Magnetic head unit, magnetic head for use in the magnetic head unit and magnetic head structure for use in the magnetic head

Abstract: Magnetic head unit comprising a magnetic head secured in a housing (41) and having a magnetic head structure (40) provided with a head face (5) and at least one transducing gap terminating in the head face. A wear- resistant layer (31) having at least one alignment mark (35, 36, 37) occupying a defined position with respect to the transducing gap is provided on the head face.

Description: The invention relates to a magnetic head unit comprising a magnetic head secured to a support and having a magnetic head structure provided with a head face and at least one transducing gap terminating in the head face. The invention also relates to a magnetic head. A support in the form of a housing comprising a magnetic head unit is known from EP-A 0,404,245 (PHN 12.996). The known magnetic head unit comprises a magnetic head intended for cooperation with a magnetic tape, which head is mounted in a housing provided with tape guides. The magnetic head has a magnetic head structure with a tape contact face and a transducing gap. In a recording/reproducing system it is important that during recording signals on a magnetic tape a write gap of a magnetic head is at the same position and at the same angle with respect to the magnetic tape as a read gap during reading the recording signals in order to inhibit signal loss. Said tape guides of the known magnetic head unit ensure that the magnetic tape always occupies the same position with respect to the magnetic head. For reasons of compatibility it is also required that the transducing gap of the magnetic head occupies a defined position with respect to the tape guides of the housing. To this end magnetic heads are aligned as to position and direction before they are built in. In the case of thin film heads use can be made of a visible layer terminating in the head face, for example, a flux guide layer. For bulk heads the visible transducing gap itself may be used as a reference. A known drawback of magnetic heads which are in contact with a magnetic medium, particularly a magnetic tape, during operation is that the head face is subject to wear. Particularly in thin-film magnetic heads the thin-film layer structure may give rise to very considerable wear within a short period of operation, thus ensuring only a short lifetime of the magnetic head unit. It is known per se to provide wear-resistant layers on the head faces of magnetic heads in order to inhibit wear. In this connection it is to be noted that it has been proposed in EP-A 0,123,826 to provide the head face of a magnetic head with a sputtered layer of titanium carbide, chromium carbide or titanium nitride having a thickness of at most 0.2 micron. A drawback of providing a wear-resistant layer, particularly a layer which is not transparent to visible light, is that the alignment of the magnetic head with respect to a support or a housing of the magnetic head unit is seriously impeded and is no longer possible with the aid of a visible-light microscope. Under circumstances only special equipment using, for example, an IR microscope or a phase-contrast microscope provides the possibility of reliable alignment. It is an object of the invention to provide a magnetic head unit having a wear-resistant magnetic head aligned by means of simple equipment. The magnetic head unit according to the invention is therefore characterized in that a wear-resistant layer forming a contact face and having at least one alignment mark occupying a defined position with respect to the transducing gap is provided on the head face of the magnetic head. When the magnetic head is being built into the magnetic head unit according to the invention, the magnetic head is aligned with respect to a reference plane by means of the alignment mark and by using a simple microscope before it is definitively secured to the support. In order to position the magnetic head accurately as regards position and direction, the wear-resistant layer is preferably provided with various, preferably small alignment marks. The magnetic head unit according to the invention is eminently suitable for analog as well as digital applications. Examples of applications are multi-track audio, video and data recording. A suitable application is particularly the longitudinal magnetic tape recording system as described in EP-A 0,381,266 (PHN 12.816). An embodiment of the magnetic head unit according to the invention is characterized in that the alignment mark is formed by an area having a structure which differs from the structure of the wear-resistant layer. The area having the different structure in the form of, for example, ridges or a pattern of elevations can be provided photolithographically. A practical embodiment of the magnetic head unit according to the invention is characterized in that the alignment mark has at least one cavity which is present in the wear-resistant layer. An embodiment of the magnetic head unit according to the invention is characterized in that the area having the different structure has a relief with a periodicity of at least 1/4 λ, in which λ is the wavelength of light, particularly visible light. The different structure is in general insufficiently visible at a periodicity of less than 1/4 λ. An embodiment of the magnetic head unit according to the invention is characterized in that the wear-resistant layer has at least one further alignment mark. An advantage thereof is that the azimuth angle, i.e. the angle at which the transducing gap extends to the normal on the direction of displacement of the magnetic medium can be accurately adjusted when the magnetic head is being mounted. An embodiment of the magnetic head unit according to the invention in which the magnetic head has a group of transducing gaps as shown, for example, in said EP-A 0,381,266, is characterized in that the group of transducing gaps is present