Improvement in performance characteristics of Zn(1-x)MgxO (x=15%) thin film transistor (TFT) with UV-ozone treatment

Abstract

Zinc magnesium oxide (ZnMgO) thin films has emerged as a promising material for optoelectronic applications in last decade. Its high electron mobility makes it a good candidate for thin film transistors applications used in active matrix of LCDs (AMLCDs). ZnMgO thin film have inherent n-type conductivity due to oxygen vacancies, oxygen interstitials and zinc vacancies. For thin film transistors (TFTs), control of doping and defects is very important to maintain carrier concentration and proper threshold voltage of device. Threshold voltage of device is greatly influenced by carrier concentrations and stoichiometry of the film. So defects need to be minimized/controlled for achieving best device performances. These defects can be controlled using reactive oxygen supplied by UV-Ozone treatment by varying the rate and time of oxygen supply. In this study we report effect of UV-Ozone treatment on bottom gate enhancement type ZnMgO TFT using air as source of oxygen for Ozone. ZnMgO thin film was deposited using RF sputter technique using ZnMgO target. Titanium (Ti)/Gold (Au) was deposited to fabricate source and drain contacts. The fabricated TFT was characterized for input characteristics. Post UVO treatment, an increase of two times in drain current is measured along with a decrease in the threshold voltage by 5.8V. The On-OFF (ION/IOFF) ratio for as-deposited film was 7.5 × 103 which increased to 2 × 104 for UVO annealed TFT.