Wafer for magnetic head and magnetic head

A wafer includes an insulating layer provided on a wafer substrate and formed of a film composition represented by a formula, Al--N.sub.(1-x) --O.sub.x (wherein 0.05.ltoreq..times..ltoreq.0.8). There is provided a wafer for a magnetic head as well as a magnetic head which is excellent in heat transferring property; in which the instability of a magnetic head characteristic due to a temperature rise is produced, and a reduction in output due to the polishing at a finishing step cannot be produced; and which is excellent in water resistance.

BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART
 The present invention relates to a wafer for use in a magnetic head capable
 of reading and writing on a magnetic medium, and to a magnetic head
 produced from such a wafer. More particularly, the present invention
 relates a wafer for a magnetic head, which is excellent in heat
 transferring property, so that the temperature is less risen during
 reading or writing, and to a magnetic head produced from such a wafer.
 In such a conventional type of a magnetic head, thin magnetic films such as
 an insulating layer, a magnetic shield film, a bottom pole and a top pole;
 an MR element; a gap layer; a coil layer and an overcoat are formed on a
 surface of a substrate formed of, for example, an alumina-titanium carbide
 and the like.
 The insulating films such as the insulating layer, the gap layer and the
 overcoat are usually formed of alumina.
 With the above conventional magnetic head, the insulating films such as the
 insulating layer, the gap layer and the overcoat are formed of alumina, as
 described above. Therefore, the conventional magnetic head suffers from
 problems of a lower heat conductivity, a poor heat transferring property
 and an instability of the characteristic of the magnetic head due to a
 temperature rise. Particularly, when the magnetic head includes an MR
 element, there is a disadvantage that the temperature rise is significant,
 whereby the motion of the MR element is unstable, because the MR element
 is a reading element. Another problem is that because the insulating layer
 is formed of alumina, when the surface of the magnetic head is polished at
 a finishing step, only the alumina material is polished in a larger amount
 to produce a difference in level, for a reason that the alumina material
 is softer than another material. As a result, the gap between a medium and
 a recording/regenerating element is widened, thereby causing a reduction
 in output. Further, the conventional magnetic head has a disadvantage that
 it is poor in water resistance.
 OBJECT AND SUMMARY OF THE INVENTION
 Accordingly, it is an object of the present invention to provide a wafer
 for a magnetic head, and to a magnetic head, which has an excellent
 heat-transferring property, in which the instability of the magnetic head
 characteristic due to a temperature rise is not caused, and a reduction in
 output due to the polishing at the finishing step cannot be produced, and
 which is excellent in water resistance.
 The present inventors have made zealous studies to solve the above problems
 and as a result, they have found that the above problems can be solved by
 using a film composition represented by a formula, Al--N.sub.(1-x)
 --O.sub.x (wherein, 0.3.ltoreq..times..ltoreq.0.6), in place of alumina
 conventionally used for the insulating film such as the insulating layer,
 the gap layer, the overcoat and the like provided on the substrate.
 To achieve the above object, according to a first aspect of the present
 invention, there is provided a wafer for a magnetic head, comprising a
 wafer substrate, and an insulating layer provided on the wafer substrate
 and formed of a film composition represented by a formula, Al--N.sub.(1-x)
 --O.sub.x, wherein 0.05.ltoreq..times..ltoreq.0.8.
 According to a second aspect of the present invention, in addition to the
 first aspect, the wafer substrate is alumina-titanium carbide.
 According to a third aspect of the present invention, there is provided a
 wafer for a magnetic head, comprising a wafer substrate, and an insulating
 layer provided on the wafer substrate ad formed of a film composition
 represented by a formula, Al--N.sub.(1-x) --O.sub.x, wherein
 0.3.ltoreq..times..ltoreq.0.6.
 According to a fourth aspect of the present invention, in addition to the
 third aspect, the wafer substrate is alumina-titanium carbide.
 According to a fifth aspect of the present invention, there is provided a
 magnetic head, comprising a magnetic head substrate, and an insulating
 layer provided on said magnetic head substrate and formed of a film
 composition represented by a formula, Al--N.sub.(1-x) --O.sub.x, wherein
 0.05.ltoreq..times..ltoreq.0.8.
