Patent Publication Number: US-6992860-B2

Title: Recording/reproducing separated magnetic head with concave portion formed in air bearing protective film

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a recording/reproducing separated type magnetic head for use in magnetic disk apparatuses. 
     2. Description of the Prior Art 
     Along with the capacity enlargement of magnetic disk apparatuses, the requirement for higher recording density is increasing year after year. The apparatuses are also required to be smaller. To meet these requirements, state-of-the-art magnetic disk apparatuses use a giant magnetoresistive (GMR) head to perform the reproducing function of the recording/reproducing separated type magnetic head, with their recording track width being reduced to 0.3 μm and the gap between the head and the recording medium (hereinafter referred to as the flying height), to 13 nm, both approximately. 
     In order to achieve a high density of recording, the heads indispensably need to be lowered in flying height. However, along with the lowering of the flying height, the deformation of heads due to heat generation of coils in the inductive write thin film head during recording is posing an increasingly serious problem, because the deformation of heads would invite localized protrusion of the air bearing surfaces of the heads by about 3 nm and the consequent narrowing of the gap between the heads and the recording medium to about 10 nm, leading to possible collision of the heads and the recording medium, which would make head positioning impossible and in the worst case result in signal disappearance due to damaging of the recording medium or sliding of the heads. Studies on this problem include, for instance, what is reported in the IEEE Transactions on Magnetics, VOL. 38. NO.1, JANUARY 2002, pp 101. 
       FIG. 6  shows a schematic sectional view of a recording/reproducing separated type magnetic head using a GMR head. FIG.  7  and  FIG. 8  respectively show thermal deformation of a head and how a head is worn by its contact with a recording medium. When heated, a head is deformed in such a way that its angled portion (the upper end of a protective film  13 ) protrudes forward with a substrate  1  as the base point. As a result, the protruding part of a multilayered protective film  19  on the air bearing surface comes into contact with the recording medium, and an area A is worn as shown in FIG.  8 . The quantity of wear is defined by the width (w), height (h) and depth (d). According to the evaluation of a head whose flying height was approximately 0, the depth (d), width (w) and height (h) of the wear of the multilayered protective film  19  on the air bearing surface over an upper magnetic film  12  were 3 nm, 8 μm and 5 μm, respectively, at a recording frequency of 300 MHz, a write current of 50 mA and an ambient temperature of 60° C. even in a head improved in thermal protrusion (TPR) whose distance from the rear part of the upper magnetic film  12  to an air bearing surface shallow groove  14  was narrowed to 4 um or less as shown in FIG.  7 . Thus, the wear of the multilayered protective film  19  on the air bearing surface over the upper magnetic film  12  due to the deformation of the head is too substantial to ignore. The wear depth of 3 nm accounts for 23% of the flying height of 13 nm between the head and the recording medium. This percentage corresponds to the 3.5-nm-thickness of the carbon film C of the multilayered protective film  19  on the air bearing surface. 
     A head can be deformed by differences among its constituent layers in the ratio of expansion when the head is heated. The heating of the head in turn would be due to its ambient temperature or its own heat generation. Among the factors of ambient temperature, the temperature within the magnetic disk apparatus is dominant. Many magnetic disk apparatuses are guaranteed against a temperature of about 60° C. The self-generated heat of the head mainly derives from Joule heating due to the electrification of coils at the time of writing, eddy current heating in the high frequency region, iron loss and an increase in resistance by the skin effect. 
