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From the discovery of giant magnetoresistance (GMR) to tunnel magnetoresistance (TMR), their subsequent application in large capacity hard disk drives (HDDs) greatly speeded up the information era over the past decades. However, the growing demand for big-data storage and processing is limited by the von-Neumann architecture due to the memory bottleneck and power dissipation. Taking advantage of nonvolatility, high speed, and low power, magnetic random access memory (MRAM) becomes a promising candidate to overcome this limitation through processing-in-memory (PIM) architectures. In this article, we provide an overview of existing technology and give a roadmap of spintronic devices for future energy-efficient computing and its relevant integration architectures. We begin with the fundamentals of Toggle-MRAM and spin-transfer torque (STT)-MRAM, which already have commercial applications. We then introduce spin-orbit torque (SOT), a critical mechanism to realize low-power data manipulation in the next generation of MRAM and summarize the recent experimental breakthroughs of field-free SOT switching schemes. Finally, we present MRAM-based PIM architectures and novel spintronic devices, provide an application outlook, and deliver the future development potential of energy-efficient computing systems.

The interplay of spin-transfer torque (STT) and spin-orbit torque (SOT) highlights the potential of current-induced magnetization reversal for the ultrahigh-speed and ultralow-power memory applications. However, the ultrafast field-free switching and its dynamic mechanism have not been clarified yet. Here, we experimentally demonstrate the sub-nanosecond field-free switching by the interplay of STT and SOT in perpendicular magnetic tunnel junctions (MTJs). The dynamic investigations of the STT and SOT switching reveal that the applied SOT current can highly decrease the incubation time and current density of STT, which leads to the achievement of ultra-fast switching. Besides, the timing scheme investigations of SOT and STT pulses are performed. The firstly applied SOT current further decreases the transition time of the magnetization switching, which could result from the different nucleation and motions of domains. The interplay and the timing operations of STT and SOT provide more flexible solutions for high-speed, large-scalability and energy efficient memory applications.

Few studies have quantitatively analyzed the relationship among the step distance, the driving voltage, and driving frequency of the inchworm linear microactuator, which cannot achieve accurate control of the micro-actuator. What’s more, the parameter setting rule is not clear. In this paper, the relationship model among step distance, voltage, and frequency is studied through theoretical derivation and experimental analysis. The parameter setting conditions of the drive signal are analyzed, and the waveform is modified to improve the stability of the micro-actuator. The theoretical model of micro-driver step prediction is established by using the non-linear Support Vector Machine (SVM) regression theory and Gaussian radial basis kernel function and verified by experiments.

In order to alleviate the problem of excessive stress and easy wear on the rotary swaging die during the process of rotary swaging high-strength tungsten wire, the die structure was changed, the transition taper was designed, and the structural parameters were optimized to achieve the purpose of reducing the stress and extending the life of the rotary swaging die. The results show that the improvement of the die structure can largely reduce the effective stress of the die, and it is found that the transition fillet has the greatest influence on the effective stress of the die, followed by the cone angle of the transition taper, and the length of the transition taper has the least effect on the effective stress of the die. Finally, the optimal die structure parameters after improvement were obtained by orthogonal experiments: the cone angle of transition taper is 4°, the length of transition taper is 10 mm, and the radius of transition fillet is 3 mm.

Chiral magnetic skyrmions are topological swirling spin textures that hold promise for future information technology. The electrical nucleation and motion of skyrmions have been experimentally demonstrated in the last decade, while electrical detection compatible with semiconductor processes has not been achieved, and this is considered one of the most crucial gaps regarding the use of skyrmions in real applications. Here, we report the direct observation of nanoscale skyrmions in CoFeB/MgO-based magnetic tunnel junction devices at room temperature. High-resolution magnetic force microscopy imaging and tunneling magnetoresistance measurements are used to illustrate the electrical detection of skyrmions, which are stabilized under the cooperation of interfacial Dzyaloshinskii-Moriya interaction, perpendicular magnetic anisotropy, and dipolar stray field. This skyrmionic magnetic tunnel junction shows a stable nonlinear multilevel resistance thanks to its topological nature and tunable density of skyrmions under current pulse excitation. These features provide important perspectives for spintronics to realize high-density memory and neuromorphic computing.

