Thin-film Inductive Heads Research Articles

Correlation of domain pattern and high-frequency response in pole-tip of inductive thin film head

The high frequency response of the soft magnetic pole tip in the thin film inductive head is crucial for the noise analysis of computer hard disk. A micromagnetic model is established in a mesoscopic soft magnetic thin film to analyze the domain pattern as well as the initial permeability in a wide frequency range from 10MHz to 18GHz. The simulated domain patterns in the pole tip, a vortex- and ladder-type, are chosen as the initial conditions for the high-frequency response studies. The scaling law of the permeability is analyzed at different amplitudes of the alternating external magnetic field. It is found that in the ladder-type domains the high frequency response is much better than that in the vortex-type domains, which agrees with experiment. A simplified explanation of the simulation result is discussed based on the analysis of the nonlinear Landau–Liftshitz equation.

Studies of Deep-Submicrometer Ultranarrow-Track Recording by Composite Simulation Models

This paper presents an analysis of the signal and noise in deep-submicrometer ultranarrow-track disk recording by composite simulation models, including the micromagnetics in longitudinal media and giant magnetoresistive (GMR) multilayers and the surface finite-element methods for inductive thin film heads and GMR head shields. The analysis assumes that the linear density of the recording process is in a range of 57 to 1200 kilo-flux changes per inch (kfci) and the width/gap ratio of the write head is between 4 and 2, corresponding to current industry practice. The first to fifth harmonics of all-one signals are found by the simulated spectrum. The signal and noise at different track densities and linear densities are analyzed by the harmonics in the spectrum. The composite heads in the disk recording system with widths 160, 240, and 320 nm are evaluated by the signal-to-noise ratio at a linear density around 1000 kfci.

Thermal pole tip protrusion finite element analysis of thin film inductive recording heads

In recent low flying height hard disk drives, the head write current causes thermal protrusion of the pole tip region that results in head–disk contact. Finite element analysis is performed in this work to study the temperature and displacement fields in heads during writing. Three-dimensional steady-state thermal-structural analysis of a head in air and over a disk is presented. Complex head geometry is modeled. Velocity slip and temperature jump boundary conditions are used in formulating heat transfer through the air bearing. Moreover, transient analysis of head thermal protrusion is presented. Step direct current is applied. Snapshots of the temperature field as well as temperature and displacement time functions of several locations in the head are exhibited. It is found that head protrusion first occurs at the pole tip, then spreads to the trailing end of the slider. For the head–disk interface studied, it takes 0.6 ms for the head to come in contact with the disk after writing starts.

Demonstration of a magnetic angular position sensor with ultra-high resolution and accuracy

In this study, a magnetic angular position sensor with 160,000 pulses/rev and 0.4 in. of the accuracy is obtained using a longitudinal disk, magnetoresistive (MR) sensors and a new method of formatting magnetic poles on the disk. The magnetic poles are formatted by a thin film inductive head with 6 μm of trackwidth and 0.7 μm gap length. Angular position signals are reproduced by two MR sensors which are commercial MR heads with 4 μm trackwidth and 0.6 μm gap length maintained in phase quadrature with each other. In order to format equally all magnetic poles on the disk, the central frequency of the writing signal must be equal to the central frequency of the speed of disk and the steadiness of the disk speed and writing frequency must be as high as possible.

Narrow-track antisymmetric dual magnetoresistive head performance on rigid media

In this work, the performance of an antisymmetric dual magnetoresistive (A-DMR) head, having a track-width of W/sub t/=2 /spl mu/m, a stripe height of h=2 /spl mu/m and a gap length of 80 nm, is presented and compared to theory. A thin film inductive head that incorporates high magnetization FeAlN poles, with a gap length of 0.25 /spl mu/m, was used to record thin film disk media with an areal magnetic moment of 0.5 memu/cm/sup 2/ and a coercivity of 3 kOe. The A-DMR roll-off and spectral curves that are fit in amplitude and shape with a 2-D analytical curve, indicated D50=190 kfci. The theoretical curves fit the experimental data with two fitting parameters, the spacing parameter of the spacing loss term and a parameter /spl zeta/=/spl zeta/ (W/sub t//h) that can be calculated with a 3-D micromagnetic model. The cross-track profile, off-track response and adjacent track interference are analyzed in the time domain and compared with previously reported theoretical results, where in this case the write head track-width is 2.5 /spl mu/m. The head showed some adjacent track interference and pulse amplitude asymmetry at lower linear densities, mainly due to a lower magnetic transverse bias level of one of the sensor layers. In spite of the good linear resolution of these heads, they offer limited sensitivity in comparison to spin valve heads.

