Wafer-Scale Micro-LEDs Transferred onto an Adhesive Film for Planar and Flexible Displays

The development of micro-sized light emitting diode (LED) displays has driven the research of micro-LED mass-transfer technology. To date, various transfer technologies are proposed, but ample room for improvements in the transfer yield and transfer accuracy still remains. Furthermore, whether these techniques are suited for the subsequent bonding process is not well investigated, which is essential for achieving a good electric connection between micro-LEDs and driver electronics. Here a systematical solution, termed as tape-assisted laser transfer, which is not only suited for high-yield micro-LED transfer but also well compatible with subsequent bonding process, is developed. Using a low-cost adhesive tape as the support substrate, the method allows fast and wafer-level transfer of micro-LED with extremely high yield (approximate to 99.8%) and minimized transfer displacement (<0.5 mu m), based on a laser lift-off (LLO) process. Combined with a shadow mask, the LLO process also allows the selective transfer of micro-LED to the tape. Such thin film micro-LEDs are well compatible with the subsequent bumpless bonding process using low-melting point solder. Representative display devices including planar display and deformable display are further developed, suggesting the method has a good potential for developing high-resolution micro-LED display panels for the applications in VR/AR, wearables, and smart glasses.