A uniaxial acceleration sensor chip based on pure axial strain beam and a working method thereof

Abstract

This invention discloses a uniaxial acceleration sensing chip based on a pure axial strain beam and its operating method. Each sensitive beam has a force-sensitive resistor. The inner frame of the fixed frame is rectangular, and all vibration units are identical and sequentially arranged at the four corners of the inner frame. A groove is provided on the mass block for the movement of the support beam. One end of the support beam is fixedly connected to a corner of the inner frame, and the other end is connected to the bottom of the groove on the mass block. Sensitive beams are arranged between the two adjacent sides of the mass blocks of the first and second vibration units; sensitive beams are also arranged between the two adjacent sides of the mass blocks of the third and fourth vibration units; all sensitive beams are parallel to each other. This invention can produce the effect of pure axial tension or compression of the sensitive beam. Furthermore, this significantly reduces the overall stiffness of the movable structure of the chip in a small size, allowing the sensitive core to still have good sensitivity and high bandwidth characteristics even in a small size.

Description

Technical Field

[0001] This invention mainly relates to the field of silicon micro-accelerometers, specifically to a uniaxial acceleration sensing chip based on a pure axial strain beam and its working method. Background Technology

[0002] Industrial vibration monitoring is a key foundation for realizing equipment condition monitoring and intelligent operation and maintenance, and an indispensable part of Industry 4.0 smart manufacturing. On the one hand, the vibration frequency of early equipment faults is often high (>10kHz) and the signal is weak, which places high demands on the frequency response bandwidth and sensitivity of sensors. On the other hand, due to factors such as early faults during equipment use, the vibration characteristics change greatly, which requires sensors with a large range.

[0003] Piezoresistive accelerometers have unique advantages in high-frequency response and high-range acceleration measurement due to their large measurement range and wide frequency response bandwidth, as well as their simple structure and post-processing circuitry. However, in traditional piezoresistive micro-accelerometer chips, the sensitive element is mounted on a support beam, which leads to a trade-off between high sensitivity and the natural frequency (the parameter that determines the upper limit of the frequency response).

[0004] Currently, by separating the sensing element from the supporting element, it is possible to achieve high sensitivity even at higher natural frequencies. Simultaneously, due to the increased sensitivity... Transverse stress of sensitive beam σ t The smaller the value, the higher the overall output sensitivity and the higher the inertial energy utilization rate. Therefore, patents CN110526200A and CN201910684531.X have proposed acceleration sensing chips based on pure axial deformation sensing beams.

[0005] The aforementioned purely axially deformable sensitive beam achieves this by relying on the mirror-symmetric motion of two mass blocks, resulting in zero longitudinal relative displacement at both ends of the sensitive beam, while creating a compression or tension effect laterally. This ingenious design can simultaneously achieve high sensitivity and high-frequency response dynamic characteristics. However, because the previously disclosed acceleration sensing structure is a linear structure, the core size is large and difficult to miniaturize, which is not conducive to cost reduction and subsequent miniaturized integration and installation. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention aims to provide a uniaxial acceleration sensing chip based on a pure axial strain beam and its working method. The uniaxial acceleration sensing chip designed in this invention has a relatively small size and also features high frequency response characteristics and high sensitivity.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A single-axis acceleration sensing chip based on a pure axial strain beam includes a sensing core, which comprises a fixed outer frame, a first vibration unit, a second vibration unit, a third vibration unit, a fourth vibration unit, a first sensing beam, a second sensing beam, a third sensing beam, and a fourth sensing beam. Each of the first, second, third, and fourth sensing beams has a force-sensitive resistor. The inner frame of the fixed outer frame is rectangular. The first, second, third, and fourth vibration units have the same structure and are arranged sequentially at the four corners of the inner frame of the fixed outer frame.

[0009] The first vibration unit includes a mass block and a support beam. The mass block has a groove for the support beam to move. One end of the support beam is fixedly connected to a corner of the inner frame of the fixed outer frame, and the other end of the support beam is connected to the bottom of the groove on the mass block.

[0010] The two ends of the side of the mass block of the first vibration unit adjacent to the mass block of the second vibration unit are respectively connected to one end of the first sensitive beam and one end of the second sensitive beam. The other end of the first sensitive beam and the other end of the second sensitive beam are respectively connected to the two ends of the side of the mass block of the second vibration unit adjacent to the mass block of the first vibration unit.

