Benchmarking of spin–orbit torque vs spin-transfer torque devices

Kumar, Piyush; Naeemi, Azad

doi:10.1063/5.0101265

Cited by 9 publications

(6 citation statements)

References 27 publications

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“…7(d), we benchmark the write performance for the SOT+VCMA/STT schemes against other memory options. 43 For the 2T SOT-MRAM, we show results for various SOT channel materials such as PtCu, 44 AuPt, 17 BiSe, 45 β-W, 46 and BiSb 47 including the perpendicular (PMA) as well as in-plane (IMA) MTJs. While the write energies for the SOT+VCMA and the SOT+STT schemes are comparable, the write time is much higher for the SOT+STT scheme.…”

Section: Write Benchmarkingmentioning

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: Write Benchmarkingmentioning

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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“…To obtain various trade-offs among write current, time, and error rate and to evaluate the VCMA selectivity of the MTJs, we use micromagnetic (OOMMF [14]) simulations augmented with rare-event enhancement [15] method. The simulation framework has already been validated with experiments [16]. We use perpendicular MTJ with a diameter of 51 nm and a free layer thickness of 1.2 nm.…”

Section: Device Simulationsmentioning

confidence: 99%

“…The write voltages and current for the SOT+VCMA scheme are listed in Table II and the same for the SOT+STT are listed in Table III. The write energy values are benchmarked against other memory options [16] as shown in Fig. 20.…”

Section: Benchmarkingmentioning

confidence: 99%

High-Density Spin–Orbit Torque Magnetic Random Access Memory With Voltage-Controlled Magnetic Anisotropy/Spin-Transfer Torque Assist

Kumar

Naeemi

2022

IEEE J. Explor. Solid-State Comput. Devices Circuits

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This paper explores an area saving scheme for spinorbit torque (SOT) magnetic random-access memory (MRAM) by sharing the SOT channel and write transistor among multiple magnetic tunnel junctions (MTJs). We use two write mechanisms to selectively write the MTJs; voltage-controlled magnetic anisotropy (VCMA) assisted write in the presence of an external magnetic field and field-free spin-transfer torque (STT) assisted write. Using micromagnetic simulations that are augmented by the rare-event enhancement, we study various tradeoffs among write current, time and energy, write error rate (WER), and the number of MTJs on an SOT channel. We quantify the issue of IR drop on the SOT channel as a function of the SOT layer thickness and number of MTJs. Our results show having more than 4 MTJs on an SOT channel poses major challenges in terms of IR drop and WER. In addition, we evaluate the impact of the proposed scheme on read performance.Index Terms-Magnetic random-access memory (MRAM), spin-transfer torque (STT), spin-orbit torque (SOT), voltagecontrolled magnetic anisotropy (VCMA).

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“…Spintronic devices have emerged as an innovative class of memory components that exploit the spin property of electrons in tandem with their charge to overcome various limitations of conventional memory devices 1 . One of the most prominent ones among spintronic memory technologies is spin-orbit torque magnetic random-access memory (SOT MRAM) which is a prospective replacement for conventional memory technologies 2 . SOT MRAM provides various advantages such as non-volatility which makes it suitable for various applications ranging from personal electronics to data centers, excellent endurance which allows for a high number of write cycles without degradation, and sufficiently fast read/ write latency.…”

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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Benchmarking of spin–orbit torque vs spin-transfer torque devices

Cited by 9 publications

References 27 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

High-Density Spin–Orbit Torque Magnetic Random Access Memory With Voltage-Controlled Magnetic Anisotropy/Spin-Transfer Torque Assist

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

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