阅读说明：本技术 一种低应力敏感度硅微谐振式加速度计结构 (Low stress sensitivity silicon micro-resonant accelerometer structure ) 是由 赵前程 宋紫阳 崔健 闫桂珍 于 2019-04-10 设计创作，主要内容包括：本发明公开了一种低应力敏感度硅微谐振式加速度计结构,主要包括质量块、杠杆放大结构、双端固支音叉谐振器(DETF)、低应力框架、支撑梁和外框架,且各结构对称分布。加速度计结构分为两层,其中上层制作了加速度计的机械结构,下层的硅衬底在键合后可为上层结构提供支撑,中间连接有金属电极,用于导出电信号。本发明通过布置对称分布于谐振器上下两侧的固定锚点,降低工作温度变化对谐振器所产生的热应力,从而减少了温度漂移对器件性能的影响问题,由此提高了谐振式加速度计的温度稳定性。(The invention discloses a low stress sensitivity silicon micro-resonant accelerometer structure which mainly comprises a mass block, a lever amplification structure, a double-end fixed support tuning fork resonator (DETF), a low stress frame, a support beam and an outer frame, wherein the structures are symmetrically distributed. The accelerometer structure is divided into two layers, wherein the upper layer is provided with a mechanical structure of the accelerometer, the lower silicon substrate can provide support for the upper layer after bonding, and the middle part is connected with a metal electrode for leading out an electric signal. The fixed anchor points symmetrically distributed on the upper side and the lower side of the resonator are arranged, so that the thermal stress generated by the working temperature change on the resonator is reduced, the problem of influence of temperature drift on the performance of a device is reduced, and the temperature stability of the resonant accelerometer is improved.)

1. A low stress sensitivity silicon micro resonance accelerometer is composed of an upper layer and a lower layer, wherein the upper layer is a mechanical structure of the accelerometer manufactured on a monocrystalline silicon piece, and the lower layer is a metal electrode manufactured on a glass substrate, and is characterized in that: the upper-layer mechanical structure comprises a mass block (1), double-clamped tuning fork resonators (2a and 2b), micro-lever amplification mechanisms (3a, 3b, 3c and 3d), a low-stress frame (4), support structures (5a, 5b, 5c and 5d) and an outer frame (6), the mass block (1) comprises the micro-lever amplification mechanisms (3a, 3b, 3c and 3d), the resonators (2a and 2b), the low-stress frame (4) and low-stress anchor points (7a and 7b) inside, and the mass block (1) comprises the support structures (5a, 5b, 5c and 5d) and the outer frame (6) outside.

2. Mass piece (1) is the structure that occupies chip area the most, its characterized in that: the mass block (1) is directly connected with the support beams (5a, 5b, 5c, 5d) and the input ends (9a, 9b, 9c, 9d) of the micro-lever amplification mechanisms, the support structures (5a, 5b, 5c, 5d) are positioned outside the mass block (1) and inside the outer frame (6) with fixed anchor points and are connected with the support beams and the input ends, the outer frame (6) plays a role of supporting the internal mechanical structure, the support structures (5a, 5b, 5c, 5d) play a role of buffering the inertial force from the outside, and in addition, inside the mass block (1), four centrosymmetric micro-lever amplification mechanisms (3a, 3b, 3c, 3d) which are respectively positioned at the upper left part, the lower left part, the upper right part and the lower right part of the structure are connected with the external mass block (1) through the input beams (9a, 9b, 9c, 9d) and are connected through the output beams (10a, 10b, 10c, 10d) are connected to the resonators (2a, 2b) for transmitting and amplifying inertial forces from the direction of the sensitive axis x.

3. The low stress frame structure (4) is also located inside the mass block, and is characterized in that: the low stress frame structure (4) is in a middle shape, is positioned at the structural center of the accelerometer and has centrosymmetric geometric properties, in addition, in order to ensure the structural stability of the low stress frame (4), each edge of the low stress frame (4) needs to have larger width so as to ensure that the whole low stress frame (4) has larger rigidity and cannot easily generate structural deformation under the action of external force, the left side and the right side of the low stress frame (4) are provided with micro-lever amplification mechanisms (3a, 3b, 3c and 3d), and the fulcrum beams (8a, 8b, 8c and 8d) of the lever structure are connected with the frame structure so as to fix the four fulcrum beams of the lever structure.

