Perpendicular Spin-transfer Torque in Asymmetric Magnetic Tunnel Junctions: Material Parameter Dependence
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스핀전달토크는 나노구조에서 자성상태를 제어하는데 유용한 수단이다. 자기터널접합에서 스핀전달토크는 자성물질층의 자화가 이루는 평면에 평행한 성분과 수직인 성분으로 나눌 수 있다. 이중 평행한 성분의 스핀전달토크의 성질은 상당히 잘 알려져 있으나, 수직인 성분의 스핀전달토크의 성질에 대해서는 여전히 이견이 많다. 비대칭 자기터널접합에서의 최근 실험에서, 수직전달토크의 전압 의존성이 전압의 이차항 성분뿐만 아니라 일차항 성분도 가짐을 보고하였다. 하지만 물질 변수에 대한 의존성은 여전히 잘 알려지지 않았다. 이 논문에서는 비대칭 자기터널접합에서의 스핀전달토크의 전압의존성을, 강자성층의 스핀 갈라짐 에너지와 일함수의 차이, 그리고 페르미 에너지를 변화시켜 가면서 체계적인 조사를 하였다. Spin-transfer torque is a useful tool to control the magnetic state in nanostructures. In magnetic tunnel junctions, the spin-transfer torque has two components, the in-plane spin torque and the perpendicular spin torque. While properties of the in-plane spin-transfer torque are relatively well understood, properties of the perpendicular spin-transfer torque still remain controversial. A recent experiment demonstrated that in asymmetric magnetic tunnel junctions, the bias voltage dependence of the perpendicular spin-transfer torque contains both linear and quadratic terms in the bias. However it still remains unexplored how the bias voltage dependence changes as a function of material parameters. In this paper, we systematically investigate the perpendicular spin-transfer torque in asymmetric magnetic tunnel junction by varying spin splitting energy, work function difference, and Fermi energy of the ferromagnetic metal leads.Keywords:
Spin-transfer torque
Tunnel magnetoresistance
Biasing
The theoretical model of spin-dependent transport in magnetic tunnel junctions (MTJ) containing magnetic or non-magnetic nanoparticle is developed. The dependences of tunnel magnetoresistance (TMR) and in-plane component of spin transfer torque (STT) on the applied voltage for various sizes of nanoparticles of the order of the mean free path of the conduction electron are calculated. The calculation is performed in the approximation of the ballistic transport of conduction electrons through the insulating layers of the MTJ and the nanoparticles.
Tunnel magnetoresistance
Spin-transfer torque
Tunnel junction
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The design and statistical analysis of a magnetic tunnel junction with pinned-layer uniaxial anisotropy, slightly tilted with respect to the perpendicular magnetic anisotropy (PMA) of the free layer, are presented in the presence of thermally induced magnetic noise. The marginal tilting of the pinned-layer easy axis reduces the critical switching current density by almost 80%, as compared to a regular PMA device for a delay of 2 ns with a switching failure probability lower than 10 -9 . Substantially lower switching current density in spin-transfer torque MRAM with tilted pinned-layer anisotropy enables the use of a higher resistance-area product with a thicker tunnel barrier that compensates for the tunneling-magnetoresistance rolloff due to the relative misalignment of free- and pinned-layer easy axes.
Spin-transfer torque
Tunnel magnetoresistance
Magnetoresistive random-access memory
Tunnel junction
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Perpendicular-anisotropy magnetic tunnel junction (MTJ) is one of the most promising candidates to build hybrid logic-in-memory architecture, because of its nonvolatility, infinite endurance, and 3-D integration with a CMOS technology. A novel magnetic full-adder (MFA) based on this architecture is proposed, with MTJs switched by spin-Hall-assisted spin-transfer torque (STT). Owing to the assistance of spin-Hall effect (SHE), MTJ switching time can significantly be reduced, and high operation frequency can be achieved. Moreover, the endurance of oxide barrier is largely enhanced as the requirement of lower write voltage. Using an industrial CMOS 28 nm design kit and a physics-based three-terminal spin-Hall-assisted STT-MTJ model, functionality and performance of the proposed MFA have been simulated and validated. A 1 ns STT current pulse assisted by 0.35 ns SHE current pulse is sufficient to switch the MTJ configuration. When compared with the previous MFAs based on STT-MTJ, the proposed MFA achieves 38% less operation time and 31% less power consumption to perform read and write operations.
