Spin-cast planarization of liquid-crystal-on-silicon microdisplays

A simplified method for planarizing liquid-crystal-on-silicon (LCOS) backplanes is presented. The method relies on the planarizing capability of spin-cast benzocyclobutene (BCB) polymeric resin. BCB planarization shows a sixfold reduction in step height on the surface of a typical LCOS backplane. Contact with the underlying pixel circuitry is made by dry etching through openings in the BCB layer. Reflective metal (87% reflectivity) is deposited over the planarized surface and patterned to form high-aperture-ratio pixel mirrors (84%). An average resistance of 0.75 Omega per via was achieved with 3.6-microm-diameter vias in 2-microm-thick BCB. The method and the results of this LCOS backplane planarization and postprocessing are described.