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Journal ArticleDOI

Effect of MgO spacer and annealing on interface and magnetic properties of ion beam sputtered NiFe/Mg/MgO/CoFe layer structures

18 Sep 2012-Journal of Applied Physics (American Institute of Physics)-Vol. 112, Iss: 6, pp 063906
TL;DR: In this article, the effect of variation in the thickness of ion assisted ion beam sputtered MgO spacer layer deposited at oxygen ion assisted energy of 50 eV on the extent of magnetic coupling of NiFe and CoFe layers in Si/NiFe(10 nm)/Mg(1.5
Abstract: The effect of variation in the thickness of ion assisted ion beam sputtered MgO spacer layer deposited at oxygen ion assisted energy of 50 eV on the extent of magnetic coupling of NiFe and CoFe layers in Si/NiFe(10 nm)/Mg(1 nm)/MgO(2,4,6 nm)/CoFe(10 nm) sandwich structure is investigated. At MgO spacer layer thickness of 4 nm, the separate reversal of magnetizations of the two ferromagnetic layers is observed in the hystresis loop recorded along easy direction. This results in a 3.5 Oe wide plateau like region during magnetization reversal, which became 4.5 Oe at 6 nm thin MgO. At 2 nm thin MgO, the absence of plateau during magnetization reversal region revealed ferromagnetic coupling between the two ferromagnetic layers, which is understood to arise due to the growth of very thin and low density (1.22 gm/cc) MgO spacer layer, indicating the presence of pinholes as revealed by x-ray reflectometry. After vaccum annealing (200 °C/1 h), the plateau region for 4 and 6 nm thin MgO case decreased to 1.5 Oe and...
Citations
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Journal ArticleDOI
TL;DR: This paper gives a full analysis of failure mechanisms for PMA-MTJ and presents some eventual solutions from device fabrication to system level integration to optimize the failure issues.
Abstract: Magnetic tunnel junction nanopillar with interfacial perpendicular magnetic anisotropy (PMA-MTJ) becomes a promising candidate to build up spin transfer torque magnetic random access memory (STT-MRAM) for the next generation of non-volatile memory as it features low spin transfer switching current, fast speed, high scalability, and easy integration into conventional complementary metal oxide semiconductor (CMOS) circuits. However, this device suffers from a number of failure issues, such as large process variation and tunneling barrier breakdown. The large process variation is an intrinsic issue for PMA-MTJ as it is based on the interfacial effects between ultra-thin films with few layers of atoms; the tunneling barrier breakdown is due to the requirement of an ultra-thin tunneling barrier (e.g., <1 nm) to reduce the resistance area for the spin transfer torque switching in the nanopillar. These failure issues limit the research and development of STT-MRAM to widely achieve commercial products. In this paper, we give a full analysis of failure mechanisms for PMA-MTJ and present some eventual solutions from device fabrication to system level integration to optimize the failure issues.

74 citations


Cites background from "Effect of MgO spacer and annealing ..."

  • ...In addition, inter-diffusion of elements during ex situ annealing also leads to rough interfaces [45], attenuation of magnetic characteristics and TMR ratio decreasing, which would cause serious failure issues that cannot be ignored....

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  • ...In addition, inter‐diffusion of elements during ex situ annealing also leads to rough interfaces [45], attenuation of magnetic characteristics and TMR ratio decreasing, which would cause serious failure issues that cannot be ignored....

