MEMS piezoelectric acoustic device and preparation method thereof

Abstract

The invention provides an MEMS piezoelectric acoustic device and a preparation method thereof, and relates to the technical field of semiconductors. The MEMS piezoelectric acoustic device comprises a substrate layer and at least two cantilever beams arranged on the substrate layer, wherein a gap is formed between the two adjacent cantilever beams; the flexible connecting layer is located in the gap and / or the side, away from the substrate layer, of the cantilever beam, the two ends of the flexible connecting layer are connected with the two adjacent cantilever beams respectively, a first connecting part is divided on the flexible connecting layer, the outer edge of the first connecting part coincides with the projection of the outer edge of the gap, and the gap is completely shielded; the winding length of the first connecting part in the gap width direction is larger than the width of the gap. The MEMS piezoelectric acoustic device has relatively high sensitivity and excellent low-frequency performance.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular, to a MEMS piezoelectric acoustic device and a method for preparing the same. Background Art

[0002] MEMS piezoelectric acoustic device is a device that can convert signals such as sound and vibration into electrical signals. It uses the piezoelectric effect to convert the mechanical energy of vibration into electrical energy and output it through piezoelectric film materials. It has the advantages of low power consumption and small size. Therefore, it is widely used in acoustic sensing, acceleration sensing, vibration detection and other fields. It is a very promising sensing technology and has broad application prospects in the 5G / Internet of Things era.

[0003] MEMS piezoelectric acoustic devices usually include at least two cantilever beams, with a gap between two adjacent cantilever beams. The setting of the gap can improve the sensitivity of the MEMS piezoelectric acoustic device, but it will also reduce the low-frequency response of the MEMS piezoelectric acoustic device. In order to improve the low-frequency response of the MEMS piezoelectric acoustic device while ensuring its sensitivity, the prior art will fill the gap with flexible materials to act as a sealing structure, so that the cantilever beams are partially or completely sealed. Although this flexible connection can improve the low-frequency response, it will significantly reduce the sensitivity of the MEMS piezoelectric acoustic device. Summary of the invention

[0004] The purpose of the present application is to provide a MEMS piezoelectric acoustic device and a preparation method thereof, which has high sensitivity and excellent low-frequency performance, in view of the deficiencies in the above-mentioned prior art.

[0005] To achieve the above purpose, the technical solution adopted in the embodiment of the present application is as follows: According to one aspect of an embodiment of the present application, a MEMS piezoelectric acoustic device is provided, comprising: a base layer and at least two cantilever beams arranged on the base layer, with a gap between two adjacent cantilever beams; and also comprising a flexible connection layer, the flexible connection layer being located in the gap and / or on the side of the cantilever beam facing away from the base layer, the two ends of the flexible connection layer being respectively connected to the two adjacent cantilever beams, a first connection portion being defined on the flexible connection layer, the outer edge of the first connection portion overlapping with the projection of the outer edge of the gap and completely blocking the gap, and the winding length of the first connection portion along the width direction of the gap being greater than the width of the gap.

[0006] Optionally, the first connecting portion extends in a broken line along the gap width direction, and the first connecting portion has a plurality of continuous corners, and the continuous corners are right angles or obtuse angles.

[0007] Optionally, the flexible connection layer is further divided into two second connection parts, the two second connection parts are respectively connected to the first connection part, and the two second connection parts are also respectively bonded and connected to the upper surfaces of two adjacent cantilever beams.

[0008] Optionally, a height of the first connecting portion is not less than a height of the gap.

