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We present an area efficient test structure that allows measurement of the statistical distribution of SRAM cell read currents and write trip voltages for 1 million SRAM core cells. The data taken from measurements of wafers fabricated with a 90-nm and 65-nm CMOS process flow show that the device variations are Gaussian distributed for more than 1 million devices, covering more than 5 sigma of variation. The analysis of the measured SRAM performances validate Monte Carlo simulations. Index Terms--65 and 90 nm, low voltage, measurement structure, read current, SRAM, variation, write trip voltage.

The effect of thermomechanically actuated pole tip protrusion on adhesive forces is characterized through model and experiment. The roughness of a thermomechanically actuated region is characterized by atomic force microscopy. Using the extracted roughness parameters and estimated apparent area associated with thermal actuation, the intermolecular forces at the head-disk interface (HDI) are calculated using the ISBL (improved sub-boundary lubrication) code. Both roughness and nominal area of contact are found to be significant factors determining adhesive forces. The adhesive forces for various HDI designs--including thermal actuation--are also characterized experimentally in situ using commercial hard disk drive samples. The experimental results are found to be consistent with the model calculations and imply certain advantages for thermally actuated HDI designs. However, the experiments also raise concerns regarding the field application of the technology. Keywords: thermal actuation, adhesion, head-disk interface (HDI), head-media spacing (HMS), pole tip protrusion

To sustain an ultra-low and stable flying height (FH) is crucial for achieving high areal densities in magnetic recording. Recently, a new method called thermal flying height control (TFC) has been introduced to the latest generations of disk drives for precise control of slider-disk spacing. It is noted that the TFC technique is able to eliminate almost all static FH loss, but is unable to circumvent dynamic FH loss such as flying height modulation (FHM) due to disk waviness. It is therefore advantageous to have both high thermal actuation efficiency and low FHM due to disk waviness characteristics in a TFC slider design. This paper investigates the effects of air bearings on the thermal actuation efficiency and the capability in following disk waviness of the TFC sliders. Air bearing surface (ABS) design strategies for TFC slider are proposed and investigated with simulations. The results show that both excellent thermal actuation efficiency and strong capability in following disk waviness can be achieved through proper arrangements of air bearing pressure distribution on the ABS of TFC sliders. Index Terms--Flying height, flying height modulation, head-disk interface, thermal flying height control, waviness.

This paper focuses on air bearing surface (ABS) design optimizations in order to reduce the lift-off force during the unloading process while satisfying the desired static flying performances. Since it takes a huge amount of computational time to solve time-dependent dynamic load/unload (L/UL) equations, an approximate lift-off force is created as a function of the air bearing suction force and flying attitude parameters by the kriging method. The design framework is employed in wrapping effectively and connecting the kriging model and the static analyzer to the optimizer. An optimization problem is formulated to minimize the amplitude of the lift-off force during the unloading process while keeping the flying height, pitch, and roll angles within suitable ranges over the entire recording band as well as reducing the possibility of slider-disk contact in steady state. Then, two different sizes of slider models are optimally designed for L/UL applications with 1-in disk drive. The L/UL simulation results show that the optimized ABS designs have reduced the lift-off force in the loading process by approximately 62% and 11% for pico and femto design respectively, while satisfying desired static flying performance. In addition, results demonstrated that the optimum slider incorporated with the suspension were not only properly unloaded onto the ramp but also smoothly loaded onto the rotating disk. Therefore, it is believed that the proposed design approach works efficiently in ABS designs for L/UL applications. Index Terms--Air bearing surface (ABS), kriging model, lift-off force, load/unload (L/UL).

Scaling the areal density, while maintaining a proper balance between media signal-to-noise ratio, thermal stability, and writability, will soon require an alternative recording technology. Heat assisted magnetic recording (HAMR) can achieve this balance by allowing high anisotropy media to be written by heating the media during the writing process (e.g., by laser light) to temporarily lower the anisotropy. Three major challenges of designing a HAMR head that tightly focuses light and collocates it with the magnetic field are discussed: 1) magnetic field delivery; 2) optical delivery; and 3) magnetic and optical field delivery integration. Thousands of these HAMR heads were built into sliders and head-gimbal assemblies, and optical and scanning electron micrograph images are shown. Scanning near-field optical microscopy (SNOM) characterization of the HAMR head shows that the predicted ~ [LAMBDA] A/4 full-width half-maximum (FWHM) spot size can be achieved using 488 nm light (124 nm was achieved). SNOM images also show that wafer level fabricated apertures were able to effectively eliminate sidelobes from the focused spot intensity profile. A magnetic force microscopy image of HAMR media shows that non-HAMR (laser power off) was not able to write transitions in the HAMR specific media even at very high write currents, hut transitions could be written using HAMR (laser power on), even at lower write currents. A cross-track profile is shown for a fully integrated HAMR head where the magnetic pole physical width is, ~350 nm, but the written track is ~200 nm, which demonstrates HAMR. A HAMR optimization contour shows that there is an optimum write current and laser power and that simply going to the highest write current and laser power does not lead to the best recording. Lastly, some prospects for advancing HAMR are given and a few key problems to be solved are mentioned. Index Terms--Heat assisted magnetic recording (HAMR), magnetic recording, recording head.

