A method for adjusting sensing voltage of piezoelectric MEMS accelerometer

Abstract

The application provides a method for adjusting the sensing voltage of a piezoelectric MEMS accelerometer. After the preparation process of the piezoelectric MEMS accelerometer is completed, the capacitance value of each suspension beam structure is finely adjusted by etching the upper electrode, so that the sensing voltage value of the suspension beam structure is consistent with the standard value. The natural inconsistency in the chip is overcome, the sensing voltage difference between the suspension arms of the accelerometer is avoided, the sensing voltage difference between different devices in the same batch is avoided, the external voltage amplifier does not need to be adjusted and calibrated, the adjustment and calibration difficulty of the peripheral matching circuit is reduced, the matching circuit is simplified, and the production and manufacturing are easy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of MEMS, in particular to a method for adjusting sensing voltage of a piezoelectric MEMS accelerometer. BACKGROUND

[0002] The working principle of the piezoelectric MEMS accelerometer is as follows: when vibrating, the mass block is subjected to an inertial force in the opposite direction of the acceleration direction, the suspension beam deforms, the piezoelectric film located on the suspension beam also deforms, and corresponding sensing charges are generated on the upper and lower electrodes. Since C = Q / V, when the capacitance is constant, the sensing voltage signal is proportional to the sensing charge. Through the voltage amplifier and the external circuit, the conversion from acceleration to voltage is realized. When working at a frequency far from the resonance frequency point, the acceleration of the mass block is proportional to the sensing voltage of the device, that is, the detection is realized.

[0003] The piezoelectric MEMS accelerometer mainly includes a suspension beam (or a suspension film), a frame, a mass block, and a piezoelectric sensitive structure. The suspension beam can be a single beam or multiple symmetrically distributed beams, and the suspension film can be a ring-shaped film or other center-symmetrically distributed films. One end of the suspension beam (or the suspension film) is connected to the mass block, and the other end is connected to the frame. The connection position of the suspension beam (or the suspension film) and the frame is covered with the piezoelectric sensitive structure, which is mainly composed of a MIM capacitor composed of a piezoelectric film and upper / lower electrodes. The dielectric layer (piezoelectric film) converts the strain into an electrical signal. In addition, the frame also has lead-out wires and PADs of the upper / lower electrodes.

[0004] Due to the non-ideality of the piezoelectric film and the consistency of the MEMS process, the sensing voltages V of the actual suspension arms will be different, and the sensing voltages V of different devices in the same batch will also be different. In order to realize accurate detection, balance the characteristics of each suspension arm, and realize standard output, it is generally necessary to adjust and calibrate the external voltage amplifier. The voltage amplifier corresponding to each suspension arm needs to be adjusted and calibrated respectively, which has a large debugging difficulty and a complex matching circuit. SUMMARY

[0005] The purpose of the embodiments of the present application is to provide a method for adjusting sensing voltage of a piezoelectric MEMS accelerometer, so as to solve the problems that the sensing voltages V of the actual suspension arms will be different, the sensing voltages V of different devices in the same batch will also be different, the external voltage amplifier needs to be adjusted and calibrated, and the voltage amplifier corresponding to each suspension arm needs to be adjusted and calibrated respectively, which has a large debugging difficulty and a complex matching circuit.

[0006] The method for adjusting sensing voltage of a piezoelectric MEMS accelerometer provided by the embodiments of the present application comprises the following steps.

[0007] After the piezoelectric MEMS accelerometer is prepared, the upper electrode is etched to change the capacitance value of the suspension beam structure, so that the sensing voltage value of the suspension beam structure is consistent with the standard value; wherein the piezoelectric MEMS accelerometer comprises a vibration sensitive structure, a frame structure and a suspension beam structure; the upper electrode of the suspension beam 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 suspension beam structure is fine-tuned by etching the upper electrode, so that the sensing voltage value of the suspension beam structure is consistent with the standard value, the natural inconsistency in the chip is overcome, the sensing voltage difference between the suspension arms of the accelerometer is avoided, the sensing voltage difference between different devices in the same batch is avoided, the external voltage amplifier does not need to be adjusted and calibrated, the adjustment and calibration difficulty of the peripheral matching circuit is reduced, the matching circuit is simplified, and production and manufacturing are easy. Specifically, when the chip is tested or the system is debugged, the exposed upper electrode surface can be cut with a laser to disconnect a small part of the metal electrode from the output end, and then the sensing voltage is tested to confirm the effect of the cutting adjustment.

