JP5011834B2 - Piezoelectric membrane sensor - Google Patents

Description

  The present invention relates to a piezoelectric membrane sensor having a membrane formed by laminating a lower electrode film, a piezoelectric film, and an upper electrode film.

  Conventionally, a membrane in this type of piezoelectric membrane sensor is generally formed by laminating a lower electrode film, a piezoelectric film made of a piezoelectric material, and an upper electrode film on a thin film structure. A thin film-like laminate including a body is configured as a membrane.

When a pressure or ultrasonic wave is applied to the membrane, an electrical change due to the piezoelectric phenomenon of the piezoelectric film, for example, a voltage change of the piezoelectric film is caused by the bending of the membrane. In this way, the applied pressure and the applied ultrasonic wave are measured (see, for example, Patent Document 1).
JP 2005-51686 A

  Here, the inventor made a prototype of a piezoelectric membrane sensor based on the prior art and examined it. FIG. 5 is a diagram showing a schematic cross-sectional configuration of a piezoelectric membrane sensor as a prototype manufactured by the present inventor. This piezoelectric membrane sensor is applied as a pressure sensor.

  In this structure, a recess 14 is formed on the back surface of the semiconductor substrate 10 by etching or the like, and the surface side corresponding to the recess 14 is configured as a thin film structure 15. A membrane 50 is formed by sequentially laminating the lower electrode film 20, the piezoelectric film 30, and the upper electrode film 40 on the thin film structure 15. That is, the membrane 50 corresponds to the laminated structure portion on the recess 14.

  Here, assuming that a positive pressure P is applied to the front side of the membrane 50, the membrane 50 bends as shown in FIG. In the vicinity of the center of the membrane 50, a downward convex shape is formed, and the bending stress generated in the piezoelectric film 30 is a compressive stress, and in the vicinity of the peripheral portion of the membrane 50, the upward convex shape is formed, and the stress generated in the piezoelectric film 30 is a tensile stress. is there.

  Therefore, similarly to the stress generated in the piezoelectric film 30 when the membrane 50 is bent, the generated charges due to the piezoelectric d31 constant have opposite polarities in the center of the membrane 50 and in the vicinity of the periphery of the membrane 50.

  In the conventional general structure in which the lower electrode film 20 and the upper electrode film 40 are arranged on the entire surface, the charges having opposite polarities cancel each other, and the output charge amount contributing to the sensor output is reduced, and as a result. The sensor sensitivity is lowered.

  With respect to this problem, in Patent Document 1 described above, one of the upper and lower electrode films sandwiching the piezoelectric film is divided into a plurality of regions, and charges having opposite polarities that have been canceled with each other in the same electrode are converted into polarities. The method of taking out so as to increase the charge amount by reversing the above is adopted.

  However, in this method, 1) a signal processing circuit for integrating the extracted charges having different polarities is required, and it becomes complicated. 2) When the divided pattern of the electrodes becomes concentric or similar, the inner electrode There is a problem that it is necessary to take measures against the charge extraction from the battery.

  For example, in the above problem 2), measures such as drawing out wiring from the inner electrode using multilayer wiring, or drawing out wiring from the inner electrode by cutting out a part of the outer electrode can be considered. However, there is a demerit that the deformation of the membrane is distorted due to the asymmetry of the pattern accompanying the drawing of the wiring, and that the process becomes complicated when a multilayer wiring is used.

  The present invention has been made in view of the above problems, and in a piezoelectric membrane sensor having a membrane formed by laminating a lower electrode film, a piezoelectric film, and an upper electrode film, the output is performed without dividing the upper and lower electrode films. The purpose is to increase the amount of charge.

  In order to achieve the above object, the present inventor has a stress-free boundary line of neutral axis J (thick broken line in FIG. 5) in the bending of the membrane 50 as shown in FIG. Focused on. The neutral axis J is a virtual axis that always exists in the membrane 50, and is generally obtained by dynamic numerical calculation.

  Specifically, the neutral axis J generates a bending stress that is compressive on the inside of the bending portion and tensile on the outside than the neutral axis J. In the conventional general configuration, as shown in FIG. 5, the neutral axis J is located below the piezoelectric film 30 on the entire surface of the membrane 50. Therefore, as shown in FIG. 5, the polarity of the stress generated in the piezoelectric film 30 is different between the central portion and the peripheral portion. As a result, the polarity of the electric charge generated in the piezoelectric film 30 is also partially different.

