Thin Film Head Research Articles

Electrochemical process for advanced package fabrication

Interconnections for high-end applications are essentially low-resistance transmission-line structures with precisely controlled cross-sectional shapes and dimensions. The relatively thick copper conductors-typically 6 µm or more-combined with the stringent control required on the 10-20-µm-wide cross sections stretches the capabilities of the subtractive etch and lift-off processes that are typically used in semiconductor fabrication to pattern evaporated and sputtered metal films. Electroplating through a photoresist mask, which has proven itself to be a highly effective, precision manufacturing process for thin-film magnetic recording heads, is, however, capable of meeting and far exceeding the requirements of package fabrication. This paper describes the fabrication of a package structure that integrates traditional dry-process technologies with electrolytic copper plating to form the conductors, polyimide backfill and planarization steps to form the dielectric, and electroless deposition to selectively clad the copper lines to prevent adverse reaction of the copper with water generated during the polyimide cure. The discussion highlights salient issues which are pertinent to the compatibility of the individual process steps and to the extension of the technology to more demanding packaging structures and to other applications.

Wear coatings for magnetic thin film magnetic recording heads

Many coatings are in use today for the wear protection of thin film heads. With the trend towards smaller head-media distances, the thickness of the coating has to diminish. In this paper some of these coatings: zirconia, chromium nitride, chromium oxide and diamond (+diamond-like carbon) will be discussed. It will be shown that the film hardness is influenced by the microcrystalline structure, the texture and the film stress. The film hardness shows a good correlation with the reciprocal wear coefficient. The wear resistance of the materials discussed increases in the order: zirconia, chromium nitride, chromium oxide, diamond.

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.

Pole tip recession studies of thin-film rigid disk head sliders II. Effects of air bearing surface and pole tip region designs and carbon coating

Pole tip recession (PTR) results in an increase in spacing between recording elements and magnetic media which is undesirable for high-density recording. The effects of air bearing surface (ABS) designs, pole tip region designs and carbon coating on the growth of PTR with increasing start-stop cycles have been investigated. A better ABS design for less PTR should reduce contact time between slider and disk during take-off and landing of the slider. Among the two-rail, tail-dragger and negative pressure sliders, the negative pressure slider has shortest contact time during take-off and landing, followed by the two-rail slider and tail-dragger slider. The growth mechanisms of PTR for two-rail slider with or without U-shaped slot consists of knocking-off protruded poles, generation of wear particles and three-body abrasive wear. The PTR reaches a saturated value after a certain start-stop cycles. However, for the tail-dragger slider with square-shaped slot, there is a fourth step of erosion which leads to no saturation of PTR and a relatively rough surface of poles. Mechanisms of PTR for negative pressure slider is similar to the two-rail slider but with a lower saturated PTR value. Carbon coating minimizes or eliminates the PTR growth through reducing static and kinetic friction during take-off and landing, providing a wear-resistant protective layer and eliminating dissimilarities of ABS, thin film structure and poles. Based on this study, we find that negative pressure slider which minimizes contact at head-disk interface and carbon coating which protects thin-film region are desirable alternatives for slider designs. Initial recession is desirable as compared to protrusion.

Pole tip recession studies of thin-film rigid disk head sliders I. Mechanisms of pole tip recession growth