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

[0010] etching a first etching area of the upper electrode;

[0011] wherein the first etching area is: from the first side of the upper electrode close to the vibration sensitive structure to the connection between the suspension beam structure and the frame structure.

[0012] In some optional embodiments, the larger V' is, the closer the etching position of the upper electrode to the connection is; the smaller V' is, the closer the etching position of the upper electrode to the first side is.

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

[0014] In the technical solution, the position of the first etching area of the upper electrode is etched to change the capacitance value and the induced charge value of the suspension beam structure, and the position is determined in relation to V'. The reason is that when the vibration sensitive structure is subjected to a force, the suspension beam structure deforms, and the deformation amount of each position of the first etching area of the suspension beam structure is different. The closer to the connection, the greater the deformation, and the farther away from the connection, the smaller the deformation. From the perspective of differentiation, the induced charge generated by the piezoelectric sensitive structure at different positions of the suspension beam 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 coefficient and thickness of the medium, and can be regarded as a uniform amount at different positions of the suspension beam. When the area of the upper electrode changes, the changes of the induced charge and the capacitance are different, and the induced voltage can be adjusted accordingly. When a certain area of the upper electrode near the connection is lost, the loss value of the induced charge is large, and the loss value of the capacitance 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 loss value of the induced charge is small, and the loss value of the capacitance 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 the first etching area of the upper electrode is etched, the induced voltage of the suspension beam structure is:

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

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

[0018] In the technical solution, the same area of the upper electrode is cut at different positions, and the loss value of the capacitance is the same. The greater the deformation, the greater the loss value of the induced charge, and the smaller the deformation, the smaller the loss of the induced charge. The ratio of the loss value of the induced charge and the loss value of the capacitance 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 greater the value of X, so as to determine the induced voltage of the suspension beam structure after etching as V=(Q-X·C') / (C-C').

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

[0020] In the case where V' is less than 0, etching the second etching area of the upper electrode;

[0021] Wherein, the second etching region is from the connection between the suspension beam structure and the frame structure to the second side of the upper electrode far 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 etching region of the upper electrode is the region where the suspension beam structure is fixedly connected with the frame structure. Since the bottom of the substrate is thick and the load is large, the deformation of the second etching region can be ignored, and the induced charge can also be ignored. Etching a certain position of the second etching region of the upper electrode can be considered as only reducing the capacitance without changing the total induced charge. In the case of constant induced charge, reducing the capacitance value can increase the value of the induced voltage. Therefore, in the case that V' is less than 0, the second etching region 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 suspension beam 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] Sputtering deposition of a lower electrode on the front surface of an SOI substrate; wherein the front surface of the SOI substrate is a device layer, the middle layer of the SOI substrate is a buried oxygen layer, and the back surface of the SOI substrate is a support layer;

[0028] Sputtering deposition of a piezoelectric layer on the lower electrode;

[0029] Sputtering deposition of an upper electrode on the piezoelectric layer;

[0030] Photographing the upper electrode;

[0031] Photographing the piezoelectric layer;

[0032] Photographing the lower electrode;

[0033] Forming a PAD on the surface of the substrate;

[0034] Photographing the device layer;

[0035] Etching the support layer to form a vibration sensitive structure, a frame structure and a suspension beam structure.

[0036] In the above technical solution, the SOI (Silicon-On-Insulator) substrate is composed of three layers, the front surface is a device layer (a silicon layer for making circuits and devices), the middle is a buried oxide layer (usually silicon dioxide, which serves as an insulating layer), and the back surface is a support layer (which provides mechanical support). On the device layer of the SOI substrate, a lower electrode is formed by sputter deposition technology. Sputter deposition is a physical vapor deposition method with high deposition rate, good film quality and controllability. On the lower electrode, a piezoelectric layer is formed by sputter deposition technology. Piezoelectric material generates electric charge when subjected to external force, and is the core sensitive element of an accelerometer. On the piezoelectric layer, an upper electrode is formed by sputter deposition technology. The upper electrode and the lower electrode together form a capacitor structure for detecting the charge change of the piezoelectric layer.

