Low-coupling biaxial silicon micro-resonant accelerometer

Abstract

The invention discloses a low-coupling biaxial silicon micro-resonant accelerometer. The low-coupling biaxial silicon micro-resonant accelerometer comprises an upper-layer micro-accelerometer structure and a lower-layer glass substrate with a signal lead, the micro-accelerometer structure is composed of two separated mass blocks, two pairs of identical tuning fork resonators and eight identical primary amplification levers. The two separated mass blocks are fixed on the same group of anchor points through U-shaped beams in different directions and are respectively used for measuring the acceleration of X / Y axes, and the whole structure is in a symmetrical figure. The four tuning fork resonators are distributed in a central symmetry mode and used for detecting the acceleration of the X axis and the acceleration of the Y axis. The X-axis and the Y-axis adopt the separated mass blocks, the sensitive mass blocks of the X-axis and the Y-axis are not connected, complete decoupling of the two detection axes is achieved, the lever structure can effectively amplify inertia force generated by the mass blocks, the sensitivity of the accelerometer is improved, and high-precision double-axis acceleration measurement is easy to achieve.

Description

Technical Field

[0001] The invention belongs to the micro-inertial sensor technology in a micro-electromechanical system (MEMS), and in particular relates to a low-coupling dual-axis resonant accelerometer. Background Art

[0002] Although traditional inertial sensors have the advantages of high precision and high performance, their large size severely limits their application. Micro-inertial devices such as silicon MEMS accelerometers and silicon MEMS gyroscopes are made using micro-machining and integrated circuit processes. The device size can be controlled within a few hundred microns or even a few microns. Therefore, they have the advantages of small size, light weight, low power consumption, high integration, and easy mass production. They can replace traditional inertial sensors in some applications with excellent performance. In recent years, with the continuous improvement of MEMS design technology, processing level and packaging technology, the performance of micro-inertial sensors has been continuously improved, and micro-accelerometers have been widely used in communications, consumer electronics, industry and agriculture, aerospace, national defense and military industries. Micro-mechanical accelerometers can be divided into capacitive, piezoresistive, piezoelectric and resonant types according to their working principles. Resonant accelerometers have become a hot topic of research due to their unique performance.

[0003] The silicon micro-resonant accelerometer measures acceleration by measuring the change of resonant frequency and directly outputs digital signals. It has high sensitivity and resolution. It also has the advantages of wide dynamic range, strong anti-interference ability and good stability. It is an accelerometer with good development prospects and high performance potential.

[0004] In recent years, the technology of micro-electromechanical systems has developed rapidly, and the performance of resonant accelerometers has also improved rapidly. For example, in the MEMS-ASIC silicon micro-resonant accelerometer developed by the National University of Singapore, a resolution of 20μg / Hz and a zero bias instability of 4μg have been achieved. With the improvement of the performance of micro-mechanical accelerometers, their applications will penetrate into medium and high-precision inertial navigation systems, aircraft control, tactical and strategic weapon guidance, gravity measurement and other application fields. Therefore, the research on silicon micro-resonant accelerometer technology has great practical significance and broad application prospects. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a dual-axis silicon micro-accelerometer structure with low cross-coupling, high sensitivity, simple structure and small size.

[0006] The technical solution for realizing the present invention is: a dual-axis silicon micro-resonant accelerometer, which is characterized in that: it is composed of an upper and lower layer, the upper layer is a dual-axis accelerometer structure made on a single crystal silicon wafer, and the lower layer is a glass substrate with signal leads, the micro-accelerometer structure is bonded to the glass substrate, and the signal leads on the glass substrate are connected to the electrodes on the micro-accelerometer structure; wherein the accelerometer structure includes two separated mass blocks, four resonators, eight primary amplifying levers, and eight U-shaped beams, the mass block transmits the inertial force to the tuning fork resonator through the amplifying lever to change the frequency of the tuning fork resonator; fixed detection electrodes and driving electrodes are symmetrically arranged on both sides of the tuning fork resonator to realize electrostatic drive and capacitance detection.

[0007] The separation mass block is fixed on the same set of anchor points through two sets of U-shaped beams, eliminating the displacement restriction of the mass block on the orthogonal axis and achieving low cross-axis coupling and high sensitivity.

[0008] The four resonators are centrally symmetrically distributed and have exactly the same size, achieving dual-axis resonant frequency differential output, offsetting common-mode interference such as temperature changes, increasing the anti-interference ability of the dual-axis silicon micro-resonance accelerometer, and achieving high-sensitivity output. Each tuning fork resonator consists of two resonant beams and external movable comb teeth, with driving electrodes and detection electrodes distributed on both sides of the movable comb teeth. The movable comb teeth are inserted into the fixed comb teeth of the driving electrode and the detection electrode to form a driving capacitor and a detection capacitor.