between the first-mentioned alignment mark and the further alignment mark. If the two alignment marks are in a plane parallel to the plane of the group of transducing gaps, the azimuth angle can be adjusted in a simple manner. If the two planes coincide, the group of gaps can be positioned with respect to a reference plane in an extremely simple manner. A technologically attractive embodiment of the magnetic head unit according to the invention is characterized in that the head face has a head face area corresponding to the area having the different structure. During manufacture of this magnetic head unit an area having a different structure is formed in the head face, for example, by means of etching before the wear-resistant layer is provided. One of its advantages is that the area having the different structure can easily be positioned and aligned with respect to the transducing gap, while parts of the magnetic head structure which are visible in the head face can generally be used. A further advantage is that it is not necessary to take special precautions when the wear-resistant layer is being provided by means of, for example, sputtering or vapour deposition, because the area having the different structure present in the head face is copied in the wear-resistant layer due to the small thickness of this layer and therefore remains visible. It is to be noted that EP-A-0 075 413 (herewith incorporated by reference) discloses a magnetoresistive card-reading head comprising a sapphire substrate, one face of which is intended for co-operation with magnetically encoded cards and an opposite face is provided with MR elements. The last-mentioned face is also provided with a registration mark for use in aligning the substrate during a stage on the manufacturing process. The invention will now be described in greater detail by way of example with reference to the accompanying drawings in which Figure 1 shows a layout of an embodiment of the magnetic head according to the invention, Figure 2 is a diagrammatic cross-section II-II through a transducing gap of the magnetic head of Figure 1, Figure 3 is a perspective elevational view of the magnetic head shown, Figure 4 is a perspective elevational view of the magnetic head of Figure 1 in a production stage in which a wear-resistant layer has not been provided yet, Figure 5 is a side elevation of an embodiment of the magnetic head unit according to the invention and Figure 6 is a plan view of the unit shown in Figure 5. The thin-film magnetic head according to the invention shown in Figures 1, 2 and 3 comprises a support or substrate 1, in this example of a magnetic material, namely NiZn ferrite on which a magnetic head structure 2 comprising magnetic layers, electric layers and insulation layers is provided, the magnetic head structure 2 being protected by a counter block 3 of a non-magnetic material, for example Al 2 O 3 /TiC. The magnetic head has a head face 5 with eleven transducing gaps in this example. Of the eleven transducing gaps a group of nine gaps S1 to S9 is intended to read information in a digital form and a group of two gaps S10 and S11 is intended to read information in an analog form from a record carrier 7 which moves along the magnetic head in a direction x. The gaps S1 to S9 for digital use generally have a smaller gap length than the gaps S10 and S11 for analog use. It is alternatively possible to choose such a gap length that both analog and digital information can be read by one and the same gap. The magnetic head according to the invention comprises an insulation layer 9 provided on the substrate 1, which layer is provided with three electric conductors C1, C2 and C3 in this example, which may extend as far as the transducing gaps. The magnetic head further comprises eleven magnetoresistive elements E1 to E11, further referred to as MR elements which comprise, for example, an Ni-Fe layer on which one or more barberpole strips of, for example, Au may be provided. Each MR element E1 to E11 may have a pair of connection tracks 11a and 11b, further referred to as first connection tracks which terminate in first connection faces 13a and 13b. In the embodiment shown the eleven first connection faces 13b are interconnected. Both the first connection tracks and the first connection faces are preferably made of Au. It is to be noted that an MR element provided with a barberpole is known per se and is described, inter alia, in US-A 4,052,748. Said electric conductors C1, C2 and C3 are used for driving the MR elements E1 to E9, E10 and E11 and are each provided with a pair of second connection tracks 15a and 15b which terminate in second connection faces 17a and 17b, respectively. The magnetic head also comprises eleven pairs of flux guides of a soft-magnetic material, for example NiFe or AlFeSi, with each pair comprising a first or front flux guide 19a and, spaced apart therefrom, a second or rear flux guide 19b. The front flux guide 19a extends as far as the head face 5 for cooperation with the magnetic record carrier 7. The MR elements E1 to E11 are present between the substrate 1 and the flux guides, each MR element forming a bridge between a first and a second flux guide 19a and 19b. In certain constructions and for specific uses it is possible to omit the rear flux guides. It also possible to start from a non-magnetic substrate and to provide an extra flux guide. The electric conductors, the MR elements and the flux guides are electrically insulated with respect to each other by a number of insulation layers of an electrically and magnetically insulating material, for example a polymer. The insulation layers are denoted by the reference numerals 21 and 23 in Figure 2. A further insulation layer 25, for example, in the form of an adhesive layer is present between the joint flux guides 19a and 19b and the counter block 3. A wear-inhibiting or wear-resistant layer 31 of substantially chromium nitride is provided on the head face 5, which layer forms