A piezoelectric MEMS microphone and its manufacturing method

Abstract

The present invention provides a piezoelectric MEMS microphone and a manufacturing method thereof, relating to the field of semiconductor technology. It includes a base layer having a cavity, and a composite vibration layer laminated on the cavity of the base layer. The composite vibration layer has at least one slit, and the slit is arranged along the lamination direction. When there are multiple slits, the multiple slits are located in the same plane along the horizontal direction perpendicular to the lamination direction. At least one slit causes the composite vibration layer to form a cantilever beam supported by the base layer. In the direction from the composite vibration layer to the cavity, the slit width of the slit gradually decreases. The slit width of the slit gradually decreases from the composite vibration layer to the cavity, and a certain slit width difference is formed in the slit, which is convenient to obtain as small a slit width as possible at the bottom of the slit. And because a slit width difference is formed in different layers of the slit, the slit is easy to manufacture in terms of process, can obtain a smaller slit width, the microphone has a wider low-frequency response, and can also ensure product quality.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly 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 mainly consist of a piezoelectric unit and an ASIC (Application Specific Integrated Circuit); among them, the piezoelectric unit includes a substrate, a support structure, and a cantilever diaphragm structure. On a cantilever microphone, slits are provided between the cantilever beams. In order to enable the microphone to obtain a wider low-frequency response range, the slit width between the cantilever beams should be as small as possible.

[0003] However, in the actual processing of cantilever microphones, due to the large aspect ratio of the slits to be processed and the presence of difficult-to-etch piezoelectric materials, etc., it is extremely difficult to obtain an as-small-as-possible slit width. During etching, thickly coated photoresist will cause insufficient light entry of the photoresist, resulting in under-exposure at the bottom or leaving residual photoresist, affecting subsequent etching; in addition, when etching slits with a large aspect ratio, the photoresist may be consumed too quickly, that is, when the slit has not been completely etched to the bottom, the photoresist has been completely consumed, resulting in the failure of opening the slit. Continuing to etch the slit will damage other parts of the device, affecting the product quality. Summary of the Invention

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

[0005] On one hand, the present invention provides a piezoelectric MEMS microphone, including a base layer having a cavity, and a composite vibration layer stacked on the cavity of the base layer. The composite vibration layer has at least one slit, and the slit is arranged along the stacking direction; when there are multiple slits, the multiple slits are arranged side by side in the same plane along the horizontal direction perpendicular to the stacking direction; at least one slit forms a cantilever beam supported by the base layer for the composite vibration layer; in the direction from the composite vibration layer to the cavity, the slit width of the slit gradually decreases.

[0006] Optionally, along the stacking direction, the slit forms a stepped slit, and the slit is arranged in at least two layers of steps.

[0007] Optionally, the side walls of the slit along the stacking direction are parallel to the stacking direction.

[0008] Optionally, the side walls of the slit along the stacking direction form an angle with the stacking direction, so that the slits of each layer of steps are in an inverted conical shape.

[0009] Optionally, the side walls of the slit along the stacking direction form an angle with the stacking direction, so that the slit is in an inverted conical shape along the stacking direction.

[0010] Optionally, the base layer at least includes any one of the following structures:

[0011] The base layer is located below the composite vibration layer along the stacking direction, and at least one slit 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;

[0012] Alternatively, the base layer includes a peripheral base layer provided around the composite vibration layer and a bottom base layer provided below the composite vibration layer along the stacking direction, a cavity is formed between the peripheral base layer and the bottom base layer, at least one slit is formed between the composite vibration layer and the peripheral base layer, and the composite vibration layer is supported by the bottom base layer;

[0013] 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.

[0014] Optionally, the composite vibration layer includes at least a first electrode layer, a piezoelectric layer, and a second electrode layer stacked on the base layer in sequence.

[0015] On the other hand, the present invention provides a method for manufacturing a piezoelectric MEMS microphone for manufacturing the above piezoelectric MEMS microphone, and the method includes:

[0016] Stack and form a composite vibration layer on the cavity of the base layer;

[0017] Etch from the composite vibration layer towards the cavity direction to form at least one slit in the composite vibration layer, so that the composite vibration layer forms a cantilever beam supported by the base layer.