 According to a sixth aspect of the present invention, in addition to the
 fifth aspect, the magnetic head further includes an MR element, and a gap
 film provided in the proximity to the MR element and formed of a film
 composition represented by a formula, Al--N.sub.(1-x) --O.sub.x, wherein
 0.05.ltoreq..times..ltoreq.0.8.
 According to a seventh aspect of the present invention, in addition to the
 sixth aspect, the magnetic head further includes an overcoat formed of a
 film composition represented by a formula, Al--N.sub.(1-x) --O.sub.x,
 wherein 0.05.ltoreq..times..ltoreq.0.8.
 According to an eighth aspect of the present invention, in addition to the
 seventh aspect, the substrate is alumina-titanium carbide.
 According to a ninth aspect of the present invention, there is provided a
 magnetic head, comprising a magnetic head substrate, and an insulating
 layer provided on the magnetic head substrate and formed of a film
 composition represented by a formula, Al--N.sub.(1-x) --O.sub.x, wherein
 0.3.ltoreq..times..ltoreq.0.6.
 According to a tenth aspect of the present invention, in addition to the
 ninth aspect, the magnetic head further includes an MR element, and a gap
 film provided in the proximity to the MR element and comprised of a film
 composition represented by a formula, Al--N.sub.(1-x) --O.sub.x, wherein
 0.3.ltoreq..times..ltoreq.0.6.
 According to an eleventh aspect of the present invention, in addition to
 the tenth aspect, the magnetic head further includes an overcoat formed of
 a film composition represented by a formula, Al--N.sub.(1-x) --O.sub.x
 wherein 0.3.ltoreq..times..ltoreq.0.6.
 According to a twelfth aspect of the present invention, in addition to the
 eleventh aspect, the substrate is alumina-titanium carbide.
 As described above, by using a film composition represented by a formula,
 Al--N.sub.(1-x) --O.sub.x, wherein 0.05.ltoreq..times..ltoreq.0.8, in
 place of the conventionally used alumina, for an insulating film such as
 an insulating layer, a gap layer, an overcoat and the like provided on a
 substrate, a wafer for a magnetic head as well as a magnetic head
 excellent in heat transferring property. In this magnetic head, the
 instability of the magnetic head characteristic due to a temperature rise
 is not caused, and a reduction in output due to a larger gap between the
 magnetic head and a medium cannot be produced by a difference in film
 level due to due to the polishing at a finishing step. Further, the
 magnetic head is also excellent in water resistance.
 Particularly, by using a film composition represented by a formula,
 Al--N.sub.(1-x) --O.sub.x, wherein 0.3.ltoreq..times..ltoreq.0.6, a wafer
 for a magnetic head as well as a magnetic head can be produced which can
 reconcile a smaller difference in film level and a higher heat
 conductivity and a higher voltage resistance.
 The insulating layer may be provided on the wafer substrate or on the
 magnetic head substrate directly or with an alumina sputtered layer
 interposed therebetween.

EMBODIMENTS
 The present invention will now be described by way of embodiments with
 reference to the accompanying drawings.
 (Fabrication of magnetic head wafer)
 First, an alumina-titanium carbide wafer substrate 11 comprising 64% by
 weight of alumina and the balance of titanium carbide and having a
 diameter of 3 inches was prepared. Then, the film-forming surface of the
 substrate 11 was subjected to a mirror polishing treatment using diamond
 abrasive grains having a grain size of 1 .mu.m, so that the degree Ra of
 surface roughness is equal to 2 nm. Subsequently, an AlNO film was formed
 on the polished surface in an Ar/O.sub.2 mixture atmosphere by an RF
 magnetron sputtering process using an AlN sintered compact as a target. In
 this case, the film was formed into a thickness of 8 to 10 .mu.m at a
 forming rate of 20 nm/min under conditions of an RF thrown power of 4
 W/cm.sup.2, a partial pressure of oxygen equal to 5% and the total
 pressure of 10 m Torr and T/S equal to 70 mm.
 The film forming method is not limited to the sputtering in the Ar/O.sub.2
 mixture atmosphere with the AlN sintered compact used as the target, and a
 similar film could be formed even by a sputtering using a metal aluminum
 target in an atmosphere of an Ar/O.sub.2 /N.sub.2 mixture.
