基于ZnO基TFT的AMOLED像素电路研究

Active matrix organic light-emitting diode (AMOLED) displays have gained considerable interest in flat panel displays due to the advantages including high brightness, wide viewing angle, low power consumption and fast response time.The TFT backplane is the key technology of AMOLED display. Until now, the types of thin-film transistors can be applied in AMOLED panel are hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs), Low-temperature polycrystalline-silicon thin-film transistors (LTPS TFTs) and ZnO-based TFTs. A-Si:H TFTs are not very suitable for AMOLED displays due to their low mobility. LTPS TFTs have large mobility,while the crystallization process is complicated. ZnO-based TFTs are hopeful to be TFTs of the next generation due to its larger mobility than that of a-Si:H TFTs and simpler fabrication process than that of LTPS TFTs. .The well-known two-TFTs one-Capacitor (2T1C) pixel circuit is not suitable for AMOLED displays because the OLED current is nonuniform due to the threshold voltage shift of TFTs. On the other hand, when a certain data voltage is input to the 2T1C pixel circuit, the OLED current will decrease with the increase of its anode potential because the threshold voltage of OLED degrades during operation. So the anode potential of OLED should be considered in the design of AMOLED pixel circuit. Therefore, how to compensate for the threshold voltage shift and OLED degradation for enhancing the uniformity of AMOLED displays is a key scientific issue. .We have developed a new voltage-programmed pixel circuit (5T2C) for AMOLED displays, which can effectively compensate for the threshold voltage shift of the driving TFT and the OLED degradation. And thus the brightness uniformity of AMOLED displays can be enhanced. It's shown that the lifetime of an OLED will be prolonged by an ac driving wave form to alleviate the space charge accumulation in the electroluminescent (EL) layers. We have also developed an ac driving pixel circuit (4T1C), which can not only make OLED work at the ac driving mode, but also effectively compensate for the threshold-voltage shift of the driving TFT and the degradation of OLED..In this project, we plan to improve the speed of the threshold voltage detection and the lifetime of OLED by some new technologies, such as external compensation, precharging method, parrellel addressing scheme and AC driving. A 5-inch 320*240 green AMOLED panel will be fabricated by the advanced ZnO-based TFTs backplane technology at the institute of new diplay technology (South China Univ.of Tech.) to verify the new pixel circuits. Where the frame frequency is 60Hz, the uniformity of display is more than 90%, the aperture ratio is more than 30% and the maxim luminance is larger than 200 cd/m^2.

有源矩阵有机发光二极管显示器（AMOLED）是全固态工艺，具有体积小，自主发光、可视角度大、响应时间短，低功耗等优点，是学术界和产业界的研究热点。如何通过像素电路设计补偿TFT阈值电压漂移和OLED开启电压退化从而提高AMOLED显示均匀性是亟待解决的关键科学问题。本项目在前期研究基础上，计划融合外围驱动电路补偿、预充电、流水线或交流驱动等技术，提高TFT阈值电压锁存速度并延长OLED的工作寿命，争取达到实用化的水平。结合像素电路研究成果，依托华南理工大学新型显示技术研究院国内领先的ZnO 基TFT背板工艺在200mm*200mm玻璃基板上制备5英寸 320*240 AMOLED 绿色屏进行实验验证。其技术指标：显示帧频60Hz，显示均匀性达90％以上，开口率 30％以上，最大亮度 200cd/m^2。

有源矩阵有机发光二极管显示器（AMOLED）是全固态工艺，具有体积小，自主发光、可视角度大、响应时间短，低功耗等优点，是学术界和产业界的研究热点。如何通过像素电路设计补偿TFT阈值电压漂移和OLED开启电压退化从而提高AMOLED显示均匀性是亟待解决的关键科学问题。本项目的主要研究内容是： 1.ZnO 基TFT和OLED的模型参数提取，2.新型AMOLED像素电路研究，3.像素电路的优化。 . 项目执行期间，取得一些创新性成果，阐述如下。 .1..利用电容耦合效应，发展阈值电压一次锁存的补偿像素电路高速驱动方法，.成果发表在IEEE Electron Device Letters。 在此基础上，提出一种高速低功耗阵列编程方法，该方法集成一次锁存和流水线编程的优点，其编程速度可接近传统的2T1C电路，编程功耗比传统的流水线编程方式低许多，尤其在高分辨率显示上更有优势。该编程方法已获中国发明专利授权。 .2．我们设计了既可实现OLED的交流驱动又可补偿TFT阈值电压漂移和OLED退化的AMOLED像素电路。该像素电路有一个明显的优点：OLED的交流驱动时序同补偿时序是完全复用的。针对金属氧化物TFT阈值电压在零附近这一个特性设计了一个新型像素电路，该像素电路不仅能够补偿正的阈值电压，还能补偿其负的阈值电压。我们也开发出面向低温多晶硅背板技术应用的全P型TFT 补偿像素电路。这些成果发表在Journal of the SID、Journal of Display Technology、Dislays等国际显示类学术期刊上。 .3．我们开展了基于ZnO基TFT的行驱动集成研究，研究设计多个新型TFT行驱动电路拓扑，其具有高速、低功耗、适用于高分辨率显示等特点，成果发表在IEEE Transaction on Electrons Devices等学术期刊上。