Acoustic converter

Abstract

To improve sensitivity. [Solution] The sound conversion device 200 includes a diaphragm 220 attached to a support substrate 211, which deforms in response to sound pressure and generates an electric charge. The diaphragm 220 has a lower electrode layer 440, a first piezoelectric layer 460 formed on the lower electrode layer 440, an intermediate electrode 250 formed on the first piezoelectric layer 460, a second piezoelectric layer 360 formed on the intermediate electrode 250, and an upper electrode layer 330 formed on the second piezoelectric layer 360. The thickness of the intermediate electrode 250 is greater than that of the upper electrode layer 330 or the lower electrode layer 440.

Description

[[Technical Field]]

[0001] The present disclosure relates to an acoustic transducer. [[Background Art]]

[0002] For example, there is known a piezoelectric element including a piezoelectric film having one end supported and the other end serving as a free end, and a pair of electrodes arranged with the piezoelectric film interposed therebetween (see, for example, Patent Document 1). [[Prior Art Documents]] [[Patent Documents]]

[0003] [[Patent Document 1]] Japanese Unexamined Patent Publication No. 2019-140638 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0004] In an acoustic transducer including a piezoelectric element, improvement in sensitivity is required. An object of the present disclosure is to provide an acoustic transducer capable of improving sensitivity. [[Means for Solving the Problem]]

[0005] An acoustic transducer according to the present disclosure includes: a support substrate; and a vibration plate attached to the support substrate, the vibration plate being deformed in response to sound pressure to generate electric charges. The vibration plate includes a lower electrode, a first piezoelectric layer formed on the lower electrode, an intermediate electrode formed on the first piezoelectric layer, a second piezoelectric layer formed on the intermediate electrode, and an upper electrode formed on the second piezoelectric layer. A thickness of the intermediate electrode is greater than a thickness of the upper electrode or the lower electrode. [[Effects of the Invention]]

[0006] The present disclosure can provide an acoustic transducer capable of improving sensitivity. [[Brief Description of the Drawings]]

[0007] [Figure 1] This is a plan view illustrating an acoustic conversion device according to the first embodiment. [Figure 2] This is a perspective view illustrating an acoustic conversion device according to the first embodiment. [Figure 3] This is a perspective view illustrating the acoustic conversion device according to the first embodiment, viewed from the bottom. [Figure 4] This is a cross-sectional view illustrating an acoustic conversion device according to the first embodiment. [Figure 5] This is a magnified cross-sectional view illustrating a diaphragm (piezoelectric film). [Figure 6] This is a side view illustrating the distribution of electric charge generated on a diaphragm that deforms under sound pressure. [Figure 7] This is a magnified cross-sectional view illustrating a larger portion of the diaphragm. [Figure 8] This is a plan view illustrating an acoustic conversion device according to the second embodiment. [Figure 9] This is a cross-sectional view illustrating an acoustic conversion device according to the second embodiment, and is a cross-sectional view along the line IX-IX in Figure 8. [Figure 10] This is a circuit diagram of the sound conversion device according to the second embodiment. [Figure 11] This is an exploded perspective view illustrating an acoustic conversion device according to the third embodiment. [Figure 12] This is an exploded perspective view illustrating an acoustic conversion device according to the fourth embodiment. [Figure 13] This is a plan view illustrating an acoustic conversion device according to a modified example. [Figure 14] This is a perspective view illustrating an acoustic conversion device according to the fifth embodiment. [Figure 15] This is a partially enlarged cross-sectional view illustrating an enlarged portion of the cantilever of the acoustic converter according to the fifth embodiment. [Figure 16] This is a cross-sectional view illustrating the cross-section of a cantilever that deforms under sound pressure. [Figure 17] This is a cross-sectional view illustrating an acoustic conversion device according to the sixth embodiment. [Figure 18] This is a cross-sectional view illustrating an acoustic conversion device according to the seventh embodiment. [Figure 19] It is a perspective view illustrating an acoustic transducer according to an eighth embodiment. [Figure 20] It is a plan view illustrating an acoustic transducer according to a ninth embodiment. [Figure 21] It is a table showing the relationship between the thickness of the intermediate layer, the signal-to-noise ratio, and the resonance frequency. [Figure 22] FIG. 22(a) is a partially exploded perspective view illustrating an acoustic transducer according to a modification, and FIG. 22(b) is an enlarged view illustrating an enlarged intermediate layer. [Figure 23] It is a graph showing the relationship between the diameter ratio of a sensing region and a normalized signal-to-noise ratio. MODE FOR CARRYING OUT THE INVENTION

[0008] Hereinafter, an acoustic transducer according to an embodiment will be described with reference to the accompanying drawings. In the present specification and the drawings, substantially identical components may be denoted by the same reference numerals to omit redundant description. In addition, in the present specification, the terms "upper" and "lower" may be used. These terms refer to "upper" and "lower" in the state shown in FIG. 4. In the Z-axis direction, the side where the upper electrode 30 is disposed is defined as "upper", and the side where the lower electrode 40 is disposed is defined as "lower". The actual arrangement of the acoustic transducer 200 is not limited to this.

[0009] [Acoustic Transducer 200 According to First Embodiment] FIG. 1 is a plan view illustrating an acoustic transducer 200 according to a first embodiment. FIG. 2 is a perspective view illustrating the acoustic transducer 200 according to the first embodiment. FIG. 3 is a perspective view illustrating the acoustic transducer 200 according to the first embodiment as viewed from the bottom surface side. FIG. 4 is a cross-sectional view illustrating the acoustic transducer 200 according to the first embodiment. In each of the drawings, mutually orthogonal X-axis direction, Y-axis direction, and Z-axis direction may be illustrated. The X-axis direction, Y-axis direction, and Z-axis direction do not need to be orthogonal to each other. The X-axis direction, Y-axis direction, and Z-axis direction may be any directions. The X-axis direction is an example of a first direction. The Y-axis direction is an example of a direction intersecting the first direction.

[0010] The acoustic transducer 200 shown in FIGS. 1 to 4 is a piezoelectric acoustic transducer having a piezoelectric element (piezoelectric film). The acoustic transducer 200 may be, for example, a microphone (MEMS microphone). The acoustic transducer 200 may be used for noise cancellation applications. The acoustic transducer 200 may be a TWS (True Wireless Stereo) device, or may be an in-vehicle device mounted on an automobile. The acoustic transducer 200 may be used, for example, as a hearing aid. The acoustic transducer 200 is not particularly limited in application as long as it can detect a physical quantity. The physical quantity may be, for example, sound pressure.

[0011] [Support substrate 211] The acoustic transducer 200 includes a support substrate 211 and a diaphragm 220. The support substrate 211 may have a rectangular shape when viewed in the Z-axis direction. The thickness direction of the support substrate 211 is along the Z-axis direction. The support substrate 211 has an upper surface 211a and a lower surface 211b that face each other in the Z-axis direction. An opening 221 is formed in the support substrate 211. The opening 221 is formed so as to penetrate the support substrate 211 in the Z-axis direction. The support substrate 211 is formed from, for example, a silicon wafer. The opening 221 is formed to have a circular shape when viewed in the Z-axis direction. Although the opening 221 is described as being circular, it may be substantially circular including elliptical or polygonal shapes.

[0012] [Diaphragm 220] The diaphragm 220 has a piezoelectric film. The diaphragm 220 is formed so as to cover the opening 221. The diaphragm 220 is formed to have a circular shape when viewed in the Z-axis direction. An outer peripheral edge 222 of the diaphragm 220 is a fixed end of the diaphragm 220, and is fixed to the upper surface 211a of the support substrate 211. As will be described later, the diaphragm 220 includes a first detection region 223, a non-detection region 224, and a second detection region 225. The diaphragm 220 is also called a "diaphragm". Although the diaphragm 220 is described as being circular, it may be substantially circular including elliptical or polygonal shapes.

[0013] [Piezoelectric film] The piezoelectric film, which is the diaphragm 220, deforms in response to sound pressure and generates an electric charge. Figure 5 is an enlarged cross-sectional view illustrating the piezoelectric film in an enlarged manner. The piezoelectric film has a lower electrode layer 440, a lower piezoelectric layer (first piezoelectric layer) 460, an intermediate electrode 250, an upper piezoelectric layer (second piezoelectric layer) 360, and an upper electrode layer 330. The intermediate electrode 250 has an upper electrode layer (lower intermediate electrode layer) 430, an intermediate layer 90, and a lower electrode layer (upper intermediate electrode layer) 340. The lower electrode layer 440, lower piezoelectric layer 460, upper electrode layer 430, intermediate layer 90, lower electrode layer 340, upper piezoelectric layer 360, and upper electrode layer 330 are stacked in this order.

[0014] [Lower electrode layer 440] The lower electrode layer 440 has lower electrodes 441 to 443, which are electrode thin films. The lower electrode layer 440 is positioned close to the opening 221 in the Z-axis direction. The lower electrodes 441 to 443 are positioned apart in the X-axis direction. Lower electrode 441 is circular in shape. When viewed in the Z-axis direction, lower electrode 441 is positioned close to the center C11 of the diaphragm 220. Lower electrode 442 is ring-shaped when viewed in the Z-axis direction. Lower electrode 442 is positioned outside lower electrode 441 in the radial direction. Lower electrode 443 is ring-shaped when viewed in the Z-axis direction. Lower electrode 443 is positioned outside lower electrode 442 in the radial direction. Although the shape of lower electrode 441 is described as circular, it may be approximately circular including ellipses or polygons to match the shape of the diaphragm 220.

[0015] [No-electrode formation area 483,484] In the radial direction of the diaphragm 220, there is an electrode-free region 483 between the lower electrode 441 and the lower electrode 442 where no electrodes are formed. In the radial direction of the diaphragm 220, there is an electrode-free region 484 between the lower electrode 442 and the lower electrode 443 where no electrodes are formed.

[0016] [Lower piezoelectric layer 460] The lower piezoelectric layer 460 is a piezoelectric thin film and is formed on the lower electrode layer 440. The lower piezoelectric layer 460 is formed continuously in the radial direction of the diaphragm 220.

