Induced voltage value adjusting method of piezoelectric MEMS accelerometer

Abstract

According to the induced voltage value adjusting method of the piezoelectric MEMS accelerometer provided by the invention, after the preparation process of the piezoelectric MEMS accelerometer is completed, the capacitance value of each cantilever structure is finely adjusted by etching the upper electrode, so that the induced voltage value of the cantilever structure is consistent with the standard value, the natural inconsistency in a chip is overcome, and the performance of the piezoelectric MEMS accelerometer is improved. Induced voltage differences among cantilevers of the accelerometer are avoided, induced voltage differences among different devices in the same batch are avoided, an external voltage amplifier does not need to be adjusted, the adjusting difficulty of a peripheral matching circuit is reduced, the matching circuit is simplified, and production and manufacturing are easy.

Description

Technical Field

[0001] The present application relates to the field of MEMS technology, and in particular to a method for adjusting an induced voltage of a piezoelectric MEMS accelerometer. Background Art

[0002] Working principle of piezoelectric MEMS accelerometer: When vibrating, the mass block is subjected to the inertial force opposite to the acceleration direction, the cantilever beam is deformed, and the piezoelectric film on the cantilever beam is also strained, and corresponding induced charges are generated on the upper and lower electrodes. Since C=Q / V, when the capacitance is constant, the induced voltage signal is proportional to the induced charge, and is connected to the external circuit through a voltage amplifier to realize the conversion of acceleration to voltage; when working at a frequency far away from the resonant frequency point, the acceleration of the mass block is proportional to the induced voltage of the device, that is, detection is achieved.

[0003] Piezoelectric MEMS accelerometers mainly include four parts: a cantilever beam (or a suspended membrane), a frame, a mass block, and a piezoelectric sensitive structure. The cantilever beam can be a single beam or multiple symmetrically distributed beams, and the suspended membrane can be a ring-shaped or other centrally symmetrically distributed membrane. One end of the cantilever beam (or suspended membrane) is connected to the mass block, and the other end is connected to the frame. The connection between the cantilever beam (or suspended membrane) and the frame is covered with a piezoelectric sensitive structure, which is mainly a MIM capacitor composed of a piezoelectric film and upper / lower electrodes, in which the dielectric layer (piezoelectric film) converts strain into electrical signals. In addition, there are lead wires and PADs for the upper / lower electrodes on the frame.

[0004] Due to the non-ideality of the piezoelectric film and the consistency of the MEMS process, the actual induced voltage V between each cantilever will be different, and the induced voltage V between different devices in the same batch will also be different. In order to achieve accurate detection, balance the characteristics of each cantilever, and achieve standard output, it is generally necessary to adjust the external voltage amplifier. The voltage amplifier corresponding to each cantilever needs to be adjusted separately, which makes debugging difficult and the matching circuit more complicated. Summary of the invention

[0005] The purpose of the embodiments of the present application is to provide a method for adjusting the induced voltage of a piezoelectric MEMS accelerometer, so as to solve the problem that there will be differences in the induced voltage V between the actual cantilevers, and there will also be differences in the induced voltage V between different devices in the same batch. It is necessary to calibrate the external voltage amplifier. The voltage amplifier corresponding to each cantilever needs to be adjusted separately, which results in difficult debugging and complex matching circuits.

[0006] An embodiment of the present application provides a method for adjusting the induced voltage of a piezoelectric MEMS accelerometer, comprising:

[0007] After the piezoelectric MEMS accelerometer is prepared, the upper electrode is etched to change the capacitance value of the cantilever structure so that the induced voltage value of the cantilever structure is consistent with the standard value; wherein the piezoelectric MEMS accelerometer includes a vibration sensitive structure, a frame structure and a cantilever structure; the upper electrode of the cantilever structure is arranged close to the frame structure.

[0008] In the above technical solution, after the preparation process of the piezoelectric MEMS accelerometer is completed, the capacitance value of each cantilever structure is fine-tuned by etching the upper electrode, so that the induced voltage value of the cantilever structure is consistent with the standard value, which overcomes the natural inconsistency inside the chip, avoids the difference in induced voltage between the cantilevers of the accelerometer, avoids the difference in induced voltage between different devices in the same batch, does not need to adjust the external voltage amplifier, reduces the difficulty of adjusting the peripheral matching circuit, simplifies the matching circuit, and is easy to manufacture. Specifically, during the chip test or system debugging, the metal can be cut with a laser on the exposed upper electrode surface so that a small part of the metal electrode is disconnected from the output end, and then the effect of the cutting adjustment is confirmed by testing the induced voltage.