[0011] The two ends of the side of the mass block of the third vibration unit adjacent to the mass block of the fourth vibration unit are respectively connected to one end of the third sensitive beam and one end of the fourth sensitive beam. The other end of the third sensitive beam and the other end of the fourth sensitive beam are respectively connected to the two ends of the side of the mass block of the fourth vibration unit adjacent to the mass block of the third vibration unit.

[0012] The first, second, third, and fourth sensitive beams are parallel to each other.

[0013] Preferably, the groove is a groove that extends through the thickness direction of the mass block.

[0014] Preferably, the support beam is set along the diagonal of the inner frame of the fixed outer frame, the mass block is a rectangular mass block, and each side of the mass block is parallel to each side of the inner frame of the fixed outer frame. The groove is opened from one of the top corners of the mass block along the diagonal of the mass block.

[0015] Preferably, movable gaps are provided between the mass blocks of the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit, between each mass block and the inner frame of the fixed outer frame, and between the groove of the mass block and the support beam.

[0016] Preferably, the two axes of symmetry of the fixed outer frame and inner frame edge lines are denoted as the first axis of symmetry and the second axis of symmetry, respectively;

[0017] The first and second vibration units are mirror-symmetric about the first axis of symmetry, the second and third vibration units are mirror-symmetric about the second axis of symmetry, the third and fourth vibration units are mirror-symmetric about the first axis of symmetry, and the fourth vibration unit and the first vibration unit are mirror-symmetric about the second axis of symmetry.

[0018] Preferably, the working direction of the single-axis acceleration sensing chip based on the pure axial strain beam is perpendicular to the first sensitive beam, the second sensitive beam, the third sensitive beam, and the fourth sensitive beam.

[0019] Preferably, the force-sensitive resistors on the first, second, third, and fourth sensitive beams are connected by a circuit to form a Wheatstone bridge, wherein the force-sensitive resistors on the first and second sensitive beams are adjacent arms, the force-sensitive resistors on the first and fourth sensitive beams are adjacent arms, and the force-sensitive resistors on the first and third sensitive beams are opposite arms.

[0020] Preferably, the uniaxial acceleration sensing chip based on a pure axial strain beam of the present invention further includes a substrate, a sensitive core bonded to the substrate, and a motion gap between the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit of the sensitive core and the substrate.

[0021] Preferably, the thickness of the first vibration unit, the second vibration unit, the third vibration unit, and the fourth vibration unit is less than the thickness of the fixed outer frame, and a gap is left between the first vibration unit, the second vibration unit, the third vibration unit, and the fourth vibration unit and the base surface.

[0022] Alternatively, a cavity may be provided on the base in the area corresponding to the inner frame of the fixed outer frame, and the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit may be located above the cavity.

[0023] The operating method of the uniaxial acceleration sensing chip based on a pure axial strain beam as described above in this invention includes the following processes:

[0024] The force-sensitive resistors on the first, second, third, and fourth sensitive beams are connected by a circuit to form a Wheatstone full bridge, wherein the force-sensitive resistors on the first and second sensitive beams are adjacent arms, the force-sensitive resistors on the first and fourth sensitive beams are adjacent arms, and the force-sensitive resistors on the first and third sensitive beams are opposite arms.

[0025] When the measured external acceleration moves in a direction perpendicular to the first, second, third, and fourth sensitive beams, the mass blocks of the first, second, third, and fourth vibration units remain stationary due to inertia, and the fixed outer frame moves in the same direction as the external environment. At this time, the mass blocks of the first, second, third, and fourth vibration units all deform in the opposite direction to the external acceleration, with the root of their respective supporting beams as the center. At this time, the first sensitive beam is under compression, the second sensitive beam is under tension, the third sensitive beam is under compression, and the fourth sensitive beam is under tension.

[0026] When the measured external acceleration moves in a direction parallel to the first, second, third, and fourth sensitive beams, the mass blocks of the first, second, third, and fourth vibration units remain stationary due to inertia. The fixed outer frame moves in the same direction as the external environment. At this time, the mass blocks of the first, second, third, and fourth vibration units deform in the opposite direction to the external acceleration, with the root of their respective supporting beams as the center. At this time, the first sensitive beam has both tensile and compressive stress on both sides, and the overall average stress is 0. The second sensitive beam has both tensile and compressive stress on both sides, and the overall average stress is 0. The third sensitive beam has both tensile and compressive stress on both sides, and the overall average stress is 0. The fourth sensitive beam has both tensile and compressive stress on both sides, and the overall average stress is 0.

