Thermoelectric power and temperature coefficient of resistivity of thin metal films

Abstract

The dependence of the electrical conductivity, σ(T) and thermopower, S(T), of Ni-SiO2 thin films on temperature, as a function of themetal content, for Ni concentration values neat" the percolation threshold has been investigated. The cermet films are deposited by r.f. sputtering, in Ar atmosphere (p ≈ 10-2 mbar), using composite targets. The samples are thermally treated in vacuum, at 600 and 700 K, respectively, in order to stabilize their electrical properties. The dependence of the samples' conductivity on the temperature has been studied between 200 and 500 K and it shows a metal-insulator transition when the Ni content in the films decreases below 50%. In order to study the thermopower of Ni-SiO2. lihns, we prepared Pt/(Ni-SiO2) thin-film 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 films 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 percolation compositional range make Ni-SiO2 thin lilms interesting for applications in the field of temperature sensors.