Acoustic conversion device

Abstract

To provide an acoustic conversion device that improves sensitivity.SOLUTION: An acoustic conversion device 100 includes a fixed frame 10 and a cantilever 20 having one end which is a fixed end 22 fixed to the fixed frame 10 and the other end which is a free end 21, and extending from the fixed frame 10 to the inside of the fixed frame 10, the cantilever 20 includes a lower electrode 40, a first piezoelectric layer 61 formed on the lower electrode 40, an intermediate electrode 50 formed on the first piezoelectric layer 61, a second piezoelectric layer 62 formed on the intermediate electrode 50, and an upper electrode 30 formed on the second piezoelectric layer 62, and the thickness of the intermediate electrode 50 in the Z-axis direction is thicker than the thickness of the upper electrode 30 in the Z-axis direction or the thickness of the lower electrode 40 in the Z-axis direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] For example, a piezoelectric element is known that includes a piezoelectric film having one end supported and the other end free, and a pair of electrodes disposed on either side of the piezoelectric film (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

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

[0004] SUMMARY OF THE INVENTION An object of the present disclosure is to provide an acoustic transducer that can improve sensitivity, in which an acoustic transducer having a piezoelectric element is required. [Means for solving the problem]

[0005] The acoustic transducer according to the present disclosure comprises a fixed frame and a cantilever having one end which is a fixed end fixed to the fixed frame and the other end which is a free end, the cantilever extending from the fixed frame to the inside of the fixed frame, the cantilever having 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, and the thickness of the intermediate electrode is thicker than the 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 explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view illustrating an acoustic transducer according to a first embodiment. [Figure 2] 1 is a cross-sectional view illustrating an acoustic transducer according to a first embodiment. [Figure 3] FIG. 2 is a cross-sectional view illustrating an example of a cantilever. [Figure 4] FIG. 10 is a cross-sectional view illustrating a cantilever according to a comparative example. [Figure 5] 10 is a graph showing the relationship between the thickness ratio of the intermediate electrode and the voltage. [Figure 6] FIG. 10 is a plan view illustrating an acoustic transducer according to a second embodiment. [Figure 7] FIG. 10 is a cross-sectional view illustrating an acoustic transducer according to a second embodiment. [Figure 8] FIG. 10 is a plan view illustrating an acoustic transducer according to a third embodiment. [Figure 9] FIG. 10 is a perspective view illustrating an acoustic transducer according to a third embodiment. [Figure 10] FIG. 11 is a perspective view illustrating an acoustic transducer according to a third embodiment, viewed from the bottom side. [Figure 11] FIG. 10 is a cross-sectional view illustrating an acoustic transducer according to a third embodiment. [Figure 12] FIG. 2 is a partially enlarged cross-sectional view illustrating an enlarged example of a diaphragm (piezoelectric film). [Figure 13] 10A and 10B are side views illustrating the distribution of electric charges generated on a diaphragm that is deformed by receiving sound pressure. [Figure 14] FIG. 10 is a plan view illustrating an acoustic transducer according to a fourth embodiment. [Figure 15] 15 is a cross-sectional view illustrating an acoustic transducer according to a fourth embodiment, taken along line IX-IX in FIG. 14. FIG. [Figure 16] FIG. 10 is a circuit diagram of an acoustic transducer according to a fourth embodiment. [Figure 17] 10 is a graph showing the relationship between the sensing area diameter ratio and the normalized SNR. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an acoustic transducer according to an embodiment will be described with reference to the accompanying drawings. In this specification and the drawings, substantially identical components may be designated by the same reference numerals to avoid redundant description. In addition, the terms "upper" and "lower" may be used in this specification. This refers to the "upper" and "lower" in the state shown in FIG. 2, for example, where the side where the upper electrode 30 is arranged in the Z-axis direction is referred to as "upper" and the side where the lower electrode 40 is arranged is referred to as "lower". The actual arrangement of the acoustic transducer 100 is not limited to this.

[0009] [Sound transducer 100 according to the first embodiment] FIG. 1 is a perspective view illustrating an acoustic transducer 100 according to the first embodiment. FIG. 2 is a cross-sectional view illustrating an acoustic transducer according to the first embodiment. FIG. 3 is a cross-sectional view illustrating a cantilever 20 (20A). Note that in each drawing, X-axis, Y-axis, and Z-axis directions that are perpendicular to each other may be illustrated. The X-axis, Y-axis, and Z-axis directions do not have to be perpendicular to each other. The X-axis, Y-axis, and Z-axis directions may be arbitrary directions. The X-axis direction is an example of a first direction. The Y-axis direction is a direction that intersects with the first direction.

[0010] The acoustic transducer 100 shown in FIGS. 1 and 2 is a piezoelectric acoustic transducer having a piezoelectric element (piezoelectric film). The acoustic transducer 100 may be, for example, a microphone (MEMS microphone). The acoustic transducer 100 may be used for noise cancellation purposes. The acoustic transducer 100 may be a TWS (Ture wireless stereo) or an in-vehicle device installed in an automobile. The acoustic transducer 100 may be used, for example, as a hearing aid. The acoustic transducer 100 may be used in any purpose as long as it is capable of detecting a physical quantity. The physical quantity may be, for example, sound pressure.

[0011] [Fixed Frame 10] The acoustic transducer 100 includes a fixed frame 10 and a pair of cantilevers 20. 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 includes a substrate 11 and an insulating film 12. The insulating film 12 is formed on the substrate 11. As shown in FIG. 2, a cavity (opening) 13 is formed in the substrate 11. The cavity 13 is formed so as to penetrate the substrate 11 in the Z-axis direction. The insulating film 12 covers the upper surface of the substrate 11. The insulating film 12 is disposed between the substrate 11 and the cantilevers 20 in the Z-axis direction.

[0012] [Cantilever 20] The pair of cantilevers 20 each have a piezoelectric film. The cantilevers 20 extend in the X-axis direction from the fixed frame 10 to the inside of the fixed frame 10. One end of the cantilever 20 is a fixed end 22, and the other end is a free end 21.

[0013] The pair of cantilevers 20 includes cantilevers 20A and 20B arranged opposite each other in the X-axis direction. The cantilever 20A is an example of a first cantilever, and the cantilever 20B is an example of a second cantilever. The free ends 21 of the pair of cantilevers 20 face each other.

[0014] As shown in FIG. 1, a pair of slits 71 and 72 are formed around the cantilevers 20A and 20B. The slit 71 is a gap formed between the fixing frame 10 and the cantilever 20, and penetrates the substrate in the Z-axis direction. The pair of slits 71 extend in the X-axis direction and are spaced apart in the Y-axis direction. The slit 72 is a gap formed between the opposing free ends 21. The fixed end 22 of the cantilever 20 is connected to the fixing frame 10. The width of the slits 71 and 72 may be, for example, 100 nm or more and 5 μm or less. The width of the slits 71 and 72 may be, for example, 0.5 μm.

[0015] Fig. 2 shows a cross section along the XZ plane of the cantilever 20 (20A) and the fixed frame 10. Fig. 3 shows a cross section along the XZ plane of the cantilever 20 (20A). The piezoelectric film of the cantilever 20 has a lower electrode 40, a first piezoelectric layer 61, an intermediate electrode 50, a second piezoelectric layer 62, and an upper electrode 30, as shown in Fig. 2.

[0016] [Lower electrode 40] The lower electrode 40 is a thin electrode film. The lower electrode 40 is formed on the lower surface of the cantilever 20. The lower electrode 40 is formed continuously in the X-axis direction.

[0017] [First piezoelectric layer 61] The first piezoelectric layer 61 is a piezoelectric thin film, and is formed on the lower electrode 40. The first piezoelectric layer 61 is formed continuously in the X-axis direction and the Y-axis direction.

