A Drift-Diffusion Based Modeling and Optimization Framework for Nanoscale Spin-Orbit Torque Devices

Kumar, Piyush; Liao, Yu-Ching; Ralph, Daniel; Naeemi, Azad

doi:10.1109/ted.2022.3227882

Cited by 3 publications

(3 citation statements)

References 33 publications

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“…In this invited paper we summarize our prior publications describing the modeling of nanoscale SOT channel 15 and SOT channel sharing schemes for SOT-MRAM. 16 After this introduction, Section II describe the SOT channel modeling and optimization.…”

Section: Introductionmentioning

confidence: 99%

Modeling of spin-orbit torque (SOT) channel and high-density SOT magnetic random-access memory

Kumar,

Naeemi

2023

Spintronics XVI

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Spin-orbit torque (SOT) devices are being pursued for various memory and in-memory compute applications. At nanoscale dimensions, electric current flowing through the SOT channel can be non-uniform due to incomplete current redistribution. Such effects were ignored in the prior modeling works. We present a comprehensive modeling framework for SOT devices that capture the effects of incomplete current redistribution along with interface spin-mixing, and non-uniform resistivity. Our transfer matrix-based formalism along with finite element simulations can account for any local variation in resistivity and spin diffusion length along with accounting for various spin-scattering mechanisms. In addition, we quantify the optimal SOT layer thickness to minimize the write energy in terms of its resistivity and spin diffusion length. To improve the bit density of SOT magnetic random-access memory (MRAM), we explore area saving schemes based on sharing SOT channel among multiple magnetic tunnel junctions (MTJs) with the help of voltage-controlled magnetic anisotropy (VCMA) effect and spin-transfer torque (STT). Using micromagnetic simulations, we study various tradeoffs among write time, current, error rate, and the number of MTJs. Our results show that the number of MTJs on the shared SOT channel is limited by the voltage drop over the SOT channel and write error rate, and having more than 4 MTJs on a SOT channel poses major challenges in terms of reliability.

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Section: Introductionmentioning

confidence: 99%

Modeling of spin-orbit torque (SOT) channel and high-density SOT magnetic random-access memory

Kumar,

Naeemi

2023

Spintronics XVI

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“…This methodology, however, turns out to be inaccurate in the case of nanoscale devices. This is because conduction current redistribution between FM and NM layers according to their resistances requires a finite length 13 . Furthermore, when relatively resistive heavy metals (such as 𝛽 − 𝑊) are utilized as the NM layer, the nonuniformity in the current redistribution can be significant.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, when relatively resistive heavy metals (such as 𝛽 − 𝑊) are utilized as the NM layer, the nonuniformity in the current redistribution can be significant. To address this issue, in 13 , the authors calculate the conduction current distribution between FM and NM layers by finite element simulation via COMSOL and apply the drift-diffusion approach to estimate the spin current profile for nanoscale devices. However, they neither focus on the non-uniformity in spin current nor on its impact on magnetization switching dynamics.…”

Section: Introductionmentioning

confidence: 99%

Investigation on the impact of spin current profile on the write time of SOT MRAMs

Shazon,

Kumar,

Naeemi

2023

Spintronics XVI

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In this work, we quantify the non-uniformity in the spin current density generated by spin-orbit torque (SOT) at the nanoscale and its impact on the switching of SOT magnetic random-access memories (MRAMs). In recent years, SOT-MRAMs have emerged as promising non-volatile candidates for last-level (L3/L4) cache due to their high endurance, sufficiently low read/write latency, long retention times, and scalability. In these devices, a conduction current is passed through the non-magnetic (NM) layer, which generates a spin current flowing towards the ferromagnetic (FM) layer due to the Spin Hall Effect (SHE). Using conventional drift-diffusion models, which consider the electric current distribution to be uniform within the FM and NM layers, can lead to erroneous results in the case of nanoscale devices. In this paper, we use the spin current distribution calculated based on finite element simulations and drift-diffusion equations in micromagnetic simulation. We demonstrate that spin current density can be significantly lower at the two edges of the magnet compared to the middle and this non-uniformity can affect the magnet switching dynamics. We investigate the impact of this non-uniformity for both perpendicular magnetic anisotropy (PMA) and in-plane magnetic anisotropy (IMA) based magnetic tunnel junctions (MTJs). Our results show that when resistive NM layers are used, the impact of nonuniform spin current density on write times is more significant for larger FMs. In addition, the variation in write times is more significant in the case of PMA FM than IMA FM.

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Design of a Compact Spin-Orbit-Torque-Based Ternary Content Addressable Memory

Narla

Kumar

Laguna

et al. 2023

IEEE Trans. Electron Devices

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A Drift-Diffusion Based Modeling and Optimization Framework for Nanoscale Spin-Orbit Torque Devices

Cited by 3 publications

References 33 publications

Modeling of spin-orbit torque (SOT) channel and high-density SOT magnetic random-access memory

Modeling of spin-orbit torque (SOT) channel and high-density SOT magnetic random-access memory

Investigation on the impact of spin current profile on the write time of SOT MRAMs

Design of a Compact Spin-Orbit-Torque-Based Ternary Content Addressable Memory

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