Acoustic sensor

Abstract

The present invention provides an acoustic sensor that can suppress a decrease in sensitivity. [Solution] The device comprises a support body 10, a support region 21a placed on and supported by the support body 10, and a vibration region 22 connected to the support region 21a and capable of vibration, and a vibration unit 20 that outputs a detection signal according to the deformation of the vibration region 22. The support body 10 has a recess 10a formed in the portion facing the vibration region, the vibration region 22 has a portion that is subjected to compressive stress, and the vibration unit 20 has a stress relaxation hole 81.

Description

Technical Field

[0006] ,

[0001] The present disclosure relates to an acoustic sensor.

Background Art

[0002] Conventionally, a piezoelectric sensor having a vibration region has been proposed as an acoustic sensor (see, for example, Patent Document 1). Specifically, this piezoelectric sensor includes a vibrating portion having a vibration region and a support region, and a support that supports the support region of the vibrating portion, and the vibration region is in a floating state from the support.

[0003] Such a piezoelectric sensor is configured such that the vibrating portion includes a piezoelectric film and an electrode film. Note that the piezoelectric film and the electrode film are formed by, for example, sputtering or the like. Therefore, the vibrating portion is configured with residual internal stress. When compressive stress as internal stress is generated in the vibration region, the acoustic sensor has a reduced sensitivity due to buckling of the vibration region and becoming structurally rigid. Therefore, in this piezoelectric sensor, the vibration region is partially thickened so that buckling is less likely to occur.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] ​​​​​​​[Means for solving the problem]

[0007] According to one aspect of this disclosure, the acoustic sensor comprises a support (10), a support region (21a) disposed on and supported by the support, and a vibrating region (22) connected to the support region and capable of vibration, and a vibrating unit (20) that outputs a detection signal according to the deformation of the vibrating region. The support has a recess (10a) formed in the portion facing the vibrating region, the vibrating region has a portion that is subject to compressive stress, and the vibrating unit has stress-relieving holes (81, 82, 83).

[0008] According to this, stress-relaxing holes are formed in the vibrating region. Therefore, compressive stress in the vibrating region can be released through the stress-relaxing holes, suppressing buckling of the vibrating region. Furthermore, since there is no need to increase the thickness of the vibrating region, the sensitivity is not reduced by the stress-relaxing holes. Thus, a decrease in sensitivity can be suppressed.

[0009] The reference numerals in parentheses attached to each component indicate an example of the correspondence between that component and the specific components described in the embodiments described later. [Brief explanation of the drawing]

[0010] [Figure 1] This is a plan view of the piezoelectric sensor in the first embodiment. [Figure 2] This is a cross-sectional view along the line II-II in Figure 1. [Figure 3] This is a perspective view showing one vibration region. [Figure 4] This figure shows the displacement in the vibration region. [Figure 5A] Figure 1 is a cross-sectional view showing the manufacturing process of the piezoelectric sensor. [Figure 5B] This is a cross-sectional view showing the manufacturing process of the piezoelectric sensor, following Figure 5A. [Figure 6] This is a cross-sectional view of the piezoelectric sensor in the second embodiment. [Figure 7]It is a plan view of the piezoelectric sensor in the third embodiment. [Figure 8] It is a cross-sectional view taken along line VIII-VIII in FIG. 7. [Figure 9] It is a plan view of the piezoelectric sensor in the fourth embodiment. [Figure 10] It is a cross-sectional view taken along line X-X in FIG. 9. [Figure 11] It is a diagram showing the displacement amount of the vibration region. [Figure 12A] It is a cross-sectional view showing the manufacturing process of the piezoelectric sensor shown in FIG. 10. [Figure 12B] It is a cross-sectional view showing the manufacturing process of the piezoelectric sensor following FIG. 12A. [Figure 12C] It is a cross-sectional view showing the manufacturing process of the piezoelectric sensor following FIG. 12B. [Figure 12D] It is a cross-sectional view showing the manufacturing process of the piezoelectric sensor following FIG. 12C. [Figure 12E] It is a cross-sectional view showing the manufacturing process of the piezoelectric sensor following FIG. 12D.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described based on the drawings. In each of the following embodiments, parts that are the same or equivalent to each other will be described with the same reference numerals.

[0012] (First Embodiment) The acoustic sensor of the first embodiment will be described. In this embodiment, as the acoustic sensor, a piezoelectric sensor applied to a microphone or the like will be described as an example.

[0013] As shown in FIGS. 1 to 3, the piezoelectric sensor includes a support 10 and a vibrating portion 20, and has a rectangular planar shape. The support 10 includes a support substrate 11 having a front surface 11a and a back surface 11b, and an insulating film 12 formed on the front surface 11a of the support substrate 11. Note that the support substrate 11 is made of, for example, a silicon substrate or the like, and the insulating film 12 is made of an oxide film or the like. Hereinafter, one direction along the plane direction of the vibrating portion 20 is also referred to as the X-axis direction, and one direction along the plane direction of the vibrating portion 20 and perpendicular to the X-axis direction is also referred to as the Y-axis direction. In FIG. 1, the left-right direction of the paper surface is the X-axis direction, and the up-down direction of the paper surface is the Y-axis direction.