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Journal ArticleDOI
TL;DR: In this article, an M-shaped curve is observed in the in-plane angular (0°−360°) dependent coercivity (ADC) by magneto-optical Kerr effect measurements.
Abstract: Angular dependent magnetization reversal has been investigated in Co2MnAl (CMA) full Heusler alloy thin films grown on Si(100) at different growth temperatures (Ts) by DC-magnetron sputtering. An M-shaped curve is observed in the in-plane angular (0°–360°) dependent coercivity (ADC) by magneto-optical Kerr effect measurements. The dependence of the magnetization reversal on Ts is investigated in detail to bring out the structure-property correlation with regards to ADC in these polycrystalline CMA thin films. This magnetization reversal ( M-shaped ADC behavior) is well described by the two-phase model, which is a combination of Kondorsky (domain wall motion) and Stoner Wohlfarth (coherent rotation) models. In this model, magnetization reversal starts with depinning of domain walls, with their gradual displacement explained by the Kondorsky model, and at a higher field (when the domain walls merge), the system follows coherent rotation before reaching its saturation following the Stoner Wohlfarth model. Fu...

23 citations

Posted Content
TL;DR: This paper presents all STT-MRAM failure mechanisms: manufacturing defects, extreme process variations, magnetic coupling,STT-switching stochasticity, and thermal fluctuation, and the resultant fault models including permanent faults and transient faults.
Abstract: As one of the most promising emerging non-volatile memory (NVM) technologies, spin-transfer torque magnetic random access memory (STT-MRAM) has attracted significant research attention due to several features such as high density, zero standby leakage, and nearly unlimited endurance. However, a high-quality test solution is required prior to the commercialization of STT-MRAM. In this paper, we present all STT-MRAM failure mechanisms: manufacturing defects, extreme process variations, magnetic coupling, STT-switching stochasticity, and thermal fluctuation. The resultant fault models including permanent faults and transient faults are classified and discussed. Moreover, the limited test algorithms and design-for-testability (DfT) designs proposed in the literature are also covered. It is clear that test solutions for STT-MRAMs are far from well established yet, especially when considering a defective part per billion (DPPB) level requirement. We present the main challenges on the STT-MRAM testing topic at three levels: failure mechanisms, fault modeling, and test/DfT designs.

13 citations


Cites background from "Effect of MgO spacer and annealing ..."

  • ...Worse still, diffusion of Ta from the seed layer to MgO layer has been reported in several papers [78,79], which scavenges O from MgO....

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Journal ArticleDOI
01 Apr 2017-Vacuum
TL;DR: In this paper, angle dependent near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to investigate the local electronic structure of magnetic Fe/MgO/Fe/Co multilayer structure.

11 citations

Journal ArticleDOI
TL;DR: In this paper, the in-plane azimuthal angular dependence of the magnetization reversal in the ion beam sputtered exchanged biased NiFe(111)/FeMn(1)/CoFeB(amorphous) stack was investigated.

8 citations

References
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Book
01 Jan 1973
TL;DR: CRC handbook of chemistry and physics, CRC Handbook of Chemistry and Physics, CRC handbook as discussed by the authors, CRC Handbook for Chemistry and Physiology, CRC Handbook for Physics,
Abstract: CRC handbook of chemistry and physics , CRC handbook of chemistry and physics , کتابخانه مرکزی دانشگاه علوم پزشکی تهران

52,268 citations

Journal ArticleDOI
TL;DR: b, R/R, is 11.8%, 20%, and 24%, respectively, consistent with Julliere's model based on the spin polarization of the conduction electrons of the magnetic films, in qualitative agreement with Slonczewski's model.
Abstract: Ferromagnetic-insulator-ferromagnetic tunneling has been measured in CoFe $/$A${\mathrm{l}}_{2}$${\mathrm{O}}_{3}$ $/$Co or NiFe junctions. At 295, 77, and 4.2 K the fractional change in junction resistance with magnetic field, $\ensuremath{\Delta}R/R$, is 11.8%, 20%, and 24%, respectively. The value at 4.2 K is consistent with Julliere's model based on the spin polarization of the conduction electrons of the magnetic films. $\ensuremath{\Delta}R/R$ changes little with a small voltage bias, whereas it decreases significantly at higher bias $(g0.1\mathrm{V})$, in qualitative agreement with Slonczewski's model. These junctions have potential use as low-power field sensors and memory elements.

