MEMS microphone

Abstract

To provide a piezoelectric MEMS microphone which can hold an excellent piezoelectric characteristic and can desirably prevent warpage in a cantilever structure.SOLUTION: A MEMS microphone 1 includes: a vibration plate 3 having a piezoelectric body-containing layer 35 including an ScAIN film 37 and extended in the shape of a cantilever from a fixation end part 32a to a free end part 32b; and a pedestal substrate 2 for tightly supporting the fixation end part of the vibration plate. The vibration plate has a structure in which a sensor part RA and a non-sensor part RB are arranged in the direction of extention, the sensor part having sensor electrodes 344 and 347 and the non-sensor part RB not having the sensor electrodes. The non-sensor part is less crystalline in the ScAIN film than is the sensor part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric MEMS microphone. MEMS stands for Micro Electro Mechanical Systems. [Background technology]

[0002] A known example of a so-called piezoelectric MEMS element is the piezoelectric element described in Patent Document 1. In this piezoelectric element, a multilayer piezoelectric film is supported and fixed via an insulating film on a support substrate made of a silicon substrate, and the piezoelectric film is sandwiched between electrodes. A cavity is formed in the support substrate, and the piezoelectric film and electrodes, separated by slits, form a diaphragm with one end fixed to the support substrate and the other end free.

[0003] However, forming a slit in such a cantilever-structured piezoelectric film releases residual stress, causing warping and widening the slit opening width. Using a piezoelectric element with a slit opening width greater than the design value as a microphone can result in degradation of characteristics, such as reduced sensitivity in the low-frequency range. Therefore, in the piezoelectric element described in Patent Document 1, a portion of the surface on the free end side of the diaphragm is made into a stress relief region. This stress relief region is an area where the crystallinity of the piezoelectric film is disturbed by implanting ions, and relieves stress in the diaphragm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-12349 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, the warpage mitigation or correction technique described in Patent Document 1 involves providing a stress-relief region on the surface side of the diaphragm by ion implantation, which relieves compressive stress. Therefore, the stress-relief region experiences compressive stress, not tensile stress. Therefore, the technique described in Patent Document 1 has limitations in mitigating or correcting warpage. Furthermore, in a structure using ScAlN (i.e., scandium aluminum nitride) as the piezoelectric material, it is known that increasing the scandium concentration increases piezoelectricity while decreasing stress. Therefore, in a cantilever beam structure using ScAlN with a high scandium concentration, attempting to forcibly correct warpage by applying an external force or the like raises concerns about buckling. The present invention has been made in light of the above-mentioned circumstances. Specifically, the present invention provides, for example, a piezoelectric MEMS microphone in which warpage in a cantilever beam structure is effectively suppressed while maintaining excellent piezoelectric properties. [Means for solving the problem]

[0006] The MEMS microphone (1) according to claim 1 comprises: a diaphragm (3) having a piezoelectric-containing layer (35) including an ScAlN film (37), formed in a plate shape having a thickness direction along a direction axis (DA), and extending in a cantilever shape from a fixed end (32a) on one end side to a free end (32b) on the other end side in an extension direction perpendicular to the direction axis; a base substrate (2) provided to fixedly support the fixed end of the diaphragm; Equipped with The diaphragm has a configuration in which a sensor portion (RA) provided with sensor electrodes (344, 347) and a non-sensor portion (RB) not provided with the sensor electrodes are arranged in the extension direction, The non-sensor portion has a lower crystallinity in the ScAlN film than the sensor portion. Ku, The non-sensor portion and the sensor portion are warped in opposite directions. .

[0007] In addition, in each section of the application documents, each element may be assigned a reference symbol in parentheses. In this case, the reference symbol merely indicates an example of the correspondence between the element and the specific configuration described in the embodiment described below. Therefore, the present invention is not limited in any way by the description of the reference symbol. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a side cross-sectional view showing a schematic configuration of a MEMS microphone according to a first embodiment of the present invention. [Figure 2] FIG. 10 is a side cross-sectional view showing a schematic configuration of a MEMS microphone according to a second embodiment of the present invention. [Figure 3] FIG. 10 is a side cross-sectional view showing a schematic configuration of a MEMS microphone according to a third embodiment of the present invention. [Figure 4] FIG. 10 is a side cross-sectional view showing a schematic configuration of a MEMS microphone according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Embodiment) Embodiments of the present invention will be described below with reference to the drawings. Note that inserting various variations applicable to one embodiment into the middle of a series of descriptions relating to that embodiment may hinder understanding of that embodiment. Therefore, variations are not inserted into the middle of a series of descriptions relating to that embodiment, but are instead described together in a "Variations" section after the series of descriptions. Furthermore, the descriptions in the drawings and the corresponding descriptions of the device configurations, functions, or operations described below are schematic or simplified for the purpose of concisely explaining the contents of the present invention and do not in any way limit the contents of the present invention. Therefore, it goes without saying that the exemplary configurations shown in the drawings and the specification do not necessarily correspond to the specific configurations actually manufactured and sold. In other words, unless expressly limited by the applicant in the prosecution history of this application, the present invention should not be construed as being limited by the descriptions in the drawings and the corresponding descriptions of the device configurations, functions, or operations described below.

