Magnetic Random Access Memory Research Articles

Exploring multiferroicity, half-metallic phase, and curie temperature in X = B/C/N/F-Doped KNbO3: a DFT aspect

Multiferroic materials provide an astonishing platform for next-generation spintronic devices such as magnetoresistive random access memory. Herein, ferroelectric, electronic, and magnetic properties of the pristine and X = B/C/N/F-doped KNbO3 (KNO) perovskite oxides are explored using ab initio calculations along with modified Becke-Johnson potential, where X is doped at O-site (X@O) in both KO- and NbO2-layers. Our calculations revealed that the pristine motif is a non-magnetic insulator having an energy band gap (E g ) of 2.80 eV and spontaneous polarization (P) of 41 μCcm−2, which are close to the experimentally observed values of 3.34 eV and 37 μCcm−2, respectively. The computed enthalpy of formation and elastic parameters confirm the thermodynamic and mechanical strength of the doped configurations, respectively. It is established that X-dopants significantly reduce structural distortions and have negative influence on the value of P. The most distinctive feature of the current work is that the B/N-doped KNO system for X@O in the KO-layer exhibits n-type half-metallic (HM) ferromagnetic (FM) behavior with an E g of 1.46/2.96 eV which is sufficiently large enough to prevent any magnetic transition. In contrast, C and F-doped structures are FM insulator and n-type non-magnetic metallic, respectively. Along with this, X = B/C/N-doped KNO system for X@O in the NbO2-layer displayed FM insulating nature, while the F-doped motif becomes an n-type non-magnetic metallic. The total magnetic moment for the B/N-doped structure is 1.0, which also hints the HM FM behavior. Finally, the estimated Curie temperature using the Heisenberg 2D Hamiltonian model in magnetic doped structures is found to be high enough to be used for practical purposes.

Data-cell-variation-tolerant triple sampling non-destructive self-reference sensing scheme of STT-MRAM

Inevitable process variations (PVT) brought by both the magnetic tunneling junction (MTJ) and MOSFET based on the complementary metal-oxide semiconductor (CMOS) technology become a major obstacle for the mass production of spin transfer torque magnetic random access memory (STT-MRAM). The detriment of the process variations leads to a serious degradation in the fundamental yield with the shrinkage of the technology nodes. However, the conventional data-cell-variation-tolerant (DCVT) sense scheme cannot get the target read yield due to the limited sense margin (SM). To resolve this problem, a DCVT triple sampling non-destructive self-reference sensing scheme (TSNS) is proposed in the paper, which doubles the SM, with lower power consumption and better SM compared with the conventional DCVT sense scheme. Monte Carlo simulation with industry-compatible 65-nm model parameters results show that the proposed sensing scheme shows over 2.5 times higher SM and less power consumption compared to the previous self-reference circuit. The proposed sensing scheme can get the target read yield with lower power consumption.

Implementing bidirectional logic with backhopping in magnetic tunnel junctions

A bidirectional logic gate has been designed based on the backhopping phenomenon observed in magnetic tunnel junctions (MTJ) at high bias. The magnetization dynamics of each magnetic layer of the MTJ—having materials and geometry of a standard spin-transfer torque magnetic random access memory device—is calculated using the coupled Landau–Lifshitz–Gilbert equation-based theoretical framework. A circuit design interconnecting the MTJs has been proposed to simulate a two-input NAND gate. The results in both forward and reverse directions agree well with those found from the Boltzmann distribution, thereby demonstrating the equiprobability of all valid states.

A Radiation-Hardened Triple Modular Redundancy Design Based on Spin-Transfer Torque Magnetic Tunnel Junction Devices

Integrated circuits suffer severe deterioration due to single-event upsets (SEUs) in irradiated environments. Spin-transfer torque magnetic random-access memory (STT-MRAM) appears to be a promising candidate for next-generation memory as it shows promising properties, such as non-volatility, speed, and unlimited endurance. One of the important merits of STT-MRAM is its radiation hardness, thanks to its core component, a magnetic tunnel junction (MTJ), being capable of good function in an irradiated environment. This property makes MRAM attractive for space and nuclear technology applications. In this paper, a novel radiation-hardened triple modular redundancy (TMR) design for anti-radiation reinforcement is proposed based on the utilization of STT-MTJ devices. Simulation results demonstrate the radiation-hardened performance of the design. This shows improvements in the design’s robustness against ionizing radiation.

