A three-axis accelerometer based on lamb wave resonators and a method of manufacturing the same

Abstract

The application discloses a three-axis accelerometer based on a Lamb wave resonator and a preparation method thereof. The three-axis accelerometer based on the Lamb wave resonator adopts the Lamb wave resonator to detect acceleration, the Lamb wave resonator has the advantages of high Q value and high frequency stability, and the resonant frequency of the Lamb wave resonator is extremely sensitive to the change of external acceleration, so that high-resolution, low-noise and low-bias acceleration detection can be realized, and the three-axis accelerometer based on the Lamb wave resonator is significantly superior to a traditional capacitive MEMS acceleration sensor. The three-axis accelerometer based on the Lamb wave resonator has the advantages of small size and low cost. The low drift and high resolution characteristics of traditional large-size mechanical accelerometers are realized on a chip scale, and the three-axis accelerometer based on the Lamb wave resonator can promote the wide application of inertial navigation level acceleration sensors.

Description

Technical Field

[0001] This invention belongs to the field of sensor chip technology, specifically relating to a triaxial accelerometer based on a Lamb wave resonator and its fabrication method. Background Technology

[0002] High-precision, low-drift navigation-grade accelerometers have wide applications in fields such as autonomous driving, military, and consumer electronics.

[0003] Typical navigation-grade accelerometers include fiber optic accelerometers, quartz resonant accelerometers, and force balance accelerometers. Although these types of accelerometers have high precision and low drift characteristics, they are relatively large and consume more power due to the use of more traditional manufacturing processes.

[0004] Microelectromechanical systems (MEMS) are miniature electromechanical systems fabricated using micro- and nano-fabrication techniques, enabling the fabrication of electromechanical sensors and actuators at the chip scale. Accelerometers based on MEMS technology include capacitive, piezoresistive, piezoelectric, and thermal accelerometers. However, existing MEMS accelerometers typically exhibit significant drift and low accuracy, failing to meet the requirements of navigation-level applications and limiting their use to consumer electronics.

[0005] For example, invention application CN116593735A discloses a MEMS capacitive accelerometer and its fabrication method. The MEMS capacitive accelerometer includes: a first substrate; a first electrode layer and a support layer disposed on the first substrate, with the support layer located outside the first electrode layer; an elastic element and an elastic element chassis, with a first end of the elastic element inserted into the first electrode layer and abutting against the first substrate, and a second end abutting against the elastic element chassis; a connecting layer disposed on the side of the support layer and the elastic element chassis away from the first substrate; a second substrate disposed on the side of the connecting layer away from the first substrate; an elastic beam and a mass block disposed on the second substrate, with the mass block corresponding to the first electrode layer and the elastic beam located outside the mass block; a second electrode layer and an insulating layer, with the insulating layer disposed on the side of the mass block facing the first substrate, and the second electrode layer sandwiched between the insulating layer and the connecting layer.

[0006] For example, invention application CN116973597A discloses a high-frequency response, high-sensitivity piezoresistive accelerometer, including an upper cover, a support frame, sensitive beams, a mass block, piezoresistors, and a lower cover. This structure has four sensitive beams located at the four corners of the mass block. The sensitive beams are short and wide, with asymmetrical structures at both ends, specifically T-shaped and Y-shaped. The short side connects to the mass block, and the long side connects to the support frame. A piezoresistor is arranged at the middle of each end of the sensitive beam. The eight piezoresistors form a Wheatstone full-bridge circuit, ensuring a high first-order natural frequency while significantly improving sensitivity. Due to the arrangement of the piezoresistors, this structure can withstand higher lateral impacts, reducing the device's lateral sensitivity. Summary of the Invention

[0007] This invention addresses the problems of large drift and low accuracy in existing MEMS accelerometers by providing a triaxial accelerometer based on a Lamb wave resonator and its fabrication method, thereby realizing a chip-scale navigation-grade accelerometer.

