Instability of the Noise Level in Polymer Field‐Effect Transistors with Non‐Stationary Electrical Characteristics

The low frequency noise (LFN) properties of field‐effect transistors (FETs) using polymers as the semiconducting substrate material are investigated and explained in terms of the charge carrier transport in polymer thin‐film structure. Three mechanisms contribute to the carrier transport — charge injection from source electrode into polymer, charge hopping between polymer molecules for drift transport toward the drain, and charge buildup, probably at polymer‐oxide interface. Charge buildup is responsible for non‐stationary electrical characteristics, but does not contribute significantly to the LFN. Charge hopping determines the maximum value of the mobility and the minimum value of mobility 1/f noise. The variations of the PFET characteristics are mainly due to dispersion in the injection barrier of source‐to‐polymer contact. High disorder in the polymer at the source contact can increase the leakage current in PFET and can introduce number fluctuation SGN in the polymer conduction on top of the mobility fluctuation. SGN is proportional to the DC power applied to the injection barrier and should be assumed as a voltage source, since carrier hopping in the polymer reduces the effect of the injection noise. At present, the physical origin of SGN is not fully understood.