JP4082424B2 - Inkjet head - Google Patents

Description

  The present invention relates to a method for manufacturing an ink jet head, which is a main part of an ink jet head recording apparatus, which ejects ink droplets only when recording is necessary and adheres them to a recording paper surface.

  The ink jet recording apparatus has many advantages such as extremely low noise during recording, high-speed printing, and use of inexpensive plain paper with a high degree of freedom of ink. Among them, a so-called ink-on-demand system that discharges ink droplets only when recording is necessary does not require collection of ink droplets that are not necessary for recording, and is currently mainstream.

  Ink-jet head recording apparatuses for ink-on-demand recording include an ink-jet head recording apparatus (Japanese Patent Laid-Open No. 6-71882) using electrostatic force as a driving means as a method for ejecting ink. Has the advantage of small size, high density, high printing quality and long life.

  Further, as a means for forming the diaphragm by etching the Si substrate, an etching stop technique described in Japanese Patent Application No. 8-43602, page 7, line 9 is used. A method has been adopted in which only the type impurity layer is left by etching, and a Si thin film to be a vibration plate is formed with high accuracy.

Japanese Patent Laid-Open No. 6-71882 Japanese Patent Application No. 8-43602

    However, when the Si substrate on which the vibration plate is formed is assembled to the head and driven for a long period of time, stress concentrates on the connection portion between the partition wall and the vibration plate constituting the discharge chamber, and this concentration of stress causes cracks in the vibration plate connection portion. Running, the ink penetrates into the gap between the diaphragm and the counter electrode necessary for electrostatic driving, and there is a problem that driving becomes impossible. Therefore, the present invention solves the problems as described above, the purpose of which is to increase the mechanical strength of the connecting portion between the partition wall and the diaphragm, improve the durability of the diaphragm against long-term driving, An object of the present invention is to provide a method for manufacturing a highly reliable inkjet head.

The inkjet of the present invention is
Single or a plurality of nozzle holes for discharging ink droplets, a discharge chamber connected to each of the nozzle holes, a vibration plate constituting at least one wall of the discharge chamber, and deformation of the vibration plate Drive means, and the drive means comprises an electrode that deforms the vibration plate to electrostatic force, and in the inkjet head in which the substrate on which the vibration plate is formed is a Si substrate, the partition wall portion that forms the discharge chamber, and the A slope portion is provided at the connection portion of the diaphragm.

  Further, in the method of manufacturing an ink jet head, the vibration plate is a Si substrate made of a high concentration p-type impurity layer, and the high concentration of the Si substrate opposite to the surface on which the high concentration p-type impurity layer is formed. Etching of the Si substrate to the vicinity of the p-type impurity layer is performed with a high concentration potassium hydroxide aqueous solution, and etching from the vicinity of the high concentration p-type impurity layer to the high concentration p-type impurity layer is performed with a low concentration potassium hydroxide aqueous solution. And the diaphragm is formed by leaving the high-concentration p-type impurity layer.

  Further, in the method of manufacturing an ink jet head, the vibration plate is a Si substrate made of a high concentration p-type impurity layer, and the high concentration of the Si substrate opposite to the surface on which the high concentration p-type impurity layer is formed. Etching of the Si substrate up to the vicinity of the p-type impurity layer is performed using an oxide mask patterned with a plurality of thicknesses using an etching mask.

  The low concentration potassium hydroxide aqueous solution has a concentration of 0.5 to 10 wt%, or the high concentration potassium hydroxide aqueous solution has a concentration of 35 to 55 wt%.

    By forming the inclined surface at the connecting portion between the partition wall and the diaphragm constituting the discharge chamber of the inkjet head, the stress concentration on the connecting portion between the partition wall and the diaphragm is reduced, and the durability of the connecting portion is improved. And the reliability in the long-term drive of an inkjet head can be improved by preventing the failure | damage of the diaphragm by the stress concentration to a connection part.

Example 1
FIG. 1 is an exploded perspective view of the ink jet head according to the first embodiment of the present invention, and is a partial cross-sectional view. This embodiment shows an example of a face inkjet head that ejects ink droplets from nozzle holes provided on the surface of a substrate. 2 is a side sectional view of the assembled entire apparatus, and FIG. 3 is a view taken along the line AA ′ in FIG. The ink jet head of this embodiment has a laminated structure in which three substrates 1, 2, 3 having a structure described in detail below are stacked and joined.

