Through-wafer optical probe characterization for microelectromechanical systems positional state monitoring and feedback control

Abstract

Implementation of closed-loop microelectromechanical sys- tem (MEMS) control enables mechanical microsystems to adapt to the demands of the environment that they are actuating, opening a broad range of new opportunities for future MEMS applications. Integrated op- tical microsystems have the potential to enable continuous in situ optical interrogation of MEMS microstructure position fully decoupled from the means of mechanical actuation that is necessary for realization of feed- back control. We present the results of initial research evaluating through-wafer optical microprobes for surface micromachined MEMS in- tegrated optical position monitoring. Results from the through-wafer free- space optical probe of a lateral comb resonator fabricated using the multiuser MEMS process service (MUMPS) indicate significant positional information content with an achievable return probe signal dynamic range of up to 80% arising from film transmission contrast. Static and dynamic deflection analysis and experimental results indicate a through- wafer probe positional signal sensitivity of 40 mV/mm for the present setup or 10% signal change per micrometer. A simulation of the applica- tion of nonlinear sliding control is presented illustrating position control of the lateral comb resonator structure given the availability of positional state information. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00312-3)