A pure CMOS surface-micromachined integrated accelerometer

A pure CMOS integrated accelerometer has been realized using surface micromachining as the structural technique. The samples are fabricated by a 14-mask 0.8 mu m CMOS standard process in a Siemens production line. Only the standard layers of the process (350 nm polysilicon and 600 nm oxide as sacrificial layer) are used to build up the surface-micromachined device. Sensor release and antisticking are also CMOS-compatible. The movement of a seismic mass normal to the chip surface is capacitively detected (open loop) and transformed on chip into a digital output signal by a robust circuit for measuring sub-femtofarad capacitance differences. Parasitics are suppressed on chip. The sensor is designed to measure accelerations up to 50g. A resolution of +/-0.6g, corresponding to a capacitance change of +/-0.1 fF, is observed.