  Therefore, the present inventor makes a neutral axis J in a certain part of the membrane 50 so that the stress generated in the piezoelectric film 30 when the membrane 50 is deformed, that is, when the membrane 50 is bent, has the same polarity over the entire area of the membrane 50. It is considered that the position of the neutral axis J may be partially changed such that is positioned above the piezoelectric film 30 and the neutral axis J is positioned below the piezoelectric film 30 in other parts.

The present invention was created in view of such knowledge. In the invention according to claim 1, the lower electrode film (20) and the piezoelectric film (30) made of a piezoelectric body are formed on the substrate (10). And a thin film-like membrane (50) having a laminated structure in which the upper electrode film (40) is sequentially laminated. When the bending occurs, the polarity of the stress generated in the central portion and the peripheral portion of the membrane (50) is reversed, and the piezoelectric phenomenon of the piezoelectric film (30) accompanying the bending generated in the membrane (50). Is detected by the upper and lower electrode films (20, 40), and the neutral axis (J) in the bending of the membrane (50) is located below the piezoelectric film (30). Piezoelectric membrane sensor In which the neutral axis (J) in the bending of the membrane (50) straddles the piezoelectric film (30) in the membrane (50) and is located above and below the piezoelectric film (30). As a result, the stress generated in the piezoelectric film (30) when the membrane (50) is bent is the same over the entire area of the membrane (50). The polarity of the laminated structure of the membrane (50) is partially different from that of the upper electrode, which is partially above the piezoelectric film (30) by placing the membrane (60) partially on the membrane (50). It is performed by arranging and adding on the membrane (40) side, and the added membrane (60) is provided in the peripheral portion of the membrane (50) and not in the central portion. And

  According to this, the laminated structure of the membrane (50) is partially different so that the neutral axis (J) is located on a different side across the piezoelectric film (30) in the membrane (50), and the piezoelectric film ( Since the stress generated in 30) has the same polarity over the entire area of the membrane (50), the charge generated in the piezoelectric film (30) can also have the same polarity over the entire surface of the membrane (50). Therefore, the output charge amount can be increased without dividing the upper and lower electrode films.

Here, the laminated structure of the membrane (50) can be partially changed by adding a film (60) partially by the membrane (50), and the film (60) to be added can be a piezoelectric film. If it is arranged on the upper electrode film (40) side above (30), in this type of piezoelectric membrane sensor, the stress generated in the piezoelectric film (30) is applied to the entire area of the membrane (50). It is easy to have the same polarity across.

  In addition, the code | symbol in the bracket | parenthesis of each means described in the claim and this column is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are given the same reference numerals in the drawings in order to simplify the description.

(First embodiment)
FIG. 1 is a diagram showing a configuration of a pressure sensor 100 as a piezoelectric membrane sensor according to a first embodiment of the present invention, and (a) is a diagram showing a schematic cross-sectional configuration along the thickness direction of the membrane 50, (B) is a top view of (a) and is a diagram showing a schematic planar configuration of the membrane 50 and its peripheral part. In FIG. 1B, the surface of the additional film 60 is hatched for convenience of identification.

  The pressure sensor 100 has a semiconductor substrate 10. Here, the semiconductor substrate 10 is an SOI (silicon on insulator) substrate in which an oxide film 13 is inserted between a first silicon layer 11 and a second silicon layer 12.

  In this semiconductor substrate 10, a concave portion 14 is formed on the back side thereof by wet etching or dry etching using KOH or TMAH (tetramethylammonium hydroxide), and the surface side portion corresponding to this concave portion 14, that is, The bottom of the recess 14 is configured as a thin film-like thin film structure 15.

  Here, in the semiconductor substrate 10, the recess 14 is formed by removing the first silicon layer 11 and the oxide film 13 on the back surface side, and has a circular hole shape as shown in FIG. Is. The thin film structure 15 is constituted by the second silicon layer 12 located on the surface side of the semiconductor substrate 10 and has a circular thin plate shape.

  A lower electrode film 20, a piezoelectric film 30, and an upper electrode film 40 are sequentially stacked on the surface of the thin film structure 15 (upper surface in FIG. 1A). The piezoelectric film 30 and the electrode films 20 and 40 sandwiching the piezoelectric film 30 are the same as those in a general piezoelectric membrane sensor, and can be formed by a normal semiconductor process.

