JP7585690B2 - Actuator and inkjet head - Google Patents

Description

The present invention relates to an actuator and an inkjet head. More specifically, the present invention relates to an actuator that can efficiently transmit the displacement of a piezoelectric body and an inkjet head using the actuator.

An inkjet device is a device that prints or draws on a surface to be printed by ejecting ink from an inkjet head. The inkjet head installed in an inkjet device has a pressure chamber for filling with ink, a flow path for guiding ink to the pressure chamber, a nozzle connected to the pressure chamber, and an actuator for applying pressure to the ink filled in the pressure chamber. By driving the actuator to increase the pressure in the pressure chamber, the ink filled in the pressure chamber is ejected from the nozzle.

The actuator, for example, has a piezoelectric element, which is a laminate consisting of a piezoelectric material that converts mechanical energy into electrical energy or converts electrical energy into mechanical energy, sandwiched between two electrodes in the thickness direction, and a vibration plate that is provided to effectively transmit the mechanical displacement generated by the piezoelectric material element to the ink. The actuator is provided, for example, on the opposite side of the pressure chamber to the nozzle, and is a mechanism in which the pressure in the pressure chamber is increased and ink is ejected from the nozzle when a voltage is applied to the piezoelectric material and the vibration plate deforms, reducing the volume of the pressure chamber.

In recent years, the demand for smaller and higher density inkjet heads has led to demands for smaller actuators as well, and a design that efficiently transmits the displacement of the piezoelectric element to the diaphragm for deformation is now required. To meet such demands, for example, Patent Document 1 employs a configuration in which the diaphragm is made of multiple layers of different materials in the film thickness direction, and the main component of the part of the diaphragm that comes into contact with the ink and the pressure chamber member are made of the same material. However, there is a demand for even more efficient displacement transmission.

JP 2009-215473 A

The present invention was made in consideration of the above problems and circumstances, and the problem to be solved is to provide an actuator that can efficiently transmit the displacement of a piezoelectric body. Also, the present invention is to provide an inkjet head that can efficiently eject ink using the actuator.

In the process of investigating the causes of the above problems in order to solve them, the inventors discovered that the displacement of the piezoelectric layer can be efficiently transmitted by configuring the diaphragm that transmits the displacement of the piezoelectric layer to have a structure of three or more layers, and further configuring the Young's modulus of the material that composes each of these layers to increase with distance from the piezoelectric layer, which led to the invention. In other words, the above problems of the present invention are solved by the following means.

1. An actuator comprising: a piezoelectric layer having a first main surface and a second main surface; a first electrode and a second electrode disposed on the first main surface and the second main surface of the piezoelectric layer, respectively; and a vibration plate disposed on the opposite side of the second electrode to the piezoelectric layer,
an actuator, characterized in that the vibration plate is formed by laminating at least three layers made of different materials in a thickness direction, and the Young's modulus of the materials constituting each of the vibration plate layers increases in order from the layer closer to the second electrode to the layer furthest from the second electrode, the three layers being a first layer, a second layer and a third layer from the second main surface of the piezoelectric layer to the layer furthest from the piezoelectric layer, and the Young's modulus of the material constituting the first layer is Y41a _, the Young's modulus of the material constituting the second layer is Y42a _, and the Young's modulus of the material constituting the third layer is Y43a _, the Young's modulus Y41a _, Y42a _and Y43a _satisfy the following relationships (1a-2) to (1a-4) .
(1a-2) 10GPa≦Y _41a
(1a-3) 1.05≦Y _42a /Y _41a ≦4.0
(1a-4) 1.05≦Y _43a /Y _42a ≦4.0

2. An actuator comprising a piezoelectric layer having a first main surface and a second main surface, a first electrode disposed on the first main surface of the piezoelectric layer, and a vibration plate disposed on the second main surface of the piezoelectric layer,
the vibration plate has a conductor layer disposed on the second main surface of the piezoelectric layer, and at least three layers stacked in a thickness direction on a side of the conductor layer opposite to the piezoelectric layer, the layers being made of a material different from the material constituting the conductor layer;
an actuator comprising: a diaphragm configured such that the Young's modulus of materials constituting the conductor layer and each of the layers increases in that order from the conductor layer toward the layer furthest from the piezoelectric layer; the conductor layer and the three layers are, from the second main surface of the piezoelectric layer toward the layer furthest from the piezoelectric layer, a first layer, a second layer, a third layer, and a fourth layer; a Young's modulus of a material constituting the first layer is Y41b _; a Young's modulus of a material constituting the second layer is Y42b _; a Young's modulus of a material constituting the third layer is Y43b _; and a Young's modulus of a material constituting the fourth layer is Y44b _; the Young's modulus Y41b _, Y42b _, Y43b _, and _Y44b satisfy the following relationships (2b-2) to (2b-5) .
(2b-2) 10GPa≦Y _41b
(2b-3) 1.05≦Y _42b /Y _41b ≦4.0
(2b-4) 1.05≦Y _43b /Y _42b ≦4.0
(2b-5) 1.05≦Y _44b /Y _43b ≦4.0

3. The actuator described in paragraph 1 or 2, characterized in that the material constituting the layer of the vibration plate closest to the piezoelectric layer is a material that suppresses a reduction reaction in the piezoelectric layer.

4. The actuator described in paragraph 3, characterized in that the material that inhibits the reduction reaction is a metal with a standard electrode potential greater than -0.126 V, or a conductive material that contains the metal.

5. The actuator according to paragraph 3 or 4, characterized in that the material that inhibits the reduction reaction is a platinum group metal selected from platinum, iridium, palladium, rhodium, and ruthenium, or a conductive material that contains the platinum group metal.

6. The actuator described in any one of paragraphs 1 to 5, characterized in that the material constituting the layer of the diaphragm farthest from the piezoelectric layer is mainly chromium or nickel.

7. An actuator according to any one of claims 1 to 6,
a pressure chamber filled with ink, the pressure of the ink being changed by driving the actuator;
a nozzle that ejects the ink filled in the pressure chamber by driving the actuator.
An inkjet head comprising:

In the following description, the actuator of the present invention defined in 1 above is referred to as the actuator of the first aspect of the present invention, and the actuator of the present invention defined in 2 above is referred to as the actuator of the second aspect of the present invention.

The above-mentioned means of the present invention can provide an actuator that can efficiently transmit the displacement of a piezoelectric body. In addition, it can provide an inkjet head that can efficiently eject ink using the actuator. The mechanism of expression or action of the effects of the present invention is inferred as follows from material mechanics considerations.

The actuator of the first aspect of the present invention has a piezoelectric layer sandwiched between a pair of electrodes, and a vibration plate consisting of at least three layers on the side of one of the electrodes opposite the piezoelectric layer. The actuator of the second aspect of the present invention has a piezoelectric layer, an electrode located on one of its main surfaces, and a vibration plate located on the other main surface, and the vibration plate is a vibration plate consisting of at least three layers, with a conductor layer and two or more layers stacked from the piezoelectric layer side.

In the actuator of the present invention, the vibration plate has a laminated structure of three or more layers, and the Young's modulus of the material that constitutes each layer is designed to increase in order from the side closest to the piezoelectric layer to the side furthest from the layer.

The amount of displacement δ of the diaphragm when it bends is determined by the deformation force F generated by the piezoelectric body and the neutral plane L that exists at a distance L in the thickness direction from the piezoelectric body/diaphragm interface in the diaphragm, and is expressed as δ ∝ F × L. Therefore, for a given deformation force F, a larger δ can be obtained by making L larger.

Generally, L is expressed by the following formula when the Young's modulus of the i-th layer and the cumulative film thickness are designated as E _i and h _i, respectively. Therefore, it is preferable to set E _i high in layers with larger i.
L=ΣE _i (h _i ² - h _i-1 ² )/2×ΣE _i (h _i - _{h i-1} )

Furthermore, in reality, it is preferable to avoid localization of the imaginary surface, which is difficult to expand and contract due to loss of generated force caused by deformation of the diaphragm, in the area close to the piezoelectric element, so it is preferable that Ei increases consistently as _i increases. Therefore, a structure of three or more layers, in which the Young's modulus increases with distance from the piezoelectric/diaphragm interface, is the best. The diaphragm can efficiently transmit the displacement of the piezoelectric layer.

FIG. 1 is a cross-sectional view showing an example of an embodiment of an actuator according to a first aspect of the present invention. FIG. 2 is a cross-sectional view showing a modified embodiment of the actuator according to the first aspect of the present invention; FIG. 2 is a plan view showing the operation of the actuator shown in FIG. 1 installed on a substrate; XX line cross-sectional view of FIG. FIG. 2 is a cross-sectional view showing an example of an embodiment of the actuator according to the second aspect of the present invention. FIG. 1 is a cross-sectional view showing a modified embodiment of the actuator according to the second aspect of the present invention; FIG. 1 is a top view of an example of an embodiment of an inkjet head according to the present invention. 7 is a cross-sectional view of the inkjet head shown in FIG. 6 taken along line YY. 7 is an enlarged cross-sectional view of the inkjet head shown in FIG. 6 taken along line YY.

The actuator of the first aspect of the present invention is an actuator including a piezoelectric layer having a first main surface and a second main surface, a first electrode and a second electrode arranged on the first main surface and the second main surface of the piezoelectric layer, respectively, and a vibration plate arranged on the opposite side of the second electrode to the piezoelectric layer, characterized in that the vibration plate is formed by stacking at least three layers made of different materials in the thickness direction, and the Young's modulus of the material constituting each layer in the vibration plate increases in order from the layer closest to the second electrode to the layer furthest from the second electrode.

The actuator of the second aspect of the present invention is an actuator including a piezoelectric layer having a first main surface and a second main surface, a first electrode disposed on the first main surface of the piezoelectric layer, and a vibration plate disposed on the second main surface of the piezoelectric layer, the vibration plate having a conductor layer disposed on the second main surface of the piezoelectric layer, and at least two layers made of a material different from the material constituting the conductor layer, stacked in the thickness direction on the side of the conductor layer opposite the piezoelectric layer, the Young's modulus of the material constituting the conductor layer and each of the layers in the vibration plate increases in order from the conductor layer to the layer farther from the piezoelectric layer.

In the following description, the term "actuator of the present invention" includes both the actuator of the first aspect of the present invention and the actuator of the second aspect of the present invention. The following embodiments are common to the actuator of the first aspect of the present invention and the actuator of the second aspect of the present invention.

In an embodiment of the actuator of the present invention, from the viewpoint of protecting the piezoelectric layer, it is preferable that the material constituting the layer of the diaphragm closest to the piezoelectric layer is a material that suppresses a reduction reaction in the piezoelectric layer. In this embodiment, it is preferable that the material that suppresses the reduction reaction is a metal having a standard electrode potential greater than -0.126 V, or a conductive material containing the metal. Furthermore, in the above embodiment, it is preferable that the material that suppresses the reduction reaction is a platinum group metal selected from platinum, iridium, palladium, rhodium, and ruthenium, or a conductive material containing the platinum group metal.

In an embodiment of the actuator of the present invention, the piezoelectric layer is preferably composed mainly of lead zirconate titanate. By having the piezoelectric layer composed mainly of lead zirconate titanate, it is possible to reduce the thickness of the piezoelectric layer and obtain good displacement efficiency.

It is known that when the piezoelectric layer mainly contains lead zirconate titanate, the deterioration of lead zirconate titanate in the reduction mode is significant. Therefore, particularly when the piezoelectric layer mainly contains lead zirconate titanate, it is preferable that the material constituting the layer of the diaphragm closest to the piezoelectric layer has a standard electrode potential of greater than -0.126 V and is less susceptible to oxidation. Specifically, it is preferable that the material be made of the above metals, particularly platinum group metals, or a conductive material containing such metals.

The above-mentioned structure of the diaphragm allows oxygen contained in the piezoelectric layer to be captured by the layer of the diaphragm closest to the piezoelectric, which is more susceptible to oxidation, through interfacial migration and interlayer diffusion, and at the same time, the piezoelectric is reduced and deteriorated. In other words, it is possible to prevent oxygen from being extracted from the piezoelectric layer by the constituent material of the diaphragm, and the piezoelectric layer can be adequately protected from deterioration over time that occurs during operation.

