Large-Stroke Capacitive MEMS Accelerometer Without Pull-In

In this study, the feasibility of obtaining electrical read-out data from a capacitive MEMS accelerometer that employs repulsive electrode configuration is demonstrated. This configuration allows for large-stroke vibrations of microstructures without suffering from pull-in failure that exists in conventional accelerometers based on the parallel-plate configuration. With initial fabrication gap of 2.75μm, the accelerometer can reach a 4.2μm dynamical displacement amplitude. The accelerometer is tested up to 95(V) without exhibiting pull-in failure. For comparison, the pull-in voltage of an accelerometer with same dimensions but with conventional parallel-plate electrode configuration is 0.8(V). The MEMS device is fabricated using the POLYMUMPs fabrication standard. An electrical circuit is built to measure the capacitance change due to motion of the accelerometer proof-mass. The accelerometer has a mechanical sensitivity of 35nm/g and electrical sensitivity of 5.3mV/g. The ability to use large bias voltages without the typical adverse effects on the stability of the moving electrode will enable the design of capacitive MEMS accelerometers with enhanced resolution and tunable frequency range.