IMPLEMENTATION OF MICROMIRROR ARRAYS AS OPTICAL BINARY SWITCHES AND AMPLITUDE MODULATORS

Five types of micromirror arrays were designed and fabricated using a three-lever, polysilicon, surface micromachined, microelectromechanica l systems (MEMS) process. The electrostatically deflectable micromirro r designs included arrays of simple cantilever beams, torsion beams, t ethered (piston-style) beams, circular membranes and oval membranes. T he smallest micromirror element was the simple cantilever beam, measur ing 50 mu m square. The largest micromirror element was the oval membr ane; it possessed an active optical surface that was 320 mu m by 920 m u m Each of the remaining micromirror designs have gold-coated polysil icon optical surfaces with geometries between these two limits. Electr ostatically induced vertical deflections on the order of 2.75 mu m wer e achieved. The torsion beam micromirror design exhibits both in-plane and out-of-plane deflection. The other micromirror designs only manif est in-plane deflections. The modeling phase focused on the microdynam ical behavior of the torsion beam micromirror. The IntelliCAD(R) finit e element analysis program was used to generate a plot of the micromir ror's deflection (d) versus applied direct current voltage (V). The da ta was least-squares fitted to the well-established V proportional to d(3/2) relationship. A resonant frequency analysis predicted an approx imate switching speed of 6 mu sec. The reliability (number of operatio nal cycles) of each micromirror design, when operated with a rectified 60 Hz alternating current (ac) signal, was measured to exceed more th an 1 million flexure events. Experimental evidence supporting the pote ntial far using micromirrors as binary optical switches and amplitude modulators was also addressed. (C) 1998 Elsevier Science S.A. All righ ts reserved.