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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Characteristics of magnetic tunnel junctions consisting of amorphous CoNbZr layers

Byong Sun Chun, Seong-Rae Lee, and Young Keun Kim

J. Appl. Phys. 93, 8361 (2003); http://dx.doi.org/10.1063/1.1558240 (3 pages) | Cited 7 times

Online Publication Date: 9 May 2003

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Magnetic tunnel junctions comprising amorphous CoNbZr layers have been investigated. Co85.5Nb8Zr6.5 (in at. %) layers were employed to substitute traditionally used Ta layers with an emphasis given on understanding underlayer effect. The typical junction structure was SiO2/CoNbZr or Ta 2/CoFe 8/IrMn 7.5/CoFe 3/Al 1.6+oxidation/CoFe 3/CoNbZr or Ta 2 (nm). For both as-deposited state and after annealing, the CoNbZr-underlayered structure showed superior surface smoothness up to the tunnel barrier than Ta-underlayered one (0.16 vs 0.34 nm). Ultrasmooth layer structure was proven beneficial for reducing temperature-dependent magnetoresistance properties. A longer annealing degraded the properties most likely due to Mn interdiffusion toward the bottom ferromagnetic electrode as confirmed by Auger electron spectroscopy. By a slight change in the bottom electrode thickness (CoNbZr 4/CoFe 10), the tunneling magnetoresistance ratio can be increased up to 32% after 10 min annealing at 300 °C. © 2003 American Institute of Physics.
Show PACS
75.45.+j Macroscopic quantum phenomena in magnetic systems
75.47.Np Metals and alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
68.35.Fx Diffusion; interface formation
75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions

Junction area dependence of breakdown characteristics in magnetic tunnel junctions

Kwang-Seok Kim, B. K. Cho, T. W. Kim, and W. J. Park

J. Appl. Phys. 93, 8364 (2003); http://dx.doi.org/10.1063/1.1540057 (3 pages) | Cited 8 times

Online Publication Date: 9 May 2003

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Breakdown characteristics of the magnetic tunnel junctions (MTJ) with different junction areas of S=200 μm2 and S=0.5 μm2 are investigated under constant voltage stress. The breakdown process is found to be quite different for the two junction areas. For the large junctions with S=200 μm2, magnetoresistance (MR) ratio decreases gradually with increasing time of constant voltage stress and lasts for 10–30 min. The low frequency 1/f noise power also increases with increasing stress time due to the Johnson and shot noises, caused by current flowing through ohmic shorts or pinholes across tunnel barrier. Meanwhile, the junctions with S=0.5 μm2 show abrupt junction breakdown after stress time of 1–7 h. There is no significant change in both MR ratio and its bias dependence during the voltage stress. In particular, soft-breakdown events are observed before total breakdown occurs. The junction breakdown of small junction area is of intrinsic nature of the junction while the one of large junction area is due to extrinsic factors. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
72.25.Mk Spin transport through interfaces
77.22.Jp Dielectric breakdown and space-charge effects
75.45.+j Macroscopic quantum phenomena in magnetic systems

Continuous thin barriers for low-resistance spin-dependent tunnel junctions

Jianguo Wang, Yaowen Liu, P. P. Freitas, E. Snoeck, and J. L. Martins

J. Appl. Phys. 93, 8367 (2003); http://dx.doi.org/10.1063/1.1555972 (3 pages) | Cited 14 times

Online Publication Date: 9 May 2003

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The occurrence of pinholes in thin barrier low-resistance junctions degrades the TMR signal and increases the coupling field between pinned and free layers. The tunnel junction coupling field (Hf), junction resistance and TMR signal dependence on the barrier thickness was studied for various types of barriers (HfOx,HfAlOx,ZrAlOx,AlOx). Micromagnetic simulation was employed to simulate the coupling field versus pinhole density. From the coupling field results, HfOx makes the thinnest continuous barriers, followed by doped HfAlOx and ZrAlOx, and then AlOx. HfAlOx and ZrAlOx offer the best compromise between low resistance (1–5 Ω μm2) and reasonable TMR (12%–14%). Pure HfOx can be made with R×A products of 0.4 Ω μm2 but the TMR does not exceed 5.5%. © 2003 American Institute of Physics.
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75.47.Np Metals and alloys
72.25.Mk Spin transport through interfaces
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
75.30.Et Exchange and superexchange interactions

Hard mask fabrication for magnetic random access memory elements using focused ion beam assisted selective chemical vapor deposition

H. Kubota, M. Hamada, Y. Ando, and T. Miyazaki

J. Appl. Phys. 93, 8370 (2003); http://dx.doi.org/10.1063/1.1540058 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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The fabrication of carbon masks for very small magnetic tunnel junctions (MTJs) was investigated using focused ion beam assisted selective chemical vapor deposition. Gaseous phenanthrene, absorbed on the sample surface, was decomposed into solid carbon by irradiation with a Ga ion beam. The carbon layer deposited showed a lower (higher) etching rate for Ar (O2) ion etching. The width of the carbon mask patterns varied from about 30 to 500 nm. Arrays of MTJs with size on the 100 nm scale were fabricated successfully using the carbon mask patterns. © 2003 American Institute of Physics.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf Surface cleaning, etching, patterning
81.05.U- Carbon/carbon-based materials
52.77.Bn Etching and cleaning
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
85.40.Sz Deposition technology
85.75.Ff Reprogrammable magnetic logic

