4‐1: Invited Paper: Micro‐LED displays: can the monolithic approach produce full‐color?

Abstract

Mature LED technologies for large area LED displays and general lighting are now commonplaces. The use of miniaturized LEDs in high‐resolution and micro‐displays is attracting more attention recently, for direct view or projection applications. LEDs have advantages in terms of efficiency, brightness, lifetime, temperature stability and robustness, compared with other existing micro‐display technologies. The most significant is visibility under bright day‐light.A few years ago, we reported the fabrication of high‐resolution truly monolithic micro‐displays with decent visual quality. We have developed two different approaches to illustrate high resolution micro‐displays with excellent bonding yield. A 1700 pixel per inch (PPI) passive‐matrix and a 400 x 240 active‐matrix micro‐LED arrays bonded on ASIC have been demonstrated.Realization of a monolithic full color LED micro‐display remains the biggest challenge because it is not straightforward (nor practical) to selectively grow three different epi‐layers emitting at different wavelengths on a single substrate for three primary colors. Dedicated for projection display application, we demonstrated a novel 3LED light engine that can project full color video on screen. 3LED consists of a trichroic prism that combines RGB images generated from three LED micro‐displays based on AIGalnP (Red) and GaN (Green and Blue) materials. For near‐to‐eye display application, RGB quantum dots were printed on micro‐LED array by aerosol jet printing, achieving full color LED micro‐displays with high image quality.To maximize the throughput and minimize the light‐guiding effect of the transparent sapphire substrate, we use LED epilayers grown on Si substrates that can be removed using a simple and low‐cost SF6‐based RIE etching process. Moreover, Si has been used for GaN growth for over two decades due to its low cost and large scale. In this talk, we report an AMLED micro‐display system consisted of micro‐LEDs array using GaN‐on‐Si epilayers and a CMOS driver. Various recent approaches to achieve full‐color micro‐LED displays and a comparison of the pros /cons of the different methods will be discussed.