Piezoelectric MEMS acoustic device

Abstract

The invention belongs to the field of acoustic transducers, and particularly relates to a piezoelectric MEMS acoustic device. The device comprises a slotted substrate, a bonding pad and a protective layer, the bonding pad is arranged on the slotted substrate, and the protective layer is deposited on the slotted substrate; the slotted base body is of a single-layer slotted structure or a double-layer slotted structure; each of the single-layer slotted structure and the double-layer slotted structure comprises a substrate, an insulating layer, a silicon substrate, an electrode layer and a piezoelectric layer; the insulating layer is arranged above the substrate, the silicon substrate is deposited on the insulating layer, the electrode layers and the piezoelectric layers are alternately stacked to form a stacked body and are stacked on the silicon substrate, and the uppermost layer and the lowermost layer of the stacked body are the electrode layers; the piezoelectric MEMS acoustic sensor solves the problem that an existing piezoelectric MEMS acoustic sensor is high in resonant frequency and difficult to meet the low-frequency working requirement, and popularization and application of the piezoelectric MEMS acoustic sensor in a low-frequency band are facilitated.

Description

Technical Field

[0001] The invention belongs to the field of acoustic transducers, and in particular relates to a piezoelectric MEMS acoustic device. Background Art

[0002] Sensors based on piezoelectric films have been one of the research hotspots in the field of MEMS sensors in recent years. Piezoelectric MEMS acoustic devices use the piezoelectric effect of piezoelectric films and the bending vibration of the composite structure formed by piezoelectric films and silicon substrates to achieve the conversion of electrical energy and mechanical energy, and transmit and receive sound waves through mechanical energy transfer with the surrounding fluid medium. They have the characteristics of small size, compact structure, adjustable shape, easy integration with circuits, suitable for 2D phase control and 3D imaging, no need for DC bias, fast response speed, and no electromagnetic interference. Overseas countries have developed ultrasonic time-of-flight (TOF) sensors, fingerprint recognition sensors, portable medical imaging equipment, etc. based on piezoelectric MEMS acoustic devices.

[0003] Piezoelectric MEMS acoustic devices are usually small in size and have high resonant frequencies. They usually operate above 100 kHz, while there are few designs with resonant frequencies below 100 kHz. Therefore, it is necessary to design new structures to reduce the resonant frequency and provide solutions for the application of piezoelectric MEMS acoustic devices in low-frequency bands. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a piezoelectric MEMS acoustic device, which comprises: a slotted substrate, a welding pad and a protective layer; the welding pad is arranged on the slotted substrate, and the protective layer is deposited on the slotted substrate; the slotted substrate is a single-layer slotted structure or a double-layer slotted structure; the slotted substrate comprises a substrate, an insulating layer, a silicon substrate, an electrode layer and a piezoelectric layer; the insulating layer is arranged above the substrate, the silicon substrate is deposited on the insulating layer, the electrode layers and the piezoelectric layers are alternately stacked to form a stacked body and stacked on the silicon substrate, and the topmost layer and the bottommost layer of the stacked body are both electrode layers.

[0005] Preferably, when the slit substrate is a single-layer slit structure, the stacked body is divided into a disc body, a connector and a pad carrier; the disc body is connected to the pad carrier through the connector, and the pad is arranged on the pad carrier; a plurality of slits are evenly arranged on the disc body along the radial direction.

[0006] Preferably, when the slit base is a double-layer slit structure, the stacked body is divided into a circular ring body, a connecting body and a pad carrier, the circular ring body is connected to the pad carrier through the connecting body, and the pad is arranged on the pad carrier; the circular ring body is composed of an inner disk, a bridging structure and an outer ring, and the inner disk is connected to the outer ring through multiple bridging structures; multiple slits are evenly arranged on the inner disk along the radial direction; a slit is arranged between the two bridging structures, and the slit between the bridging structures is connected to the slit on the inner disk and is located on the same straight line.

[0007] Furthermore, a portion of the insulating layer and the substrate is dug out below the slit to form a back cavity, and the back cavity is communicated with the slit.

[0008] Furthermore, a pad is provided on each electrode layer at the pad carrier.

[0009] Furthermore, a funnel-shaped opening which is larger at the top and narrower at the bottom is arranged in the center of the disc body.

[0010] Furthermore, a funnel-shaped opening which is larger at the top and narrower at the bottom is arranged at the center of the inner disc.