Giant anisotropic Gilbert damping and spin wave propagations in single-crystal magnetic insulator

Gilbert damping in magnetic systems describes the relaxation of magnetization. This term was phenomenologically introduced into the Landau–Lifschitz–Gilbert (LLG) equation to describe spin dynamics. In most studies, such as magnetic random access memory, spin-wave propagations, and microwave devices, it has been assumed that the Gilbert damping is an isotropic constant. In this study, we uncover a giant anisotropic Gilbert damping parameter of up to 431% in single-crystal thin films of epitaxial [100]-oriented yttrium iron garnet (YIG) using angle-dependent ferromagnetic resonance. In contrast, the Gilbert damping parameter of a [111]-oriented YIG film is almost isotropic. The observed anisotropic damping is shown to have a similar fourfold symmetry with magneto-crystalline anisotropy. The anisotropic spin-wave group velocity (vg), relaxation time (τ), and decay length (ld) were also experimentally evaluated through spin-wave spectra of [100]-oriented YIG thin film. We developed the LLG equation with the introduction of an anisotropic orbital Gilbert damping term. This anisotropic orbital damping originates from the crystal-field dominated anisotropic spin–orbit coupling and orbital-related magnon–phonon coupling. Our results extend the understanding of the mechanism of anisotropic Gilbert damping in single-crystal magnetic insulators with strong magneto-crystalline anisotropy.

Optimizing the spin Hall effect in Pt-based binary alloys

We present multicode calculations for the spin Hall effect in binary Pt-based alloys, where we explore the viability of alloying the archetype spin Hall material Pt with a large set of metals [Al, Ag, Au, Cu, Hf (hcp), Hf (fcc), Ir, Pd] in order to optimize the charge to spin current conversion for practical applications. To capture intrinsic and extrinsic mechanisms in material-specific calculations, we employ different first-principles codes based on density functional theory in the framework of Green's-function-based multiple scattering approaches. Capturing the transport properties within the relativistic and fully quantum mechanical Kubo-Bastin formalism as well as the semiclassical Boltzmann approach allows for a better understanding of the microscopic physics as well as a larger set of reliable data for the key transport parameters. If available, we compare our results to experimental data, where we generally find good agreement. As we access the full concentration range, we are able to identify the optimal doping regime, which will depend on the binary alloy but generally falls within a region of 60–90 at.% of Pt. When including the unavoidable experimental residual resistivities, the maximum spin Hall angle that we identified is 13% in Al0.2Pt0.8 and Hf0.1Pt0.9, which is comparable to the best spin Hall angles experimentally found in good metal systems. The longitudinal resistivities in this regime go beyond 70µΩ cm, which is compatible with metallic-based magnetic random access memory devices. Published by the American Physical Society 2024

Density functional study of electrode material for magnetic tunnel junction designed using Co2TiZ (Z = Ge, Si) Heusler alloys

Some of the important applications in the field of spintronics are spin current driven logic devices having logic gates and in read heads in the hard disk drives, magnetic random access memory (MRAM) containing non-volatile memory units and extremely complex magnetic sensor. In spintronic applications, a magnetic tunnel junction (MTJ) is considered the back bone of all such devices. With this motivation, in present study we have predicted very low resistance area (RA) product value and high tunnel magneto resistance (TMR) of two designed MTJs by using full Heusler alloys (FHA) Co2TiZ (Z = Ge, Si) as electrode and MgO as barrier layer. These used half metallic (HM) Heusler alloys (HA), have been investigated using Wien2K code, via primary standard calculations and studied electronic and magnetic properties followed by structural and magnetic phase stability. Spin based band structure along with density of state (DOS) profiles are determined by considering both generalized gradient approximation (GGA) + modified Becke–Johnson functional (mBJ) functional and GGA potentials. For the estimation of the Curie temperature (Tc) mean field approximation (MFA) was considered. After determining physical properties of considered FHAs, spin polarised transport properties are calculated by using PWCOND code embedded in Quantum ESPRESSO (QE) for designed MTJs and obtained extremely low resistance-area product (RA) product and a high value of TMR which is found very suitable for spintronic device applications.

