| Active-matrix organic light-emitting display (AMOLED) is now generally viewed as the next generation display because of its vivid color, high contrast ratio, thin/light module, and low energy consumption. So far, most reported pixel circuits are either based on low temperature polysilicon (LTPS) thin film transistors (TFTs) or hydrogenated amorphous silicon (a-Si:H) TFTs. Both backplane technologies have their own shortcomings, such as nonuniformity of LTPS TFTs, low field-effect mobility and threshold voltage instability of a-Si:H TFTs. As a result, TFTs based on other semiconductor materials have been explored as an alternative approach to realize reliable, high resolution AMOLEDs. Among all, amorphous In-Ga-Zn-O (a-IGZO) TFTs possess certain advantages including visible transparency, low processing temperature, uniformity over large area, and good electrical performance, which make them very attractive for AMOLEDs.;The focus of this work has been to provide a more thorough understanding of the device performance of a-IGZO TFTs, along with the underlying semiconductor physics and their possible application to AMOLEDs. Firstly, the electronic structure of crystalline In-Ga-Zn-O was studied by ab initio quantum mechanics calculation. Then the electrical properties of a-IGZO TFTs were described, including the gate voltage dependent field-effect mobility and source/drain contact resistance. The operation principles of a-IGZO TFTs were further investigated by the channel region surface potential profile obtained by scanning Kelvin probe microscopy. The effect of temperature on the electrical properties of a-IGZO TFTs was investigated. The thermally activated drain current was explored, and the density of deep states profile was calculated from measured data. Current temperature stress measurements were performed on a-IGZO TFTs. Several factors were considered when investigating the electrically stability of the devices, including the stress time, stress temperature, stress current, and TFT biasing conditions. Finally, a-IGZO TFT SPICE model was developed based on the RPI a-Si:H TFT model. Several voltage- and current-programmed AMOLED pixel circuits were simulated. The effect of threshold voltage variation on the pixel circuit performance was investigated, and the potential advantages of using a-IGZO TFTs were discussed. |