In order to achieve an areal density of 1 Tb/in (2) and beyond, not only the mechanical spacing between the slider and the disk but also the track misregistration (TMR) and the fly height modulation (FHM) should be reduced below current levels. But at reduced mechanical spacing there will be elevated excitation due to slider-disk contacts resulting in increased slider vibrations and head-disk interface (HDI) failures. Thus, there is a need to study the effect of slider-disk topography on the slider dynamics and stability at a higher level of complexity. In this paper, we do so by dividing the slider-disk surface features into three regimes based on the amplitude and the wavelength range of the features. Further, we have also proposed several ways of achieving an optimal slider-disk topography that can help reduce the slider vibrations and increase the stability of the HDI. Index Terms--Roughness, slider, stability, vibrations, waviness.

Current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) heads with a current screen layer were fabricated, and the recording performance was measured. An output voltage of 1.9 mV and head-amp signal-to-noise ratio (SNR) of about 30 dB were obtained from a 50-nm-wide head with an operating voltage of 120 mV. The MR ratio was 4%-5%, shield gap was 36 nm and resistance was 72 [ohm] With using the thermal fly-height control (TFC), the fabricated head showed a potential to yield a 382 Gb/[in.sup.2] recording (1252 kBPI x 305 kTPI). The current screen structure reduced the spin torque noise since just a low sensing current of 1-2 mA was required for obtaining a high output. Newly developed CPP-GMR films with a current screen layer showed the MR ratio of 18%-19% with the RA product of 0.2-0.3 [ohm] x [m.sup.2][micro]. Calculation showed that this film allows us to achieve 30 dB or more in the head-amp SNR when the sensor width was 40 nm or larger. The current screen CPP-GMR head is thus an attractive candidate that has a high potential suitable for an areal density of 500 Gb/[in.sup.2] or more. Below 40 nm, an all metal CPP-GMR head with the MR ratio of 10% or more would be the best candidate. Index Terms--CPP-GMR, magnetic head, magnetic recording, noise, spin torque.

Read heads using current-perpendicular-to-plane (CPP) giant magnetoresistance sensors have been fabricated and tested under highdensity 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 (2). 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 (8) A/cm (2). Index Terms--CPP-GMR, magnetic recording, read-head, spin-valve.

We created a finite-element model of the head-disk assembly (HDA) of a small-form factor drive. We conducted operational shock simulation and modal analysis with this finite-element model, and investigated the pulsewidth effect of a half-sine acceleration pulse on the shock responses. We found that the umbrella mode of the disk is the dominant mode for operational shock. Numerical results of the pulsewidth effect on the maximum shock responses further confirm the conclusions in a previous work by the authors. Index Terms--Drive, hard disks, head, shock, simulation.

This paper presents a simulation study on the coupling effects of air bearing dynamics and suspension vibrations due to slider-disk contact or disk waviness. A simulator is developed to include the interactions between the air bearing, the slider-suspension assembly and slider-disk contact by considering the suspension, slider and air bearing as a whole system. From the simulation, the dynamic motion of read/write head in both flying-height (FH) and off-track directions, even on-track direction, can be obtained. It is helpful to characterize dynamics of head positioning and understand the interactions between the head disk interface (HDI) components. In addition, the effects of contact intensity, surface roughness, skew, and disk waviness on the read/write head positioning in both FH and off-track directions are investigated. The mechanisms of these factors' effects on the dynamic stability of read/write head positioning in both FH and off-track directions are also discussed in the paper. Index Terms--Aerodynamics, contacts, dynamics, hard disks, head-disk interface, magnetic disk recording, mechanical systems.