[0018] [Intermediate electrode 50] The intermediate electrode 50 is a thin electrode film, and is formed on the first piezoelectric layer 61. The intermediate electrode 50 is formed continuously in the X-axis direction and the Y-axis direction. The thickness T50 of the intermediate electrode 50 will be described later.

[0019] [Second piezoelectric layer 62] The second piezoelectric layer 62 is a piezoelectric thin film, and is formed on the intermediate electrode 50. The second piezoelectric layer 62 is formed continuously in the X-axis direction and the Y-axis direction.

[0020] [Top electrode 30] The upper electrode 30 is a thin electrode film, and is formed on the second piezoelectric layer 62. The upper electrode 30 is formed continuously in the X-axis direction and the Y-axis direction.

[0021] The upper electrode 30 and the lower electrode 40 are spaced apart in the Z-axis direction. The intermediate electrode 50 is disposed between the lower electrode 40 and the upper electrode 30 in the Z-axis direction. The first piezoelectric layer 61 is sandwiched between the lower electrode 40 and the intermediate electrode 50 in the Z-axis direction. The second piezoelectric layer 62 is sandwiched between the intermediate electrode 50 and the upper electrode 30 in the Z-axis direction.

[0022] [Material and thickness of piezoelectric thin film] The material of the first piezoelectric layer 61 and the second piezoelectric layer 62 may be, for example, ScAlN. The material of the first piezoelectric layer 61 may be AlN. Sc may be 0 at% or more and 50 at% or less. The thickness of the first piezoelectric layer 61 and the second piezoelectric layer 62 may be, for example, 100 nm or more and 1 μm or less. The thickness of the first piezoelectric layer 61 and the second piezoelectric layer 62 may be, for example, 500 nm. The thickness of the first piezoelectric layer 61 and the second piezoelectric layer 62 may be the same. The thickness of the first piezoelectric layer 61 and the second piezoelectric layer 62 may be different.

[0023] The first piezoelectric layer 61 and the second piezoelectric layer 62 may have a fluorite structure (hafnium oxide, zirconium oxide, cesium oxide) or a wurtzite structure (zinc oxide). The material of the first piezoelectric layer 61 and the material of the second piezoelectric layer 62 may be the same. The material of the first piezoelectric layer 61 and the material of the second piezoelectric layer 62 may be different.

[0024] [Electrode thin film material] The upper electrode 30, the lower electrode 40, and the intermediate electrode 50 may be made of a material such as Al, Mo, Pt, or Ti. The material of the upper electrode 30 and the material of the lower electrode 40 may be the same or different.

[0025] [Electrode thin film thickness] The thickness T50 of the intermediate electrode 50 shown in FIG. 3 is thicker than the thicknesses T30 and T40 of the upper electrode 30 and the lower electrode 40. The thickness T50 of the intermediate electrode 50 is thicker than the thickness T30 of the upper electrode 30. The thickness T50 of the intermediate electrode 50 is thicker than the thickness T40 of the lower electrode 40. The thickness T30 of the upper electrode 30 may be the same as the thickness T40 of the lower electrode 40. The thickness T30 of the upper electrode 30 is the thickness of the upper electrode 30 along the Z-axis direction. The thickness T40 of the lower electrode 40 is the thickness of the lower electrode 40 along the Z-axis direction. The thickness T30 of the intermediate electrode 50 is the thickness of the intermediate electrode 50 along the Z-axis direction. The thickness T30 of the upper electrode 30 and the thickness T40 of the lower electrode 40 may be different.

[0026] The thicknesses T30, T40 of the upper electrode 30 and the lower electrode 40 may be, for example, 5 nm or more and 100 nm or less. The thicknesses T30, T40 of the upper electrode 30 and the lower electrode 40 may be, for example, 50 nm. The thickness T50 of the intermediate electrode 50 may be, for example, 10 nm or more and 1000 nm or less. The thickness T50 of the intermediate electrode 50 may be, for example, 100 nm. The thickness T50 of the intermediate electrode 50 may be thicker than the sum of the thickness T30 of the upper electrode 30 and the thickness T40 of the lower electrode 40.

[0027] [Ratio of thickness T50 of intermediate electrode 50 to thickness T20 of cantilever 20] The thickness T50 of the intermediate electrode 50 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 total thickness of the thickness T40 of the lower electrode 40, the thickness of the first piezoelectric layer 61, the thickness T50 of the intermediate electrode 50, the thickness of the second piezoelectric layer 62, and the thickness T30 of the upper electrode 30. The thickness T50 of the intermediate electrode 50 may be 30% to 70% of the thickness T20 of the cantilever 20. The thickness T50 of the intermediate electrode 50 may be 40% to 60% of the thickness T20 of the cantilever 20. As described above, the thickness T20 of the intermediate electrode 50 is thicker than the thicknesses T30 and T40 of the upper electrode 30 and the lower electrode 40.

[0028] [Neutral plane N20] The intermediate electrode 50 is disposed at a position including a neutral plane N20. The cantilever 20 may include the neutral plane N20. The neutral plane N20 may be a plane where, for example, neither tensile nor compressive force occurs inside the cantilever 20 in the longitudinal direction when the cantilever 20 is bent. The cantilever 20 bends, 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.

[0029] For example, when the cantilever 20 receives sound pressure upward in the Z-axis direction, the free end 21 is displaced upward, and the cantilever 20 is bent. At this time, a tensile force is generated in the first piezoelectric layer 61 below the intermediate electrode 50, and a compressive force is generated in the second piezoelectric layer 62 above the intermediate electrode 50. The magnitudes of the tensile force and compressive force vary depending on the position in the Z-axis direction. The tensile force at a position closer to the lower electrode 40 is greater than the tensile force at a position closer to the intermediate electrode 50. The compressive force at a position closer to the upper electrode 30 is greater than the compressive force at a position closer to the intermediate electrode 50.

[0030] 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 that extends along the XY plane when the cantilever 20 is not deflected. The intermediate electrode 50 is located at a position that includes the neutral plane N20. The center of the intermediate electrode 50 in the Z-axis direction may be located on the neutral plane N20. When the thickness of the first piezoelectric layer 61 and the thickness of the second piezoelectric layer 62 are the same, the thickness T30 of the upper electrode 30 and the thickness T40 of the lower electrode 40 are the same, the material of the first piezoelectric layer 61 and the second piezoelectric layer 62 are the same, and the material of the upper electrode 30 and the lower electrode 40 are the same, the neutral plane N is located at the center of the cantilever 20 in the thickness direction. The neutral plane N does not have to be located at the center of the cantilever 20 in the thickness direction. Due to the difference in thickness between the first piezoelectric layer 61 and the second piezoelectric layer 62, the difference in material between the first piezoelectric layer 61 and the second piezoelectric layer 62, the difference in thickness T30, T40 between the upper electrode 30 and the lower electrode 40, and the difference in material between the upper electrode 30 and the lower electrode 40, the neutral plane N20 is located other than the center in the thickness direction of the cantilever 20.

[0031] [Cantilever 20C of acoustic transducer according to comparative example] Next, a cantilever 20C of an acoustic transducer according to a comparative example will be described with reference to Fig. 4. Fig. 4 is a cross-sectional view illustrating the cantilever 20C according to the comparative example. In the cantilever 20C according to the comparative example, the thicknesses T30, T40, and T50C of the upper electrode 30, the lower electrode 40, and the intermediate electrode 50C are the same.

[0032] When sound pressure acts on the cantilever 20C and the cantilever 20C bends, a compressive force and a tensile force act on the first piezoelectric layer 61 and the second piezoelectric layer 62. The magnitude of the tensile force and the compressive force varies depending on the position in the Z-axis direction. The tensile force at a position closer to the lower electrode 40 is greater than the tensile force at a position closer to the intermediate electrode 50. The compressive force at a position closer to the upper electrode 30 is greater than the compressive force at a position closer to the intermediate electrode 50.

