H. Yoda

H. Yoda
Spin-Orbitronics Technologies, Inc.

Master of Science in Electrical Engineering

About

117
Publications
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Introduction
Skills and Expertise

Publications

Publications (117)
Article
We investigated a voltage-control spintronics memory (VoCSM) with a shunt-free design process and W spin-Hall electrode. We successfully reduced the write current to 62 μA at a 5-ns write pulse (48 μA at a 20-ns write pulse), utilizing a high spin-Hall efficiency by developing the shunt-free design process and optimized W spin-Hall electrode. Moreo...
Article
Magnetization switching was observed in real time in voltage-control spintronics memory (VoCSM), which utilizes a hybrid writing method that combines spin–orbit torque and voltage-controlled magnetic anisotropy (VCMA). VCMA lowers the switching energy barrier between parallel and antiparallel states, leading to a reduction in the write current and...
Conference Paper
Full-text available
Our new proposal of voltage-control spintronics memory (VoCSM) in which Spin Hall effect (SHE) in conjunction with the voltage-control-magnetic-anisotropy (VCMA) effect for in-plane magnetic tunnel junction (IP-MTJ) works as the writing principle. We demonstrate write test with IP-MTJ of aspect ratio of about one in which large retention energy as...
Article
We designed a voltage-control spintronics memory unit-cell, VoCSM, with high write-efficiency to prove a potential to reduce writing energy per bit. By optimizing a self-aligned structure, the cell has the critical switching current (I csw ) smaller than 50 µA at 20 nsec. for designed MTJ size of about 50 × 150 nm ² . The value is much smaller than...
Article
Voltage-induced magnetization switching can lead to a new paradigm enabling ultralow-power and high density instant-on nonvolatile magnetoelectric random access memory (MeRAM) devices. Two major challenges for future MeRAM devices are to achieve large perpendicular magnetic anisotropy (PMA) and high voltage-controlled magnetic anisotropy (VCMA) coe...
Article
A voltage-control spintronics memory (VoCSM) which has a potential of low energy consumption uses the spin-Hall effect (SHE) and the voltage-controlled magnetic anisotropy (VCMA) effect for its write operation. In this work, the relationship between the critical switching current (Ic sw ) and the SHE electrode thickness (t N ) is investigated in th...
Article
Full-text available
Our new proposal of voltage-control spintronics memory (VoCSM) in which spin-orbit torque (SOT) in conjunction with the voltage-control-magnetic-anisotropy (VCMA) effect works as the writing principle showed small switching current of 37 μA for about 350 KBT switching energy. This indicates VoCSM’s writing efficiency is so high that VoCSM would be...
Article
Improving the write efficiency of magnetic tunnel junctions (MTJs) by using spin-orbit torque (SOT) is essential for realizing high-density spintronic memory. Here, we investigate a voltage-controlled spintronic memory (VoCSM) with a Ta−B spin Hall electrode. The magnetic properties of MTJs with a storage layer such as Fe−B or Co−Fe−B on an amorpho...
Article
Full-text available
We fabricated magnetic tunnel junctions with a 3d-transition material(X)-doped MgO (Mg-X-O) barrier, and evaluated the effect of the doping on magnetoresistance (MR) and microstructure. Among the variations of X (X = Fe, Co, Ni, Cr, Mn, Ti, V, and Zn), X = Fe and Mn showed a high MR ratio of more than 100%, even at a low resistance-area product of...
Article
We experimentally demonstrate a giant voltage-controlled magnetic anisotropy (VCMA) coefficient in a crystallographically strained CoFe layer (~15 monolayers in thickness) in a MgO/CoFe/Ir system. We observed a strong applied voltage dependence of saturation field and an asymmetric concave behavior with giant VCMA coefficients of −758 and 1043 fJ V...
Conference Paper
Full-text available
I. Concept of VoCSM and TSSA process The voltage-control spintronic memories (VoCSM) whose writing principal of spin-Hole effect (SHE) under voltage-controlled magnetic anisotropy (VCMA) effect and device structure of multi-MTJs locate on the same SHE electrode is designed for high density, low energy consumption, and high robustness against read-d...
Article
A hybrid writing scheme that combines the spin Hall effect and voltage-controlled magnetic-anisotropy effect is investigated in Ta/CoFeB/MgO/CoFeB/Ru/CoFe/IrMn junctions. The write current and control voltage are applied to Ta and CoFeB/MgO/CoFeB junctions, respectively. The critical current density required for switching the magnetization in CoFeB...