A comprehensive electrostatic discharge control program for magnetoresistive heads

This paper describes a comprehensive electrostatic discharge (ESD) control program for the protection of magnetoresistive and giant magnetoresistive heads. These types of magnetic recording heads are far more sensitive to damage from ESD than the inductive thin film heads which previously dominated head disk drive designs. Sources of ESD damage include people, tools and work stations, packaging materials and the head itself. This document defines procedures for coping with ESD in a thorough, yet cost effective, manner.

Low inductance and high efficiency single-pole writing head for perpendicular double layer recording media

A new type of thin film inductive single-pole head for perpendicular magnetic recording has been developed to provide a writing head for perpendicular double layer media. The head consisted of a main pole, three thin-film conductive layers to drive the pole and a return path pole. A low inductance of around 1.5 nH and a small saturation magneto-motive force of less than 0.025 AT/sub 0.p/ was obtained. The D/sub 50/ was 180 kFRPI with an MR head of 210 nm shield separation. The error rate at 310 kFRPI was 10/sup -6/. Head induced erasure, which is an issue for the single-pole head, was also investigated by experiments and calculations. Around 10% output reduction in 20 Oe stray field was confirmed. Computer simulation predicted an improvement by reducing the permeability of the medium's underlayer.

Integrated, variable-reluctance magnetic minimotor

The use of lithography and electroplating to fabricate variable-reluctance, nearly planar, integrated minimotors with 6-mm-diameter rotors on silicon wafers is described. The motors consist of six electroplated Permalloy® horseshoe-shaped cores that surround the rotor. Copper coils are formed around each core. The Permalloy and copper electroplating baths, electroplating seed layers, and through-mask plating techniques are similar to those used to fabricate inductive thin-film heads. High-aspect-ratio optical lithography or X-ray lithography was used to form the various resist layers. The rotors were fabricated separately, released from the substrate, and then slipped onto the shaft, which was plated as part of the stator fabrication process. The fabrication processes for stator and rotor are described in this paper, and initial minimotor operation data are presented.

Active cancellation of mutual inductance in split-coil thin-film heads

The consequences of using split-coil thin-film inductive heads for the recording process were investigated. The heads studied have two separate coils (the head is a four-terminal device); this allows the number of turns in the write and read process to be optimized independently. Unfortunately, at high frequencies the effect of mutual inductance between the coils offsets the potential reduction in the write inductance. The mutual inductance was characterized using both recording and impedance measurements. We demonstrate a novel, active technique for reducing the effect of the mutual inductance.

A design concept of array heads

This paper describes a novel design concept and experimental hardware data of array heads for close-packed track recording. The heads are batch fabricated on wafers in a linear fashion. These 60-turn thin-film inductive heads are designed with 6 /spl mu/m pitch helical coils and planar side-by-side P1/G/P2 yokes structure. The linear head array is placed along the upstream-to-downstream direction of the track. By skewing the array slightly off the track direction, each head of the array aligns to an individual track. In this case, the track pitch is about 5 /spl mu/m, which is the yoke height. With this head arrangement, even though a thermal expansion causes the head-to-head distance to increase along the upstream-downstream direction, it does not cause a thermal induced track misregistration problem. The increased head-to-head distance only affects the timing of signals between tracks, which can be compensated by the channel electronics. Thus, the thermal induced track misregistration problem is eliminated using this design. The guard bands between tracks are not necessary, and a close-packed track recording is possible. A state of the art head impedance of the 60-turn head is obtained: 11 /spl Omega/ and 0.40 /spl mu/H. The gap-to-gap pitch is 100 /spl mu/m. The overall head-to-head isolation is greater than 50 dB at 10 MHz. Such a large isolation is realized by suppressing the capacitive coupling between lead wires using a ground plane and grounded wall structures. The tight winding of the helical coils reduces the magnetic coupling between the heads.

