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Your search keyword '"Kei Ashiba"' showing total 4 results
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4 results on '"Kei Ashiba"'

1. Multi-level resistance uniformity of double pinned perpendicular magnetic-tunnel-junction spin-valve depending on top MgO barrier thickness

Author

Han-Sol Jun, Jin-Young Choi, Kei Ashiba, Sun-Hwa Jung, Miri Park, Jong-Ung Baek, Tae-Hun Shim, and Jea-Gun Park

Subjects
Physics, QC1-999
Abstract

In order to utilize perpendicular spin-torque-transfer magnetic-random-access-memory (p-STT MRAM) as a storage class memory, the achievement of performing multi-level-cell (MLC) operation is important in increasing the integration density of p-STT MRAM. For a double pinned perpendicular magnetic tunneling junction spin-valve performing MLC (i.e., four-resistance level) operation, the uniformity in the resistance difference between four-level resistances was investigated theoretically and experimentally. The uniformity in the resistance difference between four-level resistances was strongly dependent on the top MgO tunneling-barrier thickness. Particularly, the most uniform resistance difference between four resistance states could be achieved at a critical top-MgO tunneling thickness (i.e., ∼1.15 nm).

Published
2020
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2. Double MgO-Based Perpendicular Magnetic Tunnel Junction for Artificial Neuron

Author

Dong Won Kim, Woo Seok Yi, Jin Young Choi, Kei Ashiba, Jong Ung Baek, Han Sol Jun, Jae Joon Kim, and Jea Gun Park

Subjects
neuromorphic, MRAM, spiking neuron, spiking neural network, artificial neuron, Neurosciences. Biological psychiatry. Neuropsychiatry, RC321-571
Abstract

A perpendicular spin transfer torque (p-STT)-based neuron was developed for a spiking neural network (SNN). It demonstrated the integration behavior of a typical neuron in an SNN; in particular, the integration behavior corresponding to magnetic resistance change gradually increased with the input spike number. This behavior occurred when the spin electron directions between double Co2Fe6B2 free and pinned layers in the p-STT-based neuron were switched from parallel to antiparallel states. In addition, a neuron circuit for integrate-and-fire operation was proposed. Finally, pattern-recognition simulation was performed for a single-layer SNN.

Published
2020
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3. Double MgO-Based Perpendicular Magnetic Tunnel Junction for Artificial Neuron

Author

Kei Ashiba, Woo Seok Yi, Jea-Gun Park, Jong Ung Baek, Han Sol Jun, Jin Young Choi, Jae-Joon Kim, and Dong Won Kim

Subjects
Materials science, artificial neuron, neuromorphic, 02 engineering and technology, Electron, Topology, lcsh:RC321-571, spiking neural network, 03 medical and health sciences, Neuron circuit, Artificial neuron, Perpendicular, lcsh:Neurosciences. Biological psychiatry. Neuropsychiatry, Original Research, 030304 developmental biology, Spiking neural network, 0303 health sciences, Magnetoresistive random-access memory, Quantitative Biology::Neurons and Cognition, spiking neuron, General Neuroscience, MRAM, 021001 nanoscience & nanotechnology, Tunnel magnetoresistance, Neuromorphic engineering, 0210 nano-technology, Neuroscience
Abstract

A perpendicular spin transfer torque (p-STT)-based neuron was developed for a spiking neural network (SNN). It demonstrated the integration behavior of a typical neuron in an SNN; in particular, the integration behavior corresponding to magnetic resistance change gradually increased with the input spike number. This behavior occurred when the spin electron directions between double Co2Fe6B2 free and pinned layers in the p-STT-based neuron were switched from parallel to antiparallel states. In addition, a neuron circuit for integrate-and-fire operation was proposed. Finally, pattern-recognition simulation was performed for a single-layer SNN.

Published
2020

4. Double Pinned Perpendicular-Magnetic-Tunnel-Junction Spin-Valve Providing Multi-level Resistance States

Author

Jea-Gun Park, Tae Hun Shim, Kei Ashiba, Hansol Jun, Jin-Young Choi, and Jong Ung Baek

Subjects
0301 basic medicine, Multidisciplinary, Materials science, Field (physics), Condensed matter physics, lcsh:R, Spin valve, lcsh:Medicine, High density, Coercivity, Article, Electrical and electronic engineering, 03 medical and health sciences, Tunnel magnetoresistance, 030104 developmental biology, 0302 clinical medicine, Electronic and spintronic devices, Perpendicular, lcsh:Q, lcsh:Science, Anisotropy, 030217 neurology & neurosurgery
Abstract

A new design for high density integration greater than gigabits of perpendicular-magnetic-tunnel-junction (p-MTJ) spin-valve, called the double pinned (i.e., bottom and top pinned structures) p-MTJ spin-valve achieved a multi-level memory-cell operation exhibiting four-level resistances. Three key magnetic properties, the anisotropy exchange field (Hex) of the bottom pinned structure, the coercivity (Hc) of the double free-layer, and the Hc of the top pinned structure mainly determined four-level resistances producing tunneling-magnetoresistance (TMR) ratios of 152.6%, 33.6%, and 166.5%. The three key-design concepts are: i) the bottom pinned structure with a sufficiently large Hex to avoid a write-error, ii) the Hc of the double free-layer (i.e., ~0.1 kOe) much less than the Hc of the top pinned structure (i.e., ~1.0 kOe), and iii) the top pinned structure providing different electron spin directions.

Published
2018

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