Morphologic, Compositional and Magnetic Characterization of Sputtered CoCr Thin Films for Applications in MTJs as Hard Spin Injectors

Abstract

Spin-polarized currents across an insulating tunnel barrier, needed for the development of efficient magnetic tunneling junctions (MTJs), may be obtained using hard spin injector electrodes. Thin films of CoCr solid solutions have been fabricated involving two main steps: 1) deposition of Co/Cr alternated layers via RF magnetron sputtering both onto silicon (100) substrates and thermally oxidized wafers and 2) thermal annealing in a partial Ar pressure of 1 mTorr at 450°C for 1 hour and cooling treatment in a uniform magnetic field (600 Oe). The deposition of stacks of pure elements and subsequent diffusion treatment has been preferred instead of the direct deposition of the native alloy because in the former case the right composition and magnetic bias may be tuned more easily playing on the layer thicknesses and number of repetitions.

A detailed numerical correlation of field effect SEM images and EDX micro-maps was used to evaluate the oxygen diffusion on the magnetic film, while an alternating gradient force magnetometer (AGFM) allowed us to evaluate at room temperature both coercivity and magnetic bias obtained after the field cooling treatment. The effect of standard thermal treatment on the homogeneity of the films is discussed, and a possible alternative heating technique is proposed.