A study on Fluorine doped ZnON Thin Film Transistor fabricated by Co-Sputtering method.

Abstract

ABSTRACT A study on Fluorine doped ZnON Thin Film Transistor fabricated by Co-Sputtering method. Hyeon-Su CHO Department of Material Science and Engineering The Graduated School Hanyang University During the last years, ZnON TFTs have been researched as a promising candidate for the high resolution and large area displays due to its outstanding mobility among various oxide semiconductors. However, ZnON TFTs are limited by its unstable transfer characterestic. Compared to the ZnON TFTs, Fluorine doped ZnON (ZnON:F) TFTs are available for threshold voltage control and sub-threshold swing with fluorine doping ratio adjustment. Previous researches reported that fluorine, with higher electronegativity and similar radius to the oxygen and nitrogen, was able to passivate the relative oxygen or nitrogen vacancies in oxide semiconductors. In our study, ZnON:F TFT was fabricated. Heavily doped p-type Si wafer substrate with a thermally grown SiO2 (100nm) layer is used as gate/gate insulator. Fluorine doped ZnON (ZnON:F, 30nm) was deposited in a mixed reactive gas using the Zn metal target and ZnF2 target by means of DC and RF reactive co-sputtering. Then, Aluminium (Al, 100nm) is deposited as source/drain electrode by thermal evaporation. Post annealing process is combination of UV and 175 oC thermal annealing. It was found the amount of fluorine doping concentration increases when RF power increases. As a result, the optimized ZnON:F TFTs showed 50.2cm2/Vs of mobility, 2.18V of threshold voltage, 0.31V/decade of subthreshold swing. The Fluorine may play a role to suppress nitrogen vacancies in ZnON semiconductors due to the nitrogen related defect passivation.