Instability of threshold voltage under constant bias stress in pentacene thin film transistors employing polyvinylphenol gate dielectric

The instability of threshold voltage and mobility of pentacene thin film transistors using a poly(4-vinylphenol) gate dielectric have been investigated under constant bias stress. The mobility was very stable in vacuum by exhibiting 2% variation after 6 h stress even under the high gate bias stress of VGS = − 20 V. Meanwhile, we observe a negative shift of threshold voltage 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 × 1011 cm− 2, needed to avoid the onset of stress effects, resulting in a design rule of the channel width to length ratio larger than 40.