Analysis of Recoverable Residual Image Characteristics of Flexible Organic Light-Emitting Diode Displays Using Polyimide Substrates

• Published in: IEEE electron device letters 2019-07, Vol.40 (7), p.1108-1111
• Main Authors: Hwang, Han Wook, Hong, Seonghwan, Hwang, Sang Soo, Kim, Ki Woo, Ha, Yong Min, Kim, Hyun Jae
• Format: Article
• Language: English
• Subjects: Brightness; CAD; Charge distribution; Computer aided design; Computer simulation; Displays; Electric fields; Flat panel displays; Glass substrates; Hysteresis; Light emitting diodes; Logic gates; low-temperature polycrystalline silicon (LTPS); Organic light emitting diodes; organic light-emitting diode (OLED); polyimide; Polyimides; recoverable residual image; Semiconductor devices; Substrates; Thin film transistors
• ISSN: 0741-3106; 1558-0563
• DOI: 10.1109/LED.2019.2914142

Recoverable residual image characteristics for n- and p-type low-temperature polycrystalline silicon (LTPS) thin-film transistor (TFT)-based organic light-emitting diode (OLED) displays using polyimide substrates were investigated. Unlike OLED displays using glass substrates, the n-type LTPS TFT-based OLED displays using a polyimide substrate showed inferior recoverable residual image characteristics compared to the p-type LTPS TFT-based OLED displays. By the analysis of the brightness relaxation characteristics of the residual image and technology computer-aided design (TCAD) simulations, an additional explanation for the recoverable residual image, related to the substrate, was identified. In the polyimide substrate, internal electric fields vary depending on the operation of the driving TFTs. Particularly, in the n-type LTPS driving TFTs, the direction of electric fields changes dramatically with brightness conditions. This can result in a drastic variation in charge behavior inside the polyimide substrate. Consequently, we found that when using a polyimide substrate rather than a glass substrate, the recoverable residual image characteristics of the OLED displays arise due to both the hysteresis characteristics of the LTPS TFTs and the charge generation and distribution in the polyimide substrate.