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Feedback control of 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 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 structure's 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 ±29 nm or less, and increased the robustness of the system such that it was insensitive to significant damage.

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Tristable mechanisms, or devices with three distinct stable equilibrium positions, have promise for future applications, but the complexities of the tristable behavior have made it difficult to identify configurations that can achieve tristable behavior while meeting practical stress and fabrication constraints. This paper describes a new tristable configuration that employs orthogonally oriented compliant mechanisms that result in tristable mechanics that are readily visualized. The functional principles are described and design models are derived. Feasibility is conclusively demonstrated by the successful operation of four embodiments covering a range of size regimes, materials, and fabrication processes. Tested devices include an in-plane tristable macroscale mechanism, a tristable lamina emergent mechanism, a tristable micromechanism made using a carbon nanotube-based fabrication process, and a polycrystalline silicon micromechanism.

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