Structural properties of rf magnetron sputter deposited nickel manganate thin films

Abstract

Nickel manganate thin films of ∼700 nm thickness have been deposited on [1 0 0] silicon substrates using rf magnetron sputtering in an argon atmosphere from optimised targets. Targets were sintered at different temperatures and SEM analysis revealed superior surface density for sintering temperatures of at least 1200 °C. The average grain size increased with sintering temperature and fitted a Rayleigh function. For film growth a substrate temperature of 200 °C proved to be optimal. The effect of subsequent annealing in air from 650 °C to 900 °C in steps of 50 °C on the microstructure was investigated. X-ray diffraction studies showed that the films re-crystallised from an amorphous-like structure to a cubic spinel phase. A preferred orientation of the film in the [1 0 0] out-of plane crystal direction was strongly pronounced in a temperature window around 200 °C substrate temperature. Films were studied by AFM and showed distinct crystallographic grains (sized ∼50 nm) after annealing. The lattice constant of thin films was lower than for the bulk target material, but was not correlated with annealing temperature.