Capacitance measurement techniques in MOEMS angular vertical comb-drive actuators

Abstract

This paper presents three novel techniques for the measurement of capacitance variation in high-frequency operation of angular comb-drive structures, with applications including optical projection micro-mirrors. The first technique uses a lock-in amplifier in order to measure the impedance of the comb structure by superimposing a test signal having a frequency that is at least one order of magnitude higher than the micro-mirror resonant frequency. The second measurement setup uses a digitizing oscilloscope to measure the capacitance from the instantaneous voltage and current in the comb structure. The third setup consists of a micro probe controlled by a high-resolution positioner in order to tilt the mirror to a desired angle. This allows for static capacitance measurement at different mirror deflection using a high precision LCR meter. The measurement results from the different setups were found to be in agreement with each other. The results were further verified against analytical and numerical modelling.