用以改善劣化之新式有機發光二極體驅動電路

Abstract

有機發光二極體(OLED)被視為繼液晶顯視器(LCD)後，未來最具發展潛力的平面顯示技術之ㄧ。然而，目前無法投入大量的應用其主要原因在於面板均勻度無法提升以及元件劣化等問題，前者原因為負責驅動之薄膜電晶體(TFT)電路特性會隨著長時間的驅動而有不同程度的飄移，後者為OLED在固定電流密度通過下產生之元件劣化效應。本論文將在電流鏡補償以克服TFT特性飄移的基礎下，設計以脈寬調變(PWM)原理來達到降低電流密度以改善劣化並同時具補償面板均勻度之主動式有機發光二極體驅動電路。此外，將針對面板灰階在傳統電流鏡補償電路上之電流源驅動訊號不易設計之缺點，改以正統之電壓訊號驅動以達到降低面板外部系統電路複雜度之功用。最終以低溫多晶矽薄膜電晶體(LTPS-TFT)作為模擬之基準，驗證本論文設計之電路特性，並以國家晶片研究中心之台積電TSMC 0.35um 製程之積體電路(IC)來量測並驗證改善OLED劣化程度之理論。

Organic light-emitting diode (OLED) displays have been as the ideal displays for next generation after liquid crystal display (LCD). However, OLED has two problems --- the characteristic shifts of thin film transistor (TFT) and lifetime degradation due to the two factors, the TFT stress from continuous bias and the heavy current density through OLED. To alleviate the problems, a pixel is designed with six TFTs and one capacitor is proposed in this study based on the topology of a current-mode drive circuit. This circuit employs the approach of Plus Width Modulation (PWM) to not only compensate TFT characteristic shifts but also to extend OLED lifetime. The electronic dynamics of the proposed circuit is next analyzed to find the conversion factor from input data voltage to displayed grey level of the OLED, which ought to be capable of displaying 256 gray levels. The designed circuit is simulated by HSPICE software to validate the predicted performance. In addition, the proposed pixel drive circuit is implemented by the process technology of TSMC 0.35um 2P4M CMOS integrated circuits. This realistic circuit is used to drive a 0.09 cm2 OLED panel for performance tests. The test results demonstrate a strong correlation to simulations and show superior performance for alleviate AMOLED degradation.