Jiefang Deng
Position: Grad Students
Research Type: Theory
Office: E3-03-05
Email: e0009073@u.nus.edu
Contact: tel:(65) 8451 7529
Group: Prof Liang Gengchiau
CA2DM Publications:
2020 |
Deng, Jiefang; Miriyala, Venkata Pavan Kumar; Zhu, Zhifeng; Fong, Xuanyao; Liang, Gengchiau Voltage-Controlled Spintronic Stochastic Neuron for Restricted Boltzmann Machine With Weight Sparsity Journal Article 21 IEEE ELECTRON DEVICE LETTERS, 41 (7), pp. 1102-1105, 2020, ISSN: 0741-3106. @article{ISI:000545436900036, title = {Voltage-Controlled Spintronic Stochastic Neuron for Restricted Boltzmann Machine With Weight Sparsity}, author = {Jiefang Deng and Venkata Pavan Kumar Miriyala and Zhifeng Zhu and Xuanyao Fong and Gengchiau Liang}, doi = {10.1109/LED.2020.2995874}, times_cited = {21}, issn = {0741-3106}, year = {2020}, date = {2020-07-01}, journal = {IEEE ELECTRON DEVICE LETTERS}, volume = {41}, number = {7}, pages = {1102-1105}, publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC}, address = {445 HOES LANE, PISCATAWAY, NJ 08855-4141 USA}, abstract = {This work proposes a novel three-terminal magnetic tunnel junction (MTJ) as a stochastic neuron. The neuron is probabilistically switched based on the voltage-controlled magnetic anisotropy (VCMA) effect with the assistance of Rashba effective field. We find that a restricted Boltzmann machine (RBM) implemented using our proposed neuron for handwritten character recognition can achieve synaptic weight sparsity, without sacrificing the network classification accuracy. Moreover, the RBM implemented by this novel neuron performs even better in the presence of device variations, implying that our device is highly suitable for the hardware implementation of RBM.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This work proposes a novel three-terminal magnetic tunnel junction (MTJ) as a stochastic neuron. The neuron is probabilistically switched based on the voltage-controlled magnetic anisotropy (VCMA) effect with the assistance of Rashba effective field. We find that a restricted Boltzmann machine (RBM) implemented using our proposed neuron for handwritten character recognition can achieve synaptic weight sparsity, without sacrificing the network classification accuracy. Moreover, the RBM implemented by this novel neuron performs even better in the presence of device variations, implying that our device is highly suitable for the hardware implementation of RBM. |
2018 |
Deng, Jiefang; Fong, Xuanyao; Liang, Gengchiau Electric-field-induced three-terminal pMTJ switching in the absence of an external magnetic field Journal Article APPLIED PHYSICS LETTERS, 112 (25), 2018, ISSN: 0003-6951. @article{ISI:000435987400033, title = {Electric-field-induced three-terminal pMTJ switching in the absence of an external magnetic field}, author = {Jiefang Deng and Xuanyao Fong and Gengchiau Liang}, doi = {10.1063/1.5027759}, times_cited = {6}, issn = {0003-6951}, year = {2018}, date = {2018-06-18}, journal = {APPLIED PHYSICS LETTERS}, volume = {112}, number = {25}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {Since it is undesirable to require an external magnetic field for on-chip memory applications, we investigate the use of a Rashba effective field alternatively for assisting the electric-field-induced switching operation of a three terminal perpendicular magnetic tunnel junction (pMTJ). By conducting macro-spin simulations, we show that a pMTJ with a thermal stability of 61 can be switched in 0.5 ns, consuming a switching energy of 6 fJ, and the voltage operation margin can be improved to 0.8 ns. Furthermore, the results also demonstrate that a heavy metal system that can provide a large field-like torque rather than the damping-like torque is favored for the switching. Published by AIP Publishing.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Since it is undesirable to require an external magnetic field for on-chip memory applications, we investigate the use of a Rashba effective field alternatively for assisting the electric-field-induced switching operation of a three terminal perpendicular magnetic tunnel junction (pMTJ). By conducting macro-spin simulations, we show that a pMTJ with a thermal stability of 61 can be switched in 0.5 ns, consuming a switching energy of 6 fJ, and the voltage operation margin can be improved to 0.8 ns. Furthermore, the results also demonstrate that a heavy metal system that can provide a large field-like torque rather than the damping-like torque is favored for the switching. Published by AIP Publishing. |
2017 |
Deng, Jiefang; Liang, Gengchiau; Gupta, Gaurav Ultrafast and low-energy switching in voltage-controlled elliptical pMTJ Journal Article 13 SCIENTIFIC REPORTS, 7 , 2017, ISSN: 2045-2322. @article{ISI:000416409400004, title = {Ultrafast and low-energy switching in voltage-controlled elliptical pMTJ}, author = {Jiefang Deng and Gengchiau Liang and Gaurav Gupta}, doi = {10.1038/s41598-017-16292-7}, times_cited = {13}, issn = {2045-2322}, year = {2017}, date = {2017-11-29}, journal = {SCIENTIFIC REPORTS}, volume = {7}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Switching magnetization in a perpendicular magnetic tunnel junction (pMTJ) via voltage controlled magnetic anisotropy (VCMA) has shown the potential to markedly reduce switching energy. However, the requirement of an external magnetic field poses a critical bottleneck for its practical applications. In this work, we propose an elliptical-shaped pMTJ to eliminate the requirement of providing an external field by an additional circuit. We demonstrate that a 10 nm thick in-plane magnetized bias layer (BL) separated by a metallic spacer of 3 nm from the free layer (FL) can be engineered within the MTJ stack to provide the 50 mT bias magnetic field for switching. By conducting macrospin simulation, we find that a fast switching in 0.38 ns with energy consumption as low as 0.3 fJ at a voltage of 1.6 V can be achieved. Furthermore, we study the phase diagram of switching probability, showing that a pulse duration margin of 0.15 ns is obtained and low-voltage operation (similar to 1V) is favored. Finally, the MTJ scalability is considered, and it is found that scaling down may not be appealing in terms of both the energy consumption and the switching time for precession based VCMA switching.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Switching magnetization in a perpendicular magnetic tunnel junction (pMTJ) via voltage controlled magnetic anisotropy (VCMA) has shown the potential to markedly reduce switching energy. However, the requirement of an external magnetic field poses a critical bottleneck for its practical applications. In this work, we propose an elliptical-shaped pMTJ to eliminate the requirement of providing an external field by an additional circuit. We demonstrate that a 10 nm thick in-plane magnetized bias layer (BL) separated by a metallic spacer of 3 nm from the free layer (FL) can be engineered within the MTJ stack to provide the 50 mT bias magnetic field for switching. By conducting macrospin simulation, we find that a fast switching in 0.38 ns with energy consumption as low as 0.3 fJ at a voltage of 1.6 V can be achieved. Furthermore, we study the phase diagram of switching probability, showing that a pulse duration margin of 0.15 ns is obtained and low-voltage operation (similar to 1V) is favored. Finally, the MTJ scalability is considered, and it is found that scaling down may not be appealing in terms of both the energy consumption and the switching time for precession based VCMA switching. |