Magnetoresistive Random Access Memory Technology Research Articles

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

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

Thermal optimization of two-terminal SOT-MRAM

While magnetoresistive random-access memory (MRAM) stands out as a leading candidate for embedded nonvolatile memory and last-level cache applications, its endurance is compromised by substantial self-heating due to the high programming current density. The effect of self-heating on the endurance of the magnetic tunnel junction (MTJ) has primarily been studied in spin-transfer torque (STT)-MRAM. Here, we analyze the transient temperature response of two-terminal spin–orbit torque (SOT)-MRAM with a 1 ns switching current pulse using electro-thermal simulations. We estimate a peak temperature range of 350–450 °C in 40 nm diameter MTJs, underscoring the critical need for thermal management to improve endurance. We suggest several thermal engineering strategies to reduce the peak temperature by up to 120 °C in such devices, which could improve their endurance by at least a factor of 1000× at 0.75 V operating voltage. These results suggest that two-terminal SOT-MRAM could significantly outperform conventional STT-MRAM in terms of endurance, substantially benefiting from thermal engineering. These insights are pivotal for thermal optimization strategies in the development of MRAM technologies.

Room-temperature orbit-transfer torque enabling van der Waals magnetoresistive memories

The non-volatile magnetoresistive random access memory (MRAM) is believed to facilitate emerging applications, such as in-memory computing, neuromorphic computing and stochastic computing. Two-dimensional (2D) materials and their van der Waals heterostructures promote the development of MRAM technology, due to their atomically smooth interfaces and tunable physical properties. Here we report the all-2D magnetoresistive memories featuring all-electrical data reading and writing at room temperature based on WTe2/Fe3GaTe2/BN/Fe3GaTe2 heterostructures. The data reading process relies on the tunnel magnetoresistance of Fe3GaTe2/BN/Fe3GaTe2. The data writing is achieved through current induced polarization of orbital magnetic moments in WTe2, which exert torques on Fe3GaTe2, known as the orbit-transfer torque (OTT) effect. In contrast to the conventional reliance on spin moments in spin-transfer torque and spin–orbit torque, the OTT effect leverages the natural out-of-plane orbital moments, facilitating field-free perpendicular magnetization switching through interface currents. Our results indicate that the emerging OTT-MRAM is promising for low-power, high-performance memory applications.

Atomic scale interface engineering for realizing a perpendicularly magnetized CoFeB-based skyrmion hosting material

Néel-type magnetic skyrmions in perpendicularly magnetized systems have attracted considerable interest due to their potential in fundamental research on topological objects and spintronics applications. Various systems have been explored to study Néel-type magnetic skyrmions, including repeated magnetic multilayers, two-dimensional materials, and single magnetic thin-films. Among these, single magnetic thin-films, especially a CoFeB single layer, offers multiple benefits, such as reduced defect energy, high mobility, and easy integration with existing magnetoresistive random access memory technology. However, optimizing CoFeB-based skyrmion hosting materials remains challenging and requires further systematic and comprehensive investigation. In this study, we examine the effect of atomic-scale interface engineering by inserting a Ta layer between the CoFeB/MgO interface on perpendicular magnetic anisotropy, saturation magnetization, and Dzyaloshinskii–Moriya interaction. Moreover, we provide a guideline for engineering material parameters and demonstrate the validity of atomic-scale interface engineering. Our findings contribute to the development of optimized CoFeB-based skyrmion hosting materials.

Nanoscale Materials for State-of-the-Art Magnetic Memory Technologies

The review deals with different materials science aspects of state-of-the-art magnetic memory technologies, such as magnetoresistive random-access memory (MRAM), antiferromagnetic (AFM) memory, and skyrmion racetrack memory. Particularly, the materials with high perpendicular magnetic anisotropy (PMA), such as CoFeB, L10-ordered Mn- and Fe-based alloys, are considered (Sec. 1) regarding their applications in MRAM technology. Furthermore, studies of AFM alloys, such as FeRh, CuMnAs, Mn2Au, are reviewed (Sec. 2) with an emphasis on the application of these materials in AFM-memory technology. Finally, the last (3rd) section of the review is concerning materials that could be used in skyrmion racetrack memory.

