Magnetic Random Access Memory Research Articles

Publisher Correction: Spin-transfer torque magnetoresistive random access memory technology status and future directions

Publisher Correction: Spin-transfer torque magnetoresistive random access memory technology status and future directions

Enhancement of perpendicular magnetic anisotropy in W/Co/Pt films by nitrogen doping in the W layer

The modulation of perpendicular magnetic anisotropy (PMA) in films has been the subject of considerable research interest, as it is proposed to be a key component for the design and realization of efficient magnetic switching in spintronic devices. In this study, we report the appearance of PMA in the as-deposited WNx/Co/Pt films without annealing. The strength of the PMA is quantified by means of effective magnetic anisotropy constant Keff, which is correlated with the N2 gas/Ar gas flow rate ratio PN2. The highest Keff value, 1.347 × 106 erg/cm3, is obtained for the sample deposited with PN2 of 40%. This phenomenon can be explained in two ways. On the one hand, the results of the experiment demonstrate that appropriate nitrogen doping can facilitate the formation of an ideal nitrided state at the WNx/Co interface, while simultaneously reducing the roughness of the WNx/Co interface, which, in turn, enhances the PMA of the WNx/Co/Pt films. On the other hand, the first-principles calculations indicate that the enhancement of PMA can be attributed to the modification of orbital hybridization at the Co/Pt interface by WNx. This innovative approach has the potential to advance the development of high-performance magnetic random-access memory devices.

Thermal Characterization of Ultrathin MgO Tunnel Barriers.

Magnetic tunnel junctions (MTJs) with ultrathin MgO tunnel barriers are at the heart of magnetic random-access memory (MRAM) and exhibit potential for spin caloritronics applications due to the tunnel magneto-Seebeck effect. However, the high programming current in MRAM can cause substantial heating which degrades the endurance and reliability of MTJs. Here, we report the thermal characterization of ultrathin CoFeB/MgO multilayers with total thicknesses of 4.4, 8.8, 22, and 44 nm, and with varying MgO thicknesses (1.0, 1.3, and 1.6 nm). Through time-domain thermoreflectance (TDTR) measurements and thermal modeling, we extract the intrinsic (∼3.6 W m-1 K-1) and effective (∼0.85 W m-1 K-1) thermal conductivities of annealed 1.0 nm thick MgO at room temperature. Our study reveals the thermal properties of ultrathin MgO tunnel barriers, especially the role of thermal boundary resistance, and contributes to a more precise thermal analysis of MTJs to improve the design and reliability of MRAM technologies.

Spin-transfer torque magnetoresistive random access memory technology status and future directions

Spin-transfer torque magnetoresistive random access memory technology status and future directions

Orthogonal spin–orbit torque-induced deterministic switching in NiO

The electrical switching of antiferromagnet (AFM) is very important for the development of ultrafast magnetic random-access memory (MRAM). This task becomes more difficult in antiferromagnetic oxide NiO, which has complex anisotropy. We show that by utilizing two spin–orbit torques (SOTs) from orthogonal currents, one can deterministically switch the magnetic moments of NiO in two electrical distinguishable states that can be read out using the spin Hall magnetoresistance. This deterministic switching relies on the symmetry of SOT on different sublattices, where the sign reversal of magnetic moments leads to constructive torques in the beginning and balanced torques in the end. In addition, we show that the easy-plane anisotropy plays a key role in the switching, which has been ignored in some previous works. The uniform magnetic dynamics in this work provides a clear physical picture in understanding the SOT switching of NiO. Furthermore, the electrical writing and reading function in our device advances the development of AFM-MRAM.

