Reliability study of a MEMS array under varying temperature and humidity conditions

In this work, we quantify and analyze the rate of accrual of stiction and mechanical fatigue in a MEMS micro-mirror device to understand its reliability under a set of controlled temperature and humidity splits. An accelerated aging system was employed by using a non-standard actuation procedure to more rapidly induce failure of the micro-mirrors. The array is hermetically packaged with a low surface energy self-assembled-monolayer (SAM) based anti-stiction coating, along with an encapsulated source of this anti-stiction coating that serves as a reservoir. Exposure of the micro-mirror array to the environmental conditions was made possible by drilling two 1 mm holes in the hermetic package. This enabled the retention of the encapsulated SAM source in the package which was vital to understanding the effects of SAM re-deposition on the surface in the operating environment. The fastest accrual of stiction was seen in the 90°C, 80% RH split with approximately 80% of the micro-mirrors failing within 4.4 × 10⁹ cycles (10 hours) with 2.7×10^-14 Joules of Stiction Equivalent Energy while the 60°C, 20% RH showed the least stiction accrual rate with less than 2% failure for 2.26×10¹² cycles (1500 hours). The failure data obtained from the experiments were used to do a reliability analysis by utilizing the Weibull distribution.