  The intermediate first substrate 1 is a Si substrate, and constitutes a recess 7 that constitutes a discharge chamber 6 having a bottom wall as a diaphragm 5 and an orifice 8 provided at the rear of the recess 7. A narrow groove 9 for an ink inflow port, and a recess 11 that constitutes a common ink cavity 10 for supplying ink to each discharge chamber 6. A slope 20 is provided on the connecting portion 19 between the partition wall 18 and the diaphragm 5. An oxide film having a thickness of 0.1 microns is formed on the entire surface of the first substrate by thermal oxidation to form an insulating film. This is to prevent dielectric breakdown and short-circuit during ink jet driving.

  The second substrate 2 bonded to the lower surface of the first substrate 1 uses borosilicate glass, and the recess 14 for mounting the electrode 15 on the first substrate 1 is etched by 0.3 microns. A gap G, that is, a gap G, is formed between the diaphragm 5 and the electrode 15 disposed to face the diaphragm 5. The concave portion 14 is patterned in a slightly larger shape similar to the shape of the electrode portion so that the electrode 15, the lead portion 16 and the terminal 17 can be mounted therein. The electrode is manufactured by sputtering ITO into the recess 14 by 0.1 microns to form an ITO pattern. Therefore, the gap G after the anodic bonding of the first substrate 1 and the second substrate 2 in this embodiment is 0.2 microns.

  Further, a Si substrate having a thickness of 100 microns is used as the third substrate 3 bonded to the upper surface of the first substrate, and nozzles are respectively connected to the surface portion of the substrate 3 so as to communicate with the recess 7 for the discharge chamber 6. A hole 12 is provided, and an ink supply port 13 is provided so as to communicate with the recess 11 for the ink cavity 10.

  The operation of the ink jet head configured as described above will be described. When a pulse electrode of 0V to 35V is applied to the electrode 15 by the transmission circuit 23 and the surface of the electrode 15 is positively charged, the lower surface of the corresponding diaphragm 5 is charged to a negative potential. Therefore, the diaphragm 5 bends downward due to electrostatic attraction. Next, when the electrode 15 is turned off, the diaphragm 5 is restored. For this reason, the pressure in the discharge chamber 6 rapidly increases, and the ink droplets 21 are discharged from the nozzle holes 12 toward the recording paper 22. Next, when the vibration plate 5 is bent downward again, ink is supplied from the ink cavity 10 into the discharge chamber 6 through the orifice 8. The connection between the substrate 1 and the transmission circuit 23 is made in an oxide film window (not shown) opened in a part of the substrate 1 by dry etching. Further, ink is supplied to the inkjet head through the ink supply port 13 at the end of the ink cavity 10.

  In the first embodiment of the present invention, when the inclined surface is formed on the diaphragm and the partition wall of the ink jet head, the manufacturing method of the first substrate 1 is the diffusion process diagram of the first substrate of FIG. 4 and the first of FIG. In the substrate etching process diagram, a case where a diaphragm having a thickness of 2 microns is formed using B2O3 as an impurity diffusion source will be described in detail.

  The diaphragm in the ink jet head of this example is a Si thin film in which P-type impurities are diffused at a high concentration. This Si thin film is manufactured by utilizing the fact that the etching rate in Si etching with an alkaline aqueous solution is very small in the region of high concentration (about 5 × 10 19 cm −3 or more) when the dopant is boron. The That is, a so-called etch stop technique in which the diaphragm forming region is a high-concentration boron-doped layer and the etching rate becomes extremely small when the boron-doped layer is exposed when forming discharge chambers and ink cavities by alkali anisotropic etching. Thus, the diaphragm is manufactured to a desired plate thickness.

