Piezoresistive high-g-value acceleration sensor with double-spindle structure

Abstract

The utility model discloses a piezoresistive high-g-value acceleration sensor with a double-spindle structure, which comprises a sensor core body, bonding areas are arranged on the upper surface and the lower surface of the sensor core body, two symmetrical accommodating cavities are arranged on the bonding areas on the upper surface and the lower surface in a penetrating manner, and a spindle-shaped mass block is arranged in each accommodating cavity. The two sides of the middle part of each fusiform mass block are vertically connected to the two ends of the corresponding containing cavity through a supporting beam respectively, and the two small ends of each fusiform mass block are vertically connected to the two sides of the corresponding containing cavity through two sensitive beams respectively; the upper surface of each sensitive beam is provided with a piezoresistor, and all the piezoresistors are connected in series through metal leads to form a Wheatstone bridge. The objective of the utility model is to solve the problems that a piezoresistive acceleration sensor is low in output sensitivity, the output sensitivity and the inherent frequency are mutually restricted, and the transverse crosstalk is large.

Description

Technical Field

[0001] This invention belongs to the field of acceleration sensor technology, and particularly relates to a piezoresistive high-g acceleration sensor with a double spindle structure. Background Technology

[0002] Microelectromechanical systems (MEMS) are miniature intelligent systems that integrate specialized mechanical, electronic, optical, and other components onto millimeter-scale silicon chips, manufactured using micromachining techniques. They involve various disciplines such as mechanics, electronics, optics, and materials science. Among them, the MEMS piezoresistive accelerometer is one of the earliest and fastest-developing sensor technologies.

[0003] With the development of military technology, new requirements have been placed on missile lead technology. Miniaturization, agility, intelligence, high reliability, low power consumption, and low cost are current research directions, and MEMS technology precisely meets these requirements. Due to the use of semiconductor silicon-based processing technology, MEMS accelerometers are micrometer- or submicrometer-sized, small in size and lightweight, possessing the advantages of miniaturization. Furthermore, using single-crystal silicon to fabricate accelerometers facilitates the integration of sensors, actuators, and integrated circuits, forming multifunctional systems capable of achieving more complex functions. The main materials of MEMS accelerometers are single-crystal silicon, polycrystalline silicon, and silicon nitride, etc. Based on photolithography technology, mass production can be achieved using integrated circuit manufacturing lines, greatly reducing the production cost per chip.

[0004] Currently, the most mainstream MEMS high-g accelerometers include piezoresistive, piezoelectric, capacitive, thermal convection, and resonant types. Capacitive accelerometers, due to their large range limitations and nonlinearity, are mainly used in commercial and civilian applications. Piezoelectric high-g accelerometers are primarily used in military applications where high precision is not required. Thermal convection high-g accelerometers have limited maximum range, and their response time is constrained by heat transfer, making their output sensitive to changes in ambient temperature. Resonant accelerometers measure acceleration by changing the resonant frequency of the structure, but their internal measurement implementation is complex. Compared to other sensors, MEMS piezoresistive high-g accelerometers have the following advantages: First, high linearity. Capacitive accelerometers, due to their capacitance-changing principle, exhibit poor linearity when the capacitance change is large, while piezoelectric accelerometers have poor lateral sensitivity. Piezoresistive sensors do not have these drawbacks. Second, simple readout circuitry. MEMS piezoresistive high-g accelerometers typically utilize Wheatstone bridge circuits to improve output sensitivity. The piezoresistor is fabricated on four Wheatstone bridge arms. Under acceleration, the chip undergoes elastic deformation, causing a change in the piezoresistor's resistance. The acceleration value can be obtained by measuring the differential voltage output of the Wheatstone bridge. This simplifies the readout circuit of MEMS piezoresistive high-g accelerometers, whereas capacitive and piezoelectric types require specialized and complex circuits for signal acquisition. Finally, the mature manufacturing process, particularly silicon-based semiconductor fabrication technology, significantly reduces the size and production cost of accelerometers, enabling large-scale manufacturing of MEMS piezoresistive high-g accelerometers.