[0011] Preferably, the piezoelectric layer materials include AlN, PZT, AlScN, KNN, PVDF, LN, PMN-PT and ZnO; the electrode layer materials include Au, Pt, Mo, Al, Ti, Ag, Cu and Ni; the pad materials include Au, Pt, Mo, Al, Ti, Ag, Cu and Ni; the materials of the silicon substrate and the backing are Si, SiC, SiO2 or metal materials; the protective layer and the insulating layer materials include SiO2, Si3N4 and AlN.

[0012] The beneficial effects of the present invention are as follows: the present invention can improve the sensitivity of the device by adding a piezoelectric layer, changing the single piezoelectric layer structure into a double piezoelectric layer or even a multi-piezoelectric layer structure; by adding slits to the structure, the resonant frequency of the structure can be reduced while keeping the size unchanged, thereby solving the problem that the existing piezoelectric MEMS acoustic sensor has a high resonant frequency and is difficult to meet the low-frequency working requirements, so that the device can better meet the application requirements of sound receivers and the like in the low-frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a partial structural cross-sectional view of a piezoelectric MEMS acoustic device when the slotted substrate in the present invention is a single-layer slotted structure;

[0014] Figure 2 It is a structural schematic diagram of a piezoelectric MEMS acoustic device when the slotted substrate in the present invention is a single-layer slotted structure;

[0015] Figure 3 It is a top view of the piezoelectric MEMS acoustic device when the slotted substrate is a single-layer slotted structure in the present invention;

[0016] Figure 4 It is a schematic diagram of a piezoelectric MEMS acoustic device when the slotted substrate in the present invention is a double-layer slotted structure;

[0017] Figure 5 A top view of a piezoelectric MEMS acoustic device when the slotted substrate is a double-layer slotted structure in the present invention;

[0018] Figure 6 A partial structural cross-sectional view of a piezoelectric MEMS acoustic device with double piezoelectric layers in the present invention;

[0019] Figure 7 It is a schematic diagram of the structure of a piezoelectric MEMS acoustic device with double piezoelectric layers in the present invention;

[0020] Figure 8 It is a top view of the piezoelectric MEMS acoustic device with double piezoelectric layers in the present invention. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] The present invention proposes a piezoelectric MEMS acoustic device. The main idea of ​​the present invention is to use a slotted structure as the main structure. The piezoelectric layer can also be selected as one or more layers as needed. First, a multi-layer composite film is grown on an SOI wafer or a high-resistance silicon wafer, including electrodes, piezoelectric layers, etc. The electrodes and piezoelectric layers are grown alternately to form a multi-layer composite film. After the film is grown, the multi-layer composite film is patterned using photolithography and etching technology to form a basic device structure. After the patterning, a protective layer is grown to protect the electrode and the piezoelectric layer. After the protective layer is grown, the protective layer and the silicon substrate are photolithographed and etched to pattern them, and the pad position is exposed, and the pad is grown to form a slotted structure. The back cavity is processed by photolithography and etching methods to form a cantilever beam structure that can vibrate.

[0023] like Figure 1 As shown, the piezoelectric MEMS acoustic device includes: a slotted substrate, a pad and a protective layer; the pad is arranged on the slotted substrate, and the protective layer is deposited on the slotted substrate; the slotted substrate is a single-layer slotted structure or a double-layer slotted structure; the single-layer slotted structure and the double-layer slotted structure both include a substrate, an insulating layer, a silicon substrate, an electrode layer and a piezoelectric layer; the insulating layer is arranged above the substrate, the silicon substrate is deposited on the insulating layer, the electrode layer and the piezoelectric layer are alternately stacked to form a stacked body and stacked on the silicon substrate, and the topmost layer and the bottommost layer of the stacked body are both electrode layers.

[0024] In some preferred embodiments, Figure 1 , Figure 2 and Figure 3As shown, when the slit substrate is a single-layer slit structure, the stacked body is divided into a disc body, a connector and a pad carrier; the disc body is connected to the pad carrier through the connector, and the pad is arranged on the pad carrier; a plurality of slits are evenly arranged on the disc body along the radial direction. Part of the insulating layer and the substrate are dug out below the slit to form a back cavity, and the back cavity is connected to the slit; a pad is provided on each electrode layer at the pad carrier, so the number of pads is the same as the number of electrode layers. Preferably, a slit is provided in the center of the disc body, and the slit is a funnel-shaped opening that is larger at the top and narrower at the bottom.

[0025] Figure 1 FIG. 1 is a partial structural cross-sectional diagram of a piezoelectric MEMS acoustic device when the slotted substrate is a single-layer slotted structure, such as Figure 1 As shown, 101 and 110 are pads, 102 is an upper electrode, 103 is a piezoelectric layer, 104 is a lower electrode, 105 is a silicon substrate, 106 is an insulating layer, 107 is a substrate, 108, 109, 112 and 113 are protective layers, 111 is a slit, and 114 is a back cavity.

