<title>Optical binary switch and amplitude modulator micromirror arrays</title>

Abstract

Five types of micromirror arrays were designed and fabricated using a three-level, polysilicon, surface micromachined, micro-electromechanical systems (MEMS) process. The electrostatically deflectable micromirror designs included arrays of simple cantilever beams, torsion beams, tethered (piston-style) beams, circular membranes, and oval membranes. The smallest micromirror element was the simple cantilever beam, measuring 50 micrometer square. The largest micromirror element was the oval membrane; it possessed an active optical surface that was 320 micrometer by 920 micrometer. Each of the remaining micromirror designs have gold-coated polysilicon optical surfaces with geometries between these two limits. Electrostatically induced vertical deflections on the order of 2.75 micrometer were achieved. The torsion beam micromirror design exhibits both in-plane and out-of-plane deflection. The other micromirror designs only manifest in-plane deflections. The modeling phase focused on the microdynamical behavior of the torsion beam micromirror. The IntelliCAD<SUP>R</SUP> finite element analysis program was used to generate a plot of the micromirror's deflection (d) versus applied direct current voltage (V). The data was least-squares fitted to the well- established V varies direct as d<SUP>3/2</SUP> relationship. A resonant frequency analysis predicted an approximate switching speed of 6 microseconds. The reliability (number of operational cycles) of each micromirror design, when operated with a rectified 60 Hz alternating current (ac) signal, was measured to exceed more than 1 million flexure events. Experimental evidence supporting the potential for using micromirrors as binary optical switches and amplitude modulators is also addressed.