Production of high purity nanosized SnO2 powder used as target material for gas sensor applications

In gas sensor applications, SnO2-based systems are the most promising materials which are capable of sensing a large number of gas species easily, offer high sensitivity, simpler design, and relatively inexpensive components. The most important factors affecting the critical gas sensor property known as gas sensitivity are the actual grain size and purity level of the sensing material. It is expected that grain size should be less than 6 nm and purity level is higher than 99.95% by weight for the gas materials. Thus, hydrothermal synthesis is the one of the most useful methods among the others to produce nanosized SnO2 powders with high purity, controlled particle size and distribution. The scientific objective of this study was to develop an understanding about the formation and growth mechanism of SnO2 powders as a function of initial cation concentration (0.025-1.0 M) and treatment time (1-24 h). The technological objective of this study was to determine the processing conditions of magnetron sputtered SnO2 based thin film gas sensors from target materials produced by hydrothermal synthesis. First, initial cation concentration increases from 0.025 to 1.0 M in order to understand SnO2 formation mechanism during hydothermal synthesis. As initial cation concentration increases from 0.025 to 0.1 M, particle size increases. However, as initial cation concentration increases 0.1 to 1.0 M, particle size decreases. It is observed that mechanism of particle formation shifts from Ostwald ripening to classical nucleation theory at critical cation concentration (i.e., 0.1 M in this study). It has also observed that particle growth mechanism is diffusion controlled for 1.0 M cation containing system. Hydrothermally produced SnO2 powders were used as target materials for synthesis of ZnO doped thin film gas sensors at different composition. It is observed that 0.55% Zn (by atomic) doped SnO2 film exhibits highest gas sensitivity at lower working temperature. Keywords: Tin oxide (SnO2), hydrothermal synthesis, nanosized particles and formation mechanism, gas sensor