[0008] This invention first provides a triaxial accelerometer based on a Lamb wave resonator, comprising:

[0009] The substrate has a ring structure with a cavity in the middle.

[0010] The mass block is located inside the cavity;

[0011] A suspended piezoelectric film is disposed on the top surface of the mass block and the substrate to connect the mass block and the substrate, thereby suspending the mass block in the cavity of the substrate. The suspended piezoelectric film includes four strips for connecting the mass block and the substrate from different directions, forming four Lamb wave resonators. The suspended piezoelectric film includes a support layer, a lower electrode layer, a piezoelectric layer and an upper electrode layer arranged sequentially from the bottom surface to the top surface. The support layer has a through hole for the lower electrode layer to extend downward and connect to the mass block. The lower electrode layer forms a lower electrode in the through hole, and the upper electrode layer is patterned to form interdigitated electrodes.

[0012] An encapsulation substrate is used to encapsulate the opening of the cavity on one side of the bottom surface of the substrate. A gap is left between the encapsulation substrate and the mass block to allow the mass block to move during the detection process. Furthermore, the gap allows a capacitor structure to be formed between the encapsulation substrate and the mass block.

[0013] Preferably, the cross-section of the cavity of the substrate is square, and the cross-section of the mass block is also square. The top surface of the mass block is connected to the substrate through the middle of each of the four sides by a suspended piezoelectric film. The two suspended piezoelectric films on opposite sides of the top surface of the mass block are arranged along a straight line, and the two suspended piezoelectric films on adjacent sides are arranged perpendicularly.

[0014] More preferably, the width of each of the suspended piezoelectric films is 1 μm to 200 μm;

[0015] The cross-sectional side length of the mass block is 10μm to 1000μm;

[0016] The lateral spacing (the span length of the suspended piezoelectric film) between the mass block and the substrate is 10 μm to 500 μm.

[0017] Preferably, the Lamb resonator is of one of the following types: a Lamb resonator excited by a single-sided interdigitated electrode, a Lamb resonator excited by an upper interdigitated electrode and a lower plate electrode, a Lamb resonator excited by interdigitated electrodes on both the upper and lower sides, or a Lamb resonator excited by plate electrodes on both the upper and lower sides.

[0018] The substrate is made of at least one of the following materials: silicon, silicon carbide; preferably, the substrate and the packaging substrate are doped to reduce resistivity, and the doping element is at least one of the following: boron, phosphorus;

[0019] The materials of the upper electrode layer and the lower electrode layer are each selected from at least one of the following: aluminum, platinum, tungsten, and molybdenum;

[0020] The piezoelectric layer is made of at least one of the following materials: aluminum nitride, lithium niobate, zinc oxide, and gallium lanthanum silicate.

[0021] The material of the support layer is selected from at least one of the following: silicon oxide, silicon nitride;

[0022] The material of the packaging substrate is selected from at least one of the following: silicon, silicon carbide.

[0023] Preferably, the thickness of the substrate is 100–1000 μm;

[0024] The thickness of the upper electrode layer is 50–1000 nm;

[0025] The thickness of the lower electrode layer is 50–1000 nm;

[0026] The thickness of the piezoelectric layer is 100 nm to 10 μm;

[0027] The thickness of the support layer is 500 nm to 10 μm;

[0028] The thickness of the packaging substrate is 100–1000 μm.

[0029] Preferably, the encapsulation substrate is connected to the substrate via a bonding layer;

[0030] The bonding layer may be one or more layers;

[0031] The thickness of each bonding layer is 1–20 μm.

[0032] The bonding layer is made of at least one of the following materials: gold, tin, indium, and nickel.

[0033] Preferably, the upper electrode layer is patterned to form interdigitated electrodes, and the PADs of the interdigitated electrodes are located on one side of the substrate.