[0005] For piezoresistive MEMS accelerometers, the commonly used beam-island structure, while simple, suffers from significant lateral effects that are difficult to reduce or eliminate because the center of gravity of the mass block is not level with the supporting beam. Another common piezoresistive MEMS accelerometer structure is the single cantilever beam structure. In both structures, the piezoresistor is located on the supporting beam, so the stiffness coefficient of the supporting beam determines the sensor's natural frequency, and the sensor's sensitivity is determined by the piezoresistive coefficient on the supporting beam. The stiffness coefficient of the supporting beam decreases as the beam length and cross-sectional area decrease. A larger stiffness coefficient makes it harder for the cantilever beam to bend, resulting in a higher natural frequency, smaller displacement of the mass block, lower stress on the piezoresistor, and a lower sensor output. In other words, an increase in the sensor's natural frequency leads to a decrease in sensor sensitivity; therefore, in high-frequency applications, its output sensitivity is generally very low. For these two types of sensor structures, sensitivity and natural frequency are mutually constrained due to the above reasons. Utility Model Content

[0006] To address the problems existing in the prior art, this utility model provides a piezoresistive high-g accelerometer with a double spindle structure. Its purpose is to solve the problems of low output sensitivity, mutual constraint between output sensitivity and natural frequency, and large transverse crosstalk in piezoresistive accelerometers.

[0007] To solve the above-mentioned technical problems, this utility model is achieved through the following technical solution:

[0008] A piezoresistive high-g accelerometer with a dual-spindle structure includes a sensor core. Bonding regions are formed on the upper and lower surfaces of the sensor core. Two symmetrical receiving cavities are formed through the bonding regions on the upper and lower surfaces. Each receiving cavity contains a spindle-shaped mass. The two sides of the middle portion of each spindle-shaped mass are vertically connected to the two ends of the corresponding receiving cavity via a support beam. The two smaller ends of each spindle-shaped mass are vertically connected to the two sides of the corresponding receiving cavity via two sensitive beams. A piezoresistor is formed on the upper surface of each sensitive beam. All piezoresistors are connected in series via metal leads to form a Wheatstone bridge.

[0009] Furthermore, the upper surface of the sensor core is provided with a solder pad exposed area, on which power supply pads for supplying power to the Wheatstone bridge and signal pads for outputting differential signals of the Wheatstone bridge are provided.

[0010] Furthermore, the exposed area of ​​the solder pad is also provided with a zero-adjustment solder pad for connecting the zero-adjustment resistor.

[0011] Furthermore, a transition fillet is provided at the connection between each sensitive beam and the corresponding receiving cavity.

[0012] Furthermore, the accelerometer also includes an upper cover plate. The lower surface of the upper cover plate is provided with an upper cover plate bonding area that matches the bonding area on the upper surface of the sensor core. The upper cover plate bonding area is provided with upper cover plate grooves corresponding to the two receiving cavities. The upper cover plate and the sensor core are bonded together through the upper cover plate bonding area and the bonding area on the upper surface of the sensor core.

[0013] Furthermore, the accelerometer also includes a lower cover plate. The upper surface of the lower cover plate is provided with a lower cover plate bonding area that matches the bonding area on the lower surface of the sensor core. The lower cover plate bonding area is provided with a lower cover plate groove corresponding to the two receiving cavities. The lower cover plate and the sensor core are bonded together through the lower cover plate bonding area and the bonding area on the lower surface of the sensor core.

[0014] Furthermore, the sensor core is made of SOI wafer.

[0015] Furthermore, the SOI wafer has a thickness of 400 μm, a device layer thickness of 10 μm, a buried oxide layer thickness of 1 μm, a resistivity of 3 Ω*cm to 6 Ω*cm, a total deviation of less than 1 μm, a curvature of less than 3 μm, and a warpage of less than 10 μm.

[0016] Furthermore, the varistor is made of semiconductor material.

[0017] Furthermore, the crystal orientation of the varistor is

[110] .