  For example, the lower electrode film 20 is a film made of polysilicon, aluminum, or the like, and the piezoelectric film 30 is a piezoelectric body such as lead zirconate titanate (PZT: Pb (Zr, Ti) O 3) or zinc oxide (ZnO). The upper electrode film 40 is a film made of aluminum or the like.

  As described above, in FIG. 1A, a laminated body formed on the concave portion 14, that is, a laminated film obtained by sequentially laminating the lower electrode film 20, the piezoelectric film 30, and the upper electrode film 40 on the thin film structure 15. The membrane 50 is configured. Here, since the concave portion 14 has a circular hole shape and the thin film structure 15 is a circular film, the membrane 50 is also a circular thin film. That is, the planar shape of the membrane 50 is determined by the hole shape of the recess 14.

  Furthermore, in this embodiment, in such a thin film-like membrane 50, the neutral axis J (see FIG. 2 described later) in the bending of the membrane 50 straddles the piezoelectric film 30 in the membrane 50 and is above and below the piezoelectric film 30. The laminated structure of the membrane 50 is partially different so as to be positioned on the film.

  Although the positional relationship of the neutral axis J will be described later, in the present embodiment, the membrane 30 is configured so that the stress generated in the piezoelectric film 30 when the membrane 50 is bent has the same polarity over the entire area of the membrane 50. Is configured.

  In the present embodiment, the laminated structure of the membrane 50 is partially changed by adding an additional film 60 in a part of the entire area of the membrane 50 as shown in FIG.

  Here, the additional film 60 is provided in the central portion of the membrane 50 and is not provided in the peripheral portion of the membrane 30. Further, the additional film 60 is disposed above the piezoelectric film 30, and in particular, in the example illustrated in FIG. 1, the additional film 60 is disposed above the upper electrode film 40.

  As this additional film 60, a silicon oxide film or silicon nitride film formed by plasma CVD, a metal film such as aluminum or an aluminum alloy formed by sputtering or vapor deposition, or a polyimide formed by printing or the like. A resin film made of a resin material such as can be used.

  Further, the additional film 60 is not limited to a single layer film, and one or more kinds of films selected from these silicon oxide films, silicon nitride films, metal films, resin films, and the like are laminated. It may be a laminated layer.

  Such an additional film 60 is formed by, for example, various kinds of processes used for semiconductor processes and the like after the membrane 50 excluding the additional film 60 is manufactured by a general manufacturing process of this type of piezoelectric membrane sensor. It can be formed by a film forming method.

  The configuration and operation of the additional film 60 in the pressure sensor 100 will be described in more detail with reference to FIG. FIG. 2 is a schematic cross-sectional view for explaining the operation of the pressure sensor 100 of the present embodiment.

  As shown in FIG. 2, the pressure sensor 100 measures the pressure P received by the membrane 50. FIG. 2 shows a case where a positive pressure P is applied as the pressure P to the surface side of the membrane 50.

  When a positive pressure P is applied, the membrane 50 has a downwardly convex shape near the center of the membrane 50 and an upwardly convex shape near the periphery of the membrane 50, as shown in FIG. Sag.

  Then, an electrical change due to the piezoelectric phenomenon of the piezoelectric film 30 occurs with the bending generated in the membrane 50, and this electrical change is caused by the upper and lower electrode films 20, 40 sandwiching the piezoelectric film 30. , 40 is detected as a voltage change.

  The electrical signals from the electrode films 20 and 40 are processed by a sensing circuit (not shown) that is electrically connected to the electrode films 20 and 40, and are output as sensor signals. Thereby, the pressure P is measured.

  Here, in this embodiment, the membrane 50 is provided with the additional film 60, and the laminated structure of the membrane 50 is partially different. As a result, a neutral axis J (shown by a thick broken line in FIG. 2) in the bending of the membrane 50 straddles the piezoelectric film 30 in the membrane 50 and is positioned above the piezoelectric film 30, and the neutral axis J Are formed on the lower side.

  Specifically, as shown in FIG. 2, the neutral axis J is located above the piezoelectric film 30 at the center of the membrane 50, and the piezoelectric film 30 is located at other portions of the membrane 50, that is, at the periphery of the membrane 50. The neutral axis J is located below the lower side. In other words, in the present embodiment, the additional film 60 is provided only in the central portion of the membrane 50, and the central portion is partially thickened so that the neutral axis J of the central portion of the membrane 50 is below the conventional piezoelectric film 30. It is moved from the side to the upper side as in this embodiment.

