Narrow Track Width Research Articles

A New Silicon Integrated Head For High Density Magnetic Tape Recording

A new silicon integrated magnetic head with a very narrow track width has been achieved. A collective process has been used to carry out a vertical gap fabrication which avoids a glass bonding in the gap area, and allows an integrated coil elaboration. Wear behaviour and frequency dependance for reproduced output level have been investigated.

Study of SAL-biased MR heads with patterned permanent magnet bias

SAL-biased MR heads with patterned permanent magnet (PM) bias have been studied by micromagnetic modeling. The modeling shows that in shielded MR sensors with narrow track width, the magnetic stray field generated by longitudinally magnetized PM not only produces multi-domain structures in the side-wing regions of MR heads but also degrades the biasing level as well as the sensitivity. These can be improved by either putting transverse exchange bias with FeMn on the SAL or tilting the magnetization angle of PM away from the sense current direction. It is found that proper magnetization angle of PM not only can increase the sensitivity greatly, and but also can eliminate multi-domain structures. >

A low inductance metal-in-gap head using a side-core concept

A low inductance metal-in-gap (MIG) head for rigid disk drives using a single crystal ferrite core was developed. Side mounting of a core was adopted to reduce its thickness, thus improving the inductance, and to achieve the ease of controlling the narrow track width and small throat height. It was demonstrated that the side-core composite (SCC) head has several advantages over conventional monolithic and composite heads in terms of electrical performance and manufacturability. Testing methods called swept frequency and swept current were also developed to demonstrate different interpretations of magnetic recording phenomena.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Domain Characteristics and Conformal Deposition of NiFe Thin Films

Plated has been extensively used as the pole piece material in thin film inductive head. The interaction between stress and magnetostriction, which is a strong function of composition, has a significant effect on its domain configurations. It turns out that, from a simple analysis, the optimum film composition for poles in inductive head is quite different from that for shields in magneto‐resistive head. Factors affecting the within‐device current distribution were analyzed. The diffusion layer thickness is estimated to be around 40 μm in a plating cell with reciprocating paddle under nominal operating conditions. The trend towards narrow track width and multilayer coil head design would require more stringent composition control. Pulse plating can provide thinner diffusion layer which conforms more closely to the surface contours and thus better composition uniformity can be achieved.

Laminated hard disk head for high density magnetic recording

Hard disk heads with a novel core structure have been developed for high-density magnetic recording by using magnetic alloy thin films as a core material. Sendust alloy films have been sandwiched between two nonmagnetic substrates for the sliders. This structure brings about good manufacturability, low head inductance, and good off-track characteristics. Read/write characteristics were evaluated for the structured heads with various narrow track widths. The laminated head inductance is about 40% of that for a metal-in-gap head. Normalized output voltage is 167 nVp-p/ mu mu -turn-m/sec. D/sub 70/ recording density is 47 KFCI. At 17.5 KFCI, the difference between effective track width and optical track width is 1.4 mu m. Thus, the laminated head shows great potential for achieving high-areal-density recording. >

Fabrication of thin film inductive heads with top core separated structure

A novel inductive head structure and process suitable for narrow track width have been developed based on a dry process. A top magnetic core of the head is separated into two parts, a pole tip and the rest core. This structure makes it possible to achieve smaller variation of the track width compared with a conventional head, because the pole tip can be formed at a lower step portion and a thinner photoresist pattern can be used as a masking for the etching of the pole tip part. The preferential etching ratio for a magnetic film to a masking layer was improved by using a double layer masking method. Reactive ion beam etching makes it possible to form fine and accurate pole tip patterns. The heads fabricated by using these methods revealed smaller variation of the track width and equivalent output level to a conventional head without any noise problem. >

Effect of magnetic domain configuration on read-back amplitude variations in inductive film heads (abstract)

Narrow track width, high-performance inductive film heads exhibit a noise phenomenon in which the read-back peak amplitude varies after writing with the head. This noise phenomenon was studied in 6- to 8-μm track width, 31-turn double layered coil, film heads using a scanning Kerr effect microscope. These heads, made from electroplated permalloy films with a magnetostrictive coefficient of − 1.6 × 10−6, were specially selected for the study to have varying levels of read-back amplitude variation by using the percent variation in the peak amplitude after repeated writes as a quantitative noise figure. A statistical sampling method was used to quantitatively measure the magnetic domain patterns in the top NiFe layer of the heads under simulated operating conditions. Quantitative correlation was found between the read-back variation and the magnetization orientation in the narrow-sloped pole region. The images show that a single 180° domain wall orientated longitudinally to the flux conduction direction in the narrow pole piece is the major source of read-back variation in these types of heads. The statistical sampling method shows that the pole domain configurations are reproducible in both the low-noise and high-noise heads. Patterned NiFe films on planar alumina substrates have the desired transverse oriented 180° domain wall configuration in the pole-shaped region, as found in the low-noise heads. These results imply that the variation of the domain configuration in the pole region is caused by easy axis reorientation due to variation in the stress-induced magnetic anisotropy in that region. We also find that the read-back noise is not sensitive to the longitudinal 180° walls found near the back closure region of the heads. This is probably due to the lower flux densities found in the back closure as compared to the pole region and the existence of other flux paths that circumvent the domain walls in the back closure region. We conclude that read-back distortion noise in 6-μm track width heads can be drastically reduced by maintaining a transverse magnetic easy axis in the sloped pole piece by either employing fabrication methods that control the stress state of the pole region or by using very small magnetostriction values in the NiFe films.1

