Design, fabrication and characterization of silicon nitride based MEMS spatial light modulators
Silicon nitride films were used to fabricate microelectromechanical systems (MEMS) deformable mirror (DM) spatial light modulators (SLM). Two types of DMs were studied in this work: circular diaphragms (0.5 μm thick silicon nitride) and suspended spring plates (0.5 μm and 1.0 μm thick silicon nitride). All the devices demonstrated optical modulation of amplitude and phase using a Michelson interferometer. The silicon nitride diaphragm devices were compared to a 2 μm thick Mylar diaphragm device, fabricated in a previous study, using AC and DC interferometry. The silicon nitride diaphragm device displayed larger dynamic range but less AC response than the Mylar device. The spring plate devices were characterized optically and mechanically. Dynamic mechanical analysis of the thin and thick spring plate devices yielded effective spring constants of 0.42 N/m and 3.02 N/m, respectively. Static mechanical analysis of the thin and thick spring plate devices yielded effective spring constants between 0.40–0.44 N/m and 3.15–3.32 N/m, respectively. The mechanical characterizations of the spring plates were within a factor of 2 in voltage with the optical characterizations of the devices. The observed larger deviations of the two models with the optical data at higher voltage operation may be due to electrical interference caused by the spring plate arms' fringe-fields. Lastly, the spring plate and diaphragm devices were each compared against the voltage-squared relation predicted by the theoretical models. The spring plate and diaphragm devices yielded power percent errors of −8.1% and 9.4%, respectively, as compared to the squared law.
0544: Electrical engineering