Magnetic tunnel junctions that utilize perpendicular magnetic anisotropy have attracted growing attention due to their potential for higher storage densities in future high capacity magnetic memory applications. In this study, we present an experimental demonstration of magnetic tunnel junctions composed of perpendicularly magnetized Co∕Pt multilayer electrodes and an AlOx tunnel barrier. The emphasis has been on how to maximize the thickness of the Co layers adjacent to the tunnel barrier while still magnetized perpendicularly for possible spin torque utilization in future applications. It is found that the thickness ratio between the Co and Pt layers and the number of bilayers were significant parameters to customize the magnetic properties. The difference between the switching fields of the soft and the hard layers can be adjusted by the number of repeats of the Co∕Pt bilayers. The measured hysteresis shows virtually zero exchange coupling between the two layers through the tunnel barrier. Measured tunneling magnetoresistance ratio of the fabricated submicron-size tunnel junctions ranges from 10% to 15% at room temperature.

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Annealing effects on the structural and transport properties of sputtered CoFeB / MgO / CoFeB magnetic tunnel junctions deposited on SiO 2 / Si were investigated. At the as-deposited state, the CoFeB was amorphous at the CoFeB / MgO interface. High-resolution transmission electron microscope image clearly shows that after annealing at 270°C for 1 h, crystallization of amorphous CoFeB ͑three to four monolayers͒ with lattice matching to MgO ͑100͒ occurred locally at the interface between MgO and CoFeB, producing a magnetoresistance ͑MR͒ around 35%-40%. After annealing at 360°C for 40 min, the MR increased to 102%. The increase in the MR with annealing is attributed to the complete formation of ͑100͒ crystalline structure of CoFeB well lattice matched with the ͑100͒-oriented MgO barrier. The bias voltage dependence of the MR shows a consistent correlation with each CoFeB / MgO interface.

This work demonstrates an anisotropic increase in resistivity with decreasing width in single crystal tungsten (W) nanowires having a height of 21 nm. Nanowire-widths were in the range of 15–451 nm, with the anisotropy observed for widths below 50 nm. The longitudinal directions of the nanowires coincided with the <100>, <110> and <111> orientations of the body centered cubic phase of W. The resistivity increase was observed to be minimized for the <111>-oriented single crystal nanowires, exhibiting a factor of two lower increase in resistivity at a width of ~15 nm, relative to the thin film resistivity (i.e., an infinitely wide wire). The observed anisotropy is attributed to crystallographic anisotropy of the Fermi velocity and the resultant anisotropy of the electron mean free path in W, and underscores the critical role of crystallographic orientation in nanoscale metallic conduction.

Ultrahigh density vertical magnetoresistive random access memory (invited)Long term stability of dry etched magnetoresistive random access memory elements High density submicron magnetoresistive random access memory (invited)