基于谐振-力平衡复合检测机理低交叉灵敏度三轴数字加速度传感器研究

Three-axis micromechanical accelerometer is one of the basic components concerning national security and economic. It has a wide range of applications and large demands. In view of the disadvantages of developed three-axis accelerometer, such as large cross-axis sensitivity, low measuring accuracy and so on, this project proposes a novel three-axis micromechanical accelerometer utilizing a single proof mass fabricated by bulk silicon etching techniques to sense X, Y, Z axis accelerations. Mircobridge resonators are used to detect the in-plane X and Y axis accelerations and the force balanced plate capacitors are used to detect Z axis acceleration. As the normal displacement of the proof mass is very small under applied acceleration, each detection unit can be independently designed. The cross-axis sensitivity of three-axis accelerometer can be reduced significantly by the force balanced mechanism and the integrated resonant beams-supporting beams-proof mass structure fabricated with mask-maskless etching techniques. To overcome the disadvantages of resonant detection mechanism such as low sensitivity for in-plane acceleration and large temperature drift, four flexible crab-leg beams are used to support the proof mass. A high measuring accuracy for in-plane acceleration can be achieved by the mechanical structure and push-pull resonant detection mechanisim. The project will focus on the working mechanism, design principle, fabrication process, packaging technique, signal conditioning circuit of the novel three-axis microaccelerometer. It is expected to realize a novel digital three-axis accelerometer with high measuring accuracy, high resolution and low cross-axis sensitivity to meet higher requirements of many fields such as military, navigation, microgravity measurements,disaster monitoring and so on.

三轴微机械加速度计是关系国家安全和经济建设的基础元器件之一，应用面广、需求量大。针对现有三轴加速度计交叉灵敏度大、测量精度低等缺点，课题提出采用体微机械工艺加工的单质量块敏感三轴加速度信号，微桥谐振器检测X/Y轴加速度信号，力平衡模式检测Z轴加速度信号。质量块在芯片法向运动位移极小，可对各检测单元独立进行优化设计；结合掩膜-无掩膜腐蚀技术制作的一体化谐振梁-支撑梁-质量块结构可以显著减小三轴加速度检测的交叉灵敏度。针对谐振检测机理对面内加速度检测灵敏度低、温漂大的缺点，提出一种柔性的蟹腿梁支撑结构和推挽式谐振检测机制，可实现面内加速度的高灵敏度检测。课题将研究基于谐振-力平衡检测机理的新型三轴加速度计的工作机理、设计理论、制作工艺、封装技术、测试和控制电路，最终研制出高精度、低交叉轴灵敏度、数字化输出的三轴加速度计，满足军事、导航、微重力测量、灾害监测等领域对三轴加速度检测的较高要求。

本课题首先研究了检测芯片平面内X轴和Y轴加速度信号的谐振检测机理，优选谐振器的激励和检测方法、组成材料、结构和振型。围绕提高测量精度、工作带宽、可靠性，减小温度漂移、噪声、气体阻尼等目标，并根据量程设计质量块、谐振梁、支撑梁、限位块、凸角补偿图形的结构尺寸。其次，研究Z轴加速度信号的力平衡电容检测方法、结构设计原则、测量和控制技术。理论与有限元仿真相结合对新型三轴加速度传感器进行了模态分析、应力应变分析、温度场分析和静电力分析。经5次流片和测试，不断修正版图结构尺寸，获得三轴加速度计的优化设计尺寸。. 课题重点研究了基于掩膜—无掩膜腐蚀工艺制作的低交叉轴灵敏度加速度计的关键制作工艺：（1）P+多晶硅—金属的欧姆接触制作工艺；（2）含不同添加剂的各向异性腐蚀液中谐振梁与支撑梁的一次成型方法，最终遴选出碘过饱和KOH溶液作为掩膜—无掩膜腐蚀液，快腐蚀面具有最小的腐蚀速率，腐蚀出的微梁边缘平整。（3）腐蚀过程中金属引线和多晶硅电阻保护技术。（4）三轴加速度计的封装工艺研究。研制出压阻式加速度传感器、双轴体微机械谐振式加速度计、基于谐振—力平衡检测机理三轴加速度传感器等具有低交叉轴灵敏度的加速度计样品。. 完善了检测面内加速度信号的谐振式闭环自激测量电路，设计出消除温度影响的差频电路，探索了闭环自激测量电路的集成化设计技术。研究了检测Z轴加速度的力平衡平板电容检测机理的测量电路及静电反馈控制系统，设计了传感器测量电路。测试了新型加速度传感器的灵敏度、交叉轴灵敏度、线性度等技术指标。测试结果表明：所研制的传感器具有极低的交叉轴灵敏度。