Microstructure and temperature coefficient of resistance of platinum films

Platinum thin films are prepared on alumina ceramic substrates by rf magnetron sputtering. Microstructure and morphology are found to be sensitive to the sputtering gases and substrate surface conditions. N-2-sputtered films show better microstructure quality than Ar-sputtered ones for use in forming industrial platinum resistance thermometers (IPRTs). The preferred (111) orientation in both as-deposited and recrystallized Pt films are identified using X-ray diffraction analysis. Thin-film Pt resistance thermometers are fabricated by laser beam trimming. The values of temperature coefficient of resistance (TCR) for N-2-sputtered films show values close to the desired IPRT specification of 3850 ppm/degrees C and increase proportionally to the film's thickness. The dependence of microstructure and TCR on various heat treatment conditions Is also investigated.