A monolithic surface micromachined accelerometer with digital output

A surface micromachined accelerometer with on-chip electronics realized in a 3 mu m BICMOS technology is described. The sensing element consists of a thin film of polysilicon that is deposited after fabrication of the electronic circuitry. Acceleration is measured by capacitively sensing sub-angstrom displacements of a mechanical proof-mass weighing 0.5 mu grams. The sensor uses force-feedback and achieves a resolution of 1.6 mg/root Hz (1 g = 9.8 m/s(2)). The limitations arising from the small size and mass of the sensing element and means for improvement are discussed. The small active die area of less than 3 mm(2) including the sensor along with the possibility to combine several different sensors on a single chip make this approach particularly attractive for applications demanding very small form factors.