Metastable body-centered cubic CoMnFe alloy films with perpendicular magnetic anisotropy for spintronics memory

ABSTRACT A body-centered cubic (bcc) FeCo(B) is a current standard magnetic material for perpendicular magnetic tunnel junctions (p-MTJs) showing both large tunnel magnetoresistance (TMR) and high interfacial perpendicular magnetic anisotropy (PMA) when MgO is utilized as a barrier material of p-MTJs. Since the p-MTJ is a key device of current spintronics memory, i.e. spin-transfer-torque magnetoresistive random access memory (STT-MRAM), it attracts attention for further advance to explore new magnetic materials showing both large PMA as well as TMR. However, there have been no such materials other than FeCo(B)/MgO. Here, we report, for the first time, PMA in metastable bcc Co based alloy, i.e. bcc CoMnFe thin films which are known to exhibit large TMR effect when used for electrodes of MTJs with the MgO barrier. The largest intrinsic PMA’s were about 0.6 and 0.8 MJ/m3 in a few nm thick CoMnFe alloy film and multilayer film, respectively. Our ab-initio calculation suggested that PMA originates from tetragonal strain and the value exceeds 1 MJ/m3 with optimizing strain and alloys composition. The simulation of the thermal stability factor indicates that the magnetic properties obtained satisfy the requirement of the data retention performance of X-1X nm STT-MRAM. The large PMA and high TMR effect in bcc CoMnFe/MgO, which were rarely observed in materials other than FeCo(B)/MgO, indicate that bcc CoMnFe/MgO is one of the potential candidates of the materials for X - 1X nm STT-MRAM.

Performance Analysis of Spin Orbit Torque Magneto-Resistive RAM Caches in 4-core ARM Systems

Spin Orbit Torque Magnetic Random Access Memory (SOT–)MRAM is gaining interest as it eradicates several limitations posed by its predecessor Spin Transfer Torque (STT-)MRAM, yet inherits all its advantages. This work explores in detail, the suitability of SOT–MRAM implemented caches in different levels of memory hierarchy in comparison to conventional SRAM technology, over several performance parameters like area, energy consumption and execution time for an embedded benchmark suite. Our circuit-level analysis shows that SOT–MRAM outperforms SRAM for caches ([Formula: see text] KB), and only lags in area and read-access energy for smaller caches. A typical 512 KB SOT–MRAM cache improves area by 1%, read/write latency by 33/38%, and leakage by over 99% than that of SRAM memory technology. The architecture-level analysis confirms that on average SOT–MRAM is energy efficient by 74% in L1, 97.2% in L2 and 89.3% in both (i.e., L1 + L2) implementations against SRAM, for a 22[Formula: see text]nm technology node. We also estimate that SOT–MRAM only solution offers [Formula: see text]% energy savings and [Formula: see text]% better EDP than Hybrid (L1-SRAM and L2-SOT) memory hierarchy for multi-core ARM processors.

Comparative Study of Current-Induced Torque in Cr/CoFeB/MgO and W/CoFeB/MgO.

Orbital torque (OT) in magnetic heterostructures has been actively discussed in terms of its actual existence and usefulness in comparison to the spin-orbit torque (SOT) that shows promise for next-generation magnetoresistive random access memories. The objectives of this study are 2-fold: (i) making an apples-to-apples comparison in two representative stacks where OT and SOT are expected to dominate and (ii) examining the potential emergence of OT in archetypal SOT stacks. Cr/CoFeB/MgO and W/CoFeB/MgO are chosen as the OT- and SOT-dominant systems, respectively. Systematic variations in each layer's thicknesses reveal that (i) Cr/CoFeB/MgO exhibits substantial torque comparable to or even exceeding that of the W/CoFeB/MgO stack when Cr and CoFeB layers are especially thick and (ii) the torque in W/CoFeB/MgO changes sign with increasing W and CoFeB thicknesses, suggesting a crossover of the dominant mechanism from SOT to OT. The findings clarify the opportunities and challenges of devices leveraging SOT and OT.

Materials, Processes, Devices and Applications of Magnetoresistive Random Access Memory

Abstract Magnetoresistive random access memory (MRAM) is a promising non-volatile memory technology that can be utilized as an energy and space-efficient storage and computing solution, particularly in cache functions within circuits. Although MRAM has achieved mass production, its manufacturing process still remains challenging, resulting in only a few semiconductor companies dominating its production. In this review, we delve into the materials, processes, and devices used in MRAM, focusing on both the widely adopted spin transfer torque (STT) MRAM and the next-generation spin-orbit torque (SOT) MRAM. We provide an overview of their operational mechanisms and manufacturing technologies. Furthermore, we outline the major hurdles faced in MRAM manufacturing and propose potential solutions in detail. Then, the applications of MRAM in artificial intelligent hardware is introduced. Finally, we present an outlook on the future development and applications of MRAM.

