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Publications (17)22.88 Total impact

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    ABSTRACT: Read heads using current-perpendicular-to-plane (CPP) giant magnetoresistance sensors have been fabricated and tested under high-density recording conditions. A magnetoresistance of 5.5% and shield-to-shield spacing of 45 nm have been achieved by using an all-metal single-spin-valve with Heusler-alloy-based free and reference magnetic layers. Read heads with magnetic read widths ~45 nm were tested on perpendicular media, resulting in signals above 1 mV and signal-to-noise ratio ~30 dB. Linear densities in excess of 1050 kbpi were achieved with thermal fly-height control, compatible with recording areal densities of ~400 Gb/in<sup>2</sup>. Current-induced spin-torque effects in the recording head were observed to result in rapid performance degradation above a threshold bias voltage of about 75 mV, corresponding to current densities >10<sup>8</sup> A/cm<sup>2</sup>.
    Full-text · Article · Feb 2008 · IEEE Transactions on Magnetics

  • No preview · Article · Jan 2005
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    ABSTRACT: Doping ferromagnetic nickel–iron alloys with chromium causes the Curie temperature to be reduced. We have demonstrated that solid state solutions of Ni–Fe–Cr can be formed by implanting Cr ions into ferromagnetic NiFe alloy films, thus creating paramagnetic films. We find that the magnetic moment and coercivity decrease steadily with Cr+ dose, reaching zero at room temperature with the onset of paramagnetism. Using Cr+ implantation in conjunction with a lithographic mask we have patterned continuous Ni80Fe20 films into separate regions that are ferromagnetic and paramagnetic at room temperature. This magnetic patterning process may have applications for the manufacture of magnetic write heads, such as for the notching process used to constrain the stray field from the write gap.
    No preview · Article · Oct 2003 · Journal of Physics D Applied Physics
  • M. Tsoi · R. E. Fontana · S. S. P. Parkin
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    ABSTRACT: The current-induced propagation of magnetic domain walls is studied in CoFe nanoconstrictions patterned by electron beam lithography. Propagation of the walls was confirmed by magnetic force microscopy imaging. The device geometry allows us to distinguish between various mechanisms of interaction between electric current and domain walls: a mechanism in which spin transfer associated with current traversing a domain wall dominates. As expected for such a mechanism the domain wall propagation occurs in the direction of electron current flow and has a current threshold of the order ∼ 1011 A/m2. © 2003 American Institute of Physics.
    No preview · Article · Sep 2003 · Applied Physics Letters
  • J. R. Childress · J.-S. Py · M. K. Ho · R. E. Fontana · BA Gurney
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    ABSTRACT: The properties of magnetic tunnel junctions with aluminum oxide barriers alloyed with boron are presented. When aluminum is deposited by sputtering, 10 at. % B addition is sufficient to completely transform the deposited Al film from crystalline to amorphous. We have investigated if the deposition of amorphous AlB prior to oxidation results in a variation of tunnel-valve properties. It is found that ultrathin Al90B10 films can be readily oxidized using a procedure similar to that for Al films, resulting in tunnel valves with good magnetic properties. In the ultrathin regime (when the specific junction resistance is Rj
    No preview · Article · May 2003 · Journal of Applied Physics
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    ABSTRACT: In this article, we discuss practical factors in the application of TEM as part of development of processing of magnetic nanostructures.
    No preview · Conference Paper · Jan 2003
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    ABSTRACT: In this work, to achieve practical tunnel-valve sensors for recording, the specific junction resistance of the tunnel barrier must be reduced.
    No preview · Article · Jan 2003
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    ABSTRACT: Magnetic head fabrication for 100 Gbit/in. 2 areal density requires minimum lithographic feature size 0.15 m, with aspect ratios of 8:1–10:1. Electron-beam lithography can provide adequate resolution for research and development of magnetic heads, and at 100 kV can provide greater than 10:1 aspect ratios in 1–3 m thick single-layer resist polymethylmethacrylate. Poly methylmethacrylate PMMA is well known for withstanding the rigors of plating baths, but at these thicknesses requires a nonswelling, low-stress developer such as the LIGA mixture also known as ''GG Developer U.S. Patent No. 4,393,129''. In this work we present the results of isopropyl alcohol:water development for thick PMMA, and describe the dependence of resist contrast on the temperature of the developer. We also demonstrate the advantage of ultrasonic agitation during development. These development techniques have brought resist profiles in PMMA to the theoretical limit predicted by Monte Carlo simulations. © 2002 American Vacuum Society.
