Electro Optical Performance Of An Improved Deformable Mirror Device

Abstract

The design, fabrication and performance of an improved 128 X 128 deformable mirror device (DMD) is presented. The DMD is a fast, low power, analog response, spatial light modulator. The improved DMD consists of a monolithically formed array of cantilever beams which are electrostatically deflected by an underlying MOS transistor address matrix. The on-chip address circuitry supports a single video input to the chip with all demux operations performed on-chip. The original DMD (1,2) differs in two respects from the improved version. Instead of monolithically formed cantilever beams, the original DMD utilizes a hybrid architecture wherein a continuous metalized membrane is placed over an underlying address chip by a mechanical lay-down process. In addition, instead of the single video input of the improved DMD, the original version has 128 inputs corresponding to the 128 columns of the x-y transistor matrix. The deformable mirrors of the improved DMD are cantilever beams formed by two layers of high reflectivity aluminum alloy. A thin layer forms the hinge and a thicker layer forms the cantilever beam and the surrounding support metal. The beam, hinge and support metalare formed over an underlying planarizing spacer layer, which is selectively removed by plasma etching to form an air gap underlying each cantilever beam pixel. This paper describes the design, fabrication and performance of the improved 128 X 128 cantilever beam DMD, including preliminary data on the Fourier plane behavior of this device and a discussion of its application to optical correlation. Dynamic range of the DMD in the Fourier plane at the Nyquist frequency has been measured at greater than 45 db and is limited by the CCD image detector used to record the intensity distribution.