Advances and Future Prospects of Spin-Transfer Torque Random Access Memory

An intriguing feature of spintronics [1] is the use of pure spin-currents to manipulate magnetization [2], e.g., spin-currents can switch magnetization in spin-torque MRAM [3], a next-generation DRAM alternative. Giant spin-currents via the spin Hall effect [4][5][6] greatly expand the technological opportunities [7]. Conversely, a ferromagnet/normal metal junction emits spin-currents under microwave excitation, i.e. spin-pumping [8][9][10]. While such spin-currents are modulated at the excitation frequency, there is also a non-linear, rectified component that is commonly detected using the corresponding inverse spin Hall effect (iSHE) dc voltage [11][12][13][14]. However, the ac component should be more conducive for quantitative analysis, as it is up to two orders of magnitude larger and linear [15]. But any device that uses the ac iSHE is also sensitive to inductive signals via Faradays Law and discrimination of the ac iSHE signal must rely on phase-sensitive measurements.We use the inductive signal as a reference for a quantitative measurement of the magnitude and phase of the ac iSHE.

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“…(1) to (3). We obtain χ yy directly from fitting the spectra, the damping and g ↑↓ from the linear fits to the data in Fig.…”

Section: The 180mentioning

confidence: 99%

Phase-Sensitive Detection of Spin Pumping via the ac Inverse Spin Hall Effect

et al. 2014

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“…The phenomenon of spin transfer torque (STT) [1][2][3], in which a spin-polarized current transfers angular momentum to a magnetic layer, has brought about novel applications such as spin torque oscillators (STOs) [4][5][6][7] and spin transfer torque magnetoresistive random access memory (STT-MRAM) [8][9][10]. While initially based on magnetic materials with in-plane (IP) magnetic anisotropy, the realization that such materials lead to unnecessarily high STT-MRAM switching currents, poor memory retention, poor scalability [11], and high-field operation of STOs [12], there is now a rapidly growing interest in fabricating STT devices based on perpendicular magnetic anisotropy (PMA) materials.…”

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confidence: 99%

Depth-Dependent Magnetization Profiles of Hybrid Exchange Springs

et al. 2014

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We report on the magnetization depth profile of a hybrid exchange spring system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to a CoFeB thin film with in-plane anisotropy. The competition between these two orthogonal anisotropies promotes a strong depth dependence of the magnetization orientation. The angle of the magnetization vector is sensitive both to the strength of the individual anisotropies and to the local exchange constant, and is thus tunable by changing the thickness of the CoFeB layer and by substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic depth profiles are directly probed by element specific x-ray magnetic circular dichroism (XMCD) of the Co, Fe, and Ni layers located at different average depths. The experimental results are corroborated by micromagnetic simulations.PACS numbers: 75.30. Gw, 75.30.Et, 78.20.Ls, 75.70.Cn a Author to whom correspondence should be addressed. Electronic mail: anhntn@kth.se. 2The phenomenon of spin transfer torque (STT) [1][2][3], in which a spin-polarized current transfers angular momentum to a magnetic layer, has brought about novel applications such as spin torque oscillators (STOs) [4][5][6][7] and spin transfer torque magnetoresistive random access memory (STT-MRAM) [8][9][10]. While initially based on magnetic materials with in-plane (IP) magnetic anisotropy, the realization that such materials lead to unnecessarily high STT-MRAM switching currents, poor memory retention, poor scalability [11], and high-field operation of STOs [12], there is now a rapidly growing interest in fabricating STT devices based on perpendicular magnetic anisotropy (PMA) materials. Recent tailoring of PMA materials and their interfaces have demonstrated low switching currents, high switching speed, good thermal stability, future scalability [9,[13][14][15], and low-to zero-field operation of STOs [16][17][18][19][20].Building upon these successes, the natural extension of using PMA materials is to also investigate the potential of devices in which the magnetization is tilted with respect to the surface normal. Such materials allow for additional control of the magnetization dynamics in magnetic nanostructures [17,[21][22][23], and hint at yet improved STT-MRAM switching behavior and thermal stability [24][25][26][27][28][29]. For STOs, tilted materials offer a route to improve their microwave generation properties, both in terms of higher output power and low-to zero-field operation [17,[21][22][23]28,[30][31][32].Recently, tilted materials have also been shown to have potential for current-driven domain wall motion [33]. The influence of a tilted anisotropy is stronger than simply tilting the applied field [34] as a mere 5 degree misalignment between the free and the fixed layer in magnetic tunnel junctions (MTJs) can reduce the switching current by 36%, the switching time by 30%, and improve the switching current distribution [35].Materials with tilted anisotropies have been realized using collimated oblique sputtering [36], depos...

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“…However, it is hampered by several reliability issues due to the unique characteristic of its data storage element, Magnetic Tunnel Junction (MTJ). On the one hand, the switching behavior between two states is stochastic and mainly affected by applied current intensity [1], which leads to some write errors [2], read disturbances and hold errors [3]. On the other hand, the low (tunnel magnetoresistance) TMR ratios and resistance of MTJ increase the influence of PVT variations, especially from the access transistors [4].…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, the low (tunnel magnetoresistance) TMR ratios and resistance of MTJ increase the influence of PVT variations, especially from the access transistors [4]. Several designs including error detecting circuits, auxiliary circuits, memory cells and sense amplifiers have been proposed to solve those issues in recent years [5].…”

Section: Introductionmentioning

confidence: 99%

Mitigate erroneous operations of 2T-2MTJ STT-MRAM based on dynamic voltage threshold

Tang

Deng

et al. 2016

IEICE Electron. Express

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2T-2MTJ STT-MRAM suffers from the intrinsic stochastic switching behaviors of MTJ, "source degeneration" and leakage current problem of its access transistors, which could cause erroneous operations including write error and hold error. To mitigate those erroneous operations, Dynamic Voltage Threshold based High Voltage Threshold NMOS (HVTnDTMOS) is used as access transistors of 2T-2MTJ to increase writing current and reducing leakage current. Simulation results show that the optimized design reduces write error rate by about 13.3% and 0.062‰ reduction in hold error rate for each memory cell on the same condition of cell area and operating scheduling, compared with traditional 2T-2MTJ structure.

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Advances and Future Prospects of Spin-Transfer Torque Random Access Memory

Cited by 346 publications

References 16 publications

Phase-Sensitive Detection of Spin Pumping via the ac Inverse Spin Hall Effect

Phase-Sensitive Detection of Spin Pumping via the ac Inverse Spin Hall Effect

Depth-Dependent Magnetization Profiles of Hybrid Exchange Springs

Mitigate erroneous operations of 2T-2MTJ STT-MRAM based on dynamic voltage threshold

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