[0027] When the measured external acceleration moves along the plane perpendicular to the sensitive core, the mass blocks of the first, second, third, and fourth vibration units remain stationary due to inertia, and the fixed outer frame moves in the same direction as the external environment. At this time, the mass blocks of the first, second, third, and fourth vibration units all deform in the opposite direction to the external acceleration, and the deformation constraint and displacement of the mass blocks far from the support beam are relatively smaller. At this time, the first, second, third, and fourth sensitive beams are all under pressure.

[0028] Compared with the prior art, the advantages of the present invention are as follows:

[0029] In this invention, a single-axis acceleration sensing chip based on a pure axial strain beam has four identical vibration units: a first vibration unit, a second vibration unit, a third vibration unit, and a fourth vibration unit, which are sequentially positioned at the four corners of a fixed outer frame and an inner frame. In each vibration unit, one end of the support beam is fixedly connected to a corner of the fixed outer frame and the other end is connected to the bottom of a groove on a mass block. When the single-axis acceleration sensing chip is in operation, if the measured external acceleration moves perpendicular to the first, second, third, and fourth sensitive beams, the first sensitive beam is compressed, the second sensitive beam is stretched, the third sensitive beam is compressed, and the fourth sensitive beam is stretched. If the measured external acceleration moves parallel to the first, second, third, and fourth sensitive beams, the average stress of all the first, second, third, and fourth sensitive beams is zero. If the measured external acceleration moves perpendicular to the plane of the sensitive core, all the first, second, third, and fourth sensitive beams are compressed. As can be seen, the present invention can produce the effect of pure axial tension or compression of the sensitive beam; on the other hand, this can significantly reduce the overall stiffness of the movable structure of the chip in a small size, so that the sensitive core still has good sensitivity and high bandwidth characteristics in a small size. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of the uniaxial acceleration sensing chip based on a pure axial strain beam according to the present invention.

[0031] Figure 2 This is a diagram of the force-sensitive resistor layout of the uniaxial acceleration sensing chip based on a pure axial strain beam, according to the present invention.

[0032] Figure 3(a) is a schematic diagram of the interaxial acceleration decoupling of the uniaxial acceleration sensing chip based on a pure axial strain beam according to the present invention (along the axis). Figure 2 Figure 3(b) is a schematic diagram of inter-axis acceleration decoupling of the uniaxial acceleration sensing chip based on a pure axial strain beam according to the present invention (along the Y direction); Figure 2 Figure 3(c) is a schematic diagram of inter-axis acceleration decoupling of the uniaxial acceleration sensing chip based on a pure axial strain beam according to the present invention (along the X direction); Figure 2 The Z-direction shown (perpendicular to) Figure 2 (the orientation of the paper)

[0033] Figure 4 This is a decoupled output circuit diagram of the uniaxial acceleration sensing chip based on a pure axial strain beam according to the present invention.

[0034] In the diagram, 1-sensitive core, 2-base, 3-fixed outer frame, 3-1-platform, 4-support beam, 5-mass block, 5-1-groove, 6-sensitive beam. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0036] like Figure 1 , Figure 2 Figures 3(a)-3(c) show that the uniaxial acceleration sensing chip based on a pure axial strain beam of the present invention includes a sensitive core 1. The sensitive core 1 includes a fixed outer frame 3, a first vibration unit, a second vibration unit, a third vibration unit, a fourth vibration unit, and a sensitive beam 6. Four sensitive beams 6 are provided, respectively designated as the first sensitive beam, the second sensitive beam, the third sensitive beam, and the fourth sensitive beam. Figure 2 Taking the indicated orientation as an example, from top to bottom, the four sensitive beams are the first, second, third, and fourth sensitive beams; the inner frame of the fixed outer frame 3 is rectangular, or the fixed outer frame 3 can be set as a ring-shaped rectangle. The first, second, third, and fourth vibration units have the same structure and are arranged sequentially at the four corners of the inner frame of the fixed outer frame 3. Figure 2 Taking the orientation shown as an example, the first vibration unit, the second vibration unit, the third vibration unit, and the fourth vibration unit are the vibration units at the upper left, upper right, lower right, and lower left corners, respectively; the structural size of the sensitive beam 6 is much smaller than (as small as possible under feasible conditions) the support beam, so as to concentrate the use of inertial energy to improve sensitivity; the length of the sensitive beam 6 is set to be minimized as much as possible based on the feasibility of the process to improve the device's natural frequency and sensitivity.

