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RESEARCH EXPERTISE

  1. MAGNETIC THIN FILM MEDIA:

    Deposition of high-coercivity and low-noise multi-layer ultra-thin magnetic materials,underlayers, and protective wear-resistant overcoatings on rigid disks and flexible substrates with controlled compositions and microstructures. Correlation of the micro and nano-scale physical and magnetic structures with the macro-magnetic properties, recording performance, intrinsic media noise.(JUDY, SIVERTSEN)

  2. MAGNETIC THIN FILM HEADS, SENSORS, AND MEMORIES:

    Deposition of low-coercivity, high-saturation flux density, and anisotropic high-permeability multi-layer ultra-thin film magnetic materials with controlled compositions and microstructures. Correlation of the physical and magnetic structures with the static and dynamic macromagnetic properties, magnetic domain instabilities, and device sensitivities.(JUDY, SIVERTSEN)

  3. MAGNETIC MEASUREMENT TECHNIQUES:

    Develop new ex-situ and in-situ measurement techniques for characterizing the macro, micro, and nano-scale physical and magnetic properties, and limiting mechanisms of high-speed switching and high-frequency magnetic recording, overwriting, and reproduction in ultra-thin film materials used for heads and media in ultra-high density recording storage applications.(JUDY, SIVERTSEN, VICTORA)

  4. MICROMAGNETIC MODELING:

    Develop 2-D and 3-D computer and large-scale models of ultra-thin film magnetic recording media and heads, writing, overwriting, and reading processes, transition noise, ultra-narrow-track-edge noise, and performance of magnetic sensors and memories taking into account anisotropic exchange, magnetostatic, magnetocrystalline, and magnetoelastic energy interactions.(VICTORA)

  5. MAGNETIC RECORDING AND SIGNAL PROCESSING:

    Measurements of fundamental magnetic recording processes at high areal densities. Characterizations of recording channels for optimizing coding and signal processing. Development of practical data recovery techniques well-suited to high-density, high-speed magnetic recording systems taking into account effects of transition noise, timing jitter, track edge noise, track misregistration, and channel variations. (JUDY, MOON).

  6. TRIBOLOGY OF HEAD-DISK INTERFACE:

    Develop 2-D and 3-D computer models of tribology based on measurements stiction, friction, and wear of the head-disk interface of thin film magnetic recording media and heads taking into account effects of surface roughness, grain size, and intrinsic and applied stresses. Correlate stiction, friction, and wear with mechanical properties, surface roughness, interface adhesion, elastic moduli, microhardness, fracture toughness, and corrosion.of thin films and alternative substrates (SIVERTSEN, JUDY)

