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In order to recover the patterning damage and improve the electric and magnetic properties of the patterned magnetic tunnel junctions (MTJs), the novel post-treatment process using oxygen ions has been studied. Generally, the oxygen is known as an unsuitable gas for the MTJs patterning because it causes degradation of the patterned MTJs by over-oxidation of MgO. By the way, if the damaged layer could be oxidized selectively without over-oxidation of the damage-less area, oxygen can be the most effective gas to recover the patterning damage of the MTJs. In this study, for the selective oxidation, we proposed the non-reactive oxygen treatment scheme called the oxygen showering post-treatment process (OSP) using an ozone diffusion chamber. By the specific OSP conditions, 8 l/min of the flow rate, 250 °C of the temperature, and 30 s of the time, the magneto-resistance (MR) was increased from 103% to 110%, and the switching current was decreased from 41.1 μA to 31.6 μA when compared with reference data at the same resistance level. These results show that the electric and magnetic properties of the patterned MTJs by the OSP treatment have been improved compared to the reference sample. The improvement in electric and magnetic properties by the OSP treatment is assumed because the reference sample already contains slight patterning damages at the edge of the MTJs despite the optimized patterning process, and these damages have been oxidized by the OSP treatment. Moreover, by the OSP treatment, the proportion of the electric short fail was dramatically decreased from 1.51% to 0%, which is a remarkable improvement in terms of a successful commercialization of spintronic devices. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the growth kinetics of ultrathin silicon dioxide films formed by oxidation in a nitrogen[sub2] oxygen ambient. Experimental procedure; Results and discussion; Conclusion.

To identify the degradation mechanism in magnetic tunnel junctions (MTJs) using hydrogen, the properties of the MTJs were measured by applying an additional hydrogen etch process and a hydrogen plasma process to the patterned MTJs. In these studies, an additional 50 s hydrogen etch process caused the magnetoresistance (MR) to decrease from 103% to 14.7% and the resistance (R) to increase from 6.5 kX to 39 kX. Moreover, an additional 500 s hydrogen plasma process decreased the MR from 103% to 74% and increased R from 6.5 kX to 13.9 kX. These results show that MTJs can be damaged by the hydrogen plasma process as well as by the hydrogen etch process, as the atomic bonds in MgO may break and react with the exposed hydrogen gas. Compounds such as MgO hydrate very easily. We also calculated the damaged layer width (DLW) of the patterned MTJs after the hydrogen etching and plasma processes, to evaluate the downscaling limitations of spin-transfer-torque magnetic randomaccess memory (STT-MRAM) devices. With these calculations, the maximum DLWs at each side of the MTJ, generated by the etching and plasma processes, were 23.8 nm and 12.8 nm, respectively. This result validates that the hydrogen-based MTJ patterning processes cannot be used exclusively in STTMRAMs beyond 20 nm. [ABSTRACT FROM AUTHOR]

Abstract: We report the unexpected temperature dependence of electron tunneling from the two-dimensional electron gas (2DEG) to the Si-dot in a Si-dots floating gate metal-oxide-semiconductor (MOS) capacitor. We indicate that this temperature dependence of the electron tunneling cannot be explained by the conventional one-dimensional tunneling model, and show that it is necessary for a new model which includes the geometrical factor of the system. To extract a mechanism of the electron injection process from the 2DEG to the nano-structure, we have employed the numerical simulation, which includes both the geometrical condition of the system and the experimental setup. We suggest in our new tunneling model that the main contribution to the electron tunneling is induced by the wave-packet-like state of the electron below the Si-dots. We successfully show that the temperature dependence of the electron injection voltage in the Si-dots floating gate MOS capacitor fits our model. This indicates that the spatial distribution of electron density in the two-dimensional electron gas would play a crucial role in the electron tunneling. [ABSTRACT FROM AUTHOR]

PURPOSE: The present study was designed to determine to what extent muscle damage induced by repetitive eccentric exercise with maximal voluntary effort (ECC) affects the time course of central and peripheral fatigue during sustained maximal voluntary contraction (MVC). METHODS: Ten healthy male volunteers were asked to perform brief (control MVC) and sustained MVC (fatigue test of 60 s in duration) with elbow flexion before and 2 and 4 d after ECC. Transcranial magnetic stimulation (TMS) was applied to the motor cortex to determine changes in voluntary activation (VA), the size of the motor evoked potential (MEP), and length of electromyographic (EMG) silencing. The ratio of the root mean square value for the surface EMG of the biceps brachii and exerted force within 50 ms before TMS was also calculated (RMS/F). RESULTS: In two subjects, no significant changes in MVC and muscle soreness were seen after ECC so that their data was excluded from further analysis. Control MVC and muscle soreness was significantly decreased and increased, respectively, 2 and 4 d after ECC compared with that before ECC (P < 0.001). During the fatigue test, VA, which was determined by a phasic increase in the twitch force after TMS, significantly decreased 2 and 4 d after ECC compared with that beforehand (P < 0.01). In addition, the RMS/F was significantly increased 2 and 4 d after ECC (P < 0.001). Although the degree of facilitation of the MEP was significantly increased (P < 0.05), the length of EMG silencing was less affected by ECC. CONCLUSIONS: Muscle damage and/or muscle soreness induced by repetitive eccentric exercise with maximal effort may be a strong modifier of central and peripheral fatigue during sustained MVC. [ABSTRACT FROM AUTHOR]

