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A superlattice based STT-MRAM with extra-high performance

(Nanowerk News) Researchers from National Taiwan University have developed an ultra-high performance STT-MRAM, called SS-MARM or SL-STT-MARM. The SS-MARM can simultaneously achieve ultra-high MR ratio, low writing power, high-speed switching, low RA, high endurance and simple manufacturing. Most disadvantages of traditional STT-MRAM can be solved.
As we know, single crystalline (001) MgO with 0.8-3nm thickness has been used as the insulator (barrier) layer in most MRAMs, including toggle MRAM, STT-MRAM, and SOT-MRAM, more than 10 years. The main objective of using the MgO is to provide high magnetoresistance (MR) ratio over 300%, which is required for MRAM working.
However, the MgO layer is with very large RA. In STT-MRAM, large power consumption in writing mode is required since current passes the MgO layer with and RA of the insulator is large. However, it seems impossible to find other nature insulator materials, which can provide higher MR ratio as well as lower RA for the STT-MRAM.
To avoid the weakness of traditional STT-MRAM, a superlattice (also called metamaterial or artificial material) is used to replace the MgO layer. It is amazing that the superlattice can provide not only ultra-high MR ratio but also ultra-low RA for the new type STT-MRAM, called SS-MARM or SL-STT-MRAM.
Research reports show that the SS-MRAM can reduce more than 90% writing power and RA value from traditional STT- MRAM. Moreover, the MR ratio and writing speed can be increased more than 10 times when the SS-MRAM is applied. These results have been published in various scientific journals and a conference, as shown in the references below.
It is noted that the insulator layers in the MRAM are made of arbitrary amorphous material rather than single crystalline. Fabrication of the MRAM becomes easier and simpler than traditional MgO based STT-MRAM.
Furthermore, since stable amorphous rather than unstable crystalline is used, degradation caused by repeated writing in the MRAM could be avoided. Thus, the MRAM can provide greater reliability and strong endurance.
Moreover, developing SOT-MARM to avoid part of disadvantages of traditional STT-MRAM is also not required since almost all of disadvantages of traditional STT-MRAM have been improved by the SS-MARM.

References
Peng Tseng and Wen-Jeng Hsueh, 2019, "Ultra-giant magnetoresistance in graphene-based spin valves with gate-controlled potential barriers", New J. Phys. 21 113035.
P. Tseng and W. J. Hsueh*, 2018, “Enhancement of spin-transfer torque in superlattice-barrier magnetic tunnel junctions”, Global Conference on Magnetic and Magnetism Materials (GMMM 2018), July, 23-24, Osaka, Japan.
C. H. Chen, P. Tseng, C. W. Ko, and W. J. Hsueh, 2017, “Huge spin transfer torque in a magnetic tunnel junction by a superlattice barrier”, Phys. Lett. A, Vol. 381, pp. 3124-3128.
C. H. Chen, C. H. Chang, Y. H. Cheng, and W. J. Hsueh, 2015, “Ultrahigh tunnel magnetoresistance using an artificial superlattice barrier with copper and aluminum oxide”, Europhys. Lett. Vol. 111, pp. 47005.
C. H. Chen and W. J. Hsueh, 2014, “Enhancement of tunnel magnetoresistance in magnetic tunnel junction by a superlattice barrier”, Appl. Phys. Lett., Vol. 104, pp.042405.
Source: National Taiwan University
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