Pole tip recession (PTR) results in an increase in spacing between recording elements and magnetic media which is undesirable for high magnetic recording. A methodology for an accurate measurement of PTR using an atomic force microscopy (AFM) was developed. A reliable measurement of PTR with AFM consists of: (1) mounting the sample such that air bearing surface (ABS) is as parallel as possible to fast scan direction, (2) selection of fast scan direction along the long axis of a slider and (3) the use of software correction, namely, zero order flatten and first order plane fit, to remove measurement errors. The inductive head sliders with both initially protruded and recessed poles were used for the investigation of the PTR growth as a function of increasing CSS cycles. CSS tests were conducted using laser textured and mechanically textured disks. Based on AFM measurements, microscopy and chemical analyses of the worn sample, mechanisms of PTR growth were proposed. If the poles are protruded, first, the protruded parts of pole tips are knocked off by harder carbon coated laser bumps through adhesive wear and two-body abrasive wear within initial several hundred CSS cycles. Continued contacts at head-disk interface results in the wear of Al 2O 3TiC ABS, Al 2O 3 insulating film, NiFe poles and carbon coated laser bumps which generates abrasive particles. These wear particles result in three-body abrasive wear which selectively removes relatively soft metal poles and leads to a PTR. PTR growth levels off after a certain number of CSS cycles, dependent upon the pole tip design, typical size of wear particles and propensity of stain growth. Formation of stain on the pole tip region is observed after certain number of CSS cycles which minimizes PTR growth, however, stain build up is undesirable.

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.

Extremely low inductance thin-film single-pole head on flying slider

A novel single-pole head on a flying slider is presented as a high frequency writing head. The main pole of the head is driven with three thin-film conductor layers to have a short magnetic circuit path. Thus, a low inductance of around 10 nH and a high writing sensitivity of less than 0.03 AT/sub pp/ is obtained. The writing field distribution is shown to be the same as a regular single-pole head by computer simulations. The recording performance of the head is examined and the high writing sensitivity is demonstrated.

Multitrack thin film heads for the DigaMax/sup TM/ tape storage system

The multichannel servo writer and the data read/write heads of the new DigaMax/sup TM/ tape storage system are discussed. These heads enable a storage capacity of 13 GB (uncompressed) on 300 m of 72 kA/m tape using prerecorded buried servo information for dynamic track following during reading and writing of data.

Trends in digital magnetic recording; the application of thin-film heads for tape recording

Digital tape recording systems show the same trend as hard-disk drives: a large increase of storage density with time. The use of advanced media and highly sensitive thin-film heads with magnetoresistive (MR) readout will increase the storage density dramatically. Key improvements are narrower tracks, more sensitive MR elements attained by applying the giant magnetoresistance effect, high-saturation flux density pole materials, advanced metal powder tape, intimate head-to-tape contact, and accurate tracking. By increasing the number of channels in the multitrack thin-film head, high data rates can be obtained as well. The basics of digital magnetic recording are discussed and a short historical overview is given of the Philips activities on thin-film heads for tape recording. An outlook on future improvements is given.

Characterization of Thin DLC Films Using Film Stress and Raman Techniques

AbstractDiamond like carbon (DLC) films are deposited on thin film heads in the magnetic recording industry to reduce friction and “stiction” and to provide a durable, abrasion resistant coating. The films are a mixture of graphitic phases with sp2 bonding and diamond phases with sp3 bonding. The present work provides the results of thin film stress measurements and Raman tests performed on 10 rim DLC films deposited on 75 mm silicon test wafers using standard optical lever techniques. Stress is measured after deposition and in-situ during thermal cycling. Isothermal relaxation data is also obtained. Raman is performed before and after annealing.The deposited stress of 10 nrm films was over 2000 MPa. The stress relaxed entirely to zero during thermal cycling to 500°C. Isothermal relaxation at 300°C also resulted in complete relaxation of an initial 1500 MPa stress to zero in less than 24 hours. The Raman data is consistent with prior results in the literature. The position of the G band shifts from 1513 to 1581 cm-1 during annealing, and the intensity ratio of the D band to the G band rises from 0.201 to 0.814 during annealing.The decrease of the film stress to zero during thermal processing implies that the entire thickness of the film is undergoing a structural change while the stress relaxation data implies that the stress is relaxing by a fast diffusive process. The Raman data implies that the film is becoming more graphitic and the crystallites are growing in number and size during thermal processing. We suggest that the structure of the extremely thin carbon film is modified by a surface diffusion mechanism.

