New structured metal-in-gap head for high density and high transfer rate recordings

Abstract

A b s t r a c t -A new Improved structured Metal-In-Gap (MIG) head which achieves high output voltage and low inductance Is investigated. The structure is optimized by three-dimensional finite-element calculation. In order to reduce read-back pulse distortions, a new fabrication process using nanocrystaiilne Fe-Ta-C film (Nanomax) i s Introduced. Experimental results show that this head has outstanding advantages over the conventional MIG heads with regard to low inductance (2.2 [nHlturnl at 1.0 [MHzl), high normalized output voltage (4.2 and 3.0 [pVp-p/dpH*pm* mls] at 1.0 and 6.0 [MHzl, respectively) and small read-back asymmetry instability (5.0 [nsl at 4.0 [MHz]). I. m O D U C T I O NMetal-In-Gap (MIG) heads yield strong sharp recording fields. Therefore, they have great potential for high linear density recordings when combined with high coercivity medium [l]. However, they have large inductance, which means high impedance mise that leads to the deterioration of signal-@noise ratio at high frequencies. For this reason they have yet to be used for high transfer rate recordings. Furthermore, read-back pulse distortion that comes from ferrite domain instabilities has become a serious issue [21. Single crystalline ferrite has been introduced to overcome this difficulty [3], however, the problem still exists [2]. This paper describes a new improved structured MIG head which achieves high output voltage and low inductance, the structure being optimized by three-dimensional finite-element calculation. Recording field distribution was also analyzed to maintain a good ovwwriting on a high coercivity medium. In order to reduce the read-back distortions, a new fabrication process using nanocrystalline Fe-Ta-C [4] film (Nanomax: saturation flux density, resistivity and permeability at 1 [MHz] are respectively 15 @GI, 60 w -c m ] and 5000 after annealing when a film thickness of 5 [pnl) was introduced as the metal film instead of conventional Fe-Al-Si film. Experimental results show that the developed head has outstanding advantages over the conventional MIG heads with regard to low inductance (2.2 [nWturnl at 1 .O [MHzl), high normalized output voltage (4.2 and 3.0 [pVp-p /dpH*pm-m/s] at 1.0 and 6.0 [MHz], respectively) and small read-back asymmetry instability (5.0[ns] at 4.0 [MHz]). Manuscript received February 15. 1993. II. DESIGN Figs.l(a)-(c) show the cross sections of various minimonolithic heads. Interestingly, if the coil winding spaces are assumed to be the same, calculated normalized inductance of these heads are approximately 1.2, 1.0 and 0.8, respectively.In Fig.l(c), if the trailing ferrite core thickness t becomes smaller, lower inductance can be achieved. However, no attempt has been done to reduce the inductance using this structure. Fig.2(a) shows the schematic structure of the newly developed MIG head. A conventional MIG head is shown in Fig2(b) for comparison. We assume that both have monolithic structure and that polycrystalline femte is used. The trailing core of the newly developed head consists o...