[0017] [Top electrode layer 430] The upper electrode layer 430 has upper electrodes 431 to 433, which are electrode thin films. The upper electrode layer 430 is formed on the lower piezoelectric layer 460. The upper electrodes 431 to 433 are spaced apart in the X-axis direction. The upper electrode 431 is circular in shape. When viewed in the Z-axis direction, the upper electrode 431 is positioned close to the center C11 of the diaphragm 220. The upper electrode 432 is ring-shaped when viewed in the Z-axis direction. In the radial direction, the upper electrode 432 is positioned outside the upper electrode 431. The upper electrode 433 is ring-shaped when viewed in the Z-axis direction. In the radial direction, the upper electrode 433 is positioned outside the upper electrode 432.

[0018] [No-electrode formation area 481,482] In the radial direction of the diaphragm 220, there is an electrode-free region 481 between the upper electrode 431 and the upper electrode 432 where no electrodes are formed. In the radial direction of the diaphragm 220, there is an electrode-free region 482 between the upper electrode 432 and the upper electrode 433 where no electrodes are formed.

[0019] [Middle class 90] The intermediate layer 90 is formed on top of the upper electrode layer 430. The intermediate layer 90 is formed continuously in the radial direction of the diaphragm 220. In the Z-axis direction, the intermediate layer 90 is positioned between the upper electrode layer 430 and the lower electrode layer 340.

[0020] [Lower electrode layer 340] The lower electrode layer 340 has lower electrodes 341 to 343, which are electrode thin films. The lower electrode layer 340 is formed on the intermediate layer 90. The lower electrodes 341 to 343 are spaced apart in the X-axis direction. Lower electrode 341 is circular in shape. When viewed in the Z-axis direction, lower electrode 341 is positioned close to the center C11 of the diaphragm 220. Lower electrode 342 is ring-shaped when viewed in the Z-axis direction. Lower electrode 342 is positioned outside lower electrode 341 in the radial direction. Lower electrode 343 is ring-shaped when viewed in the Z-axis direction. Lower electrode 343 is positioned outside lower electrode 342 in the radial direction.

[0021] [Electrode non-formation area 383,384] In the radial direction of the diaphragm 220, there is an electrode-free region 383 between the lower electrode 341 and the lower electrode 342 where no electrodes are formed. In the radial direction of the diaphragm 220, there is an electrode-free region 384 between the lower electrode 342 and the lower electrode 343 where no electrodes are formed.

[0022] [Upper piezoelectric layer 360] The upper piezoelectric layer 360 is a piezoelectric thin film and is formed on the lower electrode layer 340. The upper piezoelectric layer 360 is formed continuously in the radial direction of the diaphragm 220.

[0023] [Top electrode layer 330] The upper electrode layer 330 has upper electrodes 331 to 333, which are electrode thin films. The upper electrode layer 330 is formed on the upper piezoelectric layer 360. The upper electrodes 331 to 333 are spaced apart in the X-axis direction. Upper electrode 331 is circular in shape. When viewed in the Z-axis direction, upper electrode 331 is positioned close to the center C11 of the diaphragm 220. Upper electrode 332 is ring-shaped when viewed in the Z-axis direction. Upper electrode 332 is positioned outside upper electrode 331 in the radial direction. Upper electrode 333 is ring-shaped when viewed in the Z-axis direction. Upper electrode 333 is positioned outside upper electrode 432 in the radial direction. Although the shape of upper electrode 331 is circular, it may be approximately circular including ellipses or polygons to match the shape of the diaphragm 220.

[0024] [Materials and thickness of piezoelectric thin films] The piezoelectric material used as the lower piezoelectric layer 460 and the upper piezoelectric layer 360 may be, for example, aluminum nitride (AlN) or scandium aluminum nitride (ScAlN (Sc: 1-60 at%)). The piezoelectric material used as the lower piezoelectric layer 460 may be, for example, a piezoelectric material having a fluorite structure (hafnium oxide, zirconium oxide, cesium oxide) or a piezoelectric material having a wurtzite structure (zinc oxide, gallium nitride).

[0025] The thickness of the lower piezoelectric layer 460 may be, for example, 100 nm or more and 1 μm or less. The material of the lower piezoelectric layer 460 may be, for example, ScAlN (Sc: 40 at%), and the thickness of the lower piezoelectric layer 460 may be, for example, 500 nm.

[0026] The thickness of the upper piezoelectric layer 360 may be, for example, 100 nm or more and 1 μm or less. The material of the upper piezoelectric layer 360 may be, for example, ScAlN (Sc: 40 at%), and the thickness of the upper piezoelectric layer 360 may be, for example, 500 nm.

[0027] [Seed membrane 370, 470] The diaphragm 220 may include seed films 370 and 470. The lower electrode layer 440 is formed on the seed film 470. The seed film 370 is formed on the intermediate layer 90, and the lower electrode layer 340 is formed on the seed film 370.

[0028] [Materials and thickness of seed membranes 370 and 470] The material for seed films 370 and 470 may be aluminum nitride (AlN) or scandium aluminum nitride (ScAlN (Sc: 1-60 at%)). The film thickness of seed films 370 and 470 may be, for example, 5 nm to 500 nm. In the example, the material for seed films 370 and 470 is aluminum nitride (AlN), and the film thickness of seed films 370 and 470 is 5 nm.

[0029] The diaphragm 220 is equipped with seed films 370 and 470, which makes it easier to control the crystallinity of the piezoelectric layer. The seed films 370 and 470 are, for example, AlN.

[0030] [Material and thickness of electrode thin film] The material of the electrode thin film in the upper electrode layers 330, 430 and the lower electrode layers 340, 440 may be, for example, aluminum (Al), molybdenum (Mo), platinum (Pt), titanium (Ti), titanium nitride (TiN), or gold (Au). The thickness of the electrode thin film may be, for example, 5 nm to 100 nm. The thickness of the electrode thin film may also be, for example, 20 nm. The electrode thin films in the upper electrode layers 330, 430 and the lower electrode layers 340, 440 may be formed from the same material or from different materials.

[0031] The material of the electrode thin film in the upper electrode layers 330, 430 and the lower electrode layers 340, 440 may be at least one of gold, platinum, tungsten, aluminum, copper, molybdenum, ruthenium, titanium, chromium, and nickel, or a laminate of these materials.

[0032] [Material and thickness of the intermediate layer 90] The intermediate layer 90 is formed from, for example, a low-density material. Examples of low-density materials include silicon dioxide (SiO2), polysilicon (Poly-Si), aluminum (Al), aluminum nitride (AlN), silicon nitride (Si3N4), scandium aluminum nitride (ScAlN), aluminum oxide (Al2O3), and titanium (Ti). The intermediate layer 90 may be formed from the same material as the electrode thin films of the lower electrode layers 340, 440 and the upper electrode layers 330, 430.

[0033] The intermediate layer 90 is formed from a different material than the upper electrode layer 430 and the lower electrode layer 340. The volume density of the intermediate layer 90 is lower than that of the upper electrode layer 430 or the lower electrode layer 340.

[0034] The thickness of the intermediate layer 90 may be, for example, 10 nm to 3000 nm. The material of the intermediate layer 90 may be, for example, SiO2, and the thickness of the intermediate layer 90 may be, for example, 1450 nm. The intermediate layer 90 may also be a porous material.

[0035] [First detection area, non-detection area, and second detection area] The diaphragm, or vibrating plate 220, as shown in Figures 4 and 5, comprises first detection regions 323, 423, non-detection regions 324, 424, and second detection regions 325, 425. The first detection regions 323, 423 and the second detection regions 325, 425 are regions where a physical quantity can be detected. The non-detection regions 324, 424 are regions where a physical quantity is not detected. The physical quantity is, for example, sound pressure.

[0036] The first detection region 323 is a region in the Z-axis direction where the lower electrode 341, the upper piezoelectric layer 360, and the upper electrode 331 overlap. The first detection region 423 is a region in the Z-axis direction where the lower electrode 441, the lower piezoelectric layer 460, and the upper electrode 431 overlap. The acoustic converter 200 can detect the piezoelectric output charge between the lower electrode 441 and the upper electrode 431. The acoustic converter 200 can detect the piezoelectric output charge between the lower electrode 341 and the upper electrode 331.

[0037] The non-detection region 324 includes the region where the lower electrode 342, the upper piezoelectric layer 360, and the upper electrode 332 overlap in the Z-axis direction. The non-detection region 424 includes the region where the lower electrode 442, the upper piezoelectric layer 460, and the upper electrode 432 overlap in the Z-axis direction. The acoustic converter 200 cannot detect the piezoelectric output charge between the lower electrode 442 and the upper electrode 432. The acoustic converter 200 cannot detect the piezoelectric output charge between the lower electrode 342 and the upper electrode 332.

[0038] The second detection region 325 is the region in the Z-axis direction where the lower electrode 343, the upper piezoelectric layer 360, and the upper electrode 333 overlap. The second detection region 425 is the region in the Z-axis direction where the lower electrode 443, the lower piezoelectric layer 460, and the upper electrode 433 overlap. The acoustic converter 200 can detect the piezoelectric output charge between the lower electrode 443 and the upper electrode 433. The acoustic converter 200 can detect the piezoelectric output charge between the lower electrode 343 and the upper electrode 333.

[0039] The first detection regions 323, 423 are formed at a position that includes the center of the diaphragm 220. The non-detection regions 324, 424 are formed radially around the diaphragm 220, outside the first detection regions 323, 423. The second detection regions 325, 425 are formed radially around the diaphragm 220, outside the non-detection region 324.

[0040] [Outer diameter of the first detection area 323, the non-detection area 324, and the second detection area 325] As shown in Figure 1, the outer diameter Φ323 of the first detection area 323 is, for example, 0.54 mm. The outer diameter Φ324 of the non-detection area 324 is, for example, 0.81 mm. The outer diameter Φ325 of the second detection area 325 is 1 mm.