[0033] [Relationship between thickness ratio of intermediate electrode 50 and voltage] Next, referring to FIG. 5, the relationship between the thickness ratio of the intermediate electrode 50 of the acoustic transducer 100 according to the first embodiment and voltage will be described. FIG. 5 is a graph showing the relationship between the thickness ratio of the intermediate electrode 50 and voltage. In FIG. 5, the horizontal axis represents the thickness ratio [%] of the intermediate electrode 50, and the vertical axis represents voltage. The thickness ratio of the intermediate electrode 50 is the ratio of the thickness T50 of the intermediate electrode 50 to the thickness T20 of the cantilever 20. The voltage shown on the vertical axis is the voltage generated by the piezoelectric effect in the first piezoelectric layer 61 and the second piezoelectric layer 62. The graph shown in FIG. 5 may be, for example, a calculation result for the acoustic transducer 100. The shape of the graph varies depending on, for example, the material, structure, shape, and circuit configuration of the cantilever 20. For example, the generated voltage when the thickness ratio of the intermediate electrode 50 is 40% or more and 60% or less is higher than the generated voltage when the thickness ratio is 20% or less or 80% or more.

[0034] [Shape of cantilever 20] As described above, the shape of the cantilever 20 is rectangular when viewed in the Z-axis direction. When the cantilever 20 is rectangular, the area of ​​the cantilever 20 within the chip can be made larger than when the cantilever 20 is circular, and the sensitivity of the cantilever 20 can be increased. In other words, for the same sensitivity, the acoustic transducer 100 can be made smaller than conventional devices. The acoustic transducer 100 can be made smaller and cheaper.

[0035] [Total length of cantilever 20] In the acoustic transducer 100, the resonant frequency of the cantilever 20 can be easily changed by changing the overall length of the cantilever 20. At the time of design, the resonant frequency can be lowered by increasing the overall length of the cantilever 20. The resonant frequency when the overall length of the cantilever 20 is long is lower than the resonant frequency when the overall length of the cantilever 20 is short. The overall length of the cantilever 20 may be the length of the region where the upper electrode 30, the lower electrode 40, and the intermediate electrode 50 overlap.

[0036] [Cantilever 20 width] The width of the cantilever 20 is the width along the Y-axis direction. The width of the cantilever 20 may be the width of the area where the upper electrode 30, the lower electrode 40, and the intermediate electrode 50 overlap. In the acoustic transducer 100, the sensitivity of the cantilever 20 can be changed regardless of the resonant frequency by changing the width of the cantilever 20. At the time of design, the sensitivity can be increased by increasing the width of the cantilever 20. The sensitivity when the cantilever 20 is wide is higher than when the width is narrow.

[0037] [Actions and Effects of the Sound Converter 100 According to the First Embodiment] The acoustic converter 100 of the first embodiment comprises a fixed frame 10, and a cantilever 20 having one end which is a fixed end 22 fixed to the fixed frame 10 and the other end which is a free end 21, and extending from the fixed frame 10 to the inside of the fixed frame 10, the cantilever 20 having a lower electrode 40, a first piezoelectric layer 61 formed on the lower electrode 40, an intermediate electrode 50 formed on the first piezoelectric layer 61, a second piezoelectric layer 62 formed on the intermediate electrode 50, and an upper electrode 30 formed on the second piezoelectric layer 62, and the thickness T50 of the intermediate electrode 50 is thicker than the thicknesses T30, T40 of the upper electrode 30 or the lower electrode 40.

[0038] In the acoustic transducer 100, when the cantilever 20 is deformed by receiving sound pressure, a piezoelectric output charge is generated in the first piezoelectric layer 61 and the second piezoelectric layer 62, and the generated piezoelectric output charge can be detected. With this acoustic transducer 100, parts of the first piezoelectric layer 61 and the second piezoelectric layer 62 can be arranged in the region where the tensile force or compressive force is larger when the cantilever 20 is bent, and the intermediate electrode 50 can be arranged in the region where the tensile force or compressive force is smaller.

[0039] Furthermore, the acoustic transducer 100 is a piezoelectric acoustic transducer, and is more resistant to dust and water droplets than conventional electrostatic acoustic transducers.

[0040] Furthermore, because the acoustic transducer 100 has a rectangular shape, the area of ​​the cantilever 20 within the chip can be increased, enabling higher sensitivity. Since the acoustic transducer 100 can achieve high sensitivity, it can be made smaller. In the acoustic transducer 100, the resonant frequency can be easily changed by changing the length of the cantilever 20. In the acoustic transducer 100, the sensitivity can be changed regardless of the resonant frequency by changing the width W20 of the detection area 23.

[0041] [Sound transducer 100B according to the second embodiment] Next, an acoustic transducer 100B according to a second embodiment will be described. FIG. 6 is a plan view illustrating the acoustic transducer 100B according to the second embodiment. FIG. 7 is a cross-sectional view illustrating the acoustic transducer 100B according to the second embodiment. The acoustic transducer 100B according to the second embodiment shown in FIGS. 6 and 7 differs from the acoustic transducer 100 according to the first embodiment shown in FIGS. 1 and 2 in that the cantilever 20 includes a detection region 23 and a non-detection region 24, specifically, the upper electrode 30, the lower electrode 40, and the intermediate electrode 50 are divided in the X-axis direction. In the description of the acoustic transducer 100B according to the second embodiment, descriptions similar to those of the acoustic transducer 100 according to the first embodiment may be omitted.

[0042] [Lower electrode 40] The lower electrode 40 is a thin electrode film and includes a first lower electrode 41 and a second lower electrode 42. The first lower electrode 41 and the second lower electrode 42 are spaced apart in the X-axis direction. Between the first lower electrode 41 and the second lower electrode 42, there is an electrode-free region 82 where no electrode is formed. After the lower electrode 40 is formed, etching is performed to remove the electrode, thereby forming the electrode-free region 82. The electrode-free region 82 may be formed using a lift-off method.

[0043] The first lower electrode 41 is formed closer to the fixed end 22 in the X-axis direction. The second lower electrode 42 is formed closer to the free end 21 in the X-axis direction.

[0044] [Intermediate electrode 50] The intermediate electrode 50 is a thin electrode film and includes a first intermediate electrode 51 and a second intermediate electrode 52. The first intermediate electrode 51 and the second intermediate electrode 52 are spaced apart in the X-axis direction. Between the first intermediate electrode 51 and the second intermediate electrode 52, there is an electrode-free region 83 where no electrode is formed. After the intermediate electrode 50 is formed, etching is performed to remove the electrode, thereby forming the electrode-free region 83. The electrode-free region 83 may be formed using a lift-off method.

[0045] The first intermediate electrode 51 is formed closer to the fixed end 22 in the X-axis direction. The second intermediate electrode 52 is formed closer to the free end 21 in the X-axis direction.

[0046] [Top electrode 30] The upper electrode 30 is a thin electrode film and includes a first upper electrode 31 and a second upper electrode 32. The first upper electrode 31 and the second upper electrode 32 are spaced apart in the X-axis direction. Between the first upper electrode 31 and the second upper electrode 32, there is an electrode-free region 81 where no electrode is formed. After the upper electrode 30 is formed, etching is performed to remove the electrode, thereby forming the electrode-free region 81. The electrode-free region 81 may be formed using a lift-off method.

[0047] The first upper electrode 31 is formed closer to the fixed end 22 in the X-axis direction. The second upper electrode 32 is formed closer to the free end 21 in the X-axis direction.

[0048] [Detection area 23 and non-detection area 24] The cantilever 20 has a detection region 23 where a physical quantity can be detected, and a non-detection region 24 where no physical quantity is detected. The physical quantity is, for example, sound pressure. The detection region 23 may be a region where the first upper electrode 31, the first intermediate electrode 51, and the first piezoelectric layer 61 are arranged to overlap in the Z-axis direction. The first upper electrode 31 and the first lower electrode 41 are electrically connected. The acoustic transducer 100 can detect a piezoelectric output charge between the first upper electrode 31 and the first intermediate electrode 51. The acoustic transducer 100 can detect a piezoelectric output charge between the first lower electrode 41 and the first intermediate electrode 51.