Microbial dimethyl sulfide (DMS) conversion is thought to be involved in the global sulfur cycle. We isolated Pseudomonas putida strain DS1 from soil as a bacterium utilizing DMS as a sole sulfur source, and tried to elucidate the DMS conversion mechanism of strain DS1 at biochemical and genetic level. Strain DS1 oxidized DMS to dimethyl sulfone (DMSO2) via dimethyl sulfoxide, whereas the oxidation was repressed in the presence of sulfate, suggesting that a sulfate starvation response is involved in DMS utilization by strain DS1. Two of the five DMS-utilization-defective mutants isolated by transposon5 (Tn5) mutagenesis had a Tn5 insertion in the ssuEADCBF operon, which has been reported to encode a two-component monooxygenase system (SsuED), an ABC-type transporter (SsuABC), and a small protein (SsuF), and also to play a key role in utilization of sulfonates and sulfate esters in another bacterium, P. putida strain S-313. Disruption of ssuD and SsuD enzymatic activity demonstrated that methanesulfonate is a metabolic intermediate of DMS and desulfonated by SsuD. Disruption of ssuC or ssuF also led to a DMS-utilization-defective phenotype. Another two mutants had a defect in a gene homologous to pa2354 from P. aeruginosa PAO1, which encodes a putative transcriptional regulator, while the remaining mutant had a defect in cysM encoding O-acetylserine (thiol)-lyase B. [ABSTRACT FROM AUTHOR]

We investigate the switching dynamics of a 75°-canted Spin–orbit torque (SOT) device with an in-plane easy axis using the micro-magnetic simulation. The switching time (τ) is evaluated from the time evolution of the magnetization. The device with a strong out-of-plane magnetic anisotropy (μ0Hkeff = −0.08 T) shows τ = 0.19 ns while a device with a strong in-plane magnetic anisotropy (μ0Hkeff = −0.9 T) shows τ = 0.32 ns. The increase of the damping constant (α) results in the increase of τ for both devices and the sub-nanosecond switching could be retained as α < 0.14 in the device with μ0Hkeff = −0.08 T, while this was achieved as α < 0.04 in the device with μ0Hkeff = −0.9 T. Furthermore when the field-like coefficient (β) is increased, it leads to a decrease in τ, which can be reduced to 0.03 ns by increasing β to 1 in the device with μ0Hkeff = −0.08 T. In order to achieve the same result in the device with μ0Hkeff = −0.9 T, β must be increased to 6. These results indicate a way to achieve ultrafast field-free SOT switching of a few tens of picoseconds in nanometer-sized magnetic tunnel junction (MTJ) devices. [ABSTRACT FROM AUTHOR]

We have proposed a novel quad-interface magnetic tunnel junction (MTJ) technology which brings forth an increase of both thermal stability factor Δ and switching efficiency defined as the ratio of Δ to intrinsic critical current IC0 (Δ/IC0) by a factor of 1.5–2 compared with the conventional double-interface MTJ technology. The free layer of the developed quad interface consists of bottom-MgO/FL1/middle-MgO/FL2/top-MgO stack structure. We successfully fabricated the quad-interface MTJ using a 300-mm process based on a novel low-damage integration process including physical vapor deposition (PVD), reactive ion etching (RIE), and so on. By developing the quad-interface MTJ, we have achieved about two times larger Δ and Δ/IC0 at the same time. Moreover, we have achieved about two times larger tunnel magnetoresistance (TMR) ratio at the same resistance area (RA) product by developing the FL1, bottom-MgO, and middle-MgO. The developed quad-interface MTJ technology considered as post-double-interface MTJ technology will become an essential technology for the scaling of the spin-transfer-torque magnetoresistive random access memory (STT-MRAM) beyond 20 nm. [ABSTRACT FROM AUTHOR]

We improve thermal tolerance of a Co/Pt based synthetic ferrimagnetic (SyF) reference layer in a CoFeB/MgO-based perpendicular anisotropy magnetic tunnel junction by employing a surface modification treatment (SMT) using Ar plasma on a Pt buffer layer underneath the SyF layer. A higher perpendicular anisotropy and more robustness against annealing for the SyF reference layer is observed by the employment of SMT. From the cross-sectional scanning transmission electron microscope of the magnetic tunnel junction and atomic force microscopy on the Pt buffer layer, SMT has no significant effect on the surface roughness of the Pt buffer layer. On the other hand, X-ray diffraction analysis reveals that SMT increases the lattice spacing of the Pt buffer layer and shrinks that of the Co/Pt multilayer, which are maintained after annealing at 400 °C. Those structural changes could lead to the improvement of perpendicular anisotropy and thermal tolerance against annealing. A high-resolution Rutherford backscattering analysis reveals that Ar ions used for SMT penetrate to the Pt buffer layer, resulting in variation of the lattice spacing for the Pt buffer layer and Co/Pt multilayer. In addition, suppression of Fe diffusion from the CoFeB reference layer to the bottom Co/Pt multilayer is observed by using energy dispersive X-ray spectrometry, which also contributes to the higher thermal tolerance against annealing. The present observation reveals that the employment of SMT enables one to obtain both high perpendicular magnetic anisotropy and high robustness against annealing through crystallographic change of the Co/Pt multilayer and suppression of Fe diffusion from CoFeB layer into the Co/Pt multilayer. [ABSTRACT FROM AUTHOR]

