Effect of macrostructure and composition of the top metal electrode on properties of MIS gas sensors

Pd and Pd/Cu gate MIS gas sensitive structures are studied by the high-frequency CV method. The loss of the gas sensitivity due to interaction of the top electrode with the environment are characterised by Auger spectroscopy and scanning electron microscopy. Pd/Cu structures are more sensitive to the adsorption of the gas molecules compared to Pd gate. The base-line inversion after air recovery is observed and this effect is discussed. The response time of MIS structure with a thin fresh Pd/Cu electrode (∼500 Å) is slower compared to the structures with a thick Pd gate (∼1000 Å). Similar results have also been obtained for thick aged Pd electrodes. Slow responses of these structures may be associated with a Pd oxide growth on a Pd surface and/or an enhanced adsorption of oxygen and water species at the boundaries of Pd/Cu grains. The higher active hydrogen sensitivity catalyst Pd/Cu has been modelled on a more intensive dissociation of hydrogen molecules on Pd surface doped with Cu.