Comparison of Synthetic Antiferromagnets and Hard Ferromagnets as Reference Layer in Magnetic Tunnel Junctions With Perpendicular Magnetic Anisotropy

Abstract

International audienc

Origin of the collapse of tunnel magnetoresistance at high annealing temperature in CoFeB/MgO perpendicular magnetic tunnel junctions

“…In order to reduce the effect of the dipolar coupling, we increase d from 40 nm to 100 nm. 24 The T dependence of TMR ratio of the MTJ with d ¼ 100 nm and T a ¼ 400 C shows monotonic temperature dependence up to RT, where the TMR ratio takes 99% as shown in Fig. 4.…”

“…4) in the previous report is most probably due to a thicker bottom CoFeB layer and a thinner top CoFeB layer than the present MTJs, both of which increase the magnitude of H S . H S can be reduced by adopting synthetic anti-ferromagnetic coupled layers 24 and/or by utilizing a stepped structure. 25 In summary, we have studied the origin of the collapse of TMR ratio at RT of the 40 nm diameter CoFeB/MgObased p-MTJ annealed at 400 C by measuring the T dependence of R-H loops.…”

Strong interlayer exchange coupling and high post-annealing stability in perpendicularly magnetized [Pt/Co]/Ru/[Co/Pt] structures

“…Since the stray field intensity increases when the MTJ cell size decreases, reducing the field intensity becomes an important issue for high-density MRAM devices. 1,2 This problem can be solved using a synthetic ferrimagnet (SyF) as a PL. A SyF is composed of two magnetic entities of upper and lower magnetic layers (UL and LL) that are separated by a nonmagnetic spacer such as Ru.…”

“…In a SyF with antiparallel interlayer exchange coupling (AP-IEC) between the UL and LL, the UL and LL stray fields can cancel out, thus reducing the stray field intensity in the FL. 1 However, the SyF structure also has some disadvantages. Stray fields in the UL that are generated in adjacent magnetic layers in both the pinned and free structures as well as those in the FL that are generated in the pinned structure, can increase dramatically as the cell size enters the nanoscale range.…”

Enhancement of perpendicular magnetic anisotropy thanks to Pt insertions in synthetic antiferromagnets

“…In this configuration, by properly adjusting the relative thickness of the two ferromagnetic layers, the stray fields generated from the SAF on the storage layer can be greatly reduced, leading to two low and high resistance states with equivalent thermal stability and critical switching currents or reversal fields. 6,7 In the framework of p-MTJs, such a SAF structure can be based on (Co/Pt) or (Co/Pd) multilayers. However, in these multilayers, an appropriate buffer layer (most often Pt or Pd) is required to obtain large PMA values.…”