In one embodiment of the actuator of the present invention, it is preferable that the material constituting the layer of the diaphragm farthest from the piezoelectric layer is mainly chromium or nickel. By configuring the diaphragm in this way, when the actuator of the present invention is made into, for example, an inkjet head, it becomes easy to form a pressure chamber that contains ink and is connected to the actuator, and has the advantage of being excellent in terms of high precision.

The inkjet head of the present invention is characterized by comprising the actuator of the present invention described above, a pressure chamber filled with ink and in which the pressure of the ink changes when the actuator is driven, and a nozzle that ejects the ink filled in the pressure chamber when the actuator is driven.

The present invention, its components, and the forms and modes for implementing the present invention are described in detail below. Note that in this application, "~" is used to mean that the numerical values before and after it are included as the lower and upper limits.

[Actuator of the first embodiment]
The actuator of a first aspect of the present invention is an actuator comprising a piezoelectric layer having a first main surface and a second main surface, a first electrode and a second electrode respectively arranged on the first main surface and the second main surface of the piezoelectric layer, and a vibration plate arranged on the opposite side of the second electrode to the piezoelectric layer, characterized in that the vibration plate is formed by stacking at least three layers made of different materials in the thickness direction, and the Young's modulus of the material constituting each of the layers in the vibration plate increases in the order from the layer closer to the second electrode to the layer furthest from the second electrode.

In the diaphragm of the actuator of the first embodiment, the material constituting each layer may be a single element such as a metal, an alloy or compound containing two or more elements, or a combination of these. Furthermore, even if the materials constituting each layer are composed of the same elements, if they have different densities or crystal structures, they are considered to be different materials.

The actuator of the first aspect, with the above configuration, effectively propagates mechanical displacement generated in the piezoelectric layer by electrical energy supplied from the first and second electrodes via the vibration plate. The object to which the mechanical displacement is propagated is not particularly limited, but an example is ink. Specifically, the actuator of the first aspect of the present invention is effectively used for ejecting ink from an inkjet head to perform printing or drawing on a printing surface. In the inkjet head, ink is filled in a pressure chamber connected to a nozzle. The pressure chamber is a mechanism in which, for example, part of the wall surface is composed of an actuator, and when printing, the actuator is driven to increase the pressure in the pressure chamber, thereby ejecting ink from the pressure chamber to the outside via the nozzle.

The actuator of the first aspect may have any other components as necessary in addition to the first electrode, the piezoelectric layer, the second electrode, and the diaphragm. Examples of the optional components include an insulating protection layer and a gas barrier layer that are arranged on the main surface of the first electrode opposite the piezoelectric layer for the purpose of insulating and protecting the first electrode.

The actuator of the first aspect will be described below with reference to Figures 1, 2, 3A, and 3B, but the actuator of the first aspect is not limited to these. The actuator of the first aspect shown in these figures can be modified as appropriate without departing from the spirit of the present invention. Figures 1 and 2 are cross-sectional views showing an example of an embodiment and a modified example of the actuator of the first aspect of the present invention. Figures 3A and 3B are plan and cross-sectional views showing the operation of the actuator shown in Figure 1 installed on a substrate.

The actuator 11A shown in FIG. 1 has a piezoelectric layer 1 having a first main surface S1 and a second main surface S2, and a first electrode 2 and a second electrode 3 arranged on the first main surface S1 and the second main surface S2 of the piezoelectric layer 1, respectively. The actuator 11A has a vibration plate 4A on the side of the second electrode 3 opposite the piezoelectric layer 1.

The diaphragm 4A is formed by stacking a first layer 41a, a second layer 42a, and a third layer 43a in the thickness direction from the second electrode 3 side. The materials constituting the first layer 41a, the second layer 42a, and the third layer 43a are different from each other.

In the diaphragm 4A, if the Young's modulus of the material constituting the first layer 41a is _Y41a , the Young's modulus of the material constituting the second layer 42a is _Y42a , and the Young's modulus of the material constituting the third layer 43a is _Y43a , the following relationship holds between _Y41a , _Y42a , and _Y43a .
Y _41a <Y _42a <Y _43a

The actuator 11B shown in FIG. 2 has the same configuration as the actuator 11A shown in FIG. 1, except that it has an insulating protective layer 5 on the main surface of the first electrode 2 opposite the piezoelectric layer 1, and the vibration plate is a vibration plate 4B composed of four layers instead of the vibration plate 4A composed of three layers.

In the actuator 11B, the vibration plate 4B is formed by stacking a first layer 41a, a second layer 42a, a third layer 43a, and a fourth layer 44a in the thickness direction from the side of the second electrode 3. In the vibration plate 4B, if the Young's modulus of the material constituting the first layer 41a is _Y41a , the Young's modulus of the material constituting the second layer _42a is Y42a, the Young's modulus of the material constituting the third layer _43a is Y43a _{, and} the Young's modulus of the material constituting the fourth layer 44a is Y44a, the following relationship is established among _Y41a , _Y42a , _Y43a , and _Y44a .
Y _41a <Y _42a <Y _43a <Y _44a

3A and 3B are diagrams showing the operation of the actuator 11A placed on the substrate 6. FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view of line X-X in FIG. 3A. The substrate 6 on which the actuator 11A is mounted is, for example, a plate-like body having a rectangular planar shape and a cylindrical through-hole 7 in the center. In the actuator 11A, for example, the second electrode 3 and the vibration plate 4A have a rectangular planar shape of the same size and shape as the outer periphery of the substrate 6, and the piezoelectric layer 1 and the first electrode 2 have a circular planar shape smaller than the outer periphery of the through-hole 7 of the substrate 6. In FIG. 3A and FIG. 3B, the outer periphery of the piezoelectric layer 1 and the first electrode 2 of the actuator 11A is located inside the outer periphery of the through-hole 7.

The first electrode 2 and the second electrode 3 of the actuator 11A are connected to a drive circuit 8. The actuator 11A is driven based on a voltage (drive signal) applied from the drive circuit 8 to the first electrode 2 and the second electrode 3. Specifically, when a potential difference is applied between the first electrode 2 and the second electrode 3 by applying a voltage from the drive circuit 8, the piezoelectric layer 1 expands and contracts in a direction perpendicular to the thickness direction, i.e., in a direction parallel to the first main surface S1 and the second main surface S2, according to the potential difference between the first electrode 2 and the second electrode 3. As a result of this expansion and contraction, the piezoelectric layer 1 attempts to displace in the thickness direction.

Then, a curvature is generated in the portion of the vibration plate 4A facing the through-hole 7 of the substrate 6, and the portion of the vibration plate 4A facing the through-hole 7 is displaced (bent, vibrates) toward the through-hole 7. This displacement of the vibration plate 4A reduces the volume of the through-hole 7. When the actuator of the present invention is applied to an inkjet head, for example, the through-hole 7 of the substrate 6 shown in Figures 3A and 3B serves as a pressure chamber to contain ink, and further, a substrate having a nozzle on the opposite side of the pressure chamber from the vibration plate 4A is bonded to the substrate 6. In an inkjet head having this configuration, the vibration of the vibration plate 4A described above is transmitted to the ink in the pressure chamber, and the ink is ejected from the nozzle to the outside as ink droplets.

In the actuators 11A and 11B, the vibration plate is composed of three or more layers in the thickness direction, and the relationship of the Young's modulus of each layer satisfies _Y41a < _Y42a < _Y43a and _Y41a < _Y42a < _Y43a < _Y44a , respectively. This allows the neutral plane of the piezoelectric layer to be set further outward, resulting in more efficient energy generation. In other words, the displacement of the piezoelectric layer can be transmitted to the vibration plate more efficiently.

Below, we will explain each component of the actuator of the first aspect in detail.

(Piezoelectric Layer)
The piezoelectric layer 1 is composed of a piezoelectric material. The piezoelectric material preferably contains a perovskite compound such as barium titanate (BaTiO ₃ ) and lead zirconate titanate ([Pb(Zr.Ti)O ₃ ], hereinafter also referred to as "PZT"), and preferably contains mainly PZT. The molar ratio of Zr to Ti in PZT is preferably Zr/Ti=30/70 to 70/30. "Containing mainly PZT" means that PZT accounts for 85 mass % or more of the total amount of the piezoelectric material.

To improve the performance of the piezoelectric body, donor ions may be added to PZT. Examples of donor ions include metal ions such as lanthanum (La), niobium (Nb), tantalum (Ta), tungsten (W), aluminum (Al), and strontium (Sr), and it is preferable that the PZT contains one or more ions selected from the group consisting of La, Nb, Ta, and W. It is preferable that the PZT contains one or more metal ions selected from the group consisting of iron (Fe), cobalt (Co), and manganese (Mn).

The piezoelectric layer 1 may be composed of a single layer or multiple layers. Whether it is a single layer or multiple layers, the piezoelectric layer 1 preferably includes a layer mainly made of PZT. In addition, examples of layers that can be combined with a layer mainly made of PZT include layers made of lead lanthanate titanate (PLT), lead magnesium niobate titanate (PMN), lead zinc niobate titanate (PZN), etc.

The thickness of the piezoelectric layer 1 can be appropriately selected depending on the application of the actuator of the first embodiment. For example, when the actuator of the first embodiment is used in an inkjet head, the thickness of each layer and the total thickness of the piezoelectric layer 1 are preferably in the range of 1 to 10 μm. If the total thickness of the piezoelectric layer 1 is 1 μm or more, it is possible to sufficiently displace the vibration plate when made into an actuator, and if the thickness of each layer and the total thickness of the piezoelectric layer 1 are 10 μm or less, defects such as cracks and peeling off during film formation hardly occur.

Methods for forming the piezoelectric layer 1 include chemical methods such as CVD, physical methods such as sputtering and ion plating, and liquid phase growth methods such as the sol-gel method.

The planar shape and size (area) of the piezoelectric layer 1 are not particularly limited. They can be selected appropriately depending on the application. For the same area, a circular shape is preferable because it is advantageous for drive efficiency. When the actuator of the first embodiment is used in an inkjet head, the planar shape and size (area) are appropriately set depending on the amount of ink ejected.

(First Electrode)
In the actuators 11A and 11B, the first electrode 2 is formed on the entire first main surface S1 of the piezoelectric layer 1. The range of the first electrode on the first main surface S1 is not particularly limited, but in order to efficiently use the entire piezoelectric layer 1, the first electrode is usually disposed on the entire surface.

The material constituting the first electrode 2 is not particularly limited as long as it is a conductive material. Specifically, conductive materials containing one or more of metals such as platinum (Pt), gold (Au), copper (Cu), palladium (Pd), ruthenium (Ru), titanium (Ti), nickel (Ni), aluminum (Al), chromium (Cr), tungsten (W), and iridium (Ir) can be used. The conductive material can be a material containing one or more of these metals. The conductive material may be a mixture of metals or an alloy. In that case, it may be a mixture or alloy of at least one of the above metals with another metal.

The conductive material may be a material containing one or more of metal oxides such as iridium oxide (IrO ₂ ), ruthenium oxide (RuO ₂ ), lanthanum nickelate (LaNiO ₃ ; LNO), and strontium ruthenate (SrRuO ₃ ; SRO).

Conductive materials include materials in which silicon is doped with trace elements (phosphorus, boron, etc.), such as p-type silicon. Conductive materials may also be materials made of carbon. Materials made of carbon include diamond and diamond-like carbon that are doped with boron or the like to give them electrical conductivity.

The first electrode 2 may consist of a single layer or multiple layers. The thickness of the first electrode 2 is preferably in the range of 0.005 to 2 μm. When the first electrode 2 consists of multiple layers, the total thickness is preferably in the above range. The first electrode 2 can be formed by a chemical method such as a CVD method, a physical method such as a sputtering method or an ion plating method, or a liquid phase growth method such as a sol-gel method.

The first electrode 2 preferably has a two-layer laminate structure, for example, having a layer made of a highly adhesive conductive material on the piezoelectric layer 1 side, and a highly conductive layer on top of that. Examples of the layer on the piezoelectric layer 1 side include a Ti layer and an Ir layer. Examples of the layer laminated on the adhesive layer include a Pt layer and an Au layer. The thickness of the adhesive layer is preferably, for example, about 0.002 to 1 μm, and the thickness of the layer laminated on top of that is preferably, for example, about 0.1 to 0.2 μm.