[0026] Figure 2 Schematic diagram of the structure of the piezoelectric MEMS acoustic device when the slotted substrate is a single-layer slotted structure, Figure 2 As shown, 201 and 208 are pads, 202 is an upper electrode, 203 is a piezoelectric layer, 204 is a lower electrode, 205 is a silicon substrate, 206 is an insulating layer, 207 is a substrate, 209 is a slit, and 210 is an opening. In order to more intuitively display the three-dimensional structure, Figure 2 No protective layer is introduced in the present invention. In actual design, the protective layer can be deposited and patterned as needed.

[0027] When the size of the slit exceeds the center circular multilayer composite film, a beam structure needs to be added to realize the electrical connection between the fan-shaped structure obtained by dividing the circle and the pad.

[0028] In some preferred embodiments, Figure 4 and Figure 5As shown, when the slit matrix is ​​a double-layer slit structure, the stacked body is divided into a ring body, a connector and a pad carrier, the ring body is connected to the pad carrier through the connector, and the pad is arranged on the pad carrier; the ring body is composed of an inner disk, a bridge structure and an outer ring, and the inner disk is connected to the outer ring through a plurality of bridge structures; preferably, the number of bridge structures can be adjusted as needed, with the normal through the center of the middle through hole as the symmetry point, and the center is symmetrically evenly distributed. There are multiple slits evenly arranged radially on the inner disk; a slit is arranged between the two bridge structures, and the slit between the bridge structures is connected to the slit on the inner disk and is located on the same straight line. Part of the insulating layer and the substrate are dug out below the slit to form a back cavity, and the back cavity is connected to the slit. A pad is provided on each electrode layer at the pad carrier, so the number of pads is the same as the number of electrode layers. Preferably, a slit is arranged at the center of the inner disk, and the slit is a funnel-shaped opening that is large at the top and narrow at the bottom.

[0029] Figure 4 Schematic diagram of a piezoelectric MEMS acoustic device when the slot size is large, that is, when the slot substrate is a double-layer slot structure, as shown in FIG. Figure 4 As shown, 301 and 310 are pads, 302 is an upper electrode, 303 is a piezoelectric layer, 304 is a lower electrode, 305 is a silicon substrate, 306 is an insulating layer, 307 is a substrate, and 308 and 309 are slits. In order to more intuitively display the three-dimensional structure, Figure 4 No protective layer is introduced in the present invention. In actual design, the protective layer can be deposited and patterned as needed.

[0030] The above embodiments are all cases where the piezoelectric layer has only one layer. In some preferred embodiments, the piezoelectric layer may have two layers or even more layers. When the piezoelectric layer has two layers, such as Figure 6 and Figure 8 As shown, Figure 6 401, 414 and 416 are pads, 402 is an upper electrode, 403 is a piezoelectric layer, 404 is a middle electrode, 405 is a piezoelectric layer, 406 is a lower electrode, 407 is a silicon substrate, 408 is an insulating layer, 409 is a substrate, 410, 411, 412, 415 and 417 are protective layers, 413 is an opening, and 418 is a back cavity. Figure 7 Shown Figure 6 Schematic diagram of the three-dimensional structure, where 501, 502 and 503 are pads, 504 is the upper electrode, 503 is the piezoelectric layer, 506 is the middle electrode, 507 is the piezoelectric layer, 511 is the lower electrode, 508 is the silicon substrate, 509 is the insulating layer, 510 is the substrate, 512 is the opening, and 513 is the slit. In order to show the three-dimensional structure more intuitively, Figure 6 No protective layer is introduced in the present invention. In actual design, the protective layer can be deposited and patterned as needed.

[0031] In some preferred embodiments, the piezoelectric layer materials include AlN (aluminum nitride), PZT (lead zirconate titanate), AlScN (scandium aluminum nitride), KNN (potassium sodium niobate), PVDF (polyvinylidene fluoride), LN (lithium niobate), PMN-PT (lead magnesium niobate-lead titanate) and ZnO (zinc oxide); the electrode layer materials include Au (gold), Pt (platinum), Mo (molybdenum), Al (aluminum), Ti (titanium), Ag (silver), Cu (copper) and Ni (nickel); the pad materials include Au (gold), Pt (platinum), Mo (molybdenum), Al (aluminum), Ti (titanium), Ag (silver), Cu (copper) and Ni (nickel); the materials of the silicon substrate and the substrate are Si (silicon), SiC (silicon carbide), SiO2 (silicon dioxide) or metal materials; the protective layer and the insulating layer materials include SiO2 (silicon oxide), Si3N4 (silicon nitride) and AlN (aluminum nitride).

