Investigation of ultrasmall sidewall-insulated GaN via with large aspect ratio for the strategy of vertically stacked full-color Micro-LEDs

Micro light-emitting diode (Micro-LED) is considered as an ideal candidate for near-eye, outdoor display, and light field photography applications. At present, the commercialization of full-color Micro-LED is limited by the mass transfer of red, green, and blue (R-B-G) sub-pixels. Hence, we proposed a full-color scheme of vertically stacked tricolor Micro-LED layers to avoid mass transfer, which owns over 1000 PPI (pixel per inch). In this solution, the sidewall-insulated via in the epilayer plays a critical role to achieve the electrical and mechanical integration of three monochromatic Micro-LEDs with Si-based complementary metal-oxide semiconductor (CMOS) driver. Therefore, the via processes of GaN-based epilayer were investigated systematically using available semiconductor processes in this article. The inductively coupled plasma (ICP) etching was employed to create the ultra-small micro-structure array using SiO₂ thin film as hard mask. Sidewall-insulated vias were fabricated with different aperture sizes (9.3, 7.5, and 3.4 μm) and a depth of about 4-μm. The vias with large aspect ratio are completely satisfy the requirement of designed vertical interconnection. This study aims to provide valuable reference for the commercial progress of high-resolution and full-color Micro-LEDs.