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

Double-barrier magnetic tunnel junction (MTJ) cells incorporating one thermal barrier (GeSbTe) were fabricated for improved thermally assisted magnetic switching. The MTJ has two Al2O3 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 (TB) of the storage layer is reduced to 110 °C by thinning the MnIr layer to 80 Å, while a strong exchange coupling and TB∼300°C are obtained at the reference layers with a synthetic antiferromagnetically coupled CoFeB∕Ru∕CoFeB structure pinned to 250-Å-thick MnIr. For the write experiments, the current flowing through the MTJ (patterned down to 2μm2) increases the temperature above the storage layer TB, under an external field of +∕−80Oe. Current densities <1mA∕μm2 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 0.3–1.8mW∕μm2 were achieved.