| Summary: | A comparative study on the effects of e-beam deposited gate dielectrics for amorphous indium gallium zinc oxide (<i>a</i>-IGZO) thin-film transistors (TFTs) has been carried out using SiO<sub>2</sub>, Si<sub>3</sub>N<sub>4</sub>, and Ta<sub>2</sub>O<sub>5</sub> dielectric materials. The channel width dependent device electrical performances were investigated using three different sizes of 500 μm, 1000 μm, and 1500 μm. The reliability characteristics were revealed by the threshold voltage variation and drain current variation under positive bias stress. The e-beam deposited high-k dielectric Ta<sub>2</sub>O<sub>5</sub> exhibited the highest stability at the stress voltage of 3 V for 1000 s due to its high capacitance density at 34.1 nF/cm<sup>2</sup>. The threshold voltage variation along the channel width decreased from SiO<sub>2</sub>, then Si<sub>3</sub>N<sub>4</sub>, to Ta<sub>2</sub>O<sub>5</sub>, because of the increased insulating property and density of capacitance. The SiO<sub>2</sub>-based <i>a</i>-IGZO TFT achieved a high field effect mobility of 27.9 cm<sup>2</sup>/V·s and on⁻off current ratio > 10<sup>7</sup> at the lower channel width of 500 μm. The gate leakage current also decreased with increasing the channel width/length ratio. In addition, the SiO<sub>2</sub> gate dielectric-based <i>a</i>-IGZO TFT could be a faster device, whereas the Ta<sub>2</sub>O<sub>5</sub> gate dielectric would be a good candidate for a higher reliability component with adequate surface treatment.
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