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] This invention provides a piezoresistive high-g accelerometer with a double-spindle structure. By employing a double-spindle-shaped mass block design, the mass blocks can generate greater displacement under acceleration, thereby improving the sensor's sensitivity. The spindle-shaped mass block design concentrates the mass in the middle, with relatively smaller masses at both ends. This optimized mass distribution allows the sensor to more effectively convert acceleration into displacement of the mass blocks when subjected to acceleration, thus improving the sensor's output sensitivity. By introducing a combination of double-spindle-shaped mass blocks and a sensitive beam, a high natural frequency is maintained while improving sensitivity. Specifically, the combination of the spindle-shaped mass blocks and the sensitive beam allows the sensor to generate sufficient displacement to improve sensitivity while maintaining sufficient stiffness to maintain a high natural frequency under acceleration. Furthermore, sensitivity can be improved by adjusting only the size of the sensitive beam, with almost no impact on the structure's natural frequency. Two perfectly symmetrical cavities, which run through the upper and lower surfaces of the sensor core, provide a stable mounting space for the spindle-shaped mass block. Their symmetrical layout effectively reduces the lateral crosstalk of the sensor, enabling it to more accurately measure acceleration in the target direction when subjected to acceleration, while reducing the influence of acceleration in other directions on the measurement results.

[0020] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the specific embodiments of this utility model, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1A schematic diagram of the structural assembly of a piezoresistive high-g accelerometer with a dual-spindle structure provided for an embodiment of this utility model;

[0023] Figure 2 A schematic diagram of the sensor core of a piezoresistive high-g acceleration sensor with a dual-spindle structure provided for an embodiment of this utility model;

[0024] Figure 3 A schematic diagram of the sensitive beam structure of a piezoresistive high-g accelerometer with a double spindle structure provided for an embodiment of this utility model;

[0025] Figure 4 A schematic diagram of the upper cover plate structure of a piezoresistive high-g accelerometer with a double spindle structure provided for an embodiment of this utility model;

[0026] Figure 5 A schematic diagram of the lower cover plate structure of a piezoresistive high-g acceleration sensor with a double spindle structure provided for an embodiment of this utility model;

[0027] Figure 6 A schematic diagram of zeroing a piezoresistive high-g accelerometer with a dual-spindle structure provided for an embodiment of this utility model;

[0028] Figure 7 S1 is a cross-sectional side view of a piezoresistive high-g accelerometer with a dual-spindle structure provided for an embodiment of this utility model.

[0029] Figure 8 S2 sensor cross-sectional side view of a piezoresistive high-g accelerometer with a dual-spindle structure provided for an embodiment of this utility model;

[0030] Figure 9 A side view of the S3 sensor cross-section of a piezoresistive high-g accelerometer with a dual-spindle structure provided for an embodiment of this utility model;

[0031] Figure 10 S4 sensor cross-sectional side view of a piezoresistive high-g accelerometer with a dual-spindle structure provided for an embodiment of this utility model;

[0032] Figure 11 S5 sensor cross-sectional side view of a piezoresistive high-g accelerometer with a dual-spindle structure provided for an embodiment of this utility model;

[0033] Figure 12 A stress simulation diagram of a piezoresistive high-g accelerometer with a double spindle structure provided for an embodiment of this utility model.

