JP5435802B2 - Piezoelectric thin film element, ultrasonic sensor using the same, and manufacturing method thereof - Google Patents

Description

  The present invention relates to a piezoelectric thin film element, and more particularly to a diaphragm type thin film element using a piezoelectric thin film, an ultrasonic sensor using the same, and a method of manufacturing the same.

  Patent Document 1 discloses a cantilever type ultrasonic sensor formed on a silicon substrate. In this ultrasonic sensor, the base end portion of the cantilever is connected to two sides of the concave portion of the silicon substrate, and the cantilever is prevented from being broken and the yield is improved by the dispersion of stress applied to the base end portion.

  Patent Document 2 discloses a piezoelectric ultrasonic sensor in which a plurality of diaphragm-shaped ultrasonic receiving elements are arranged on a silicon substrate. In this structure, since all directions (four sides) of the piezoelectric film of the ultrasonic receiving unit are fixed to the substrate, it is difficult to obtain a large displacement when ultrasonic waves are received and pressure is applied to the piezoelectric film. It is difficult to obtain a large voltage (detection signal) from the piezoelectric film. Therefore, it is usually necessary to ensure sensitivity by increasing the size (area) of the diaphragm.

Japanese Patent No. 3272141 Japanese Patent No. 42282727

  In general, the sensitivity of a diaphragm type sensor is proportional to the square of the area of the diaphragm and inversely proportional to the cube of the thickness of the diaphragm. In the case of a rectangular diaphragm, it is expressed by the following relational expression.

(Sensitivity) ∝ (one side of diaphragm) ⁴ / (Thickness of diaphragm) ³
If one side of the diaphragm is increased in order to increase sensitivity, the deflection (displacement) increases and sensitivity is improved, but the size of the element increases. In order to increase the sensitivity, it is necessary to reduce the thickness of the diaphragm. However, if the diaphragm is simply made thin, there is a problem of occurrence of cracks and the like, and the reliability and manufacturing yield are lowered.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a piezoelectric thin film element having a high sensitivity and a small size, an ultrasonic sensor using the piezoelectric thin film element, and a manufacturing method thereof.

In order to achieve the above object, a piezoelectric thin film element according to the present invention includes a piezoelectric film, counter electrodes disposed on both sides of the piezoelectric film with the piezoelectric film interposed therebetween, and the counter electrode. A substrate that supports the piezoelectric film, and a recess formed at the corresponding position of the substrate corresponding to the displaceable portion of the piezoelectric film provided on the substrate, and is displaceable. The thickness of the remaining portion excluding the counter electrode and the piezoelectric film from the diaphragm portion including the counter electrode and the piezoelectric film at a site is greater than 0 and 0.1 μm or less .
Moreover, in order to achieve the said objective, the following invention aspects are provided.

  (Invention 1): A piezoelectric thin film element according to Invention 1 includes a piezoelectric film, a counter electrode disposed on both sides of the piezoelectric film with the piezoelectric film interposed therebetween, and the piezoelectric device including the counter electrode. A substrate supporting the body film, and a recess formed at the corresponding position of the substrate corresponding to the displaceable portion of the piezoelectric film provided on the substrate, and the displaceable portion of the substrate The remaining portion excluding the counter electrode and the piezoelectric film from the diaphragm portion including the counter electrode and the piezoelectric film has a thickness of 0 to 1 μm.

  According to the present invention, in the diaphragm-type piezoelectric thin film element, there is no film element other than the counter electrode and the piezoelectric film in the displaceable film part (diaphragm part) corresponding to the recess formed in the substrate ( The remaining thickness is zero), or there is only a layer with a thickness (1 μm or less) that does not substantially affect the displacement performance.

  That is, conventionally, there is no member element corresponding to a “diaphragm” having a function of holding the piezoelectric film. Therefore, the piezoelectric film of the present invention can obtain a large displacement without hindering / suppressing its movement (displacement). Thereby, a large output voltage can be obtained, and a small sensor with high sensitivity can be realized.

  (Invention 2): The piezoelectric thin film element according to Invention 2 is characterized in that, in Invention 1, the diaphragm portion is a self-supporting film substantially composed of only the piezoelectric film and the counter electrode. .