1/f-type of low frequency noise is widely observed in today's state-of-the-art tunneling-magneto-resistive (TMR) and current-perpendicular-to-plane (CPP), and giant-magneto-resistive (GMR) heads. In this paper, the 1/f-type magnetic noise arising from the thermally excited low frequency edge magnetization switch of the free layer is studied by micromagnetic simulation. It is found that although the free layer dimension is in the single domain regime, the edge magnetization random switching related to the thermal excitation and insufficient hard bias field on sensor edge can be a significant low frequency noise contributor in TMR/CPP GMR heads. A strong local hard bias (HB) field at sensor edge that pins the free layer edge magnetization is found to be more critical than a strong averaged HB field across the sensor to avoid magnetic 1/f-type noise. The simulation study shows that a high HB field gradient from sensor edge to center is preferred to maintain a low noise sensor while still achieving high sensitivity. This paper will also discuss the roles of free layer thickness, sensor geometry, current field, temperature, and air-bearing surface physical defect in the behavior of this edge flipping noise. Index Terms--1/f noise, current-perpendicular-to-plane (CPP), hard bias (HB), thermal excitation, tunneling-magneto-resistive (TMR).

We refined a previously developed finite-element (FE) model of a Seagate Bali II hard-disk drive (HDD) to include compliance contributed by roller bearings at the spindle and pivot motors. We then performed drop-test simulations with the nonlinear structural dynamic codes LS-DYNA and ABAQUS/Explicit. In parallel, we subjected a nonoperating Bali II HDD to physical tilt-drop tests from drop angles of 10[degrees] and 45[degrees], representing a mild and a substantial shock input, respectively. We measured velocity responses with a laser Doppler vibrometer (LDV) at two points on the HDD. The first point was on the topmost read/write head at the center of its trailing edge, and the second point was on the top surface of the baseplate directly above the line of contact with the impact bar. In the FE studies, the baseplate velocity histories measured during the tests were used to prescribe input motions at the corresponding baseplate nodes. We compared computed and measured head velocity histories in order to evaluate the effectiveness of present state-of-the-art simulation tools for modeling head-slap events. Index Terms--Finite element, hard disk drive, shock, tilt drop test.

A pseudoray method is suggested for the initial design for the composition of combined optical CD-DVD read-write heads. The effectiveness of the method is shown in the design of the optical system for the CD-DVD read-write heads.

To aid understanding the physical mechanisms responsible for the perpendicular write head remanent field and thereby improve the write head design, we studied the remanence of single-pole perpendicular recording heads with trailing shield by using a contact scanning recording tester. We used two different pole-tip size heads in the study. We found that the remanence areas of the heads tested usually locate at the trailing edge corners of the pole tip. We also found that the remanence areas of both types of heads are also the head field easy-rising areas when the heads are driven by low write currents. Additionally, the current level that leads to remanence is the same for both types of heads. However, the remanence of the small pole-tip heads can be demagnetized by a much lower amplitude reverse current than that of the large pole-tip heads. Index Terms--Head remanence, perpendicular recording, pole-tip size, shielded head.

The selected aspects of the recording physics of magnetic data storage specific to writing and reading in patterned medium are discussed. The influence of a recording layer design on playback resolution is evaluated, which offers guidelines for the design and optimization of patterned magnetic recording medium.

Grain boundaries play a crucial role in determining the macroscopic properties of magnetic recording media. The authors employ electronic structure theory, based on the local spin density approximation, to calculate the exchange energy, anisotropy energy, and magnetization at two types of grain boundaries. They incorporate these values into a micromagnetic simulation, thus correlating hysteresis loops and switching properties to atomic features. The authors show that small intergranular spacings (less than 0.2 nm) effectively break exchange, while a larger Cr thickness is required to achieve the same effect. Index Terms--Electronic structure, grain boundaries, intergranular exchange, micromagnetic simulation.

Ferromagnetic/antiferromagnetic coupled multi-layers provide a unique solution to several problems found with soft underlayers for perpendicular media. Properly designed, they demonstrate outstanding characteristics: a unique single-domain remanent direction, reversible hysteretic behavior over a wide angular range, optimum permeability [micro] ~ 100, and high saturation flux density 4[pi][M.sub.s]. Initially, FeTaN-IrMn multilayers were prepared with these characteristics and a target ferromagnetic thickness of 200 nm, but 19 total layers were required and they were thermally unstable. These problems were first overcome by replacing FeTaN with high-anisotropy [Fe.sub.10][Co.sub.90], although 4[pi][M.sub.s] was reduced from ~19 to ~16 kG. Further work, however, revealed that soft anisotropic [Fe.sub.65][Co.sub.35] films with an induced anisotropy field [H.sub.k] of 30 Oe and 4[pi][M.sub.s] ~ 23 kG could be successfully produced on Cu, NiFe, Ru, Ta-Cu, Ta-NiFe, or Cu-IrMn underlayers. An optimized structure was found to be glass/Cu(20 nm)/IrMn(10 nm)/[[[Fe.sub.65][Co.sub.35](50nm)/ IrMn(10nm)]].sub.4]/[Fe.sub.65][Co.sub.35](25 nm). Furthermore, postannealing will allow the number of layers to be reduced from 11 to 7. Index Terms--Exchange coupling, FeCo alloy, high saturation magnetization, perpendicular media, soft underlayers.

