Full-color high brightness Micro-LED displays with high bonding yield realized via photosensitive conductive polymeric bumps

Micro light-emitting diode (Micro-LED) display technology is regarded as a promising next-generation display technology due to its advantages of high brightness, high contrast, low power consumption, long life, and fast response. However, with the aggressive downscaling of Micro-LED size to only a few microns, when the pixel density is high, the lift-off fabrication of metal bumps used as the soldered joints between the Micro-LEDs and the driver substrate becomes increasingly difficult. Therefore, achieving a high-yield bump array becomes challenging under high-density conditions. In this study, we innovatively use a photosensitive conductive polymer (PCP) to replace conventional metal bumps, serving as a new bonding material between Micro-LEDs and the driving substrate, which can be used to fabricate polymeric micro-bump arrays through well-established photolithography, elegantly bypassing the complex lift-off process in the preparation of traditional metal bumps, and yet keeping a low risk of short circuits. We innovatively use isopropyl alcohol to regulate the wettability of the developer to obtain the best development effect and prepare bump arrays with a bump size of 20 µm × 12 µm and a height of (1.9288 ± 0.0213) µm on thin-film transistor drivers (TFTs) with a yield of over 99.99%. In addition, we successfully resolved the issue of low bonding yield resulting from polydimethylsiloxane (PDMS) thermal expansion, achieving a bonding yield exceeding 99.8%, and a 0.99-inch full-color Micro-LED display with a density of 114 pixels per inch (PPI) and a display brightness of 5537 cd/m² was successfully prepared. It is noteworthy that the high-yield bump arrays and Micro-LED arrays, as well as their high bonding yield, are highly reproducible, which can promote the development of Micro-LED displays and related fields.