Article
Voltage-control spintronics memory (VoCSM) is a spintronics-based memory that uses the voltage-control-magnetic-anisotropy (VCMA) effect as a selection method and the spin-Hall effect as a write method, and is a candidate for future nonvolatile main memory because of its advantages such as high density, low energy consumption, and robustness agains...
Article
Epitaxial Fe/magnesium gallium spinel oxide (MgGa2O4)/Fe(001) magnetic tunnel junctions (MTJs) were fabricated by magnetron sputtering. Tunnel magnetoresistance (TMR) ratio up to 121% at room temperature (196% at 4 K) was observed, suggesting a TMR enhancement by the coherent tunneling effect in the MgGa2O4 barrier. The MgGa2O4 layer had a spinel s...
Article
We propose a new spintronics-based memory employing the voltage-control-magnetic-anisotropy effect as a bit selecting principle and the spin-orbit-torque effect as a writing principle. We have fabricated the prototype structure, and successfully demonstrated the writing scheme specific to this memory architecture.
Conference Paper
We propose a new spintronics-based memory employing the voltage-control-magnetic-anisotropy effect as a bit selecting principle and the spin-orbit-torque effect as a writing principle. We have fabricated the prototype structure, and successfully demonstrated the writing scheme specific to this memory architecture.
Article
Full-text available
Patterning damage at the sidewall in a magnetic tunnel junction (MTJ) was observed precisely using a rectangular MTJ where deterioration in crystallinity is easier to identify than in the case of a dot-shaped conventional MTJ. A 200-500 nm-square rectangular MTJ was patterned by a 200 eV ion beam (IB). Cross-sectional transmission electron microsco...
Chapter
This chapter covers the entire gamut of MRAM, from the fundamental physics of magnetism, magnetic materials used in MTJ elements, history of MRAM developments, and innovations which were keys to MRAM, to important designing points, MRAM scalability, and expected future evolutions of MRAM. The chapter is expected to help engineers who are not famili...
Conference Paper
Critical switching current, I sw , of STT (Spin Transfer Torque)-MRAM has been reduced by several orders with perpendicular MTJ and the state-of-the-art write charge, Q w , becomes the order of 100–150fC. With the small Q w , MRAM starts to save energy consumption by 70–80% compared with a conventional memory system. Analysis of the write pulse-wid...
Patent
One embodiment provides a magnetic memory element, including: a first ferromagnetic layer whose magnetization is variable; a second ferromagnetic layer which has a first band split into a valence band and a conduction band and a second band being continuous at least from the valence band to the conduction band; and a nonmagnetic layer provided betw...
Article
Although mobile devices such as smartphones are convenient in many respects, short battery lifetime remains an issue. Moreover, the energy consumption of the mobile processor is increasing as its performance improves. Accordingly, there are high expectations that the energy consumption of mobile devices will be reduced in order to prolong battery l...
Patent
Full-text available
A magnetoresistive device of an embodiment includes: first and second devices each including, a first magnetic layer having a changeable magnetization perpendicular to a film plane, a second magnetic layer having a fixed and perpendicular magnetization, and a nonmagnetic layer interposed between the first and second magnetic layers, the first and s...
Patent
Full-text available
According to one embodiment, a magnetoresistive effect element includes a recording layer including ferromagnetic material with perpendicular magnetic anisotropy to a film surface and a variable orientation of magnetization, a reference layer including ferromagnetic material with perpendicular magnetic anisotropy to a film surface and an invariable...
Patent
Full-text available
According to one embodiment, a magnetoresistive element includes an electrode layer, a first magnetic layer, a second magnetic layer and a nonmagnetic layer. The electrode layer includes a metal layer including at least one of Mo, Nb, and W. The first magnetic layer is disposed on the metal layer to be in contact with the metal layer and has a magn...
Patent
Full-text available
According to one embodiment, a method of manufacturing a magnetic memory, the method includes forming a first magnetic layer having a variable magnetization, forming a tunnel barrier layer on the first magnetic layer, forming a second magnetic layer on the tunnel barrier layer, the second magnetic layer having an invariable magnetization, forming a...
Article
Full-text available
Most parts of present computer systems are made of volatile devices, and the power to supply them to avoid information loss causes huge energy losses. We can eliminate this meaningless energy loss by utilizing the non-volatile function of advanced spin-transfer torque magnetoresistive random-access memory (STT-MRAM) technology and create a new type...
Patent
A magnetoresistive element according to an embodiment includes: a first and second magnetic layers having an easy axis of magnetization in a direction perpendicular to a film plane; and a first nonmagnetic layer interposed between the first and second magnetic layers, at least one of the first and second magnetic layers including a structure formed...
