A high-precision multi-axis sensitive micro acceleration sensor chip and a preparation method thereof

Abstract

The application discloses a high-precision multi-axis sensitive micro acceleration sensor chip and a preparation method thereof, and belongs to the technical field of electric acceleration sensors. The multi-axis d33 mode micro piezoelectric acceleration sensor chip is characterized in that a SiO2 layer and an aluminum layer are arranged between a base contact area and a cap-shaped mass contact area, and a silicon dioxide-metal bonding process is realized through metal bonding, and a longitudinal piezoelectric mode is applied to the micro accelerometer, so that the technical problem that the existing speed sensor chip is difficult to meet the application requirement of the d33 piezoelectric sensor is solved.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric acceleration sensor technology, specifically relating to a high-precision multi-axis sensitive micro acceleration sensor chip and its fabrication method. Background Technology

[0002] With the rapid development of modern manufacturing towards intelligence, miniaturization, and integration, Micro-Electro-Mechanical Systems (MEMS) technology, with its advantages of miniaturization, mass production capability, low power consumption, and high integration—advantages that traditional machining technologies cannot match—has gained widespread application in fields such as industrial automation, consumer electronics, and aerospace. As an important branch of MEMS sensors, accelerometer chips can be classified into various types based on their working principles, mainly including piezoresistive types based on strain-resistance change effects, piezoelectric types based on strain-charge change effects, capacitive types based on electrode spacing changes, resonant types based on resonant frequency shifts, tunneling types based on quantum tunneling effects, and thermal conduction types based on the principle of thermal convection.

[0003] Among the many types of sensors, piezoelectric accelerometer chips exhibit significant advantages due to their unique electromechanical conversion mechanism. This type of sensor directly utilizes the intrinsic properties of piezoelectric materials; when subjected to mechanical stress, their crystal structure undergoes asymmetric deformation, leading to the separation of internal positive and negative charge centers and the generation of polarized charges. This self-generating characteristic, requiring no external power supply, gives the sensor advantages such as simple structure, fast dynamic response, and high signal-to-noise ratio. In particular, its excellent high-frequency response characteristics make it outstanding in scenarios requiring the capture of rapid dynamic changes, such as vibration monitoring and impact measurement.

[0004] Current mainstream piezoelectric accelerometer chips generally adopt the transverse piezoelectric effect, utilizing the piezoelectric coefficient d31 (the sensitive axis is orthogonal to the polarization direction) and piezoelectric materials (such as quartz crystals or lead zirconate titanate ceramics) cut with specific crystal orientations. In terms of structural implementation, three classic configurations are mainly adopted: cantilever beam-mass block, cross beam-mass block, or membrane-mass block. The former causes stress concentration at the beam root through the inertial displacement of the concentrated mass block at the end, while the latter relies on the displacement of the mass block caused by membrane deformation to generate strain. All three topologies have mature mechanical models and good process compatibility, perfectly fitting standard MEMS manufacturing processes.

[0005] However, for commonly used thin-film piezoelectric materials, the longitudinal piezoelectric effect boasts a higher piezoelectric coefficient (d33) and a higher quality factor, providing more charge signals, and its operating mode often exhibits a higher resonant frequency. Therefore, d33 piezoelectric sensors offer significant advantages in output voltage, energy conversion efficiency, high-precision applications, and high-frequency performance, making them particularly suitable for applications requiring high sensitivity, high power output, and high-precision control. However, due to the limitations of traditional MEMS crossbeam structure sensor chip fabrication and design, which cannot meet the needs of d33 mode MEMS piezoelectric accelerometers, there is a lack of exploration regarding d33 mode piezoelectric accelerometer chips and their fabrication methods. Summary of the Invention

[0006] The purpose of this invention is to provide a high-precision multi-axis sensitive micro accelerometer chip and its fabrication method, in order to solve the technical problem that existing accelerometer chips cannot meet the application requirements of piezoelectric sensors using the d33 mode.

