The recording characteristics of helical scan silicon (HSS) heads with perfect alignment of the magnetic poles were investigated. Their overall performances were found to be superior to those of ferrite MIG heads, especially the side writing. Erase bands of 0.25 /spl mu/m were measured using a HSS head and ME tape with 50 nm thick magnetic layer. Side writing and erasing were studied from the frequency response of microtracks, as well as from triple-track profiles

Hozoi, Adrian

Lodder, J.C.

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Hozoi, A.

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Recording performances of perfectly aligned HSS heads

The recording characteristics of Helical Scan Silicon (HSS) heads with perfect alignment of the magnetic poles were investigated. Their overall performances were found to be superior to those of ferrite MIG heads, especially the side writing. Erase bands of 0.25 um were measured using a HSS head and ME tape with 50 nm thick magnetic layer. Side writing and erasing were studied from the frequency response of microtracks, as well as from triple-track profiles

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2422 IEEE TRANSACTIONS ON MAGNETICS, VOL. 40, NO. 4, JULY 2004Recording Performances ofPerfectly Aligned HSS HeadsAdrian Hozoi and J. C. LodderAbstract—The recording characteristics of Helical Scan Silicon(HSS) heads with perfect alignment of the magnetic poles were in-vestigated. Their overall performances were found to be superiorto those of ferrite MIG heads, especially the side writing. Erasebands of 0.25 m were measured using a HSS head and ME tapewith 50 nm thick magnetic layer. Side writing and erasing werestudied from the frequency response of microtracks, as well as fromtriple-track profiles.Index Terms—Erase bands, magnetic tape recording, micro-tracks, side writing, thin-film heads.I. INTRODUCTIONTHE process of increasing the track density in magnetic taperecording must be supported by a parallel reduction of theerase bands. It was shown in [1] that the erase bands were cutdown to 0.4 in order to reach a track width of 5 in theMICROMV video system. The improvement came from a betteralignment of the magnetic poles of the MIG write head, achievedby mechanical trimming. A recording density of 11.5was reported in [2] using thin ME tape and a GMR read head,without addressing the side writing/erasing issue. However, suchdensity can practically be achieved only if the erase bands arereduced close to 0.1 . Side writing is influenced by a numberof factors including the magnetic spacing between head andmedium, the medium’s thickness and magnetic properties, andthe write field gradient at the track edges. The magnetic spacingin tape recording is unlikely to ameliorate much. Tape mediawith very thin magnetic layers of 20 nm and high coercivityaround 200 kA/m was obtained by metal sputtering [3], andmay be suitable to better control the erase bands. However, mostimprovements are expected from the write heads that shouldgenerate better-confined fields, using well-aligned magneticpoles and short gap length. The Helical Scan Silicon (HSS)heads are an innovative step toward these features [4], [5]. Inthis work, the recording performances of HSS heads with verygood pole alignment were investigated, with great emphasis ontheir edge effects. Ferrite MIG heads were examined as well. Weintroduced a technique to study the side writing phenomenonfrom the frequency response of microtracks. The method allowsanalyzing the deterioration of the transitions at each track edgeas a function of the frequency. Triple-track profiles were alsomeasured to estimate the erase bands of the heads.Manuscript received October 16, 2003. This work was supported by the DutchTechnology Foundation (STW).The authors are with the Systems and Materials for Information Storage,MESA+ Research Institute, University of Twente, 7500 AE Enschede, TheNetherlands (e-mail: a.hozoi@el.utwente.nl; j.c.lodder@el.utwente.nl).Digital Object Identifier 10.1109/TMAG.2004.828967Fig. 1. Magnetic poles of the (a) HSS head and (b) MIG head.II. EXPERIMENTHSS heads were developed by CEA-LETI and Alditech usingadvanced thin-film technology [4]. They feature unique proper-ties such as integrated solenoid coil, integrated azimuth angle,and very good alignment of the magnetic poles. Two HSS headswere investigated, having a pole width of 6.2 , electrical gaplength of 0.23 , and azimuth angle of 15 . They have sole-noid coils with 40 turns, dc resistance below 6 , and inductancearound 0.6 (at 20 MHz). Two MIG ferrite heads with trackwidths of 5.5 and 7.0 were studied as well, and bothpresented very similar edge effects. Their electrical gap lengthwas the same as that of the HSS heads, i.e., 0.23 . They hadan azimuth angle of 10 , a coil with 15 turns and inductancearound 