No abstract

Series results for the anisotropic Ising model are analysed by investigating the logarithmic derivative of the susceptibility. If the odd and even coefficients are extrapolated separately, results consistent with scaling and universality predictions are obtained.

We investigated AC bias stress instability of indium-gallium-zincoxide (IGZO) Thin-film transistors (TFTs). AC bias frequency dependence showed different aspect in IGZO TFTs and a-Si:H TFTs. Influencing factors to AC bias frequency dependence of instability is charge accumulation characteristic under negative bias stress, and detrapping characteristics of shallow trapped charges under positive bias stress.

We successfully fabricated a-IGZO TFTs with a Ti/Cu source/drain (S/D) in order to reduce the data-line resistance. SiNx passivation was used to protect the Cu from Cu-oxygen diffusion. The TFTs exhibited normal enhancement-mode characteristics compared to the TFT employing a Mo S/D, which behaved like a conductor. Our experiments suggest that the Ti/Cu S/Ds control the channel resistivity of the fabricated TFT lower than the Mo case. We found an indium-deficient IGZO layer under the Ti contact; this is thought to be the origin which reduces oxygen vacancy concentration in the channel.Amorphous Indium-Gallium-Zinc-Oxide Thin Film Transistors (a-IGZO TFTs) have attracted a considerable amount of attention because they exhibit excellent electrical properties, such as high field-effect mobility and large on-current, along with small leakage current. 1, 2 Their low sub-threshold swing enables fast on/off switching; the uniformity of a-IGZO TFTs is also good. 3 TFT-LCDs and AMOLEDs employing a-IGZO TFTs suggest that an oxide semiconductor is a good candidate for the switching devices used in displays. 4,5 High resolutions and large display sizes require a low data-line resistivity and high mobility TFTs. When display devices increase in size, resolution, and refresh rate, the required short charging time makes it difficult to charge the pixel electrodes up to the necessary data voltage. High mobility TFTs can overcome this charging problem. However, the signal distortions due to the RC-delay of the data-line are still a liability. The RC-delay, therefore, needs to be decreased in order to avoid image distortion. Since the capacitance is usually fixed by the data-line width, the resistivity of the data-line needs to be reduced in order to decrease the RC-delay. Al is widely used for the data-line in displays. Cu, which is about 30% more conductive than Al, is being considered for data-line resistance reduction. 6 Because the data line is formed simultaneously with the source/drain (S/D) electrodes, employing Cu for the oxide TFT's S/D is very important.A problem to employ Cu in oxide TFTs is that Cu diffuse into SiO 2 passivation, 7 so that the Cu resistivity and RC-delay will increase. The reason why oxide TFTs widely use SiO 2 for passivation layer is that SiO 2 can be easily deposited using conventional PECVD methods and exhibits superior environmental stability. 8,9 Therefore, in spite of usefulness of SiO 2 , when Cu-based metallization is used, it is desirable to employ SiNx passivation which is widely used in a-Si TFTs. However, there is another problem to apply SiNx passivation in the oxide TFTs, because their electrical properties are easily changed by the hydrogen species such as SiH 4 , NH 3, and H 2 during the SiNx deposition. It has been found that an oxide semiconductor TFT with SiNx passivation has negative turn-on voltage or even becomes a conductor due to the resulting increased number of carriers.The purpose of this paper is to report upon the fabrication of a-IGZO TFTs using a Ti/Cu S/D as well as Si...

We have investigated a stability of oxide TFTs (IGZO) under electrical bias and monochromatic light illumination. Under -20 V gate bias, when 650 nm monochromatic illumination with intensity of 1 mW/cm 2 was radiated, threshold voltage (V th ) was shifted by about -1.55 V while V th was almost constant without illumination. Even though the photon energy of 650 nm is much smaller than optical band gap of oxide active layer (E opt~3 .0 eV), V th was changed due to generation of carriers through localized state. However, under positive gate bias of 20 V, V th was not changed with and without 650 nm light illumination. In terms of 300 nm wavelength light, V th was shifted positively under negative bias stress and negatively under positive bias stress. It is considered that light affected not only the active layer but also the gate insulator layer.