Piezoelectric MEMS microphone and preparation method thereof

Abstract

The invention provides a piezoelectric MEMS microphone and a preparation method thereof, and relates to the technical field of semiconductors, the piezoelectric MEMS microphone comprises a base layer with a cavity and a composite vibration layer laminated on the cavity of the base layer, the composite vibration layer is provided with at least one gap, and the gap is arranged along the lamination direction; when there are multiple gaps, the multiple gaps are located in the same plane in the horizontal direction perpendicular to the stacking direction. At least one gap enables the composite vibration layer to form a cantilever beam supported by the base layer; the opening width of the gap is gradually reduced in the direction from the composite vibration layer to the cavity. The slit width of the slit is gradually reduced from the composite vibration layer to the cavity, and the slit forms a certain slit width difference, so that the slit width as small as possible can be obtained at the bottommost part of the slit; and the slit width difference is formed in different layers by the slit, so that the slit is easy to prepare in process, smaller slit width can be obtained, the microphone has wider low-frequency response, and the product quality can be ensured.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a piezoelectric MEMS microphone and a preparation method thereof. Background Art

[0002] As an advanced acoustic sensor technology, MEMS (Micro-Electro-Mechanical System) piezoelectric microphones have developed rapidly due to their many advantages such as low power consumption, fast response, and high reliability. MEMS piezoelectric microphones are mainly composed of piezoelectric units and ASICs (Application Specific Integrated Circuits); the piezoelectric unit includes a substrate, a supporting structure, and a cantilever beam diaphragm structure. On a cantilever beam microphone, slits are set between each cantilever beam. In order to make the microphone obtain a wider low-frequency response range, the width of the slits between the cantilever beams should be as small as possible.

[0003] However, in the actual processing of cantilever microphones, it is extremely difficult to obtain the smallest possible slit width due to the large aspect ratio of the gap to be processed and the presence of difficult-to-etch piezoelectric materials. During etching, thick coating of photoresist will result in insufficient light entering the photoresist, causing underexposure at the bottom, or leaving residual photoresist, affecting subsequent etching; in addition, when etching gaps with a large aspect ratio, the photoresist may be consumed too quickly, that is, when the gap has not been completely etched to the bottom, the photoresist has been completely consumed, resulting in slit failure. Continuing to etch the gap will damage other parts of the device and affect product quality. Summary of the invention

[0004] The object of the present invention is to provide a piezoelectric MEMS microphone and a preparation method thereof, which can obtain a smaller slot width and ensure product quality.

[0005] According to one aspect of the present invention, a piezoelectric MEMS microphone is provided, comprising a base layer having a cavity, and a composite vibration layer stacked on the cavity of the base layer, wherein the composite vibration layer has at least one slit, and the slit is arranged along a stacking direction; when there are multiple slits, the multiple slits are arranged side by side in the same plane along a horizontal direction perpendicular to the stacking direction; at least one slit enables the composite vibration layer to form a cantilever beam supported by the base layer; and the opening width of the slit gradually decreases in a direction from the composite vibration layer to the cavity.

[0006] Optionally, along the stacking direction, the gaps form stepped gaps, and the gaps are arranged in at least two layers of steps.

[0007] Optionally, a side wall of the gap along the stacking direction is parallel to the stacking direction.

[0008] Optionally, the sidewall of the gap along the stacking direction forms an angle with the stacking direction, so that the gap of each step is in an inverted cone shape.

[0009] Optionally, a side wall of the gap along the stacking direction forms an angle with the stacking direction, so that the gap is in an inverted cone shape along the stacking direction.

[0010] Optionally, the base layer includes at least any one of the following structures: The base layer is located below the composite vibration layer along the stacking direction, and at least one of the gaps divides the composite vibration layer into at least two cantilever beams supported by the base layer; the base layer includes a substrate and a film layer stacked on the substrate, and the film layer completely covers the substrate along the stacking direction; Alternatively, the base layer includes a peripheral base layer arranged around the composite vibration layer, and a bottom base layer arranged below the composite vibration layer along the stacking direction, the cavity is formed between the peripheral base layer and the bottom base layer, at least one gap is formed between the composite vibration layer and the peripheral base layer, and the composite vibration layer is supported by the bottom base layer; Alternatively, the base layer includes a substrate and a film layer stacked on the substrate, the film layer partially covers the substrate along the stacking direction, and the composite vibration layer is stacked on the film layer.

