Hybrid dielectrics composed of Al₂O₃ and phosphonic acid self-assembled monolayers for performance improvement in low voltage organic field effect transistors

Low voltage operational organic transistors (< 4 V) based on pentacene were successfully fabricated with hybrid dielectric films composed of aluminum oxide using atomic layer deposition and various phosphonic acid-based self-assembled monolayers as the gate dielectrics. High capacitances up to 279 nF/cm², low leakage current densities of 10⁻⁸ A/cm² at 6 V, and high breakdown fields up to 7.5 MV/cm were obtained. The transistors with the octadecylphosphonic acid hybrid dielectric exhibited an improved saturation mobility of 0.58 cm²/Vs, a subthreshold slope of 151 mV/decade, a threshold voltage of − 1.84 V and an on–off current ratio of 10⁶. The low surface energies of the self-assembled monolayers having non-polar terminal groups, such as methyl and pentafluorophenoxy, improved the carrier conduction of the transistors due to the pentacene growth with an edge-on orientation for low voltage operation. The pentafluorophenoxy end-group showed an accumulation of holes at the semiconductor-dielectric interface.