Side writing/reading in magnetic recording

Side writing is a significant effect for narrow track widths used in high- areal-density magnetic recording. Lorentz electron micrographs can help to understand the nature of side writing and are used in this paper, in conjunction with analytical modeling, to characterize side writing in isotropic and strongly oriented recording media. Isotropic media exhibit a wide side-written fringe, including a strip often termed an ‘‘erased band,’’ although it is not truly erased. Strongly oriented media, however, show no erased band.

1.2 Gbit/s HDTV digital VTR

Some of the essential features of the record/playback system of a new 1.2 Gbit/s digital VTR are described. The VTR can record the full bandwidth of 1125/60 HDTV signals, namely 30 MHz luminance, and 15 MHz for each of the two color difference signals. As for low error rate recording techniques, a cross-shape multilayered amorphous head, a 5 stage transversal filter, a playback head with a narrow trackwidth and a special PLL to cope with stunt motion are employed. At a high data rate of 148.5 Mbit/s and a high linear density of 0.345 μm per bit, the recorder confirms reliable operation with a word error rate of less than 10 −4.

Side Crosstalk Response in Perpendicular Magnetic Recording with Narrow Track Width Single-pole Head

We investigated the off-track side crosstalk response and Bitter patterns in perpendicular magnetic recording media after recording with a single-pole head, for various head track widths and recorded bit lengths. A Co-Cr/permalloy flexible 3.5" disk medium and single-sided single-pole heads with track widths of 3.8, 5.5 and 7.0 μm were used in evaluations. Experiments yielded the following results: 1) the recorded track width coincided precisely with the width of the main pole, even at the very narrow track width of 3.8 μm; 2) side crosstalk in perpendicular magnetic recording is governed by the side-reading behavior of the single-pole head used.

Design issues for practical rigid disk magnetoresistive heads

Some of the issues of magnetoresistive (MR) head design are discussed from the point of view of practical, high-reliability, low-cost, manufacturable heads for rigid disk files. The major advantages of MR heads over single element inductive thin-film heads are that the MR head gives an ideal, easy to equalize output waveshape, can be used on disks with high coercivities for high linear densities, and is less subject to stability problems at narrow trackwidths. The major advantages of MR heads over metal-in-gap ferrite heads are in narrow trackwidth and high-frequency potential. Disadvantages of MR heads in the rigid disk environment include concerns about reliability and, more specifically, possible environmental fragility, loss of performance due to imperfect alignment between the read and write elements and/or due to signal asymmetry, and the possibility of higher cost/price. >

Improved bias and stability in dual-exchange-biased unshielded magnetoresistive heads

Data are presented on dual-exchange-biased NiFe-TbCo UMR (unshielded magnetoresistive) tape heads with improved signal response and process stability. It was found that a Si/sub 3/N/sub 4/ passivation layer offered better stability of the exchange bias through head processing than SiO/sub 2/. In order to improve sensor sensitivity, the longitudinal component of the exchange bias was reduced by increasing the exchange angle to 75 degrees from the sense current direction. This resulted in a +6-dB improvement in signal over previous heads without sacrificing Barkhausen-noise-free operation in narrow trackwidths. Heads with trackwidths as narrow as 8 mu m were shown to operate at linear densities of up to 50 kFCI with excellent signal-to-noise ratios (>45 dB). Investigations of different passivation materials showed Si/sub 3/N/sub 4/ to provide the best protection against environmental corrosion and thermally induced oxidation of the TbCo layer. >

Gigabit density recording using dual-element MR/inductive heads on thin-film disks

Inductive-write and magnetoresistive (MR)-read dual-element heads of very narrow trackwidths and narrow gaps have been designed, fabricated, and recording-tested on thin-film media of high coercivity and squareness. Results show excellent writability at modest write currents of 50 mA, large readback amplitudes with good signal-to-noise performance, very high linear-density resolution up to 5000 fc/mm (-6-dB density), and trackwidths close to the design dimensions. These results show that such head-disk systems are capable of recording operations at a target areal density of 1 Gb/in/sup 2/. Another result is that novel techniques for measuring nonlinear transition shifts as well as offtrack and squeeze performance have been developed. >

Magnetic Domain Structures of Multilayered permalloy Films Observed by Spin-Polarized SEM

The domain structures in patterned permalloy films were investigated by spin-polarized SEM, as part of the development of thin film magnetic heads with narrow track widths. Spin-polarized SEM made it possible to determine the direction of the magnetization in magnetic cores accurately. For single-layer permalloy films, triangular domains dominate and no 180° walls are observed in pole pieces when the track width is less than 10 ?m. For two-layer permalloy films with an alumina intermediate layer of thickness 4 nm, domain structures indicate that the magnetization direction remains oriented along the track width even when the track width is 7 ?m. Furthermore, in six-layer permalloy films with alumina intermediate layers 20 nm thick, the length of the 180° walls in the pole pieces becomes longer than that in two-layer permalloy films with a 4 nm alumina layer. It is thus concluded that multilayer permalloy films with single-domain structures are best suited for use in thin film magnetic heads with narrow track widths.