[0014] The vibrating portion 20 is disposed on the support 10. The support 10 is formed with a recess 10a for floating the inner edge side of the vibrating portion 20. Therefore, the vibrating portion 20 has a configuration including a support region 21a disposed on the support 10 and a floating region 21b that is connected to the support region 21a and floats on the recess 10a. In other words, in the stacking direction of the support 10 and the vibrating portion 20, the portion overlapping the recess 10a is the floating region 21b, and the region different from the floating region 21b is the support region 21a. That is, the recess 10a is formed in a portion facing the floating region 21b (that is, the vibrating region 22 described later).

[0015] Note that the recess 10a of the present embodiment is formed so as to penetrate the support substrate 11 and the insulating film 12 and expose the vibrating portion 20, and the shape of the opening end on the vibrating portion 20 side is a rectangular planar shape. Therefore, the entire floating region 21b has a rectangular planar shape. More specifically, the entire floating region 21b has a square shape in which the lengths in the X-axis direction and the Y-axis direction are equal. In addition, the stacking direction of the support 10 and the vibrating portion 20 is, in other words, the same direction as the normal direction to one surface 22a of the vibrating region 22 described later.

[0016] In this embodiment, a slit 30 is formed in the floating region 21b, penetrating the floating region 21b in the thickness direction. The slit 30 in this embodiment is formed to divide the floating region 21b into four sections. Specifically, two slits 30 are formed so as to pass through the center C1 of the floating region 21b and extend toward the opposing corners of the floating region 21b. In other words, the slits 30 extend from each corner of the planar rectangular floating region 21b toward the center C1, and are formed so as to intersect at the center C1. As a result, the floating region 21b is separated into four vibration regions 22 which are substantially planar triangular in shape. In this embodiment, the slits 30 are formed to reach the recess 10a, but the slits 30 may be configured to terminate within the floating region 21b. That is, each vibration region 22 may be connected at the portion on the recess 10a side. Furthermore, although not particularly limited, in this embodiment, the distance between each vibration region 22 (i.e., the width W of the slit 30) is set to about 1 μm.

[0017] Each vibration region 22 has a cantilever structure in which one end 221 on the support region 21a side is a fixed end, and the other end 222 on the opposite side of the support region 21a is a free end. Hereinafter, the surface of the vibration region 22 opposite to the support 10 will be described as one surface 22a of the vibration region 22, and the surface of the vibration region 22 on the support 10 side will be described as the other surface 22b of the vibration region 22. In this embodiment, one end 221 of the vibration region 22 can also be said to be the part that coincides with the open end on the vibrating part 20 side of the recess 10a in the normal direction.

[0018] The vibrating section 20 has a bimorph structure having a piezoelectric film 40 and an electrode film 50 connected to the piezoelectric film 40. Specifically, the piezoelectric film 40 has a lower piezoelectric film 41 and an upper piezoelectric film 42 laminated on the lower piezoelectric film 41. The lower piezoelectric film 41 and the upper piezoelectric film 42 are made of lead-free piezoelectric ceramics such as scandium aluminum nitride (ScAlN) or aluminum nitride (AlN).

[0019] The electrode film 50 is formed at a predetermined location in the vibration region 22 so as to be connected to the piezoelectric film 40, and is made of molybdenum, copper, platinum, titanium, etc. In this embodiment, the electrode film 50 is formed as a lower electrode film 51 formed below the lower piezoelectric film 41, an intermediate electrode film 52 formed between the lower piezoelectric film 41 and the upper piezoelectric film 42, and an upper electrode film 53 formed above the upper piezoelectric film 42.

[0020] The lower electrode film 51 and the intermediate electrode film 52 are positioned opposite each other with the lower piezoelectric film 41 in between. The intermediate electrode film 52 and the upper electrode film 53 are positioned opposite each other with the upper piezoelectric film 42 in between. Furthermore, the lower electrode film 51, the intermediate electrode film 52, and the upper electrode film 53 have the same shape in the direction normal to one surface 22a of the vibration region 22 (hereinafter also simply referred to as the normal direction). In other words, the direction normal to one surface 22a of the vibration region 22 can also be said to be when viewed from the direction normal to one surface 22a of the vibration region 22. Also, the statement that the lower electrode film 51, the intermediate electrode film 52, and the upper electrode film 53 have the same shape includes not only cases where they are completely identical in shape, but also cases where there are slight differences in shape.

[0021] In this embodiment, when the vibration region 22 is cantilevered, the stress generated when the vibration region 22 (i.e., the piezoelectric film 40) vibrates tends to be greater on the fixed end side where the vibration region 22 is supported than on the free end side. In other words, the stress generated when the vibration region 22 (i.e., the piezoelectric film 40) vibrates tends to be greater on the one end 221 side than on the other end 222 side. For this reason, the vibration region 22 can be said to have a configuration that includes a first region R1 on the one end 221 side where the stress tends to be greater, and a second region R2 on the other end 222 side where the stress tends to be smaller. In this embodiment, electrode films 50 are formed in both the first region R1 and the second region R2. However, in this embodiment, the electrode film 50 formed in the first region R1 and the electrode film 50 formed in the second region R2 are insulated from each other.