We report the effect of introducing a thin carbon interlayer to the recording layer on the read-write characteristics of Co-Pd multilayered perpendicular magnetic recording media. A 1-nm-thick carbon interlayer markedly reduced the medium noise and improved the output resolution, [D.sub.50]. As a result, the signal-to-noise ratio at the recording density of 200 kFRPI for the medium was higher by 5 dB than that for the medium without the interlayer. We attribute these improvements in read-write characteristics to a decrease in the crystal grain diameter of the recording layer, resulting in suppression of the transition fluctuation of recorded bits. The Co-Pd multilayered perpendicular magnetic recording medium with carbon interlayer has a high thermal stability despite a slight degradation of perpendicular magnetic anisotropy. Index Terms--Carbon interlayer, Co-Pd multilayer, medium noise, perpendicular magnetic recording.

A reptation algorithm applied to a simplified bead-spring off-lattice polymer model an NVT Monte Carlo simulation for perfluoropolyether (PFPE) Z and Zdol (qualitative) has been performed to simulate the bulk and the ultrathin film polymer conformations. A bead-bead Lennard-Jones (LJ) potential is used in the bulk, and a substrate-bead LJ potential is added in the ultrathin film condition. In addition, a dipole--dipole polar interaction potential is adopted at the two chain ends of Zdol. The simulation is performed with similar molecular weights of PFPE Z and Zdol under the assumption of room temperature and pressure condition. A maximum volume fraction of approximately 80%--82%, typical of a melt at room condition, is considered for both the bulk and the ultrathin film condition. It is observed that the calculated average radius of gyration (Rg) is nearly equal to the experimental value for the bulk situation. The average components of Rg in the x, y, and z directions Rgx, Rgy, and Rgz are almost equal to each other in the bulk denoting the average shape of a polymer as a sphere. In the ultrathin films of several nanometers of film thickness, a substrate surface at the bottom and a top restriction at film heights of different thicknesses are introduced, keeping the maximum volume fraction similar to that of the bulk. Rg and Rgz decrease and Rgx and Rgy increase (here, xy plane is taken parallel to the substrate surface and z denotes the distance from the same surface) in comparison to their bulk values with the decrease of film thickness initiated at a specific ultrathin film thickness, which depends on the polar (Zdol) or nonpolar interaction. The results will be important for the design of the ultrathin liquid films of PFPE. Index Terms--Conformation, perfluoropolyethers, polar interaction and ultrathin liquid films.

Hard disk drive (HDD) servo technology for media-level servo track writing (MLSTW) is developed. MLSTW is the process of writing servo signals on magnetic disks before they are assembled in drives. It supplies a solution to achieve low-cost and accurate means of servo-signal writing. The HDD servo controller for MLSTW drives compensates for radial and rotational distortions of the servo signals (e.g., track-address, eccentricities, and servo-signal timing) that are inherent in the MLSTW method. The authors prove that the positioning accuracy is improved and the seek time is unchanged by using the new servo controller for HDDs with MLSTW disks. Index Terms--Calibration, delay effects, disk drives, distortion, feedforward systems, magnetic disk recording, position control, STW.

Novel fast seek and settling controls for hard disk drives (HDDs) have been developed. The controls are suitable for digital control and can be implemented into the servo program of a HDD's microcontroller easily. The controls use a feedback control and a feedforward control that uses feedforward trajectory with little power at actuator resonance frequencies. A finite-impulse-response notch filter is used to design the feed-forward trajectories. The seek control uses the pair of feedforward trajectories of position and current. The settling control that connects a long-distance seek control with a following control uses two pairs of feed-forward trajectories for initial position and initial velocity and a new bias-estimation method. The authors prove both controls are fast and free from residual vibrations and bias offset. Index Terms--Digital control, disk drives, feedforward systems, FIR digital filters, position control, resonance, state estimation, velocity control.

The authors investigate the flow structure in 3.5-in hard disk drives with a rotation speed of 10 033 rpm, especially the unsteady flow around actuator arms with and without a weight-saving hole, and clarify the unsteady flow in detail. In the method of approach utilized in this investigation, they used: 1) a direct numerical simulation of the Navier--Stokes equations to analyze the flow field; 2) a laser Doppler velocimeter to measure the velocity field; and 3) a laser Doppler vibrometer to monitor unsteady displacement of the actuator arm. The authors find a three-dimensional spiral vortex in the wake region of the arm and the flow spilled from the weight-saving hole. These flows can be considered to be an excitation source for the actuator arm. The power spectrum of the arm torque generated by calculated wind disturbance agrees with that of measured wind disturbance. This verifies the existence of the predicted vortices and the flow spilled from the weight-saving hole. Index Terms--Airflow, fluid analysis, hard disk drive, spiral vortex.

