The effect of γ-irradiation on amorphous silicon field effect transistors

The paper deals with the effect of γ-radiation from a Co⁶⁰ source on the electronic properties of amorphous silicon field effect transistors. These thin film devices, deposited by the glow discharge technique, are being developed for addressable liquid crystal displays, logic circuits and other applications. 1 Mrad (Si) and 5 Mrad (Si) doses were used and the transistors were held at gate voltages between -8V and +8V during irradiation. Measurements on irradiated specimens showed shifts in threshold voltage of less than 3 V and a change in transconductance below 10%, both of which could be removed by annealing above 130 °C. These results are compared with presently available “radiation hardened” crystalline silicon device structures and it is concluded that in spite of the thicker gate insulation layer (0.3 μm of silicon nitride) of the amorphous devices, the latter are remarkably radiation tolerant, with little degradation in performance. Measurements on irradiated α-Si films deposited on glass show pronounced conductivity changes, not observed in the transistors. It is suggested that these effects arise at the Si/glass interface, and are prevented by the presence of the silicon nitride film in the devices.