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RESEARCH ACCOMPLISHMENTS

  1. Thin Film Media
    • Study of Effects Nitrogen and Initial Layer in RF-Sputtered Perpendicular CoCr Thin Films (1982, 1984)
    • Directly RF-Sputtered Gamma Ferric Oxide Thin Films from a Magnetite Target (1984)
    • Epitaxial Growth of Single Crystal Perpendicular CoCr Thin Films by RF-Sputtering (1984)
    • Effects of C3O4 Seed Layers on Perpendicular Magnetic Anisotropy of RF-Sputtered CoCr Thin Films (1985)
    • Effective Expitaxial Thickness of RF-Sputtered Longitudinal CoCrTa/Cr Thin Films (1989)
    • Effects of Substrate Bias on Magnetic and Recording Properties of Longitudinal CoCrTa/Cr Thin Films (1990)
    • Magnetic Properties and Remanent Magnetization of Quaternery CoCrPtB/Cr Thin Films (1993)
    • Effect of Substrate Temp on Microstructure and Noise of Quaternery CoCrTaPt/Cr Thin Film Media (1993)
    • Analysis of Electronic Structure of CoCrPt Films Using Parallel Electron Energy Loss Spectroscopy (1993)
    • Advanced Multilayer Thin Films for Ultra-High-Density Magnetic Recording Thin Film Media (1994)
    • Intergranular Interactions and Structures of Multilayer CoCrPt/CoCrTa/Cr Thin Film Media (1995)
  2. Measurements
    • TEM Micromagnetic Structures of Recorded Transitions in High-Coercivity CoCrTa/Cr Thin Films (1991)
    • Method for Investigating the Switching Modes of Isolated Ba-Ferrite Fine Particles Utilizing MFM (1993)
    • Measurements of Magnetic Recording on High Coercivity Media Using Magnetic Force Microscopy (1996)
    • Impedance Measurements of Inductive Write and MR Read Heads using a Network Analyzer (1998)
    • Measurements of Nanosecond Transient Response of Soft Ferromagnetic Thin Films (1999)
  3. Recording
    • Read Flux Noise Measurements of DC-Erased Rigid Disk Media Using Autocorrelation (1990)
    • Correlation Length of Magnetization Fluctuations and Reverse DC Erase Noise of CoCrTa/Cr Media (1991)
    • Magnetization Cross-Track Correlations and Transition Noise of Longitudinal Thin Film Media (1993)
    • Comparison of Reproduce Signal and Noise of Conventional and Keepered Thin Film Media (1993)
    • Magnetic Force Microscopy Study of High Coercivity Perpendicular & Longitudinal Thin Film Media (1995)
    • Advancements and Limitations of High-Coercivity and Low-Noise Longitudinal Thin Film Media (1996)
  4. Tribology
    • Initiation of Sliding Wear Damage of the Head-Disk Interface at Very Low Rotational Velocity (1988)
    • Study of Effect of Nitrogen Sputtering Gas on Durability and Structure of Carbon Thin Films (1989-1993)
    • Durability and Structure Studies of RF-Sputtered CN Thin Film Overcoats on Thin Film Media (1991)
    • Comparison of Tribological Performance of Pure C and CN Coated Thin Film Head Sliders (1995)
  5. Read Signal/Noise Characterization
    • System level modeling of nonadditive transition noise and nonlinearities
    • Investigation of media noise/nonlinearity effects on various coding/detection schemes
    • Development of a parametric read signal simulator (NSIC standard known as "Nair-Moon Model")
  6. Data Detection/Equalization
    • Development of FDTS/DF idea as a suboptimal detector well-suited for ultra-high density recording
    • Development of modified PR4ML to improve immunity against jitter
    • Develpment of DFE with pattern-dependent threshold to improve BER in presence of severe nonlinearity
    • Develpment of a reduced complexcity EPR4ML
    • Develpment of nonlinear equalizers for PRML to improve BER in the presence of severe noise & nonlinearity
    • Develpment of fast adaptive equalizers based on knowledge-based channel identification
  7. Coding
    • Recent development of maximum transition-run (MTR) coding to improve distance properties of sequence detectors at high densities