[0009] According to another aspect of an embodiment of the present application, a method for preparing a MEMS piezoelectric acoustic device is provided, comprising: providing a base layer, and forming a piezoelectric film stack on the base layer along a first direction; patterning the piezoelectric film stack to form a gap, wherein the gap penetrates the piezoelectric film stack along the first direction and a second direction perpendicular to the first direction, respectively, to divide the piezoelectric film stack into at least two sub-piezoelectric film stacks; forming a supporting film on the sub-piezoelectric film stack, and patterning the supporting film to form a supporting layer, wherein the supporting layer is provided with two first through holes, one first through hole exposing the sub-piezoelectric film stack on one side of the gap, and the other first through hole exposing the sub-piezoelectric film stack on the other side of the gap, and the area of ​​the supporting layer facing the gap The upper surface of the substrate is uneven; a flexible film is formed on the supporting layer, and the flexible film is patterned to form a flexible connecting layer, wherein two ends of the flexible connecting layer are respectively connected to the sub-piezoelectric film stack exposed by the two first through holes, and a first connecting portion is divided on the flexible connecting layer, the outer edge of the first connecting portion coincides with the outer edge projection of the gap and completely blocks the gap, the winding length of the first connecting portion along the third direction is greater than the width of the gap along the third direction, and the third direction is perpendicular to the first direction and the second direction respectively; a back cavity corresponding to the position of the gap is formed on the base layer, wherein the back cavity makes the sub-piezoelectric film stack suspended to form a cantilever beam, and the width of the back cavity along the third direction is greater than the width of the gap; the supporting layer is released through the back cavity to make the flexible connecting layer suspended.

[0010] Optionally, a second through hole is further provided on the supporting layer, and the second through hole exposes the base layer below the gap and penetrates the supporting layer along the second direction.

[0011] Optionally, the thickness of the support layer is greater than or equal to 20 μm.

[0012] Optionally, the first through hole is located above the sub-piezoelectric film stack, and two ends of the flexible connection layer respectively cover the upper surface of the sub-piezoelectric film stack.

[0013] Optionally, the support layer wraps around corners of the piezoelectric film stack formed by the gap.

[0014] Optionally, the material of the supporting film is silicon oxide; providing a base layer and forming a piezoelectric film stack on the base layer along a first direction includes: providing a silicon substrate and forming a silicon oxide film on the silicon substrate; and forming a piezoelectric film stack on the silicon oxide film.

[0015] The beneficial effects of this application include: The present application provides a MEMS piezoelectric acoustic device, comprising: a base layer and at least two cantilever beams arranged on the base layer, with a gap between two adjacent cantilever beams; and also comprising a flexible connection layer, the flexible connection layer being located in the gap and / or on the side of the cantilever beam facing away from the base layer, the two ends of the flexible connection layer being respectively connected to the two adjacent cantilever beams, the flexible connection layer being divided into a first connection portion, the outer edge of the first connection portion being overlapped with the outer edge projection of the gap and completely blocking the gap, and the winding length of the first connection portion along the gap width direction being greater than the width of the gap. The above-mentioned MEMS piezoelectric acoustic device uses a flexible connection layer to connect two adjacent cantilever beams, and the first connection portion on the flexible connection layer facing the gap completely blocks the gap, achieving complete closure of the gap, thereby significantly improving the low-frequency performance of the MEMS piezoelectric acoustic device. The winding length of the first connection portion along the gap width direction is greater than the gap width, so that the flexible connection layer has a lower elastic coefficient and a certain stretchability, and has less restriction and influence on the cantilever beam during deformation, which can give the cantilever beam a larger deformation space and replace the cantilever beam to bear most of the strain, thereby ensuring the sensitivity of the MEMS piezoelectric acoustic device. Therefore, the above-mentioned MEMS piezoelectric acoustic device has high sensitivity and excellent low-frequency performance.