[0018] Optionally, the etching from the composite vibration layer towards the cavity direction to form at least one slit in the composite vibration layer, so that the composite vibration layer forms a cantilever beam supported by the base layer, includes:

[0019] Etch at least twice from the composite vibration layer towards the cavity direction, so that the slits are arranged in at least two layers of steps along the stacking direction, and the slits of each layer of steps are etched in one go;

[0020] Vertically etch the slits of each layer of steps, so that the side walls of the slits along the stacking direction are parallel to the stacking direction;

[0021] Alternatively, obliquely etch the slits of each layer of steps, so that an included angle is formed between the side walls of the slits along the stacking direction and the stacking direction.

[0022] Optionally, the etching from the composite vibration layer towards the cavity direction to form at least one slit in the composite vibration layer, so that the composite vibration layer forms a cantilever beam supported by the base layer, includes:

[0023] Etch once from the composite vibration layer towards the cavity direction, so that the side walls of the slit along the stacking direction are arranged at an included angle with the stacking direction, and the slit is in an inverted conical shape along the stacking direction.

[0024] For the piezoelectric MEMS microphone and its manufacturing method provided by the present invention, the slit width of the slit gradually decreases from the composite vibration layer towards the cavity direction of the base layer, forming a certain slit width difference, which facilitates obtaining as small a slit width as possible at the bottom of the slit; and because the slit width difference is formed in different layers of the slit, it makes the slit easy to prepare in the process, and there is no situation of under-exposure or residue of photoresist at the bottom of the slit in the prior art, or the slit opening fails due to incomplete slit opening. The piezoelectric MEMS microphone provided by the present invention can obtain a smaller slit width, the microphone has a wider low-frequency response, and can also ensure the product quality. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions 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 therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0026] Figure 1 is a schematic structural diagram of a piezoelectric MEMS microphone in the prior art;

[0027] Figure 2 is a frequency response comparison diagram of a prior piezoelectric MEMS microphone at different slit widths;

[0028] Figure 3 is a schematic diagram of photoresist residue of a prior piezoelectric MEMS microphone;

[0029] Figure 4Schematic diagram of the failure of the slitting of the existing piezoelectric MEMS microphone;

[0030] Figure 5a One of the schematic diagrams of the structure of the piezoelectric MEMS microphone provided by the present invention;

[0031] Figure 5b Another schematic diagram of the structure of the piezoelectric MEMS microphone provided by the present invention;

[0032] Figure 5c Another schematic diagram of the structure of the piezoelectric MEMS microphone provided by the present invention;

[0033] Figure 5d Another schematic diagram of the structure of the piezoelectric MEMS microphone provided by the present invention;

[0034] Figure 5e One of the schematic diagrams of the structure of the top view projection plane of the piezoelectric MEMS microphone provided by the present invention;

[0035] Figure 5f Another schematic diagram of the structure of the top view projection plane of the piezoelectric MEMS microphone provided by the present invention;

[0036] Figure 6 One of the schematic diagrams of the slit structure of the piezoelectric MEMS microphone provided by the present invention;

[0037] Figure 7 Another schematic diagram of the slit structure of the piezoelectric MEMS microphone provided by the present invention;

[0038] Figure 8 One of the low-frequency response comparison diagrams of the slit of the piezoelectric MEMS microphone provided by the present invention and the slit of the prior art;

[0039] Figure 9 Another schematic diagram of the slit structure of the piezoelectric MEMS microphone provided by the present invention;

[0040] Figure 10 Another schematic diagram of the slit structure of the piezoelectric MEMS microphone provided by the present invention;

[0041] Figure 11 Picture of the slit of the piezoelectric MEMS microphone provided by the present invention under the electron microscope;

[0042] Figure 12 Another schematic diagram of the structure of the piezoelectric MEMS microphone provided by the present invention;

[0043] Figure 13 Another schematic diagram of the slit structure of the piezoelectric MEMS microphone provided by the present invention;

[0044] Figure 14It is a comparison diagram of the low-frequency response of the slit of the piezoelectric MEMS microphone provided by the present invention;

[0045] Figure 15 It is the second comparison diagram of the low-frequency response between the slit of the piezoelectric MEMS microphone provided by the present invention and the slit of the prior art.

