Shock-protection of nano-gap capacitive MEMS accelerometers using sloped electrode design

This paper presents a novel sloped electrode scheme to enable the implementation of shock stops in MEMS devices that use a sacrificial layer to define in-plane capacitive gaps. Since the thickness of the sacrificial layer grown or deposited on the sidewall of a microstructure is constant, by sloping the interdigitated fingers, one can get a larger travelling range for the proof-mass than the thickness of the sacrificial layer. This allows the realization of larger sensing gap than the shock stop without using additional photomasks or fabrication steps. Proposed scheme is incorporated into the accelerometer design with 270 nm gaps and number of different characterizations were done to verify the survivability of the sensor under high-g environment. Further characterization shows a scale factor of 55.3 mV/g, noise density level of 187.09 μg/√Hz at 1 Hz for devices with a full-scale range of +/- 16g.