[0009] In some optional embodiments, etching the upper electrode includes:

[0010] Etching a first etching region of the upper electrode;

[0011] The first etching area is from the first side of the upper electrode close to the vibration sensitive structure to the connection between the cantilever structure and the frame structure.

[0012] In some optional embodiments, the larger the V' is, the closer the first etched region is to the connection portion, and the smaller the V' is, the closer the first etched region is to the first side, to the position of the upper electrode being etched.

[0013] Wherein, V'=V1-V0; V1 is the measured value of the induced voltage, and V0 is the standard value of the induced voltage.

[0014] In the above technical solution, a certain position of the first etched area of ​​the upper electrode is etched to change the capacitance value and the induced charge value of the cantilever structure. The determination of this position is related to V'. The reason is that when the vibration sensitive structure is subjected to the force, the cantilever structure will deform accordingly, and the deformation amount of each position of the first etched area of ​​the cantilever structure is different. The closer to the connection, the greater the deformation, and the farther away from the connection, the smaller the deformation. From a differential point of view, the induced charge generated by the piezoelectric sensitive structure at different positions of the cantilever is also different. The induced charge near the connection is the largest, and the capacitance of the piezoelectric sensitive structure is only related to the electrode area and the dielectric constant and thickness of the medium, and can be regarded as a uniform amount at different positions of the cantilever. When the area of ​​the upper electrode changes, the changes in the induced charge and capacitance are not synchronized, and the induced voltage can be adjusted accordingly. When a certain area of ​​the upper electrode near the connection is lost, the induced charge loss value is large, and the loss value of the capacitor is proportional to the area, and the induced voltage after laser adjustment is relatively large; when a certain area of ​​the upper electrode near the first side is lost, the induced charge loss value is small, and the loss value of the capacitor is proportional to the area, and the induced voltage after laser adjustment is relatively small. Therefore, when V' is larger, for example, V' is greater than 0, to reduce the induced voltage, a certain position of the upper electrode near the connection is etched; when V' is smaller, for example, V' is less than 0, to increase the induced voltage, a certain position of the upper electrode near the first side is etched.

[0015] In some optional embodiments, after etching the first etching region of the upper electrode, the induced voltage of the cantilever structure is:

[0016] V=(Q-Q') / (C-C')

[0017] Wherein, Q'=X·C'; Q is the induced charge before etching, Q' is the induced charge loss value after etching, C is the capacitance value before etching, and C' is the capacitance loss value after etching; X is the coefficient of different etching positions. In the first etching area, the value of X gradually increases from the first side to the connection.

[0018] In the above technical solution, the same area of ​​the upper electrode is cut at different positions, and the capacitance loss is the same. However, the greater the deformation, the greater the loss of the induced charge, and the smaller the deformation. The ratio of the induced charge loss value to the capacitance loss value is set as the coefficient X. The closer to the first side, the smaller the value of X, and the closer to the connection, the larger the value of X, so that the induced voltage of the cantilever structure after etching is determined to be V = (QX·C') / (C-C').

[0019] In some optional embodiments, etching the upper electrode includes:

[0020] When V' is less than 0, etching the second etching region of the upper electrode;

[0021] The second etching area is from the connection between the cantilever structure and the frame structure to the second side of the upper electrode away from the vibration sensitive structure; V'=V1-V0; V1 is the measured value of the induced voltage, and V0 is the standard value of the induced voltage.

[0022] In the above technical solution, the second etched area of ​​the upper electrode is the area where the cantilever structure is fixedly connected to the frame structure. Since the bottom of the substrate is thick and the load is large, the deformation of the second etched area can be ignored, and the induced charge can also be ignored. Etching a certain position of the second etched area of ​​the upper electrode can be considered to only reduce the capacitance without changing the total induced charge. When the induced charge remains unchanged, reducing the capacitance value can increase the value of the induced voltage. Therefore, when V' is less than 0, the second etched area of ​​the upper electrode can be etched to increase the induced voltage.

[0023] In some optional embodiments, after etching the second etching region of the upper electrode, the induced voltage of the cantilever structure is:

[0024] V=Q / (C-C')

[0025] Wherein, Q is the induced charge before etching, C is the capacitance value before etching, and C' is the capacitance loss value after etching.

[0026] In some optional embodiments, a piezoelectric MEMS accelerometer is prepared, comprising:

[0027] The lower electrode is deposited by sputtering on the front side of the SOI substrate; wherein the front side of the SOI substrate is a device layer, the middle layer of the SOI substrate is a buried oxide layer, and the back side of the SOI substrate is a support layer;

[0028] sputter depositing a piezoelectric layer on the lower electrode;

[0029] sputtering depositing an upper electrode on the piezoelectric layer;

[0030] Patterning the upper electrode;

[0031] patterning the piezoelectric layer;

[0032] patterning the lower electrode;

[0033] Forming a PAD on the substrate surface;

[0034] Patterning the device layer;

[0035] The supporting layer is etched to form a vibration sensitive structure, a frame structure and a cantilever beam structure.

