Thermally stable voltage-controlled perpendicular magnetic anisotropy in Mo|CoFeB|MgO structures

Abstract

We study voltage-controlled magnetic anisotropy (VCMA) and other magnetic properties in annealed MojCoFeBjMgO layered structures. The interfacial perpendicular magnetic anisotropy (PMA) is observed to increase with annealing over the studied temperature range, and a VCMA coefficient of about 40 fJ/V-m is sustained after annealing at temperatures as high as 430 C. Ab initio electronic structure calculations of interfacial PMA as a function of strain further show that strain relaxation may lead to the increase of interfacial PMA at higher annealing temperatures. Measurements also show that there is no significant VCMA and interfacial PMA dependence on the CoFeB thickness over the studied range, which illustrates the interfacial origin of the anisotropy and its voltage dependence, i.e., the VCMA effect. The high thermal annealing stability of MojCoFeBjMgO structures makes them compatible with advanced CMOS back-end-of-line processes, and will be important for integration of magnetoelectric random access memory into on-chip embedded applications. V

Effect of Mo insertion layers on the magnetoresistance and perpendicular magnetic anisotropy in Ta/CoFeB/MgO junctions

“…2(b)), K i increased to 1.63 (60:1) erg/cm 2 . As it was previously reported, [28][29][30] MTJ structures with Mo as buffer and capping layers have higher interfacial magnetic anisotropy, especially at higher temperatures (above 350 C). Therefore, for Ta with 1.2 nm Mo-dust ( Fig.…”

“…2(d)) showed the highest K i of 1.92 (60:1) erg/cm 2 , which is also close to K i values obtained previously. [28][29][30] The results from VSM studies suggest that insertion of Mo dusting layer helps the Ta layer to improve thermal stability by reducing intermixing of Ta with CoFeB layers and consequently enhancing the K i value. Additionally, the range of CoFeB thicknesses showing PMA for pure Mo sample and 1.2 nm Mo-dust sample is wider (up to 1.2 nm compared to 1 nm) than those for 0.6 nm Mo-dust and pure Ta buffers.…”

“…However, both TMR and PMA were reported to be deteriorated upon annealing at temperatures above 400 C for Ta/CoFeB/MgO junctions. 22,23 Several other underlayers such as Pt (Pd), 24 Hf, [25][26][27] Mo, [28][29][30][31][32] and W 33,34 have been studied to improve thermal stability, TMR, PMA, electric field, and spin orbit torque effects in pMTJs. Furthermore, doping of Ta buffer with nitrogen 35 or using a thin sacrificial Mg layer 36 was also reported to improve PMA and TMR in pMTJs.…”

Influence of inserted Mo layer on the thermal stability of perpendicularly magnetized Ta/Mo/Co20Fe60B20/MgO/Ta films

“…• C. 17 We studied a Ta-based CoFeB/MgO stack that consisted of a 5 nm thick Ta underlayer, which maintains a high CoFeB magnetization but with an additional Mo layer inserted between Ta and CoFeB. This configuration effectively suppressed the diffusion of Ta atoms.…”

“…Different underlayers, e.g., Ta, Mo, Hf, W, Pt, or Pd, have differing effects on PMA and thermal stability. [12][13][14][15][16][17] Ta is often used as a buffer layer to optimize the structure and magnetic properties in magnetic multilayers with single-crystal Si substrates. However, PMA degradation occurs in Ta buffer layers at annealing temperatures higher than 300…”