  “Substantially” means that the presence or absence of a film element that has little influence to inhibit or suppress the displacement of the piezoelectric film does not matter. For example, the remaining portion of the oxide film used as an etching stopper layer in the manufacturing process, or a film piece added in an island shape pattern on the counter electrode does not substantially function as a diaphragm. Therefore, even if these oxide films and film pieces are present, it is interpreted as a substantially self-supporting film.

  (Invention 3) A piezoelectric thin film element according to Invention 3 is characterized in that, in Invention 1, the remaining portion is a thermal oxide film of a material of the substrate.

(Invention 4): A piezoelectric thin film element according to Invention 4, in any one of Inventions 1 to 3,
The difference in displacement amount of the piezoelectric film depending on the presence or absence of the remaining portion is 5% or less.

  When the diaphragm part is a self-supporting film composed only of a piezoelectric film and a counter electrode (when there is no remaining part), the displacement amount with respect to a specified pressure is set as a reference displacement amount, and other than the piezoelectric film and the counter electrode When the amount of displacement with respect to the specified pressure is compared when there is an element (when there is a remaining part), if the difference in the amount of displacement is less than 5% of the reference displacement, there is virtually no effect. It can be handled as a degree.

  (Invention 5) A piezoelectric thin film element according to Invention 5 is characterized in that, in any one of Inventions 1 to 4, the thickness of the piezoelectric film exceeds 1 μm.

  If the piezoelectric film is too thin, cracks are likely to occur, and therefore the thickness is preferably more than 1 μm. More preferably, it is 2 micrometers or more, More preferably, it is 3 micrometers or more.

(Invention 6): A piezoelectric thin film element according to Invention 6, in any one of Inventions 1 to 5, wherein the piezoelectric film is a PZT-based perovskite oxide and an A site in an ABO ₃ type crystal structure The composition ratio of the material entering is not less than 1.0 and less than 1.1.

  If the material entering the A site (for example, mainly Pb, but also including materials substituted by the A site such as Bi) is small, the surface of the piezoelectric film tends to be rough and easily cracked.

  On the other hand, if the molar ratio of the material at the A site is 1.1 or more, the characteristics may change due to humidity or the like. Therefore, the conditions described in Invention 6 are preferable.

  (Invention 7): The piezoelectric thin film element according to Invention 7 is characterized in that, in any one of Inventions 1 to 6, the piezoelectric film is a PZT-based perovskite oxide and contains 2% or more of Nb. And

  As the amount of Nb increases, the piezoelectric constant tends to increase. Further, by adding Nb, the Young's modulus of the material is lowered as compared with the case where Nb is not added, so that cracks are hardly generated.

  (Invention 8): The piezoelectric thin film element according to Invention 8 is the piezoelectric thin film element according to any one of Inventions 1 to 7, wherein a plurality of the concave portions are formed on the substrate, and a plurality of the diaphragm portions corresponding to the respective concave portions are formed. It is characterized by being.

  In the piezoelectric thin film element of the present invention, a plurality of diaphragm structures can be formed in an array on one substrate, and a small and highly sensitive array type sensor can be realized.

  (Invention 9): Invention 9 provides an ultrasonic sensor that achieves the above object. That is, the ultrasonic sensor according to the ninth aspect of the invention receives a ultrasonic wave at the displaceable portion of the piezoelectric thin film element according to any one of the first to eighth aspects, and generates a voltage according to the displacement of the piezoelectric film. The signal is obtained from the counter electrode.

  (Invention 10): Invention 10 provides a production method for achieving the object. That is, the method for manufacturing a piezoelectric thin film element according to the tenth aspect includes a step of superposing and forming a first electrode, a piezoelectric film, and a second electrode on a first surface of a substrate, the first electrode, the piezoelectric film, and A step of bonding a surface protection member covering the first surface side of the substrate on which the second electrode is formed to the substrate; a second side opposite to the first surface of the substrate to which the surface protection member is bonded; Etching the substrate from the surface side to form a recess, and removing the surface protection member after forming the recess.

