Temperature-dependent electrical resistivity of tungsten oxide thin films

Tungsten oxide (WO3) thin films have been previously investigated for various applications. Optoelectronic and electrochromic applications require detailed knowledge of the electrical properties of such films, whereas gas-sensing applications require understanding the electrical resistivity and its variation with temperature. In numerous studies on the electrical properties of WO3 thin films, the results were widely scattered and critically dependent on deposition and resistivity measurement conditions. This paper presents a systematic investigation of the electrical resistivity of WO3 thin films and its variation with temperature. WO3 thin films were deposited on heated substrates using thermal evaporation both in vacuum and under an oxygen atmosphere. Subsequently, the films were annealed in air or in vacuum. The structural, chemical, optical, and room-temperature electrical properties were measured. The temperature-dependent electrical resistivity was measured at 300-700 K in air or in vacuum. The activation energies for electrical conduction were derived from these measurements and were used to investigate the mechanisms responsible for electrical conduction.