[0034] The interdigitated electrodes are patterned during the formation of the upper electrode layer. Specifically, they can be fabricated using a lift-off process. The steps are as follows: first, a photoresist pattern complementary to the electrode pattern is created using photolithography; then, metal is deposited; and finally, the entire structure is immersed in a resist remover (acetone, NMP, etc.) to remove the photoresist and the metal on it, leaving only the patterned electrodes.

[0035] Preferably, in the fabrication of the triaxial accelerometer based on the Lamb wave resonator of the present invention, the same layer structure in each suspended piezoelectric film is formed at one time. The portion of the support layer, lower electrode layer, piezoelectric layer and upper electrode layer located between the substrate and the mass block constitutes the suspended piezoelectric film, and the portion located in the mass block region is part of the mass block.

[0036] More preferably, the lower electrode formed by the lower electrode layer is located in the middle of the mass block, the lower electrode extends along one of the suspended piezoelectric films as a connecting line, and a PAD of the lower electrode is formed above the region where the substrate is located. The lower electrode also extends symmetrically along the opposite direction of the connecting line as a counterweight. The present invention further provides a method for fabricating the triaxial accelerometer based on the Lamb wave resonator, comprising the following steps:

[0037] (1) A support layer, a lower electrode layer, a piezoelectric layer and an upper electrode layer are sequentially formed on the top surface of the substrate used to form the substrate and the mass block; wherein the lower electrode layer forms a lower electrode and the upper electrode layer is patterned to form an interdigitated electrode;

[0038] (2) Etch the substrate from the bottom surface to remove excess substrate between the substrate and the mass block;

[0039] (3) The encapsulation substrate is used to encapsulate the bottom surface of the substrate to obtain the triaxial accelerometer based on the Lamb wave resonator.

[0040] This invention relates to a triaxial accelerometer based on a Lamb wave resonator, which uses a Lamb wave resonator for acceleration detection. The Lamb wave resonator has the advantages of high Q value and high frequency stability, and its resonant frequency is extremely sensitive to changes in external acceleration. Therefore, it can achieve high resolution, low noise, and low offset acceleration detection, which is significantly better than traditional capacitive MEMS accelerometers.

[0041] Compared to traditional quartz resonant velocity sensors, this invention, due to its MEMS fabrication process, offers advantages such as smaller size and lower cost. The miniaturized Lamb wave resonant accelerometer fabricated using MEMS technology achieves sub-millimeter dimensions, solving the miniaturization problem of traditional navigation-grade accelerometers, reducing their cost, and expanding their application scenarios.

[0042] The Lamb wave resonant accelerometer proposed in this invention achieves the low drift and high resolution characteristics of traditional large-size mechanical accelerometers at the chip scale, which can promote the widespread application of inertial navigation-grade accelerometers. Attached Figure Description

[0043] Figure 1 This is a top view of the triaxial accelerometer based on the Lamb wave resonator of the present invention after the lower electrode layer has been formed.

[0044] Figure 2 This is a top view of the triaxial accelerometer based on a Lamb wave resonator according to the present invention.

[0045] Figure 3 This is a longitudinal cross-sectional view of the triaxial accelerometer based on the Lamb wave resonator of the present invention.

[0046] Figure 4 Four Lamb wave resonator configurations for the triaxial accelerometer of this invention are proposed.

[0047] Figure label:

[0048] Substrate 101, mass block 102, suspended piezoelectric film 103, interdigitated electrode 104, PAD 105, PAD 106, lower electrode 107.

[0049] Upper electrode layer 201, piezoelectric layer 202, lower electrode layer 203, support layer 204, bonding layer 205, bonding layer 206, packaging substrate 207, parallel plate capacitor 208.

[0050] Lamb resonator 301 is excited by a single interdigitated electrode, Lamb resonator 302 is excited by an upper interdigitated electrode and a lower plate electrode, Lamb resonator 303 is excited by interdigitated electrodes on both sides, and Lamb resonator 304 is excited by plate electrodes on both sides. Detailed Implementation

[0051] This invention proposes a triaxial accelerometer based on a Lamb wave resonator, the top view of which after the lower electrode layer is formed is shown below. Figure 1 As shown, the overall top view of the structure after all parts are completed is as follows: Figure 2 As shown, it includes a substrate 101, a mass block 102, and four suspended piezoelectric thin films 103 uniformly distributed on the four sides of the mass block 102.

