Structural and electrical properties of NiCu films deposited onto MgO(001) by d.c. biased plasma sputter deposition

Abstract

NiCu alloy films were deposited onto MgO(001) substrates at 230 °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 °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 η (η > 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 η for the films deposited for 30 min increases appreciably with increasing V s compared with the films deposited for 15 min, although η is highest at V s = −140 V for both cases.