CN102590555A - Resonance-force balance capacitance type three-axis acceleration transducer and manufacture method - Google Patents

Abstract

The invention discloses a structure and a manufacturing method of a resonance-force balance capacitive three-axis acceleration sensor, belonging to the field of micro-electromechanical systems. Its structural feature is that the three-axis acceleration sensor is composed of a middle silicon chip (1), an upper cover plate (2) and a lower bottom plate (3); wherein, the middle silicon chip (1) is composed of a double-end fixed support beam resonator (4), The mass block (6) is composed of a support beam (5), a movable electrode (7) and a frame (8). The characteristic of this sensor in terms of detection principle is that the X-axis and Y-axis acceleration signals in the chip plane are detected by a double-end fixed beam resonator (4), and the change of the resonant frequency of the double-end fixed beam resonator (4) reflects the magnitude of the acceleration and direction; the Z-axis acceleration signal perpendicular to the chip plane is detected by the capacitive sensitive principle, and works in the closed-loop force balance mode. The movement displacement of the mass block (6) in the normal direction of the chip is very small, and the acceleration signal input by the Z axis has very little cross interference on the acceleration detection of the X axis and the Y axis.

Description

Resonance-force balance capacitive three-axis acceleration sensor and manufacturing method

technical field

The present invention relates to the working principle, structure and manufacturing method of a three-axis acceleration sensor, in particular to the working mechanism, structure and manufacturing method of a resonant-force balance capacitive three-axis acceleration sensor, belonging to Micro-Electro-Mechanical Systems (Micro-Electro-Mechanical Systems, MEMS) field.

Background technique

Miniature accelerometers are an important class of mechanical quantity sensors. As early as the end of the 1960s, people began to study one-dimensional micro-silicon acceleration sensors. The large-scale production of one-dimensional miniature acceleration sensors began in the late 1980s. In the 1990s, with the development of science and technology and the needs of the military and commercial markets, research on three-dimensional micro-acceleration sensors began to be used in military, automotive electronics, industrial automation, robotics, consumer electronics and other fields. Due to the advantages of small size, light weight, low power consumption and cost, strong overload capacity, easy integration, and large-scale mass production, the miniature acceleration sensor has not only become the core component of the micro-inertial measurement combination, but also quickly applied to vehicle control, high-speed Civilian fields such as railways, robots, industrial automation, mining, toys, and medical care.

Miniature accelerometers are sensors that use the inertial force of a sensing mass to measure acceleration. According to the movement mode of the detection quality, it can be divided into linear accelerometer and pendulum accelerometer; according to the signal detection method, it can be divided into piezoresistive, capacitive, tunnel current, resonant, thermal convection and piezoelectric acceleration sensors. According to whether there is a feedback signal, it can be divided into open-loop deviation type and closed-loop force balance type acceleration sensor. According to the number of sensitive axes, it is divided into single-axis, double-axis and three-axis acceleration sensors. After the 1990s, with the continuous development of MEMS technology and the needs of the military and commercial markets, the acceleration test in a single direction can no longer meet the increasing demand for acceleration sensors, and the acceleration sensors are developing in a three-dimensional direction for use in Detect spatial acceleration, and serve military projects such as satellite navigation, missile guidance, and shell orientation, as well as civil projects such as automobile anti-shock protection, automatic braking, and medical treatment. The triaxial miniature accelerometer can simultaneously measure the acceleration of three axial directions orthogonal to each other. Its measurement principles include capacitive, piezoresistive, piezoelectric and thermal convection, and can be divided into multi-mass and single-mass systems according to the number of masses.

和

同年，该研究小组还成功研制出单质量块电容传感力平衡式三轴微加速度计，采用三个含有Sigma-Delta调制器的反馈闭环控制系统，每个方向的检测电容各使用一个。传感部分包括质量块、四个对角支撑的弹性梁以及叉指电容。平面加速度依靠叉指电容检测，垂直方向的加速度依靠质量块与下电极组成的电容检测。微结构为2.3μm厚的多晶硅，叉指静止时的间隙为2.2μm，质量块为0.2μg。电路为2μm的CMOS技术制作，5V供电。X、Y、Z轴的电容分别为98fF、98fF和177fF。最大量程为11g、11g、5.5g。灵敏度分别为0.24fF/g、0.24fF/g和0.82fF/g。噪声为和