4. The upper and lower two low-stress anchor points (7a, 7b) which are positioned on the structure central line and are distributed in central symmetry are also positioned inside the mass block (1), and the mass block is characterized in that: the low stress anchor points (7a, 7b) are respectively connected with the upper end point and the lower end point of the middle-shaped low stress frame structure (4) and are used for fixing the low stress frame (4), so that the whole mechanical structure is fixed on the glass substrate through the anchor points, and the upper mechanical mechanism part is suspended above the lower glass substrate, in addition, the low stress anchor points (7a, 7b) are symmetrically distributed on the low stress frame (4), the rigidity of the low stress frame (4) is higher, when the two low stress anchor points (7a, 7b) have thermal expansion due to temperature change, the low stress frame (4) is only acted by the thermal stress in the Y-axis direction, the thermal stress in the X-axis direction is smaller, and the influence of the thermal stress transmitted to the resonator is minimized.

5. Double-ended clamped tuning fork resonators (2a, 2b), characterized in that: the resonators (2a, 2b) are positioned in the low-stress frame structure (4) and connected with the low-stress frame structure into a whole, the structural parameters of the pair of double-ended fixed-support tuning fork resonators (2a, 2b) are completely identical and are symmetrically distributed on the left side and the right side in the low-stress frame structure (4), and the frequencies of the resonators are driven and detected in a film pressing or sliding mode of a comb capacitor.

The technical field is as follows:

the invention belongs to the technical field of micro-electro-mechanical systems, and relates to a stress-free silicon micro-resonance type accelerometer structure, which applies micro-inertia sensor technology and is widely applied to the fields of automobile industry, aerospace, earthquake monitoring, consumer electronics and the like as a micro-inertia device.

Background art:

the accelerometer is a core instrument of the inertial system, and the technical indexes of the accelerometer directly influence the overall performance of the inertial system. In recent 30 years, due to the demands for low cost and high performance of devices, micro-mechanical accelerometers based on IC process and micro-machining process have the characteristics of small volume, light weight, low power consumption, low cost, strong overload capability, mass production and the like compared with the traditional inertial instrument, thereby having wide application prospect. Meanwhile, through continuous development and improvement, the MEMS resonant accelerometer is advancing from low precision to high precision. The types of silicon microaccelerometers include resonant type, capacitive type, piezoresistive type, piezoelectric type, heat convection type, tunnel current type, and the like.

The silicon micro-resonance accelerometer (MSRA) can directly convert acceleration into frequency output, avoids the error of amplitude measurement from being easily interfered by environmental noise, and has the advantages of small volume, low power consumption, quasi-digital quantity output, low cost, batch manufacture, high sensitivity, high precision improvement and the like, thereby being a high-precision MEMS inertial instrument with good application prospect.

MEMS resonant accelerometers generally consist of a proof mass, a lever amplification structure, a resonant beam (DETF), and a support structure. When acceleration is input from the outside, the sensitive mass block can transmit the axial inertia force to the lever amplification structure, the inertia force acts on the resonance beam structure after being amplified by the micro lever, the resonance beam is stressed and deformed to generate the change of tension or compression, so that the resonance frequency of the resonance beam is changed, and the acceleration of the carrier can be obtained by measuring the frequency change of the resonance beam by utilizing the force frequency characteristic of the resonance beam.

The research of the Draper laboratory in America on the resonant accelerometer is always in the international leading position, the stability of the silicon micro-resonant accelerometer in research and development reaches 0.73 multiplied by 10 < -6 > in the month of scale factor, and the stability of the silicon micro-resonant accelerometer in the month of zero bias reaches 2 mu g. The sensitivity of the resonant accelerometer based on the two-stage micro-lever mechanism, which is developed by applying an SOI-MEMS processing technology in Berkeley division of university of California, USA, reaches 160 Hz/g. In addition, related studies have been conducted by milan physicist of italy, the french space agency, seoul university of korea, and the like.