This paper describes design and fabrication of active head sliders using PZT thin films for in situ flying-height control. Silicon sliders with piezoelectric unimorph cantilevers were fabricated monolithically using micromachining process. The deflection of 70 nm was obtained at the tip of the 0.6-mm-long cantilever with a drive voltage of 4 V. Furthermore, an air-bearing surface design that makes it possible to reduce the aerodynamic lift force under the head is discussed. Index Terms--Hard disks, microactuators, microelecto-mechanical devices, piezoelectric films.

A phase-stabilized servo controller was developed based on a Nyquist plot for moving-suspension dual-stage actuators. The controller uses the suspension resonances of a PZT microactuator to compensate for the track misregistration (TMR) due to windage disturbance caused by suspension vibration. Experimental results obtained using a prototype 3.5-in hard disk drive show that the crossover frequency of the open loop is 2.0 kHz, and that the root mean square of the TMR due to windage disturbance is reduced by 23% compared to that of a conventional notch-based dual-stage controller. Index Terms--Decoupled feedback control, dual-stage actuator, hard disk drive, windage.

A computationally effective fixed-order multirate digital control scheme is presented for disk drive actuator control. The proposed multirate controller outputs control commands at each control update instant, while the multirate control scheme is evenly computed for every measurement sampling period, thereby eliminating the need for very powerful processors for implementation. Application results demonstrate that the proposed multirate control scheme is useful to smooth control inputs so as not to excite the flexible mode dynamics of the actuator arm and suspensions. Index Terms--Digital control, disk drives, multirate, resonance mode, Sampled data systems, stability.

An actuator consisting of a linear air bearing and a voice coil motor (VCM) of the linear type was designed for precise tracking. The stiffness of the air bearing was strong enough so that the moving coil of a VCM fixed to the air bearing slider arm could form a cantilever system. The linear actuator showed a much higher resonance frequency than a conventional rotary actuator. Due to the high resonance frequency, the servo bandwidth became significantly wider. The linear actuator could be stepped at 1-nm resolution without overshoots and undershoots and the rise time was less than 0.5 ms. Index Terms--Linear actuator, linear tracking, position control, precise positioning, servo writing, track following.

Unsteady airflow in an actual hard disk drive (HDD) which has a rotary actuator is numerically simulated by using the large eddy simulation technique, and the aerodynamic force affecting head gimbal assembly (HGA) is estimated from the simulation. The calculated force is fed to a structure analysis to predict the airflow-induced vibration of the HGA. The authors calculate the head positioning error or the head displacements for the different HGA orientations to explain and classify the mechanism of airflow-induced positioning error (i.e., windage) in HDD. Index Terms--Aerodynamics, CAE, displacement control, hard disk drive, numerical analysis.

This paper demonstrates an accurate mathematical model predicting forced vibration of rotating-shaft hard disk drive spindle motors with flexible stationary parts. The mathematical model consists of three parts: a rotating part, a stationary part, and bearings. The rotating part includes a flexible hub, a flexible shaft press-fit into the hub, and N elastic disks mounted on the hub. The stationary part can include motor bracket (stator), base casting, and a top cover. The bearings under consideration can be ball bearings or fluid-dynamic bearings (FDB). The rotating disks are modeled through the classical plate theory. The rotating part (except the disks) and the stationary part are modeled through finite-element analyses (FEA). With mode shapes and natural frequencies obtained from FEA, the kinetic and potential energies of the rotating and stationary parts are formulated and discretized to compensate for the gyroscopic effects from rotation. Finally, use of the Lagrange equation results in the equations of motion. To verify the mathematical model, frequency response functions are measured experimentally for an FDB spindle carrying two identical disks at motor and drive levels. Experimental measurements agree very well with theoretical predictions not only in resonance frequency but also in resonance amplitude. Index Terms--Fluid-dynamic bearing spindles, HDD spindle motors, vibration.

In the operation of fluid-dynamic-bearing (FDB) motors, the acoustic noise caused by the electromagnetic forces takes a big ratio in the noise level. The authors analyze the relationship between the acoustic noise frequency, harmonic current, and harmonic field, and propose a drive mode for reducing the acoustic noise of the FDB motors. The drive mode can also reduce the copper loss in the motor operation. Index Terms--Acoustic noise, drive mode, fluid dynamic bearing, spindle motor, torque ripple.

