A case study: dynamic behavior of a typical Micro-LED chips during laser induced forward transfer process

In Laser Induced Forward Transfer (LIFT) technology, low transfer yield of micrometer-scale chips, especially with tens of millions, limits Micro-LED large-scale use. Many studies explore LIFT process parameters, but few examine the chip descent process. We analyze this process and find a neglected issue: during LIFT transfer of commercial Micro-LED chips, chips rotate after release from the donor substrate, reducing yield. Our analysis reveals the cause: asymmetric geometry and uneven mass distribution in these chips misalign the geometric center and center of mass, creating torque that drives unavoidable rotation and lowers yield. We propose a fix: adjusting laser fluence and transfer distance, key LIFT parameters, to control chip rotation and improve yield. Tests show slow, manageable rotation at 70mJ/cm² fluence and under 100 μm distance. Beyond 100 μm at this fluence, rotation speeds up to 1.2°/μm, raising failure risk. Higher fluence and distance increase rotation, peaking at 2.5°/μm. Optimal parameters for these uneven chips are 70–75mJ laser energy and 80–100 μm transfer distance, achieving industry-standard yields. Our work bridges a gap in prior LIFT process research, explaining why shorter transfer distances improve yield, unresolved in prior studies.