(Insulating protective layer)
In the actuator of the first embodiment, the insulating protective layer 5 of the actuator 11B shown in Fig. 2 is an optional layer provided on the side of the first electrode 2 opposite to the piezoelectric layer 1. The insulating protective layer 5 is preferably configured to cover the entire main surface of the first electrode 2. The insulating protective layer 5 may also be configured to cover the end faces of the first electrode 2 as necessary.

The insulating protective layer 5 is made of an insulating material. Examples of the insulating material include resin, ceramics, glass, etc., and these may be used in combination. Specific examples of the resin include polyimide resin, polyester resin, acrylic resin, epoxy resin, melamine resin, nylon resin, urethane resin, polyolefin resin, polycarbonate resin, etc. Examples of the ceramic include metal oxides such as SiO ₂ and Al ₂ O ₃ , and mixtures containing these.

The insulating protective layer 5 may be a single layer or may be made up of multiple layers. The total thickness of the insulating protective layer 5 is preferably in the range of 0.5 to 2.5 μm. In the case of a resin layer, the insulating protective layer 5 can be formed by any general precision coating technique, including, for example, a spin coat method. In the case of a ceramic layer, it can be formed by, for example, a sol-gel method, as well as a vapor phase deposition method such as a deposition method, a CVD method, or a sputtering method.

(Second Electrode)
In the actuators 11A and 11B, the second electrode 3 is formed to cover the entire second main surface S2 of the piezoelectric layer 1 and to transmit the displacement of the piezoelectric layer 1 when a voltage is applied to the vibration plate 4A and the vibration plate 4B, respectively. The shape and size of the second electrode 3 in a plan view are usually such that the entire second main surface S2 of the piezoelectric layer 1 can be covered.

The vibration plate 4A and the vibration plate 4B are configured so that the area of the main surface is larger than, for example, the area of the second main surface S2 of the piezoelectric layer 1. The vibration plate 4A and the vibration plate 4B and the piezoelectric layer 1 are stacked so that the outer periphery of the piezoelectric layer 1 is located inside the outer periphery of the vibration plate 4A and the vibration plate 4B in a planar view. The shape and size of the second electrode 3 in a planar view may be, for example, the same size and shape as the second main surface S2 of the piezoelectric layer 1. The second electrode 3 may also be configured so that the area in a planar view is larger than the area of the second main surface S2 of the piezoelectric layer 1 so that the outer periphery in a planar view exceeds the outer periphery of the second main surface S2 of the piezoelectric layer 1. Specifically, the shape and size of the second electrode 3 in a planar view may be configured to be approximately the same size and shape as the main surfaces of the vibration plate 4A and the vibration plate 4B on the piezoelectric layer 1 side.

The second electrode 3 can be made of the same conductive material as the first electrode 2. The second electrode 3 may be made of a single layer, as with the first electrode 2, or may be made of multiple layers. The thickness of the second electrode 3 is preferably in the range of 0.005 to 2 μm. Examples of the second electrode 3 made of multiple layers include the same examples as the first electrode 2.

It is more preferable that the thickness of the second electrode 3 is in the range of 0.005 to 3 μm. The Young's modulus of the second electrode 3 is preferably in the range of 150 to less than 300 GPa, for example.

(Vibration plate)
In the actuator of the first aspect of the present invention, the vibration plate is configured such that three or more layers made of different materials are laminated in the thickness direction, and the Young's modulus of the material of each layer increases in order from the layer closer to the second electrode to the layer farther from the second electrode. The number of layers constituting the vibration plate in the actuator of the first aspect is not particularly limited as long as it is three or more, and is appropriately selected depending on the application. The number of layers constituting the vibration plate depends on the thickness of the entire vibration plate, the thickness and Young's modulus of each layer, but four or more is preferable in order to efficiently propagate the displacement by adjusting the physical properties such as the stress of the piezoelectric layer and the composite Young's modulus.

The Young's modulus of the diaphragm is such that the Young's modulus of the material constituting each layer increases from the layer closest to the second electrode to the layer furthest from the second electrode. The Young's modulus of each single layer of the diaphragm, while satisfying the above conditions, is preferably in the range of approximately 10 to 900 GPa, and more preferably in the range of 60 to 800 GPa. In other words, the lower limit of the Young's modulus of the material constituting the layer closest to the second electrode is most preferably 10 GPa, and in practical terms, it is preferable that it be less than 300 GPa at most. The upper limit of the Young's modulus of the material constituting the layer furthest from the second electrode is preferably 900 GPa, and more preferably 800 GPa. The Young's modulus of the entire diaphragm can be in the range of approximately 80 to 700 GPa.

The thickness of the diaphragm is adjusted as appropriate depending on the application of the actuator of the first embodiment and the Young's modulus of the diaphragm. When the actuator of the first embodiment is used in an inkjet head, it is preferable that the overall thickness of the diaphragm be within the range of 1.5 to 12 μm, from the viewpoint of achieving a thin design while increasing the displacement efficiency.

In the actuator of the first embodiment, actuator 11A shown in FIG. 1 is an example in which the diaphragm has three layers, and actuator 11B shown in FIG. 2 is an example in which the diaphragm has four layers.

In the diaphragm 4A of the actuator 11A, the Young's moduli Y _41a , Y _42a and Y _43a of the materials constituting the first layer 41a, the second layer 42a and the third layer 43a, respectively, satisfy the following relationship (1a-1).
(1a-1) Y _41a <Y _42a <Y _43a

From the viewpoint of increasing the displacement transmission efficiency (hereinafter also referred to as "displacement efficiency") of the piezoelectric layer 1, it is preferable that the Young's moduli _Y41a , _Y42a , and _Y43a satisfy the above-mentioned (1a-1) and further satisfy any one of the following relationships (1a-2) to (1a-4), more preferably satisfy two or more of them, and further preferably satisfy all of them.

(1a-2) 10GPa≦Y _41a
(1a-3) 1.05≦Y _42a /Y _41a ≦4.0
(1a-4) 1.05≦Y _43a /Y _42a ≦4.0

In (1a-2), the Young's modulus Y _41a of the material constituting the first layer 41a is 10 GPa or more, preferably 60 GPa or more, which is preferable in that the Young's modulus of the entire diaphragm 4A can be increased and a high resonance frequency can be obtained for the purpose of driving the diaphragm. The Young's modulus Y _41a is more preferably 100 GPa or more. The upper limit of the Young's modulus Y _41a is preferably about 300 GPa from the viewpoint of satisfying the above (1a-1).

(1a-3) and (1a-4) are indexes showing how much the Young's modulus of the material constituting each layer increases as the layers constituting the diaphragm 4A become farther from the second electrode 3 in the order of the first layer 41a, the second layer _42a , and the third layer 43a. Hereinafter, the Young's modulus Y41a of the material constituting the first layer 41a is also referred to as the "Young's modulus _Y41a of the first layer 41a." The same applies to the other layers.

(1a-3) defines the value " _Y42a / _Y41a " of the ratio of the Young's modulus _Y42a of the second layer _42a to the Young's modulus Y41a of the first layer 41a. When _Y42a / _Y41a is in the above range, the Young's modulus between the first layer 41a and the second layer 42a is sufficiently increased, and the relationship of (1a-1) is also satisfied, which is preferable. It is more preferable that _Y42a / _Y41a is in the range of 1.05 to 1.85.

(1a-4) defines the value "Y _43a /Y _42a " of the ratio of the Young's modulus Y _43a of the third layer 43a to the Young's modulus Y _42a of the second layer 42a. When Y _43a /Y _42a is equal to or greater than the lower limit, the Young's modulus between the second layer 42a and the third layer 43a increases sufficiently, which is preferable. When Y _43a /Y _42a is equal to or less than the upper limit, it is preferable that the total film thickness satisfies a preferable range, for example, 1.5 to 12 μm, while allowing room to increase the number of layers for the purpose of stress adjustment, etc. It is more preferable that Y _43a /Y _42a is within the range of 1.05 to 2.0.

Furthermore, the relationship between _Y42a / _Y41a and _Y43a / _Y42a , (1a-5) _Y42a / _Y41a : _Y43a / _Y42a, is preferably in the range of 1:1 to 1:2. With _Y42a / _Y41a : _Y43a / _Y42a in this range, the Young's modulus increases nearly uniformly from the first layer to the third layer.

Taking the above (1a-1) as an essential requirement and taking into account (1a-2) to (1a-4) and further (1a-5), specifically, it is preferable that the Young's modulus Y41a of the first layer 41a is in the range of 60 to 300 GPa, the Young's modulus Y42a of the second layer 42a is in the range of 63 to 555 GPa, and the Young's modulus Y43a of the third layer 43a is in the range of 66 to 900 GPa.

It is more preferable that the Young's modulus Y41a of the first layer 41a is in the range of 100 to 300 GPa, the Young's modulus Y42a of the second layer 42a is in the range of 105 to 555 GPa, and the Young's modulus Y43a of the third layer 43a is in the range of 110 to 900 GPa.

The thicknesses of the first layer 41a, the second layer 42a, and the third layer 43a in the diaphragm 4A are indicated by _T41a , _T42a , and _T43a , respectively. In the case where the actuator 11A is used in an inkjet head, for example, in order to increase the displacement efficiency, it is preferable that _T41a , _T42a , and _T43a are each within the range of 0.5 to 4 μm, and more preferably within the range of 0.5 to 3.5 μm. Moreover, it is preferable that the total thickness of the diaphragm 4A, that is, _T41a + _T42a + _T43a , is within the range of 1.5 to 12 μm, from the viewpoint of achieving a thin structure while increasing the displacement efficiency.

As described above, the materials constituting the first layer 41a, second layer 42a, and third layer 43a of the diaphragm 4A may each be composed of a single element such as a metal, an alloy or compound containing two or more elements, or a combination of these. Furthermore, even if the materials constituting each layer are composed of the same elements, they are considered to be different materials if they have different densities or crystal structures.

The materials constituting the first layer 41a, second layer 42a, and third layer 43a of the diaphragm 4A may be organic or inorganic, or may be a composite or mixture of these, as long as they satisfy the relationship (1a-1) above.

Inorganic substances that can be used as constituent materials for each layer of the diaphragm 4A are described below, divided into metals and non-metallic inorganic substances. Metals include aluminum, gold, titanium, copper, platinum, chromium, nickel, tungsten, zirconium, silver, tantalum, osmium, niobium, molybdenum, iron, cobalt, palladium, zinc, and vanadium. The metal may be an alloy of two or more metals selected from these, or a mixture.

Non-metallic inorganic substances include silicon, carbon, boron, and nitrides, oxides, oxynitrides, and carbides of the above metals or silicon. Non-metallic inorganic substances further include materials in which silicon is doped with trace elements (phosphorus, boron, etc.), such as p-type silicon. Inorganic substances composed of carbon include diamond and diamond-like carbon that are doped with boron or the like to give them electrical conductivity.

The above nitrides, oxides, oxynitrides, and carbides may contain one or more metals. Furthermore, these nitrides, oxides, oxynitrides, and carbides may be compounds with compositions that deviate from the stoichiometric ratio.

Various types of resins can be used as organic materials for the layers of the diaphragm 4A. Examples of resins include polyimide resin, polyester resin, acrylic resin, epoxy resin, melamine resin, nylon resin, urethane resin, polyolefin resin, and polycarbonate resin.

As mentioned above, even if the materials constituting each layer of the diaphragm 4A are composed of the same elements, if the densities and crystal structures are different, the Young's modulus will be different. For example, in the case of metals, the Young's modulus is affected by the density and crystal structure. In addition, nitrides, oxides, oxynitrides, and carbides contain compounds with compositions that deviate from the stoichiometric ratio, and it is possible to change the Young's modulus by changing the composition.

Generally speaking, the Young's modulus of organic materials is lower than that of inorganic materials, and that of resins is generally in the range of 0.1 to 10 GPa. Table I shows the Young's modulus [GPa] of inorganic materials obtained using typical manufacturing methods. In Table I, materials with a range of Young's modulus values include those that contain compounds with compositions other than the stoichiometric ratio, and those with different densities due to differences in manufacturing methods.

