Optimized oxygen deprived low temperature sputtered WO₃ thin films for crystalline structures

Abstract

We report a detailed analysis on the effects of processing parameters for sputtered tungsten trioxide (WO3) thin nanoscale films on their structural, vibrational and electrical properties. The research aims to understand the fundamental aspects of WO3 sputtering at relatively low temperatures and in an oxygen deprived environment targeting applications of temperature and oxygen sensitive substrates. Structural analysis indicates that films deposited at room temperature, or substrate temperatures at or below 400 °C with low oxygen partial pressure are amorphous. Crystallization of the films was observed with distinct Raman peaks when the films were annealed at 300 °C or above using rapid thermal annealing for 10 min. Films revealed monoclinic phases of WO3 with the presence of W–O–W stretching, bending and lattice vibrational modes in the Raman spectra. Interestingly, a change of transport behavior from insulating to semiconducting was observed for as deposited films on post annealing. Annealed films revealed stoichiometric WO3 phases with no external defects detected. The present study adopts a route to intercalate WO3 in a variety of applications from electrochromic coloration to a nanocrystalline thin film for electronic devices sensitive to higher temperatures and gas flow in the sputtering system.

Sputtered Ultrathin WO3 for Realizing Room-Temperature High-Sensitive NO2 Gas Sensors

“…A notable observation is that of a series of five identical peaks in the typical Raman spectrum of the WO 3 crystalline film, namely at 137, 182, 273, 302, and 808 cm –1 . The peaks at 808 cm –1 correspond to W–O–W stretching frequencies. , The peaks at 273 and 302 cm –1 can be attributed to the W–O–W bending mode of the bridging oxygen, while the peaks observed at 137 and 182 cm –1 are caused by the lattice vibration of crystalline WO 3 . Thus, these observations confirm that the sputtered WO 3 samples are in the monoclinic phase.…”

“…The peaks at 808 cm −1 correspond to W−O−W stretching frequencies. 38,39 The peaks at 273 and 302 cm −1 can be attributed to the W−O−W bending mode of the bridging oxygen, while the peaks observed at 137 and 182 cm −1 are caused by the lattice vibration of crystalline WO 3 . Thus, these observations confirm that the sputtered WO 3 samples are in the monoclinic phase.…”

Highly stable electrochromic cells based on amorphous tungsten oxides prepared using a solution‐annealing process

“…Numerous methods have been being carried out to prepare electrochromic WO 3 electronic devices, and different approaches have been being employed to boost the efficiency of devices to prepare practical, commercial, and friendly enviroment devices. Various methods such as the hydrothermal method, 25,26 chemical vapor deposition, 27,28 thermal evaporation, 29,30 sputtering, 31,32 sol-gel method, 33,34 and electrochemical deposition 35,36 have been used to prepare electrochromic tungsten oxide films and the electrochromic performance of tungsten oxide films with different morphologies such as amorphous films, 37,38 crystalline films, 39 nanoparticle films, 40,41 nanowire films, 42 or nanorod films. 43,44 However, these methods present several disadvantages such as the use of expensive equipment, toxic environment, or complicated processing.…”