Tuning the Electrical Properties of Tungsten Oxide Thin Films Deposited by Reactive Magnetron Sputtering

Tungsten oxide films are deposited onto glass and silicon substrates using reactive magnetron sputtering. Several studies have revealed difficulties in studying the electrical properties of resistive WO films. The main objective of this work is to propose the capacitance meter as a method for studying the electrical properties of resistive WO films. In addition, we aim to establish the correlation between the deposition process and WO physico-chemical properties. The study of the W-Ar-O system hysteresis permitted us to gather the films into four zones, which were delimited by different oxygen flow rate intervals. The identification of these zones was confirmed by the deposition rate, target voltage, chemical composition and electrical properties of the films. A gradual evolution of the capacitance-voltage curves of the metal-oxide-semiconductor structures, with the WO thin films as the oxide layer, was globally observed with increasing oxygen flow rate. Ion density (N) and flat band voltage (V) evolved inversely to oxygen flow rate. The relationship between the evolution of N and V and the increase in oxygen flow rate reflects the improvement in oxygen stoichiometry in the WO films. The WO-Si interface trap density distribution (D) was also studied using the Terman method. It was observed that the films closest to stoichiometry, i.e., WO or WO, showed the lowest values of D and N.