We investigated the effects of sputtering conditions for the deposition of an Iridium (Ir) layer in a [Co/Pt]m/Co/Ir/[Co/Pt]n/Co/W/CoFeB synthetic antiferromagnetic reference layer (Ir-SyF) on the magnetic properties and tunnel magnetoresistance ratio (TMR ratio) of magnetic tunnel junctions (MTJs) stacks annealed at 400 °C for 1 h. The exchange coupling field ($H_{\mathrm {ex}}$) 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. This could cause the deterioration of the $H_{\mathrm {ex}}$ of the Ir-SyF. Despite the larger $H_{\mathrm {ex}}$ , 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. [ABSTRACT FROM AUTHOR]

Dynamic magnetic properties of Ta-O/Co20Fe60B20 bilayer films are strongly influenced by the oxidation condition of the Ta-O layer. The oxidation of the Ta-O layer by a slight amount of oxygen with a pressure (POxygen) of 0.03 Pa decreases in-plane damping constant (αIP), and increases the effective magnetization (4πMs,eff). Then, both αIP and 4πMs,eff maintain their values by increasing POxygen up to 0.3 Pa. The out-of-plane damping constant (αOP) showed a similar tendency to that of αIP against POxygen, although αOP is much smaller than αIP in every POxygen. αOP reaches to 0.0033 for sample oxidized at 0.03 Pa. It was suggested that αIP consists of both the intrinsic damping and the extrinsic damping, while αOP is closer to the intrinsic damping. The control of αOP and αIP by the oxidation would be beneficial in designing the high frequency spintronic devices. [ABSTRACT FROM AUTHOR]

We investigated the effect of magnetic coupling (the energy constant of unit area $J_{\text {cpl}}$) between CoFeB free layers on thermal stability factor $\Delta $ in magnetic tunnel junction (MTJ) with CoFeB/MgO double interfacial perpendicular magnetic anisotropy (IPMA). We newly introduced $J_{\text {cpl}}$ in models for calculations, which were based on magnetic domain propagation model when MTJ diameter $d$ is larger than critical diameter $d_{\text {c}}$ and magnetization coherent rotation model when $d \le d_{\text {c}}$. With increasing $J_{\text {cpl}}$ , $\Delta $ increases and saturates when $J_{\text {cpl}}$ is over a critical value $J_{\mathrm {cpl\_{}c}}$. Magnetostatic coupling constants ($J_{\text {stat}}$) between the free layers were also calculated. $J_{\text {stat}}$ is much smaller than $J_{\mathrm {cpl\_{}c}}$ and cannot maximize $\Delta $ by itself, so an interlayer exchange coupling (the critical energy constant of unit area $J_{\mathrm {ex\_{}c}}$) is required to cover the difference between $J_{\mathrm {cpl\_{}c}}$ and $J_{\text {stat}}$. $J_{\mathrm {ex\_{}c}}$ also rapidly increases with the decrease in $d$ and reaches a plateau of 0.15 mJ/m2 in $d \le 30$ nm. MTJ devices with the smallest $J_{\text {ex}}\,\,(=0.01 \text {mJ/m}^{2}$) and a moderate PMA (constant per unit area $K_{\text {eff}} t^{\ast }$) were made and $\Delta s$ were evaluated by experiments. The experimental $\Delta s$ were fitted by the calculations with adjusting stiffness constants $A_{s}$. The calculated $\Delta s$ and the experimental $\Delta s$ were in good agreement when $A_{s}$ had a smaller value than that of the blanket film. Since the experimentally used $J_{\text {ex}}$ value was almost 0, $\Delta $ values were estimated when $J_{\text {ex}}$ was a greater value of 0.15 mJ/m2. As a result, 30% enhancement of $\Delta $ was obtained at the smallest $d = 20$ nm. [ABSTRACT FROM AUTHOR]

