Constant Bias Stress Effects on Threshold Voltage of Pentacene Thin-Film Transistors Employing Polyvinylphenol Gate Dielectric

We investigate the stability of pentacene thin-film transistors using a poly(4-vinylphenol) (PVP) gate dielectric under constant bias stress. The threshold voltage is shifted to the positive gate voltage when stressed in air, as caused by water vapors in the PVP gate dielectric. Meanwhile, we observe a negative shift under stress in vacuum. This shift is attributed to charges trapped in deep electronic states in pentacene near the gate interface. We propose a model for the negative shift of the threshold voltage and extract the hole concentration 4.5 x 10¹¹ cm^-2 that is needed to avoid the critical degradation, resulting in a W/L larger than 40.