The materials constituting each layer of the diaphragm 4A are selected from the materials exemplified above so that the relationship between the Young's moduli of each layer satisfies the above (1a-1). More preferably, they are selected so that the above (1a-2) to (1a-4) and even (1a-5) are satisfied. The method of forming each layer can be appropriately selected from chemical methods such as CVD, physical methods such as sputtering and ion plating, and liquid phase growth methods such as sol-gel methods, depending on the constituent materials. In the case of a resin layer, it can be formed by, for example, spin coating, dipping, or electrodeposition.

In addition to the Young's modulus of the material constituting each layer of the diaphragm 4A, it is preferable that the material constituting the first layer 41a has the following characteristic (A):

(A): The material constituting the first layer 41a of the diaphragm 4A is preferably a material that suppresses the reduction reaction in the piezoelectric layer 1, specifically, the reduction reaction at the interface between the piezoelectric layer 1 and the first layer 41a itself.

More specifically, the material that inhibits the reduction reaction is preferably a metal having a standard electrode potential greater than -0.126 V, or a conductive material containing such a metal. Furthermore, the material that inhibits the reduction reaction is preferably a platinum group metal selected from platinum, iridium, palladium, rhodium, and ruthenium, or a conductive material containing such a platinum group metal. In this case, one type of metal or platinum group metal having a standard electrode potential greater than -0.126 V may be used alone, or two or more types may be used in combination. When two or more types are used in combination, they may be a mixture or an alloy.

When using a material containing a metal, a material that suppresses such a reduction reaction is preferably a material containing a metal element whose standard electrode potential is greater than that of titanium (-1.630 V), zirconium (-1.534 V), or even lead (-0.216 V) when the piezoelectric layer 1 is mainly composed of PZT.

Specific examples of such materials include Cr (-0.740 V), Ni (-0.257 V), Cu (+0.340 V), Ag (+0.799 V), Pd (+0.915 V), Ir (+1.156 V), Pt (+1.188 V), and Au (+1.510 V). In the above, the numbers in parentheses after the material names indicate the standard electrode potential.

Moreover, it is more preferable that the material constituting the first layer 41a that is in direct contact with the piezoelectric layer 1 is a platinum group metal, through which oxygen does not easily diffuse. The elements contained in platinum group metals and their standard electrode potentials are ruthenium (+0.460 V), rhodium (+0.900 V), palladium (+0.915 V), iridium (+1.156 V), and platinum (+1.188 V). As described above, these are more preferable because oxygen does not easily diffuse through the film, and because they suppress the reduction reaction at the interface between the piezoelectric layer 1 and the first layer 41a itself.

In addition to the Young's modulus of the material constituting each layer of the vibration plate 4A, it is preferable that the material constituting the layer furthest from the piezoelectric layer 1, i.e., the third layer 43a, is mainly chromium or nickel. For example, when the actuator of the first embodiment is applied to an inkjet head, the layer furthest from the piezoelectric layer 1 of the vibration plate faces the pressure chamber in which ink is stored, as described below. In that case, it is preferable that the material constituting the layer furthest from the piezoelectric layer 1 of the vibration plate and the material constituting the partition wall of the pressure chamber (for example, the main body substrate 51 shown in Figures 6 to 8 described later) have good adhesion. For this reason, the material constituting the partition wall of the pressure chamber and the material constituting the layer furthest from the piezoelectric layer 1 of the vibration plate have a common main component, thereby improving the adhesion between the two.

The partition walls of the pressure chambers of the inkjet head are typically formed by plating using an alloy whose main component is chromium or nickel. Therefore, in the vibration plate 4A, if the material constituting the third layer 43a is mainly chromium or nickel, good adhesion with the partition walls of the pressure chambers of the inkjet head will be achieved. It is preferable that the partition walls of the pressure chambers of the inkjet head and the third layer 43a of the vibration plate 4A mainly contain the same metal.

Specific examples of combinations of the configurations of the layers of the diaphragm 4A include the combinations shown in Table II below. The Young's modulus of each of these materials can be adjusted by the composition and manufacturing method, and the Young's modulus value required for each layer is specified in a relative relationship. Therefore, these examples do not cover all or limit the materials that can be used in each layer.

Next, the diaphragm 4B of the actuator 11B will be described. In the diaphragm 4B, the Young's moduli Y _41a , Y 42a , Y _43a and Y 44a of the materials constituting the first layer 41a, the second layer 42a, the third layer _43a and the fourth layer _44a respectively satisfy the following relationship (2a-1).
(2a-1) Y _41a <Y _42a <Y _43a <Y _44a

From the viewpoint of enhancing the displacement efficiency of the piezoelectric layer 1, it is preferable that the Young's moduli _Y41a , _Y42a , and _Y43a satisfy the above-mentioned (2a-1) and further satisfy any one of the following relationships (2a-2) to (2a-5), more preferably satisfy two or more of them, and further preferably satisfy all of them.

(2a-2) 10GPa≦Y _41a
(2a-3) 1.05≦Y _42a /Y _41a ≦4.0
(2a-4) 1.05≦Y _43a /Y _42a ≦4.0
(2a-5) 1.05≦Y _44a /Y _43a ≦4.0

The conditions shown in (2a-2) to (2a-4) above are the same as the conditions shown in (1a-2) to (1a-4) above. In other words, when the diaphragm is composed of four layers, the relationship of the Young's modulus of the first to third layers can be the same as the relationship of the Young's modulus of the first to third layers when the diaphragm is composed of three layers.

In (2a-2), the Young's modulus Y _41a of the material constituting the first layer 41a is 10 GPa or more, preferably 60 GPa or more, which is preferable in that the Young's modulus of the entire diaphragm 4B can be increased and a high resonance frequency can be obtained for the purpose of driving the diaphragm. The Young's modulus Y _41a is more preferably 100 GPa or more. The upper limit of the Young's modulus Y _41a is preferably about 300 GPa from the viewpoint of satisfying the above (2a-1).

(2a-3), (2a-4), and (2a-5) are indices that indicate the extent to which the Young's modulus of the material constituting each layer increases as the layers constituting the diaphragm 4B become farther away from the second electrode 3 in the order of the first layer 41a, the second layer 42a, the third layer 43a, and the fourth layer 44a.

(2a-3) defines the value " _Y42a / _Y41a " of the ratio of the Young's modulus _Y42a of the second layer _42a to the Young's modulus Y41a of the first layer 41a. When _Y42a / _Y41a is in the above range, the Young's modulus between the first layer 41a and the second layer 42a is sufficiently increased, and the relationship of (2a-1) is also satisfied, which is preferable. It is more preferable that _Y42a / _Y41a is in the range of 1.05 to 1.5.

(2a-4) defines the value " _Y43a / _Y42a " of the ratio of the Young's modulus _Y43a of the third layer _43a to the Young's modulus Y42a of the second layer 42a. When _Y43a / _Y42a is in the above range, the Young's modulus between the second layer 42a and the third layer 43a is sufficiently increased, and the relationship of (2a-1) is also satisfied, which is preferable. It is more preferable that _Y43a / _Y42a is in the range of 1.05 to 1.8.

(2a-5) defines the value " _Y44a / _Y43a " of the ratio of the Young's modulus _Y44a of the fourth layer _44a to the Young's modulus Y43a of the third layer 43a. When _Y44a / _Y43a is equal to or greater than the lower limit, the Young's modulus between the third layer 43a and the fourth layer 44a increases sufficiently, which is preferable. When _Y44a / _Y43a is equal to or less than the upper limit, it is preferable that the total film thickness is within a preferable range, for example, 2.0 to 12 μm, while there is room to increase the number of layers for the purpose of stress adjustment, etc. It is more preferable that _Y44a / _Y43a is within the range of 1.05 to 1.8.

In addition, the relationship between _Y42a / _Y41a and _Y43a / _Y42a , and the relationship between _Y43a / _Y42a and _Y44a / _Y43a are preferably in the range of 1:1 to 1:1.2 for (2a-6) _Y42a / _Y41a : _Y43a / _Y42a and 1:1 to 1:1.5 for _{Y43a/Y42a:Y44a/Y43a. By having Y42a / Y41a : Y43a / Y42a and Y43a} / _Y42a : _Y44a / _Y43a in the range, the Young's modulus increases almost uniformly from the first layer to the fourth layer.

Taking the above (2a-1) as an essential requirement and also taking into consideration (2a-2) to (2a-5) and further (2a-6), specifically, it is preferable that the Young's modulus Y _41a of the first layer 41a is in the range of 60 to 300 GPa, the Young's modulus Y _42a of the second layer 42a is in the range of 63 to 450 GPa, the Young's modulus Y _43a of the third layer 43a is in the range of 66 to 810 GPa, and the Young's modulus Y _44a of the fourth layer 44a is in the range of 69 to 900 GPa.

More preferably, the Young's modulus Y _41a of the first layer 41a is in the range of 100 to 300 GPa, the Young's modulus Y _42a of the second layer 42a is in the range of 105 to 450 GPa, the Young's modulus Y _43a of the third layer 43a is in the range of 110 to 810 GPa, and the Young's modulus Y _44a of the fourth layer 44a is in the range of 116 to 900 GPa.

The thicknesses of the first layer 41a, the second layer 42a, the third layer 43a, and the fourth layer 44a in the vibration plate 4B are indicated by _T41a , _T42a , _T43a , and _T44a , respectively. In the case where the actuator 11B is used in an inkjet head, for example, in order to increase the displacement efficiency, it is preferable that _T41a , _T42a , _T43a , and _T44a are each within the range of 0.5 to 5.3 μm, and more preferably within the range of 0.5 to 4.7 μm. Moreover, it is preferable that the total thickness of the vibration plate 4B, that is, _T41a + _T42a + _T43a + _T44a , is within the range of 2.0 to 12 μm, from the viewpoint of achieving a thin structure while increasing the displacement efficiency.

The materials constituting each layer of the diaphragm 4B are selected from the materials exemplified above so that the relationship between the Young's moduli of each layer satisfies the above (2a-1). More preferably, they are selected so that the above (2a-2) to (2a-5) and further (2b-6) are satisfied. The method of forming each layer can be appropriately selected from chemical methods such as CVD, physical methods such as sputtering and ion plating, and liquid phase growth methods such as sol-gel methods, depending on the constituent materials. In the case of a resin layer, it can be formed by, for example, spin coating, dipping, or electrodeposition.

As a characteristic other than the Young's modulus of the material constituting each layer of the diaphragm 4B, it is preferable that the material constituting the first layer 41a has the above characteristic (A). Also, as a characteristic other than the Young's modulus of the material constituting each layer of the diaphragm 4B, it is preferable that the material constituting the layer furthest from the piezoelectric layer 1, i.e., the fourth layer 44a, is mainly chromium or nickel.

Specific examples of the combinations of the configurations of the layers of the diaphragm 4B include the combinations shown in Table III below. The Young's modulus of each of these materials can be adjusted by the composition and manufacturing method, and there are no limitations on the materials used in each layer.

The actuator of the first embodiment has been described above using an example in which the diaphragm is composed of three or four layers. In the case in which the diaphragm is composed of five or more layers, the Young's modulus of each layer may be appropriately selected taking into consideration the preferred range of Young's modulus of the entire diaphragm shown above, approximately 80 to 700 GPa, and the range of Young's modulus of the entire diaphragm calculated from Tables II and III, 86 to 640 GPa, and also the balance of the increase in Young's modulus from the layer closest to the second electrode to the layer furthest from the second electrode, for example, an increase that is nearly uniform. In addition, even in the case in which the diaphragm is composed of five or more layers, the preferred characteristics of the material that constitutes the layer closest to the second electrode are as described above, and the preferred characteristics of the material that constitutes the layer furthest from the second electrode are as described above.

Each layer constituting the diaphragm of the actuator of the first embodiment may be configured so that the Young's modulus within the layer gradually increases from the main surface closer to the second electrode 3 toward the main surface farther from the second electrode 3. In that case, for example, taking diaphragm 4A as an example, the Young's modulus of the first layer on the side farther from the second electrode 3 is smaller than the Young's modulus of the second layer on the side farther from the second electrode 3, and the Young's modulus of the second layer on the side farther from the second electrode 3 is smaller than the Young's modulus of the third layer on the side near the second electrode 3.

