A novel capacitive accelerometer with a highly symmetrical double-sided beam-mass structure

This paper reports a novel capacitive accelerometer with highly symmetrical double-sided beam-mass structure. The highly symmetrical structure is fabricated from single wafer by a novel vertical sidewall protection technique. The good device performance is obtained by highly symmetrical double-sided beam-mass structure and fabrication process that enable formation of a large proof mass, controllable thickness of beam, and a narrow uniform capacitive gap over a large area. The resonance frequency of the accelerometer is measured in open loop system by a network analyzer. The quality factor and the resonant frequency are 34 and 787 Hz, respectively. The accelerometer with closed loop interface circuit is calibrated on B&K Vibration Transducer Calibration System (Type 3629). The typical measurement range of the device is 1 g, and the maximum range is 2 g. The capacitance sensitivity of the fabricated accelerometer is 11.7 pF/g. The sensitivity of the device with closed loop interface circuit is 1 V/g, and the nonlinearity is 0.39% over the range of 1 g. The cross-sensitivity x/z is 0.72% and y/z is 0.50%, respectively. The accelerometer with closed loop circuit has wide bandwidth of DC to 1 kHz (3 dB). Also the bias stability is 255 μg. The device with closed loop circuit has signal to noise ratio (SNR) of 106 dB, the average noise floor is 3.1 μg/Hz (0–100 Hz).