Effects of polyimide curing on image sticking behaviors of flexible displays

Hyojung Kim; Jongwoo Park; Sora Bak; Jungmin Park; Changwoo Byun; Changyong Oh; Bo Sung Kim; Chanhee Han; Jongmin Yoo; Dongbhin Kim; Jangkun Song; Pyungho Choi; Byoungdeog Choi

doi:10.1038/s41598-021-01364-6

Effects of polyimide curing on image sticking behaviors of flexible displays

Sci Rep. 2021 Nov 8;11(1):21805. doi: 10.1038/s41598-021-01364-6.

Authors

Hyojung Kim^{1

2}, Jongwoo Park¹, Sora Bak¹, Jungmin Park², Changwoo Byun³, Changyong Oh⁴, Bo Sung Kim⁴, Chanhee Han⁵, Jongmin Yoo⁵, Dongbhin Kim⁵, Jangkun Song⁵, Pyungho Choi⁵, Byoungdeog Choi⁶

Affiliations

¹ Technology Reliability Team, OLED Business, Samsung Display Co., Ltd., Asan, South Korea.
² Department of Semiconductor and Display Engineering, Sungkyunkwan University, Suwon, South Korea.
³ Research Center for Materials, Components and Equipment, Advanced Institutes of Convergence Technology (AICT), Seoul National University, Suwon, South Korea.
⁴ Department of Applied Physics, Korea University, Sejong, South Korea.
⁵ Department of Electrical and Computer Engineering, Sungkyunkwan University, Suwon, South Korea.
⁶ Department of Electrical and Computer Engineering, Sungkyunkwan University, Suwon, South Korea. bdchoi@skku.edu.

Abstract

Flexible displays on a polyimide (PI) substrate are widely regarded as a promising next-generation display technology due to their versatility in various applications. Among other bendable materials used as display panel substrates, PI is especially suitable for flexible displays for its high glass transition temperature and low coefficient of thermal expansion. PI cured under various temperatures (260 °C, 360 °C, and 460 °C) was implemented in metal-insulator-metal (MIM) capacitors, amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFT), and actual display panels to analyze device stability and panel product characteristics. Through electrical analysis of the MIM capacitor, it was confirmed that the charging effect in the PI substrates intensified as the PI curing temperature increased. The threshold voltage shift (ΔV_th) of the samples was found to increase with rising curing temperature under negative bias temperature stress (NBTS) due to the charging effect. Our analyses also show that increasing ΔV_th exacerbates the image sticking phenomenon observed in display panels. These findings ultimately present a direct correlation between the curing temperature of polyimide substrates and the panel image sticking phenomenon, which could provide an insight into the improvement of future PI-substrate-based displays.