Numerical Modeling of Flexible ZnO Thin-Film Transistors Using COMSOL Multiphysics

Abstract

Increasing attention has been directed towards the development of optically transparent and mechanically flexible thin film transistors (TFTs) and associated circuits based on the transition metal oxides. These flexible see-through structures offer reduced weight, potential low-cost fabrication, and high performance compared to commonly used hydrogenated amorphous silicon (a-Si:H) in applications for large-area electronics and displays. As these emerging technologies evolve towards commercialization, a thorough investigation of the impacts of the thermo-mechanical stress and strain and their effects on the electrical and mechanical stability of the flexible microelectronic devices have become increasingly necessary. However, not much progress has been reported in this area, and the numerical modeling of the flexible transistors with the Finite Element Method (FEM) would provide unique insight to the design and operation of the flexible TFTs. In this thesis, numerical models of flexible TFTs are built up by COMSOL Multiphysics and compared with analytical models to reach the best agreement between the experimental measurements and the numerical analyses. These simulations provide additional insight into the local stress induced strain within the device due to both intrinsic and applied stress. It was shown that the thermal and mechanical impacts on the TFT performance can be reduced by placing the vital active layer of the flexible device near the neutral mechanical plane or by proper designing the device structure and processing conditions based on the data derived from the numerical models. The mathematical analysis and numerical simulation will be used to improve the electrical and mechanical performance and the reliability of the transistors for flexible applications.