[0011] Optionally, the composite vibration layer includes at least a first electrode layer, a piezoelectric layer and a second electrode layer which are sequentially stacked on the base layer.

[0012] Another aspect of the present invention provides a method for preparing a piezoelectric MEMS microphone, which is used to prepare the above-mentioned piezoelectric MEMS microphone, and the method comprises: A composite vibration layer is stacked on the cavity of the base layer; The composite vibration layer is etched toward the cavity to form at least one gap in the composite vibration layer, so that the composite vibration layer forms a cantilever beam supported by the base layer.

[0013] Optionally, etching from the composite vibration layer toward the cavity to form at least one gap in the composite vibration layer so that the composite vibration layer forms a cantilever beam supported by the base layer includes: Etching at least twice from the composite vibration layer toward the cavity, so that the gaps are arranged in at least two layers of steps along the stacking direction, and the gaps in each layer of steps are etched once; Vertically etching the gap of each step so that the sidewall of the gap along the stacking direction is parallel to the stacking direction; Alternatively, the gap of each step is etched obliquely so that the sidewall of the gap along the stacking direction forms an angle with the stacking direction.

[0014] Optionally, etching from the composite vibration layer toward the cavity to form at least one gap in the composite vibration layer so that the composite vibration layer forms a cantilever beam supported by the base layer includes: The composite vibration layer is etched once toward the cavity so that the sidewall of the gap along the stacking direction is arranged at an angle with the stacking direction, and the gap is in an inverted cone shape along the stacking direction.

[0015] In the piezoelectric MEMS microphone and its preparation method provided by the present invention, the slit width gradually decreases from the composite vibration layer to the cavity direction of the base layer, forming a certain slit width difference, so that it is easy to obtain the smallest possible slit width at the bottom of the slit; and because the slit width difference is formed in different layers, the slit is easy to prepare in terms of process, and there is no problem of underexposure or residue of photoresist at the bottom of the slit, or slit failure caused by inadequate slit opening in the prior art. The piezoelectric MEMS microphone provided by the present invention can obtain a smaller slit width, and the microphone has a wider low-frequency response, and can also ensure product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the present invention will be briefly introduced below. It should be understood that the following drawings only show some examples of the present invention and should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 It is a schematic diagram of the structure of a piezoelectric MEMS microphone in the prior art; Figure 2 This is a comparison chart of the frequency responses of existing piezoelectric MEMS microphones at different slot widths; Figure 3 This is a schematic diagram of the photoresist residue of an existing piezoelectric MEMS microphone; Figure 4 This is a schematic diagram of the failure of the existing piezoelectric MEMS microphone to open the seam; Figure 5a This is one of the structural schematic diagrams of the piezoelectric MEMS microphone provided by the present invention; Figure 5b This is the second structural schematic diagram of the piezoelectric MEMS microphone provided by the present invention; Figure 5cThis is the third structural schematic diagram of the piezoelectric MEMS microphone provided by the present invention; Figure 5d This is the fourth structural schematic diagram of the piezoelectric MEMS microphone provided by the present invention; Figure 5e This is one of the structural schematic diagrams of the top projection plane of the piezoelectric MEMS microphone provided by the present invention; Figure 5f This is the second structural schematic diagram of the top projection plane of the piezoelectric MEMS microphone provided by the present invention; Figure 6 This is one of the schematic diagrams of the gap structure of the piezoelectric MEMS microphone provided by the present invention; Figure 7 This is the second schematic diagram of the gap structure of the piezoelectric MEMS microphone provided by the present invention; Figure 8 This is one of the low-frequency response comparison diagrams of the piezoelectric MEMS microphone gap provided by the present invention and the gap in the prior art; Fig. 9 This is the third schematic diagram of the gap structure of the piezoelectric MEMS microphone provided by the present invention; Fig.10 This is the fourth schematic diagram of the gap structure of the piezoelectric MEMS microphone provided by the present invention; Fig.11 This is a picture of the gap of the piezoelectric MEMS microphone provided by the present invention under an electron microscope; Fig.12 This is the fifth structural schematic diagram of the piezoelectric MEMS microphone provided by the present invention; Fig.13 This is the fifth schematic diagram of the gap structure of the piezoelectric MEMS microphone provided by the present invention; Fig.14 is a comparison diagram of the low-frequency response of the piezoelectric MEMS microphone gap provided by the present invention; Fig.15 This is the second comparison diagram of the low-frequency response of the piezoelectric MEMS microphone gap provided by the present invention and the gap in the prior art.