[0007] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a high-precision multi-axis sensitive micro accelerometer chip, comprising a base and a cap-shaped mass block; the base includes a base contact area and a base handle; the base contact area is located at the center of the base; the base handle is located around the base contact area on the outer periphery of the base; the cap-shaped mass block has a cap-shaped mass block contact area at its center; a bottom electrode, a piezoelectric film, and a top electrode are sequentially disposed on the base contact area; a SiO2 layer is disposed on the top electrode and the base handle; the cap-shaped mass block contact area and the base contact area are bonded together by metal bonding, and an aluminum layer is disposed in the bonded area.

[0008] Furthermore, the thickness of the SiO2 layer is 500~1000nm.

[0009] Furthermore, the bottom electrode and the top electrode are respectively connected to the top electrode circuit used to derive the charge signal.

[0010] Furthermore, at the point where the contact area of ​​the cap-shaped mass block and the contact area of ​​the base are bonded together by metal bonding, a bonding allowance is left.

[0011] Furthermore, the piezoelectric film is a PZT piezoelectric film, a ZnO piezoelectric film, an AlN piezoelectric film, a KNN piezoelectric film, or a PMNPT piezoelectric film.

[0012] Furthermore, the bottom electrode and the top electrode are made of Pt electrode, Ti-Pt electrode, TiW alloy or Cr-Au electrode.

[0013] Furthermore, the material of the hat-shaped mass block is metal.

[0014] This invention also discloses a method for fabricating a high-precision multi-axis sensitive micro accelerometer chip, comprising the following steps: A piezoelectric thin film was prepared on the bottom electrode by sol-gel method, and the top electrode was sputtered by magnetron sputtering. Subsequently, a SiO2 layer was prepared on the top electrode by ion-enhanced chemical vapor deposition, and an aluminum layer was sputtered at the same location using a sputtering method. The SiO2 layer and piezoelectric thin film are patterned using wet etching to expose the bottom electrode; An aluminum layer is deposited on the base, and front overlay is performed. Then, the Al mask is obtained by peeling off. An aluminum layer is vapor-deposited in the contact area of ​​the cap-shaped mass block on the cap-shaped mass block. Finally, metal bonding is performed on the base contact area and the cap-shaped mass block contact area, leaving a bonding allowance.

[0015] Furthermore, the SiO2 layer is deposited using plasma-enhanced chemical vapor deposition. After sputtering the top electrode, a top electrode circuit is also sputtered.

[0016] Furthermore, the front etching process also includes front etching to release the base.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a high-precision multi-axis sensitive micro accelerometer chip. By setting a SiO2 layer and an aluminum layer between the base contact area and the cap-shaped mass block contact area, and achieving silicon dioxide-metal bonding through metal bonding, the longitudinal piezoelectric mode is applied to the micro accelerometer, providing a better option for applications requiring high sensitivity, high power output, and multi-directional measurement. A d33 mode multi-axis piezoelectric MEMS accelerometer is designed, providing a low-cost, high-reliability, and space-saving solution for applications requiring multi-vibration direction measurement. The sensitivity after fabrication is affected by the mass block structure mass, the mass block structure center of gravity size, and the contact surface size, exhibiting high flexibility and strong designability. The d33 mode MEMS piezoelectric accelerometer chip based on this design has the advantages of high precision, wide frequency response, strong designability, and suitability for multi-directional measurement. It solves the technical problem that existing accelerometer chips cannot meet the application requirements of piezoelectric sensors utilizing the d33 mode.