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RESEARCH PROJECTS

  1. UNDERGRADUATE CO-OP STUDENTS (8)
    • High Frequency Properties Thin Film Head Materials, Electrical Eng. ,RHO
    • Structural PropertiesThin Film Head Materials , Materials Science, RHO
    • High Frequency Permeability & Switching Thin Film Heads, Electrical Eng. , RHO
    • Uniformity of Magnetic Properties of Thin Film Disk Media , Materials Science , TCO
    • SNR and BER of Narrow-Track Magnetic Recording , Electrical Eng., TCO
    • Tribology of DLC Films of CH & CN on Media & Sliders , Materials Science , TCO
    • Manufacture of Sputtered Multilayer Thin Film Media , Electrical Eng. , RMG
    • Structural & Mangetic Properties Multilayer Thin Film Media , Materials Science , RMG
  2. MASTER OF SCIENCE GRADUATE STUDENT INTERNSHIPS (12)
    • Sputtering New Pinning Layers for GMR Spin Valve Heads , Judy, Sivertsen , RHO
    • Sputtering High Bs Thin Film Head Materials (FeNC,CoZrTa) , Judy, Sivertsen RHO
    • Optimizing Sensitivity & Reliability GMR Spin Valve Heads , Judy, Sivertsen , RHO
    • Plating High Bs Thin Film Head Materials(Ni50Fe50,NiFeCo) , Smyrl, Sivertsen , RHO
    • High-Frequency & High-Speed Switching of TF Write Heads , Judy, Gopinath , RHO
    • Limitations of Optical Lithography for MR/GMR/TMR Heads, Campbell, Judy, RHO
    • Measurement Uniformity and Temperature Dependence of Hcr, Judy, Sivertsen, TCO
    • Correlation of Bit-Error-Rate with Defects of Thin Film Media, Moon, Judy , TCO
    • Tribology FTS Sputtered Ultra-Thin CH/CN on Media/Sliders , Judy, Sivertsen ,TCO
    • High-Precision High-SpeedTwo-Stage Head-Gimbol Actuators , Polla, Judy , TCO
    • Sputtered Higher-Coercivity & Lower-Noise Thin Film Media , Judy, Sivertsen , TCO
    • Measurement & Modeling CoZrNb Keepered Thin Film Media , Judy, Sivertsen , RMG
  3. PH.D. GRADUATE STUDENT INTERNSHIPS (8)
    • UHV Sputtered Multilayers High Bs Thin Film Head Materials, Judy, Siversten, RHO
    • UHV Sputtered Multilayers GMR & TMR S-V Head Materials, Judy, Sivertsen, RHO
    • Micromagnetics Modeling High Bs, GMR/TMR S-V Heads, Judy, Sivertsen, RHO
    • Measurements & Modeling High-Speed Switching TF Heads, Judy, Sivertsen, RHO
    • UHV Sputtered Ultra-Thin Ultra-Low-Noise Thin Film Media, Judy, Sivertsen, RMG
    • Measurement & Modeling Micromagnetics Thin Film Media, Judy, Sivertsen, RMG
    • Measurement & Modeling Thermal-Time Decay Recorded Bits, Judy, Sivertsen, RMG
    • Fabrication/Testing/Modeling Nano-Patterned Thin Film Media, Judy, Gopinath, RMG

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 PROPOSED RESEARCH PROJECTS

  1. Ultra-High-Vacuum Multi-Target Co-Sputtering of Films for Heads and Media (Jack Judy, John Sivertsen, MINT, TEL: 612-625-7381)

    As the multilayer film thickness of magnetoresistive (MR),giant magnetoresistive (GMR) spin-valve heads, inductive heads, and thin film media approach that of a few monolayers (10-100 Å), the grain size and thickness uniformity becomes a very sensitive function of the cleanliness and atomic roughness of the surface of the substrate. The presence of water vapor and other residual gases on the surface of the substrate and films can have a profound effect on the morphology, grain size, and defects of the resulting films. Only with an ultra-high-vacuum (UHV) system can these effects be controlled and studied to determine the limiting physical processes involved and the vacuum quality required in manufacturing deposition equipment to fabricate reproducible low-defect and low-noise films for future heads and media. We propose to utilize a molecular beam epitaxy (MBE) evaporation system retrofitted to be an 8-target computer controlled co-sputtering system to carry out this proposed research to understand and optimize depositiion of multilayer multicomponent future generation thin films for heads and media.

  2. Comparison of Proximity-Recorded Longitudinal & Perpendicular Thin Film Media (Jack Judy, John Sivertsen, MINT, TEL: 612-625-7381)

    As the recording density required to meet the rapidly increasing capacity demanded of small disk drives approaches ultra-high densities (UHD) of 10 -100 Gigabits/square-inch, the physical separation or flying height between the head and disk surface must be reduced to be essentially in-contact. It has not yet been established experimentally whether in-contact perpendicular recording has any particular intrinsic advantage over in-contact longitudinal recording other than capability of storing much higher densities in thicker media. We propose to fabricate the thin film media required and use available narrow-track high-moment pole tip thin film heads (Seagate, Read-Rite, Silmag, Quantum) and single-pole (Silmag, Seagate) heads to compare the UHDR proximity recording performance of multilayer longitudinal and perpendicular media as a function of fly-height right down to contact in terms of signal amplitude, pulse width, non-linear bit shift, overwrite, noise, signal-to-noise, and bit-error-rate. In-situ magnetic force microscopy (MFM) will be used to measure minimum switching volumes of magnetic cluster domains.

