In a previous study, the authors investigated that abnormal V th behaviour could occur due to polyimide charging when a voltage was applied to the gate in thin film transistors fabricated on polyimide substrates. The authors propose a barrier structure that could prevent this charging effect when fabricating flexible thin film transistors on polyimide substrates. The barrier layer was changed to an SiOCH/SiO 2 double layer to reduce the influence of fluorine ions generated in PI by negative

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... temperature stress. To confirm the effect of the SiOCH layer, Al/PI/SiO 2 /Al, Al/PI/SiOCH/SiO 2 /Al metal-insulator-metal capacitors were fabricated and electrical properties were measured. When bias stress was applied, changes in current and capacitance were observed only in the device with a single SiO 2 barrier layer. In addition, it was confirmed through secondary ion mass spectrometry measurements that the Si-CH 3 bonds in the SiOCH layer were replaced with Si-F bonds by the fluorine ions originating from PI. It was also verified that the abnormal behaviour of V th did not occur after negative bias temperature stress of the thin film transistor fabricated using an SiOCH/SiO 2 double layer.