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Advances in reducing the resistance and enhancing the magnetoresistance (MR%) of the magnetic tunnel junction (MTJ) material has made it useful for magnetoresistive random access memory as well as magnetic field sensing applications. One of the most important aspects for producing the MTJ material is the method used for forming the tunnel barrier, and its impact on the properties of MTJ such as resistance and area product (RA), MR%, and RA uniformity across a large area. We have explored forming the aluminum oxide tunnel barrier with air; reactive sputtering; plasma oxidation with plasma source; plasma oxidation with power introduced from the target side; and plasma oxidation with power introduced from the substrate side. Our results show that all techniques can be made to work. Plasma oxidation is favored due to its simplicity and manufacturing compatibility. It was also discovered that different oxidation methods used in this study caused little difference in MTJ resistance uniformity. The latter is mainly determined by the Al metal-thickness uniformity. Modeling based on Simmons’ theory supports our experimental finding. This illustrates the importance in improving Al metal-film uniformity for producing MTJ with ultra-uniform resistance. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper, a review of the developments in MRAM technology over the past 20 years is presented. The various MRAM generations are described with a particular focus on spin-transfer torque MRAM (STT-MRAM) which is currently receiving the greatest attention. The working principles of these various MRAM generations, the status of their developments, and demonstrations of working circuits, including already commercialized MRAM products, are discussed. [ABSTRACT FROM PUBLISHER]

MRAIvI technology is based on the storage of data in stable magnetic states using devices that have a large magnetoresistance effect, so that the data can be read by determining the resistance of the device. MRAM is inherently nonvolatile and the magnetic states can be switched extremely fast and with no wear out. In this article, we review the fundamentals of MRAM technology, explain the innovations that have overcome barriers to commercialization, and describe areas where further innovation can advance the technology most significantly. The influence of key structural and magnetic properties of materials used in magnetic tunnel junctions, and optimization of those devices for read and write performance in memory arrays, is discussed in detail. The various approaches to writing data in MRAM arrays are described and compared, with emphasis on toggle MRAM, the type that is in commercial production, and on spin-torque MRAM, which shows great promise for future improvements in power and density. In the final section, we summarize recent demonstrations of advanced MRAM technology. [ABSTRACT FROM AUTHOR]

We report the first demonstration of a magnetoresistive random access memory (MRAM) circuit incorporating MgO-based magnetic tunnel junction (MTJ) material for higher performance. We compare our results to those of AlOx-based devices, and we discuss the MTJ process optimization and material changes that made the demonstration possible. We present data on key MTJ material attributes for different oxidation processes and free-layer alloys, including resistance distributions, bias dependence, free-layer magnetic properties, interlayer coupling, breakdown voltage, and thermal endurance. A tunneling magnetoresistance (TMR) greater than 230% was achieved with CoFeB free layers and greater than 85 % with NiFe free layers. Although the TMR with NiFe is at the low end of our MgO comparison, even this MTJ material enables faster access times, since its TMR is almost double that of a similar structure with an AlOx barrier. Bit-to-bit resistance distributions are somewhat wider for MgO barriers, with sigma about 1.5% compared to about 0.9% for AlOx. The read access time of our 4 Mb toggle MRAM circuit was reduced from 21 ns with AlOx to a circuit-limited 17 ns with MgO. [ABSTRACT FROM AUTHOR]

Abstract-A 4-Mb magnetoresistive random access memory (MRAM) with a novel magnetic bit cell and toggle switching mode is presented. The circuit was designed in a five level metal, 0.18-μm complementary metal-oxide-semiconductor process with a bit cell size of 1.55 μm². The new bit cell uses a balanced synthetic antiferromagnetic free layer and a phased write pulse sequence to provide robust switching performance with immunity from half-select disturbs. This switching mode greatly improves the operational performance of the MRAM as compared to conventional MRAM. Adetailed description of this 4-Mb toggle MRAM is presented. [ABSTRACT FROM AUTHOR]

Presents information on a study which discussed the progress on improving the material structures, thermal stability and competitive architectures for Giant Magnetoresistance (GMR) and Magnetic Tunnel Junction (MTJ) based Magnetoresistance Random Access Memory (MRAM). MRAM memory architectures; MRAM material characteristics; Conclusions.

We reduced the switching field (Hsw) in arrays of single-layer magnetoresistive random access memory elements using enhanced permeability dielectric (EPD) films. This reduction is due to an increased magnetic flux density produced at the bit by increasing the permeability μ of the surrounding dielectric. The authors produced EPD films by embedding superparamagnetic nanoparticles of various sizes in oxides of Al, Mg, or Si. For bits surrounded by EPD, Hsw decreased linearly as μ increased. Using this approach, we reduced Hsw by ≈40% for μ=3.5, without changing the energy barrier to magnetization reversal. [ABSTRACT FROM AUTHOR]

Synthetic antiferromagnet (SAF) structures are a key element of TMR and GMR read heads and MRAM devices. Control of the SAP coupling strength and thermal endurance are key issues for these technologies. We find that the coupling strength increases with stronger crystalline texture in polycrystauine NiFe SAFs, and, surprisingly, we observe a strong dependence on seed layer in amorphous CoFeB SAFs. We also have developed an analysis method for evaluating thermal endurance of SAFs and show that failure of the SAF can be modeled as a thermally activated diffusion process. The analysis is used to predict the time to failure at any temperature, thus allowing accelerated failure analysis for SAF-based devices. The stability improves dramatically with ins creasing Ru spacer thickness. The time to failure for typical NiFe SAFs was found to be >10 years at 120 °C. [ABSTRACT FROM AUTHOR]

We have measured thermally activated magnetization reversal of the free layers in submicron magnetic tunnel junctions to be used for magnetoresistive random access memory. We applied magnetic field pulses to the bits with a pulse duration t[sub p] ranging from nanoseconds to 0.1 ms. We have measured the switching probability as a function of t[sub p] with a fixed field amplitude H, and as a function of H for fixed t[sub p]. For both cases, we find good agreement with the switching probability predicted by the Arrhenius-N&eeacute;el theory for thermal activation over a single energy barrier. [ABSTRACT FROM AUTHOR]