[0034] In the figure: 1-Sensor core; 100-Bonding area; 101-Receiving cavity; 102-Spindle-shaped mass block; 103-Support beam; 104-Sensitive beam; 105-Varistor; 106-Metal lead; 107-Exposed pad area; 108-Power supply pad; 109-Signal pad; 110-Zeroing pad; 111-Transition fillet; 2-Upper cover plate; 200-Upper cover plate bonding area; 201-Upper cover plate groove; 3-Lower cover plate; 300-Lower cover plate bonding area; 301-Lower cover plate groove; 4-N-type substrate; 5-Buried oxide layer; 6-Device layer; 7-Silicon dioxide insulating layer; 8-Silicon dioxide mask; 9-Ohmic contact area; 10-Front-side metal layer; 11-Back-side metal layer; 12-Back-side bonding area. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0036] Combination Figure 1 and Figure 2 As shown, this utility model provides a piezoresistive high-g accelerometer with a dual-spindle structure. Through optimized structural design, the sensor's output sensitivity is improved, while simultaneously addressing the mutual constraint between output sensitivity and natural frequency, and effectively reducing lateral crosstalk. The dual-spindle piezoresistive high-g accelerometer includes a sensor core 1. Bonding regions 100 are provided on the upper and lower surfaces of the sensor core 1. Two symmetrical receiving cavities 101 are formed through the bonding regions 100. Each receiving cavity 101 contains a spindle-shaped mass block 102. The two sides of the middle portion of each spindle-shaped mass block 102 are vertically connected to the two ends of the corresponding receiving cavity 101 via a support beam 103. The two smaller ends of each spindle-shaped mass block 102 are vertically connected to the two sides of the corresponding receiving cavity 101 via two sensitive beams 104. A piezoresistive resistor 105 is provided on the upper surface of each sensitive beam 104. All piezoresistive resistors 105 are connected in series via metal leads 106 to form a Wheatstone bridge.

[0037] Specifically, the sensor core 1 is the core component of the entire accelerometer. Bonding areas 100 are provided on both the upper and lower surfaces of the sensor core 1. These bonding areas 100 are used to connect with the packaging structure, ensuring stable sensor operation and signal output. Two completely symmetrical receiving cavities 101 are formed through the bonding areas 100 on the upper and lower surfaces of the sensor core 1. These two receiving cavities 101 not only provide installation space for the spindle-shaped mass block 102, but also effectively reduce lateral crosstalk of the sensor through their symmetrical layout. Each receiving cavity 101 contains a spindle-shaped mass block 102. The spindle-shaped mass block 102 resembles a spindle in shape, with a larger mass concentrated in the middle and relatively smaller at both ends. This spindle-shaped design allows the mass block to generate a larger displacement under acceleration, thereby improving the sensor's sensitivity. Each spindle-shaped mass block 102 is vertically connected to the two ends of the corresponding receiving cavity 101 via a support beam 103 on both sides of its middle portion. The support beam 103 ensures the stable movement of the spindle-shaped mass 102 under acceleration, while also restricting its degrees of freedom in non-measuring directions, enhancing the sensor's resistance to lateral interference. Furthermore, its stiffness coefficient influences the sensor's natural frequency. The two small ends of each spindle-shaped mass 102 are vertically connected to the sides of the corresponding receiving cavity 101 via two sensitive beams 104. As a key component for stress transmission, the slender structure of the sensitive beam 104 allows for greater strain under acceleration, thereby improving the response sensitivity of the piezoresistor 105. The sensitive beam 104 enables the deformation of the spindle-shaped mass 102 under acceleration to be more effectively transmitted to the piezoresistor 105, thus improving the sensor's output sensitivity. A piezoresistor 105 is mounted on the upper surface of each sensitive beam 104; the resistance of the piezoresistor 105 changes with stress, i.e., its resistance changes when subjected to pressure. When the sensor is subjected to acceleration, the sensitive beam 104 deforms, causing a change in the resistance value of the piezoresistor 105 on its upper surface. All piezoresistors 105 are connected in series via metal leads 106 to form a Wheatstone bridge. It should be understood that the Wheatstone bridge circuit is a commonly used bridge circuit that can improve the output sensitivity of the sensor and accurately reflect the acceleration value by measuring the output differential voltage.

[0038] When the sensor is subjected to, for example Figure 2 During the acceleration shown, the spindle-shaped mass 102 compresses and stretches the sensitive beam 104 under the action of inertial force, causing one end of the sensitive beam 104 at both ends of the spindle-shaped mass 102 to be under tension and the other end to be under compression. Due to the piezoresistive effect, the presence of stress causes the resistance of the piezoresistor 105 to change with the pressure, and the output differential voltage of the Wheatstone bridge will also change. By measuring the output differential voltage, the acceleration value can be obtained. For example, as shown... Figure 2As shown, the Wheatstone bridge arm resistors R1 and R3 are deformed in the same way, and R2 and R4 are deformed in the same way. R1 and R2 form one side of the bridge, and R3 and R4 form the other side of the bridge. In this way, the bridge will output a differential signal.

