A differential capacitive mini-displacement sensor

The paper describes a micromachined device that offers high sensitivity and wide dynamic range for electronically monitoring the planar displacement caused by other microstructures. The device uses a differential capacitance between overlapped electrodes to sense displacement. The differential capacitance is composed of a suspension electrode mounted on a moving cantilever, and two fixed electrodes located under the suspension electrode. The suspension and fixed electrodes are arranged such that output is a differential readout, eliminating common mode parasitic capacitance. Analytical and numerical modeling results are presented and results of simulating the capacitance prove that it has sensitivity in the range of 90-100 fF//spl mu/m and a measurement range of about /spl plusmn/10 /spl mu/m. A sensor circuit for precise measurement of changes in capacitance is also presented.