Piezoelectric MEMS acoustic device and manufacturing method thereof

Abstract

The invention relates to the field of manufacturing of sensitive elements and sensors in the electronic core industry, in particular to a piezoelectric MEMS acoustic device and a manufacturing method thereof. The device structurally comprises a substrate, an insulating layer, a silicon substrate, a multi-layer composite film structure and a protective layer from bottom to top in sequence, wherein the multi-layer composite film structure is formed by alternately growing electrode layers and piezoelectric layers, and the first layer and the last layer of the multi-layer composite film are the electrode layers; a bonding pad is arranged on the multi-layer composite film structure; the protective layer covers the upper surface of the device; a suspended back cavity structure is arranged between the substrate and the insulating layer; the silicon substrate, the multi-layer composite film structure and the protective layer are connected through an opening communicated with the back cavity; according to the device provided by the invention, the volume of the piezoelectric material is increased mainly by adding the piezoelectric layer, and the energy conversion efficiency of the structure is effectively improved, so that the sensitivity of the transducer is improved.

Description

Technical Field

[0001] The present invention belongs to the field of sensitive element and sensor manufacturing in the core electronic industry, and specifically relates to a piezoelectric MEMS acoustic device and a manufacturing method thereof. Background Art

[0002] Piezoelectric MEMS acoustic devices are acoustic sensors that apply the piezoelectric effect to micro-electromechanical systems (MEMS). They use the bending vibration of the composite structure formed by the piezoelectric film and the silicon substrate to achieve the conversion of electrical energy into mechanical energy, and transmit and receive sound waves through the mechanical energy transfer with the surrounding fluid medium. Currently, piezoelectric MEMS acoustic devices are widely used in smart devices, audio equipment, medical equipment and other fields. Compared with traditional acoustic devices, piezoelectric MEMS acoustic devices have the advantages of compact structure, adjustable shape, no need for DC voltage, easy integration with circuits, fast response speed, and no electromagnetic interference.

[0003] At present, the structures used in piezoelectric MEMS acoustic devices are mostly cantilever beams or diaphragm structures, which have reliable stability, dustproofness and moisture resistance. The above-mentioned piezoelectric MEMS acoustic devices mainly have the problem of low transmission and receiving sensitivity. Although the sensitivity can be improved by optimizing the design scheme, the improvement is very limited. Therefore, a new structure is expected to effectively improve the sensitivity of the device. Summary of the invention

[0004] In view of the sensitivity problem existing in the field of existing piezoelectric MEMS acoustic devices, the present invention provides a piezoelectric MEMS acoustic transducer structure based on a dual piezoelectric layer and a manufacturing method thereof; the main idea of ​​the present invention is based on a dual piezoelectric layer structure, and the piezoelectric layer can be further increased as needed, and more piezoelectric layer structures are similar to the design idea of ​​the present invention; specifically:

[0005] A piezoelectric MEMS acoustic device, the device structure from bottom to top is: a substrate, an insulating layer, a silicon substrate, a multi-layer composite membrane structure, and a protective layer; wherein the multi-layer composite membrane structure is formed by alternating growth of an electrode layer and a piezoelectric layer, and the first layer and the last layer of the multi-layer composite membrane are both electrode layers; a solder pad is arranged on the multi-layer composite membrane structure; the protective layer covers the upper surface of the device; a suspended back cavity structure is arranged in the middle of the substrate and the insulating layer; the silicon substrate, the multi-layer composite membrane structure, and the protective layer are connected via an opening connected to the back cavity.

[0006] Preferably, the piezoelectric MEMS acoustic device further comprises a beam structure, which is evenly distributed around the device opening and symmetrical with the device opening as the center point;

[0007] Furthermore, the beam structure adopts a disconnected beam structure, that is, the beam is disconnected from the multi-layer composite membrane structure.

[0008] A method for manufacturing a piezoelectric MEMS acoustic device, the method comprising:

[0009] S1. Growing a multilayer composite film on an SOI wafer or a high-resistance silicon wafer;

[0010] S2, performing photolithography and etching on the multi-layer composite film to pattern the multi-layer composite film;

[0011] S3, growing a protective layer on the patterned composite film;

[0012] S4, performing photolithography and etching on the protective layer to pattern the protective layer;

[0013] S5, growing a pad on the reserved area of ​​the patterned protection layer;

[0014] S6. Perform back cavity processing on the device obtained in S5 to form a suspended diaphragm structure that can vibrate.