[0046] Icon: 10 - base layer; 100 - cavity; 101 - substrate; 102 - film 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 - slit; F1 - stacking direction; F2 - horizontal direction; H - photoresist thickness; D - slit width; d - slitting width; d1 - first slitting width; d2 - second slitting width; d3 - third slitting width; d4 - fourth slitting width; h - thickness. Specific embodiments

[0047] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the accompanying drawings in the present invention.

[0048] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "inside", "outside", etc. is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product is usually placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, terms such as "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0049] It should also be noted that unless otherwise clearly specified and defined, the terms "arrangement", "connection" should be understood in a broad sense. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0050] As Figure 1 , on a cantilever beam microphone, the slitting design between the cantilever beams has a great influence on the low-frequency response ability of the microphone. Among them, the slitting width d is a parameter that directly affects the low-frequency response of the microphone. The smaller the slitting width d, the lower the low-frequency response of the microphone and the wider the response range. A smaller slitting width d can help the microphone capture and reproduce low-frequency sounds more accurately, and achieve a more natural and clear sound sensing of the microphone system by obtaining a wider frequency response.

[0051] Figure 2It is a frequency response comparison diagram of existing piezoelectric MEMS microphones at different slit widths d. It can be seen that at the same frequency, the smaller the slit width d of the microphone, the smaller the signal attenuation. Taking the response at 100 Hz as an example, the microphone with a slit width d of 1 μm here has the highest response signal. Compared with the former, the response attenuation of the microphone with a slit width d of 2 μm exceeds an order of magnitude, that is, when the slit width d doubles, it will cause more than a ten-fold attenuation of the response signal of the microphone. Therefore, in order to enable the microphone to obtain a wider low-frequency response range, the slit width d between the cantilever beams should be as small as possible.

[0052] However, in the actual processing of cantilever microphones, due to the large aspect ratio of the gap to be processed and the presence of piezoelectric materials that are difficult to etch, it is extremely difficult to obtain an as small as possible slit width d.

[0053] For example, before etching a gap with a large aspect ratio, a layer of photoresist is often thickly coated according to a certain proportion of the gap depth. However, too thick photoresist may lead to insufficient light entry during lithography, resulting in the phenomenon of under-exposure of the bottom photoresist; for positive photoresist, it will cause partial photoresist not to soften completely, and when developing, the exposed photoresist cannot be completely removed, leaving a small amount of residue, affecting the accuracy of the subsequent etching process.

[0054] And when etching a gap with a large aspect ratio, there will be a problem of too fast consumption of photoresist, that is, when the gap has not been completely etched to the bottom, the photoresist has been completely consumed, resulting in the failure of the slit opening; continuing to etch the gap will damage other parts of the device, affecting the quality of the chip.

[0055] In addition, due to the limitations of the process itself, it is impossible to process a gap with an infinitely small slit width d; and as the thickness of the cantilever beam increases, the processing difficulty of the gap will be further increased. Therefore, from the perspective of processing feasibility, the minimum limit of the slit width d also limits the low-frequency response width of the microphone.

[0056] As Figure 1 、 Figure 3 shown, when processing a piezoelectric device with a thickness h = 1.5 μm using a photolithography etching process, due to the difficulty of etching the piezoelectric material itself, it is difficult to achieve a very high selectivity ratio of the photoresist. Therefore, in order to achieve a slit opening through one processing, the photoresist thickness H is usually greater than 2h = 3.0 μm; however, as mentioned above, too thick photoresist may lead to insufficient light entry during lithography, resulting in the phenomenon of under-exposure of the bottom photoresist; when using positive photoresist, partial photoresist cannot be completely softened, so when developing, the exposed photoresist cannot be completely removed, leaving a small amount of residue, affecting the subsequent etching process.

[0057] Under the condition that the depth to be etched is the same, the smaller the etching width, the slower the etching rate, the longer the required time, and the more the photoresist is consumed. Therefore, the smaller the slit width d of the slit to be etched, the thicker the photoresist is usually required. When the slit width d = 1.0 μm, the etching rate may be too slow, resulting in the premature consumption of the photoresist, directly causing Figure 4 the situation of slit opening failure shown, and continuing to etch the slit will damage other parts of the device and affect the quality of the chip.