  According to the tenth aspect, the piezoelectric thin film element according to the first to eighth aspects and the ultrasonic sensor according to the ninth aspect can be manufactured. In particular, the surface protection member can protect the piezoelectric film from mechanical impacts, can prevent damage during manufacturing, etc., improves the handleability of the substrate, and increases manufacturing efficiency. The first electrode and the second electrode correspond to the “counter electrode” referred to in the first aspect of the invention.

  (Invention 11): The method for manufacturing a piezoelectric thin film element according to Invention 11 is the method according to Invention 10, wherein a thermal oxide film is formed on the first surface of the substrate, and the first electrode is overlapped with the thermal oxide film. The thermal oxide film is formed as a stopper layer during the etching.

  (Invention 12): The method for manufacturing a piezoelectric thin film element according to Invention 12 is characterized in that, in Invention 11, a piezoelectric thin film element having a diaphragm structure in which the thermal oxide film is left in the recess is obtained.

  According to the present invention, a small and highly sensitive piezoelectric thin film element can be provided. In addition, according to the present invention, it is possible to provide an ultrasonic sensor that is highly sensitive and small in size.

Sectional drawing of the diaphragm type sensor using the piezoelectric thin film element which concerns on embodiment of this invention Plan view of FIG. Sectional drawing which shows the structural example whose diaphragm is a self-supporting film | membrane which consists only of an electrode and a piezoelectric material Diagram of manufacturing process of diaphragm type sensor Sectional drawing which shows the sensor structure of a comparative example Perspective view of diaphragm structure used for simulation calculation Plan view of FIG. Graph showing the result of calculating the resonance frequency and output voltage of the diaphragm by changing the thickness of the diaphragm by simulation

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view of a diaphragm type sensor using a piezoelectric thin film element according to an embodiment of the present invention, and FIG. 2 is a plan view thereof. 1 is a cross-sectional view taken along line 1-1 in FIG. Although only one element element is shown here, an array-like sensor in which a plurality of elements having the same structure are arranged on a substrate is configured.

<About sensor structure>
The diaphragm type sensor 10 has a configuration in which a lower electrode 20, a piezoelectric film 22, and an upper electrode 24 are laminated on one side surface of the substrate 12 (the upper surface in FIG. . The piezoelectric element 26 that converts the displacement of the piezoelectric film 22 into a voltage signal is formed by the configuration in which the lower electrode 20 and the upper electrode 24 are arranged to face each other with the piezoelectric film 22 interposed therebetween.

  On the other hand, the substrate 12 has a recess formed by removing a part of the substrate 12 from the surface opposite to the surface on which the piezoelectric element 26 is formed (the lower surface in FIG. 1, hereinafter referred to as “rear surface” in some cases). 14 is formed.

  The recess 14 in this example is substantially rectangular (in this example, a square) in plan view, but is not limited to a rectangle, and may be other polygons, circles, ellipses, or the like. The portion of the piezoelectric film 22 (reference numeral 28) corresponding to the position of the gap portion of the recess 14 is in a state where the lower surface thereof is not restrained (unconstrained) and becomes a displaceable region. The unconstrained region indicated by reference numeral 28 corresponds to a “displaceable part” and serves as a receiving element that receives ultrasonic waves as an ultrasonic sensor.

  The lower electrode 20 is configured as a common electrode integrally connected to a plurality of elements on the substrate 12. The upper electrode 24 is individually patterned in accordance with the recess 14 of each element. When the piezoelectric film 22 is displaced, a voltage is generated according to the distortion. When the piezoelectric film 22 bends downward in FIG. 1, stress is applied in the compression direction in the vicinity of the middle, and stress is applied in the extending direction at the end (peripheral part near the restraint part). Therefore, it is preferable that the upper electrode 24 is provided only in the vicinity of the center or only at the end portion, rather than being formed on the entire surface of the diaphragm.

  In this example (FIGS. 1 and 2), an upper electrode 24 having an area smaller than the opening area (diaphragm area) is formed at the center of the opening shape (diaphragm planar shape) of the recess 14. In FIG. 1 and FIG. 2, illustration of an extraction electrode and the like for wiring is omitted.

