ON-CHIP METALLIZATION LAYERS FOR REFLECTIVE LIGHT VALVES

The metallization layers required for a silicon-based reflective liqui d crystal light valve have been developed and integrated with a medium -voltage CMOS process using standard microelectronic manufacturing too ls. Unique requirements include the following: 1) shielding the Si dev ices from incident light so that electron-hole pairs are not formed; 2 ) high optical throughput and contrast, which are dependent on the mir ror fill factor, reflectivity, and flatness; 3) pixel storage capacita nce to maintain the voltage across the liquid crystal cell with suffic ient accuracy to select the desired gray level until the data are upda ted; and 4) precise control of the liquid crystal cell thickness witho ut spacers obscuring the mirrors. Wafers have been successfully fabric ated to support a technology demonstration of a 2048 x 2048-pixel (''f ourmillion-pixel'') projection display. The process is based on a medi um-voltage CMOS process and uses six masks (for three metal levels, on e via level, and two insulator levels) after Si device processing has been completed.