Thin film temperature sensor for cryogenic region with small magnetoresistance

Chromium nitride (CrN) thin films were fabricated onto Si wafers by RF magnetron sputtering equipment in pure N2 gas. By adjusting the fabrication conditions, the film had negative temperature coefficient of resistance (TCR) below 300 K. It showed reasonable sensitivity between 300 and 1.8 K. The temperature resolution in the cryogenic temperature region was better than 1 mK. A good thermal cycle stability was observed. After 27 thermal cycles between 4 and 300 K, the coefficient of variation (CV) value was as small as 0.098% at 4 K, which corresponds to a 2.1 mK temperature shift. In addition, the thermometer was nearly insensitive to the magnetic field. The temperature shift due to magnetoresistance in a magnetic field of 9 T was less than 5 mK at 4 and 2 K. Therefore CrN can be an excellent choice of material for cryogenic temperature sensors under magnetic fields.

► We have succeeded to make a thin film temperature sensor made of CrN.
► The sensor showed reasonable sensitivity between 1.8 and 300 K.
► The CV value at 4.00 K after 27 thermal cycles was 0.098%, which corresponds to 2 mK.
► Temperature shift due to magnetic field up to 9T was less than 5 mK at 2 and 4 K.