[0016] The present application also provides a method for preparing a MEMS piezoelectric acoustic device, comprising: providing a substrate layer, and forming a piezoelectric film stack on the substrate layer along a first direction; performing patterning on the piezoelectric film stack to form a gap, wherein the gap penetrates the piezoelectric film stack along the first direction and a second direction perpendicular to the first direction, respectively, to divide the piezoelectric film stack into at least two sub-piezoelectric film stacks; forming a supporting film on the sub-piezoelectric film stack, and performing patterning on the supporting film to form a supporting layer, wherein two first through holes are provided on the supporting layer, one first through hole exposes the sub-piezoelectric film stack on one side of the gap, and the other first through hole exposes the sub-piezoelectric film stack on the other side of the gap, and the upper surface of the region of the supporting layer facing the gap The surface is uneven; a flexible film is formed on the support layer, and the flexible film is patterned to form a flexible connection layer, wherein the two ends of the flexible connection layer are respectively connected to the sub-piezoelectric film stack exposed by the two first through holes, and a first connection portion is divided on the flexible connection layer, the outer edge of the first connection portion coincides with the outer edge projection of the gap and completely blocks the gap, the winding length of the first connection portion along the third direction is greater than the width of the gap along the third direction, and the third direction is perpendicular to the first direction and the second direction respectively; a back cavity corresponding to the gap position is formed on the base layer, wherein the back cavity makes the sub-piezoelectric film stack suspended to form a cantilever beam, and the width of the back cavity along the third direction is greater than the width of the gap; the support layer is released through the back cavity to make the flexible connection layer suspended. The preparation method of the above-mentioned MEMS piezoelectric acoustic device is simple and easy to implement, and the MEMS piezoelectric acoustic device prepared by the above-mentioned preparation method of the MEMS piezoelectric acoustic device has high sensitivity and excellent low-frequency performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore 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.

[0018] Figure 1 A schematic diagram of the structure of a MEMS piezoelectric acoustic device provided in an embodiment of the present application; Figure 2 One of the structural schematic diagrams of the cantilever beam and the flexible connection layer in the MEMS piezoelectric acoustic device provided in the embodiment of the present application; Figure 3 The second structural schematic diagram of the cantilever beam and the flexible connection layer in the MEMS piezoelectric acoustic device provided in the embodiment of the present application; Figure 4 A schematic diagram of the deformation of a cantilever beam and a flexible connection layer in a MEMS piezoelectric acoustic device provided in an embodiment of the present application; Figure 5 One of the flow charts of the method for preparing a MEMS piezoelectric acoustic device provided in an embodiment of the present application; Figure 6 One of the schematic diagrams of the preparation process of the MEMS piezoelectric acoustic device provided in the embodiment of the present application; Figure 7 The second schematic diagram of the preparation process of the MEMS piezoelectric acoustic device provided in the embodiment of the present application; Figure 8 The third schematic diagram of the preparation process of the MEMS piezoelectric acoustic device provided in the embodiment of the present application; Fig. 9 A fourth schematic diagram of the preparation process of the MEMS piezoelectric acoustic device provided in an embodiment of the present application; Fig.10 A fifth schematic diagram of the preparation process of the MEMS piezoelectric acoustic device provided in an embodiment of the present application; Fig.11 Schematic diagram six of the preparation process of the MEMS piezoelectric acoustic device provided in the embodiment of the present application; Fig.12 Schematic diagram of the preparation process of the MEMS piezoelectric acoustic device provided in the embodiment of the present application No. 7; Fig.13 The second flowchart of the method for preparing the MEMS piezoelectric acoustic device provided in the embodiment of the present application.

[0019] Icon: 10-MEMS piezoelectric acoustic device; 11-base layer; 111-back cavity; 1111-sub-back cavity; 112-silicon substrate; 113-silicon oxide film; 12-cantilever beam; 121-electrode layer; 122-piezoelectric layer; 13-gap; 131-outer edge of the gap; 14-flexible connection layer; 141-first connection part; 1411-outer edge of the first connection part; 142-second connection part; 15-piezoelectric film stack; 151-sub-piezoelectric film stack; 16-support film; 161-support layer; 1611-first through hole; 1612-second through hole; 17-flexible film; X-gap width direction; Y-second direction; Z-first direction; H1-height of the first connection part; H2-height of the gap; θ-continuous rotation angle. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. It should be noted that, in the absence of conflict, the various features in the embodiments of the present application can be combined with each other, and the combined embodiments are still within the scope of protection of the present application.

