Low-cost technological approaches to micromachined spatial light modulators

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Approaches toward the fabrication of low-cost integrated micromachined spatial light modulators are presented. An optimized fabrication procedure minimizes requirements on integrated electronics and mechanical layers. This surface can rest on a viscoelastic carrier material under which an electrode array is placed. Under application of appropriate potentials on the underlying electrodes, localized sinusoidal phase gratings can be produced. The depth of modulation can be converted to an intensity value by using Schlieren bars and integrating properties of the projection lens. The pixel sizes can vary from 20μm to 1mm. In the fabrication procedure, a top chip is used, which is coated with a 50nm nitride layer and an 80nm Al layer. A droplet of the carrier layer is placed on the bottom chip, on which the top chip is then pressed, planarizing the surface. A 33 wt% KOH solution is used to bulk-etch the silicon of the top chip, using the thin nitride membrane as an etch stop, thus transferring the metal layer to the carrier substrate, a technique potentially also usable for adaptive deformable mirrors. A special elastomer based etch holder technology was developed to provide low stress protection of the sidewalls and aluminum bond pads during etching. Applications of these devices lie in the field of projection displays, optical lithography and optical communication networks.