Planar thin film magnetic head

Abstract: A planar thin film magnetic head is disclosed wherein an axis of easy magnetization in the vicinity of a magnetic gap (g) of a magnetic yoke (37)is forcibly made coincident with the direction of a track width by a magnetic field due to current flowing in a conductor layer (38). Accordingly, even though the track width is small, a high magnetic permeability, low Barkhausen noise and linear responsiveness can be realized to thereby improve the sensitivity, output and linearity. In another aspect of the invention, a throat portion is eliminated from a thin film magnetic core forming a magnetic gap. The thin film magnetic core is configured such that a pair of magnetic members constituting the magnetic core are diverged from the magnetic gap so that a divergent angle ϑ, of first opposite side edges of the magnetic members, from a direction of the gap length of the magnetic gap, is set to the range of 30° ≦ ϑ ≦ 80°, and the magnetic members have second opposite side edges extending in substantially parallel to the direction of the gap length of the magnetic gap. Accordingly, even though a track width is reduced less than 10µm, adjoining crosstalk or off track crosstalk can be avoided to thereby realize low-noise and high quality reproduction and improve the operating characteristics.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a thin film magnetic head, and more particularly to a magnetic head of a magneto-resistance effect type suitable for a small track width. There is shown in Figs. 6 to 8 a conventional thin film magnetic head of a horizontal type or a so-called planar type. Fig. 6 is a perspective view of a magnetic head slider; Fig. 7 is a schematic enlarged sectional view of the thin film magnetic head taken along a direction of a track width; and Fig. 8 is a schematic enlarged perspective view of a magnetic gap of the thin film magnetic head. Referring to Fig. 6, reference numeral 100 generally designates a magnetic head slider having a base 101. The base 101 is formed with a groove 102 extending in a travelling direction on a surface opposed to a magnetic recording medium (not shown), so that a rail-like ABS (Air Bearing Surface) 81 is formed on the opposite sides of the groove 102. The ABS 81 is formed with a slant surface 104 at a rear end with respect to the travelling direction, so as to effect smooth flying over the magnetic recording medium. Furthermore, a planar thin film magnetic head 90 is formed on the ABS 81 at a front end thereof with respect to the travelling direction. Referring to Fig. 7, the thin film magnetic head 90 is formed in a recess 101a of the base 101 formed of an insulating material such as silicon. The thin film magnetic head 90 includes a thin film magnetic core 113 formed of a magnetic material such as permalloy, a magnetic gap 118 formed in the thin film magnetic core 113, a conductor layer 114, insulator layers 115 and 75, a coil 116, and a protector layer 117 forming a part of the ABS 81. A through hole 112 is formed through the base 101, so as to form the conductor layer 114 and the insulator layer 115 therein. As apparent from Fig. 8 showing a gap forming portion of the thin film magnetic core 113 forming the magnetic gap 118, the thin film magnetic core 113 is generally configured such that it is gradually widened in a direction of a track width Tw as it comes away from the magnetic gap 118. Furthermore, the gap forming portion of the thin film magnetic core 113 is formed as a throat portion 119 having a constant width defining the track width Tw. The coil 116 is a thin film coil wound in a plane below the thin film magnetic core 113. Fig. 11 is a vertical sectional view of a thin film magnetic head of a magneto-resistance effect type (which will be hereinafter referred to as an MR type) as an example of the planar thin film magnetic head 90. Referring to Fig. 11, an MR device 126 as an MR thin film is formed on the base 101, and a thin film magnetic yoke 127 is formed to be connected to opposite ends of the MR device 126. The thin film magnetic yoke 127 is formed at its central portion with a magnetic gap g flush with an ABS 122. A bias conductor 128 for applying a required bias magnetic field to the MR device 126 is formed between the MR device 126 and the thin film magnetic yoke 127 under the magnetic gap g, so that the MR device 126 is operated in a magneto-resistance characteristic area with good linearity and high sensitivity. A non-magnetic protection film 129 is formed on the thin film magnetic yoke 127 except the gap forming portion to constitute a part of the ABS 122. As shown in Fig. 9, a throat portion 129 of the thin film magnetic yoke 127 forming the magnetic gap g has a width defining the track width Tw. In the case that the track width Tw is relatively large such as about 10µm or more, a principal magnetic domain 130 becomes a closed magnetic domain structure along a direction of the track width Tw, that is, an axis of easy magnetization can be formed in the direction of the track width Tw. Accordingly, the magnetic head can be operated by rotation of magnetization for a magnetic flux of a signal introduced from the magnetic gap g. As a result, a Barkhausen noise is reduced to provide a linear responsiveness. However, it has been recently demanded to further increase a recording density, causing the track width Tw to be more reduced. When