    Full-text · Article · Nov 2002 · Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures
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    ABSTRACT: Magnetic recording areal densities using magnetoresistive (MR) head technology are increasing at annual rates in excess of 60% per year and in some applications as great as 100% per year. Today, the critical features of the thin-film head can be patterned with the same optical lithography techniques used by the semiconductor industry. However, with the assumption that areal density increases in magnetic recording are maintained, within the next rive years, thin-film head lithography requirements will exceed semiconductor roadmap projections. This paper describes the use of e-beam lithography as an alternative to optical lithography for the fabrication of critical features in the thin-film head. In particular, the unique geometry of the head structure, the low density of critical head features on the wafer, and the relatively low wafer volume requirements for thin-film heads allow e-beam lithography to become a viable manufacturing alternative for thin-film head fabrication. More important, e-beam lithography is ideally suited for producing thin-film head structures at a development level prior to the optimization of manufacturable optical processing.
    No preview · Article · Feb 2002 · IEEE Transactions on Magnetics
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    ABSTRACT: We have investigated the use of ultrathin Al2O3 barriers to fabricate low-resistance tunnel-valve sensors suitable for recording heads. Tunnel valves of the type underlayer/(IrMn or PtMn)/CoFe/Al2O3/CoFe/NiFe/Cap layer have been fabricated by magnetron sputtering. Tunnel barriers are formed by Al metal deposition followed by in situ oxidation, and tunnel-junction test devices are built by photolithography with areas down to 1×1 mum2. Specific resistances as low as 13 Omega mum2 with 25% tunnel magnetoresistance have been obtained using Al thicknesses of 6-7 Å.
    Full-text · Article · Jun 2001 · Journal of Applied Physics
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    ABSTRACT: Nonoxide tunnel barriers such as AlN are of interest for magnetic tunnel junctions to avoid the oxidation of the magnetic electrodes. We have investigated the fabrication and properties of thin AlN-based barriers for use in low resistance magnetic tunnel junctions. Electronic, magnetic and structural data of tunnel valves of the form Ta (100 Å)/PtMn (300 Å)/CoFe20 (20 Å–25 Å)/barrier/CoFe20 (10–20 Å)/NiFe16 (35–40 Å)/Ta (100 Å) are presented, where the barrier consists of AlN, AlNxOy or AlN/AlOx with total thicknesses between 8 and 15 Å. The tunnel junctions were sputter deposited and then lithographically patterned down to 2×2 μm2 devices. AlN was deposited by reactive sputtering from an Al target with 20%–35% N2 in the Ar sputter gas at room temperature, resulting in stoichiometric growth of AlNx (x=0.50±0.05), as determined by RBS. TEM analysis shows that the as-deposited AlN barrier is crystalline. For AlN barriers and AlN followed by natural O2 oxidation, we obtain tunnel magnetoresistance >10% with specific junction resistance Rj down to 60 Ωμm2. © 2001 American Institute of Physics.
    No preview · Article · May 2001 · Journal of Applied Physics
  • K.-S. Moon · R. E. Fontana · S. S. P. Parkin
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    ABSTRACT: Magnetic tunnel junction structures comprising a ferromagnetic layer pinned by exchange biasing and a “free” ferromagnetic layer were prepared using dc-magnetron sputtering and patterned with conventional optical lithography. Structures were prepared, square and rectangular in shape, with various widths and lengths. It was observed that the magnetic properties of the free layer vary systematically with the size of the junction. In particular, the offset field of the free-layer magnetic hysteresis loop, as measured resistively, is controlled by a combination of magnetostatic and ferromagnetic coupling between the pinned and free layers. © 1999 American Institute of Physics.  
    No preview · Article · Jul 1999 · Applied Physics Letters
  • C. H. Tsang · Fontana, R.E., Jr · T. Lin · D. E. Heim · BA Gurney · M. L. Williams
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    ABSTRACT: Since the early 1990s, the introduction of dual-element recording heads with inductive write elements and magnetoresistive (MR) read elements has almost doubled the rate of areal density improvements for hard-disk-drive data storage products. In the past several years, prospects of even more rapid performance improvements have been made possible by the discovery and development of sensors based on the giant magnetoresistance (GMR) effect, also known as the spin-valve effect, for a particular class of sensor configurations. In this paper, we explore the potentials as well as challenges of spin-valve sensors as magnetic recording read heads. We first examine the data rate and areal density potentials of large read-back signals resulting from increases in the MR coefficient. We then discuss associated magnetic sensor performance, including linearity and noise suppression. Finally, we study in detail the magnetic and recording performance of a spin-valve read head designed for 1-Gb/in.<sup>2</sup>density performance.
