Demonstration of Trench Isolated Monolithic GaN μLED Displays Enabled by Photoresist Planarization

Micro-Light-Emitting Diode (μLED) displays are of increasing interest in applications which require extremely high resolutions such as virtual and alternate reality headsets. Most modern full-color μLED displays rely on red, green, and blue (RGB) pixels based on different material systems combined together on a thin-film transistor back panel, a costly process which often has very poor yield. An alternative approach is to create a monolithic display in the InGaN/GaN material system. However, efficient pixel isolation is a concern for monolithic GaN displays, as the lack of truly insulating undoped GaN (u-GaN) makes it difficult to electrically isolate rows or columns of μLEDs from one another. In this work, we demonstrate a novel solution to pixel isolation in a single-color passive matrix display. Photoresist is used to fill deep trenches isolating columns of μLEDs from one another. The resist is then patterned, and baked at high temperature, making it extremely durable. This photoresist planarization process allows for formation of p-interconnects using liftoff, and avoids the issues involved in bridging high aspect ratio trenches. This process could contribute to creation of improved monolithic full color μLED displays which require multiple deep isolation features to be bridged by conductive interconnects.