  By realizing such an arrangement of the neutral axis J, as shown in FIG. 2, the stress generated in the piezoelectric film 30 when the membrane 50 is bent by the application of the positive pressure P extends over the entire area of the membrane 50. Tensile stress, that is, the same polarity.

  Therefore, in the present embodiment, the generated charges due to the piezoelectric d31 constant have the same polarity over the entire surface of the membrane 50, similarly to the stress generated in the piezoelectric film 30 when the membrane 50 is bent.

  Here, FIG. 2 shows the action in a state where the positive pressure P is applied to the membrane 50, but the same applies to the case of the negative pressure P. FIG. 3 shows a state in which the negative pressure P is applied to the surface side of the membrane 50 in the pressure sensor 100 of the present embodiment.

  In this case, as shown in FIG. 3, when negative pressure P is applied, the membrane 50 has an upwardly convex shape near the center of the membrane 50, as shown in FIG. 3. The vicinity is bent so as to have a downwardly convex shape. Also in this case, as in the case of the positive pressure, the electrical change of the piezoelectric film 30 due to the bending can be taken out by the upper and lower electrode films 20 and 40 and the pressure can be measured.

  Here, also in the case of application of the negative pressure P, the neutral axis J is located above the piezoelectric film 30 in the central part of the membrane 50 and located below the piezoelectric film 30 in the peripheral part. Thereby, in the case of the negative pressure P, the stress generated in the piezoelectric film 30 becomes a compressive stress over the entire area of the membrane 50. Then, as in the case of the positive pressure described above, the generated charges have the same polarity over the entire surface of the membrane 50.

  As described above, according to the present embodiment, the membrane 50 is provided with the additional film 60 as a neutral axis adjusting film, thereby causing a problem of a decrease in the amount of output charge due to cancellation of charges having opposite polarities as in the prior art. The output charge amount can be increased without dividing the upper and lower electrode films as in the prior art. As a result, in this embodiment, it is possible to prevent a decrease in sensor sensitivity.

  Here, the region to which the additional film 60 is added in the membrane 50 corresponds to the polarity of the stress generated in the piezoelectric film 30. Therefore, in the membrane 50 in the state before adding the additional film 60, the stress distribution between the tensile stress region and the compressive stress region is predicted by numerical analysis, and the arrangement pattern of the additional film 60 is designed according to this stress distribution. That's fine.

  In the present embodiment, the circular membrane 50 is formed by forming the concave portion 14 into a circular hole shape. However, when the membrane 50 is circular, the stress distribution is 2 between the tensile stress region and the compressive stress region. Two regions are concentrically separated. Therefore, in the present embodiment, as shown in FIG. 1B, the circular additional film 60 is provided so as to be concentric with the membrane 50.

  By the way, as the additional film 60, each of the above-described films can be adopted, but a silicon oxide film, a silicon nitride film, and a metal film such as aluminum or an aluminum alloy, which are used in a general semiconductor process, are prominent.

  The formation of the additional film 60 is close to the end of the process as described above, and a relatively low temperature process is required. Therefore, a silicon oxide film and a silicon nitride film formed by plasma CVD are particularly effective as the additional film 60. Polysilicon is not preferable because it is difficult to form after formation of the piezoelectric film 30 in view of the film formation temperature.

  Further, as described above, a resin film such as polyimide used in a semiconductor process can be used as the additional film 60, but generally, an organic material is soft, that is, has a small Young's modulus. Therefore, since the influence on the rigidity is small, that is, the effect of moving the neutral axis J is small, the resin film needs to be relatively thick.

  By the way, as this type of piezoelectric membrane sensor, as shown in FIG. 1, the membrane 50 is formed by sequentially laminating a lower electrode film 20, a piezoelectric film 30, and an upper electrode film 40. In general, the thin film structure 15 is included on the lower side (the back side of the membrane 50). For this reason, normally, the lower part of the piezoelectric film 30 is thicker than the upper part (the surface side of the membrane 50).

  As described above, when the lower part of the membrane 50 is thicker than the piezoelectric film 30, the additional film 60 for adjusting the neutral axis is disposed above the piezoelectric film 30, so that the stress generated in the piezoelectric film 30 described above is applied. The effect of having the same polarity over the entire area of the membrane 50 is obtained. It seems that the same effect can be obtained even below the piezoelectric film 30, but since it is a completely opposite effect, it is meaningful to arrange it on the upper side.