最大交叉轴干扰为-36dB。2003年，密西根大学的Junseok Chae等人研制成功一种电容式三轴微加速度计。该加速度计包含三个独立的单轴加速度计，多晶硅传感和驱动电极面积较大，由牺牲氧化层形成的微小感应间隙仅1.5μm。该加速度计系统的尺寸是7×9mm²，量程1g，灵敏度大于5pF/g，三个轴的最低噪声都低于

与接口电路集成之后的加速度计工作时其XY平面内和Z轴向的最低噪声分别是

和

2008年台湾工业技术研究所微系统技术研究中心的Y.W.Hsu采用SOG体微机工艺和DRIE刻蚀技术研制了一种三轴电容式加速度传感器，其平面尺寸仅为1.3×1.28mm²，量程±2g，其Z轴输出灵敏度高达1.434V/g，分辨率为

X轴灵敏度和交叉灵敏度分别为1.442V/g和0.03％，Y轴灵敏度和交叉灵敏度分别为1.241V/g和0.21％。2008年Hongwei Qu报道了一种采用单一质量块实现的单片集成电容式CMOS-MEMS三轴加速度传感器。在芯片上设计有低功耗、低噪声、双斩波的放大电路以降低传感器的噪声。传感器X、Y、Z轴的灵敏度分别为520mV/g，460mV/g，320mV/g。相应地，其噪声水平分别为2010年Chih-Ming Sun报道了一种单质量块三轴电容式加速度传感器。包含传感部分和测量电路在内的芯片面积只有1.78×1.38mm²，量程为0.8～6g。X、Y、Z轴的灵敏度分别为0.53mV/，0.28mV/g和0.2mV/g，非线性度分别为2.64％、3.15％和3.36％。交叉灵敏度在1％～8.3％之间，X、Y、Z轴的噪声分别为和

The three-axis acceleration sensor with capacitance detection is the easiest to implement and has better performance. In 1996, T.Mineta developed a three-axis capacitive acceleration sensor. The acceleration measurement sensitivity of the three axes is the same, the center of gravity of the mass block is above the support beam, the X-axis and Y-axis accelerations are detected by the translation of the mass block, and the Z-axis acceleration is detected by the inclination of the mass block. For every 1g change in the three axial accelerations, the capacitance gap changes by 0.3μm, the sensitivity is 40mV/g, and the transverse sensitivity is about 10%. In 1997, researchers at the University of California, Berkeley developed a monolithic three-axis capacitive accelerometer made by surface micromachining technology based on the research of single-axis micro-accelerometers, using three different masses to detect three axes. to the acceleration. The measurement of X and Y-axis acceleration is measured by comb-shaped interdigital capacitance, and the vertical Z-axis acceleration is measured by flat-plate capacitance. The sensor is manufactured by surface micro-mechanical technology, the microstructure is integrated with CMOS circuit, the structure layer is 2μm polysilicon, the circuit contains the feedback closed-loop control circuit of the Sigma-Delta modulator and the on-chip integrated AD conversion circuit. The capacitances of the X, Y, and Z axes are 101fF, 78fF, and 322fF, respectively; the interdigital gaps are 2.13, 2.13, and 2.3μm; the noise is

and

In the same year, the research team also successfully developed a three-axis micro-accelerometer with single-mass capacitive sensing force balance, using three feedback closed-loop control systems containing Sigma-Delta modulators, and using one detection capacitor in each direction. The sensing part includes a proof mass, four diagonally supported elastic beams, and interdigital capacitors. Plane acceleration is detected by interdigital capacitance, and acceleration in the vertical direction is detected by capacitance composed of mass block and lower electrode. The microstructure is 2.3 μm thick polysilicon, the interdigitation gap is 2.2 μm at rest, and the mass is 0.2 μg. The circuit is made of 2μm CMOS technology and powered by 5V. The capacitances for the X, Y, and Z axes are 98fF, 98fF, and 177fF, respectively. The maximum capacity is 11g, 11g, 5.5g. The sensitivities are 0.24fF/g, 0.24fF/g and 0.82fF/g, respectively. Noise is and

The maximum cross-axis interference is -36dB. In 2003, Junseok Chae and others at the University of Michigan successfully developed a capacitive three-axis micro-accelerometer. The accelerometer contains three independent uniaxial accelerometers, the polysilicon sensing and driving electrodes have a large area, and the tiny sensing gap formed by the sacrificial oxide layer is only 1.5μm. The size of the accelerometer system is 7×9mm ² , the measuring range is 1g, the sensitivity is greater than 5pF/g, and the lowest noise of the three axes is lower than

