Unusual Behavior of a MEMS Resonator in Superfluid $^{4}$He

Mechanical resonators based on micro-electro-mechanical systems (MEMS) technology were developed for the study of superfluid $^{4}$He [1]. The MEMS device is composed of a movable plate (200 $\times$ 200 $\mu$m$^{2})$ suspended above the substrate by four serpentine springs. The suspended plate moves parallel to the substrate while maintaining a uniform gap between them. A specific device with a 1.25 $\mu$m gap was tested in the superfluid phase of $^{4}$He down to 100 mK. The device exhibits an extreme sensitivity to the excitation level below 400 mK, displaying a nonlinear and hysteretic behavior accompanied by switching. This phenomenon might be related to quantum turbulence generated by a rather simple oscillating plate.\\[4pt] [1] M. Gonzalez, B. Moon, P. Zheng, E. Garcell, H. B. Chan, and Y. Lee. \textit{Journal of Low Temperature Physics, Online First}$^{TM}$\textit{, 22 August 2012}, DOI: 10.1007/s10909-012-0682-8.