[0018] Icon: 10-base layer; 100-cavity; 101-substrate; 102-membrane layer; 103-peripheral base layer; 104-bottom base layer; 11-composite vibration layer; 110-support layer; 111-first electrode layer; 112-piezoelectric layer; 113-second electrode layer; 12-gap; F1-stacking direction; F2-horizontal direction; H-photoresist thickness; D-gap width; d-slit width; d1-first slit width; d2-second slit width; d3-third slit width; d4-fourth slit width; h-thickness. DETAILED DESCRIPTION

[0019] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention.

[0020] In the description of the present invention, it should be noted that the terms "inside", "outside", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product is usually placed when in use, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0021] It should also be noted that, unless otherwise clearly specified and limited, the terms "setting" and "connection" should be understood in a broad sense. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] like Figure 1 On a cantilever beam microphone, the slot design between each cantilever beam has a great influence on the microphone's low-frequency response capability. Among them, the slot width d is a parameter that directly affects the microphone's low-frequency response. The smaller the slot width d, the lower the microphone's low-frequency response and the wider the response range. A smaller slot width d can help the microphone capture and reproduce low-frequency sounds more accurately, and by obtaining a wider frequency response, the microphone system can sense more natural and clear sounds.

[0023] Figure 2 The frequency response comparison diagram of existing piezoelectric MEMS microphones at different slot widths d shows that at the same frequency, the smaller the slot width d, the smaller the signal attenuation. Taking the response at 100 Hz as an example, the microphone with a slot width d of 1 μm has the highest response signal, while the microphone with a slot width d of 2 μm has a response attenuation of more than an order of magnitude compared to the former, that is, when the slot width d is doubled, the microphone's response signal will be attenuated by more than ten times. Therefore, in order to make the microphone obtain a wider low-frequency response range, the slot width d between the cantilever beams should be as small as possible.

[0024] However, in the actual processing of the cantilever microphone, it is extremely difficult to obtain the smallest possible slot width d because the slot to be processed has a large depth-to-width ratio and contains piezoelectric materials that are difficult to etch.

[0025] For example, before etching a gap with a large aspect ratio, a layer of photoresist is often applied thickly in proportion to the gap depth. However, a photoresist that is too thick may result in insufficient light entering during photolithography, causing underexposure of the bottom photoresist; for positive photoresists, this may cause part of the photoresist to not be completely softened, and the exposed part of the photoresist cannot be completely removed during development, leaving a small amount of residue, which affects the accuracy of subsequent etching processes.

[0026] In addition, when etching gaps with a large aspect ratio, the photoresist will be consumed too quickly, that is, the photoresist has been completely consumed before the gap is completely etched to the bottom, which leads to the failure of opening the gap; continuing to etch the gap will damage other parts of the device and affect the quality of the chip.

[0027] In addition, due to the limitations of the process itself, it is impossible to produce a gap with an infinitely small slit width d; and as the thickness of the cantilever beam increases, the difficulty of processing the gap will increase further. Therefore, in terms of processing feasibility, the minimum limit of the slit width d also limits the low-frequency response width of the microphone.

[0028] like Figure 1 , Figure 3 As shown in the figure, when a piezoelectric device with a thickness of h=1.5μm is processed by a photolithography process, the piezoelectric material itself is difficult to etch, and its photoresist selectivity is difficult to achieve a high level. Therefore, if you want to achieve slits in one process, the photoresist thickness H is usually greater than 2h=3.0μm; however, as mentioned above, too thick a photoresist may lead to insufficient light entering during photolithography, resulting in underexposure of the bottom photoresist; when a positive photoresist is used, part of the photoresist cannot be completely softened, and the exposed part of the photoresist cannot be completely removed during development, leaving a small amount of residue, affecting the subsequent etching process.