Evidence of Spin Reorientation from Γ4 to Γ2 and Sign Reversal Exchange Bias in CeCrO3 Nanoparticles

Herein, the temperature‐dependent magnetic structure and sign reversal exchange bias in CeCrO3 using magnetization data and time‐of‐flight neutron diffraction data which is given less attention among RCrO3 are investigated. While nuclear structural analysis using Rietveld refinement exhibits distorted orthorhombic structure within Pnma space group, temperature dependence of the magnetic structure using neutron diffraction reveals possible spin configurations, namely, Γ4, Γ2, and Γ1, within the temperature range of 6–300 K. Temperature‐dependent magnetization shows compensation temperature, Tcomp, at 58 K, spin reorientation temperature, TSR, at 15 K along with a Neel temperature, TN, at 260 K which is the outcome of the competition between canted antiferromagnetic ordering of Cr3+ ions and Ce3+ ions in CeCrO3. Furthermore, the magnetization versus magnetic field (M vs H) measurements indicate transition of the Γ4 spin structure to Γ2 spin structure around TSR which is further supported by reversible‐to‐irreversible changes observed in temperature‐dependent MFCC and MFCW. Moreover, a temperature‐driven sign reversal of exchange bias in CeCrO3 is observed, resulting from the competition between antiferromagnetic coupling between chromium moment (MCr) and cerium moment (MCe) in these nanoparticles. This intriguing behavior holds significant potential for the development of thermally assisted magnetic random access memory.

Study of the influence of nitrogen doping on magnetic anisotropy in CoFe/MgO thin films with different deposition sequences

Abstract The ferromagnetic (FM)/MgO structure multilayers with perpendicular magnetic anisotropy (PMA) play a crucial role in magnetic random-access memory. It is essential to explore the methods for modulating magnetic anisotropy and to clarify the underlying mechanisms. We study the regulation of the magnetic anisotropy with nitrogen (N) doping concentration (CN) in two samples: Ta/CoFe(N)/MgO/Ta (S1) and Ta/MgO/CoFe(N)/Ta (S2) with different deposition sequences. The S1 sample exhibits in-plane magnetic anisotropy (IMA) without N doping. And the sample presents PMA when CN = 15%. The S2 sample shows weak PMA without N doping, and the sample converts to IMA when CN = 15%. X-ray photoelectron spectroscopy is performed to evaluate the oxidation level of Fe at the CoFe/MgO interface by the peak area ratio of Fe oxide to Fe (ϵ). It is believed that excessively high and low ϵ values correspond to over-oxidation and under-oxidation of Fe, respectively. For films deposited in different sequences, both over-oxidation and under-oxidation lead to IMA, while moderate oxidation facilitates the formation of PMA. The microstructure analysis reveals that the N doping does not affect the crystallization of the films, indicating that magnetocrystalline anisotropy has a minor influence on the changes of K eff.

The single event upset hardened design of spin transfer torque magnetic random access memory read circuits at 40 nm technology

With the advancement of technology nodes, the challenging space radiation environment poses a significant threat to memory reliability. Spin transfer torque magnetic random access memory (STT-MRAM) is a formidable candidate for non-volatile memory for space applications due to its advantages of non-volatility, durability, speed and compatibility with CMOS technology. Although the STT-MRAM memory unit magnetic tunnel junction (MTJ) is naturally immune to radiation effects, the single event upset (SEU) affects the peripheral circuitry. A radiation-hardened circuit is proposed, which theoretically does not have ‘0' upset nodes and automatically recovers from ‘1' upset. Moreover, the circuit's radiation-hardened performance was corroborated through hybrid simulation utilizing 40-nm technology. The findings of this investigation hold significance for the use of space radiation-hardened STT-MRAM.

