New FET accelerometer based on surface micromachining

A new accelerometer based on an FET sensing element and surface-micromachining technology has been designed and fabricated. A new process to avoid sticking during processing has been developed. In this new process, the sacrificial layer is etched before polysilicon structuring, defining a sealed vacuum cavity. Finally the accelerometer structure is defined with dry etching on this cavity, avoiding any wet etching process and, in consequence, the sticking of the polysilicon structure on the substrate. The sensing element of the accelerometer is a transistor FET. So the mass of the accelerometer acts as a gate of the transistor, changing the value of the threshold voltage, VT, with the acceleration. Preliminary results show a high sensitivity with a much simpler readout compared to capacitive sensors.