Metal-free phthalocyanine and palladium sensor structure with a polyethylene membrane for hydrogen detection in SAW systems

The results concerning bilayer sensor structures (metal-free phthalocyanine (H2Pc) + palladium (Pd)) with various thicknesses of metal-free phthalocyanine (∼120 nm, ∼160 nm and ∼200 nm), but the same thickness of palladium (∼20 nm), have been studied with respect to the application of hydrogen gas-sensing at a relatively low interaction temperature ∼30–38 °C, employing a method based on the surface acoustic wave (SAW) system. All the films are produced by physical vapour deposition (PVD) in a SAW gas sensor system with a dual-delay line configuration. In the case of the best structure, H2Pc ∼ 160 nm and Pd ∼ 20 nm (the greatest change in frequency due to hydrogen gas interaction at the same temperature), single and double novel polyethylene (PE) membranes are placed on the top of the bilayer structure to reduce the influence of humidity. These PE membranes are made in a special way also by means of the PVD technology (at a temperature of ∼190–250 °C). The thickness of a single PE film amounts to about several score nanometers (60–80 nm). These membranes can also reduce the influence of other gases, like CO, NO2 and ammonia.