[0052] like Figure 3 The figure shown is a cross-sectional view of the triaxial accelerometer of the present invention. The substrate 101 has an upper electrode layer 201, a piezoelectric layer 202, a lower electrode layer 203 and a support layer 204.

[0053] The substrate 101 has a ring structure with a cavity in the middle, and the mass block 102 is located inside the cavity in the middle of the substrate 102. A suspended piezoelectric film 103 is disposed on the top surface of the mass block 102 and the substrate 101, connecting the mass block 102 and the substrate 101, thereby suspending the mass block 102 in the cavity of the substrate 101. The suspended piezoelectric film 103 has four strips for connecting the mass block 102 and the substrate 101 from different directions.

[0054] In a preferred embodiment, the cavity of the substrate 101 has a square cross-section, and the mass block 102 also has a square cross-section. The top surface of the mass block 102 is connected to the substrate 101 through a suspended piezoelectric film 103 at the middle of each of the four sides. The two suspended piezoelectric films 103 on opposite sides of the top surface of the mass block 102 are arranged along a straight line, and the two suspended piezoelectric films 103 on adjacent sides are arranged perpendicularly.

[0055] The width of each suspended piezoelectric film 103 is 1 μm to 200 μm. The side length of the cross-section of the mass block 102 is 10 μm to 1000 μm. The lateral spacing between the mass block 102 and the substrate 101 (i.e., the span of the suspended piezoelectric film 103) is 10 μm to 500 μm.

[0056] The suspended piezoelectric film 103 includes a support layer 204, a lower electrode layer 203, a piezoelectric layer 202 and an upper electrode layer 201 formed sequentially from the bottom surface to the top surface.

[0057] Each suspended piezoelectric thin film 103 is formed in one continuous process: first, a support layer 204 is formed, then a lower electrode layer 203 is formed, followed by a piezoelectric layer 202, and finally an upper electrode layer 201 is formed. In each layer structure, the portion located between the substrate 101 and the mass block 102 constitutes the suspended piezoelectric thin film 103, and the portion located in the region of the mass block 102 is part of the mass block 102.

[0058] The support layer 204 is used to adjust the mechanical strength and operating frequency of the overall structure. The support layer 204 has through holes for the lower electrode layer 203 to extend downward and connect to the mass block 102.

[0059] The lower electrode layer 203 includes a planar or interdigitated electrode for exciting Lamb waves, and a PAD 106 for externally connecting the capacitor plates of the mass block. In a preferred embodiment, the lower electrode layer 203 forms a lower electrode 107 within a through-hole in the support layer 204. The lower electrode 107 is located in the middle of the mass block 102. The lower electrode 107 extends a connecting line along one of the suspended piezoelectric films 103, and the PAD 106 of the lower electrode 107 is formed above the region where the substrate 101 is located. The lower electrode 107 also extends a counterweight line symmetrically in the opposite direction to the connecting line. The connecting line, the counterweight line, and the PAD 106 are located above the support layer 204. The piezoelectric layer 202 utilizes the piezoelectric effect to convert electrical energy into mechanical energy, generating Lamb wave vibrations. When the piezoelectric layer 202 is formed, the region corresponding to the PAD 106 is removed, thereby exposing the PAD 106.

