Abstract
Ta–Al2O3 cermet thin films were produced by diode sputtering. Cathodes were fabricated by powder techniques, plasma spraying and as mechanical composites. Film compositions of 1–20 wt% Al2O3 produced resistivities of 250 to 25 000 μΩ·cm and TCR's of +100 to −450 ppm/°C, respectively. The films showed good thermal stability and could be anodized. Electron microscopy and x-ray analyses suggest a film structure consisting of long columnar grains of bcc Ta, approximately 100 Å in diameter, surrounded by Al2O3. A quantitative analysis is made of tunneling currents in an idealized film. Resistivity-composition and resistivity-temperature data are explained in terms of this analysis. The height of the Al2O3 barrier between grains is estimated to be 0.23 eV for an effective electron mass of 1/9. Barrier thicknesses are estimated at 15–30 Å.
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