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Feedback control of microelectromechanical systems (MEMS) devices has the potential to significantly improve device performance and reliability. One of the main obstacles to its broader use is the small number of on-chip sensing options that are available to MEMS designers. A method of using integrated piezoresistive sensing is proposed and demonstrated as another option. Integrated piezoresistive sensing utilizes the inherent piezoresistive property of polycrystalline silicon from which many MEMS devices are fabricated. As compliant MEMS structures flex to perform their functions, their resistance changes. That resistance change can be used to transduce the structures' deflection into an electrical signal. The piezoresistive microdisplacement transducer (PMT) is a demonstration structure that uses integrated piezoresistive sensing to monitor the output displacement of a thermomechanical inplane microactuator (TIM). Using the PMT as a feedback sensor for closed-loop control of the TIM provided excellent tracking with no evident steady-state error, maintained the positioning resolution to plusmn29 nm or less, and increased the robustness of the system such that it was insensitive to significant damage.
Date of Publication: Dec. 2009