[0022] As shown in Figure 3, the electrode film 50 formed in the first region R1 is connected to an electrode section (not shown) provided in the support region 21a via external wiring 61 formed in the support region 21a. In this embodiment, the lower electrode film 51, intermediate electrode film 52, and upper electrode film 53 in each vibration region 22 are connected to the electrode section via external wiring 61, etc., so that the change in charge in the first region R1 of each vibration region 22 is output as a single detection signal.

[0023] Furthermore, in this embodiment, the upper electrode film 53 formed in the first region R1 is divided into first to third upper electrode films 531 to 533. The first to third upper electrode films 531 to 533 are connected in series via internal wiring 71 formed in the support region 21a. Note that in Figure 1, the external wiring 61 and internal wiring 71 are omitted. In addition, although not specifically shown, the intermediate electrode film 52 and the lower electrode film 51 have the same shape as the first to third upper electrode films 531 to 533, and are divided into first to third intermediate electrode films and first to third lower electrode films, respectively. The first to third intermediate electrode films and first to third lower electrode films are connected in series via internal wiring, which is not shown. In this embodiment, by dividing the electrode film 50 formed in the first region R1 in this way, multiple capacitors are connected in parallel, thereby improving detection sensitivity. Hereinafter, in the second region R2 of the vibration region 22, the area along the normal direction where the first upper electrode film 531 is located will be referred to as the first region R11, the area along the normal direction where the second upper electrode film 532 is located will be referred to as the second region R12, and the area along the normal direction where the third upper electrode film 533 is located will be referred to as the third region R13.

[0024] The lower electrode film 51, intermediate electrode film 52, and upper electrode film 53 formed in the second region R2 are not electrically connected to each electrode portion and are in a floating state. For this reason, the lower electrode film 51, intermediate electrode film 52, and upper electrode film 53 formed in the second region R2 are not necessarily required, but in this embodiment they are provided to protect the portions of the lower piezoelectric film 41 and upper piezoelectric film 42 located in the second region R2.

[0025] Although not specifically shown in the figures, the piezoelectric sensor may have a base film on which the lower piezoelectric film 41 and the lower electrode film 51 are arranged. In other words, the piezoelectric sensor may have the piezoelectric film 40 and the electrode film 50 arranged on the base film. The base film is provided to facilitate crystal growth when forming the lower piezoelectric film 41, etc., and is made of, for example, aluminum nitride. When a base film is provided, the thickness of the base film is about several tens of nanometers, making it extremely thin compared to the piezoelectric film 40. Therefore, when a configuration with a base film is adopted, the base film located in the floating region 21b also constitutes each vibration region 22, so the vibration region 22 has a configuration that includes the base film.

[0026] The vibrating section 20 is formed by depositing a piezoelectric film 40 and an electrode film 50 using a sputtering method or the like, and then patterning them, as will be described later. It has been reported that the piezoelectric properties of the piezoelectric film 40 tend to decrease when the tensile stress increases. For this reason, the piezoelectric sensor is configured in a state where compressive stress remains in the vibrating region 22. However, if compressive stress is present in the vibrating region 22, the sensitivity may decrease if the vibrating region 22 buckles. In this embodiment, the vibrating region 22 is in an open state on the free end side, making it less likely for buckling to occur due to compressive stress, but buckling may occur in the fixed end side due to compressive stress. In other words, in this embodiment, buckling is more likely to occur in the first region R1 than in the second region R2 of the vibrating region 22.

[0027] Therefore, in this embodiment, a through-hole portion 81 is formed in the first region R1, penetrating between one surface 22a and the other surface 22b of the vibration region 22. In this embodiment, three through-hole portions 81 are formed in each vibration region 22 so as to penetrate the first portion R11, the second portion R12, and the third portion R13, respectively. Furthermore, the through-hole portions 81 in this embodiment are cylindrical in shape with the opening being a perfect circle, and are formed along the normal direction. Moreover, in this embodiment, the width (i.e., diameter) d of the opposing portions of the opening of the through-hole portion 81 is equal to or greater than the slit width W. In this embodiment, the through-hole portion 81 corresponds to a stress relaxation hole.

[0028] The above describes the configuration of the piezoelectric sensor in this embodiment. When sound pressure is applied to each vibration region 22 in such a piezoelectric sensor, each vibration region 22 vibrates. In this case, for example, if the free end side of each vibration region 22 is displaced upward, tensile stress is generated in the lower piezoelectric film 41 and compressive stress is generated in the upper piezoelectric film 42, causing the charge of the lower piezoelectric film 41 and the upper piezoelectric film 42 to change. Therefore, the sound pressure applied to the vibration region 22 is detected based on the charge of the lower piezoelectric film 41 and the upper piezoelectric film 42.