[0058] In view of this, to solve the above problems, please refer to Figure 5a 、 Figure 5b As shown, the present invention provides a piezoelectric MEMS microphone, including: a base layer 10 having a cavity 100, and a composite vibration layer 11 laminated on the cavity 100 of the base layer 10. The composite vibration layer 11 has at least one slit 12, and the slit 12 is arranged along the lamination direction F1; when there are multiple slits 12, the multiple slits 12 are arranged side by side in the same plane along the horizontal direction F2 perpendicular to the lamination direction F1.

[0059] At least one slit 12 makes the composite vibration layer 11 form a cantilever beam supported by the base layer 10; in the direction from the composite vibration layer 11 to the cavity 100, the slit width of the slit 12 gradually decreases, and the slit width is Figure 5a the dimension of the slit 12 in the horizontal direction F2.

[0060] The middle region of the base layer 10 is etched away, and the base layer 10 forms an annular body with a cavity 100; a composite vibration layer 11 is formed on the cavity 100 of the base layer 10, and the composite vibration layer 11 is provided with slits 12. The composite vibration layer 11 is divided into cantilever beams through the slits 12, and the lower part of the cantilever beams is supported and connected by the base layer 10.

[0061] Exemplarily, as Figure 5a shown, in the back etching of the base layer 10, the cavity 100 is located on the back of the base layer 10 to form a back cavity. In the front etching of the base layer 10, the cavity 100 is located on the front of the base layer 10 to form Figure 5b the structure of.

[0062] The base layer 10 can also be set to different structures according to different scenario requirements. In the present invention, the base layer at least includes the following one structure:

[0063] Figure 5a 、 Figure 5b In, the base layer 10 is located below the composite vibration layer 11 along the lamination direction F1, and at least one slit 12 divides the composite vibration layer 11 into at least two cantilever beams supported by the base layer 10; one slit 12 divides the composite vibration layer 11 into two cantilever beams, and two slits 12 divide the composite vibration layer 11 into four cantilever beams, and so on, which will not be elaborated here.

[0064] The base layer 10 includes a substrate 101 and a film layer 102 laminated on the substrate 101. Exemplarily, the substrate 101 can be a silicon substrate, and the film layer 102 can be a single-layer film layer or a stack of multiple-layer film layers according to different functional requirements; the film layer 102 completely covers the position of the substrate 101 that supports the composite vibration layer 11 along the lamination direction F1.

[0065] Or, as Figure 5c In the example of, the base layer 10 includes a peripheral base layer 103 disposed around the composite vibration layer 11, and a bottom base layer 104 disposed below the composite vibration layer 11 along the lamination direction F1. A cavity 100 is formed between the peripheral base layer 103 and the bottom base layer 104, and at least one gap 12 is formed between the composite vibration layer 11 and the peripheral base layer 103. The composite vibration layer 11 is supported by the bottom base layer 104.

[0066] The structures of the bottom base layer 104 and the peripheral base layer 103 are specifically set according to needs. For example, the bottom base layer 104 can be a central column, and the peripheral base layer 103 can be a substrate and corresponding film layers, etc.

[0067] Or, it can also be as Figure 5d In the example of, the base layer 10 includes a substrate 101 and a film layer 102 laminated on the substrate 101. The film layer 102 partially covers the substrate 101 along the lamination direction F1, and the composite vibration layer 11 is laminated on the film layer 102. Since the film layer 102 does not completely cover the substrate 101, the space vacated on the substrate 101 forms a cavity 100; and the film layer 102 can also be a single-layer film layer or a stack of multiple-layer film layers, which is not limited here.

[0068] Generally, as Figure 5a shown, the composite vibration layer 11 includes a support layer 110 sequentially disposed on the base layer 10, and at least a first electrode layer 111, a piezoelectric layer 112, and a second electrode layer 113 disposed on the support layer 110; Exemplarily, the thicknesses of the support layer 110, the first electrode layer 111, and the second electrode layer 113 are substantially equal in the lamination direction F1, and the thickness of the piezoelectric layer 112 is about 3 to 4 times the thickness of the first electrode layer 111 or the second electrode layer 113.

[0069] The composite vibration layer 11 may not include the support layer 110. As Figure 5d shown, it only includes a first electrode layer 111, a piezoelectric layer 112, and a second electrode layer 113 sequentially disposed on the base layer 10.

