Aqueous-based synthesis of gallium tungsten oxide thin film dielectrics

Abstract

An aqueous-based approach to the deposition of gallium tungsten oxide thin film dielectrics was developed where the metal content (Ga_2−xW_x/2O_3−δ, x = 0.31–0.66) can be controlled by the initial precursor concentrations, while the oxygen deficiency (δ) can be controlled by post annealing. The spin-coated precursor converts to an amorphous oxide thin film with uniform distribution of metal cations after heating to 400 °C. The Ga_2−xW_x/2O_3−δ band gap decreased with increasing W content from 4.9 eV for the undoped film (Ga₂O₃) to 4.6 eV for the film with the highest W content (Ga_1.34W_0.33O_3−δ). The electronic properties of the dielectric films significantly improved with incorporation of W, where a decrease in leakage current and an increase in breakdown field strength from 2.9 MV cm⁻¹ (Ga₂O₃) to 5.2 MV cm⁻¹ (Ga_1.34W_0.33O_3−δ) was observed. Prior studies have suggested that Ga_2−xW_x/2O_3−δ thin films can form dense low-k dielectric materials, where the relative amount of W in the film can significantly modify the dielectric constant. However our studies found no significant decrease in the dielectric constant with W doping of Ga₂O₃. We found that annealing the films >400 °C in air resulted in the formation of sub-stoichiometric WO_x and metallic W throughout the films which may complicate dielectric measurements.