Structural and electrical properties of Ni-Cu films deposited onto MgO(001) by dc biased plasma sputter deposition

Ni-Cu alloy films were deposited onto MgO(001) substrates at 230 degrees C by d.c. plasma sputtering at 2.7 kV and 8 mA in pure Ar gas using an Ni-10wt.%Cu alloy target. The deposition time was 15 or 30 min. A d.c. bias voltage V-s ranging from 0 to -140 V was applied to the substrate during deposition. The structure, composition and electrical properties of the films were studied as a function of V-s using cross-sectional transmission electron microscopy (XTEM) and X-ray photoelectron spectroscopy (XPS), and measurements of the temperature coefficient of electrical resistance (TCR) from -135 to -15 degrees C. The alloy films, which have the f.c.c. lattice of the components, are monocrystalline with the relationship Ni-Cu(001)/MgO(001) and Ni-Cu [010]/MgO[010] unless V-sp=-110 V. The Cu content in the films decreases from 8 wt.% to 3 wt.% as V-s increases from 0 to -140 V. The growth rate of the films and the value of TCR eta (eta>0) depend on V-s; the film thickness d for the films deposited for 30 min reaches 50+/-1 nm at V-s=0 V and 74+/-2 nm at V-s=-140 V, while eta for the films deposited for 30 min increases appreciably with increasing V-s compared with the films deposited for 15 min, although eta is highest at V-s=-140 V for both cases.