  When the additional film 60 is provided above the piezoelectric film 30, the additional film 60 may be inserted between the piezoelectric film 30 and the upper electrode film 40. However, when an insulating film is inserted as the additional film 60 between the piezoelectric film 30 and the upper electrode film 40, a capacitor is connected in series between the piezoelectric film 30 and the upper electrode film 40. The charge generated on the surface of the piezoelectric film 30 is reduced, and the output charge amount is likely to decrease.

  Therefore, when the insulating film such as the above-described silicon oxide film, silicon nitride film, or resin film is used as the additional film 60, it is more efficient that the additional film 60 is disposed above the upper electrode film 40. However, in the case where a metal film is used as the additional film 60, even if it is disposed between the piezoelectric film 30 and the upper electrode film 40, there is almost no electrical influence as described above, and a decrease in the amount of output charge can be prevented.

  When the neutral axis J is above the piezoelectric film 30 on the entire surface of the membrane 50 before the additional film 60 is formed, the additional film 60 is partially below the piezoelectric film 30 in the membrane 50. It may be provided.

(Second Embodiment)
FIG. 4 is a diagram showing a configuration of a pressure sensor 200 as a piezoelectric membrane sensor according to a second embodiment of the present invention, (a) is a diagram showing a schematic cross-sectional configuration along the thickness direction of the membrane 50, (B) is a top view of (a) and is a diagram showing a schematic planar configuration of the membrane 50 and its peripheral part. FIG. 4A shows a state in which the membrane 50 is bent with a positive pressure. In FIG. 4B, the surface of the additional film 60 is hatched for convenience of identification.

  In the first embodiment, the additional film 60 is provided in the central portion of the membrane 50 and is not provided in the peripheral portion, thereby straddling the piezoelectric film 30 and in the central portion of the membrane 50 above the piezoelectric film 30. The vertical axis J is positioned, and the neutral axis J is positioned below the piezoelectric film 30 in the other peripheral portions.

  On the other hand, in the pressure sensor 200 of this embodiment, as shown in FIG. 4, the additional film 60 is provided in the peripheral portion of the membrane 50 and is not provided in the central portion. That is, in the concentric stress distribution generated in the circular membrane 50 before forming the additional film 60 as described above, in the above embodiment, the additional film 60 is provided in a circular region where compressive stress is generated when positive pressure is applied. In this embodiment, the additional film 60 is provided in a concentric region that becomes tensile stress when a positive pressure is applied.

  Thereby, in the present embodiment, the peripheral portion of the membrane 60 is partially thick, straddling the piezoelectric film 30, the neutral axis J is located below the piezoelectric film 30 at the center of the membrane 50, and the others In the portion of the membrane 50, the neutral axis J is positioned above the piezoelectric film 30.

  In this case, as shown in FIG. 4, the stress generated in the piezoelectric film 30 when the membrane 50 is bent by applying positive pressure is a compressive stress, that is, the same polarity over the entire area of the membrane 50.

  Therefore, in this embodiment as well, as in the above embodiment, the charge generated in the piezoelectric film 30 can have the same polarity over the entire surface of the membrane 50, and the output charge can be output without dividing the upper and lower electrode films. The amount can be increased.

(Other embodiments)
In the above embodiment, the pressure sensor may be formed integrally with the sensing circuit. As described above, when the sensing circuit is integrally formed, a film used in the circuit forming process can be used as the additional film. In this case, the additional film may be patterned using a process of patterning a film used in the circuit formation process.

  In this case, specifically, for example, when a silicon nitride film is used as the additional film 60, the passivation film included in the circuit process can be shared. Furthermore, the additional film 60 can be formed by sharing the passivation film patterning step. That is, a desired effect can be obtained without adding any process.

  In addition, when the sensing circuit is formed integrally, when an oxide film is used as the additional film 60, an interlayer insulating film or the like can be shared. Further, when a metal film is used as the additional film 60, any of the multilayer wiring forming steps performed when multilayer wiring is used in the circuit process can be used.

