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.