Sub-micron lithography using InGaN micro-LEDs : mask-free fabrication of LED arrays

Guilhabert, Benoit Jack Eloi and Massoubre, David and Richardson, Elliot and McKendry, Jonathan and Valentine, Gareth and Henderson, Robert and Watson, Ian and Gu, Erdan and Dawson, Martin (2012) Sub-micron lithography using InGaN micro-LEDs : mask-free fabrication of LED arrays. IEEE Photonics Technology Letters, 24 (24). pp. 2221-2224. ISSN 1041-1135

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Abstract

The fabrication of gallium-nitride (GaN)-based light-emitting diode (LED) arrays by a direct writing technique, itself using micron-sized LEDs (micro-LEDs), is reported. CMOSdriven ultraviolet GaN-based micro-LED arrays are used to pattern photoresist layers with feature sizes as small as 500 nm. Checkerboard-type square LED array devices are then fabricated using such photoresist patterns based on either single pixel or multipixel direct writing, and implemented as part of a completely mask-less process flow. These exemplar arrays are composed of either 450-nm-emitting 199 × 199 μm2 pixels on a 200-μm pitch or 520-nm-emitting 21 × 18 μm2 pixels on a 23-μm pitch. Fill factors of 99% and 71.5% are achieved with optical output power densities per pixel of 5 and 20 W/cm2 at 90- and 6-mA dc-injected currents, respectively.