Patent
According to one embodiment, a magnetic memory element includes a memory layer, a first nonmagnetic layer, a reference layer, a second nonmagnetic layer, and an adjustment layer which are stacked. The adjustment layer is configured to reduce a leakage magnetic field from the reference layer. The adjustment layer is formed by stacking an interface l...
Conference Paper
This paper presents a review and future prospects for the tunnel magnetoresistance (TMR) effect in magnetic tunnel junction (MTJ) and spin manipulation technologies such as spin-transfer torque (STT) for magnetoresistive random access memory (MRAM). Major challenges for ultrahigh-density STT-MRAM with perpendicular magnetization and novel functiona...
Article
We report on the spin-transfer magnetization switching properties of CoFe/Pd-based perpendicularly magnetized giant magnetoresistive cells over a wide current pulse duration time range. Analytic expressions without empirical parameters like attempt frequency are tested experimentally for the thermally assisted and precessional regimes. Good agreeme...
Patent
Full-text available
A magnetoresistive element which records information by supplying spin-polarized electrons to a magnetic material, includes a first pinned layer which is made of a magnetic material and has a first magnetization directed in a direction perpendicular to a film surface, a free layer which is made of a magnetic material and has a second magnetization...
Patent
Full-text available
A magneto-resistive element according to an aspect of the present invention includes a free layer whose magnetized state changes and a pinned layer whose magnetized state is fixed. The free layer comprises first and second ferromagnetic layers and a non-magnetic layer which is arranged between the first and second ferromagnetic layers. An intensity...
Conference Paper
We demonstrated lower power consumption of mobile CPU by replacing high-performance (HP)-SRAMs with spin transfer torque (STT)-MRAMs using perpendicular (p)-MTJ. The key points that enable the low power consumption are adapting run time power gating architecture (shown in Fig. 1), and satisfying both fast and low-power writing, namely, 3 nsec and 0...
Conference Paper
In this paper, the progress of P-MTJs is reviewed and prospects for the normally-off memory hierarchy based on new results are discussed.
Article
This paper presents novel processor architecture for HP-processor with MRAM/SRAM-based hybrid cache memory. By simulations of HP-processor using MTJs, it has been clarified that total power of the HP-processor using perpendicular-(p-)STT-MRAM [H. Yoda, et al., Current Appl. Phys. 10, e87 (2010)] can be reduced by 50.2% without any degradation of op...
Conference Paper
Spin-RAM technologies for operation speed faster than 30 ns, memory capacity larger than 1 Gbits and practically infinite read/write endurance have been developed by using magnetic tunnel junctions with perpendicular magnetization layers. Combination of Spin-RAM and power-gating technology will enable ultra low power computer called Normally-Off Co...
Article
We studied the spin-transfer switching probability (P<sub>sw</sub>) in giant magnetoresistance (GMR) device with perpendicular magnetizations using short nanosecond and sub-nanosecond current pulses. A switching time of 510 picoseconds was achieved with the application of 7.5 mA, which is 4.3 times larger than the critical current at 0 K, without t...
Article
Full-text available
A high-speed random number generator (RNG) circuit based on magnetoresistive random-access memory (MRAM) using an error-correcting code (ECC) post processing circuit is presented. ECC post processing increases the quality of randomness by increasing the entropy of random number. We experimentally show that a small error-correcting capability circui...
Article
Spin torque transfer switching magnetic random access memory (Spin-MRAM) using MgO-magnetic tunnel junction (MTJ) is considered to be the most promising candidate for high-density, high-speed, and non-volatile RAM. Notwithstanding its excellent potential, the breakdown mechanism of MgO-MTJ has not been well understood although a thorough understand...
Conference Paper
In order to realize a sub-Giga bit scale NVRAM, the novel MRAM based on the spin-transfer-torque (STT) switching has been intensively investigated due to its excellent scalability compared with a conventional magnetic field induce switching MRAM [1]. However, the memory cell size of STT-MRAM reported so far is still over 1μm2, and the memory capaci...
Article
An Fe-based perpendicular alloy with small damping constant was applied to an MTJ storage layer and small switching current of 9 μA was obtained for a write current width of 5 ms. The efficiency of spin transfer torque writing was proved to be higher than those for in-plane MTJs. The estimated Ic for the MTJ with 50 nsec pulse width is lower than 2...
Article
A spin transfer torque magnetoresistive random access memory (STT-MRAM) is the most promising candidate for a non-volatile random access memory, because of its scalability, high-speed operation, and unlimited read/write endurance. An ion beam etching (IBE) is one of the promising etching methods for a magnetic tunnel junction (MTJ) of the STT-MRAM,...