[0036] In the above technical solution, the SOI (Silicon-On-Insulator) substrate consists of three layers, the front side is the device layer (silicon layer used to make circuits and devices), the middle side is the buried oxide layer (usually silicon dioxide, which plays an insulating role), and the back side is the support layer (provides mechanical support). On the device layer of the SOI substrate, the lower electrode is formed by sputtering deposition technology. Sputtering deposition is a physical vapor deposition method with the advantages of high deposition rate, good film quality and controllability. On the lower electrode, the piezoelectric layer is further formed by sputtering deposition technology. Piezoelectric materials will generate electric charges when subjected to external forces, and are the core sensitive elements of the accelerometer. On the piezoelectric layer, the upper electrode is formed again by sputtering deposition technology. The upper electrode and the lower electrode together constitute a capacitor structure for detecting the charge changes generated by the piezoelectric layer.

[0037] In some optional embodiments, sputtering deposits a lower electrode on the front side of the SOI substrate, comprising:

[0038] Growing silicon oxide as an isolation layer on the surface of the SOI substrate by thermal oxidation;

[0039] On the isolation layer on the front side of the SOI substrate, titanium is sputtered, or titanium is sputtered and then annealed with oxygen to form titanium oxide, thereby forming an adhesion layer;

[0040] On the adhesion layer, a metal material is deposited by sputtering to form a lower electrode.

[0041] In the above technical solution, titanium is first sputtered on the isolation layer on the front side of the SOI substrate, or titanium is sputtered and then oxygen-containing annealing is performed to form titanium oxide, thereby forming an adhesion layer. This step significantly enhances the adhesion between the lower electrode and the isolation layer below.

[0042] In some optional embodiments, forming a PAD on a surface of a substrate includes:

[0043] By photolithography, the patterns of the connection lines and PAD are formed on the surface of the substrate;

[0044] Depositing a metal layer on the substrate surface by electron beam evaporation;

[0045] The photoresist and the metal layer thereon are stripped off to form a PAD.

[0046] In the above technical solution, a layer of photoresist is uniformly coated on the surface of the substrate. Photoresist is an organic material that is sensitive to light and its properties change after exposure. A photolithography machine is used to expose the substrate coated with photoresist, and the patterns of the wiring and PAD are transferred to the photoresist. After exposure, the photoresist in the exposed area is removed using a developer to form the desired pattern. The electron beam evaporation device is started, and the electron beam directly hits the metal target material to evaporate it under heat. The evaporated metal atoms diffuse in the vacuum chamber and are deposited on the surface of the substrate to form a uniform metal layer. The photoresist and the metal layer thereon are removed together using a physical or chemical method (such as ultrasonic vibration or chemical solvent). During the stripping process, it is necessary to ensure that the photoresist and the metal layer thereon can be completely separated without damaging the metal layer on the surface of the substrate. After the above steps, the desired PAD pattern will be left on the surface of the substrate, and these PADs will be used to connect to external circuits.

[0047] In some optional embodiments, etching the support layer to form a vibration sensitive structure, a frame structure and a cantilever beam structure includes:

[0048] A front protection structure is provided on the front side of the substrate;

[0049] Coating photoresist on the back of the substrate, patterning the photoresist, etching away the support layer of a set depth that is not shielded by the photoresist to form a vibration sensitive structure, and cleaning away the remaining photoresist;

[0050] Coating photoresist on the back of the substrate, patterning the photoresist, etching away the support layer not covered by the photoresist to form a cantilever structure and a frame structure, and cleaning away the remaining photoresist;

[0051] Etch away the buried oxide layer on the back side of the substrate;

[0052] Remove the front protection structure.

[0053] In the above technical solution, photolithography is used to expose and develop the photoresist through a mask to form the desired pattern. An appropriate etching process (such as wet etching or dry etching) is used to etch away the support layer of a set depth that is not shielded by the photoresist. This step will form a preliminary outline of the vibration-sensitive structure. Use an appropriate cleaning agent to remove the remaining photoresist to ensure the cleanliness of the back of the substrate.