[0037] Specifically, the first vibration unit includes a mass block 5 and a support beam 4. The mass block 5 has a groove 5-1 for the support beam 4 to move through, and the groove 5-1 extends through the thickness of the mass block 5. The support beam 4 is positioned along the diagonal of the inner frame of the fixed outer frame 3. The mass block 5 is rectangular, with each side of the mass block 5 parallel to the corresponding side of the inner frame of the fixed outer frame 3. The groove 5-1 is formed from a apex of the mass block 5 along its diagonal. One end of the support beam 4 is fixedly connected to a corner of the inner frame of the fixed outer frame 3, and the other end of the support beam 4 is connected to the bottom center of the groove 5-1 on the mass block 5. Mobility gaps are provided between each mass block 5, between each mass block 5 and the inner frame of the fixed outer frame 3, and between the groove 5-1 of the mass block 5 and the support beam 4 to ensure normal vibration of the entire chip. The two axes of symmetry of the inner frame of the fixed outer frame 3 are respectively denoted as the first axis of symmetry (e.g., ...). Figure 2 The vertical axis of symmetry shown) and the second axis of symmetry (as shown) Figure 2(As shown by the horizontal axis of symmetry), the first and second vibration units are mirror-symmetrical about the first axis of symmetry, the second and third vibration units are mirror-symmetrical about the second axis of symmetry, the third and fourth vibration units are mirror-symmetrical about the first axis of symmetry, and the fourth vibration unit and the first vibration unit are mirror-symmetrical about the second axis of symmetry. In the above structure, by arranging the support beams in a rectangular diagonal pattern, the stiffness of the support beam-mass block system can be significantly reduced in small sizes, making it possible to achieve high frequency response and high sensitivity in small chip sizes.

[0038] by Figure 2 Taking the orientation shown as an example, the upper and lower ends of the right side surface of the mass block 5 of the first vibration unit are connected to the left end of the first sensitive beam and the left end of the second sensitive beam, respectively. The right end of the first sensitive beam and the right end of the second sensitive beam are connected to the upper and lower ends of the left side surface of the mass block 5 of the second vibration unit, respectively.

[0039] The upper and lower ends of the left side surface of the mass block 5 of the third vibration unit are connected to the right ends of the third and fourth sensitive beams, respectively; the left ends of the third and fourth sensitive beams are connected to the upper and lower ends of the right side surface of the mass block 5 of the fourth vibration unit, respectively. Figure 2 As shown, the first, second, third, and fourth sensitive beams are all horizontally arranged and parallel to each other.

[0040] The single-axis acceleration sensing chip of this invention operates in a direction perpendicular to the sensing beam. Preferably, the sensing beam is positioned along its length (x-direction), and the sensor operates in the y-direction.

[0041] As can be seen from the structure of the uniaxial acceleration sensing chip based on a pure axial strain beam in this invention, the invention adopts a polygonal sensing structure configuration, that is, the support beam is placed along the diagonal of the rectangular fixed outer frame, and the mass blocks are connected along the diagonal of the rectangular mass blocks. On the one hand, it can achieve mirror deformation of the two mass blocks, thereby producing the effect of pure axial tension or compression of the sensing beam between them; on the other hand, this can significantly reduce the overall stiffness of the movable structure of the chip in a small size, so that the sensing core still has good sensitivity and high bandwidth characteristics in a small size.