[0029] In this case, the stress generated in the vibration region 22 (i.e., the piezoelectric film 40) is greater on the fixed end side than on the free end side because the stress is released on the free end side. In other words, the free end side generates less charge, and the signal-to-noise ratio (SNR), which is the ratio of signal to noise, tends to decrease. For this reason, in the piezoelectric sensor of this embodiment, each vibration region 22 is divided into a first region R1 where stress tends to be large and a second region R2 where stress tends to be small, as described above. In the piezoelectric sensor, the charge generated in the lower piezoelectric film 41 and upper piezoelectric film 42 located in the first region R1 is extracted from the lower electrode film 51, upper electrode film 53, and intermediate electrode film 52 located in the first region R1. This makes it possible to suppress the influence of noise.

[0030] In this embodiment, the through-hole 81 is formed in the first region R1, which is the region where charge is extracted and where compressive stress tends to be large. Therefore, the compressive stress in the first region R1 can be released from the through-hole 81, and buckling in the vibration region 22 can be suppressed. Consequently, a decrease in the sensitivity of the piezoelectric sensor can be suppressed.

[0031] Here, the inventors diligently studied the displacement amount of the vibration region 22 in the piezoelectric sensor of this embodiment and obtained the results shown in Figure 4. In Figure 4, a piezoelectric sensor in which the through-hole portion 81 of this embodiment is not formed and the other configurations are the same as in this embodiment is used as a comparative example piezoelectric sensor, and the displacement amount of each vibration region 22 when no sound pressure is applied to the vibration region 22 is shown. Furthermore, Figure 4 shows the displacement amount of the portion along the line IV-IV in Figure 3, with the boundary between the support body 10 and the vibrating part 20 as the reference (i.e., 0), and the case where the vibration region 22 is displaced toward the support body 10 is shown as negative. In addition, as shown in Figure 1, in Figure 4, the length L of one end portion 221 in the vibration region 22 is 900 μm, the width d of the through-hole portion 81 is 60 μm, and the position at 400 μm is shown as the central part of the second portion R12.

[0032] As shown in Figure 4, in this embodiment, since the through-hole 81 is formed, it can be confirmed that the amount of displacement in the vibration region 22 can be reduced. In other words, it can be confirmed that deformation due to buckling is less likely to occur in the vibration region 22.

[0033] In this embodiment, the through-hole portion 81 is cylindrical with a perfectly circular opening, but the shape of the opening can be changed as appropriate; it may be elliptical or polygonal. Furthermore, the number of through-hole portions 81 can be changed as appropriate.

[0034] Next, we will briefly explain the manufacturing method of the piezoelectric sensor described above.

[0035] First, as shown in Figure 5A, a support 10 without a recess 10a is prepared, and the piezoelectric film 40 and electrode film 50 are arranged by appropriately performing sputtering, etching, etc. At this time, the piezoelectric film 40 is formed such that compressive stress remains in at least the portion that will become the vibration region 22, by appropriately adjusting the sputtering conditions. Next, as shown in Figure 5B, a resist (not shown) is placed on the vibration portion 20, and slits 30 and through holes 81 are appropriately formed by etching, etc. After that, although not specifically shown, the recess 10a is formed by etching, etc. from the other side 11b of the support substrate 11, thereby forming the floating region 21b (i.e., the vibration region 22), and the piezoelectric sensor is manufactured.

[0036] According to the embodiment described above, a through-hole 81 is formed in the vibrating section 20. Therefore, the compressive stress in the vibrating region 22 can be released from the through-hole 81, and buckling of the vibrating region 22 can be suppressed. Furthermore, since there is no need to thicken the vibrating region 22, the sensitivity is not reduced by the through-hole 81. Thus, a decrease in sensitivity can be suppressed.

[0037] (1) In this embodiment, the vibration region 22 has a cantilever structure, and the through-hole portion 81 is formed in the first region R1 on the end portion 221 side. In other words, the through-hole portion 81 is formed in a region where buckling is likely to occur due to compressive stress. Therefore, a further decrease in sensitivity can be suppressed.

[0038] (Second Embodiment) A second embodiment will now be described. This embodiment is a modification of the first embodiment in which the shape of the through-hole portion 81 is changed. Other aspects are the same as in the first embodiment, so a detailed explanation will be omitted here.

[0039] In the piezoelectric sensor of this embodiment, as shown in Figure 6, the through-hole portion 81 is formed at an angle in the normal direction. Therefore, compared to the case where the through-hole portion 81 is formed along the normal direction, as in the first embodiment described above, the length of the through-hole portion 81 is increased, and the hole resistance (i.e., pipe resistance) related to the passage of sound increases. Specifically, the through-hole portion 81 is formed such that the hole resistance is greater than the slit resistance (i.e., pipe resistance) related to the passage of sound through the slits 30 that demarcate each vibration region 22. Therefore, by forming the through-hole portion 81, it is possible to suppress sound from escaping from the through-hole portion 81, thereby suppressing a decrease in sensitivity and a change in the detection bandwidth.

[0040] The through-hole portion 81 is formed such that, for example, the hole resistance is about 1 / 10 of the slit resistance. Also, in Figure 6, the through-hole portion 81 is shown to be formed so that it extends from the other surface 22b side towards the other end 222 side towards the one surface 22a side. However, the through-hole portion 81 may also be formed so that it extends from the one surface 22a side towards the other end 222 side towards the other surface 22b side.