First, both surfaces of the Si substrate 41 having a plane orientation of (110) are mirror-polished to produce a substrate having a thickness of 180 microns (FIG. 4A). The Si substrate 41 is set in a thermal oxidation furnace, and is subjected to thermal oxidation treatment at 1100 degrees Celsius for 4 hours in an oxygen and water vapor atmosphere to form an oxide film 42 on the surface of the Si substrate 41 with a thickness of 1.2 microns (FIG. 4). (B)). Next, in order to remove the oxide film 42 on the surface 43 on which the boron doped layer is to be formed, a resist is coated on the surface 44 opposite to the surface 43 on which the boron doped layer is to be formed on the Si substrate 41, and a boron doped layer is formed using the resist as a protective film. The oxide film 42 on the surface 43 is removed by etching with a hydrofluoric acid aqueous solution, and the resist is peeled off (FIG. 4C). A diffusion agent 45 in which 3.15 wt% of B2O3 serving as a diffusion source is dispersed in an organic solvent is spin-coated on the surface 43 on which the boron-doped layer from which the oxide film has been removed is formed at 2000 rpm for 1 minute. Bake for 30 minutes at a temperature of 140 degrees Celsius (FIG. 4D). At this time, the thickness of the diffusing agent 45 is 1.2 microns.

  The Si substrate 41 coated with the diffusing agent 45 is set in a thermal oxidation furnace, heated in an oxygen atmosphere at a temperature of 600 degrees Celsius, the organic binder in the diffusing agent 45 is oxidized and removed, and B 2 O 3 is baked. Subsequently, the inside of the furnace is put into a nitrogen atmosphere, the temperature is raised to 1100 degrees Celsius, the temperature is maintained for 12 hours, and boron is diffused into the Si substrate to form the boron doped layer 46. At this time, a boron compound 47 is formed at the interface between the diffusing agent 45 (B 2 O 3) and the boron-doped layer 46 on the surface of the Si substrate 41 (FIG. 4E).

A resist is coated on the side opposite to the surface on which the boron doped layer 46 is formed, and the diffusing agent 45 is removed by etching with a hydrofluoric acid aqueous solution (FIG. 4F). Since the boron compound 47 appearing on the surface of the Si substrate 41 has high etching resistance and cannot be removed by wet etching, the following measures are taken. First, after removing the resist on the Si substrate 41, the Si substrate 41 is set in an oxidation furnace, and the boron compound 47 is oxidized for 1 hour in an oxygen and water vapor atmosphere at 600 degrees Celsius, so that etching with a hydrofluoric acid aqueous solution is possible. Chemical change to B2O3 + SiO2. Since the oxidation temperature is low, diffusion does not proceed and the boron compound 47 can be removed by dry etching without being oxidized. In a state where the boron compound 47 on the diffusion surface is oxidized and chemically changed to B 2 O 3 + SiO 2, it is further thermally oxidized.
A 2 micron oxide film 48 is formed (FIG. 4G).

  The above is the case where the high-concentration boron dope layer 46 is formed by a coating method. As another means for forming the high-concentration dope layer, there is a method of performing thermal diffusion with a boron diffusion plate facing the Si substrate. .

  Next, the manufacturing method of the diaphragm and diaphragm slope part by an etching is demonstrated.

A boron-doped layer 46 is formed, a resist is coated on the surface opposite to the boron-doped side of the Si substrate 41 on which the oxide film 42 is formed, the cavity 51 is patterned, and the oxide film 42 is etched with a hydrofluoric acid aqueous solution. Further, the resist is removed, and the oxide film 42 is patterned (FIG. 5A). Next, etching reaches the boron dope layer 46 (thickness 3 microns) with a 40 wt% potassium hydroxide aqueous solution, and is performed up to an etching depth at which etching stops (the remaining 3 microns) (FIG. 5B). At this time, the etching with the high-concentration potassium hydroxide aqueous solution has the property that the slope 53 remains in the cavity bottom 52, and the slope 53 having a height of 18 microns is formed in the 40 wt% potassium hydroxide aqueous solution. Next, the etching of the Si substrate 41 is continuously stopped with a 5 wt% potassium hydroxide aqueous solution having a high etching stop property in the high-concentration boron-doped layer 46 (FIG. 5C). However, an etchant with a low concentration such as a 5 wt% potassium hydroxide aqueous solution has a property that the slope 53 is not formed at the cavity bottom 52, and the slope 53 disappears when the etching is continued until the diaphragm 54 has a predetermined thickness. As a result, the taper angle of the slope 53 becomes smaller.

  Through the above steps, an ink jet cavity having an inclined surface with a small taper angle at the connecting portion between the partition wall and the diaphragm can be formed. As a result, the durability of the diaphragm was improved, and stable long-term driving of the inkjet head could be realized.