[0042] The working principle of the uniaxial acceleration sensing chip based on a pure axial strain beam described above is as follows:

[0043] See Figure 4The force-sensitive resistors corresponding to the first, second, third, and fourth sensitive beams are R1, R2, R3, and R4, respectively. These resistors are connected in a circuit to form a Wheatstone bridge. Specifically, R1 and R2 of the first and second sensitive beams are adjacent arms, as are R1 and R4 of the fourth sensitive beam, and R1 and R3 of the first and third sensitive beams are opposite arms. By applying input voltages between R1-R4 and R3-R3, and outputting differential voltages between R1-R2 and R3-R4, the inter-axis decoupling of the sensor is achieved, reducing the influence of environmental factors (temperature, humidity, etc.) on the sensor output. The sensitive structure proposed in this invention uses a mirror-symmetric arrangement of the two sensitive units and their internal structures to form a Wheatstone bridge, effectively eliminating drift caused by environmental changes and improving the sensor's output accuracy and sensitivity. In addition, by using a support beam of considerable thickness and a triangular beam-mass block structure arrangement, the acceleration response in the Z direction and the non-working direction in the plane is suppressed respectively. Furthermore, the Wheatstone bridge is used for decoupling, which significantly reduces the cross-axis sensitivity of the accelerometer.

[0044] See Figure 2 And as shown in Figure 3(a), when the measured external acceleration is along the direction perpendicular to the first, second, third, and fourth sensitive beams (i.e. Figure 2 When the chip moves in the Y direction (as shown in Figure 3(a)), the mass blocks 5 of the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit remain stationary due to inertia. The fixed outer frame 3 moves in the same direction as the outside world. At this time, the mass blocks 5 of the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit all deform in the opposite direction to the acceleration direction of the outside world, with the root of their respective supporting beams 4 as the center. At this time, R1 on the first sensitive beam is compressed, R2 on the second sensitive beam is stretched, R3 on the third sensitive beam is compressed and R4 on the fourth sensitive beam is stretched.

[0045] See Figure 2 And Figure 3(b), when the measured external acceleration is along the direction parallel to the first sensitive beam, the second sensitive beam, the third sensitive beam and the fourth sensitive beam (i.e. Figure 2When the X-direction movement is shown in Figure 3(b), the mass blocks 5 of the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit remain stationary due to inertia. The fixed outer frame 3 moves in the same direction as the outside world. At this time, the mass blocks 5 of the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit all deform in the opposite direction to the acceleration direction of the outside world with the root of their respective supporting beams 4 as the center. At this time, the first sensitive beam has both tensile stress and compressive stress on both sides, and the overall average stress is 0. The second sensitive beam has both tensile stress and compressive stress on both sides, and the overall average stress is 0. The third sensitive beam has both tensile stress and compressive stress on both sides, and the overall average stress is 0. The fourth sensitive beam has both tensile stress and compressive stress on both sides, and the overall average stress is 0.

[0046] See Figure 2 And as shown in Figure 3(c), when the measured external acceleration is along the direction perpendicular to the plane where the sensitive core 1 is located (i.e. Figure 2 As shown in Figure 3(b), when moving in the direction perpendicular to the XY plane, the mass blocks 5 of the first, second, third, and fourth vibration units remain stationary due to inertia, while the fixed outer frame 3 moves in the same direction as the outside world. At this time, the mass blocks 5 of the first, second, third, and fourth vibration units all deform in the opposite direction to the acceleration direction of the outside world. The deformation constraint and displacement of the part of the mass block 5 away from the support beam 4 (i.e., the part of the mass block 5 near the center of the entire chip) are relatively smaller. At this time, the first, second, third, and fourth sensitive beams are all under pressure. As can be seen from Figures 3(a) to 3(c), when the acceleration is along the working direction (Y direction), the resistance values ​​of R1, R2, R3, and R4 show obvious positive and negative changes. Therefore, the acceleration measurement cross-axis decoupling can be achieved through reasonable circuit design.

[0047] As a preferred embodiment of the present invention, platforms 3-1 (equivalent to inner chamfers, with the chamfer being a plane) are provided at each corner of the fixed outer frame 3. This reduces the processing difficulty and decreases the resistance to the swing of the support beam along the width direction. Furthermore, certain rounded corners are provided at the connections between the support beam 4 and the mass block 5, between the support beam 4 and the platform 3-1 of the fixed outer frame 3, and between the sensitive beam 6 and the mass block 5 to reduce stress concentration, improve stress uniformity, and thus improve the overload resistance and reliability of the device. Preferably, the rounded corner size is half the minimum width of the connection structure at both ends of the rounded corner. For example, the rounded corners at the connections between the support beam and the fixed outer frame, and between the support beam and the mass block, are half the width of the support beam. The substrate 2 and the sensitive core 1 have the same dimensions in the XY plane, and the substrate 2 is made of glass or ceramic. Preferably, the substrate 2 is made of BF33 glass.

