A pure CMOS surface micromachined integrated accelerometer

A pure CMOS integrated accelerometer was realised using surface micromachining as structural technique. The samples were fabricated by a 14 mask 0.8 μm 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-fF capacitance differences. Parasitics are suppressed on chip. The sensor was designed to measure accelerations up to 50 g. A resolution of ±0.6 g corresponding to a capacitance change of ±0.1 fF was observed