[0022] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0023] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the application is usually placed when in use. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0024] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0025] In one aspect of the embodiment of the present application, please refer to Figure 1 , a MEMS piezoelectric acoustic device 10 is provided, comprising: a base layer 11 and at least two cantilever beams 12 arranged on the base layer 11, with a gap 13 between two adjacent cantilever beams 12. The MEMS piezoelectric acoustic device 10 also includes a flexible connection layer 14, the flexible connection layer 14 is located in the gap 13 and / or on the side of the cantilever beam 12 away from the base layer 11, the two ends of the flexible connection layer 14 are respectively connected to the two adjacent cantilever beams 12, and a first connection portion 141 is divided on the flexible connection layer 14, the outer edge 1411 of the first connection portion overlaps with the outer edge 131 of the gap in projection and completely blocks the gap 13, and the winding length of the first connection portion 141 along the gap width direction X is greater than the width of the gap 13.

[0026] The cantilever beam 12 is used to convert the vibrating mechanical signal into an electrical signal. The cantilever beam 12 includes at least two electrode layers 121 and at least one piezoelectric layer 122. The electrode layers 121 and the piezoelectric layers 122 are alternately stacked on the base layer 11 along the first direction Z. The electrode layers 121 are distributed on both sides of each piezoelectric layer 122. The first direction Z is preferably perpendicular to the upper surface of the base layer 11. The cantilever beam 12 has a fixed end and a free end relative to each other. The fixed end is connected to the base layer 11, and the free end is suspended. There are at least two cantilever beams 12, all of which are fixed on the base layer 11. The cantilever beam 12 can be directly bonded to the base layer 11, or indirectly connected through other film layers in the middle. There is a gap 13 between two adjacent cantilever beams 12. During preparation, the gap 13 divides the complete piezoelectric film stack to form a cantilever beam 12. The presence of the gap 13 can reduce the resonant frequency of the MEMS piezoelectric acoustic device 10 and improve its response sensitivity.

[0027] The flexible connection layer 14 connects the free ends of two adjacent cantilever beams 12 together. The flexible connection layer 14 may be completely located in the gap 13, or completely located outside the gap 13, or a portion of the flexible connection layer 14 may be located in the gap 13 and a portion of the flexible connection layer 14 may be located outside the gap 13. The ends of the flexible connection layer 14 may be connected to the surfaces of the cantilever beams 12 (e.g., Figure 1 As shown), it can also be connected to the side of the cantilever beam 12 corresponding to the gap 13 (as shown Figure 2 ), or connected to the surface of the cantilever beam 12 and the side of the corresponding gap 13 at the same time (as shown in Figure 3 as shown).

[0028] At least a first connection portion 141 can be divided on the flexible connection layer 14. The first connection portion 141 can be completely located in the gap 13, or completely located outside the gap 13, or a part of the area is located in the gap 13 and a part of the area is located outside the gap 13. The outer edge 1411 of the first connection portion coincides with the projection of the outer edge 131 of the gap (projected in the direction opposite to the first direction Z) and completely blocks the gap 13, so that when the cantilever beam 12 is viewed from the side away from the base layer 11, the gap 13 cannot be seen. The first connection portion 141 does not extend in a straight line in the gap width direction X (perpendicular to the first direction Z), but extends in a winding manner, for example, along a broken line or a curve. The winding length of the first connection portion 141 is greater than the width of the gap 13, so that the first connection portion 141 has a certain stretchability, giving the cantilever beam 12 a larger deformation space. Among them, the winding length refers to the total length of the extension path of the first connection portion 141 in the gap width direction X, that is, Figure 2 The total length of the red polyline.

