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We fabricated PMOS SPC-Si TFTs which show better current uniformity than ELA poly-Si TFTs and superior stability compare to a-Si:H TFT on a glass substrate employing alternating magnetic field crystallization. However the leakage current of SPC-Si TFT was rather high for circuit element of AMOLED display due to many grain boundaries which could be electron hole generation centers. We applied off-state bias annealing of VGS=5V, VDS=-20V in order to suppress the leakage current of SPC-Si TFT. When the off-state bias annealing was applied on the SPC-Si TFT, the electron carriers were trapped in the gate insulator by high gate-drain voltage (25V). The trapped electron carriers could reduce the gate-drain field, so that the leakage current of SPC-Si TFT was reduced after off-state bias annealing. . We also applied same off state bias annealing at SPC-Si TFT with 20,000 lx light illumination in order to verify the reduction of leakage current of SPC-Si TFT under light illumination. The leakage current of SPC-Si TFT was reduced successfully even under light illumination during off-state bias annealing. The off-state bias annealed SPC-Si TFT could be used as pixel element of high quality AMOLED display.
We fabricated highly transparent and high haze ZnO:Al film for front TCO of amorphous and microcrystalline silicon solar cells. We have sputtered ZnO:Al film of 1.3 μm on the thin seed layer of about 60nm which was previously sputtered on the glass substrate by using 4% dilution of oxygen to argon gas. The ZnO:Al film grown on the seed layer had much higher crystalline phase than one without any seed layer. Our bi-layer ZnO:Al film showed low resistivity of 2.66×10-4 Ω•cm and sheet resistance of 2.08 Ω/⇐ while conventional ZnO:Al film showed resistivity of 3.24×10-4 Ω•cm and sheet resistance of 2.46 Ω/⇐. After surface texturing by 0.5% HCl wet-chemical etching, the transmittance of ZnO:Al film was increased from 83.7% to 88.1% at wavelength of 550nm through the seed layer. Also the transmittance at 800nm was increased from 82.3% to 88.9%. Especially, haze values of the ZnO:Al film were drastically increased from 58.7% to 90.6% at wavelength of 550nm by employing the seed layer. Also haze values at 800nm were increased from 22.1% to 68.1%. It is expected that the seed layer method to improve the quality of ZnO:Al film will contribute to an increase of solar cell efficiency due to the high capability of light trapping and low electrical resistivity.
We fabricated nc-Si TFTs in order to investigate the effect of the active-layer thickness on the characteristic of the nc-Si TFT. Bottom gate nc-Si TFTs were fabricated at 350°C using ICP-CVD. The thicknesses of the nc-Si layer were remained to 700, 1200 and 1700 Å. As the active-layer thickness increases, the mobility and the on-current level were not altered. However, the off-current level increased considerably and on/off ratio decreased. It may be attributed to highly doped characteristic of thick nc-Si film. As the nc-Si film thicker, the conductivity increases considerably and the Fermi level approaches to the conduction band minimum, which indicates the increases of doping level. The oxygen concentration shows high level of unintentional doping. Also, columnar growth of nc-Si film makes that the crystallinity of top region is much higher than that of bottom region. So, the conductivity of thick nc-Si film becomes high compared to that of thin nc-Si film. The structure of the nc-Si TFT with thick nc-Si film can be similar to the serial connection of N+, N- and N+ resistance, so that it suffers difficulty to suppress the off current and to secure high on/off ratio. Therefore, the off current can be suppressed by thinning of the high conducting active nc-Si layer and nc-Si TFT with channel thickness of 700 Å shows good on/off characteristic. It is deduced that bottom gate nc-Si TFT is necessary to have intrinsic channel layer as well as thin channel layer to reduce the leakage current.
We fabricated PMOS SPC-Si TFTs which show better current uniformity than ELA poly-Si TFTs and superior stability compare to a-Si:H TFT on a glass substrate employing alternating magnetic field crystallization. However the leakage current of SPC-Si TFT was rather high for circuit element of AMOLED display due to many grain boundaries which could be electron hole generation centers. We applied off-state bias annealing of VGS=5V, VDS=−20V in order to suppress the leakage current of SPC-Si TFT. When the off-state bias annealing was applied on the SPC-Si TFT, the electron carriers were trapped in the gate insulator by high gate-drain voltage (25V). The trapped electron carriers could reduce the gate-drain field, so that the leakage current of SPC-Si TFT was reduced after off-state bias annealing. We applied AC-bias stress on the gate node of SPC-Si TFT for 20,000 seconds in order to verify that the leakage current of SPC-Si TFT could be remained low at actual AMOLED display circuit after off-state bias annealing. The suppressed leakage current was not altered after AC-bias stress. The off-state bias annealed SPC-Si TFT could be used as pixel element of high quality AMOLED display.
Silicon dioxide (SiO2) films were deposited on crystalline silicon substrate by inductively coupled plasma chemical vapor deposition (ICP-CVD). In this paper, various process parameter-gas flow rate, ICP RF power, Process pressure were discussed for the investigation of refractive index. And some properties of the SiO2 film are investigated. Since there was no external substrate heating during the deposition, the SiO2 film showed poor electrical characteristics, such as shifted flat-band voltage and high effective charge density. We have proposed He plasma pre-treatment in order to reduce the interface fixed charge and some post-treatment. Our experimental results shows that He plasma pre-treatment supply thermal energy for decomposition of reactant gas and to remove effective charges. Hydrogen post-treatment also enhances electrical characteristics. We measured the effect of the plasma treatment using FT-IR spectrum and C-V characteristics.
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