Tunable MEMS diffraction gratings with improved displacement profile of the fixed-fixed beams

MEMS diffraction gratings whose period can be tuned during operation find applications in microspectrometers and in display1 devices. These structures were designed using fixed-fixed beams of 10 μm width and spacing of 2 μm between them and were actuated in an out-of-plane motion. It was found that non-planar bending of fixed-fixed beams reduces the amount of light diffracted into the first order by about 4% compared to ideal planar beam displacement. A new fixed-fixed beam design with modified spring constant and actuation mechanism was proposed to improve the planarity of the beam during actuation. The profiles of the two structures (proposed design and normal beam), when displaced by λ/4 (relative displacement between two beams required for diffraction), were extracted using Intellisuite simulations and this data was fitted with a ninth order polynomial to model the beam displacement. The grating transfer function was modeled with the acquired displacement profiles and it was found that the new design improved the efficiency in the first order by about 2% when simulated in MATLAB for 633 nm wavelength. The grating structures were fabricated using a 4-mask process and were released using a wet release process developed in the lab. The electrical characterization of the devices indicates that the devices were released. The grating structures were tested optically using an optical setup built in the lab. © 2013 SPIE.