Single- and multi-layer electroplated microaccelerometers

Electroplating techniques have been used to fabricate both single- and multi-layer, differential output acceleration sensors. The accelerometers detect accelerations normal to the substrate by a capacitance change between electrodes. Accelerometer beam shapes were determined using finite element (FEM) simulation, and took into account the potential for residual stress in the beams. These devices have been realized using standard ultraviolet lithography and photosensitive polyimide (PSPI) resist, electroplating, and sacrificial etch processes. Electroplated nickel was employed as a structural material (beams, proof mass, anchors and electrodes) and an evaporated copper was used both for the electroplating seed layer and as a sacrificial layer. The sensors were made on top of polyimide-coated silicon to reduce stray capacitance. The maximum capacitance change of the single- and multi-layer accelerometer (four 2 mm length beams, a 2 mm/spl times/2 mm proof mass, and 2 micron gaps) were 0.90 and 1.77 pF per g, respectively. The sensitivity of the differential accelerometer was 1.85 V/g (1 g=9.8 m/s/sup 2/) after hybrid packaging with an integrated diode-quad bridge circuit.