A novel single axis capacitive MEMS accelerometer with double-sided suspension beams fabricated using μWEDM

Abstract

Design and fabrication of the first micromachined accelerometer made from steel and the first MEMS accelerometer fabricated using micro-wire electrical discharge machining (μWEDM) process is presented in this paper. By utilizing this fabrication method, it is possible to achieve a huge proof mass that has a prominent effect on reducing noise. The proof mass in this design has a mass of 7.85 mg which leads to the Brownian noise of 0.8 μg/Hz that is comparable to low noise MEMS accelerometers. Another advantage is the higher density of the steel relative to the silicon, so a heavier proof mass can be achieved in a smaller size, providing a better control over the damping. The finite element analysis of the accelerometer shows that this sensor is able to measure high-amplitude accelerations up to 131 g without the risk of failure and fatigue because of the high yield stress and fracture toughness of the steel. Consequently, due to its low noise, resulting from its heavy mass, and also the ability to measure high amplitude acceleration, resulting from the high yield stress, the fabricated accelerometer has a dynamic range of more than 100 dB. Experimental tests showed that the accelerometer has the sensitivity, nonlinearity and range of 18 mV/g, 3% and 100 g respectively. This sensor provides the ability to operate in the air, which makes the packaging process easier. Also, the accelerometer shows the cross axis sensitivity of 0.44% accruing from the symmetrical arrangement of suspension beams used to suspend the proof mass.