Solution-Processable Zirconium Oxide Gate Dielectrics for Flexible Organic Field Effect Transistors Operated at Low Voltages

We investigate solution based fabrication of high-k ZrO2 thin films for low-voltage-operated organic field effect transistors (OFETs). An alternative UV curing method for the densification of Zr-based gel films, which allows for low-temperature processing, is compared to the conventional thermal annealing method. Elemental and microstructural analysis shows that UV-curing induces the decomposition of organic-metal bonds and causes the densification of the metal oxide film, just as the conventional thermal annealing of gel films does, resulting in a high-k dielectric layer from Zr-based solutions. Furthermore, we found that the low temperature associated with UV-curing prevents the interface layer from intermixing with the substrate. Fabricated ZrO2 films (5-6 nm in thickness) treated with an octadecylphosphonic acid self-assembled monolayer exhibit low leakage current density (below 10(-6) to 10(-7) A/cm(2)) at 3 V and high dielectric breakdown strength (V > 4 V). Using this dielectric layer, solution processable polymer OFETs with PBTTT-C-14 as the organic semiconductor function well at low voltage (below 3 V.) The effect of self-assembled monolayers (SAMs) on the morphology and microstructure of the organic semiconductor deposited on the ZrO2 dielectrics are investigated. Finally, we demonstrate solution-processable, low temperature fabrication of OFETs on a flexible substrate.