An exploration for the degradation behavior of 2-D electrostatic microscanners by accelerated lifetime test. (January 2018) - Qiao, Dayong
Abstract: Failure analysis for the MEMS device is a crucial step in understanding the root causes of failure and improving the performance of the device. In order to explore the degradation failure mechanisms of 2-D electrostatic microscanners, three steps were addressed in this paper. Firstly, the stress distribution of the microscanner under its operation state was simulated using the finite element method (FEM), and the results showed that the middle part on the frame torsion beam was the most critical place. In the second step, accelerated lifetime test (ALT) was performed to shorten the time-to-failure period. Thirty well-conditioned devices participated in the experiment with continuous operation modes. Finally, five failures were observed by scanning electron microscope (SEM), and pull-in was found to be the main failure mode. In particular, a new appearance (wrinkling) was found at the most critical place obtained by previous simulation, and the natural frequencies of failed microscanners declined in accordance with the characteristic degradation trend before they failed. In this paper, it was proved that for electrostatic microscanners, the degradation of the mechanical properties after a long period of cyclic torsion work was the cause that induced pull-in failure, and the degradation was embodied by the wrinkling appearance. Besides, based on the experimental data, a working life of 15.8 years at 298 K for microscanners was obtained by further calculation. Highlights: Accelerated lifetime test is effective in life prediction and failure analysis. Microscanners suffer from wrinkling and pull-in failure after a long-term work. The degradation of material mechanical properties induces pull-in failure.