XPS analysis of the interface of ceramic thin films for humidity sensors

MgAl2O4 thin films, deposited on Si/SiO2 substrates, were studied as humidity sensors. This paper discusses the evaluation of the chemical composition at increasing depths, carried out by a combination of Ar+ ion etching and XPS analysis. These analyses showed the simultaneous presence of Mg, Al and Si at the film/substrate interface. The thickness of the interfaces were calculated between 7 and 10 nm. The shift in the binding energies of the XPS peaks observed at the interface seems to demonstrate the occurrence of a chemical interaction between film and substrate. At the interface, Si 2p binding energy values are characteristic of a silicate, and this effect may be responsible for the good adhesive properties of MgAl2O4 films to silica, as demonstrated by peel tests with Scotch tape.