Utilizing the piezoresistive properties of polysilicon as an on-chip sensing mechanism facilitates the implementation of feedback control on surface-micromachined MEMS devices. We have performed nanopositioning resolution tests on a MEMS thermal actuator, both open and closed loop, to demonstrate the performance improvements possible with feedback control. A thermomechanical in-plane microactuator (TIM), fabricated using the MUMPS fabrication process, was used in this study. The actuator was coupled to a piezoresistive displacement sensor (PRDS) that was fabricated as part of the same process. Measurements of the actuator output, taken using a scanning electron microscope, show that nanopositioning repeatability improved from ±59 nm to ±31 nm when feedback control is employed.

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