Abstract
We examine highly stable perpendicular magnetic anisotropy (PMA) features of [Co/Pd]10 multilayers (MLs) versus Pd thickness at various ex-situ annealing temperatures. Thermally stable PMA characteristics were observed up to 500 °C, confirming the suitability of these systems for industrial applications at this temperature. Experimental observations suggest that the choice of equivalent Co and Pd layer thicknesses in a ML configuration ensures thermally stable PMA features, even at higher annealing temperatures. X-ray diffraction patterns and cross-sectional transmission electron microscopy images were obtained to determine thickness, post-annealing PMA behavior, and to explore the structural features that govern these findings.
Highlights
Perpendicular spin-transfer torque magnetic random access memories (p-STT MRAMs) have garnered considerable interest as alternatives to conventional memories due to a fast write time of ∼10 ns, non-volatile memory characteristics, and extremely low power consumption.[1,2,3] one goal in the development of p-STT-MRAMs beyond a feature size of 20 nm is to meet the demands of device performance, including a high tunneling magnetoresistance ratio (TMR) of 150%, a low critical current density (JC) of 4.7 MA/cm[2], and a good thermal stability (∆ = E/kBT) of 74
Experimental observations suggest that the choice of equivalent Co and Pd layer thicknesses in a ML configuration ensures thermally stable perpendicular magnetic anisotropy (PMA) features, even at higher annealing temperatures
A perpendicular magnetic tunnel junction (p-MTJ) suitable for PMA characteristics is a key factor to obtain a low JC and a high thermal stability, which cannot be achieved with in-plane MTJ (i-MTJ).[3]
Summary
E = KeffV is the energy barrier, MS is the saturation magnetization, Hk is the anisotropy field, Keff is the effective perpendicular magnetic anisotropy (PMA) energy density, V is the volume of the magnetic layer, kB is the Boltzmann constant, and T is temperature.[3,4] In particular, a perpendicular magnetic tunnel junction (p-MTJ) suitable for PMA characteristics is a key factor to obtain a low JC and a high thermal stability, which cannot be achieved with in-plane MTJ (i-MTJ).[3]. Much effort has been dedicated towards ensuring annealing stability in p-MTJs that can be operated at more than 400◦C for a wide range of applications, such as high-density and low-power p-STT MRAM devices.[3]. In this letter, we present the correlation between Pd metal thickness and PMA features of [Co/Pd] MLs at annealing temperatures ranging from 200 to 500◦C. In order to clarify Pd thickness-dependent structural characteristics under various annealing temperatures, the structural features underlying the experimental findings are discussed
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