Analysis of amorphous tungsten oxide thin films deposited by magnetron sputtering for application in transparent electronics

In this paper, the structural, surface, optical, and electrical properties of tungsten oxide thin films were analyzed. Eight sets of WOx thin films were prepared using the magnetron sputtering method. In each case, the sputtering process parameters were the same, except the Ar:O-2 gas mixture ratios, which were intentionally changed from 1:1 to 10:1 to obtain various properties of the deposited thin film coatings. Structural properties analyzed with the aid of X-ray diffraction measurements results showed that all thin films were amorphous. X-ray photoelectron spectroscopy measurements revealed a shift of the binding energy for the W4f (7/2) peak towards lower energies for increasing Ar:O-2 ratio, indicating a possible change of stoichiometry and change of the oxygen vacancy concentration. It was also determined that the O/W atomic ratio at the surface of the thin films decreased from 3.01 to 2.55 with an increase of argon content in the magnetron sputtering atmosphere. Scanning electron microscope images revealed that all thin films had a smooth, homogenous, crack-free, and featureless, confirming the structural analysis. It was shown that the sputtering process atmosphere had a significant influence on the optical and electrical properties. Analysis of the transmittance spectra revealed that an increase of Ar:O-2 ratio caused a gradual decrease of the average transparency in the visible wavelength range, an increase of the fundamental absorption edge, and decrease of the optical band gap energy. Moreover, the refractive index and extinction coefficient were analyzed, showing that the change of the argon content in the sputtering atmosphere significantly influenced on those parameters. The sheet resistance and resistivity of the prepared WOx thin films decreased with the increase of Ar:O-2 ratio. The electrostatic charge dissipation times were measured for each coating to assess their antistatic properties. In turn, the hardness of tungsten oxide thin films increased with the increase of Ar:O-2 ratio. It was found that thin films deposited with Ar:O-2 ratio above 6:1 had good ability to dissipate static charge. Performed studies showed that a proper control of the gas atmosphere during magnetron sputtering of tungsten oxide thin films leads to tailoring their optoelectronic properties and creates an opportunity to design coatings destined for application in transparent electronics.