When the accelerometer integrated with the interface circuit works, the lowest noise in the XY plane and the Z axis are respectively

and

In 2008, YWHsu of the Microsystem Technology Research Center of Taiwan Industrial Technology Research Institute developed a three-axis capacitive acceleration sensor using SOG bulk microcomputer technology and DRIE etching technology. Its plane size is only 1.3×1.28mm ² and the range is ±2g. Its Z-axis output sensitivity is as high as 1.434V/g, and the resolution is

The X-axis sensitivity and cross-sensitivity are 1.442V/g and 0.03%, respectively, and the Y-axis sensitivity and cross-sensitivity are 1.241V/g and 0.21%, respectively. In 2008, Hongwei Qu reported a monolithic integrated capacitive CMOS-MEMS three-axis acceleration sensor realized by a single mass. A low power consumption, low noise, double chopping amplifier circuit is designed on the chip to reduce the noise of the sensor. The sensitivities of the X, Y, and Z axes of the sensor are 520mV/g, 460mV/g, and 320mV/g, respectively. Correspondingly, their noise levels are In 2010, Chih-Ming Sun reported a single-mass three-axis capacitive acceleration sensor. The chip area including the sensing part and the measuring circuit is only 1.78×1.38mm ² , and the measuring range is 0.8～6g. The sensitivities of the X, Y, and Z axes are 0.53mV/, 0.28mV/g, and 0.2mV/g, respectively, and the nonlinearities are 2.64%, 3.15%, and 3.36%, respectively. The cross-sensitivity is between 1% and 8.3%, and the noises of the X, Y, and Z axes are respectively and

When the three-axis piezoresistive acceleration sensor realized by piezoresistor measures the plane acceleration, the action direction is not along the side length of the mass block, but along the diagonal direction of the mass block, so that the mass block is along the two sides of the acceleration direction. One of the vertices rises and the other falls, so the pressure resistance of the elastic beam changes in different directions. The piezoresistive acceleration sensor can also use P-type MOS transistors to measure the strain of the microbeam. In 1999 Hidekuni Takao implemented a monolithically integrated triaxial accelerometer using a CMOS-compatible stress-sensitive differential amplifier. Its CMOS signal processing circuit is made in the center, and the inertial mass for sensing acceleration is located in the periphery. There are four support beams between them, and a P-type MOS transistor is made at the root of the beam to measure the deformation of the beam caused by inertial force. This structure, called a perimeter mass structure, reduces the effects of package stress. The sensitivity of the Z axis is 192mV/g, and the resolution is 0.024g; the sensitivity of the X and Y axes is 23mV/g, and the resolution is 0.23g. In 2001, Hidekuni Takao produced a low-g three-axis accelerometer on a commercial 0.8-micron CMOS process line using bulk micromechanical technology. The P-type MOS transistor on the folded beam was used to detect the magnitude of the acceleration. The device size was 3×3mm ² and 6 ×6mm ² , Z-axis resolution is 2 mg, X-axis and Y-axis resolution are 10.8 mg.

In 2004, Q.Zou et al. of the University of Southern California reported a triaxial piezoelectric bimorph acceleration sensor, which uses a highly symmetrical four-beam bimorph structure to support a mass. The sensitivities of the X, Y and Z axes are 0.9mV/g, 1.13mV/g and 0.88mV/g, respectively. In 2008, Abdul Haseeb Ma reported a three-axis thermal acceleration sensor based on a buckled cantilever beam made of polymer-based surface micromechanical technology. The X, Y and Z-axis sensitivities were 10 μV/g, 14.4 μV/g and 9.8μV/g. A. Chaehoi et al. developed a triaxial acceleration sensor with a mixed working mechanism. The X-axis and Y-axis accelerations are measured by thermal convection, with a sensitivity of 370mV/g and a resolution of 30mg. The measurement of the Z-axis acceleration uses a piezoresistor with a sensitivity of 24mV/g and a resolution of 1g.

In short, the implementation methods of miniature three-axis acceleration sensors can be divided into three categories: [1] Place three single-degree-of-freedom acceleration sensors orthogonally and package them together, which is actually just a combined module of three miniature single-axis acceleration sensors. This method has disadvantages such as poor stability, small application range, and difficult assembly. [2] To realize the acceleration of three axial axes on the same silicon chip, the easiest way is to make three independent sensitive element structures on the same substrate. This method requires a larger chip area. [3] used a sensitive element structure to realize the measurement of the three-axis acceleration.

At present, the detection method of three-axis acceleration is relatively simple, and the three axial accelerations are mostly detected by the same principle. Cross-interference is more serious, generally between 3% and 25%.