[0010] (First embodiment: configuration) Referring to FIG. 1, the schematic configuration of a MEMS microphone 1 according to a first embodiment will be described. The MEMS microphone 1, serving as an electro-acoustic transducer, is configured to convert sound or ultrasonic vibrations propagated from an external space S into an electrical signal. For ease of explanation, a right-handed XYZ Cartesian coordinate system is set so that the Z axis is parallel to the directional axis DA, as shown in the figure. The directional axis DA is an imaginary line that serves as a reference for the directivity of the MEMS microphone 1 receiving sound or ultrasonic waves, and may also be referred to as the "center directional axis." The directional axis DA typically corresponds to an imaginary line that indicates the axis center of a three-dimensional shape, such as a substantially conical or spindle-shaped shape, that represents the range of directivity (e.g., the range in which a predetermined gain can be obtained). Specifically, the directional axis DA is, for example, the central axis of the sound pressure half-value angle.

[0011] Hereinafter, the direction along the pointing axis DA, i.e., the direction parallel to the pointing axis DA, will be referred to as the "axial direction." Therefore, the axial direction is a direction parallel to the Z-axis in the drawings. Furthermore, a direction intersecting the axial direction, typically any direction perpendicular to the axial direction, will be referred to as the "in-plane direction." The "in-plane direction" is a direction parallel to the XY plane in the drawings. The "in-plane direction" may also be referred to as the "radial direction" in some cases. The "radial direction" is a direction perpendicular to the pointing axis DA and moving away from the pointing axis DA. In other words, the "radial direction" is the direction in which a half-ray extends when a virtual plane perpendicular to the pointing axis DA intersects with the pointing axis DA as its origin. In other words, the "radial direction" is the radial direction of a circle drawn in the virtual plane with the intersection of the virtual plane and the pointing axis DA as its center. The "in-plane direction" may also be referred to as the "circumferential direction" in some cases. The "circumferential direction" is the circumferential direction of a circle drawn within the imaginary plane with the intersection of the imaginary plane and the directional axis DA as its center. Furthermore, viewing the MEMS microphone 1 and its components from above in FIG. 1 in the same direction as the negative Z-axis direction is referred to as a "planar view." The shape of a certain component in a "planar view" (i.e., the planar shape) corresponds to the shape of the component when it is mapped onto the XY plane in the figure.

[0012] In this embodiment, the MEMS microphone 1 has a so-called piezoelectric configuration. Specifically, as shown in Fig. 1, the MEMS microphone 1 includes a base substrate 2, a diaphragm 3, and an oxide film 4. The specific configuration of each part of the MEMS microphone 1 will be described below in order.

[0013] (Base board) The base substrate 2 is formed into a cylindrical or annular shape surrounding the pointing axis DA using a ceramic substrate such as alumina or a silicon-based semiconductor substrate. In this embodiment, the base substrate 2 has a square cylindrical or annular shape with the pointing axis DA as its central axis. The base substrate 2 is also formed so that its outer shape in a plan view is square.

[0014] The base substrate 2 has an outer wall surface 21 that is parallel to the pointing axis DA and is exposed radially outward, and an inner wall surface 22 that is parallel to the pointing axis DA and surrounds the pointing axis DA. A cavity 23, which is the space surrounded by the inner wall surface 22, is formed in the shape of a quadrangular prism that is square in plan view. The base substrate 2 also has an upper end surface 24 that is the end surface on one side in the axial direction, i.e., the positive Z-axis side in the figure, and a lower end surface 25 that is the end surface on the other side in the axial direction, i.e., the negative Z-axis side in the figure. The upper end surface 24 and the lower end surface 25 are formed in a flat plane with the axial direction as the normal direction. The upper end surface 24 is joined to the diaphragm 3 via an insulating oxide film 4. Here, "insulating" means a material having an electrical resistivity (i.e., volume resistivity) of 10 4 This means that the resistance is Ω·m or greater. Hereinafter, one side of the axial direction, i.e., the positive Z-axis direction in the drawing, will be referred to simply as "up" or "upper," and the other side of the axial direction, i.e., the negative Z-axis direction in the drawing, will be referred to simply as "down" or "lower." In this case, "up" refers to the direction from the MEMS microphone 1 toward the external space S.

[0015] (diaphragm) The diaphragm 3 is formed in the shape of a thin plate whose thickness direction is along the directional axis DA, i.e., in the axial direction. The diaphragm 3 has a fixed portion 31 and a vibrating portion 32. The fixed portion 31 is fixed to the base substrate 2 by being bonded to the upper end surface 24 of the base substrate 2 via an oxide film 4. The vibrating portion 32 is provided at a position corresponding to the cavity 23 in the in-plane direction, i.e., so as to face the cavity 23 in the axial direction. The vibrating portion 32 is configured to flexibly vibrate in a manner such that the antinode of vibration moves along the directional axis DA. That is, the vibrating portion 32 has a fixed end portion 32a and a free end portion 32b.

