Heterogeneous and Monolithic 3D Integrated Full-Color Micro-Light-Emitting Diodes via CMOS-Compatible Oxide Bonding for μLEDoS

Abstract

Micro-light emitting diode (mu LED) based LED on silicon (LEDoS) is a promising candidate for next-generation AR and VR displays due to superior pixel performance and potential for high resolution. Traditional RGB pixels are placed on a single plane, which limits the resolution. To overcome this, vertically stacked RGB pixels using heterogeneous and monolithic 3D integration (M3D) have been explored. However, previously reported vertical mu LED pixels have not considered the heat dissipation capability of the pixels, which is indeed important in future micro displays, and utilized materials incompatible with standard CMOS processes, further limiting their practicality for LEDoS. The critical regions for constraint, the bonding medium, are typically organic polymer materials. Therefore, to handle issue, vertically stacked full-color mu LEDs are demonstrated using silicon oxide (SiO2) and yttrium oxide (Y2O3), as bonding mediums. These materials are CMOS-compatible and offer thermal conductivity at least 10 times higher than conventional polymers. The InGaN/GaN blue mu LEDs bonded with oxides show improved thermal management, leading to higher external quantum efficiency (EQE) and better color characteristics, including narrower full width at half maximum (FWHM) and higher color purity. Precise control over bonding layer thickness is achieved, minimizing pixel thickness and enhancing manufacturability for high-resolution displays.