Role of oxygen vacancies on the bias illumination stress stability of solution-processed zinc tin oxide thin film transistors

Solution-processed ultra-thin (similar to 3 nm) zinc tin oxide (ZTO) thin film transistors (TFTs) with a mobility of 8 cm(2)/Vs are obtained with post spin-coating annealing at only 350 degrees C. The effect of light illumination (at wavelengths of 405 nm or 532nm) on the stability of TFT transfer characteristics under various gate bias stress conditions (zero, positive, and negative) is investigated. It is found that the Delta Vth (Vth(stress) (3400 s - stress 0 s)) window is significantly positive when ZTO TFTs are under positive bias stress (PBS, Delta Vth = 9.98 V) and positive bias illumination stress (lambda = 405 nm and Delta Vth = 6.96 V), but Delta Vth is slightly negative under only light illumination stress (lambda = 405 nm and Delta Vth = 2.02 V) or negative bias stress (Delta Vth = -2.27 V). However, the Delta Vth of ZTO TFT under negative bias illumination stress is substantial, and it will efficiently recover the Delta Vth caused by PBS. The result is attributed to the photo-ionization and subsequent transition of electronic states of oxygen vacancies (i.e., V-o, V-o(+), and V-o(++)) in ZTO. A detailed mechanism is discussed to better understand the bias stress stability of solution processed ZTO TFTs. (C) 2014 AIP Publishing LLC.