A Single-Side Fabricated Triaxis (111)-Silicon Microaccelerometer With Electromechanical Sigma–Delta Modulation

This paper presents a novel single-side (111)-silicon (non-SOI) fabricated triaxis capacitive microaccelerometer with a dual quantization electromechanical sigma-delta modulator (EM-ΣΔM) interface circuit. The fully CMOS compatible single-sided micromachining process with toroidal shaped electrical isolation structures is described. A 2.6 mm × 2.6 mm sized triaxis accelerometer was designed and fabricated using only the front side of a 4-in (111) silicon wafer. The interface circuit was based on a front-end ASIC readout circuit and a back-end dual quantization high-order EM-SDM digital circuit implemented on an FPGA. The EM-ΣAM loop adopts a multifeedback noise shaping architecture, for which different numbers of bits for the loop quantization were analyzed. The parameters of the EM-ΣAM loop are optimized by a genetic algorithm. Acceleration sensitivities of 170 mV/g (2785 LSB/g), 142 mV/g (2327 LSB/g), and 26 mV/g (426 LSB/g) were measured in EM-ΣAM closed-loop operation for the in-plane (X/Y) and out-of-plane (Z) axes, respectively. The cross-axis sensitivity was in the order of 1%-6% and the output noise was 0.5 mg-2 mg/√Hz, with a 1-h bias drift of 3-6 mg.