JP2017216728A - Electromechanical converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromechanical converter or the like that can prevent light from entering a reception surface without deteriorating mechanical characteristics of a vibration film.SOLUTION: An electromechanical converter includes at least one cell structure 2 of movably supporting a vibration film 7 including one electrode 8 of two electrodes 3 and 8 having a gap 5 in between. In the electromechanical converter, on the vibration film 7 provided is a stress relaxation layer 9 having acoustic impedance matched with the vibration film 7, and a light reflection layer 6 is provided on the stress relaxation layer 9.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electromechanical transducer such as a capacitive electromechanical transducer used as an ultrasonic transducer or the like.

Conventionally, micromechanical members manufactured by micromachining technology can be processed on the micrometer order, and various micro functional elements are realized using these. A capacitive electromechanical transducer such as a CMUT (Capacitive Micromachined Ultrasonic Transducer) using such a technique has been studied as an alternative to a piezoelectric element. According to such a capacitance type electromechanical transducer, acoustic waves such as ultrasonic waves can be transmitted and received using the vibration of the vibrating membrane, and excellent broadband characteristics can be easily obtained particularly in liquid. On the other hand, an ultrasonic transducer that receives a photoacoustic wave emitted from the inside of a subject by illuminating a measurement object with illumination light (such as near infrared rays) has been proposed (see Patent Document 1). In this transducer, a light reflecting member for reflecting light is provided, and this light reflecting member is configured to be larger than the receiving surface of the ultrasonic transducer that receives the photoacoustic wave.

JP 2010-075681 A

When a capacitive electromechanical transducer is used as a sensor for receiving a photoacoustic wave, when light for generating the photoacoustic wave is incident on the device, a photoacoustic wave is generated on the receiving surface of the device, resulting in noise. Become. In order to prevent such a situation, when the reflecting member is arranged immediately above the receiving surface of the capacitive electromechanical transducer so that light does not enter, this time, the change in the spring constant of the vibrating membrane constituting the device, the vibrating membrane Variation in the amount of deformation occurs. This may cause a decrease in sensitivity, variation, and a decrease in bandwidth of the capacitive electromechanical transducer.

In view of the above problems, an electromechanical transducer according to the present invention is a capacitance-type electromechanical transducer including a plurality of cell structures, and the cell structures are arranged in a stacking direction on a substrate. And a vibration film configured to include a second electrode provided with a gap from the first electrode, and a light reflection layer corresponding to the plurality of cell structures includes the vibration film. A stress relaxation layer that is provided on the film and is commonly used for the plurality of cell structures is provided between the vibration film and the light reflection layer.

In the electromechanical transducer of the present invention, the stress relaxation layer is provided on the vibration film as the device receiving surface, and the light reflection layer is provided thereon. Accordingly, the influence of the stress of the light reflecting layer does not reach the receiving surface so much that the vibration film is hardly deformed. Thereby, the performance variation of the electromechanical transducer which formed the light reflection layer can be reduced, and elastic waves, such as a photoacoustic wave, can be received.

It is a figure for demonstrating the electromechanical converter of Embodiment and Example 1 of this invention. It is sectional drawing for demonstrating the electromechanical converter of Example 2 of this invention. It is a schematic diagram for demonstrating the photoacoustic apparatus of this invention.

A feature of the electromechanical conversion device of the present invention is that a stress relaxation layer is provided on a vibration film having a cell structure, and a light reflection layer is provided on the stress relaxation layer. In the cell structure, for example, a gap is formed between the substrate, the first electrode on one surface side of the substrate, the vibrating membrane having the second electrode, and the first electrode and the vibrating membrane. And a diaphragm supporting portion that supports the diaphragm. The cell structure can be manufactured by a so-called surface type or junction type manufacturing method. The example of FIG. 1 described later has a structure that can be manufactured by a bonding type manufacturing method, and the example of FIG. 2 described later has a structure that can be manufactured by a surface type manufacturing method.

Hereinafter, an embodiment of the present invention will be described with reference to FIG. Fig.1 (a) is a top view of the electrostatic capacitance type electromechanical transducer of this embodiment, FIG.1 (b) is AB sectional drawing of Fig.1 (a). The electromechanical transducer has a plurality of elements 1 having a cell structure 2. In FIG. 1, only four elements 1 are shown, but any number of elements may be used. Each element 1 is composed of nine cell structures 2, but the number of cell structures 2 may be any number.