[0070] In some other examples, a piezoelectric layer 112 and a third electrode layer can be further laminated on the second electrode layer 113, and a piezoelectric layer 112 and a fourth electrode layer can be laminated on the third electrode layer, to form a stacked structure with electrode layers respectively on the upper and lower sides of the piezoelectric layer 112, and the stacking number is not limited.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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, i.e. Figure 7 As shown, the third slot width d3<the second slot width d2<the first slot width d1.

[0076] When preparing the stepped slit 12, one layer of steps is processed and formed at a time. If there are N layers of steps, it needs to be processed N times. Through multiple slitting processes with decreasing slit widths, a smaller slit width can be obtained. That is, in each processing, on the basis of the previous processing, the slit width of the slit 12 is reduced to a certain extent. Therefore, with the same first slit width d1, the stepped slit 12 has a smaller slit width.

[0077] Compared with the prior art where the depth of the slit 12 (the dimension in the stacking direction F1) needs to be processed and formed at one time, in the present invention, by processing the slit 12 multiple times, the depth of the slit 12 processed in a single time in the prior art can be reduced. When using the photolithography etching process, the thickness of the photoresist to be coated in each process can be reduced, thus avoiding the problems of under-exposure of the bottom-layer photoresist or photoresist residue caused by thick coating of the photoresist in the prior art. Moreover, in the multiple photolithography etching processes, when etching the slit 12 with the widest slit width in the first processing, a groove with a larger depth can be selectively etched first. In this way, when processing the slit 12 with a smaller slit width in subsequent processing, the aspect ratio will not be too large, reducing the difficulty of single processing and solving the problem of slit opening failure, and improving the accuracy of single processing.

[0078] 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.

[0079] When comparing with the prior art, such as when using the photolithography etching process, for processing Figure 6 a device with an example thickness (the total thickness of the first electrode layer 111, the piezoelectric layer 112, and the second electrode layer 113) h = 1.5 μm, when processing a slit 12 with a second slit width d2 = 1.0 μm in the same way, by using the two-step stepped slit 12, two processes with smaller aspect ratios can be achieved. First, a groove with a first slit width d1 = 1.5 μm and a depth (in the stacking direction F1) of 0.75 μm is etched. In the second processing, on the basis of the first groove, a slit 12 with a second slit width d2 = 1.0 μm and a depth of 0.75 μm is processed. The aspect ratios of both etching processes are less than 1.

[0080] Figure 8 This is one of the low-frequency response comparison diagrams of the piezoelectric MEMS microphone slit 12 provided by the present invention and the prior art slit. When the existing slit width d is the same as the first slit width d1, Structure 2 ( Figure 6 the structure shown), Structure 3 ( Figure 7 the structure shown) compared with Structure 1 ( Figure 1The signal attenuation of the shown structure is smaller at low frequencies; when the second slit width d2 is the same, the response limit that structure 3 can achieve at low frequencies is smaller than that of structure 2. It can be seen that the main parameter affecting the low-frequency response of the microphone is the minimum slit width of the microphone, and it has nothing to do with the maximum first slit width d1. Thus, it can be proved that using the stepped slit 12 can help the microphone obtain a wider low-frequency response and improve the performance of the microphone.

[0081] In summary, the cross-section of the slit 12 is stepped. According to the thickness change of the device to be processed, different processing times can be selected. The number of steps of the stepped cross-sectional structure changes with the processing times, and the slit width of the slit 12 obtained by each processing is smaller than that of the previous processing.

[0082] In order to obtain the smallest possible slit width, through the setting of the stepped slit 12, multiple processing is selected to minimize the slit width; in the stepped slit 12, the number of steps gradually increases with the increase of the processing times and can theoretically tend to infinity.

[0083] In each of the above implementation manners, the slit 12 can be a vertical stepped slit, that is, the side wall of the slit 12 along the stacking direction F1 is parallel to the stacking direction F1, as Figure 6 、 Figure 7 shown.

[0084] In some other implementation manners, the side wall of the slit 12 along the stacking direction F1 and the stacking direction F1 can form an angle, and the slit 12 of each step forms an Figure 9 、 Figure 10 shown inverted cone shape.

[0085] This inverted cone-shaped slit 12 is based on the above vertical stepped slit. Compared with the above vertical stepped slit, the inverted cone-shaped slit 12 can also obtain a smaller slit width when reaching the processing limit, that is, in Figure 9 shown (structure 5), the second slit width d2 < the third slit width d3; in Figure 10 shown (structure 6), there is the second slit width d2 < the fourth slit width d4.