[0029] When the depth to be etched is the same, the smaller the etching width, the slower the etching rate, the longer the time required, and the more photoresist is consumed. Therefore, the smaller the opening width d of the slit to be etched, the thicker the photoresist is usually required; when the opening width d=1.0μm, the etching rate may be too slow, resulting in the premature consumption of the photoresist, which directly causes Figure 4 In the case of failed slit opening shown in the figure, continuing to etch the slit will damage other parts of the device and affect the quality of the chip.

[0030] In view of this, to solve the above problems, please refer to Figure 5a , Figure 5bAs shown, the present invention provides a piezoelectric MEMS microphone, comprising: a base layer 10 having a cavity 100, and a composite vibration layer 11 stacked on the cavity 100 of the base layer 10, the composite vibration layer 11 having at least one slit 12, and the slit 12 is arranged along a stacking direction F1; when there are multiple slits 12, the multiple slits 12 are arranged side by side in the same plane along a horizontal direction F2 perpendicular to the stacking direction F1. At least one slit 12 enables the composite vibration layer 11 to form a cantilever beam supported by the base layer 10; the slit width of the slit 12 gradually decreases from the composite vibration layer 11 to the cavity 100, and the slit width is Figure 5a The dimension of the gap 12 in the horizontal direction F2.

[0031] The middle area of ​​the base layer 10 is etched away, and the base layer 10 forms a ring body with a cavity 100; a composite vibration layer 11 is formed on the cavity 100 of the base layer 10, and a gap 12 is opened in the composite vibration layer 11, and the composite vibration layer 11 is divided into cantilever beams by the gap 12, and the bottom of the cantilever beam is supported and connected by the base layer 10.

[0032] For example, Figure 5a As shown, in the back etching of the base layer 10, the cavity 100 is located in the back of the base layer 10, forming a back cavity. In the forward etching of the base layer 10, the cavity 100 is located in the forward direction of the base layer 10, forming Figure 5b structure.

[0033] The base layer 10 can also be configured to have different structures according to different scene requirements. In the present invention, the base layer includes at least one of the following structures: Figure 5a , Figure 5b In the figure, the base layer 10 is located below the composite vibration layer 11 along the stacking direction F1, and at least one gap 12 divides the composite vibration layer 11 into at least two cantilever beams supported by the base layer 10; one gap 12 divides the composite vibration layer 11 into two cantilever beams, two gaps 12 divide the composite vibration layer 11 into four cantilever beams, and so on, which will not be repeated.

[0034] The base layer 10 includes a substrate 101 and a film layer 102 stacked on the substrate 101. For example, the substrate 101 can be a silicon substrate, and the film layer 102 can be a single film layer or a stack of multiple film layers according to different functional requirements; the film layer 102 fully covers the position of the substrate 101 supporting the composite vibration layer 11 along the stacking direction F1.

[0035] Or, if Figure 5cIn the example, the base layer 10 includes an outer base layer 103 arranged around the composite vibration layer 11, and a bottom base layer 104 arranged below the composite vibration layer 11 along the stacking direction F1, a cavity 100 is formed between the outer base layer 103 and the bottom base layer 104, at least one gap 12 is formed between the composite vibration layer 11 and the outer base layer 103, and the composite vibration layer 11 is supported by the bottom base layer 104.

[0036] The structures of the base layer 104 and the peripheral base layer 103 are specifically configured according to needs. For example, the base layer 104 can be a central column, and the peripheral base layer 103 can be a substrate and a corresponding film layer, and so on.

[0037] Alternatively, you can Figure 5d In the example of FIG. 1 , the base layer 10 includes a substrate 101 and a film layer 102 stacked on the substrate 101, the film layer 102 partially covers the substrate 101 along the stacking direction F1, and the composite vibration layer 11 is stacked on the film layer 102. Since the film layer 102 does not fully cover the substrate 101, the space on the substrate 101 forms a cavity 100; and the film layer 102 can also be a single-layer film layer or a multi-layer film layer, which is not limited here.