[0049] The detection area 23 is disposed closer to the fixed end 22 than the non-detection area 24. In other words, the non-detection area 24 is disposed closer to the free end 21 than the detection area 23.

[0050] The non-detection region 24 is a region of the cantilever 20 excluding the detection region 23. The second upper electrode 32, the second intermediate electrode 52, and the second lower electrode 42 are not electrically connected.

[0051] [Electrode thin film thickness] The thickness T51 of the first intermediate electrode 51 is thicker than the thicknesses T31, T41 of the first upper electrode 31 or the first lower electrode 41. The thickness T51 of the first intermediate electrode 51 is thicker than the thickness T31 of the first upper electrode 31. The thickness T51 of the first intermediate electrode 51 is thicker than the thickness T41 of the first lower electrode 41. The thickness T31 of the first upper electrode 31 may be the same as the thickness T41 of the first lower electrode 41.

[0052] The thickness T52 of the second intermediate electrode 52 is thicker than the thicknesses T32, T42 of the second upper electrode 32 or the second lower electrode 42. The thickness T52 of the second intermediate electrode 52 is thicker than the thickness T32 of the second upper electrode 32. The thickness T52 of the second intermediate electrode 52 is thicker than the thickness T42 of the second lower electrode 42. The thickness T32 of the second upper electrode 32 may be the same as the thickness T42 of the second lower electrode 42.

[0053] [Electrode end shape] The end of the electrode in the X-axis direction may be tapered. The electrodes include an upper electrode 30, a lower electrode 40, and an intermediate electrode 50. The thickness of the end of the electrode in the X-axis direction may be thinner than the thickness of the central part of the electrode in the X-axis direction. The end of the electrode may be formed to form an acute angle. The tapered shape may be inclined so that the lower end is positioned outward in the X-axis direction relative to the upper end.

[0054] The end of the electrode may be disposed more inward than the free end 21 in the X-axis direction. The first piezoelectric layer 61 and the second piezoelectric layer 62 may be formed more outward than the end of the electrode in the X-axis direction. The first piezoelectric layer 61 and the second piezoelectric layer 62 may be connected in the Z-axis direction in a region more outward than the end of the electrode. In this way, by tapering the end of the electrode, it is possible to suppress a decrease in the crystallinity of the first piezoelectric layer 61 and the second piezoelectric layer 62. Therefore, it is possible to stably generate electric charges in the first piezoelectric layer 61 and the second piezoelectric layer 62.

[0055] [Actions and Effects of the Sound Converter 100B According to the Second Embodiment] The acoustic transducer 100B according to the second embodiment also has the same effects as the acoustic transducer 100 according to the first embodiment. In the acoustic transducer 100B according to the second embodiment, the electrodes are separated in the length direction (X-axis direction) of the cantilever 20, thereby forming a detection region 23 and a non-detection region 24, thereby improving sensitivity.

[0056] Furthermore, in the acoustic transducer 100, the cantilever 20 has a piezoelectric film, which includes a lower electrode 40, a first piezoelectric layer 61 formed on the lower electrode 40, an intermediate electrode 50 formed on the first piezoelectric layer 61, a second piezoelectric layer 62 formed on the intermediate electrode 50, and an upper electrode 30 formed on the second piezoelectric layer 62, and has electrode-free regions 82, 83, and 81 between the detection region 23 and the non-detection region 24, in which at least one of the lower electrode 40, the intermediate electrode 50, and the upper electrode 30 is not formed.

[0057] In the acoustic transducer 100 having this configuration, the cantilever 20, which is a piezoelectric film, is deformed, and piezoelectric output charges generated between the first upper electrode 31 and the first intermediate electrode 51 and between the first lower electrode 41 and the first intermediate electrode 51 in the detection region 23 are connected to the first intermediate electrode 51. In the acoustic transducer 100, the detection region 23 and the non-detection region 24 can be separated by forming electrode-free regions 82, 83, and 81 in which no electrode is formed on at least one of the lower electrode 40, the intermediate electrode 50, and the upper electrode 30.

[0058] [Acoustic transducer 200 according to the third embodiment] Next, an acoustic transducer 200 according to a third embodiment will be described. FIG. 8 is a plan view illustrating the acoustic transducer 200 according to the third embodiment. FIG. 9 is a perspective view illustrating the acoustic transducer 200 according to the third embodiment. FIG. 10 is a perspective view illustrating the acoustic transducer 200 according to the third embodiment from the bottom side. FIG. 11 is a cross-sectional view illustrating the acoustic transducer 200 according to the third embodiment. Note that in each drawing, X-axis, Y-axis, and Z-axis directions that are orthogonal to each other may be illustrated. The X-axis, Y-axis, and Z-axis directions do not have to be orthogonal to each other. The X-axis, Y-axis, and Z-axis directions may be arbitrary 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. In the description of the acoustic transducer 200 according to the third embodiment, descriptions similar to those of the acoustic transducer 100 according to the above embodiment will be omitted.

[0059] [Support substrate 211] The acoustic transducer 200 includes a support substrate (fixed frame) 211 and a diaphragm (piezoelectric element) 220. The support substrate 211 may be rectangular when viewed in the Z-axis direction. The plate 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 so as to form a circle when viewed in the Z-axis direction.

[0060] [Diaphragm 220] The diaphragm 220 has a piezoelectric film. The diaphragm 220 is formed to cover the opening 221. The diaphragm 220 is formed to have a circular shape when viewed in the Z-axis direction. The diaphragm 220 may include a portion that covers the outside of the opening 221. The outer periphery 222 of the diaphragm 220 is the 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 has a first detection area 323, a non-detection area 324, and a second detection area 325. The diaphragm 220 is also called a "diaphragm." The shape of the opening 221 is not limited to a circle, and may be an ellipse or another shape.

[0061] [Piezoelectric film] The piezoelectric film, which is diaphragm 220, deforms in response to sound pressure and generates an electric charge. Fig. 12 is an enlarged cross-sectional view illustrating an example of the piezoelectric film. The piezoelectric film has a lower electrode layer 440, a lower piezoelectric layer (first piezoelectric layer) 460, an intermediate electrode layer 250, an upper piezoelectric layer (second piezoelectric layer) 360, and an upper electrode layer 330. The lower electrode layer 440, the lower piezoelectric layer 460, the intermediate electrode layer 250, the upper piezoelectric layer 360, and the upper electrode layer 330 are laminated in this order.

[0062] [Lower electrode layer 440] Lower electrode layer 440 has lower electrodes 441 to 443 which are thin electrode films. Lower electrode layer 440 is disposed at a position close to opening 221 in the Z-axis direction. Lower electrodes 441 to 443 are disposed apart in the X-axis direction. Lower electrode 441 has a circular shape. Lower electrode 441 is disposed at a position close to center C11 of diaphragm 220 as viewed in the Z-axis direction. Lower electrode 442 has a ring shape as viewed in the Z-axis direction. Lower electrode 442 is disposed outside lower electrode 441 in the radial direction. Lower electrode 443 has a ring shape as viewed in the Z-axis direction. Lower electrode 443 is disposed outside lower electrode 442 in the radial direction.

[0063] [No-electrode formation area 483,484] In the radial direction of diaphragm 220, there is an electrode-free region 483 where no electrode is formed between lower electrode 441 and lower electrode 442. In the radial direction of diaphragm 220, there is an electrode-free region 484 where no electrode is formed between lower electrode 442 and lower electrode 443.

[0064] [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 vibration plate 220.

