Article
Physics, Applied
Tatsuya Yamamoto, Tomohiro Ichinose, Jun Uzuhashi, Takayuki Nozaki, Tadakatsu Ohkubo, Kay Yakushiji, Shingo Tamaru, Hitoshi Kubota, Akio Fukushima, Kazuhiro Hono, Shinji Yuasa
Summary: In this study, we investigate the perpendicular magnetic anisotropy (PMA) in MgO/CoFeB (CFB)/MgO junctions by introducing an angstrom-thick Mo spacer layer. It is found that perpendicularly magnetized CFB/Mo/CFB films can be obtained for a wide range of CFB thicknesses, achieving a large PMA energy density. The voltage-controlled magnetic anisotropy effect shows a sign inversion between the 'top free' and 'bottom free' magnetic tunnel junctions, indicating the importance of the flatness of the CFB/MgO interface for improving the efficiency of the effect.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2022)
Article
Engineering, Electrical & Electronic
Tomohiro Ichinose, Tatsuya Yamamoto, Takayuki Nozaki, Kay Yakushiji, Shingo Tamaru, Makoto Konoto, Shinji Yuasa
Summary: We developed a cryogenic temperature deposition process for high-performance CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) on φ300 mm thermally oxidized silicon wafers. The effect of deposition temperature on CoFeB layers and its impact on nanostructure, magnetic, and magneto-transport properties of MTJs were investigated. Cryogenic deposition of CoFeB at 100 K resulted in enhancements of perpendicular magnetic anisotropy (PMA) and voltage-controlled magnetic anisotropy (VCMA) of the MTJs compared to room temperature deposition. Improved interfacial qualities at the MgO/CoFeB interfaces were observed with cryogenic temperature deposition.
ACS APPLIED ELECTRONIC MATERIALS
(2023)
Article
Chemistry, Multidisciplinary
Geunwoo Kim, Soogil Lee, Sanghwa Lee, Byonggwon Song, Byung-Kyu Lee, Duhyun Lee, Jin Seo Lee, Min Hyeok Lee, Young Keun Kim, Byong-Guk Park
Summary: This study investigates the effects of annealing on the tunnel magnetoresistance ratio in CoFeB/MgO/CoFeB-based magnetic tunnel junctions with different capping layers and correlates them with microstructural changes. The findings indicate that the proper selection of a capping layer can increase the annealing temperature of MTJs, making it compatible with the complementary metal-oxide-semiconductor backend process.
Article
Materials Science, Multidisciplinary
Tatsuya Yamamoto, Takayuki Nozaki, Kay Yakushiji, Shingo Tamaru, Hitoshi Kubota, Akio Fukushima, Shinji Yuasa
Summary: The study shows that Ta layer in MgO/Ta/CoFeB/MgO junctions can enhance the PMA of magnetic films and eliminate the diffusion of Ta, leading to superior thermal stability and the release of VCMA effect. In addition, the Co-Fe compositional variation in CoFeB layer associated with Ta insertion is related to the changes in PMA and VCMA.
Article
Materials Science, Multidisciplinary
A. Meo, S. Sampan-a-pai, P. B. Visscher, R. Chepulskyy, D. Apalkov, J. Chureemart, P. Chureemart, R. W. Chantrell, R. F. L. Evans
Summary: The study investigates the spin transfer torque switching dynamics in CoFeB/MgO/CoFeB magnetic tunnel junctions using atomistic simulations based on Slonczewski's model. The results demonstrate a magnetization reversal driven by the combination of coherent and nonuniform excitation modes, affected by factors such as current density, temperature, and structural imperfections. This deeper understanding can be valuable for spin transfer torque dynamics in nanoscale devices.
Article
Physics, Applied
Hua Lv, Joao Fidalgo, Thomas Kampfe, Juergen Langer, Jerzy Wrona, Berthold Ocker, Paulo P. Freitas, Susana Cardoso
Summary: This study systematically investigates the Seebeck effect in nano scale p-MTJs induced by Joule heating. Experimental results show a sign change of the thermovoltage between different magnetic states, indicating the significant dependence of the Seebeck effect on the magnetic state of the p-MTJ. The efficiency of energy re-use can be improved by optimizing the non-magnetic layers.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2022)
Article
Engineering, Electrical & Electronic
K. Nishioka, S. Miura, H. Honjo, H. Naganuma, T. V. A. Nguyen, T. Watanabe, S. Ikeda, T. Endoh
Summary: The effect of magnetic coupling on the thermal stability factor Delta in magnetic tunnel junctions (MTJs) was investigated. It was found that increasing the energy constant J(cpl) of magnetic coupling can enhance Delta, but saturates when J(cpl) exceeds a critical value J(cpl_c). The magnetic static coupling constant J(stat) was much smaller than J(cpl_c), and an interlayer exchange coupling constant J(ex_c) is required to cover the difference between J(cpl_c) and J(stat). Experimental results were in good agreement with calculations, showing that Delta can be enhanced by adjusting the stiffness constant As.
