Radiation-Hard ZnO Thin Film Transistors

We report effects for up to 100 Mrad (SiO₂) gamma-ray exposure on polycrystalline ZnO thin film transistors (TFTs) deposited by two different techniques. The radiation related TFT changes, either with or without electrical bias during irradiation, are primarily a negative VON shift and a smaller VT shift (ΔV_ON ~ - 2.5 V and ΔV_T ~ - 1.5 V for 100 Mrad (SiO₂) exposure). Field-effect mobility remains nearly unchanged. Both, VON and VT shifts are nearly completely removed by annealing at 200°C for 1 minute and some recovery is seen even at room temperature. We find that our ZnO TFTs are insensitive to electrical bias during irradiation; that is, unbiased measurements are useful worst case test results. To the best of our knowledge, these are the most radiation-hard thin film transistors reported to date.