Dipolar Chromophore Functional Layers in Organic Field Effect Transistors

The study of organic field effect transistors has expanded from its original objectives in developing organic semiconductors in which charge carriers have high mobility to focusing increasingly on opportunities arising from the design of electronic interfaces. Interfaces can have an important functional role in devices, for example a reconfigurable interface which responds reversibly to external stimuli. At a molecular level, reversible responses include intramolecular charge transfer, photoinduced charge transfer, and isomerization of the organic molecules. These molecular processes can be detected and probed in a field effect transistor (FET) through changes in the electronic transport properties of devices. Self assembled monolayers (SAMs) with permanent electric dipole moments in the range of 2–3 Debye have been attached to the gate insulator of FETs to add to the field induced by the gate voltage, shifting the gate voltage dependence of the transistor characteristics. We have recently designed a controllable layer of electron acceptors using a C60-terminated SAM at the interface between a pentacene thin film and a SiO2 gate dielectric and shown that these acceptors can participate in photoinduced charge transfer. Our interest here is in incorporating reconfigurable dipolar chromophores into FETs. These chromophores are organic molecules with donor and acceptor groups connected by extended p-conjugation which are used in many non-linear optical (NLO) and electro-optic (EO) applications and routinely have a tunable dipole moment of well over 9 Debye. Mechanisms for reversible changes can be built into the interfacial layers between the gate insulator and semiconductor layers of FETs. In purely inorganic approach, a ferroelectric oxide with a large reconfigurable polarization can be incorporated in the transistor. Similarly, organic polymer ferroelectrics with electrically switchable polarization can be