[0039] It should be noted that by adjusting the size and shape of the support beam 103 and the sensing beam 104, the balance between the sensor's natural frequency and sensitivity can be optimized. For example, increasing the stiffness of the support beam 103 can increase the sensor's natural frequency, but may reduce the sensitivity; while increasing the flexibility of the sensing beam 104 can increase the sensitivity, but may reduce the natural frequency. Therefore, in practical applications, a trade-off needs to be made based on specific requirements.

[0040] In one possible implementation, such as Figure 1 and Figure 2 As shown, the upper surface of the sensor core 1 is also provided with a pad exposed area 107, and the pad exposed area 107 is provided with a power supply pad 108 for supplying power to the Wheatstone bridge, and a signal pad 109 for outputting the differential signal of the Wheatstone bridge.

[0041] In other words, on the upper surface of the sensor core 1, in addition to the bonding area 100 and its internal receiving cavity 101, spindle-shaped mass block 102, support beam 103, sensitive beam 104, and varistor 105, a solder pad exposed area 107 is also provided. The purpose of the solder pad exposed area 107 is to provide space for electrical connection with external circuits or devices, ensuring that the sensor can receive power and output measurement signals.

[0042] On the exposed pad area 107, there are power supply pads 108 and signal pads 109. Power supply pad 108 supplies power to the Wheatstone bridge. When the sensor is operating, a stable voltage or current needs to be supplied to the Wheatstone bridge via an external power source to drive the varistor 105 to change its resistance and generate an output signal. Signal pad 109 outputs the differential signal of the Wheatstone bridge. When the sensor is operating, the differential voltage output by the Wheatstone bridge is output through signal pad 109 to external circuits or devices for processing and analysis.

[0043] For example, the exposed pad area 107 is located at the edge of the upper surface of the sensor core 1, away from areas susceptible to acceleration such as the receiving cavity 101 and the spindle-shaped mass block 102, in order to reduce the impact of mechanical stress and deformation generated under acceleration on the electrical connection.

[0044] In one possible implementation, such as Figure 1 and Figure 2As shown, the exposed pad area 107 also has a zero-adjustment pad 110 for connecting a zero-adjustment resistor. In a piezoresistive accelerometer, the zero-adjustment resistor is used to adjust the sensor's zero-point output. Due to minor differences in the manufacturing process, changes in ambient temperature, and aging during long-term use, the sensor's zero-point output may shift. The zero-adjustment resistor is introduced to compensate for this shift, eliminate the influence of manufacturing errors and environmental factors such as temperature on the measurement results, and ensure that the sensor can output a stable zero signal when there is no acceleration input. During sensor installation and debugging, the resistance value of the zero-adjustment resistor is adjusted to ensure that the sensor can output a stable zero signal when there is no acceleration input.

[0045] For example, under the influence of the same plane and Figure 2 When the acceleration is perpendicular to the sensor plane or perpendicular to the direction of acceleration shown, R1, R2, R3, and R4 deform uniformly, and the bridge circuit outputs no signal. Therefore, theoretically, this structure has no lateral influence. However, considering the actual manufacturing process, the initial resistance values ​​of R1, R2, R3, and R4 may be inconsistent, resulting in a non-zero initial output, which affects subsequent signal amplification. Therefore, a zero-adjustment pad is reserved in the design. It should be understood that the specific zero-adjustment principle is as follows: Figure 6 As shown:

[0046] When S- is connected to 1:

[0047]

[0048] When S- is connected to 2:

[0049]

[0050] In the formula, V out This is the differential output between S+ and S-. R t This is the resistance value of the zero-adjustment resistor.

[0051] In one possible implementation, such as Figure 3 As shown, each sensitive beam 104 is provided with a transition fillet 111 at the connection between it and the corresponding receiving cavity 101.