The cell structure 2 of the present embodiment includes a vibration film 7, a gap 5 such as a gap, a vibration film support portion 4 that supports the vibration film 7 so as to vibrate, and a silicon substrate 3. The vibration film 7 is made of single crystal silicon, but may be a vibration film (for example, a silicon nitride film) formed by lamination. The vibration film 7 has a metal (aluminum thin film 8 or the like) serving as a second electrode inside or on the vibration film. In the present invention, the membrane portion made of a silicon nitride film or a single crystal silicon film and the second electrode portion are collectively expressed as a vibration film. In addition, when the vibration film 7 is low-resistance single crystal silicon, single crystal silicon can be used as the second electrode, and therefore a metal serving as the second electrode need not be disposed. The silicon substrate 3 has a low resistance and can be used as the first electrode. When a silicon substrate is not used as the first electrode, a metal can be formed on the substrate as the first electrode. In addition, when an insulating substrate such as a glass substrate is used as the substrate, the first electrode is formed on the substrate. The first and second electrodes are provided across the gap 5.

The electromechanical transducer of this embodiment includes a stress relaxation layer 9 on the acoustic wave receiving surface. The stress relaxation layer 9 is formed directly on the vibration film when the first electrode is formed in the vibration film, and on the first electrode when the first electrode is formed on the vibration film. Formed. The stress relaxation layer 9 is desirably arranged larger than the entire receiving surface including the entire cell structure. The stress relaxation layer does not increase the deformation amount of the vibration film 7 and does not change the mechanical characteristics such as the spring constant. Moreover, it is preferable that the acoustic impedance is approximately the same as that of the receiving surface having the vibrating membrane 7. Specifically, the Young's modulus is preferably 0 MPa or more and 100 MPa or less, and the acoustic impedance is 1 MRayls or more and 2 MRayls or less. If the stress relaxation layer has a Young's modulus of 100 MPa or less, the influence of the stress of the light reflecting layer 6 (described later) on the vibration film is relaxed and the rigidity (Young's modulus) is sufficiently small. Almost no change in mechanical properties. Further, by having an acoustic impedance of 1 MRayls or more and 2 MRayls or less, the acoustic impedance is almost the same as the acoustic impedance of the acoustic wave receiving surface, and reflection of acoustic waves at the interface between the vibration film 7 and the stress relaxation layer 9 can be suppressed. The acoustic impedance of the receiving surface is an acoustic impedance that can be converted from the spring constant of the vibrating membrane, the mass, the capacitance of the element, and the like. For example, in the case of a CMUT having a center frequency of 1 to 10 MHz, it is 0.01 to 5 MRayls. However, the acoustic impedance of the receiving surface varies depending on the shape of the cell. Further, when the electromechanical transducer of this embodiment is used in a medium having a low acoustic impedance such as water (the acoustic impedance of water is about 1.5 MRayls), if the stress relaxation layer is 1 MRayls or more and 2 MRayls or less, Reflection at the interface between the stress relaxation layer and the medium can be reduced.

Furthermore, the electromechanical transducer of this embodiment has a light reflecting layer 6 on the stress relaxation layer 9. The light reflecting layer 6 is mainly for reflecting light having a wavelength of a light source used for generating a photoacoustic wave by irradiating the subject with light, and is a film having a high reflectance with respect to the wavelength of the light source. I just need it. As the light reflecting layer 6, Al, Au, a dielectric multilayer film, or the like is used. The light reflecting layer 6 is desirably disposed on the entire surface of the stress relaxation layer 9. It is more desirable that the light reflecting layer 6 is disposed on all members located on the subject side of the receiving surface in the electromechanical transducer. With this configuration, it is possible to prevent noise generated when the electromechanical transducer is irradiated with laser light. The reflectance of the light reflecting layer 6 is preferably 80% or more, and more preferably 90% or more in the light used. In addition, since the light reflection layer 6 is disposed on the receiving surface, it is necessary to propagate the acoustic wave with almost no attenuation. Specifically, it is preferably 10 μm or less.