[0037] In some optional embodiments, the lower electrode is sputter deposited on the front surface of the SOI substrate, including:

[0038] Silicon oxide is grown as an isolation layer on the surface of the SOI substrate by thermal oxidation;

[0039] Titanium is sputtered on the isolation layer on the front surface of the SOI substrate, or titanium is sputtered and then oxygen annealing is performed to form titanium oxide, forming an adhesion layer;

[0040] A metal material is sputter deposited on the adhesion layer to form a lower electrode.

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

[0042] In some optional embodiments, the PAD is formed on the surface of the substrate, including:

[0043] A pattern of the PAD and the connecting lines is formed on the surface of the substrate by photolithography;

[0044] A metal layer is deposited on the surface of the substrate by electron beam evaporation;

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

[0046] In the above technical solution, a layer of photoresist is uniformly coated on the substrate surface. Photoresist is a photosensitive organic material whose properties change after exposure. A photolithography machine is used to expose the substrate coated with photoresist, transferring the interconnect and PAD patterns onto the photoresist. After exposure, a developer is used to remove the photoresist from the exposed areas, forming the desired pattern. An electron beam evaporation device is activated, with the electron beam directly striking a metal target, causing it to evaporate upon heating. The evaporated metal atoms diffuse in a vacuum chamber and deposit on the substrate surface, forming a uniform metal layer. Physical or chemical methods (such as ultrasonic vibration or chemical solvents) are used to remove the photoresist and the metal layer on it. During the stripping process, it is necessary to ensure complete separation of the photoresist and the metal layer on it without damaging the metal layer on the substrate surface. After these steps, the desired PAD pattern will remain on the substrate surface; these PADs will be used for connection to external circuits.

[0047] In some alternative implementations, the support layer is etched to form a vibration-sensitive structure, a frame structure, and a cantilever structure, including:

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

[0049] Photoresist is coated on the back of the substrate and patterned. The support layer at a set depth that is not covered by the photoresist is etched away to form a vibration-sensitive structure. The remaining photoresist is then cleaned away.

[0050] Photoresist is coated on the back of the substrate and patterned. The support layer not covered by the photoresist is etched away to form a cantilever structure and a frame structure. The remaining photoresist is then cleaned away.

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

[0052] Remove the front protective structure.

[0053] In the above technical solution, photolithography is used to expose and develop photoresist using a photomask to form the desired pattern. An appropriate etching process (such as wet or dry etching) is then employed to etch away the support layer at a predetermined depth that is not masked by the photoresist. This step forms the preliminary outline of the vibration-sensitive structure. Finally, a suitable cleaning agent is used to remove any remaining photoresist, ensuring the cleanliness of the back side of the substrate.

[0054] Photoresist is applied again to the back of the substrate and patterned to form the cantilever and frame structures. Using an appropriate etching process, the support layer not covered by the photoresist is etched away. This step forms the initial outline of the cantilever and frame structures. The remaining photoresist is removed, ensuring the back of the substrate is clean. Using an appropriate etching process, the buried oxide layer on the back of the substrate is etched away. This step requires precise control of the etching depth and uniformity to ensure the stability and performance of the subsequent structure. Attached Figure Description

[0055] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

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

[0057] Figure 2 This is a schematic diagram of a single cantilever beam structure provided in an embodiment of this application;

[0058] Figure 3 A comparison image showing the etching of the first invalid region and the etching of the second invalid region;

[0059] Figure 4 This is a schematic diagram of the substrate after processing in steps 1, 2, and 3;

[0060] Figure 5 This is a schematic diagram of the substrate after step 4.

[0061] Figure 6 This is a schematic diagram of the substrate after step 5.

[0062] Figure 7 This is a schematic diagram of the substrate after step 6.

[0063] Figure 8 This is a schematic diagram of the substrate after step 7.

[0064] Figure 9 This is a schematic diagram of the substrate after steps 91 and 92.

[0065] Figure 10 This is a schematic diagram of the substrate after step 92.

[0066] Figure 11 This is a schematic diagram of the substrate after step 93.

