MIS gas sensors based on porous silicon with Pd and WO3/Pd electrodes

Pd and WO3/Pd gate metal-oxide-semiconductor (MIS) gas sensitive structures based on porous silicon layers are studied by the high frequency C(V) method. The chemical compositions of composite WO3/Pd electrodes are characterized by secondary-ion mass spectrometry (SIMS). The atomic force microscopy (AFM) was used for morphologic studies of WO3/Pd films. As shown in the experiments, WO3/Pd structures are more sensitive and selective to the adsorption of hydrogen sulphide compared to Pd gate. The analyses of kinetic characteristics allow us to determine the response and characteristic times for these structures. The response time of MIS-structures with thin composite WO3/Pd electrodes (the thickness of Pd is about 50 nm with WO3 clusters on its surface) is slower compared to the structures with Pd electrodes. Slower sensor responses of WO3-based gas sensors may be associated with different mechanism of gas sensitivity of given structures. The enhanced sensitivity and selectivity to H2S action of WO3/Pd MIS-structures can also be explained by the chemical reaction that occurs at the catalytic active surface of gate electrodes. The possible mechanisms of enhanced sensitivity and selectivity to H2S adsorption of MIS gas sensors with WO3/Pd composite gate electrodes compared to pure Pd have been analyzed.