The driving principle of this embodiment will be described. Here, the element 1 is formed on the silicon substrate 3 used as the first electrode, and the vibration film 7 is used as the second electrode. The element 1 can draw an electric signal from the first electrode or the second electrode by providing a lead wiring (not shown) on the substrate or in the through-hole substrate. When receiving an acoustic wave, a DC voltage is applied to the first electrode or the second electrode by a voltage applying means (not shown). When the acoustic wave is received, the vibration film 7 is deformed, so that the distance of the gap 5 between the vibration film 7 including the second electrode and the substrate 3 that is the first electrode changes, and the capacitance changes. Due to this change in capacitance, a current flows through a lead wiring (not shown). An acoustic wave can be received using this current as a voltage by a current-voltage conversion element (not shown). In addition, the single-crystal silicon vibrating membrane 7 can be vibrated by electrostatic force by applying a DC voltage and an AC voltage to the silicon substrate 3 as the first electrode or the vibrating membrane 7 as the second electrode. Thereby, an acoustic wave can also be transmitted.

The capacitive electromechanical transducer of this embodiment can be used to receive photoacoustic waves. A photoacoustic wave is an acoustic wave (typically an ultrasonic wave) generated from a subject that has irradiated the subject with a short pulse laser and absorbed the light. Therefore, it is necessary to irradiate a subject (not shown) with light such as a laser. When scattered light or the like from a light source such as a laser enters the receiving surface of the apparatus, the vibration film 7 or the like constituting the receiving surface absorbs scattered light or the like from the light source and generates an acoustic wave on the receiving surface. , It becomes noise. In order to prevent this, a light reflecting layer is used. However, in the case of a capacitive electromechanical transducer in which a light reflecting layer is provided directly on the receiving surface, the deformation amount or vibration of the vibrating film is affected by the stress of the light reflecting layer. Mechanical properties such as the spring constant of the membrane change. Therefore, as described above, sensitivity variations and band variations occur between the cell structures and between the elements, resulting in deterioration of the device characteristics. On the other hand, the capacitive electromechanical transducer of this embodiment has the light reflecting layer 6 on the stress relaxation layer 9. Since the stress relaxation layer 9 has a small Young's modulus, even when the stress relaxation layer is formed by curing, the deformation of the vibration film and the change of the spring constant due to the stress at the time of curing can be suppressed. In addition, since the acoustic impedance is approximately the same as that of the reception surface, reflection of the reception acoustic wave at the interface between the stress relaxation layer and the reception surface can be suppressed. Further, since the light reflecting layer 6 is provided, light does not enter the receiving surface. Therefore, when the apparatus of this embodiment is used as a sensor that receives photoacoustic waves, noise can be reduced. Further, since the light reflecting layer 6 is disposed in the vicinity of the receiving surface, it is possible to prevent light such as scattered light entering from various angles from entering the receiving surface. Further, since the light reflecting layer 6 is integrated with the receiving surface, the capacitive electromechanical transducer that receives the photoacoustic wave can be reduced in size and can be easily incorporated into other devices.

In the capacitive electromechanical transducer of this embodiment, a light reflecting layer supporting layer that supports the light reflecting layer can also be provided between the stress relaxation layer 9 and the light reflecting layer 6 (Examples described later). 2). When the light reflection layer is formed directly on the stress relaxation layer, the stress reflection layer has a low Young's modulus, so that the light reflection layer may be bent or deformed by the stress of the light reflection layer. In addition, when the adhesion between the light reflection layer and the stress relaxation layer is low, the light reflection layer may peel off. In this configuration, since the light reflection layer is formed on the light reflection layer support layer having higher rigidity than the stress relaxation layer, the light reflection layer bends even if the light reflection layer support layer is bonded onto the stress relaxation layer. Alternatively, deformation can be prevented. The Young's modulus of the light reflection layer support layer that supports the light reflection layer 6 is preferably 100 MPa or more and 20 GPa or less. Moreover, the light reflection layer is supported by the light reflection layer support layer, and the light reflection layer support layer and the stress relaxation layer can be bonded by an adhesive method or an adhesive having high adhesion. Therefore, compared with the case where the light reflecting layer is directly formed on the stress relaxation layer, the light reflecting layer can be more reliably prevented from being bent or deformed, and the adhesion can be improved. it can. The light reflection layer support layer that supports the light reflection layer 6 preferably has an acoustic impedance of about 1 MRayls or more and 5 MRayls or less. By making the acoustic impedance of the light reflection layer support layer that supports the light reflection layer 6 close to the value of the acoustic impedance of the stress relaxation layer 9, the light reflection layer support layer that supports the light reflection layer 6 and the stress relaxation layer 9 The amount of acoustic wave reflection at the interface can be reduced.

