Laminated magneto-resistive head

Abstract: The head (100) used for a magnetic reproducing apparatus is structured by laminating 2 magneto-resistive heads (100a,101b), at least with the position of 2 magneto-resistive elements (123a,123b) substantially shifted each other for lamination and also enabling a plurality of track formats to be conformed, thus making it possible to assure stable outputs up to a low frequency range.

Description: The present invention relates to a laminated magneto-resistive head used for a magnetic recording/reproducing apparatus. Recently, a magneto-resistive head has come to attract the attention in compliance with the trend to a higher recording density, higher data transfer speed an multi-channel in the magnetic recording/reproducing apparatus. Especially, with the magnetic recording/reproducing apparatus in which a magnetic recording medium runs at a low speed, magneto-resistive heads are being used of which reproduced outputs are independent of the speed. Fig. 6 (a) and (b) show a conventional magneto-resistive head. Fig. 6(a) is a perspective view of the main area and Fig. 6(b) is a sectional drawing shown at a section I-I' of Fig. 6(a). The conventional magneto-resistive head is formed with a first magnetic layer 27 composed of Permalloy, Sendust or amorphous magnetic materials, etc. on a substrate 21 which is comprised of glass or ceramics, a bias conductor 22 composed of a conductive material such as gold thin film or copper thin film which is a means of applying a bias magnetic field to a magneto-resistive element 23, a magneto-resistive element 23 comprised of Permalloy thin film, electrodes 24a and 24b formed of the gold thin film or copper thin film for running a driving current to the magneto-resistive element 23, a second magnetic layer 25 and a third magnetic layer 26 composed of soft magnetic material through such an insulating layer 32 as SiO 2 or the like together with a first gap 28 and a second gap 29 consecutively. Furthermore, a protection layer 31 is formed and finally a cover plate 30 is bonded, thereby completing the magneto-resistive head. Especially, in the vicinity of the second gap 29 between the second magnetic layer 25 and the third magnetic layer 26 said magneto-resistive element 23 is formed in such a manner that said magneto-resistive element 23 overlaps each edge of the second magnetic layer 25 and the third magnetic layer 26. Likewise, the first gap 28 which conducts into the magnetic head a recording magnetic field generated from a magnetic recording medium is formed between the first and second magnetic layers 27 and 25. The surface 33 is the sliding surface of magnetic medium. Recently, such a magnetic head is desired that enables a plurality of track formats having a different track width to be conformed. However, it has been impossible for the above-mentioned conventional magnetic head to conform to a plurality of track formats which allow reproduction at almost the same position of the magnetic recording medium having a different track width. In order to conform to such demand, a lamination type magneto-resistive head 80 as shown in Fig. 7 is known. This is the same structure as that of the conventional example, and the first magneto-resistive type head 81a and the second magneto-resistive type head 81b which are different in track width from each other are consecutively laminated on a common substrate through a separate layer 83 so that the second magnetic gap 29a of the first magneto-resistive head 81a faces with the first magnetic layer 27b of the second magneto-resistive type head 81b each other. In such a case, each magneto-resistive head has a different reproducing track width, allowing a plurality of track formats having a different track width to be conformed. That is, the magneto-resistive head 81b is used for the one track format, while the 81a is used for the other one. However, as mentioned above, the magneto-resistive element 23a on the first magneto-resistive type head 81a is faced with the first magnetic layer 27b of the second magneto-resistive type head 81b, and the first magnetic layer 27b of the second magneto-resistive type head 81b acts as a magnetic shield to the first magneto-resistive head, thereby preventing the signal magnetic field generated from the magnetic recording medium from flowing into the first magneto-resistive head. Therefore, there has been such a problem that a reproducing sensitivity is lowered at an area where a 1/2 of recorded wave length on the magnetic recording medium is larger than a distance L between the first gap 28a of the first magneto-resistive head 81a and the first magnetic layer 27b of the second magneto-resistive head 81b. JP-A-1-303617 discloses a thin film magnetic head having three heads arranged such that there are two recording heads one on either side of a central reproducing head, the three heads being formed on the same side substrate. The general construction of this head is generally similar to the construction described above. In consideration of the defects of the conventional laminated magneto-resistive head, an object of the