[0015] The beneficial effects of the present invention are:

[0016] The present invention increases the volume of the piezoelectric material and effectively improves the energy conversion efficiency of the structure by introducing a multi-layer composite membrane structure, thereby solving the problem of relatively low sensitivity of the piezoelectric MEMS acoustic sensor, especially in terms of emission sensitivity; by introducing a centrally symmetrical beam structure, the problem of unbalanced distribution of the diaphragm vibration displacement is effectively solved; by introducing a beam structure disconnected from the multi-layer composite membrane, the influence of the vibration anti-phase zone on the structural sensitivity is effectively eliminated; and a design idea is provided for improving the sensitivity of the piezoelectric MEMS acoustic sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A cross-sectional view of a basic embodiment of a dual-piezoelectric-layer piezoelectric MEMS acoustic device;

[0018] Figure 2 is a schematic diagram of the structure of a basic embodiment, and Figure 1 The difference is that in order to show the three-dimensional structure more intuitively, Figure 2 No protective layer is introduced;

[0019] Figure 3 It is a structural schematic diagram of an embodiment in which a symmetrical beam structure is introduced into the basic embodiment;

[0020] Figure 4 A cross-sectional view of an embodiment that introduces a symmetrical beam structure and a disconnected beam structure based on a basic embodiment;

[0021] Figure 5It is a structural schematic diagram of an embodiment that introduces a symmetrical beam structure and a disconnected beam structure on the basis of a basic embodiment;

[0022] Figure 6 A top view of a basic embodiment;

[0023] Figure 7 A top view of an embodiment in which a symmetrical beam structure is introduced on the basic embodiment;

[0024] Figure 8 A top view of an embodiment that introduces a symmetrical beam structure and a disconnected beam structure based on a basic embodiment;

[0025] Icons: 01-pad one, 02-upper electrode, 03-piezoelectric layer, 04-middle electrode, 05-piezoelectric layer, 06-lower electrode, 07-silicon substrate, 08-insulating layer, 09-substrate, 10, 11, 12-protective layer, 13-opening, 14-back cavity, 15-pad two, 16-pad three, 17-beam, 18-symmetric beam one, 19-symmetric beam two, 20-symmetric beam three, 21-multilayer composite thin film structure, 22-disconnection point of the disconnected beam structure. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution, characteristics and advantages of the present invention more clear, the present invention is further described below in conjunction with the accompanying drawings and embodiments. It is obvious that the embodiments mentioned are only some embodiments of the present invention rather than all embodiments. All other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0027] A piezoelectric MEMS acoustic transducer device with multiple piezoelectric layers:

[0028] Specifically, it includes: a substrate, an insulating layer, a silicon substrate, a multi-layer composite film structure, a protective layer, and a pad structure; the composite film includes an electrode layer and a piezoelectric layer grown alternately; the cross-sectional view of the basic structure of the device is as follows Figure 1 As shown, the structural diagram is as follows Figure 2 As shown, the top view is Figure 6 As shown;

[0029] Preferably, the piezoelectric MEMS acoustic device further comprises a beam structure uniformly distributed around the device opening and symmetrical with the device opening as the center point;

[0030] Specifically, Figure 3As shown, in order to reduce the influence of the beam 17 for electrode lead-out on the uniformity of bending vibration, beam structures 18, 19 and 20 are also designed in three symmetrical directions. In this embodiment, four beams are used as an example to illustrate the design. The number of beams can be adjusted as needed. The positions of the beams need to be symmetrically distributed with the center of the middle through hole as the symmetrical point. Here, the beams 17, 18, 19 and 20 are connected to the multilayer composite film structure 21. Figure 3 The structure shown combines the device base structure with the symmetrical beam structure. Figure 7 As shown, it is a preferred embodiment;

[0031] Furthermore, the beam structure adopts a disconnected beam structure, that is, the beam is disconnected from the multi-layer composite membrane structure, which is used to solve the problem that the deformation at the center position is in reverse phase with the edge position when the diaphragm is bent and vibrated;

