Immunity of nanoscale magnetic tunnel junctions with perpendicular magnetic anisotropy to ionizing radiation

Abstract

Spin transfer torque magnetic random access memory (Stt-MRAM) is a promising candidate for next generation memory as it is non-volatile, fast, and has unlimited endurance. Another important aspect of Stt-MRAM is that its core component, the nanoscale magnetic tunneling junction (MtJ), is thought to be radiation hard, making it attractive for space and nuclear technology applications. However, studies on the effects of ionizing radiation on the STT-MRAM writing process are lacking for MTJs with perpendicular magnetic anisotropy (pMtJs) required for scalable applications. particularly, the question of the impact of extreme total ionizing dose on perpendicular magnetic anisotropy, which plays a crucial role on thermal stability and critical writing current, remains open. Here we report measurements of the impact of high doses of gamma and neutron radiation on nanoscale pMtJs used in Stt-MRAM. We characterize the tunneling magnetoresistance, the magnetic field switching, and the currentinduced switching before and after irradiation. our results demonstrate that all these key properties of nanoscale MtJs relevant to Stt-MRAM applications are robust against ionizing radiation. Additionally, we perform experiments on thermally driven stochastic switching in the gamma ray environment. these results indicate that nanoscale MtJs are promising building blocks for radiation-hard non-von neumann computing. Spin transfer torque random access memory (STT-MRAM) is a next-generation non-volatile memory technology 1-4 that has the advantage of fast write times 5-7 , relatively low power consumption 8-11 , and shows promise of scalability down to at least 7 nm CMOS technology node 12,13. STT-MRAM has already found its applications in the form of stand-alone nonvolatile memory 14 , and efforts to realize embedded versions of STT-MRAM are under way 15,16. The core component of STT-MRAM is a nanoscale magnetic tunnel junction (MTJ) 17-19 that consists of ferromagnetic metallic layers separated by a non-magnetic insulating tunnel barrier as illustrated in Fig. 1(a). Since the MTJ does not contain semiconductor components, STT-MRAM can be radiation hard, i.e. robust to the effects of ionizing radiation. This makes STT-MRAM potentially attractive for applications in space and military technologies, particle accelerators, and nuclear reactors 20,21. In fact previous studies have shown the promise of the radiation hardness of MTJs 22-24 ; however, the effects of ionizing radiation on spin transfer torque switching in MTJs with properties required for scalable STT-MRAM technology have not been experimentally studied. An STT-MRAM bit is written by a current pulse that applies spin torque 25 to magnetization of the free layer ferromagnet and reverses its direction thereby changing the relative alignment of magnetic moments of the free and pinned layers of the MTJ between parallel and antiparallel 26-28. This free layer switching leads to a change of the MTJ resistance due to the tunneling magneto-resistance (TMR) effect 28 , which allows resi...

Energy-efficient and Reliable Inference in Nonvolatile Memory under Extreme Operating Conditions

“…al. [96] demonstrated that MTJs are even resilient to radiation that is 100× greater than what is observed on particularly harsh inter-planetary travel [11,156]. Therefore, MTJs represent leading candidates for space applications [39,67].…”

“…Without the earth's atmosphere to shield radiation from space, satellites are exposed to much higher levels of radiation. Non-volatile memory is at an advantage in this domain, as the memory devices it uses are highly resistant to radiation [96]. However, non-volatile memory still relies on CMOS circuitry for memory access and external control, which also applies to non-volatile PIM.…”

High-dose X-ray radiation induced MgO degradation and breakdown in spin transfer torque magnetic tunnel junctions

“…Both studies concluded that ionizing radiation has a negligible impact either on TMR or on field-induced switching properties of i-MTJs. Recently, Montoya et al 14 characterized the current-induced switching property of nanoscale MTJs with perpendicular magnetic anisotropy (p-MTJs) before and after gamma radiation, which also demonstrated that all key properties of p-MTJs are robust against ionizing radiation of cobalt-60 gamma-ray. It has been pointed out that gamma-ray radiation is involved more in electron-hole pair creation rather than in trap generation.…”

A Radiation-Hardened Triple Modular Redundancy Design Based on Spin-Transfer Torque Magnetic Tunnel Junction Devices

“…Fanghui Ren et al [10] demonstrated that the electrical and the magnetic properties of MgO-based MTJs were not affected by gamma radiation and epithermal neutrons. Eric Arturo Montoya et al [11] proved that the critical properties of nanoscale perpendicular magnetic anisotropy in STT-MTJs, such as magnetoresistance, magnetic field switching, and current-induced switching, are robust against ionizing radiation.…”