[0054] Apply photoresist to the back of the substrate again and pattern it to form the pattern of the cantilever structure and the frame structure. Use the same appropriate etching process to etch away the support layer that is not covered by the photoresist. This step will form the preliminary outline of the cantilever structure and the frame structure. Remove the remaining photoresist to ensure the cleanliness of the back of the substrate. Use an appropriate etching process to etch away the buried oxide layer on the back of the substrate. This step requires precise control of the etching depth and uniformity to ensure the stability and performance of the subsequent structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application 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.

[0056] Figure 1 A flowchart of a method for adjusting the induced voltage of a piezoelectric MEMS accelerometer provided in an embodiment of the present application;

[0057] Figure 2 A schematic diagram of a single cantilever beam structure provided in an embodiment of the present application;

[0058] Figure 3 A comparison diagram of etching the first invalid area and etching the second invalid area;

[0059] Figure 4 Schematic diagram of the substrate after being processed in steps 1, 2 and 3;

[0060] Figure 5 Schematic diagram of the substrate after being processed in step 4;

[0061] Figure 6 Schematic diagram of the substrate after being processed in step 5;

[0062] Figure 7 Schematic diagram of the substrate after processing in step 6;

[0063] Figure 8 Schematic diagram of the substrate after being processed in step 7;

[0064] Fig. 9 is a schematic diagram of a substrate after being processed in steps 91 and 92;

[0065] Fig.10 is a schematic diagram of the substrate after being processed in step 92;

[0066] Fig.11 is a schematic diagram of the substrate after being processed in step 93;

[0067] Fig.12 FIG. 2 is a schematic diagram of a substrate after being processed in step 200 . DETAILED DESCRIPTION

[0068] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0069] Please refer to Figure 1 , Figure 1A flowchart of a method for adjusting the induced voltage of a piezoelectric MEMS accelerometer provided in an embodiment of the present application includes:

[0070] Step 100: prepare a piezoelectric MEMS accelerometer, wherein the piezoelectric MEMS accelerometer includes a vibration sensitive structure, a frame structure, and a cantilever structure; an upper electrode of the cantilever structure is disposed close to the frame structure;

[0071] Step 200 , etching the upper electrode to change the capacitance value of the cantilever structure so that the induced voltage value of the cantilever structure is consistent with the standard value.

[0072] Among them, the method of etching the upper electrode can adopt laser etching technology, dry etching technology, etc.

[0073] Laser etching technology uses the high energy density of the laser beam to directly act on the upper electrode, causing it to partially melt, vaporize or react chemically, thereby achieving the purpose of etching. The laser beam can be focused to a very small point to achieve high-precision etching. Laser etching does not require direct contact with the upper electrode, avoiding mechanical wear and contamination.

[0074] Dry etching technology is to remove the electrode layer material in gaseous form by physical or chemical methods (such as plasma etching, reactive ion etching, etc.). Dry etching can achieve high-precision etching and a fast etching speed.

[0075] In the above technical solution, after the preparation process of the piezoelectric MEMS accelerometer is completed, the capacitance value of each cantilever structure is fine-tuned by etching the upper electrode, so that the induced voltage value of the cantilever structure is consistent with the standard value, which overcomes the natural inconsistency inside the chip, avoids the difference in induced voltage between the cantilevers of the accelerometer, avoids the difference in induced voltage between different devices in the same batch, does not need to adjust the external voltage amplifier, reduces the difficulty of adjusting the peripheral matching circuit, simplifies the matching circuit, and is easy to manufacture. Specifically, during the chip test or system debugging, the metal can be cut with a laser on the exposed upper electrode surface so that a small part of the metal electrode is disconnected from the output end, and then the effect of the cutting adjustment is confirmed by testing the induced voltage.

[0076] The piezoelectric MEMS accelerometer includes at least one cantilever beam structure. The capacitance value adjustment method for each cantilever beam structure is the same. The following embodiments are described in detail by taking one of the cantilever beam structures as an example.

[0077] Please refer to Figure 2 , Figure 2Schematic diagram of a single cantilever beam structure provided in an embodiment of the present application. The upper electrode is divided into a first etching region and a second etching region, the first etching region and the second etching region are bounded by the connection between the cantilever beam structure and the frame structure, the first side of the upper electrode to the connection is the first etching region, and the second side of the upper electrode to the connection is the second etching region.

[0078] In some optional embodiments, etching the upper electrode includes: etching a first etching region of the upper electrode; wherein the first etching region is: from the first side of the upper electrode close to the vibration sensitive structure to the connection between the cantilever structure and the frame structure.

[0079] In some optional embodiments, the larger the V' is, the closer the first etched region is to the connection portion, and the smaller the V' is, the closer the first etched region is to the first side, to the position of the upper electrode being etched.

[0080] Wherein, V'=V1-V0; V1 is the measured value of the induced voltage, and V0 is the standard value of the induced voltage.