[0009] Compared with the prior art, the present invention has the following significant advantages: (1) the present invention adopts two separate mass blocks, the movements of the two mass blocks do not interfere with each other, and the movement decoupling in two directions is realized, thereby reducing the influence of cross-axis coupling; (2) four tuning fork resonators are centrally distributed, and are connected to the separate mass blocks in pairs, for detecting the acceleration of the X / Y axis. The structural parameters of the tuning fork resonators are exactly the same. Two tuning fork resonators along the same axis are a group. When there is acceleration input, the resonant frequency of one tuning fork resonator increases, and the resonant frequency of the other tuning fork decreases. The magnitude of the acceleration can be obtained by detecting the differential output of the resonant frequencies of the two tuning fork resonators. This method is convenient for eliminating the common mode influence and improving the sensitivity; (3) The two separated mass blocks are fixed on the same set of anchor points by a U-shaped beam, which can not only effectively release the thermal stress generated during processing, but also suppress the movement of the orthogonal axes, thereby reducing the nonlinearity of the movement; (4) The movable comb teeth of the tuning fork resonator are externally mounted on the resonant beam, which reduces the distance between the two resonant beams, thereby widening the frequency of the resonator's working mode and the interference mode, and improving the working stability of the tuning fork resonator; (5) The tuning fork resonator uses electrostatic drive and capacitive detection to detect acceleration. Fixed driving electrodes and detection electrodes are distributed on both sides of each movable comb tooth. The movable comb teeth are inserted into the fixed comb teeth of the driving electrode and the detection electrode to form a driving capacitor and a detection capacitor, which can achieve higher driving strength and detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is an isometric three-dimensional stereoscopic view of the low-coupling dual-axis resonant accelerometer of the present invention.

[0011] Figure 2 It is a schematic diagram of the structural layers of the low-coupling dual-axis resonant accelerometer of the present invention.

[0012] Figure 3 It is a schematic diagram of a resonator of a low-coupling dual-axis resonant accelerometer of the present invention.

[0013] In the figure, A-accelerometer structure layer made of single crystal silicon, B-glass substrate layer with signal leads; 1-first mass block, 2-second mass block, 3a-first tuning fork resonator, 3b-second tuning fork resonator, 3c-third tuning fork resonator, 3d-fourth tuning fork resonator, 4a-first first-stage amplifying lever, 4b-second first-stage amplifying lever, 4c-third first-stage amplifying lever, 4d-fourth first-stage amplifying lever, 4e-fifth first-stage amplifying lever, 4f-sixth first-stage amplifying lever, 4g-seventh first-stage amplifying lever, 4h-eighth first-stage amplifying lever; 5a-first U-shaped beam, 5b-second U-shaped beam, 5c-third U-shaped beam, 5d-fourth U-shaped Beam, 5e-fifth U-shaped beam, 5f-sixth U-shaped beam, 5g-seventh U-shaped beam, 5h-eighth U-shaped beam; 6a-first anchor point, 6b-second anchor point, 6c-third anchor point, 6d-fourth anchor point; 7a-first resonant beam of tuning fork resonator 3a, 7b-second resonant beam of tuning fork resonator 3a; 8a-first fixed drive comb teeth of tuning fork resonator 3a, 8b-second fixed drive comb teeth of tuning fork resonator 3a, 8c-third fixed drive comb teeth of tuning fork resonator 3a, 8d-fourth fixed drive comb teeth of tuning fork resonator 3a; 9a-first fixed detection comb teeth of tuning fork resonator 3a, 9b-second fixed detection comb teeth of tuning fork resonator 3a. DETAILED DESCRIPTION

[0014] The present invention will be further described below in conjunction with the embodiments and the accompanying drawings.