[0018] Furthermore, the chip of this invention proposes a method for applying the longitudinal piezoelectric mode to micro-accelerometers, enriching the design means of fabricating piezoelectric accelerometers using piezoelectric sensitive films; it also proposes a design method for multi-axis piezoelectric micro-accelerometers based on the d33 mode; simultaneously, with the same area of ​​sensitive film used (the usable area of ​​d33 is large, and the piezoelectric coefficient of PZT film d33 is 3-4 times higher than that of other directions), it improves important parameters such as output voltage, energy conversion efficiency, accuracy application and high-frequency performance, thus enhancing the application capabilities of piezoelectric sensitive films with high longitudinal piezoelectric coefficient and low transverse piezoelectric coefficient. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the preparation of PZT piezoelectric thin films using the sol-gel method of this invention; Figure 2 This is a three-dimensional schematic diagram of the base and the cap-shaped mass block of the present invention; Where: a-base; b-hat-shaped mass block; Figure 3 This is a schematic diagram of the overall structure and an AA cross-sectional view of the high-precision multi-axis sensitive micro accelerometer chip of the present invention; Where: a - overall structure; b - AA section; Figure 4 A schematic diagram illustrating the fabrication process of a high-precision multi-axis sensitive micro accelerometer chip. Wherein: a- PZT sensitive film prepared on Pt bottom electrode using sol-gel method; b- Top electrode, lead wire and pad diagram by magnetron sputtering deposition; c- Release base structure; d- Bonding diagram of base and cap-shaped mass block; Figure 5 This is a schematic diagram of the working principle of a high-precision multi-axis sensitive miniature accelerometer chip. Wherein: a - Working principle diagram of longitudinal acceleration measurement; b, c - Working principle diagram of lateral acceleration measurement; 1-Base; 2-Base contact area; 3-Base handle; 3-1, First base handle; 3-2, Second base handle; 3-3, Third base handle; 3-4, Fourth base handle; 4-Cap-shaped mass block contact area; 5-Bottom electrode; 5-1, First bottom electrode; 5-2, Second bottom electrode; 5-3, Third bottom electrode; 5-4, Fourth bottom electrode; 6-Piezoelectric film; 6-1, First piezoelectric film; 6-2, Second piezoelectric film; 6-3, Third piezoelectric film; 7-Top electrode; 7-1, First top electrode; 7-2, Second top electrode; 7-3, Third top electrode; 7-4, Fourth top electrode; 8-SiO2 layer; 9-Cap-shaped mass block; 10-Silicon substrate of the base; 12-Opening of the cap-shaped mass block; 12-1, Opening of the first cap-shaped mass block; 12-2, Opening of the second cap-shaped mass block; 12-3, Opening of the third cap-shaped mass block; 12-4, Opening of the fourth cap-shaped mass block; 13-Silicon substrate of the cap-shaped mass block. Detailed Implementation

[0020] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0021] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0022] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0023] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0024] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0025] like Figures 2-4 As shown, this invention provides a high-precision multi-axis sensitive micro accelerometer chip, which uses two wafers to manufacture a cap-shaped mass block and a base, respectively, and bonds the two parts tightly together; specifically including: The system comprises a base 1 and a cap-shaped metal mass block 9. The base 1 includes a base contact area 2 and a base handle 3. A bottom electrode 5 is sequentially sputtered onto the base contact area 2. A piezoelectric thin film 6 is grown on the bottom electrode 5 using sputtering and PECVD. A top electrode 7 and a SiO2 layer 8 are then formed. When an acceleration signal is received, the cap-shaped mass block 9 vibrates, causing stress on the piezoelectric thin film 6 and generating a charge signal. The piezoelectric thin film 6 acts as a sensing element, outputting charge when stress is generated. The bottom electrode 5 and the top electrode 7 collect these charge signals and export them through the top electrode circuit. The bottom electrode 5, in addition to serving as an electrode, also acts as a guiding layer in the sol-gel fabrication of the piezoelectric thin film 6. The base 1 is disposed on a silicon substrate 10.

[0026] After the bottom electrode 5, piezoelectric film 6, and top electrode 7 are fabricated, a 500nm-1000nm SiO2 layer 8 is grown as a protective layer using PECVD. A cap-shaped mass block 9 is precision-machined to create a cap-shaped mass block contact area 4. An aluminum layer is sputtered onto both the cap-shaped mass block contact area 4 and the base contact area 2 as an interlayer. The SiO2 layer 8 is bonded to the aluminum layer and tightly bonded to the base. The cap-shaped mass block contact area 4 and the base contact area 2 are then bonded together. The cap-shaped mass block 9 is disposed on the silicon substrate 13 of the cap-shaped mass block.