Spin-transfer torque
Tunnel magnetoresistance
Magnetoresistive random-access memory
Hall effect sensor
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The integration of magnetic tunnel junctions (MTJ) above CMOS circuits in embedded magnetic RAM (MRAM) or magnetic FPGA (MFPGA) could bring to digital circuits major advantages associated to non-volatile capability such as instant on/off, multi-context FPGA and zero standby power consumption. A complete simulation model for the hybrid MTJ/CMOS design is presented in this paper. Based on the recently demonstrated spin-transfer torque (STT) writing approach which promises to lower the switching current down to ~120 uA, we have added to the previous static model the dynamic behaviors as well as the switching probability and the thermal effects. The model has been developed in Verilog-A language and implemented on Cadence Virtuoso platform. Many experimental parameters are included in this model to improve the simulation accuracy. Simulations demonstrate that the model can be efficiently used to design hybrid MTJ/CMOS circuits.
Spin-transfer torque
Tunnel magnetoresistance
Magnetoresistive random-access memory
Standby power
Verilog
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A two‐transistor and two‐magnetic‐tunnel‐junction (MTJ) multi‐level cell (MLC) structure of spin‐transfer torque magnetic random access memory (STT‐RAM) is proposed. Compared with the conventional one‐transistor and two‐magnetic‐tunnel‐junction MLC STT‐RAMs, by adding an extra access transistor and adjusting the connection of the two MTJs, the extra write power consumption on the soft bit MTJ can be reduced, which will also have a benefit to the lifetime of the soft bit. Specifically, the simulation results show that more than 75% write power consumption on the soft bit can be wiped out, and the area cost caused by the extra access transistor is negligible.
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Tunnel magnetoresistance
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Spin-transfer torque
Tunnel magnetoresistance
Magnetoresistive random-access memory
Macro
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Spin-transfer torque
Tunnel magnetoresistance
Tunnel junction
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Abstract The tunnel magnetoresistance (TMR) in the magnetic tunnel junction (MTJ) with embedded nanoparticles (NPs) was calculated in range of the quantum-ballistic model. The simulation was performed for electron tunneling through the insulating layer with embedded magnetic and non-magnetic NPs within the approach of the double barrier subsystem connected in parallel to the single barrier one. This model can be applied for both MTJs with in-plane magnetization and perpendicular one. We also calculated the in-plane component of the spin transfer torque (STT) versus the applied voltage in MTJs with magnetic NPs and determined that its value can be much larger than in single barrier system (SBS) for the same tunneling thickness. The reported simulation reproduces experimental data of the TMR suppression and peak-like TMR anomalies at low voltages available in leterature.
Tunnel magnetoresistance
Spin-transfer torque
Tunnel junction
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Spin-transfer torque
Tunnel magnetoresistance
Magnetoresistive random-access memory
Macro
Hysteresis
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Spin transfer torque magnetic random access memory (STT-MRAM) has shown great potential in building future universal memory. However, the core of STT-MRAM, conventional perpendicular magnetization anisotropy (PMA) magnetic tunnel junction (MTJ) is facing challenges in keeping high thermal stability factor (ΔE), which is essential for reliable data storage. Despite solving the problem of ΔE, perpendicular shape anisotropy (PSA) MTJ still has drawbacks of slow STT switching and high breakdown risk. In this paper, we proposed a spin obit torque (SOT)-assisted-STT switching mechanism for PSA MTJ. A SIPCE model of PSA MTJ is developed. This model shows great agreements with experimental measurements. Besides, it is a very useful tool for circuit design and simulation. This model shows ΔE of PMA MTJ can be up to 70. Thanks to SOT-assisted-STT switching mechanism, the switching time can be greatly reduced. At last, simulations of non-volatile master flip-flop (NVMFF) circuit is performed to validate the device modeling.
Tunnel magnetoresistance
Spin-transfer torque
Magnetoresistive random-access memory
Switching time
Magnetic storage
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