[0015] like Figure 1 and Figure 2As shown, the low-coupling dual-axis resonant accelerometer of the present invention is used to detect the acceleration input on the same horizontal plane, and is composed of an upper and a lower layer, wherein the upper layer is an accelerometer structure A made on a single crystal silicon wafer, and the lower layer is a glass substrate B with a signal lead. The mechanical structure of the accelerometer includes: a first mass block 1, a second mass block 2; a first tuning fork resonator 3a, a second tuning fork resonator 3b, a third tuning fork resonator 3c, and a fourth tuning fork resonator 3d; a first first-stage amplifying lever 4a, a second first-stage amplifying lever 4b, a third first-stage amplifying lever 4c, a fourth first-stage amplifying lever 4d, a fifth first-stage amplifying lever 4e, a sixth first-stage amplifying lever 4f, a seventh first-stage amplifying lever 4g, and an eighth first-stage amplifying lever 4h; a first U-shaped beam 5a, a second U-shaped beam 5b, a third U-shaped beam 5c, a fourth U-shaped beam 5d, a fifth U-shaped beam 5e, a sixth U-shaped beam 5f, a seventh U-shaped beam 5g, and an eighth U-shaped beam 5h. The first mass block 1 is distributed inside the anchor point of the accelerometer structure, and is roughly rectangular in shape. The second mass block 2 is distributed outside the anchor point, and is square in shape. The first tuning fork resonator 3a and the third tuning fork resonator 3c are distributed on the upper and lower sides of the first mass block 1 along the Y axis, and are used to measure the acceleration of the Y axis. The second tuning fork resonator 3b and the fourth tuning fork resonator 3d are distributed on the left and right sides of the second mass block 2 along the X axis, and are used to measure the acceleration of the X axis. The first mass block 1 amplifies the inertial force of the Y axis through the first first-stage amplifying lever 4a, the second first-stage amplifying lever 4b, the fifth first-stage amplifying lever 4e, and the sixth first-stage amplifying lever 4f, and then inputs it into the first tuning fork resonator 3a and the third tuning fork resonator 3c, so as to realize the differential detection of the acceleration in the Y axis direction. The second mass block 2 amplifies the inertial force of the X axis through the third first-stage amplifying lever 4c, the fourth first-stage amplifying lever 4d, the seventh first-stage amplifying lever 4g, and the eighth first-stage amplifying lever 4h, and then inputs it into the second tuning fork resonator 3b and the fourth tuning fork resonator 3d, so as to realize the differential detection of the acceleration in the X axis direction. The first mass block 1 is fixed on the first anchor point 6a, the second anchor point 6b, the third anchor point 6c and the fourth anchor point 6d through the second U-shaped beam 5b, the fourth U-shaped beam 5d, the sixth U-shaped beam 5f and the eighth U-shaped beam 5h, and the second mass block 2 is fixed on the same set of anchor points through the first U-shaped beam 5a, the third U-shaped beam 5c, the fifth U-shaped beam 5e and the seventh U-shaped beam 5g. The U-shaped beams enable the mass block to move only in the sensitive direction to achieve the decoupling function. The first anchor point 6a, the second anchor point 6b, the third anchor point 6c and the fourth anchor point 6d are bonded to the bonding point of the glass substrate, so that the accelerometer structure is suspended above the lower glass substrate.

[0016] The first mass block 1 is fixed on the anchor point through the second U-shaped beam 5b, the fourth U-shaped beam 5d, the sixth U-shaped beam 5f, and the eighth U-shaped beam 5h. The four U-shaped beams have a smaller stiffness in the Y axis and a larger stiffness in the X axis. The second mass block 2 is fixed on the same set of anchor points through the first U-shaped beam 5a, the third U-shaped beam 5c, the fifth U-shaped beam 5e, and the seventh U-shaped beam 5g. The four U-shaped beams have a smaller stiffness in the X axis and a larger stiffness in the Y axis. The first mass block 1 and the second mass block 2 do not interfere with each other. They are fixed on the same set of anchor points through two sets of U-shaped beams in different directions, so that the movement of the mass block on the sensitive axis is not restricted by the U-shaped beams of the orthogonal axis, which greatly improves the sensitivity of the accelerometer and weakens the coupling of the orthogonal axes.

[0017] The first tuning fork resonator 3a, the second tuning fork resonator 3b, the third tuning fork resonator 3c, and the fourth tuning fork resonator 3d have the same size and composition. The first resonator 3a is used as an example for explanation. The structure of the first resonator 3a is as follows: Figure 3 As shown, the tuning fork resonator is composed of a first resonant beam 7a and a second resonant beam 7b with external movable comb teeth. In addition, the first resonant beam 7a has fixed first drive comb teeth 8a, second drive comb teeth 8b and first detection comb teeth 9a on both sides of the external movable comb teeth; the second resonant beam 7b has fixed third drive comb teeth 8c, fourth drive comb teeth 8d and second detection comb teeth 9b on both sides of the external movable comb teeth. The drive comb teeth and the detection comb teeth are fixed on the glass substrate, and the movable comb teeth are inserted into the fixed drive comb teeth and the detection comb teeth to form a drive capacitor and a detection capacitor. An AC voltage with a DC bias is applied to the fixed drive comb teeth, and an electrostatic drive and a capacitance detection working mode are adopted to achieve a higher drive strength and detection accuracy.