Co-optimizing of H-curing, stress, and thermal annealing—A more effective way for realizing FEOL-BEOL compatible eMRAM chip

Metallization, plasma, and thermal annealing used in magneto-resistive random access memory integration differs significantly from traditional interconnection processes, usually resulting in the device performance deterioration of metal-oxide-silicon field-effect transistors. Commonly used methods, such as hydrogen postalloying, may not be effective to recover performance when magneto-resistive random access memory is integrated. The study focused on the interplay between hydrogen content in the dielectric films, wafer configuration induced by film stress, and thermal annealing during the chip fabrication process. Post-thermal annealing can enhance the release of hydrogen from the dielectric films, which can repair the silicon–hydrogen bond breakage resulting from magneto-resistive random access memory integration. However, this process can also worsen wafer bowing in an undesired direction which is detrimental to the performance of metal-oxide-silicon field-effect transistors. Consequently, utilizing silicon nitride with specific hydrogen content, in conjunction with post-thermal annealing, can improve effectively both p-type and n-type metal-oxide-silicon field-effect transistors. This approach holds significant potential for application in more advanced technological nodes since it is compatible with traditional process and does not require more advanced fabrication equipment. Additionally, the resulting embedded magneto-resistive random access memory chips maintain competitive magnetic tunneling junction reliability in term of endurance and reflow resistivity.

Tunneling Barrier Thickness Dependence of Spin Polarization of Ferromagnet in Magnetic Tunnel Junctions

Abstract For designing low-impedance magnetic tunnel junctions (MTJs), it has been found that tunneling magnetoresistance strongly correlates with the insulating barrier thickness, imposing a fundamental problem about the relationship between spin polarization of ferromagnet and the insulating barrier thickness in MTJs. Here, we investigate the influence of alumina barrier thickness on tunneling spin polarization (TSP) through a combination of theoretical calculations and experimental verification. Our simulating results reveal a significant impact of barrier thickness on TSP, exhibiting an oscillating decay of TSP with the barrier layer thinning. Experimental verification is realized on FeNi/AlO x /Al superconducting tunnel junctions to directly probe the spin polarization of FeNi ferromagnet using Zeeman-split tunneling spectroscopy technique. These findings provide valuable insights for designs of high-performance spintronic devices, particularly in applications such as magnetic random access memories, where precise control over the insulating barrier layer is crucial.

Robust Electric-Field Control of Colossal Exchange Bias in CrI3 Homotrilayer.

Controlling exchange bias (EB) by electric fields is crucial for next-generation magnetic random access memories and spintronics with ultralow energy consumption and ultrahigh speed. Multiferroic heterostructures have been traditionally used to electrically control EB and interfacial ferromagnetism through weak/indirect coupling between ferromagnetic and ferroelectric films. However, three major bottlenecks (lattice mismatch, interface defects, and weak/indirect coupling in multiferroic heterostructures) remain, resulting in only a few tens of milli-tesla EB field. Here, this study reports a robust electric-field control recipe to dynamically tailor the EB effect in a pure CrI3 homotrilayer on a ferroelectric Y-doped HfO2 (HYO) substrate, and demonstrate a colossal and tunable EB field (HE) from -0.15 to +0.33 T, giving rise to an EB modulation of 0.48 T. The charge doping due to ferroelectric HYO film divides a homo-configuration of CrI3 homotrilayer into one antiferromagnetic (AFM) bilayer CrI3 and one ferromagnetic (FM) monolayer CrI3, favoring direct exchange coupling. The synergies of charge doping and electric field induce a transition of magnetic orders from AFM to FM phase in bilayer CrI3, which is also supported by first-principles calculations, leading to the robust electric control of colossal EB effect. The results therefore open numerous opportunities for exploring 2D spintronics, memories, and braininspired in-memory computing.

