一种采用圆片级真空封装的全硅MEMS三明治电容式加速度计

摘要

Full-silicon MEMSaccelerometers have advantages of good temperature characteristics, small size, low cost and small package,and havebecome a key component of GNC(guidance, navigation and control)micro-systems. In this work, a wafer-level hermetic packaging method of MEMS sandwich accelerometer with three silicon layers is presented.Using SiO2hard mask with thickness steps, the 3D structures of silicon middle waferare fabricated by KOH wet etching from both polished wafer surfaces. The fabrication processes of the cap wafers mainly consist of KOH anisotropic etching and ICP (Inductively coupled plasmaetching) silicon etching. Finally, thecap wafers are bonded with silicon middle wafer by Au-Si eutectic bonding from both sides. The cavity of the sandwich accelerometer encapsulateshigh-pure low-pressurenitrogen(N2) of200Pa. Themeasurement results show that the closed-loop sensitivity of the proposed accelerometer is 0.575V/g,and the zero bias is 0.43g. The-3dB bandwidthof the accelerometer is 278.14Hz. The output stabilityfor1his 2.23×10-4g(1σ). The output drift ofthe accelerometer infull temperature range (-40℃to 60℃) is 45.78 mg, and the maximum temperature hysteresis is 3.725 mg.%全硅MEMS加速度计具有温度特性好、封装体积小、成本低的优点,从而成为小型化GNC(制导、导航与控制)系统的关键器件.给出了一种具有三层硅结构的MEMS三明治加速度计的设计、加工以及圆片级真空封装方法,其中,中间硅摆片的3D结构通过双面KOH湿法腐蚀制造,腐蚀过程中使用台阶化的SiO2作为硬掩模.硅盖板的加工主要通过KOH各向异性腐蚀和电感耦合等离子体垂直刻蚀完成.最后,上、下硅盖板通过基于Au-Si共晶反应的全硅键合技术从两侧与硅中间摆片进行键合,并实现圆片级真空封装.三明治加速度计的腔体内封装了压力为200 Pa的高纯氮气.测试结果表明,所述加速度计的闭环输出灵敏度为0.575 V/g,零位误差为0.43 g.加速度计的-3 dB带宽为278.14 Hz.加速度计1 h的输出稳定性为2.23×10-4 g(1σ).加速度计在全温范围(-40℃～60℃)内的输出漂移为45.78 mg,最大温度滞环为3.725 mg.