Preparation And Stability Of α-IGZO TFT On Flexible Substrate

Flexible display devices have attracted a lot of interest in future display area, and at the same time, α-IGZO TFT is also considered a good substitute for α-Si:H TFT because of its high mobility, good uniformity and fabricating at room temperature, which makes the researchers pay a lot of attention to the α-IGZO TFT on flexible substrate. We fabricated α-IGZO TFT on polyimide film using kinds of film deposition methods,, modified depositing technology to solve the existed problems and investigated the influence to the electrical performance and stability.We fabricated α-IGZO TFT on flexible substrate using SiNx/SiO2 stack as gate insulator. By adopting suitable SiNx and SiO2 thickness(SiNx/SiO2 200nm/50nm), we make the full use of the high dielectric constant from SiNx and good surface contact with IGZO film from Si O2, which leads to a much better electrical performance and stability of flexible α-IGZO TFT compared to those with single SiNx or SiO2 layer as insulator.In order to solve the problem that flexible substrate may easily deform under film intrinsic stress’ s influence during fabricating process, we investigated the relationships between the film intrinsic stress and the high frequency power time ratio when depositing SiNx or SiO2 using PECVD. Based on this, we found out an optimized parameter conditon which can produce a low stress in whole for our depositing SiNx/SiO2/SiNx as water oxygen isolate buffer, and the best flexible α-IGZO TFT electrical performance and stability.We investigated the post-annealing of α-IGZO TFT fabricated on polyimide substrate and found out that a second time air annealing can improve the TFT electrical performance such as a higher saturation mobility(3.9 cm2/V·s) and a lower S.S value(1.27 V/decade), also it could help the device to acquire a better stability. By comparing TFT devices with different annealing condition and making use of other test method, we confirmed the improvement comes from the second time air annealing which has a positive effect on IGZO film and GI/IGZO interface.