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

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.