[0016] The fixed end 32a constitutes a vibration node of the vibrating section 32 and is located at a position corresponding to the inner wall surface 22 of the base substrate 2 in a plan view. The free end 32b, which constitutes a vibration antinode of the vibrating section 32, is located at a position close to the directional axis DA. In this manner, the fixed end 32a of the diaphragm 3 is fixedly supported by the base substrate 2 at one end in an extension direction perpendicular to the directional axis DA. In the diaphragm 3 shown in FIG. 1, the "extension direction" is the positive direction of the X-axis in the drawing. The diaphragm 3 extends in a cantilevered manner from the fixed end 32a to the free end 32b at the other end in the extension direction. The vibrating section 32, which is a flexural vibration region of the diaphragm 3, is vibrated such that the fixed end 32a is fixedly supported by the base substrate 2 and the free end 32b moves up and down along the directional axis DA.

[0017] In this embodiment, corresponding to the square-shaped external shape of the base substrate 2 in a plan view, the diaphragm 3 has a substantially right-angled isosceles triangle shape with the fixed end 32a as the base and the free end 32b as the apex in a plan view. That is, the vibrating portion 32 is formed so that its width narrows from the fixed end 32a to the free end 32b. The "width" of the vibrating portion 32 refers to its dimension in the width direction perpendicular to the thickness direction and the extension direction. The MEMS microphone 1 according to this embodiment is provided with a diaphragm 3 extending in the positive X-axis direction toward the directional axis DA as shown in FIG. 1 , as well as a diaphragm 3 extending in the negative X-axis direction toward the directional axis DA, a diaphragm 3 extending in the positive Y-axis direction toward the directional axis DA, and a diaphragm 3 extending in the negative Y-axis direction toward the directional axis DA. Each of these multiple diaphragms 3 is divided in the in-plane direction by slits 33 that axially communicate the external space S with the cavity 23. Therefore, the slit 33 is formed in a substantially X-shape corresponding to the diagonal of the square in plan view.

[0018] The diaphragm 3 has a plurality of electrode layers 34 and a piezoelectric-containing layer 35. The electrode layers 34 are formed of a conductive material such as a molybdenum film, an amorphous molybdenum film, or a polycrystalline silicon film. Here, "conductive" means that the electrical resistivity (i.e., volume resistivity) is 10 -2 This means that the resistivity is Ω·m or less. "Amorphous" refers to a state of matter that does not have a crystalline structure and is also called non-crystalline. Whether or not a material is amorphous can be confirmed by electron diffraction measurement. Multiple electrode layers 34 are arranged in the thickness direction. The piezoelectric-containing layer 35 is sandwiched between a pair of electrode layers 34 arranged in the thickness direction. The piezoelectric-containing layer 35 is formed by an underlayer 36 and an ScAlN film 37. That is, the piezoelectric-containing layer 35 has a multilayer structure including the underlayer 36 and the ScAlN film 37. The piezoelectric-containing layer 35 is formed by forming the underlayer 36 on the electrode layer 34 and then forming the ScAlN film 37 as a piezoelectric layer on the underlayer 36. The underlayer 36 is formed of an amorphous insulating material such as SiN or SiO2.

[0019] (electrode layer) In this embodiment, the multiple electrode layers 34 include a total of three layers, namely, a lower electrode layer 341, an intermediate electrode layer 342, and an upper electrode layer 343, provided in this order from the lower side, i.e., from the side of the base substrate 2. The lower electrode layer 341 is formed on the oxide film 4. The intermediate electrode layer 342 is provided between the lower electrode layer 341 and the upper electrode layer 343. The upper electrode layer 343 is provided on the outermost layer of the diaphragm 3 so as to face the external space S.

[0020] The lower electrode layer 341 has a lower sensor electrode 344 and a lower dummy electrode 345. The lower sensor electrode 344 is provided on the base side of the cantilever structure, i.e., closer to the fixed portion 31 or fixed end 32a than the lower dummy electrode 345. Specifically, the lower sensor electrode 344 is formed in a range extending from the fixed portion 31 to a position protruding a predetermined amount toward the free end 32b. A lower gap 346 is provided between the lower sensor electrode 344 and the lower dummy electrode 345. The lower gap 346 is formed by removing a portion of the lower electrode layer 341 by etching or the like so as to interrupt electrical connection between the lower sensor electrode 344 and the lower dummy electrode 345. The lower dummy electrode 345 is provided in a range or region extending from the inner edge of the lower gap 346 in the radial direction to the free end 32b.