Magnetoresistive Random Access Memory: Present and Future

Magnetoresistive random access memory (MRAM) is regarded as a reliable persistent memory technology because of its long data retention and robust endurance. Initial MRAM products utilized toggle mode writing of a balanced synthetic antiferromagnet (SAF) free layer to overcome problems with half-selected bits that challenged traditional Stoner–Wohlfarth switching. With the development of spin transfer torque (STT) switching in perpendicular magnetic tunnel junctions, the capability for scaling MRAM products increased markedly, enabling a 1-Gb device in 2019. Ongoing research will allow scaling to even higher capacities. Compared to traditional memories, STT-MRAM can save power, improve performance, and enhance system data integrity, which supports the growing computing demands for everything from data centers to Internet of Things (IoT) devices. This article provides a review of the technology that enabled present toggle and STT-MRAM products, future STT-MRAM products, and new MRAM technologies beyond STT.

Out-of-Plane Focusing Grating Couplers for Silicon Photonics Integration With Optical MRAM Technology

We present the design methodology and experimental characterization of compact out-of-plane focusing grating couplers for integration with magnetoresistive random access memory technology. Focusing grating couplers have recently found attention as layer-couplers for photonic-electronic integration. The components we demonstrate are designed for a wavelength of 1550 nm, fabricated in a standard 220 nm SOI photonic platform and optimized given the fabrication restrictions for standard 193-nm UV lithography. For the first time, we extend the design based on the phase matching condition to a two-dimensional (2-D) grating design with two optical input ports. We further present the experimental characterization of the focusing behaviour by spatially probing the emitted beam with a tapered-and-lensed fiber and demonstrate the polarization controlling capabilities of the 2-D FGCs.

Low-Barrier Magnet Design for Efficient Hardware Binary Stochastic Neurons

Binary stochastic neurons (BSN's) form an integral part of many machine learning algorithms, motivating the development of hardware accelerators for this complex function. It has been recognized that hardware BSN's can be implemented using low barrier magnets (LBM's) by minimally modifying present-day magnetoresistive random access memory (MRAM) devices. A crucial parameter that determines the response of these LBM based BSN designs is the \emph{correlation time} of magnetization, $\tau_c$. In this letter, we show that for magnets with low energy barriers ($\Delta \approx k_BT$ and below), circular disk magnets with in-plane magnetic anisotropy (IMA) lead to $\tau_c$ values that are two orders of magnitude smaller compared to $\tau_c$ for magnets having perpendicular magnetic anisotropy (PMA) and provide analytical descriptions. We show that this striking difference in $\tau_c$ is due to a precession-like fluctuation mechanism that is enabled by the large demagnetization field in IMA magnets. We provide a detailed energy-delay performance evaluation of previously proposed BSN designs based on Spin-Orbit-Torque (SOT) MRAM and Spin-Transfer-Torque (STT) MRAM employing low barrier circular IMA magnets by SPICE simulations. The designs exhibit sub-ns response times leading to energy requirements of $\sim$a few fJ to evaluate the BSN function, orders of magnitude lower than digital CMOS implementations with a much larger footprint. While modern MRAM technology is based on PMA magnets, results in this paper suggest that low barrier circular IMA magnets may be more suitable for this application.