[0038] Generally, if Figure 5a As shown, the composite vibration layer 11 includes a support layer 110 sequentially arranged on the base layer 10, and at least a first electrode layer 111, a piezoelectric layer 112 and a second electrode layer 113 arranged on the support layer 110; illustratively, the thicknesses of the support layer 110, the first electrode layer 111 and the second electrode layer 113 in the stacking direction F1 are substantially equal, and the thickness of the piezoelectric layer 112 is approximately 3 to 4 times the thickness of the first electrode layer 111 or the second electrode layer 113.

[0039] The composite vibration layer 11 may also not include the support layer 110. Figure 5d As shown, only the first electrode layer 111, the piezoelectric layer 112 and the second electrode layer 113 are sequentially arranged on the base layer 10.

[0040] In other examples, the piezoelectric layer 112 and the third electrode layer may continue to be stacked on the second electrode layer 113, and the piezoelectric layer 112 and the fourth electrode layer may be stacked on the third electrode layer, so that the electrode layers are stacked on the upper and lower sides of the piezoelectric layer 112 respectively, and the number of stacks is not limited.

[0041] The first electrode layer 111, the piezoelectric layer 112 and the second electrode layer 113 as a whole serve as a diaphragm structure. When sound acts on the diaphragm, the diaphragm begins to vibrate under the action of sound pressure and generates corresponding strain. At this time, the piezoelectric layer 112 generates charges on its upper and lower sides due to the strain, and the output becomes an electrical signal to achieve sensing.

[0042] In addition, it should be clarified that the above-mentioned levels are all arranged in the stacking direction F1. On the top projection plane of the stacking direction F1, the shape and position of the gap 12 are not specifically limited. The gap 12 can be formed as follows: Figure 5e The I-shaped shape shown can also be formed Figure 5f The shape of the gap 12 is shown; the specific shapes of the other layer structures on the top projection plane of the stacking direction F1 are not limited.

[0043] As mentioned above, the composite vibration layer 11 is divided into cantilever beams by the slit 12; and the slit width of the slit 12 gradually decreases from the composite vibration layer 11 to the base layer 10. In other words, the slit width does not remain a constant value in the stacking direction F1, but gradually decreases from top to bottom to form a certain slit width difference, which makes it easy to obtain the smallest possible slit width in the bottom layer; and because the slits form slit width differences in different layers, the slits are easy to prepare in terms of process, and there is no problem of underexposure or residue of the bottom layer photoresist, or slit failure caused by inadequate slits in the prior art. The piezoelectric MEMS microphone provided by the present invention can obtain a smaller slit width, and the microphone has a wider low-frequency response, and can also ensure product quality. The following Figure 5a Taking the structure of as an example, in some implementations, a smaller slit width can be obtained by forming a stepped slit 12. Along the stacking direction F1, the slit 12 forms a stepped slit, and the slit 12 is arranged in at least two layers of steps.

[0044] The cross section of the gap 12 is as follows: Figure 6 , Figure 7 It is in the shape of a step, with no limit on the number of steps (number of processing times) and the height of each step (the depth of a single processing in the stacking direction F1); when processing a film of the same thickness h, the more steps there are, the smaller the minimum slit width is, that is, Figure 7 As shown, the third slot width d3<the second slot width d2<the first slot width d1.

[0045] When preparing the stepped gap 12, one layer of steps is processed and formed at a time, and N layers of steps need to be processed N times; through multiple slit processing with decreasing slit width, a smaller slit width can be obtained, that is, each processing reduces the slit width of the gap 12 to a certain extent on the basis of the previous processing. Therefore, when the first slit width d1 is the same, the stepped gap 12 has a smaller slit width.

[0046] Compared with the prior art which requires one-time processing and shaping of the depth of the gap 12 (the dimension in the stacking direction F1), the present invention can reduce the depth of the single-processed gap 12 in the prior art by processing the gap 12 multiple times. When adopting the photolithography etching process, the thickness of the photoresist required to be applied in each process can be reduced, thereby avoiding the problem of underexposure of the underlying photoresist or residual photoresist due to thick coating of the photoresist in the prior art. Moreover, the multiple photolithography etching processes can choose to etch a groove with a larger depth first when processing the gap 12 with the widest slit width for the first time. In this way, when processing the gap 12 with a smaller slit width subsequently, the aspect ratio will not be too large, thereby reducing the difficulty of single processing, solving the problem of slit failure, and improving the accuracy of single processing.

