Robustness and reliability of MOEMS for miniature spectrometers

Tunable MOEMS Fabry-Perot interferometers (FPIs) are key elements in the miniaturization of spectroscopic instrumentation. Robustness and high reliability of the MOEMS structure are important factors especially for sensors utilized in challenging environments such as in space- and automotive applications. This paper presents reliability assessment of two types of MOEMS optical filters; a tunable ALD (atomic layer deposition) -based surface micromachined FPI for visible - near-infrared range, and a tunable FPI for mid- infrared applications based on LPCVD (low-pressure chemical vapor deposition) thin-film micromachining. High-G shock tests were performed on both MOEMS FPIs. The FPI structures can survive mechanical impact up to 18 000 G without any detectable changes in the capacitance, while detected failure mechanisms in this range arise from packaging and not from the MOEMS structures. The effect of DDMS SAM (dichlorodimethylsilane self-assembled monolayer) coating to prevent in-use stiction was evaluated in both humidity- and impact tests. In humidity tests, 20% stiction rate in non-coated devices vs. 0% stiction rate in DDMS-coated LPCVD FPIs under pull-in was observed. These results indicate good shock-impact robustness for both types of surface-micromachined structures, while DDMS SAM can be utilized to improve in-use reliability of MOEMS.