Ultra low power composite free layer spin-orbit torque MRAM

Wei-Heng Hsu, R. Bell, R. H. Victora

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Spin-transfer torque MRAM (STT-MRAM) serves as a promising candidate for next generation memory. However, STT-MRAM suffers from tunnel barrier degradation under rapid operations and a poor spin polarization. In contrast, spin-orbit torque MRAM (SOT-MRAM) utilizes spin-orbit interaction at the interface of heavy metal (HM) and ferromagnetic (FM) layers via mechanisms such as the Rashba effect and spin Hall effect (SHE)1,2. Since current only flows through the heavy metal in SOT-MRAM, device performance is no longer limited by insulator breakdown. Because no charge current through the FM layer is needed in SOT devices, the other unrecognized benefit of SOT is its compatibility with low-damping magnetic insulators (MI). SOT experiments with YIG/Pt, YIG/Ta, and YIG/W have demonstrated the potential for ultra-low damped switching of YIG in SOT systems3,4. SOT switching has also been demonstrated in TmIG based system5. Here, we propose a composite free layer SOT-MRAM (Fig. 1a). The MTJ is a cylinder structure with a diameter D. The free layer consists of an easily switched YIG layer and a thermally stable high anisotropy (Ku∼107 ergs/cc) L10-FePt or L10-FePd layer. These two layers are ferromagnetically coupled through the RKKY exchange provided by the Pd layer. It has been shown that exchange coupling between magnetic soft and hard layers can reduce the critical current6. Current CoFeB based devices necessitate larger diameters due to the low anisotropy. By adopting FePt or FePd, we can reduce the device area, which is favorable for high density applications. We optimized our device by running micromagnetic simulations in the macrospin approximation. A device of small diameter (D < 30nm) with low write energy (Ew < 1 fJ) can be achieved for 1 ns switching while maintaining thermal stability Δ = 60kBT at room temperature.

Original languageEnglish (US)
Title of host publication2018 IEEE International Magnetic Conference, INTERMAG 2018
PublisherInstitute of Electrical and Electronics Engineers Inc.
ISBN (Electronic)9781538664254
StatePublished - Oct 24 2018
Event2018 IEEE International Magnetic Conference, INTERMAG 2018 - Singapore, Singapore
Duration: Apr 23 2018Apr 27 2018

Publication series

Name2018 IEEE International Magnetic Conference, INTERMAG 2018


Conference2018 IEEE International Magnetic Conference, INTERMAG 2018

Bibliographical note

Publisher Copyright:
© 2018 IEEE.


Dive into the research topics of 'Ultra low power composite free layer spin-orbit torque MRAM'. Together they form a unique fingerprint.

Cite this