The Heavy ions irradiation Effects on Advanced Spin Transfer Torque Materials

Abstract We investigate the heavy ions irradiation effect on the spin transfer torque film stacks with perpendicular magnetic anisotropy. Samples are exposed to 175MeV Cl ion and 235MeV Ge ion at the fluence of 1x105 ions/cm2 and 1x106 ions/cm2. Measurements of magnetization vs. magnetic field are performed on the film stacks before and after irradiation. The results exhibit that magnetic properties of free layer (CoFeB) in the spin transfer torque film keeps unchanged while magnetic properties of the synthetic antiferromagnet layer (Co/Pt) and the ferromagnetic exchange coupling between reference layer (CoFeB) and synthetic antiferromagnet layer through W layer have changed significantly when the fluence of the two kinds of ions reach 1x106 ions/cm2. We analysis the irradiation damage of the film stacks by SRIM simulation and give a reasonable explanation for this phenomenon. Thus, our work demonstrates that perpendicular spin transfer torque MRAM technology itself, the memory element construction, is subject to damage from heavy ions irradiation.