NTC thin film temperature sensors for cryogenics region with high sensitivity and thermal stability

HfOxNy thin films were deposited on polished and oxidized silicon wafers at different nitrogen-oxygen gas flow rates by DC magnetron reactive sputtering, and temperature sensors based on these HfOxNy thin films were fabricated using a microelectromechanical system micromachining process. The resistance–temperature dependencies of these sensors were studied in the temperature range of 4.2 K–300 K, and the effect of the sputtering gas flow rate on the initial resistivity and sensitivity [temperature coefficient of resistance and absolute sensitivity (Sa)] was discussed. One of these sensors was subjected to 15 cycles between 300 K and 4.2 K for thermal cycle stability testing. The performances of these sensors were compared to the now available negative temperature coefficient thin film temperature sensors (ZrNx, CrNx, RuO2, and ZrOxNy), and they show very outstanding sensitivity and thermal cycle stability. Furthermore, the conduction mechanism of HfOxNy thin films in the cryogenic region was studied for the first time.