Optimization of Tunneling Magnetoresistance in Perpendicular Magnetic Tunnel Junctions With Co|Pd Reference Layers

Abstract

We report on the optimization of Co|Pd-multilayer-based reference layers in magnetic tunnel junctions with perpendicular magnetic anisotropy. By inserting a thin Ta-spacer layer between the CoFeB interfacial layer and Co|Pd multilayer, a high tunneling magnetoresistance up to 98.5% can be achieved. Electron energy loss spectroscopy and synchrotron X-ray diffraction studies show that the high magnetoresistance is related primarily to the suppression of Pd diffusion and secondarily to improved CoFeB texture during annealing.

Correlation between Pd metal thickness and thermally stable perpendicular magnetic anisotropy features in [Co/Pd]n multilayers at annealing temperatures up to 500 °C

“…1(b) and 1(c). Thus, since it is widely believed that the Co/Pd intermixing or Pd diffusion is one of the main factors for PMA degradation during annealing process, 16 Co and Pd thicknesses were frequently used in the MLs. 4,14,16 Therefore, more detailed studies are necessary to clarify the structural characteristics in ML configurations.…”

Challenging issues for terra-bit-level perpendicular STT-MRAM

“…In general, in p-STT-MRAM cells, p-MTJ spin-valves have been developed with the vertically stacking of amorphous CoFeB free layer/MgO tunneling barrier/CoFeB pinned layer with a [Co/Pd] n -SyAF (synthetic anti-ferro-magnetic) layer [13]. The TMR of >150% in p-MTJ spin-valves should be achieved above the BEOL of >350 o C, which is the first challenging issue.…”

“…1(f)). Although the Ta seed based Co 2 Fe 6 B 2 /MgO p-MTJ spin-valves stacked with a [Co/Pd] n -SyAF layer was a surprising invention [13], they could not satisfy the requirement of the BEOL of > 350 o C since the TMR ratio rapidly decreased when the ex-situ annealing temperature increased from 275 to 325 o C, as shown in Fig. 1(e).…”

Perpendicular magnetic tunnel junction (p-MTJ) spin-valves designed with a top Co2Fe6B2 free layer and a nanoscale-thick tungsten bridging and capping layer

“…A bridging layer ferro-couples the Co 2 Fe 6 B 2 pinned layer with an upper synthetic anti-ferromagnetic (SyAF) layer in the p-MTJ spin-valve, and a capping layer is sputtered on the Co 2 Fe 6 B 2 free layer, as shown in Figure 1a and b. [19][20][21] In addition, the mechanism by which the bridging and capping materials determine the TMR ratio is analyzed by the static perpendicular magnetic anisotropy (PMA) behavior, the face-center-cubic (fcc) crystallinity of the MgO tunneling barrier and the atomic compositional depth profile of the p-MTJ spin-valves. 22 …”