驱动AM-OLED的2-a-Si∶H TFT的设计与制作

Design and Facture of 2-a-Si∶H TFT Driving AM-OLED

a-Si∶H/SiNx∶HTFT在长时间栅偏应力作用下,会产生阈值电压漂移,这主要是由绝缘层电荷注入和有源层亚稳态产生而引起的。针对电荷注入现象,文章首先通过控制源气体SiH4和NH3流量的不同,利用PECVD制作了不同N/Si比(0.87～1.68)的氮化硅绝缘材料,对其进行了椭偏、红外和光电子散射能谱(EDS)测试。制作了不同的MIS结构电容,对其进行老化实验和C-V测试分析,结果表明稍富氮(N/Si比稍大于标准Si3N4的化学计量比1.33)的氮化硅做成的MIS样品在老化前后C-V曲线偏移不是很明显,表明其缺陷态密度相对较小,能够有效减小半导体/绝缘层界面间的电荷注入。设计了驱动OLED的2-a-Si∶HTFT像素电路及其阵列版图,优化了电路中的几个关键参数,即T1的W/L=2.5、T2的W/L=25和存储电容Cs=0.8pF。运用7PEP生产工艺,制作了13cm(5.2in)的TFT阵列样品。对TFT进行I-V特性测试,其开态电流为10μA,开关比为106;对AMOLED显示屏样品进行了静态驱动下的亮度测试,其最高亮度为341cd/m2。

The threshold voltage of a-Si：H/SiNx：H TFT will shift under long time gate bias stress, it is mostly leaded by charge trapping in gate insulator and defect creation in semiconductor. In allusion to the phenomenon of charge trapping, a series of SiNx insulating materials in different N/Si（0.87～1.68） were deposited by PECVD, controlling different flow ratio of source gas SiH4 and NH3 in this paper, and a great deal of measurements （ellipsometer test, infrared absorption test and electron dispersion spectrum（EDS） test） were done on these samples. Three different capacitance samples in MIS structure were done, degradation experiments and C-V measurements on these samples were done, and the results of C-V measurement indicated that the shift of MIS sample C-V curves with slightly Nrich SiNx （N/Si is bigger slightly than 1.33）was not evident before and after degradation, its defect density was smaller, and could effectively restrain charge chapping in the interface of a-Si：H and SiNx. This paper designed the pixel circuit and layout of 2-a-Si：H TFT driving OLED, and optimized its key parameters： W/L=2.5,W/L=25 and storage capacity 0.8 pF; TFT matrix sample of 13 cm （5.2 in） was made with 7PEP productive technology. I-V characteristics of the TFT was measured, the Ion was 10μA and the ratio of Ion and Ioff was 106. The luminance measurement of the AM-OLED display in static driving was made, and the highest luminance was 341 cd/m^2.