Thin Film Head Research Articles

A Methodology to Improve Manufacturing Precision in the Presence of Workpiece Imperfections

In modern manufacturing applications of products such as LCD’s, semiconductor wafers, and thin film heads, the workpiece has to be processed in multiple steps. The quality and yield of the products depends on how precisely the workpiece is aligned in each setup. The effect of imperfections of the workpiece on the manufacturing precision are analyzed, and our analysis shows that the imperfections of the workpiece can be a major cause of tolerance problems. A methodology that can help to greatly reduce the sensitivity of imperfections in the workpiece has been proposed. The methodology is applied to the 2-D domain, and is substantiated by characterization and analysis of samples from the LCD industry.

ChemInform Abstract: Evaluation of Amorphous Diamond‐Like Carbon‐Nitrogen Films as Wear Protective Coatings on Thin Film Media and Thin Film Head Sliders

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

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.

Current dependence of the magnetization rise time in thin film heads

Time-domain optical measurements of magnetization dynamics can now be performed with sufficient resolution to reveal the intrinsic speed of many structures relevant to magnetic recording. Here we describe the behavior of the magnetization rise time at the air-bearing surface of a thin film recording head, as a function of the amplitude of current pulses in the write coil. The spatial profile of the magnetization on both sides of the gap is also examined through time-resolved, current dependent measurements. Spatial resolution enhancement via a solid immersion lens allows domain features to be discerned in the data.

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.

Stress and microstructure of nanocrystalline FeXN (X = Ta, Si, and Al) thin films

Magnetic domain structures in thin-film heads are influenced by magnetoelastic anisotropy which is proportional to the film stress. In this study we have undertaken systematic measurements of thin film stress in the as-deposited state for sputtered FeXN (X = Ta, Si, and Al) thin films as a function of Ta, Si, Al, and N content. All as-deposited films exhibited the α-Fe structure with a (1 1 0) growth texture. It was found that pure Fe exhibits a tensile stress and this stress becomes more compressive as the amounts of Ta, Si, Al, and N in the films are increased. These stresses appear to be a cumulative effect of the amounts of Ta, Si, Al, and N added to the pure Fe. It was also found that N decreases the biaxial modulus of FeN and Fe-10TaN thin films.

Microtribological properties of hard amorphous carbon protective coatings for thin-film magnetic disks and heads

For long durability of magnetic media and head sliders, protective overcoats of hydrogenated amorphous carbon (a-C:H) are generally used. In this study, microtribological studies of hydrogenated amorphous carbon coatings deposited on a single-crystal silicon using three different deposition techniques—sputtering, ion beam and cathodic arc—were studied using atomic force/friction force microscopy (AFM/FFM). Roughnesses of all coatings at two scan sizes of 1 μm × 1 μm and 10 μm × 10 μm are comparable. Surface topography of sputtered carbon coating shows some particulates on the surface. Cathodic arc carbon coating exhibits the lowest coefficient of friction value followed by ion beam and sputtered carbon coatings. Microscratch and wear resistance and nanohardness of cathodic arc carbon coating are superior to those of ion beam and sputtered carbon coatings. Cathodic arc deposited carbon coatings are potential candidates for magnetic disks and heads.

High resolution imaging of thin-film recording heads by superparamagnetic magnetic force microscopy tips

We have used superparamagnetic magnetic force microscopy (MFM) tips to obtain high spatial resolution MFM images of recording heads. Profiles of the magnetic field gradient above a thin-film recording head under 3 mA bias current to the head and various tip-head distance conditions are presented. At a low tip-head distance, the gap width, gap location, and gap-field structure can be well resolved in these MFM images. Superparamagnetic tips show promise for the magnetic imaging of recording heads with gap widths below 200 nm.

Inductance-saturation characteristics in thin film heads

Inductance-saturation characteristics in thin film heads are measurements of inductance as a function of write current. These measurements typically exhibit a series of step-like inductance discontinuities as various segments of the magnetic core saturate. In this work, we present a framework for interpreting the location and magnitude of these discontinuities and discuss what they reveal about the physical constitution of the core.

Thin-Film Head with Domain Structure Stabilized by the Magnetoelastic Effect

A new technique for creating a thin-film head with a controlled domain structure was investigated. The difference between the thermal expansion coefficients of the magnetic film and the photoresist insulation layer greatly affects the stress distribution across the upper magnetic core after annealing. Tensile stress is induced in the lower part of the upper magnetic core, and compressive stress is induced in the upper part of the core. The composition distribution of NiFe alloy across the upper core can be controlled by means of the electroplating conditions. Consequently, magnetoelastic effect anisotropy can be induced to stabilize the domain structure of the upper magnetic core. This new technique was used to fabricate a thin-film head with low wiggle noise.