     Deformation can be reduced by lowering the head temperature, the ambient temperature among various temperature elements is specified by the customer, and the manufacturer has to configure a structure that can meet the customer&#39;s requirement. On the other hand, to reduce the self-generated heat of heads, effective ways include reducing the resistance of coils, shaping the magnetic film compactly and using high-resistance magnetic materials. It is effective as well to reduce the volumic proportion of a material with a big difference in thermal expansion coefficient. More specifically, it is advisable to reduce the size of metallic films having a high thermal expansion coefficient, for instance, upper and lower shield films. Further, it is also effective to enhance the heat radiation effect. This can be achieved by providing a radiator plate near the source of heat. However, though the deformation of the head can be restrained to some extent by these means, deformation still occur as long as there are differences in thermal expansion coefficient among the constituent members, and it is impossible to completely eliminate contact between the head and the magnetic disk. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a highly sliding resistance reliability of recording/reproducing separated type magnetic head by preventing the head coming into contact with a recording medium, which arises with the deformation of the head and with a decrease in the flying height of the head, which is an indispensable requirement for high density recording. 
     The object stated above can be achieved by providing a level gap on the air bearing surface of an inductive write thin film head and the air bearing surface of a read GMR head with a protective film, forming the air bearing surface of the inductive write thin film head, which is subject to deformation by heat generation, in a concave shape in advance (forming a first concave), and thereby preventing the air bearing surface of the inductive write thin film head, which is subject to deformation by heat generation, from protruding through the air bearing surface of the read GMR head. 
     Thus, by removing only the carbon film of the multilayered protective film on the air bearing surface in a wear-susceptible area A of a recording/reproducing separated type magnetic head to form a concave air bearing surface of about 3.5 nm in depth in advance, it is possible to provide a highly reliable recording/reproducing separated type magnetic head that can avoid contact with the recording medium even when heated by the use. A similar effect can be achieved by totally removing the multilayered protective film on the air bearing surface of the recording/reproducing separated type magnetic head in the part matching the inductive write thin film head to form a concave. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of a recording/reproducing separated type magnetic head to which the present invention is applied. 
         FIG. 2  shows a section of a recording/reproducing separated type magnetic head, which is a preferred embodiment of the invention. 
         FIG. 3  shows a sectional view of the deformation of the recording/reproducing separated type magnetic head embodying the invention when under the influence of heating. 
         FIGS. 4A  to  4 C constitute a process diagram showing the method forming a level gap portion of the multilayered protective film on the air bearing surface of the recording/reproducing separated type magnetic head embodying the invention. 
         FIG. 5  shows a perspective view of a recording/reproducing separated type magnetic head, which is another preferred embodiment of the invention. 
         FIG. 6  shows a section of a recording/reproducing separated type magnetic head according to the prior art. 
         FIG. 7  shows a sectional view of the deformation of the recording/reproducing separated type magnetic head according to the prior art. 
         FIG. 8  shows a schematic view of the worn state of the recording/reproducing separated type magnetic head according to the prior art. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a perspective view of a recording/reproducing separated type magnetic head to which the present invention is applied, though the illustration of its multilayered protective film on the air bearing surface is dispensed with.  FIG. 2  shows the sectional structure of a recording/reproducing separated type magnetic head, which is a first preferred embodiment of the invention, before it is heated. The recording/reproducing separated type magnetic head has a structure in which an inductive write thin film head is stacked over a giant magnetoresistive (GMR) head solely for reading use. 
     The read GMR head is configured by stacking over a substrate  1  a lower shield film  2 , a lower gap film  4 , a magnetoresistive film (GMR film)  7  for detecting signals, a hard bias film  6  for controlling the domain in the end portion of the GMR film  7 , an electrode film  8  for flowing an electric current to the GMR film  7 , an upper gap film  5 , an upper shield film-cum-lower magnetic film  3  and so forth. On the other hand, the inductive write thin film head uses the upper shield of the GMR head also as the lower magnetic film, and is configured by stacking over this upper shield film-cum-lower magnetic film  3  a write gap film  9 , coils  10 , an insulating layer  11 , an upper magnetic film  12  and so on. Over the inductive write thin film head is stacked a protective film  13 . Further, over the air bearing surface is formed a multilayered protective film  19  on the air bearing surface by stacking a silicon film Si and a carbon film C by sputtering or otherwise. The silicon film Si is a layer in tight contact with the carbon film C. 
