Transistors are the fundamental building block in modern circuitry and are used either as switches or signal amplifiers. The field effect is a phenomenon in which the conductivity of a semiconductor changes due to the application of an electric field normal to its surface. Organic Field Effect Transistors (OFETs) can be prepared either by vacuum evaporation of small molecules, by solution-casting of polymers or small molecules, or by mechanical transfer of a peeled single-crystalline organic layer onto a substrate. These devices have been developed to realize low-cost, large-area electronic products and biodegradable electronics. Organic polymers, such as poly(methyl-methacrylate) (PMMA), can also be used as dielectric.
OFETs are composed of three terminals: the source, the drain and the gate, as well as a semiconductor layer and an insulating layer between the semiconductor and the gate. An OFET is deposited to bridge the source and drain electrodes, and is itself spaced from the gate electrode by an insulating gate dielectric layer. The organic semiconductor can be a pi-conjugated polymer or oligomer. Two voltages are applied relative to the source electrode which is kept at common (0 V): the drain voltage (Vds) is applied to the drain electrode, while the gate voltage (Vgs) is applied to the gate electrode. This gate voltage provides an electric field that leads to the accumulation of charge carriers at the semiconductor/ dielectric interface which modulates the source-to-drain conductance. Depending on whether p-channel or n-channel FET characteristics are being measured, the Vds and Vgs are swept in the negative or positive voltages to accumulate the appropriate sign of charge carriers at the semiconductor/ dielectric interface, i.e., holes or electrons.