In the above configuration, the stress relaxation layer 9 is preferably polydimethylsiloxane (PDMS). PDMS to which silica particles or the like are added, fluorosilicone obtained by substituting a part of hydrogen of PDMS with fluorine, or those obtained by adding silica particles to fluorosilicone may be used. The acoustic impedance can be adjusted by adding silica particles or the like. PDMS has an acoustic impedance of about 1 MRayls to 2 MRayls, and can suppress reflection of acoustic waves at the interface between the stress relaxation layer and the receiving surface. Furthermore, the compatibility with a living body is high. The light reflection layer support layer that supports the light reflection layer 6 is preferably higher in rigidity than the stress relaxation layer 9. When polydimethylsiloxane is used as the stress relaxation layer, for example, a resin light reflecting layer support layer such as polymethylpentene, polycarbonate, acrylic, polyimide, polyethylene, and polypropylene can be used. However, the present invention is not limited to this as long as the rigidity of the light reflection layer support layer is higher than that of the stress relaxation layer. In particular, the acoustic impedance of trimethylpentene is about 1.8 MRayls, the polycarbonate is about 2.5 MRayls, and the acoustic impedance is 3 MRayls or less, which is very low. Therefore, it is possible to reduce the amount of acoustic wave reflection at the interface between the light reflection layer support layer that supports the light reflection layer 6 and the stress relaxation layer 9. Furthermore, when the electromechanical transducer according to this embodiment is used in a medium with low acoustic impedance, the difference in acoustic impedance between the light reflecting layer supporting layer that supports the light reflecting layer 6 and the medium is small. The amount of reflected acoustic waves can be reduced. Furthermore, since the surface roughness of polycarbonate can be reduced, the surface roughness of the reflective film can also be reduced, and a decrease in reflectance can be prevented.

Hereinafter, the present invention will be described in detail with reference to more specific examples.
Example 1
The configuration of the capacitance type electromechanical transducer of Example 1 will be described with reference to FIG. The electromechanical transducer of this embodiment has a plurality of elements 1. In FIG. 1, only four elements are shown, but any number of elements may be used.

The cell structure 2 includes a single crystal silicon vibration film 7 having a thickness of 1 μm, a gap 5, a vibration film support portion 4 that supports the single crystal silicon vibration film 7 having a resistivity of 0.01 Ωcm, and a silicon substrate 3. . The silicon substrate 3 has a thickness of 300 μm and a resistivity of 0.01 Ωcm. The shape of the vibrating membrane 7 of the present embodiment is a circle having a diameter of 30 μm, but the shape may be a square, a hexagon, or the like. The single crystal silicon vibration film 7 is mainly made of single crystal silicon, and since a layer having a large residual stress is not formed on the vibration film 7, the uniformity between the elements 1 is high, and the variation in transmission / reception performance can be reduced. . In order to improve the conductive characteristics of the single crystal silicon vibration film 7, an aluminum thin film 8 of about 200 nm can be formed. In this configuration, the diaphragm support 4 is silicon oxide, the height of the diaphragm support 4 is 300 nm, and the gap 5 is 200 nm.

Since the single crystal silicon vibration film 7 and the silicon substrate 3 have low resistance, they can be used as the first electrode or the second electrode. In the capacitance type electromechanical transducer of this embodiment, the lead-out wiring is formed on the silicon substrate, or the silicon substrate having the through-wiring is used, so that an electric signal is transmitted from the first electrode or the second electrode. It can be pulled out. The driving principle of reception and transmission is as described in the above embodiment.

In the capacitive electromechanical transducer of the present embodiment, the stress relaxation layer 9 is disposed on the receiving surface, and the light reflection layer 6 is disposed on the stress relaxation layer 9. The stress relaxation layer 9 is PDMS, and the light reflection layer 6 is gold. The acoustic impedance of the stress relaxation layer 9 is 1.8 MRayls and the thickness is 100 μm. Since the difference in acoustic impedance between the stress relaxation layer 9 and the silicon vibration film 7 is very small, reflection of acoustic waves at the interface between the stress relaxation layer and the receiving surface hardly occurs. Further, when the electromechanical transducer of this embodiment is used in a medium having a low acoustic impedance such as water, the difference between the acoustic impedance of the stress relaxation layer 9 and the medium is very small. Reflection at the interface can be reduced. Therefore, when receiving an acoustic wave, the received signal does not deteriorate in intensity. The light reflecting layer 6 is for reflecting light having a wavelength of a light source used for generating a photoacoustic wave, and may be a film having a high reflectance with respect to the wavelength of the light source. As the light reflecting layer 6, Al, a dielectric multilayer film, or the like can also be used. The capacitance type electromechanical transducer of this example can be used to receive photoacoustic waves as described in the above embodiment.

