Thermal Reliability Study of an Electrothermal MEMS Mirror

Micro-electrical-mechanical mirrors based on electrothermal bimorph actuators have unparalleled advantages of large scan range, low driving voltage, and high fill factor, but their reliability issues are not well understood. One of the main failure phenomena is the burnout of the refractory metal resistor embedded in electrothermal bimorph actuator structures. In this paper, the burnout process was thoroughly studied via both electrical and optical testing. In particular, the current passing through the embedded resistor was monitored throughout the entire burnout process. It was found that the burnout was caused by multiple steps of anomalies, including electrical breakdown at poor step coverage, short circuit, overheating, and electromigration. Electrical models and lumped-element thermal models were established and electrothermomechanical finite-element method simulations were performed. The modeling and simulation results are all in good agreement with the experimental results. These findings will help greatly improve future design for better reliability.