The central role of tilted anisotropy for field-free spin–orbit torque switching of perpendicular magnetization

The discovery of efficient magnetization switching upon device activation by spin Hall effect (SHE)-induced spin–orbit torque (SOT) changed the course of magnetic random-access memory (MRAM) research and development. However, for electronic systems with perpendicular magnetic anisotropy (PMA), the use of SOT is still hampered by the necessity of a longitudinal magnetic field to break magnetic symmetry and achieve deterministic switching. In this work, we demonstrate that robust and tunable field-free current-driven SOT switching of perpendicular magnetization can be controlled by the growth protocol in Pt-based magnetic heterostructures. We further elucidate that such growth-dependent symmetry breaking originates from the laterally tilted magnetic anisotropy of the ferromagnetic layer with PMA, a phenomenon that has been largely neglected in previous studies. We show experimentally and in simulation that in a PMA system with tilted anisotropy, the deterministic field-free switching exhibits a conventional SHE-induced damping-like torque feature, and the resulting current-induced effective field shows a nonlinear dependence on the applied current density. This relationship could be potentially misattributed to an unconventional SOT origin.

Spin orbit magnetic random access memory based binary CNN in-memory accelerator (BIMA) with sense amplifier

The research tends to suggest a spin-orbit torque magnetic random access memory (SOT-MRAM)-based Binary CNN In-Memory Accelerator (BIMA) to minimize power utilization and suggests an In-Memory Computing (IMC) for AdderNet-based BIMA to further enhance performance by fully utilizing the benefits of IMC as well as a low current consumption configuration employing SOT-MRAM. And recommended an IMC-friendly computation pipeline for AdderNet convolution at the algorithm level. Additionally, the suggested sense amplifier is not only capable of the addition operation but also typical Boolean operations including subtraction etc. The architecture suggested in this research consumes less power than its spin-orbit torque (STT) MRAM and resistive random access memory (ReRAM)-based counterparts in the Modified National Institute of Standards and Technology (MNIST) data set, according to simulation results. Based to evaluation outcomes, the pre-sented strategy outperforms the in-memory accelerator in terms of speedup and energy efficiency by 17.13× and 18.20×, respectively.

Interfacial modulation of magnetic relaxation and electrical characteristic in RuO2/CrO2 antiferromagnet-half metal bilayer

Half-metallic chromium dioxide (CrO2) is a promising candidate in magnetic random-access memory (MRAM) devices due to its nearly full spin polarization and ultralow Gilbert damping at room temperature. In this study, we succeeded in fabricating (110) and (100)-oriented RuO2/CrO2 bilayers with different thicknesses of CrO2 film using two-step method. The CrO2 film epitaxially grown on a RuO2 layer exhibits a perfect in-plane magnetic uniaxial anisotropy. The magnetic relaxation of CrO2 films can be strongly modulated via the proximity to RuO2 layer, which may relate to the enhancement of the two-magnon scattering due to effects of antiferromagnetic order in RuO2 film. In addition, electronic transport measurements indicate that the electronic characteristic is strongly related to the film growth orientation, and a linear magnetoresistance is observed stemming from intergrain tunneling magnetoresistance and double-exchange mechanism. Angle-dependent ferromagnetic resonance measurements indicates that the uniaxial anisotropy in CrO2 film is strongly related to the strain effect, which is consistent with reciprocal space mapping results. This work lays a foundation for current-drive MRAM based on RuO2/CrO2 bilayer and provides a feasible damping modulation method for CrO2 film.

Thermodynamic properties and switching dynamics of perpendicular shape anisotropy MRAM

The power consumption of modern random access memory (RAM) has been a motivation for the development of low-power non-volatile magnetic RAM (MRAM). Based on a CoFeB/MgO magnetic tunnel junction, MRAM must satisfy high thermal stability and a low writing current while being scaled down to a sub-20 nm size to compete with the densities of current RAM technology. A recent development has been to exploit perpendicular shape anisotropy along the easy axis by creating tower structures, with the free layers’ thickness (along the easy axis) being larger than its width. Here we use an atomistic model to explore the temperature dependent properties of thin cylindrical MRAM towers of 5 nm diameter while scaling down the free layer from 48 to 8 nm thick. We find thermal fluctuations are a significant driving force for the switching mechanism at operational temperatures by analysing the switching field distribution from hysteresis data. We find that a reduction of the free layer thickness below 18 nm rapidly loses shape anisotropy, and consequently stability, even at 0 K. Additionally, there is a change in the switching mechanism as the free layer is reduced to 8 nm. Coherent rotation is observed for the 8 nm free layer, while all taller towers demonstrate incoherent rotation via a propagated domain wall.