[0021] The upper electrode layer 343 has an upper sensor electrode 347 and an upper dummy electrode 348. The upper sensor electrode 347 is provided on the base side of the cantilever structure, i.e., closer to the fixed portion 31 or fixed end 32a than the upper dummy electrode 348. Specifically, the upper sensor electrode 347 is formed in a range extending from the fixed portion 31 to a position protruding a predetermined amount toward the free end 32b. An upper gap 349 is provided between the upper sensor electrode 347 and the upper dummy electrode 348. The upper gap 349 is formed by removing a portion of the upper electrode layer 343 by etching or the like so as to interrupt electrical connection between the upper sensor electrode 347 and the upper dummy electrode 348. The upper dummy electrode 348 is provided in a range or region extending from the inner edge of the upper gap 349 in the radial direction to the free end 32b. That is, the upper sensor electrode 347 is formed so that its position and shape in the in-plane direction overlap with those of the lower sensor electrode 344. Similarly, the upper dummy electrode 348 is formed so that its position and shape in the in-plane direction overlap with the lower dummy electrode 345 .

[0022] The region in the in-plane direction or extension direction where the sensor electrodes, i.e., the lower sensor electrode 344 and the upper sensor electrode 347, are provided is hereinafter referred to as the "sensor portion RA." That is, the sensor portion RA is a region that effectively functions as a sensor element that converts sound wave vibrations or ultrasonic vibrations propagated from the external space S into an electric signal, i.e., an inter-electrode voltage, in order to generate an output signal of the MEMS microphone 1. In contrast, the region where no sensor electrodes are provided is hereinafter referred to as the "non-sensor portion RB."

[0023] Specifically, non-sensor portion RB is a region in the in-plane direction or extension direction where lower dummy electrode 345, lower gap 346, upper dummy electrode 348, and upper gap 349 are provided. That is, non-sensor portion RB is a region that does not contribute to the generation of an output signal of MEMS microphone 1; in other words, a region that does not effectively function as a sensor element. Diaphragm 3 has a configuration in which sensor portion RA and non-sensor portion RB are arranged in the extension direction of diaphragm 3. More specifically, sensor portion RA is provided on the root side of diaphragm 3 in the extension direction, i.e., on the fixed end 32a side. In contrast, non-sensor portion RB is provided on the tip side of diaphragm 3 in the extension direction, i.e., on the free end 32b side. The boundary between sensor portion RA and non-sensor portion RB can be set to pass through lower gap 346 and upper gap 349, as shown in FIG. 1 . Alternatively, the boundary between the sensor portion RA and the non-sensor portion RB can be set to pass through the boundary between the lower sensor electrode 344 and the lower gap 346 and the boundary between the upper sensor electrode 347 and the upper gap 349.

[0024] (Piezoelectric-containing layer) In this embodiment, the diaphragm 3 has a multilayer structure in which a plurality of piezoelectric-containing layers 35 are stacked in the axial direction. Specifically, the diaphragm 3 has two piezoelectric-containing layers 35, namely, a first layer 351 and a second layer 352. The first layer 351 is disposed below the second layer 352, i.e., closer to the base substrate 2. In other words, the first layer 351 is disposed between the lower electrode layer 341 and the intermediate electrode layer 342. Meanwhile, the second layer 352 is disposed between the intermediate electrode layer 342 and the upper electrode layer 343.

[0025] In the first layer 351, the sensor portion RA and the non-sensor portion RB have different formation states of the base film 36. That is, the base film 36 in the first layer 351 has a high-crystallinity formation portion 361 and a low-crystallinity formation portion 362. The high-crystallinity formation portion 361 is provided in the sensor portion RA. The low-crystallinity formation portion 362 is provided in the non-sensor portion RB. In this embodiment, the high-crystallinity formation portion 361 and the low-crystallinity formation portion 362 are formed of the same material and with the same thickness. However, the high-crystallinity formation portion 361 and the low-crystallinity formation portion 362 are formed so that the surface roughness of the surface facing the ScAlN film 37 is different. Specifically, the low-crystallinity formation portion 362 is formed so that the surface roughness is larger (i.e., rougher) than that of the high-crystallinity formation portion 361. On the other hand, in the second layer 352, the sensor portion RA and the non-sensor portion RB have the same formation state of the base film 36. That is, the base film 36 in the second layer 352 is formed so that the surface facing the ScAlN film 37 is smooth, similar to the highly crystalline formed portion 361. The base film 36 in the second layer 352 is formed seamlessly and integrally with the same material and thickness across the sensor portion RA and the non-sensor portion RB.

[0026] The non-sensor portion RB is configured so that the crystallinity of the ScAlN film 37 is lower than that of the sensor portion RA. Specifically, in this embodiment, the ScAlN film 37 in the first layer 351 has a high-crystallinity portion 371 provided in the sensor portion RA and a low-crystallinity portion 372 provided in the non-sensor portion RB and having lower crystallinity than the high-crystallinity portion 371. That is, the low-crystallinity portion 372 provided in the non-sensor portion RB in the first layer 351 is formed so as to have lower crystallinity than the high-crystallinity portion 371 provided in the sensor portion RA and the ScAlN film 37 provided in the second layer 352, thereby generating tensile residual stress. As a result, the non-sensor portion RB and the sensor portion RA are configured so that their warping directions are opposite to each other.

