With the increasing attention of environmental protection, air quality is also get more and more attention; for the purposes of environmental protection, improve air quality, the development of gas sensor with high sensitivity, low cost, easy to maintain is also increasingly urgent, thus to effectively test and inspect a variety of gases of toxic, hazardous, flammable, explosive and so on. Chemical gas sensor of metal oxide semiconductor sensor has been extensively studied, due to its high sensitivity, fast response, and low cost etc..

 

Tungsten oxide (WO₃) is a common metal oxide semiconductor gas material, and because of its low operating temperature, high sensitivity, it has become one of the key research direction in recent years. WO₃ is a transition metal oxide, with the melting point of 1473°C, boiling point of 1837°C; WO₃ has a strong acid resistance which reacts with any inorganic acids exclude the hydrofluoric acid (HF). Tungsten trioxide is a wide band gap of the n-type semiconductor, the band gap of about 2.4eV ~ 2.8eV. Atmosphere at a specific target, the target molecule and surface of tungsten trioxide will have an oxidation or reduction reaction, and cause the changes of tungsten trioxide’s conductivity, which shows like follows:

1. When the target gas is an oxidizing gas, WO₃ conductivity decreased with the resistance value rise;

2. When the target gas is a reducing gas, WO₃ electrical conductivity increased with resistance decreased.

 

Results showed that tungsten trioxide gas sensor can be used to detect gas of sulfur dioxide. Sulfur dioxide is one of the main pollutants in the atmosphere, and there are two common detection methods which are physical and chemical or electrochemical methods. Wen Changbao and his team used tungsten powder, hydrogen peroxide, methanol and PVP (polyvinyl pyrrolidone) as the raw materials to prepare the tungsten trioxide films by chemical and thermal spray method, the films have a microporous structure, small heat absorption, adsorbing gas fastly, etc. which are conducive to the absorption of sulfur dioxide. Within the gas concentration range of 1.43 *10³~57.2*10³μg/m³, its sensitivity to sulfur dioxide reaches to 6.8. Boudiba with their team prepared WO3 gas sensor on an alumina ceramic substrate by screen printing method, after tested, it proved that this kind of sensor has good response to the sulfur dioxide with the concentration of 2.86 * 10³~28.6*10³μg/m³ under the temperature of 200~300°C.