0.6 (at 5 MHz). Only results obtained with one HSShead and one MIG head (of 5.5 track width) are presentedhere, as they are representative of each technology investigated.Images of their magnetic poles are given in Fig. 1.The recording experiments were performed at 3 m/s speed, ona rotating tape-drum tester with cross-track resolution beyond0.1 . We used ME tape with the magnetic layer’s thickness, and the coercivity (1700 Oe).This sample was fabricated by Sony Corporation and is similarto the tape used in the MICROMV video system [1].III. RESULTS AND DISCUSSIONThe frequency responses of the HSS and MIG heads aregiven in Fig. 2. The optimum recording current was 10 mA forthe HSS head and 20 mA for the MIG head. The HSS headneeds very low write current, which is unusual for thin-filmtechnology. This is due to its solenoid thin-film coil with highnumber of turns and good efficiency. The output signal of theHSS head has much higher amplitude and decays less with thefrequency, even though the track width is almost the same. Thebetter performance of the HSS head should come from superiorsensitivity and weaker edge effects.The side writing phenomenon was explored by studying thefrequency response of microtracks created at the edges of thetrack as well as in the center. The center-microtracks were pre-pared by erasing at both sides of the recorded track; the edge-0018-9464/04$20.00 © 2004 IEEEHOZOI AND LODDER: RECORDING PERFORMANCES OF PERFECTLY ALIGNED HSS HEADS 2423Fig. 2. Frequency response of HSS and MIG heads.Fig. 3. Influence of the number of erase cycles on microtracks.microtracks were prepared by erasing at one side only. Theerase method used to narrow the recorded track may influencethe quality of the microtracks. The erasure has to be completeand leave the edge of the microtrack abrupt and free of distor-tions. Different erase techniques were studied in order to min-imize related artifacts. They were tested by comparing the mi-crotracks prepared using one erase cycle and ten erase cycles.Minimal differences should result with a good erase method.We preferred a method consisting in a cycle of erasing two timeswith dc currents of opposite sense. The frequency responses ofcenter-microtracks prepared using one and ten erase cycles areshown in Fig. 3, for both HSS and MIG heads. In the case ofthe HSS head, there is hardly any difference between one andten erase cycles. This is probably due to a very well confinedwrite field, related to the good pole alignment. The situation isdifferent with the MIG head, where the signal from the micro-track created with ten erase cycles is evidently lower. However,the reduction does not seem to depend much on frequency.The frequency responses of edge-microtracks obtained withthe HSS head are plotted in Fig. 4. After writing a full track, thehead was offset with plus or minus 0.8 to erase part of thetrack. The erase offset, , is given in the figure for each curve.The read offset, , was null when the head was replaced at theoriginal write position for reading. Reading was also performedwith the head centered on the microtrack, in which casewas or . The frequency responses of two center-microtracks are also included in the same figure for reference.Their erase offsets were , and.The edge-microtracks measured with the HSS head exhibitvery similar frequency behavior for both edges and read posi-Fig. 4. Frequency response of microtracks measured with the HSS head.Fig. 5. Frequency response of microtracks measured with the MIG head.tions. Their frequency decay is higher than of the center-mi-crotracks, due to the degradation of the transitions at the trackedges. This can be seen as an effective track width reductionat short wavelengths. The roll-off curves of the edge-micro-tracks are contained in between the roll-off curves of the twocenter-microtracks, for the frequency range investigated. Thedifference between the widths of the center microtracks was de-duced from the values of their erase offsets to be 0.5 . Wecould thus estimate that the effective track width reduction ateach edge is less than 0.5 up to a wavelength of 0.2 .The effective track width reduction at a recording wavelengthof 0.33 was found to be about 0.3 (from a center micro-track with ).Edge and center-microtracks measurements were performedwith the MIG head as well, and the results are plotted in Fig. 5.The erase offsets had to be increased considerably comparedwith the HSS head (1.6 instead of 0.8 ), due to muchstronger side erasing. At both edges, the output is considerablyhigher when the head is centered on the edge-microtrack forreading. This means that the MIG head is able to write signalmore faraway from its gap edge than it can read. In other words,side writing is stronger than side reading. The edge-microtracksare very different for each side of the MIG head. The