Abstract:
An overcoat overcoat for a head and/or media surface is made of a hard, dense and durable silicon-carbide (SiC) layer. The SiC layer does not require an interlayer to promote adhesion to underlying magnetic or ceramic layers, thus reducing head-media spacing and increasing areal storage density and resolution. The SiC is formed in a manner that creates an overcoat with density, hardness, durability and corrosion resistance similar to DLC. The SiC overcoat formation process also penetrates less into underlying magnetic layers than is conventional, reducing further the spacing of active elements by inactive coatings. In an alternative embodiment, SiC may be formed by this process as an interlayer for a carbon overcoat such as DLC or ta-C. This allows the overcoat to be made thinner, since the interlayer is hard and dense, while retaining the chemical and other surface properties of the carbon overcoat.

Description:
TECHNICAL FIELD 
     The present invention relates to electromechanical information storage systems. 
     BACKGROUND OF THE INVENTION 
     It is well known in the field of magnetic information storage systems that a means for increasing storage density and signal resolution is to reduce the separation between a transducer and associated media. For many years, devices incorporating flexible media, such as floppy disk or tape drives, have employed a head in contact with the flexible media during operation in order to reduce the head-media spacing. Recently, hard disk drives have been designed which can durably operate with high-speed contact between the hard disk surface and the head. 
     A head for a hard disk drive typically includes microscopic solid layers formed on a ceramic or ferrite substrate, and can easily be damaged by such high-speed contact. Moreover, a head can also damage a disk during such contact, which may occur at speeds exceeding ten meters per second. In an attempt to prevent such damage, which can destroy a disk and the data stored thereon, hard disk media is conventionally coated with a carbon or carbon-based overcoat that is hard and durable. Similarly, a slider that carries a transducer for a disk drive head is usually formed of a hard durable material, such as alumina (Al 2 O 3 )/titanium-carbide (TiC), which is commonly referred to as AlTiC. Another suitable slider or disk material is silicon carbide (SiC), which may be sintered or formed by high-temperature chemical vapor deposition (CVD), as described in. U.S. Pat. No. 5,465,184 to Pickering et al. 
     Another means for increasing signal resolution that has become increasingly common is the use of magnetoresistive (MR) or other sensors for a head. MR elements may be used along with inductive writing elements, or may be separately employed as sensors. While MR sensors offer greater sensitivity than inductive transducers, they are even more prone to damage from high-speed contact with a hard disk surface, and may also suffer from corrosion. For these reasons, air bearing surfaces (ABS) for heads containing MR sensors are conventionally coated with a hard, durable carbon or carbon-based overcoat. 
     Current methods for making overcoats for slider or disk surfaces include sputtering or ion beam chemical vapor deposition (IBCVD) to form diamond-like carbon (DLC) films. More recently, cathodic arc deposition has been used to form tetrahedral-amorphous carbon (ta-C) films having even greater hardness. Employment of harder films allows the thickness of the films to be reduced, which can help to reduce head-media spacing. 
     DLC and ta-C films have a high stress as well as high hardness, and do not adhere well to slider ABS or magnetic layers, and so an adhesion layer of Si or Si 3 N 4  is conventionally formed to help with stress relief and adhesion. FIG. 1 depicts such a conventional DLC coating  20  that has been formed on an interlayer  22  of Si or Si 3 N 4 , which in turn was formed on a substrate  25  that may be a magnetic or ceramic layer of a head. The DLC coating  20  conventionally has a thickness that is about four times that of the interlayer  22 . Thus a 80 Å layer  20  of DLC may be formed on a 20 Å interlayer  22  of Si 3 N 4 , to create a minimum head spacing of 100 Å, while a similar spacing may be present on the media. Further head-media spacing conventionally occurs due to penetration of energetic interlayer ions into underlying magnetic layers, deadening a portion of those magnetic layers. 
     It is not clear that the minimum head-medium spacing due to these layers can be reduced substantially without encountering problems in overcoat durability and interlayer continuity. For example, a 10 Å interlayer may be only a few atoms thick, and may not provide adequate adhesion even if one assumes that the somewhat thicker carbon overcoat can withstand high-speed head-disk contact without damage or removal. 
     SUMMARY OF THE INVENTION 
     The present invention provides a thinner overcoat for a head and/or media surface, substantially reducing head-media spacing and increasing areal storage density and resolution. The overcoat is hard and durable silicon-carbide (SiC), and does not require an interlayer to promote adhesion to underlying magnetic or ceramic layers. 
     The SiC is formed in a manner that creates an overcoat with density, hardness, durability and corrosion resistance similar to DLC. The SiC overcoat may also be formed with a process that penetrates less into an underlying magnetic layer than is conventional, reducing further the spacing of active elements by inactive coatings. 