[0086] It can be seen from this that the inverted cone-shaped stepped slit can obtain more sizes of slit widths than the vertical stepped slit, and thus it is easier to obtain a smaller slit width.

[0087] Figure 11 is a picture of the slit 12 of the piezoelectric MEMS microphone provided by the present invention under an electron microscope. It is a picture of the slit 12 processed by using the inverted cone-shaped stepped slit for two times under an electron microscope. It can be seen that the cross-section of the slit 12 is an obvious inverted cone-shaped step, and the overall slit is flat.

[0088] The groove with a first machining slot width of 3.5 μm is processed, and an inverted conical groove is obtained by using an inverted conical stepped slot; the groove with a second machining slot width of 2.5 μm is processed, and the slot width at the bottom is 1 μm, and the slot size is smaller than the machining size.

[0089] The above vertical stepped slot or inverted conical stepped slot is arranged in at least two layers of steps. In some other implementation manners, a single-layer inverted conical slot 12 can also be used. At this time, the side wall of the slot 12 along the stacking direction F1 forms an angle with the stacking direction F1, so that the slot 12 is in an inverted conical shape along the stacking direction F1.

[0090] The cross-section of the slot 12 approaches Figure 12 As shown in the figure, it is in an inverted conical shape. When processing by a photolithography etching process, a single-layer inverted conical slot 12 can be processed once to obtain a slot width smaller than the slot width D of the photolithography feature size; that is, when the slot width D is fixed, by using an inverted conical etching process, the slot width obtained at the bottom is definitely smaller than the slot width D, that is Figure 13 as shown in the figure, the second slot width d2 < the first slot width d1.

[0091] Through Figure 14 simulation, it can be seen that, also when the first slot width d1 is the same, the structure 5 ( Figure 9 the structure shown in the figure), the structure 6 ( Figure 10 the structure shown in the figure) have smaller signal attenuation at low frequencies compared to the structure 4 ( Figure 13 the structure shown in the figure); when the third slot width d3 is the same, the structure 6 has a smaller response limit at low frequencies compared to the structure 5. 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, and it has nothing to do with the first slot width d1 at the maximum.

[0092] And in Figure 15 , the responses of the microphone cantilever beams with the same thickness in two slot structures of the structure 4 ( Figure 13 the structure shown in the figure), the structure 1 ( Figure 1 the structure shown in the figure) are compared, when the first slot width d1 and the slot width d are both equal to 2 μm; it can be seen that Figure 13 the single-layer inverted conical slot 12 formed has smaller signal attenuation than Figure 1 the straight slot shown in the figure.

[0093] Based on this, the present invention also provides a preparation method of a piezoelectric MEMS microphone for preparing the above piezoelectric MEMS microphone, and the method includes:

[0094] Step 200: Stack and form a composite vibration layer 11 on the cavity 100 of the base layer 10.

[0095] With Figure 5aFor example, the composite vibration layer 11 can be prepared on the entire base layer 10 first, and then the material in the middle area of the base layer 10 can be etched away to form a cavity 100 in the base layer 10.

[0096] For base layers 10 with different structures, such as Figure 5a , Figure 5b , Figure 5c , Figure 5d , they are prepared according to the corresponding structures, which will not be elaborated here.

[0097] Step 210: Etch from the composite vibration layer 11 towards the cavity 100 to form at least one slit 12 in the composite vibration layer 11, so that the composite vibration layer 11 forms a cantilever beam supported by the base layer 10.

[0098] In step 210, different preparation methods can be divided according to different structures. For example, if a stepped slit structure is adopted, it includes at least two layers of steps; correspondingly, etch from the composite vibration layer 11 towards the cavity 100 at least twice, and each etching forms one layer of step, so that the slits 12 are arranged in at least two layers of steps along the stacking direction F1, and the slits 12 of each layer of step are completed by one etching.

[0099] The stepped slit can be a vertical step, then etch the slits 12 of each layer of step vertically, so that the side walls of the slits 12 along the stacking direction F1 are parallel to the stacking direction F1, forming the structures shown in Figure 6 , Figure 7 .

[0100] Or, the stepped slit is an inverted conical step, and etch the slits 12 of each layer of step obliquely, so that the side walls of the slits 12 along the stacking direction F1 form an angle with the stacking direction F1, forming the structures shown in Figure 9 , Figure 10 .