We developed perpendicular magnetic tunnel junctions (MTJs) with four synthetic anti-ferromagnetically coupled Co/Pt layers (quad-SyF) and investigated their magnetic and transport properties. The quad-SyF comprised four Co/Pt layers and three 0.9 nm-thick Ru coupling layers, which consisted of Co/[Co/Pt] ${}_{a}$ /Ru/Co/[Co/Pt] ${}_{b}$ /Ru/Co/[Co/Pt] ${}_{c}$ /Ru/Co/[Co/Pt] ${}_{d}$ from top to bottom. The exchange coupling field ($H_{\mathrm {ex}}$) reached a maximum of 1 T when the values of $a$ , $b$ , $c$ , and $d$ were 1, 2, 2, and 1, respectively. The tunnel magnetoresistance ratio of the MTJ with the quad-SyF and the second-peak conventional double-SyF increased as the annealing temperature was increased up to 400 °C, whereas that of the MTJ with the first-peak conventional double-SyF degraded at temperatures of more than 350 °C in blanket films. A 55 nm diameter MTJ with quad-SyF was found to be stable even against an external magnetic field up to 300 mT. On the contrary, in the conventional double-SyF, the reference-layer (RL) magnetization direction flips at around 250 mT. The shift magnetic field of the MTJ with quad-SyF becomes approximately zero when the values of $a$ , $b$ , $c$ , and $d$ are 1, 4, 1, and 2, respectively. No back-hopping of the MTJ with quad-SyF was observed even for the write pulsewidth ($t_{W}$) down to 10 ns. On the contrary, an MTJ with conventional double-SyF exhibited back-hopping. In the patterned MTJ with conventional double-SyF, as the MTJ size decreases, the coercive field of Co/Pt significantly increases and $H_{\mathrm {ex}}$ decreases, causing the $m$ – $H$ curve of the RL to cross the zero magnetic field. This enables both parallel and antiparallel configurations for the top and bottom Co/Pt layers in double-SyF at the zero magnetic field, which could induce back-hopping. However, the $m$ – $H$ curves of the RL in the patterned MTJ with quad-SyF are far from the zero magnetic field owing to the high $H_{\mathrm {ex}}$ and low $H_{c}$ , which could lead to the suppression of back-hopping. [ABSTRACT FROM AUTHOR]

Abstract: GaSb thin films have been grown on Si(111) substrates by molecular beam epitaxy (MBE), using an Sb template as an initiation layer. The film's crystal properties were investigated by in situ reflection high energy electron diffraction (RHEED), atomic force microscope (AFM), X-ray reciprocal space mapping (RSM) and X-ray diffraction (XRD). RSMs around Si and GaSb 224 reciprocal lattice points indicated that the GaSb thin film grown on the Sb template is nearly unstrained, in contrast to that grown on an AlSb initiation layer which is under tensile strain. The extra peaks on the XRD profiles can be assigned to {224} diffraction originating from a sub-domain region that corresponds to the region rotated by 180° with respect to the fundamental domain of epitaxial film. The very weak intensity of the extra peaks suggests that using the Sb template is an effective way to suppress sub-domain generation in the epitaxial film, resulting in a higher quality GaSb thin film on Si(111) substrates. The spotty RHEED patterns observed were analyzed as a superposition of zinc-blende type diffraction spots on the plane and plane, indicating that the GaSb quantum dots at the initial growth stage are not randomly orientated polycrystalline structures but a two-domain structure with zinc-blende type crystals. [Copyright &y& Elsevier]

Abstract: Ohmic contacts are crucial for both device applications and the study of fundamental physics. In this study, we propose a new physical model for Ohmic contacts based on the detailed considerations of a metal/semiconductor interface, such as charge neutrality level concept, with which it is possible to describe the real situation precisely. Our proposed model contains many defect energy levels that originate from vacancies and impurities located in the vicinity of the metal/semiconductor interface, within the energy range of the Schottky barrier height. Moreover, we calculate the current–voltage characteristics based on our model. Our calculated results show that our model reveals linear Ohmic I–V characteristics and dense defect energy level distribution in the energy range of the Schottky barrier height is crucial for obtaining Ohmic I–V characteristics. [ABSTRACT FROM AUTHOR]

Abstract: We report on the molecular beam epitaxy (MBE) of GaSb films and GaSb/AlGaSb multiple quantum well (MQW) structures grown on Si(111) and Si(011) substrates using an AlSb initiation layer. The structural and optical properties of the films on the different oriented Si substrates were characterized by cross-sectional transmission electron microscopy (TEM), high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), and photoluminescence (PL) measurements. The GaSb films and the MQW structures grown on Si(011) were found to have rather rough surfaces and of poor crystallinity under the present growth condition with the AlSb initiation layer. In contrast, the films grown on Si(111) indicated a mirror surface, definite MQW structures, and HRXRD patterns. The PL emissions within the 1.3–1.5μm for the MQW structures on Si(111) and Si(011) were observed at the temperatures up to 300 and 200K, respectively. We found that the PL peak energy, around 1.5μm, of the MQW structures grown on Si(111) is almost temperature independent up to ∼120K and exhibits a smaller variation with increasing temperature compared to those of the samples grown on Si (001) substrates. In the case of the MQW on Si (011), the PL peak energy as a function of temperature showed an intermediate behavior between those grown on Si(111) and Si(001) substrates. [Copyright &y& Elsevier]

Amorphization, following a decrease in the dislocation density and fragmentation of the matrix, has been revealed in a thin layer just below the tensile-fractured surface of a hydrogen-charged ferritic steel. The creation of a high density of vacancies associated with hydrogen is discussed as the origin. [Copyright &y& Elsevier]