This paper presents the development of an ultraslim spindle motor for a 3.3-mm-height CF Type I disk drive. The mechanical structure of the developed motor is extremely miniaturized not only by eliminating the unnecessary space but also by optimizing the hub and clamp in order to fit in a small form factor. Electrically, it has the auxiliary winding in the linking part between the adjacent teeth of slotted stator, which increases the torque constant and efficiency. Simulation and experiment are performed to prove the advantages of the developed motor. Index Terms--Auxiliary winding, computer hard disk drive, high efficiency, high torque constant, spindle motor.

Ultrathin carbon nitride (C[N.sub.x]) overcoats were grown using pulsed dc magnetron sputtering. Substrates were mounted on a holder that allowed 45[degrees] tilt angle and rotation at different speeds. Effects of sputter gas composition, target power, substrate bias, substrate tilt, and rotation on film growth and properties were explored. Atomic force microscopy scans over large sampling areas show that thin C[N.sub.x] films obtained at--100 V substrate bias with 45[degrees] substrate tilt and 20 r/min rotation have root-mean-square roughness almost four times lower than those prepared without substrate tilt and rotation. Several percent of helium in an Ar-5%[N.sub.2] sputter gas was found to improve surface roughness of these coatings. These 1-nm-thick ultrasmooth coatings reduced corrosion damage compared with coatings of the same thickness grown without substrate tilt and rotation. This improved performance appears to be directly related to the growth of smoother and denser coatings synthesized under the present conditions. Index Terms--Coatings, corrosion, hard disks, sputtering.

Vibration analysis and experimental study of a disk-spindle system in hard disk drives are presented in this paper. The natural frequencies, mode shapes, and frequency response are calculated with the consideration of the flexibility of rotor and base structures of a disk-spindle system. The analytical model is verified by comparing the simulation results with the experimental data for a variety of motor configurations and sizes. It is shown that they agree very well with each other. Index Terms--Disk-spindle system, frequency response, mode shape, natural frequency.

An assessment of the chemical environment, within which a disk drive's head/disk interface must operate, is presented. This provides the framework for discussing the benefit of an internal, integrated chemical filter (ICF) to the long-term integrity of the head/disk interface. The ICF in the present embodiment has a diffusion limiting channel at the drive's breather inlet to minimize the rate of volatile contamination ingress, a mass of chemically treated, activated charcoal to permanently absorb acid gases and volatile organic compounds, and a particle filter to stop the ingress of external particles and charcoal fragments. The activated charcoal has the additional property of reversibly absorbing water vapor, which is used to moderate changes in the humidity within the drive. The design and performance of the ICF are discussed. Index Terms--Activated carbon or charcoal, chemical integration, contamination, corrosion, corrosive gas, disk drives, filter technology, humidity control.

The thickness of carbon overcoats has been reduced to 30 [Angstrom] or less to achieve high areal density in magnetic media. Presently, technologies such as ion beam deposition and plasma enhanced chemical vapor deposition (PECVD) produce thin carbon overcoats with a high fraction of [sp.sup.3] bonding. These hard and dense overcoats exhibit good wear durability and corrosion resistance. This paper discusses processing, characterization, and tribological and corrosion performance of ultrathin overcoats (30 [Angstrom] or less) produced by PECVD. The physical and chemical properties of the carbon overcoat affect the carbon-lubricant bonding, which subsequently determines the head--disk interaction. Since optimal properties of the carbon vary at the lubricant and magnetic layer interfaces, an interfacial functionality approach is needed for the design of thin overcoats. Functionalized carbon overcoat is a design that consists of a PECVD carbon layer with a sputtered functional layer on top. Characterization and tribological performance and comparison of functionalized carbon overcoat with PECVD carbon is also presented. Index Terms--Carbon overcoat, characterization, ion beam, magnetic disks, precursors, processing, thin, tribology.

The static spacing loss of slider-disk interface is investigated through careful characterization of disk shape for disks of different form factors with different peak-to-valley flatness values. Measured radial profiles are normalized and found to be confined within a relatively narrow region. The representation of these shapes is reduced to a simple set of quadratic equations. Static flyability models associated with the disk radial slope (crown effect) and radial curvature (camber effect) are presented. Spacing loss is calculated for a negative pressure pico-slider and a positive pressure catamaran nano-slider. Results show that slider geometries and crown/camber sensitivity, as well as disk flatness and shape, all affect static slider-disk spacing loss. The analysis is focused on the effect of disk shape on the static spacing loss and its relationship to slider design. Index Terms--Disk drive, disk shape, flatness, flyability.