[0081] In the above technical solution, a certain position of the first etched area of ​​the upper electrode is etched to change the capacitance value and the induced charge value of the cantilever structure. The determination of this position is related to V'. The reason is that when the vibration sensitive structure is subjected to the force, the cantilever structure will deform accordingly, and the deformation amount of each position of the first etched area of ​​the cantilever structure is different. The closer to the connection, the greater the deformation, and the farther away from the connection, the smaller the deformation. From a differential point of view, the induced charge generated by the piezoelectric sensitive structure at different positions of the cantilever is also different. The induced charge near the connection is the largest, and the capacitance of the piezoelectric sensitive structure is only related to the electrode area and the dielectric constant and thickness of the medium, and can be regarded as a uniform amount at different positions of the cantilever. When the area of ​​the upper electrode changes, the changes in the induced charge and capacitance are not synchronized, and the induced voltage can be adjusted accordingly. When a certain area of ​​the upper electrode near the connection is lost, the induced charge loss value is large, and the loss value of the capacitor is proportional to the area, and the induced voltage after laser adjustment is relatively large; when a certain area of ​​the upper electrode near the first side is lost, the induced charge loss value is small, and the loss value of the capacitor is proportional to the area, and the induced voltage after laser adjustment is relatively small. Therefore, when V' is larger, for example, V' is greater than 0, to reduce the induced voltage, a certain position of the upper electrode near the connection is etched; when V' is smaller, for example, V' is less than 0, to increase the induced voltage, a certain position of the upper electrode near the first side is etched.

[0082] In some optional embodiments, after etching the first etching region of the upper electrode, the induced voltage of the cantilever structure is:

[0083] V=(Q-Q') / (C-C')

[0084] Wherein, Q'=X·C'; Q is the induced charge before etching, Q' is the induced charge loss value after etching, C is the capacitance value before etching, and C' is the capacitance loss value after etching; X is the coefficient of different etching positions. In the first etching area, the value of X gradually increases from the first side to the connection.

[0085] In the above technical solution, the same area of ​​the upper electrode is cut at different positions, and the capacitance loss is the same. However, the greater the deformation, the greater the loss of the induced charge, and the smaller the deformation. The ratio of the induced charge loss value to the capacitance loss value is set as the coefficient X. The closer to the first side, the smaller the value of X, and the closer to the connection, the larger the value of X, so that the induced voltage of the cantilever structure after etching is determined to be V = (QX·C') / (C-C').

[0086] For details, please refer to Figure 3 , Figure 3 This is a comparison diagram of etching the first invalid area and etching the second invalid area. The first invalid area is far from the connection, and the second invalid area is close to the connection. Therefore, when etching the first invalid area, the induced charge loss value is small; when etching the second invalid area, the induced charge loss value is large; if the first invalid area and the second invalid area have the same area, the capacitance loss value of etching the first invalid area and etching the second invalid area is the same, but the induced charge loss value is different, resulting in different induced voltages after etching. Therefore, the specific position of etching the first etched area can be determined based on the difference between the induced voltage and the standard value.

[0087] In some optional embodiments, etching the upper electrode includes: etching a second etching region of the upper electrode when V' is less than 0;

[0088] The second etching area is from the connection between the cantilever structure and the frame structure to the second side of the upper electrode away from the vibration sensitive structure; V'=V1-V0; V1 is the measured value of the induced voltage, and V0 is the standard value of the induced voltage.

[0089] In the above technical solution, the second etched area of ​​the upper electrode is the area where the cantilever structure is fixedly connected to the frame structure. Since the bottom of the substrate is thick and the load is large, the deformation of the second etched area can be ignored, and the induced charge can also be ignored. Etching a certain position of the second etched area of ​​the upper electrode can be considered to only reduce the capacitance without changing the total induced charge. When the induced charge remains unchanged, reducing the capacitance value can increase the value of the induced voltage. Therefore, when V' is less than 0, the second etched area of ​​the upper electrode can be etched to increase the induced voltage.

[0090] In some optional embodiments, after etching the second etching region of the upper electrode, the induced voltage of the cantilever structure is:

[0091] V=Q / (C-C')

[0092] Wherein, Q is the induced charge before etching, C is the capacitance value before etching, and C' is the capacitance loss value after etching.

[0093] Please refer to Figures 4 to 12 , Figures 4 to 12 Schematic diagram of the substrate during the preparation of the piezoelectric MEMS accelerometer.