We successfully developed 25-nm quad CoFeB/MgO-interfaces perpendicular magnetic tunnel junction (quad-MTJ) with enough thermal stability. To fabricate the quad-MTJ, a physical vapor deposition (PVD) process for depositing novel free layer and low resistance-area (RA) product MgO layer and low-damage fabrication processes were developed. The developed quad-MTJ technology and advanced process bring better tunnel magneto resistance (TMR) ratio and RA to quad-MTJ than those of double-interface MTJ (double-MTJ), even though quad-MTJ has an additional MgO layer. Scaling down the MTJ size to 25 nm, we demonstrated the advantages of quad-MTJ compared with double-MTJ as follows: 1) two times larger thermal stability factor (Δ), which results in over ten years retention; 2) superiority of large Δ in the measuring temperature range up to 200 °C; 3) ~1.5 times higher write efficiency; 4) lower write current at short write pulse regions at less than 100 ns; and e) excellent endurance of over 1011 thanks to higher write efficiency, which results from the reduced voltage owing to low RA and the low damage integration process technology. As a result, the developed quad-MTJ technologies will open the way for the realization of high-density STT-MRAM with low power, high speed, high reliability, and excellent scalability down to 2 × nm node. [ABSTRACT FROM AUTHOR]

Vertical nitrate fluxes associated with turbulent mixing and upwelling around a small reef in the Kuroshio are quantified by continuously deploying a turbulence microstructure profiler with an attached submersible ultraviolet nitrate analyzer while drifting from the upstream to the downstream of the reef. Flow separations and trains of Kelvin‐Helmholtz billows (thickness = 60 m) are identified using a shipboard ADCP and an echo‐sounder. The turbulence diffusivity associated with the vigorous turbulent mixing reaches up to O(10−1 m2 s−1), resulting in strong nitrate fluxes of O(1–103 mmol m−2 day−1). In addition, large differences between the upstream and downstream density profiles suggest a strong upwelling velocity of O(10−3 m s−1), as well as an upwelling nitrate flux of O(102 mmol m−2 day−1) in the entire subsurface layer. Plain Language Summary: Vertical nitrate fluxes associated with flow‐topography interactions around a small reef in the Kuroshio Current are quantified using state‐of‐the‐art oceanographic instruments. When the flow passes over a shallow sill on the flank of the reef, the velocity differences between layers intensify, resulting in a substantial vertical overturning and mixing of the water column. This turbulent mixing causes the observed nitrate flux from deep water to reach a value among the highest observed worldwide. Key Points: Flow separations and trains of Kelvin‐Helmholtz billows mix the water column around a small reef in the KuroshioDoming of isopycnals/nitraclines suggests strong upwelling in the lee of the reefTurbulent nitrate fluxes reach up to O(103 mmol m−2 day−1) [ABSTRACT FROM AUTHOR]

Magnetic coupling between two CoFeB layers through the W insertion layer is important in the conventional double CoFeB/MgO interface, magnetic tunneling junctions (MTJs) (double-MTJs) with MgO/CoFeB/W/CoFeB/MgO free layer stack because it increases the effective magnetic volume of the free layer. The magnetic coupling energy constant per unit area, Jcpl, between two CoFeB layers through the W layer and the effective perpendicular magnetic anisotropy (PMA) energy constant per unit area, Kefft*, were investigated for conventional double-MTJs with various W insertion layer thicknesses. As the W layer thickness increased, Kefft* increased and Jcpl decreased. There exists a trade-off relationship between Jcpl and Kefft*. In conventional double-MTJs with a single W insertion layer, large values for Jcpl and Kefft* were difficult to obtain simultaneously. To improve this tradeoff, we employed a free layer stack with a thin ferromagnetic layer (ferromagnetic bridge layer: FBL) located in the W insertion layer. In the double-MTJs with FBL annealed at 400 °C, a large Jcpl value of 0.37 mJ/m2 was achieved while maintaining the maximum values of Kefft*. Accordingly, the MTJ with FBL provides an MTJ stack structure for obtaining high thermal stability. [ABSTRACT FROM AUTHOR]

We investigated the effects of surface modification treatment (SMT) on the perpendicular magnetic anisotropy (PMA) and the thermal tolerance of top-pinned magnetic tunnel junctions (MTJs) with a Co/Pt synthetic ferrimagnetic coupling reference layer. Applying an SMT to the bottom Pt layer increased the PMA of the overlying Co/Pt multilayer. X-ray diffraction spectrum analysis revealed that the SMT resulted in a higher crystallinity and smaller lattice spacing in the Co/Pt multilayer in the thinner bottom Pt layer, which may have increased the PMA in the Co/Pt multilayer. The tunnel magnetoresistance (TMR) ratio of the MTJ with SMT increased as the annealing temperature was increased up to 400 °C; conversely, the TMR ratio of the MTJ without SMT decreased at an annealing temperature of 400 °C. Evaluation of the m-H loops revealed that, after annealing at 400 °C, the reference layers in the MTJs after SMT possessed better magnetic properties than those in the MTJs without an SMT; this is attributable to the higher PMA of the reference layers with SMT. EDX line analysis revealed that SMT suppressed Pt diffusion to the MgO barrier, resulting in a higher thermal tolerance and larger PMA of the reference layer. [ABSTRACT FROM AUTHOR]

