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

In this paper, bottom-gate thin-film transistors (TFTs) with zinc oxide (ZnO) channels were grown on Si substrates with an
${\rm SiO}_{2}$
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
$^{\circ}$
), smallest strain
$(2.61\times 10^{-3})$
, highest thin-film density
$(5.78~{\rm g}/{\rm cm}^{3})$
, lowest surface roughness (1.75 nm), and largest surface energy
$(65.3~{\rm mJ}/{\rm m}^{2})$
. The saturation mobility, subthreshold voltage, ON/OFF current ratio, and trap density of the ZnO TFTs with optimal UV-ozone treatment were 4.54
${\rm cm}^{2}~{\rm V}^{-1}~{\rm S}^{-1}$
, 0.28 V/decade,
$2.02\times 10^{7}$
, and
$2.61\times 10^{11}~{\rm eV}^{-1}~{\rm cm}^{-2}$
, respectively, indicating the potential of this structure to be applied to large-area flat-panel displays.