Laser-Assisted Mass Transfer Technology for Microlight-Emitting Diodes

Abstract Microlight-emitting diodes (MicroLEDs), as a next-generation inorganic self-emissive display technology, offer high contrast, low power consumption, longevity, and excellent brightness stability by miniaturizing traditional light-emitting diode pixels to micrometer scales and achieving high integration. These advantages make them ideal candidates for ultra-high-definition large displays, augmented and virtual reality, and smart wearable devices. However, their large-scale manufacturing faces the core challenge of mass transfer: the efficient and precise transfer of millions of micrometer-sized chips onto a driving substrate. To overcome this challenge, this review is aimed at summarizing recent advancements in laser lift-off (LLO) and laser-assisted mass transfer technologies, which are crucial for improving MicroLED manufacturing throughput and yield, emphasizing the underlying mechanisms, process optimization strategies, and scalability. The role of patterned sapphire substrates in improving chip quality and light-extraction efficiency after separation is first explored, and several laser-assisted mass transfer techniques are summarily compared. Thereafter, the influences of laser parameters (e.g., wavelength, pulse width, and energy distribution) and structural optimizations (e.g., support and sacrificial layers) on lift-off performance are examined from the LLO perspective. Additionally, key strategies for mitigating thermal damage and residual stress are discussed. The principles and process-optimization strategies (e.g., energy modulation and interfacial-adhesion switching) of three key laser-assisted mass transfer techniques (direct ablation laser-induced forward transfer (LIFT), blister-based LIFT, and laser-assisted stamp transfer) are comprehensively analyzed to identify their critical challenges, including shock waves, residues, and narrow process windows. Additionally, parallel transfer schemes, such as solid-state laser beam splitting and excimer laser mask projection, are introduced, thereby highlighting the mechanism by which optical field modulation enables high-precision, high-throughput transfer. Finally, current technical challenges, including thermal management, cost control, and yield improvement, are summarized, and future directions in optical path design, material engineering, and system-level integration are examined, providing valuable insights for the industrialization of MicroLED technology.