Title :
Lifetime Amelioration for an AMOLED Pixel Circuit by Using a Novel AC Driving Scheme
Author :
Lin, Chih-Lung ; Chou, Kuan-Wen ; Hung, Chia-Che ; Tu, Chun-Da
Author_Institution :
Dept. of Electr. Eng., Nat. Cheng Kung Univ., Tainan, Taiwan
Abstract :
This paper describes how a reversed-bias voltage affects organic light-emitting diodes (OLEDs) with green emitting Alq3:C545T (40 nm). The luminance efficiency and the active area of the test OLED devices are 8-11 cd/A and 2.5 mm × 2.5 mm, respectively. The OLED lifetime under an ac driving scheme can be apparently improved, in contrast with that under a dc driving scheme. Experimental results indicate that adjusting the duty ratio of the ac driving scheme can ameliorate the brightness uniformity; meanwhile, the normalized luminance of a 20% duty ratio after a 3600-s stress is 94.3%, and that of dc stress is 76.4%. Therefore, a novel pixel circuit with three p-type thin-film transistors (TFTs) for an active-matrix OLED application is proposed to ameliorate the brightness uniformity. Variations of the threshold voltage of the driving TFT are compensated for, and the performance and lifetime of the OLED are improved by using an ac driving method. Simulation results indicate that the output current is almost constant over the data range. Furthermore, the current error rate of the proposed pixel circuit is less than 6.5%.
Keywords :
brightness; driver circuits; organic light emitting diodes; thin film transistors; AC driving scheme; AMOLED pixel circuit; OLED lifetime amelioration; TFT; active-matrix OLED application; brightness; duty ratio; green light emission; luminance efficiency; organic light emitting diode; p-type thin film transistor; reversed-bias voltage affect; threshold voltage; Brightness; Current measurement; Degradation; Organic light emitting diodes; Pixel; Thin film transistors; Voltage measurement; AC driving method; OLED degradation; active-matrix organic light-emitting diode (AMOLED); aperture ratio; threshold voltage;
Journal_Title :
Electron Devices, IEEE Transactions on
DOI :
10.1109/TED.2011.2151862