Influence of Heavy Ion Irradiation on Perpendicular-Anisotropy CoFeB-MgO Magnetic Tunnel Junctions

Abstract

A non-volatile memory element called a perpendicular-anisotropy magnetic tunnel junction was fabricated using CoFeB/MgO/CoFeB film stack technology. It exhibits two stable resistance values, high or low, depending on the relative directions of the magnetizations of the two ferromagnetic CoFeB layers. After being programmed into the high resistance state with a current injection scheme based on the spin transfer torque theory, the tunnel junction was exposed to 15-MeV Si ions under different voltage stress conditions. The tested structure remained in the programmed high resistance state after being bombarded with 10-100 Si ions, even under the stressed situations. A time-domain analysis proved that this result is due to the perfect immunity of the tested magnetic tunnel junction to single event upsets. Some degradation in resistance due to the heavy-ion irradiation was detected through a precise parameter analysis based on a tunneling theory but it was negligibly small (1%). There were no statistically significant changes in the thermal stability factor before and after irradiation, and this means the long-term retention properties remained unchanged.

Radiation Effects in Advanced and Emerging Nonvolatile Memories

“…Damage and bit upsets induced by heavy ions were studied by Kobayashi et al [91], specifically investigating the effect of 15-MeV silicon atoms on the CoFeB/MgO/CoFeB pMTJ devices with a diameter of 70 nm and did not find resistance change. Later, the same group found that singleevent bit flips can occur in an MTJ cell resulting from heavyion exposure, depending on both the LET and properties of the bit [92].…”

Prospect of Spin-Orbitronic Devices and Their Applications

“…Particularly, the devices used in the aerospace are required to be radiation resistant to cosmic rays. Since MTJs are equipped with intrinsic magnetic immunity to radiation effect ( Kobayashi et al., 2014 ; Hughes et al., 2012 ; Ren et al., 2012 ; Park et al., 2019 ), MRAMs have already been used in satellites early in March 2008 ( Greenemeier, 2008 ). Moreover, featured with almost unlimited endurance, spin-orbitronic devices are particular favorable to be applied in avionics, e.g., a spacecraft, which may travel more than tens of years in the universe.…”

SEU Mechanisms in Spintronic Devices: Critical Parameters and Basic Effects

“…Nevertheless, these effects will become more significant in electronic structures when the characteristic feature sizes will be reaching deeper into the nano-scale. Some studies tried to explain a posteriori the effects on MTJ irradiation sites by means of traditional LET cross-section plot or by exploiting TEM microscopy [4] [5]. In this paper, new insights are proposed to bring clear understanding on the possible basic degradation mechanisms that can trigger SEU in STT-MTJ, regardless of the radiation source, building a bridge between radiation effects and spintronic theory.…”