Electrical aging of a piezoelectric MEMS fast steering mirror and its impact on reliability

Abstract

Reliability is a critical characteristic of aerospace-grade components, particularly fast steering mirror (FSM), which is one of the key devices in Free-Space laser communication terminals. The previous long-term work of FSM exposes noteworthy reliability issues about degradation of this device. This paper first demonstrates the electrical aging effect that occurs in piezoelectric-driven micro electro mechanical system (MEMS) FSM during prolonged operation. This is a significant reliability issue as it causes the decay of mechanical angle of MEMS FSM, ultimately resulting in functional failure. In order to study the electrical aging effect, firstly, a mechanical angle monitoring system is developed for the rapid and accurate identification of electrical aging failure. Secondly, we performed failure analysis by using scanning electron microscope - focused ion beam (FIB - SEM) and conducted thermal analysis experiments to confirm heat accumulation within the MEMS FSM actuator, where the electrical aging effect takes place. Thirdly, by setting up a finite element simulations (FEM) model of the step region in the actuator, the electrical aging effect resulting from heat accumulation caused by high current density under a significant electric field at the lower step is confirmed. Finally, the critical reliability issue of electrical aging, which affects the lifetime of piezoelectric-driven MEMS FSM, is improved by adjusting the layout to eliminate large electric field intensity in local region.