Contents of the invention

The object of the present invention is to invent a novel three-axis acceleration sensor to achieve high precision, high resolution, low cross-axis interference, low noise measurement and digital output of the three-axis acceleration.

In order to achieve the above object, the technical solution adopted by the present invention is: the three-axis acceleration sensor is composed of a middle silicon wafer (1), an upper cover plate (2) and a lower base plate (3). The middle silicon wafer (1) is composed of a double-end fixed beam resonator (4), a support beam (5), a quality block (6), a movable electrode (7) and a frame (8). A single mass block (6) is used to sense three axial acceleration signals. The double-end fixed-supported beam resonator (4) is located on the upper surface of the middle silicon wafer (1), and one end of the double-ended fixed-supported beam resonator (4) is fixedly supported on the four sides of the upper surface of the frame (8), and the other end is fixed Support on the four limits of mass block (6). The neutral plane of the support beam (5) and the center of gravity of the mass block (6) are in the same horizontal plane. The beam resonator (4) with fixed supports at both ends detects the X-axis and Y-axis accelerations in the plane of the chip. A movable electrode (7), an upper electrode (9) and a lower electrode (10) for detecting Z-axis acceleration are respectively fabricated on the middle silicon chip (1), the upper cover plate (2) and the lower base plate (3).

The working principle of the resonance-force balance capacitive three-axis acceleration sensor involved in the present invention is that the mass block (6) moves in the X-axis direction under the positive acceleration of the X-axis. One of the double-ended fixed-supported beam resonators (4) in the X-axis direction is subjected to an increase in axial tensile stress or a decrease in axial compressive stress, and the resonance frequency increases; the other double-ended fixed-supported beam resonator (4) in the X-axis direction ) The axial tensile stress decreases or the axial compressive stress increases, and the resonant frequency decreases. The difference between the resonant frequencies of the two double-end fixed beam resonators (4) in the X-axis direction reflects the magnitude and direction of the X-axis acceleration. Similarly, when the mass block (6) moves in the Y-axis direction under the action of the Y-axis acceleration, the axial tensile stress of one of the double-ended fixed beam resonators (4) in the Y-axis direction increases or the axial compressive stress decreases, The resonant frequency increases; the other double-ended fixed beam resonator in the Y-axis direction (4) the axial tensile stress decreases or the axial compressive stress increases, and the resonant frequency decreases. The two double-ended fixed-supported beam resonators in the Y-axis direction (4) The difference in resonance frequency reflects the magnitude and direction of the Y-axis acceleration. The Z-axis acceleration signal perpendicular to the chip plane is detected by the capacitive sensitive principle, and works in the closed-loop force balance mode. When the mass block (6) is subjected to the Z-axis acceleration to cover the plate (2), the capacitance between the mass block (6) and the upper cover plate (2) increases, and the capacitance between the mass block (6) and the lower bottom plate (3) The capacitance between them decreases. The control circuit will generate an electrostatic force opposite to the movement tendency of the mass block (6) to prompt the sensitive mass block (6) to return to the equilibrium position. Therefore, the movement displacement of the mass block (6) in the normal direction of the chip is very small, and the acceleration signal input by the Z axis causes very little cross interference to the acceleration detection of the X axis and the Y axis.

The X-axis acceleration signal of the resonant-force balance capacitive three-axis acceleration sensor involved in the present invention can also only be detected by a double-ended fixed-support beam resonator (4), which can reflect the X-axis acceleration according to its resonant frequency increase or decrease. size and orientation, but with less detection sensitivity. Similarly, the Y-axis acceleration signal can also be detected by only one double-ended fixed beam resonator (4), and the increase or decrease according to its resonant frequency reflects the magnitude and direction of the Y-axis acceleration

The double-end fixed-supported beam resonator (4) of the resonance-force balance capacitive three-axis acceleration sensor involved in the present invention can be either a double-end fixed-supported single-beam resonator, or a double-end fixed-supported double-beam resonator or A three-beam resonator is fixed at both ends. Slots or openings can be made in the beams to improve the quality factor or to achieve electrical isolation. Double-beam resonators fixed at both ends consist of two parallel beams whose ends are merged and fixed to the substrate. When the two tuning fork arms are vibrated in antiphase through a suitable excitation method, the stress and moment generated in their merged area are in opposite directions and cancel each other out, so the energy coupling between the entire structure and the outside world through the fixed end is minimal, and the energy of the vibration system The loss is small and has a high Q value. The width of the middle beam of the beam resonator (4) with double-end fixed support in the three-beam structure is equal to the sum of the widths of the left and right adjacent beams, and the three beams are connected to each other at the ends through the energy isolation area to form a whole. When the third-order vibration mode of the antisymmetric phase of the three-beam resonator is selected as the resonance mode of the beam, the reaction force and moment generated by the middle beam and the two beams on both sides at the fixed end cancel each other due to the opposite vibration direction , The vibration energy is stored inside the resonator, thereby reducing energy loss and improving the Q value.