IEEE TRANSACTIONS ON MAGNETICS
(2022)
Article
Nanoscience & Nanotechnology
Hua Lv, Joao Fidalgo, Ana Silva, Diana C. Leitao, Thomas Kampfe, Juergen Langer, Jerzy Wrona, Berthold Ocker, Paulo P. Freitas, Susana Cardoso
Summary: The research demonstrated multi-level switching in single perpendicular magnetic tunnel junctions (p-MTJs) and showed the potential of high-performance multi-level p-MTJs for new generation spintronic devices. Using CoFeB/MgO/CoFeB based nano-scale p-MTJs, the study achieved multi-level switching with reliable set-reset operations, suggesting feasible strategies for improving multi-level switching through materials optimization and device geometry.
ADVANCED ELECTRONIC MATERIALS
(2021)
Article
Materials Science, Multidisciplinary
Yoichi Shiota, Kaoru Noda, Yuushou Hirata, Kyosuke Kuwano, Shinsaku Funada, Ryusuke Hisatomi, Takahiro Moriyama, Maksim Stebliy, Alexey Ognev, Alexander S. Samardak, Teruo Ono
Summary: In this study, the temperature dependence of magnetic domain wall creep motion in ferrimagnetic microwires was examined. The results showed that the DW velocity changed significantly with temperature and was mainly attributed to the variation in the creep-scaling constant.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Engineering, Electrical & Electronic
M. Niwa, K. Kimura, T. Naijo, A. Oshurahunov, S. Nagamachi, H. Inoue, H. Honjo, S. Ikeda, T. Endoh
Summary: The study successfully observed the microstructure of nano-scale CoFeB-MgO-based magnetic tunnel junctions, identified the root cause of resistance changes, determined the composition of the altered region inside the MTJ, and confirmed the effectiveness of STEM tomography in failure analysis.
IEEE TRANSACTIONS ON MAGNETICS
(2021)
Article
Chemistry, Physical
Mahsa Konh, Yang Wang, Hang Chen, Subhash Bhatt, John Q. Xiao, Andrew Teplyakov
Summary: The study focused on thermal dry etching of CoFeB alloy thin films using sequential doses of chlorine and 2,4-pentanedione, achieving selective removal of the alloy without affecting the insulating barrier MgO. Analysis was conducted using atomic force microscopy and temperature-programmed desorption experiments.
APPLIED SURFACE SCIENCE
(2022)
Article
Nanoscience & Nanotechnology
Hiroshi Naganuma, Hiroaki Honjo, Chioko Kaneta, Koichi Nishioka, Shoji Ikeda, Tetsuo Endoh
Summary: The influence of sidewall damage on the thermal stability factor of quad-interface magnetic tunnel junctions is investigated through micromagnetic simulation. Sidewall damage causes a split in the energy barrier, resulting in decreased thermal stability.
Article
Physics, Applied
S. Tacchi, F. Casoli, M. G. Pini, A. Rettori, M. Madami, J. Akerman, T. T. Le, Q. N. Pham, H. L. Pham, T. N. Anh Nguyen
Summary: Utilizing alternating gradient force magnetometry and Brillouin light scattering experiments, this study investigated perpendicular magnetic anisotropy localized at the CoFeB-MgO interface in different heterostructures. Thermal treatment was found to significantly increase the PMA, and analysis of spin wave frequencies allowed estimation of the thickness dependence of PMA in a single CoFeB film. Additionally, the study of magnetic tunnel junctions revealed an antiferromagnetic interlayer exchange coupling between CoFeB layers that increased after annealing.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2021)
Article
Engineering, Electrical & Electronic
Junlin Wang, Guanqi Li, Bosen Zhang, Kunpeng Zhang, Kaiyu Tong, Bo Liu, Hao Meng, Jing Wu, Yongbing Xu
Summary: In this study, the influence of interface edge defects on the critical current and switching time in a CoFeB MRAM device was investigated by atomistic spin model simulations. The results showed that the effect of interface edge defects depends on the thickness of the magnetic layer, the operating temperature, and the driven current density. This finding can contribute to the control of fabrication processes in STT-based technologies.
