Electrical instabilities in amorphous Si-Zn-sn-O thin film transistors under ultra-violet irradiation depending on oxygen content

Abstract

The effect of different oxygen (O2) flow rates during the radio-frequency (RF) sputter deposition of amorphous silicon-zinc-tin-oxide (a-SZTO) thin film transistors (TFTs) has been studied. The threshold voltage (Vth) shifts towards the positive bias by increasing the O2 flow rate during the deposition, which decreases the electron concentration by reducing oxygen vacancies (VOs). The post-treatment of the devices under ultraviolet (UV) irradiation in the air atmosphere has been performed to analyze the reliability of light. The post-treatment of UV irradiation on the a-SZTO TFT for different time intervals significantly shifts the threshold voltage (Vth) from enhance-to depletion mode owing to the creation of VOs. Interestingly, we observed that UV irradiation is more effective on the parameters of Vth and the current ON/OFF (ION/OFF) ratio for the TFTs prepared at lower O2 flow rates. The reason may be that by introducing more oxygen flow, the de-trapping of electrons is reduced under UV irradiation due to the reduced VOs. UV irradiation does not significantly impact the field-effect mobility (mu FE) for different O2 flow rates. The negative bias stress measurement of the devices was performed and analyzed for different O2 flow rates under UV irradiation treatment.