Surface Condition Influence on the Nonlinear Response of MEMS CC-Beam Resoswitches

This letter characterizes the effect of surface conditions on the nonlinear responses of micromechanical resonant switches (aka “resoswitches”). In particular, a CMOS-MEMS clamped–clamped beam (CC-beam) resoswitch used as a testing vehicle exhibits variations in the magnitude of the frequency tapping bandwidth upon modification of the surface stiction force by salinization with (1H, 1H, 2H, 2H)-perfluorodecyltrichlorosilane (FDTS) and by altering the operating temperature of the resoswitch. The tapping bandwidth of the CC-beam resoswitch increases from 17.37 to 29.75 kHz after salinization and reduces from 36.75 to 26.06 kHz as the device temperature rises from 35 °C to 80 °C. The experiment of salinization, together with the theory prediction, verifies that FDTS coating would result in a lower surface energy and thus a lower attractive force between the contact surfaces. As a result, the resoswitch would exhibit a larger tapping bandwidth due to the reduction of the attractive force. In contrast, raising the temperature would induce an increase in the surface energy and in the contact asperity radius of curvature due to material softening, both of which cause the attractive force to increase. Understanding the surface condition dependence of the nonlinear tapping frequency response could pave the way toward applications not achieved by the existing technologies, such as
in situ
monitoring of the anti-stiction coating quality in MEMS motion sensors.