We have successfully observed the process-induced microstructure of the ultrafine CoFeB–MgO-based magnetic tunnel junctions with a perpendicular easy axis (p-MTJs) down to junction size of less than 20 nm using scanning transmission electron microscope (STEM) tomography combined with energy-dispersive X-ray spectroscopy (EDX). This made it possible to examine 3-dimensionally the precise structural information inside the entire MTJ. By this, the root cause of the change in the resistance of the MTJ was found to be the altered region consisting of Fe-dipping attached to the edge of the MgO and ultrathin TaO layer uniformly formed on the MTJ surface. This altered region is caused by etching during patterning of the MTJ, and the resistance value of the MTJ changes depending on the degree of adhesion of insulating TaO and Fe atoms at the edge of the MgO barrier layer. Furthermore, it was found that the unevenness of the MgO/CoFeB interface inside the MTJ was not a factor that caused the change in the thickness of the MgO barrier layer in the current process. Our results show that STEM tomography is an effective tool for failure analysis to clarify the relationship between the detailed structure of fine MTJs and magnetic properties. Unlike the conventional cross-sectional STEM observation, since the STEM tomographic observation includes the whole view of the MTJ, this enables higher resolution observation as the MTJ size decreases without overlooking the cause of failure inside the MTJ. [ABSTRACT FROM AUTHOR]

A compact 6-input lookup table (LUT) circuit using nonvolatile logic-in-memory (LIM) architecture with series/parallel-connected magnetic tunnel junction (MTJ) devices is proposed for a standby-power-free field-programmable gate array. Series/parallel connections of MTJ devices make it possible not only to reduce the effect of resistance variation, but also to enhance the programmability of resistance values, which achieves a sufficient sensing margin even when process variation is serious in the recent nanometer-scaled VLSI. Moreover, the additional MTJ devices do not increase the effective chip area because the configuration circuit using MTJ devices is simplified and these devices are stacked over the CMOS plane. As a result, the transistor counts of the proposed circuit are reduced by 62% in comparison with those of a conventional nonvolatile LUT circuit where CMOS-only-based volatile static random access memory cell circuits are replaced by MTJ-based nonvolatile ones. [ABSTRACT FROM AUTHOR]

We investigated the influence of hard mask (HM) materials on tunnel magnetoresistance (TMR) properties and magnetic properties for the magnetic tunnel junctions with pependicular easy axis (p-MTJs) with double CoFeB/MgO interface annealed at 400 °C for 0.5–10 h. After annealing at 400 °C for 5 h, the TMR ratio of the MTJ with TiN HM was significantly decreased, whereas the TMR ratio of the MTJ with Ta-HM was maintained at a value of more than 120%. The analysis results by secondary-ion mass spectrometry (SIMS) and energy-dispersive X-ray spectroscopy (EDX) revealed that Ru in Ru-cap for the MTJ with TiN-HM diffused into the free layer through the MgO-cap layer, resulting in the degradation of the magnetic and TMR properties of the MTJ with TiN-HM. In contrast, Ru did not diffuse into the free layer for the MTJ with Ta-HM, which results from suppression of Ru diffusion into the free layer due to the formation of Ta–Ru alloy. Furthermore, in both the MTJs with TiN-HM and Ta-HM annealed at 400 °C for 10 h, EDX analysis revealed Pt diffusion into the CoFeB reference layer, which could degrade the magnetic properties of the reference layer, resulting in the degradation of TMR properties. To obtain a double CoFeB/MgO interface p-MTJ with higher thermal tolerance, it is necessary to design an HM material that suppresses the diffusion of the cap material into the free layer in addition to suppressing the Pt diffusion of the reference layer. [ABSTRACT FROM AUTHOR]

Magnetic properties of Co film in Pt/Co/α-Cr2O3/Pt/α-Al2O3 structure were investigated. Co layer thickness tCo dependence of perpendicular magnetic anisotropy energy density K reveals that the bulk magnetic anisotropy plays an important role in the system in addition to the interfacial anisotropy. Damping constant α monotonically increases with the decrease of tCo but not proportionally to 1/tCo. Both K and α increase with the increase of Pt layer thickness tPt from 3 nm to 5 nm and keeps almost constant in the tPt range between 5 nm to 20 nm. These results are of importance to understand the magnetization switching behavior driven by the magneto-electric (ME) effect as well as to design the spintronics device using the ME effect. [ABSTRACT FROM AUTHOR]

We investigate the effect of the capping layer on the thermal tolerance of magnetic tunnel junctions (MTJs) with free layer of MgO/CoFeB/spacer layer/CoFeB/MgO/capping layers (CoFeB, Ru, or Ta). We observe the largest perpendicular magnetic anisotropy energy density for the free layer with CoFeB capping layer using Ta spacer after annealing at 400°C for 1 h. Energy-dispersive X-ray (EDX) line analysis along film normal direction reveals the absorption of oxygen in MgO by Ta in the stack with Ta capping layer and Ru diffusion into CoFeB free layer in the stack with Ru capping layer, which could cause the reduction of perpendicular magnetic anisotropy. We also evaluate annealing temperature dependence of magnetic properties for the MTJ stacks with different spacer layer. We again observe the largest perpendicular magnetic anisotropy energy density for the MTJ stack using the CoFeB capping layer. The present study reveals that CoFeB capping layer is effective for achieving improved robustness against annealing. [ABSTRACT FROM AUTHOR]