[0041] [Split position] As shown in Figure 5, electrode-free regions 483 and 484 are formed in the lower electrode layer 440. Electrode-free regions 481 and 482 are formed in the upper electrode layer 430. Electrode-free regions 383 and 384 are formed in the lower electrode layer 340. Electrode-free regions 381 and 382 are formed in the upper electrode layer 330.

[0042] The electrode-free regions 381-384 and 481-484 may also be called "divided positions." These electrode-free regions 381-384 and 481-484 are located at different positions in the radial direction of the diaphragm 220.

[0043] The electrode-free region 481 is located inward of the electrode-free region 483 in the radial direction of the diaphragm 220. The electrode-free region 482 is located outward of the electrode-free region 484 in the radial direction of the diaphragm 220.

[0044] The electrode-free region 383 is located inward of the electrode-free region 481 in the radial direction of the diaphragm 220. The electrode-free region 384 is located outward of the electrode-free region 482 in the radial direction of the diaphragm 220.

[0045] The electrode-free region 381 is located inward of the electrode-free region 383 in the radial direction of the diaphragm 220. The electrode-free region 382 is located outward of the electrode-free region 384 in the radial direction of the diaphragm 220.

[0046] In the diaphragm 220, multiple electrode-free regions 381-384 and electrode-free regions 481-484 are formed in positions that do not overlap with each other when viewed in the Z-axis direction. This suppresses a decrease in the strength of the diaphragm 220. Piezoelectric thin films are formed in electrode-free regions 381-384 and electrode-free regions 481-484.

[0047] The crystallinity of the piezoelectric thin film above the boundary between the end of the lower electrode 441 and the electrode-free region 483 is lower compared to the crystallinity of the piezoelectric thin film above the lower electrode 441. Similarly, the crystallinity of the piezoelectric thin film above the boundary between the electrode and the electrode-free region is lower compared to the crystallinity of the piezoelectric thin film above the electrode.

[0048] The division position, which is the electrode-free region 483, is located outside the first detection region 423 in the radial direction of the diaphragm 220. The division position, which is the electrode-free region 484, is located inside the second detection region 425 in the radial direction of the diaphragm 220. This does not hinder the crystal growth of the piezoelectric thin film that generates charge. In the acoustic converter 200, the piezoelectric thin film in the first detection region 423 and the second detection region 425 that generate charge has high crystallinity.

[0049] The division position, which is the electrode-free region 383, is located outside the first detection region 323 in the radial direction of the diaphragm 220. The division position, which is the electrode-free region 384, is located inside the second detection region 325 in the radial direction of the diaphragm 220. This does not hinder the crystal growth of the piezoelectric thin film that generates charge. In the acoustic converter 200, the piezoelectric thin film in the first detection region 423 and the second detection region 425 that generate charge has high crystallinity.

[0050] In the first embodiment, in the diaphragm 220, multiple electrode-free regions 381-384 and electrode-free regions 481-484 are formed in positions that do not overlap with each other when viewed in the Z-axis direction. However, in each laminate 300, 400, the multiple electrode-free regions 381-384 and electrode-free regions 481-484 may overlap with each other when viewed in the Z-axis direction, and between the laminate 300 and 400, the multiple electrode-free regions 381-384 and electrode-free regions 481-484 do not need to overlap with each other when viewed in the Z-axis direction. Furthermore, the regions where each piezoelectric element is formed that overlap in the Z-axis direction do not need to be formed symmetrically with respect to the intermediate layer 90.

[0051] [Effects of the sound conversion device 200 according to the first embodiment] The acoustic converter 200 according to the first embodiment includes a support substrate 211 and a diaphragm 220 attached to the support substrate 211, which deforms in response to sound pressure and generates an electric charge. The diaphragm 220 has a lower electrode layer (lower electrode) 440, a piezoelectric layer (first piezoelectric layer) 460 formed on the lower electrode layer 440, an intermediate electrode 250 formed on the piezoelectric layer 460, a piezoelectric layer (second piezoelectric layer) 360 formed on the intermediate electrode 250, and an upper electrode layer (upper electrode) formed on the piezoelectric layer 360. The thickness of the intermediate electrode 250 is greater than that of the upper electrode layer 330 or the lower electrode layer 440.

[0052] In such an acoustic converter 200, the signal-to-noise ratio (SNR) can be increased by thickening the intermediate electrode 250 of the acoustic converter 200, thereby improving the sensitivity for detecting charge in response to sound pressure. Specifically, when the diaphragm 220 deforms in response to sound pressure, causing its center to protrude upward, tensile stress acts on the upper piezoelectric layer 360 and compressive stress acts on the lower piezoelectric layer 460 in the central part of the acoustic converter 200. In this case, because the intermediate electrode 250 is thick in the acoustic converter 200, the stress acting on the piezoelectric layers 360 and 460 becomes even greater. Furthermore, in the acoustic converter 200, the distance between the piezoelectric layer 360 and the piezoelectric layer 460 can be increased, thereby increasing the charge generated in the piezoelectric layers 360 and 460 and improving the SNR.

[0053] Furthermore, in the acoustic converter 200, the intermediate electrode 250 is thick, which increases the rigidity of the diaphragm 220. This improves the resonant frequency when the diaphragm 220 deforms. As a result, the sensitivity of the acoustic converter 200 can be improved.

[0054] In the acoustic converter 200, the intermediate electrode 250 includes an upper electrode layer (lower intermediate electrode layer) 430 formed on the piezoelectric layer 460 side in the Z-axis direction (thickness direction of the diaphragm), an intermediate layer 90 formed on the upper electrode layer 430, and a lower electrode layer (upper intermediate electrode layer) 340 formed on the intermediate layer 90. The intermediate layer 90 is made of a different material from the upper and lower electrode layers 430 and 340.

[0055] In the acoustic converter 200 with this configuration, the thickness of the intermediate layer 90 can be adjusted during film formation. In the acoustic converter 200, the thickness of the intermediate electrode 250 can be easily adjusted, and an acoustic converter 200 with a desired sensitivity can be easily manufactured.

[0056] In the acoustic converter 200, the volume density of the intermediate layer 90 may be less than the volume density of the upper electrode layer 430 or the lower electrode layer 340. In the acoustic converter 200 with this configuration, by using a material with low volume density for the intermediate layer 90, it is possible to suppress an increase in the weight of the diaphragm 220 even if the intermediate layer 90 is made thicker. In the acoustic converter 200, a relatively light material can be used for the intermediate layer 90, making the diaphragm 220 lighter. In the acoustic converter 200, the rigidity of the diaphragm 220 can be increased while suppressing an increase in weight. This makes it possible to improve the resonant frequency of the diaphragm 220. In the acoustic converter 200, a decrease in the resonant frequency of the diaphragm 220 can be suppressed.

[0057] In the acoustic converter 200, the thickness of the intermediate layer 90 may be between 10 nm and 3000 nm. With this configuration, the acoustic converter 200 can achieve both an improvement in the signal-to-noise ratio and suppression of a decrease in the resonant frequency. As a result, the acoustic converter 200 can improve the sensitivity of detecting charge in response to sound pressure.

[0058] Furthermore, in the acoustic converter 200, the intermediate layer 90 may be formed from a porous material. With this configuration of the acoustic converter 200, it is possible to reduce the weight of the intermediate layer 90 while ensuring sufficient volume, thereby suppressing a decrease in the resonant frequency of the diaphragm 220.

[0059] In the acoustic converter 200, the electrodes included in the upper electrode layer 430 or the lower electrode layer 340 may be formed from at least one of gold, platinum, tungsten, aluminum, copper, molybdenum, ruthenium, titanium, chromium, and nickel, or from a laminated film thereof. The upper electrode layer 430 and the lower electrode layer 340 are included in the intermediate electrode 250, as described above. This allows for electrical connection between the electrode of the lower electrode layer 340 of the upper laminate 300 and the electrode of the upper electrode layer 430 of the lower laminate 400 via the intermediate layer 90, eliminating the need to form the intermediate layer 90 from an insulating material. Therefore, compared to the case where the intermediate layer 90 is formed from an insulating material, there is no need to employ electrical connection structures such as through electrodes, thus suppressing an increase in the manufacturing process. Such an acoustic converter 200 can simplify the manufacturing process.

[0060] In the acoustic converter 200, the piezoelectric layer (first piezoelectric layer) 460 and the piezoelectric layer (second piezoelectric layer) 360 may be formed from aluminum nitride or scandium aluminum nitride. With this configuration, the piezoelectric response when the diaphragm 220 deforms under sound pressure can be improved.

[0061] Furthermore, the acoustic converter 200 according to the first embodiment includes a support substrate 211 having an opening 221, and a diaphragm 220 provided on the support substrate 211 so as to cover the opening 221, which deforms in accordance with sound pressure and generates an electric charge. The diaphragm 220 may have a first detection region 323, 423 located near the center C11 of the opening 221 and capable of detecting an electric charge, a non-detection region 324, 424 located outside the first detection region 323, 423 in the radial direction of the diaphragm 220 (the radial direction of the opening 221) and not capable of detecting an electric charge, and a second detection region 325, 425 located outside the non-detection region 324, 424 in the radial direction of the opening 221 and capable of detecting an electric charge.

[0062] In this embodiment, the acoustic converter 200 generates an electric charge in response to the deformation of the diaphragm 220, and detects the charges generated in the first detection regions 323, 423 and the second detection regions 325, 425. In the acoustic converter 200, the electrodes divide the diaphragm 220 in the radial direction, thereby forming the first detection regions 323, 423, the non-detection regions 324, 424, and the second detection regions 325, 425. Such an acoustic converter 200 can improve the sensitivity of charge detection in response to sound pressure.

[0063] Figure 6 is a side view illustrating the distribution of electric charge generated on a diaphragm 220 that deforms under sound pressure. In the diaphragm 220, the radially outer peripheral edge is fixed to the support substrate 211. As shown in Figure 6, the area near the inflection point P12 is difficult to deform and therefore does not generate electric charge. The region near the inflection point P12 where no electric charge is generated is included in the second detection regions 325 and 425.

