Radiation Hardness of Sol-Gel Derived Zinc Oxide Thin Film Transistors*

Solution-derived bottom-gate zinc oxide thin film transistors (ZnO TFTs) with different number of spin-coated layers (4 layers and 8 layers) were successfully fabricated and exposed to gamma irradiation with a dosage as high as 2.2 MGy (220 MRad (air)). Zinc oxide layers were grown via sol-gel spin coating technique and were used as the active channel layer. The fabricated devices were characterized before and after being exposed to 1.2 MGy and 2.2 MGy gamma irradiation. The zinc oxide films were characterized by photoluminescence and device characteristics were extracted from the current-voltage measurements before and after irradiation. After 1.2 MGy gamma ray exposure, both 4-layer and 8-layer sample devices were functioning. Degradation in drain current ON/OFF ratio was observed for 4-layer devices while 8-layer devices exhibited an enhancement. The 8-layer ZnO TFTs remained functional after the 2.2 MGy exposure, while the 4-layer devices no longer functioned. Degradation/enhancement of device characteristics such as saturation mobility, drain current ON/OFF ratio and threshold voltage shift due to gamma ray exposure will be discussed.