[0067] Figure 12 This is a schematic diagram of the substrate after step 200. Detailed Implementation

[0068] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0069] Please refer to Figure 1 , Figure 1A flow chart of a method for adjusting the sensing voltage of a piezoelectric MEMS accelerometer is provided in the embodiments of the present application, and the flow chart comprises the following steps:

[0070] In step 100, a piezoelectric MEMS accelerometer is prepared, which comprises a vibration-sensitive structure, a frame structure and a beam structure; the upper electrode of the beam structure is arranged close to the frame structure.

[0071] In step 200, the upper electrode is etched to change the capacitance value of the beam structure, so that the sensing voltage value of the beam structure is consistent with the standard value.

[0072] The method for etching the upper electrode can be laser etching technology, dry etching technology, etc.

[0073] The laser etching technology uses the high energy density of the laser beam to directly act on the upper electrode, so that the upper electrode is locally melted, vaporized or chemically reacted, 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 pollution.

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

[0075] In the above technical solution, after the preparation process of the piezoelectric MEMS accelerometer is completed, the capacitance value of each beam structure is fine-tuned by etching the upper electrode, so that the sensing voltage value of the beam structure is consistent with the standard value. This overcomes the natural inconsistency within the chip, avoids the difference in sensing voltage between the beams of the accelerometer, avoids the difference in sensing voltage between different devices in the same batch, eliminates the need for adjustment and calibration of the external voltage amplifier, reduces the difficulty of adjustment and calibration of the peripheral matching circuit, simplifies the matching circuit, and is easy to produce and manufacture. Specifically, when the chip is tested or the system is debugged, a small part of the metal electrode is disconnected from the output end by cutting the metal on the exposed surface of the upper electrode with a laser, and the cutting and adjustment effect is confirmed by testing the sensing voltage.

[0076] The piezoelectric MEMS accelerometer comprises at least one beam structure, and the adjustment method for the capacitance value of each beam structure is the same. The following embodiments will be described in detail taking one of the beam structures as an example.

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

[0078] In some optional embodiments, etching the upper electrode comprises: etching a first etching area of the upper electrode; wherein the first etching area is: 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 greater V' is, the position of etching the upper electrode, which is the first etching area, is closer to the connection; the smaller V' is, the position of etching the upper electrode, which is the first etching area, is closer to the first side.

[0080] 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 etching the first etching area of the upper electrode is used to change the capacitance value and the induced charge value of the cantilever structure, and the determination of the position is related to V'. The reason is that when the vibration sensitive structure is subjected to a force, the cantilever structure deforms along with it, and the deformation amount of each position of the first etching area of the cantilever structure is different. The closer to the connection, the greater the deformation; the farther away from the connection, the smaller the deformation. From the perspective of differentiation, the induced charge generated by the piezoelectric sensitive structure at different positions of the cantilever is also different. The induced charge is the largest near the connection, while the capacitance of the piezoelectric sensitive structure is only related to the electrode area and the dielectric coefficient 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 of the induced charge and the capacitance are different, and the induced voltage can be adjusted accordingly. When a certain area of the upper electrode close to the connection is lost, the loss value of the induced charge is large, while the loss value of the capacitance is proportional to the area, and the induced voltage after laser adjustment is relatively large; when a certain area of the upper electrode close to the first side is lost, the loss value of the induced charge is small, while the loss value of the capacitance is proportional to the area, and the induced voltage after laser adjustment is relatively small. Therefore, when V' is greater, for example, V' is greater than 0, to reduce the induced voltage, a certain position of etching the upper electrode close to the connection; when V' is smaller, for example, V' is less than 0, to increase the induced voltage, a certain position of etching the upper electrode close to the first side.

[0082] In some optional embodiments, after etching the first etching area 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 loss value of the induced charge after etching, C is the capacitance value before etching, C' is the loss value of the capacitance after etching; X is the coefficient of different etching positions, and the value of X gradually increases from the first side to the connecting part on the first etching area.

[0085] In the above technical solution, the same area of the upper electrode is cut at different positions, and the loss value of the capacitance is the same. The greater the deformation, the greater the loss value of the induced charge, and the smaller the deformation, the smaller the loss of the induced charge. The ratio of the loss value of the induced charge and the loss value of the capacitance is set as the coefficient X, the value of X is smaller near the first side, and the value of X is larger near the connecting part, so as to determine the induced voltage of the suspended beam structure after etching as V = (Q-X*C') / (C-C').