[0064] In contrast, the region including the center C11 of the diaphragm 220 and the vicinity of the outer edge 222 of the diaphragm 220 exhibit large deformation and generate a large amount of charge. The region including the center C11 of the diaphragm 220 and its surrounding area are included in the first detection region 323,423. The vicinity of the outer edge 222 of the diaphragm 220 is included in the second detection region 325,425. In the acoustic converter 200, the region including the inflection point P12, where charge generation is small, is not included in the first detection region 323,423 and the second detection region 325,425. As a result, the signal-to-noise ratio can be improved in the acoustic converter 200, and the sensitivity of charge detection can be increased.

[0065] Furthermore, in the acoustic converter 200, the diaphragm 220 has lower electrode layers 340, 440, piezoelectric layers 360, 460 formed on the lower electrode layers 340, 440, and upper electrode layers 330, 430 formed on the piezoelectric layers 360, 460. The lower electrode layers 340, 440 have lower electrodes 341, 441 for the first detection regions 323, 423, lower electrodes 342, 442 for the non-detection regions 324, 424, and lower electrodes 343, 443 for the second detection regions 325, 425. The upper electrode layer 330 has upper electrodes 331, 431 for the first detection regions 323, 423, upper electrodes 332, 432 for the non-detection region 324, and upper electrodes 333, 433 for the second detection regions 325, 425.

[0066] In the acoustic converter 200 with this configuration, the lower electrodes 342, 442 and upper electrodes 332, 432 are formed in the non-detection regions 324, 424, thereby improving the rigidity of the diaphragm 220 compared to a case where electrodes are not formed in the non-detection regions. As a result, the acoustic converter 200 can improve the resonant frequency when the diaphragm 220 deforms under sound pressure. Consequently, the sensitivity of the acoustic converter 200 can be improved.

[0067] In the acoustic converter 200, the lower electrode layers 340, 440 have electrode-free regions (first lower non-electrode regions) 383, 483 formed between the lower electrodes 341, 441 of the first detection regions 323, 423 and the lower electrodes 342, 442 of the non-detection regions 324, 424 in the radial direction (X-axis direction and Y-axis direction) of the diaphragm 220, and (second lower non-electrode regions) 384, 484 formed between the lower electrodes 343, 443 of the second detection regions 325, 425 and the lower electrodes 342, 442 of the non-detection regions 324, 424. The upper electrode layers 330, 430 have, in the radial direction of the diaphragm 220, electrode-free regions (first upper non-electrode regions) 381, 481 formed between the upper electrodes 331, 431 of the first detection regions 323, 423 and the upper electrodes 332, 432 of the non-detection regions 324, 424, and electrode-free regions (second upper non-electrode regions) 382, ​​482 formed between the upper electrodes 333, 433 of the second detection regions 325, 425 and the upper electrodes 332, 432 of the non-detection regions 324, 424. The electrode-free regions (first upper non-electrode regions) 381, 481 have portions that do not overlap with the electrode-free regions (first lower non-electrode regions) 383, 483 when viewed in the Z-axis direction (thickness direction of the diaphragm 220), and the electrode-free regions (second upper non-electrode regions) 382, ​​482 have portions that do not overlap with the electrode-free regions (second lower non-electrode regions) 384, 484 when viewed in the Z-axis direction.

[0068] In the acoustic converter 200 with this configuration, the electrode-free regions 381-384 and 481-484 are arranged so as not to overlap when viewed in the Z-axis direction. This ensures mechanical strength against deformation of the lower electrode layers 340, 440 and the upper electrode layers 330, 430. Furthermore, a step may occur at the boundary between the electrode-free regions 381-384 and 481-484 and the electrodes, and the crystallinity of the piezoelectric thin film may be low above this boundary. In such regions of the piezoelectric thin film, charge may not be efficiently generated. In the acoustic converter 200, since the electrode-free regions 381-384 and 481-484 are formed so as not to overlap, regions with low crystallinity can be prevented from overlapping. Therefore, regions where charge cannot be efficiently generated can be dispersed in the radial direction of the diaphragm 220, suppressing a decrease in detection sensitivity in the acoustic converter 200.

[0069] In the acoustic converter 200, the electrode-free regions (first upper electrode-free regions) 381, 481 are located inward of the electrode-free regions (first lower electrode-free regions) 383, 483 in the radial direction of the diaphragm 220, while the electrode-free regions (second upper electrode-free regions) 382, ​​482 are located outward of the electrode-free regions (second lower electrode-free regions) 384, 484.

[0070] In the acoustic converter 200 with this configuration, the boundaries between the electrode-free regions 381-384 and 481-484 and the electrodes are arranged so that they do not overlap. This suppresses a decrease in the mechanical strength of the diaphragm 220. Furthermore, in the acoustic converter 200, regions with low crystallinity are formed so that they are not included in the first detection region 323 and the second detection region 325. As a result, a decrease in the detection sensitivity of the acoustic converter 200 is suppressed.

[0071] In the acoustic converter 200, the diaphragm 220 comprises a plurality of laminates 300, 400 having lower electrode layers 340, 440, piezoelectric layers 360, 460, and upper electrode layers 330, 430. The plurality of laminates 300, 400 are stacked in the Z-axis direction. Laminate 300 has a lower electrode layer 340, an upper piezoelectric layer 360, and an upper electrode layer 330. Laminate 400 has a lower electrode layer 440, an upper piezoelectric layer 460, and an upper electrode layer 430.

[0072] In an acoustic converter 200 with this configuration, the signal-to-noise ratio can be increased by the bimorph effect, thereby improving detection sensitivity.

[0073] The acoustic converter 200 includes an intermediate layer 90 positioned between multiple laminates 300 and 400 in the Z-axis direction. In this configuration of the acoustic converter 200, the laminates 300 and 400 are spaced apart in the Z-axis direction. This allows for a higher bimorph effect, a larger signal-to-noise ratio, and improved detection sensitivity.

[0074] Furthermore, in the acoustic converter 200, the piezoelectric layers 360 and 460 may be aluminum nitride or scandium aluminum nitride. In an acoustic converter 200 with this configuration, the piezoelectric response when the acoustic converter 200 deforms in response to sound pressure can be improved. In an acoustic converter 200 with this configuration, the piezoelectric effect can be further enhanced.

[0075] [Shape of the electrode ends] Next, the shape of the electrode ends will be described. Figure 7 is a partially enlarged cross-sectional view illustrating an enlarged portion of the diaphragm. As shown in Figure 7, the ends of the upper electrodes 331, 332 and the lower electrode 341 may have a tapered shape. Similarly, the ends of the other upper electrodes 333, 431-433 and the lower electrodes 343, 441-443 may also have a tapered shape. The electrode ends are the ends facing each other in the radial direction of the diaphragm 220. The tapered shape of the electrode ends is formed so that the lower side protrudes more than the upper side.

[0076] Thus, by having tapered ends for the lower electrodes 341 and 342, the step at the boundary between the lower electrodes 341 and 342 and the electrode-free region 383 can be made gentler. Therefore, a decrease in crystallinity in the piezoelectric layer 360 can be suppressed. The same applies to the boundaries between other electrodes and electrode-free regions.

[0077] [Acoustic converter 200B according to the second embodiment] Next, the acoustic converter 200B according to the second embodiment will be described. Figure 8 is a plan view illustrating the acoustic converter 200B according to the second embodiment. Figure 9 is a cross-sectional view illustrating the acoustic converter according to the second embodiment, and is a cross-sectional view along the line IX-IX in Figure 8. The differences between the acoustic converter 200B according to the second embodiment shown in Figures 8 and 9 and the acoustic converter 200 according to the first embodiment shown in Figure 1 are that it includes a plurality of upper electrodes 331B, 333B, 431B, 433B divided in the circumferential direction, a plurality of lower electrodes 341B, 343B, 441B, 443B divided in the circumferential direction, and electrode-free regions 385, 386 extending in the radial direction. Note that in the description of the acoustic converter 200B according to the second embodiment, explanations similar to those in the description of the acoustic converter 200 according to the first embodiment may be omitted.

[0078] [Laminate 300B] The acoustic converter 200B comprises laminates 300B and 400B, as shown in Figure 9. Laminate 300B has an upper electrode layer 330B, a piezoelectric layer 360, and a lower electrode layer 340B. The upper electrode layer 330B has a plurality of upper electrodes 331B, upper electrodes 332, and a plurality of upper electrodes 333B divided in the circumferential direction.

[0079] [First detection area 323B] The laminate 300B has a first detection region 323B, a non-detection region 324, and a second detection region 325B. The first detection region 323B has a plurality of upper electrodes 331B, a piezoelectric layer 360, and a plurality of lower electrodes 341B. The first detection region 323B includes a plurality of piezoelectric elements. In the first detection region 323B, the piezoelectric elements have an upper electrode 331B, a piezoelectric layer 360, and a lower electrode 341B.

[0080] [Second detection area 325B] The second detection region 325B has a plurality of upper electrodes 333B, a piezoelectric layer 360, and a plurality of lower electrodes 343B. The second detection region 325B includes a plurality of piezoelectric elements. In the second detection region 325B, the piezoelectric elements have an upper electrode 333B, a piezoelectric layer 360, and a lower electrode 343B.

[0081] The upper electrode layer 330B includes electrode-free regions 381, 383 and electrode-free regions 385, 386, as shown in Figure 8.

[0082] [Electrode non-formation area 385] The electrode-free region 385 divides the upper electrode into multiple parts in the first detection region 323B. The electrode-free region 385 extends radially from the center of the diaphragm 220. The multiple electrode-free regions 385 are arranged at equal intervals in the circumferential direction. The areas of the multiple upper electrodes 331B are equal. The acoustic converter 200B has, for example, 10 upper electrodes 331B.

[0083] [Electrode non-formation area 386] The electrode-free region 386 divides the upper electrode into multiple parts in the second detection region 325B. The electrode-free region 386 extends radially from the electrode-free region 382 toward the outer edge 222 of the diaphragm 220. The multiple electrode-free regions 386 are arranged at equal intervals in the circumferential direction. The areas of the multiple upper electrodes 333B are equal. The acoustic converter 200B has, for example, 12 upper electrodes 333B.

