| Summary: | 碩士 === 中華大學 === 電機工程學系碩士班 === 94 === Low-temperature poly-Si (LTPS) thin-film transistors (TFTs) are used for active matrix liquid crystal displays (AMLCDs) on glass substrates. However , a difficult technological challenge is to develop high-performance TFTs that are useful for both pixel and display circuits . Pixel TFTs need to operate at high voltages with low gate-leakage currents, to drive the liquid crystal. In contrast, high-speed display circuits require TFTs to operate at low voltages and high drive currents, with a low threshold voltage（Vth）. In this letter, we report high-K LaAlO3 gate dielectric TFTs which show a high breakdown voltage and transistor drive current at 5 V. In addition to the very high-K（~23）, the LaAlO3 has good device reliability of low bias-temperature instability among high- CMOS devices. The performance is due to the increase, by a factor of Kdielectric/KSiO2, in the gate capacitance density. This lowers the Vth and improves both the gate-leakage current and breakdown field, since the thickness of the high-K dielectric layer can be increased. Although the high-K Al2O3 TFT was previously reported , the relative lower K of 9–10 and gate capacitance have smaller effect to lower down the Vth. The LaAlO3 TFTs showed a low of 1.2 V, a high gate-dielectric breakdown field of 6.3 MV/cm, low subthreshold swing of 0.31 V/dec, high field-effect mobility of 40 cm /Vs, a large on-off-state drive current ratio（Ion/Ioff）of 1.5×106 and high drive current up to 21 A/ m. The high breakdown voltage and high transistor drive current suggest that the LaAlO3 TFTs can meet the device requirements for both pixel and display circuits.
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