[Actuator of the Second Aspect]
The actuator of a second aspect of the present invention is an actuator comprising a piezoelectric layer having a first main surface and a second main surface, a first electrode arranged on the first main surface of the piezoelectric layer, and a vibration plate arranged on the second main surface of the piezoelectric layer, wherein the vibration plate has a conductor layer arranged on the second main surface of the piezoelectric layer, and at least two layers made of a material different from the material constituting the conductor layer, stacked in the thickness direction on the side of the conductor layer opposite the piezoelectric layer, and wherein the Young's modulus of the materials constituting the conductor layer and each of the layers in the vibration plate increases in order from the conductor layer to the layer farther from the piezoelectric layer.

The actuator of the second aspect of the present invention differs from the actuator of the first aspect in that the actuator of the first aspect has a second electrode on the second main surface of the piezoelectric layer and a vibration plate on the side of the second electrode opposite the piezoelectric layer, whereas the actuator of the second aspect has a vibration plate on the second main surface of the piezoelectric layer with a conductor layer on the side of the piezoelectric layer. In other words, the vibration plate in the actuator of the second aspect has the functions of both the second electrode and the vibration plate in the actuator of the first aspect.

The first electrode and piezoelectric layer in the actuator of the second embodiment can be the same as the first electrode and piezoelectric layer in the actuator of the first embodiment, including preferred aspects. The actuator of the second embodiment may have any optional members as necessary, in addition to the first electrode, piezoelectric layer, and diaphragm. Examples of optional members include an insulating protective layer arranged on the main surface of the first electrode opposite the piezoelectric layer for the purpose of insulating and protecting the first electrode, and a moisture-proof layer arranged for the purpose of preventing deterioration of the piezoelectric layer due to humidity. The insulating protective layer in the actuator of the second embodiment can also be the same as the insulating protective layer in the actuator of the first embodiment, including preferred aspects.

The actuator of the second aspect will be described below with reference to Figs. 4 and 5, but the actuator of the second aspect is not limited thereto. The actuator of the second aspect shown in these figures can be modified as appropriate without departing from the spirit of the present invention. Figs. 4 and 5 are cross-sectional views showing an example of an embodiment of the actuator of the second aspect of the present invention and a modified example.

The actuator 12A shown in FIG. 4 has a piezoelectric layer 1 having a first main surface S1 and a second main surface S2, and a first electrode 2 and a vibration plate 4C arranged on the first main surface S1 and the second main surface S2 of the piezoelectric layer 1, respectively.

The vibration plate 4C is formed by stacking a first layer 41b, a second layer 42b, and a third layer 43b in the thickness direction from the piezoelectric layer 1 side. The first layer 41b is a conductor layer, and the second layer 42b and the third layer 43b are each made of a material different from that of the first layer 41b.

In the diaphragm 4C, if the Young's modulus of the material constituting the first layer 41b is _Y41b , the Young's modulus of the material constituting the second layer 42b is _Y42b , and the Young's modulus of the material constituting the third layer 43b is _Y43b , the following relationship holds between _Y41b , _Y42b , and _Y43b .
Y _41b <Y _42b <Y _43b

The actuator 12B shown in FIG. 5 has the same configuration as the actuator 12A shown in FIG. 3, except that it has an insulating protective layer 5 on the main surface of the first electrode 2 opposite the piezoelectric layer 1, and the vibration plate is a vibration plate 4D composed of four layers instead of the vibration plate 4C composed of three layers.

In the actuator 12B, the vibration plate 4D is formed by stacking a first layer 41b, a second layer 42b, a third layer 43b, and a fourth layer 44b in the thickness direction from the piezoelectric layer 1 side. In the vibration plate 4D, the first layer 41b is a conductor layer, and the second layer 42b, the third layer 43b, and the fourth layer 44b are each made of a material different from that of the first layer 41b.

In the diaphragm 4D, if the Young's modulus of the material making up the first layer 41b is _Y41b , the Young's modulus of the material making up the second layer _42b is Y42b, the Young's modulus of the material making up the third layer 43b is Y43b _{, and} the Young's modulus of the material making up the fourth layer 44b is _Y44b , then the following relationship holds between _Y41b , _Y42b , _Y43b , and _Y44b .
Y _41b <Y _42b <Y _43b <Y _44b

In the actuator of the second embodiment, the conductor layer on the piezoelectric layer side of the diaphragm functions in the same manner as the second electrode of the actuator of the first embodiment, and operates in the same manner as the actuator of the first embodiment described above. In the actuator of the second embodiment, the conductor layer on the piezoelectric layer side of the diaphragm also functions as a diaphragm.

In the actuators 12A and 12B, which are the actuators of the second embodiment, the vibration plate is composed of three or more layers in the thickness direction, and the relationship of the Young's modulus of each layer satisfies _Y41b < _Y42b < _Y43b and _Y41b < _Y42b < _Y43b < _Y44b , respectively. As a result, the displacement surface of the piezoelectric layer is set further outward, so that more efficient energy generation is obtained. In other words, the displacement of the piezoelectric layer can be transmitted to the vibration plate more efficiently. In addition, by adopting such a configuration, the stress concentration of the piezoelectric layer is alleviated during the formation of the vibration plate, and a stable manufacturing process can be established.

The amount of displacement δ of the diaphragm when it bends is determined by the deformation force F generated by the piezoelectric body and the neutral plane L that exists at a distance L in the thickness direction from the piezoelectric body/diaphragm interface in the diaphragm, and is expressed as δ ∝ F × L. Therefore, for a given deformation force F, a larger δ can be obtained by making L larger.

Generally, L is expressed by the following formula when the Young's modulus of the i-th layer and the cumulative film thickness are designated as E _i and h _i, respectively. Therefore, it is preferable to set E _i high in layers with larger i.
L=ΣE _i (h _i ² - h _i-1 ² )/2×ΣE _i (h _i - _{h i-1} )
Furthermore, in reality, it is preferable to avoid localization of the imaginary surface, which is difficult to expand and contract due to loss of generated force caused by deformation of the diaphragm, in the area close to the piezoelectric element, so it is preferable that Ei increases consistently as _i increases. Therefore, a structure of three or more layers, in which the Young's modulus increases with distance from the piezoelectric/diaphragm interface, is the best. The diaphragm can efficiently transmit the displacement of the piezoelectric layer.

The second embodiment of the actuator has a different configuration from the first embodiment of the actuator, namely the diaphragm, which will be described in detail below.

(Vibration plate)
In the actuator of the second aspect of the present invention, the vibration plate is configured such that three or more layers made of different materials are laminated in the thickness direction on the second main surface of the piezoelectric layer, at least the layer closest to the piezoelectric layer is a conductor layer, and the Young's modulus of the material of each layer increases in order from the layer closest to the piezoelectric layer to the layer furthest from the piezoelectric layer. The number of layers constituting the vibration plate in the actuator of the second aspect is not particularly limited as long as it is three or more, and is appropriately selected depending on the application. The number of layers constituting the vibration plate depends on the thickness of the entire vibration plate, the thickness and Young's modulus of each layer, but is preferably four or more in order to efficiently propagate the displacement of the piezoelectric layer.

The diaphragm in the actuator of the second embodiment can be the diaphragm in the actuator of the first embodiment, in which the layer closest to the piezoelectric layer is a conductor layer. The Young's modulus of the diaphragm in the actuator of the second embodiment is preferably within the range of approximately 80 to 700 GPa overall, while satisfying the above conditions. In other words, the lower limit of the Young's modulus of the material constituting the layer closest to the piezoelectric layer is preferably 10 GPa, and more preferably 300 GPa. Also, the upper limit of the Young's modulus of the material constituting the layer furthest from the piezoelectric layer is preferably 900 GPa.

The thickness of the diaphragm is adjusted as appropriate depending on the application of the actuator of the second embodiment and the Young's modulus of the diaphragm. When the actuator of the second embodiment is used in an inkjet head, it is preferable that the overall thickness of the diaphragm be within the range of 1.5 to 12 μm, from the viewpoint of achieving a thin design while increasing the displacement efficiency.

In the actuator of the second embodiment, the actuator 12A shown in FIG. 4 is an example in which the diaphragm has three layers, and the actuator 12B shown in FIG. 5 is an example in which the diaphragm has four layers.

In the diaphragm 4C of the actuator 12A, the first layer 41b is a conductive layer, and the Young's moduli Y _41b , Y _42b and Y _43b of the materials constituting the first layer 41b, the second layer 42b and the third layer 43b respectively satisfy the following relationship (1b-1).
(1b-1) Y _41b <Y _42b <Y _43b

From the viewpoint of enhancing the displacement efficiency of the piezoelectric layer 1, it is preferable that the Young's moduli _Y41b , _Y42b , and _Y43b satisfy the above-mentioned (1b-1) and further satisfy any one of the following relationships (1b-2) to (1b-4), more preferably satisfy two or more of them, and further preferably satisfy all of them.

(1b-2) 10GPa≦Y _41b
(1b-3) 1.05≦Y _42b /Y _41b ≦4.0
(1b-4) 1.05≦Y _43b /Y _42b ≦4.0

In (1b-2), the Young's modulus Y _41b of the conductive material constituting the first layer 41b is 10 GPa or more. The Young's modulus Y _41b being 60 GPa or more is preferable in that the Young's modulus of the entire diaphragm 4C can be increased and a high resonance frequency can be obtained. The Young's modulus Y _{41b is more preferably 100 GPa or more. The upper limit of the Young's modulus Y 41b is} preferably about 300 GPa from the viewpoint of satisfying the above (1b-1).

(1b-3) and (1b-4) are indices that indicate the extent to which the Young's modulus of the material constituting each layer increases as the layers constituting the diaphragm 4C become farther from the piezoelectric layer 1 in the order of the first layer 41b, the second layer 42b, and the third layer 43b.

(1b-3) defines the value " _Y42b / _Y41b " of the ratio of the Young's modulus _Y42b of the second layer _42b to the Young's modulus Y41b of the first layer 41b. When _Y42b / _Y41b is in the above range, the Young's modulus between the first layer 41b and the second layer 42b is sufficiently increased, and the relationship of (1b-1) is also satisfied, which is preferable. It is more preferable that _Y42b / _Y41b is in the range of 1.05 to 1.85.

(1b-4) defines the value "Y _43b /Y _42b " of the ratio of the Young's modulus Y _43b of the third layer 43b to the Young's modulus Y _42b of the second layer 42b. When Y _43b /Y _42b is equal to or greater than the lower limit, the Young's modulus between the second layer 42b and the third layer 43b increases sufficiently, which is preferable. When Y _43b /Y _42b is equal to or less than the upper limit, it is preferable that the total film thickness satisfies a preferable range, for example, 1.5 to 12 μm, while allowing room to increase the number of layers for the purpose of stress adjustment, etc. It is more preferable that Y _43b /Y _42b is within the range of 1.05 to 2.0.

Furthermore, the relationship between Y42b/ _Y41b and _Y43b / _Y42b , (1b-5) _Y42b / _Y41b : _Y43b / _Y42b, is preferably in the range of _{1:1 to 1:2. With Y42b/Y41b:Y43b/Y42b in this range ,} the Young's modulus increases nearly uniformly from the first layer to the third layer.

Considering the above (1b-1) as an essential requirement and (1b-2) to (1b-4) and further (1b-5), specifically, it is preferable that the Young's modulus Y _41b of the first layer 41b is in the range of 60 to 300 GPa, the Young's modulus Y _42b of the second layer 42b is in the range of 63 to 555 GPa, and the Young's modulus Y _43b of the third layer 43b is in the range of 66 to 900 GPa.

More preferably, the Young's modulus Y _41b of the first layer 41b is in the range of 100 to 300 GPa, the Young's modulus Y _42b of the second layer 42b is in the range of 105 to 555 GPa, and the Young's modulus Y _43b of the third layer 43b is in the range of 110 to 900 GPa.

The thicknesses of the first layer 41b, the second layer 42b, and the third layer 43b in the diaphragm 4C are indicated by _T41b , _T42b , and _T43b , respectively. In the case where the actuator 12A is used in an inkjet head, for example, in order to increase the displacement efficiency, it is preferable that _T41b , _T42b , and _T43b are each within the range of 0.5 to 4 μm, and more preferably within the range of 0.5 to 3.5 μm. Moreover, it is preferable that the total thickness of the diaphragm 4C, that is, _T41b + _T42b + _T43b , is within the range of 1.5 to 12 μm, from the viewpoint of achieving a thin structure while increasing the displacement efficiency.