[0101] If a single-tilt slit as shown in Figure 13 is adopted, correspondingly, etch from the composite vibration layer 11 towards the cavity 100 once, so that the side walls of the slits 12 along the stacking direction F1 are arranged at an angle with the stacking direction F1, and the slits 12 are in an inverted conical shape along the stacking direction F1, forming the structure shown in Figure 13 .

[0102] It should be noted that the preparation method of the present invention uses photolithography to etch the slits 12. In other implementation manners, other non-photolithography methods can also be used to obtain the slits 12. The preparation method of the present invention is not limited to obtaining the slits 12 by photolithography.

[0103] Moreover, the present invention Figure 6 , Figure 7 , Figure 9 and Figure 10Two - layer and three - layer stepped slits are exemplified; in the actual process, the number of steps is not limited and can be set according to specific needs.

[0104] The preparation method of this piezoelectric MEMS microphone has the same beneficial effects as the piezoelectric MEMS microphone in the foregoing implementation. The structure and beneficial effects of the piezoelectric MEMS microphone have been described in detail in the foregoing implementation and will not be elaborated here.

[0105] The above is only an example of the present invention and is not used to limit the protection scope of the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A piezoelectric MEMS microphone, characterized in that, Comprising: A base layer having a cavity, and a composite vibration layer laminated on the cavity of the base layer, the composite vibration layer having at least one slit, the slit being arranged along the lamination direction; when there are multiple slits, the multiple slits are arranged side by side in the same plane in a horizontal direction perpendicular to the lamination direction; at least one of the slits forms a cantilever beam supported by the base layer through the composite vibration layer; in the direction from the composite vibration layer to the cavity, the slit width of the slit gradually decreases; along the lamination direction, the slit forms a stepped slit, the slit is arranged in at least two layers of steps, and at least two layers of the steps are formed by lithography at least twice in the direction from the composite vibration layer to the cavity.

2. The piezoelectric MEMS microphone according to claim 1, wherein The side wall of the slit along the lamination direction is parallel to the lamination direction.

3. The piezoelectric MEMS microphone according to claim 1, characterized in that, The side wall of the slit along the lamination direction and the lamination direction form an angle so that the slit of each layer of the step is in an inverted conical shape.

4. The piezoelectric MEMS microphone according to claim 1, characterized in that, The base layer at least includes any one of the following structures: The base layer is located below the composite vibration layer along the lamination direction, and at least one of the slits 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 laminated on the substrate, and the film layer completely covers the substrate along the lamination direction; Or, 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 lamination direction, the cavity is formed between the peripheral base layer and the bottom base layer, at least one of the slits is formed between the composite vibration layer and the peripheral base layer, and the composite vibration layer is supported by the bottom base layer; Or, the base layer includes a substrate and a film layer laminated on the substrate, the film layer partially covers the substrate along the lamination direction, and the composite vibration layer is laminated on the film layer.

5. The piezoelectric MEMS microphone according to any one of claims 1 to 4, characterized in that, The composite vibration layer includes at least a first electrode layer, a piezoelectric layer, and a second electrode layer laminated on the base layer in sequence.

6. A method for manufacturing a piezoelectric MEMS microphone, which is used to manufacture the piezoelectric MEMS microphone according to any one of claims 1 to 5, characterized in that, The method includes: Laminating and forming a composite vibration layer on the cavity of the base layer; Etching from the composite vibration layer towards the cavity to form at least one slit in the composite vibration layer, so that the composite vibration layer forms a cantilever beam supported by the base layer.

7. The manufacturing method of the piezoelectric MEMS microphone according to claim 6, characterized in that, The etching from the composite vibration layer towards the cavity to form at least one slit in the composite vibration layer, so that the composite vibration layer forms a cantilever beam supported by the base layer, includes: Etching from the composite vibration layer towards the cavity at least twice, so that the slit is arranged in at least two layers of steps along the lamination direction, and the slit of each layer of the step is completed by one etching; Vertically etching the slit of each layer of the step, so that the side wall of the slit along the lamination direction is parallel to the lamination direction; Or, obliquely etching the slit of each layer of the step, so that the side wall of the slit along the lamination direction and the lamination direction form an angle.

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