ITO-Ag-ITO Annealing Effects During Delamination of Flexible Colorless Polyimide Substrates by Xenon Flash Lamp for Flexible Displays

In fabrication of high resolution flexible display or various wearable electronic devices, polyimide(PI) has been coated and cured as a substrate on carrier glass and active devices such as thin film transistors(TFTs) have been realized using deposition of channel material, laser annealing, and photolithography. After encapsulation process, for a separation of flexible substrates from carrier glass, an excimer laser has been used as a method of lift-off. Although laser lift-off shows an effective delamination process using differences of thermal resistance between PI substrate and mother glass, it is difficult to optimize the excimer laser beam parameters such as wavelength and fluence for the complete release of PI substrate from carrier glass. Most of all, the expense lift-off process time by laser line scanning is proportional to scanning area and it takes a long time for a large sized display.
Recently, a xenon(Xe) flash lamp has been applied to the lift-off process of flexible substrate from carrier glass for the realization of high throughput delamination. When a Xe light was irradiated on a sacrificial layer between PI substrate and carrier glass, the irradiated light energy is converted into thermal energy in the sacrificial layer and PI substrate is released from sacrificial layer and carrier glass. The non-laser lift-off process has been also used in the debonding process in semiconductor packaging.
In this study, using the converted thermal energy resulted from the irradiated Xe light, indium tin oxide(ITO)-Ag-ITO thin films sputtered on the colorless polyimide(CPI) substrates were annealed simultaneously when the CPI substrates were released from sacrificial layers and carrier glasses by Xe flash lamp. From our previous research results, the annealing effect of Xe flash lamp on ITO-Ag-ITO was substantiated. Before 40 mm CPI was formed on carrier glass by coating and curing, molybdenum(Mo) was sputtered on cover glass as a sacrificial layer. When PulseForge 1300 (PulseForge Corporation) was used for the irradiation from Xe flash lamp, the CPI was completely released from carrier glass at a pulse length of 110 ms or above (3.11 J/cm). To block excess thermal energy on the embedded Ag layer in ITO-Ag-ITO structure, an intrinsic zinc oxide(i-ZnO) was added between CPI substrate and ITO-Ag-ITO layer and no damages on CPI was investigated. ITO-Ag-ITO layers on CPI substrates showed advanced smaller sheet resistances after the lift-off process by Xe flash lamp. The optimized process condition of Xe flash lamp and the ITO-Ag-ITO-i-ZnO structure was confirmed using thermal simulation.

Acknowledgement : The Xe-FLA process was operated with the help of Hanseul Kim, Minyoung Lee, and Jaerin Kim from the Pulse Forge Corporation.

[1] R. Delmdahl, M, Fricke, and B. Fechner, J. Information Display, 2013
[2] S. L. Lee, S. H. Jang, Y. J. Han, J. y. Lee, J. Choi, and K. H. Cho, Micromachines, 2020
[3] Z. Zhao, A. Rose, S. J. Kwon, Y. Jeon, and E.-S. Cho, Scientific Reports, 2023