[0065] [Intermediate electrode layer 250] The intermediate electrode layer 250 has intermediate electrodes 251 to 253 which are thin electrode films. The intermediate electrode layer 250 is formed on the lower piezoelectric layer 460. The intermediate electrodes 251 to 253 are arranged to be spaced apart in the X-axis direction. The intermediate electrode 251 has a circular shape. The intermediate electrode 251 is arranged at a position close to the center C11 of the vibration plate 220 when viewed in the Z-axis direction. The intermediate electrode 252 has a ring shape when viewed in the Z-axis direction. The intermediate electrode 252 is arranged radially outward of the intermediate electrode 251. The intermediate electrode 253 has a ring shape when viewed in the Z-axis direction. The intermediate electrode 253 is arranged radially outward of the intermediate electrode 252.

[0066] [Electrode non-formation area 281,282] In the radial direction of diaphragm 220, there is an electrode-free region 281 where no electrode is formed between intermediate electrode 251 and intermediate electrode 252. In the radial direction of diaphragm 220, there is an electrode-free region 282 where no electrode is formed between intermediate electrode 252 and intermediate electrode 253.

[0067] [Upper piezoelectric layer 360] The upper piezoelectric layer 360 is a piezoelectric thin film, and is formed on the intermediate electrode layer 250. The upper piezoelectric layer 360 is formed continuously in the radial direction of the vibration plate 220.

[0068] [Top electrode layer 330] The upper electrode layer 330 has upper electrodes 331 to 333 which are thin electrode films. The upper electrode layer 330 is formed on the upper piezoelectric layer 360. The upper electrodes 331 to 333 are arranged to be spaced apart in the X-axis direction. The upper electrode 331 has a circular shape. The upper electrode 331 is arranged at a position close to the center C11 of the diaphragm 220 when viewed in the Z-axis direction. The upper electrode 332 has a ring shape when viewed in the Z-axis direction. The upper electrode 332 is arranged radially outward of the upper electrode 331. The upper electrode 333 has a ring shape when viewed in the Z-axis direction. The upper electrode 333 is arranged radially outward of the upper electrode 332.

[0069] [Material and thickness of piezoelectric thin film] The piezoelectric material used for 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 to 60 at%)), or 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).

[0070] The thickness of the lower piezoelectric layer 460 may be, for example, 100 nm to 1 μm 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.

[0071] The thickness of the upper piezoelectric layer 360 may be, for example, 100 nm to 1 μm 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.

[0072] [Electrode thin film material and thickness] The thickness of the electrode thin film in the upper electrode layer 330, the intermediate electrode layer 250, and the lower electrode layer 440 may be, for example, 5 nm or more and 100 nm or less. The thickness of the electrode thin film may be, for example, 20 nm. The electrode thin films in the upper electrode layer 330, the intermediate electrode layer 250, and the lower electrode layer 440 may be formed to different thicknesses.

[0073] The material of the electrode thin films in the upper electrode layer 330, the intermediate electrode layer 250, and the lower electrode layer 440 may be formed from, for example, at least one of gold, platinum, tungsten, aluminum, copper, molybdenum, ruthenium, titanium, chromium, and nickel, or an alloy containing one of these. The electrode thin films in the upper electrode layer 330, the intermediate electrode layer 250, and the lower electrode layer 440 may be formed from the same material or different materials.

[0074] [First detection area, non-detection area, and second detection area] As shown in Figures 11 and 12, diaphragm 220 includes first detection areas 323, 423, non-detection areas 324, 424, and second detection areas 325, 425. First detection areas 323, 423 and second detection areas 325, 425 are areas where a physical quantity can be detected. Non-detection areas 324, 424 are areas where a physical quantity is not detected. The physical quantity is, for example, sound pressure.

[0075] The first detection region 323 is a region where the intermediate electrode 251, the upper piezoelectric layer 360, and the upper electrode 331 are arranged to overlap in the Z-axis direction. The first detection region 423 is a region where the lower electrode 441, the lower piezoelectric layer 460, and the intermediate electrode 251 are arranged to overlap in the Z-axis direction. The acoustic transducer 200 can detect the piezoelectric output charge between the lower electrode 441 and the intermediate electrode 251. The acoustic transducer 200 can detect the piezoelectric output charge between the intermediate electrode 251 and the upper electrode 331.

[0076] The non-detection region 324 includes a region where the intermediate electrode 252, the upper piezoelectric layer 360, and the upper electrode 332 are overlapping in the Z-axis direction. The non-detection region 424 includes a region where the lower electrode 442, the lower piezoelectric layer 460, and the intermediate electrode 252 are overlapping in the Z-axis direction. The acoustic transducer 200 cannot detect the piezoelectric output charge between the lower electrode 442 and the intermediate electrode 252. The acoustic transducer 200 cannot detect the piezoelectric output charge between the intermediate electrode 252 and the upper electrode 332.

[0077] The second detection region 325 is a region where the intermediate electrode 253, the upper piezoelectric layer 360, and the upper electrode 333 are arranged to overlap in the Z-axis direction. The second detection region 425 is a region where the lower electrode 443, the lower piezoelectric layer 460, and the intermediate electrode 253 are arranged to overlap in the Z-axis direction. The acoustic transducer 200 can detect the piezoelectric output charge between the lower electrode 443 and the intermediate electrode 253. The acoustic transducer 200 can detect the piezoelectric output charge between the intermediate electrode 253 and the upper electrode 333.

[0078] The first detection regions 323, 423 are formed at positions close to the center of the diaphragm 220. The non-detection regions 324, 424 are formed further outward than the first detection regions 323, 423 in the radial direction of the diaphragm 220. The second detection regions 325, 425 are formed further outward than the non-detection regions 324, 424 in the radial direction of the diaphragm 220.

[0079] [Outer diameters of first detection area 323, non-detection area 324, and second detection area 325] 8, the outer diameter Φ323 of the first detection region 323 is, for example, 0.59 mm, the outer diameter Φ324 of the non-detection region 324 is, for example, 0.81 mm, and the outer diameter Φ325 of the second detection region 325 is 1 mm.

[0080] [Split position] 12, the lower electrode layer 440 has no-electrode regions 483 and 484. The intermediate electrode layer 250 has no-electrode regions 281 and 282. The upper electrode layer 330 has no-electrode regions 381 and 382.

[0081] The electrode-free regions 281, 282, 381, 382, ​​483, and 484 may be referred to as “division positions.” These electrode-free regions 281, 282, 381, 382, ​​483, and 484 are arranged at different positions in the radial direction of the diaphragm 220.

[0082] The electrode-free region 381 is disposed more inward than the electrode-free region 281 in the radial direction of the diaphragm 220. The electrode-free region 281 is disposed more inward than the electrode-free region 483 in the radial direction of the diaphragm 220.

[0083] The electrode-free region 382 is disposed further outward than the electrode-free region 282 in the radial direction of the diaphragm 220. The electrode-free region 282 is disposed further outward than the electrode-free region 484 in the radial direction of the diaphragm 220.

[0084] In diaphragm 220, multiple electrode-free regions 281, 282, 381, 382, ​​483, and 484 are formed in positions that do not overlap one another when viewed in the Z-axis direction, thereby preventing a decrease in strength of diaphragm 220. Note that piezoelectric thin films are formed in electrode-free regions 281, 282, 483, and 484.

[0085] 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 than 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 than the crystallinity of the piezoelectric thin film above the electrode.

[0086] The division position of electrode-free region 483 is located outside first detection region 423 in the radial direction of diaphragm 220. The division position of electrode-free region 484 is located inside second detection region 425 in the radial direction of diaphragm 220. This does not hinder the crystal growth of the piezoelectric thin film that generates electric charge. In acoustic transducer 200, the crystallinity of the piezoelectric thin film is high in first detection region 423 and second detection region 425 that generate electric charge.