[0027] This invention also discloses a method for fabricating the aforementioned high-precision multi-axis sensitive micro accelerometer chip, comprising the following steps: Step 1: Prepare a piezoelectric thin film 6 on the bottom electrode 5 using the sol-gel method; Step 2: Sputter the top electrode 7 and the top electrode circuit using magnetron sputtering, and pattern the metal layer using photolithography; each top electrode 7 is arranged in the base contact area 2; Step 3: A dense SiO2 layer 8 is deposited on the substrate 1, including the substrate contact area 2, using the plasma-enhanced chemical vapor deposition (PECVD) method, and a layer of metallic aluminum is sputtered at the same location using the sputtering method. Step 4: Pattern the SiO2 layer 8 and the piezoelectric thin film 6 using wet etching to expose the bottom electrode 5; Step 5: Evaporate Al onto base 1, perform front overlay etching, use acetone to remove Al masking, etch the front side, release base 1, and remove Al with Al etching solution. Step 6: Deposit an Al layer onto the metal cap-shaped mass block 9, which has been precision machined to leave the cap-shaped mass block contact area 4; Step 7: With bonding allowance left between the base contact area 2 and the cap-shaped mass block contact area 4, the two wafers are bonded together to complete the processing of the sensor chip; Step 8: Scribing and releasing the sensor structure.

[0028] Preferably, the bottom electrode 5 and the top electrode 7 are made of Pt, Ti-Pt electrode, TiW alloy, or Cr-Au electrode, etc.

[0029] Preferably, the piezoelectric film 6 is a PZT piezoelectric film, a ZnO piezoelectric film, an AlN piezoelectric film, a KNN piezoelectric film, or a PMNPT piezoelectric film.