The double-end solid-supported beam resonator (4) of the resonant-force balance capacitive triaxial acceleration sensor involved in the present invention adopts one of electrothermal excitation, photothermal excitation, inverse piezoelectric excitation, electromagnetic excitation, and electrostatic excitation to make it In the resonant state, the resonant frequency signal output by it is realized by one of piezoresistive detection, electromagnetic detection, piezoelectric detection, optical interference and capacitance detection.

The basic manufacturing process steps of the resonance-force balance capacitive triaxial acceleration sensor involved in the present invention are as follows:

1) Adopting a silicon wafer with low resistivity as the intermediate silicon wafer (1), thermal oxidation or chemical vapor deposition method is used to make an insulating film on the low resistivity silicon wafer;

2) Combining photolithography, corrosion, diffusion, and thin film deposition processes to fabricate the exciter and vibration detection element of the double-end fixed beam resonator (4) on the silicon wafer.

3) On the front side of the middle silicon wafer (1) photolithography double-terminal fixed beam resonator (4) and mass block (6) patterns, anisotropic wet etching or dry etching double-terminal fixed beam resonator (4 ) and the forming groove of the mass block (6).

4) Metal film is deposited by evaporation or sputtering process, and the metal inner lead (13) is produced by combining photolithography and corrosion process.

5) Front protection, back photolithography, etch or etch the insulating film in the back window. Anisotropic wet etching or dry etching releases the double-ended fixed beam resonator (4) and the support beam (5).

6) A silicon wafer with low resistivity is used to make the upper cover plate (2). Wet etching with silicon dioxide and silicon nitride film as a mask or dry etching with photoresist and metal film as a mask to remove the front side of the silicon wafer facing the mass block (6) and the double-terminal fixed beam resonator ( 4) A part of the silicon provides a movement space and a capacitance gap for the tiny movement of the proof mass (6) in the normal direction of the chip under the Z-axis acceleration, and also provides a movement space for the double-end fixed beam resonator (4). A metal thin film is deposited on the back of the silicon wafer by sputtering or evaporation process, and the upper electrode (9) is photolithographically etched, and an alloying process makes the metal thin film and the low-resistance silicon wafer form good ohmic contact.

7) The lower base plate (3) is fabricated by using silicon wafers with low resistivity. Wet etching with silicon dioxide and silicon nitride film as a mask or dry etching with photoresist and metal film as a mask to remove a part of the silicon on the front side of the silicon wafer facing the lower surface of the mass block (6), which is the mass block (6) The slight movement in the normal direction of the chip under the acceleration of the Z axis provides a space for movement and a capacitance gap. A metal thin film is deposited on the back of the silicon wafer by sputtering or evaporation process, and an alloying process makes the metal thin film form a good ohmic contact with the low-resistance silicon wafer to form a lower electrode (10).

8) The fronts of the upper cover (2) and the lower base (3) face the front and back of the middle silicon wafer (1) respectively, bond the three together, and use eutectic bonding technology or conductive adhesive to seal the The connected sensor chip is sealed in a metal casing or a ceramic casing with a metal layer at the bottom of the tube core. Lead wires are welded between the pads on the sensor chip and the packaging tube shell, and the metal layer at the bottom of the tube shell is connected to a terminal on the tube shell to realize the extraction of electrical signals from the lower electrode (10) of the sensor.

The upper cover plate (2) and the lower base plate (3) of the resonance-force balance capacitive triaxial acceleration sensor involved in the present invention can also be made of silicon wafers with higher conductivity, but the upper electrode (9) and the lower electrode (9) need to be The electrode (10) is made on the side facing the mass block (6), and through-hole interconnection technology is required to realize the electrical signal extraction of the upper electrode (9) and the lower electrode (10).