  The diaphragm sensor 10 according to the present embodiment does not have a member element corresponding to a diaphragm for holding the lower surface of the piezoelectric film 22 in the displaceable portion 28 corresponding to the recess 14. In FIG. 1, a film indicated by reference numeral 30 formed on the lower surface of the lower electrode 20 is a thermal oxide film of the substrate 12. This thermal oxide film 30 is used as an etching stopper layer when the recess 12 is formed by etching the substrate 12 in the manufacturing process. The thickness of the thermal oxide film 30 is about 0.1 μm (100 nm), does not substantially function as a diaphragm, and hardly affects the displacement of the piezoelectric film 22.

  From the viewpoint of not inhibiting / suppressing the displacement of the piezoelectric film 22, the thickness of the diaphragm part (corresponding to the “remaining part”) excluding the piezoelectric film 22 and the electrodes (20, 24) is set to less than 1 μm. Preferably it is 0.5 μm or less, more preferably 0.1 μm or less, and more preferably 0 “zero”.

  The thickness of the remaining portion being 0 “zero” means that the diaphragm is a self-supporting film including only the electrodes (20, 22) and the piezoelectric film 22, as shown in FIG. The configuration shown in FIG. 3 is most preferable.

  In addition, the piezoelectric film 22 is preferably thicker than 1 μm from the viewpoint of preventing cracks.

<Physical properties of piezoelectric material>
The piezoelectric film 22 is a PZT system, and the amount of Pb is 1.0 or more and less than 1.1. This is because if the amount of Pb is small, the surface of the film is rough and cracks are likely to occur. Even if Pb is 1.0 or less, it is sufficient if there is a material substituted for the A site such as Bi. Further, if Pb is 1.1 or more, the characteristics may change depending on the temperature or the like.

  In the piezoelectric material, it is preferable that at least Nb in PZT is 2% or more, more preferably 5% or more, and further preferably 10% or more. Increasing the amount of Nb increases the piezoelectric constant. Further, the addition of Nb lowers the Young's modulus and makes the film strong against cracks. For example, the Young's modulus of the material to which Nb is not added is 70 to 90 GPa, but when Nb is added, it becomes about 50 GPa.

  In consideration of the resonance frequency on a diaphragm structure suitable as an ultrasonic sensor, the Young's modulus of the piezoelectric body is preferably 60 GPa or less.

<About manufacturing method>
FIG. 4 is a diagram showing a manufacturing process of the diaphragm type sensor using the piezoelectric thin film element according to the embodiment of the present invention.

(Step 1): A silicon (Si) wafer 112 having a thermal oxide film (SiO ₂ film) 130 formed on the substrate surface with a predetermined thickness (for example, 100 nm) was used as the substrate (FIG. 4A).

  (Step 2): Ti 20 nm and Ir 150 nm were laminated as the lower electrode 120 on one side surface (upper surface in FIG. 4) of the Si wafer 112. Thereafter, a PZT film 122 added with 10% Nb was formed on the lower electrode 120 at a deposition temperature of 500 degrees (FIG. 4B). The thickness of the PZT film 122 was 3 μm. Further, Pt was formed as the upper electrode 124 on the upper surface of the PZT film 1222 and patterned into a desired structure. The film thickness of the upper electrode 124 is approximately the same as the film thickness of the lower electrode 120, and the upper electrode 124 is patterned in accordance with the planar shape of the diaphragm portion serving as the ultrasonic light receiving portion and the arrangement form.

  (Step 3): Next, as shown in FIG. 4C, the surface protection member 150 was attached to the upper surface of the PZT film 122. The surface protection member 150 has a cap-like structure that covers the top surface of the PZT film 122 while forming a gap 152 between the surface protection member 150 and the top surface of the PZT film 122. By enclosing the upper portion of the PZT film 122 with the surface protection member 150, the PZT film 122 is prevented from being mechanically damaged during or after the etching process (FIG. 4D) described later. Yes.

  Although there is no restriction | limiting in particular as a protection member, things, such as Si, glass, stainless steel, resin, can be used as a material. The protective member and the sensor part can be bonded together using a resist, an adhesive, a foam tape, or the like.