[0029] Please refer to Figure 1 and Figure 4The above-mentioned MEMS piezoelectric acoustic device 10 uses a flexible connection layer 14 to connect two adjacent cantilever beams 12. The first connection portion 141 on the flexible connection layer 14 facing the gap 13 completely blocks the gap 13, thereby achieving complete closure of the gap 13, thereby significantly improving the low-frequency performance of the MEMS piezoelectric acoustic device 10. The winding length of the first connection portion 141 along the gap width direction X is greater than the width of the gap 13, so that the flexible connection layer 14 has a lower elastic coefficient and a certain stretchability, and has less restriction and influence on the cantilever beam 12 during deformation, which can give the cantilever beam 12 a larger deformation space and replace the cantilever beam 12 to bear most of the strain, thereby ensuring the sensitivity of the MEMS piezoelectric acoustic device 10. Therefore, the above-mentioned MEMS piezoelectric acoustic device 10 has high sensitivity and excellent low-frequency performance.

[0030] Optionally, see Figure 1 and Figure 2 The first connection portion 141 extends in a broken line along the gap width direction X, and the first connection portion 141 has a plurality of continuous turning angles θ, and the continuous turning angles θ are right angles or obtuse angles.

[0031] The first connection portion 141 extends in a broken line along the gap width direction X and turns multiple times. The first connection portion 141 extending in a broken line is easier to prepare, and multiple turns can make the winding length of the first connection portion 141 longer, thereby giving the cantilever beam 12 a larger deformation space. The first connection portion 141 forms a continuous turning angle θ at the turning position. The continuous turning angle θ is greater than or equal to 90° to further reduce the difficulty of processing.

[0032] Optionally, a height H1 of the first connection portion is not less than a height H2 of the gap.

[0033] The higher first connection portion 141 can improve the flexibility of the MEMS piezoelectric acoustic device 10, thereby further improving the sensitivity and low-frequency performance of the MEMS piezoelectric acoustic device 10. Preferably, the height H1 of the first connection portion is greater than or equal to 20 μm.

[0034] Optionally, the flexible connection layer 14 is further divided into two second connection parts 142 , and the two second connection parts 142 are respectively connected to the first connection part 141 , and the two second connection parts 142 are also respectively connected to the upper surfaces of two adjacent cantilever beams 12 .

[0035] The first connection portion 141 is connected to two adjacent cantilever beams 12 through two second connection portions 142, thereby being fixed on the cantilever beam 12. The second connection portion 142 is attached to the upper surface of the cantilever beam 12, which can improve the reliability of the connection between the flexible connection layer 14 and the cantilever beam 12.

[0036] For another aspect of the present application, please refer to Figure 5, providing a method for preparing a MEMS piezoelectric acoustic device, comprising: S100: providing a base layer, and forming a piezoelectric film stack along a first direction on the base layer.

[0037] Please refer to Figure 6 The first direction Z is preferably a direction perpendicular to the upper surface of the substrate layer 11. The piezoelectric film stack 15 includes at least two electrode layers 121 and at least one piezoelectric layer 122. The electrode layers 121 and the piezoelectric layers 122 are alternately stacked on the substrate layer 11 along the first direction Z, and the electrode layers 121 are distributed on both sides of each piezoelectric layer 122. Of course, the piezoelectric film stack 15 may also include other film layers.

[0038] The film layers in the piezoelectric film stack 15 may be formed by material deposition, for example, by a plasma enhanced chemical vapor deposition (PECVD) process.

[0039] S200: performing patterning on the piezoelectric film stack to form a gap, wherein the gap penetrates the piezoelectric film stack along a first direction and a second direction perpendicular to the first direction, respectively, to divide the piezoelectric film stack into at least two sub-piezoelectric film stacks.

[0040] Please refer to Figure 7 , the complete piezoelectric film stack 15 is divided by the gap 13, so that the piezoelectric film stack 15 is divided into two sub-piezoelectric film stacks 151. It can be understood that if the number of the gap 13 is one, the piezoelectric film stack 15 is divided into two sub-piezoelectric film stacks 151; if the number of the gap 13 is two or more, the two or more gaps 13 cooperate with each other to divide the piezoelectric film stack 15 into multiple sub-piezoelectric film stacks 151.