Single-nanometer CoFeB/MgO magnetic tunnel junctions with high-retention and high-speed capabilities

Making magnetic tunnel junctions (MTJs) smaller while meeting performance requirements is critical for future electronics with spin-transfer torque magnetoresistive random access memory (STT-MRAM). However, it is challenging in the conventional MTJs using a thin CoFeB free layer capped with an MgO layer because of increasing difficulties in satisfying the required data retention and switching speed at smaller scales. Here we report single-nanometer MTJs using a free layer consisting of CoFeB/MgO multilayers, where the number of CoFeB/MgO interfaces and/or the CoFeB thicknesses are engineered to tailor device performance to applications requiring high-data retention or high-speed capability. We fabricate ultra-small MTJs down to 2.0 nm and show high data retention (over 10 years) and high-speed switching at 10 ns or below in sub-5-nm MTJs. The stack design proposed here proves that ultra-small CoFeB/MgO MTJs hold the potential for high-performance and high-density STT-MRAM.

Tailoring Interlayer Chiral Exchange by Azimuthal Symmetry Engineering.

Recent theoretical and experimental studies of the interlayer Dzyaloshinskii-Moriya interaction (DMI) have sparked great interest in its implementation into practical magnetic random-access memory (MRAM) devices, due to its capability to mediate long-range chiral spin textures. So far, experimental reports focused on the observation of interlayer DMI, leaving the development of strategies to control interlayer DMI's magnitude unaddressed. Here, we introduce an azimuthal symmetry engineering protocol capable of additive/subtractive tuning of interlayer DMI through the control of wedge deposition of separate layers and demonstrate its capability to mediate field-free spin-orbit torque (SOT) magnetization switching in both orthogonally magnetized and synthetic antiferromagnetically coupled systems. Furthermore, we showcase that the spatial inhomogeneity brought about by wedge deposition can be suppressed by specific azimuthal engineering design, ideal for practical implementation. Our findings provide guidelines for effective manipulations of interlayer DMI strength, beneficial for the future design of SOT-MRAM or other spintronic devices utilizing interlayer DMI.

Advanced hybrid MRAM based novel GPU cache system for graphic processing with high efficiency

With the rapid development of portable computing devices and users’ demand for high-quality graphics rendering, embedded Graphics Processing Units (GPU) systems for graphics processing are increasingly turning into a key component of computer architecture to enhance computability. The cache system based on traditional static random access memory (SRAM) plays a crucial role in GPUs. But high leakage, low lifetime and poor integration problems deeply plague the science and engineering field. In the paper, a novel magnetic random access memory (MRAM) based cache architecture of GPU systems is proposed for highly efficient graphics processing and computing accelerating, with the merits of high speed, long endurance, strong interference resistance, and ultra-low power consumption. Spin transfer torque-MRAM and spin orbit torque-MRAM are utilized in off-chip and on-chip caches, respectively. A controller design scheme with prefetching modules and optimized cache coherency protocols are adopted. After testing and evaluating with multiple loads, neural network models and datasets, the simulation results show that the proposed system can achieve up to 28%, 56%, and 66.45% optimizations mostly in terms of speed, energy and leakage power, respectively.

