14:00 〜 14:15
▼ [16p-C41-3] Dependence of switching properties of CoFeB-MgO based magnetic tunnel junctions on insertion layer material
キーワード：spintronics, magnetic tunnel junctions, spin transfer torque-induced magnetization switching
CoFeB-MgO is crucial for high-performance magnetic tunnel junctions (MTJs), whose properties are known to depend on a material adjacent to the CoFeB. Recently, it was reported that the use of Mo adjacent layer improves heat-treatment resistance of magnetic properties, and the robustness is determined also by the crystallinity of Mo, bcc or amorphous. CoFeB-MgO MTJs with double MgO interfaces and ultrathin Ta insertion layer were shown to exhibit excellent characteristics at reduced dimensions less than 30 nm in diameter D; high thermal stability factor Delta and low intrinsic critical current IC0 of spin-transfer torque (STT) switching. However, the insertion material dependence of the characteristics is yet to be elucidated. Here, we study the properties of double-interfaced CoFeB-MgO MTJs with Mo or Ta insertion layer and various D down to less than 20 nm.
We fabricate MTJs with D ranging from 15 to 40 nm by electron-beam lithography and Ar ion milling, and anneal them at 300oC; a recording layer is CoFeB(1.4)/Mo or Ta(0.45)/CoFeB(1) (nm) and a reference layer possesses a synthetic ferrimagnetic structure. We confirm the ferromagnetic coupling between the two CoFeB layers in both recording layers with Ta and Mo. Delta and IC0 are evaluated from the switching probability measurement using 10-ms-long pulse currents. We obtain similar values of Delta irrespective of the insertion materials. The Delta decreases with decreasing D from ~60 at D = 40 nm to ~30 at D = 15 nm, indicating single-domain-like magnetization reversal. IC0 is almost independent of the insertion materials or slightly smaller for Ta-inserted CoFeB, and decreases monotonically with decreasing D. The results indicate that the properties of MTJs at reduced dimensions do not depend much on insertion materials, Ta or Mo, for the present stack structures with an ultrathin insertion layer.
We fabricate MTJs with D ranging from 15 to 40 nm by electron-beam lithography and Ar ion milling, and anneal them at 300oC; a recording layer is CoFeB(1.4)/Mo or Ta(0.45)/CoFeB(1) (nm) and a reference layer possesses a synthetic ferrimagnetic structure. We confirm the ferromagnetic coupling between the two CoFeB layers in both recording layers with Ta and Mo. Delta and IC0 are evaluated from the switching probability measurement using 10-ms-long pulse currents. We obtain similar values of Delta irrespective of the insertion materials. The Delta decreases with decreasing D from ~60 at D = 40 nm to ~30 at D = 15 nm, indicating single-domain-like magnetization reversal. IC0 is almost independent of the insertion materials or slightly smaller for Ta-inserted CoFeB, and decreases monotonically with decreasing D. The results indicate that the properties of MTJs at reduced dimensions do not depend much on insertion materials, Ta or Mo, for the present stack structures with an ultrathin insertion layer.