[0087] The division position of electrode-free region 281 is located outside first detection region 323 in the radial direction of diaphragm 220. The division position of electrode-free region 282 is located inside second detection region 325 in the radial direction of diaphragm 220. This does not hinder crystal growth of the piezoelectric thin film that generates electric charge. In acoustic transducer 200, the crystallinity of the piezoelectric thin film is high in first detection region 323 and second detection region 325 that generate electric charge.

[0088] [Piezoelectric film connection] In vibration plate 220, which is a piezoelectric film (piezoelectric element), the electrodes of first detection regions 323, 423 are electrically connected in parallel. The electrodes of first detection region 323 include upper electrode 331 and intermediate electrode 251. The electrodes of first detection region 423 include lower electrode 441 and intermediate electrode 251. The electrodes of second detection regions 325, 425 are electrically connected in parallel. The electrodes of second detection region 325 include upper electrode 333 and intermediate electrode 253. The electrodes of second detection region 425 include lower electrode 443 and intermediate electrode 253.

[0089] The electrodes in the first and second detection regions are electrically connected in series: specifically, upper electrode 331 and upper electrode 333 are connected in series, and lower electrode 441 and lower electrode 443 are connected in series, or intermediate electrode 251 and intermediate electrode 253 are connected in series.

[0090] [Actions and Effects of the Acoustic Converter 200 According to the Third Embodiment] Acoustic transducer 200 according to the third embodiment includes support substrate (fixed frame) 211 and diaphragm 220, which is a piezoelectric element fixed to support substrate 211. Diaphragm 220 has first detection regions 323, 423 and second detection regions 325, 425, which are multiple detection regions capable of detecting physical quantities, and non-detection regions 324, 424, which do not detect physical quantities. Electrodes in the multiple detection regions are electrically connected in series.

[0091] In the acoustic transducer 200 of this embodiment, the physical quantity can be detected by detecting the deformation of the diaphragm 220 due to deformation of the diaphragm 220. In the acoustic transducer 200, first detection areas 323, 423 and second detection areas 325, 425 are formed, and the electrodes of these multiple detection areas are electrically connected in series, thereby improving the sensitivity of the diaphragm 220.

[0092] In the acoustic transducer 200, the piezoelectric element is a vibration plate (diaphragm) 220, and an outer periphery 222 of the vibration plate 220 (outer periphery of the diaphragm) is a fixed end fixed to a support substrate 211.

[0093] In the acoustic transducer 200, the multiple detection regions include first detection regions 323 and 423 which are inner detection regions arranged at positions close to the center C11 of the diaphragm 220 in the radial direction of the diaphragm 220, and second detection regions 325 and 425 which are outer detection regions arranged at positions far from the center C11 of the diaphragm 220 in the radial direction of the diaphragm 220. Non-detection regions 324 and 424 are formed between the inner detection regions and the outer detection regions in the circumferential direction of the diaphragm 220.

[0094] In the acoustic transducer 200 of this embodiment, as the diaphragm 220 deforms, charges are generated in response to the diaphragm 220, and the charges generated are detected in the first detection areas 323, 423 and the second detection areas 325, 425. In the acoustic transducer 200, the electrodes are divided in the radial direction of the diaphragm 220, thereby forming the first detection areas 323, 423, the non-detection areas 324, 424, and the second detection areas 325, 425. In such an acoustic transducer 200, the sensitivity for detecting charges in response to sound pressure can be improved.

[0095] 13 is a side view illustrating the distribution of electric charges generated on diaphragm 220 as it deforms under sound pressure. Diaphragm 220 has outer periphery 222 fixed to support substrate 211 in the radial direction. As shown in FIG. 13, the area near inflection point P12 is less likely to deform, and the amount of electric charge generated is small. Inflection point P12 and the area nearby, where the amount of electric charge generated is small, are included in non-detection areas 324, 424.

[0096] In contrast, the area close to the center C11 of the diaphragm 220 and near the outer periphery 222 of the diaphragm 220 are largely deformed and generate a large amount of electric charge. The center C11 of the diaphragm 220 and the area around it are included in the first detection areas 323, 423. The area near the outer periphery 222 of the diaphragm 220 is included in the second detection areas 325, 425. In the acoustic transducer 200, the area including the inflection point P12, where little electric charge is generated, is not included in the first detection areas 323, 423 and the second detection areas 325, 425. This makes it possible to improve the signal-to-noise ratio in the acoustic transducer 200 and to detect electric charge with high sensitivity.

[0097] [Electrode end shape] Next, the shape of the electrode end portions will be described. As shown in Fig. 12, the end portions of the upper electrodes 331-333, the lower electrodes 441-443, and the intermediate electrodes 251-253 may be tapered. The electrode end portions are end portions that face each other in the radial direction of the diaphragm 220. The tapered shape of the electrode end portions is formed so that the lower side protrudes more than the upper side.

[0098] In this way, by tapering the ends of the lower electrodes 441 to 443, it is possible to make the steps gentler at the boundaries between the lower electrodes 441 to 443 and the electrode-free regions 483, 484. This makes it possible to suppress deterioration in the crystallinity of the piezoelectric layer 460. The same applies to the boundaries between the other electrodes and the electrode-free regions.

[0099] [Sound transducer 200B according to the fourth embodiment] Next, an acoustic transducer 200B according to a fourth embodiment will be described. FIG. 14 is a plan view illustrating the acoustic transducer 200B according to the fourth embodiment. FIG. 15 is a cross-sectional view illustrating the acoustic transducer according to the fourth embodiment, taken along line IX-IX in FIG. 14. The acoustic transducer 200B according to the fourth embodiment shown in FIGS. 14 and 15 differs from the acoustic transducer 200 according to the third embodiment shown in FIG. 8 in that the acoustic transducer 200B according to the fourth embodiment includes a plurality of upper electrodes 331B, 333B divided in the circumferential direction, a plurality of lower electrodes 441B, 443B divided in the circumferential direction, a plurality of intermediate electrodes 251B, 253B divided in the circumferential direction, and electrode-free regions 385, 386 extending in the radial direction. Note that, in the description of the acoustic transducer 200B according to the fourth embodiment, descriptions similar to those of the acoustic transducer 200 according to the third embodiment may be omitted.

[0100] [Laminate 300B] As shown in Fig. 15, the acoustic transducer 200B includes laminates 300B and 400B. The laminate 300B includes an upper electrode layer 330B, a piezoelectric layer 360, and an intermediate electrode layer 250B. The upper electrode layer 330B includes a plurality of upper electrodes 331B divided in the circumferential direction, a circumferentially continuous upper electrode 332, and a plurality of upper electrodes 333B divided in the circumferential direction. The intermediate electrode layer 250B includes a plurality of intermediate electrodes 251B divided in the circumferential direction, a circumferentially continuous intermediate electrode 252, and a plurality of intermediate electrodes 253B divided in the circumferential direction.

[0101] [First detection area 323B] The laminate 300B has a first detection region 323B, a non-detection region 324B, 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 intermediate electrodes 251B. 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 an intermediate electrode 251B.

[0102] [Second detection area 325B] The second detection region 325B includes a plurality of upper electrodes 333B, a piezoelectric layer 360, and a plurality of intermediate electrodes 253B. The second detection region 325B includes a plurality of piezoelectric elements. In the second detection region 325B, the piezoelectric elements include the upper electrodes 333B, the piezoelectric layer 360, and the intermediate electrodes 253B.

[0103] As shown in FIG. 14, the upper electrode layer 330B has electrode-free regions 381 and 382 and electrode-free regions 385 and 386 formed therein.

[0104] [Electrode non-formation area 385] The electrode-free regions 385 divide the upper electrode into multiple regions in the first detection region 323B. The electrode-free regions 385 extend radially from the center of the diaphragm 220B. The multiple electrode-free regions 385 are arranged at equal intervals in the circumferential direction. The multiple upper electrodes 331B have approximately the same area. The sound transducer 200B has, for example, ten upper electrodes 331B.