[0060] The upper electrode layer 201 includes interdigitated electrodes 104 for applying an alternating electric field to generate a Lamb wave through electric field excitation, and also includes PADs 105 for external connections. The upper electrode layer 201 is patterned to form the interdigitated electrodes 104. The PADs 105 of the interdigitated electrodes 104 are located on one side of the substrate 101. The interdigitated electrodes 104 are obtained by patterning during the formation of the upper electrode layer 201. Specifically, they can be fabricated using a lift-off process. The steps are as follows: first, a photoresist pattern complementary to the electrode pattern is created using photolithography; then, metal is deposited; and finally, the entire structure is immersed in a resist remover (acetone, NMP, etc.) to remove the photoresist and the metal on it, leaving only the patterned electrodes.

[0061] The substrate 101 is made of materials such as silicon or silicon carbide, and can be doped to achieve a low resistivity. The doping element is at least one of the following: boron or phosphorus. The thickness of the substrate 101 is 100–1000 μm. The upper electrode layer 201 and the lower electrode layer 203 can be made of metals such as aluminum, platinum, tungsten, or molybdenum, with a thickness of 50–1000 nm. The piezoelectric layer 202 can be made of materials such as aluminum nitride, lithium niobate, zinc oxide, or gallium lanthanum silicate, with a thickness of 100 nm–10 μm. The support layer 204 can be made of materials such as silicon oxide or silicon nitride, with a thickness of 500 nm–10 μm.

[0062] The suspended piezoelectric thin film 103 is formed by removing the underlying substrate material through dry or wet etching, and its interdigitated electrodes 104 are patterned from the upper electrode layer 201. The substrate material surrounding the mass block 102 is etched, leaving only the suspended piezoelectric thin film 103 to connect it to the substrate. The mass block 102 and the lower electrode layer 203 are connected by vias, meaning that the support layer 204 has vias that allow the lower electrode layer 203 to extend downwards and connect to the mass block 102.

[0063] Since the chip needs to be bonded to the substrate for packaging, in order to facilitate packaging while maintaining the free movement of the mass block 102, this invention introduces a packaging substrate 207, a bonding layer 205, and a bonding layer 206 below the substrate 101. The thickness of both the bonding layer 205 and the bonding layer 206 is set to 1–20 μm to ensure sufficient vertical clearance between the mass block 102 and the packaging substrate 207. The bonding layer 205 can be made of metal materials such as gold, tin, indium, or nickel, and the packaging substrate 207 is made of materials such as silicon or silicon carbide, and can be doped to have lower resistance, with a thickness of 100–1000 μm.

[0064] The gap between the encapsulation substrate 207 and the mass block 102 also forms a planar capacitor 208. The capacitor plate on the encapsulation substrate side is directly connected to the external metal ground through the encapsulation substrate 207, while the plate on the mass block side is connected to the lower electrode layer 203 through a through hole and led out to the capacitance detection circuit.

[0065] The present invention discloses a method for fabricating a triaxial accelerometer based on a Lamb wave resonator, comprising the following steps:

[0066] (1) A support layer 204, a lower electrode layer 203, a piezoelectric layer 202 and an upper electrode layer 201 are sequentially formed on the top surface of the substrate used to form the substrate 101 and the mass block 102; wherein, the lower electrode layer 203 forms the lower electrode and the upper electrode layer 201 is patterned to form the interdigitated electrode 104.

[0067] (2) Etch the substrate from the bottom surface to remove excess substrate between substrate 101 and mass block 102;

[0068] (3) The substrate 101 is packaged using a packaging substrate 207 to obtain the triaxial accelerometer based on the Lamb wave resonator of the present invention.

[0069] The working principle of the triaxial accelerometer based on a Lamb wave resonator is as follows: Interdigitated electrodes located on four suspended piezoelectric films generate Lamb waves in the suspended piezoelectric films through the piezoelectric effect. Due to the presence of two reflective boundaries between the mass block and the substrate, the Lamb waves in the films form standing wave resonances at a specific frequency. The resonant frequency is determined by parameters such as the period of the interdigitated electrodes, the electrode width, and the thickness and size of the piezoelectric films. When the external acceleration changes, the mass block generates a compressive force opposite to the acceleration due to inertia, causing the four suspended piezoelectric films to deform accordingly.