3,285 citations

Journal ArticleDOI
TL;DR: A giant MR ratio up to 180% at room temperature in single-crystal Fe/MgO/Fe MTJs is reported, indicating that coherency of wave functions is conserved across the tunnel barrier.
Abstract: The tunnel magnetoresistance (TMR) effect in magnetic tunnel junctions (MTJs)1,2 is the key to developing magnetoresistive random-access-memory (MRAM), magnetic sensors and novel programmable logic devices3,4,5. Conventional MTJs with an amorphous aluminium oxide tunnel barrier, which have been extensively studied for device applications, exhibit a magnetoresistance ratio up to 70% at room temperature6. This low magnetoresistance seriously limits the feasibility of spintronics devices. Here, we report a giant MR ratio up to 180% at room temperature in single-crystal Fe/MgO/Fe MTJs. The origin of this enormous TMR effect is coherent spin-polarized tunnelling, where the symmetry of electron wave functions plays an important role. Moreover, we observed that their tunnel magnetoresistance oscillates as a function of tunnel barrier thickness, indicating that coherency of wave functions is conserved across the tunnel barrier. The coherent TMR effect is a key to making spintronic devices with novel quantum-mechanical functions, and to developing gigabit-scale MRAM.

2,956 citations

Journal ArticleDOI
TL;DR: Sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to ∼220% at room temperature and ∼300% at low temperatures, which will accelerate the development of new families of spintronic devices.
Abstract: Magnetically engineered magnetic tunnel junctions (MTJs) show promise as non-volatile storage cells in high-performance solid-state magnetic random access memories (MRAM). The performance of these devices is currently limited by the modest (< approximately 70%) room-temperature tunnelling magnetoresistance (TMR) of technologically relevant MTJs. Much higher TMR values have been theoretically predicted for perfectly ordered (100) oriented single-crystalline Fe/MgO/Fe MTJs. Here we show that sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented (100) MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to approximately 220% at room temperature and approximately 300% at low temperatures. Consistent with these high TMR values, superconducting tunnelling spectroscopy experiments indicate that the tunnelling current has a very high spin polarization of approximately 85%, which rivals that previously observed only using half-metallic ferromagnets. Such high values of spin polarization and TMR in readily manufactureable and highly thermally stable devices (up to 400 degrees C) will accelerate the development of new families of spintronic devices.

2,931 citations

Journal ArticleDOI
TL;DR: In this paper, first-principles based calculations of the tunneling conductance and magnetoconductance of epitaxial ''mathrm{Fe}(100)|\mathm{MgO''(100), ''mgO''.
Abstract: We present first-principles based calculations of the tunneling conductance and magnetoconductance of epitaxial $\mathrm{Fe}(100)|\mathrm{MgO}(100)|\mathrm{Fe}(100)$ sandwiches. Our results indicate that tunneling is much more interesting and complicated than the simple barrier model used previously. We obtain the following general results: (1) Tunneling conductance depends strongly on the symmetry of the Bloch states in the electrodes and of the evanescent states in the barrier layer. (2) Bloch states of different symmetry decay at different rates within the barrier. The decay rate is determined by the complex energy bands of the same symmetry in the barrier. (3) There may be quantum interference between the decaying states in the barrier. This leads to an oscillatory dependence of the tunneling current on ${k}_{\ensuremath{\Vert}}$ and a damped oscillatory dependence on barrier thickness. (4) Interfacial resonance states can allow particular Bloch states to tunnel efficiently through the barrier. For $\mathrm{Fe}(100)|\mathrm{MgO}(100)|\mathrm{Fe}(100)$ our calculations indicate that quite different tunneling mechanisms dominate the conductance in the two spin channels. In the majority channel the conductance is primarily via Bloch electrons with small transverse momentum. One particular state with ${\ensuremath{\Delta}}_{1}$ symmetry is able to effectively couple from the Fe into the MgO. In the minority channel the conductance is primarily through interface resonance states especially for thinner layers. We predict a large magnetoresistance that increases with barrier thickness.

1,823 citations