Active-matrix TFT driven GaN blue Micro-LED display realized with electroplated copper-tin-silver micro bumps-based bonding structure

Abstract

With the rapid advancement of display and smart lighting technologies, micro-light-emitting diodes (Micro-LEDs) have garnered substantial attention due to their exceptional performance characteristics. However, a significant challenge persists in achieving reliable interconnections between Micro-LED chips and driver backplanes. This article proposes and implements the Double-Layer Photoresist Structure Electroplating (DPSE) technique for fabricating Cu-SnAg metal bumps, thereby facilitating the heterogeneous integration of oxide thin film transistors (TFTs) with GaN-based blue LEDs. The DPSE process was optimized by addressing several critical factors, including the correlation between bump height and electroplating time, the occurrence of cracks in the photoresist surface, and the removal of the conductive layer. Metal bumps were successfully fabricated on TFT backplanes with dimensions of 16.5 μm × 10 μm, an average height of 5.39 μm, and a uniformity of approximately 2.266%. To demonstrate the efficacy of this approach, a 0.495-inch blue active-matrix Micro-LED display was designed and fabricated. This display features a mesa size of 15 µm × 30 µm, a pixel pitch of 222 µm, and a pixel density of 114 pixels per inch (PPI). The resultant blue Micro-LED display exhibits excellent optical characteristics, achieving a brightness of 1625 cd/m² (nits). It is anticipated that the methodology and findings presented in this study will contribute significantly to the advancement of Micro-LED display technology in consumer electronics. This research not only represents a significant advancement in the field of Micro-LED display technology, but also paves the way for future innovations in high-resolution, energy-efficient display systems.