[0105] [Electrode non-formation area 386] The electrode-free regions 386 divide the upper electrode into multiple sections in the second detection region 325B. The electrode-free regions 386 extend radially from the electrode-free regions 382 toward the outer periphery 222 of the diaphragm 220. The multiple electrode-free regions 386 are arranged at equal intervals in the circumferential direction.

[0106] [Laminate 400B] 15, the laminate 400B has an intermediate electrode layer 250B, a piezoelectric layer 460, and a lower electrode layer 440B. The intermediate electrode layer 250B serves as both the laminate 300B and the laminate 400B. The lower electrode layer 440B has a plurality of lower electrodes 441B divided in the circumferential direction, a lower electrode 442 that is continuous in the circumferential direction, and a plurality of lower electrodes 443B divided in the circumferential direction.

[0107] [First detection area 423B] The laminate 400B has a first detection region 423B, a non-detection region 424B, and a second detection region 425B. The first detection region 423B has a plurality of intermediate electrodes 251B, 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 intermediate electrode 251B, a piezoelectric layer 460, and a lower electrode 441B. In the first detection region 423B, the areas of the plurality of lower electrodes 441B are approximately equal to each other.

[0108] [Second detection area 425B] The second detection region 425B has a plurality of intermediate electrodes 253B, 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 the intermediate electrode 253B, the piezoelectric layer 460, and a lower electrode 443B. In the second detection region 425B, the areas of the plurality of lower electrodes 443B are equal to each other.

[0109] The lower electrode layer 440B and the intermediate electrode layer 250B of the stack 400B include a radially extending electrode-free region, similar to the upper electrode layer 330B of the stack 300B.

[0110] [Capacitance of piezoelectric element] In the laminate 300B, the capacitances of the plurality of piezoelectric elements aligned in the circumferential direction of the diaphragm 220 are equal to each other. In the laminate 400B, the capacitances of the plurality of piezoelectric elements aligned in the circumferential direction of the diaphragm 220 are approximately equal to each other.

[0111] [Series connection of multiple piezoelectric elements] In the vibration plate 220B, the plurality of piezoelectric elements arranged in the circumferential and radial directions are electrically connected in series.

[0112] [Actions and Effects of the Sound Converter 200B According to the Fourth Embodiment] The sound transducer 200B according to the fourth embodiment also provides the same effects as the sound transducer 200 according to the third embodiment.

[0113] In acoustic transducer 200B, the multiple detection regions include first detection regions 323B and 423B, which are inner detection regions located near center C11 of diaphragm 220B in the radial direction of diaphragm 220B, and second detection regions 325B and 425B, which are outer detection regions located far from center C11 of diaphragm 220B in the radial direction of diaphragm 220B. Non-detection regions 324, 424 include electrode-free regions 381, 382 formed between the inner and outer detection regions in the circumferential direction of diaphragm 220, and multiple electrode-free regions 385, 386 extending in the radial direction of the diaphragm and formed at intervals in the circumferential direction of the diaphragm.

[0114] According to such an acoustic transducer 200B, by having the electrode-free areas 385 and 386 extending in the radial direction, the electrodes in the detection area can be divided into a plurality of areas.

[0115] [Modification of the acoustic transducer 200B according to the fourth embodiment] In acoustic transducer 200B, diaphragm (piezoelectric element) 220B has a piezoelectric film, and the piezoelectric film includes a lower electrode layer 440B, a lower piezoelectric layer 460 formed on lower electrode layer 440, an intermediate electrode layer 250B formed on lower piezoelectric layer 460, an upper piezoelectric layer 360 formed on intermediate electrode layer 250B, and an upper electrode layer 330 formed on upper piezoelectric layer 360. Between a plurality of detection regions (first detection regions 323B, 423B and second detection regions 325B, 425B), there is provided an electrode-free region (first electrode-free region) where the upper electrode and lower electrode are not formed, or an electrode-free region (second electrode-free region) where the intermediate electrode is not formed.

[0116] In acoustic transducer 200B, when an electrode no-formation region (first electrode no-formation region) is formed in the upper electrode and the lower electrode, an electrode no-formation region (second electrode no-formation region) may not be formed in the intermediate electrode. In acoustic transducer 200B, when an electrode no-formation region (second electrode no-formation region) is formed in the intermediate electrode, an electrode no-formation region (first electrode no-formation region) 381, 382, ​​483, 484 may not be formed in the upper electrode and the lower electrode.

[0117] Furthermore, in the detection region, the upper electrode, intermediate electrode, and lower electrode may be divided in the circumferential direction. In the circumferential direction, the division position (electrode-free region) of the upper electrode and the division position of the intermediate electrode may be different. Similarly, in the circumferential direction, the division position of the lower electrode and the division position of the intermediate electrode may be different.

[0118] [Circuit diagram of acoustic transducer 200B according to the fourth embodiment] Next, a circuit diagram of the sound transducer 200B according to the fourth embodiment will be described below. Fig. 16 is a circuit diagram of the sound transducer 200B according to the fourth embodiment.

[0119] 16, the acoustic transducer 200B has a MEMS microphone chip 201. A diaphragm 220B is mounted on the MEMS microphone chip 201. The diaphragm 220B has a plurality of first detection areas 323B, 423B and second detection areas 325B, 425B.

[0120] The multiple first detection regions 323B, 423B include an upper electrode 331B, an intermediate electrode 251B, and a lower electrode 441B. The multiple second detection regions 325B, 425B include an upper electrode 333B, an intermediate electrode 253B, and a lower electrode 443B. The upper electrode 331B includes upper electrodes 331B-1, 331B-2, ..., 331B-n that are divided into n pieces in the circumferential direction, where n is a natural number. The same applies to the other upper electrodes, intermediate electrodes, and lower electrodes.

[0121] In the first detection areas 323B and 423B of the acoustic transducer 200B, the piezoelectric output charge between the upper electrode 331B and the intermediate electrode 251B, and the piezoelectric output charge between the intermediate electrode 251B and the lower electrode 441B can be detected. The multiple piezoelectric elements arranged in the circumferential direction are connected in series.

[0122] In the second detection areas 325B and 425B of the acoustic transducer 200B, the piezoelectric output charge between the upper electrode 333B and the intermediate electrode 253B, and the piezoelectric output charge between the intermediate electrode 253B and the lower electrode 443B can be detected. The multiple piezoelectric elements arranged in the circumferential direction are connected in series.

[0123] Furthermore, MEMS microphone chip 201 has pads 213 and 214. Electrodes of a plurality of piezoelectric elements are connected to pads 213 and 214. Acoustic transducer 200B includes IC 202 connected to pad 213. IC 202 is an amplifier that amplifies the output signal of the piezoelectric element of diaphragm 220B. Note that IC 202 may be provided with a function of amplifying the output signal of the piezoelectric element of diaphragm 220B and then performing AD (analog-to-digital) conversion.

[0124] The polarity of the charge generated in the second detection regions 325B, 425B is opposite to the polarity of the charge generated in the first detection regions 323B, 423B. Therefore, the second detection regions 325B, 425B and the first detection regions 323B, 423B are connected in series with the wiring reversed.

[0125] [Electrode connection] In the acoustic transducer 200B, the upper electrodes 331B and the intermediate electrodes 251B of the first detection areas 323B may be electrically connected in series. Similarly, the upper electrodes 333B and the intermediate electrodes 253B of the second detection areas 325B may be electrically connected in series.

[0126] In acoustic transducer 200B, lower electrodes 441B and intermediate electrodes 251B of multiple first detection areas 423B may be electrically connected in series. Similarly, lower electrodes 433B and intermediate electrodes 253B of multiple second detection areas 425B may be electrically connected in series.

[0127] In the sound transducer 200B, the upper electrodes and lower electrodes of each of the plurality of detection regions may be electrically connected in parallel.