Low on/off ratio gravely hinders the application of magnetoresistance (MR) devices for the accurate and reliable data fetch. In this paper, a rectified tunnel MR (R-TMR) device is fabricated by integrating perpendicular-magnetic-anisotropy magnetic tunnel junction (PMA MTJ) and Schottky diode. High on/off ratio, intrinsic non-volatility and multi-dimensional regulation capabilities can be obtained, which makes this emerging spintronic device suitable for in-memory computing (IMC). By reversing the rectifying direction of the diode and tuning the proportions of alternating current (AC) and direct current (DC), reconfigurable logic operations have been achieved. Two proofs of concept, i.e. “NOR” and “NAND”, are experimentally performed.

Perpendicular magnetic tunnel junctions with double-interface free layer (p-DMTJs), which exhibit enhanced tunnel magnetoresistance (TMR) and thermal stability (Δ) at the nanoscale, have received considerable interest as building blocks for spintronic data storage devices. Heat-assisted magnetic recording (HAMR) techniques have been widely employed in mainstream magnetic storage to enable ultrahigh storage density. However, the data access is achieved by sensing the stray field of the selected magnetic element using a mechanical “read head”, resulting in an unfavorable speed limitation and design complexity. To address this issue, integrating laser-assisted switching with a high-performance magnetic tunnel junction has received interest in spintronic R&D; however, it has not yet been achieved. In this study, we experimentally explored femtosecond (fs) laser-assisted switching in a p-DMTJ device using a direct electrical TMR readout. We demonstrate two reconfigurable switching operations, i.e., binary “write” and unidirectional “reset”, by the interplay of the fs laser and synchronized magnetic field sequence. We further explored the joint effect, and a switching phase diagram was obtained. The effect of the stray field of p-DMTJ, as well as laser helicity, on switching is also discussed. Results show the feasibility of fs laser-assisted writing p-DMTJs, which can pave the way in high-density optospintronic storage applications.

The uncertainty of the hydrological environment and unbalanced water resource allocation result in a high risk of irrigation water shortages in regional agriculture, which seriously affects the sustainable development of agricultural systems. In this paper, we propose a risk regulation based modeling approach for the optimal allocation of agricultural water resources in a complex stochastic environment. The approach includes a conditional value-at-risk (CVaR) model, two-stage stochastic programming (TSP) model, two-dimensional joint distribution probability (JP) model, fractal criteria, and a multiple forms of chance-constrained programming (CCP) model. The model can weigh the contradiction between the intended target and associated penalties attributed to unknown hydrological events, measure the risk between system benefits and expected losses in agricultural water allocation at different confidence levels, and address the randomness in the objective function and constraints (including the left end term, right end term, and left and right end terms). To verify the applicability of the method, it is applied to the Jinxi Irrigation District in China to optimize the allocation and risk regulation of limited water resources under the variable runoff conditions of the Songhua River and crop water demands in the irrigation area. By adjusting parameters such as risk preference and probability of violation, the risk of water shortages in the irrigation area can be regulated, and the multidimensional impacts of different water allocation schemes on agricultural economic benefits, social benefits, ecology and environment can be determined. The case study reveals that the CTSP-CCJP method is sensitive, applicable to complex and uncertain environments and important for the efficient use of agricultural water resources and risk reduction.

We demonstrate in-plane field-free-switching spin-orbit torque (SOT) magnetic tunnel junction (MTJ) devices that are capable of low switching current density, fast speed, high reliability, and, most importantly, manufactured uniformly by the 200-mm-wafer platform. The performance of the devices is systematically studied, including their magnetic properties, switching behaviors, endurance and data retention. The successful integration of SOT devices within the 200-mm-wafer manufacturing platform provides a feasible way to industrialize SOT MRAMs. It is expected to obtain excellent performance of the devices by further optimizing the MTJ film stacks and the corresponding fabrication processes in the future.