present invention is to provide easily at low cost a laminated magneto-resistive head having a stable reproduction frequency characteristics and capable of conforming to a plurality of track formats which are different from one another in track width and/or the number of channels. The present invention provides a laminated magneto-resistive head comprising two magneto-resistive heads, each head comprising: a first magnetic layer; a second magnetic layer; a third magnetic layer; a magneto-resistive element; and means arranged to apply a bias magnetic field to said magneto-resistive element; said layers in each head being arranged to define a first gap between the first and second magnetic layers, the first gap being exposed at a magnetic medium sliding surface of the laminated magneto - resistive head, and a second gap between the second and third magnetic layers; and the magneto-resistive element in each head being disposed near the respective second gap so as to overlap ends of the respective second and third magnetic layers; characterised in that the laminated magneto-resistive head has a central layer with first and second surfaces, said central layer being formed between the respective second magnetic layers of said two magneto-resistive heads, at least the portions of the central layer adjacent the first and second surfaces being formed of magnetic material to provide said first magnetic layers of said two magneto-resistive heads and the first gaps of the two magneto-resistive heads being formed between the two second magnetic layers and said first and second surfaces respectively. The laminated magneto-resistive head of the present invention allows a plurality of track formats having different track widths and/or different numbers of channels from one another to be conformed based on the above-mentioned structure, thus giving stable frequency characteristics of the reproducing output because of no magnetic interference given to the magneto-resistive element area of laminated magneto-resistive head from another magneto resistive head. Fig. 1 illustrates a cross-sectional view of a lamination type magneto-resistive head showing the first embodiment of the present invention. Fig. 2 illustrates a cross-sectional view of a lamination type magneto-resistive head showing the second embodiment of the present invention. Fig. 3 illustrates a cross-sectional view of a lamination type magneto-resistive head showing the third embodiment of the present invention. Fig. 4 illustrates a general view of a multi-channel lamination type magneto-resistive head as seen from the contact surface of magnetic recording medium, showing the fourth embodiment of the present invention. Fig. 5 (a) and (b) illustrate views of two kinds of track formats which conform to a multi-channel lamination type magneto-resistive head of the fourth embodiment. Fig. 6(a) illustrates a general view of the main area of a conventional magneto-resistive head. Fig. 6(b) illustrates a cross-sectional view of I-I' of Fig. 6(a). Fig. 7 illustrates a cross-sectional view of the conventional lamination type magneto-resistive head. Description for the embodiment of the present invention follows below. Fig. 1 illustrates the first embodiment of the present invention, showing a cross-sectional structure drawing similar to the one illustrated in Fig. 6(b). The lamination type magneto-resistive head 100 in the embodiment of the present invention is composed of a lamination of the first and second magneto-resistive heads 101a and 101b made consecutively through an alumina thin film 110. Namely, after forming a backing layer 131a like alumina, etc. on a substrate 121 composed of glass or ceramics, the second magnetic layer 125a composed of Permalloy or Sendust or amorphous magnetic materials, etc., and the third magnetic layer 126a are formed together with the second gap 129a. And, furthermore, a magneto-resistive element 123a composed of a Permalloy thin film, a bias conductor 122a composed of conductive materials such as gold thin film or copper thin film as means of applying a bias magnetic field to said magneto-resistive element 123a, and then, the first magnetic layer 127a which is composed of Permalloy, Sendust or amorphous magnetic materials, etc. and formed together with the gap 128a consecutively through an insulating layer 133 a such as SiO 2 , etc., thus becoming the first magneto-resistive head 101a. Especially, said magneto-resistive element 123a is formed in the vicinity of the second gap 129a situated between the second magnetic layer 125a and third magnetic layer 126a, in such a manner that said magneto-resistive element 123a overlaps the ends of the second magnetic layer 125a and of the third magnetic layer 126a each other. Then, an intermediate layer 110 of alumina thin film, etc. is formed, and then the first magnetic layer 127b of the second magneto-resistive head 101b , the second magnetic layer 125b and the third magnetic layer 126b, the first gap 128b, the second magnetic gap 129b, bias conductor 122b, magneto-resistive element 123b, and protection layer 131b, etc. are formed through an insulating layer 