[0048] In a preferred embodiment of the present invention, the sensitive core 1 can be disposed on a substrate 2 and bonded to the substrate 2. A movement gap is maintained between the first vibration unit, second vibration unit, third vibration unit, and fourth vibration unit of the sensitive core 1 and the substrate 2 to ensure normal vibration of the mass block. This movement gap can be configured in one of the following two ways:

[0049] The first form: the thickness of the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit is less than the thickness of the fixed outer frame 3, and there is a gap between the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit and the surface of the base 2.

[0050] The second form: A cavity is provided on the base 2 in the area corresponding to the inner frame of the fixed outer frame 3, and the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit are suspended above the cavity.

[0051] In a preferred embodiment of the present invention, the thickness and width of the sensitive beam are on the order of several μm, and the length is on the order of tens of μm, while the thickness, width, and length of the support beam are on the order of hundreds of μm, tens of μm, and hundreds of μm, respectively. Preferably, the thickness, width, and length of the sensitive beam are 5 μm, 3 μm, and 50 μm, respectively; and the thickness, width, and length of the support beam are 500 μm, 30 μm, and 300 μm, respectively.

[0052] Example

[0053] This embodiment takes a single-axis acceleration sensor chip with substrate 2 as an example. In this embodiment, the sensitive core 1 is made of an N-type (100) crystal SOI wafer with dimensions of 1mm (length) * 1mm (width) * 0.5mm (thickness); the substrate 2 has dimensions of 1mm (length) * 1mm (width) * 0.3mm (thickness); the sensitive beam 6 has dimensions of 50μm (length) * 3μm (width) * 5μm (thickness); the support beam 4 has dimensions of 300μm (length) * 30μm (width) * 500μm (thickness); the mass block 5 has dimensions of 0.38mm (length) * 0.38mm (width) * 0.5mm (thickness) and a cutting edge length of 0.12mm; the movement gaps between mass blocks, between mass blocks and the fixed outer frame, and between mass blocks and the support beam are 0.05mm.

[0054] The manufacturing process of the uniaxial acceleration sensing chip based on a pure axial strain beam in this embodiment includes the following steps:

[0055] Step 1) Double-sided thermal oxidation of N-type SOI silicon wafer: After RCA cleaning of the wafer, the SOI wafer device layer and the bottom surface oxide layer are prepared by dry-wet composite thermal oxidation.

[0056] Step 2) Fabrication of lightly doped force resistors: The silicon dioxide layer thermally oxidized in the corresponding region of the force resistor in the device layer is removed using photolithography and plasma etching. Boron ions are then implanted using a low-dose plasma to form a lightly doped force resistor region; the low-dose plasma is 8 × 10⁻⁶. 14 cm -2 ;

[0057] Step 3) Fabrication of heavily doped ohmic contact region: The silicon oxide layer thermally oxidized on the surface of the heavily doped region at both ends of the force-sensitive resistor is removed using photolithography and plasma etching. Boron ions are then implanted using a high-dose plasma to form the heavily doped ohmic contact region, where the high-dose plasma is 1×10⁻⁶. 16 cm -2 ;

[0058] Step 4) Metal lead pad preparation: Metal is deposited on the heavily doped ohmic contact and pad areas on the device layer surface using photolithography and sputtering to form leads and pads; the metal lead and pad materials are Au / Pt / Ti or Au / Cr;

[0059] Step 5) Preparation of passivation layer for force-sensitive resistor: A passivation layer is prepared on top of the device layer by PECVD; the passivation layer is SiOx;

[0060] Step 6) Device Layer Stress Relief: Rapid annealing repairs the damage to the silicon lattice caused by the plasma injection doping process, thereby improving ohmic electrical contact and reducing the stress within the passivation layer film prepared by PECVD. During rapid annealing, the heating rate is 100~150℃ / s, the holding temperature is 1000~1150℃, and the holding time is 10s.

[0061] Step 7) Etching of the active area of ​​the back cavity: Use photolithography and RIE to etch the active area of ​​the support beam and mass block.

