Growth and Electronic Properties of Sputtered Ni–NiO Films as a Potential Resistive Memory

Abstract

NiO films were deposited by radio-frequency reactive magnetron sputtering from a Ni target in an Ar–O2 mixed atmosphere. The flow rate of Ar was controlled at 20 sccm and that of oxygen was controlled at 1.0 (S1.0), 1.5 (S1.5), 1.6 (S1.6), 2.0 (S2.0), 2.3 (S2.3), and 3.0 (S3.0) sccm. The formation of defects, change in preferential orientation, and electrical conduction properties of the deposited films were examined with X-ray absorption spectra. The results indicate that the deposited films altered from being Ni-rich to O-rich as the oxygen flow rate increased. S1.0 is a Ni-like structure whereas other samples are NiO. X-ray absorption spectra reveal small amounts of Ni metal in S1.5 and S1.6, forming metal clusters or isolated Ni0 atoms in the films. When the oxygen flow rate was increased from 2.0 to 3.0 sccm, the deposited films became p-type, coinciding with a preferential orientation altered from (200) to (111). This alternation is attributed to the formation by excess oxygen of an oxygen layer, which benefits the growth of the (111) plane. A Ni-rich NiO film deposited at oxygen flow rate 1.6 sccm contains isolated Ni atoms and a non-conductive NiO matrix, which is promising for the resistive-based memory.