133b, etc. in an approximately reverse order of structuring the first magneto-resistive head 101a. Also, the second magneto-resistive head is formed in such a manner that its track width differs from that of the first magneto-resistive head, so that the widths of the first magnetic layer 127b, second magnetic layer 125b and third magnetic layer 126b are formed in such a way that they differ from that of the first magneto-resistive head. Finally, a cover plate 130 is bonded, followed by polishing of the magnetic medium sliding surface 132 so that the first gap 128a and 128b are exposed, thus completing the lamination type magnetic head 100. The lamination type thin film magnetic head of the embodiment of the present invention allows a plurality of track formats having a different track width to be conformed. Namely, a magneto-resistive head is used of which track width conforms to the width of one track format, while at that time a magneto-resistive head of another one is used. Furthermore, in case of this embodiment, it is structured that the first magnetic layers 127a and 127b of two magneto-resistive heads 101a and 101b are laminated by being faced with each other, magneto-resistive elements 123a and 123b do not face with other magnetic layers 127a and 127b each other. Therefore, the first magnetic layer of another magneto-resistive head does not act as a shield of another magneto-resistive head, thus providing the possible effect of stable reproducible output up to a low frequency range. Fig. 2 illustrates the second embodiment of the present invention. The same numbers are applied to the same structural elements as the ones used in the first embodiment. The lamination type magneto-resistive head 200 of the second embodiment is structured by laminating two magneto-resistive heads 201a and 201b in the same manner as used in the first embodiment. In this embodiment, the formed position of magneto-resistive element 123a of magneto-resistive head 201a is different from that used in the first embodiment. That is, the magneto-resistive element 123a is situated on a flat alumina layer 131a which is formed on the substrate 121. In general, magneto-resistive elements are subjected to noise generation and lowering in reproducible output when the flatness of backing surface became worse. Therefore, the magneto-resistive element of the present embodiment has an effect not subject to the influence of a difference in the backing surface level and allows stable reproducible characteristics to be obtained with a few noises. Fig. 3 illustrates the third embodiment of the present invention. The present embodiment is a lamination type magneto-resistive head 350 , in which in the second embodiment the first magnetic layer of each magneto-resistive head is made common each other, and thereby made a common magnetic layer 51. In this case, it is not necessary to form a intermediate layer in the first and the second embodiment and a lamination type magneto-resistive head 350 is structured by forming only one layer, with the first magnetic layer made common. Therefore, in this case, production process is remarkably shortened, allowing a plurality of track formats to be easily confomed at low cost, with the effect of providing stable reproducing outputs up to a low frequency range. Fig. 4 illustrates the fourth embodiment as seen from the sliding surface of the magnetic medium. The multi-channel lamination type magneto-resistive head 70 of the present embodiment is structured by at first arranging 4 pieces of magneto-resistive heads 71a (72a), 71b (72b), 71c (72c), and 71d (72d) having a certain track width, and also two pieces of magneto-resistive heads 73a, (74a) and 73b (74b) having a different track width in a track width direction, thus making a multi-channel type, followed by laminating 2 pieces thereof so as to have a common magnetic layer 60 which is made common each other. In this case, the positions of magneto-resistive heads having the same track width are such that heads 71a, 71b, 71c and 71d and heads 72a, 72b, 72c and 72d or heads 73a and 73b and heads 74a and 74b are arranged in a rotation symmetry with respect to an axis Z as seen from the sliding surface of magnetic medium, thus conforming to a magnetic recording medium which runs forward and backward. Namely, Fig. 5(A) and (B) show track formats on 2 kinds of magnetic recording media conformable to this case. A total of 4 tracks of track formats shown in Fig. 5(A) are situated on each side of magnetic medium, bringing about reproduction during running forward and backward. The track formats shown in Fig. 5(b) are situated with 2 tracks on each side of the magnetic recording medium, bringing about reproduction. The multi-channel lamination type magneto-resistive head 70 is the fourth embodiment, which enables 2 kinds of track formats of reciprocally running magnetic recording medium to be conformed, providing stable reproducing outputs up to a low frequency range. Explanation follows below of the operation in this case. When the running direction of magnetic medium for the track format in Fig. 5(A) is F, reproduction is