Solution processed amorphous tantalum oxide films as alternative high-k gate dielectrics

Dikko, Umar and Halcovitch, Nathan Ross and Milne, W.I. and Adamopoulos, George (2018) Solution processed amorphous tantalum oxide films as alternative high-k gate dielectrics. In: 7th International Symposium on Transparent Conductive Materials, 2018-10-14 - 2018-10-19, Chania, Crete, Greece.

Abstract

The high-k oxides are considered as alternative gate dielectrics as replacements to SiO2 due to their high dielectric constants and breakdown voltage. Among those, tantalum oxide is one of the first to be used extensively in capacitors production, however the issues in forming material with a uniform structure has led to variations in its reported properties such as the dielectric constant as well as the optical band gap. Additionally, tantalum oxide thin films deposition has been monopolised by reactive sputtering and CVD-based techniques inevitably leading to high manufacturing costs. Here we report the application a solution-based deposition method namely the spray pyrolysis for the deposition of amorphous tantalum oxide (TaOx) films and their implementation in thin-film transistors employing spray-coated ZnO and In2O3 semiconducting channels. A variety of methods, including XRD, FTIR, UV-Vis, XPS, and impedance spectroscopy have been applied to assess the structure, dielectric and electron transport properties of the amorphous tantala films. Analyses revealed that the optimum substrate temperature to achieve both high relative dielectric constant and high breakdown voltage was 400 °C. Simultaneously, and for the optimum deposition conditions tantala films exhibit wide band gap of about 5 eV consistent with the amorphous phase, and high dielectric constant of about 26. The remarkable finding however was related to the extremely low leakage currents that were found to be on the order of 10-10 A. Similarly, thin film transistors implementing TaOx gate dielectrics and ZnO as well as In2O3 channels showed excellent operating characteristics such as high electron mobility in excess of 25 cm2/Vs, high on/off current modulation ratio (>106) and excellent high bias stress stability.