[0062] Step 8) Sensitive Core-Substrate Bonding: A metal layer is deposited on the substrate by sputtering, and then the substrate is bonded to the bottom layer of the sensitive core wafer by anodic bonding.

[0063] Step 9) Device layer etching to release movable structure: The SOI device layer and buried silicon oxide layer in the middle movement gap region of the movable structure are etched using photolithography and RIE to release the movable structure. The depth of the back cavity etching is 300nm.

[0064] Step 10) Device structural stress release: The wafer after etching and bonding is treated with a low-temperature annealing process to release structural stress. During the low-temperature annealing, the holding temperature is 300℃ and the holding time is 4h.

[0065] Step 11) Scribing: Use mechanical or laser scribing to cut out the sensitive chip, and the piezoresistive accelerometer chip is completed.

[0066] In the above fabrication process, the four force-sensitive resistors R1, R2, R3, and R4 are all fabricated in the same step, ensuring resistance uniformity and facilitating the subsequent decoupling of the Wheatstone bridge from environmental and cross-axial acceleration. The manufacturing process proposed in this invention etches the gap in the z-axis direction of the underlying mass block of the sensitive core before bonding the substrate to the sensitive core. This eliminates the need for precise alignment during subsequent bonding, significantly reducing the difficulty of the bonding process, facilitating the optimization of low-stress bonding, and improving the chip processing yield.

Claims

1. A uniaxial acceleration sensing chip based on a pure axial strain beam, characterized in that, The sensitive core (1) comprises a fixed outer frame (3), a first vibration unit, a second vibration unit, a third vibration unit, a fourth vibration unit, a first sensitive beam, a second sensitive beam, a third sensitive beam and a fourth sensitive beam, and the first sensitive beam, the second sensitive beam, the third sensitive beam and the fourth sensitive beam each have a force-sensitive resistor; the inner frame of the fixed outer frame (3) is rectangular in shape, the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit are the same in structure and are sequentially arranged at the four corner positions of the inner frame of the fixed outer frame (3). The first vibration unit comprises a mass block (5) and a support beam (4), the mass block (5) is provided with a groove (5-1) for the movement of the support beam (4), one end of the support beam (4) is fixedly connected with one corner of the inner frame of the fixed outer frame (3), and the other end of the support beam (4) is connected with the bottom of the groove (5-1) on the mass block (5). The two ends of the side surface adjacent to the mass block (5) of the second vibration unit of the mass block (5) of the first vibration unit are respectively connected with one end of the first sensitive beam and one end of the second sensitive beam, and the other end of the first sensitive beam and the other end of the second sensitive beam are respectively connected with the two ends of the side surface adjacent to the mass block (5) of the first vibration unit on the mass block (5) of the second vibration unit. The two ends of the side surface adjacent to the mass block (5) of the fourth vibration unit of the mass block (5) of the third vibration unit are respectively connected with one end of the third sensitive beam and one end of the fourth sensitive beam, and the other end of the third sensitive beam and the other end of the fourth sensitive beam are respectively connected with the two ends of the side surface adjacent to the mass block (5) of the third vibration unit on the mass block (5) of the fourth vibration unit. The first sensitive beam, the second sensitive beam, the third sensitive beam and the fourth sensitive beam are parallel to each other. The support beam (4) is arranged along the diagonal line of the inner frame of the fixed outer frame (3), the mass block (5) is a rectangular mass block, the edges of the mass block (5) are parallel to the corresponding edges of the inner frame of the fixed outer frame (3), and the groove (5-1) is formed from one top corner of the mass block (5) along the diagonal line of the mass block (5).

2. The uniaxial acceleration sensing chip based on pure axial strain beam according to claim 1, characterized in that, The groove (5-1) is a groove penetrating through the thickness direction of the mass block (5).

3. The uniaxial acceleration sensing chip based on pure axial strain beam according to claim 1, characterized in that, An active gap is arranged between the mass blocks (5) of the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit, between each mass block (5) and the inner frame of the fixed outer frame (3), and between the groove (5-1) of the mass block (5) and the support beam (4).

4. The uniaxial acceleration sensing chip based on pure axial strain beam according to claim 1, characterized in that, Two symmetrical axes of the edge line of the inner frame of the fixed outer frame (3) are respectively denoted as a first symmetrical axis and a second symmetrical axis; The first vibration unit and the second vibration unit are mirror-symmetric about the first symmetrical axis, the second vibration unit and the third vibration unit are mirror-symmetric about the second symmetrical axis, the third vibration unit and the fourth vibration unit are mirror-symmetric about the first symmetrical axis, and the fourth vibration unit and the first vibration unit are mirror-symmetric about the second symmetrical axis.