[0047] As the number of processing times increases, the slit width can be further reduced; the smaller the slit width, the wider the low-frequency response of the microphone.

[0048] Compared with the existing technology, such as using photolithography and etching process, processing Figure 6 For example, when a device with a thickness (the total thickness of the first electrode layer 111, the piezoelectric layer 112 and the second electrode layer 113) of h=1.5μm is processed in the same way to form a second slit 12 with a width of d2=1.0μm, a two-step stepped slit 12 can be used to achieve two processings with a smaller aspect ratio; the first time, a groove with a first slit width of d1=1.5μm and a depth (in the stacking direction F1) of 0.75μm is etched out, and the second time, based on the first groove, a slit 12 with a second slit width of d2=1.0μm and a depth of 0.75μm is processed, and the aspect ratios of both etchings are less than 1.

[0049] Figure 8 This is a comparison diagram of the low-frequency response of the piezoelectric MEMS microphone gap 12 provided by the present invention and the gap in the prior art. When the existing gap width d is the same as the first gap width d1, the structure 2 ( Figure 6 Structure shown), Structure 3 ( Figure 7 Compared with structure 1 ( Figure 1 The signal attenuation of structure 3 at low frequency is smaller than that of structure 2 when the second slit width d2 is the same. It can be seen that the main parameter affecting the low-frequency response of the microphone is the minimum slit width of the microphone, which has nothing to do with the maximum first slit width d1. This proves that the use of a stepped slit 12 can help the microphone obtain a wider low-frequency response and improve the performance of the microphone.

[0050] In summary, the cross section of the gap 12 is stepped. Different processing times can be selected according to the thickness of the device to be processed. The number of steps in the cross-sectional stepped structure changes with the number of processing times. Each processing has a smaller opening width of the gap 12 than the previous processing.

[0051] In order to obtain the smallest possible slit width, the stepped slit 12 is set and multiple processing is selected to minimize the slit width; in the stepped slit 12, the number of steps gradually increases with the increase in the number of processing times, and can theoretically approach infinity.

[0052] In the above-mentioned implementations, the gap 12 may be a vertical step gap, that is, the sidewall of the gap 12 along the stacking direction F1 is parallel to the stacking direction F1, such as Figure 6 , Figure 7 shown.

[0053] In other implementations, the sidewalls of the gap 12 along the stacking direction F1 may form an angle with the stacking direction F1, and the gap 12 of each step may be Fig. 9 , Fig.10 Inverted cone shown.

[0054] The inverted tapered gap 12 is based on the vertical step gap, and compared with the vertical step gap, the inverted tapered gap 12 can also obtain a smaller opening width when the processing limit is reached. Fig. 9 In the structure 5 shown in FIG. 1 , the second slit width d2 is less than the third slit width d3 ; Fig.10 In the structure shown (Structure 6), the second slit width d2 is less than the fourth slit width d4.

[0055] It can be seen from this that the inverted tapered step gap can obtain a wider range of opening widths than the vertical step gap, and therefore it is easier to obtain a smaller opening width.

[0056] Fig.11 This is a picture of the piezoelectric MEMS microphone gap 12 provided by the present invention under an electron microscope. It is a picture of the gap 12 processed by twice using an inverted cone step gap under an electron microscope. It can be seen that the cross-section of the gap 12 is obviously inverted cone step shape, and the overall gap is flat.

[0057] The first processing was to produce a groove with a slit width of 3.5 μm, and an inverted cone-shaped groove was obtained by using an inverted cone step gap; the second processing was to produce a groove with a slit width of 2.5 μm, and the bottom slit width was 1 μm, and the slit size was smaller than the processing size.

