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

摘要

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.