2822 PPI active matrix micro-LED display fabricated via Au-Au micro-bump bonding technology

Abstract

Currently, due to their cost-effectiveness and excellent physical properties, indium and tin are frequently utilized as bump materials for micro-light emitting diodes (Micro-LEDs) and silicon complementary metal–oxide–semiconductor (CMOS) devices to realize flip-chip bonding technology. However, as micro-LED pixel sizes and spacings decrease, forming indium and tin bumps that meet bonding requirements becomes challenging. These bumps are difficult to form an ideal spherical shape in the reflow process and easy to cause interconnection problems between adjacent pixels, adversely affecting device performance. To address this, we propose a novel Au-Au bump technology for micro-LED flip-chip bonding. This technology aims to effectively avoid interconnection issues while simplifying the micro-LED process flow and reducing production costs. Therefore, this paper designed a micro-LED device with 2822 PPI, 640 × 360 resolution, and 9 μm pixel pitch to verify the feasibility of Au-Au micro-bump bonding. During this process, Au bump with diameter of 3.9 μm and 6.5 μm were fabricated for micro-LED array and CMOS driver chip respectively, followed by integrating them using the flip-chip bonding process. Cross-sectional analysis confirmed the high reliability and stability of the Au-Au connection, enabling the micro-LED device to function properly. Furthermore, the Au bump micro-LED exhibits greater electroluminescence (EL) intensity and brightness than the In bump micro-LED, potentially due to the optical losses incurred during the preparation of indium bumps within the micro-LED chip.