[0027] 1, neutral axis LA, which passes through approximately the center in the thickness direction of diaphragm 3, is shown at the boundary between intermediate electrode layer 342 and second layer 352, but this is for convenience of illustration, and the actual position of neutral axis LA in the thickness direction is not limited to the position shown in Fig. 1 and may vary depending on the formation state of each layer. Here, neutral axis LA corresponds to a line obtained by mapping, onto the XZ plane in the figure, a boundary surface that is not subjected to either tensile stress or compressive stress when diaphragm 3 is flexurally deformed in a manner such that free end 32b moves up and down in the figure, assuming that there is no residual stress inside diaphragm 3.

[0028] (effect) Below, an outline of the operation of the configuration of this embodiment will be described together with the effects achieved by the configuration, with reference to the drawings.

[0029] The MEMS microphone 1 according to this embodiment has a function of converting distortion caused by flexural deformation when the free end 32b of the vibrating part 32 moves along the directional axis DA into a voltage between a pair of electrode layers 34 provided on both sides of the piezoelectric-containing layer 35. That is, for example, flexural vibration of the vibrating part 32 caused by receiving sound waves or ultrasonic waves is extracted as an inter-electrode voltage between the lower sensor electrode 344 and the intermediate electrode layer 342, and an inter-electrode voltage between the upper sensor electrode 347 and the intermediate electrode layer 342. An output signal of the MEMS microphone 1 is generated by processing these inter-electrode voltages using a signal processing circuit such as an amplifier circuit (not shown).

[0030] 1, it is possible to improve the sensitivity of the MEMS microphone 1 by using a piezoelectric diaphragm 3 with a cantilever structure as shown in Fig. 1. However, when a moment difference occurs above and below the neutral axis LA (i.e., in the thickness direction) due to stress in the diaphragm 3, the diaphragm 3 warps. If the diaphragm 3 warps and the opening width of the slit 33 widens beyond the design value, low-frequency sound will escape, leading to deterioration of characteristics such as a decrease in sensitivity in the low-frequency range.

[0031] The configuration described in Patent Document 1 attempts to mitigate or correct warpage by creating a stress relief region in which ions are implanted from the surface side of the piezoelectric film to disrupt the crystallinity, thereby relieving compressive stress on the surface side of the piezoelectric film. However, such stress relief region produces compressive stress, not tensile stress. Therefore, the technology described in Patent Document 1 has limitations in mitigating or correcting warpage. Furthermore, in a cantilever beam structure using ScAlN with a high concentration of scandium, there is a concern that buckling may occur if warpage is forcibly corrected by external force or the like.

[0032] In this regard, the inventors have found through extensive research that even if the deposition conditions for the ScAlN film 37 are the same, by changing the state of the base film 36 to form a low-crystallinity region 372, a region with low crystallinity, tensile stress can be generated in the low-crystallinity region 372, reversing the warpage direction and thereby suppressing or reducing warpage throughout the diaphragm 3. Specifically, for the sensor portion RA at the base of the cantilever-shaped diaphragm 3, the base film 36 is formed as an amorphous film with a smooth surface to ensure good piezoelectricity by depositing the ScAlN film 37 with good crystallinity. This results in compressive stress at the initial stage of deposition, which generates moment asymmetry about the neutral axis LA, causing the sensor portion RA to warp upward in the figure. Meanwhile, for the non-sensor portion RB at the tip, the ScAlN film 37 is deposited in the first layer 351, the lower of the first and second layers 351 and 352, with poor crystallinity, forming a low-crystallinity region 372 with tensile stress. This causes downward warping, which is opposite to the upward warping described above, and makes it possible to reduce the overall amount of warping of the diaphragm 3.

[0033] In this embodiment, by forming a low-crystallinity portion 372 of tensile stress in the ScAlN film 37 in the first layer 351, which is the lower layer of the first and second layers 351 and 352, it is possible to reduce the overall warpage of the diaphragm 3 without causing buckling. Furthermore, by adjusting the warpage at the tip end of the cantilever structure, it is possible to achieve a large amount of warpage correction. On the other hand, even if the low-crystallinity portion 372 is formed in the ScAlN film 37, it is located in the non-sensor portion RB, which does not contribute to the generation of the output signal of the MEMS microphone 1, so there is no problem with microphone performance. To form the low-crystallinity portion 372, a low-crystallinity portion 362 is formed in the base film 36. The low-crystallinity portion 362 can be easily formed by omitting or shortening the smoothing process after deposition of the base film 36 and increasing the surface roughness. Therefore, this embodiment makes it possible to provide a piezoelectric MEMS microphone 1 that maintains excellent piezoelectric characteristics while effectively suppressing warpage in the cantilever structure.

[0034] Second Embodiment The second embodiment will be described below with reference to FIG. 2. In the following description of the second embodiment, differences from the first embodiment will be mainly described. In addition, identical or equivalent parts in the first and second embodiments are denoted by the same reference numerals. Therefore, in the following description of the second embodiment, the description of the first embodiment can be appropriately applied to components having the same reference numerals as those in the first embodiment, unless there is a technical contradiction or a special additional explanation. The same applies to the third embodiment, etc., described below.

