MgO/CoFeB/Ta/CoFeB/MgO recording structure with low intrinsic critical current and high thermal stability

Abstract

CoFeB-MgO based magnetic tunnel junctions with perpendicular easy axis are attracting much interest for application to nonvolatile very large scale integrated circuits. MgO/CoFeB/Ta/CoFeB/MgO recording structure with double-interface shows a high thermal stability factor without an increase of intrinsic critical current with comparison to MgO/CoFeB recording structure with single-interface. In this paper, we review our recent progress on the CoFeBMgO magnetic tunnel junctions with a double MgO barrier (MgO/CoFeB/Ta/CoFeB/MgO) recording structure. It enabled us to obtain magnetic tunnel junctions with a high thermal stability factor of 59 at a device dimension of 29 nm in diameter.

Cobalt substituted L10-MnAl thin films with large perpendicular magnetic anisotropy

“…1.2 × 10 7 erg=cm 3 . M s decreased with increasing Co content; the M s 's were 550 emu=cm 3 for x = 0.03, 430 emu=cm 3 for x = 0.05, and 350 emu=cm 3 for x = 0.08. K u also decreased with increasing Co content.…”

“…1) Perpendicularly magnetized magnetic tunnel junctions (p-MTJs) with ferromagnetic electrodes with a high magnetic anisotropy (K u ), a small magnetic damping constant (α), and a small magnetization (M s ) are very useful for STT-MRAM because the thermal stability factor Δ (= K u V=k B T, V: volume of free layers in MTJs, k B : Boltzmann constant) should be above 60 to keep information in the memory for 10 years, and the switching current density is expressed as J c0 ∼ αM s tH eff according to theory (t: thickness, H eff : effective magnetic field for free layers). [2][3][4][5] In addition, ferromagnetic materials with a small magnetization are useful for suppressing the stray field problem, which causes the loop shift of magnetoresistance curves.…”

“…To date, various ferromagnetic thin films that show perpendicular magnetic anisotropy (PMA) such as artificial superlattices, 6,7) multilayers, 8,9) CoFeB=MgO systems, 3,10) and L1 0 -ordered alloys such as FePt, CoPt, and FePd [11][12][13][14] have been investigated. Among the many types of perpendicular materials, Mn-based L1 0 -and D0 22 -ordered alloys such as L1 0 -and D0 22 -MnGa, [15][16][17][18] D0 22 -Mn 3 Ge [19][20][21][22][23][24] are promising materials for STT-MRAM because of their high K u , small α, and small M s .…”

L10-ordered MnAl thin films with high perpendicular magnetic anisotropy

“…Many ferromagnetic materials with perpendicular magnetic anisotropy (PMA) such as an artificial superlattice, 4,5) a multilayer, 6,7) a CoFeB=MgO system, 8,9) and L1 0 -ordered alloys such as FePt, CoPt, and FePd [10][11][12][13] have been investigated to apply them to the MTJs. Among the perpendicular ferromagnetic materials, Mn-based ferromagnetic ordered alloys, such as L1 0 -and D0 22 -MnGa [14][15][16][17] and D0 22 -Mn 3 Ge, [18][19][20][21][22] have a great potential in showing a high performance in STT-MRAMs because of their high perpendicular magnetic anisotropy (K u ), small magnetic damping constant (α), and small magnetization (M s ).…”