5. The uniaxial acceleration sensing chip based on pure axial strain beam according to claim 1, characterized in that, The working direction of the single-axis acceleration sensing chip based on the pure axial strain beam is perpendicular to the first sensitive beam, the second sensitive beam, the third sensitive beam and the fourth sensitive beam.

6. The uniaxial acceleration sensing chip based on pure axial strain beam according to claim 1, characterized in that, The force-sensitive resistors on the first, second, third and fourth sensitive beams are connected into a Wheatstone full bridge through a circuit, wherein the force-sensitive resistors on the first and second sensitive beams are adjacent arms to each other, the force-sensitive resistors on the first and fourth sensitive beams are adjacent arms to each other, and the force-sensitive resistors on the first and third sensitive beams are opposite arms to each other.

7. The uniaxial acceleration sensing chip based on pure axial strain beam according to claim 1, characterized in that, The substrate (2) is further included, and the sensitive core (1) is bonded to the substrate (2), and a movement gap is left between the first, second, third and fourth vibration units of the sensitive core (1) and the substrate (2).

8. The uniaxial acceleration sensing chip based on pure axial strain beam according to claim 7, characterized in that, The thicknesses of the first, second, third and fourth vibration units are less than the thickness of the fixed outer frame (3), and a gap is left between the first, second, third and fourth vibration units and the surface of the substrate (2). Alternatively, the substrate (2) is provided with a recessed cavity in a region corresponding to the inner frame of the fixed outer frame (3), and the first, second, third and fourth vibration units are located above the recessed cavity.

9. The working method of a uniaxial acceleration sensing chip based on pure axial strain beam according to claim 1, characterized in that, The following processes are included: The force-sensitive resistors on the first, second, third and fourth sensitive beams are connected into a Wheatstone full bridge through a circuit, wherein the force-sensitive resistors on the first and second sensitive beams are adjacent arms to each other, the force-sensitive resistors on the first and fourth sensitive beams are adjacent arms to each other, and the force-sensitive resistors on the first and third sensitive beams are opposite arms to each other; When the measured acceleration of the external environment moves in a direction perpendicular to the first, second, third and fourth sensitive beams, the mass blocks (5) of the first, second, third and fourth vibration units remain stationary due to inertia, and the fixed outer frame (3) moves in accordance with the external environment, at this time, the mass blocks (5) of the first, second, third and fourth vibration units deform in the opposite direction to the direction of the acceleration of the external environment with the root of the corresponding support beam (4) as the center, at this time, the first sensitive beam is compressed, the second sensitive beam is stretched, the third sensitive beam is compressed, and the fourth sensitive beam is stretched; When the measured acceleration of the outside world moves along the direction parallel to the first sensitive beam, the second sensitive beam, the third sensitive beam and the fourth sensitive beam, the mass block (5) of the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit remains stationary due to inertia, the fixed outer frame (3) moves with the outside world, at this time the mass block (5) of the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit deforms in the opposite direction to the direction of the acceleration of the outside world with the root of the corresponding support beam (4) as the center, at this time the first sensitive beam has both tensile stress and compressive stress on both sides, the overall average stress is 0, the second sensitive beam has both tensile stress and compressive stress on both sides, the overall average stress is 0, the third sensitive beam has both tensile stress and compressive stress on both sides, the overall average stress is 0, and the fourth sensitive beam has both tensile stress and compressive stress on both sides, the overall average stress is 0; When the measured acceleration of the outside world moves along the direction perpendicular to the plane where the sensitive core (1) is located, the mass block (5) of the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit remains stationary due to inertia, the fixed outer frame (3) moves with the outside world, at this time the mass block (5) of the first vibration unit, the second vibration unit, the third vibration unit and the fourth vibration unit deforms in the opposite direction to the direction of the acceleration of the outside world, and the part of the mass block (5) away from the support beam (4) deforms relatively less and has relatively larger displacement, at this time the first sensitive beam, the second sensitive beam, the third sensitive beam and the fourth sensitive beam are all under compression.

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