Tailoring magnetism in chromium-doped zinc cobalt ferrite nanostructure for advanced spintronic memory devices

Soft magnetic ferrites serve as a crucial component in a wide array of sensing and actuating applications across various industries, including consumer electronics, automotive systems, spintronics, and more. These materials also find utility in spintronics, particularly for next-generation magnetic random-access memory (MRAM) due to their excellent inductive properties, which enhance the performance and scalability of spintronic memory devices. This study focuses on fine-tuning soft magnetic ferrites for inductive applications by doping them with Cr ions. By utilizing advanced experimental techniques such as the vibrating sample magnetometer (VSM) for bulk magnetometry and X-ray magnetic circular dichroism (XMCD) alongside X-ray absorption spectroscopy for atomic studies, the research aims to investigate the structural, electronic, and magnetic properties of the nanoferrites. Addition of doping in the soft ferrites observes reduction in the general magnetic parameters, with the only exception being coercivity, which decreases from 381 Oe to 275 Oe as the doping concentration increases from x = 0 to x = 0.02, and then increases to 350 Oe at x = 0.03. Through such precise tuning of the nanoparticles, this study aims to investigate the controllable soft magnetic properties of the nanoferrites, thereby paving the way for fast access times, non-volatility, and low energy consumption, presenting a compelling alternative to conventional memory technologies.

Back-Side Stress to Ease p-MOSFET Degradation on e-MRAM Chips

Abstract Magnetoresistive random access memory process makes great contribution to threshold voltage deterioration of metal-oxide-silicon field-effect transistors, especially on p-type devices. Herein, a method was proposed to reduce threshold voltage degradation by utilizing back-side stress. Through the deposition of tensile material on the back side, positive charges generated by silicon-hydrogen bond breakage were inhibited, resulting in a potential reduction of threshold voltage shift by up to 20%. In addition, it was found that the method could only relieve silicon-hydrogen bond breakage physically, failing to provide a complete cure. However, it holds significant potential for applications where additional thermal budget is undesired. Furthermore, it was also concluded that the method used in this work was irreversible, with its effect sustained to the chip package phase, and it ensures competitive reliability of the resulting magnetic tunnel junction devices.

Thermal effects on damping determination of perpendicular MRAM devices by spin-torque ferromagnetic resonance

We report device-level damping measurements using spin-torque driven ferromagnetic resonance on perpendicular magnetic random-access memory cells. It is shown that thermal agitation enhances the apparent damping for cells smaller than about 55 nm. The effect is fundamental and does not reflect a true damping increase. In addition to the thermal effect, it is still found that device-level damping is higher than film-level damping and increases with decreasing cell size. This is attributed to edge damage caused by device patterning.

Swift heavy ion irradiation-induced enhancement of spin–orbit torque efficiency in Pt/Co/Ta trilayers

Increasing the efficiency of spin–orbit torque (SOT) is of great interest in applications for magnetic random access memory and logic devices due to decreased energy consumption. Here, we present that the SOT efficiency of Pt/Co/Ta films with perpendicular magnetic anisotropy can be improved by swift high-energy heavy Fe11+ ion irradiation, which is an effective method to alter crystallinity, interface roughness, and defects in ferromagnet/heavy metal heterostructures. Specifically, the Pt/Co/Ta films show an optimal SOT efficiency at ion fluence around 1.0 × 1013 ions/cm2 with the largest spin Hall angles reaching 0.59, which is the largest improvement of spin Hall angle by ion irradiation compared to previous studies using light ions. We demonstrate that the increase in SOT efficiency arises from structural changes in the Pt layer due to ion irradiation-induced damage effects at proper fluence, while the decrease in SOT efficiency is mainly attributed to the restoration of Pt crystallinity induced by beam-heating effects at high fluence. This work demonstrates that an appropriate ion irradiation process could improve the SOT efficiency and the spin Hall angle, thereby providing a way to develop future SOT-based spintronic devices.

Magnetic tunnel junctions with superlattice barriers

The urgent demand for high-performance emerging memory, propelled by artificial intelligence in internet of things (AIoT) and machine learning advancements, spotlights spin-transfer torque magnetic random-access memory as a prime candidate for practical application. However, magnetic tunnel junctions (MTJs) with a single-crystalline MgO barrier, which are central to magnetic random-access memory (MRAM), suffer from significant drawbacks: insufficient endurance due to breakdown and high writing power requirements. A superlattice barrier-based MTJ (SL-MTJ) is proposed to overcome the limitation. We first fabricated the MTJ using an SL barrier while examining the magnetoresistance and resistance-area product. Lower writing power can be achieved in SL-MTJs compared to MgO-MTJs. Our study may provide a new route to the development of MRAM technologies.