Grain size effects on low temperature electrical transport in sputtered ZrNxOy thin films

Abstract

Accurate low-temperature measurements are crucial in fields such as high energy physics, nuclear engineering, and aerospace. ZrN_xO_y thin films exhibit resistance highly sensitive to temperature variations due to meticulously controlled growth parameters. The grain size of these films, significantly influences their low-temperature electrical transport properties, a relationship that remains insufficiently explored. In this study, the effects of grain size evolution by controlling deposition temperature are investigated, focusing on the temperature dependence of resistivity and magnetoresistance behavior in a low-temperature strong magnetic field. As grain size decreases, room temperature resistivity, the intensity of transverse phonon modes, and disorder all increased. The electron − phonon interactions strength weakens as the grain size decreases. The w(T) function, which is the logarithmic derivative of electrical conductance with respect to temperature, exhibits anomalous behavior in the temperature range of 300 K−100 K (i.e., dw/dT > 0), contrasting with the negative slope observed from 100 K to 2 K. By analyzing w(T), it is determined that multiple conduction mechanisms overlap in this series of samples. At 2 K, 0.2 % positive saturated magnetoresistance shows in weak magnetic fields, transitioning to unsaturated negative magnetoresistance as the magnetic field increases until 9 T, is consistent with the correlation effects and spin-flip hopping theory. Meanwhile, positive magnetoresistance is unaffected by grain size, whereas negative magnetoresistance weakens as grain size increases. Grain size evolution effect offers an approach for evaluating and developing high-sensitivity thermometers for a wide temperature range.