Micromechanical accelerometer integrated with MOS detection circuitry

A cantilever beam accelerometer has been demonstrated in which the small cantilever sensing element is integrated with and fabricated alongside MOS detection circuitry. Fully compatible and conventional materials and processing steps are employed throughout the fabrication schedule. Accelerations of the chip normal to its surface induce motions in the cantilever beam. These motions result in capacitance variations (40 attofarads/g of acceleration) which drive the simple MOS detection circuit. Sensitivities greater than 2 mV/g of acceleration were measured, corresponding to beam motions of about 58 nm/g, in close agreement with calculations. The total area of the detector/circuit combination was about 15,000 µm2(24 mil2), at least two orders of magnitude smaller than any other solid state analog accelerometer yet reported.