[0030] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0031] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0032] Example 1 like Figure 1 As shown, using Figure 1 The sol-gel method shown deposits a layer of Pb(Zr) with a thickness of approximately 1 μm on substrate 1. 0.52 Ti 0.48 O3 thin film (piezoelectric thin film 6); the Pb(Zr) 0.52 Ti 0.48 The preparation process of O3 thin film is as follows: Appropriate amounts of formamide and acetylacetone were added to the solution to prevent film cracking. Each layer was dried at 150 °C, and then pyrolyzed in a box furnace at different temperatures from 300 to 500 °C for 10 minutes to fully remove organic matter. Samples were taken after pyrolysis for characterization, and the remaining portion was returned to the box furnace and annealed at 650 °C for 30 minutes. Annealing was performed after every two layers of pyrolysis, for a total of 5 annealing cycles to obtain piezoelectric film 6. Figure 4 As shown in (a); Using a photomask, the first photolithography is performed on the piezoelectric thin film 6, leaving an area for sputtering the metal thin film. The photolithographically patterned silicon wafer is placed in the coating chamber, a vacuum is drawn, and Pt electrodes are sputtered using magnetron sputtering. The sample is then removed from the coating chamber and stripped with acetone to obtain patterned electrodes, leads, and pads. The top electrode 7 covers the entire base contact area to collect all the charge generated by the stress on the sensitive material on the base contact surface when the sensor vibrates. A dense SiO2 layer 8 is deposited on the base 1, including the base contact area 2, using the PECVD method. The SiO2 layer 8 serves two functions: protecting and bonding materials. The SiO2 layer 8 protects the piezoelectric film 6, the top electrode 7, and the top electrode circuit from external contamination and damage during subsequent processes and operation. At the same time, it participates in bonding as part of the silicon dioxide-silicon bonding process, combining the base 1 and the cap-shaped mass block 9. The PECVD silica film and the sol-gel PZT piezoelectric film 6 were patterned using wet etching to expose the bottom electrode 5 and the top electrode 7. The bottom electrode 5 and the top electrode 7 are located at the top and bottom poles of the PZT piezoelectric film, respectively, to collect piezoelectric charges. Figure 4 (b) shows that the PZT etching solution used in the experiment consisted of 100 mL BOE (6:1) + 6 mL CH3COOH + 6 mL HNO3 (65%) + 6 mL HCl (35%) + 4 g (NH4Cl) + 2 g C10H18N2O10 (EDTA) + 75 mL deionized water; the silica etching solution used in the experiment was BOE (6:1). Al is sputtered onto the surface of the wafer, followed by front-side etching. The Al mask is obtained by acetone stripping, and after dry etching, the remaining Al on the silicon wafer surface is washed away with aluminum etchant. The base 1 is released through front-side etching; the aluminum layer is retained as an intermediary layer for bonding. The cap-shaped mass block 9 is obtained by MEMS wafer fabrication, where an Al layer is sputtered onto the existing silicon wafer structure. A cap-shaped mass block contact area 4 is located at the center of the cap-shaped mass block 9. The base 1 and the cap-shaped mass block 9 only contact at this contact area. This is to amplify the stress during vibration, ensuring that the mechanical energy of the vibration is completely collected by the PZT piezoelectric film. The center of the gauge block 9 is adjusted to be consistent with the contact area 2 of the base through the design of the contact area 4 of the cap-shaped mass block and the opening 12 of the cap-shaped mass block. The openings 12-1, 12-2, 12-3, and 12-4 of the first, second, and third cap-shaped mass blocks correspond one-to-one with the handles 3-1, 3-2, 3-3, and 3-4 of the first, second, and third bases, respectively. The periphery of the cap-shaped mass block 9 is higher than the center, which is to adjust the height distance between the center of gravity of the mass block and the contact surface. Four quarter-circle piezoelectric films 6-1, 6-2, 6-3, and 6-4 are evenly arranged on the contact area 2 of the base. Four top electrodes of the same size are arranged on the films and led out through the circuit, namely the first top electrode 7-1, the second top electrode 7-2, the third top electrode 7-3, and the fourth top electrode 7-4. The first bottom electrode 5-1, the second bottom electrode 5-2, the third bottom electrode 5-3, and the fourth bottom electrode 5-4 are arranged next to the top electrode 7.

[0033] The upper and lower surfaces of the two wafers have bonding allowances, and metal bonding is performed at 450℃ and 30MPa. The Al-Al interface undergoes plastic deformation and forms a bond through atomic diffusion. The Al-SiO2 interface forms a chemical bond Al-O-Si. The upper and lower wafers only contact each other at the cap-shaped mass block contact area 4 and each chip frame. Contacts in other places are to increase the contact area, improve the stability of the bonding process, and facilitate subsequent dicing processes. The protruding design of the opening 12 of the cap-shaped mass block is to adjust the horizontal position of the center of gravity to be consistent with the base contact area 2, and at the same time, it cooperates with the slope of the base as an auxiliary positioning during bonding. The sensor structure is diced and released using a laser scribing machine. In the released sensor chip structure, the cap-shaped mass block 9 and the base 1 remain in contact only in the cap-shaped mass block contact area 4.

[0034] The working principle of the high-precision multi-axis sensitive micro accelerometer chip disclosed in this invention is as follows: Reference Figure 5According to Newton's second law, when the hat-shaped mass 9 is subjected to acceleration in a certain direction, an inertial force proportional to the acceleration will be generated on the hat-shaped mass 9, causing displacement of the hat-shaped mass 9, and its stress... 3. Size is: (1); Where m is the mass of the block, a is the vibration acceleration, and s is the area of ​​the contact zone.

[0035] From the first kind of piezoelectric equation, we get: (2); in, and Stress and strain of directional piezoelectric thin film 6 It is the flexibility constant of PZT under a constant electric field. The electric field applied in the direction is (the corresponding voltage is V). The dielectric constant of PZT is... The longitudinal piezoelectric coefficient, The surface polarization intensity; Integrating along the L direction and substituting the two equations, we get: (3); Wherein, the surface area of ​​the contact area is s.