[0041] The graphic processing can adopt a photolithography + etching process. First, a layer of photoresist is coated on the surface of the piezoelectric thin film stack 15, and the photoresist is exposed and developed to form a photoresist layer with etched holes. The piezoelectric thin film stack 15 is then etched through the etched holes to transfer the etched holes to the piezoelectric thin film stack 15 to form a gap 13. After the gap 13 is formed, the photoresist layer is removed.

[0042] S300: forming a supporting film on the sub-piezoelectric film stack, and performing a patterning process on the supporting film to form a supporting layer, wherein the supporting layer is provided with two first through holes, one first through hole exposing the sub-piezoelectric film stack on one side of the gap, and the other first through hole exposing the sub-piezoelectric film stack on the other side of the gap, and the upper surface of the supporting layer facing the gap is uneven.

[0043] Please refer to Figure 8 and Fig. 9, the support film 16 can also be formed by material deposition, and the support film 16 can be one layer, two layers or multiple layers. The complete support film 16 is patterned to form a support layer 161. The patterning method is not described here. The support layer 161 serves as a support skeleton to support the flexible connection layer 14 formed subsequently. At the same time, the first through hole 1611 on the support layer 161 exposes the cantilever beams 12 on both sides of the gap 13, so that when the flexible connection layer 14 is formed later, the flexible connection layer 14 can be in contact with and fit the sub-piezoelectric film stack 151, thereby achieving a fitting connection. The first through hole 1611 can expose the surface of the sub-piezoelectric film stack 151, or the side of the sub-piezoelectric film stack 151 corresponding to the gap 13, or the surface of the sub-piezoelectric film stack 151 and the side of the corresponding gap 13 are exposed at the same time. The upper surface of the support layer 161 facing the gap 13 is not flat, that is, it is not a plane.

[0044] S400: forming a flexible film on the support layer, and performing patterning on the flexible film to form a flexible connection layer, wherein two ends of the flexible connection layer are respectively connected to the sub-piezoelectric film stack exposed by the two first through holes, and a first connection portion is divided on the flexible connection layer, the outer edge of the first connection portion coincides with the outer edge projection of the gap and completely blocks the gap, the winding length of the first connection portion along the third direction is greater than the width of the gap along the third direction, and the third direction is perpendicular to the first direction and the second direction, respectively.

[0045] Please refer to Fig.10 and Fig.11 , a complete flexible film 17 is formed on the support layer 161. The material of the flexible film 17 needs to have good covering ability and conformally cover the support layer 161 and the surface of the underlying film layer exposed by the support layer 161 as much as possible. The flexible film 17 is patterned to retain only the flexible material near the gap 13, and to ensure that the remaining flexible material covers the sub-piezoelectric film stack 151 on both sides of the gap 13, thereby obtaining a flexible connection layer 14 connected to the sub-piezoelectric film stack 151.

[0046] The area of ​​the flexible connection layer 14 facing the gap 13 is the first connection portion 141. The outer edge 1411 of the first connection portion overlaps with the outer edge 131 of the gap in projection and completely blocks the gap 13, so that the gap 13 cannot be seen when the sub-piezoelectric film stack 151 is viewed from the side of the sub-piezoelectric film stack 151 away from the base layer 11. Since the upper surface of the area of ​​the support layer 161 facing the gap 13 is uneven, the first connection portion 141 does not extend in a straight line in the third direction (i.e., the aforementioned gap width direction X), but extends in a winding manner. The winding length of the first connection portion 141 is greater than the width of the gap 13, so that the first connection portion 141 can have a certain degree of stretchability after the support layer 161 is released.

[0047] S500: forming a back cavity corresponding to the position of the gap on the base layer, wherein the back cavity suspends the sub-piezoelectric film stack to form a cantilever beam, and the width of the back cavity along the third direction is greater than the width of the gap.

[0048] Please refer to Fig.12 The back cavity 111 can be prepared by an etching process. The back cavity 111 allows a portion of the sub-piezoelectric film stack 151 to be suspended, thereby forming a cantilever beam 12.

[0049] S600: releasing the support layer through the back cavity so that the flexible connection layer is suspended.