Narrow track dual magnetoresistive heads for tape

An experimental investigation of a dual magnetoresistive head tested on a Metrum tape test stand, is presented. The dual magnetoresistive (DMR) head has a trackwidth of 4 μm and a gap length of 0.1 μm. Metal particle tape, with a Mrδ of 16 memu/cm2 and a coercivity of 1.8 kOe, was used. A square wave was recorded with an FeAlN thin film inductive head, with a trackwidth of 33 μm and a gap of 1.9 μm. A shielded shunt biased MR head used in quarter inch cartridge drives (QIC), with a trackwidth of 19 μm and a shield to element gap of 0.25 μm was used as a benchmark. The DMR head showed a larger signal to dc erased noise per unit trackwidth than the QIC MR head, at linear densities of 20 to 100 kfci. Isolated transitions and dibits with a bit spacing of 0.3 μm were recorded for time domain measurements. The dibit response of the DMR head, characterized by a unipolar pulse with small side over/undershoots demonstrated the differential character of the DMR head. The QIC MR head PW50, measured directly from the isolated transition response and indirectly from the dibit response, was 1.4 μm. This large PW50 value was essentially write process limited, to first order independent of the read head gap length.

Batch-processed close-track array heads (abstract)

This article describes novel array heads for close packed track recording. The heads are batch fabricated on wafers in a linear fashion (Fig. 1). These 60-turn thin-film inductive heads are designed with 6 μm pitch helical coils and planar side-by-side P1/G/P2 yoke structures. The linear head array is placed along the upstream-to-downstream direction of the track. By skewing the array slightly off the track direction, each head of the array aligns to an individual track (Fig. 2). In this case, the track pitch is about 5 μm, which is the yoke height. With this head arrangement, even though thermal expansion causes the head-to-head distance to increase along the upstream–downstream direction, it does not cause a thermally induced track misregistration problem. The increased head-to-head distance only affects the timing of signals between tracks, which can be compensated by the channel electronics. Thus, the thermally induced track misregistration problem is eliminated using this design. The guardbands between tracks are not necessary and a close-packed track recording is possible. A state of the art head impedance of the 60-turn head is obtained: 11 Ω and 0.40 μH. The gap-to-gap pitch is 100 μm. The overall head-to-head isolation is greater than 50 dB at 10 MHz. Such a large isolation is realized by suppressing the capacitive coupling between lead wires using a ground plane and grounded wall structures. The tight winding of the helical coils reduces the magnetic coupling between the heads.

Inter-track interference studies using MFM image reconstruction

The Magnetic Force Microscopy (MFM) image reconstruction technique has overcome difficulties in interpreting MFM images of data tracks written on longitudinal recording media. In this work, MFM image reconstruction is used to study the vector magnetization components of closely spaced tracks. Untrimmed and Focused-Ion Beam (FIB) milled, trimmed thin-film inductive heads of widths 4.5 /spl mu/m and 2.5 /spl mu/m are used to write tracks with wavelengths ranging from 0.75 /spl mu/m to 3 /spl mu/m. In order to analyze the limitations of high density recording, the magnetization at the edges of neighboring tracks is considered. It is shown that the width of the cross-track component of magnetization is strongly dependent on the relative phase difference of adjacent tracks, the track width, and the linear recording density.

FeN/Ta multilayers: magnetic properties and application to magnetic recording heads

Magnetic recording performance of inductive heads with hybrid top-pole structures consisting of thin sputtered FeN/Ta multilayers and thick electroplated NiFe was studied. Conventional 42-turn, 4-layer thin-film inductive heads were used and emphasis was placed on writability. Heads with hybrid top-displayed structures showed improved overwrite and nonlinear transition shift performance compared with NiFe-only heads.

Micromechanical and tribological characterization of alternate pole tip materials for magnetic recording heads