[0084] The lower electrode layer 340B, like the upper electrode layer 330B, includes a radially extending electrode-free region.

[0085] [Laminate 400B] As shown in Figure 9, the laminate 400B has an upper electrode layer 430B, a piezoelectric layer 460, and a lower electrode layer 440B. The upper electrode layer 430B has a plurality of upper electrodes 431B, upper electrodes 432, and a plurality of upper electrodes 433B divided in the circumferential direction.

[0086] [First detection area 423B] The laminate 400B has a first detection region 423B, a non-detection region 424, and a second detection region 425B. The first detection region 423B has a plurality of upper electrodes 431B, a piezoelectric layer 460, and a plurality of lower electrodes 441B. The first detection region 423B includes a plurality of piezoelectric elements. In the first detection region 423B, the piezoelectric elements have an upper electrode 431B, a piezoelectric layer 460, and a lower electrode 441B. In the first detection region 423B, the areas of the plurality of upper electrodes 431B are equal to each other. In the first detection region 423B, the areas of the plurality of lower electrodes 441B are equal to each other.

[0087] [Second detection area 425B] The second detection region 425B has a plurality of upper electrodes 433B, a piezoelectric layer 460, and a plurality of lower electrodes 443B. The second detection region 425B includes a plurality of piezoelectric elements. In the second detection region 425B, the piezoelectric elements have an upper electrode 433B, a piezoelectric layer 460, and a lower electrode 443B. In the second detection region 425B, the areas of the plurality of upper electrodes 433B are equal to each other. In the second detection region 425B, the areas of the plurality of lower electrodes 443B are equal to each other.

[0088] The upper electrode layer 430B and the lower electrode layer 440 of the laminate 400B include radially extending electrode-free regions, similar to the laminate 300B.

[0089] [Capacitance of piezoelectric element] In laminate 300B, the capacitances of the multiple piezoelectric elements arranged in the circumferential direction of the diaphragm 220 are equal to each other. In laminate 400B, the capacitances of the multiple piezoelectric elements arranged in the circumferential direction of the diaphragm 220 are equal to each other. Note that "equal" includes "approximately equal".

[0090] [Series connection of multiple piezoelectric elements] In the diaphragm 220B, multiple piezoelectric elements arranged in the circumferential direction are electrically connected in series.

[0091] [Effects of the sound converter 200B according to the second embodiment] The sound converter 200B according to this second embodiment also provides the same effects and advantages as the sound converter 200 according to the first embodiment described above.

[0092] In the acoustic converter 200B, the lower electrode layers 340B, 440B of the first detection regions 323B, 423B include a plurality of lower electrodes (multiple parts) 341B, 441B arranged in the circumferential direction of the diaphragm 220B; the lower electrode layers 340B, 440B of the second detection regions 325B, 425B include a plurality of lower electrodes (multiple parts) 343B, 443B arranged in the circumferential direction of the diaphragm 220B; the upper electrode layers 330B, 430B of the first detection regions 323B, 423B include a plurality of upper electrodes (multiple parts) 331B, 431B arranged in the circumferential direction of the diaphragm 220; and the upper electrode layers 330B, 430B of the second detection regions 325B, 425B include a plurality of upper electrodes (multiple parts) 333B, 433B arranged in the circumferential direction of the diaphragm 220. The area of ​​each of the multiple lower electrodes 341B, 441B contained in the lower electrode layers 340B, 440B of the first detection regions 323B, 423B may be the same as the area of ​​each of the multiple lower electrodes 343B, 443B contained in the lower electrode layers 340B, 440B of the second detection regions 325B, 425B. The area of ​​each of the multiple upper electrodes 331B, 431B contained in the upper electrode layers 330B, 430B of the first detection regions 323B, 423B may be the same as the area of ​​each of the multiple upper electrodes 333B, 433B contained in the upper electrode layers 330B, 430B of the second detection regions 325B, 425B.

[0093] According to the acoustic converter 200B with this configuration, by making the areas of multiple electrodes equal, the design freedom of amplification circuits and the like connected to multiple piezoelectric elements having these electrodes can be increased. Specifically, when connecting the capacitances of piezoelectric elements having electrodes arranged above and below the piezoelectric layer 360 and piezoelectric layer 460 in series, it becomes easier to calculate the capacitance of the multiple piezoelectric elements compared to when the areas of the divided multiple electrodes are not equal. Therefore, the circuit design of amplification circuits and the like designed based on the total capacitance of the diaphragm 220B becomes easier.

[0094] Furthermore, when multiple capacitances are electrically connected in series, if the areas of the divided electrodes are not equal, the charge generated at each capacitance will differ when subjected to sound pressure. In such cases, excess charge may be generated, which may reduce the overall detection accuracy of the diaphragm 220. In the acoustic converter 200B, since the areas of the multiple electrodes are equal, the generation of excess charge is suppressed. As a result, the reduction in the overall detection accuracy of the diaphragm 220B can be suppressed.

[0095] [Circuit diagram of the sound converter 200B according to the second embodiment] Next, the circuit diagram of the sound converter 200B according to the second embodiment will be described. Figure 10 is the circuit diagram of the sound converter 200B according to the second embodiment.

[0096] As shown in Figure 10, the acoustic converter 200B has a MEMS microphone chip 201. The MEMS microphone chip 201 is equipped with a diaphragm 220B. The diaphragm 220B has a plurality of first detection regions 323B, 423B and second detection regions 325B, 425B.

[0097] Multiple first detection regions 323B, 423B each have an upper electrode 331B, a lower electrode 341B, an upper electrode 431B, and a lower electrode 441B. Multiple second detection regions 325B, 425B each have an upper electrode 333B, a lower electrode 343B, an upper electrode 433B, and a lower electrode 443B.

[0098] In the first detection regions 323B and 423B of the acoustic converter 200B, the piezoelectric output charge between the upper electrode 331B and the lower electrode 341B, and the piezoelectric output charge between the upper electrode 431B and the lower electrode 441B can be detected. Multiple piezoelectric elements arranged in the circumferential direction are connected in series.

[0099] In the second detection regions 325B and 425B of the acoustic converter 200B, the piezoelectric output charge between the upper electrode 333B and the lower electrode 343B, and the piezoelectric output charge between the upper electrode 433B and the lower electrode 443B can be detected. Multiple piezoelectric elements arranged in the circumferential direction are connected in series.

[0100] Furthermore, the MEMS microphone chip 201 has pads 213 and 214. Multiple piezoelectric elements are connected to the electrodes of the pads 213 and 214. The acoustic converter 200B includes an IC 202 connected to pad 213. IC 202 is an amplifier that amplifies the output signal of the piezoelectric element of the diaphragm 220. IC 202 may also be provided with a function to perform AD (analog-to-digital) conversion after amplifying the output signal of the piezoelectric element of the diaphragm 220.

[0101] The polarity of the charge generated in the second detection region 325B,425B is the opposite of the polarity of the charge generated in the first detection region 323B,423B. Therefore, the second detection region 325B,425B and the first detection region 323B,423B are connected in series with the wiring reversed.

[0102] [Acoustic converter 200C according to the third embodiment] Next, the acoustic converter 200C according to the third embodiment will be described. Figure 11 is an exploded perspective view illustrating the acoustic converter 200C according to the third embodiment. The difference between the acoustic converter 200C according to the third embodiment shown in Figure 11 and the acoustic converter 200B according to the second embodiment is that an opening 91 is formed in the intermediate layer 90C. Note that in the description of the acoustic converter 200C according to the third embodiment, explanations similar to those given in the descriptions of the acoustic converters 200 and 200B according to the above embodiments may be omitted.

[0103] The diaphragm 220C of the acoustic converter 200C according to the third embodiment includes an intermediate layer 90C in which an opening 91 is formed. The opening 91 is formed on the inside in the radial direction of the diaphragm 220C. The opening 91 penetrates in the Z-axis direction. The peripheral edge of the opening 91 is formed on the inside of the electrode-free region 381 in the radial direction of the diaphragm 220C.

[0104] The opening 91 is circular when viewed in the Z-axis direction. The interior of the opening 91 is hollow, and no other objects are placed inside. The shape of the opening 91 is not limited to a circle. The shape of the opening 91 may be, for example, a polygon, a ring shape arranged concentrically, or an ellipse. In addition, multiple openings may be formed in the intermediate layer 90C.

[0105] In the acoustic converter 200C according to this third embodiment, the weight of the intermediate layer 90C can be reduced. In other words, the weight of the diaphragm 220C can be reduced. This makes it possible to improve the resonant frequency of the diaphragm 220C and improve the sensitivity of the acoustic converter 200C.

[0106] [Acoustic converter 200D according to the fourth embodiment] Next, the acoustic converter 200D according to the fourth embodiment will be described. Figure 12 is an exploded perspective view illustrating the acoustic converter 200D according to the fourth embodiment. The difference between the acoustic converter 200D according to the fourth embodiment shown in Figure 12 and the acoustic converter 200C according to the third embodiment is that it includes an intermediate layer 90D having a plurality of pillars 92. In the description of the acoustic converter 200D according to the fourth embodiment, explanations similar to those given in the descriptions of the acoustic converters 200, 200B, and 200C according to the above embodiments may be omitted.

[0107] The diaphragm 220D of the acoustic converter 200D according to the fourth embodiment includes an intermediate layer 90D having a plurality of pillars 92. The pillars 92 are cylindrical in shape. The direction of the centerlines of the plurality of pillars 92 is along the Z-axis direction. Gaps are formed around the plurality of pillars 92. The plurality of pillars 92 are formed on the upper electrodes 431B, 432, and 433B.

[0108] The shape of the pillar 92 is not limited to a cylindrical shape. For example, the pillar 92 may be prismatic, cylindrical, or rectangular.