We have studied the magnetic and electrical properties of double CoFeB–MgO interface magnetic tunnel junctions (MTJs) with various W insertion layer thicknesses $t_{\mathrm {W}}$ annealed at 400 °C and evaluated $t_{\mathrm {W}}$ dependence of thermal stability factor $\Delta $ , intrinsic critical current $I_{\mathrm {C0}}$ and damping constant $\alpha $. It was found that spin-transfer torque efficiency ($\Delta /I_{\mathrm {C0}}$) values increased with decreasing $t_{\mathrm {W}}$ as compared with the same MTJ size $D$. $\alpha $ measured by ferromagnetic resonance increased with an increase in $t_{\mathrm {W}}$ , which is consistent with those calculated from $\Delta /I_{\mathrm {C0}}$. This result indicates that lower damping constant of MTJ with thin W insertion layer contributes to higher $\Delta /I_{\mathrm {C0}}$. [ABSTRACT FROM AUTHOR]

The robustness of data load of metal-oxide-semiconductor/magnetic tunnel junction (MOS/MTJ) hybrid latches at power-on is examined by using Monte Carlo simulation with the variations in magnetoresistances for MTJs and in threshold voltages for MOSFETs involved in 90 nm technology node. Three differential pair type spin-transfer-torque-magnetic random access memory cells (4T2MTJ, 6T2MTJ, and 8T2MTJ) are compared for their successful data load at power-on. It is found that the 4T2MTJ cell has the largest pass area in the shmoo plot in TMR ratio (tunnel magnetoresistance ratio) and Vdd in which a whole 256 kb cell array can be powered-on successfully. The minimum TMR ratio for the 4T2MTJ in 0.9V

A compact nonvolatile programmable switch (NVPS) using 90 nm CMOS technology together with perpendicular magnetic tunnel junction (p-MTJ) devices is fabricated for zero-standby-power field-programmable gate array. Because routing information does not change once it is programmed into an NVPS, high-speed read and write accesses are not required and a write-control transistor can be shared among all the NVPSs, which greatly simplifies structure of the NVPS. In fact, the effective area of the proposed NVPS is reduced by 40% compared to that of a conventional MTJ-based NVPS. The instant on/off behavior without external nonvolatile memory access is also demonstrated using the fabricated test chip. [ABSTRACT FROM AUTHOR]

We investigated an effect of sputtering gas species (Ar, Kr, and Xe) for deposition of a W insertion layer in the CoFeB/W/CoFeB free layer on magnetic properties of the free layer and tunnel magnetoresistance (TMR) ratio of magnetic tunnel junctions (MTJs) stacks using the free layer annealed at 400 °C for 1 h. As the W insertion layer thickness tW increased, we found the degradation of perpendicular anisotropy and larger reduction of saturation magnetic moment per unit area mS in the free layer using Ar compared to those using Kr and Xe. We also found a smaller TMR ratio for the MTJ stack using Ar compared to those using Kr and Xe. Energy-dispersive X-ray spectrometry line analysis revealed more significant interdiffusion between W and CoFeB layers in the free layer using Ar than those using Kr and Xe, that could result in the smaller mS and perpendicular anisotropy in the free layer and smaller TMR ratio for the MTJ stack using Ar than those using Kr and Xe. We also investigated concentration of Ar, Kr, and Xe in W layers deposited using Ar, Kr, and Xe, respectively, by high-resolution Rutherford backscattering spectrometry, revealing that 0.2 at% Ar was detected in the W layer using Ar, while Kr and Xe were not detected in W layers using Kr and Xe. Such a difference in concentration of inert gas atoms in the W layer could be one possible reason for the difference about degree of interdiffusion between W and CoFeB layers. [ABSTRACT FROM AUTHOR]

We investigated properties of perpendicular-anisotropy magnetic tunnel junctions (p-MTJs) with [Co/Pt]-multilayer based synthetic ferrimagnetic reference (SyF) layer at elevated annealing temperature Ta from 350°C to 400°C. Shift field HS defined as center field of minor resistance versus magnetic field curve of the MTJs increased with increase of Ta from 350°C to 400°C. The variation of HS is attributed to the variation of saturation magnetic moment in the SyF reference layer. Cross sectional energy dispersive X-ray spectroscopy analysis revealed that Fe element of CoFeB in the reference layer diffuses to Co/Pt multilayers in the SyF reference layer. [ABSTRACT FROM AUTHOR]

We investigated annealing temperature Ta dependence of tunnel magnetoresistance (TMR) ratio and magnetic properties for perpendicular-anisotropy (CoFe)100–XBX/MgO magnetic tunnel junctions (MTJs) with single (CoFe)100–XBX/MgO interface (s-MTJ) and double CoFeB–MgO interface (d-MTJ) structures with various boron compositions X. High TMR ratio over 100% was observed in the s-MTJ with $X= 35$ at.% after annealing at 360 °C–400 °C, whereas the s-MTJ with X = 30$ at.% showed the degradation of TMR ratio with the increase of X = 25$ at.% maintained high TMR ratio up to owing to its higher perpendicular anisotropy compared with the s-MTJ. The difference of perpendicular anisotropy between the s-MTJ and the d-MTJ can be attributed to higher interfacial anisotropy together with lower saturation magnetization of the d-MTJs. The lower saturation magnetization is attributable to two MgO layers that suppress boron diffusion from CoFeB layers, which was verified by cross-sectional line analysis using electron energy-loss spectroscopy. [ABSTRACT FROM PUBLISHER]