IEEE TRANSACTIONS ON MAGNETICS
(2023)
Article
Nanoscience & Nanotechnology
Hiroshi Shimada, Takehiro Koike, Keisuke Kikkawa, Hiroki Konno, Naoki Ito, Ryusuke Kobayashi, Yoshinao Mizugaki, Kensaku Kanomata, Masanori Miura, Fumihiko Hirose
Summary: Nanoscale metallic tunnel junctions are essential in cutting-edge technologies like superconducting qubits, single electronics, nanospintronics, and caloritronics. This study introduced a new method for fabricating nanoscale tunnel junctions using a combination of shadow evaporation and in-situ grown Al2O3 tunnel barrier. This innovative process allows for precise control of tunnel barrier thickness and has been successfully applied to fabricate various nanoscale tunnel junctions.
ACS APPLIED NANO MATERIALS
(2021)
Article
Physics, Applied
Butsurin Jinnai, Junta Igarashi, Kyota Watanabe, Eli Christopher I. Enobio, Shunsuke Fukami, Hideo Ohno
Summary: The study shows that in shape-anisotropy magnetic tunnel junctions, magnetization reversal proceeds coherently in the 15-nm-thick CoFeB layer, which is different from conventional interfacial-anisotropy MTJs. Evaluation of the thermal stability factor Delta using two methods is crucial for the development of ultra-small and high-reliability MTJ devices.
APPLIED PHYSICS LETTERS
(2021)
Article
Physics, Applied
Chaoliang Zhang, Yutaro Takeuchi, Shunsuke Fukami, Hideo Ohno
Summary: In this study, we investigate the magnetization switching using a combination of STT and SOT, finding that SOT allows for fast switching of magnetization and STT eliminates the need for an external field. The results show that in the short pulse regime, the Type X structure achieves a switching current one-fourth smaller than the Type Y structure at 200 ps.
APPLIED PHYSICS LETTERS
(2021)
Article
Nanoscience & Nanotechnology
H. Honjo, H. Naganuma, T. V. A. Nguyen, H. Inoue, M. Yasuhira, S. Ikeda, T. Endoh
Summary: The study showed that applying SMT to the bottom Pt layer increased the PMA of the overlying Co/Pt multilayer, leading to better thermal tolerance and magnetic properties of the MTJs with a Co/Pt synthetic ferrimagnetic coupling reference layer.
Article
Engineering, Electrical & Electronic
Masanori Natsui, Akira Tamakoshi, Hiroaki Honjo, Toshinari Watanabe, Takashi Nasuno, Chaoliang Zhang, Takaho Tanigawa, Hirofumi Inoue, Masaaki Niwa, Toru Yoshiduka, Yasuo Noguchi, Mitsuo Yasuhira, Yitao Ma, Hui Shen, Shunsuke Fukami, Hideo Sato, Shoji Ikeda, Hideo Ohno, Tetsuo Endoh, Takahiro Hanyu
Summary: The article introduces a nonvolatile memory technology called SOT-MRAM based on spin-orbit torque, which has read-disturbance-free characteristic and implements a new read-energy reduction technique. The measurement results demonstrate that under a magnetic-field-free condition, SOT-MRAM achieves high-speed write and read operations.
IEEE JOURNAL OF SOLID-STATE CIRCUITS
(2021)
Article
Engineering, Electrical & Electronic
K. Nishioka, S. Miura, H. Honjo, H. Inoue, T. Watanabe, T. Nasuno, H. Naganuma, T. V. A. Nguyen, Y. Noguchi, M. Yasuhira, S. Ikeda, T. Endoh
Summary: The developed 25-nm quad-MTJ technology has better thermal stability and performance advantages compared to double-MTJ, with higher write efficiency and endurance.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2021)
Article
Physics, Applied
Yutaro Takeuchi, Ryotaro Okuda, Junta Igarashi, Butsurin Jinnai, Takaharu Saino, Shoji Ikeda, Shunsuke Fukami, Hideo Ohno
Summary: In this study, a thin-film deposition technique for a-few-nanometer-thin L1(0)-MnAl was developed and its structure and magnetic properties were investigated. The results show that L1(0)-MnAl has a large crystalline anisotropy and small spontaneous magnetization, making it a promising material for high-density and high-speed STT-MRAM.
