Low-Magnetoresistance RuO2-Al2O3 Thin-Film Thermometer and its Application

Thermometers consisting of RuO2-Al2O3 composite thin films were prepared by RF sputtering. It was found that different electrode-patterning techniques have dissimilar effects on the magnetoresistance (MR) and the temperature coefficient of resistance (TCR). In general, the thermometers with electrodes fabricated by photo-resist lithography exhibit superior performance compared to those with electrodes prepared using a metal mask. By adjusting the relative compositions of RuO2 and Al2O3, the thermometers can be applied to a wide temperature range from 60 mK to 500 K. In a pulsed magnetic field up to 55 T, the MR at 4.2 K of a typical thermometer for the temperature range from 1.4 K to 300 K increases linearly with magnetic field to a maximum of similar to 15 %, corresponding to a temperature deviation of similar to - 4 %. As frequency increases from dc to 1.9 MHz, the MR decreases from - 13% to similar to - 0.5% at T = 1.3 K and H = 55 T. By integrating the thermometer with a heater on a sapphire chip, a micro-calorimeter can be developed and successfully used to measure the heat capacity of small mg-sized sample. The RuO2-Al2O3 composite film can also be employed as an infrared bolometer operated at room temperature.