Properties and performance for alloy and multilayer perpendicular recording media designs utilizing a soft magnetic underlayer are compared. Among samples considered here, grain size and grain size dispersion are more highly refined for alloy media deposited at high substrate temperature, and are beginning to approach those now available in longitudinal recording. Multilayer media made at ambient temperature typically sacrifice film density and surface smoothness for interface quality. Although microstructural development and the manufacturing process for multilayer media are less mature versus alloy, multilayer media remain attractive due to their high anisotropy potential and the ease with which [H.sub.n] and [H.sub.c] can be controlled. For thermally stable alloy media made on a pilot production sputtering machine, a spin-stand areal density of 61 Gb/[in.sup.2] has been demonstrated at 350 Mb/s data rate with an on-track bit-error-rate reference level of 1e-6. Using the same media, a working perpendicular drive has been demonstrated at 32 Gb/[in.sup.2] and 500--800 Mb/s data rate. Index Terms--Alloy, micromagnetic modeling, multilayer, noise, perpendicular magnetic recording, signal decay, soft magnetic underlayer.

A recording density of 130 Gb/[in.sup.2] was achieved using thermally stable conventional CoCrPtB longitudinal media. The high in-plane orientation ratio (OR) of the media resulted in an excellent recording performance due to a narrow switching field distribution as well as a high thermal stability caused by narrow energy barrier distribution. The low noise is attributed to the fully isolated fine grains with a narrow size distribution. A good in-plane c axis crystallographic texture was achieved by using an optimum multilayered structure of underlayer and magnetic layers. A detailed study of high OR media is reported by characterizing the magnetic, microstructural, and read/write properties. Index Terms--Areal density, longitudinal recording media, orientation ratio, thermal stability.

Chemically synthesized high-anisotropy magnetic nanoparticles have demonstrated thermal stability and extremely narrow size distributions that are critical for reducing noise in future media applications. Due to their monodispersity, they also exhibit emergent self-patterning that could potentially support bit-per-particle densities up to 2 to 8 Tb/[cm.sup.2] (10 to 50 Tb/ [in.sup.2]). The authors report on the challenges and progress in developing self-organized nanoparticle arrays for magnetic recording at densities up to and beyond 30 Gb/[cm.sup.2] (200 Gb/[in.sup.2]), and in particular describe the beneficial use of biological templates in developing such media. CoPt grains are prepared within monodisperse protein spheres from aqueous reactants, with synthesis conditions controlling grain size, structure, and composition. Dispersions of these protein-encapsulated grains can be induced to form patterned precursor films that retain long range order irrespective of a distribution in grain size. Assemblies are annealed to form films of L[1.sub.0] phase nanomagnets within carbonized shells that can support stable transitions up to 1 Gb/[cm.sup.2] (6 Gb/[in.sup.2]). Index Terms--Magnetic films, magnetic liquids, magnetic recording, nanotechnology.

As the recording density of hard disk drives is being rapidly increased, the current servo track writing method using a conventional servo track writer has become more costly and technically difficult. In order to solve the problem, the authors propose a new magnetic contact duplication technology using a lithographically patterned master disk and discuss the printing process reliability for practical implementation to the product drives, in particular, from the viewpoint of master-slave contact issues. The air channel structure provided on the master disk surface allows close surface contact between the master and the slave disks, yielding very small amplitude modulation of the printed signal. The master disk was found durable over 1 million printing shots without giving any serious damage to the lithographically patterned ferromagnetic film. Moreover, organic and inorganic contamination tests that the contact printing operation does not increase contamination on the printed disks. The magnetic printing technique can also be successfully applied to perpendicular recording media using the same master disk as for longitudinal media. Index Terms--Hard disk drives, lithographically patterned film, magnetic printing, master disk, servo track writing.

A diamond-like carbon film of 20 [Angstrom] deposited by the ion-beam method demonstrated good wear and corrosion protection on a magnetic medium. No wear or high stiction was observed after the contact-start-stop (CSS) test terminated at 20 000 cycles. The corrosion tests on the medium indicated that an ion-beam carbon overcoat, as thin as 20 [Angstrom], provides better corrosion protection than a 50-[Angstrom] sputtered carbon overcoat. The carbon deposition ion energy influenced the overall magnetic performance of the recording medium. Magnetic defects and media noise increased with increasing carbon deposition ion energy. Index Terms--Carbon overcoat, corrosion, ion-beam method, magnetic recording, tribology.

