0.26‐inch LED microdisplay using pixel level Cu–Cu connections of transferred GaN/Si and CMOS backplane wafer

Abstract We have developed an integration process for LED microdisplays toward augmented reality (AR) applications and present the first demonstration of a blue mono‐color active‐matrix LED microdisplay fabricated with this process methodology. One of the primary manufacturing challenges in realizing LED microdisplays is to develop a process that provides pixel‐level heterogeneous connections between III‐V compound LEDs and Si CMOS circuits at a fine pixel pitch. In this work, a die‐to‐silicon process is employed, in which GaN on Si chips are reconstituted on a larger‐diameter support Si wafer (referred to as GaN/Si wafer), allowing the use of Si CMOS wafer processes, including novel Cu‐Cu hybridization. After the Cu‐Cu hybridization process to bond a die‐to‐silicon transferred GaN/Si wafer and a Si CMOS backplane wafer, LED mesas and on‐chip lenses (OCLs) are fabricated. We achieved high yields of pixel‐level connections at 3.8‐μm and 4.5‐μm pitches through the Cu‐Cu hybridization. Finely tapered 1.2‐μm LED mesas with OCLs exhibited a 4.2‐fold enhancement in light extraction efficiency (LEE) compared with a Lambertian emitter within the emission angle of ±20°. Also, we introduce the key features and results of the prototyped 0.26‐in., 5,644‐ppi LED microdisplay.