As described above, the materials constituting the first layer 41b, second layer 42b, and third layer 43b of the diaphragm 4C may each be composed of a single element such as a metal, an alloy or compound containing two or more elements, or a combination of these. Furthermore, even if the materials constituting each layer are composed of the same elements, if they have different densities or crystal structures, they are considered to be different materials.

The materials constituting the first layer 41b, second layer 42b, and third layer 43b of the diaphragm 4C are not particularly limited, so long as the first layer 41b is a conductive material and the relationship with the materials constituting the other layers satisfies the relationship (1b-1).

The material constituting the first layer 41b of the diaphragm 4C may be any of the materials exemplified as the material constituting the diaphragm 4A that are conductive. Specifically, the conductive materials exemplified as the material constituting the first or second electrode may be used as the conductive material. Specifically, the materials constituting the second layer 42b and third layer 43b of the diaphragm 4C may be any of the materials exemplified as the material constituting the diaphragm 4A that satisfy the relationship (1b-1).

More preferably, the materials constituting each layer of the diaphragm 4C are selected so as to satisfy the above (1b-2) to (1b-4) and further (1b-5). The method for forming each layer can be appropriately selected from chemical methods such as CVD, physical methods such as sputtering and ion plating, and liquid phase growth methods such as the sol-gel method, depending on the constituent materials.

As a characteristic other than the Young's modulus of the material constituting each layer of the diaphragm 4C, it is preferable that the conductive material constituting the first layer 41a has the above characteristic (A). Also, as a characteristic other than the Young's modulus of the material constituting each layer of the diaphragm 4C, it is preferable that the material constituting the layer furthest from the piezoelectric layer 1, i.e., the third layer 43b, is mainly chromium or nickel.

Specific examples of combinations of the configurations of the layers of the diaphragm 4C include the combinations shown in Table VI below. The Young's modulus of each of these materials can be adjusted by the composition and manufacturing method, and the Young's modulus value required for each layer is specified in a relative relationship. Therefore, these examples do not exhaustively limit the materials used in each layer. In the table, DLC stands for diamond-like carbon. Also, since the conductor layer of the diaphragm requires an insulating layer to function as an electrode, at least one of the second and third layers in the above combinations must be made of a non-conductive material.

Next, the diaphragm 4D of the actuator 12B will be described. In the diaphragm 4D, the first layer 41b is a conductor layer, and the Young's moduli _Y41b , _Y42b , Y43b and Y44b of the materials constituting the first layer 41b, the second layer 42b, the third layer _43b and the fourth layer _44b respectively satisfy the following relationship (2b-1).
(2b-1) Y _41b <Y _42b <Y _43b <Y _44b

From the viewpoint of enhancing the displacement efficiency of the piezoelectric layer 1, it is preferable that the Young's moduli _Y41b , _Y42b , and _Y43b satisfy the above-mentioned (2b-1) and further satisfy any one of the following relationships (2b-2) to (2b-5), more preferably satisfy two or more of them, and further preferably satisfy all of them.

(2b-2) 10GPa≦Y _41b
(2b-3) 1.05≦Y _42b /Y _41b ≦4.0
(2b-4) 1.05≦Y _43b /Y _42b ≦4.0
(2b-5) 1.05≦Y _44b /Y _43b ≦4.0

The conditions shown in (2b-2) to (2b-4) above are the same as the conditions shown in (1b-2) to (1b-4) above. In other words, when the diaphragm is composed of four layers, the relationship of the Young's modulus of the first to third layers can be the same as the relationship of the Young's modulus of the first to third layers when the diaphragm is composed of three layers.

In (2b-2), the Young's modulus Y _41b of the conductive material constituting the first layer 41b is 10 GPa or more, preferably 60 GPa or more, which is preferable in that the Young's modulus of the entire diaphragm 4D can be increased and a high resonance frequency can be obtained for the purpose of driving the diaphragm. The Young's modulus Y _41b is more preferably 100 GPa or more. The upper limit of the Young's modulus Y _41b is preferably about 300 GPa from the viewpoint of satisfying the above (2b-1).

(2b-3), (2b-4), and (2b-5) are indices that indicate the extent to which the Young's modulus of the material constituting each layer increases as the layers constituting the diaphragm 4D become farther away from the piezoelectric layer 1 in the order of the first layer 41b, the second layer 42b, the third layer 43b, and the fourth layer 44b.

(2b-3) defines the value " _Y42b / _Y41b " of the ratio of the Young's modulus _Y42b of the second layer _42b to the Young's modulus Y41b of the first layer 41b. When _Y42b / _Y41b is in the above range, the Young's modulus between the first layer 41b and the second layer 42b is sufficiently increased, and the relationship of (2b-1) is also satisfied, which is preferable. It is more preferable that _Y42b / _Y41b is in the range of 1.05 to 1.5.

(2b-4) defines the value " _Y43b / _Y42b " of the ratio of the Young's modulus _Y43b of the third layer _43b to the Young's modulus Y42b of the second layer 42b. When _Y43b / _Y42b is in the above range, the Young's modulus between the second layer 42b and the third layer 43b is sufficiently increased, and the relationship of (2b-1) is also satisfied, which is preferable. It is more preferable that _Y43b / _Y42b is in the range of 1.05 to 1.8.

(2b-5) defines the value " _Y44b / _Y43b " of the ratio of the Young's modulus _Y44b of the fourth layer _44b to the Young's modulus Y43b of the third layer 43b. When _Y44b / _Y43b is equal to or greater than the lower limit, the Young's modulus between the third layer 43b and the fourth layer 44b is sufficiently increased, which is preferable. When _Y44b / _Y43b is equal to or less than the upper limit, it is preferable that the total film thickness is within a preferable range, for example, 2.0 to 12 μm, while there is room to increase the number of layers for the purpose of stress adjustment, etc. It is more preferable that _Y44b / _Y43b is within the range of 1.05 to 1.8.

In addition, the relationship between _Y42b / _Y41b and _Y43b / _Y42b , and the relationship between _Y43b / _Y42b and _Y44b / _Y43b are preferably in the range of 1:1 to 1:1.2 for (2b-6) _Y42b / _Y41b : _Y43b / _Y42b and 1:1 to 1:1.5 for _{Y43b/Y42b:Y44b/Y43b. By having Y42b / Y41b : Y43b / Y42b and Y43b} / _Y42b : _Y44b / _Y43b in the range, the Young's modulus increases almost uniformly from the first layer to the fourth layer.

Taking the above (2b-1) as an essential requirement and taking into consideration (2b-2) to (2b-5) and further (2b-6), specifically, it is preferable that the Young's modulus Y _41b of the first layer 41b is in the range of 60 to 300 GPa, the Young's modulus Y _42b of the second layer 42b is in the range of 63 to 450 GPa, the Young's modulus Y _43b of the third layer 43b is in the range of 66 to 810 GPa, and the Young's modulus Y _44b of the fourth layer 44b is in the range of 69 to 900 GPa.

More preferably, the Young's modulus Y _41b of the first layer 41b is in the range of 100 to 300 GPa, the Young's modulus Y _42b of the second layer 42b is in the range of 105 to 450 GPa, the Young's modulus Y _43b of the third layer 43b is in the range of 110 to 810 GPa, and the Young's modulus Y _44b of the fourth layer 44b is in the range of 116 to 900 GPa.

The thicknesses of the first layer 41b, the second layer 42b, the third layer 43b, and the fourth layer 44b in the vibration plate 4D are indicated by _T41b , _T42b , _T43b , and _T44b , respectively. In the case where the actuator 12B is used in an inkjet head, for example, in order to increase the displacement efficiency, it is preferable that _T41b , _T42b , _T43b , and _T44b are each within the range of 0.5 to 5.3 μm, and more preferably within the range of 0.5 to 4.7 μm. Moreover, it is preferable that the total thickness of the vibration plate 4D, that is, _T41b + _T42b + _T43b + _T44b , is within the range of 2.0 to 12 μm, from the viewpoint of achieving a thin structure while increasing the displacement efficiency.

The materials constituting each layer of the diaphragm 4D are not particularly limited, as long as the first layer 41b is a conductive material and the relationship with the materials constituting the other layers satisfies the relationship (2b-1).

The material constituting the first layer 41b of the diaphragm 4D may be any of the conductive materials given as examples of the materials constituting the diaphragm 4A. Specifically, the conductive materials given as examples of the materials constituting the first or second electrode may be used. Specifically, the materials constituting the second layer 42b, third layer 43b, and fourth layer 44b of the diaphragm 4D may be any of the materials given as examples of the materials constituting the diaphragm 4A that satisfy the relationship (2b-1).

The material constituting each layer of the diaphragm 4D is more preferably selected so as to satisfy the above (2b-2) to (2b-5) and further (2b-6). The method of forming each layer can be appropriately selected from chemical methods such as CVD, physical methods such as sputtering and ion plating, and liquid phase growth methods such as the sol-gel method, depending on the constituent material. In the case of a resin layer, it can be formed by, for example, spin coating, dipping, or electrodeposition.

As a characteristic other than the Young's modulus of the material constituting each layer of the diaphragm 4D, it is preferable that the conductive material constituting the first layer 41b has the above characteristic (A). Also, as a characteristic other than the Young's modulus of the material constituting each layer of the diaphragm 4D, it is preferable that the material constituting the layer furthest from the piezoelectric layer 1, i.e., the fourth layer 44b, is mainly chromium or nickel.

Specific examples of combinations of the layers of the diaphragm 4D are shown in Table V below. The Young's modulus of each of these materials can be adjusted by the composition and manufacturing method, and the Young's modulus value required for each layer is specified in a relative relationship. Therefore, this example does not cover or limit the materials used in each layer. In the table, DLC stands for diamond-like carbon. In addition, since the conductor layer of the diaphragm needs an insulating layer to function as an electrode, at least one of the second and third layers in the above combinations must be made of a non-conductive material.

The actuator of the second embodiment has been described above using an example in which the diaphragm is composed of three or four layers. In the case in which the diaphragm is composed of five or more layers, the Young's modulus of each layer may be appropriately selected taking into consideration the preferred range of Young's modulus for the entire diaphragm shown above, approximately 80 to 700 GPa, and the range of Young's modulus for the entire diaphragm calculated from Tables IV and V, 127 to 640 GPa, and also taking into consideration the balance of the increase in Young's modulus from the layer closest to the piezoelectric layer to the layer furthest from the piezoelectric layer, for example, an increase that is nearly uniform. In addition, even in the case in which the diaphragm is composed of five or more layers, the preferred characteristics of the material that constitutes the layer closest to the piezoelectric layer are as described above, and the preferred characteristics of the material that constitutes the layer furthest from the piezoelectric layer are as described above.

The layers constituting the diaphragm of the actuator of the second embodiment may be configured so that the Young's modulus within the layer gradually increases from the main surface closer to the piezoelectric layer 1 toward the main surface farther from the piezoelectric layer 1. In that case, for example, in the case of diaphragm 4C, the Young's modulus of the first layer on the side farther from the piezoelectric layer 1 is smaller than the Young's modulus of the second layer on the side farther from the piezoelectric layer 1, and the Young's modulus of the second layer on the side farther from the piezoelectric layer 1 is smaller than the Young's modulus of the third layer on the side closer to the piezoelectric layer 1.

When the actuator of the present invention is used in, for example, an inkjet head, it is preferable that at least one of the layers in the diaphragm is made of a brittle material that exhibits brittle fracture when subjected to stress at room temperature. This makes it possible to obtain a large generated pressure from the mechanical displacement energy of the piezoelectric layer 1. Examples of brittle materials include inorganic ceramic materials made of oxides such as aluminum oxide and zirconium oxide, and nitrides such as silicon nitride, as well as cast iron and tungsten.

By incorporating a layer of such a brittle material into the diaphragm of the actuator of the first embodiment and the actuator of the second embodiment so as to meet the above essential conditions and, if necessary, any conditions, it becomes possible to optimize the process for manufacturing the diaphragm and optimize ink ejection.

The actuator of the first aspect of the present invention can be manufactured, for example, by a method having the following steps (1) to (6).

