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We report reliable 5 ns switching of spin-transfer torque magnetoresistive random-access memory devices of nominal size 43 nm and a resistance area product of 11 Ω·µm2. We measured 256 devices with a 100% write-error-rate (WER) yield at a WER floor of $10^{-6}$ and a steep WER slope as a function of voltage. A single device had a WER less than $10^{-10}$ for 5 ns write pulses. We show promising 3 ns switching performance, with a 94% WER yield at a $10^{-6}$ WER floor, for 64 devices of nominal size 50 nm.

The dependence of the write-error rate (WER) on the applied write voltage, write pulse width, and device size was examined in individual devices of a spin-transfer torque (STT) magnetic random-access memory (MRAM) 4 kbit chip. We present 10 ns switching data at the ${10^{ - 6}}$ error level for 655 devices, ranging in diameter from 50 nm to 11 nm, to make a statistically significant demonstration that a specific magnetic tunnel junction stack with perpendicular magnetic anisotropy is capable of delivering good write performance in junction diameters range from 50 to 11 nm. Furthermore, write-error-rate data on one 11 nm device down to an error rate of $7{\times}10^{ - 10}$ was demonstrated at 10 ns with a write current of $7.5\;\upmu{\rm A}$ , corresponding to a record low switching energy below 100 fJ.

With the promise of nonvolatility, practically infinite write endurance, and short read and write times, magnetic tunnel junction magnetic random access memory could become a future mainstream memory technology.

Wide-field magneto-optic Kerr observation techniques are described for the imaging of magnetic recording heads and other small magnetic devices. The imaging problems encountered for these samples are quite different from those for continuous films and lead to a different set of experimental approaches. Observation techniques that preserve the magnetic state of the sample allow for the implementation of new image acquisition algorithms based on multiple additions and subtractions that progressively build up a weak Kerr contrast even under unfavorable experimental conditions. Examples of results are presented. >

The authors report on a newly discovered domain configuration, observed with a magnetooptical microscope, in narrow stripes of NiCoFe, CoFeCu and NiFe. The stripes-1 to 25 mu m wide and 0.5 to 2.0 mu m thick-are used as a model for a narrow-track pole of a recording head. The new domain configuration, with its magnetization oriented mostly in a plane perpendicular to the long dimension of the stripe, suggests the possibility of obtaining a large high-frequency susceptibility even in recording head poles as a narrow as 1 mu m. >

The magnetic domain structure at the media-facing surfaces of the single-crystal ferrite MIG heads is investigated using the magnetooptical Kerr effect. Domain behavior depends strongly on the stress state and surface treatment of the head. The pole tips display coercive zig-zag domain walls, which are nucleated at the gap by write current pulses. For the samples studied, nucleation and motion of these walls are different between heads which exhibit small secondary pulses in the read-back signal and heads which do not. >

A novel magnetooptic imaging technique was used to investigate the dynamics of magnetization response in thin-film head yokes. Completed head devices were excited with a sinusoidal current applied to the integrated coils. The amplitude (20 to 40 mA pp) and frequency (1 to 50 MHz) of excitation were chosen to simulate the write process. Pulsed laser illumination permitted stroboscopic observation of domain-wall and flux-flow dynamics with a time resolution limited only by the 5-ns pulse width (full width at half maximum). Results suggest that high-frequency write performance is degraded by two mechanisms not considered previously for thin-film heads: first, 180 degrees walls appear to impede the flux-flow across the plane of the wall and, second, the inhomogeneous rotational magnetization response observed is known to be much slower than the typically assumed coherent rotation. The effect of NiFe composition on dynamics was also investigated by comparing responses of two heads, one having positive and the other negative magnetostriction. Flux in the head with positive magnetostriction flows in a constricted path along yoke edges, rather than at its center, which is consistent with the significantly lower efficiency measured electrically for this head. >

A magnetooptic microscope was used to observe the time-averaged magnetization distribution in an inductive thin-film head excited by continuous sine waves. Domain activity in yokes driven with sinusoidal currents (1 to 20 MHz) was observed using the Kerr effect at video frame rates (0 to 30 Hz). Thus, the average location and shape of domains in the top yoke of the head could be recorded. It is shown that the domain pattern generally undergoes significant changes in a slow, repeatable evolution. Some changes lead to abrupt conversions of domain states. Although specific behavior varies from head to head, these conversions follow measurable curves having a common trend in the amplitude versus frequency space. Previous work on analysis of head response has not considered this type of dynamic response, although it appears to be common to many magnetic system. In addition to possible response at the excitation frequency, the wall network can also undergo large changes with a time scale much longer than the excitation period. Three possible mechanisms driving the domain conversions are outlined. >