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

Implementation of closed-loop microelectromechanical system (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 fut ure MEMS applications. Integrated optical microsystems have the potential t o enable continuous in situ optical interrogation of MEMS microstructure po sition fully decoupled from the means of mechanical actuation that is neces sary for realization of feedback control. We present the results of initial research evaluating through-wafer optical microprobes for surface micromac hined MEMS integrated optical position monitoring. Results from the through -wafer free-space optical probe of a lateral comb resonator fabricated usin g the multiuser MEMS process service (MUMPS) indicate significant positiona l information content with an achievable return probe signal dynamic range of up to 80% arising from film transmission contrast. Static and dynamic de flection analysis and experimental results indicate a through-wafer probe p ositional signal sensitivity of 40 mV/mum for the present setup or 10% sign al change per micrometer. A simulation of the application of nonlinear slid ing control is presented illustrating position control of the lateral comb resonator structure given the availability of positional state information. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(0 0)00312-3].