High-Yield and High-Accuracy Mass Transfer of Full-Color Micro-LEDs Using a Blister-Type Dynamic Release Polymer

Micro light-emitting diode (Micro-LED) is widely regarded as a highly promising technology in the current display field due to its excellent performance, but the core issue hindering the further development of Micro-LED is how to achieve high-precision and high-yield transfer. In this study, laser-induced forward transfer (LIFT) is adopted as the main technique, and a novel blister-type dynamic release layer (DRL) material is selected, characterized by a gentle transfer process and minimal residue on the chip after transfer. Chip-on-wafer (COW) is a structure that fabricates a large number of Micro-LEDs (15 × 30 μm²) on a sapphire substrate. The COW-on-head (COH) chip bonding method can control the uniformity of the overall chip height before transfer within 3.5%, which is favorable for subsequent stable transfer. Based on the analysis of the close relationship between the transfer gap and laser energy density, this study successfully achieved the transfer of red/green/blue (R/G/B) Micro-LED chips (6400, respectively) onto the corresponding chip-on-carrier 2 (COC-2), and all of them have achieved a one-step transfer yield of over 99.3% and an average chip transfer offset of 2 μm or less. It is worth mentioning that the one-step transfer yield mentioned in this paper is different from the yield after testing and repairing the chips. The one-step transfer yield can fully reflect the transfer quality. In order to verify the validity of this study, a 1 in., full-color, active Micro-LED display with a pixel size of 114 pixels per inch (PPI) and a display brightness of 5598 cd/m² was successfully fabricated. This study proposes an optimized solution for Micro-LED transfer technology, which will help accelerate the mass production and marketization of Micro-LED.