Double-barrier magnetic tunnel junctions with GeSbTe thermal barriers for improved thermally assisted magnetoresistive random access memory cells

摘要

Double-barrier magnetic tunnel junction (MTJ) cells incorporating one thermal barrier (GeSbTe) were fabricated for improved thermally assisted magnetic switching. The MTJ has two Al_2O_3 barriers with a common weakly pinned structure (storage layer) and two pinned layers (reference). The structural quality of the double junction stack and the roughness at the (buffer/thermal barrier) level were investigated and optimized. To minimize the required heating during writing, the blocking temperature (T_B) of the storage layer is reduced to 110℃ by thinning the MnIr layer to 80 A, while a strong exchange coupling and T_B ～ 300℃ are obtained at the reference layers with a synthetic antiferromagnetically coupled CoFeB/Ru/CoFeB structure pinned to 250-A-thick MnIr. For the write experiments, the current flowing through the MTJ (patterned down to 2 μm~2) increases the temperature above the storage layer T_B, under an external field of +/- 80 Oe. Current densities < 1 mA/μm~2 were enough to write in the MTJs with a thermal barrier (almost half the values needed without thermal barriers, which also showed a stronger dependence of the write power on the junction area). Write power values of the order of 0.3-1.8 mW/μm~2 were achieved.