     The multilayered protective film  19  on the air bearing surface is formed for the purpose of preventing the read GMR head from corrosion and discharge, of which the silicon film Si is about 1.5 nm and the carbon film C, about 3.5 nm. In the upper end portion of the protective film  13  is formed an air bearing surface shallow groove  14  (second concave) d 2 . Further by removing the part of the carbon film C in what will constitute a C film-removed area  20  from the multilayered protective film  19  on the air bearing surface, a protective film level gap (first concave) d 1  of a depth corresponding to the thickness of the carbon film C (about 3.5 nm) is formed in the air bearing surface matching the upper magnetic film  12  of the inductive write thin film head. Incidentally, the second concave d 2  can be dispensed with. 
       FIG. 3  shows how the recording/reproducing separated type magnetic head embodying the invention is deformed when under the influence of heating. By forming the protective film level gap d 1 , the protrusion of the upper end portion of the head can be reduced by about 3.5 nm. It is thereby made possible to avert contact or collision between the recording/reproducing separated type magnetic head and the recording medium. Further by properly aligning the C film-removed area  20  and distributing the thicknesses of the carbon film C and the silicon film Si over the multilayered protective film  19  on the air bearing surface, the protrusion of the angled portion of the head can be further restrained. 
     A number of methods are available for the formation of the level gap of the multilayered protective film  19  on the air bearing surface. A first method to form the level gap is, in the process of floating rail formation for the head, to mask other parts than the C film-removed area  20  with a resist (masking material), etch the exposed portion with oxygen (RIE) and remove the carbon film C while leaving the silicon film Si. A second method is to remove the carbon film C by reactive ion etching (RIE) with oxygen after forming a mask as in the first method, then remove the silicon film Si as well with CF4 reactive gas, and finally remove the whole multilayered protective film  19  on the air bearing surface. A third method is to form the whole air bearing surface protective film  19  of a carbon film C, and then remove the air bearing surface protective film  19  in the same way as described above. The last two methods require consideration of possible adverse impacts, such as damage or corrosion, on the surface of the upper magnetic film  12  which becomes exposed on the air bearing surface. No particular exactness is required for the depth of this protective film level gap d 1 , which may be 3 to 5 nm. 
     Next will be described in detail a manufacturing method for the recording/reproducing separated type magnetic head embodying the invention with reference to FIG.  2  and FIG.  4 . First, reference is made to FIG.  2 . 
     (1) The substrate  1  is formed in a wafer shape by stacking an Al 2 O 3  film (base alumina) over sintered Al 2 O 3 .TiC (alumina titanium carbide) by sputtering. The lower shield film  2  is formed over this substrate  1  by plating. The lower shield film  2  is an NiFe alloy film of 2 μm in thickness. 
     (2) Next, the lower gap film  4  is formed of Al 2 O 3  (alumina) by sputtering to a thickness of 0.05 μm. After that, it is processed into a desired shape by photolithography and ion milling. 
     (3) Then, the GMR film  7  is formed by sputtering, and processed into a desired shape by photolithography and ion milling. The GMR film  7  is a spin valve film having a CoFe free layer. 
     (4) Next, the hard bias film  6  and the electrode film  8  are formed by sputtering. Patterning is done by a lift-off method. The hard bias film  6  is a CoPt film. The electrode film  8  is a laminated layer of Ta and a thin film of its alloy. 
     (5) Then, the upper gap film  5  is formed of Al 2 O 3  (alumina) by sputtering to a thickness of 0.05 μm. After that, it is processed into a desired shape by photolithography and ion milling. 
     (6) Further the upper shield film-cum-lower magnetic film  3  is formed an NiFe alloy film by plating to a thickness of 2 μm. 
     The formation of the read GMR head is now completed. 
     Then, the inductive write thin film head is stacked over the read GMR head. 
     (7) The write gap film  9  is formed of Al 2 O 3  (alumina) to a thickness of 0.2 μm by sputtering over the upper shield film-cum-lower magnetic film  3 . 
     (8) Then, the coil  10  is formed of Cu by plating. The number of turns of the coil  10  is nine. 