[0036] The above analysis shows that when the sensor chip is subjected to a longitudinal load, the sensor output signal is directly proportional to the magnitude of the longitudinal acceleration. This formula indicates that the longitudinal sensitivity is adjustable, and its magnitude is affected by the mass of the cap-shaped mass block 9. In this mode, the output charge of the MEMS piezoelectric accelerometer chip is proportional to the acceleration it experiences, thus converting acceleration into an electrical signal output. The stress magnitude of the MEMS piezoelectric accelerometer chip operating in longitudinal piezoelectric mode is related to the longitudinal piezoelectric coefficient. The size, weight, and acceleration of the cap-shaped mass block are related.

[0037] When the mechanism is subjected to lateral acceleration, the sensor cap-shaped mass 9 is subjected to acceleration load stress. The center of gravity of the cap-shaped mass 9 is h above the joint surface, and the radius of the mass is r. The magnitude of the bending moment from the acceleration load at the center of the joint surface is: (4); Assume the mass block is a rigid body. On a single, semi-circular piezoelectric film, a load at a distance x from the center is... (5); Combined with the bending moment formula (4) (7); have to: (8); Substitute the piezoelectric equation (2) and the charge formula (3) into the equation. (9); have to (10); As can be seen from this formula, when the sensor chip is subjected to a lateral load, the sensor output signal is proportional to the magnitude of the acceleration signal. The lateral sensitivity is adjustable, and its magnitude is affected by the mass of the hat-shaped mass block 9, the size of the center of gravity of the hat-shaped mass block 9, and the size of the contact area 2 of the base.

[0038] Example 2 In this embodiment, the sensor structure and dielectric layer are the same as in Embodiment 1. The difference lies in the use of different piezoelectric thin films to meet the needs of different application scenarios. Based on this, a piezoelectric MEMS accelerometer chip is fabricated, as detailed below: AlN thin films were deposited using reactive magnetron sputtering. During the magnetron sputtering process, electrons move rapidly towards the substrate under the influence of an electric field. These electrons collide with inert argon atoms, causing ionization and forming Ar atoms. + And new electrons, on the one hand producing Ar + Under the influence of electric and magnetic fields, the atoms gain significant kinetic energy and accelerate to the Al target surface, bombarding it with high energy. This impact triggers a series of cascade reactions on the Al target surface. Some Al atoms gain sufficient energy to detach from the target surface (sputtered Al atoms) and react with the working gas nitrogen, depositing onto the substrate. Meanwhile, newly formed secondary electrons, influenced by the magnetic field of the magnetron target, have longer trajectories and collide again with inert Ar atoms, producing new Ar atoms. + The electrons react with the AlN to form a new deposition reaction, thus producing an AlN thin film.

[0039] The difference in step 1 is that in Si / SiO 2 / A uniform and dense aluminum nitride film with a thickness of 500-1000 nm was obtained by sputtering on a Pt substrate with a sputtering pressure of 0.3 Pa, a sputtering voltage of 250 W, and a nitrogen content of 50% for 45-90 min.

[0040] Step 6 differs in that it uses inductively coupled plasma etching (ICP), with chlorine gas as the etching gas and Cr / Au metal as the hard mask to etch the AlN epitaxial layer. The silicon wafer is then placed in a Cr / Au etching solution to remove the mask. The Cr etching solution is prepared based on high-purity cerium ammonium nitrate, containing a small amount of nitric acid to maintain the acidic environment of the etching solution. The Au etching solution is typically prepared from potassium iodide and iodine. AlN thin films prepared by magnetron sputtering can produce high-quality, dense, and uniform films with good adhesion and mechanical properties, high purity, and uniform film thickness. By adjusting sputtering parameters such as target material composition, gas pressure, deposition rate, and substrate temperature, the properties of the film can be precisely controlled to meet the performance requirements of different applications. Deposition can be performed at relatively low temperatures, avoiding substrate damage and film defects that may occur with high-temperature processes, which is particularly important for some temperature-sensitive substrate materials.