[0094] In some optional embodiments, a piezoelectric MEMS accelerometer is prepared, comprising:

[0095] Step 1, sputtering and depositing a lower electrode on the front side of the SOI substrate; wherein the front side of the SOI substrate is a device layer, the middle layer of the SOI substrate is a buried oxide layer, and the back side of the SOI substrate is a support layer;

[0096] Step 2, sputtering and depositing a piezoelectric layer on the lower electrode;

[0097] Step 3, sputtering and depositing an upper electrode on the piezoelectric layer;

[0098] Step 4, patterning the upper electrode;

[0099] Step 5, patterning the piezoelectric layer;

[0100] Step 6, patterning the lower electrode;

[0101] Step 7, forming a PAD on the surface of the substrate;

[0102] Step 8, patterning the device layer;

[0103] Step 9: Etch the support layer to form a vibration sensitive structure, a frame structure and a cantilever beam structure.

[0104] In the above technical solution, the SOI (Silicon-On-Insulator) substrate consists of three layers, the front side is the device layer (silicon layer used to make circuits and devices), the middle side is the buried oxide layer (usually silicon dioxide, which plays an insulating role), and the back side is the support layer (provides mechanical support). On the device layer of the SOI substrate, the lower electrode is formed by sputtering deposition technology. Sputtering deposition is a physical vapor deposition method with the advantages of high deposition rate, good film quality and controllability. On the lower electrode, the piezoelectric layer is further formed by sputtering deposition technology. Piezoelectric materials will generate electric charges when subjected to external forces, and are the core sensitive elements of the accelerometer. On the piezoelectric layer, the upper electrode is formed again by sputtering deposition technology. The upper electrode and the lower electrode together constitute a capacitor structure for detecting the charge changes generated by the piezoelectric layer.

[0105] For details, please refer to Figure 4 , Figure 4Schematic diagram of the substrate after processing in steps 1, 2 and 3.

[0106] Steps 1, 2 and 3 are the film forming process. A 100-1000nm oxide layer is grown on the surface of the SOI substrate by thermal oxidation as an isolation layer. A 20-50nm seed layer or adhesion layer is deposited on the front of the substrate by sputtering + oxygen-containing annealing. It can be Ti, TiOx, AlN, ScAlN, etc. A 50-500nm bottom electrode is deposited on the front of the substrate by sputtering. It can be Pt, Mo or other metals. A 50-200nm buffer layer is deposited on the surface of the substrate by sputtering as a buffer. A 0.5-5um piezoelectric layer is deposited on the surface of the substrate by sputtering. It can be PZT, AlN, ScAlN or other thin film materials with piezoelectric properties. A 50-500nm top electrode is deposited on the front of the substrate by sputtering. It can be Pt, Mo or other metals.

[0107] Among them, the isolation layer, seed layer, adhesion layer and buffer layer may also be omitted, and the corresponding process steps can be removed accordingly.

[0108] Please refer to Figure 5 , Figure 5 Schematic diagram of the substrate after processing in step 4.

[0109] The upper electrode is patterned, including: forming an upper electrode design pattern on the substrate surface by photolithography, removing excess upper electrode metal by dry etching or wet etching to form an upper electrode layer of the piezoelectric MEMS accelerometer, and removing photoresist by organic solvent or oxygen plasma.

[0110] Please refer to Figure 6 , Figure 6 Schematic diagram of the substrate after processing in step 5.

[0111] The piezoelectric layer is patterned, including: forming a piezoelectric layer design pattern on the substrate surface by photolithography, removing excess piezoelectric material by dry etching or wet etching to form the piezoelectric layer of the piezoelectric MEMS accelerometer, and removing the photoresist by organic cleaning or oxygen plasma.

[0112] Please refer to Figure 7 , Figure 7 Schematic diagram of the substrate after processing in step 6.

[0113] The lower electrode is patterned, including: forming a lower electrode design pattern on the substrate surface by photolithography, removing excess lower electrode metal by dry etching or wet etching to form the lower electrode of the piezoelectric MEMS accelerometer, and removing the photoresist by organic cleaning or oxygen plasma.

[0114] Please refer to Figure 8 , Figure 8 Schematic diagram of the substrate after processing in step 7.

[0115] In some optional embodiments, forming a PAD on a surface of a substrate includes:

[0116] By photolithography, the patterns of the connection lines and PAD are formed on the surface of the substrate;

[0117] Depositing a metal layer on the surface of the substrate by electron beam evaporation; the material of the metal layer can be Ti, Ni, Cr, Al, Ag, Pt, Au, etc. or a laminated mixed structure of several materials;

[0118] The photoresist and the metal layer thereon are stripped off to form a PAD.