APPLIED PHYSICS LETTERS
(2022)
Article
Engineering, Electrical & Electronic
H. Honjo, H. Naganuma, K. Nishioka, T. V. A. Nguyen, M. Yasuhira, S. Ikeda, T. Endoh
Summary: We investigated the effects of sputtering conditions for the deposition of an Iridium (Ir) layer on the magnetic properties and tunnel magnetoresistance ratio (TMR ratio) of magnetic tunnel junctions (MTJs) stacks. the exchange coupling field (H-ex) of Ir-SyF was improved by reducing the energy of Ir recoil ions and two times larger than that with Ru-SyF. Energy dispersive X-ray (EDX) spectrometry line analysis revealed greater interlayer diffusion in Ir when Ir was sputtered by using a conditions with large recoiled energy. Despite the larger H-ex, the TMR ratio of the MTJ with Ir-SyF is smaller than that with Ru-SyF. The m-H curve of MTJ with Ru-SyF showed a large plateau region around zero magnetic field, whereas that with Ir-SyF did not. These results indicated the degradation of perpendicular magnetic anisotropy (PMA) in the top part of the Co/Pt multilayer with CoFeB reference layer and a large biquadratic coupling effect in the thin Ir layer. This causes the deterioration of the TMR ratio of the MTJ with Ir-SyF. TEM image of the Co/Pt layer in the MTJ with Ir shows some lattice defects. The EDX line analysis revealed that a large amount of Pt in the top Co/Pt layer diffused toward CoFeB reference layer in the Ir-SyF, resulting in the degradation of PMA. The structural analysis by X-ray diffraction showed the lattice spacing of CoPt (111) in Ir-SyF to be larger than that in Ru-SyF, indicating the occurrence of strain relaxation at the Co/Pt interface. These crystallographic changes in Ir-SyF might be related to a larger Pt diffusion. Suppression of Pt diffusion as well as low damage Ir deposition in the reference layer is crucial to utilize Ir-SyF.
IEEE TRANSACTIONS ON MAGNETICS
(2022)
Article
Engineering, Electrical & Electronic
H. Honjo, K. Nishioka, S. Miura, H. Naganuma, T. Watanabe, Y. Noguchi, T. V. A. Nguyen, M. Yasuhira, S. Ikeda, T. Endoh
Summary: Perpendicular magnetic tunnel junctions (MTJs) with four synthetic anti-ferromagnetically coupled Co/Pt layers were developed and showed higher tunnel magnetoresistance ratio and stability at high temperatures compared to conventional double-SyF. In contrast, conventional double-SyF exhibited magnetization direction flipping and back-hopping under external magnetic fields.
IEEE TRANSACTIONS ON MAGNETICS
(2022)
Article
Engineering, Electrical & Electronic
K. Nishioka, S. Miura, H. Honjo, H. Naganuma, T. V. A. Nguyen, T. Watanabe, S. Ikeda, T. Endoh
Summary: The effect of magnetic coupling on the thermal stability factor Delta in magnetic tunnel junctions (MTJs) was investigated. It was found that increasing the energy constant J(cpl) of magnetic coupling can enhance Delta, but saturates when J(cpl) exceeds a critical value J(cpl_c). The magnetic static coupling constant J(stat) was much smaller than J(cpl_c), and an interlayer exchange coupling constant J(ex_c) is required to cover the difference between J(cpl_c) and J(stat). Experimental results were in good agreement with calculations, showing that Delta can be enhanced by adjusting the stiffness constant As.
IEEE TRANSACTIONS ON MAGNETICS
(2022)
Article
Nanoscience & Nanotechnology
T. V. A. Nguyen, Y. Saito, H. Naganuma, S. Ikeda, T. Endoh, Y. Endo
Summary: The dynamic magnetic properties of Ta-O/Co20Fe60B20 bilayer films are greatly influenced by the oxidation condition of the Ta-O layer. The oxidation of the Ta-O layer leads to a decrease in the in-plane damping constant and an increase in the effective magnetization. The out-of-plane damping constant shows a similar trend but with a much smaller magnitude compared to the in-plane damping constant.
Article
Nanoscience & Nanotechnology
Hiroshi Naganuma, Hiroaki Honjo, Chioko Kaneta, Koichi Nishioka, Shoji Ikeda, Tetsuo Endoh
Summary: The influence of sidewall damage on the thermal stability factor of quad-interface magnetic tunnel junctions is investigated through micromagnetic simulation. Sidewall damage causes a split in the energy barrier, resulting in decreased thermal stability.
Article
Materials Science, Multidisciplinary
Yoshiaki Saito, Shoji Ikeda, Tetsuo Endoh
Summary: Investigation on spin-orbit torque in synthetic antiferromagnetic structures reveals higher spin-torque efficiency in stack systems with Pt/Ir/Pt spacer layer. This finding contributes to the improvement of magnetic memory device performance.
