2 Mb SPRAM (SPin-Transfer Torque RAM) With Bit-by-Bit Bi-Directional Current Write and Parallelizing-Direction Current Read

Kawahara, Takayuki; Takemura, Riichiro; Miura, Katsuya; Hayakawa, Jun; Ikeda, Shoji; Lee, Young Min; Sasaki, R.; Goto, Yuki; Ito, K.; Meguro, T.; Matsukura, F.; Takahashi, Hiromasa; Matsuoka, Hiroaki; Ohno, Hideo

doi:10.1109/jssc.2007.909751

Cited by 216 publications

(89 citation statements)

References 13 publications

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“…[1][2][3] However, one goal in the development of p-STT-MRAMs beyond a feature size of 20 nm is to meet the demands of device performance, including a high tunneling magnetoresistance ratio (TMR) of 150%, a low critical current density (J C ) of 4.7 MA/cm 2 , and a good thermal stability (∆ = E/k B T) of 74. Here, E = K eff V is the energy barrier, M S is the saturation magnetization, H k is the anisotropy field, K eff is the effective perpendicular magnetic anisotropy (PMA) energy density, V is the volume of the magnetic layer, k B is the Boltzmann constant, and T is temperature.…”

Section: Introductionmentioning

confidence: 99%

Correlation between Pd metal thickness and thermally stable perpendicular magnetic anisotropy features in [Co/Pd]n multilayers at annealing temperatures up to 500 °C

Lee

Yang

et al. 2015

AIP Advances

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We examine highly stable perpendicular magnetic anisotropy (PMA) features of [Co/Pd]10 multilayers (MLs) versus Pd thickness at various ex-situ annealing temperatures. Thermally stable PMA characteristics were observed up to 500 °C, confirming the suitability of these systems for industrial applications at this temperature. Experimental observations suggest that the choice of equivalent Co and Pd layer thicknesses in a ML configuration ensures thermally stable PMA features, even at higher annealing temperatures. X-ray diffraction patterns and cross-sectional transmission electron microscopy images were obtained to determine thickness, post-annealing PMA behavior, and to explore the structural features that govern these findings.

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Section: Introductionmentioning

confidence: 99%

Correlation between Pd metal thickness and thermally stable perpendicular magnetic anisotropy features in [Co/Pd]n multilayers at annealing temperatures up to 500 °C

Lee

Yang

et al. 2015

AIP Advances

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“…[1][2][3][4][5][6][7][8][9] The record room temperature TMR of 604% is found in single-barrier MTJs ͑SMTJs͒ with a pseudo spin valve stack, 6 which is close to the theoretical maximum. 1,2 However, the TMR ratio in an MTJ falls off with increasing bias.…”

mentioning

confidence: 86%

1 / f noise in MgO double-barrier magnetic tunnel junctions

Diao

Feng

et al. 2011

Applied Physics Letters

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Low frequency noise has been investigated in MgO double-barrier magnetic tunnel junctions ͑DMTJs͒ with tunneling magnetoresistance ͑TMR͒ ratios up to 250% at room temperature. The noise shows a 1 / f frequency spectrum and the minimum of the noise magnitude parameter is 1.2ϫ 10 −10 m 2 in the parallel state for DMTJs annealed at 375°C. The bias dependence of noise and TMR suggests that DMTJs with MgO barriers can be useful for magnetic field sensor applications. © 2011 American Institute of Physics. ͓doi:10.1063/1.3562951͔The large tunneling magnetoresistance ͑TMR͒ in MgO barrier magnetic tunnel junctions ͑MTJ͒ has greatly improved the performance of spintronic devices, such as magnetic random access memories ͑MRAMs͒, sensors, and logic devices. [1][2][3][4][5][6][7][8][9] The record room temperature TMR of 604% is found in single-barrier MTJs ͑SMTJs͒ with a pseudo spin valve stack, 6 which is close to the theoretical maximum. 1,2 However, the TMR ratio in an MTJ falls off with increasing bias. 10 Double barrier MTJs ͑DMTJs͒ offer TMR of 105%-212% at room temperature 10-13 but bias dependence of TMR is reduced because the applied voltage is divided over two single barriers. This helps to preserve the high TMR ratio at high bias. 10 A high bias is needed to inject a sufficiently large critical current to facilitate spin transfer torque ͑STT͒ switching in magnetic nanopillars with MgO barriers, which is the basis for high-speed non-volatile STT-MRAM. 14 In conventional DMTJs with a thick free layer, TMR is often lower than that in SMTJs. [10][11][12][13] However, a DMTJ can potentially improve the signal-to-noise ratio of a magnetic field sensor due to the increase in output voltage compared to an SMTJ. Hence, the low frequency noise of DMTJs is worth exploring, in comparison with that of SMTJs. It has been previously reported that 1 / f noise dominates the low frequency response of MTJs. [15][16][17][18][19][20][21][22][23] The 1 / f noise can be characterized by a noise magnitude parameter ␣ = AfS V / V 2 , where A is the junction area, f is the frequency, S V is the noise power spectrum density, and V is the applied bias. 15 Recently, Guerrero et al. 24 suggested that 1 / f noise can be greatly reduced in field sensors, when a large number of MTJs are connected either in series or in parallel. However, devices constructed with a large number of MTJs may lack integrity and suffer from a much higher chance of failure. DMTJs may be able to halve the 1 / f noise without these drawbacks, opening up a way to reduce the noise.Until now, a few reports have been published on the low frequency noise in DMTJs with a thick free layer 12,20 but their TMR ratio of around 80%-120% is considerably less than we report here. Earlier studies of MgO DMTJs did not produce high TMR because the middle CoFeB layer remains amorphous after annealing. [10][11][12]20 The adjacent MgO barriers cannot absorb boron, which maintains the amorphous nature of CoFeB. 25 Here we investigate the low frequency noise in DMTJs, with TMR ratios as high...

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“…Magnetic tunnel junctions are two terminal resistive elements that operate on the principle of spin dependant conduction through magnetic domains [1]- [3]. The device is a stack of ferromagnetic metal on both sides of a tunneling oxide spacer.…”

Section: Mtj Operationmentioning

confidence: 99%

Field driven STT-MRAM cell for reduced switching latency and energy

Patel

Ïpek

Friedman

2014

2014 IEEE International Symposium on Circuits and Systems (ISCAS)

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Abstract-A field driven approach to STT-MRAM switching is proposed as a method for reducing the switching latency of an MTJ in high performance caches. An MRAM array model is presented to characterize the switching energy and maximum achievable reduction in energy using the field driven approach. The switching latency per bit is reduced by more than a factor of ten. The resultant switching energy per bit is reduced by 82% as compared to a standard STT-MRAM.

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2 Mb SPRAM (SPin-Transfer Torque RAM) With Bit-by-Bit Bi-Directional Current Write and Parallelizing-Direction Current Read

Cited by 216 publications

References 13 publications

Correlation between Pd metal thickness and thermally stable perpendicular magnetic anisotropy features in [Co/Pd]n multilayers at annealing temperatures up to 500 °C

Correlation between Pd metal thickness and thermally stable perpendicular magnetic anisotropy features in [Co/Pd]n multilayers at annealing temperatures up to 500 °C

1 / f noise in MgO double-barrier magnetic tunnel junctions

Field driven STT-MRAM cell for reduced switching latency and energy

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