Diffusion and redistribution of constituent elements on the CoFeB surface after natural oxidation and annealing were investigated by means of X-ray photoelectron spectroscopy with argon beam sputtering. Boron and iron atoms were found to redistribute into the $\sim 3$ nm-thick oxidized surface by the natural oxidation even at room temperature. After annealing up to 400 °C in vacuum, boron atoms drastically diffused into the oxidized surface to reduce the oxidized iron/cobalt. The migration of boron atoms was observed within the depth of $\sim 6$ nm. In contrast, iron atoms diffused little. The diffusion and redistribution behaviors during the redox reactions, such as the natural oxidation and annealing, are speculated to be related to the values of the standard free energy of formation of oxides. In other words, the reduction nature of elements on the CoFeB surface is speculated to be the driving force in the diffusion and redistribution of iron and boron on the surface during the redox reaction. [ABSTRACT FROM AUTHOR]

A variation‐resilient single‐ended six‐input lookup table circuit, which makes it possible to implement any arbitrary six‐input logic gates, is proposed. Since operating point is optimally tuned by the redundant magnetic tunnel junction devices after chip fabrication, adequate p‐channel metal‐oxide semiconductor (PMOS) feedback can be performed, which results in variation‐resilient, energy‐efficient operation. In fact, the energy consumption of the proposed circuit is 66% smaller than that of the conventional single‐ended circuit. [ABSTRACT FROM AUTHOR]

Abstract: We have deposited boron- and/or nitrogen-incorporated DLC films by radio-frequency magnetron sputtering, and systematically investigated the structure and the mechanical and tribological properties. The N content in DLC films increased with increasing N2 flow ratio [N2/(Ar+N2)], and it tended to be saturated at higher N2 flow ratios. The N content further increased with an increase in the B content of the targets. The B/C ratios of the films were almost the same as those of the B-containing targets regardless of the N content. Scratch tests revealed that the adhesion strength of N-incorporated DLC films decreased with increasing N2 flow ratio and the critical loads of B-incorporated films were lower than that of an unincorporated film. It was found that for B, N-coincorporated films there was an optimum N2 flow ratio at which the critical load became a maximum value, which was higher than that of the unincorporated film. The optimum N2 flow ratio increased with an increase in the B composition of the targets. The N-incorporated films peeled off during ball-on-plate friction tests. On the other hand, the B, N-coincorporated films showed good wear-resistant properties that the specific wear rates were lower than those of the unincorporated and B-incorporated films. [Copyright &y& Elsevier]

Abstract: We present our observation of an anomalous temperature and optical excitation intensity dependence of the electron tunneling between a two-dimensional electron gas (2DEG) and Si dots in the direct tunneling mode. We find that the gate voltages required for the electron injection from the 2DEG to Si-dots become smaller with increase in the temperature or in the optical excitation intensity. The experimental results are discussed in terms of the geometrical matching of the wave functions of a 2DEG and an electron in a Si-dot. [Copyright &y& Elsevier]

Abstract: We have deposited Si-DLC films by pulsed laser deposition using KrF excimer laser, and have investigated etching of the Si-DLC films by atomic hydrogen. We have examined the structure and chemical bonding of the films by Raman spectroscopy, X-ray photoelectron spectroscopy and photoelectron spectroscopy using synchrotron radiation. Photoelectron spectra of Si 2p with 135 eV photons showed two distinguishing components. The main components were identified with Si–C and silicon oxides. The intensity of the oxide component increased when the detection angle to the surface normal was increased from 0 to 60°, indicating that thin oxide layers were formed at the surface. The oxide component decreased by annealing at a substrate temperature above 850 °C in an ultra-high vacuum and it disappeared at 1050 °C. We found that the etching rate of the films drastically decreased by the incorporation of Si. It was also found that the etching rate of the Si-DLC films markedly increased after dipping in a HF solution, indicating that the hydrogen etching of the Si-DLC films is suppressed by thin oxide layers formed at the surfaces. When the HF-treated Si-DLC films were annealed at a temperature above 400 °C in a high vacuum chamber, the etching rate decreased, suggesting that oxide layers were formed again at the surfaces. [Copyright &y& Elsevier]

A variation-resilient single-ended six-input lookup table circuit, which makes it possible to implement any arbitrary six-input logic gates, is proposed. Since operating point is optimally tuned by the redundant magnetic tunnel junction devices after chip fabrication, adequate p-channel metal-oxide semiconductor (PMOS) feedback can be performed, which results in variation-resilient, energy-efficient operation. In fact, the energy consumption of the proposed circuit is 66% smaller than that of the conventional single-ended circuit. [ABSTRACT FROM AUTHOR]