  Of course, a laminate of all of these may be used as the additional film 60. This method can be used when a thick film is required as the additional film 60. When laminating, it is difficult in terms of process to align the pattern edges of each layer to the same. This is because the alignment between the patterns is difficult in the first place because, for example, the step becomes large, the resist application in the photolithography process is hindered. For this reason, the pattern edges of each layer need only be slightly shifted. Usually, the size of the membrane 50 is often large, such as several hundred um or more, and the above-mentioned deviation hardly causes a problem.

  Moreover, as the membrane 50 in the said embodiment, it is good also as a rectangular membrane by making the recessed part 14 into a rectangular hole shape. In the case of the rectangular shape, the stress distribution in the tensile stress region and the compressive stress region is somewhat complicated as compared with the circular shape described above, but the point is divided into two regions. Therefore, in this case as well, the stress distribution may be predicted by numerical analysis, and the arrangement pattern of the additional film 60 may be designed according to the stress distribution.

  Further, in the above-described embodiment, partially changing the laminated structure of the membrane 50 is performed by adding the additional film 60 partially on the membrane 50, but the point is to change the laminated structure. Thus, the membranes may be partially different in thickness so that the neutral axis movement effect described above can be exhibited. Therefore, in addition to the additional film 60, for example, a method of partially changing the number of layers in the membrane 50 to partially change the thickness may be employed.

  Further, the present invention can be applied to the membrane 50 as long as the membrane 50 is a thin film having a laminated structure in which a lower electrode film, a piezoelectric film, and an upper electrode film are sequentially laminated. In the illustrated example described above, the portion of the membrane 50 excluding the additional film 60 shows three layers of the lower electrode film 20, the piezoelectric film 30, and the upper electrode film 40. However, in addition to these three layers 20 to 40, The membrane 50 may be provided with a layer such as a protective film for protecting the surface or an interlayer film interposed between the internal layers.

  Further, the semiconductor substrate 10 is limited to the above-described SOI substrate as long as the recess 14 is formed on the back surface thereof by etching or the like, and the surface side corresponding to the recess 14 can be configured as the thin film structure 15. It is not a thing.

  In the above embodiment, the pressure sensor has been mainly described. However, the present invention is not limited to the pressure sensor as long as it is a piezoelectric membrane sensor, and may be applied to an ultrasonic sensor or the like. .

It is a figure which shows the structure of the pressure sensor which concerns on 1st Embodiment of this invention, (a) is a schematic sectional drawing, (b) is a top view of (a). It is a schematic sectional drawing which shows the state which applied the positive pressure in the pressure sensor of the said 1st Embodiment. It is a schematic sectional drawing which shows the state which applied the negative pressure in the pressure sensor of the said 1st Embodiment. It is a figure which shows the structure of the pressure sensor which concerns on 2nd Embodiment of this invention, (a) is a schematic sectional drawing, (b) is a top view of (a). It is a schematic sectional drawing of the piezoelectric membrane sensor as a prototype of this inventor.

Explanation of symbols

20 ... Lower electrode film, 30 ... Piezoelectric film, 40 ... Upper electrode film, 50 ... Membrane,
60: Additional film as an additional film, J: Neutral axis.

Claims (1)

A thin film membrane (50) having a laminated structure in which a lower electrode film (20), a piezoelectric film (30) made of a piezoelectric body, and an upper electrode film (40) are sequentially laminated on a substrate (10),
Polarity of stress generated at the central portion and the peripheral portion of the membrane (50) when the membrane (50) is bent by fixing the outer peripheral end of the membrane (50) to the substrate (10). Is supposed to be reversed,
An electrical change due to the piezoelectric phenomenon of the piezoelectric film (30) accompanying the bending occurring in the membrane (50) is detected by the upper and lower electrode films (20, 40),
In the piezoelectric membrane sensor in which the neutral axis (J) in the bending of the membrane (50) is located below the piezoelectric film (30),
The neutral axis (J) in the bending of the membrane (50) is located above and below the piezoelectric film (30) across the piezoelectric film (30) in the membrane (50). By partially varying the laminated structure of the membrane (50) so that a part is formed,
The stress generated in the piezoelectric film (30) when the membrane (50) is bent has the same polarity over the entire area of the membrane (50),
When the laminated structure of the membrane (50) is partially different, the upper electrode film (40) in which the film (60) is partially above the piezoelectric film (30) in the membrane (50). It is done by placing and adding to the side,
Furthermore, the membrane (60) to be added is provided in the peripheral portion of the membrane (50), and is not provided in the central portion.

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