Electrostatic digital micromirror using interdigitated cantilevers and its applications

Abstract

New digital micromirror device, the key device for digital projection display has been devised and developed to provide its applications using surface micromachining technology. The proposed micromirror has an operational mechanism of a seesaw allowing accurate and reliable control of the final rotating angle because of the unique design of the interdigitated cantilevers. Contrast to the previous DMD structure that utilizing a torsional motion of the hinge spring to rotate the overhanging micromirror, only cantilevers are utilized to rotate the micromirror excluding any torsional actions. The modeling and analytic calculation of the cantilevers for guiding of proper structural design are suggested and the calculated pull-in voltage have a good match with FEM simulation results. Therefore, the model is applied for designing the operating property of the micromirror device. Next, new microfabrication processes for three-dimensional metallic microstructures have been proposed. One method is to use extended soft bake process of thick positive-type photoresist, which is to remove thermal reflow of the lower layer of photoresist mold during the next thermal step. Also, using the stabilization step after spin coating of photoresist, the upper molds have no concerned with the surface profile of the lower layer. Therefore, it can be easily fabricated the flat multi-level metallic microstructures. The other method is to use thermally stable negative-type photoresist mold as a sacrificial layer for three-dimensional metallic microstructures. The flat multi-level metallic microstructure has been also successfully fabricated using this method. Next, we have fabricated the micromirror array using these microfabrication techniques and evaluated the static and dynamic operating characteristics of the fabricated micromirrors. The fabricated micromirror has shown a successful operation with tilting angles of 8 degree at the voltage bias of 85V in the size of 80 square micromete...