Polarization-induced transport in ferroelectric organic field-effect transistors

Abstract

Ferroelectric dielectrics, permitting access to nearly an order of magnitude range of dielectric constants with temperature as the tuning parameter, offer a great platform to monitor the changes in interfacial transport in organic field-effect transistors (OFETs) as the polarization strength is tuned. Temperature-dependent transport studies have been carried out from pentacene-based OFETs using the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) as a gate insulating layer. The thickness of the gate dielectric was varied from 20 nm to 500 nm. By fits to an Arrhenius-type dependence of the charge carrier mobility as a function of temperature, the activation energy in the ferroelectric phase is found to increase as the thickness of the PVDF-TrFE layer decreases. The weak temperature-dependence of the charge carrier mobility in the ferroelectric phase of PVDF-TrFE may be attributed to a polarization fluctuation driven transport, which results from a coupling of the charge carriers to the surface phonons of the dielectric. By comparing single layer PVDF-TrFE pentacene OFETs with stacked PVDF-TrFE/inorganic dielectric OFETs, the contribution from Fröhlich polarons is extracted. The temperature-dependent mobility of the polarons increases with the thickness of the PVDF-TrFE layer. Using a strongly coupled polaron model, the hopping lengths were determined to vary between 2 Å and 5 Å.