The research on the micro-mechanical accelerometer is started from the end of the 20 th century and the 80 th century in China, and the research and development work of the micro-mechanical accelerometer is actively carried out at present in Beijing university, Nanjing university of science and technology, southeast university, Zhejiang university, Chinese academy and the like. Although researchers have developed single-axis, double-axis and even three-axis resonant accelerometers, and have made a breakthrough in improving the scale factor and the measuring range of a resonator, the problems of mismatching of the thermal expansion coefficient of silicon and glass, poor frequency stability, incapability of releasing residual stress and the like of the domestic existing silicon micro-resonant accelerometers are still difficult to overcome due to the structural design and the process parameters, so that the accelerometers have serious zero-bias stability and temperature drift problems in performance, thereby severely restricting the performance and the application environment of the resonant accelerometers and being difficult to prepare high-precision devices meeting the requirements of tactical equipment.

The invention content is as follows:

the technical problem to be solved by the invention is as follows: the bottleneck of the prior art is broken through, and a silicon micro-resonance type accelerometer structure with low stress sensitivity is provided, so that the problems of low sensitivity, large influence by working temperature and processing environment, poor impact resistance and the like of the existing micro-mechanical accelerometer are solved, and high-precision measurement of the accelerometer is realized.

The technical solution of the invention is as follows: a silicon micro-resonance type accelerometer structure with low stress sensitivity is divided into two layers, wherein the upper layer of mechanical structure is manufactured on a monocrystalline silicon chip, and the lower layer of glass substrate is manufactured with electrode leads. The upper-layer mechanical structure comprises a mass block, a double-end fixedly-supported tuning fork resonator, a micro-lever amplification mechanism, a support beam, a low-stress frame and an outer frame, and the mechanical structure is fixed on the substrate through anchor points. The mass block is used for transferring inertia force and is respectively connected with the micro-lever amplification mechanism and the supporting structure, and the double-end fixed-support tuning fork resonator is driven and detected through comb tooth structures on two sides. When the measured acceleration is input into the device, the mass block can generate displacement under the action of the inertia force, the generated inertia force is subjected to force amplification through the micro-lever mechanism and then acts on the resonator, the natural frequency of the resonator is changed, and the measured acceleration is obtained through signal processing by the detection electrode.

The mass block, the micro-lever amplification structure, the double-end fixed-support tuning fork resonator, the comb tooth structure and the support structure are all manufactured by adopting a standard bulk silicon process, and the used material is monocrystalline silicon.

The substrate material can be boron low-acid glass with the temperature characteristic close to that of silicon, the substrate is connected with the tuning fork resonator, the low-stress anchor points and the outer frame through anchor points by adopting a bonding process, and the upper low-stress anchor point and the lower low-stress anchor point are located on the middle line of the structure and are distributed in a centrosymmetric mode.

Compared with the prior art, the invention has the advantages that: the low-stress anchor points symmetrically distributed on the two sides of the resonator are adopted, so that the thermal stress of the resonator along the X-axis direction generated in the processing process and the environmental temperature change can be effectively removed. The micro-lever amplification mechanism realizes the amplification of micro inertia force and reduces the inertia force loss caused by the rigid connection of the structure, thereby improving the working range of the resonator. The four symmetrically distributed support structures are connected with the outer frame, the mass block is suspended on the substrate, the influence of cross coupling on the measurement precision of the resonator is greatly reduced, and the shock resistance of the whole structure is improved.

Drawings

FIG. 1 is a schematic structural diagram of a resonant accelerometer with low stress sensitivity

