Sub-Micron Lithography Using InGaN Micro-LEDs: Mask-Free Fabrication of LED Arrays

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. CMOS-driven 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 $,\times,$ 199 $\mu{\rm m}^{2}$ pixels on a 200- $\mu{\rm m}$ pitch or 520-nm-emitting 21 $,\times,$ 18 $\mu{\rm m}^{2}$ pixels on a 23- $\mu{\rm m}$ pitch. Fill factors of 99% and 71.5% are achieved with optical output power densities per pixel of 5 and 20 ${\rm W}/{\rm cm}^{2}$ at 90- and 6-mA dc-injected currents, respectively.