Perpendicular magnetic tunnel junctions with multi-interface free layer

Abstract

Future generations of magnetic random access memory demand magnetic tunnel junctions that can provide simultaneously high magnetoresistance, strong retention, low switching energy, and small cell size below 10 nm. Here, we study perpendicular magnetic tunnel junctions with composite free layers, where multiple ferromagnet/nonmagnet interfaces can contribute to the thermal stability. Different nonmagnetic materials (MgO, Ta, and Mo) have been employed as the coupling layers in these multi-interface free layers. The evolution of junction properties under different annealing conditions is investigated. A strong dependence of the tunneling magnetoresistance on the thickness of the first CoFeB layer has been observed. In junctions where Mo and MgO are used as coupling layers, a large tunneling magnetoresistance above 200% has been achieved after 400 °C annealing.

Electric field control of perpendicular magnetic tunnel junctions with easy-cone magnetic anisotropic free layers

“…Numbers in parentheses are the nominal thicknesses in nanometers and CoFeB denotes Co 20 Fe 60 B 20 . The CoFeB/W/CoFeB is used as the FL owing to the increased thermal stability factor ( 50 – 52 ) as well as the large tunability of magnetic anisotropy via changing the thickness of two CoFeB layers. The RL CoFeB, compensatory layer Co, and (Co/Pt) 3 are ferromagnetically coupled via spacer layers W and Ta.…”

“…Through local reciprocal space mapping (LRSM) under different electric fields for PMN-PT beneath the MTJ pillar, the modulation of resistance can be ascribed to the magnetic anisotropy variation of the FL induced by the nonvolatile strain-mediated magnetoelectric coupling due to electric field-induced rhombohedral-orthorhombic (R-O) phase transition. (50)(51)(52) as well as the large tunability of magnetic anisotropy via changing the thickness of two CoFeB layers. The RL CoFeB, compensatory layer Co, and (Co/Pt) 3 are ferromagnetically coupled via spacer layers W and Ta.…”

Electric-field control of nonvolatile resistance state of perpendicular magnetic tunnel junction via magnetoelectric coupling

“…Figure 1A shows our p-MTJ multilayer stacks composed of Ta (25)/CuN (20)/Ta (3)/CuN(20)/Ta(0.7)/Pt(1.5)/[Co(0.5)/Pt(0.35)] 6 /Co(0.6)/Ru(0.8)/Co(0.6)/[Pt(0.35)/Co(0.5)] 3 /Pt(0.25)/Ta(0.2)/Co(1.2)/W(0.25)/CoFeB(0.9)/MgO(2.0)/CoFeB(1.4)/W(0.3)/CoFeB(0.9)/MgO(1)/Pt(1.5)/Ta(3)/Ru(4) (number in parenthesis denotes layer thickness in nanometers, and CoFeB denotes Co 20 Fe 60 B 20 ; see Materials and Methods for details of sample preparation). The ferromagnetically coupled double CoFeB structure, i.e., CoFeB/W/CoFeB, is used as the free layer owing to its increased thermal stability factor ( 44 , 45 ). A synthetic antiferromagnetic (SAF) pinning layer, i.e., (Co/Pt) 6 /Co/Ru/Co/(Pt/Co) 3 , is used as a building block in p-MTJ for effective reduction of stray field.…”

“…see Materials and Methods for details of sample preparation). The ferromagnetically coupled double CoFeB structure, i.e., CoFeB/W/ CoFeB, is used as the free layer owing to its increased thermal stability factor (44,45). A synthetic antiferromagnetic (SAF) pinning layer, i.e., (Co/Pt) 6 /Co/Ru/Co/(Pt/Co) 3 , is used as a building block in p-MTJ for effective reduction of stray field.…”

Strain-mediated magnetoelectric control of tunneling magnetoresistance in magnetic tunneling junction/ferroelectric hybrid structures

“…In particular, the isotropic strain induced by E-fields in the (001)-oriented FE layer may be more efficient than the anisotropic strain (most commonly used (011)-cut FE) to achieve 180 • magnetization switching in the perpendicular magnetic tunnel junction, which has received extensive attention due to high thermal stability at a reduced dimension, low-current-induced magnetization switching and a high TMR ratio all at the same time. [27][28][29][30] Additionally, the exploration of different architectures of in-plane or perpendicular MTJ/FE multiferroic heterostructures offers new possibilities for high-performance memory and logic devices. Therefore, further optimization of hybrid MTJ/PMN-xPT multiferroic heterostructures is meaningful for potential spintronic and electronic applications, even without the assistance of external magnetic fields.…”