[0041] According to the embodiment described above, since the through-hole 81 is formed in the vibration region 22, the same effects as in the first embodiment can be obtained.

[0042] (1) In this embodiment, the through-hole portion 81 is formed such that the resistance of the hole is greater than the resistance of the slit. Therefore, by forming the through-hole portion 81, it is possible to suppress sound leakage from the through-hole portion 81. In other words, by forming the through-hole portion 81, it is possible to suppress a decrease in sensitivity and a change in the detection bandwidth.

[0043] (Third embodiment) A third embodiment will now be described. This embodiment is a modification of the first embodiment in which the shape of the through-hole portion 81 is changed. Other aspects are the same as in the first embodiment, so a detailed explanation will be omitted here.

[0044] In the piezoelectric sensor of this embodiment, as shown in Figures 7 and 8, the through-hole portion 81 is formed along the normal direction. However, the width d of the through-hole portion 81 is narrower than the width W of the slit 30. Therefore, compared to the case where the width d of the through-hole portion 81 is greater than or equal to the width W of the slit 30, as in the first embodiment, the hole resistance is larger. Specifically, the through-hole portion 81 of this embodiment is formed such that the hole resistance is greater than the slit resistance. Therefore, forming the through-hole portion 81 makes it easier to suppress sound leakage from the through-hole portion 81. The through-hole portion 81 is formed such that, for example, the hole resistance is about 1 / 10 of the slit resistance.

[0045] Furthermore, in this embodiment, since the width d of the through-hole portion 81 is reduced, there is a possibility that the function of releasing compressive stress in the vibration region 22 will be reduced. For this reason, in this embodiment, the number of through-hole portions 81 is increased compared to the first embodiment.

[0046] According to the embodiment described above, since the through-hole 81 is formed in the vibration region 22, the same effects as in the first embodiment can be obtained.

[0047] (1) In this embodiment, the through-hole portion 81 is formed such that the resistance of the hole is greater than the resistance of the slit. Therefore, by forming the through-hole portion 81, it is possible to suppress sound leakage from the through-hole portion 81. In other words, by forming the through-hole portion 81, it is possible to suppress a decrease in sensitivity and a change in the detection bandwidth.

[0048] (Fourth Embodiment) A fourth embodiment will now be described. This embodiment is a modification of the stress-relieving hole configuration compared to the first embodiment. Other aspects are the same as in the first embodiment, so a detailed explanation will be omitted here.

[0049] In this embodiment, as shown in Figures 9 and 10, the through-hole 81 is not formed in the vibration region 22, and the through-hole 83 is formed in the support region 21a. Specifically, in this embodiment, a cavity 82 is formed in the portion of the insulating film 12 of the support 10 that is on the recess 10a side, and communicates with the recess 10a. More specifically, the cavity 82 is composed of a recessed portion obtained by removing the surface of the insulating film 12 that is on the vibration region 20 side.

[0050] Furthermore, the depth t of the cavity 82 is made shallower than the width W of the slit 30 so that the cavity resistance (i.e., piping resistance) related to sound passage is greater than the slit resistance. For example, the depth t of the cavity 82 is adjusted so that the piping resistance in the pressure relief hole, which is formed by communication with the through-hole 83 described later, is about 1 / 10 of the slit resistance.

[0051] Furthermore, in this embodiment, the cavity 82 is formed such that, at one end 221 in each vibration region 22, the inner edge 221a of the end 221 is supported by the support 10 (i.e., the insulating film 12). In other words, the cavity 82 is not formed in such a way that the inner edge 221a of the end 221 in each vibration region 22 is suspended.

[0052] Furthermore, in this embodiment, the cavity 82 is formed such that, at one end 221 in each vibration region 22, the outer edge 221b of the end 221 is supported by the support 10 (i.e., the insulating film 12). In other words, the cavity 82 is not formed in such a way that the outer edge 221b of the end 221 in each vibration region 22 is suspended.

[0053] Therefore, in this embodiment, one end portion 221 on the support region 21a side in the vibration region 22 consists of a support portion supported by the support 10, a floating portion floating away from the support 10, a support portion supported by the support 10, a floating portion floating away from the support 10, and a support portion supported by the support 10, moving from one end portion 221 to the other.

[0054] In this embodiment, when the piezoelectric film 40 and the electrode film 50 are stacked to form the vibration region 22, differences in the stacked structure result in differences in internal stress. For example, at one end 221 of the vibration region 22, the internal stress differs between the area where the electrode film 50 is located and the area where the electrode film 50 is not located. That is, at one end 221 of the vibration region 22, there is a region with high compressive stress and a region with lower compressive stress. Note that the region with low compressive stress also includes the region with tensile stress.

[0055] In this embodiment, the compressive stress is higher in the areas where the electrode film 50 is not placed than in the areas where the electrode film 50 is placed. For example, in the vibration region 22 of this embodiment, the compressive stress is higher in the region between the first part R11 and the second part R12, and in the region between the second part R12 and the third part R13, than in the first part R11, the second part R12, and the third part R13. The cavity 82 of this embodiment is formed to levitate the region between the first part R11 and the second part R12, and the region between the second part R12 and the third part R13, where the compressive stress is higher on the end 221 side.