[0052] Specifically, during the operation of the accelerometer, when subjected to a large acceleration impact, the connection between the sensitive beam 104 and the receiving cavity 101 often becomes a critical area of ​​stress concentration. If the design of this area is not reasonable enough, it may lead to structural damage, thereby affecting the sensor's performance and lifespan. To solve this problem, this invention provides a transition fillet 111 at the connection between each sensitive beam 104 and the corresponding receiving cavity 101. The transition fillet 111 disperses stress through a smooth transition, reducing stress concentration and thus improving the sensor's overload resistance.

[0053] In other words, the transition fillet 111 can effectively disperse the stress at the connection point and avoid structural damage caused by stress concentration. The fillet makes the connection point smoother, improves the overall toughness of the structure, and enables the sensor to better absorb and disperse energy when subjected to high overloads.

[0054] In one possible implementation, such as Figure 1 and Figure 4 As shown, the accelerometer also includes an upper cover plate 2. The lower surface of the upper cover plate 2 is provided with an upper cover plate bonding area 200 that matches the bonding area 100 on the upper surface of the sensor core 1. The upper cover plate bonding area 200 is provided with upper cover plate grooves 201 corresponding to the two receiving cavities 101. The upper cover plate 2 and the sensor core 1 are bonded together through the upper cover plate bonding area 200 and the bonding area 100 on the upper surface of the sensor core 1.

[0055] Specifically, the main function of the upper cover plate 2 is to provide additional protection, ensuring that the sensor core 1 can operate stably under complex environmental conditions. For example, the upper cover plate 2 is made of the same material as the sensor core 1 or a material with similar physical properties to ensure good compatibility between the two. The lower surface of the upper cover plate 2 is provided with an upper cover plate bonding area 200 that matches the bonding area 100 on the upper surface of the sensor core 1, ensuring that the upper cover plate 2 can be accurately positioned and aligned with the sensor core 1. To correspond to the two receiving cavities 101 on the sensor core 1, the lower surface of the upper cover plate 2 is also provided with two upper cover plate grooves 201 within the upper cover plate bonding area 200. The upper cover plate grooves 201 ensure that during the bonding process, the upper cover plate 2 will not interfere with the spindle-shaped mass block 102 or other sensitive structures within the receiving cavity 101, thereby ensuring the normal operation of the sensor.

[0056] In one possible implementation, such as Figure 1 and Figure 5As shown, the accelerometer also includes a lower cover plate 3. The upper surface of the lower cover plate 3 is provided with a lower cover plate bonding area 300 that matches the bonding area 100 on the lower surface of the sensor core 1. The lower cover plate bonding area 300 is provided with a lower cover plate groove 301 corresponding to the two receiving cavities 101. The lower cover plate 3 and the sensor core 1 are bonded together through the lower cover plate bonding area 300 and the bonding area 100 on the lower surface of the sensor core 1.

[0057] Specifically, the lower cover plate 3 is similar to the upper cover plate 2, and its main function is to provide additional protection while ensuring the stable operation of the sensor core 1 under complex environmental conditions. The lower cover plate 3 is made of the same material as the sensor core 1 or a material with similar physical properties to ensure good compatibility between the two. The upper surface of the lower cover plate 3 is provided with a lower cover plate bonding area 300 that matches the bonding area 100 on the lower surface of the sensor core 1, ensuring that the lower cover plate 3 can be accurately positioned and aligned with the sensor core 1. In order to correspond to the two receiving cavities 101 on the sensor core 1, the upper surface of the lower cover plate 3 is also provided with two lower cover plate grooves 301 in the lower cover plate bonding area 300, ensuring that the lower cover plate 3 will not interfere with the spindle-shaped mass block 102 or other sensitive structures in the receiving cavity 101 during the bonding process, thereby ensuring the normal operation of the sensor.

