Magnetic Random Access Memory Development Research Articles

Cubic-type Heusler compound Mn2FeGa thin film with strain-induced large perpendicular magnetic anisotropy

This study reports the development of ferrimagnetic cubic Heusler compound ${\mathrm{Mn}}_{2}{\mathrm{Fe}}_{x}\mathrm{Ga}$ (MFG) thin films with large perpendicular magnetic anisotropy (PMA). By growing MFG on a Cr buffer layer, a cubic ${\mathrm{X}}_{\mathrm{a}}$ phase with a tetragonal distortion $c/a\ensuremath{\approx}1.04$ induced by the buffer layer was obtained in the range of $x=1.0--1.3$, leading to large PMA which exceeds $0.75\phantom{\rule{4pt}{0ex}}\mathrm{MJ}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}3}$ in stoichiometric ${\mathrm{Mn}}_{2}\mathrm{FeGa}$ $(x=1)$. Synchrotron M\"ossbauer spectroscopy revealed that these cubic MFG thin films show good chemical ordering close to the ${\mathrm{X}}_{\mathrm{a}}$-ordered state. First-principles calculations demonstrated that, in ${\mathrm{X}}_{\mathrm{a}}$-ordered cubic MFG, the characteristic electronic structure of Fe around the Fermi level causes a large uniaxial magnetocrystalline anisotropy under the tetragonal strain consistent with experiment. The half-metallic-like band structure of cubic MFG was also shown to be preserved under the strain. Cubic ${\mathrm{Mn}}_{2}\mathrm{FeGa}$ with its small saturation magnetization, large PMA, and possibility of being highly spin polarized make this material an ideal candidate for the development of magnetic random-access memory and other spintronic devices.

Steady State and Dynamics of Joule Heating in Magnetic Tunnel Junctions Observed via the Temperature Dependence of RKKY Coupling

Understanding quantitatively the heating dynamics in magnetic tunnel junctions (MTJ) submitted to current pulses is very important in the context of spin-transfer-torque magnetic random access memory development. Here we provide a method to probe the heating of MTJ using the RKKY coupling of a synthetic ferrimagnetic storage layer as a thermal sensor. The temperature increase versus applied bias voltage is measured thanks to the decrease of the spin-flop field with temperature. This method allows distinguishing spin transfer torque (STT) effects from the influence of temperature on the switching field. The heating dynamics is then studied in real-time by probing the conductance variation due to spin-flop rotation during heating. This approach provides a new method for measuring fast heating in spintronic devices, particularly magnetic random access memory (MRAM) using thermally assisted or spin transfer torque writing.

Magnetic random access memory: Commercialization trend from the perspective of patents

As one of the most promising new nonvolatile memory technologies in the future, magnetic random access memory (MRAM) can address a wide range of potential memory applications, potentially worth thousands of billions of dollars with the substantial advantages of nonvolatility, radiation hardness, unlimited endurance, high speed, high density and low power consumption, attracting worldwide investments, especially from the United States, Europe, Japan and South Korea. From the perspective of patents, the commercialization trend and competitiveness of MRAM emerging industry are explored based on the analysis of global patent application data in this technology field. The first commercially available MRAM device with a storage capacity of 4 Mbit was actually realized in 2006. Current 16 Mbit MRAM devices based on magnetic field-driven switching have been applied on a small scale in niche areas ranging from aerospace to industrial and automotive systems. The further commercial development of MRAM with a storage capacity of 1 Gbit has now become the research goal. The scalability embodied in switching using the spin torque transfer (STT) effect has transformed the prospects for MRAM commercialization. Novel designs based on STT current switching can be expected to open a new route for fabricating scalable MRAM devices with high density, high performance, but low power consumption. Although STT-MRAM is only just beginning to be commercialized, the rapid increase of patent applications in this domain signals the desire for commercialization. Most recently, novel MRAM devices based on the spin orbit coupling (SOC) effects such as spin Hall effect, Rashba effect, Dzyaloshinskii-Moriya interaction (DMI), etc. are emerging, and a highly dynamic and competitive market in the near future will be expected.

Two-level BEOL processing for rapid iteration in MRAM development

The implementation of magnetic random access memory (MRAM) hinges on complex magnetic film stacks and several critical steps in back-end-of-line (BEOL) processing. Although intended for use in conjunction with silicon CMOS front-end device drivers, MRAM performance is not limited by CMOS technology. We report here on a novel test site design and an associated thin-film process integration scheme which permit relatively inexpensive, rapid characterization of the critical elements in MRAM device fabrication. The test site design incorporates circuitry consistent with the use of a large-area planar base electrode to enable a processing scheme with only two photomask levels. The thin-film process integration scheme is a modification of standard BEOL processing to accommodate temperature-sensitive magnetic tunnel junctions (MTJs) and poor-shear-strength magnetic film interfaces. Completed test site wafers are testable with high-speed probing techniques, permitting characterization of large numbers of MTJs for statistically significant analyses. The approach described in this paper provides an inexpensive means for rapidly iterating on MRAM development alternatives to converage on an implementation suitable for a production environment.

Rapid-turnaround characterization methods for MRAM development

Magnetic random access memory (MRAM) technology, based on the use of magnetic tunnel junctions (MTJs), holds the promise of improving on the capabilities of existing charge-based memories by offering the combination of nonvolatility, speed, and density in a single technology. In this paper we review rapid-turnaround methods which have been developed or applied in new ways to characterize MRAM chips at various stages during processing, with particular emphasis on the MTJs. The methods include current-in-plane tunneling (CIPT), Kerr magnetometry, vibrating sample magnetometry (VSM), and conducting atomic force microscopy (CAFM). Use of the methods has enabled rapid learning with respect to the materials used for the MTJs, as well as tuning of the MTJ geometry in terms of size and shape and of the patterning methods employed. Examples of the use of each of the methods are presented along with interpretation of the data via critical operating parameters.

Magnetic Nanostructures and Materials in Magnetic Random Access Memory

AbstractFor Abstract see ChemInform Abstract in Full Text.

Magnetic nanostructures and materials in magnetic random access memory.

The advances in magnetic random access memory provide a remarkable showcase for the rapid development and application of nanodevices. Several aspects of state-of-the-art magnetic nanoscience and nanotechnology are developed and utilized in this single device. Current magnetic random access memory design is built upon the discovery and understanding of physics issues such as giant magnetoresistance, spin-dependent tunneling, exchange bias, and magnetic anisotropy in small elements. Successful magnetic random access memory development requires future research in some of the key areas involving nanotechnology. For example, the uniformity of the barrier thickness across the entire device and magnetic switching stability of a nanosized element are challenging issues that lie ahead. The spin degree of freedom of electrons is an added dimension that is both unique and useful in electronic transport and information technology. Nonvolatile, high-density, high-speed, and low-power magnetic random access memory is one of the first examples of the application of spintronics.