The resonance-force balance capacitive three-axis acceleration sensor involved in the present invention has the following three advantages: [1] The Z-axis acceleration signal adopts the force balance mode of operation, and the mass block (6) is very small in the normal movement displacement of the chip, and the Z-axis The input acceleration signal introduces minimal cross-interference to the X-axis and Y-axis acceleration detection. Similarly, the mass block (6) feels the X-axis and Y-axis acceleration signals and the displacement within the chip plane will not bring cross-sensitivity to the detection of the Z-axis acceleration signals. [2] The X-axis and Y-axis acceleration signals are measured by a double-ended fixed beam resonator (4) that is highly sensitive to axial stress. The measured acceleration is directly converted into a frequency signal with high stability and reliability. Distortion errors are not easy to occur during the transmission process, and it can be interfaced with the digital system without an A/D converter. The measurement accuracy is extremely high, and it can meet the high performance requirements of the acceleration sensor. [3] The Z-axis acceleration signal adopts the closed-loop force balance working mode, which has the advantages of good linearity, large dynamic range, and low noise.

Description of drawings

Fig. 1 is a structural schematic diagram of the middle silicon chip (1) of the resonance-force balance capacitive triaxial acceleration sensor involved in the present invention.

Fig. 2 is the structural representation of the embodiment of the resonant-force balance capacitive three-axis acceleration sensor involved in the present invention, and this embodiment utilizes the double-end solid-supported beam resonator (4) detection of polysilicon resistance electrothermal excitation and piezoresistive detection X-axis and Y-axis acceleration signals.

Fig. 3 is a flow chart of the manufacturing process of the resonance-force balance capacitive triaxial acceleration sensor as an embodiment of the present invention.

In the attached picture:

1- middle silicon wafer 2- upper cover plate 3- lower bottom plate

4-Double-end fixed support beam resonator 5-Support beam 6-Mass block

7-movable electrode 8-frame 9-upper electrode

10-lower electrode 11-excitation resistor 12-varistor

13-Inner lead 14-Silicon dioxide film 15-Polysilicon film

16-Silicon dioxide grown from polysilicon 17-Ion implantation window 18-Silicon nitride film

19-Sealing ring

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but is not limited to the embodiments.

Example:

The technical scheme of the invention is used to manufacture a resonance-force balance capacitive triaxial acceleration sensor. Wherein, the X-axis and Y-axis acceleration signals are detected by a miniature double-end solid-supported beam resonator (4) that is electrothermally excited by polysilicon resistance and piezoresistively detected. Its production process is as follows:

1) An N-type silicon wafer with a (100) plane and a resistivity of 0.1Ω.cm is used as the intermediate silicon wafer (1). (See Attachment 3[1])

2) Thermal oxidation to produce a silicon dioxide film (14) with a thickness of 1 micron. (See attached drawing 3[2])

3) Depositing a polysilicon film (15) with a thickness of 1 micron by low-pressure chemical vapor deposition. (See attached drawing 3[3])

4) thermal oxidation, part of the polysilicon film (15) is oxidized to silicon dioxide (16), photolithography and etching processes are combined to make the ion implantation window (17) of the excitation resistor (11) and the piezoresistor (12). (see attached drawing 3[4])

5) Ion-implanting boron to make a polysilicon excitation resistor (11) and a piezoresistor (12). Anneal at 950°C for 30 minutes in an oxygen atmosphere to activate doped boron ions. (see attached drawing 3[5])

6) The front photoresist is protected, and the silicon dioxide (16) on the back is corroded by a slow-release hydrofluoric acid solution to remove the glue. The anisotropic solution etches the polysilicon film (15) on the back. (see attached drawing 3[6])

7) Depositing a silicon nitride film (18) with a thickness of 250 nm by low-pressure chemical vapor deposition. On the front side of the middle silicon wafer (1) photolithographically etches the double-terminal fixed-support beam resonator (4) and the mass block (6), and anisotropic wet etching or dry etching of the double-terminal fixed-support beam resonator (4) and The molding groove of mass block (6); (see accompanying drawing 3 [7])

8) Photoetching the contact hole, dry etching the silicon nitride film and the silicon dioxide film in the contact hole. The metal inner lead (13) is fabricated by combining photolithography and thin film deposition process. (See attached drawing 3[8])

9) The pattern of the sealing ring (19) is photolithographically etched on the front side, Schott 8329 glass is deposited by electron beam evaporation technology, and the sealing ring (19) is manufactured by a stripping process. (see attached drawing 3[9])

10) Front protection, back photolithography, dry etching of the silicon nitride film (18) and silicon dioxide film (14) on the back, and stripping. A double-end fixed-support beam resonator (4) and a support beam (5) are formed by combining etching with a mask and etching without a mask. (See attached drawing 3[10])

