Analytical investigations of tunnel magnetoresistance layers

Abstract

The basic elements of tunnel magnetoresists are two magnetic layers separated by an insulating barrier layer. The uniformity of this only 1-2 nm thick barrier layer up to dot edges and the chemical composition of the layers are properties important for the efficiency of tunnel magnetoresistance devices. These key-properties have been investigated by analytical TEM methods like high resolution TEM imaging and energy-filtered imaging. With regard to the chemical composition the TEM results have been confirmed by XPS investigations. The subsequent oxidation of the barrier is one of the most critical steps of the deposition procedure of the layer stacks. An undersized oxygen dose leads to an incomplete oxidation of the barrier layer with uncontrollable tunnel behaviour. An overdose of oxygen leads to oxygen diffusion in the layers beneath the barrier and uncontrollable magnetic hardness of the lower magnetic electrode.

Quantitative ARXPS investigation of systems with ultrathin aluminium oxide layers

“…Analysis of the Co 3p spectra has shown that the cap layer is oxidized, 3 as expected from the sample's contact with the atmosphere. From the ARXPS model calculation using the total peak areas of O 1s, C 1s, Al 2p and Co 3p core levels, we obtain a fit to the experimental atomic concentrations (Fig.…”

“…1,2 For aluminium oxide barriers much work is devoted to achieve very thin layers by optimization of deposition and new plasma oxidation methods. 3 Angle-resolved x-ray photoelectron spectroscopy (ARXPS) is a very powerful method that allows the in-depth composition of the investigated sample to be determined non-destructively. However, because of the limitation of the surface sensitivity to an information depth of up to ¾3 , where denotes the attenuation length of an electron within a material, 4 it is only possible to investigate the sample up to a maximum depth of ¾10 nm with standard XPS excitation sources.…”