[0032] Specifically, Figure 4 As shown, the upper electrode 02, the piezoelectric layers 03 and 05, the middle electrode 04, and the lower electrode 06 are not connected to the middle multilayer film structure 21; Figure 5 As shown, the beams 18, 19 and 20 are not connected to the multilayer membrane structure 21. Optionally, the connection between the lower electrode 06 and the piezoelectric layer 05 and the middle multilayer membrane structure 21 may be retained. Figure 5 The structure shown in Figure 3 The structure shown in the figure is combined with a broken beam structure, and the top view is as follows Figure 8 Shown is the most preferred embodiment.

[0033] An embodiment of a method for manufacturing a piezoelectric MEMS acoustic device is as follows:

[0034] Embodiment 1, a manufacturing step of a piezoelectric MEMS acoustic device with a central hole, comprising:

[0035] S1. Growing a multilayer composite film on an SOI wafer or a high-resistance silicon wafer;

[0036] Specifically, a silicon substrate is thinned, and an electrode layer, a piezoelectric layer, an electrode layer, a piezoelectric layer, and an electrode layer are grown on the thinned silicon substrate in sequence, and the electrode layer and the piezoelectric layer are grown alternately to form a multilayer composite film; optionally, the substrate and the backing material can be Si, SiC, SiO2 or a metal material; the electrode layer material can be Au, Pt, Mo, Al, Ti, Ag, Cu, Ni, and the electrode layer thickness is 200-400nm; the piezoelectric layer material can be AlN, PZT, AlScN, KNN, PVDF, LN, PMN-PT, ZnO, and the thickness is 1-3μm; the composite film thickness is 300-600μm;

[0037] S2, performing photolithography and etching on the multi-layer composite film to pattern the multi-layer composite film;

[0038] Specifically, for graphics, you can choose centrally symmetrical polygons such as circles, squares, hexagons, and octagons;

[0039] S3, growing a protective layer on the patterned composite film;

[0040] Specifically, in order to protect the electrode and the piezoelectric layer, a protective layer is grown. The materials of the protective layer and the insulating layer can be AlN, SiO2, Si3Ni4, and the thickness of the protective layer is 100 to 300 nm.

[0041] S4, performing photolithography and etching on the protective layer to pattern the protective layer;

[0042] S5, growing a pad on the reserved area of ​​the patterned protection layer;

[0043] Specifically, a pad is grown and an open-hole structure is formed, and the pad material can be Au, Pt, Mo, Al, Ti, Ag, Cu, Ni;

[0044] S6, performing back cavity processing on the device obtained in S5 to form a suspended diaphragm structure that can vibrate;

[0045] Specifically, the back cavity is processed by photolithography and etching to form a suspended diaphragm structure that can vibrate. Taking the hexagon as an example, when a hexagonal lower electrode, piezoelectric layer and upper electrode are used, the back cavity can be circular, or hexagonal or other centrally symmetrical polygons.

[0046] Embodiment 2, a manufacturing step of a piezoelectric MEMS acoustic device without a central hole, comprising:

[0047] S1. Growing a multilayer composite film on an SOI wafer or a high-resistance silicon wafer;

[0048] Specifically, a silicon substrate is thinned, and an electrode layer, a piezoelectric layer, an electrode layer, a piezoelectric layer, and an electrode layer are grown (including sputtering or evaporation) on the thinned silicon substrate in sequence, and the electrode layer and the piezoelectric layer are grown alternately to form a multilayer composite film; optionally, the substrate and the backing material can be Si, SiC, SiO2 or a metal material; the electrode layer material can be Au, Pt, Mo, Al, Ti, Ag, Cu, Ni, and the electrode layer thickness is 200-400nm; the piezoelectric layer material can be AlN, PZT, AlScN, KNN, PVDF, LN, PMN-PT, ZnO, and the thickness is 1-3μm; the composite film thickness is 300-600μm;

[0049] S2, performing photolithography and etching on the multi-layer composite film to pattern the multi-layer composite film;

[0050] Specifically, for graphics, you can choose centrally symmetrical polygons such as circles and squares;

[0051] S3, growing a protective layer on the patterned composite film;

[0052] Specifically, in order to protect the electrode and the piezoelectric layer, a protective layer is grown. The materials of the protective layer and the insulating layer can be AlN, SiO2, Si3Ni4, and the thickness of the protective layer is 100 to 300 nm.

