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Low-magnification TEM micrograph in cross-section geometry obtained from a working TMR element grown on thermally oxidized silicon with some of the deposited layers indicated. On this scale, the MgO tunneling barrier looks homogeneous. The inset shows the corresponding vs loop of the same junction before FIB thinning.
High-resolution TEM micrograph of the crystalline MgO barrier sandwiched between two amorphous CoFeB layers obtained from a working TMR element.
Low-magnification TEM micrograph in cross-section geometry obtained from a TMR element after dielectric breakdown due to high voltage stresses. On this scale, local regions of the MgO tunneling barrier appear to be thinner compared to their neighborhood; in addition, crystalline diffraction contrast in the CoFeB can be seen at these spots (white arrows). The inset shows the corresponding vs loop of the same junction before FIB thinning and before voltage stress.
TEM image of the tunnel barrier region of a voltage stressed MTJ. The white arrow indicates a pinhole in the MgO layer. In addition, a region of crystalline CoFeB is shown in the region enclosed by the dashed line.
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