抄録
Microstructures of Pt/Ti thin-films on SiO2/Al2O3 substrates and their relationship to the temperature coefficient of resistance (TCR) were investigated by means of X-ray diffraction analysis, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and measurement of electrical resistance. We prepared four different specimens: one as-sputtered and three annealed in vacuum, argon gas and air, respectively. The TCRs were determined to be the largest for the air-annealed specimen and decrease in order of the as-sputtered, the argon-annealed and the vacuum-annealed ones. It is observed that, in the as-sputtered specimen, the Pt film with the preferred (111) orientation deposits on the ultra-thin Ti film with the (00·1) orientation. In the annealed specimens, Ti partly migrates into the Pt film and forms TiO2 precipitates with the rutile-type structure at the Pt/SiO2 interface and in the Pt film. The TiO2 precipitates in the Pt film are relatively small in size, and the amount is observed to be the largest in the air-annealed specimen and decreases in order of the argon-annealed and the vacuum-annealed ones. It is considered that the remaining Ti atoms construct Pt-Ti solid solution in the Pt film, and thereby decrease the TCR from that of the pure Pt film. From these observations, the formation of a large amount of TiO2 precipitates in the air-annealed specimen results in a substantial decrease of Pt-Ti solid solution, and thereby gives rise to a higher value of TCR. It is clarified from the present investigation that oxgen in air play an important role in the improvement of the TCR value by forming a sufficient amount of TiO2 precipitates.
