An investigation into the effect of electrostatic actuation and mechanical shock on microstructures

Understanding the behavior and modes of failure of micro-electro-mechanical systems (MEMS) under different conditions is a crucial element to enhance their reliability and sensitivity, which may also lead to widen their use to more applications. One of the major causes of failure in these devices is mechanical shock. In this work we present a theoretical and experimental investigation into the effects of mechanical shock on microstructures under the influence of squeeze film damping and electrostatic forces. For the theoretical investigation, a single-degree-of-freedom system is used to model a microstructure. Simulation results are demonstrated in a series of shock spectra that help indicate the nonlinear effects due to electrostatic and squeeze film forces on the motion of the microstructure. In practical applications, the microstructure is mounted on a printed circuit board (PCB). For that purpose, the effect of the motion of a PCB on the microstructure response is also investigated, both theoretically and experimentally. For the theoretical part, a two-degree-of-freedom system is used to model the PCB and microstructure assembly.;The effect of mechanical shock on the response of resonant sensors is another reliability issue that is addressed in this work. Resonant sensors typically operate at low pressures for enhanced sensitivity, which makes their response to external disturbances such as shock a greater issue. For the theoretical investigation, a single-degree-of-freedom system is used to model the resonant sensor, which is electrostatically driven by a DC load superimposed to an AC harmonic load. Experimental work is also conducted for this case.;Finally, we present an investigation in using the nonlinearities arising from electrostatic actuation to enhance the sensitivity of a resonant accelerometer. Several results are shown for the effect of the DC and AC voltages on enhancing the sensitivity of the accelerometer. The use of the accelerometer as a switch triggered by low accelerations while operating at primary or sub-harmonic resonance is also investigated.;The experimental investigations in this work were conducted on a capacitive accelerometer. It is found that the experimental data are in good agreement with the simulation results in all the investigated cases. It is found that accounting for the nonlinearities, arising from the DC load and the AC harmonic load, and for the PCB motion is crucial. In some cases, whether the microstructure is operated as a capacitive sensor or a resonant sensor, the microstructure may experience an early dynamic instability. This in turn may lead to unexpected failure of the sensor.