NANODISPERSE CRSI(O, N) THIN-FILMS CONDUCTIVITY, THERMOPOWER AND APPLICATIONS

The electrical conductivity sigma(T) and thermopower S(T) of Cr-Si-O and Cr-Si-N thin films were investigated as a function of their microstructure for different ratios [Si]/[Cr] > 1 and concentrations c(O) and c(N) up to 50 at.%. The films were prepared by reactive d.c. sputtering of CrSi targets and non-reactive r.f.-diode sputtering of CrSi/SiO2 targets respectively. The as-deposited amorphous structure a-Cr-SiO(x)(SiN(y)) is changed by stepwise annealing into a nanodisperse structure nc-Cr(n)Si(m)-SiO(x)(SiN(y)). The temperature dependence sigma(T), investigated between 2 K and 400 K, shows a metal-insulator transition with increasing C(O)(C(N)). In the amorphous state sigma(T) is described by weak and strong localization, analogous to doped amorphous semiconductors. In the nanodisperse state a temperature coefficient of resistivity near zero was obtained within the temperature range -50-120-degrees-C up to 5 x 10(4) muOMEGA cm and in a smaller range around 27-degrees-C up to 2 x 10(5) muOMEGA cm. These properties are used in high ohmic and precision thin film resistors. Results are also given for nc-Cr(n)Si(m)-SiAlO(x) thin films. The thermopower of the nanodisperse films is found to be essentially determined by the metallic components. With increasing c(O) (c(N)) these components are CrSi2, Cr5Si3 and Cr3Si with S(300 K) of 80 muV K-1, 5 muV K-1 and 17 muV K-1, respectively. As a consequence, in the film values between 90 muV K-1 and 10 muV K-1 were obtained. The temperature dependence S(T) above 300 K is reversible at least up to T(ann). These results also make the nanodisperse films very suitable for application in thermoelectric sensors.