  3. High-Speed Switching and High-Frequency Performance of Thin Film Heads & Thin Film Media (Jack Judy, John Sivertsen, MINT, TEL: 612-625-7381)

    As the data rate required for future generation magnetic recording disk drives approaches several hundred meagabits per second(240 Mb/s), the switching times required for the heads and media are approaching a few nanoseconds which is close to the limiting time determined by gryoscopic dynamics. New measurements techniques need to be developed to measure the high-speed switching and high-frequency performance of thin film heads and media and the resulting effects on the recording processes such as increases in pulse width and non-linear bit shift. In particular, the eddy currents in thick conductive thin film heads and thin media increase the rise time of switching, decrease the permeability, and increase the resistive losses at high frequencies which increase the pulse width and head noise. We propose to measure and model the high-speed switching and high-frequency performance of heads and media and correlate with magnetic properties, grain sizes, and magnetic microstructures. In addition, MFM imaging will be used to correlate the minimum switching volumes with high-speed performance.

  4. High-Saturation Flux Density Multilayer Inductive Thin Film Head Materials (Jack Judy, John Sivertsen, MINT, TEL: 612-625-7381)

    As the coercivity of longitudinal thin film media is increased beyond 3000 Oe to meet the demands of future ultra-high densities, thick pole tip inductive write heads will need to be sputtered with multilayers of high-saturation flux density materials which are both corrosion-resistant and manufacturable. We propose to investigate new material alloys films for thick multilayer inductive write heads such as FeCoCrN, FeCoCrTaN, FeCoZrNbN, FeCoZrTaN to meet the requirements at high frequencies of high permeability and low eddy current resistive losses to minimize pulse widths and switching times.

  5. High-Sensitivity & Low Resisitivity MR & Multilayer GMR Spin-Valve Head Materials (Jack Judy, John Sivertsen, MINT, TEL: 612-625-7381)

    As the areal storage density of magnetic recording systems is increased beyond 1 Gigabit/in2 with remanent magnetization-thickness products less than 1 memu/cm2, MR and GMR spin-valve read heads will need to be fabricated with higher sensitivities and lower-resistivities. In addition, new MR and soft-adjacent-layer (SAL) materials (NiFeCoCr, CoZrTa) with lower coercivities, higher permeabilities, and lower electrical resistivities at higher ultra-high frquencies (200-300 MHz) need to be investigated. Furthermore, new GMR spin-valve materials (CoFe, CoFeN, CoFePt) and antiferromagnetic (NiCoMn, NiIrMn) or ferrimagnetic (NiZnFe, MnZnFe)with optimized buffer layers for higher sensitivities need to be investigated using an ultra-high vacuum co-sputtering system. Also, ultra-thin (< 50 nm) insulating films of Al2O3 with high thermal conductivity and permanent magnetic films such as CoPt need to be made with lower electrical resistance to conduct current to MR & GMR sensors with planer topologies.

  6. Soft Keeper to Prevent Thermally-Activated Decay of Recording in Longitudinal Thin Film Media (Jack Judy, John Sivertsen, MINT, TEL: 612-625-7381)

    As areal storage densities of longitudinal magnetic recording media is increased beyond 5 Gigabit/in2, it is proposed to use a multilayer overlayer of a magnetic sendust keeper to prevent decay of the remanent magnetizations of UHDR recorded bits through thermally-activated magnetic after-effect-induced switching of magnetic domains clusters. Keepered longitudinal media exhibits increased signal output, decreased isolated pulse widths, pulse shape and amplitude asymmetry, and increased bit-shift margins.