     Alternatively, SiC may be formed by this process as an interlayer for a carbon overcoat such as DLC or ta-C. This allows the overcoat to be made thinner, since the interlayer is hard and dense, while retaining the chemical and other surface properties of the carbon overcoat. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cutaway cross-sectional view of a prior art device having a conventional overcoat and interlayer. 
     FIG. 2 is a cutaway cross-sectional view of a device of the present invention having an SiC overcoat without an interlayer. 
     FIG. 3 is a diagram of an apparatus used to form the SiC overcoat of FIG.  2 . 
     FIG. 4 is a cutaway cross-sectional view of a device of the present invention including an interlayer of SiC and a ta-C overcoat. 
     FIG. 5 is a diagram of an apparatus used to form the SiC interlayer and ta-C overcoat of FIG.  4 . 
     FIG. 6 is a cutaway cross-sectional view of a partially formed head of the present invention. 
     FIG. 7 is a cutaway cross-sectional view of the head of FIG. 6 with an SiC overcoat forming a media-facing surface. 
     FIG. 8 is a perspective view of the head of FIG. 7 showing the media-facing surface. 
     FIG. 9 is a cutaway cross-sectional view of a disk of the present invention having an SiC overcoat. 
     FIG. 10 is a cutaway cross-sectional view of the head of FIGS. 7 and 8 interacting with the disk of FIG. 9 during operation in a disk drive. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 2, a SiC overcoat  30  has been formed on a substrate  33  that may be a magnetic or ceramic layer of a head. Alternatively, substrate  33  may represent a magnetic media layer of a disk. The SiC overcoat  30  adheres well to the substrate  33  without the need for an adhesion layer, dramatically lowering the physical spacing between the head and media. For reasons discussed below, unlike bulk SiC that may be obtained as wafers and may conventionally form a support substrate for a head or disk, the SiC overcoat  30  does not chip or fragment in a hard disk drive environment. Further, unlike typical SiC films, the overcoat  30  is extremely dense and defect-free, providing an excellent barrier to corrosion for example. Due to these attributes, the overcoat  30  can be made very thin, and may even be less than about 10 Å in thickness for the situation in which high-speed contact is avoided and the overcoat functions primarily as a corrosion barrier. A currently preferred thickness for the SiC overcoat  30  is in a range between about 20 Å and 60 Å, although a higher or lower thickness may be desirable for certain applications. 
     FIG. 3 illustrates an apparatus  40  that is used for forming the hard, dense, nonporous SiC layers employed in the present invention. A rotatable platen or platter  42  that may hold one or more substrates is disposed within a chamber  44  that may be maintained at a pressure on the order of 10 −4 Torr or less, the chamber pressure maintained by a conventional pump, not shown. A grounded SiC wafer target  46  faces the substrate-holding platter  42 , and is also aligned with an ion beam source  48 . The ion beam source  48  directs a beam of ions such as argon (Ar+) onto the target  46 , ejecting atoms and/or molecules from the target, some of which impinge upon the substrates held on the rotating platter to form a SiC coating. This process is termed ion beam sputtering (IBS). 
     At the same time, a second ion beam source  50  directs ions from a material such as Ar or other chemically nonreactive elements at the platter  42 . The ions from source  50  pass through an electron cloud created by electron source  52  so that electrically as well as chemically neutral atoms are directed at the substrate-holding platter  42 . It is believed that these atoms tend to remove deposited SiC that is weakly bound to the substrates on platter  42 , leaving SiC that is strongly bonded to the substrates. The neutral atom bombardment may also dislodge SiC molecules from microscopic peaks such as those forming over nucleation centers, filling in nearby valleys to form a stronger, denser SiC film. While atoms from the SiC target are preferably directed at an angle somewhat close to perpendicular to the substrate surfaces to be coated, the neutral atoms from sources  50  and  52  may be directed at a further angle from perpendicular, which may dislodge atoms from microscopic peaks without removing atoms from valleys, smoothing, hardening and densifying the SiC coating. The neutral atom beam may optionally be directed at a grazing angle that is much closer to parallel than perpendicular to the substrate surfaces, in order to further the differential impingement upon nanoscale peaks compared to valleys. Note that prior to formation of an SiC film, the neutral ion beam from sources  50  and  52  may be used to clean the substrate surfaces, at a similar or different angle than that later employed during hardening and densification of the SiC. 
     Table 1 compares some properties of the SiC films of the present invention with convention overcoat materials such as DLC and more recently employed ta-C. Note that the SiC has a density, hardness and stress somewhat between the DLC and ta-C. The contact angle with water offers a measure of stiction performance of the material, as a high contact angle implies a low surface energy, and less capillary adhesion between the surface and the opposed surface of the head-disk interface. A head with a high contact angle for a disk-facing overcoat may also accumulate less lubricant from the disk surface. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 DLC 
                 SiC 
                 Ta—C 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Density [g/cm 3 ] 
                 1.5-2.1 
                 1.7-2.4 
                 3.0-3.5 
               