Impact of Technology Scaling and Back-End-of-the-Line Technology Solutions on Magnetic Random-Access Memories

Impact of Technology Scaling and Back-End-of-the-Line Technology Solutions on Magnetic Random-Access Memories

A High-Speed, Low-Power, High-Reliability and Fully Single Event Double Node Upset Tolerant Design for Magnetic Random Access Memory

A High-Speed, Low-Power, High-Reliability and Fully Single Event Double Node Upset Tolerant Design for Magnetic Random Access Memory

Novel CPU cache architecture based on two-dimensional MTJ device with ferromagnetic Fe3GeTe2

With the development of Artificial Intelligence (AI) in recent years, the fields of computer, biology, medicine, and aerospace have demanded higher requirements for the processing and storage of information. In this paper, a novel Magnetic Tunnel Junction (MTJ) based Spin-Orbital Torque Magnetic Random Access Memory (SOT-MRAM) composed of Fe3GeTe2 (FGT) is employed as a storage medium in the computer architecture. On the basis of the analysis of the fundamentals, model configuration, characteristics and performance advantages of the FGT based SOT device, a hybrid storage (L1, L2, Last Level Cache) is constructed, with FGT-SOT-MRAM, conventional SOT-MRAM and STT-MRAM replacing the original static random access memory (SRAM) in the novel triple-level CPU cache architecture. This can override the increasing leakage problem of SRAM, while opening up the application of two-dimensional van der Waals ferromagnets in computer systems at the L1 cache level. Meanwhile, an innovative cache optimization scheme is put forward for magnetic memory to better match the performance of FGT-SOT-MRAM to CPU. The simulation results demonstrate that the FGT-based MRAM can achieve up to 38.03% IPC optimization and 53.41% power optimization in the CPU cache system in contrast to the conventional ones.

Field-free magnetic switching dependence on lateral interfaces in synthetic antiferromagnets by ion implantation

Field-free spin–orbit torque switching in synthetic antiferromagnets (SAF) holds significant promise for high-density spintronic memory and logic devices. In this paper, we realize the field-free magnetization switching in SAFs due to the local ion implantation-induced 45° lateral interface and symmetry breaking. Moreover, the magnetization switching ratio is enlarged by the lateral interface owing to the superimposition of a damping-like effective field and a symmetry-breaking effective field. Our work is significant for the development of magnetic random-access memory technology with high-speed and anti-interference ability.

Magnetization switching driven by spin-orbit torque of Weyl semimetal WTe<sub>2</sub>

The Wely semimetal WTe<sub>2</sub> exhibits significant spin-orbit coupling characteristics and can generate unconventional spin current with out-of-plane polarization, which has become a hotspot in recent years. Meanwhile, WTe<sub>2</sub> also has high charge-spin conversion efficiency, allowing perpendicular magnetization to be switched deterministically without the assistance of an external magnetic field, which is critical for the high-density integration of low-power magnetic random-access memories. The purpose of this paper is to review the recent advances in the research on spin orbit torque in heterostructures composed of WTe<sub>2</sub> and ferromagnetic layers, focusing on progress of research on the detection and magnetization switching in the spin orbit torque of heterojunctions composed of WTe<sub>2</sub> prepared by different methods (e.g. mechanical exfoliation and chemical vapor deposition) and ferromagnetic layers such as conventional magnets (e.g, FeNi and CoFeB, etc.) and two-dimensional magnets (e.g. Fe<sub>3</sub>GeTe<sub>2</sub>, etc.). Finally, the prospect of related research is discussed.

External fields effectively switch the spin channels of transition metal-doped β-phase tellurene from first principles.

Non-volatile magnetic random-access memories have proposed the need for spin channel switching. However, this presents a challenge as each spin channel reacts differently to the external field. Tellurene is a semiconductor with a tunable bandgap, excellent stability, and high carrier concentration, but its lack of magnetic properties has hindered its application in spintronics. In this work, the influence of an external field on transition metal (TM)-doped β-tellurene is systematically analysed from first principles. First, the active-learning moment-tensor-potential (MTP) is used to verify the thermal stability of the V-doped system with the MTP proving to be 900 times faster than the traditional method. Subsequently, under biaxial strain ranging from -2% to 10%, the V-doped system undergoes a gradual transition from a magnetic semiconductor to a spin-gapless semiconductor, and further to a half-metal and magnetic metal. The band structure can be maintained under an electric field. By examining the magnetic anisotropy energy, the lattice changes profoundly impact the electromagnetic properties, particularly with the TMs being sensitive to strain. Moreover, the band structure is reflected in the spin resolution current of the magnetic tunnel junction. This work investigates the response of doped β-Te to external fields, revealing its potential applications in spintronics.