11) Use another N-type silicon wafer with a (100) plane and a resistivity of 0.1Ω.cm to make the top cover (2). Growth of silicon dioxide thin films by thermal oxidation. Use the silicon dioxide film as a mask to wet etch and remove a part of the silicon on the front side of the silicon wafer facing the mass block (6) and the double-end fixed beam resonator (4), so that the mass block (6) is subjected to Z-axis acceleration in the chip method The small movement of the direction provides the activity space and the capacitance gap, and also provides the movement space for the double-end fixed support beam resonator (4). The slow-release hydrofluoric acid solution etches the silicon dioxide film. A metal thin film is deposited on the back of the silicon wafer by sputtering or evaporation process, and the upper electrode (9) is photolithographically etched, and an alloying process makes the metal thin film and the low-resistance silicon wafer form good ohmic contact. (See attached drawing 3[11])

12) Use another N-type silicon wafer with a (100) surface and a resistivity of 0.1Ω.cm to make the lower base plate (3). Growth of silicon dioxide thin films by thermal oxidation. Using the silicon dioxide film as a mask to wet etch and remove a part of the silicon on the front of the silicon wafer facing the mass block (6), to provide an active space and a capacitance gap for the micro movement of the mass block (6) subjected to Z-axis acceleration in the normal direction of the chip. Slow-release hydrofluoric acid etches the silica film. A metal thin film is deposited on the back of the silicon wafer by sputtering or evaporation process, and an alloying process makes the metal thin film form a good ohmic contact with the low-resistance silicon wafer to form a lower electrode (10). (See attached drawing 3[12])

13) The fronts of the upper cover (2) and the lower base (3) face the front and back of the middle silicon wafer (1) respectively, bond the three together, and use eutectic bonding technology or conductive adhesive to seal the The connected sensor chip is sealed in a metal casing or a ceramic casing with a metal layer at the bottom of the tube core. Lead wires are welded between the pads on the sensor chip and the packaging tube shell, and the metal layer at the bottom of the tube shell is connected to a terminal on the tube shell to realize the extraction of electrical signals from the lower electrode (10) of the sensor. Solder the outer leads. (See Figure 3 [13])

Claims (6)

