Effect of hydrogen on the electrical properties of a Ag/WO x /W thin-film structure exhibiting resistive switching behavior

Abstract

Thin-film structures based on gas-sensitive tungsten oxide Ag/WOx/W exhibiting a bipolar resistive switching effect were prepared. The current-voltage characteristics of the structures were studied in air with laboratory humidity and after hydrogen feeding into the chamber to a concentration of 2% in the air. The chemical state of the surface layers of the resulting structures was analyzed by X-ray photoelectron spectroscopy. The morphology and structural condition were studied by atomic force and scanning electron microscopy and micro-Raman spectroscopy. A severe reaction to hydrogen was found in the Ag/WOx/W structure subjected to additional heat treatment in the air at 200°C. The annealing of this structure gave rise to the formation of silver nanoparticles with an oxide coating on the surface of tungsten oxide. The formation of nano-particles resulted in a change in contact properties and offered hydrogen efficient access to the contact areas, as is evidenced by an increase in the flow of current in the low- and high-resistive states of this structure. A comparison of the reaction to hydrogen exhibited by WOx/W and Ag/WOx/W structures suggested that hydrogen had a significant effect on the mechanism of formation of conductive silver threads in the oxide layer and the chemical state of the interface owing to a change in the kinetics of the electrochemical oxidation-reduction processes in the contact areas of Ag/WOx. The results show the possibility of designing hydrogen sensors operating on new physical principles.