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 (ΔVth) 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 ΔVth 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.
Highlights
As described above, PI is mainly used as a substrate for flexible displays, and to investigate whether the properties of display substrates have a distinguishable effect on the V th shift anomaly in the thin-film transistor (TFT), we manufactured and analyzed devices and products fabricated on PI substrates for three different curing temperatures (260 °C, 360 °C, and 460 °C)
This is further clarified in this study as the results indicate the active hole carriers in the amorphous indium gallium zinc oxide (a-IGZO) film are trapped in the barrier layer because the electric field induced by the accumulated F− at the PI and barrier interface is greater than the negative field applied to the TFT gate
Physical property analysis and electrical analysis were conducted by varying the curing temperature of PI, which is used as a substrate for flexible displays
Summary
PI is mainly used as a substrate for flexible displays, and to investigate whether the properties of display substrates have a distinguishable effect on the V th shift anomaly in the TFTs, we manufactured and analyzed devices and products fabricated on PI substrates for three different curing temperatures (260 °C, 360 °C, and 460 °C). Through secondary-ion mass spectrometry (SIMS) analysis of MIM capacitors before and after NBTS, we confirmed that the cause of the abnormal Vth shift lies in the increasing amount of F − accumulating in the upper part of PI as the curing temperature increases. Image sticking evaluation was carried out with actual display panels to investigate the effect of PI curing temperature on product-level display panels. We confirmed that the curing temperature of PI is correlated with the image sticking issue and investigated the cause of this relationship through chemical, electrical, and physical analysis methods
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