Corrosion resistance of low coercivity, high moment FeXN (X=Rh, Mo) thin film head materials

Electrochemical corrosion of low coercivity, high moment FeXN (X=Rh, Mo) films were tested in 0.5 M NaCl electrolyte. The testing conditions emulate the extreme environment to which thin film heads are exposed during packaging, storage and subsequent application. The addition of Rh or Mo to FeN films improves the corrosion resistance significantly. In 0.5 M NaCl electrolyte and with the protection of the native oxide layer, the corrosion resistance of FeRhN films is as good as Permalloy. More importantly, FeRhN films show better overall pitting resistance than Permalloy.

Photoacoustic detection of microcracks of thin film head alumina using Nd:YAG laser irradiation

Acoustic wave generation during Nd:YAG laser irradiation on thin film head alumina is studied. It is found that with proper selection of laser parameters, the acoustic waveforms observed are completely different for pristine head and head with preexisting microcracks. It has potential applications of thin-film heads and head wafers.

Magnetic thin film head with controlled domain structure by electroplating technology

Thin film heads with electroplated NiFe magnetic cores are the main parts of hard disk drives. It is generally agreed that a uniform negative magnetostriction magnetic core is essential to minimize stress-induced anisotropy and to obtain a controlled magnetic domain structure. Only weak tensile stress is induced to the core with the traditional process. In this paper, a new process is presented to obtain a more stabilized domain structure core that has a large magnetization distribution from negative to positive. Annealing at the final stage of water fabrication generates a stress distribution from tensile to compressive across the core. Therefore the magnetization distribution is effective to induce stress-induced anisotropy at right angles to the magnetic path. A desired magnetization distribution can be formed by electroplating technologies. Results of the finite elements method show the origin of this stress distribution to be plastic deformation or creep deformation of the core layer on the organic insulation layer.

Thin-film heads for helical scan recording

The paper describes the technology of newly developed thin film heads with azimuth in the process for helical tape recording and outlines their integration into the digital video (DV) system.

Thin-film heads with anisotropy-determined track widths

Multitrack yoke-type MR readout heads having a single shared front fluxguide with a highly anisotropic permeability, have been designed and evaluated. The well defined microtrack response profiles of these heads show that the anisotropy of the permeability confines the flux-detection to the area on tape in between the contact leads of the MR element. This can be exploited in "full-density" tape recording heads which read directly a number of adjacent tracks.

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.

Evaluation of amorphous diamond-like carbon-nitrogen films as wear protective coatings on thin film media and thin film head sliders

As the magnetic data storage industry strives to achieve ultra-high recording densities requiring fly heights of less than one microinch, the tribology of the head-disk interface (HDI) is a limiting factor in disk drive design. Amorphous diamond-like-carbon (DLC) films have been the materials of choice for wear-protective coatings. Various amorphous DLC type coatings have been developed. The earliest DLC material was DC magnetron sputtered pure carbon films. Recent developments have produced C:H (hydrogenated-carbon) and C:N (carbon-nitrogen) films with greater wear-resistance than pure C film. Our intent is to describe and evaluate the wear-resistance performance of amorphous C:N films as wear-protective overcoats on thin film media and thin film sliders. Both C:H and C:N films have demonstrated superiority over DC magnetron sputtered pure carbon films. The bond character, microhardness, surface roughness features, and the physical nature of initial wear damage influence wear-resistance performance significantly. A recent report of nano-indentor measurements and wear-resistance performance confirmed the superiority of RF diode and DC magnetron Facing Target Sputtering (FTS) of thin C:N coatings over other DLC films.

Multilayer Resist Frame Fabrication Using RIE

We investigate multilayer resist processes using reactive ion etching (RIE) for the narrow-track resist frame of thin-film heads. In terms of the shape of the resist, the three-layer resist (photoresist/SiO2/photoresist) process is better than the two-layer resist (Si containing resist/photoresist) process. Reducing the pressure of O2 plasma during RIE causes the residue of the resist to vanish. A resist frame with a width of 1μm and a height of 6μm can be produced by using the three-layer resist process. Plating was performed within this frame.

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.