Wafer‐Scale Micro‐LEDs Transferred onto an Adhesive Film for Planar and Flexible Displays. Issue 12 (18th August 2020) - Pan, Zhangxu
Abstract: 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 (≈99.8%) and minimized transfer displacement (<0.5 µm), 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. Abstract : Wafer‐level micro‐sized light emitting diodes (LEDs) on an adhesive film are fabricated using a tape‐assisted laser lift‐off technique. Such thin‐film micro‐LEDs can be readily integrated onto the backplane using a bumpless bonding process. Representative planar display or flexible display devices are demonstrated, showing the potential for high‐resolution microdisplays.