(Example 2)
The configuration of the capacitive electromechanical transducer of Example 2 will be described with reference to FIG. The configuration of the electromechanical transducer of Example 2 is almost the same as that of Example 1. The cell structure includes an upper electrode 37, a vibration film 36 having a thickness of 1 μm, a gap 34, a vibration film support portion 35 that supports the vibration film 36, an insulating film 33, a lower electrode 32, and a substrate 30. The substrate 30 is a silicon substrate, the vibration film 36 and the vibration film support portion 35 are silicon nitride films, and the upper electrode 37 and the lower electrode 32 are aluminum. An oxide film 31 is disposed between the substrate 30 and the lower electrode 32 to insulate them from each other. When the substrate 30 is a low resistance silicon substrate or an insulating substrate such as glass, the oxide film 31 may not be provided.

The substrate 30 has a thickness of 300 μm. In this configuration, the vibration film 36 has a circular shape with a diameter of 30 μm. The height of the vibration film support portion 35 is 300 nm, and the gap 34 is 200 nm. Further, the stress relaxation layer 38 is disposed on the receiving surface, and the light reflection layer 41 is disposed on the stress relaxation layer 38. In order to maintain the rigidity of the light reflection layer 41, the light reflection layer 41 is formed on the high-rigidity light reflection layer support layer 40. The high-rigidity light reflection layer support layer 40 having the light reflection layer 41 is bonded to the stress relaxation layer 38 with a resin 39.

The stress relaxation layer 38 is PDMS. The acoustic impedance of the stress relaxation layer 38 is 1.8 MRayls and the thickness is 50 μm. The acoustic impedance of the stress relaxation layer 38 is preferably 1 MRayls to 2 MRayls, so that almost no acoustic wave reflection occurs at the interface between the stress relaxation layer and the receiving surface. Therefore, when receiving an acoustic wave, the received signal does not deteriorate in intensity. The stress relaxation layer 38 can be produced by spin coating, dripping, press-fitting using a mold, or pasting a formed stress relaxation layer.

The light reflection layer 41 is gold, and the high-rigidity light reflection layer support layer 40 that supports the light reflection layer 41 is polycarbonate. This has a Young's modulus of 2.5 × 10 ⁹ Pa and a thickness of 100 μm. Since the stress relaxation layer 38 has a low Young's modulus, the light reflection layer may be bent or deformed by the stress of the light reflection layer 41 or the like. In addition, when the adhesion between the light reflection layer 41 and the stress relaxation layer 38 is low, the light reflection layer may be peeled off. In this configuration, since the light reflection layer 41 is formed on the light reflection layer support layer 40 having a higher rigidity than the stress relaxation layer 38, the light reflection layer support layer 40 can be bonded to the stress relaxation layer 38 even if the light reflection layer support layer 40 is bonded. It is possible to prevent the reflective layer 41 from being bent or deformed. Further, the light reflecting layer 41 is supported by the light reflecting layer support layer 40, and the light reflecting layer support layer 40 and the stress relaxation layer 38 can be bonded by a bonding method or an adhesive having high adhesion. Therefore, the adhesion can be improved as compared with the case where the light reflecting layer is directly formed on the stress relaxation layer.

The acoustic impedance of the polycarbonate of the light reflection layer support layer 40 is 2.4 MRayls. Since the difference in acoustic impedance between the stress relaxation layer 38, the high-rigidity light reflecting layer support layer 40, and the receiving surface is relatively small, reflection of acoustic waves at each interface is very small. Therefore, it can be received without reducing the intensity of the acoustic wave signal. The high-rigidity light reflecting layer support layer 40 may have any acoustic impedance that is substantially equal to the acoustic impedance of the stress relaxation layer 38, and may be acrylic, polyimide, polyethylene, or the like. The acoustic impedance of the high-rigidity light reflecting layer support layer 40 is preferably 1 MRayls to 5 MRayls. As the resin 39 for bonding the high-rigidity light reflection layer support layer 40 and the stress relaxation layer 38, a silicon-based adhesive can be used. Also, an adhesive such as epoxy can be used. Also in this example, the same effects as those of the above embodiment and examples can be obtained.

