WO3-Pd Structure in SAW Sensor for Hydrogen Detection

In the paper a new sensor structure for surface acoustic wave gas system is presented. A bilayer structure WO3-Pd thin films may be useful for hydrogen detection in low concentration in air. A bilayer sensor structure of tungsten oxide WO3 with a very thin catalytic film of palladium on the top has been studied for gas-sensing application at room temperature (about 25 degrees C) in surface acoustic wave system. The bilayer structure of WO3 layers with a thickness of about 50 nm, 100 nm and 150 nm was made onto a LiNbO3 Y-cut Z-propagating substrate by means of the vacuum sublimation method using a special aluminum mask. The vapor source consisted of commercially available WO3 powder (Fluka 99.9%) and molybdenum heater. The thin palladium (Pd) layer (about 10 nm) was made separately on each WO3 layer by means of vapor deposition in high vacuum. There have been investigated three structures: 50 nm WO3 + 10 nm Pd, 100 nin WO3 + 10 nm Pd and 150 nm WO3 + 10 nm Pd in three canal surface acoustic wave system with reference oscillator. Numerical results obtained by analysis of the surface acoustic wave gas sensor model have been compared with experimental results.