Micromechanical Electrostatic Voltmeter

A microminiature, noncontracting electrostatic voltmeter (ESV), produced by IC processes on a silicon wafer, is described.  The ESV works on the principle of intermittent shuttering and exposing a sensing electrode to an electric field between a remote electrode at a different potential from the sensing electrode.  The resultant time-varying field at the electrode produces an electrical signal.  The principle of ESV measurements by intermittent shuttering is well establihsed and hybrid designs are presently used commerically.  This invention teaches how the entire structure, and eventually the drive and measuring-circuits, can be fabricated on a silicoin chip leading to substantially lower cost and possibly to significantly higher resolution.  The entire ESV is capable of being batch processed, in contrast to conventional macroscopic ESV circuits that have been built.  The prototype ESVs, studied thus far, do not have on-chip circuitry.  The microshutter is driven by electrostatic forces and made from polycrystalline silicon suing micromechanical fabrication procedures similar to those described by How and Tang to make resonators.  The ESVs that have been made and tested have electrostatic-comb drives and shutters with areas ranging from 0.022 to 0.067 mm^2 that are suspended roughly 2 microns above the surface of the silicon substate. Sensitivity to the remote voltage is a function of spacing to the surface electrode.  Initital tests showed sensitivity to about 20V for electrodes sapced 0.2 mm away; sensitivity can be greatly improved by redesigns that are already being investigated and, with the shuttered element encapsulated in a vacuum ambient, there is a possibility of detection of mV signals.