Electroluminescent devices using a high-temperature stable GaN-based phosphor and thick-film dielectric layer

Abstract

Red, green, and blue light emission has been obtained from electroluminescent devices on glass using a high-temperature stable (HTS) GaN-based phosphor doped with rare earths (Eu, Er, Tm) and a screen-printed thick-film dielectric layer. The thick-dielectric electroluminescent (TDEL) structure consists of metal/dielectric/GaN/indium-tin-oxide/Corning 1737 glass. The BaTiO/sub 3/-based /spl sim/20-40 /spl mu/m thick-film dielectric layer has a dielectric constant of /spl epsiv//sub r//spl sim/500-1000 and breakdown voltage >300 V. Despite granularity of the dielectric layer, the emission is uniform to well-below pixel dimensions (<10 /spl mu/m). Red GaN:Eu TDEL operated at 240 V and 1 kHz exhibits a luminance of 35-40 cd/m/sup 2/. Under 140 lux illumination, the TDEL device structure exhibits a contrast ratio of 5:1 at 120 V, 1 kHz biasing, without the assistance of contrast-enhancement techniques. Accelerated aging tests of TDEL devices show 60 Hz operating lifetimes exceeding 1000 h at >95% brightness. The TDEL structure has advantages over current thin-film and thick-dielectric electroluminescent structures in flat panel display applications.