[0070] Specifically, when the system is subjected to acceleration in the +x direction, the mass block will compress the suspended piezoelectric film in the -x direction and stretch the film in the +x direction. Because the compression reduces the interdigital spacing, the resonant wavelength of the Lamb wave shortens, thus increasing the resonant frequency of the film in the -x direction and decreasing the resonant frequency in the +x direction. At this time, the suspended piezoelectric film in the y direction will experience shear force in the same direction, causing a frequency shift in the same direction for its resonators. Furthermore, the shear deformation will cause irregular changes in the interdigital spacing, resulting in a significant decrease in the Q value of the resonators. By combining the changes in the frequencies and Q values ​​of the four resonators, the specific acceleration value experienced by the system can be extracted. Similarly, we can determine the frequency and Q value trends when the system is subjected to accelerations in the -x, +y, and -y directions. When the system is subjected to accelerations in the ±z directions, all four resonators will undergo equal warping deformation, with corresponding equal changes in resonant frequency and Q value. Since the frequency shifts caused by accelerations in the x and y directions have different signs across the four resonators, this characteristic can be used to distinguish and extract the accelerations in the x, y, and z directions. Since the frequency shifts generated by +z and -z may be in the same direction, it is necessary to distinguish them by the change in the parallel plate capacitance between the mass block and the packaging substrate: when the system generates +z acceleration, the spacing between the parallel plate capacitors decreases and the capacitance increases; conversely, acceleration in the -z direction causes the parallel plate capacitance to decrease.

[0071] In reality, acceleration typically includes three components: x, y, and z. Since the overall displacement of the system is relatively small, the frequency shifts generated by the three components are linearly superimposed on the four resonators. The acceleration of the three components can be linearly solved based on the frequency shifts of the four resonators. The change in the Q value of the resonators can be used to further improve the accuracy of the calculation.

[0072] In the simple case of linear superposition of the components, the frequency shift of each resonator can be expressed by the following set of equations (1):

[0073]

[0074] Where Δf x+ , Δf x- The frequency shifts of the Lamb wave resonator along the positive and negative x-axis directions are Δf, respectively. y+ , Δf y- These represent the frequency offsets of the Lamb wave resonator along the positive and negative y-axis directions, respectively. MN This represents the change in Lamb wave resonator frequency offset on the M-axis with respect to the N-axis acceleration a. N The sensitivity of M can be x or y, and N can be x, y, or z. Equation (1) assumes that the absolute values ​​of the Lamb wave resonator's sensitivity to the frequency shift caused by accelerations leading to film extrusion and stretching are the same, but with opposite signs; therefore, positive a xThe frequency shift components caused by acceleration on the Lamb wave resonators on the positive and negative x-axis are S, respectively. xx a x With -S xx a x The situation is the same for the y-axis. Because of +a z and -a z This results in the same frequency shift across each Lamb wave resonator, therefore its absolute value |a| is used in equation (1). z Perform calculations.

[0075] The values ​​of each acceleration component can be obtained from the system of equations (1):

[0076]

[0077] Since the system of equations (1) has four equations but only three acceleration variables, therefore |a z This can yield two different expressions. Ideally, they are equal, but when the system has errors, they may differ. The actual expression with smaller error, 'a', can be obtained by averaging the two expressions. z Acceleration value. z The sign can be obtained through the direction of change of capacitor 208. In practice, if the components produce nonlinear superposition, the numerical solution of the three acceleration components can be obtained by further introducing the response quantity of Q value and by curve fitting method.