(Step 4): The PZT film 122 is covered with the surface protection member 150, and silicon is etched from the back surface side of the Si wafer 112 to the SiO ₂ film 130 on the front surface side by the Bosch method with the PZT film 122 protected (FIG. 4 (e)). The space of the recess 114 removed by the etching is a space (gap) that allows the displacement of the PZT film 122. The lower surface of the PZT film 122 is fixed (restrained) by the Si layer present around the recess 114, and the recess 114 is fixed, thereby forming a diaphragm structure.

  (Step 5): Thereafter, the surface protection member 150 is removed, and the diaphragm type sensor 110 is completed.

  The removal method is not particularly limited, but the member of the adhesive portion can be melted with a solvent, mechanically peeled off, or peeled off by heat or the like.

In step 4, the SiO ₂ film in the recess 114 may be further removed to produce the structure of FIG.

<Comparative example>
For comparison, a diaphragm type sensor shown in FIG. 5 was prepared. In FIG. 5, the same or similar elements as those in the sensor according to the embodiment of FIG. In the comparative example of FIG. 5, a member corresponding to the diaphragm 165 is provided on the lower surface (back surface) side of the PZT film 122 in the diaphragm portion. As a manufacturing method having such a configuration, for example, instead of the step 4 (FIG. 4D) described in FIG. 4, the etching is stopped while leaving the silicon layer corresponding to the diaphragm 165. be able to. Alternatively, an SOI (Silicon On Insulator) substrate may be used as the substrate, the recess 114 may be formed in the support substrate layer, and the active layer may be used as the diaphragm 165.

<Comparison evaluation 1>
In the structure shown in FIG. 5, two examples (Example 2 and Comparative Example 1) were created by changing the thickness (reference numeral t in FIG. 5) other than the piezoelectric element (piezoelectric body and electrode) in the diaphragm portion. The sensor sensitivity was compared and evaluated for Example 1 (FIG. 4 (e)), Example 2 and Comparative Example 1, and the results are summarized in Table 1.

   When the thickness (t) of the diaphragm part excluding the piezoelectric body and the electrode exceeds 1 μm, the sensitivity of the sensor is lowered.

<Comparison evaluation 2>
Further, as another comparative example, a configuration was made in which the thickness of the PZT film in the sensor structure shown in FIG. 1 was 1 μm (Comparative Example 2). The comparative example 2 and the example were compared and summarized in a table.

<Comparison evaluation 3>
In the formation of the PZT film in the sensor structure shown in FIG. 1, Example 3 and Comparative Examples 3 to 4 in which the PZT film was formed by changing the Pb amount were prepared. Comparative Examples 3 to 4 and Example 1 were compared and summarized in a table.

<Comparison evaluation 4>
When forming the PZT film in FIG. 1, Examples 4 to 7 and Comparative Example 5 in which the PZT film was formed by changing the amount of Nb added were prepared. The comparative example 5 and each example were compared and summarized in a table.

<Comparison evaluation 5>
When the sensor was produced without using the surface protection member 150 described in the example of FIG. 4, the sensor was broken in the middle and the yield was poor.

<Relationship between diaphragm thickness, sensor performance, and resonance frequency>
Calculations were performed using the rectangular diaphragm structure shown in FIGS. 6 and 7 as a model and using simulation software of Murata Software Co., Ltd. 6 is a perspective view, and FIG. 7 is a plan view. Diaphragm resonance frequency and output voltage were calculated by changing the diaphragm size to 200 μm square (square with one side of the rectangular recess 14 being 200 μm) and changing the thickness of the diaphragm. FIG. 8 shows the result.

  A curve indicated by a thick line (line connecting ■) in FIG. 8 indicates a change in output voltage with respect to the thickness of the diaphragm. A curve indicated by a thin line in FIG. 8 (line connecting ◆) indicates a change in resonance frequency with respect to the thickness of the diaphragm.

  From FIG. 8, it can be seen that as the diaphragm is made thinner, a larger output voltage is obtained and a signal having a larger S / N is obtained. Further, the resonance frequency of the diaphragm decreases as the diaphragm thickness decreases.

