Effect of UV-Ozone Treatment on the Performance of ZnO TFTs Fabricated by RF Sputtering Deposition Technique

Abstract

In this paper, bottom-gate thin-film transistors (TFTs) with zinc oxide (ZnO) channels were grown on Si substrates with an SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> dielectric layer via the radio-frequency sputtering technique. The ZnO films were then subjected to 16 min of ultraviolet (UV)-ozone treatment, which resulted in fewer oxygen vacancies, enhanced crystallization, lower strain, lower surface roughness, and higher thin-film density, as well as improved surface energy and adhesion properties of the gallium zinc oxide source/drain electrodes. The UV-ozone 16-min ZnO active layer TFT with the preferable resistivity values by Hall measurement results. The optimal UV-ozone treatment time (16 min) led to the smallest full-width at half-maximum (0.4138°), smallest strain (2.61 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ), highest thin-film density (5.78 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ), lowest surface roughness (1.75 nm), and largest surface energy (65.3 mJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). The saturation mobility, subthreshold voltage, ON/OFF current ratio, and trap density of the ZnO TFTs with optimal UV-ozone treatment were 4.54 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> S <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , 0.28 V/decade, 2.02 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> , and 2.61 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , respectively, indicating the potential of this structure to be applied to large-area flat-panel displays.