(Example 2)
A method of forming a slope portion using an oxide film patterned with a plurality of thicknesses as an etching mask according to the second embodiment of the present invention will be described with reference to the etching process diagram of FIG.

  Since the size of the slope at the bottom of the cavity formed with the high-concentration potassium hydroxide aqueous solution is almost regulated by the concentration of the etching solution, the following method is used when attempting to form a larger slope.

The boron doped layer 46 is formed on the Si substrate 41 and the process up to the formation of the oxide film 46 is performed in the same manner as the diffusion process of the above embodiment. A resist is coated on the surface opposite to the boron-doped side of the Si substrate 41, the cavity 61 is patterned, and the oxide film 42 is half-etched with an aqueous hydrofluoric acid solution (FIG. 6A). After removing the resist once, the resist is coated again, and the oxide film 42 in the portion 62 to be the vibration plate is completely removed with a hydrofluoric acid aqueous solution, and the resist is peeled off (FIG. 6B). The Si substrate 41 patterned with the oxide film 42 is etched with a 30 wt% potassium hydroxide aqueous solution at a depth 62 of 60 μm (FIG. 6C). Next, the etching time is adjusted and the Si substrate 41 is immersed so that only the oxide film portion 63 thinned by half etching can be removed (FIG. 6D). Then, the etching with the potassium hydroxide aqueous solution is continued so that the thickness of the portion 62 to be the first etched diaphragm becomes about 3 microns. At this time, the portion from which the oxide film 42 is removed is also etched, and the corner 64 is gradually etched (FIG. 6E), and finally becomes a large tapered slope 65 (FIG. 6F). ). Next, the Si substrate 41 is continuously etched with a 5 wt% potassium hydroxide aqueous solution having a high etching stop property in the high-concentration boron-doped layer 46 to form a diaphragm 66 having a predetermined thickness (FIG. 6G). Since the taper of the slope 65 after the high-concentration etching is large, the finally remaining taper shape can be increased. As a result, the strength of the connecting portion between the partition wall and the diaphragm is increased, and the durability of the diaphragm is further improved.

(Example 3)
FIG. 7 showing the relationship between the etchant concentration and the slope width for the concentrations of the high-concentration potassium hydroxide aqueous solution and the low-concentration potassium hydroxide aqueous solution according to the third embodiment of the present invention, and the etchant concentration and the etch stop selection ratio ( The relationship of the ratio of the etching rate of undoped Si to the etching rate of boron-doped Si) will be described with reference to FIG.

  In the etching of the Si substrate with an aqueous potassium hydroxide solution, the slope width and concentration of the slope formed at the bottom of the etching groove have a relationship as shown in FIG. 7, and the slope is formed at 32 wt% or more, and the slope is formed at 30 wt% or less. Not formed at all. That is, the maximum concentration of the potassium hydroxide aqueous solution is 55 wt%, and the optimum concentration of the high concentration potassium hydroxide aqueous solution for the purpose of forming the slope portion in the diaphragm formation is 32 to 55 wt%.

On the other hand, the point of selecting the concentration of the low-concentration etching solution of the potassium hydroxide aqueous solution is how to increase the etching stop selection ratio. That is, it means how much variation in the Si substrate thickness can be absorbed by the etching stop, and it is desirable that the etching stop selection ratio is high. Considering that the thickness variation of the Si substrate is about 10 microns, the necessary selectivity is 16 or more in order to suppress the vibration plate thickness accuracy to within ± 0.3 microns at the worst. That is, in order to ensure a selectivity of 16 or more, it can be seen from FIG. 8 that the concentration of the potassium hydroxide aqueous solution may be 10 wt% or less. On the other hand, when the concentration of the potassium hydroxide aqueous solution becomes extremely low, the etching ability with respect to Si tends to become unstable, and it is not practical at a concentration lower than 0.5 wt%. Therefore, the optimum concentration of the low-concentration potassium hydroxide aqueous solution for the purpose of etching stop in the diaphragm formation is 0.5 to 10 wt%.