  7. Nano-Tribology of Proximity and In-Contact Recording (Jack Judy, John Sivertsen, MINT, TEL: 612-625-7381)

    As small magnetic recording disk drives are driven to approach actual in-contact recording, the mechanical and tribologicaly properties of ultra-thin overcoats and the thin film media itself must be characterized in the nano-scale range. We propose to fabricate ultra-thin (50-10 Å) overcoats of C, CN, CB, & TiN/TiC thin films on media and head sliders using UHV, DIB, and FTS sputtering. A two-axis STM diamond nano-indentor which is capable of 0.1-0.5 nm indentations will be used to measure the modulus and nano-tribology of ultra-thin overcoats as well as metal alloy and ceramic thin film media.

  8. Development, Fabrication & Characterization of Nano-Patterned Quantum Disk Media (Jack Judy, John Sivertsen, MINT, TEL: 612-625-7381)

    As the physical limits of fabricating continuous thin film media for durable in-contact recording are approached, the alternative of nano-patterned quantum disk media composed of aligned ion-beam-etched or mechanically-embossed nano-bits (0.1-0.01 µm diameter) of physically-separated high-coercivity magnetic storage pillars (CoCrTaPt/Cr) should be investigated. We propose to use ion-beam etching and the nano-lithographic embossing technique proposed by Professor Steven Chou at the University of Minnesota for fabrication of quantum disk media. The switching characteristics and magnetic stability of clusters and individual nano-storage bits will be determined by writing with MFM tips and narrow track (1-0.1 µm) thin film heads fabricated by focused-ion beam etching of inductive thin film heads and reading by MFM & narrow-track (1-0.1 µm) dual-stripe DS GMR (Headway, Seagate, NSIC) heads.

  9. Nonlinear Equalization (Jay Moon, MINT, TEL: 612-625-7322)

    Our research to date on nolinear equalization has produced some important results including successful application of neural-net-like equalizers to nonlinear magnetic channels, simplification of such nonlinear equalizers for low-cost implementation, introduction of a new, efficient training technique. We want to apply nonlinear equalizers to DFE, FDTS/DF and other sequence detectors. Training algorithms will be improved to include the patern dependent nature of bit errors. Efforts will be directed to reducing the convergence time as well. We will also investigate other types of nonlinear structures such as function estimators based on constrained topological mapping for possible application to disk drive channels.

  10. Combined Detection and Timing Recovery (Jay Moon, MINT, TEL: 612-625-7322)

    Combined sequence detection and timing recovery can potentially eliminate the need for a phase-locked loop-based subsystem in the data recovery process.In the proposed setting, a coarse first-order frequency-locked loop can be used to generate the symbol rate read samples. A sequence detector incorporating the "expectation-maximization" algorithm then generates the estimation of both the data symbols and timing phase from the read samples. The data symbols and the timing information are obtained in a recursive fashion. Preliminary results show potential of this approach when applied to DFE & FDTS/DF. The ultimate goal is to design a digital equalization/detection system using a free-running analog to digital converter.

  11. Analog Implementation of FDTS/DF (Jay Moon, Ramesh Harjani, MINT, TEL: 612-625-7322)

    Sequence detection techniques such as FDTS/DF require a large number of signal processing functions. Analog implementations of such signal processing functions provide a number of advantages. In general, they consume less power, occupy less area, and can potentially run at higher speeds than their digital counterparts. Our research has concentrated on design considerations & circuit implementations for the individual components of the read channel such as forward equalizer, timing recovery, and FDTS sequence detection. The final goal of this project is to develop a prototype analog VLSI chip implementing the entire data recovery path, including timing, gain control, equalization and FDTS/DF detection circuitries at a data rate comparable to or exceeding that of a state-of-the-art disk drive system.

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Copyright © 1997-1999 by MINT
Last modified on February 15, 1998; jchen@ece.umn.edu.