[0056] In this embodiment, two cavities 82 are formed so that each vibration region 22 is supported by the support 10 as described above. Specifically, one cavity 82 is formed to float between the inner edge 221a and the outer edge 221b at one end 221. The other cavity 82 is formed to float between the inner edge 221a and the other outer edge 221b. Furthermore, the cavities 82 in this embodiment are formed to be approximately triangular in the normal direction.

[0057] Furthermore, the through-hole 81 formed in the support region 21a is formed to communicate with the cavity 82. In this embodiment, the through-hole 81 is formed so that its width d is greater than or equal to the width W of the slit 30. In this embodiment, a stress-relieving hole is formed including the through-hole 81 and the cavity 82, and the stress-relieving hole is formed to penetrate the vibrating section 20. Moreover, in this embodiment, the cavity resistance (i.e., the piping resistance) is formed to be greater than the slit resistance, so the overall piping resistance of the stress-relieving hole is greater than the slit resistance.

[0058] The above describes the configuration of the piezoelectric sensor in this embodiment. Even in such a piezoelectric sensor, compressive stress can be released from the through-hole portion 83 and the cavity portion 82, and buckling in the vibration region 22 can be suppressed. Therefore, a decrease in the sensitivity of the piezoelectric sensor can be suppressed.

[0059] Here, the inventors diligently studied the displacement amount of the vibration region 22 in the piezoelectric sensor of this embodiment and obtained the results shown in Figure 11. In Figure 11, a piezoelectric sensor in which the through-hole portion 83 and cavity portion 82 of this embodiment are not formed, and the other configurations are the same as in this embodiment, is used as a comparative example piezoelectric sensor, and the displacement amount of each vibration region 22 when no sound pressure is applied to the vibration region 22 is shown. Furthermore, Figure 11 shows the displacement amount of the portion along the line XI-XI in Figure 9, with the boundary between the support body 10 and the vibrating part 20 as the reference (i.e., 0), and the case where the vibration region 22 is displaced toward the support body 10 is shown as negative. In addition, in Figure 11, the length L of one end portion 221 in the vibration region 22 is 900 μm, and the width d of the through-hole portion 81 is 60 μm. Furthermore, Figure 11 shows the results when the length L1 along the longitudinal direction of one end 221 in one cavity 82 is 300 μm, the length L2 in the direction intersecting the longitudinal direction is 150 μm, and the position at 400 μm is considered to be the central part of the second part R12. In addition, Figure 11 shows the results when a tensile stress of 50 MPa is generated in the part where the electrode film 50 is placed, and a compressive stress of 100 MPa is generated in the part where the electrode film 50 is not placed.

[0060] As shown in Figure 11, in this embodiment, since the through-hole portion 83 and the cavity portion 82 are formed, it can be confirmed that the displacement amount of the vibration region 22 can be reduced overall. In other words, it can be confirmed that deformation due to buckling is less likely to occur in the vibration region 22.

[0061] Next, the manufacturing method of the piezoelectric sensor described above will be explained.

[0062] In this embodiment, first, a support 10 without recesses 10a is prepared, as shown in Figure 12A. Then, as shown in Figure 12B, a resist (not shown) is placed on the insulating film 12 and patterned, and etching is performed using the resist as a mask to remove the insulating film 12 in the portion constituting the cavity 82. Subsequently, as shown in Figure 12C, an embedding material 90 made of a nitride film or the like, which is more easily etched than the insulating film 12, is embedded in the portion that will become the cavity 82.

[0063] Then, as shown in Figure 12D, after arranging the piezoelectric film 40 and electrode film 50 by appropriately performing sputtering, etching, etc., the slit 30 and through-hole portion 83 are formed. The through-hole portion 83 is formed in the portion that will become the support area 21a and is formed to reach the embedding material 90. Subsequently, as shown in Figure 12E, a recess 10a is formed by etching from the other side 11b of the support substrate 11. In this embodiment, the embedding material 90 is made of a material that is more easily etched than the insulating film 12. Therefore, when the recess 10a is formed, the embedding material 90 is removed by side etching, and a cavity portion 82 is formed.

[0064] As described above, in this embodiment, a through-hole portion 83 and a cavity portion 82 are formed as stress-relaxing holes. Therefore, the compressive stress in the vibration region 22 can be released from the through-hole portion 83 and the cavity portion 82, and the same effects as in the first embodiment can be obtained.

[0065] (1) In this embodiment, the through-hole portion 81 is not formed in the vibration region 22. Therefore, the configuration of the vibration region 22 is the same as in the conventional model, making it easier to use the same method as in the conventional model.

[0066] (2) In this embodiment, the cavity 82 is formed such that the inner edge 221a of one end 221 in the vibration region 22 is supported by the support 10. Therefore, the length of the vibration region 22 that actually vibrates is the same as in the first embodiment, and the resonance frequency of the vibration region 22 is less likely to change. Therefore, it is easy to use the same method as before.

