Study On Gate Dielectrics Of Flexible Amorphous In GaZnO Thin Film Transistors

The amprohous InGaZnO thin film transistors(a-IGZO TFTs)are considered as the active-matrix driving electronic devices for the next-generation flat panel displays(FPDs)because of their high carrier mobility,low temperature processing,transparent and flexibility.Because gate insulators have a significant impact on the characteristics of flexible a-IGZO TFTs,it is particularly important to choose the appropriate gate insulator materials and optimize the processing conditions.At present,SiO_X and SiN_X are the most common gate insulators of TFTs.However,the dielectric constant of SiO_X is too low(only about 3.9),and the band gap of SiN_X is so small(only about 5eV).Therefore,the research and development on new materials and processing methods of dielectircs for flexible TFTs are still necessiary.Firstly,the flexible a-IGZO TFTs with various gate insulators(GI)were prepared on the polyimide(PI)substrates at room temperature by magnetron sputtering.Here,the GI layers were consisted of variously thick SiO_X and TaO_X films.Then,we compared the properties of different dielectrics as well as the performance and bias-stress stability of the corresponding TFTs.The experimental results indicated that the growth rate of TaO_X was faster than SiO_X;the GI surface roughness decreased and the GI dielectric constant increased with the film thickness of TaO_X increasing.For instance,the relative dielectric constant of the GI consisted of 300-nm-thick SiO_X and 300-nm-thick TaO_X became 10.Accordingly,the corresponding a-IGZO TFTs showed larger on-current and smaller threshold voltage,whereas their off-current and bias-stress stability became worse.Then,we studied the effect of bending on the operating characteristics and bias stress stability of flexible a-IGZO TFTs.According to the aforementioned results,we designed two kinds of gate insulators,i.e.,one consisted of 300-nm-thick SiO_X and 300-nm-thick TaO_X,and the otherwas600-nm-thick SiO_X as the reference.We comparatively studied the effect of bending on the properties of the flexible a-IGZO TFTs with different GIs.We tested the elecrical perforance and bias stress stability of the devices before,while and after bending.The experimental results showed that the GI consisted of 300-nm-thick SiO_X and 300-nm-thick TaO_X could effectively improve the stability of flexible a-IGZO TFTs.Through theoretical analysis,we believe that the experimental results are closely related to the higher Young’s modulus of TaO_X.We believe that the flexible a-IGZO TFTs with stacked gate dielectricsmight be applied to drive the flexible FPDs.