Bistable MEMS Gas Detector Based on Nonlinear Bifurcations

This work presents the exploitation of the nonlinear bifurcations of snap-through and pull-in instability in a doubly-clamped microbeam to realize a new thermal conductivity-based gas detection technique. The microbeam is electrothermally heated, buckled, electrostatically actuated, and operated near the snap-through limit. We demonstrate the capability of the proposed concept for detecting cooling gases, such as helium (He) and hydrogen (H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>). Results are presented showing the microbeam undergoing direct pull-in following a snap-through bifurcation upon reaching predetermined gas concentration thresholds of 11.4%He, as demonstrated experimentally and 5%H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>, as demonstrated by simulations. The pull-in is utilized to realize a binary switch for simplified signal readout and direct actuation. Additionally, results are shown for the application of a resonant sensor, which provides more quantitative data when needed. The helium sensitivity is measured to be 2.516 %/%He, with a limit of detection (LOD) of 0.62%He. In addition, the response and recovery times are determined as 212 s and 215 s, respectively. The simulated results for H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> predict a higher sensitivity of 12.45%/%H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and a lower LOD of 0.13%H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>. The effect of exposing the microstructure to gases with heating effects, such as carbon dioxide (CO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>), is also investigated. The proposed approach provides a simple and practical gas sensing method suitable for gas leakage warning systems.