Spin-orbit torque magnetization switching in Co/Pt multilayers for multistate memory and logic devices

Spintronics is a highly researched topic for its rich underlying physics as well as for practical applications such as in magnetic random-access memory (MRAM). It has proven to be a serious contender in emerging memory technology due to its intrinsic non-volatility, low power dissipation, and high s...

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Main Author: Lim, Gerard Joseph
Other Authors: Lew Wen Siang
Format: Thesis-Doctor of Philosophy
Language:English
Published: Nanyang Technological University 2021
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Online Access:https://hdl.handle.net/10356/146231
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Institution: Nanyang Technological University
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spelling sg-ntu-dr.10356-1462312023-02-28T23:58:09Z Spin-orbit torque magnetization switching in Co/Pt multilayers for multistate memory and logic devices Lim, Gerard Joseph Lew Wen Siang School of Physical and Mathematical Sciences WenSiang@ntu.edu.sg Science::Physics::Electricity and magnetism Spintronics is a highly researched topic for its rich underlying physics as well as for practical applications such as in magnetic random-access memory (MRAM). It has proven to be a serious contender in emerging memory technology due to its intrinsic non-volatility, low power dissipation, and high speed. The spin degree of freedom further opens opportunities that exploit its ultrafast dynamics and spin transport. Instead of transistors and charge-based elements, spintronic devices use the magnetization state in a ferromagnetic material to store and interpret information. More recently, spintronic devices have been proposed for logical, neuromorphic, and compute-in-memory applications. Further investigation on material and device physics are crucial for developing new spintronic memory and computation elements. In this thesis, the quantification and optimization of current-induced spinorbit torques (SOT) in [Co/Pt] multilayers are investigated. The thin film multilayer exhibiting perpendicular magnetic anisotropy (PMA) is characterized using adiabatic harmonic Hall measurements for SOT efficiency optimization. Due to the complex structure, the effect of Pt seed and interlayer thickness on the magnetic properties and SOT efficiency is studied. Manipulation of magnetization for multistate memory and logic functionality is also explored. Multistate magnetization switching, useful for synaptic applications due to the analogue-like behaviour, is experimentally demonstrated in a Hall cross device. Through finite element and Mumax simulations, the analogue-like response is shown to be a result of the geometrically-induced inhomogeneous current-density profile of the Hall cross structure. The thermal impact on the multi-state device operation is also studied through multi-state switching at elevated device temperatures. A compound structure using similar switching techniques is used to develop a reconfigurable logic device, in which an integrated bias field line allows for on-chip local Oersted field generation for breaking the switching symmetry in PMA devices. The logic device is then used to construct a half-adder through the circuit simulator “Simulation Program with Integrated Circuit Emphasis” (SPICE). The results from the works presented in this thesis aims to provide a platform from which to develop more efficient SOT-driven spintronic memory and logic devices. Doctor of Philosophy 2021-02-03T04:41:49Z 2021-02-03T04:41:49Z 2020 Thesis-Doctor of Philosophy Lim, G. J. (2020). Spin-orbit torque magnetization switching in Co/Pt multilayers for multistate memory and logic devices. Doctoral thesis, Nanyang Technological University, Singapore. https://hdl.handle.net/10356/146231 10.32657/10356/146231 en This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0). application/pdf Nanyang Technological University
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic Science::Physics::Electricity and magnetism
spellingShingle Science::Physics::Electricity and magnetism
Lim, Gerard Joseph
Spin-orbit torque magnetization switching in Co/Pt multilayers for multistate memory and logic devices
description Spintronics is a highly researched topic for its rich underlying physics as well as for practical applications such as in magnetic random-access memory (MRAM). It has proven to be a serious contender in emerging memory technology due to its intrinsic non-volatility, low power dissipation, and high speed. The spin degree of freedom further opens opportunities that exploit its ultrafast dynamics and spin transport. Instead of transistors and charge-based elements, spintronic devices use the magnetization state in a ferromagnetic material to store and interpret information. More recently, spintronic devices have been proposed for logical, neuromorphic, and compute-in-memory applications. Further investigation on material and device physics are crucial for developing new spintronic memory and computation elements. In this thesis, the quantification and optimization of current-induced spinorbit torques (SOT) in [Co/Pt] multilayers are investigated. The thin film multilayer exhibiting perpendicular magnetic anisotropy (PMA) is characterized using adiabatic harmonic Hall measurements for SOT efficiency optimization. Due to the complex structure, the effect of Pt seed and interlayer thickness on the magnetic properties and SOT efficiency is studied. Manipulation of magnetization for multistate memory and logic functionality is also explored. Multistate magnetization switching, useful for synaptic applications due to the analogue-like behaviour, is experimentally demonstrated in a Hall cross device. Through finite element and Mumax simulations, the analogue-like response is shown to be a result of the geometrically-induced inhomogeneous current-density profile of the Hall cross structure. The thermal impact on the multi-state device operation is also studied through multi-state switching at elevated device temperatures. A compound structure using similar switching techniques is used to develop a reconfigurable logic device, in which an integrated bias field line allows for on-chip local Oersted field generation for breaking the switching symmetry in PMA devices. The logic device is then used to construct a half-adder through the circuit simulator “Simulation Program with Integrated Circuit Emphasis” (SPICE). The results from the works presented in this thesis aims to provide a platform from which to develop more efficient SOT-driven spintronic memory and logic devices.
author2 Lew Wen Siang
author_facet Lew Wen Siang
Lim, Gerard Joseph
format Thesis-Doctor of Philosophy
author Lim, Gerard Joseph
author_sort Lim, Gerard Joseph
title Spin-orbit torque magnetization switching in Co/Pt multilayers for multistate memory and logic devices
title_short Spin-orbit torque magnetization switching in Co/Pt multilayers for multistate memory and logic devices
title_full Spin-orbit torque magnetization switching in Co/Pt multilayers for multistate memory and logic devices
title_fullStr Spin-orbit torque magnetization switching in Co/Pt multilayers for multistate memory and logic devices
title_full_unstemmed Spin-orbit torque magnetization switching in Co/Pt multilayers for multistate memory and logic devices
title_sort spin-orbit torque magnetization switching in co/pt multilayers for multistate memory and logic devices
publisher Nanyang Technological University
publishDate 2021
url https://hdl.handle.net/10356/146231
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