Theoretical and experimental studies of laser lift-off of nonwrinkled ultrathin polyimide film for flexible electronics

This paper theoretically and experimentally studies an innovative laser lift-off (LLO) technique that utilizes a line-shaped laser to scan the interfacial polyimide (PI) film through the transparent substrate to peel off the thin-film electronics. A comprehensive illustration of the mechanism of the occurrence of wrinkles in ultrathin PI films is provided, based on which the LLO process for ultrathin flexible electronics is optimized. A mechanical model is established to describe the deformation of the laser-induced blister and validated by experimental results. The results show that the wrinkles are due to the plastic deformation inside the film, which is caused by the instantaneous pressure of gas products generated by laser ablation. By measuring the instantaneous pressure through piezoelectric sensors, the maximum allowable laser fluence without inducing plastic deformation has been found, which decreases linearly with the film thickness. Accordingly, the process window of the traditional single-pass LLO has been obtained, which confirms that the wrinkles in ultrathin PI films (<5 μm) are inevitable through traditional LLO process. To obtain non-wrinkled ultrathin films, two optimization approaches are proposed, which are also verified through the tests of strain sensors.