Spring Constant Characterization of a Thermally Tunable MEMS Regressive Spring

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MEMS and Nanotechnology

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Springs are a widely utilized component in the Microelectromechanical systems (MEMS) industry, especially in inertial devices. Many of these devices rely on the restoring forces of springs to return the device to equilibrium, such as in an accelerometer. By adding external springs with negative spring constant behavior, the total spring constant can be modified. Previous work at AFIT investigated the spring characteristics of a buckled MEMS Si/SiO2 membrane. This research followed on previous work and attempted to modify the spring behavior. A Ti/Au meander resistor was deposited atop the membrane in an effort to actuate the membrane and change the spring constant. Membrane buckling was investigated through analytical equations and Finite Element analysis (FEA) to predict device behavior. Membrane deflections and thermal effects were measured using an interferometric microscope (IFM) and showed a deflection change of 13.3–22.2 μm in the square style of resistor and 15.1–23.5 μm in the spiral type of resistor. The results concluded that by introducing a thermal stress, the membrane could be actuated with a subsequent change in spring constant. From the initial position to the fully thermally actuated position, we expect the spring to undergo a threefold increase in spring stiffness in the linear region.


MEMS and Nanotechnology, Conference Proceedings of the Society for Experimental Mechanics Series, Vol. 8 (2015): 7-15. DOI.

Ronald A. Coutu was affiliated with the Air Force Institute of Technology at the time of publication.