[0109] In the acoustic converter 200D according to this fourth embodiment, the weight of the intermediate layer 90D can be reduced. In other words, the weight of the diaphragm 220D can be reduced. This makes it possible to improve the resonant frequency of the diaphragm 220D and improve the sensitivity of the acoustic converter 200D.

[0110] [Sound conversion device 200E related to a modified example] Next, a modified acoustic converter 200E will be described. Figure 22(a) is a partially exploded perspective view illustrating a modified acoustic converter 200E, and Figure 22(b) is an enlarged view illustrating an enlarged intermediate layer 90E. The modified acoustic converter 200E may include a porous intermediate layer 90E. Multiple cavities may be formed in the intermediate layer E90. Multiple uneven shapes may also be formed in the intermediate layer 90E. Multiple openings may also be formed in the intermediate layer 90E. The openings may or may not penetrate the intermediate layer 90 in the Z-axis direction.

[0111] In the modified acoustic converter 200E, the weight of the intermediate layer 90E can be reduced, thereby reducing the weight of the diaphragm 220E. This improves the resonant frequency of the diaphragm 220E and improves the sensitivity of the acoustic converter 200E.

[0112] [Sound conversion device 200B related to a modified example] Figure 13 is a plan view illustrating a modified acoustic converter 200B. As shown in Figure 13, the diaphragm 220B of the acoustic converter 200B may have vent holes 93 formed therein. The vent holes 93 are through holes formed in the diaphragm for degassing. The vent holes 93 penetrate the diaphragm 220B in the Z-axis direction.

[0113] The vent hole 93 is provided, for example, at the center of the diaphragm 220B. The vent hole 93 is provided, for example, in the non-detection regions 324,424. The diaphragm 220B may have one vent hole 93 or multiple vent holes 93.

[0114] [Acoustic converter 100 according to the fifth embodiment] Figure 14 is a perspective view illustrating the acoustic converter 100 according to the fifth embodiment. In describing the acoustic converter 100 according to the fifth embodiment, explanations similar to those given in the descriptions of the acoustic converters 200, 200B to 200D according to the above embodiments may be omitted.

[0115] [Fixed frame 10] The acoustic converter 100 comprises a fixed frame 10 and a pair of cantilevers 20A and 20B. The fixed frame 10 is a rectangular frame when viewed in the Z-axis direction. The length of the fixed frame 10 in the X-axis direction is shorter than the length of the fixed frame 10 in the Y-axis direction. The fixed frame 10 has a first base 11 and a second base 12. The first base 11 may be a substrate. The second base 12 is formed on the first base 11. When the pair of cantilevers 20A and 20B are not distinguished, they may be referred to as cantilever 20.

[0116] [Cantilever 20A, 20B] The pair of cantilevers 20A and 20B have piezoelectric films. The pair of cantilevers 20A and 20B are arranged to face each other in the X-axis direction. The cantilevers 20A and 20B protrude from the fixed frame 10 in the X-axis direction toward the inside of the fixed frame 10. One end of the cantilevers 20A and 20B is a fixed end 22, and the other end is a free end 21. The fixed end 22 of the pair of cantilevers 20A and 20B is connected to the fixed frame 10. The free ends 21 of the cantilevers 20A and 20B face each other.

[0117] A pair of slits 71 and 72 are formed around the cantilevers 20A and 20B. Slits 71 and 72 are gaps formed between the fixed frame 10 and the cantilevers 20A and 20B, and penetrate the substrate in the Z-axis direction. The pair of slits 71 extend in the X-axis direction and are formed apart in the Y-axis direction. Slit 72 is a gap formed between the free ends 21 of the pair of cantilevers 20A and 20B. Slit 72 extends in the Y-axis direction. The width of slits 71 and 72 may be, for example, 100 nm or more and 5 μm or less. The width of slits 71 and 72 may be, for example, 0.5 μm.

[0118] Figure 15 is a partially enlarged cross-sectional view illustrating an enlarged portion of the cantilever 20 of the acoustic converter 100 according to the fifth embodiment. The piezoelectric film of the cantilever 20 has a lower electrode layer 440, a piezoelectric layer (first piezoelectric layer) 460, an intermediate electrode 250, a piezoelectric layer (second piezoelectric layer) 360, and an upper electrode layer 330.

[0119] The material of the intermediate layer 90 may be, for example, SiO2, and the thickness of the intermediate layer 90 may be, for example, 1450 nm. The material of the lower piezoelectric layer 460 may be, for example, ScAlN (Sc: 50 at%), and the thickness of the lower piezoelectric layer 460 may be, for example, 500 nm. The material of the upper piezoelectric layer 360 may be, for example, ScAlN (Sc: 50 at%), and the thickness of the upper piezoelectric layer 360 may be, for example, 500 nm.

[0120] The material of the electrode layers 430 and 440 positioned above and below the lower piezoelectric layer 460 is, for example, molybdenum, and the thickness of the electrode layers 430 and 440 may be, for example, 20 nm. The material of the electrode layers 330 and 340 positioned above and below the upper piezoelectric layer 360 is, for example, molybdenum, and the thickness of the electrode layers 330 and 340 may be, for example, 20 nm.

[0121] The material for seed films 370 and 470 is, for example, aluminum nitride (AlN), and the film thickness of seed films 370 and 470 may be 5 nm.

[0122] [Bimorph structure] Figure 16 is a cross-sectional view illustrating a cross-section of a cantilever 20 that deforms under sound pressure. When the cantilever 20 deforms under sound pressure, the two piezoelectric layers 360 and 460 form a bimorph structure due to the intermediate layer 90. With an acoustic converter equipped with such a cantilever 20, the intermediate layer 90 can be made thicker, and the generated charge can be increased. As a result, the signal-to-noise ratio can be improved.

[0123] [Effects of the sound conversion device 100 according to the fifth embodiment] The acoustic converter 100 according to the fifth embodiment includes a fixed frame 10 and a cantilever 20 that extends from the fixed frame 10 inward. The cantilever 20 has a lower electrode layer (lower electrode) 440, a piezoelectric layer (first piezoelectric layer) 460 formed on the lower electrode layer 440, an intermediate electrode 250 formed on the piezoelectric layer 460, a piezoelectric layer (second piezoelectric layer) 360 formed on the intermediate electrode 250, and an upper electrode layer (upper electrode) 330 formed on the piezoelectric layer 360. The intermediate electrode 250 includes an upper electrode layer (lower intermediate electrode layer) 430 formed on the piezoelectric layer 460 side in the Z-axis direction (thickness direction of the diaphragm), an intermediate layer 90 formed on the upper electrode layer 430, and a lower electrode layer (upper intermediate electrode layer) 340 formed on the intermediate layer 90. The intermediate layer 90 is formed from a different material than the upper electrode layer 430 and the lower electrode layer 340, and the thickness of the intermediate electrode 250 is greater than that of either the upper electrode layer 430 or the lower electrode layer 340.

[0124] The sound converter 100 according to this fifth embodiment also provides the same effects and advantages as the sound converter 200 according to the first embodiment described above.

[0125] The cantilever 20 has a pair of cantilevers (first cantilever and second cantilever) 20A and 20B that face each other in the X-axis direction (first direction), which is the direction in which the cantilever 20 extends. With this configuration of the acoustic converter 100, sensitivity can be improved by providing a pair of cantilevers 20A and 20B.

[0126] [Ratio of the thickness T250 of the intermediate electrode 250 to the thickness T20 of the cantilever 20] The thickness T250 of the intermediate electrode 250 may be 10% to 90% of the thickness T20 of the cantilever 20. The thickness T20 of the cantilever 20 is the thickness along the Z-axis direction of the cantilever 20. The thickness T20 of the cantilever 20 is the sum of the thickness T440 of the lower electrode layer 440, the thickness of the piezoelectric layer 460, the thickness T250 of the intermediate electrode 250, the thickness of the piezoelectric layer 360, and the thickness T330 of the upper electrode layer 330. The thickness of the lower electrode layer 440 may include the thickness of the seed film 470. The thickness T250 of the intermediate electrode 250 may include the thickness of the seed film 370.

[0127] The thickness T250 of the intermediate electrode 250 may be 30% to 70% of the thickness T20 of the cantilever 20. The thickness T250 of the intermediate electrode 250 may be 40% to 60% of the thickness T20 of the cantilever 20. As mentioned above, the thickness T220 of the intermediate electrode 50 is thicker than the thickness T330 or T440 of the upper electrode layer 330 or the lower electrode layer 440.

[0128] [Neutral plane N20] The intermediate electrode 250 is positioned to include the neutral plane N20. The cantilever 20 may also include the neutral plane N20. The neutral plane N20 may be a plane in which neither tensile nor compressive forces in the longitudinal direction of the cantilever 20 are generated internally when the cantilever 20 is deflected. The cantilever 20 deflects, for example, when subjected to sound pressure. The free end 21 of the cantilever 20 is displaced relative to the fixed end 22 in the Z-axis direction.

[0129] For example, when the cantilever 20 is subjected to sound pressure from above in the Z-axis direction, the free end 21 is displaced upward and the cantilever 20 bends. At this time, a tensile force is generated in the piezoelectric layer 460 below the intermediate electrode 50, and a compressive force is generated in the piezoelectric layer 360 above the intermediate electrode 250. The magnitudes of the tensile and compressive forces differ depending on the position in the Z-axis direction. The tensile force near the lower electrode 40 is greater than the tensile force near the intermediate electrode 50. The compressive force near the upper electrode 30 is greater than the compressive force near the intermediate electrode 50.

[0130] The neutral plane N20 is located near the center of the cantilever 20 in the thickness direction. The neutral plane N20 is a virtual plane along the XY plane when the cantilever 20 is not bent. The intermediate electrode 50 is positioned within the neutral plane N20. The center of the intermediate electrode 250 in the Z-axis direction may also be on the neutral plane N20. The neutral plane N20 is located at the center of the cantilever 20 in the thickness direction when the thickness of the piezoelectric layer 460 and the piezoelectric layer 360 are the same, the thickness of the upper electrode layer 330 T330 and the thickness of the lower electrode layer 440 T440 are the same, the material of the piezoelectric layer 460 and the piezoelectric layer 360 are the same, and the material of the upper electrode layer 330 and the lower electrode layer 440 are the same. The neutral plane N20 does not have to be located at the center of the cantilever 20 in the thickness direction. Due to differences in the thickness of piezoelectric layers 360 and 460, differences in the materials of piezoelectric layers 360 and 460, differences in the thickness T330 and T440 of the upper electrode layer 330 and lower electrode layer 440, and differences in the materials of the upper electrode layer 330 and lower electrode layer 440, the neutral plane N20 is located outside the center in the thickness direction of the cantilever 20.