Thermally Robust Perpendicular STT-MRAM Free Layer Films Through Capping Layer Engineering

In order to enable the spin-transfer torque (STT) magnetoresistive random access memory technologies, it is essential to control the thermal budget, perpendicular magnetic anisotropy, and magnetic damping parameter of perpendicular magnetic tunnel junction (pMTJ) thin films. This paper demonstrates the enhancement of pMTJ free layer (FL) properties through selective engineering of capping materials placed between a CoFeB FL and the top electrode. By introducing a capping layer of Mg or MgO, thermal budget and tunneling magnetoresistance (TMR) ratio are significantly improved over the conventional FL schemes due to reduced atomic intermixing at interfaces. In full-stack pMTJ films, thin Mg above the FL enables the TMR above 170% after 400 °C annealing. Capping via MgO increases the interface anisotropy, allowing for the use of thicker CoFeB FLs with magnetic damping constants as low as 0.003. We discuss the implications of these capping layer improvements and suggest that Mg and MgO show the potential for optimizing the FLs with high-thermal budget and good STT efficiency.

Perpendicular Magnetic Anisotropy for CoFeBZr/MgO

Magnetic tunnel junctions (MTJs) using perpendicular magnetic anisotropy (PMA) have been studied for high density magnetoresistive random access memory (MRAM) with the expectations of scalability for driving current and reducing switching anomalies by local magnetization non-uniformity. CoFeB which has been well developed for MTJ using in-plane magnetization, is also a favorable choice for perpendicular magnetization with the stalking structure of Ta/CoFeB/MgO because its interfacial anisotropy results low current density (J c ) for magnetization reversal by spin transfer torque (STT) [1]. However the practical MRAM technology requires further reduction of J c without degradation of thermal stability. The Gilbert damping measurement showed that Zr insertion provides reduction of the damping constant (α) for the Co film with in-plane magnetization [2]. We present the effects of Zr insertion (5%) in Co(65)Fe(20)B(10) for PMA due to interfacial anisotropy with MgO. Perpendicular magnetization is successfully formed up to 1.56 nm of CoFeBZr with the stalking structure of Ta/CoFeBZr/MgO. The damping is determined as α = 0.004 from the line width of ferromagnetic resonance (FMR) which is lower than value (∼ 0.008) for CoFeB [3]. Moreover, the effective anisotropy energy (K eff ) for maximum value shows 0.163 MJ/m3 for CoFeBZr which is comparable to that 0.183 MJ/m of CoFeB [4]. This study results that insertion of Zr in CoFeB suggests a method for low current switching of MTJ using PMA.

Spin-transfer torque magnetoresistive random-access memory technologies for normally off computing (invited)

Most parts of present computer systems are made of volatile devices, and the power to supply them to avoid information loss causes huge energy losses. We can eliminate this meaningless energy loss by utilizing the non-volatile function of advanced spin-transfer torque magnetoresistive random-access memory (STT-MRAM) technology and create a new type of computer, i.e., normally off computers. Critical tasks to achieve normally off computers are implementations of STT-MRAM technologies in the main memory and low-level cache memories. STT-MRAM technology for applications to the main memory has been successfully developed by using perpendicular STT-MRAMs, and faster STT-MRAM technologies for applications to the cache memory are now being developed. The present status of STT-MRAMs and challenges that remain for normally off computers are discussed.

High-density magnetoresistive random access memory operating at ultralow voltage at room temperature

The main bottlenecks limiting the practical applications of current magnetoresistive random access memory (MRAM) technology are its low storage density and high writing energy consumption. Although a number of proposals have been reported for voltage-controlled memory device in recent years, none of them simultaneously satisfy the important device attributes: high storage capacity, low power consumption and room temperature operation. Here we present, using phase-field simulations, a simple and new pathway towards high-performance MRAMs that display significant improvements over existing MRAM technologies or proposed concepts. The proposed nanoscale MRAM device simultaneously exhibits ultrahigh storage capacity of up to 88 Gb inch−2, ultralow power dissipation as low as 0.16 fJ per bit and room temperature high-speed operation below 10 ns.