[0067] (3) In this embodiment, the cavity 82 is formed such that the outer edge 221b of one end 221 in the vibration region 22 is supported by the support 10. Therefore, it is possible to further suppress changes in the resonant frequency of the vibration region 22.

[0068] (4) In this embodiment, the stress relief holes are formed such that the pipe resistance is greater than the slit resistance. Therefore, by forming the cavities 82 and through-holes 83 that serve as stress relief holes, it is possible to suppress sound from escaping from the stress relief holes. In other words, it is possible to suppress a decrease in sensitivity and a change in the detection bandwidth by forming the stress relief holes.

[0069] (5) In this embodiment, the cavity 82 is formed to levitate the region of one end 221 in the vibration region 22 where the compressive stress is high. This further suppresses buckling in the vibration region 22.

[0070] (Other embodiments) This disclosure is described in accordance with embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and concept of this disclosure.

[0071] For example, in each of the above embodiments, a piezoelectric sensor was used as an example of an acoustic sensor. However, as long as the configuration has a vibration region 22, the acoustic sensor may be, for example, a capacitive sensor or the like.

[0072] Furthermore, in each of the above embodiments, a configuration in which the vibration region 22 is cantilevered was used as an example for explanation. However, the vibration region 22 may also be configured to be double-supported.

[0073] Furthermore, in each of the above embodiments, the recess 10a may be formed such that a part of the support 10 remains, and the vibration region 22 may be configured to include a part of the support 10. For example, the recess 10a may be formed such that the insulating film 12 remains while the support substrate 11 is removed, and the vibration region 22 may be configured to include the insulating film 12.

[0074] Furthermore, in each of the above embodiments, the electrode film 50 formed in the second region R2 may be electrically connected to the electrode film 50 formed in the first region R1.

[0075] Furthermore, in the first to third embodiments described above, a configuration was described in which the through-hole portion 81, which serves as a stress-relieving hole, penetrates the vibrating portion 20. However, the through-hole portion 81 does not have to be formed to penetrate the vibrating portion 20. Similarly, in the fourth embodiment described above, a configuration was described in which the cavity portion 82 and the through-hole portion 83, which serve as stress-relieving holes, are connected to penetrate the vibrating portion 20. However, the cavity portion 82 and the through-hole portion 83 may be formed separately, or only one of them may be formed.

[0076] Furthermore, in the first to third embodiments described above, the through-hole 81 may be formed in the second region R2.

[0077] Furthermore, in the fourth embodiment described above, the cavity 82 may be formed such that the cavity resistance is smaller than the slit resistance. Also, the location and shape of the cavity 82 can be changed as appropriate. For example, the cavity 82 may be formed so as to levitate the inner edge 221a of the vibration region 22, or it may be formed so as to levitate the outer edge 221b of the vibration region 22.

[0078] Furthermore, the above embodiments can be combined. For example, the second embodiment and the third embodiment can be combined so that the through-hole portion 81 is inclined with respect to the normal direction and its width d is narrower than the width W of the slit. The second embodiment can also be combined with the fourth embodiment so that the through-hole portion 83 is inclined with respect to the normal direction. The fourth embodiment can also be combined with the third embodiment so that the width of the through-hole portion 83 is narrower than the width W of the slit 30. In other words, the through-hole portion 83 may be formed such that the hole resistance is greater than the slit resistance. The first embodiment and the fourth embodiment can also be combined so that the through-hole portion 81 is formed in the vibration region 22, while a cavity portion 82 is formed in the support 10 and the through-hole portion 83 is formed in the support region 21a. Furthermore, combinations of the above embodiments can be combined even further.

