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.