Organization of pentacene molecules on anisotropic ultrathin HfO ₂ / Al₂O₃ templates for organic thin-film transistors using an ion-beam treatment

This article investigates improving organic thin-film transistor (OTFT) characteristics by using an alignable high dielectric constant film to control the self-organization of pentacene molecules. The process, based on the growth of a pentacene film with high vacuum sublimation, is a method of self-organization that uses ion-beam (IB) bombardment of the HfO₂ / Al₂O₃ surface that serves as the gate dielectric layer. X-ray photoelectron spectroscopy indicates that the IB increases the structural anisotropy of the HfO₂ / Al₂O₃ film, and X-ray diffraction patterns show that increasing the anisotropy may lead to the self-organization of pentacene molecules in the first polarized monolayer. An effective mobility of 2.3× 10-3 cm2 V-1 s-1 was achieved, which is significantly different from the mobility in pentacene films that are not aligned. The proposed OTFT devices with an ultrathin HfO₂ structure as the gate dielectric layer were operated at a gate voltage lower than 5 V.