[0086] Specifically, refer to Figure 3 , Figure 3 The first invalid area is far away from the connecting part, and the second invalid area is close to the connecting part, so that the loss value of the induced charge is smaller when etching the first invalid area, and the loss value of the induced charge is larger when etching the second invalid area. If the areas of the first invalid area and the second invalid area are the same, the loss value of the capacitance is the same when etching the first invalid area and etching the second invalid area, but the loss value of the induced charge is different, resulting in different induced voltages after etching. Therefore, the specific position of etching the first etching area can be determined according to the difference between the induced voltage and the standard value.

[0087] In some optional embodiments, etching the upper electrode comprises: etching the second etching area of the upper electrode when V' is less than 0.

[0088] Wherein, the second etching area is: the connecting part of the suspended beam 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 etching area of the upper electrode is the area where the suspended beam structure is fixedly connected with the frame structure. Since the bottom of the substrate is thick and the load is large, the deformation of the second etching area can be ignored, and the induced charge can also be ignored. Etching a certain position of the second etching area of the upper electrode can be considered as only reducing the capacitance without changing the total induced charge. In the case that the induced charge is unchanged, reducing the capacitance value can increase the value of the induced voltage. Therefore, in the case that V' is less than 0, the second etching area of the upper electrode can be etched to increase the induced voltage.

[0090] In some optional embodiments, after etching the second etching area of the upper electrode, the induced voltage of the suspended beam 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 The process of preparing a piezoelectric MEMS accelerometer.

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

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

[0096] Step 2, sputtering deposition of the piezoelectric layer on the lower electrode;

[0097] Step 3, sputtering deposition of the upper electrode on the piezoelectric layer;

[0098] Step 4, patterning of the upper electrode;

[0099] Step 5, patterning of the piezoelectric layer;

[0100] Step 6, patterning of the lower electrode;

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

[0102] Step 8, patterning of the device layer;

[0103] Step 9, etching of the support layer to form the vibration sensitive structure, the frame structure and the cantilever structure.

[0104] In the above technical solution, the SOI (Silicon-On-Insulator) substrate is composed of three layers, the front side is the device layer (a silicon layer used for making circuits and devices), the middle is the buried oxygen layer (usually silicon dioxide, which serves as an insulator), and the back side is the support layer (which 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 high deposition rate, good film quality and controllability. On the lower electrode, the piezoelectric layer is formed by sputtering deposition technology. Piezoelectric material generates electric charge when subjected to external force, which is the core sensitive element 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 form a capacitor structure for detecting the change in electric charge generated by the piezoelectric layer.

[0105] In particular, please refer to Figure 4 , Figure 4Schematic diagram of the substrate after step 1, 2 and 3.

[0106] Step 1, 2 and 3 are film forming processes, growing 100-1000 nm oxide layer on the surface of SOI substrate as isolation layer by thermal oxidation. Depositing 20-50 nm seed layer or adhesion layer on the front surface of the substrate by sputtering + oxygen containing annealing, which can be Ti, TiOx, AlN, ScAlN, etc. Depositing 50-500 nm bottom electrode on the front surface of the substrate by sputtering method, which can be Pt, Mo or other metals. Depositing 50-200 nm buffer layer on the surface of the substrate by sputtering method as buffer. Depositing 0.5-5 um piezoelectric layer on the surface of the substrate by sputtering method, which can be PZT, AlN, ScAlN or other piezoelectric thin film materials. Depositing 50-500 nm top electrode on the front surface of the substrate by sputtering method, which can be Pt, Mo or other metals.

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

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

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

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

[0111] The piezoelectric layer is patterned, including: forming the piezoelectric layer design pattern on the surface of the substrate by photolithography method, removing the excess piezoelectric material by dry etching or wet etching method, forming 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 step 6.

[0113] The lower electrode is patterned, including: forming the lower electrode design pattern on the surface of the substrate by photolithography method, removing the excess lower electrode metal by dry etching or wet etching method, forming 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 step 7 processing.

[0115] In some optional embodiments, the PAD is formed on the surface of the substrate, including:

[0116] The pattern of the connection line and the PAD is formed on the surface of the substrate by a photolithography method.