[0119] In the above technical solution, a layer of photoresist is uniformly coated on the surface of the substrate. Photoresist is an organic material that is sensitive to light and its properties change after exposure. A photolithography machine is used to expose the substrate coated with photoresist, and the patterns of the wiring and PAD are transferred to the photoresist. After exposure, the photoresist in the exposed area is removed using a developer to form the desired pattern. The electron beam evaporation device is started, and the electron beam directly hits the metal target material to evaporate it under heat. The evaporated metal atoms diffuse in the vacuum chamber and are deposited on the surface of the substrate to form a uniform metal layer. The photoresist and the metal layer thereon are removed together using a physical or chemical method (such as ultrasonic vibration or chemical solvent). During the stripping process, it is necessary to ensure that the photoresist and the metal layer thereon can be completely separated without damaging the metal layer on the surface of the substrate. After the above steps, the desired PAD pattern will be left on the surface of the substrate, and these PADs will be used to connect to external circuits.

[0120] In some optional embodiments, the device layer is patterned, including: forming a device layer design pattern on the substrate surface by a photolithography method, removing excess device layer Si by a dry etching or wet etching method, forming a cantilever (or suspended membrane) structure, a mass block, and a frame structure of the piezoelectric MEMS accelerometer, and removing the photoresist by organic cleaning or oxygen plasma.

[0121] In some optional embodiments, etching the support layer to form a vibration sensitive structure, a frame structure and a cantilever beam structure includes:

[0122] Step 91, setting a front protection structure on the front side of the substrate;

[0123] Step 92, coating a photoresist on the back side of the substrate, patterning the photoresist, etching away the support layer of a set depth that is not shielded by the photoresist to form a vibration sensitive structure, and cleaning away the remaining photoresist;

[0124] Step 93, coating a photoresist on the back side of the substrate, patterning the photoresist, etching away the support layer not shielded by the photoresist, forming a cantilever structure and a frame structure, and cleaning away the remaining photoresist;

[0125] Step 94, etching away the buried oxide layer on the back side of the substrate;

[0126] Step 95: Remove the front protection structure.

[0127] In the above technical solution, photolithography is used to expose and develop the photoresist through a mask to form the desired pattern. An appropriate etching process (such as wet etching or dry etching) is used to etch away the support layer of a set depth that is not shielded by the photoresist. This step will form a preliminary outline of the vibration-sensitive structure. Use an appropriate cleaning agent to remove the remaining photoresist to ensure the cleanliness of the back of the substrate.

[0128] Apply photoresist to the back of the substrate again and pattern it to form the pattern of the cantilever structure and the frame structure. Use the same appropriate etching process to etch away the support layer that is not covered by the photoresist. This step will form the preliminary outline of the cantilever structure and the frame structure. Remove the remaining photoresist to ensure the cleanliness of the back of the substrate. Use an appropriate etching process to etch away the buried oxide layer on the back of the substrate. This step requires precise control of the etching depth and uniformity to ensure the stability and performance of the subsequent structure.

[0129] Please refer to Fig. 9 , Fig. 9 Schematic diagram of the substrate after processing in steps 91 and 92, specifically including: protecting the front side of the substrate, forming a quality block design pattern on the back side of the substrate by photolithography, removing excess support layer Si by dry etching or wet etching to form a quality block structure of the piezoelectric MEMS accelerometer, and removing the photoresist by organic cleaning or oxygen plasma.

[0130] Please refer to Fig.10 , Fig.10 Schematic diagram of the substrate after processing in step 92, specifically including: forming a hollow design pattern on the back of the substrate by a photolithography method, removing excess support layer Si by a dry etching or wet etching method, forming a cantilever (or suspended membrane) structure and a frame structure of the piezoelectric MEMS accelerometer, and removing the photoresist by organic cleaning or oxygen plasma.

[0131] Please refer to Fig.11 , Fig.11 Schematic diagram of the substrate after processing in step 93, which specifically includes: removing excess SiO2 by vapor phase etching or wet etching or dry etching, releasing the cantilever (or suspended film) structure, and removing the protective structure on the front side of the substrate.

[0132] Please refer to Fig.12, Fig.12 This is a schematic diagram of the substrate after processing in step 200, which specifically includes: by laser etching the upper electrode, the area of ​​the upper electrode is reduced, which plays a role in adjusting the capacitance of the MIM structure, and then the induced voltage is adjusted to the standard voltage value required by the design. Laser etching is performed from the end of the upper electrode close to the mass block to increase the induced voltage; laser etching is performed from the end of the upper electrode close to the frame to reduce the induced voltage.

[0133] In the embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some communication interfaces, and the indirect coupling or communication connection of the devices or units can be electrical, mechanical or other forms.