the track width Tw becomes less than 10µm, eg., about 5µm, the width of the throat portion 129 forming the magnetic gap g becomes small and causes a large influence of shape anisotropy, resulting in a difficulty of orientation of magnetization in the direction of the track width Tw because of an increased static magnetic energy. That is, the axis of easy magnetization is oriented in the direction of the gap length perpendicular to the track width Tw (Fig. 10). As a result, a magnetic domain wall in the vicinity of the magnetic gap g in the magnetic yoke 127 irreversibly functions for magnetic flux of a signal introduced from the magnetic gap g upon reproduction, thus exhibiting a non-linear responsiveness. That is, a Barkhausen noise due to movement of the magnetic domain wall is induced in a reproductive waveform, or the magnetic permeability in the vicinity of the magnetic gap g is reduced so that a sufficient reproductive output cannot be obtained. The above problem occurs not only in the MR type thin film reproducing magnetic head as mentioned above, but also in an electromagnetic induction type planar recording (reproducing) thin film magnetic head having a structure such that a thin-film coil or the like is substantially wound around a magnetic yoke. EP-A-0 298 417 discloses a magnetoresistive (MR) sensor the central active region thereof is magnetically biassed by a bias current in order to provide for magnetical bias in the desired direction. SUMMARY OF THE INVENTION There is shown an essential part of the thin film magnetic head according to the present invention in Fig. 1. As shown in Fig. 1, there is provided a thin film magnetic head comprising a thin film magnetic core 72 having a magnetic gap 71 substantially parallel to a magnetic recording medium (not shown); said thin film magnetic core 72 comprising a pair of magnetic members 72A having opposed end surfaces 73 between which the magnetic gap 71 is defined, said opposed end surfaces 73 having a width defining a track width Tw; said magnetic members 72A being gradually widened as they come away from the magnetic gap 71 so that a divergent angle  of first opposite side edges 74A and 75A of the magnetic members 72A, from the direction of the gap length of the magnetic gap 71, is set to the range of 30° ≤  ≤ 80°. The magnetic members 72A have second opposite side edges 74B and 75B extending substantially parallel to the direction of the gap length of the magnetic gap 71. As mentioned above, no throat portion is formed in the thin film magnetic core 72, and the thin film magnetic core 72 is configured such that the width of the opposed end surfaces 73, with the magnetic gap 71 therebetween, defines the track width Tw, and the magnetic members 72A are gradually widened as they come away from the magnetic gap 71. Accordingly, even though the width of the opposed end surfaces 73 is set to be less than 10µm, a magnetic domain structure can be made into the structure as shown in Fig. 2. That is, assuming that the direction of the gap length of the magnetic gap 71 is the X direction, and that the direction of the track width Tw perpendicular to the gap length is the Y direction, the axis of easy magnetization is made coincident with the Y direction. Accordingly, even though the track width Tw is small, magnetization of the thin film magnetic core 72 in the vicinity of the magnetic gap 71 linearly responds to a magnetic flux introduced from the magnetic gap 71 upon reproduction, thereby suppressing the generation of Barkhausen noise due to movement of a magnetic domain wall in a reproductive waveform, and also suppressing a reduction in magnetic permeability in the vicinity of the magnetic gap 71, that is, at the opposed end portions of the magnetic members 72A of the thin film magnetic core 72, with the result that a sufficient reproductive output can be obtained. Furthermore, a throat portion is eliminated from the thin-film magnetic core 72 forming the magnetic gap 71, and the thin film magnetic core 72 is configured such that the magnetic members 72A are diverged from the magnetic gap 71 so that the divergent angle  of the first opposite side edges 74A and 75A of the magnetic members 72A, from the direction of the gap length (i.e., X direction) of the magnetic gap 71, is set to the range of 30° ≤  ≤ 80°, and that the magnetic members 72A have the second opposite side edges 74B and 75B extending in substantially parallel to the X direction. Accordingly, even though the track width Tw is reduced less than 10 µm, no magnetic gap is formed by the magnetic members 72A in an area remote from the gap forming portion as shown by the line A-A in Fig. 1, and accordingly adjoining crosstalk or off track crosstalk can be avoided to thereby realize low-noise and high-quality reproduction and improve the operating characteristics. