High Performance Organic Thin Film Transistors Using Pentacene-Based Rare-Earth Oxide Bilayer Gate Dielectric

Abstract

High-k dielectrics, neodymium oxide (Nd₂O₃) and lanthanum oxide (La₂O₃) are regarded as useful materials to reduce the operating voltage of organic thin film transistors (OTFTs). However, the high-k dielectrics often have the drawback of high interface trap density leading to high leakage current and low carrier mobility. Here, a bilayer La₂O₃/Nd₂O₃ gate dielectric for OTFTs is employed to address the issues. A top contact pentacene-based organic thin film transistor is exhibiting a variation in carrier mobility as the thickness of Nd₂O₃ changes from 100 nm to 175 nm. Compared to the pentacene thin film transistor with solely 118 nm thick La₂O₃ gate dielectric, the OTFTs with the bilayer La₂O₃/Nd₂O₃ (118 nm/150 nm) gate dielectric improves the threshold voltage from − 0.42 V to − 1.1 and V, the carrier mobility from 0.54 cm²/Vs to 1.08 cm²/Vs. These bilayer devices produced the current on–off ratio of 2.4 × 10⁵ and the subthreshold slope of 0.5 V/decade. The OTFT device exhibits good stability under a low voltage bias-stress effect. The OTFTs are investigated in the atomic force microscope to understand the dielectric–pentacene interface to verify the improved OTFT parameters. The morphology and structure of the La₂O₃/Nd₂O₃ bilayer dielectric films are studied using a field emission scanning electron microscope and x-ray diffraction techniques.