LCD面板TFT特性相关残像研究

Influence of TFT character on LCD image sticking

残像是影响TFT-LCD画面品质的重要因素,也是发生原因最为复杂的一种不良。本论文提出了一种定量测量残像水平的方法,同时对TFT特性引起的残像不良进行了实验研究,得到了由TFT特性引起的交流(AC)残像发生规律及发生机理。本文通过对比研究残像画面黑白格亮度与TFT漏电流变化曲线,同时结合像素充放电计算公式进行电压差模拟,发现黑白格像素放电差异导致的像素保持电位差异(ΔV>12.5mV)是发生残像的根本原因。根据以上机理,本论文提出了两种方法改善此类残像。第一种是通过改善TFT a-Si成膜工艺减小漏电流(<50pA),同时提升TFT特性的稳定性,可以减小棋盘格画面残像评价导致的TFT转移特性曲线偏移;第二种是通过改变栅压低电平,避开关态时不同显示区域的TFT漏电流差异峰值;以上两种方法均可以有效改善残像(ΔL<0.5cd/m^2)。

Image sticking(I.S.)is a main factor that lowers the display quality in TFT-LCD,and it is also the most complicated issue that occurred on LC display.In this study,measuring method of I.S.level is proposed,and experiments are performed to find the relationship between image sticking and TFT transfer curve.The feature of AC image sticking is discovered,and the mechanism of the image sticking is obtained.By analyzing the luminance and TFT I off(Leakage current at TFT off state)on white(W)and black(B)area at chessboard image and comparing the simulation results,we find that the recharging difference of pixels on W and B area,which can be result in different pixel holding voltage(ΔV>12.5 mV),is responsible for image sticking.Based on this mechanism,we introduced two methods to improve image sticking.One way is to lower the TFT I off(<50 pA)and stabilize the TFT character during a-Si formation process,which can effectively decrease the shift of TFT transfer curve during the I.S.image aging.Another way is to adjust the gate low voltage(VGL)to a proper value that can deviate from the peak ofΔI off curve of W and B area.This two methods is proved to solve the AC image sticking effectively(ΔL<0.5 cd/m 2).