Phosphonic acid self-assembled monolayer and amorphous hafnium oxide hybrid dielectric for high performance polymer thin film transistors on plastic substrates

A vacuum-free solution processed hybrid dielectric composed of an n -octadecyl-phosphonic acid self-assembled monolayer on amorphous sol-gel processed hafnium oxide (HfO_x) is demonstrated for low-voltage polymer semiconductor-based thin film transistors (TFTs). The phosphonic acid/ HfO_x hybrid dielectric provides high capacitance (0.41 μF/ cm ²), low leakage current (5× 10^-8 A/ cm²), and is compatible with plastic substrates. The utility of this dielectric is demonstrated by fabricating high performance polymer TFTs based on a spin coated thiophene-thiazolothiazole copolymer with operating voltages under -2 V, negligible hysteresis, subthreshold slopes as low as 100 mV/dec, and hole mobilities up to 0.11 cm² V s. © 2009 American Institute of Physics.