[0053] S4, performing photolithography and etching on the protective layer to pattern the protective layer;

[0054] S5, growing a pad on the reserved area of ​​the patterned protection layer;

[0055] Specifically, a pad is grown and an open-hole structure is formed, and the pad material can be Au, Pt, Mo, Al, Ti, Ag, Cu, Ni;

[0056] S6, performing back cavity processing on the device obtained in S5 to form a suspended diaphragm structure that can vibrate;

[0057] Specifically, the back cavity is processed by photolithography and etching to form a suspended diaphragm structure that can vibrate. Taking the hexagon as an example, when a hexagonal lower electrode, piezoelectric layer and upper electrode are used, the back cavity can be circular, or hexagonal or other centrally symmetrical polygons.

[0058] The above-mentioned embodiments only describe some embodiments of the present invention. Those skilled in the art can conceive of various changes, modifications, substitutions and deformations of the embodiments without departing from the principles and spirit of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents, and the above-mentioned behaviors should all be included in the scope of protection of the present invention.

Claims

1. A piezoelectric MEMS acoustic device, characterized in that: The device structure is, from bottom to top, a substrate, an insulating layer, a silicon substrate, a multilayer composite film structure, and a protective layer; wherein the multilayer composite film structure is formed by alternating growth of an electrode layer and a piezoelectric layer, and the first layer and the last layer of the multilayer composite film are both electrode layers; a solder pad is provided on the multilayer composite film structure; the protective layer covers the upper surface of the device; a suspended back cavity structure is provided in the middle of the substrate and the insulating layer; the silicon substrate, the multilayer composite film structure, and the protective layer are connected via an opening connected to the back cavity.

2. The piezoelectric MEMS acoustic device according to claim 1, characterized in that: It also includes a beam structure, which is evenly distributed around the device opening and is symmetrical with the device opening as a center point.

3. The piezoelectric MEMS acoustic device according to claim 2, characterized in that: The beam structure adopts a disconnected beam structure, that is, the beam is disconnected from the multi-layer composite membrane structure.

4. The piezoelectric MEMS acoustic device according to claim 1, characterized in that: The opening is located in the center of the composite membrane structure and is narrower to wider from bottom to top.

5. The piezoelectric MEMS acoustic device according to claim 1, characterized in that: The thickness of the electrode layer is 200 to 400 nm, and the thickness of the piezoelectric layer is 1 to 3 μm.

6. The piezoelectric MEMS acoustic device according to claim 1, characterized in that: The electrode layer material is any one of Au, Pt, Mo, Al, Ti, Ag, Cu, and Ni; the piezoelectric layer material is any one of AlN, PZT, AlScN, KNN, PVDF, LN, PMN-PT, and ZnO; the protective layer and insulating layer material is any one of AlN, SiO2, and Si3Ni4; the pad material is any one of Au, Pt, Mo, Al, Ti, Ag, Cu, and Ni; the substrate is any one of Si, SiC, SiO2, and metal materials; the backing material is any one of Si, SiC, SiO2, and metal materials.

7. A method for manufacturing a piezoelectric MEMS acoustic device, the method being used to manufacture the piezoelectric MEMS acoustic device according to any one of claims 1 to 6, characterized in that: include: S1. Growing a multilayer composite film on an SOI wafer or a high-resistance silicon wafer; S2, performing photolithography and etching on the multi-layer composite film to pattern the multi-layer composite film; S3, growing a protective layer on the patterned composite film; S4, performing photolithography and etching on the protective layer to pattern the protective layer; S5, growing a pad on the reserved area of ​​the patterned protection layer; S6. Perform back cavity processing on the device behind the growth pad to form a suspended diaphragm structure that can vibrate.

8. The method for manufacturing a piezoelectric MEMS acoustic transducer with multiple piezoelectric layers as claimed in claim 7, characterized in that: The graphical shape is a circular structure.

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