Formation of the accumulation layer in polymer field-effect transistors

We present an experimental study of charge transfer in polymer thin-film field-effect devices. The rearrangement of the charge-carrier density in the transistor channel upon a gate-voltage swing has been monitored in real time and space by means of noncontact scanning potentiometry. The experimental results are in excellent agreement with a simple theory, in which the charging currents are assumed to be driven by drift in the self-induced electric field. The charge density exponentially approaches its final value with a time constant given by L2/μ|Vg|π2, where L is the characteristic device dimension, μ the field-effect mobility, and Vg the final gate voltage.