Stress Simulation And Reliability Analysis Of Flexible Thin-Film Transistors Under Mechanical Stresses

In recent years,flexible displays have attracted increasing attention due to their potential merits such as lightweight,being unbreakable,and their ability to be bent or folded.However,for flexible displays mechanical stress may generate defects or cracks in thin-film transistors(TFTs),causing device reliability issues.Hence,the research on mechanical reliability of flexible TFT devices is of great significance.Before studying the effects of mechanical stress on device characteristics,we should first understand the stress/strain distribution characteristics of the device under different deformation modes(such as bending and stretching).In this paper,with the aid of finite element simulation software ANSYS,the stress/strain distribution of flexible low-temperature polysilicon(LTPS)TFTs under the condition of bending and stretching is simulated,and the results are compared and analyzed with the theoretical values calculated according to the mathematical formula in material mechanics.Then,mechanical reliability of flexible amorphous indium-gallium-zinc-oxide(a-IGZO)TFTs is investigated by monitoring the electrical characteristic of TFTs during dynamic stretch process.Experimental results show that,with increasing the stretch cycles degradation features in a decrease in the on-state current,an increase in the off-state current,but almost no change in the subthreshold region or the threshold voltage.An approximately linear dependence between the on-state current degradation and the stretch force is observed,from which the critical strain of composite membranes of a-IGZO and SiO2 is determined to be 0.21%.It is proposed that a very few number of nano-scaled mechanical-stress-induced cracks,which originate from the interface between the channel and the gate insulator,but introduce only insignificant amount of interface defects,can fully explain the observed degradation.