  The sensitivity is preferably such that the diaphragm is thin, and the thickness of the diaphragm portion excluding the electrode and the piezoelectric body is preferably 1 μm or less. The reason is that the output voltage increases. When the diaphragm thickness exceeds 1 μm, the output voltage is gradually lowered. Further, focusing on the resonance frequency, the thinner the diaphragm, the smaller the resonance frequency. For example, when the diaphragm thickness is zero, the diaphragm size needs to be reduced in order to increase the resonance frequency. . If the diaphragm size is made smaller, the number of wafers taken per wafer at the time of manufacture increases, leading to cost reduction. In addition, since the resonant frequency and the thickness of the diaphragm are design parameters related to each other, there are actually various solutions (combinations). However, as a direction to increase the output voltage and reduce the size, It is essential to reduce the thickness of the diaphragm.

As described above, the thickness of the diaphragm portion excluding the electrode and the piezoelectric body is preferably smaller. In the manufacturing method described with reference to FIG. 4, the thickness of the diaphragm portion excluding the electrodes and the piezoelectric body is zero, or the thermal oxide film (SiO ₂ layer) 30 is on the order of 100 nm at most. Demonstrate the effect. Further, it is possible to manufacture while protected by the SiO ₂ layer of 1μm thickness less than, there is a great advantage.

<About the surface shape of the diaphragm>
In the above-described embodiment, the case where the shape of the diaphragm is a flat shape (planar surface shape) is illustrated, but the form of the diaphragm is not limited to this, and the initial shape is an upwardly convex dome shape, It may be a concave-convex shape.

<About the composition of the piezoelectric film>
The piezoelectric material used in the embodiment of the present invention will be described. The piezoelectric body used in this example is based on lead zirconate titanate (Pb (Zr, Ti) O3, commonly referred to as “PZT”). In PZT, both Zr and Ti are tetravalent ions, and Ti: Zr can take all concentration ratios from PbTiO3 to PbZrO3. Among these, the composition with Zr: Ti of 52:48 or 53:47, which is the composition between the tetragonal crystal that is the crystal system of PbTiO3 and the rhombohedron that is the crystal system of PbZrO3, has particularly good piezoelectric characteristics. This characteristic is used as a piezoelectric body for an actuator. This composition is called the MPB composition.

The intrinsic PZT to which no dopant is added is a modified PZT in which a small amount of ions having a valence higher than tetravalent such as Nb ⁵⁺ are added to improve the piezoelectric characteristics. In PZT used in this example, about 10% or more of Nb can be added, and high-quality PZT (modified PZT) can be obtained. For example, a high piezoelectricity of d31 = 200 to 300 pm / V can be obtained.

  As a piezoelectric film that can be used in the practice of the present invention, a piezoelectric film made of one or more perovskite oxides represented by the following general formula (P) (may contain unavoidable impurities) Is mentioned. Such a piezoelectric film can be formed on the substrate by a sputtering method using plasma. This piezoelectric film (general formula (P)) has a negative coercive electric field with a small absolute value, and has a piezoelectric characteristic in which Pr-E hysteresis is biased toward the positive electric field.

General formula A _a B _b O ₃ (P)
In the formula, A is an A site element containing Pb as a main component, B is an element of a B site, and Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Sc, Co, Cu, In, At least one element selected from the group consisting of Sn, Ga, Zn, Cd, Fe, and Ni, O is oxygen is typically a ≧ 1.0 and b = 1.0, These numerical values may deviate from 1.0 within a range where a perovskite structure can be taken.

  Examples of the perovskite oxide represented by the general formula (P) include lead titanate, lead zirconate titanate (PZT), lead zirconate, and lead niobate zirconium titanate. The piezoelectric film may be a mixed crystal system of perovskite oxides represented by the above general formula (P).

  In carrying out the present invention, in particular, a piezoelectric film composed of one or more perovskite oxides (which may contain inevitable impurities) represented by the following general formula (P-1). More preferred.

Pb _a (Zr _b1 Ti _b2 X _b3 ) O ₃ (P-1)
In formula (P-1), X is at least one metal element selected from the group of elements of group V and group VI. a> 0, b1> 0, b2> 0, b3 ≧ 0. Although it is standard that a ≧ 1.0 and b1 + b2 + b3 = 1.0, these numerical values may deviate from 1.0 within a range where a perovskite structure can be taken.