[0131] [Acoustic converter 100B according to the sixth embodiment] Next, the acoustic converter B according to the sixth embodiment will be described. Figure 17 is a cross-sectional view illustrating the acoustic converter 100B according to the sixth embodiment. In describing the acoustic converter 100B according to the sixth embodiment, explanations similar to those given in the descriptions of the acoustic converters 100, 200, 200B to 200D according to the above embodiments may be omitted.

[0132] The acoustic converter 100B includes a cantilever 20. The cantilever 20 has a first detection region 223 located on the fixed end 22 side and a non-detection region 224 located on the free end 21 side.

[0133] The first detection region 223 includes upper electrodes 331, 431, lower electrodes 341, 441, and piezoelectric layers 360, 460. A capacitive element having upper electrodes 331, lower electrodes 341, and piezoelectric layer 360 is connected in series with a capacitive element having upper electrodes 431, lower electrodes 441, and piezoelectric layer 460. The first detection region 223 is a region for detecting physical quantities.

[0134] The non-detection region 224 includes the upper electrodes 332, 432, the lower electrodes 342, 442, and the piezoelectric layers 360, 460. The non-detection region 224 is a region where no physical quantity is detected.

[0135] In an acoustic converter 100B equipped with a cantilever 20, a first detection region 223 may be formed on the fixed end 22 side, and a non-detection region 224 may be formed on the free end 21 side.

[0136] [Sound converter 100C according to the seventh embodiment] Next, the acoustic converter B according to the seventh embodiment will be described. Figure 17 is a cross-sectional view illustrating the acoustic converter 100C according to the seventh embodiment. The difference between the acoustic converter C according to the seventh embodiment and the acoustic converter 100B according to the sixth embodiment is that a cavity 91C is formed in the intermediate layer 90.

[0137] The acoustic converter 100C includes an intermediate layer 90 having a cavity 91C. The cavity 91C may be formed continuously in the Y-axis direction or intermittently. The cavity 91C is formed in the non-detection region 224 at a position close to the free end 21. When viewed in the Z-axis direction, the cavity 91C is formed at a position overlapping the lower electrode 342 and the upper electrode 432.

[0138] In the acoustic converter 100C according to this seventh embodiment, the weight of the intermediate layer 90 can be reduced. In other words, the weight of the cantilever 20 can be reduced. This makes it possible to improve the resonant frequency of the cantilever 20 and improve the sensitivity of the acoustic converter 100C.

[0139] [Sound conversion device 100B related to a modified example] The modified acoustic converter 100B may include a porous intermediate layer 90. The intermediate layer 90 may have multiple cavities formed in it. The intermediate layer 90 may also have multiple uneven surfaces formed in it. The intermediate layer 90 may also have multiple openings formed in it. The openings may or may not penetrate the intermediate layer 90 in the Z-axis direction.

[0140] In the modified acoustic converter 100, the weight of the intermediate layer 90 can be reduced, thereby reducing the weight of the cantilever 20. This improves the resonant frequency of the cantilever 20 and improves the sensitivity of the acoustic converter 100.

[0141] [Acoustic converter 100D according to the 8th embodiment] Next, the sound converter 100D according to the eighth embodiment will be described. Figure 19 is a perspective view illustrating the sound converter 100D according to the eighth embodiment. The differences between the sound converter 100D according to the eighth embodiment shown in Figure 19 and the sound converter 100 according to the fifth embodiment shown in Figure 14 are that it is equipped with four cantilevers 20A to 20D, and that the shape of the fixed frame 10 is different. Note that in the description of the sound converter 100D according to the eighth embodiment, explanations similar to those given for the sound converters 100 and 200 according to the above embodiments may be omitted.

[0142] The acoustic converter 100D includes a fixed frame 10. The fixed frame 10 has a plurality of frame sections 10B. The plurality of frame sections 10B are arranged in the X-axis direction. The plurality of frame sections 10B include a common section 10E. The common section 10E extends in the Y-axis direction at the center of the fixed frame 10. Inside each of the plurality of frame sections 10B, a pair of cantilevers 20A to 20D are formed. The free ends 21 of the pair of cantilevers 20A to 20D are arranged to face each other. The cantilevers 20B and 20C that extend from the common section 10E extend in opposite directions from each other.

[0143] [Effects of the sound converter 100D according to the 8th embodiment] The acoustic converter 100D according to this eighth embodiment also provides the same effects as the acoustic converter 100 according to the fifth embodiment described above. In the acoustic converter 100D according to the eighth embodiment, sensitivity can be improved by providing four cantilevers 20A to 20. The acoustic converter 100D may also be provided with multiple pairs of cantilevers 20A to 20D. The acoustic converter 100D may also be provided with four or more cantilevers 20A to 20D.

[0144] [Acoustic converter 100E according to the 9th embodiment] Next, the sound converter 100E according to the ninth embodiment will be described. Figure 20 is a plan view illustrating the sound converter 100E according to the ninth embodiment. The differences between the sound converter 100E according to the ninth embodiment shown in Figure 20 and the sound converter 100 according to the fifth embodiment shown in Figure 14 are that it is equipped with a pair of cantilevers 20 (cantilevers 20A, 20F) with different widths W20, W20F, and that the shape of the fixed frame 10F is different. Note that in the description of the sound converter 100E according to the ninth embodiment, explanations similar to those given for the sound converters 100 and 200 according to the above embodiments may be omitted.

[0145] The acoustic converter 100E comprises a pair of cantilevers 20, namely cantilevers 20A and 20F. The laminated structure of cantilevers 20A and 20F is the same as that of cantilever 20 as described above, and includes an upper electrode layer 330, a lower electrode layer 440, an intermediate electrode 250, a piezoelectric layer 460, and a piezoelectric layer 360. Cantilever 20A has a detection region 223 and a non-detection region 224. Cantilever 20F has a detection region 223F and a non-detection region 224F.

[0146] The width W20F of cantilever 20F is wider than the width W20 of cantilever 20A (W20F > W20). The width W20F is the width of the upper electrode 331 of the detection region 223F. The width W20 is the width of the upper electrode 331 of the detection region 223. The capacitive element of cantilever 20A and the capacitive element of cantilever 20F are connected in series.

[0147] Furthermore, the length L20 of cantilever 20A may be equal to the length L20F of cantilever 20F (L20 = L20F). The length L21 of the detection region 23 of cantilever 20A may be approximately the same as the length L21F of the detection region 223F of cantilever 20F (L21 ≈ L21F).

[0148] The shape of the fixed frame 10F corresponds to the shape of the cantilevers 20A and 20F. The slits 71 formed on both sides of the cantilever 20A and the slits 71 formed on both sides of the cantilever 20F are positioned at different locations in the Y-axis direction.

[0149] [Effects of the sound converter 100E according to the 9th embodiment] The sound converter 100E according to this ninth embodiment also provides the same effects as the sound converter 100 according to the first embodiment. In the sound converter 100E according to the ninth embodiment, the widths W20 and W20F of a pair of opposing cantilevers 20A and 20F along the Y-axis direction may be different.

[0150] [Interlayer thickness, signal-to-noise ratio, and resonant frequency] Next, we will explain the relationship between the thickness of the interlayer, the signal-to-noise ratio (SNR), and the resonant frequency. Figure 21 is a table showing the relationship between the thickness of the interlayer, the SNR, and the resonant frequency.

[0151] The signal-to-noise ratio (SNR) and resonant frequency were measured using the acoustic converter 200 according to Examples 1-11 and Comparative Examples 1-7. The acoustic converter 200 according to Examples 1-11 and Comparative Examples 1-7 has the same configuration as the acoustic converter 200 according to the first embodiment described above, but differs in the material of the piezoelectric layer and the thickness of the intermediate layer. In Examples 1-5 and Comparative Examples 1-4, the piezoelectric layer was made of AlN. In Examples 6-11 and Comparative Examples 5-7, the piezoelectric layer was made of ScAlN. The thickness of the intermediate layer was changed as appropriate. As an evaluation result, a result above the reference value was evaluated as A, and a result below the reference value was evaluated as B. The acoustic converters according to the examples and comparative examples were placed in an anechoic chamber, and the SNR and resonant frequency were measured using an Audio Precision audio analyzer.

[0152] In Example 1, the signal-to-noise ratio (SNR) was high, and in Examples 2 and 3, the SNR was very high. In Examples 4 and 5, the resonant frequency was high. Examples 1 to 5 received an evaluation of A.

[0153] Examples 8-10 showed a high signal-to-noise ratio (SNR), and Examples 6 and 7 showed an extremely high SNR. Examples 9 and 10 showed a high resonant frequency, and Example 11 showed an extremely high resonant frequency.

[0154] [Relationship between sensing area diameter ratio and normalized SNR] Next, the relationship between the sensing area diameter ratio and the normalized SNR will be explained. Figure 21 is a graph showing the relationship between the sensing area diameter ratio and the normalized SNR. In Figure 21, the horizontal axis shows the sensing area diameter ratio [%], and the vertical axis shows the normalized SNR [%]. The graph shown in Figure 21 shows the relationship between the sensing area diameter ratio and the normalized SNR in the acoustic converter 200 according to the first embodiment shown in Figure 1.

[0155] The "percentage of sensing area" can be expressed by the following formula (1). Sensing area ratio = (radius of electrode separation part / diaphragm radius) × 100 ... (1) The "electrode separation radius" may also be the radius of the inner detection region 323. The "diaphragm radius" may also be the radius of the diaphragm 220. In Figure 1, the diameter φ323 of the inner detection region 323 and the diameter φ325 of the diaphragm 220 are shown.

