应用于AMOLED像素驱动电路中的多晶硅薄膜晶体管的退化机理研究

Active matrix organic light-emitting diode (AMOLED) display has become the key technology for the next-generation display. Ultra-high resolution and system on panel are the tendency of the next-generation flat-panel display. To fulfill the above requirements, polycrystalline silicon (poly-Si) technology, which has always been a hot research hotspot from academia to industry, become a top contender. The reliability of poly-Si thin film transistors (TFTs) has been extensively investigated for several years. However, the stress conditions depicted in those research works are far from the practical operation conditions in the pixel driver circuits. In this project, the degradation mechanisms of poly-Si TFTs in pixel driver circuits of AMOLED display will be systematically investigated. First, the working conditions of different poly-Si TFTs in pixel driver circuits of AMOLED display will be analyzed and the various simulated stress conditions, which are based on the real working conditions, will be proposed. Then, the degradation behaviors of poly-Si TFTs under different practical stresses will be fully studied. At the same time, the static/transition simulations for different stress conditions using commercial software will be performed. Next, based on degradation behaviors and simulations, the degradation mechanism will be elucidated and the physical degradation model will be developed. At last, from the degradation mechanisms, several methods, such as improved fabrication process and modified device structures, will be proposed to suppress such pixel-stress-induced degradation. The implementation and outcome of this project will offer a more precise model for prediction of pixel device life time in AMOLED displays, will provide direct and significant reference for pixel circuit designers, and will give a deeper insight into the reliability of poly-Si TFTs.

有源矩阵有机发光二极管显示（AMOLED）已经成为下一代显示的核心技术。超高清和片上系统将是下一代平板显示的主流趋势。多晶硅技术可为实现上述要求提供解决方案。虽然对多晶硅薄晶体管（TFT）的可靠性进行了广泛的研究，但其相关应力条件与TFT在像素驱动电路中的实际工作状态仍有区别。本项目将系统研究多晶硅TFT在AMOLED像素驱动电路工作中的退化机理。首先通过分析AMOLED像素驱动电路中的器件工作状态，提取相应的应力模拟条件；然后系统地研究对应应力条件下的多晶硅TFT的退化行为；结合相关的静态瞬态模拟，澄清退化机理并建立物理退化模型；最后通过改善制程工艺和改造器件结构来抑制相关的退化。本项目的开展与实施将对应用于AMOLED像素驱动电路中的多晶硅TFT的寿命预测提供更为精确的理论模型，将对AMOLED像素驱动电路设计提供直接有效的参考，并将进一步加深和延展对多晶TFT可靠性的认知。

多晶硅技术是实现高清有源矩阵有机发光二极管 (AMOLED: Active-Matrix Organic Light-Emitting Diode) 显示的核心技术之一。AMOLED像素驱动电路中的多晶硅薄晶体管 (TFT: Thin Film Transistor) 的可靠性尤为重要，其好坏关系着AMOLED显示的显示质量和使用寿命。本项目系统研究了多晶硅TFT在AMOLED像素驱动电路工作中的退化行为和退化机理。首次提出“驱动”电压应力、关态电压应力、正向同步电压应力和反向同步电压应力来模拟AMOLED像素驱动电路中驱动TFT和开关TFT的实际工作状态。分别系统研究了多晶硅TFT在“驱动”电压力、关态电压应力、正向同步电压应力和反向同步电压应力的器件退化行为。研究结果发现在“驱动”电压应力下，器件退化只和应力脉冲的上升沿有关；在关态应力下，器件退化只和应力脉冲的下降沿有关；在正向同步电压应力下，器件退化不仅和应力脉冲频率有关而且和应力脉冲上升沿下降沿都有关；在反向同步电压应力下，器件退化最为严重，300秒的应力就可以引发器件几乎100%的开态电流退化，器件退化只和脉冲上升沿有关。通过数据比对，动态热载流子效应主导了上述四种应力条件下的器件退化。结合相关的瞬态模拟，我们提出和完善了非平衡态PN结退化模型来解释上述四种应力条件下的器件退化机理。从退化模型得到启发，通过对多晶硅TFT有源区进行搭桥晶粒 (BG: Bridged Grain)掺杂，可以有效抑制漏端电场，从而大幅度改良多晶硅TFT在上述四种应力条件下的器件可靠性。此外，我们进一步BG TFT进行优化，发明无源漏掺杂的BG多晶硅TFT。对项目的研究结果为多晶硅TFT在AMOLED像素驱动电路中的寿命预测提供更为精确的理论模型；为AMOLED像素电路设计者提供直接有效的参考；丰富了对多晶硅TFT物理退化机制的认知。