1. A resonant-force balance capacitive triaxial acceleration sensor is characterized in that: the described triaxial acceleration sensor is made up of middle silicon chip (1), upper cover plate (2) and lower base plate (3), middle silicon The sheet (1) consists of a double-end fixed beam resonator (4), a support beam (5), a mass (6), a movable electrode (7) and a frame (8); the double-end fixed beam resonator (4 ) is located on the upper surface of the middle silicon wafer (1), and one end of the double-ended fixed-supported beam resonator (4) is fixedly supported on the upper surface of the frame (8), and the other end is fixedly supported on the four sides of the mass block (6); the supporting beam The neutral plane of (5) and the center of gravity of mass block (6) are in the same horizontal plane; four double-ended fixed beam resonators (4) detect the X-axis and Y-axis accelerations in the plane of the sensor chip; in the middle silicon chip (1 ), the upper pole plate (2) and the lower base plate (3) respectively make a movable electrode (7), an upper pole plate (9) and a lower electrode (10) for detecting Z-axis acceleration. 2. The resonance-force balance capacitive triaxial acceleration sensor according to claim 1, characterized in that: under the positive acceleration of the X axis, the mass block (6) moves in the X axis direction, and the two ends of the X axis direction When the axial tensile stress on one of the fixed-supported beam resonators (4) increases or the axial compressive stress decreases, the resonant frequency increases, and the axial tensile stress of the other double-ended fixed-supported beam resonator (4) in the X-axis direction decreases. When the small or axial compressive stress increases, the resonant frequency decreases, and the difference between the resonant frequencies of the two double-ended fixed beam resonators (4) in the X-axis direction reflects the magnitude and direction of the X-axis acceleration; under the action of the Y-axis acceleration, the The mass block (6) moves in the Y-axis direction, the axial tensile stress of one of the double-end fixed beam resonators (4) in the Y-axis direction increases or the axial compressive stress decreases, and the resonant frequency increases, and the other one in the Y-axis direction A double-ended fixed beam resonator (4) decreases the axial tensile stress or increases the axial compressive stress, and the resonant frequency decreases, and the difference in the resonant frequency of the two double-ended fixed beam resonators (4) in the Y-axis direction reflects The magnitude and direction of the Y-axis acceleration; the Z-axis acceleration signal perpendicular to the plane of the sensor chip is detected by the capacitive sensitive principle, and works in the closed-loop force balance mode. ), the capacitance between the mass block (6) and the upper cover plate (2) increases, the capacitance between the mass block (6) and the lower bottom plate (3) decreases, and the control circuit will generate a ) electrostatic force in the opposite direction of motion, prompting the sensitive mass (6) to return to the equilibrium position. 3. resonance-force balance capacitive three-axis acceleration sensor according to claim 1, is characterized in that: the X-axis acceleration signal of described three-axis acceleration sensor also can only use a double-ended fixed beam resonator (4 ) detection, according to the increase or decrease of its resonant frequency to reflect the size and direction of the X-axis acceleration; the Y-axis acceleration signal can also only be detected by a double-ended fixed beam resonator (4), and the increase or decrease according to its resonant frequency reflects The magnitude and direction of the Y-axis acceleration. 4. The resonant-force balance capacitive triaxial acceleration sensor according to claim 1, characterized in that: the double-end fixed beam resonator (4) of the triaxial acceleration sensor adopts electrothermal excitation, photothermal excitation, One of inverse piezoelectric excitation, electromagnetic excitation, and electrostatic excitation is used to make it in a resonant state, and the resonant frequency signal it outputs is realized by one of piezoresistive detection, electromagnetic detection, piezoelectric detection, optical interference, and capacitance detection. 5. The resonance-force balance capacitive three-axis acceleration sensor according to claim 1, wherein the basic manufacturing process steps of the three-axis acceleration sensor are as follows: 1) Adopting a silicon wafer with low resistivity as the intermediate silicon wafer (1), thermal oxidation or chemical vapor deposition method is used to make an insulating film on the low resistivity silicon wafer; 2) Combining photolithography, corrosion, diffusion, and thin film deposition processes to fabricate the exciter and vibration detection element of the double-end fixed beam resonator (4) on the silicon wafer; 3) On the front side of the middle silicon wafer (1) photolithography double-terminal fixed beam resonator (4) and mass block (6) patterns, anisotropic wet etching or dry etching double-terminal fixed beam resonator (4 ) and the forming groove of the mass block (6); 4) Deposit metal thin film by evaporation or sputtering process, and combine photolithography and corrosion process to make metal inner lead (13); 5) Front protection, back photolithography, etching or etching the insulating film in the back window, anisotropic wet etching or dry etching to release the double-terminal fixed beam resonator (4) and the support beam (5); 6) Use silicon wafers with low resistivity to make the upper cover plate (2), use silicon dioxide and silicon nitride films as masks for wet etching or use photoresist and metal films as masks for dry etching to remove silicon wafers The front side faces the mass block (6) and a part of the silicon of the double-ended fixed beam resonator (4), which provides a movable space and a capacitive gap for the mass block (6) to be subjected to Z-axis acceleration in the chip normal direction, and also provides a space for the dual The end-fixed beam resonator (4) provides a space for movement; sputtering or evaporation process deposits a metal film on the back of the silicon wafer; the photolithographic upper electrode (9), and the alloying process makes the metal film and the low-resistance silicon wafer form a good ohmic touch; 7) Use silicon wafers with low resistivity to make the bottom plate (3), use silicon dioxide and silicon nitride films as masks for wet etching or use photoresist and metal films as masks for dry etching to remove the front side of the silicon wafers A part of the silicon facing the lower surface of the proof mass (6) provides an active space and a capacitance gap for the micro motion of the proof mass (6) subjected to Z-axis acceleration in the normal direction of the chip; sputtering or evaporation process deposits a metal film on the back of the silicon wafer , the alloying process enables the metal thin film to form a good ohmic contact with the low-resistance silicon wafer to form the lower electrode (10); 8) The fronts of the upper cover (2) and the lower base (3) face the front and back of the middle silicon wafer (1) respectively, bond the three together, and use eutectic bonding technology or conductive adhesive to seal the The connected sensor chip is sealed in a metal shell or a ceramic shell with a metal layer at the bottom of the tube core; solder the lead between the pad on the sensor chip and the package shell, and connect the metal layer at the bottom of the shell to the tube A binding post on the shell is connected to realize the extraction of electrical signals from the lower electrode (10) of the sensor. 6. The resonance-force balance capacitive three-axis acceleration sensor according to claim 1, characterized in that: the upper cover plate (2) and the lower base plate (3) of the three-axis acceleration sensor can also adopt relatively high conductivity Large silicon wafers are made, but it is necessary to make the upper electrode (9) and the lower electrode (10) on the side facing the proof mass (6), and through-hole interconnection technology is required to realize the upper electrode (9) and the lower electrode (10) ) Leading out of electrical signals.

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