[0035] As shown in FIG. 2 , in this embodiment, the high-crystallinity formation portion 361 and the low-crystallinity formation portion 362 have different film thicknesses. That is, the low-crystallinity formation portion 362 is formed with a film thickness thinner than the high-crystallinity formation portion 361. Varying the film thickness changes the crystallinity of the ScAlN film 37 formed thereon, thereby varying the stress. Therefore, this configuration can achieve the same effects as the first embodiment. For example, the base film 36 in the first layer 351 can be formed with a uniform thickness across the sensor portion RA and the non-sensor portion RB, and then subjected to a smoothing process required for the high-crystallinity formation portion 361, followed by forming the low-crystallinity formation portion 362 by partial etching or the like. In this case, the low-crystallinity formation portion 362 will be thinner than the high-crystallinity formation portion 361 and will have a greater surface roughness than the high-crystallinity formation portion 361. That is, in this case, the first embodiment and this second embodiment can be applied in a superimposed manner.

[0036] (Third embodiment) The third embodiment will be described below with reference to Fig. 3. In this embodiment, the low-crystallinity portion 372 is formed on the lower electrode layer 341, i.e., the lower dummy electrode 345. In other words, in the non-sensor portion RB, the base film 36 is removed at a position or region corresponding to the low-crystallinity portion 372.

[0037] Here, if the electrode layer 34 and the underlayer 36 formed below the ScAlN film 37 are collectively referred to as the "underlayer," changing the film type, i.e., material, of the underlayer can change the crystallinity of the ScAlN film 37 formed thereon, thereby changing the stress. Specifically, if the underlayer is an amorphous film or has a small difference in lattice constant from the ScAlN film 37, the generation of abnormal grains due to the lattice constant mismatch can be effectively avoided, resulting in good crystallinity of the ScAlN film 37. Therefore, by removing the amorphous underlayer 36 from the non-sensor portion RB, a low-crystallinity portion 372 with low crystallinity and tensile stress can be formed. Therefore, with this configuration, the same effects as those of the first embodiment and the like can be achieved.

[0038] (Fourth embodiment) A fourth embodiment will be described below with reference to FIG. 4. In the above-described embodiments, the low-crystallinity portion 372 was provided in the first layer 351, not in the second layer 352. In contrast, in this embodiment, the low-crystallinity portion 372 is provided in both the first layer 351 and the second layer 352. That is, the ScAlN film 37 in the upper second layer 352 has a high-crystallinity portion 371 and a low-crystallinity portion 372. Correspondingly, the base film 36 in the second layer 352 has a high-crystallinity formation portion 361 and a low-crystallinity formation portion 362. In other words, the low-crystallinity formation portion 362 and the low-crystallinity portion 372 are provided in the non-sensor portion RB in the first layer 351 and the second layer 352.

[0039] In this embodiment, a stress adjustment film 381 is formed on an outer surface 380 of the non-sensor portion RB. The outer surface 380 is the surface closer to the second layer 352 than the first layer 351 in the thickness direction of the diaphragm 3, specifically, the outermost surface on the external space S side. The stress adjustment film 381 is a compressive stress film, and can be formed of an insulating film such as SiO2 or SiN, or a metal film such as Ti or TiW. Alternatively, the stress adjustment film 381 may be one whose stress is controlled by heat treatment, impurity implantation, or the like.

[0040] The configuration according to this embodiment can achieve the same effects as those of the first embodiment, etc. Furthermore, the non-sensor portion RB can be subjected to a large tensile stress, improving the degree of freedom in design.

[0041] (Variation) The present invention is not limited to the above-described embodiment. Therefore, the above-described embodiment can be modified as appropriate. Representative modifications will be described below. In the following description of the modifications, differences from the above-described embodiment will be mainly described. Furthermore, the same reference numerals are used for parts that are identical or equivalent to each other in the above-described embodiment and the modifications. Therefore, in the following description of the modifications, the description of the above-described embodiment can be used as appropriate for components that have the same reference numerals as the above-described embodiment, unless there is a technical contradiction or special additional explanation.

[0042] The present invention is not limited to the specific device configuration described in the above embodiment. Specifically, for example, the base substrate 2 may have a shape such as a cylindrical shape, an elliptical shape, a triangular shape, a pentagonal shape, a hexagonal shape, or an octagonal shape surrounding the pointing axis DA. Alternatively, the base substrate 2 may have a shape such as a circular ring shape, an elliptical ring shape, a triangular ring shape, a pentagonal ring shape, a hexagonal ring shape, or an octagonal ring shape surrounding the pointing axis DA.

