Experimental study of chromium oxide thin films as an intermediate layer for Pt-based temperature sensor applications

This paper reports, the impact of high-temperature annealing on temperature coefficient of resistance (TCR) of platinum thin films, by using chromium oxide as an intermediate adhesion layer. Chromium oxide thin films were prepared by using the RF magnetron sputtering technique. These thin films were then characterized with the scanning electron microscopy and X-ray photoelectron spectroscopy to optimize thickness and identify their elemental compositions. Thin film platinum resistance temperature detector (RTD) prototype devices, with sensing element of width ~ 40 µm and thickness of ~ 164 nm were fabricated and their TCR values were evaluated with and without thermal annealing treatment. The average value of temperature coefficient of resistance (TCR) was observed to be ~ 1976 ppm/°C without annealing, which increased to ~ 2839 ppm/°C with annealing up to 1000 °C. Finally, for practical applications, an electronic interface circuit for the resistance temperature detector (RTD) device was used, to demonstrate the functioning of the devices for their end application in temperature sensing. These results clearly demonstrate that chromium oxide can be used as an alternate adhesion layer, for enhancement in TCR of platinum thin films that are required for various MEMS applications.