MIS gas sensors based on porous silicon with Pd and WO 3/Pd electrodes

Abstract

Pd and WO 3/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 WO 3/Pd electrodes are characterized by secondary-ion mass spectrometry (SIMS). The atomic force microscopy (AFM) was used for morphologic studies of WO 3/Pd films. As shown in the experiments, WO 3/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 WO 3/Pd electrodes (the thickness of Pd is about 50 nm with WO 3 clusters on its surface) is slower compared to the structures with Pd electrodes. Slower sensor responses of WO 3-based gas sensors may be associated with different mechanism of gas sensitivity of given structures. The enhanced sensitivity and selectivity to H 2S action of WO 3/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 H 2S adsorption of MIS gas sensors with WO 3/Pd composite gate electrodes compared to pure Pd have been analyzed.