An all-silicon single-wafer fabrication technology for precision microaccelerometers

This paper reports a novel all-silicon single-wafer fabrication technology for high precision capacitive accelerometers. This technology combines both surface and bulk micromachining to attain a large proofmass, controllable/small damping, and a small airgap for large capacitance variation. The microfabrication process provides large proofmass by using the whole wafer thickness, and a large sense capacitance by utilizing a thin sacrificial layer. The sense/feedback electrodes are formed by a deposited 2 μm polysilicon film with embedded 20-30 μm thick vertical stiffeners. These electrodes, while thin, are made very stiff by the thick embedded stiffeners so that force rebalancing of the proofmass becomes possible. The polysilicon electrodes are patterned to create damping holes. Several prototype microaccelerometers are fabricated successfully. Sensitivity of the devices with 2 mm×1 mm proofmass and full-bridge support are measured to be 2pF/g