[0128] [Relationship between sensing area diameter ratio and normalized SNR] Next, the relationship between the sensing area diameter ratio and the normalized SNR will be described. Fig. 17 is a graph showing the relationship between the sensing area diameter ratio and the normalized SNR. In Fig. 17, the horizontal axis represents the sensing area diameter ratio [%], and the vertical axis represents the normalized SNR [%]. The graph shown in Fig. 17 is a graph showing the relationship between the sensing area diameter ratio and the normalized SNR in the sound transducer 200 according to the third embodiment shown in Fig. 8.

[0129] The "sensing area ratio" can be expressed by the following formula (1). Sensing area ratio = (electrode separation radius / diaphragm radius) × 100 (1) The "electrode section separation section radius" may be the radius of inner detection area 323. The "diaphragm radius" may be the radius of diaphragm 220. In Figure 8, the diameter φ323 of inner detection area 323 and the diameter φ325 of diaphragm 220 are shown.

[0130] The inner diameter of opening 221 covered by diaphragm 220 was set as 100% of the sensing area diameter ratio. When 71% of the area is covered by an electrode-free area, the normalized SNR is set to 100%. In FIG. 17, "◯" indicates the position of the boundary between inner detection area 323 and non-detection area 324. In FIG. 17, "X" indicates the position of the boundary between outer detection area 325 and non-detection area 324.

[0131] The SNR normalized value of inner detection region 323 is a value obtained when the boundary between outer detection region 325 and non-detection region 324 is set to 71% and the outer diameter Φ323 of inner detection region 323 is changed.

[0132] The SNR normalized value of outer detection region 325 is a value obtained when the boundary between inner detection region 323 and non-detection region 324 is set to 71% and the inner diameter Φ324 of outer detection region 325 is changed.

[0133] 17, the SNR normalized value of the inner detection area 323 was maximum at point P21. The sensing area diameter ratio at point P21 was 59%.

[0134] 17, the SNR normalized value of the outer detection area 325 was maximum at point P22. The sensing area diameter ratio at point P22 was 81%.

[0135] When the sensing area diameter ratio of the inner detection area 323 was 44% or more and 71% or less, the normalized SNR value was 100% or more. When the sensing area diameter ratio of the inner detection area 323 was 49% or more and 67% or less, the normalized SNR value was 104% or more. When the sensing area diameter ratio of the inner detection area 323 was 51% or more and 65% or less, the normalized SNR value was 106% or more.

[0136] The sensing area diameter ratio of the inner detection area 323 is preferably 44% or more and 71% or less, more preferably 49% or more and 67% or less, and even more preferably 51% or more and 65% or less.

[0137] When the sensing area diameter ratio of the outer detection area 325 was 71% or more and 89% or less, the normalized SNR value was 100% or more. When the sensing area diameter ratio of the outer detection area 325 was 75% or more and 87% or less, the normalized SNR value was 104% or more. When the sensing area diameter ratio of the outer detection area 325 was 78% or more and 84% or less, the normalized SNR value was 106% or more.

[0138] The sensing area diameter ratio of outer detection area 325 is preferably 71% or more and 89% or less, more preferably 75% or more and 87% or less, and even more preferably 78% or more and 84% or less.

[0139] When the sensing area diameter ratio of inner detection area 323 is 71% and the sensing area diameter ratio of outer detection area 325 is 71%, the electrode division position may be at the 71% position.

[0140] In the acoustic transducer 200, when 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 an outer value of the range of 44% or more and 71% or less. In such a case, the SNR normalized value may become high.

[0141] In the acoustic transducer 200, when 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 a case, the SNR normalized value may become high.

[0142] It should be noted that the present invention is not limited to the configurations shown here, and other embodiments may be possible in which other components are combined with the configurations described in the above embodiments. In this regard, the present invention can be modified within the scope of the present invention, and can be appropriately determined depending on the application form.

[0143] In the above embodiment, the acoustic transducers 100, 100B are illustrated as including a cantilever 20 with a cantilever structure having a free end 21 and a fixed end 22, but the acoustic transducers 100, 100B are not limited to this. The acoustic transducers 100, 100B may also be provided with a doubly supported beam structure in which both ends of the beam structure are connected to opposing portions of the fixed frame 10 as fixed ends 22. In the acoustic transducers 100, 100B with this structure, when sound pressure is applied, the central portion of the doubly supported beam bends in the thickness direction. The acoustic transducers 100, 100B may also be provided with a doubly supported beam instead of the cantilever 20.

[0144] In the above embodiment, acoustic transducers 100, 100B are described which have a pair of cantilevers 20A, 20B, but acoustic transducers 100, 100B may also have one cantilever 20 or three or more cantilevers 20.

[0145] The intermediate electrode 50 may be thicker than the upper electrode 30 and the same thickness as the lower electrode 40. The intermediate electrode 50 may be thicker than the upper electrode 30 and thinner than the lower electrode 40. The intermediate electrode 50 may be thicker than the lower electrode 40 and the same thickness as the upper electrode 30. The intermediate electrode 50 may be thicker than the lower electrode 40 and thinner than the upper electrode 30. [Explanation of symbols]

[0146] 100, 100B: acoustic transducer, 10: fixed frame, 20: cantilever, 20A: cantilever (first cantilever), 20B: cantilever (second cantilever), 21: free end, 22: fixed end, 23: detection area, 24: non-detection area, 30: upper electrode, 40: lower electrode, 50, 50B: intermediate electrode, X: X-axis direction (first direction), Y: Y-axis direction (direction intersecting the first direction), Z: Z-axis direction (plate thickness direction).

Claims

1. A fixed frame and a piezoelectric element fixed to the fixed frame, The piezoelectric element is 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; an upper electrode formed on the second piezoelectric layer; An acoustic transducer in which the thickness of the intermediate electrode is greater than the thickness of the upper electrode or the lower electrode.

2. the piezoelectric element is a cantilever having one end fixed to the fixed frame and the other end free, the cantilever extending from the fixed frame to the inside of the fixed frame; The cantilever is 2. The acoustic transducer according to claim 1, further comprising a first cantilever and a second cantilever that face each other in a first direction in which the cantilevers extend.

3. the piezoelectric element is a diaphragm, 3. The acoustic transducer according to claim 2, wherein the outer periphery of the diaphragm is a fixed end fixed to the fixed frame.

4. 4. The acoustic transducer according to claim 2, wherein the thickness of the intermediate electrode is 10% to 90% of the thickness of the piezoelectric element.

5. 4. The acoustic transducer according to claim 2, wherein the thickness of the intermediate electrode is 30% to 70% of the thickness of the piezoelectric element.

6. 4. The acoustic transducer according to claim 2, wherein the thickness of the intermediate electrode is 40% to 60% of the thickness of the piezoelectric element.

7. the piezoelectric element includes a neutral surface where neither a tensile force nor a compressive force occurs inside when the piezoelectric element is bent, The acoustic transducer according to claim 1 , wherein the intermediate electrode includes the neutral surface.

8. The acoustic transducer according to claim 7 , wherein the neutral plane is at the center of the piezoelectric element in the thickness direction.

9. The acoustic transducer according to claim 8 , wherein the thickness of the upper electrode and the thickness of the lower electrode are the same.

10. 10. The acoustic transducer according to claim 8, wherein the thickness of the first piezoelectric layer is the same as the thickness of the second piezoelectric layer.

11. the upper electrode and the lower electrode are made of the same material; The acoustic transducer according to claim 10 , wherein the first piezoelectric layer and the second piezoelectric layer are made of the same material.

12. A fixed frame and a doubly supported beam, both ends of which are fixed to opposing portions of the fixed frame; The doubly supported beam is 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; an upper electrode formed on the second piezoelectric layer; An acoustic transducer in which the thickness of the intermediate electrode is greater than the thickness of the upper electrode or the lower electrode.

Images