[0058] like Figure 12 As shown, in one embodiment, when the accelerometer of this invention is subjected to an acceleration of 100,000g, the average stress on the sensitive beam 104 is 64.73MPa, and the maximum structural stress is only 98.64MPa, which is far lower than the allowable yield stress of silicon material of 340MPa. Therefore, the accelerometer can resist high overload impact.

[0059] In one embodiment, the sensor core 1 uses an SOI wafer. To maximize sensitivity, the crystal orientation with the largest piezoresistive coefficient, i.e., the SOI wafer processing plane, is selected as (100), and the crystal orientation of the varistor 105 is

[110] . Based on simulation design, the SOI wafer thickness is selected as 400 μm, the device layer thickness as 10 μm, and the buried oxide layer thickness as 1 μm. To ensure the yield of the subsequently processed chips and meet the processing requirements, the selected SOI wafer has a resistivity of 3 Ω*cm to 6 Ω*cm, a total deviation of less than 1 μm, a bending degree of less than 3 μm, and a warpage of less than 10 μm. The varistor 105 uses semiconductor material.

[0060] like Figures 7 to 11 As shown, this embodiment provides a fabrication process for a piezoresistive high-g accelerometer with a dual-spindle structure, including the following steps:

[0061] S1: An N-type (100) crystal plane SOI wafer is selected as the processing material. The silicon wafer includes an N-type substrate 4, a buried oxide layer 5, and a device layer 6. Then, the SOI wafer is thermally oxidized on both sides to form a silicon dioxide insulating layer 7 on the upper and lower surfaces. Finally, as shown in the figure... Figure 7 As shown.

[0062] S2: A window is made in the silicon dioxide insulating layer 7, and low-concentration boron ion implantation is performed in the varistor region, followed by annealing to form the varistor 105. Photoresist is spin-coated onto the lightly doped silicon wafer, and high-concentration boron ion implantation is performed using the photoresist as a mask, followed by annealing to form the heavily doped region. Then, a silicon dioxide mask 8 is generated using LPCVD. A window is made in the LPCVD-generated silicon dioxide mask 8, and etch trenches are performed in the heavily doped region to form the ohmic contact region 9. Finally, as shown... Figure 8 As shown.

[0063] S3: A gold film is deposited on the silicon wafer surface using magnetron sputtering. Then, the bottom silicon dioxide is removed. Wet etching is used here to remove the bottom silicon dioxide because the silicon dioxide generated by the front-side LPCVD is protected by a metal layer. Using photoresist as a barrier layer, the metal layer is patterned using Au dry etching to form the front-side metal layer 10, which includes metal leads 106, power supply pads 108, signal pads 109, zero-adjustment pads 110, and bonding areas 100 (gold-to-gold bonding areas). After etching, a varistor IV characteristic test is performed to determine the success of the ohmic contact process through resistance calculation. Finally, bonding metal is deposited on the back side to form the back-side metal layer 11, as shown in the final image. Figure 9 As shown.

[0064] S4: First, the back metal is etched to form the back bonding region 12. Next, the back active region is etched. Then, using the metal layer behind the bottom as a bonding layer as a mask, RIE is used to etch the active region of the back mass block. Afterwards, deep back etching is performed. DRIE is used to etch the bottom down to the buried oxide layer, initially forming a spindle-shaped mass block 102. Finally, RIE is used to etch away the buried oxide layer, resulting in the final shape as shown. Figure 10 As shown.

[0065] S5: First, metal deposition is performed on the silicon cover plate, and etching is performed to leave the bonding area to obtain the lower cover plate 3. Then, the lower cover plate 3 is gold-bonded to the lower surface of the chip. Next, the silicon dioxide protective layer is etched away on the front side using RIE, and then a 10um silicon device layer is etched to release the spindle-shaped mass block 102 and the sensitive beam 104. A bonding alloy film is deposited on the silicon cover plate, a gold film is etched, and the active area of ​​the mass block, the lead area, and the pad area are etched to obtain the upper cover plate 2. Then, the upper cover plate 2 is gold-bonded to the upper surface of the chip. Finally, the front side is etched to expose the pads, and the final result is as follows. Figure 11 As shown.