(Example 3)
The electromechanical transducer of each of the above embodiments can be used for a photoacoustic apparatus using a photoacoustic imaging technique. In photoacoustic imaging, a subject is first irradiated with pulsed light, and an acoustic wave generated by the absorption of light energy propagated and diffused in the subject is received. This is a technique for imaging information inside the subject by using the received acoustic wave signal. With this technique, optical characteristic distribution information such as an initial pressure generation distribution and a light absorption coefficient distribution in the subject can be obtained as image data.

A schematic diagram of a photoacoustic apparatus to which the present invention can be applied is shown in FIG. The photoacoustic apparatus of the present invention includes at least the light source 51, the electromechanical transducer 57 of each of the above embodiments that is an acoustic wave receiver, a signal processing unit 59, and a data processing unit 50. In this embodiment, the light 52 oscillated from the light source 51 is applied to the subject 53 via an optical member 54 such as a lens, a mirror, or an optical fiber. In the subject, the irradiated light is absorbed by a light absorber 55 (for example, a tumor or a blood vessel) in the subject, and an acoustic wave 56 is generated. The acoustic wave receiver 57 receives the acoustic wave 56 and converts it into an electrical signal, and outputs the electrical signal to the signal processing unit 59. The signal processing unit 59 performs signal processing such as A / D conversion and amplification on the input electric signal and outputs the signal to the data processing unit 50. The data processing unit 50 converts the input signal into image data and outputs it to the display unit 58. The display unit 58 displays an image based on the input image data.

As described above, according to the photoacoustic apparatus of the present invention, since the electromechanical transducer that is an acoustic wave receiver has the light reflection film, light is not incident on the receiving surface and image data with less noise can be generated.

DESCRIPTION OF SYMBOLS 1 ... Element, 2 ... Cell structure, 3 ... Board | substrate (electrode), 4 ... Vibration film support part, 5 ... Gap, 6 ... Light reflection layer, 7 ... Vibration film, 8 ... Aluminum thin film (electrode), 9 ... Stress relaxation layer

Claims (14)

A capacitance type electromechanical transducer including a plurality of cell structures,
The cell structure includes a first electrode in a stacking direction on a substrate, and a vibration film configured to include a second electrode provided with a gap from the first electrode,
A light reflection layer corresponding to the plurality of cell structures is provided on the vibration film, and is commonly used for the plurality of cell structures between the vibration film and the light reflection layer. A capacitance-type electromechanical transducer having a stress relaxation layer. The capacitance type electromechanical transducer according to claim 1, wherein the stress relaxation layer is disposed in a region larger than a receiving surface formed by the plurality of cell structures. The capacitance type electromechanical transducer according to claim 1, wherein the stress relaxation layer is thicker than the vibration film. 4. The capacitance-type electrostatic capacitor according to claim 1, wherein the stress relaxation layer is a layer for relaxing an influence on the vibration film due to stress of the light reflection layer. 5. Electromechanical converter. 5. The capacitance type electromechanical transducer according to claim 1, wherein the stress relaxation layer includes polydimethylsiloxane (PDMS). 6. The electrostatic electromechanical transducer according to claim 1, wherein the light reflecting layer is provided on the entire surface of the stress relaxation layer. The capacitance type electromechanical transducer according to claim 1, wherein the cell structures are two-dimensionally arranged. 8. The electrostatic capacitance type electromechanical transducer according to claim 1, wherein the vibration film includes the second electrode and a silicon nitride film. 9. The capacitance type electromechanical transducer according to claim 1, wherein the substrate includes a silicon substrate or an insulating substrate. The electrostatic electromechanical transducer according to any one of claims 1 to 9, wherein the light reflecting layer is Al, Au, or a dielectric multilayer film. 11. The capacitance type electromechanical transducer according to claim 1, wherein the light reflecting layer has a thickness in the stacking direction of 10 μm or less. The capacitance type according to any one of claims 1 to 11, wherein a light reflection support layer having higher rigidity than the stress relaxation layer is provided between the stress relaxation layer and the light reflection layer. Electromechanical converter. The acoustic impedance of the stress relaxation layer is adjusted so that reflection of acoustic waves at an interface between the vibration film and the stress relaxation layer can be reduced. The capacitance-type electromechanical transducer according to Item 1. light source,
An optical fiber for guiding the light from the light source and irradiating the subject;
The electromechanical transducer according to any one of claims 1 to 13,
A signal processing unit that performs A / D conversion on a signal from the electromechanical converter, and a data processing unit that generates image data relating to information inside the subject using an output signal from the signal processing unit. A photoacoustic apparatus.

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