Laminated dual-axial anisotropy film for submicrometer-trackwidth thin-film heads

A dual-axial anisotropy film which consists of two uniaxial sandwiches of Co/sub 91/Nb/sub 6/Zr/sub 3//SiO/sub 2//Co/sub 91/Nb/sub 6/Zr/sub 3/ with their easy axes orthogonally oriented, was fabricated by RF-sputtering using a water-cooled, magnetic substrate holder, for application in a new type of submicron trackwidth thin film head. The thermal stability of the induced uniaxial anisotropy of the film was studied by heat treatment in a magnetic field and subsequent magnetic measurements. The magnetic properties of the films before and after rotational field annealing (RFA) mere studied by their B-H loops and permeability spectrum along various directions in the film plane. It was found that the B-H loops of the as-deposited dual-axial film along either axis were the superposition of the easy axis and hard axis B-H loops of the two uniaxial sandwiches along that axis. The two uniaxial sandwiches appear to behave independently before RFA. In-plane isotropic B-H loops and isotropic permeability of 2640 at 10 MHz were obtained for the dual-axial films after RFA at 320/spl deg/C. The small H/sub k/ and the magneto-static interaction between the two sandwiches may be mainly responsible for the isotropic magnetic properties of the dual-axial film after RFA.

Experimental study of the validity of simple design rules for the biasing of spin-valve-type GMR heads

From an analytical description of magnetic interactions combined with finite-element modelling, design rules for a giant magnetoresistance (GMR) element can be derived. For some practical designs we arrive at the conditions t P M S P < t f M S f and t p M S P ≈ γhH F. Here t p, t f, M S P and M S f are the layer thicknesses and the saturation magnetizations of the pinned and the free layer, respectively; h is the element height, H F is the ferromagnetic interlayer coupling and γ accounts for the soft magnetic environment of the sensor. We have fabricated yoke-type GMR heads in an adapted design conforming to these rules. The GMR elements were Ta/8 nm Ni 80Fe 20/2.8 nm Cu/6 nm Ni 80Fe 20/10 nm FeMn/Ta. From finite-element calculations we find that for our heads γ ≈ 2, which together with H F = 6 Oe and h = 5 μm obeys the design rules. Measurements of these heads show that indeed the optimum bias state is obtained without using the integrated bias conductor to apply a d.c. bias current. Measurements also show that the limiting factor for the head output in this case may no longer be the head efficiency (geometry), but the maximum driving amplitude (saturation) of the GMR element. This sheds new light on the current discussion whether for application of spin-valve materials in thin-film heads, a yoke-type or a shielded-type design would be advantageous.

ウルトラクリーンプロセスと微細構造制御 薄膜媒体並びに薄膜ヘッド材料を例として

ウルトラクリーンプロセスと微細構造制御 薄膜媒体並びに薄膜ヘッド材料を例として

Design of thin-film tape heads

In this paper tools to handle the magnetostatic aspects of thin-film tape head design are reviewed. Some illustrative results from transmission-line calculations on inductive write heads and yoke-type magnetoresistive read heads are shown. New is the application to nonlinear saturation effects in write heads. The design of an emboss head for writing servo tracks on tape is described. Finally, a new type of read head is discussed that utilizes anisotropy of the permeability instead of structuring of the fluxguides for obtaining very small track widths.

The Self-Acting, Subambient Foil Bearing in High Speed, Contact Tape Recording with a Flat Head

The mechanics and tribology of a flat head for high-speed, contact tape recording is presented. Experiments performed on a “row-bar” of thin-film disk heads where the tape is wrapped only on the edge opposite to the heads showed very stable contact for a wide range of tape speeds and very low wear. A model of the interface showed that a self-acting, subambient air bearing forms near the leading wrapped corner. This suction is caused by the expansion of air into the diverging gap on the upstream side of the head-tape interface, which is unique to this wrap geometry, and it is responsible for the stability and low contact pressures. A bidirectional version of a flat head geometry is analyzed via modeling and suggestions are made for that design. This work also showed strong evidence of a threshold of contact pressure below which wear becomes negligible.

