Threshold voltage instability and polyimide charging effects of LTPS TFTs for flexible displays
Hyojung Kim, Jongwoo Park, Taeyoung Khim, Sora Bak, Jang‐Kun Song, Byoungdeog Choi
Abstract
Abstract In this paper, we investigate the V th shift of p-type LTPS TFTs fabricated on a polyimide (PI) and glass substrate considering charging phenomena. The V th of the LTPS TFTs with a PI substrate positively shift after a bias temperature stress test. However, the V th with a glass substrate rarely changed even with increasing stress. Such a positive V th shift results from the negative charging of fluorine stemmed from the PI under the gate bias. In fact, the C–V characterization on the metal–insulator-metal capacitor reveals that charging at the SiO 2 /PI interface depends on the applied gate bias and the PI material, which agrees well with the TCAD simulation and SIMS analyses. As a result, the charging at the SiO 2 /PI interface contributes to the V th shift of the LTPS TFTs leading to image sticking.