[0058] The vertical step gaps or inverted tapered step gaps mentioned above are arranged in at least two layers of steps. In other implementations, a layer of inverted tapered gaps 12 may also be used. In this case, the side walls of the gaps 12 along the stacking direction F1 form an angle with the stacking direction F1, so that the gaps 12 are inverted tapered along the stacking direction F1.

[0059] The cross section of the gap 12 approaches Fig.12As shown, it is in an inverted cone shape. When a photolithography process is used, a layer of inverted cone-shaped slits 12 can be processed once to obtain a slit width smaller than the slit width D of the photolithography feature size; that is, when the slit width D is constant, the inverted cone etching process is used, and the slit width obtained at the bottom must be smaller than the slit width D, that is, Fig.13 The second slot width d2 shown is less than the first slot width d1.

[0060] pass Fig.14 From the simulation, we can see that, when the first slit width d1 is the same, structure 5 ( Fig. 9 Structure shown), Structure 6 ( Fig.10 The structure shown) is compared to structure 4 ( Fig.13 The signal attenuation of structure 6 at low frequency is smaller than that of structure 5 when the third slot width d3 is the same. It can be seen that the main parameter affecting the low-frequency response of the microphone is still the minimum slot width of the microphone, which has nothing to do with the maximum first slot width d1.

[0061] And in Fig.15 In the figure, the microphone cantilever beam with the same thickness is compared in structure 4 ( Fig.13 Structure shown), Structure 1 ( Figure 1 The response of the two slit structures when the first slit width d1 and the slit width d are both equal to 2μm; it can be seen that Fig.13 The gap of the first inverted cone is 12 Figure 1 The straight slot shown has less signal attenuation.

[0062] Based on this, the present invention also provides a method for preparing a piezoelectric MEMS microphone, which is used to prepare the above-mentioned piezoelectric MEMS microphone, and the method comprises: Step 200 : forming a composite vibration layer 11 by stacking on the cavity 100 of the base layer 10 .

[0063] by Figure 5a For example, the composite vibration layer 11 may be prepared on the entire base layer 10 first, and then the material in the middle area of ​​the base layer 10 may be etched away to form the cavity 100 of the base layer 10 .

[0064] For base layers 10 of different structures, for example Figure 5a , Figure 5b , Figure 5c , Figure 5d , prepared according to the corresponding structure, which will not be described here.

[0065] Step 210 : etching the composite vibration layer 11 toward the cavity 100 to form at least one gap 12 in the composite vibration layer 11 , so that the composite vibration layer 11 forms a cantilever beam supported by the base layer 10 .

[0066] In step 210, different preparation methods can be used according to different structures. For example, if a stepped gap structure is used, it includes at least two layers of steps. Correspondingly, the composite vibration layer 11 is etched at least twice toward the cavity 100, and each etching forms a layer of steps, so that the gap 12 is arranged in at least two layers of steps along the stacking direction F1, and the gap 12 of each layer of steps is etched once.

[0067] The stepped gap may be a vertical step, and the gap 12 of each step is etched vertically so that the sidewall of the gap 12 along the stacking direction F1 is parallel to the stacking direction F1, forming Figure 6 , Figure 7 The structure shown.

[0068] Alternatively, the stepped gap is an inverted tapered gap, and the gap 12 of each step is etched obliquely so that the side wall of the gap 12 along the stacking direction F1 forms an angle with the stacking direction F1, forming Fig. 9 , Fig.10 The structure shown.

[0069] If adopted Fig.13 The first inclined gap shown in the figure is correspondingly etched from the composite vibration layer 11 toward the cavity 100 so that the side wall of the gap 12 along the stacking direction F1 is set at an angle with the stacking direction F1, and the gap 12 is in an inverted cone along the stacking direction F1, forming Fig.13 The structure shown.

[0070] It should be noted that the preparation method of the present invention uses photolithography to etch the gap 12. In other implementations, other non-photolithography methods can also be used to obtain the gap 12. The preparation method of the present invention is not limited to obtaining the gap 12 by photolithography.

[0071] Furthermore, the present invention Figure 6 , Figure 7 , Fig. 9 and Fig.10 Two-layer and three-layer stepped gaps are exemplified; in actual process, the number of steps is not limited and can be set according to specific needs.