Pole tip recession or PTR (relative wear of the pole tip with respect to the air bearing surface) causes signal loss when using inductive heads. Loss of signal caused by spacing between a head gap and the recording medium is magnified in high-density short wavelength recording. Nickel iron (NiFe) is the most commonly used pole material. NiFe is softer than the head substrate material (typically NiZn ferrite or Al 2O 3TiC) which leads to PTR as a result of differential wear of the materials. Alternate pole tip materials which are more wear resistant and superior in magnetic properties (such as high saturation magnetization), as compared with NiFe, need to be developed. In this research, NiFe, cobalt zirconium tantalum (CoZrTa) and iron aluminum nitride (FeAlN) materials were studied. In the first phase of this study, micromechanical characterization of the three pole tip materials, the alumina (Al 2O 3) insulating under/overcoat and gap material and the Al 2O 3TiC substrate was conducted using a depth-sensing nanoindenter. The nanohardness of NiFe, CoZrTa and Al 2O 3 are similar and about one half that of FeAlN, and the hardness of the Al 2O 3TiC substrate is about twice that of FeAlN. Microscratch studies showed that the critical load required to cause failure of the NiFe and CoZrTa films are similar and about one fourth that of FeAlN, and the critical load for FeAlN is comparable with that of the Al 2O 3 and Al 2O 3TiC substrate. Thus, FeAlN is superior in mechanical properties to NiFe and CoZrTa. In the second phase of this study, dummy tape heads fabricated with the three pole materials were run against metal particle (MP) tape in a linear tape drive. The PTR was measured by atomic force microscope (AFM) imaging before and after the sliding tests. Any nonuniformities in the thin-film region gets removed in the first few kilometres of sliding. FeAlN poles exhibited a low (∼10 nm) and constant PTR over 1 000 km of tape sliding distance, whereas the NiFe and CoZrTa poles exhibited growth in recession to about 30 and 40 nm, respectively, over the same sliding distance. The superior wear resistance and high saturation magnetization of FeAlN are ideal for high-density thin-film inductive heads.

Effect of head domain asymmetry on a recording track

The effects of the domain structure in the write head on a recording track are modeled by studying the magnetic field distribution generated by a thin film inductive head such as those used in high density recording on hard disks. The magnetic field around the head gap is calculated in three dimensions from a magnetization configuration generated by a two-dimensional micromagnetic model. Domain variations inside the recording head produce asymmetries in the recording track due to the presence of closure domains in the head. The effects of this asymmetry on overwrite are discussed.

Thin-film inductive heads

The development of IBM thin-film inductive recording heads is traced from 1964, through their first introduction in 1979, to the present. We review a number of innovations in thin-film technology materials and processes associated with this type of head. Design and technology changes made since 1979 have led to the development and implementation of heads in several successful recording systems. We also describe efforts to predict the performance of thin-film inductive heads and to understand and control head instabilities and noise.

Domain structures at the cross sections of thin film inductive recording heads

Using a scanning Kerr effect microscope with external ac-tickle field excitation, zigzagged and slanted intersections of domain walls were observed at the symmetry-axis cross sections of thin film inductive heads. These domain walls are believed to be the intersections of edge-closure domain walls, with the magnetization on the two sides of the walls (or lines) oriented in ‘‘head-to-head’’ or ‘‘tail-to-tail’’ configurations. They are thus slanted or zigzagged in order to spread the charges along the walls over a larger region, thereby reducing magnetostatic energy. This interpretation is further evident by the observation that upon applying a small dc bias field in the symmetry-axis direction, the slanted or zigzagged intersections of domain walls were observed to displace according to the field direction, and sometimes deformed to different configurations. Upon lapping the heads from their air-bearing surfaces, slanted domain walls at the sloped backgap cross sections were occasionally observed.

Frequency losses of readback efficiency for thin-film inductive heads

Magnetic recording measurements on a rigid disk are used to derive the readback efficiency of thin film inductive heads as a function of frequency. The technique relies on a pseudo-contact air bearing system which keeps the transducer in contact with the disk over a range of velocities. It is found that the readback efficiency decreases monotonically with frequency, showing a 3 dB loss at 40 MHz for the heads used in this experiment. A four section transmission line model has been developed to include the geometry variations in different areas of the head. Domain wall motion and rotational contributions to flux transmission have been included. The calculated efficiency and impedance values are found to be in good agreement with measured values.

Track profile study of ABS-patterned narrow track thin film inductive heads

ABS-patterning is a known method for achieving the ever-increasing track density requirements of today's disk drives. This patterning leaves a shoulder on either side of the head which can affect the track profile of the head. Therefore, the height and width of this shoulder are important parameters to control when fabricating heads in this fashion. In this study, we examine the effect of the shoulder width and the shoulder height on the cross-track performance. We conclude that a shoulder height of 0.75 /spl mu/m is sufficient to minimize the effect of a shoulder width of up to 1 /spl mu/m. A 3D model was constructed and shows good agreement with the data. The model was used to predict throat-height tolerance and to model wider shoulder widths.