Deformable Grating Light Valves for High Resolution Displays

摘要

The Grating Light Valve (GLV) is a micromechanical phase grating that can be usedfor black white or color display applications. Operation is based on electrically controlling the mechanical positions of the grating elements to modulate the diffraction efficiency. Proper choice of the grating dimensions allows the structure to operate as a digital optical device. Since the grating is inherently dispersive, the GLV can be used for color displays. In addition, the devices are bistable and may he able to operate with a passive matrix of contacts and still achieve the performance of an active matrix light valve. Eight bits of gray scale are possible using time division multiplexing and the fast (20 ns) switching speed of the GLV. The contrast ratio of the device is very sensitive to processing errors; to date, a ratio of 20:1 has been measured. With better processing, a color contrast of 200:1 should be achieved for a monochrome pixel. Stiction of the micromachined grating elements to the substrate during the final wet processing step and during operation remains a problem. However, our current approach uses rough (150 A-RMS) polysilicon films to reduce the area of contact. When doped, the polysilicon can be patterned to function as a bottom electrode for two-dimensional array applications. Although this structure suffers from some of the difficulties of a non-planar process, it was used to demonstrate two-dimensional arrays of devices with switching voltages as low as IIV.