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

Abstract

We investigated the Ru spacer-thickness effect on the anti-ferro-magnetic coupling strength (Jex) of a [Co/Pd]n-synthetic-anti-ferro-magnetic layer fabricated with Co2Fe6B2/MgO based perpendicular-magnetic-tunneling-junction spin-valves on 12-in. TiN electrode wafers. Jex peaked at a certain Ru spacer-thickness: specifically, a Jex of 0.78 erg/cm2 at 0.6 nm, satisfying the Jex criteria for realizing the mass production of terra-bit-level perpendicular-spin-transfer-torque magnetic-random-access-memory. Otherwise, Jex rapidly degraded when the Ru spacer-thickness was less than or higher than 0.6 nm. As a result, the allowable Ru thickness variation should be controlled less than 0.12 nm to satisfy the Jex criteria. However, the Ru spacer-thickness did not influence the tunneling-magneto-resistance (TMR) and resistance-area (RA) of the perpendicular-magnetic-tunneling-junction (p-MTJ) spin-valves since the Ru spacer in the synthetic-anti-ferro-magnetic layer mainly affects the anti-ferro-magnetic coupling efficiency rather than the crystalline linearity of the Co2Fe6B2 free layer/MgO tunneling barrier/Co2Fe6B2 pinned layer, although Co2Fe6B2/MgO based p-MTJ spin-valves ex-situ annealed at 275 °C achieved a TMR of ∼70% at a RA of ∼20 Ω μm2.

Double MgO-based Perpendicular Magnetic-Tunnel-Junction Spin-valve Structure with a Top Co2Fe6B2 Free Layer using a Single SyAF [Co/Pt]n Layer

“…Thus, we investigated the face-centered-cubic (f.c.c) crystallinity of the p-MTJ spin-valves by using x-HRTEM. Here we should recall that the f.c.c crystallinity of the MgO tunneling barrier directly affects the probability of coherent tunneling of the spin electrons, determining dominantly the TMR ratio of a p-MTJ spin-valve 14 , 17 – 30 .…”

“…In addition, better f.c.c crystallinity of the MgO tunneling barrier leads to a higher coherent tunneling ability of spin-electrons. Thus, both surface roughness and f.c.c crystallinity directly and dominantly affect the TMR ratio of the p-MTJ spin-valves; i.e., smaller surface roughness and better f.c.c crystallinity of the MgO tunneling barrier leads to a higher TMR ratio 14 , 17 – 30 . Thus, as revealed in the x-HRTEM image, the MgO tunneling barrier of the spin-valve using the single SyAF [Co/Pt] n layer obviously showed a smaller surface roughness and better f.c.c crystallinity compared with the barrier of the spin-valve with the double SyAF [Co/Pt] n layer.…”

Dependency of tunneling magneto-resistance on Fe insertion-layer thickness in Co2Fe6B2/MgO-based magnetic tunneling junctions

“…The buffer layer (Co/Pt) and [Co/Pd] n -SyAF layers were also well-textured along fcc (111), which means they could operate perfectly well as a ferromagnetic coupling between the CFB pinned and lower SyAF layers and an antiferromagnetic coupling between the lower and upper SyAF layers. 23 In addition, the Ta seed showed an amorphous structure, being well matched with an amorphous CFB free layer. Figure 5(b) shows an x-HR-TEM image of a p-MTJ spin valve with a CFB free layer/MgO tunneling barrier/Fe insertion-layer/CFB pinned layer structure of 1.0/1.0/0.0/1.0 nm thicknesses.…”

“…The Co/ Ru/Co spacer thickness was 0.4/0.6/0.4 nm to obtain a maximum J ex and a perfect antiferromagnetic coupling between the lower and upper SyAF layers. 23 Finally, the Ru electrode was sputtered on the a-Ta buffer layer to avoid lattice mismatch between the hcp Ru and the fcc [Co/Pd] n -SyAF layers. Note that the inserted thick arrows represent typical magnetization configurations at zero magnetic fields.…”

“…This issue is a critical device parameter for attaining a terabit-level nonvolatile memory because a smaller J ex leads to a high occurrence of crosstalk in p-MTJ cell arrays. [21][22][23] In particular, achieving a J ex of > 0.7 erg/cm 2 in a CFB pinned layer with SyAF layers is essential to ensure the read/write failure margin of p-STT MRAMs. 24 Furthermore, to mass produce terabit-level p-STT MRAMs, p-MTJ spin valves should be fabricated on a TiN electrode sputtered on 12-in.…”