[0117] A metal layer is deposited on the surface of the substrate by an electron beam evaporation method; the material of the metal layer can be Ti, Ni, Cr, Al, Ag, Pt, Au, etc. or a mixed structure of several materials in a stack.

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

[0119] In the above technical solution, a layer of photoresist is uniformly coated on the surface of the substrate. The photoresist is a kind of organic material sensitive to light, and its properties will change after exposure. The substrate coated with the photoresist is exposed by a photoetching machine, and the pattern of the connection line and the PAD is transferred to the photoresist. After exposure, the photoresist in the exposed area is removed by using a developing solution to form the required pattern. The electron beam evaporation equipment is started, and the electron beam directly hits the metal target to make it evaporate. The evaporated metal atoms diffuse in the vacuum chamber and deposit on the surface of the substrate to form a uniform metal layer. The photoresist and the metal layer thereon are removed by using physical or chemical methods (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, while the metal layer on the surface of the substrate is not damaged. After the above steps, the PAD pattern required on the surface of the substrate is left, and these PADs will be used for connection with external circuits.

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

[0121] In some optional embodiments, the support layer is etched to form the vibration sensitive structure, the frame structure and the suspended beam structure, including:

[0122] Step 91, a front protection structure is arranged on the front surface of the substrate.

[0123] Step 92, the photoresist is coated on the back surface of the substrate, and the photoresist is patterned, the support layer with a set depth not covered by the photoresist is etched to form the vibration sensitive structure, and the remaining photoresist is cleaned.

[0124] Step 93, coat photoresist on the back of the substrate, and pattern the photoresist, etch away the support layer not covered by the photoresist, form the cantilever structure and frame structure, and clean away the remaining photoresist;

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

[0126] Step 95, remove the front protective structure.

[0127] In the above technical solution, photolithography technology is used to expose and develop the photoresist through a mask to form the required pattern. A suitable etching process (such as wet etching or dry etching) is used to etch away the support layer of a certain depth not covered by the photoresist. This step will form the preliminary profile of the vibration sensitive structure. A suitable cleaning agent is used to remove the remaining photoresist to ensure the cleanliness of the back of the substrate.

[0128] Again, coat photoresist on the back of the substrate and pattern it to form the pattern of the cantilever structure and frame structure. Similarly, a suitable etching process is used to etch away the support layer not covered by the photoresist. This step will form the preliminary profile of the cantilever structure and frame structure. Remove the remaining photoresist to ensure the cleanliness of the back of the substrate. A suitable etching process is used to etch away the buried oxide layer on the back of the substrate. This step requires precise control of etching depth and uniformity to ensure the stability and performance of the subsequent structure.

[0129] Please refer to Figure 9 , Figure 9 The schematic diagram of the substrate after steps 91 and 92 is shown below. Specifically, the front of the substrate is protected, the mass block design pattern is formed on the back of the substrate by photolithography, the excess support layer Si is removed by dry etching or wet etching to form the mass block structure of the piezoelectric MEMS accelerometer, and the photoresist is removed by organic cleaning or oxygen plasma.

[0130] Please refer to Figure 10 , Figure 10 The schematic diagram of the substrate after step 92 is shown below. Specifically, the hollow design pattern is formed on the back of the substrate by photolithography, the excess support layer Si is removed by dry etching or wet etching to form the suspended beam (or suspended membrane) structure and frame structure of the piezoelectric MEMS accelerometer, and the photoresist is removed by organic cleaning or oxygen plasma.

[0131] Please refer to Figure 11 , Figure 11 The schematic diagram of the substrate after step 93 is shown below. Specifically, the excess SiO2 is removed by vapor etching or wet etching or dry etching to release the suspended beam (or suspended membrane) structure, and the protective structure on the front of the substrate is removed.

[0132] Please refer to Figure 12, Figure 12 As shown in Fig. 6, the schematic diagram of the substrate processed in step 200 is shown, which specifically includes: reducing the area of the upper electrode by laser etching the upper electrode, playing a role of MIM structure capacitor adjustment, and then adjusting the induced voltage to the standard voltage value required by the design. The induced voltage can be adjusted to be larger by laser etching from the end of the upper electrode close to the mass block, and the induced voltage can be adjusted to be smaller by laser etching from the end of the upper electrode close to the frame.