狭トラック単磁極ヘッドのオフトラック特性

We investigated the off-track side crosstalk response and Bitter patterns in perpendicular magnetic recording media after recording with a single-pole head, for various head track widths and recorded bit lengths. A Co-Cr/permalloy flexible 3.5 disk medium and single-sided single-pole heads with track widths of 3.8, 5.5 and 1.0 ?m were used in evaluations. Experiments yielded the following results: 1) the recorded track width coincided precisely with the width of the main pole, even at the very narrow track width of 3.8 ?m; 2) side crosstalk in perpendicular magnetic recording is governed by the side-reading behavior of the single-pole head used.

Magnetic Domain Structures of Multilayered Permalloy Films for Magnetic Recording Thin Film Heads

The domain structures of cores with patterned Permalloy films have been investigated in order to develop magnetic recording thin film heads with narrow track widths. For single-layered Permalloy films, domain patterns indicate that the writing and reading abilities decrease when the track width becomes less than 10 ?m. For six-layer Permalloy films with an alumina interlayer of 0.02 ?m, domain patterns show that domain walls remain oriented along the direction of the track width, even for a width of 7 ?m. Furthermore, six-layer Permalloy films with small anisotropy fields show no change in wall position when an external magnetic field is applied along the hard axis. It is thus concluded that six-layer Permalloy films with small anisotropy fields are most suitable for use in magnetic thin film heads with narrow track widths.

スピンＳＥＭ法で観察した多層パーマロイ膜の磁区構造

The domain structures of cores with patterned permalloy films are investigated in order to develop thin film magnetic heads with narrow track widths using spin-polarized SEM. This method made it possible to determine the direction of the magnetization in magnetic cores accurately. For single layered permalloy films, triangular domains are dominant and no 180° walls are observed at pole pieces when the track width becomes less than 10μm. For two layered permalloy films with an alumina interlayer of 4 nm thickness, domain structures show that the direction of the magnetization remains oriented along the track width even at the width of 7μm. Furthermore, for six layered permalloy films with an alumina interlayer of 20 nm thickness, the length of 180° walls at pole pieces becomes longer than two layered permalloy films with an alumina interlayer of 4 nm thickness. It is thus concluded that multilayered permalloy films with single domain structures are most suitable for thin film magnetic heads with narrow track widths.

Domain structures in multi-layered Co-Ni-Fe-Pd films observed by spin-polarized SEM

The domain structures of cores with patterned six-layered CoNiFePd films with alumina interlayers are investigated using spin-polarized scanning electron microscopy. The films exhibit virtually single domains in the middle of the magnetic cores with magnetization parallel to the easy axis of the films. Around the pattern edge, the magnetization orients along the pattern edge. At the pole tip, the ratio of the edge domain to the pole width increases as the track width becomes narrow. It is important to prevent the enlargement of such a region so as to maintain the permeability at the pole tip. This domain structure remains stable for different magnetization conditions, a necessary condition for readout waveforms without distortions. Thus the films are suitable for magnetic thin-film heads with narrow track widths. >

High sensitivity single-pole head with transverse return-path core of flux

A highly sensitive low noise and narrow-track width, main pole driven type single-pole head has been developed. This head is called TRF head (single-pole head with Transverse Return-path core of Flux flow). It is a kind of main pole driven type single-pole head which operates only on one side of the recording medium[1][2], and is based on a new idea incorporated in the flux return-path portion, to improve the recording and reproducing sensitivity and to reduce its system noise. The TRF head is especially effective for the recording and reproducing with narrow track widths. The development of this head has resolved the problem of insufficient sensitivity in conventional single-pole heads which was a barrier to using narrow track widths, and has provided the prospect of using narrow track width heads necessary for high density digital video recording.

Wide-band read/write characteristics of an ultra narrow track width video head using sputtered Fe-Si-Al alloy film

Read/write performance of an ultra narrow track width (5μm) video head using a sputtered Fe-Si-Al alloy film in connection with high-coercivity metal powder tape is presented. Both the high output voltage (90nVo-p/μm.turn.m/s) and the wide-band reproduction sensitivity (3dB roll-off at 40MHz) have been demonstrated. This proves that an excellent isotropic high-frequency permeability has been realized in the alloy film core.