Development and process control of magnetic tunnel junctions for magnetic random access memory devices

Witold Kula, Jerome Wolfman, Kamel Ounadjela, Eugene Chen, and William Koutny

J. Appl. Phys. 93, 8373 (2003); http://dx.doi.org/10.1063/1.1558241 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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We report on the development and process control of magnetic tunnel junctions (MTJs) for magnetic random access memory (MRAM) devices. It is demonstrated that MTJs with high magnetoresistance ∼40% at 300 mV, resistance–area product (RA) ∼1–3 kΩ μm2, low intrinsic interlayer coupling (Hin) ∼2–3 Oe, and excellent bit switching characteristics can be developed and fully integrated with complementary metal–oxide–semiconductor circuitry into MRAM devices. MTJ uniformity and repeatability level suitable for mass production has been demonstrated with the advanced processing and monitoring techniques. © 2003 American Institute of Physics.
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85.75.Dd Magnetic memory using magnetic tunnel junctions
75.45.+j Macroscopic quantum phenomena in magnetic systems
75.47.Np Metals and alloys
85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits

On the shape optimization of magnetic random access memory element design

Xiaochun Zhu and Jian-Gang Zhu

J. Appl. Phys. 93, 8376 (2003); http://dx.doi.org/10.1063/1.1555973 (3 pages) | Cited 7 times

Online Publication Date: 9 May 2003

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In designing the shape of magnetic random access memory elements, a sufficient difference in switching current threshold between a full-select element and a half-select memory element is critical. In this article, we present a systematic micromagnetic study of the margin of switching threshold for two specific shapes: eye shaped and ellipse. It is found that at small magnetic thickness, the eye-shaped element exhibits a higher switching threshold margin than the ellipse. However, for relatively thick storage layers, the opposite becomes true. The switching threshold is also a strong function of the initial magnetization state for the ellipse. © 2003 American Institute of Physics.
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85.75.Dd Magnetic memory using magnetic tunnel junctions
75.47.Np Metals and alloys
75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Magnetic tunnel junction pattern technique

Eugene Chen, Benjamin Schwarz, Chang Ju Choi, Witold Kula, Jerome Wolfman, Kamel Ounadjela, and Sam Geha

J. Appl. Phys. 93, 8379 (2003); http://dx.doi.org/10.1063/1.1543867 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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We have developed a magnetic tunnel junction (MTJ) pattern technique that involves transforming the magnetic layer above the tunnel barrier in unwanted areas into an insulator, thus providing insulation between different MTJ devices without suffering common tunnel barrier shorting problems. With this technique, 90%–100% yielding MTJ devices have been observed. MTJ results using this process are superior to an etching based process. Switching distribution of patterned magnetic bits is also narrower using this novel technique. Process control and the ability to stop on the tunnel barrier have been demonstrated. © 2003 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.Dd Magnetic memory using magnetic tunnel junctions

Chopping techniques for low-frequency nanotesla spin-dependent tunneling field sensors

A. Jander, C. A. Nordman, A. V. Pohm, and J. M. Anderson

J. Appl. Phys. 93, 8382 (2003); http://dx.doi.org/10.1063/1.1555975 (3 pages) | Cited 8 times

Online Publication Date: 9 May 2003

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Three chopping techniques to address 1/f noise in spin-dependent tunneling magnetoresistive sensors are investigated. These include modulation of the sensitivity using orthogonal fields, modulation, and second-harmonic generation using the nonlinear response of the magnetoresistive element and modulation of the flux concentrator permeability. Of these, only the second technique resulted in a slight reduction in low-frequency noise. In order to achieve significant noise reduction by chopping, domain noise will have to be reduced. © 2003 American Institute of Physics.
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85.75.Ss Magnetic field sensors using spin polarized transport
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Current-induced switching in low resistance magnetic tunnel junctions

Yaowen Liu, Zongzhi Zhang, Jianguo Wang, P. P. Freitas, and J. L. Martins

J. Appl. Phys. 93, 8385 (2003); http://dx.doi.org/10.1063/1.1543868 (3 pages) | Cited 20 times

Online Publication Date: 9 May 2003

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Current-induced magnetization switching (CIMS) in low resistance tunnel junctions is reported at critical current densities of 1.9×106 A/cm2 for tunnel junction areas ranging from 2 to 3 μm2, and junction resistances from 6 to 20 Ω μm2. Typical tunnel magnetic resistance values for these junctions range from 15% to 21% (measured in an external magnetic field) and 10% to 14% resistance changes are obtained by CIMS. Micromagnetic simulation indicates that vortex fields and spin transfer effects cannot fully account for the observed current-induced switching. Although able to explain the observed transition from a parallel or antiparallel state to a vortex state, it fails to explain the switch back to the original state, at a comparable but symmetrical critical current density. © 2003 American Institute of Physics.
Show PACS
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.70.Ay Magnetic device characterization, design, and modeling
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
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