[0134] In addition, the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0135] Furthermore, the functional modules in the various embodiments of the present application may be integrated together to form an independent part, or each module may exist separately, or two or more modules may be integrated to form an independent part.

[0136] In this document, relational terms such as first and second, etc. are used merely to distinguish one entity or operation from another entity or operation, but do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0137] The above description is only an embodiment of the present application and is not intended to limit the protection scope of 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 method for adjusting the induced voltage of a piezoelectric MEMS accelerometer, characterized in that: include: After the piezoelectric MEMS accelerometer is prepared, the upper electrode is etched to change the capacitance value of the cantilever structure so that the induced voltage value of the cantilever structure is consistent with the standard value; wherein the piezoelectric MEMS accelerometer includes a vibration sensitive structure, a frame structure and a cantilever structure; the upper electrode of the cantilever structure is arranged close to the frame structure.

2. The method according to claim 1, characterized in that The etching of the upper electrode comprises: Etching a first etching region of the upper electrode; The first etching area is from the first side of the upper electrode close to the vibration sensitive structure to the connection between the cantilever structure and the frame structure.

3. The method according to claim 2, characterized in that The larger V' is, the position of the upper electrode to be etched is the position where the first etched region is closer to the connection; the smaller V' is, the position of the upper electrode to be etched is the position where the first etched region is closer to the first side; Wherein, V'=V1-V0; V1 is the measured value of the induced voltage, and V0 is the standard value of the induced voltage.

4. The method according to claim 3, characterized in that After etching the first etching area of ​​the upper electrode, the induced voltage of the cantilever structure is: V=(Q-Q') / (C-C') Wherein, Q'=X·C'; Q is the induced charge before etching, Q' is the induced charge loss value after etching, C is the capacitance value before etching, and C' is the capacitance loss value after etching; X is the coefficient of different etching positions, and in the first etching area, the value of X gradually increases from the first side to the connection.

5. The method according to claim 1, characterized in that The etching of the upper electrode comprises: When V' is less than 0, etching the second etching region of the upper electrode; The second etching area is from the connection between the cantilever structure and the frame structure to the second side of the upper electrode away from the vibration sensitive structure; V'=V1-V0; V1 is the measured value of the induced voltage, and V0 is the standard value of the induced voltage.

6. The method according to claim 5, characterized in that After etching the second etching area of ​​the upper electrode, the induced voltage of the cantilever structure is: V=Q / (C-C') Wherein, Q is the induced charge before etching, C is the capacitance value before etching, and C' is the capacitance loss value after etching.

7. The method according to claim 1, characterized in that The piezoelectric MEMS accelerometer is prepared, comprising: The lower electrode is deposited by sputtering on the front side of the SOI substrate; wherein the front side of the SOI substrate is a device layer, the middle layer of the SOI substrate is a buried oxide layer, and the back side of the SOI substrate is a support layer; sputtering and depositing a piezoelectric layer on the lower electrode; sputtering and depositing an upper electrode on the piezoelectric layer; Patterning the upper electrode; Patterning the piezoelectric layer; Patterning the lower electrode; Forming a PAD on the substrate surface; Patterning the device layer; The support layer is etched to form a vibration sensitive structure, a frame structure and a cantilever beam structure.

8. The method according to claim 7, characterized in that The step of sputtering and depositing the lower electrode on the front side of the SOI substrate comprises: growing silicon oxide as an isolation layer on the surface of the SOI substrate by thermal oxidation; On the isolation layer on the front side of the SOI substrate, titanium is sputtered, or titanium is sputtered and then annealed with oxygen to form titanium oxide, thereby forming an adhesion layer; The lower electrode is formed by depositing a metal material on the adhesion layer by sputtering.

9. The method according to claim 7, characterized in that The forming of PAD on the surface of the substrate comprises: By photolithography, the patterns of the connection lines and PAD are formed on the surface of the substrate; Depositing a metal layer on the substrate surface by electron beam evaporation; The photoresist and the metal layer thereon are stripped off to form a PAD.

10. The method according to claim 7, characterized in that The etching of the support layer to form a vibration sensitive structure, a frame structure and a cantilever beam structure includes: A front protection structure is provided on the front side of the substrate; Coating a photoresist on the back of the substrate, patterning the photoresist, etching away the support layer of a set depth that is not shielded by the photoresist to form the vibration sensitive structure, and cleaning away the remaining photoresist; Coating photoresist on the back of the substrate, patterning the photoresist, etching away the support layer not shielded by the photoresist to form a cantilever structure and a frame structure, and cleaning away the remaining photoresist; Etch away the buried oxide layer on the back side of the substrate; The front protection structure is removed.

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