Thermal conductivity-based gas sensing utilizing multi-threshold MEMS switches: Helium as a case study

We present a gas sensing paradigm based on thermal conductivity cooling and multi-threshold micromachined switches and demonstrate it for helium detection as a case study. The proposed concept aims to provide discrete data at multiple gas thresholds while maintaining the sharpness of readout signals of threshold switches, besides offering the capability to generate direct actuation signals. The method relies on the pull-in and snap-through nonlinear bifurcation instabilities. In this work, a proof-of-concept device is presented with three thresholds based on doubly clamped bistable microbeams that are electrothermally heated and buckled. The switching thresholds can be adjusted using the softening effect of the electrostatic force. The proposed device is also shown to have the potential to be used as a resonant sensor for real-time continuous sensing. The demonstrated concept offers a simple practical solution for the detection of gas leakage for safety warning applications, especially for gases of cooling effect, such as hydrogen.