Structure and Properties of Sputtered Ta–Al2O3 Cermet Thin Films

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.