[0041] Preferably, the sensitive thin film piezoelectric layer 6 can also be a ZnO piezoelectric thin film, a KNN piezoelectric thin film, or a PMNPT piezoelectric thin film.

[0042] In summary, this invention proposes a method for applying longitudinal piezoelectric modes to triaxial micro-accelerometers, enriching the design methods for fabricating piezoelectric accelerometers using piezoelectric sensitive films; it proposes a method for designing sensitivity by adjusting the mass weight, center of gravity height, and contact surface area; it improves important parameters such as output voltage, energy conversion efficiency, accuracy, and high-frequency performance under the same sensitive film area; and it enhances the application capabilities of some piezoelectric sensitive films with high longitudinal piezoelectric coefficients and low transverse piezoelectric coefficients.

[0043] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A high-precision multi-axis sensitive miniature accelerometer chip, characterized in that, The device includes a base (1) and a cap-shaped mass block (9); the base (1) includes a base contact area (2) and a base handle (3); the base contact area (2) is located at the center of the base (1); the base handle (3) is located around the base contact area (2) on the outer periphery of the base (1); the center of the cap-shaped mass block (9) is provided with a cap-shaped mass block contact area (4); a bottom electrode (5), a piezoelectric film (6), and a top electrode (7) are sequentially provided on the base contact area (2); a SiO2 layer (8) is provided on the top electrode (7) and the base handle (3); the cap-shaped mass block contact area (4) and the base contact area (2) are bonded together by metal bonding, and an aluminum layer is provided in the bonded area.

2. The high-precision multi-axis sensitive micro accelerometer chip according to claim 1, characterized in that, The thickness of the SiO2 layer (8) is 500~1000nm.

3. The high-precision multi-axis sensitive micro accelerometer chip according to claim 1, characterized in that, The bottom electrode (5) and the top electrode (7) are respectively connected to the top electrode circuit used to extract charge signals.

4. The high-precision multi-axis sensitive micro accelerometer chip according to claim 1, characterized in that, The contact area (4) of the cap-shaped mass block and the contact area (2) of the base are bonded together by metal bonding, with a bonding allowance.

5. A high-precision multi-axis sensitive micro accelerometer chip according to claim 1, characterized in that, The piezoelectric film (6) is a PZT piezoelectric film, a ZnO piezoelectric film, an AlN piezoelectric film, a KNN piezoelectric film, or a PMNPT piezoelectric film.

6. A high-precision multi-axis sensitive micro accelerometer chip according to claim 1, characterized in that, The bottom electrode (5) and top electrode (7) are made of Pt electrode, Ti-Pt electrode, TiW alloy or Cr-Au electrode.

7. A high-precision multi-axis sensitive micro accelerometer chip according to claim 1, characterized in that, The material of the cap-shaped mass block (9) is metal.

8. A method for fabricating a high-precision multi-axis sensitive micro accelerometer chip according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Prepare a piezoelectric thin film (6) on the bottom electrode (5) by sol-gel method; Step 2: Sputter the top electrode (7) and the top electrode circuit using magnetron sputtering, and pattern the metal layer using photolithography; each top electrode (7) is arranged in the base contact area (2); Step 3: Deposit a dense SiO2 layer (8) on the substrate (1), including the substrate contact area (2), using plasma-enhanced chemical vapor deposition, and sputter a metal Al layer at the same location using sputtering. Step 4: Pattern the SiO2 layer (8) and the piezoelectric film (6) using wet etching to expose the bottom electrode (5). Step 5: Evaporate Al onto the base (1), perform front overlay etching, peel off with acetone to obtain Al masking, etch the front side, release the base (1), and remove Al with Al etching solution; Step 6: Deposit an Al layer on the metal cap-shaped mass block (9) that has been precision machined to leave the cap-shaped mass block contact area (4); Step 7: The base contact area (2) and the cap-shaped mass block contact area (4) have a bonding allowance. The two wafers are bonded together to complete the processing of the sensor chip. Step 8: Scribing and releasing the sensor structure.

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