The effect of Ta and Ta/Cu seed layers, and Ta and Cu cap layers on the effective magnetic thickness of ultrathin permalloy (Ni81Fe19) was investigated for MRAM applications. The films were deposited by Ion Beam Deposition. The magnetic moment of each as-deposited permalloy film was measured using a B-H looper and a SQUID magnetometer. The films were further annealed at either 525 K for 1/2 h or 600 K for 1 h to study the effect of thermally driven interdiffusion on the magnetic moment of the permalloy film. Our theoretical calculations showed that the presence of 12% intermixing at the interface reduces the Ni moments to zero. Experimentally, it was shown that the tantalum rather than the copper interfaces are primarily responsible for the magnetically dead layers. The Ta seed layer interface produces a loss of moment equivalent to a magnetically dead layer of thickness 0.6±0.2 nm. The Ta metal in the cap layer results in a loss of moment equivalent to a dead layer of thickness 1.0±0.2 nm. Upon annealing, thermally driven interdiffusion is concluded to have a strong effect on the Ta(seed)/ Ni81Fe19 as-deposited interface, based on the doubling of the magnetically dead layer to 1.2±0.2 nm. The Ni81Fe19/Ta(cap) as-deposited interface slightly increases its equivalent magnetically dead layer upon annealing to 1.2±0.2 nm. As-deposited interfaces of Ta(seed)/permalloy and permalloy/Ta(cap) are not chemically equivalent and result in different magnetically dead layers, whereas after annealing to 600 K both interfaces attain comparable intermixing and magnetically dead layers. It was also shown that a half-hour anneal at the lower 525 K annealing temperature, which is closer to the actual processing temperature, results in only slight increase of the magnetically dead layer at both interfaces.
Write and read characteristics of current-in-plane pseudo-spin-valve (PSV) devices are demonstrated in terms of switching, resistive, and magnetoresistive properties of individual PSV devices and ensembles of PSV devices. Characteristics of PSV devices are described that are necessary and consistent with requirements for a giant magnetoresistive random access memory (GMRAM) which is an integrated magnetics-on-semiconductor memory. An architecture for a GMRAM is described that uses PSV devices for writing, readback, and nonvolatile data retention. Write and read switching, read magnetoresistance, write and read selectivity, switching repeatability, resistance, and change-in-resistance properties have been characterized and described in PSV devices and populations of PSV devices fabricated on bulk Si and complementary metal–oxide semiconductor underlayers. PSV device switching characteristics are shown to be consistent with coupled-switching models and have trends that show similarities with micromagnetic simulation results.
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