[0079] [Disclosure of the Invention] The above disclosure can be understood from the following perspectives, for example. [First point of view] It is an acoustic sensor, Support (10) and The device comprises a support region (21a) placed on the support and supported by the support, and a vibration region (22) connected to the support region and capable of vibration, and a vibration unit (20) that outputs a detection signal corresponding to the deformation of the vibration region, The support has a recess (10a) formed in the portion facing the vibration region. The aforementioned vibration region has a portion that experiences compressive stress, The vibrating part of the acoustic sensor has stress-relaxing holes (81, 82, 83) formed therein. [Second perspective] The acoustic sensor according to the first aspect, wherein the vibrating part comprises a piezoelectric film (40) having a lower piezoelectric film (41) and an upper piezoelectric film (42) disposed on the lower piezoelectric film, and an electrode film (50) having a lower electrode film (51) connected to the lower piezoelectric film, an intermediate electrode film (52) connected to the lower piezoelectric film and the upper piezoelectric film, and an upper electrode film (53) connected to the upper piezoelectric film, which extracts the charge generated by the deformation of the piezoelectric film. [Third perspective] The vibration region is connected to the support region, and multiple floating regions (21b) that float away from the support are divided by slits (30). The acoustic sensor according to the second aspect, wherein the vibration region has a cantilever structure in which one end (221) on the support region side is fixed to the support body and the other end (222) side is a free end. [Fourth perspective] The vibration region is defined as a first region (R1) on one end side and a second region (R2) on the other end side. The electrode film is formed in at least the first region, The acoustic sensor according to the third aspect, wherein the stress relaxation hole is a through hole (81) formed in the first region and penetrating the vibration region. [Fifth perspective] The acoustic sensor according to a third or fourth aspect, wherein the through-hole portion has a hole resistance for sound passage that is greater than the slit resistance for sound passage through the slit. [Sixth perspective] The acoustic sensor according to the fifth aspect, wherein the through-hole portion is formed at an angle with respect to the stacking direction of the support and the vibrating portion. [Seventh perspective] The acoustic sensor according to a fifth or sixth view, wherein the width (d) of the through-hole is narrower than the width (W) of the slit between adjacent vibration regions. [Perspective 8] The support has a cavity (82) on the vibrating part side that communicates with the recess, The support region has a through hole (83) that penetrates the support region and communicates with the cavity. The acoustic sensor according to the third aspect, wherein the stress-relieving hole portion comprises the cavity portion and the through-hole portion. [Perspective 9] The acoustic sensor according to the eighth aspect, wherein the cavity resistance for sound passage is greater than the slit resistance for sound passage through the slit. [Perspective 10] The acoustic sensor according to the ninth aspect, wherein the depth (t) of the cavity is shallower than the width (W) of the slit between adjacent vibration regions. [Perspective 11] The acoustic sensor according to any one of the eighth to tenth views, wherein the cavity is formed such that the inner edge (221a) at one end of the vibration region is supported by the support. [Perspective 12] The acoustic sensor according to any one of the eighth to eleventh views, wherein the cavity is formed such that the outer edge (221b) at one end of the vibration region is supported by the support. [Perspective 13] The vibration region has, at one end, a region where the compressive stress is high and a region where the compressive stress is lower than that region. The acoustic sensor according to any one of the eighth to twelfth views, wherein the cavity is formed to allow the region with high compressive stress to float. [Explanation of Symbols]

[0080] 10 Support 10a recess 20 Vibration section 21a Support area 22 Vibration area 81 Hole (stress relaxation hole)

Claims

1. It is an acoustic sensor, Support (10) and The device comprises a support region (21a) positioned on the support and supported by the support, and a vibration region (22) connected to the support region and capable of vibration, and a vibration unit (20) that outputs a detection signal corresponding to the deformation of the vibration region, The support has a recess (10a) formed in the portion facing the vibration region. The aforementioned vibration region has a portion that experiences compressive stress, The vibrating part of the acoustic sensor has stress-relaxing holes (81, 82, 83) formed therein.

2. The acoustic sensor according to claim 1, wherein the vibrating part comprises a piezoelectric film (40) having a lower piezoelectric film (41) and an upper piezoelectric film (42) disposed on the lower piezoelectric film, and an electrode film (50) having a lower electrode film (51) connected to the lower piezoelectric film, an intermediate electrode film (52) connected to the lower piezoelectric film and the upper piezoelectric film, and an upper electrode film (53) connected to the upper piezoelectric film, which extracts the charge generated by the deformation of the piezoelectric film.

3. The vibration region is connected to the support region, and a plurality of floating regions (21b) that float from the support are divided by slits (30). The acoustic sensor according to claim 2, wherein the vibration region has a cantilever structure in which one end (221) on the support region side is a fixed end fixed to the support body and the other end (222) side is a free end.

4. The vibration region is defined as a first region (R1) on one end side and a second region (R2) on the other end side. The electrode film is formed in at least the first region, The acoustic sensor according to claim 3, wherein the stress relief hole is a through hole (81) formed in the first region that penetrates the vibration region.

5. The acoustic sensor according to claim 4, wherein the resistance of the through-hole portion to the passage of sound is greater than the slit resistance to the passage of sound through the slit.

6. The acoustic sensor according to claim 5, wherein the through-hole portion is formed at an angle with respect to the stacking direction of the support and the vibrating portion.

7. The acoustic sensor according to claim 5, wherein the width (d) of the through-hole is narrower than the width (W) of the slit between adjacent vibration regions.

8. The support has a cavity (82) on the vibrating part side that communicates with the recess, The support region has a through hole (83) that penetrates the support region and communicates with the cavity. The acoustic sensor according to claim 3, wherein the stress-relieving hole portion includes the cavity portion and the through-hole portion.

9. The acoustic sensor according to claim 8, wherein the cavity resistance for sound passage is greater than the slit resistance for sound passage through the slit.

10. The acoustic sensor according to claim 8, wherein the depth (t) of the cavity is shallower than the width (W) of the slit between adjacent vibration regions.

11. The acoustic sensor according to claim 8, wherein the cavity is formed such that the inner edge (221a) at one end of the vibration region is supported by the support.

12. The acoustic sensor according to claim 8, wherein the cavity is formed such that the outer edge (221b) at one end of the vibration region is supported by the support.

13. The vibration region has, at one end, a region where the compressive stress is high and a region where the compressive stress is lower than that region. The acoustic sensor according to claim 8, wherein the cavity is formed to allow the region with high compressive stress to float.

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