Nonvolatile static random access memory based on spin-transistor architecture

The authors proposed and computationally analyzed nonvolatile static random access memory (NV-SRAM) architecture using a new type of spin transistor comprised of a metal-oxide-semiconductor field-effect transistor (MOSFET) and magnetic tunnel junction (MTJ) that is referred to as a pseudo-spin-MOSFET (PS-MOSFET). The PS-MOSFET is a circuit approach to reproduce the functions of spin transistors, based on recently progressed magnetoresistive random access memory technology. The proposed NV-SRAM cell can be simply configured by connecting two PS-MOSFETs to the storage nodes of a standard SRAM cell.

Magnetoresistive Random Access Memory: The Path to Competitiveness and Scalability

This paper provides an in-depth review of the magnetoresistive random access memory technology and its developments over the past decade. Both the traditional field-driven and more recent spin torque transfer driven designs are discussed. By pointing out key technical challenges, important aspects and characteristics of various designs are used to illustrate mechanisms that overcome the technical obstacles. A significant portion of this paper is devoted to the principles of various designs based on spin torque transfer effect, including memory elements with in-plane and perpendicular magnetic electrodes.

Current aspects and future perspectives of high-density MRAM

Magnetoresistive random access memory (MRAM) is regarded as one of the leading candidates for universal memory [1] that will be commercialized in the foreseeable future. The figure of merits for MRAM technology includes non-volatility, high speed, high density, radiation hardness, and unlimited endurance. Very promising R & D results have been announced wordlwide. For a high density MRAM as a stand-alone memory, uniform resistance and switching control for sub-micron and deep sub-micron devices must be guaranteed. To achieve this goal, several material and device issues related with MRAM core cell should be resolved. Resistance (R) as well as magnetoresistance (MR) are limited by the uniformity of barrier thickness induced by bottom electrode. Switching issues appear controllable with a choice of appropriate shape and fine patterning process.

Magnetoresistive random access memory using magnetic tunnel junctions

Magnetoresistive random access memory (MRAM) technology combines a spintronic device with standard silicon-based microelectronics to obtain a combination of attributes not found in any other memory technology. Key attributes of MRAM technology are nonvolatility and unlimited read and write endurance. Magnetic tunnel junction (MTJ) devices have several advantages over other magnetoresistive devices for use in MRAM cells, such as a large signal for the read operation and a resistance that can be tailored to the circuit. Due to these attributes, MTJ MRAM can operate at high speed and is expected to have competitive densities when commercialized. In this paper, we review our recent progress in the development of MTJ-MRAM technology. We describe how the memory operates, including significant aspects of reading, writing, and integration of the magnetic material with CMOS, which enabled our recent demonstration of a 1-Mbit memory chip. Important memory attributes are compared between MRAM and other memory technologies.

Fundamentals of MRAM Technology

Developments in portable communication and computing systems are creating a growing demand for nonvolatile random access memory that is dense and fast. None of the existing solid-state memories can provide all the needed attributes in a single memory solution. Therefore, to achieve the required multiple functionality requirements, a number of different memories are being used while compromising performance and adding cost to the system. Magnetoresistive Random Access Memory (MRAM) has the potential to replace these memories in various systems with a single, universal memory solution. Key attributes of MRAM technology are nonvolatility and unlimited read and write endurance. In addition, MRAM can operate at high-speed and is expected to have competitive densities. In this paper we describe several fundamental technical and scientific aspects of MRAM with emphasis on recent accomplishments that enabled our successful demonstration of a 256 kbit memory chip.

Progress and outlook for MRAM technology

We summarize the features of existing semiconductor memories and compare them to Magnetoresistive Random Access Memory (MRAM),a semiconductor memory with magnetic bits for nonvolatile storage. MRAM architectures based on Giant Magnetoresistance (GMR) and Magnetic Tunnel Junction (MTJ) cells are described. This paper will discuss our progress on improving the material structures, memory bits, thermal stability of the bits, and competitive architectures for GMR and MTJ based MRAM memories as well as the potential of these memories in the commercial memory market.