  The perovskite oxide represented by the general formula (P-1) is lead zirconate titanate (PZT) when b3 = 0, and when b3> 0, part of the B site of PZT is group V. And an oxide substituted with X which is at least one metal element selected from the group of elements of group VI.

  X may be any metal element of Group VA, Group VB, Group VIA, and Group VIB, and is preferably at least one selected from the group consisting of V, Nb, Ta, Cr, Mo, and W. .

<Other application examples>
In the above-described embodiment, application to an ultrasonic sensor has been exemplified, but the scope of application of the present invention is not limited to this, and the present invention can also be used for an ultrasonic probe, a pyroelectric sensor, and the like.

  DESCRIPTION OF SYMBOLS 10 ... Diaphragm type sensor, 12 ... Substrate, 14 ... Recess, 20 ... Lower electrode, 22 ... Piezoelectric film, 24 ... Upper electrode, 26 ... Piezoelectric element, 28 ... Displaceable part, 30 ... Thermal oxide film, 110 ... Diaphragm Type sensor, 112 ... Si wafer, 114 ... concave, 120 ... lower electrode, 122 ... PZT film, 124 ... upper electrode, 130 ... thermal oxide film, 150 ... surface protective member

Claims (12)

A piezoelectric film;
Counter electrodes disposed on both sides of the piezoelectric film across the piezoelectric film;
A substrate that supports the piezoelectric film including the counter electrode;
Corresponding to the displaceable portion of the piezoelectric film provided on the substrate, a recess formed at the corresponding position of the substrate;
With
The remaining portion excluding the counter electrode and the piezoelectric film from the diaphragm portion including the counter electrode and the piezoelectric film at the displaceable portion has a thickness of more than 0 and 0.1 μm or less. A piezoelectric thin film element. In claim 1,
The piezoelectric thin film element, wherein the remaining portion is a thermal oxide film made of a material of the substrate. In claim 1 or 2 ,
A difference in displacement of the piezoelectric film depending on the presence or absence of the remaining portion is 5% or less. In any one of Claims 1 thru | or 3 ,
A piezoelectric thin film element having a thickness of the piezoelectric film exceeding 1 μm. In any one of Claims 1 thru | or 4 ,
The piezoelectric film is a PZT-based perovskite oxide, and the composition ratio of the material entering the A site in the ABO ₃ type crystal structure is 1.0 or more and less than 1.1. element. In any one of Claims 1 thru | or 5 ,
The piezoelectric thin film element, wherein the piezoelectric film is a PZT-based perovskite oxide and contains 2% or more of Nb. In any one of Claims 1 thru | or 6,
A piezoelectric thin film element, wherein the piezoelectric film has a Young's modulus of 60 GPa or less. In any one of Claims 1 thru | or 7,
A plurality of the concave portions are formed on the substrate, and a plurality of the diaphragm portions corresponding to the respective concave portions are formed.   An ultrasonic wave is received at the displaceable portion of the piezoelectric thin film element according to any one of claims 1 to 8, and a voltage signal generated according to the displacement of the piezoelectric film is obtained from the counter electrode. A featured ultrasonic sensor. A thermal oxide film is formed on the first surface of the substrate, and a step of forming a first electrode, a piezoelectric film and a second electrode on the thermal oxide film ,
Bonding a surface protective member covering the first surface side of the substrate on which the first electrode, the piezoelectric film and the second electrode are formed, to the substrate;
Etching the substrate from the second surface side opposite to the first surface of the substrate to which the surface protection member is bonded to form a recess;
Removing the surface protection member after forming the recess;
Only including,
A diaphragm portion including the first electrode, the piezoelectric film, and the second electrode is formed at the position of the recess, and the first electrode, the piezoelectric film, and the second electrode are formed from the diaphragm portion. A method for manufacturing a piezoelectric thin film element, comprising: obtaining a piezoelectric thin film element having a remaining thickness of greater than 0 and 0.1 μm or less . In claim 10,
Method of manufacturing a piezoelectric thin film element the thermal oxide layer during the pre-Symbol etching is characterized by comprising a stopper layer. In claim 11,
A method for manufacturing a piezoelectric thin film element, comprising: obtaining a piezoelectric thin film element having a diaphragm structure in which the thermal oxide film is left in the recess.

Images