Fig. 1.

Schematic illustrations and images of tandem RGB thin-film micro-LEDs and device arrays, assembled by the transfer printing method. (A) Comparison of a conventional parallel RGB micro-LED array (Left) and our proposed tandem RGB micro-LED array (Right), with the same display resolution. (B) Exploded schematic of tandem RGB micro-LED arrays, with the inset showing a single pixel, comprising an InGaP red LED, a multilayer SiO₂/TiO₂ filter, an InGaN green LED, and an InGaN blue LED (from bottom to top). The stacked devices can be assembled on various substrates. (C) Fluorescent microscopic images for an array of tandem RGB micro-LEDs. From top to bottom: bright field view, RGB emissions under green/blue/ultraviolet (UV) illuminations, respectively. (D) Cross-sectional scanning electron microscope (SEM) image of tandem RGB micro-LEDs with colorized regions showing thin films of RGB micro-LEDs as well as the filter interlayer. Different device layers are separated by layers of SU-8 epoxy.