The spin-transfer torque magnetoresistive random access memory(STT-MRAM) has a potential business value due to its low power consumption and non-volatile. It can apply in the smart wearable device, industrial equipment, and other fields. By combining the double data rate three (DDR3) controller and STT-MRAM to make a complete storage system. We propose a method of parallel reading and writing in the storage system. By comparing the delayed data of parallel and serial read and write modes in different storage capacities. The proposed method can improve the efficiency of the system.

With downscaling of process technology, conventional memories encounter challenges, such as soaring static power, low reliability, and charge sharing effect induced by radiation effects. Magnetic random access memory (MRAM) is considered as an outstanding candidate for addressing these challenges. In particular, emerging spin–orbit torque (SOT) MRAMs have shown ultra-fast switching and read-disturbance immunity compared with spin-transfer torque MRAMs. However, the write operation of the SOT-MRAM is more vulnerable to single-event upsets (SEUs) as its ultra-short write pulse is comparable to the radiation current pulse. In addition, its read circuit can also be disturbed by SEUs or even double-node upsets (DNUs) induced by the charge sharing effect. In this paper, we investigate radiation effects on read/write circuits of the SOT-MRAM. Then, we propose novel radiation hardening designs for SOT-MRAM. The hardening technique is first studied at the write circuit by adding six PMOS transistors as a feedback structure to charge/discharge. Afterwards, we propose a radiation hardening read circuit addressing the issue of SEUs and DNUs, which uses redundant six transistors and two feedback connections as the hardening structure. Based on a physics-based SOT magnetic tunnel junction model and a 65-nm complementary metal–oxide–semiconductor design kit, simulation results indicate that radiation-induced soft errors can be corrected at sensitive nodes. Moreover, the error rate of the proposed read circuit is $40\times $ smaller than the previous work, and restoring time is reduced by 30.6% with negligible area overhead.

Recently, exploiting emerging nonvolatile memories to implement the process-in-memory (PIM) paradigm have shown great potential to address the von Neumann bottleneck and have attracted extensive research and development. In this paper, we present a novel PIM platform—spintronic processing unit (SPU), within spin transfer toque magnetic random access memory (STT-MRAM). This energy-efficient and reconfigurable PIM platform can perform different tasks—data storage and logic computing—using the same physical fabric that is programmable at the finest grain, i.e., the individual memory cell level, without the need to move data outside the memory fabric. The proposed SPU works just like a typical memory and all the logic functions are achieved through regularmemory-like write and read operations with minimal modifications. The functionality and performance are evaluated via hybrid circuit simulations under the 40-nm process technology node. Our proposed SPU is expected to be a feasible PIM platform in the near future, owing to the increasing maturity of STT-MRAM.

The temperature dependence of magnetoresistance and switching characterization based on spin transfer torque (STT) effect of perpendicular magnetic tunnel junctions (p-MTJs) with MgO/CoFeB/W/CoFeB/MgO double-interface free layer was studied. The tunneling magnetoresistance (TMR) ratio increases from 95% to 176% for both 84 and 64 nm-diameter p-MTJs, upon decreasing the temperature from 400 to 20 K. This change of TMR is dominated by a steady increase in the resistance of antiparallel state while the parallel state conductance remains almost constant. Switching behavior at various temperatures is investigated for pulse voltage-dependent STT measurements; resistance versus voltage loops for both the switching directions become more symmetric with decreasing temperature. Furthermore, low-temperature measurements of magnetic properties suggest that the effect of stray field for STT becomes weaker as the temperature decreases, which suggests the p-MTJs design for cryogenic memories.

In this work, a novel method consisting of side-wall passivation and a top-metal reveal process is proposed for spintronics devices based on magnetic tunnel junctions (MTJs). The method can efficiently protect ferromagnetic metals and magnesium oxide, which are the key materials of MTJs, and effectively establish electrical contact with the interconnect metals for perpendicular MTJs (p-MTJs). The scheme consists of the passivation of MTJs with dual dielectrics – silicon nitride and silicon oxide – followed by planarization and selective wet etching. The proposed integration scheme was successfully demonstrated with 80-nm-diameter p-MTJ devices.