Micromechanical accelerometer integrated with MOS detection circuitry

A cantilever beam accelerometer is described in which the small cantilever sensing element is integrated with and fabricated alongside MOS detection circuitry. The total area of the detector/circuit combination is about 15000 µm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (24 mil <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). 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 which drive the simple MOS detection circuit. Sensitivities of about 2.2 mV/g of acceleration were measured, corresponding to beam motions of about 68 nm/g, with a beam mechanical resonant frequency of 2.2 kHz. These results were in close agreement with detailed mechanical calculations and circuit modeling.