Nanodisperse CrSi(O, N) thin films—conductivity, thermopower and applications

Abstract

The electrical conductivity σ( 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/SiO 2 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 σ( T), investigated between 2K and 400 K. Shows a metal-insulator transition with increasing c o( c N). In the amorphous state σ( 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°C up to 5 × 10 4 microOhm cm and in a smaller range around 27°C up to 2 × 10 5 microOhm 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 CrSi 2, Cr 5Si 3 and Cr 3Si with S(300 K) of 80 microV K −1, 5 microV K −1 and 17 microV K −1, respectively. As a consequence, in the film values between 90 microV K −1 and 10 microV 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.