Conference Paper
We investigate extremely low programming current and fast switching time of a perpendicular tunnel-magnetoresistance (P-TMR) for spin-transfer torque using a P-TMR cell of 50 nm-diameter. A L1<sub>0</sub>-crystalline ordered alloy is used as a free layer that has excellent thermal stability and a damping constant of about 0.03. The programming curr...
Article
Perpendicular L1<sub>0</sub>-FePt/MgO/Fe/L1<sub>0</sub> -FePt magnetic tunnel junction (MTJ) films with the (001) texture were successfully developed to obtain a large tunnel magnetoresistance (TMR) above 100 % at room temperature. The TMR ratio in the L1<sub>0</sub>-FePt/MgO/Fe/L1<sub>0</sub>-FePt MTJ was strongly dependent on the Fe interfacial l...
Conference Paper
A comprehensive statistical model of the switching probability was proposed for a 1 Gb spin transfer torque magneto resistive random access memory (STT-MRAM). Since the switching current varies with every write cycle owing to the thermal instability, the read disturbance and the write error are critical issues in the STT-MRAM. In this paper, the op...
Conference Paper
Magnetoresistive Random Access Memory (MRAM) is a promising device for high-density (over Gbits scale), high-speed (equal to DRAM or better) non-volatile RAM, and much research has been done over several years with a view to overcoming the problems regarding practical use. Spin Torque Transfer switching MRAM (STT-MRAM) is considered to be the most...
Article
In this paper, the switching current distribution by spin transfer torque is investigated for CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs). The distribution of the spin transfer switching current for a MTJ with junction size of 85×110 nm2 is 16% when the duration of applied pulse current is 5 ms. In the case of magnetization reversal with magne...
Article
It has been reported that spin transfer torque switching in the perpendicular magnetic device has the advantage of improving the spin-torque efficiency in comparison with the in-plane one [1, 2]. Our previous study was the first time to demonstrate the spin transfer switching in perpendicular magnetic tunnel junctions (MTJs) using TbCoFe alloy. In...
Article
Spin transfer (ST) switching in the TbCoFe/CoFeB/MgO/CoFeB/TbCoFe magnetic tunnel junction (MTJ) was studied. The TbCoFe/CoFeB free layer with a large coercive field of 1.2 kOe and a large thermal stability factor of 107 at room temperature was switched by a 100 ns pulse current with a current density of 4.7 MA/cm2. This is the first report of ST s...
Article
To enlarge the read margin of magnetic random access memory (MRAM), we developed a SiO2/Si3N4 hard mask process for magnetic tunnel junction (MTJ) stack patterning. This process can protect MTJ materials from oxidation during the resist removal process and reduces the distribution of MTJ resistance for 0.32-mum-wide bits on an 8-in.-diameter wafer...
Conference Paper
Study of the reliability of ultra-thin MgO tunneling barriers for spin transfer switching magnetoresistive random access memory (MRAM) revealed MgO to be an excellent film with little resistance drift. Precise control of CoFeB/MgO/CoFeB interface was found to be important for making highly reliable tunneling barriers.
Article
In the CoFeB/MgO/CoFeB magnetoresistive tunneling junctions, the bias-dependent magnetic switching curves are investigated and the spin transfer torque effect and the thermal activation effect on the magnetic switching are estimated. The different switching behaviors at the positive and negative biases were observed, which are the asymmetric change...
Article
Tunnel resistance for CoFeB/MgO/CoFeB junctions with a wide variety of resistance has been investigated as a function of bias voltage Vb and temperature to elucidate bias voltage dependence of the magnetoresistance ratio. Comparison with a conventional NiFe/AlOx/CoFe junction is also discussed. In the case of a parallel alignment of the magnetic mo...
Article
For each case of current and voltage detection in series connections, and current and voltage in parallel connections in the multi-layered structure of a magnetoresistive random access memory (MRAM) cell having two serially connected magnetic tunnel junction (MTJ) layers, first, we demonstrate the existence of an optimum value for the weighting coe...
Article
Technologies for realizing high density MRAM were developed. First, new circuitry to lower the resistance of programming wires was developed. Second, both MTJ plane shape and cross-sectional structure were optimized to lower the programming current. Based on these two technologies, 16 Mb MRAM was designed, fabricated with 130 nm CMOS process and 24...
Article
Switching astroid curve of "C-shape" cell with weakly coupled synthetic antiferomagnetic layer is studied. Micromagnetic model simulation and experimental measurements clearly show that the switching mechanism of this magnetic element strongly depends on the C-type magnetic domain, derived from characteristic shape anisotropy, and strength of inter...