[0066] In the description of this utility model, it should be understood that the terms "upper", "lower", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0067] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0068] In this utility model, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0069] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0070] In this utility model, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0071] Finally, it should be noted that the above-described embodiments are merely specific implementations of this utility model, used to illustrate the technical solution of this utility model, and not to limit it. The protection scope of this utility model is not limited thereto. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the technical scope disclosed in this utility model. These modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model, and should all be covered within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the protection scope of the claims.

Claims

1. A piezoresistive high-g accelerometer with a dual-spindle structure, characterized in that, The sensor includes a sensor core (1), on which bonding areas (100) are provided on the upper and lower surfaces. Two symmetrical receiving cavities (101) are opened through the bonding areas (100) on the upper and lower surfaces. A spindle-shaped mass block (102) is provided in each receiving cavity (101). The two sides of the middle part of each spindle-shaped mass block (102) are vertically connected to the two ends of the corresponding receiving cavity (101) through a support beam (103). The two small ends of each spindle-shaped mass block (102) are vertically connected to the two sides of the corresponding receiving cavity (101) through two sensitive beams (104). A varistor (105) is provided on the upper surface of each sensitive beam (104). All varistors (105) are connected in series through metal leads (106) to form a Wheatstone bridge.

2. The piezoresistive high-g accelerometer with a double spindle structure according to claim 1, characterized in that, The upper surface of the sensor core (1) is also provided with a solder pad exposed area (107), and the solder pad exposed area (107) is provided with a power supply pad (108) for supplying power to the Wheatstone bridge, and a signal pad (109) for outputting the differential signal of the Wheatstone bridge.

3. The piezoresistive high-g accelerometer with a double spindle structure according to claim 2, characterized in that, The exposed area (107) of the pad is also provided with a zero-adjustment pad (110) for connecting the zero-adjustment resistor.

4. The piezoresistive high-g accelerometer with a double spindle structure according to claim 1, characterized in that, Each sensitive beam (104) is provided with a transition fillet (111) at the connection between itself and the corresponding receiving cavity (101).

5. A piezoresistive high-g accelerometer with a double spindle structure according to claim 1, characterized in that, The accelerometer also includes an upper cover plate (2), the lower surface of which is provided with an upper cover plate bonding area (200) that matches the bonding area (100) on the upper surface of the sensor core (1), the upper cover plate bonding area (200) is provided with an upper cover plate groove (201) corresponding to the two receiving cavities (101), and the upper cover plate (2) and the sensor core (1) are bonded together through the upper cover plate bonding area (200) and the bonding area (100) on the upper surface of the sensor core (1).

6. A piezoresistive high-g accelerometer with a double spindle structure according to claim 1, characterized in that, The accelerometer also includes a lower cover plate (3). The upper surface of the lower cover plate (3) is provided with a lower cover plate bonding area (300) that matches the bonding area (100) on the lower surface of the sensor core (1). The lower cover plate bonding area (300) is provided with a lower cover plate groove (301) corresponding to the two receiving cavities (101). The lower cover plate (3) and the sensor core (1) are bonded together through the lower cover plate bonding area (300) and the bonding area (100) on the lower surface of the sensor core (1).

7. A piezoresistive high-g accelerometer with a dual-spindle structure according to claim 1, characterized in that, The sensor core (1) is made of SOI wafer.

8. A piezoresistive high-g accelerometer with a dual-spindle structure according to claim 7, characterized in that, The SOI wafer has a thickness of 400 μm, a device layer thickness of 10 μm, a buried oxide layer thickness of 1 μm, a resistivity of 3 Ω*cm to 6 Ω*cm, a total deviation of less than 1 μm, a curvature of less than 3 μm, and a warpage of less than 10 μm.

9. A piezoresistive high-g accelerometer with a double spindle structure according to claim 1, characterized in that, The varistor (105) is made of semiconductor material.

10. A piezoresistive high-g accelerometer with a double spindle structure according to claim 9, characterized in that, The crystal orientation of the varistor (105) is [110].

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