[0050] Please refer to Figure 1 , chemicals capable of dissolving the support layer 161 are introduced into the back cavity 111 , and the chemicals dissolve the support layer 161 after contacting the support layer 161 , thereby achieving the release of the support layer 161 .

[0051] The preparation method of the MEMS piezoelectric acoustic device is simple and easy to implement. The MEMS piezoelectric acoustic device 10 prepared by the preparation method of the MEMS piezoelectric acoustic device has high sensitivity and excellent low-frequency performance.

[0052] Optionally, see Fig.10 and Fig.11 A second through hole 1612 is further provided on the support layer 161 . The second through hole 1612 exposes the base layer 11 below the gap 13 and penetrates the support layer 161 along the second direction Y.

[0053] The area of ​​the supporting film 16 facing the gap 13 is patterned to form a second through hole 1612. The second through hole 1612 and the first through hole 1611 are preferably obtained simultaneously in one patterning process. The existence of the second through hole 1612 enables the flexible connection layer 14 to cover not only the surface of the supporting layer 161, but also the hole wall of the second through hole 1612 and the base layer 11 exposed by the second through hole 1612. Therefore, the winding length of the first connection portion 141 of the flexible connection layer 14 is effectively increased, and it is easy to achieve in terms of process.

[0054] Optionally, the thickness of the support layer 161 is greater than or equal to 20 μm. This arrangement can obtain a higher first connecting portion 141 , thereby improving the flexibility of the MEMS piezoelectric acoustic device 10 .

[0055] Optionally, please refer to Figure 6 The first through hole 1611 is located above the sub-piezoelectric film stack 151 , and both ends of the flexible connection layer 14 respectively cover the upper surface of the sub-piezoelectric film stack 151 .

[0056] This arrangement can improve the reliability of the connection between the flexible connection layer 14 and the sub-piezoelectric film stack 151. The width of the first through hole 1611 can be set larger, thereby increasing the contact area between the flexible connection layer 14 and the sub-piezoelectric film stack 151.

[0057] Alternatively, if Fig.12 As shown in the dotted line area, the support layer 161 wraps the corner of the piezoelectric film stack 151 formed by the gap 13. Figure 1 When the supporting layer 161 is released, the supporting layer 161 between the second connecting portion 142 and the cantilever beam 12 can be released smoothly.

[0058] Optionally, see Figure 1 , Fig.12 and Fig.13 , the material of the supporting film 16 is silicon oxide.

[0059] Providing a base layer and forming a piezoelectric film stack along a first direction on the base layer comprises: S110: providing a silicon substrate, and forming a silicon oxide film on the silicon substrate.

[0060] S120: forming a piezoelectric thin film stack on the silicon oxide film.

[0061] The back cavity 111 penetrates the silicon substrate 112 and the silicon oxide film 113. Since the silicon substrate 112 and the silicon oxide film 113 are made of different materials, the back cavity 111 can be formed in two steps. First, a sub-back cavity 1111 is formed on the silicon substrate 112 to expose the silicon oxide film 113, and then another sub-back cavity 1111 is formed on the silicon oxide film 113. The two sub-back cavities 1111 together constitute the back cavity forming the cantilever beam 12. The silicon oxide film 113 is made of the same material as the supporting film 16. The same chemical can be used to simultaneously etch the silicon oxide film 113 and the supporting layer 161 formed by the supporting film 16, thereby releasing the supporting layer 161.

[0062] Please refer to Fig. 9 The silicon oxide film 113 is usually grown by a thermal oxidation process, and the support film 16 is usually formed by deposition by a process such as PECVD. Therefore, the density of the support layer 161 is not as high as that of the silicon oxide film 113, and the etching speed of the support layer 161 is faster than that of the silicon oxide film 113. When forming the second through hole 1612, the difference in etching rate can be used to stop on the surface of the silicon oxide film 113. The partial over-etching of the silicon oxide film 113 caused by etching the support film 16 does not affect the subsequent process.