[0078] The accelerometer described in this invention uses the frequency shift of a suspended piezoelectric thin-film Lamb wave resonator as the sensing signal. Different configurations of Lamb wave resonators have different frequency sensitivities. Figure 4 Four different Lamb wave resonators with different configurations that can be used in the accelerometer described in this invention are presented, including a Lamb wave resonator 301 excited by a single-sided interdigital electrode, a Lamb wave resonator 302 excited by an upper interdigital electrode and a lower plate electrode, a Lamb wave resonator 303 excited by interdigital electrodes on both the top and bottom, and a Lamb wave resonator 304 excited by plate electrodes on both the top and bottom. In addition to operating in Lamb wave mode, the latter three Lamb wave resonators (the excitation electrode configurations described in 302, 303, and 304) can also enable the thin film to operate in bulk acoustic resonator mode and perform acceleration detection using the same frequency shift principle.

[0079] Example 1

[0080] In this embodiment, the substrate 101 of the triaxial accelerometer based on a Lamb wave resonator is an 8-inch silicon wafer with a thickness of 300 μm. The support layer 204 is made of silicon dioxide with a thickness of 1 μm and is prepared by chemical vapor deposition. The vias on the support layer 204 used to form the lower electrode are first formed by reactive ion etching to create the hole structure. The lower electrode layer 203 is made of 200 nm molybdenum metal and is prepared by magnetron sputtering. During the preparation of the lower electrode layer, the vias on the support layer 204 are also filled with molybdenum metal. The piezoelectric layer 202 is made of 1 μm aluminum nitride and is prepared by magnetron sputtering. The upper electrode layer 201 is made of 200 nm molybdenum metal and is prepared by magnetron sputtering. The interdigitated electrodes 104 and the PAD 105 for external connection are formed by patterning the upper electrode layer and prepared by photolithography and reactive ion etching.

[0081] After the thin films on the substrate are fabricated, reactive ion etching is used to remove the front silicon oxide layer in the cavity region surrounding the mass block 102. The bonding layer 205 is made of 5μm tin and is fabricated on the back side of the substrate 101 using back-aligned photolithography and a lift-off process. After the bonding layer 205 is fabricated, back-aligned photolithography and deep silicon etching are used to remove the silicon substrate surrounding the mass block, allowing the mass block to be completely suspended. The bonding layer 206 is made of 1μm gold and is fabricated on the surface of the packaging substrate 207 using a lift-off process. The packaging substrate 207 is made of a 200μm thick 8-inch silicon wafer. The packaging substrate 207 and the substrate 101 with the accelerometer are formed by low-temperature eutectic bonding. A ground PAD is connected to the packaging substrate 207 via conductive adhesive, and then connected to an external signal ground for measuring the capacitance change of the capacitor 208.

[0082] After the device is fabricated, the four Lamb wave resonators are connected to an external circuit to form four oscillators capable of outputting sinusoidal signals. Their resonant frequencies are read by a dedicated frequency reading circuit and used as sensing signals. The planar capacitor 208 formed between substrate 101 and package substrate 102 is connected to an external dedicated capacitor reading circuit to detect the direction of the z-axis acceleration. Combining the measured resonant frequency shift with the capacitance change, the reading algorithm can ultimately calculate the acceleration in the x, y, and z axes.

Claims

1. A triaxial accelerometer based on a Lamb wave resonator, characterized in that, include: The substrate has a ring structure with a cavity in the middle. The mass block is located inside the cavity; A suspended piezoelectric film is disposed on the top surface of the mass block and the substrate to connect the mass block and the substrate, thereby suspending the mass block in the cavity of the substrate. The suspended piezoelectric film includes four strips for connecting the mass block and the substrate from different directions, forming four Lamb wave resonators. The suspended piezoelectric film includes a support layer, a lower electrode layer, a piezoelectric layer and an upper electrode layer formed sequentially from the bottom surface to the top surface. The support layer has a through hole for the lower electrode layer to extend downward and connect to the mass block. The lower electrode layer forms a lower electrode in the through hole, and the upper electrode layer is patterned to form interdigitated electrodes. An encapsulation substrate is used to encapsulate the opening of the cavity on one side of the bottom surface of the substrate. A gap is left between the encapsulation substrate and the mass block to allow the mass block to move during the detection process. Furthermore, the gap allows a capacitor structure to be formed between the encapsulation substrate and the mass block. The cavity of the substrate has a square cross-section, and the mass block also has a square cross-section. The top surface of the mass block is connected to the substrate through the middle of each of the four sides by a suspended piezoelectric film. Among the four sides of the top surface of the mass block, the two suspended piezoelectric films on opposite sides are arranged along a straight line, and the two suspended piezoelectric films on adjacent sides are arranged perpendicularly. During fabrication, the same layer structure in each suspended piezoelectric film is formed at once. The portion of the support layer, lower electrode layer, piezoelectric layer and upper electrode layer located between the substrate and the mass block constitutes the suspended piezoelectric film, and the portion located in the mass block region is part of the mass block. The lower electrode formed by the lower electrode layer is located in the middle of the mass block. The lower electrode extends along one of the suspended piezoelectric films as a connecting line and forms a PAD of the lower electrode above the area where the substrate is located. The lower electrode also extends a counterweight line symmetrically in the opposite direction of the connecting line as a counterweight.

