S.W. Tsao

Influence of positive bias stress on N2O plasma improved InGaZnO thin film transistor

A post-treatment using N2O-plasma is applied to enhance the electrical characteristics of amorphous indium gallium zinc oxide thin film transistors. Improvements in the field-effect mobility and the subthreshold swing demonstrate that interface states were passivated after N2O-plasma treatment, and a better stability under positive gate-bias stress was obtained in addition. The degradation of mobility, resulted from bias stress, reduces from 6.1% (untreated devices) to 2.6% (N2O-plasma treated devices). Nevertheless, a strange hump characteristic occurs in transfer curve during bias stress, inferring that a parasitic transistor had been caused by the gate-induced electrical field.

The Instability of a-Si : H TFT under Mechanical Strain with High Frequency ac Bias Stress

The instability of amorphous Si thin film transistors under uniaxial strain has been studied. Compared to the effect of tensile bias stress, larger threshold voltage shift is observed under compressive bias stress. These results are related to the damage of weak Si-Si bonds during the ac bias stress. However, the V th shift of devices on the re-flattened substrate is larger after tensile strain than that of compressive strain. In addition, the defeat diminished effect of tensile situation is decreased after re-flattening the device. Therefore, after re-flattening the substrate the V th shift resulting from tensile bias stress is larger than that of the compressive one.

Analysis of Parasitic Resistance and Channel Sheet Conductance of a-Si : H TFT under Mechanical Bending

The effect of mechanical strain on the performance of a-Si:H thin-film transistors (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 originates from the evolution of defect state density in a*-Si:H channel material.

Photo-leakage-current characteristic of F incorporated hydrogenated amorphous silicon thin film transistor

The photo-leakage-current (IPLC) characteristic of F incorporated a-Si:H thin film transistor (TFT) has been studied. The device activation energy (Ea) of a-Si:H(:F) TFTs is higher than those of typical a-Si:H TFTs, and resulted in the shift down of Fermi level in a-Si:H(:F). Experimental results show that the IPLC of a-Si:H(:F) TFTs is smaller than that of conventional a-Si:H TFTs in the density of states 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.