(1) Step of forming a first electrode on a substrate The substrate used here is removed in the following step (6). A vapor phase growth method such as sputtering deposition can be used to form the first electrode on the substrate.
(2) Step of forming a piezoelectric layer on the first electrode. To form the piezoelectric layer, a vapor phase growth method such as sputtering deposition or a sol-gel method can be used depending on the constituent material.

(3) Process for forming wiring part insulating pattern layer The second electrode and the first electrode formed subsequently need to have wiring extending to the drive circuit in addition to the part that sandwiches the piezoelectric body and activates it. Since this wiring part is also formed on the first surface and the second surface of the piezoelectric layer, respectively, sandwiching the piezoelectric layer, in the region other than the piezoelectric activation part facing the pressure chamber, it is preferable that an insulating pattern layer having a sufficient thickness is provided in the desired region to prevent the piezoelectric body from being activated by being sandwiched between the wiring and to prevent unexpected short circuits.

This wiring insulation pattern layer can be obtained, for example, by applying an insulating resin such as a photosensitive polyimide resin, exposing the resin to light in a pattern before curing, and selectively curing the resin. Note that instead of the process of forming such a wiring insulation pattern layer, a desired patterning may be used for the second electrode to avoid overlapping of the desired first electrode with the piezoelectric layer. The following is a description of the case where a wiring insulation pattern layer is provided.

(4) Step of forming a second electrode on the piezoelectric layer and the wiring portion insulating pattern layer. The second electrode can be formed by a vapor phase growth method such as sputtering deposition.

(5) Step of forming a diaphragm on the second electrode The diaphragm is composed of three or more layers made of different materials. Each layer of the diaphragm is formed in a stacking order in which the Young's modulus increases from the side closer to the second electrode to the direction away from the second electrode. Each layer constituting the diaphragm can be formed by electrochemical deposition, coating deposition methods such as spin coating, or vapor deposition methods such as sputtering deposition, depending on the material constituting the layer.
(6) Step of Removing the Substrate Dry or wet etching can be used to remove the substrate.

Furthermore, when an insulating protective layer is provided on the first electrode, the actuator of the first embodiment is usually obtained by the following steps.
(7) Step of Patterning the First Electrode To pattern the first electrode, a method of resist patterning followed by dry etching can be used.
(8) Step of Patterning the Piezoelectric Layer After (7), in order to further pattern the piezoelectric layer, a method of resist patterning followed by dry etching can be used.

(9) Step of forming an insulating protection layer on the surface of the patterned first electrode The insulating protection layer can be formed by a coating method such as spin coating, or a vapor phase growth method such as sputtering. The insulating protection layer may be formed not only on the surface of the first electrode but also on the surface of the piezoelectric layer depending on the patterns of the first electrode and the piezoelectric layer.

The actuator of the second aspect of the present invention can be manufactured in the same manner as above, except that in the manufacturing process of the actuator of the first aspect, step (4) is omitted and the formation of the diaphragm of step (5) is performed on the piezoelectric layer and the wiring insulating pattern layer. However, the diaphragm in the actuator of the second aspect is configured such that the side closest to the piezoelectric layer is composed of a conductor layer, and the diaphragm is composed of three or more layers including the conductor layer, and the Young's modulus increases in the order from the conductor layer to the layer furthest from the piezoelectric layer.

[Inkjet head]
The inkjet head of the present invention is characterized by comprising: the actuator of the present invention; a pressure chamber filled with ink and in which the pressure of the ink changes when the actuator is driven; and a nozzle that ejects the ink filled in the pressure chamber when the actuator is driven.

Figure 6 is a top view of an example of an embodiment of an inkjet head of the present invention. Figure 7 is a cross-sectional view taken along line Y-Y of the inkjet head shown in Figure 6. Figure 8 is an enlarged cross-sectional view taken along line Y-Y of the inkjet head shown in Figure 6. Note that the inkjet head of the present invention is not limited to these. The inkjet head of the present invention shown in these figures can be modified as appropriate without departing from the spirit of the present invention.

As shown in Figures 6 to 8, the inkjet head 100 includes an actuator 12C in which multiple sets of a piezoelectric layer 1, a first electrode 2, and an insulating protective layer 5 are arranged on a vibration plate 4D, and a main substrate 51 and a nozzle substrate 52 that have main surfaces of the same size and shape as the actuator 12C in a plan view.

The main substrate 51 has a through hole that becomes a pressure chamber 70 filled with ink, and the vibration plate 4D side of the actuator 12C is bonded to one main surface of the main substrate 51, and the nozzle substrate 52 is bonded to the other main surface to form the inkjet head 100. The pressure chamber 70 is a space formed by the wall surface S3 of the through hole in the main substrate 51, the main surface S4 of the vibration plate 4D of the actuator 12C, and the main surface S5 of the nozzle substrate 52 on the side bonded to the main substrate 51.

In the inkjet head 100, the main surface of the main substrate 51 is rectangular, and the pressure chambers 70 are generally circular when viewed from above (see FIG. 6). Multiple pressure chambers 70 (seven on each side in FIG. 6) are arranged at approximately equal intervals on two straight lines parallel to the long sides of the main substrate 51.

In actuator 12C, the piezoelectric layer 1 is formed on vibration plate 4D in a similar shape (approximately circular) that is approximately equidistant from the outer periphery of pressure chamber 70 in plan view. A first electrode 2 and an insulating protective layer 5 having a main surface of the same size and shape as the first main surface S1 are laminated on the first main surface S1 of the multiple piezoelectric layers 1. Actuator 12C corresponds to the actuator of the second aspect of the present invention, and the piezoelectric layer 1, first electrode 2, insulating protective layer 5, and vibration plate 4D of actuator 12C can be configured similarly to the piezoelectric layer 1, first electrode 2, insulating protective layer 5, and vibration plate 4D of actuator 12B.

The nozzle substrate 52 has nozzles 60 that correspond to each pressure chamber 70 and penetrate from the main surface S5 that faces the pressure chamber 70 to the main surface S6 on the opposite side of the main surface S5.

The pressure chamber 70 of the inkjet head 100 is filled with ink. During printing, a voltage is applied to the actuator 12C, displacing the vibration plate 4D so that it has a curvature toward the nozzle substrate 52. This increases the pressure of the ink in the pressure chamber 70, causing it to be ejected from the nozzle 60.

In the inkjet head of the present invention, the actuator of the present invention has high displacement efficiency, so ink can be ejected efficiently.

The inkjet head of the present invention can be manufactured, for example, by a method including the following steps (11) and (12).

(11) Step of forming pressure chambers in actuator Possible means for laminating and forming pressure chambers in the actuator include aligning a patterned main body substrate for the pressure chambers (plate-shaped pressure chamber member) with the diaphragm surface of the actuator and bonding/adhering the same.

In addition, as in the embodiment described below, when the outermost layer of the diaphragm that contacts the pressure chamber is formed from a metal having the same composition as the main component of the material forming the main body substrate for the pressure chamber, the main body substrate for the pressure chamber (plate-shaped pressure chamber member) can be obtained by directly plating (electroforming) the surface of the actuator facing the diaphragm. Specifically, the metal layer of the outermost layer of the diaphragm is used as a seed layer for plating, a negative pattern of the pressure chamber pattern is formed on the surface with photoresist, electroplating is performed, and the resist is removed, so that a structure equivalent to the wall surface of the pressure chamber (main body substrate for the pressure chamber) can be directly processed into the actuator. The pressure chamber formed in this way has favorable dimensional accuracy and hardness.

(12) A process of merging a nozzle substrate having a nozzle with a main substrate for a pressure chamber equipped with an actuator The nozzle substrate is bonded and adhered to a main substrate for a pressure chamber equipped with an actuator. If necessary, a flow path substrate having a flow path communicating with the nozzle of the nozzle substrate may be provided between the main substrate for the pressure chamber and the nozzle substrate. In this case, the nozzle substrate and the flow path substrate are bonded and adhered to each other, and are further bonded and adhered to a main substrate for a pressure chamber equipped with an actuator.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these. In the examples, the terms "parts" and "%" are used, but unless otherwise specified, they represent "parts by mass" or "% by mass."

[Example 1]
Actuator I of the first embodiment having the configuration shown in Table VI was fabricated by the following method. Table VI shows the active parts of the piezoelectric layer that correspond to the pressure chambers. The same applies to Tables VII to XI and XIII below. In any case, different elements may be laminated in the inactive parts of the piezoelectric layer (corresponding to the partition walls of the pressure chambers).

Actuator I has a laminated structure with an insulating protective layer on the first electrode 2 in actuator 11A shown in FIG. 1. However, the wiring insulating pattern layer is omitted in FIG. 1.

The first electrode was obtained by using a Pt target and forming the electrode in argon gas at 1 Pa with 200 W high-frequency power for 12 minutes while heating the substrate to 600°C.

The piezoelectric layer was fabricated using a multi-target sputtering device. A sintered PZT target (Zr/Ti=53/47, 20 mol% excess Pb) with a larger Pb content than the stoichiometric composition was used as the target. The substrate was preheated in a vacuum using a heater, and the piezoelectric layer was formed for 180 minutes at a substrate temperature of 580° C. in a mixed atmosphere of argon and oxygen (gas volume ratio Ar:O ₂ =15:5) with a vacuum degree of 0.3 Pa and a high-frequency power of 250 W.

Next, a wiring insulating pattern layer that insulates the first electrode from the second electrode in the inactive part of the piezoelectric layer was formed in the area other than the active part of the piezoelectric layer corresponding to the pressure chamber by applying a photosensitive polyimide resin (Pimel (product name, manufactured by Asahi Kasei Corporation) by spin coating and performing selective hardening patterning with a photoresist.

The second electrode was obtained by forming it using an Au target at room temperature in argon gas at 1 Pa with a high-frequency power of 100 W for 10 minutes.

The first layer of the diaphragm was obtained by forming it with a silicon nitride (hereinafter referred to as "SiN") target at room temperature in argon gas at 0.5 Pa with a high frequency power of 250 W for 90 minutes. The second layer of the diaphragm was obtained by forming it with an aluminum nitride (hereinafter referred to as "AlN") target at room temperature in argon gas at 0.5 Pa with a high frequency power of 250 W for 55 minutes. The third layer of the diaphragm was obtained by forming it with a titanium nitride (hereinafter referred to as "TiN") target at room temperature in argon gas at 0.5 Pa with a high frequency power of 250 W for 90 minutes.

The insulating protective layer was obtained by spin coating and ultraviolet irradiation using a photosensitive polyimide resin (Pimel (product name, manufactured by Asahi Kasei Corporation), indicated as "PI" in the table).

[Example 2]
The actuator II of the first embodiment having the configuration shown in Table VII was fabricated by the following method. The actuator II has the same layered configuration as the actuator 11B shown in Fig. 2, except that the number of layers of the diaphragm in the actuator 11B is five. However, in Fig. 2, the wiring portion insulating pattern layer is omitted.

The first electrode, piezoelectric layer, wiring insulation pattern layer, and second electrode of Actuator II were fabricated in the same manner as Actuator I.

The first layer of the diaphragm was obtained by spin coating and ultraviolet irradiation using a photosensitive polyimide resin (Pimel (product name, manufactured by Asahi Kasei Corporation), indicated as "PI" in the table). The second layer of the diaphragm was obtained by forming the layer using a _SiO2 target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W for 90 minutes.

The third layer of the diaphragm was obtained by forming it for 80 minutes using a _ZrO2 target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W. The fourth layer of the diaphragm was obtained by forming it for 100 minutes using a _MgO target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W. The fifth layer of the diaphragm was obtained by forming it for 40 minutes using an _Al2O3 target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W.

The substrate was removed by plasma etching, and an insulating protective layer was fabricated in the same manner as for actuator I.

[Example 3]
The actuator III of the second embodiment having the configuration shown in Table VIII was fabricated by the following method. The actuator III has the same layered structure as the actuator 12B shown in Fig. 5. However, in Fig. 5, the wiring portion insulating pattern layer is omitted.

The first electrode, piezoelectric layer, and wiring insulating pattern layer in actuator III were fabricated in the same manner as actuator I.

The first layer of the diaphragm was obtained by forming it with a Cu target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 200 W for 50 minutes. The second layer of the diaphragm was obtained by forming it with a Cr target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 200 W for 55 minutes.

The third layer of the diaphragm was obtained by forming it for 40 minutes using an AlN target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W. The fourth layer of the diaphragm was obtained by forming it for 100 minutes using _{an Al2O3} target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W.