    No preview · Article · Feb 1998 · Ibm Journal of Research and Development
  • S. S. P. Parkin · R. E. Fontana · AC Marley
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    ABSTRACT: Interest in magnetic tunnel junctions(MTJ) has been increased by the recent observation of large room-temperature magnetoresistance(MR) in structures comprised of sandwiches of two ferromagnetic(FM) layers with different coercivities separated by a thin Al 2 O 3 tunnel barrier. Using an ultrahigh vacuum dc magnetron sputtering system, a variety of MTJ structures have been explored. Junctions were fabricated directly using computer-controlled placement of successive contact masks, and by patterning using optical lithography techniques and processes, compatible with MR head structures. Structures were prepared in which one of the FM layers is exchange biased with an antiferromagnet MnFe layer. Thus, the junctions exhibit two well-defined magnetic states in which the FM layers are either parallel or antiparallel to one another. The tunnel barrier was prepared by in situplasmaoxidation of thin Al layers sputter deposited at room temperature. Using FM layers comprised of Co or permalloy ( Ni 81 Fe 19 ) , MR values exceeding 30% were obtained at room temperature in low fields (5–10 Oe ) . Similar magnetic and MR properties are found in junctions ranging in size from 80×80 μ m 2 (contact masks) to 2×2 μ m 2 (lithography). The smallest junctions, of area 2×2 μ m 2 , have resistance values of ∼5 M Ω and 25% MR. Thus, changes in resistance of ∼1 M Ω are found. Such structures may form an excellent magnetic switch. However, for many device applications, much lower resistances are required. The junction resistance can readily be varied by several orders of magnitude by varying the thickness and oxidation conditions of the Al layer as well as by varying the thicknesses and nature of the layers within the electrodes themselves. Note that it is important that the voltage drop laterally across the electrodes must be small compared to that across the tunnel barrier itself. This requires measurement of junctions with low sheet resistances in lithographically patterned devices.
    No preview · Article · May 1997 · Journal of Applied Physics
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    ABSTRACT: The effects of ion beam irradiation on the magnetic properties of thin Permalloy films have been examined experimentally, using the ion species He+, Ar+, Xe+, C+, N+, O+ and Si+, at energies chosen either to implant within the film or to produce kinetic effects in the film during transmission. Hysteresis loop parameters, magnetoresistance measurements and XRD were used to characterize the samples before and after exposure. The principal results seen were a loss of uniaxial anisotropy and an increase of coercivity, being attributed to collisional damage of the Permalloy lattice structure and the introduction of extended defects. Effects of film stress and implanted impurities were also identified.
    No preview · Article · Jan 1997 · Materials Science Forum
  • D.D. Tang · P.K. Wang · V.S. Speriosu · S. Le · R.E. Fontana · S. Rishton
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    ABSTRACT: This paper presents the characteristics of a silicon IC process compatible, nonvolatile memory. The basic storage element is a thin-film stripe that consists of a pair of 9-nm ferromagnetic (NiFe) layers spaced with 2.2-2.5 nm of non-magnetic Cu film. The magnetization, M, of one of the layers is pinned along the longitudinal direction of the stripe with an antiferromagnetic material (FeMn), while the M of the other layer is free to rotate. This structure is known as a spin valve. When the Ms of the pair are in the same (parallel) direction, the resistance is lower than when they are in the opposite (anti-parallel) direction by 5-8%. This property is well known as the giant magneto-resistive effect. The memory cell is made up of a storage resistor stripe and the x/y select wires, typically 100 nm thick. The current pulses in the select wires generate a vector sum of magnetic field that switches the cell state. The switching field in the longitudinal direction is lowered when a transverse field is applied. The memory cells were fabricated on thermal oxide on silicon wafers. The sputter deposition and etch process of the spin valve does not affect the leakage nor does it alter the Vt of FETs, and thus may be integrated into the metallization steps of the silicon wafer processing
    No preview · Conference Paper · Jan 1996
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    ABSTRACT: Not Available
    No preview · Conference Paper · Aug 1995