Micro-LED displays offer exceptional performance, but key technological breakthroughs are still required. One of the critical challenges is the detachment of epitaxial substrates. Micro-LED chips, based on GaN (gallium nitride) light-emitting materials, typically use sapphire substrates due to their low lattice mismatch with GaN and low cost. However, . Furthermore, the brittleness of sapphire makes it unsuitable for flexible displays. Given the high resolution, brightness, and contrast of Micro-LEDs, the laser lift-off (LLO) process to detach sapphire substrates is essential. This technology amplifies the advantages of Micro-LEDs and is crucial for their development.
01 Selective Laser Lift-Off Technology (SLLO)
Compared to OLED technology widely used in flexible displays, Micro-LED offers a broader color gamut, higher brightness, lower power consumption, and better environmental stability—making its technological advantages and potential improvements evident. Traditional laser lift-off (LLO) methods typically employ linear or rectangular beam shapes, which are inadequate for precisely transferring or lifting micron-scale Micro-LED particles. Selective Laser Lift-Off (SLLO) technology, however, focuses on precision. It adjusts the spot size based on the size of the device or region being lifted.
Key to advancing SLLO is controlling laser energy input and adding an appropriate sacrificial layer. Although still in the early stages of development, SLLO’s precision in transferring small device units and arrays makes it highly promising for use in large-scale integrated circuits and chip manufacturing.
02 Laser-Induced Forward Transfer (LIFT) Technology
Laser-Induced Forward Transfer (LIFT) technology works by using a laser pulse to irradiate the thin-film absorption layer on a transparent substrate. The absorbed layer is then melted, and a jet of material is ejected to transfer the functional layer.
Unlike traditional LLO, which avoids using high-viscosity materials, LIFT exploits the dynamic power of the ablated molten layer, making it ideal for transferring high-viscosity materials. Compared to conventional LLO, LIFT offers more precise transfer selection and is particularly effective for transferring small-sized polymer patterns and microstructures. Additionally, LIFT requires far less laser energy—typically one-twentieth to one-fifth of the energy required by LLO—resulting in significantly less damage to the material being lifted.
03 Ultra-Fast Laser Lift-Off Technology
Currently, the mainstream laser lift-off techniques use excimer nanosecond pulsed lasers, whose primary stripping mechanism involves thermal effects. This can cause damage through uneven energy distribution, unstable scanning, and thermal stress during laser irradiation. To address these thermal damage issues, researchers have proposed the use of ultra-fast lasers with pulse widths of less than 10-11 seconds, which possess “cold” processing characteristics.
Researchers from Beijing University of Technology, led by Dr. Ji Lingfei, have been investigating the feasibility and mechanism of applying ultra-fast lasers to LLO technology. Their studies suggest that while cumulative thermal effects from ultra-fast laser pulses persist, moderate thermal effects can actually improve the detachment efficiency. This is because these effects help to accelerate material vaporization and the formation of high-density plasma, which absorbs the laser energy more effectively than the medium. The high-density plasma absorbs the laser energy more efficiently, preventing the functional layer from absorbing excessive energy and concentrating it into nanometer-scale areas.
Ultra-fast laser detachment technology offers advantages of high efficiency, zero damage, and high selectivity. It is expected to become a key breakthrough in overcoming the bottlenecks of flexible electronics and large-scale Micro-LED transfer and assembly.
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