[0063] It should be understood that, although the various steps in the above flowchart are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear description in this article, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowchart may include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0064] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A MEMS piezoelectric acoustic device, characterized in that: include: A base layer and at least two cantilever beams arranged on the base layer, with a gap between two adjacent cantilever beams; It also includes a flexible connection layer, which is located in the gap and / or on the side of the cantilever beam away from the base layer, and the two ends of the flexible connection layer are respectively connected to two adjacent cantilever beams. The flexible connection layer is divided into a first connection part, and the outer edge of the first connection part overlaps with the projection of the outer edge of the gap and completely blocks the gap. The winding length of the first connection part along the gap width direction is greater than the width of the gap.

2. The MEMS piezoelectric acoustic device according to claim 1, characterized in that: The first connecting portion extends in a broken line along the gap width direction, and the first connecting portion has a plurality of continuous corners, and the continuous corners are right angles or obtuse angles.

3. The MEMS piezoelectric acoustic device according to claim 1, characterized in that: The flexible connection layer is further divided into two second connection parts, the two second connection parts are respectively connected to the first connection part, and the two second connection parts are also respectively bonded and connected to the upper surfaces of two adjacent cantilever beams.

4. The MEMS piezoelectric acoustic device according to claim 1, characterized in that: The height of the first connecting portion is not less than the height of the gap.

5. A method for preparing a MEMS piezoelectric acoustic device, characterized in that: include: Providing a base layer, and forming a piezoelectric film stack along a first direction on the base layer; Performing a patterning process on the piezoelectric film stack to form a gap, wherein the gap penetrates the piezoelectric film stack along the first direction and a second direction perpendicular to the first direction, respectively, so as to divide the piezoelectric film stack into at least two sub-piezoelectric film stacks; A support film is formed on the sub-piezoelectric film stack, and the support film is patterned to form a support layer, wherein two first through holes are provided on the support layer, one of the first through holes exposes the sub-piezoelectric film stack on one side of the gap, and the other first through hole exposes the sub-piezoelectric film stack on the other side of the gap, and the upper surface of the support layer facing the gap is uneven; A flexible film is formed on the support layer, and the flexible film is patterned to form a flexible connection layer, wherein two ends of the flexible connection layer are respectively connected to the sub-piezoelectric film stack exposed by the two first through holes, a first connection portion is divided on the flexible connection layer, an outer edge of the first connection portion overlaps with the outer edge projection of the gap and completely blocks the gap, a winding length of the first connection portion along a third direction is greater than a width of the gap along the third direction, and the third direction is perpendicular to the first direction and the second direction respectively; forming a back cavity corresponding to the position of the gap on the base layer, wherein the back cavity suspends the sub-piezoelectric film stack to form a cantilever beam, and the width of the back cavity along the third direction is greater than the width of the gap; The supporting layer is released through the back cavity so that the flexible connection layer is suspended in the air.

6. The method for preparing a MEMS piezoelectric acoustic device according to claim 5, characterized in that: The support layer is also provided with a second through hole, which exposes the base layer below the gap and penetrates the support layer along the second direction.

7. The method for preparing a MEMS piezoelectric acoustic device according to claim 6, characterized in that: The thickness of the support layer is greater than or equal to 20 μm.

8. The method for preparing a MEMS piezoelectric acoustic device according to claim 5, characterized in that: The first through hole is located above the sub-piezoelectric film stack, and two ends of the flexible connection layer respectively cover the upper surface of the sub-piezoelectric film stack.

9. The method for preparing a MEMS piezoelectric acoustic device according to claim 8, characterized in that: The support layer wraps the corners of the sub-piezoelectric film stack formed by the gap.

10. The method for preparing a MEMS piezoelectric acoustic device according to claim 5, characterized in that: The material of the supporting film is silicon oxide; The step of providing a base layer and forming a piezoelectric film stack on the base layer along a first direction comprises: Providing a silicon substrate, and forming a silicon oxide thin film on the silicon substrate; A piezoelectric thin film stack is formed on the silicon oxide thin film.

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