[0072] The method for preparing the piezoelectric MEMS microphone has the same beneficial effects as the piezoelectric MEMS microphone in the aforementioned implementation. The structure and beneficial effects of the piezoelectric MEMS microphone have been described in detail in the aforementioned implementation, and will not be repeated here.

[0073] The above description is only an example of the present invention and is not intended to limit the scope of protection of the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A piezoelectric MEMS microphone, characterized in that: include: A base layer having a cavity, and a composite vibration layer stacked on the cavity of the base layer, wherein the composite vibration layer has at least one gap, and the gap is arranged along the stacking direction; when there are multiple gaps, the multiple gaps are arranged side by side in the same plane along a horizontal direction perpendicular to the stacking direction; at least one gap enables the composite vibration layer to form a cantilever beam supported by the base layer; and the opening width of the gap gradually decreases in the direction from the composite vibration layer to the cavity.

2. The piezoelectric MEMS microphone according to claim 1, characterized in that: Along the stacking direction, the gaps form stepped gaps, and the gaps are arranged in at least two layers of steps.

3. The piezoelectric MEMS microphone according to claim 2, characterized in that: The sidewalls of the slit along the stacking direction are parallel to the stacking direction.

4. The piezoelectric MEMS microphone according to claim 2, characterized in that: The sidewalls of the gap along the stacking direction form an angle with the stacking direction, so that the gap of each step is in an inverted cone shape.

5. The piezoelectric MEMS microphone according to claim 1, characterized in that: The sidewall of the slot along the stacking direction forms an angle with the stacking direction, so that the slot is in an inverted cone shape along the stacking direction.

6. The piezoelectric MEMS microphone according to claim 1, characterized in that: The base layer includes at least one of the following structures: The base layer is located below the composite vibration layer along the stacking direction, and at least one of the gaps divides the composite vibration layer into at least two cantilever beams supported by the base layer; the base layer includes a substrate and a film layer stacked on the substrate, and the film layer completely covers the substrate along the stacking direction; Alternatively, the base layer includes a peripheral base layer arranged around the composite vibration layer, and a bottom base layer arranged below the composite vibration layer along the stacking direction, the cavity is formed between the peripheral base layer and the bottom base layer, at least one gap is formed between the composite vibration layer and the peripheral base layer, and the composite vibration layer is supported by the bottom base layer; Alternatively, the base layer includes a substrate and a film layer stacked on the substrate, the film layer partially covers the substrate along the stacking direction, and the composite vibration layer is stacked on the film layer.

7. The piezoelectric MEMS microphone according to any one of claims 1 to 6, characterized in that: The composite vibration layer includes at least a first electrode layer, a piezoelectric layer, and a second electrode layer which are stacked in sequence on the base layer.

8. A method for preparing a piezoelectric MEMS microphone, used for preparing the piezoelectric MEMS microphone according to any one of claims 1 to 7, characterized in that: The method comprises: A composite vibration layer is stacked on the cavity of the base layer; The composite vibration layer is etched toward the cavity to form at least one gap in the composite vibration layer, so that the composite vibration layer forms a cantilever beam supported by the base layer.

9. The method for preparing a piezoelectric MEMS microphone according to claim 8, characterized in that: The etching from the composite vibration layer toward the cavity to form at least one gap in the composite vibration layer so that the composite vibration layer forms a cantilever beam supported by the base layer, comprises: Etching at least twice from the composite vibration layer toward the cavity, so that the gaps are arranged in at least two layers of steps along the stacking direction, and the gaps in each layer of steps are etched once; Vertically etching the gap of each step so that the sidewall of the gap along the stacking direction is parallel to the stacking direction; Alternatively, the gap of each step is etched obliquely so that the sidewall of the gap along the stacking direction forms an angle with the stacking direction.

10. The method for preparing a piezoelectric MEMS microphone according to claim 8, characterized in that: The etching from the composite vibration layer toward the cavity to form at least one gap in the composite vibration layer so that the composite vibration layer forms a cantilever beam supported by the base layer, comprises: The composite vibration layer is etched once toward the cavity so that the sidewall of the gap along the stacking direction is arranged at an angle with the stacking direction, and the gap is in an inverted cone shape along the stacking direction.

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