Soft-magnetic fluxguide materials

This paper reviews the research done on soft-magnetic fluxguide materials for use in sandwich heads and in thin-film recording heads for digital magnetic recording. After dealing with the basic principles of magnetic recording, the requirements on modern soft-magnetic materials are discussed. The roles of magnetic anistropy and magnetostriction in relation to permeability are discussed. Next, we review the recent advances in soft-magnetic materials processing, in particular for amorphous cobalt (CoNbZr) and nanocrystalline iron alloys, such as FeMX, with M being group IVa-Va metals such as Zr, Hf, Nb, Ta, etc., and X being N and O.

Isolated pulse distortion and medium noise analysis for submicrometer-width narrow-track recording

Isolated pulse shapes and medium noise are analyzed for narrow track recording by micro-magnetic simulation. Low density recording is simulated and studied with thin film heads of widths 1.5, 1.0, and 0.5 /spl mu/m. Isolated pulse shape for a 0.5 /spl mu/m width recording is severely distorted compared with that for a wide recording. A formula for the PW50 of an isolated pulse is empirically obtained. For a fixed gap length, the first null in the spectrum shifts to lower frequency with a smaller head width. Increases in total noise power are sensitive to narrower heads, especially in the submicron region of the head width.

スプレー造粒粉末を用いた焼結センダストの磁気特性

The iron-silicon-aluminum alloys (especially Sendust) have been widely used for the application requiring high saturation flux density, low coercive force and high electric resistivity. For this reason they have been appreciated for magnetic thin film heads, however, they are too hard and brittle to be made into thin film by rolling or three dimensional complex shaped products by mechanical work or conventional powder metallurgy process. The reduction in the size and weight of apparatus that can be accomplished by its use has had an important effect on technical developments. In this report, magnetic characteristics of Sendust ring samples produced by the powder metallurgy process with spray drying method were investigated. After gas atomized Sendust powders were mixed with paraffin compounds, these powders were granulated by spray drying method using organic binder consisting of poly (vinyl alcohol) (PVA) and plasticizer in the range from 0.1wt% to 0.5wt% of PVA, in order to improve the powder flowability and mechanical strength of green bodies. Results show that the present method is an excellent process for producing near-net-shape parts with high performance and high precision in dimension after sintering.

Design and technology of sensor-last thin film magnetic heads

The first thin film heads produced commercially by Philips were of the socalled sensor-first type, the sensor being processed on the substrate and the remaining parts of the head being processed on top of the sensor. This design has various drawbacks in comparison with a design where the sensor is processed at the end (sensor-last), such as a higher power consumption (low head efficiency) and limitations of use of high-temperature processes/materials. However, initially, topographic structures, step coverage and problems with wet chemical etching were obstacles in realizing the sensor-last design. The introduction of planarization in wafer processing technology opened the way to the sensor-last design. The design was introduced in heads for the DIGAMAX TM system and showed all the expected advantages in comparison with the sensor-first design. It also offers the possibility of applying new materials in the head, an option which is necessary for realizing new generations of recording systems.

A stroboscopic scanning solid immersion lens microscope

A high resolution scanning optical microscope for stroboscopic time-resolved studies is presented. High optical efficiency is the prime motivation in selecting a solid immersion lens to surpass conventional diffraction limited resolution. A microscope design including details concerning the fabrication, mounting, and operation of both the hemispherical and the truncated-sphere solid immersion lenses is discussed. A thin-film magnetic recording head is used as a convenient, planar test specimen with well-defined optically reflective and magnetic features on a submicrometer length scale that allows characterization of the lateral spatial resolution of the instrument. In addition, the versatility of the microscope is demonstrated through examples of time-resolved magneto-optic imaging of the head. Further enhancement of the spatial resolution through the incorporation of confocal imaging is also described. The tradeoffs governing the selection of a particular style of microscope for specific circumstances are outlined.