[0043] In the above embodiment, the diaphragm 3 is fixed to the upper end surface 24 of the base substrate 2, but the present invention is not limited to this configuration. For example, it is not impossible in principle to configure the outer edge of the diaphragm 3 in the in-plane direction or the radial direction, which constitutes the fixed end portion 32a, to be fixed by a groove or adhesive layer provided on the inner wall surface 22 of the base substrate 2. In other words, the fixed portion 31 of the diaphragm 3, which does not flexurally vibrate, can be omitted. In this case, the entire diaphragm 3 constitutes the vibrating portion 32 that flexurally vibrates.

[0044] There are no particular limitations on the number or planar shape of the diaphragms 3. That is, for example, the MEMS microphone 1 may include a pair of rectangular diaphragms 3 facing each other. In this case, a total of two diaphragms 3 are provided: a substantially rectangular diaphragm 3 extending in the positive direction of the X-axis toward the directional axis DA, and a substantially rectangular diaphragm 3 extending in the negative direction of the X-axis toward the directional axis DA. The slit 33 is formed in a substantially H-shape. Alternatively, for example, the MEMS microphone 1 may include only one substantially square diaphragm 3. In this case, the slit 33 is formed in a substantially U-shape or a substantially inverted U-shape.

[0045] There is no particular limitation on the number of electrode layers 34 or piezoelectric-containing layers 35. That is, for example, three or more piezoelectric-containing layers 35 may be provided. In this case, multiple intermediate electrode layers 342 are also provided. Furthermore, the intermediate electrode layers 342 may also be divided into a sensor electrode and a dummy electrode.

[0046] The electrode layer 34 and the underlayer 36 below the ScAlN film 37 may be integrated. That is, the underlayer 36 can be interpreted as including the electrode layer 34. For example, by using an amorphous conductive film such as an amorphous molybdenum film as the underlayer of the ScAlN film 37, it is possible for one layer of such amorphous conductive film to function as both the electrode layer 34 and the underlayer 36. This aspect is applicable to each of the above-described embodiments. In addition to an amorphous molybdenum film, examples of amorphous conductive films that can be used as the underlayer of the ScAlN film 37 include Ru oxide and ITO (i.e., indium tin oxide).

[0047] The oxide film 4 may be omitted. Alternatively, a film may be provided in place of the oxide film 4 to improve the bonding state between the base substrate 2 and the diaphragm 3. There are also no particular limitations on the materials that make up each part. Furthermore, the terms "film" and "layer" are interchangeable.

[0048] In the above description, multiple components that were formed seamlessly and integrally with each other may be formed by bonding separate members together. Similarly, multiple components that were formed by bonding separate members together may be formed seamlessly and integrally with each other. Furthermore, in the above description, multiple components that were formed from the same material may be formed from different materials. Similarly, multiple components that were formed from different materials may be formed from the same material.

[0049] It goes without saying that the elements constituting the above-described embodiments are not necessarily essential unless they are particularly clearly stated as essential or are considered to be clearly essential in principle. Furthermore, when numerical values ​​such as the number, value, amount, range, etc. of components are mentioned, the present invention is not limited to those specific numbers unless they are particularly clearly stated as essential or are clearly limited to specific numbers in principle. Similarly, when the shape, direction, positional relationship, etc. of components are mentioned, the present invention is not limited to those shapes, directions, positional relationship, etc. unless they are particularly clearly stated as essential or are clearly limited to specific shapes, directions, positional relationship, etc. in principle.

[0050] The modified examples are not limited to the above examples. That is, for example, multiple embodiments may be applied in combination. In other words, a part of one embodiment may be combined with a part of another embodiment. There are no particular limitations on the number or manner in which multiple embodiments are combined. Furthermore, any one of the multiple embodiments and any one of the multiple modified examples may be combined with each other as long as there is no technical contradiction. Similarly, one of the multiple modified examples may be combined with another one of the multiple modified examples as long as there is no technical contradiction.

