Design, Fabrication, and Calibration of a Full Silicon WLP MEMS Sandwich Accelerometer

Full silicon micro electromechanical system (MEMS) accelerometers have advantages of good temperature characteristics, small size, low cost and small package, and become a key component of GNC microsystems. In this work, a wafer level hermetic packaging method of MEMS sandwich accelerometer with three silicon layers is presented. 3D structures on the silicon middle wafer are fabricated by KOH wet etching from both polished wafer surfaces, using the SiO2 hard mask with thickness steps. The fabrication processes of the cap wafers mainly consist of KOH anisotropic etching, and inductively coupled plasma (ICP) etching. Finally, cap wafers are bonded with the silicon middle wafer by Au-Si eutectic bonding from both sides. The cavity of the sandwich accelerometer encapsulates N-2 with a low pressure of 200Pa. The measurement results show that the closed-loop sensitivity of the proposed accelerometer is 0.575V/g and the zero bias is 0.43g. The -3dB bandwidth of the accelerometer is 278.14Hz. The output stability for 1 hour is 2.23x10(-4)g (1 sigma). The output drift of the accelerometer in the full temperature range (-40 to 60 degrees C) is 45.78 mg, and the maximum of the temperature hysteresis is 3.725mg.