The effects of gate insulator on transistor parameters of organic field-effect transistors with PEDOT:PSS gate electrode

Organic field-effect transistors (OFETs), recently have been studied intensively for their usage as an electronic component in electronic circuits because of their flexibility and low production costs. In OFETs, besides the organic semiconductor, gate insulators are also important components since they have a high impact on the charge transport in the semiconductor-dielectric interface. Performance of the transistors can be improved significantly via adding compatible gate insulators in OFETs. In this regard, in order to enhance the parameter values of the OFETs, poly(methyl-acrylate (PMA) which was synthesized by chemist of our university and more flexible compared to the heavily used poly(methyl-methacrylate) (PMMA) in the literature was used as gate insulators in OFETs both as thin-film and gel states. Copolymers of the PMA (P18, P28, P29, and P30) were originally synthesized and obtained by adding particular amount of soybean oil to the methyl acrylate (MA) in the polymerization process. Even though coated thin-film PMA was proven to have a higher mobility and lower threshold voltage (VTH) compared to the coated PMMA thin-film, on-to-off current ratio (ION⁄IOFF) and subthreshold swing (SS) parameters were exhibited a lower performance since the higher gate leakage current (IOFF). Therefore, PMA and above-mentioned copolymers of the PMA were transformed into the gel state and used as gate insulators in order to decrease the IOFF and operating voltage of the devices. Consequently, it was demonstrated that operating voltage of the devices can be decreased in this way. Furthermore, relative dielectric constant of the gel dielectric can also be decreased by increasing the soybean oil to MA weight ratio in the polimerization process and it was proven that this led the enhancement of mobility. Moreover, it was shown that transforming the gate insulators into gel state lowers the value of IOFF. Besides all of that, it was shown that using the poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) formulation as a gate electrode in designs enhanced the performance of the devices further. Finally, it can be said that by using above mentioned gate insulators and simple techniques, OFETs can be fabricated with a low budget and then they can be potentially used in electronic oscillator and inverter circuits.