[0156] The inner diameter of the opening 221 covered by the diaphragm 220 was defined as 100% of the sensing area diameter ratio. A normalized SNR of 100% was defined as the case where an electrode-free area was formed in 71% of the area. In Figure 12, "○" indicates the position of the boundary between the inner detection area 323 and the non-detection area 324. In Figure 12, "×" indicates the position of the boundary between the outer detection area 325 and the non-detection area 324.

[0157] The SNR normalized value of the inner detection region 323 is the value obtained when the outer diameter Φ323 of the inner detection region 323 is varied, with the boundary between the outer detection region 325 and the non-detection region 324 set at 71%.

[0158] The SNR normalized value of the outer detection region 325 is the value obtained when the inner diameter Φ324 of the outer detection region 325 is varied, with the boundary between the inner detection region 323 and the non-detection region 324 set at 71%.

[0159] In the example shown in Figure 21, the normalized SNR value of the inner detection region 323 was maximized at point P21. The sensing region diameter ratio at point P21 was 59%.

[0160] In the example shown in Figure 21, the normalized SNR value of the outer detection region 325 was maximized at point P22. The sensing region diameter ratio at point P22 was 81%.

[0161] When the sensing area diameter ratio of the inner detection area 323 was between 44% and 71%, the SNR normalized value was 100% or higher. When the sensing area diameter ratio of the inner detection area 323 was between 49% and 67%, the SNR normalized value was 104% or higher. When the sensing area diameter ratio of the inner detection area 323 was between 51% and 65%, the SNR normalized value was 106% or higher.

[0162] The ratio of the sensing area diameter of the inner detection area 323 is preferably 44% to 71%, more preferably 49% to 67%, and even more preferably 51% to 65%.

[0163] When the sensing area diameter ratio of the outer detection area 325 was between 71% and 89%, the SNR normalized value was 100% or higher. When the sensing area diameter ratio of the outer detection area 325 was between 75% and 87%, the SNR normalized value was 104% or higher. When the sensing area diameter ratio of the outer detection area 325 was between 78% and 84%, the SNR normalized value was 106% or higher.

[0164] The ratio of the sensing area diameter of the outer detection area 325 is preferably 71% to 89%, more preferably 75% to 87%, and even more preferably 78% to 84%.

[0165] The case where the sensing area diameter ratio of the inner detection area 323 is 71% and the sensing area diameter ratio of the outer detection area 325 is 71% may also mean that the electrode division position is located at the 71% position.

[0166] In the acoustic converter 200, if the sensing area diameter ratio of the outer detection area 325 is 71% or more and 89% or less, the sensing area diameter ratio of the inner detection area 323 may be a value outside the range of 44% or more and 71% or less. In such cases, the SNR normalized value may be high.

[0167] In the acoustic converter 200, if the sensing area diameter ratio of the inner detection area 323 is 44% or more and 71% or less, the sensing area diameter ratio of the outer detection area 325 may be a value outside the range of 71% or more and 89% or less. In such cases, the SNR normalized value may be high.

[0168] Furthermore, other embodiments may be used in which other components are combined with the configurations listed in the above embodiments, and the present invention is not limited in any way to the configurations shown herein. In this regard, modifications can be made without departing from the spirit of the present invention, and can be appropriately determined according to the application form.

[0169] In the above embodiment, an example is given where the intermediate electrode 250 has an upper electrode layer (lower intermediate electrode layer) 430, an intermediate layer 90, and a lower electrode layer (upper intermediate electrode layer) 340. However, the intermediate electrode 250 may have only an electrode and may not have an intermediate layer 90.

[0170] Furthermore, although the above embodiment illustrates a case where the piezoelectric film (diaphragm or cantilever) has a detection region and a non-detection region, the piezoelectric film may include a detection region but not include a non-detection region.

[0171] In the above embodiment, an acoustic converter 100 having a cantilever (single-sided beam) 20 is illustrated, but the acoustic converter 100 may also be equipped with a piezoelectric film (diaphragm) with a double-sided beam. [Explanation of Symbols]

[0172] 200, 200B, 200C, 200D, 200E: Acoustic converter, 90, 90C, 90D, 90E: Intermediate layer, 221: Aperture, 211: Support substrate, 220, 220B, 220C, 220D, 220E: Diaphragm, 222: Outer edge, 323, 323B, 423, 423B: First detection area, 324, 424: Non-detection area, 325, 325B, 425, 425B: Second detection area, 330, 330B, 430, 430B: Upper electrode layer, 331, 331B, 431, 431B: Upper electrode (upper electrode of the first detection area), 332, 432: Upper electrode (upper electrode of the non-detection area) Electrode), 333,333B,433,433B: Upper electrode (upper electrode of the second detection region), 340,340B,440,440B: Lower electrode layer, 341,341B,441,441B: Lower electrode (lower electrode of the first detection region), 342,442: Lower electrode (lower electrode of the non-detection region), 343,343B,443,443B: Lower electrode (lower electrode of the second detection region), 360: Upper piezoelectric layer (piezoelectric layer), 460: Lower piezoelectric layer (piezoelectric layer), 381~384: Non-electrode formed region, 481~484: Non-electrode formed region, X: X-axis direction, Y: Y-axis direction, Z: Z-axis direction (plate thickness direction).

Claims

1. Support substrate and The system includes a diaphragm attached to the support substrate, which deforms in response to sound pressure and generates an electric charge, The aforementioned diaphragm is Lower electrode and A first piezoelectric layer formed on the lower electrode, An intermediate electrode formed on the first piezoelectric layer, A second piezoelectric layer formed on the intermediate electrode, The upper electrode formed on the second piezoelectric layer, The thickness of the intermediate electrode is greater than that of the upper electrode or the lower electrode in this acoustic converter.

2. The aforementioned intermediate electrode is In the thickness direction of the diaphragm, a lower intermediate electrode layer formed on the first piezoelectric layer side, An intermediate layer formed on the lower intermediate electrode layer, It includes an upper intermediate electrode layer formed on the intermediate layer, The acoustic conversion device according to claim 1, wherein the intermediate layer is formed from a material different from the upper intermediate electrode layer and the lower intermediate electrode layer.

3. The acoustic conversion device according to claim 2, wherein the volume density of the intermediate layer is smaller than the volume density of the upper intermediate electrode layer or the lower intermediate electrode layer.

4. The acoustic conversion apparatus according to claim 2, wherein the thickness of the intermediate layer is 10 nm or more and 3000 nm or less.

5. The acoustic conversion apparatus according to claim 2, wherein the intermediate layer comprises a porous material.

6. The acoustic converter according to claim 2, wherein the lower intermediate electrode layer or the upper intermediate electrode layer is formed from at least one of gold, platinum, tungsten, aluminum, copper, molybdenum, ruthenium, titanium, chromium, and nickel, or from a laminated film thereof.

7. The acoustic converter according to claim 1 or 2, wherein the first piezoelectric layer and the second piezoelectric layer are formed from aluminum nitride or scandium aluminum nitride.

8. The acoustic converter according to claim 2, wherein the intermediate layer is formed from at least one of silicon dioxide, polysilicon, aluminum, aluminum nitride, silicon nitride, scandium aluminum nitride, aluminum oxide, titanium, or a laminated film thereof.

9. Fixed frame and The system includes a cantilever that extends from the fixed frame inward, The aforementioned cantilever is Lower electrode and A first piezoelectric layer formed on the lower electrode, An intermediate electrode formed on the first piezoelectric layer, A second piezoelectric layer formed on the intermediate electrode, The upper electrode formed on the second piezoelectric layer, The aforementioned intermediate electrode is In the thickness direction of the cantilever, the lower intermediate electrode layer formed on the first piezoelectric layer side, An intermediate layer formed on the lower intermediate electrode layer, It includes an upper intermediate electrode layer formed on the intermediate layer, The intermediate layer is formed from a different material than the upper intermediate electrode layer and the lower intermediate electrode layer. The thickness of the intermediate electrode is greater than that of the upper electrode or the lower electrode in this acoustic converter.

10. The acoustic converter according to claim 9, wherein the cantilever has a first cantilever and a second cantilever that face each other in a first direction which is the direction in which the cantilever extends.

11. The acoustic conversion device according to claim 9, wherein the thickness of the intermediate electrode is 10% or more and 90% or less of the thickness of the cantilever.

12. The cantilever includes a neutral surface in which neither tensile nor compressive forces are generated when the cantilever is deflected. The acoustic conversion device according to claim 9, wherein the intermediate electrode includes the neutral surface.

13. The acoustic conversion device according to claim 12, wherein the neutral plane is the center in the thickness direction of the cantilever.

14. The acoustic conversion device according to claim 9, wherein the thickness of the upper electrode and the thickness of the lower electrode are the same.

15. The acoustic conversion device according to claim 9, wherein the thickness of the first piezoelectric layer and the thickness of the second piezoelectric layer are the same.

16. The material of the upper electrode and the material of the lower electrode are the same. The acoustic converter according to claim 9, wherein the material of the first piezoelectric layer and the material of the second piezoelectric layer are the same.

17. Fixed frame and The fixed frame comprises two cantilevered beams, the two cantilevered beams having both ends fixed to the opposing parts of the fixed frame, The aforementioned two support beams are, Lower electrode and A first piezoelectric layer formed on the lower electrode, An intermediate electrode formed on the first piezoelectric layer, A second piezoelectric layer formed on the intermediate electrode, The upper electrode formed on the second piezoelectric layer, The aforementioned intermediate electrode is In the thickness direction of the double-supported beam, the lower intermediate electrode layer formed on the first piezoelectric layer side, An intermediate layer formed on the lower intermediate electrode layer, It includes an upper intermediate electrode layer formed on the intermediate layer, The intermediate layer is formed from a different material than the upper intermediate electrode layer and the lower intermediate electrode layer. The thickness of the intermediate electrode is greater than that of the upper electrode or the lower electrode in this acoustic converter.

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