Inertia mass bio-sensors based on snap-through phenomena in electrostatic MEMS shallow arch resonators

This research examines on a new class of MEMS inertia mass sensors that are simple, sensitive, and selective in possibly detecting tiny objects. The sensor consists of two beams attached by an end-plate and is mounted on an electrostatically actuated shallow micro-arch. The presence of the end-plate overcomes the shortcoming of building inertia mass sensors using in-plane beam resonators. It gives more room to deposit detector material and, therefore, controls and mobilizes the quantity of the detector toward sensing a target. The design exploits the bistable behavior, resulting from the combination of the snap-through instability and the nonlinear force to move from one stable equilibrium to another. The transition can be controlled statically or dynamically depending on an operational modes. The eigenvalue problem assessment shows a considerable reduction in the first and third symmetrical resonant frequencies under DC voltage when a few picograms of the object substance are introduced. It is also corroborating that placing the added mass at the center of the end-plate and operating the sensor at vibration mode shape that dominated by the platform are more effective for mass detection through measuring the change in its frequency and bifurcation points. We found that superimposing the excitation signal to a small AC harmonic load, linear dynamic responses show a shift in the neighborhood of the first resonant frequency. On the other hand, increasing the actuation signal, dynamic responses show nonlinear trends offering possibilities to use the proposed design as a bifurcation-based type inertia sensor. This added mass leads to significant shifts at the locations of the bifurcation points compared to those in the absence of the object.