Analysis of the hysteresis in organic thin-film transistors with polymeric gate dielectric

Abstract

Controlling threshold voltage (VTH) and field-effect mobility (μFET) in organic thin-film transistors (OTFTs) is of primary importance to attain reliable devices that can be harnessed in more complicated circuits and eventually commercialized. In particular hysteresis in OTFT transfer curves is an issue that has to be better understood and analyzed. In this regard, even if the interface between organic dielectric and organic semiconductor seems to play an important role, our study shows that a further and relevant factor is played by the transport of charges across the bulk of the dielectric layer. Here, an analytical approach is applied to identify and understand the different components that give rise to the hysteresis in the transfer curves of pentacene-based OTFTs using poly(vinyl alcohol) (PVA) and poly(vinyl alcohol) cross-linked with ammonium dichromate (PVAad) as the (polymeric) gate dielectric. Transfer curves simulations which include charge transport in the PVA show a hysteretic behavior in good agreement with the experimental data. Moreover, the hysteresis measured in OTFTs can be reduced by the insertion of an underlying dielectric layer of SiO2 that blocks the above-mentioned effect. The residual contribution to the hysteresis is then analyzed by investigating the chemistry nature of both PVA and PVAad, which show different electron trapping efficiency at the interface with the pentacene layer. Therefore, a consistent explanation of how the polymeric dielectric is able to impact the transfer curves requires considering all mentioned factors.