Perpendicular magnetic tunnel junctions with synthetic antiferromagnetic pinned layers based on [Co/Pd] multilayers

Abstract

We fabricated MgO-based perpendicular magnetic tunnel junctions (p-MTJ) with Ta/CoFeB magnetic electrodes. Synthetic antiferromagnetic (SAF) pinned layers with perpendicular magnetic anisotropy (PMA) were included into the p-MTJs by using two Co/Pd multilayers (MLs) separated by a thin Ru spacer layer. The MTJs stack has the structure bottom contact/free layer CoFeB (1.0)/MgO (1)/pinned layer CoFeB (1.0)/Ta spacer layer/SAF/Ru cap layer/top contact (the units in parenthesis are in nanometers). The SAF was optimized by changing the repetition period n in one of the Co/Pd multilayers and the Ru thickness in order to obtain PMA with antiferromagnetic (AFM) coupling. The Ru spacer values were 0.7, 0.75, 0.8, 0.85, and 0.9 nm. The magnetic studies show that all magnetic films, including the Ta/CoFeB layers, are perpendicularly magnetized. The two Co/Pd MLs are AFM coupled for n > 2. Controlling the Ru thickness, the interlayer exchange coupling strength Jiec can be tailored. Jiec vs. Ru thickness exhibits a simple exponential decay. The electrical properties of the full p-MTJ with SAF show a low resistance-area (RA) product of 44.7 Ω μm2 and a tunnel magnetoresistance (TMR) ratio of 10.2%.

Annealing stability study of Co20Fe60B20\MgO\Co20Fe60B20perpendicular magnetic tunnel junctions

“…pMTJs also benefit from having a better thermal stability. pMTJs have been prepared using (Co\Pd) or (Co\Pt) multilayers, superlattices [1, 14-15], or L1 0 -ordered alloys [16] as the ferrimagnets.…”

Dependency of anti-ferro-magnetic coupling strength on Ru spacer thickness of [Co/Pd]n-synthetic-anti-ferro-magnetic layer in perpendicular magnetic-tunnel-junctions fabricated on 12-inch TiN electrode wafer

“…11 Furthermore, in order to realize the mass production of p-STT MRAM, p-MTJ should be fabricated on TiN electrodes sputtered on 12-in. Si wafers due to being connected with a selective n-MOSFET cell-transistor.…”

“…[5][6][7][8][9] Recent studies have provided evidence that CFB/MgO based p-MTJ spin-valves with a synthetic anti-ferro-magnetic (SyAF) layer based on [Co/Pd] n -multilayers (MLs), which enhance the thermal and magnetic stabilities of the sensors, have a high TMR ratio and low RA for realizing p-STT MRAM devices. [10][11][12][13][14][15][16][17] In addition, anti-ferro-magnetic coupling strength (J ex ) in a SyAF layer is a critical device parameter to attain a terra-bit-level nonvolatile memory since a smaller J ex leads to a high occurrence of cross-talk in p-MTJ-cell array. 11 The J ex in a SyAF layer of >0.7 erg/cm 2 is essential to ensure the read/write failure margin of p-STT MRAM.…”

“…[10][11][12][13][14][15][16][17] In addition, anti-ferro-magnetic coupling strength (J ex ) in a SyAF layer is a critical device parameter to attain a terra-bit-level nonvolatile memory since a smaller J ex leads to a high occurrence of cross-talk in p-MTJ-cell array. 11 The J ex in a SyAF layer of >0.7 erg/cm 2 is essential to ensure the read/write failure margin of p-STT MRAM. 18 A SyAF layer consisting of a upper SyAF layer, a Ru spacer layer, and a lower SyAF layer, which are antiferro-magnetically coupled, is shown in the left box of Figure 1.…”

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 …”