Determining the influence of relative humidity on the working parameters of a gas sensor based on zinc oxide

Abstract

This paper investigates the depen dence of operating parameters of a gas sensor based on zinc oxide obtained by the method of direct current mag netron sputtering. The production of gas sensor films was carried out using a VUP-5M vacuum unit with an orig inal material-saving magnetron. The study of the dependence of the working parameters of the gas sensor was car ried out under standard conditions. It was found that with increasing humid ity, the electrical resistance of the gas sensor decreases and, accordingly, the sensitivity to the target gas decreases. A significant reaction of the gas sensor to an increase in humidity was observed in the range of 65–80 % relative humid ity. The mechanism of influence of rela tive humidity on the sensitivity of a gas sensor based on ZnO was investigated. The change in resistance of the gas sen sor is caused by trapped electrons on adsorbed oxygen molecules on the sur face of the sensitive layer. The capture of electrons from the conduction zone leads to bending of the conduction zone and an increase in the space charge zone, respectively, to a change in the resistance of the sensitive layer of the gas sensor. In the atmosphere, when O2 molecules are adsorbed on the ZnO sur face, they remove an electron from the conduction band. The reaction of oxy gen adsorbed on the ZnO surface with reducing gases and the replacement of adsorbed oxygen with other molecules changes the bending of the conduc tion band and reduces the area of space charge. Adsorption of water on the sur face of zinc oxide occurs according to the dissociation mechanism, which consists in the adsorption of steam molecules or hydroxyl groups with the subsequent displacement of previously adsorbed oxygen and free electrons and, accord ingly, leads to a decrease in the sensi tivity of the gas sensor. In addition, the adsorption of water vapor (H2O) mole cules leads to less chemisorption of oxy gen species on the ZnO surface due to the reduction of the surface area, which is responsible for the sensor response. Approaches to reduce the influence of relative humidity on the sensitivity of a gas sensor based on zinc oxide have been proposed