2. The triaxial accelerometer based on a Lamb wave resonator according to claim 1, characterized in that, The width of each of the aforementioned suspended piezoelectric films is 1 μm to 200 μm; The cross-sectional side length of the mass block is 10μm~1000μm; The lateral spacing between the mass block and the substrate is 10μm to 500μm.

3. The triaxial accelerometer based on a Lamb wave resonator according to claim 1, characterized in that, The Lamb wave resonator can be one of the following types: a Lamb wave resonator excited by a single-sided interdigitated electrode, a Lamb wave resonator excited by an upper interdigitated electrode and a lower plate electrode, or a Lamb wave resonator excited by interdigitated electrodes on both sides.

4. The triaxial accelerometer based on a Lamb wave resonator according to claim 1, characterized in that, The substrate is made of at least one of the following materials: silicon, silicon carbide; The materials of the upper electrode layer and the lower electrode layer are each selected from at least one of the following: aluminum, platinum, tungsten, and molybdenum; The piezoelectric layer is made of at least one of the following materials: aluminum nitride, lithium niobate, zinc oxide, and gallium lanthanum silicate. The material of the support layer is selected from at least one of the following: silicon oxide, silicon nitride; The material of the packaging substrate is selected from at least one of the following: silicon, silicon carbide.

5. The triaxial accelerometer based on a Lamb wave resonator according to claim 4, characterized in that, The substrate and the packaging substrate have their resistivity reduced by doping, and the doping element is at least one of the following: boron or phosphorus.

6. The triaxial accelerometer based on a Lamb wave resonator according to claim 1, characterized in that, The thickness of the substrate is 100~1000μm; The thickness of the upper electrode layer is 50~1000 nm; The thickness of the lower electrode layer is 50~1000 nm; The thickness of the piezoelectric layer is 100 nm to 10 μm; The thickness of the support layer is 500 nm to 10 μm; The thickness of the encapsulation substrate is 100~1000μm.

7. The triaxial accelerometer based on a Lamb wave resonator according to claim 1, characterized in that, The encapsulation substrate is connected to the substrate via a bonding layer; The bonding layer may be one or more layers; The thickness of each bonding layer is 1~20μm; The bonding layer is made of at least one of the following materials: gold, tin, indium, and nickel.

8. The method for fabricating a triaxial accelerometer based on a Lamb wave resonator as described in any one of claims 1 to 7, characterized in that, Includes the following steps: (1) A support layer, a lower electrode layer, a piezoelectric layer and an upper electrode layer are sequentially formed on the top surface of the substrate used to form the substrate and the mass block; wherein the lower electrode layer forms a lower electrode and the upper electrode layer is patterned to form an interdigitated electrode; (2) Etch the substrate from the bottom surface to remove excess substrate between the substrate and the mass block; (3) The packaging substrate is used to encapsulate the bottom surface of the substrate to obtain the triaxial accelerometer based on the Lamb wave resonator.

Images