The shape of the slope 93 at the connecting portion between the partition wall 91 and the diaphragm 92 after the high concentration etching is as shown in FIG. 9 (0), and the slope width d and slope height h are substantially equal. Here, in order to estimate the shape after the low-concentration etching, when the etching stop selection ratio in the low-concentration etchant is S and the etching amount after reaching the high-concentration boron-doped layer 95 is a, the relationship between h and S There are three types of shapes after low-concentration etching, as shown in FIGS. 9 (Ι), (П), and (Ш). If the height of the slope after low concentration etching is x,
When S × a <h,
x = h− (S × a) + a
When S × a = h,
x = a
When S × a> h,
The amount of etching of the high-concentration boron-doped layer before the slope portion upper portion 94 reaches the high-concentration boron-doped layer is a1, and the etching amount after the slope-top portion 94 reaches the high-concentration boron-doped layer is a2.
S × a1 = d, a = a1 + a2
a1 = h / S
x = a−a2
= A1
= H / S
Here, since the thickness of the high-concentration boron doped layer 95 is 3 microns and the target thickness of the diaphragm 96 is 2 microns, the etching amount of the high-concentration boron doped layer 95 is a = 1 micron. For example, when the concentration of the high concentration etching solution is 40 wt% and the concentration of the low concentration etching solution is 5 wt%, from the graphs of FIGS. 7 and 8,
h = 18 microns, S = 22,
Since S × a = 22> h = 18,
x is
x = h / S = 18/22 = 0.82
Therefore, in this case, the height of the slope after etching is 0.82 microns.

  From the above, the slope shape can be arbitrarily controlled by selecting the concentration of the high-concentration etching solution and the low-concentration etching solution.

1 is an exploded perspective view showing the structure of an inkjet head according to a first embodiment of the present invention. 1 is a cross-sectional side view of an ink jet head according to a first embodiment of the present invention. FIG. 3 is a view taken along line A-A ′ in FIG. 2. FIG. 6 is a diffusion process diagram that constitutes a manufacturing process of the first substrate of the ink jet head according to the first embodiment of the present invention. FIG. 5 is an etching process chart constituting the manufacturing process of the first substrate of the inkjet head in the first embodiment of the present invention. The etching process figure which comprises the manufacturing process of the 1st board | substrate of the inkjet head in the 2nd Example of this invention. The relationship figure of potassium hydroxide aqueous solution concentration and slope width in the 3rd example of the present invention. The relationship figure of potassium hydroxide aqueous solution concentration and selectivity in the 3rd example of the present invention. Schematic which simulates and demonstrates the etching shape of the slope part of the partition part and diaphragm connection part in 3rd Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st board | substrate 2 2nd board | substrate 3 3rd board | substrate 5 Diaphragm 6 Discharge chamber 7 Recessed part 8 Orifice 9 Narrow groove 10 Ink cavity 11 Recessed part 12 Nozzle hole 13 Ink supply port 14 Recessed part 15 Electrode 16 Lead part 17 Terminal 18 Partition part 19 Connection part 20 Slope 21 Ink droplet 22 Recording paper 23 Transmission circuit 41 Si substrate 42 Oxide film 43 Surface to form boron doped layer 44 Opposite surface 45 Diffusion agent 46 Boron doped layer 47 Boron compound 48 Oxide film 51 Become a cavity Part 52 Cavity bottom part 53 Slope 54 Vibration plate 55 Bulkhead part 56 Slope 61 Part to be cavity 62 Part to be diaphragm 63 Thinned oxide film part 64 Angle 65 Slope 66 Diaphragm 91 Bulkhead part 92 Diaphragm part 93 Slope 94 Slope upper part 95 Boron doped layer

Claims (2)

Single or a plurality of nozzle holes for discharging ink droplets, a discharge chamber connected to each of the nozzle holes, a vibration plate constituting at least one wall of the discharge chamber, and deformation of the vibration plate In the inkjet head, the driving means comprises an electrode that deforms the diaphragm to electrostatic force, and the substrate on which the diaphragm is formed is a Si substrate.
A p-type impurity layer is formed on the diaphragm side of the substrate,
The partition wall part that separates each of the discharge chambers and the connecting part of the diaphragm are constituted by two inclined surfaces having different inclination angles,
The inkjet head according to claim 2, wherein the two inclined surfaces are in contact with each other at a boundary portion of the p-type impurity layer of the substrate. 2. The inkjet head according to claim 1, wherein the substrate has a (110) plane orientation.

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