Raw product of rare-earth ore works as a high-k gate insulator for low-voltage operable organic field-effect transistors

Abstract

Rare earth metal oxides were found to be good candidates for high-k gate insulators in field-effect transistors. However, refinement of individual elements of rare earth metals either requires complicated processes, or discards a large fraction of the components, which drastically increases the fabrication cost and wastes natural resources. We demonstrate here the successful use of rare-earth raw product to fabricate high-quality gate insulators, which contain a number of different elements without strict refinement. The oxide dielectric thin film showed a very high dielectric constant (k) value of 35 and high dielectric strength >1 MV cm⁻¹, which even rivals those of pure rare-earth oxides. High-k gate insulators are essential for low-voltage operated organic field-effect transistors (OFETs). Capping with a high-k cyanoethylated pullulan (CEP) polymer layer further increased the film quality and created a favorable semiconductor/dielectric interface, and benefits the stacking of overgrown semiconductor molecules. The OFETs were successfully operated at low voltage of 2–4 V, exhibiting nice mobility ∼0.5 cm² V⁻¹ s⁻¹, on/off current ratio >10⁴, and a steep subthreshold slope of 0.096 V dec⁻¹. The utilization of rare-earth raw product as a source material would drastically reduce the production cost of gate insulators in OFETs, and reduce environmental pollution, which is meaningful in view of green chemistry.