a contact face or tape contact face 33 for cooperation with the tape-shaped record carrier 7. The chromium nitride layer 31, which is not transparent to visible light, has a thickness of 40 nm. The layer 31 has three alignment marks 35, 36 and 37 in this example, which with respect to the gaps S1 to S11 have an accurately defined position as regards location as well as direction, the gaps S1 to S11 being present in the area between the alignment marks 35 and 36 and the alignment mark 37. The formation of the alignment marks 35, 36 and 37 in the wear-resistant layer 31 will be described in greater detail, particularly with reference to Figures 2 and 4. When the magnetic head structure 2 is being formed layer by layer, three extra layers 35a, 36a and 37a, for example strips of a polymer are formed at a defined distance from the gaps S1 to S11 at the same time when the insulation layer 21 is being provided, which extra layers terminate in the head face 5 at least after the head face 5 has been formed by means of, for example, grinding and/or lapping. By finishing the head face thus formed, cavities 35b, 36b and 37b can be formed in the head face 5 at the area of the polymer layers 35a, 36a and 37a. After the head face 5 has been formed, it is cleaned in the given example by means of selective etching in an O 2 plasma in which the head face is hollowed at the area of the polymer layers 35a, 36a and 37a due to the difference in etching rate of the material used, in this example a polymer, of the layers 35a, 36a and 37a and the material surrounding the layers 35a, 36a and 37a, for example, NiFe or an oxide. The thin chromium nitride layer 31 is provided by way of sputtering on the head face 5 which is obtained in this manner with areas 35b, 36b and 37b having a different structure. Due to the small thickness of this layer 31, the areas 35b, 36b and 37b formed in the head face 5 appear as similar visible areas 35, 36 and 37 having the different structure in the non-transparent layer 31. Due to this property the magnetic head according to the invention can be accurately aligned and built in a housing of a magnetic head unit in spite of the presence of a non-transparent layer 31 on the head face 5. The magnetic head structure according to the invention shown in Figures 5 and 6 comprises the magnetic head described with reference to Figures 1 to 4 and here being denoted by the reference numeral 40. The magnetic head structure is provided with a support in the form of a housing 41 having a pair of tape guides 43 and 44 at both sides of the magnetic head 40. These tape guides are used for accurately guiding a magnetic tape along the magnetic head. Notably the height of the tape with respect to the magnetic head, particularly its transducing gaps, and the angle between a bounding edge of the tape and the magnetic head, particularly its joint transducing gaps, are maintained accurately. Before the magnetic head 40 is secured in the housing 41 during manufacture, it is positioned with reference to the alignment marks 35, 36 and 37 and by using a microscope and is oriented with respect to a reference plane related to the tape guides 43 and 44. After the correct position and orientation have been set, with the transducing gaps occupying the correct position and direction with respect to the recording tracks of the magnetic tape to be scanned, the magnetic head 41 is secured in the housing. By using two alignment marks which are spaced apart over a short distance, such as the marks 35 and 36, it is possible to determine an average distance to the reference plane and thus enhance the aligning accuracy. It is to be noted that the invention is not limited to the embodiments shown. For example, instead of a cavity 35, 36 or 37 as an alignment mark, it is possible to provide an alignment mark having a structure or a relief of elevations alternating with depressions, with the space between two consecutive elevations or depressions being at least equal to 1/4 λ of visible light. Furthermore, different soft materials such as a photolacquer or soft metals are suitable as materials for the extra layers 35a, 36a and 37a.

Claims: A magnetic head unit comprising a magnetic head secured to a support and having a magnetic head structure provided with a head face and at least one transducing gap terminating in the head face, characterized in that a wear-resistant layer forming a contact face and having at least one alignment mark occupying a defined position with respect to the transducing gap is provided on the head face of the magnetic head. A magnetic head unit as claimed in Claim 1, characterized in that the alignment mark is formed by an area having a structure which differs from the structure of the wear-resistant layer. A magnetic head unit as claimed in Claim 1 or 2, characterized in that the alignment mark has at least one cavity which is present in the wear-resistant layer. A magnetic head unit as claimed in Claim 2, characterized in that the area having the different structure has a relief with a periodicity of at least 1/4 λ, in which λ is the wavelength of light. A magnetic head unit as claimed in Claim 1, 2, 3 or 4, characterized in that the wear-resistant layer has at least one further alignment mark. A magnetic head unit as claimed in Claim 5, in which the magnetic head has a group of transducing gaps, characterized in that the group of transducing gaps is present between the first-mentioned alignment mark and the further alignment mark. A magnetic head unit as claimed in Claim 2, 3 or 4, characterized in that the head face has a head face area corresponding to the area having the different structure.

Inventors: BROESE VAN GROENOU ARNOLD, DE JONGH MATHIJS, RUIGROK JACOBUS JOSEPHUS MARIA, ZIEREN VICTOR, BROESE VAN GROENOU, ARNOLD, DE JONGH, MATHIJS, RUIGROK, JACOBUS JOSEPHUS MARIA, ZIEREN, VICTOR
Applicants: PHILIPS ELECTRONICS NV, PHILIPS ELECTRONICS N.V.
Application year: 1992
Main classification: G11B5
IPC codes: G11B5