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a plan view of an essential part of a preferred embodiment of the thin film magnetic head according to the present invention; Fig. 2 is a schematic plan view showing a magnetic domain structure at a magnetic gap forming portion of the thin film magnetic head shown in Fig. 1; Fig. 3 is a cross section taken along the line B-B in Fig. 1; Fig. 4 is a sectional view of an MR device shown in Fig. 3; Fig. 5 is a sectional view explaining a reproducing operation of the thin film magnetic head shown in Fig. 3; Fig. 6 is a perspective view of the magnetic head slider in the prior art; Fig. 7 is a sectional view of the thin film magnetic head in the prior art; Fig. 8 is a perspective view of the magnetic gap in the prior art; Fig. 9 is a schematic plan view illustrating the magnetic domain structure at the magnetic gap forming portion of the thin film magnetic head in the prior art; Fig. 10 is a view similar to Fig. 9, showing the magnetic domain structure in the case that the track width is more reduced; and Fig. 11 is a sectional view of an essential part of the MR type thin film magnetic head in the prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT There will now be described a preferred embodiment of the thin film magnetic head according to the present invention with reference to Figs. 1 to 5. Referring to Fig. 3 which is a cross section taken along the line B-B in Fig. 1 showing a yoke type planar MR head including an MR device, a thin film magnetic core 72 consists of a pair of upper yokes 72A and a lower yoke 72B which are formed of NiFe plating films or the like. A thin film coil 78 formed of Cu or the like is provided between the upper yokes 72A and the lower yoke 72B. Each upper yoke 72A is formed with a gradually upwardly inclined portion extending to an upper surface opposed to a magnetic recording medium, that is, extending to an ABS 81, and is also formed with a gap forming portion for forming a magnetic gap 71. The gap forming portion has an upper surface flush with the ABS 81. An MR device 76 is located below the magnetic gap 71, and a bias conductor 77 for generating a bias magnetic field is located below the MR device 76 in crossing relationship with each other. Reference numerals 82 designate insulator layers such as SiO₂ layers. Such a thin film magnetic head is manufactured in the following manner. First, the lower yoke 72B is formed by flame plating or the like on an insulating base 91 formed of Al₂O₃ · TiC, CaTiO₃, ferrite ceramic, crystallized glass, etc. Then, the first insulator layer 82 such as SiO₂ layer is formed on the lower yoke 72B, and the thin film coil 78 having a given pattern is formed on the first insulator layer 82. Then, the second insulator layer 82 such as SiO₂ layer is so formed as to entirely cover the coil 78. Then, the first and second insulator layers 82 are bored at opposite ends thereof by RIE (reactive ion etching) or the like, and the bores thus formed are then filled with a magnetic material such as NiFe to thereby form connecting portions 72C for connecting the upper yokes 72A with the lower yoke 72B. Then, the bias conductor 77 is formed on the second insulator layer 82, and the third insulator layer 82 is then formed to entirely cover the bias conductor 77. Then, the MR device 76 is formed on the third insulator layer 82, and the fourth insulator layer 82 is then formed to entirely cover the MR device 76. The formation of the bias conductor 77 and the MR device 76 can be effected by pattern etching using photolithography. Referring to Fig. 4 which is a schematic enlarged sectional view of the MR device 76, the MR device 76 is composed of first and second MR thin films 76A and 76B of NiFe layers each having a thickness of about 300 angstroms and of a non-magnetic layer 84 interposed between the first and second MR thin films 76A and 76B. The non-magnetic layer 84 is formed of SiO₂, and has a thickness of about 30 angstroms so that the first and second MR thin films 76A and 76B each having an axis of easy magnetization in a direction of a track width (i.e., Y direction) may generate static magnetic connection but hardly generate exchange interaction. Referring to Fig. 3, the second to fourth insulator layers 82 surrounding the bias conductor 77 and the MR device 76 are taperingly etched so as to upwardly taper toward the gap forming portion. Then, the fourth insulator layer 82 is anisotropically etched except a projection thereof forming the magnetic gap 71. Then, the upper yokes 72A are formed on the second to fourth insulator layers 82 as etched above so as to be connected to the connecting portions 72C by plating NiFe or the like and then patterning the plated NiFe to a desired pattern. Then, the fifth insulator layer 82 as a protection film of SiO₂ or the like is formed on the upper yokes 72A, and an upper surface of the fifth insulator layer 82 is polished to form the ABS 81, thus obtaining a thin film magnetic head. In the thin film magnetic head as obtained above, a width of opposed end surfaces 73 of the upper yokes 72A of the thin film magnetic core 72 defining the magnetic gap 71 therebetween, that is, a track width Tw as shown in Fig. 1 is set to 5µm. Further, the upper yokes 72A on the right and left sides with respect to the magnetic gap 71 as viewed in Fig. 1 are gradually widened as they come away from the magnetic gap 71. A divergent angle  of one side edge 74A of the right upper yoke 72A from a direction of a gap length of the magnetic gap 71 (i.e., X direction) is set to about 45°. Similarly, a divergent angle  of one side edge 75A of the left upper yoke 72A from the X direction is set to about 45° The side edge 75A is formed on the opposite side of the side edge 74A with respect to the magnetic gap 71. Furthermore, the other side edge 74B of the right upper yoke 72A and the other side edge 75B of the left upper yoke 72A extend in substantially parallel to the X direction. The MR