Researchers from Fuzhou University, in collaboration with researchers from Sweden's Chalmers University of Technology, report on improvement in laser lift off (LLO) process for mass transfer of microLED chips, finding the optimal conditions for successful processes - both the LLO itself and the preparatory process.
The researchers started by studying current LLO processes, and identifying the issues of chip damage and missing LEDs during the laser transfer process. The researchers then analyzed the underlying causes of these problems, and continued to discover the optimal process conditions.
The researchers say that the chip retention rate is at its highest when the energy density of the controlled laser lift-off is within the range of 1200-1500 mJ/cm2. Additionally, the secondary transfer yield was 100 % when the energy density of the laser transfer and the depth of the chip subsidence satisfied empirical relationship, and the laser spot size was 30 μm × 38 μm.