carried out on tracks 81a, 81b, 81c and 81d conformed by use of magnetic resist heads 71a, 71b, 71c, and 71d. When a medium running direction is R, reproduction is carried out on tracks 82a, 82b, 82c, and 82d by use of magneto-resistive heads 72a, 72b, 72c, and 72d. When the track format is as shown in Fig.5(B) and the magnetic recording medium runs in the direction F, reproduction from tracks 83a and 84b is carried out by magneto-resistive heads 73a and 73b. Therefore, in any case, the magnetic medium first makes contact with a common magnetic layer 60 of operating magneto-resistive head, and then contact with the first gap and the second magnetic layer. As mentioned above, the positional relation-ship between the magnetic medium and the multi-channel lamination type magneto-resistive head is always constant, and reproduced outputs are independent of a running direction, thereby providing a stable output effect up to a low frequency range because of no magnetic interference given from another magneto-resistive head. As mentioned above, the lamination type magneto-resistive head of the present invention conform to a plurality of track formats which are different from one another in track width and/or the number of channels, having such an effect that reproducing outputs become stable for a full frequency range, because the inadequate resistive element of the lamination type magneto-resistive head is not subjected to the interference given from another first magnetic layer. Also, by making the first magnetic layer common, it eliminates the need for forming an intermediate layer and will further reduce the formation of a magnetic layer, thereby processing such effects that it remarkably shorten the production process and easily provide a lamination type magneto-resistive head at low cost. Furthermore, laminating 2 sets of plural magneto-resistive heads having the same track width arranged on one plane provides an effect which enables a plurality of multi-channel track formats to be conformed.

Claims: A laminated magneto-resistive head comprising two magneto-resistive heads (101a,101b;201a,201b), each head comprising: a first magnetic layer (127a,127b;51;60); a second magnetic layer (125a,125b); a third magnetic layer (126a,126b); a magneto-resistive element (123a,123b); and means (122a,122b) arranged to apply a bias magnetic field to said magneto-resistive element; said layers in each head being arranged to define a first gap (128a,128b) between the first and second magnetic layers, the first gap being exposed at a magnetic medium sliding surface (132) of the laminated magneto - resistive head, and a second gap (129a,129b) between the second and third magnetic layers; and the magneto-resistive element in each head being disposed near the respective second gap so as to overlap ends of the respective second and third magnetic layers; characterised in that the laminated magneto-resistive head has a central layer (127a,127b,110;51;60) with first and second surfaces, said central layer being formed between the respective second magnetic layers (125a,125b) of said two magneto-resistive heads (101a,101b;201a,201b) at least the portions of the central layer adjacent the first and second surfaces being formed of magnetic material to provide said first magnetic layers of said two magneto-resistive heads (101a,101b) and the first gaps (128a,128b) of the two magneto-resistive heads (101a-101b) being formed between the two second magnetic layers (125a,125b) and said first and second surfaces respectively. A laminated magneto-resistive head according to Claim 1 in which said central layer comprises an intermediate layer (110) between two magnetic layers (127a,127b), said magnetic layers forming the first magnetic layers of the two magneto-resistive heads respectively. A laminated magneto-resistive head according to Claim 1 or 2 wherein each of the two magneto-resistive heads has its magneto-resistive element (123a,123b disposed between the first magnetic layer (127a,127b) and the second gap (129a,129b). A laminated magneto-resistive head according to Claim 2 wherein one (101a;201a) of said two magneto-resistive heads is formed on a substrate (121), and the other (101b;201b) of said two magneto-resistive heads is formed on said one of said two magneto-resistive heads with the intermediate layer (110) disposed there between. A laminated magneto-resistive head according to Claim 4, wherein said one of said two magneto-resistive heads which is formed on said substrate (121) has said magneto-resistive element (123a) disposed on a flat insulating layer (131a) formed on said substrate. A laminated magneto-resistive head according to Claim 1 in which said central layer is a magnetic layer (51) which forms the first magnetic layer of each of said two magnetic heads. A laminated multi-channel magneto-resistive head comprising a plurality of pairs of magneto-resistive heads according to Claim 6.

Inventors: FUKAZAWA TOSHIO, MITANI SATORU, NAGATA YUJI, FUKAZAWA, TOSHIO, MITANI, SATORU, NAGATA, YUJI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1992
Main classification: G11B5
IPC codes: G11B5