device 76 located below the magnetic gap 71 extends in the X direction, and the bias conductor 77 located below the MR device 76 extends in a Y direction perpendicular to the X direction. As mentioned above, the side edges 74A and 75A of the right and left upper yokes 72A formed in symmetrical relationship with each other with respect to the magnetic gap 71 are inclined at about 45° from the X direction. Accordingly, the upper yokes 72A as a whole is inclined at about 45° clockwise from the X direction. Therefore, the lower yoke 72B is also inclined at about 45° clockwise from the X direction with the thin film coil 78 interposed between the same and the upper yokes 72A. With this construction, a gap forming portion of the thin film magnetic core 72 forming the magnetic gap 71 can be made substantially wide even though the track width Tw is narrow such that it is set to about 5µm. Accordingly, referring to Fig. 2 which shows a magnetic domain structure of the magnetic head, the axis of easy magnetization can be made coincident with the direction of the track width, i.e., the Y direction, thereby avoiding a reduction in magnetic permeability and obtaining a good reproductive output. Referring back to Fig. 1, the side edge 74B of the right upper yoke 72A extends in substantially parallel to the X direction. In other words, in an off track area as shown by the line A-A in Fig. 1, the right upper yoke 72A is not present, and no magnetic gap is defined, thereby avoiding adjoining crosstalk and off track crosstalk. It is considered that a shield effect of the upper yokes 72A to the MR device 76 will be lost because either, of the upper yokes 72A lacks in the off track area. However, since a magnetic flux by an off track signal is not actually applied in the direction of the axis of easy magnetization of the MR device 76, this signal is hardly reproduced. That is, referring to Fig. 5 which shows a reproducing operation of the magnetic head, a reproductive signal is obtained when a magnetization transit portion 86 of a magnetic recording medium 85 comes to a position offset from a position just over the magnetic gap 71, and a magnetic flux having entered a part of the upper yokes 72A in a direction of the arrow a flows in a direction along an axis of difficult magnetization of the MR device 76. Although the divergent angle  of the side edges 74A and 75A of the right and left upper yokes 72A from the X direction is set to about 45° in the above preferred embodiment, this angle  may be set to the range of 30° ≤  ≤ 80°. In this range, it is confirmed that significant crosstalk is hardly generated. Further, although the side edges 74B and 75B of the right and left upper yokes 72A are substantially parallel to the X direction in the above preferred embodiment, they may be slightly inclined from the X direction provided that significant crosstalk is hardly generated. Further, the NiFe plated film of the thin film magnetic core 72 in the above preferred embodiment may be replaced with FeCoNi plated film, NiFe sputtered film, FeAlSi sputtered film, Fe alloy sputtered film, or amorphous magnetic film such as CoZrNb or CoZvTa. The recording coil 78 and the bias conductor 77 may be formed of Al sputtered or plated film instead of Cu sputtered or plated film. Further, although the present invention is applied to the yoke type planar thin film magnetic head employing the MR device in the above preferred embodiment, it may be also applied to a thin film magnetic head employing a coil for carrying out recording and reproducing. It will be apparent that various modifications and/or additional may be made in the apparatus of the invention without departing from the essential feature of novelty involved, which are intended to be defined and secured by the appended claims.

Claims: A thin film magnetic head comprising a thin film magnetic core having a magnetic gap (g) , said thin film core and gap defining a recording surface, substantially parallel to, and for cooperating with, a magnetic recording medium; said thin film magnetic core comprising a pair of magnetic members (72A) having opposed end surfaces between which said magnetic gap is defined, the width of said opposed end surfaces defining a track width characterized in that; said magnetic members are gradually widened as they extend over said recording surface away from said magnetic gap so that a divergent angle of a each of a first pair of diagonally opposite side edges of said magnetic members from a direction of a gap length across said magnetic gap is set to the range of 30° - 80°; and the second pair of diagonally opposite side edges of said magnetic members extend substantially parallel to the direction of the gap length across said magnetic gap. The magnetic head according to claim 1, said magnetic head being in the form of a planar type thin film, and said magnetic members constitute upper magnetic yokes (72A), wherein said magnetic head further comprises: a lower magnetic yoke (72B); a MR element (76) provided between ends of said upper magnetic yokes remote from said gap (71) and said lower magnetic yoke; a bias conductor (77) for applying a bias magnetic field to said MR element.

Inventors: MATSUZONO ATSUSHI, MIYAUCHI TEIICHI, YAMAKAWA KIYOSHI, MATSUZONO, ATSUSHI, MIYAUCHI,TEIICHI, YAMAKAWA, KIYOSHI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1991
Main classification: G11B5
IPC codes: G11B5