 The composition of the film represented by a formula, Al--N.sub.(1-x)
 --O.sub.x (wherein 0.05.ltoreq..times..ltoreq.0.8) is regulated by
 controlling the partial pressure of oxygen in the atmosphere of the
 Ar/O.sub.2 mixture flowing during formation of the film.
 The surface of the film formed in the above manner was subjected to a
 so-called MCP polishing treatment using oxide fine abrasive grains such as
 CeO or a cloth, so that the degree Ra of roughness of the film surface is
 equal to 5 nm, thereby producing a magnetic head wafer 10 having an
 insulating layer 12 with a film composition represented by the formula,
 Al--N.sub.(1-x) --O.sub.x (wherein 0.05.ltoreq..times..ltoreq.0.8) on its
 surface.
 (Fabrication of magnetic head)
 An alumina-titanium carbide substrate 21 was prepared which was formed into
 a substrate shape from the alumina-titanium carbide wafer substrate 11
 comprising 64% by weight of alumina and the balance of titanium carbide
 and having the diameter of 3 inches. Then, the film-forming surface of the
 alumina-titanium carbide substrate 21 was subjected to a mirror polishing
 treatment using diamond abrasive grains having a grain size of 1 .mu.m, so
 that the degree Ra of surface roughness is equal to 2 nm. Subsequently, an
 AlNO film was formed on the polished surface in an Ar/O.sub.2 mixture
 atmosphere by an RF magnetron sputtering process using an AlN sintered
 compact as a target. In this case, the film was formed into a thickness of
 8 to 10 .mu.m at a forming rate of 20 nm/min under conditions of an RF
 thrown power of 4 W/cm.sup.2, a partial pressure of oxygen equal to 5% and
 the total pressure of 10 m Torr and T/S equal to 70 mm.
 Subsequently, the surface of the film formed in the above manner was
 subjected to a so-called MCP polishing treatment using oxide fine grains
 such as CeO or a cloth, so that the degree Ra of roughness of the film
 surface is equal to 5 nm, thereby forming an insulating layer 22 having a
 composition represented by the formula, Al--N.sub.(1-x) --O.sub.x (wherein
 0.05.ltoreq..times..ltoreq.0.8) on its surface.
 In the above manner, the insulating layer 22 having the composition
 represented by the formula, Al--N.sub.(1-x) --O.sub.x (wherein
 0.05.ltoreq..times..ltoreq.0.8) was provided on the surface of the
 alumina-titanium carbide substrate 21.
 Then, a film having a composition comprising 80% by weight of Ni and the
 balance of Fe was formed on the insulating layer 22 and subjected to an
 MCP mirror polishing treatment similar to that described above, thereby
 forming a magnetic shield film
 Subsequently, an AlNO film having a composition similar to that described
 above was formed into a thickness of 100 nm as a gap film 24 on the
 magnetic shield film 23 by a sputtering. An MR element 25 was formed on
 the AlNO film by a photolithography and a sputtering. Further, an AlNO
 film having a composition similar to that described above was formed again
 into a thickness 80 nm as a gap film 26 on the MR element 25 by a
 sputtering.
 In this manner, the gap films 24 and 26 adjacent the MR element 25 were
 formed of the composition represented by the formula, Al--N.sub.(1-x)
 --O.sub.x (wherein 0.05.ltoreq..times..ltoreq.0.8).
 Then, a bottom pole 27 having a composition comprising 80% by weight of Ni
 and the balance of Fe was formed as a writing element on the gap film 26
 by a photolithography and an electroplating. An AlNO film having a
 composition similar to that described above was formed into a thickness of
 400 nm as a writing gap film 28 on the bottom pole 27.
 An organic insulating film 29 was formed on the writing gap film 28 by a
 spin coating technique. A coil pattern 30 of Cu was formed on the organic
 insulating film 29 by an electroplating process. Further, an organic
 insulating film 31 was formed on the coil pattern 30 in the same manner as
 described above.
 Then, a top pole 32 having a composition comprising 80% by weight of Ni and
 the balance of Fe was formed as a writing element by a photolithography
 and an electroplating, so that a predetermined track width was provided.