[0018] Working principle of the invention: The working principle of the dual-axis resonant accelerometer of the invention is based on a resonant system, which detects acceleration by measuring the change in the vibration frequency of a tuning fork resonator. This accelerometer contains two mutually orthogonal sensitive axes and can measure the acceleration of the X / Y axis simultaneously. When there is acceleration input on the Y-axis, the first mass block 1 is subjected to the inertial force, the second U-shaped beam 5b, the fourth U-shaped beam 5d, the sixth U-shaped beam 5f, and the eighth U-shaped beam 5h are deformed, and the first mass block 1 is displaced in the Y-axis direction. The inertial force is amplified by 4a-the first-stage amplifying lever, 4b-the second-stage amplifying lever, 4e-the fifth-stage amplifying lever, and 4f-the sixth-stage amplifying lever, and then input into the first tuning fork resonator 3a and the third tuning fork resonator 3c respectively. One of the resonant beams in the resonator is subjected to tension and the other is subjected to pressure. The resonant frequency of the resonator subjected to tension increases, and the resonant frequency of the resonator subjected to pressure decreases. The resonant beam is driven by the fixed driving electrodes distributed on both sides of the resonant beam, and the vibration is picked up by the fixed detection electrodes distributed on both sides of the resonant beam. Finally, the difference between the frequency outputs of the two resonators is output, and the measured acceleration is calculated by the output resonant frequency.

[0019] When there is acceleration input on the X-axis, the second mass block 2 is subjected to the inertial force, the first U-shaped beam 5a, the third U-shaped beam 5c, the fifth U-shaped beam 5e, and the seventh U-shaped beam 5g are deformed, and the second mass block 2 is displaced in the X-axis direction. The inertial force is amplified by 4c-the third first-stage amplifying lever, 4d-the fourth first-stage amplifying lever, 4g-the seventh first-stage amplifying lever, and 4h-the eighth first-stage amplifying lever, and then input into the second tuning fork resonator 3b and the fourth tuning fork resonator 3d respectively. One of the resonant beams in the resonator is subjected to tension and the other is subjected to pressure. The resonant frequency of the resonator subjected to tension increases, and the resonant frequency of the resonator subjected to pressure decreases. The resonant beam is driven by the fixed driving electrodes distributed on both sides of the resonant beam, and the vibration is picked up by the fixed detection electrodes distributed on both sides of the resonant beam. Finally, the difference between the frequency outputs of the two resonators is output, and the measured acceleration is calculated by the output resonant frequency.

[0020] In summary, the present invention proposes a novel dual-axis silicon micro-resonant accelerometer with low orthogonal axis coupling. The dual-axis resonant accelerometer adopts four resonators, which are centrally symmetrically distributed to detect the acceleration of the X-axis and the Y-axis. Separated mass blocks are used, and the sensitive mass blocks of the X / Y axes are not connected to each other, which can effectively reduce the cross-axis sensitivity and improve the sensitivity of the accelerometer, and it is easy to achieve high-precision dual-axis acceleration measurement.

[0021] In addition, those skilled in the art may also make other changes within the spirit of the present invention. Of course, these changes made according to the spirit of the present invention should be included in the scope of protection required by the present invention.

Claims

1. A dual-axis silicon micro-resonance accelerometer, comprising an upper micro-accelerometer structure and a lower glass substrate with signal leads, characterized in that: It includes a glass substrate, two separate mass blocks, eight U-shaped beams, four resonators, eight first-stage amplification levers, drive electrodes, and detection electrodes. The entire structure is a symmetric figure, and the accelerations of the X and Y axes are measured through the two separate mass blocks. The mass block for measuring the X-axis acceleration is in a "return" shape and is distributed outside the anchor points. The mass block for measuring the Y-axis acceleration is roughly rectangular and is distributed inside the anchor points. The two different mass blocks are fixed to the same set of anchor points through two groups of U-shaped beams. The mass blocks transfer the amplified inertial force to one end of the tuning fork resonator through the first-stage amplification levers. Drive electrodes and detection electrodes are respectively arranged on both sides of the tuning fork resonator.

2. The dual-axis silicon micro-resonance accelerometer according to claim 1, characterized in that: The X-axis does not share the same mass block but is fixed to the same set of anchor points through U-shaped beams in different directions, reducing the overall area of the biaxial resonant accelerometer while achieving low cross-axis sensitivity.

3. The dual-axis silicon micro-resonance accelerometer according to claim 1, characterized in that: The eight first-stage amplification levers are centrally distributed. The two ends of the levers are respectively connected to the mass blocks and the resonators, and the inertial force generated by the mass blocks is amplified and then acts on the tuning fork resonator.

4. The dual-axis silicon micro-resonance accelerometer according to claim 1, characterized in that: The U-shaped beams fixing the mass blocks have a small stiffness in the sensitive axis and a large stiffness in the orthogonal axis, effectively restricting the movement of the mass blocks in the orthogonal axis and greatly reducing the coupling.

5. The dual-axis silicon micro-resonance accelerometer according to claim 1, characterized in that: The four tuning fork resonators have exactly the same size and are centrally symmetrically distributed. Each tuning fork resonator consists of two resonant beams, two fixed drive electrodes, four fixed detection electrodes, and movable comb teeth. The movable comb teeth are hung outside the resonant beams, reducing the distance between the two resonant beams, separating the interference mode and the working mode of the resonator, and improving the stability of the resonator.

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