Investigation of oxide tunnel barriers by atom probe tomography (TAP)

Oxide tunnel barriers (TMR) are currently of interest for application in magnetic sensor and storage devices. Compared to giant magneto resistance (GMR) devices, tunnel barriers are distinguished by an improved effect amplitude and a higher base resistivity, so that they may be used in 'current perpendicular to plane' arrangements. We investigated the nano-structure of such TMR devices using field ion microscopy in combination with a 2D-detection setup. Spin valve structures consisting of Co and Ni(79)Fe(21) electrodes and Al(2)O(3) barriers were prepared by sputter deposition on tips of 30-50 nm radius of curvature suitable for field ion microscopy. Inspite of the isolating character of the barrier material, the chemical structure can be reasonably characterized by analytical field ion microscopy. The 3D spatial distribution of the atomic species, in particular the distribution of oxygen, is discussed in dependence on various deposition methods.