ESD testing and combdrive snap-in in a MEMS tunable grating under shock and vibration

This work describes a method for tracking the dynamics of electrostatic discharge (ESD) sensitive MEMS structures during ESD events, as well as a model for determining the reduced combdrive snap-in voltage under vibration and shock. We describe our ESD test setup, based on the human body model, and optimized for high impedance devices. A brief description of the MEMS tunable grating, the test structure used here, and its operation is followed by results of the measured complex device dynamics during ESD events. The device fails at a voltage up to four times higher than that required to bring the parts into contact. We then present a model for the snap-in of combfingers under shock and vibration. We combine the results of the analytical model for combdrive snap-in developed here with a shock response model to compute the critical shock acceleration conditions that can result in combdrive snap-in as a function of the operating voltage. We discuss the validity regimes for the combdrive snap-in model and show how restricting the operation voltage below the snap-in voltage is not a sufficient criterion to ensure reliable operation especially in environments with large disturbances.