Decision feedback equalization (DFE) is a promising low-cost solution for signal detection in magnetic recording channels. In terms of the bit error rate after detection, (0, k)-DFE and MDFE (Multilevel Decision Feedback Equalization) [1] are comparable to (0, k)-PR4ML. Error propagation, however, is one of the major concerns for all DFE approaches. In this paper, an analysis of error propagation for RLL-constrained DFE at all stages of data processing, including RLL decoder and error correction, is performed. To evaluate error propagation, a Markov chain is constructed that explicitly models any type of RLL constraints. From this model, a Markov chain, describing the error distribution inside the bursts, is derived and a relation between these chains and error propagation decay rate is established. Performance of interleaved ECC (Error Correction Code) is also evaluated. The results obtained are compared with those from simulation. By using the newly developed model, a special technique of equalizer design, aimed to reduce error propagation, is analyzed. The comparison between (0,k)-DFE and MDFE in terms of the bit error rate after ECC is also provided.

In this paper, we present signal space detectors for use with maximum transition run (MTR) codes. A three-dimensional signal space detector is first derived for an MTR = 2 coded channel. The bit error rate performance of this detector is close to MTR-coded FDTS/DF(2) throughout the user density range of interest. The detector is then modified to be used with a time-variant MTR code. Simulation as well as experimental results are presented.

We present a novel method to determine the motion of the slider's flying height and off-track direction simultaneously in a hard disk drive. The results show the relative movement of the slider in two dimensions, both during thermal actuator controlled contact and full flying condition. The method separates the position error signal (PES) and the flying height signal from the readback signal. The method includes writing dual-frequency pattern tracks adjacently, with the readback signals from the tracks filtered for the in situ motion measurement. The harmonic ratio method is used to determine the flying height variation of the head, whereas the conventional servo burst detection method is used to determine the PES. Index Terms--Flying height, measurement, position error signal, two-dimensional.

To demonstrate the highest areal recording density of tape media, we have developed a metal evaporated tape with higher magnetic anisotropy of 2.5 x [10.sup.5] J/[m.sup.3] and finer magnetic activation volume of 2.7 x [10.sup.-24][m.sup.3] of a Co-CoO recordin la er de osited on a g yp smoother base film. A capability of an areal recording density of 23.0 Gb/[in.sup.2] was confirmed using a giant magnetoresistive head as a read head. The smoother surface roughness improved signal-to-noise ratio more than 2 dB. Index Terms--Areal recording density, giant magnetoresistive head, magnetic tape recording, metal evaporated.

The spin transfer modified Landau--Lifshitz--Gilbert equation is used to model a permalloy bar with configurations for current, transverse field, and magnetizations resembling those of a read head. The trends of noise power and noise peak frequency against sensing currents and transverse fields with different polarities are calculated and analyzed by symmetry and asymmetry properties, by magnetization dynamics, and by extended linear stability analysis that is applicable to shape anisotropy. With the linear stability analysis, it is found that smaller track width (with aspect ratio fixed) has larger field stability and larger current-density stability. Index Terms--Spin transfer noise, stability analysis, thermal noise.

Exchange-coupled composite (ECC) media consisting of hard and soft coupled regions has been predicted to exhibit attempt frequencies that are much larger than conventional perpendicular media due to the presence of two degrees of freedom. As a result, adjacent track erasure (ATE) and archivability are adversely affected, whereas writability is significantly enhanced due to thermal fluctuation assisted recording. Recording heads for ECC and perpendicular media, designed dimensionally for recording at 250 Gbits/[In.sup.2], are evaluated within this context. In comparison, recording on ECC media is shown to yield about a factor 2 advantage in areal density. Index Terms--Attempt frequency, exchange-coupled composite (ECC) media, perpendicular recording, thermal fluctuations.

A new method to detect magnetic recording head/media contact point is introduced in this paper. By comparing it with a common method using an acoustic emission sensor, the new method is simple, but yet still effective enough to control fly high or clearance between head and disk so as to improve the performance of perpendicular magnetic recording (PMR) at ultra-high density. The method can be easily implemented on head/disk spin-stand testers or in hard disk drives. Index Terms--Disk drives, magnetic head, magnetic recording, perpendicular magnetic recording.

The lattice Boltzmann method (LBM) is utilized to simulate the nanoscale flow physics of air bearings in the head-disk interface. In the high Knudsen number flow analysis of air bearings, the slip boundary model is very important to guarantee the accuracy of solution. In this paper, the Laugmuir slip model for the rarefied gas flow was incorporated and its feasibility and accuracy was examined in nanoscale flow simulations. It was shown that our LBM can solve the fluid flow of air bearing with high efficiency due to its complex geometry handling capability and high accuracy comparable to the Boltzmann transport equation in the slip flow regime. The LBM model developed in this paper could serve as a powerful tool for the design of advanced air-bearing systems. Index Terms--Air bearing, head-disk interface, Langmuir slip model, lattice Boltzmann method.