signalis decaying much faster at one edge causing an effective track2424 IEEE TRANSACTIONS ON MAGNETICS, VOL. 40, NO. 4, JULY 2004Fig. 6. Erase bands of HSS head measured from triple-track profiles.width reduction around 1.5 at a wavelength of 0.3(estimated using the center-microtracks as references). Theeffective track width reduction is considerably less at the otheredge. It was found that the situation becomes the other wayaround when changing the tape moving direction. The sidewriting of the MIG head is anti-symmetric with respect to thetape moving direction. Each edge presents worse degradationin one direction than in the other, due to asymmetric writefields at the trailing edges. Side writing causes the transitionsto bend and to broaden at the track edge. The bend of thetransitions introduces a phase shift between the edge and thetrack-center, which contributes to the decrease of the signalat short wavelengths together with the transition broadening.The effects are strong at poor pole alignment and depend onthe write field gradient at the trailing pole. These issues will betreated in more detail in a future publication.The effective track width reduction induced by side writingeffects causes the erase bands to broaden. It is therefore ex-pected that the MIG head generates larger erase bands thanthe HSS head. The erase bands of the HSS and MIG headswere deduced from triple-track patterns using the interpreta-tion technique described in [5]. A central track with wavelengthwas used to overwrite with partial overlap twoside tracks of wavelength . The experimental re-sults are shown in Figs. 6 and 7 for each head. The HSS headexhibited erase bands as low as 0.25 , which are suitable fornarrow track recording. The MIG head presented much largererase bands of 0.76 , due to the poor alignment of its mag-netic poles. Erase bands of the same order of magnitude werepreviously reported for MIG heads, extracted from MFM im-ages [6]. The track profiles of the HSS head are better fitted bytrapezoids than in the case of the MIG head, probably becauseits read response is closer to a square function. This is a conse-quence of the uniform gap and good pole alignment of the HSSFig. 7. Erase bands of MIG head measured from triple-track profiles.head. The relative side read width, , is small and almostthe same for both heads, as the wavelength of the central trackis close to that of the side tracks.IV. CONCLUSIONA technique to investigate the side writing from the fre-quency response of microtracks was described. The methodallows studying the degradation of the transitions at each trackedge as a function of the frequency. It was applied to study theside writing of HSS and MIG heads, with identical electricalgap lengths of 0.23 . HSS heads presented very weak edgeeffects due to the good alignment of their magnetic poles. Theirerase bands measured from triple-track profiles were around0.25 at 0.6 wavelength, about three times smallerthan those of the MIG heads. The erase bands could be furtherdecreased by using shorter gap length, which is relatively easyto achieve in thin-film technology.REFERENCES[1] K. Tsuneki, K. Iesaka, Y. Yanagi, Y. Senshu, and Y. Kotani, “Develop-ment of a consumer VCR format and a high-density magnetic recordingusing an MR head,” IEEE Trans. Consumer Electron., vol. 48, pp.783–789, Aug. 2002.[2] T. Ozue, M. Kondo, Y. Soda, S. Fukuda, S. Onodera, and T. Kawana,“11.5-Gb=in recording using spin-valve heads in tape systems,” IEEETrans. Magn., vol. 38, pp. 136–140, Jan. 2002.[3] L. T. Nguyen, A. Lisfi, and J. C. Lodder, “Obliquely sputtered Co/Crthin film tape for bidirectional recording,” J. Appl. Phys., vol. 93, no.10, pp. 7786–7788, May 2003.[4] J. B. Albertini, H. Sibuet, P. Renaux, and P. Gaud, “A new solenoid mag-netic integrated head for digital video recording,” IEEE Trans. Magn.,vol. 33, pp. 2836–2838, Sept. 1997.[5] A. Hozoi, J. P. J. Groenland, J. B. Albertini, and J. C. Lodder, “Novelprofiling model and side effects of helical scan silicon heads,” IEEETrans. Magn., vol. 38, pp. 1916–1918, Sept. 2002.[6] N. Nagai, T. Shirai, S. Fukuda, T. Ozue, and S. Onodera, “A narrowerside erase band for use with helical scan tape systems,” IEEE Trans.Magn., vol. 35, pp. 2691–2693, Sept. 1999.

11.5-Gb=in recording using spin-valve heads in tape systems,”

A narrower side erase band for use with helical scan tape systems,”

Development of a consumer VCR format and a high-density magnetic recording using an MR head,”

J.B.Albertini,H.Sibuet,P.Renaux,andP.Gaud,“Anewsolenoidmagnetic integrated head for digital video recording,”

Novel profiling model and side effects of helical scan silicon heads,”

Obliquely sputtered Co/Cr thin film tape for bidirectional recording,”

Recording performances of perfectly aligned HSS heads

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