 Finally, an AlNO film having a composition similar to that described above
 was formed into a thickness of 60 .mu.m as an overcoat 33 by a sputtering,
 thus forming a magnetic head element.
 Further, the substrate 21 having the elements formed thereon in the above
 manner was cut into a slider size by machining, so that a surface to come
 into contact with a medium has a predetermined floating property and shows
 a predetermined contact state. Thereafter, the substrate 21 was polished
 with a fine diamond paste having a diameter of 0.5 .mu.m, thereby
 completing a magnetic head.
 Then, magnetic heads were produced as examples 1 to 5 and comparative
 examples 1 and 2 in the same manner, except that the composition of the
 film represented by the formula, Al--N.sub.(1-x) --O.sub.x (wherein
 0.05.ltoreq..times..ltoreq.0.8) was varied in a range shown in Table 1,
 and as a comparative example 3 having a conventional alumina layer as an
 insulating film. The characteristics of the produced magnetic heads were
 estimated below.
 TABLE 1
 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Co. Ex. 1 Co. Ex. 2
 Co. Ex. 3
 Film X = 0.05 0.3 0.4 0.6 0.8 0.01 0.9
 alumina
 composition
 film
 Hv 1380 1320 1150 1120 980 1450 680
 700
 Difference in -5 0 1.5 5 10 -10 17
 15
 level (nm)
 heat 5.12 4.83 3.88 4.21 2.05 4.43 1.1
 1.1
 conductivity
 (W/m .multidot. K)
 withstand 6 10 10 8 8 5 5
 5
 voltage (v)
 water not not not not not X X
 X
 resistance varied varied varied varied varied
 Ex. = Example
 Co. Ex. = Comparative Example
 The characteristic shown in Table 1 was measured in the following manner.
 Film composition: It was measured quantitatively by EPMA (Electron Probe
 Micro Analyzer).
 Vickers hardness Hv: It was measured by Vickers impression made at a load
 of 100 g.
 Difference in level: A difference in level between the substrate and the
 film was measured by AFM (Atomic Force Microscope) after polishing of a
 cut face, wherein + indicates that the film protruded from the substrate,
 and - indicates that the film is recessed from the substrate.
 Heat conductivity: The film formed on the thin plate-like substrate having
 the known thickness value of 50 .mu.m was measured by a thermal efficiency
 process.
 Withstand voltage: A film was formed into a thickness of 100 nm on a
 conductor substrate and a pattern of 2.times.4 mm was formed on this film.
 The voltage was measured until the pattern was fractured.
 Water resistance: The magnetic head was immersed in pure water for 24
 hours, and a difference in film level between before and after the
 immersion was measured by AFM.
 As apparent from Table 1, it can be seen that when the insulating layer was
 provided by the film composition represented by the formula,
 Al--N.sub.(1-x) --O.sub.x (wherein 0.05.ltoreq..times..ltoreq.0.8), the
 heat resistance was excellent; the instability of the characteristic of
 the magnetic head was not produced due to a temperature rise; a reduction
 in output due to the polishing at the finishing step was not produced; and
 moreover, the water resistance was excellent, as compared with the prior
 art in which the insulating film was formed from alumina.
 Particularly, it is apparent that when the film composition represented by
 the formula, Al--N.sub.(1-x) --O.sub.x (wherein
 0.3.ltoreq..times..ltoreq.0.6) is used, a smaller difference in film and a
 higher heat conductivity as well as a higher voltage resistance is
 reconciled.
 In the embodiment, all of the insulating films such as the insulating
 layer, the gap films and the overcoat were formed by the film having the
 above-described composition. Alternatively, only the insulating film just
 on the substrate, or this insulating film and the gap film may be formed
 for the purpose of escaping the heat of the MR element to the substrate.
 The arrangement of the magnetic head is not limited to that in the
 embodiment, but any other arrangement may be used such as an arrangement
 in which the positions of the MR element and the writing element are
 changed with each other.
 In addition, the magnetic head including the MR element has been
 illustrated as an example in the embodiment, but the present invention is
 applicable to a thin-film magnetic head of a type which includes no MR
 element and which is capable of reading and writing by the induction-type
 element. This thin-film magnetic head is effective, because a stability of
 a soft magnetism can be obtained from the viewpoint of the prevention of
 the temperature rise.