[0032] In some preferred embodiments, the shape of the slotted base includes but is not limited to a ring or a disk, and other shapes such as a square or a polygon may also be selected.

[0033] The manufacturing method of the piezoelectric MEMS acoustic device with double piezoelectric layers can refer to the following process:

[0034] 1. Grow a multilayer composite film with a thickness of 300-600μm on an SOI wafer or a high-resistance silicon wafer, and sequentially grow (sputtering, evaporation) an electrode layer (molybdenum can be selected, thickness 200-400nm), a piezoelectric layer (AlN, PZT, AlScN, KNN, etc.) (thickness 1-3μm), an electrode layer (molybdenum can be selected, 200-400nm), a piezoelectric layer (AlN, PZT, AlScN, KNN, etc.) (thickness 1-3μm), and an electrode layer (molybdenum can be selected, 200-400nm) on a thinned silicon substrate.

[0035] 2. After the thin film is grown, the multilayer composite thin film is patterned using photolithography and etching techniques to form the basic device structure;

[0036] 3. After patterning, a protective layer is grown to protect the electrode and piezoelectric layer. AlN, SiO2, etc. can be selected with a thickness of 100 to 300 nm;

[0037] 4. After the protective layer is grown, the protective layer and the silicon substrate are photolithographically etched and patterned, and the pad position is exposed, and the pad is grown and a slit structure is formed;

[0038] 5. The back cavity is processed by photolithography and etching to form a cantilever beam structure that can vibrate.

[0039] The above embodiments further illustrate the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above embodiments are only preferred implementation modes of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A piezoelectric MEMS acoustic device, characterized in that: include: A slotted substrate, a soldering pad and a protective layer; the soldering pad is arranged on the slotted substrate, and the protective layer is deposited on the slotted substrate; the slotted substrate is a single-layer slotted structure or a double-layer slotted structure; the single-layer slotted structure and the double-layer slotted structure both include a substrate, an insulating layer, a silicon substrate, an electrode layer and a piezoelectric layer; the insulating layer is arranged above the substrate, the silicon substrate is deposited on the insulating layer, the electrode layers and the piezoelectric layers are alternately stacked to form a stack and stacked on the silicon substrate, and the topmost layer and the bottommost layer of the stack are both electrode layers.

2. A piezoelectric MEMS acoustic device according to claim 1, characterized in that: When the slotted substrate is a single-layer slotted structure, the stacked body is divided into a disc body, a connector and a pad carrier; the disc body is connected to the pad carrier through the connector, and the pad is arranged on the pad carrier; and a plurality of slots are evenly arranged on the disc body along the radial direction.

3. The piezoelectric MEMS acoustic device according to claim 1, characterized in that: When the slit base is a double-layer slit structure, the stacked body is divided into a ring body, a connector and a pad carrier. The ring body is connected to the pad carrier through the connector, and the pad is arranged on the pad carrier; the ring body is composed of an inner disk, a bridge structure and an outer ring, and the inner disk is connected to the outer ring through multiple bridge structures; multiple slits are evenly arranged on the inner disk along the radial direction; a slit is arranged between the two bridge structures, and the slit between the bridge structures is connected to the slit on the inner disk and is located on the same straight line.

4. A piezoelectric MEMS acoustic device according to claim 2 or 3, characterized in that: A portion of the insulating layer and the substrate is dug out below the slit to form a back cavity, and the back cavity is communicated with the slit.

5. A piezoelectric MEMS acoustic device according to claim 2 or 3, characterized in that: A pad is provided on each electrode layer at the pad carrier.

6. A piezoelectric MEMS acoustic device according to claim 2, characterized in that: A funnel-shaped opening which is larger at the top and narrower at the bottom is arranged in the center of the disc body.

7. The piezoelectric MEMS acoustic device according to claim 3, characterized in that: A funnel-shaped opening which is larger at the top and narrower at the bottom is arranged in the center of the inner disc.

8. The piezoelectric MEMS acoustic device according to claim 1, characterized in that: Piezoelectric layer materials include AlN, PZT, AlScN, KNN, PVDF, LN, PMN-PT and ZnO; electrode layer materials include Au, Pt, Mo, Al, Ti, Ag, Cu and Ni; pad materials include Au, Pt, Mo, Al, Ti, Ag, Cu and Ni; the materials of the silicon substrate and the backing are Si, SiC, SiO2 or metal materials; the protective layer and insulating layer materials include SiO2, Si3N4 and AlN.

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