[0133] In the embodiments provided by the present application, it should be understood that the disclosed device and method can be implemented in other ways. The device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There can be another division manner for actual implementation, or a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections between the units can be indirect couplings or communication connections through some interfaces, devices or units, and can be electrical, mechanical or in other forms.

[0134] In addition, the units described as separate components can or can not be physically separate, and the components displayed as units can or can not be physical units, that is, they can be located in one place, or can be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the embodiments.

[0135] In addition, the functional modules in each embodiment of the present application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0136] In this paper, the relationship terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations.

[0137] The above only describes the embodiments of the present application and is not used to limit the protection scope of the present application. For those skilled in the art, the present application can have various modifications and changes. 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 sensing voltage calibration of a piezoelectric MEMS accelerometer, characterized in that, include: After the piezoelectric MEMS accelerometer is fabricated, 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 set close to the frame structure; The etching of the upper electrode includes: If the difference V' between the measured value of the induced voltage and the standard value of the induced voltage is less than 0, the first etched area of ​​the upper electrode or the second etched area of ​​the upper electrode is etched. When the difference V' between the measured value of the induced voltage and the standard value of the induced voltage is greater than 0, the first etched area of ​​the upper electrode is etched. The first etched area is defined as the area from the first side of the upper electrode near the vibration-sensitive structure to the connection between the cantilever structure and the frame structure. The larger the difference V' between the measured value of the induced voltage and the standard value of the induced voltage, the closer the upper electrode is to the connection point in the first etched area. The smaller V' is, the closer the upper electrode is to the first side in the first etched area. The second etching region 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; Where V' = V1 - V0; V1 is the measured value of the induced voltage, and V0 is the standard value of the induced voltage.

2. The method of claim 1, wherein, After etching the first etched area of ​​the upper electrode, the induced voltage of the cantilever structure is: V=(Q-Q') / (C-C') Where 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, C' is the capacitance loss value after etching; X is a coefficient for different etching positions, and the value of X gradually increases from the first side to the connection point in the first etching region.

3. The method of claim 1, wherein, After etching the second etched area of ​​the upper electrode, the induced voltage of the cantilever structure is: V = Q / (C - C') Where Q is the induced charge before etching, C is the capacitance value before etching, and C' is the capacitance loss value after etching.

4. The method of claim 1, wherein, Fabrication of the piezoelectric MEMS accelerometer includes: Electrodes are sputtered and deposited on the front side of an 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. A piezoelectric layer is sputtered and deposited on the lower electrode; An electrode is sputtered and deposited on the piezoelectric layer; The upper electrode is patterned; The piezoelectric layer is patterned; The lower electrode is patterned; PADs are formed on the substrate surface; The device layer is patterned; The support layer is etched to form a vibration-sensitive structure, a frame structure, and a cantilever structure.

5. The method of claim 4, wherein, The electrode deposited by sputtering on the front side of the SOI substrate includes: Silicon oxide is grown on the surface of the SOI substrate by thermal oxidation as an isolation layer; Titanium is sputtered onto the isolation layer on the front side of the SOI substrate, or titanium is sputtered and then annealed with oxygen to form titanium oxide, thus forming an adhesion layer. The lower electrode is formed on the adhesive layer by sputtering and depositing metallic material.

6. The method of claim 4, wherein, The method for forming the PAD on the surface of the substrate comprises: forming the pattern of the connection line and the PAD on the surface of the substrate by the photoetching method; depositing a metal layer on the surface of the substrate by the electron beam evaporation; stripping the photoresist and the metal layer thereon to form the PAD.

7. The method of claim 4, wherein, The method for etching the support layer to form the vibration sensitive structure, the frame structure and the cantilever structure comprises: setting the front protection structure on the front surface of the substrate; coating the photoresist on the back surface of the substrate, patterning the photoresist, etching the support layer of the set depth which is not shielded by the photoresist to form the vibration sensitive structure, and cleaning the remaining photoresist; coating the photoresist on the back surface of the substrate, patterning the photoresist, etching the support layer which is not shielded by the photoresist to form the cantilever structure and the frame structure, and cleaning the remaining photoresist; etching the buried oxygen layer on the back surface of the substrate; removing the front protection structure.

Images