FIG. 2 is a schematic structural view of a micro-lever amplification mechanism

FIG. 3 is a schematic diagram of a dual-clamped tuning fork resonator

Detailed Description

Referring to fig. 1, the present invention is a structure of a silicon micro-resonant accelerometer with low stress sensitivity, which is divided into an upper single crystal silicon layer and a lower glass substrate layer. The upper-layer mechanical structure comprises a mass block (1), double-clamped tuning fork resonators (2a and 2b), micro-lever amplification mechanisms (3a, 3b, 3c and 3d), a low-stress frame (4), support beams (5a, 5b, 5c and 5d) and an outer frame (6). The whole structure of the invention is a symmetrical graph, and the sensitive axis is an X axis. The mass block (1) is respectively connected with the micro-lever amplification mechanisms (3a, 3b, 3c and 3d) and the supporting beams (5a, 5b, 5c and 5d), and the effective amplification of the inertial force generated by the accelerometer to be tested and the decoupling of the two orthogonal sensitive directions are realized by optimizing the structural parameters of the micro-lever amplification mechanisms and the supporting structures, so that the accelerometer has higher sensitivity and larger measuring range. The double-end fixed branch tuning fork resonators (2a and 2b) are a pair of sensitive structures with the same structural parameters and are symmetrically distributed, and form a group of differential resonant tuning fork structures. Wherein one end of the mass block is connected with the mass block (1) through a lever mechanism (3a, 3b, 3c, 3d), and the other end is connected with a silicon structure frame (4) fixed with low stress anchor points (7a, 7 b). The outer frame is fixed on the substrate through anchor points. All anchor points are bonded with the glass substrate, so that the mechanical structure of the upper silicon layer is suspended on the lower glass substrate. The supporting structure is a U-shaped beam and is an axisymmetric structure. The micro-lever amplification mechanism is a primary lever amplification mechanism and is fixed on the substrate through low-stress anchor points (7a and 7 b).

Referring to fig. 2, the fulcrum beams (8a, 8b, 8c, 8d), the input beams (9a, 9b, 9c, 9d), and the output beams (10a, 10b, 10c, 10d) of the amplification mechanism of the micro-lever all adopt a thin beam structure, and the fulcrum beams are perpendicular to the axial direction of the lever, thereby making the amplification of the lever close to the ideal level.

With reference to fig. 3, the resonant accelerometer structure of the present invention includes a pair of resonators with identical structures and symmetrical positions, namely a left-side resonator (2a) and a right-side resonator (2b), and the pair of resonators includes six fixed driving electrodes (11a, 11b, 11c, 11d, 11e, 11f) and six fixed detecting electrodes (12a, 12b, 12c, 12d, 12e, 12f), wherein the detecting electrodes are close to the structure center, the driving electrodes are far from the structure center, the left-side fixed driving electrodes (11a, 11b, 11c) are symmetrical to the right-side fixed driving electrodes (11d, 11e, 11f), and the left-side fixed detecting electrodes (12a, 12b, 12c) are symmetrical to the right-side fixed detecting electrodes (12d, 12e, 12 f). Each fixed electrode is connected on the substrate through an anchor point. The change of the capacitance can be driven and detected by adopting a film pressing or sliding mode, so that the frequency change quantity is obtained.

The mass block is used for generating inertia force when the accelerometer to be measured is input, the inertia force is amplified through the micro-lever amplification mechanism and then acts on the resonator, the natural frequency of the resonator is changed, and the change of the detection capacitance is measured to obtain the acceleration value to be measured.

The mass block, the micro-lever amplifying structure, the double-end fixedly-supported tuning fork resonator and the supporting structure are all manufactured by adopting a standard bulk silicon process, and monocrystalline silicon is selected as a material. The substrate material can be borosilicate glass with temperature characteristic close to that of silicon, and the substrate is connected with each mechanical structure through anchor points by adopting a silicon-glass bonding process.

The working principle of the invention is as follows: when external force is input into the accelerometer, the mass block can convert the measured acceleration into inertial force, the inertial force acts on the resonance sensitive structure after being amplified by the force of the micro-lever amplification mechanism, so that the inherent frequency of the resonance sensitive structure is changed, and the measured acceleration value can be obtained by measuring the variation of the inherent frequency of the resonator. As shown in FIG. 1, when there is an acceleration component in the X-axis direction, the mass block generates an inertial force along the X-axis, and after the force amplification, one tensile force natural frequency of the resonator is increased, and the other compressive force natural frequency of the resonator is decreased, so that the two resonators form a pair of differential sensitive structures. The comb teeth are driven to drive the resonator to vibrate at a natural frequency, and the natural frequency change of the resonator under the input of the inertia force is detected by the comb teeth, so that the value of the acceleration component along the X axis is obtained.

Wherein, the resonant frequency of the resonator without external force can be calculated by the following formula

In conclusion, the invention provides a low stress sensitivity silicon micro-resonant accelerometer which has the characteristics of high sensitivity, wide measuring range, simple structure, good temperature stability and the like, and can be applied to the fields of aerospace, earthquake monitoring and the like.