Oxygen-rich polycrystalline magnesium oxide - A high quality thin-film dielectric.

Sputtering of a magnesium target with a beam of argon ions in the presence of a partial pressure of reactive oxygen gas has been found to yield smooth Mg0(x) thin-film dielectrics with low electrical loss, good mechanical stability, and excellent reproducibility. The films are polycrystalline with a grain size ~50A and an oxygen-rich stoichiometry. The thickness dependence of the areal capacitance is discussed in the context of a two-layer model in which an oxygen-rich phase (chi)~=1. 4) overlays a thin (~40A) stoichiometric phase (chi)~=1.0). Observation of superconducting tunneling characteristics in trilayer Au-Mg0(x)-Pb structures confirms pinhole-free coverage which may have possible application as artificial tunnel barriers.