Ionic Liquid Crystal Film Gated Electric Double Layer Transistors

Ionic liquid crystal (ILC) films were employed as solid-state electrolyte dielectrics in organic field-effect transistors (OFETs) because their LC phases are found to have the capability of forming electric double layers (EDLs). In this demonstration, [C 16 mim][PF 6 ] was used as an ILC gate electrolyte in thin film form, whose thickness was over 1000 nm, in the ILC-gated OFET with P3HT as an active semiconductor layer. At 80 °C, a temperature at which [C 16 mim][PF 6 ] is in the smectic A (SmA) LC phase, the OFET exhibited p-type transistor behavior, typically with a low threshold voltage of −1.8 V. The low-voltage transistor operation, even for such a thick ILC dielectric, is the result expected from the EDL formation at its interface with P3HT, into which high-density carriers were efficiently accumulated. Furthermore, the on-state could be maintained even with no gate voltage applied at near room temperature through the following process: cooling with a gate voltage applied from the temperature of 80 °C to a temperature below the crystal phase transition of the ILC and then removing the gate voltage. The nonvolatile memory behavior is evidence of the EDL formation playing a key role in the operation. These results present an additional material option for electrolyte gate transistors, and expand their device applications.