Abstract
Due to the RC propagation line delay for the fabrication of large-area and high-resolution active- matrix liquid-crystal displays (AM-LCD’s), the low resistivity metal Cu was introduced to reduce the RC propagation line delay .The feasibility of using Cu/CuMg as the gate electrode and source/drain metal for a-Si:H thin film transistors (TFTs) has been investigated. The issue of adhesion with the glass substrates and the n+-a-Si layer has been overcome by introducing the Cu/CuMg alloy. Furthermore, a wet etching process of Cu-based metal has been proposed by using the copper etchant in the conventional printed circuit boards (PCBs). The suppression of Schottky leakage current in metal/a-Si:H structure was also observed in the island-in a-Si:H TFT.The main objectives for flat panel display application are to enhance the field effect mobility and to reduce the off-state leakage current under back light illumination. In addition to reduce the RC propagation line delay for the fabrication of large-area and high-resolution active- matrix liquid-crystal displays (AM-LCD’s), the reduction of the TFT off-state leakage current under back light illumination is also an important issue for keeping signal. For effectively reducing the off-state signal loss resulted from the a-Si:H TFTs photo leakage current, the photo leakage current (IPLC) characteristic of F incorporated a-Si:H thin film transistor is smaller than that of conventional a-Si:H TFTs in the density of states (DOS) limited region, stemmed from the higher recombination centers present in a-Si:H(:F) material. However, the higher IPLC is observed in the hole conduction region, resulted from the larger Ea in the a-Si:H(:F) TFTs. The a-Si:H TFTs with the use of ITO as source-drain metal have been also fabricated. A remarkable transformation in photo leakage current has been observed under the backlight illumination. The photo generation holes blocked in the Schottky barrier could be effectively resulted in the different characteristic of photo leakage current.The numerous trap states existed in a-Si layer seriously strict the transporting of carriers The application of microcrystalline silicon thin film transistors (μ-Si:H TFTs) is attractive due to the higher mobility. On the other hand, the ohmic-contact characteristic of the μ-Si:H was also important for the application of μ-Si:H TFTs. The feasibility of using CuMg as source/drain metal electrodes for n+-doped-layer free μ-Si:H TFTs has been investigated. The ohmic-contact characteristic has been achieved by using the CuMg alloy as source/drain metal. The proposed μ-Si:H TFT has shown the similar electrical characteristic with the μ-Si:H TFT with n+-doped layer.For flexible display application, display panels are required to sustain a certain degree of bending. The effect of mechanical strain on the performance of a-Si:H TFTs with different channel lengths was studied under uniaxial compressive and tensile strain applied parallel to the TFT source-drain current path. The source/drain parasitic resistance, and channel sheet conductance were extracted to explain the device performance under mechanical strain. These results indicate that the compressive bending leads to a significant decrease (~16%) in the source-drain parasitic resistance. The channel sheet conductance has shown a 6% variation under mechanical bending. The variation under mechanical bending strain is originated from the evolution of defect state density in a-Si:H channel material. Furthermore, the instability of a-Si:H TFTs under uniaxial strain has been studied. Compared to the effect of tensile bias stress, larger threshold voltage (Vth) shift is observed under compressive bias stress. However, the Vth shift of devices on the re-flattened substrate is larger after tensile strain than that of compressive strain. The defeat diminished effect of tensile situation is decreased after re-flattening the device. Therefore, after re-flattening substrate the Vth shift resulted from tensile bias stress is larger than that of compressive one.