[0051] (Disclosure details) As is clear from the above description of the embodiments and modifications, this specification discloses at least the following matters. [Point 1] A MEMS microphone (1), a diaphragm (3) having a piezoelectric-containing layer (35) including an ScAlN film (37), formed in a plate shape having a thickness direction along a direction axis (DA), and extending in a cantilever shape from a fixed end (32a) on one end side to a free end (32b) on the other end side in an extension direction perpendicular to the direction axis; a base substrate (2) provided to fixedly support the fixed end of the diaphragm; Equipped with The diaphragm has a configuration in which a sensor portion (RA) provided with sensor electrodes (344, 347) and a non-sensor portion (RB) not provided with the sensor electrodes are arranged in the extension direction, the non-sensor portion has a lower crystallinity in the ScAlN film than the sensor portion; MEMS microphone. [Point 2] The non-sensor portion and the sensor portion are warped in opposite directions. A MEMS microphone according to aspect 1. [Point 3] the sensor unit is provided on the fixed end side in the extension direction, The non-sensor portion is provided on the free end side in the extension direction. A MEMS microphone according to aspect 1 or 2. [Point 4] The vibration plate has a configuration in which a first layer (351) and a second layer (352) as the piezoelectric-containing layer are laminated in the thickness direction, the first layer is disposed closer to the base substrate than the second layer, The ScAlN film in the first layer has a high crystallinity portion (371) provided in the sensor portion and a low crystallinity portion (372) provided in the non-sensor portion and having a lower crystallinity than the high crystallinity portion. A MEMS microphone according to any one of aspects 1 to 3. [Point 5] the low-crystallinity portion is formed to have a crystallinity lower than that of the sensor portion and the second layer, so that tensile residual stress is generated; A MEMS microphone according to aspect 4. [Point 6] the ScAlN film in the second layer has the high crystallinity portion and the low crystallinity portion; A MEMS microphone according to aspect 4. [Point 7] The low-crystallinity portion is formed so as to generate tensile residual stress by lowering the crystallinity of the low-crystallinity portion compared to the sensor portion. A MEMS microphone according to aspect 6. [Point 8] The vibration plate further includes a stress adjustment film (381) having a compressive residual stress formed on a surface (380) of the vibration plate closer to the second layer than the first layer in the thickness direction. A MEMS microphone according to aspect 7. [Point 9] the piezoelectric-containing layer has an underlayer (36) and the ScAlN film formed on the underlayer, The sensor portion and the non-sensor portion have different formation states of the base film. A MEMS microphone according to any one of aspects 1 to 8. [Point 10] the underlayer has a high-crystallinity formation portion (361) provided in the sensor portion and a low-crystallinity formation portion (362) provided in the non-sensor portion, The high-crystallinity formation portion and the low-crystallinity formation portion have different film thicknesses. A MEMS microphone according to aspect 9. [Point 11] the underlayer has a high-crystallinity formation portion (361) provided in the sensor portion and a low-crystallinity formation portion (362) provided in the non-sensor portion, The high-crystallinity formation portion and the low-crystallinity formation portion have different surface roughnesses. A MEMS microphone according to aspect 9 or 10. [Explanation of symbols]

[0052] 1 MEMS microphone 3 Vibration plate 32a Fixed end 32b Free end 344 Lower Sensor Electrode 347 Upper sensor electrode 35 Piezoelectric-containing layer 37 ScAlN membrane RA sensor section RB non-sensor part

Claims

1. A MEMS microphone (1), a vibration plate (3) having a piezoelectric-containing layer (35) including a ScAlN film (37), formed in a plate shape having a thickness direction along a direction axis (DA), and extending in a cantilever shape from a fixed end (32a) on one end side to a free end (32b) on the other end side in an extension direction perpendicular to the direction axis; a base substrate (2) provided to fixedly support the fixed end of the diaphragm; Equipped with The vibration plate has a configuration in which a sensor portion (RA) provided with sensor electrodes (344, 347) and a non-sensor portion (RB) not provided with the sensor electrodes are arranged in the extension direction, the non-sensor portion has a lower crystallinity in the ScAlN film than the sensor portion; The non-sensor portion and the sensor portion are warped in opposite directions. MEMS microphone.

2. the sensor unit is provided on the fixed end side in the extension direction, The non-sensor portion is provided on the free end side in the extension direction. The MEMS microphone of claim 1 .

3. The vibration plate has a configuration in which a first layer (351) and a second layer (352) as the piezoelectric-containing layer are laminated in the thickness direction, the first layer is disposed closer to the base substrate than the second layer, The ScAlN film in the first layer has a high crystallinity portion (371) provided in the sensor portion and a low crystallinity portion (372) provided in the non-sensor portion and having a lower crystallinity than the high crystallinity portion.

3. The MEMS microphone according to claim 1 or 2.

4. the low-crystallinity portion is formed to have a crystallinity lower than that of the sensor portion and the second layer, so that tensile residual stress is generated; The MEMS microphone of claim 3 .

5. the ScAlN film in the second layer has the high crystallinity portion and the low crystallinity portion; The MEMS microphone of claim 3 .

6. The low-crystallinity portion is formed so as to generate tensile residual stress by lowering the crystallinity of the low-crystallinity portion compared to the sensor portion. The MEMS microphone of claim 5 .

7. The vibration plate further includes a stress adjustment film (381) having a compressive residual stress formed on a surface (380) of the vibration plate closer to the second layer than the first layer in the thickness direction.

7. The MEMS microphone of claim 6.

8. the piezoelectric-containing layer has an underlayer (36) and the ScAlN film formed on the underlayer; The sensor portion and the non-sensor portion have different formation states of the base film.

3. The MEMS microphone according to claim 1 or 2.

9. The underlayer film has a high-crystallinity formation portion (361) provided in the sensor portion and a low-crystallinity formation portion (362) provided in the non-sensor portion, The high-crystallinity formation portion and the low-crystallinity formation portion have different film thicknesses. The MEMS microphone of claim 8.

10. The underlayer film has a high-crystallinity formation portion (361) provided in the sensor portion and a low-crystallinity formation portion (362) provided in the non-sensor portion, The high-crystallinity formation portion and the low-crystallinity formation portion have different surface roughnesses. The MEMS microphone of claim 8.

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