ON TEMPERATURE-DEPENDENCE OF CONDUCTIVITY AND THERMOPOWER OF CO-SPUTTERED NI-X-(SIO2)(1-X) COMPOSITE THIN-FILMS

The dependence of the electrical conductivity, sigma(T) and thermopowe r, S(T), of Ni-SiO2, thin films on temperature, as a function of the m etal content, for Ni concentration values near the percolation thresho ld has been investigated. The cermet films are deposited by r.f. sputt ering, in Ar atmosphere (p approximate to 10(-2) mbar), using composit e targets. The samples are thermally treated in vacuum, at 600 and 700 K, respectively, in order to stabilize their electrical properties. T he dependence of the samples' conductivity on the temperature has been studied between 200 and 500 K and it shows a metal-insulator transiti on when the Ni content in the films decreases below 50%. In order to s tudy the thermopower of Ni-SiO2 films, we prepared Pt/(Ni-SiO2) thin-f ilm test thermocouples, on alumina substrates, also by r.f. sputtering . The dependence of S on temperature does not show the metal-insulator transition for the entire compositional range we investigated. The fi lms also present a good resistance to the oxidation agents. The values of the TCR (temperature coefficient of resistance) and S(T) obtained the near the a percolation compositional range make Ni-SiO2 thin films interesting for applications in the field of temperature sensors. (C) 1997 Elsevier Science S.A.