Improved Tolerance Against UV and Alpha Irradiation of Encapsulated Organic TFTs

In this work, we analyzed the effects of alpha and ultraviolet irradiation on encapsulated and non-encapsulated thin film-transistors. Up to -35% mobility variation occurs on unencapsulated devices after UV irradiation. The same UV irradiation induced less than -3% on encapsulated devices. By investigating the charge trapping kinetics, we show that the increased robustness comes from the reduced air absorption, rather than solely attenuating UV the components. Beside the degradation mechanisms seen on conventional MOS structures, alpha irradiation also induces another form of degradation in air, on devices without encapsulation, due to the reaction of the exposed pentacene with ozone or ionized oxygen generated by alpha, through air ionization. The encapsulation partially mitigates this mechanism, but it is ineffective in reducing the ionizing radiation effects intrinsic to the MOS structure.