The substrate was removed by plasma etching, and an insulating protective layer was fabricated in the same manner as for actuator I.

[Example 4]
Actuator IV of the second embodiment having the configuration shown in Table IX was fabricated by the following method. Actuator IV has the same layered structure as actuator 12B shown in Fig. 5. However, in Fig. 5, the wiring portion insulating pattern layer is omitted.

The first electrode, piezoelectric layer, and wiring insulating pattern layer of actuator IV were fabricated in the same manner as actuator I.

The first layer on the diaphragm was obtained by forming it with a Pd target at room temperature in argon gas at 0.5 Pa and high-frequency power of 200 W for 30 minutes. The second layer on the diaphragm was obtained by forming it with a Cr target at room temperature in argon gas at 0.5 Pa and high-frequency power of 250 W for 50 minutes.

The third layer of the diaphragm was obtained by forming it for 55 minutes using an AlN target at room temperature in argon gas at 0.5 Pa with a high frequency power of 250 W. The fourth layer of the diaphragm was obtained by forming it for 100 minutes using _{an Al2O3} target at room temperature in argon gas at 0.5 Pa with a high frequency power of 250 W.

The substrate was removed by plasma etching, and an insulating protective layer was fabricated in the same manner as for actuator I.

[Comparative Example 1]
Comparative actuator Cf-I having the configuration shown in Table X was fabricated by the following method. The first electrode, piezoelectric layer, wiring portion insulating pattern layer, and second electrode of actuator Cf-I were fabricated in the same manner as actuator I.

The first layer on the diaphragm was obtained by forming it with a TiN target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W for 90 minutes. The second layer on the diaphragm was obtained by forming it with an AlN target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W for 55 minutes. The third layer on the diaphragm was obtained by forming it with a SiN target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W for 90 minutes.

The substrate was removed by plasma etching, and an insulating protective layer was fabricated in the same manner as for actuator I.

[Comparative Example 2]
Comparative actuator Cf-II having the configuration shown in Table XI was fabricated by the following method. The first electrode, the piezoelectric layer, the wiring insulating pattern layer, and the second electrode of actuator Cf-II were fabricated in the same manner as actuator I.

The first layer of the diaphragm was obtained by forming it for 42 minutes using _{an Al2O3} target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W. The second layer of the diaphragm was obtained by forming it for 90 minutes using a _SiO2 target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W. The third layer of the diaphragm was obtained by forming it for 80 minutes using a _ZrO2 target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W. The fourth layer of the diaphragm was obtained by forming it for 105 minutes using an MgO target at room temperature in argon gas at 0.5 Pa with a high-frequency power of 250 W.

The substrate was removed by plasma etching, and an insulating protective layer was fabricated in the same manner as for actuator I.

[Evaluation of Displacement Amount (1)]
The actuators of the examples and comparative examples prepared above are designed so that the assumed driving frequency when the actuator is incorporated into an inkjet head and used is equal to the natural frequency of the actuator diaphragm when filled with ink. The displacement amount was evaluated by applying a driving voltage consisting of a corrected resonance frequency obtained by correcting the head driving frequency to a system not filled with ink to the actuator alone, and directly measuring the minute displacement amount [nm] of the actuator at that time with a laser Doppler vibrometer.

Specifically, the percentage increase in the displacement of each actuator relative to the average (average between levels) of the displacements [nm] of all actuators was calculated using the following formula (I), and the results were evaluated according to the following criteria. The results are shown in Table XII.
Formula (I) (displacement amount-average of displacement amount)/average of displacement amount×100

(Evaluation Criteria)
◎: 5% or more 〇: 0% or more but less than 5% ×: Less than 0% (negative)

As can be seen from Table XII, all of the examples of the present invention showed superior displacement characteristics compared to the comparative examples under the same driving frequency conditions.

[Example 5]
Furthermore, using actuator IV shown in the embodiment as an example, it was evaluated as follows that the use of a platinum group metal in the first layer of the diaphragm in the actuator of the present invention reduces the deterioration of the piezoelectric body.

To compare with Actuator IV, Actuator V was fabricated as follows, in which the material of the first layer of the diaphragm in Actuator IV was changed from Pd to Ti. Furthermore, the effect of this difference in structure on the reduction degradation of the actuator was evaluated.

The Young's modulus of Pd and Ti are relatively close (Pd: 121 GPa, Ti: 116 GPa) and the electrical resistivity is also similar (bulk resistivity is on the order of 100 nΩ·m for both, Pd: 105 nΩ·m, Ti: 420 nΩ·m), so they are essentially equivalent materials in terms of basic function when used as materials for the diaphragm, the first layer of which is a conductor in the actuator of the second embodiment. However, there is a difference in the standard electrode potential between palladium, which is a platinum group metal, and titanium, which is a titanium group metal (Pd: +0.987 V, Ti: -1.630 V).

Specifically, the actuator V of the second embodiment having the configuration shown in Table XIII was fabricated by the following method. The actuator V has the same layered structure as the actuator 12B shown in FIG. 5. However, in FIG. 5, the wiring portion insulating pattern layer is omitted.

The first electrode, piezoelectric layer, and wiring insulation pattern layer of actuator V were fabricated in the same manner as actuator I.

The first layer of the diaphragm was obtained by forming it with a Ti target at room temperature in argon gas at 0.5 Pa and high frequency power of 200 W for 30 minutes. The second layer of the diaphragm was obtained by forming it with a Cr target at room temperature in argon gas at 0.5 Pa and high frequency power of 250 W for 50 minutes. The third layer of the diaphragm was obtained by forming it with an AlN target at room temperature in argon gas at _0.5 Pa and high frequency power of 250 W for 55 minutes. The fourth layer of the diaphragm was obtained by forming it with an _Al2O3 target at room temperature in argon gas at 0.5 Pa and high frequency power of 250 W for 100 minutes.

The substrate was removed by plasma etching, and an insulating protective layer was fabricated in the same manner as for actuator I.

[Evaluation of Displacement Amount (2)]
The amount of displacement when a predetermined voltage was applied to Actuator IV and Actuator V was evaluated by direct measurement using a laser Doppler vibrometer similar to the method for evaluating the amount of displacement (1) above. The results are shown in Table XIV. The materials used are almost equivalent as the materials for the diaphragm in the actuator of the second embodiment, and both Actuator IV and Actuator V were formed with the Young's modulus of all layers constituting the diaphragm within a preferred range, so both showed good displacement.

[Evaluation of heat resistance]
Actuator IV and actuator V in which the first layer of the diaphragm was replaced with Ti were each placed under a condition of 60° C., and a pulse voltage (15 V applied, duty ratio 0.2, frequency 100 kHz) was continuously applied to perform a durability test.

To evaluate durability, the actuator was removed after a certain period of time, and the capacitance of the actuator was compared using LCR measurements when it was treated as a capacitor. The results are shown in Table XV.

In all time series data exceeding 10 hours, the rate of decrease in capacitance of Actuator IV, in which Pd, a platinum group metal, is used in the first diaphragm layer located at the boundary between the diaphragm and the piezoelectric layer, was lower than the rate of decrease in capacitance of Actuator V, in which Ti, a titanium group metal, is used in the first diaphragm layer located at the boundary between the diaphragm and the piezoelectric layer.

The decrease in capacitance indicates an apparent decrease in the dielectric constant of the piezoelectric body, which is a dielectric material sandwiched between the electrodes. Therefore, in actuator V, which showed a greater decrease in capacitance through durability testing, oxygen was extracted from the piezoelectric body to the Ti layer of the first diaphragm layer in the area close to the electrodes of the piezoelectric body, resulting in the formation of an area with slightly increased conductivity.

However, in actuator IV, Pd, a platinum group metal, is used in the first diaphragm layer located at the boundary between the diaphragm and the piezoelectric layer. This suppresses the diffusion of oxygen at the interface and between the layers of the piezoelectric and diaphragm, suppressing reductive deterioration of the piezoelectric layer and increasing the reliability of the actuator, including the risk of leakage current. Therefore, it has been confirmed that in the actuator of the second embodiment, when the first layer of the diaphragm contains a platinum group metal, it is more preferable in that reductive deterioration of the piezoelectric can be prevented.

Reference Signs List 11A, 11B Actuator of first embodiment 12A, 12B, 12C Actuator of second embodiment 1 Piezoelectric layer 2 First electrode 3 Second electrode 4A, 4B, 4C, 4D Vibration plate 41a, 41b First layer 42a, 42b Second layer 43a, 43b Third layer 44a, 44b Fourth layer 5 Insulating protective layer 6 Substrate 7 Penetration portion 8 Driving circuit 100 Inkjet head 70 Pressure chamber 51 Main body substrate 52 Nozzle substrate 60 Nozzle

Claims (7)

An actuator comprising: a piezoelectric layer having a first main surface and a second main surface; a first electrode and a second electrode disposed on the first main surface and the second main surface of the piezoelectric layer, respectively; and a vibration plate disposed on an opposite side of the second electrode to the piezoelectric layer,
an actuator, characterized in that the vibration plate is formed by laminating at least three layers made of different materials in a thickness direction, and the Young's modulus of the materials constituting each of the vibration plate layers increases in order from the layer closer to the second electrode to the layer furthest from the second electrode, the three layers being a first layer, a second layer and a third layer from the second main surface of the piezoelectric layer to the layer furthest from the piezoelectric layer, and the Young's modulus of the material constituting the first layer is Y41a _, the Young's modulus of the material constituting the second layer is Y42a _, and the Young's modulus of the material constituting the third layer is Y43a _, the Young's modulus Y41a _, Y42a _and Y43a _satisfy the following relationships (1a-2) to (1a-4) .
(1a-2) 10GPa≦Y _41a
(1a-3) 1.05≦Y _42a /Y _41a ≦4.0
(1a-4) 1.05≦Y _43a /Y _42a ≦4.0 An actuator comprising: a piezoelectric layer having a first main surface and a second main surface; a first electrode disposed on the first main surface of the piezoelectric layer; and a vibration plate disposed on the second main surface of the piezoelectric layer,
the vibration plate has a conductor layer disposed on the second main surface of the piezoelectric layer, and at least three layers stacked in a thickness direction on a side of the conductor layer opposite to the piezoelectric layer, the layers being made of a material different from the material constituting the conductor layer;
an actuator comprising: a diaphragm configured such that the Young's modulus of materials constituting the conductor layer and each of the layers increases in that order from the conductor layer toward the layer furthest from the piezoelectric layer; the conductor layer and the three layers are, from the second main surface of the piezoelectric layer toward the layer furthest from the piezoelectric layer, a first layer, a second layer, a third layer, and a fourth layer; a Young's modulus of a material constituting the first layer is Y41b _; a Young's modulus of a material constituting the second layer is Y42b _; a Young's modulus of a material constituting the third layer is Y43b _; and a Young's modulus of a material constituting the fourth layer is Y44b _; the Young's modulus Y41b _, Y42b _, Y43b _, and _Y44b satisfy the following relationships (2b-2) to (2b-5) .
(2b-2) 10GPa≦Y _41b
(2b-3) 1.05≦Y _42b /Y _41b ≦4.0
(2b-4) 1.05≦Y _43b /Y _42b ≦4.0
(2b-5) 1.05≦Y _44b /Y _43b ≦4.0 The actuator according to claim 1 or 2, characterized in that the material constituting the layer of the vibration plate closest to the piezoelectric layer is a material that suppresses a reduction reaction in the piezoelectric layer. The actuator according to claim 3, characterized in that the material that inhibits the reduction reaction is a metal whose standard electrode potential is greater than -0.126 V, or a conductive material that contains the metal. The actuator according to claim 3 or 4, characterized in that the material that inhibits the reduction reaction is a platinum group metal selected from platinum, iridium, palladium, rhodium, and ruthenium, or a conductive material containing the platinum group metal. An actuator according to any one of claims 1 to 5, characterized in that the material constituting the layer of the diaphragm farthest from the piezoelectric layer is mainly chromium or nickel. An actuator according to any one of claims 1 to 6;
a pressure chamber filled with ink, the pressure of the ink being changed by driving the actuator;
a nozzle that ejects the ink filled in the pressure chamber by driving the actuator.
An inkjet head comprising:

Images