Dynamic magnetic information storage or retrieval – Head – Head surface structure
Reexamination Certificate
1996-07-31
2002-07-23
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Head surface structure
Reexamination Certificate
active
06424489
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a magnetic head having a head face and comprising a head structure composed of thin layers and provided with a transducing element, in which different materials in different areas are present in the head face.
A magnetic head of this type is known from JP-A 63-37811 (herewith incorporated by reference). The known magnetic head has a thin-film structure provided on a substrate and comprises a magnetic yoke with a magnetoresistive element and a transducing gap. The magnetic head also has a head face in which the transducing gap and magnetic flux guides for guiding magnetic information towards the magnetoresistive element terminate. The head face of the known magnetic head is used for guiding a magnetic record carrier, particularly a magnetic tape.
In magnetic heads which have a layer structure, soft materials, notably soft-magnetic materials of flux guides, for example permalloy, occur in addition to relatively hard materials, notably substrate materials, for example Al
2
O
3
/TiC. Due to the abrasive effect of the record carrier moving along the head face during operation, the relatively soft materials may wear on the head face, which results in a hollowing of the layer structure of the head face. Such a hollowing leads to a larger distance between the record carrier and the layer structure and hence to a reduced transfer of information from the record carrier to the magnetic head. Consequently, a long lifetime cannot be guaranteed for the known magnetic head whose head face also serves as a tape contact face.
It is known per se to provide wear-resistant layers on the head faces of magnetic heads in order to inhibit wear. It is known from IBM Technical Disclosure Bulletin, vol. 11, no. 10, March 1969, pp. 1199 (herewith incorporated by reference) to provide Cr
2
O
3
by means of flame plating on heat-resistance magnetic heads for forming wear-resistant layers. JP-A 66-73917 (herewith incorporated by reference) proposes to provide core limbs of permalloy comprising Cr with a layer of Cr oxide having a thickness of more than 0.5 &mgr;m and to form a layer of Cr oxide by means of sputtering on core limbs of permalloy not comprising Cr. EP-A 0 123 826 (herewith incorporated by reference) proposes to provide the head face of a magnetic head with a sputtered layer of titanium carbide, chromium carbide or titanium nitride which is thinner than 0.2 &mgr;m. However, magnetic heads whose head faces have a wear-resistant layer have the problem that the transfer of information from the record carrier to the magnetic head is worse than in corresponding magnetic heads without a wear-resistant layer on the head face. In order that more favourable output signals are still achieved during operation, it is required that the wear-resistant layer should not be made thicker than is strictly necessary due to the wear-inhibiting function. Thin wear-resistant layers, notably thinner than 100 nm, are generally not gas and moist-proof so that corrosively reacting substances, notably from the record carrier, can reach the head face via pores in the wear-resistant layer. Notably soft-magnetic materials such as NiFe alloys are readily affected by corrosively reacting substances, resulting in a decrease of the transfer of information from the magnetic tape to the transducing element. It has been found that many magnetic tapes contain, inter alia chlorine, and that during scanning of these magnetic tapes Cl ions diffuse from the magnetic tapes into the head faces of the magnetic heads where they cause local corrosion.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to improve the magnetic head described in the opening paragraph in such a way that it has a wear-resistant and corrosion-resistant head face.
The magnetic head according to the invention is characterized in that the head face is provided with a first layer of a material which is more sensitive to corrosion than said materials in the head face, and the first layer is provided with a second layer of a wear-resistant material which is more insensitive to corrosion than the material of the first layer.
The second layer, which constitutes a contact face for cooperation with a record carrier, protects the magnetic head according to the invention from abrasive and corrosive wear, while the first layer present between the head face and the second layer protects the magnetic head from corrosively reacting substances such as chlorine originating from the record carrier. It has also been found that the adhesion of wear-resistant materials to materials occurring in the head face can be improved by suitable choice of the material of the first layer; in other words, the first layer may also serve as an adhesive layer.
To ensure a favourable signal transmission from the record carrier to the transducing element and/or from the transducing element to the record carrier, said layers should have a minimal thickness. Favourable results were achieved with magnetic heads according to the invention, whose first layer had a thickness of between 1 nm and 20 nm and whose second layer had a thickness of between 10 nm and 100 nm. However, a magnetic head is preferred whose first layer has a thickness of less than 5 nm and whose second layer has a thickness of less than 60 nm, because only very limited output losses occur in such cases.
An embodiment of the magnetic head according to the invention is characterized in that the material of the first layer mainly comprises a metal from the group of Ti, Zr, Hf, V, Nb, Ta, Cr, Al, Zn. All the metals of this group are non-magnetic metals having lower standard reduction potential, —E° values in accordance with the U.S. definition, than Fe; thus, they are less noble than Fe as well as Fe alloys, for example an NiFe alloy—permalloy—. Thus, soft-magnetic flux guides of permalloy terminating in the head face are protected from corrosion by the material of the first layer. The metals may be provided on the head face by means of known deposition methods, particularly physical or chemical vapour deposition such as sputtering or CVD.
An embodiment of the magnetic head according to the invention is characterized in that the material of the second layer is one of the materials from the group of chromium oxide, chromium nitride, hafnium nitride, titanium nitride, chromium carbide, titanium carbide, tungsten carbide, diamond. All these materials have good wear-resistant properties and adhere satisfactorily to the metals of the first layer. The materials may be provided on the first layer by known techniques such as sputtering deposition, vapour deposition or CVD. For process reasons the following combinations of materials for the first and second layers are preferred: titanium and titanium nitride or titanium carbide; hafnium and hafnium nitride; chromium and chromium oxide or chromium nitride or chromium carbide.
An embodiment of the magnetic head according to the invention is characterized in that the chromium oxide is mainly Cr
2
O
3
, the material of the first layer being Cr. This magnetic head according to the invention has a wear-resistant contact face formed by the layer mainly comprising Cr
2
O
3
for cooperation with a record carrier, particularly a magnetic tape. At a layer thickness of 10 nm to 100 nm a favourable signal transmission between the record carrier and the transducing element is ensured. It has also been found that the contact face has a good wear resistance, not only in the temperature range between 5° C. and 85° C., but also at temperatures in the range between 5° C. and −20° C. This is particularly important for magnetic heads which are used in portable apparatuses and in magnetic scanning devices intended for outdoor use, such as car radio cassette recorders.
It has been found by experiment that a layer of eminent quality mainly comprising Cr
2
O
3
on the head face can be obtained by sputtering. Already at layer thicknesses of less than 60 nm, high wear resistances are found to be achievable by means of sputtering. A further advantage
Broese Van Groenou Arnold
De Jongh Mathijs
Dirne Franciscus W. A.
Lasinski Peter
Roozeboom Freddy
Cao Allen
U.S. Philips Corporation
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