     (9) Next, the insulating layer  11  is formed by coating with a photoresist followed by heat treatment to a thickness of 10 μm. 
     (10) Then, the upper magnetic film  12  is formed of NiFeCo by plating. 
     (11) Next, a lower terminal  15  is formed of Cu by plating to be electrically connected to the electrode film  8 . 
     (12) Next, the protective film  13  is formed of Al 2 O 3  (alumina) to a thickness of 60 μm by sputtering. 
     (13) Then, the protective film  13  is lapped to expose the lower terminal  15 , over which an upper terminal  16  is formed of Au to a thickness of 6 μm by plating. 
     The formation of the read head and the write head is now completed. 
     This is followed by the formation of the multilayered protective film  19  on the air bearing surface, and the level gap d 2  is formed in the protective film  13  by shaped rail (SR) machining, and the level gap d 1 , in the multilayered protective film  19  on the air bearing surface. 
     (14) As shown in  FIG. 4A , a bar block  18  is cut out of the wafer-shaped substrate  1 . 
     (15) Next, as shown in  FIG. 4B , rails  21  are formed in the air bearing surface in the state of the bar block  18 . First the multilayered film  19  of a silicon film Si and a carbon film C on the element face side of the bar block  18  is formed, followed by the formation of the rails  21  and the second concave d 2  for floating by photolithography and ion milling. 
     (16) Then, as shown in  FIG. 4C , to remove the carbon film C of the multilayered protective film  19  on the air bearing surface in the part matching the upper magnetic film  12 , the other area than the C film-removed area  20  is masked with a resist (masking material)  22 . In this state, the C film-removed area  20  is subjected to RIE with oxygen, and the carbon film C is removed, with the silicon film Si serving as the stopper film. The etched quantity is about 3.5 nm, corresponding to the thickness of the carbon film C of the multilayered protective film  19  on the air bearing surface. 
     (17) By removing the resist (masking material)  22  after that, the level gap (first concave) d 1  of the air bearing surface protective film is formed as shown in FIG.  1 . 
     (18) By cutting this bar block  18  into chips, the recording/reproducing separated type magnetic head, which is this first embodiment of the invention, is completed. 
     While the first embodiment described above is a recording/reproducing separated type magnetic head wherein the upper shield of the read head is also used as the lower magnetic film of the write head, the invention can also be applied to a type where the two elements are separated by an insulating separation film  23  as shown in  FIG. 5 , and this configuration would give a similar effect to the first embodiment described above. Referring to  FIG. 5 , the GMR film  7 , the hard bias film  6  and the electrode film  8  are formed over the substrate  1  with the lower shield film  2  and a lower gap film (not shown) in-between, and the upper shield film  3 , the separation film  23 , a lower magnetic film  24 , a write gap film (not shown), the coils  10 , an interlayer insulator (not shown), the upper magnetic film  12 , a protective film (not shown) and a multilayered protective film on the air bearing surface (not shown) are formed with an upper gap film (not shown) in-between. Reference numeral  26  denotes a lower pole protruded by trimming the lower magnetic film  24 , and  27 , a tip pole of the upper magnetic film  12 . A magnetic gap  25 , formed of the lower pole  26  and the tip pole  27 , determines the write track width. On the air bearing surface is formed the multilayered protective film  19  on the air bearing surface (not shown) as in the first embodiment, the second concave d 2  is formed in the protective film over the upper magnetic film  12 , again as in the first embodiment, and further the level gap (first concave) d 1  of the air bearing surface protective film is formed in the part of the air bearing surface matching the inductive write thin film head. As in the first embodiment, the second concave d 2  can be dispensed with. 
     As hitherto described, by forming a level gap in the part of the multilayered protective film on the air bearing surface matching the inductive write thin film head of the head air bearing surface, it is made possible to provide a recording/reproducing separated type magnetic head in which the protrusion of the head to the air bearing surface due to thermal deformation can be cancelled and, at the same time, the lowest floating point of the read GMR head can be made