               
                   
                 Hardness [Gpa] 
                 15-20 
                 18-23 
                 30-60 
               
               
                   
                 Stress [Gpa] 
                 2.0-3.0 
                 1.5-2.0 
                 3.0-4.0 
               
               
                   
                 Contact Angle 
                 60-70 
                 60-70 
                 75-85 
               
               
                   
                 [degrees] 
               
               
                   
                   
               
             
          
         
       
     
     FIG. 4 illustrates the employment of a hard, dense and defect free SiC material of the present invention as an interlayer  60  between a substrate  63  and a hard carbon overcoat layer  66 . The substrate  63  may be a transducer or ceramic layer of a head or may be a media layer of a medium. The overcoat layer  66  may contain DLC or ta-C, which are denoted in this application as sp 3  carbon in reference to the type of bonds that predominate, and which can be made much thinner than is conventional due to the reinforcement provided by the underlying SiC interlayer  60 . In addition, the interlayer  60  forms an adhesion layer for the hard carbon overcoat layer  66  that may have improved adhesive properties over conventional silicon-based adhesion layers. Both the interlayer  60  and the overcoat layer  66  can have a thickness as little as about 10 Å or less, although a greater thickness may be preferable for some applications. Having a hard carbon overcoat layer  66  allows the employment of a known surface chemistry and texture for a head-disk interface. 
     FIG. 5 depicts an apparatus  70  that may be used to form the interlayer  60  and overcoat layer  66  shown in FIG.  4 . For conciseness, the apparatus  40  illustrated in FIG. 3 for forming hard, dense SiC layers is reproduced in FIG. 5 in combination with a filtered cathodic arc device  80  employed for forming ta-C, apparatuses  40  and  80  together forming apparatus  70 . To form the structure shown in FIG. 4, the dense interlayer  60  of SiC is first formed in a manner much as described above with regard to layer  30  of FIG. 2, which for brevity will not be repeated here. 
     Apparatus  80  provides for deposition of hard carbon overcoat layer  66  on interlayer  60 , which has been formed on substrates positioned on the moveable palate  42 . A carbon cathode  82  is disposed near an anode  84 , the anode and cathode disposed in an evacuated chamber  86  in fluid communication with the chamber  44  that houses the substrate-holding palate  42 . An arc is created between the anode and cathode that generates carbon ions as well as some macroparticles at the cathode, the ions and macroparticles traveling generally toward the cylindrical, water cooled anode. A focusing solenoid  88  located near the anode directs carbon ions and to some extent the macroparticles toward a filtering solenoid  90 , which filters out most macroparticles that are generated by the arc, while guiding the carbon ions toward the substrate. Stated differently, the charge to mass ratio of the carbon ions is much higher than that of the macroparticles, causing the ions to be guided through the path defined by the solenoid  90  while the macroparticles fly out of that path. Neutral atoms provided by ion beam source  50  and electron source  52  may be employed during this ta-C deposition to dislodge any macroparticles that were not removed by the filter, strengthening the hard carbon coating  66 . 
     In FIG. 6, some conventional initial steps in forming a head of the present invention are shown. The head has been formed on a wafer substrate  100  that may be made of AlTiC, SiC or other known materials, the head typically being mass-produced along with thousands of other heads. After polishing and preparing a surface of the substrate  100 , a first magnetically permeable layer  102  is formed which will function as a magnetic shield. A first read gap layer  105  of nonmagnetic, electrically insulating material such as alumina is then formed, on top of which a magnetoresistive (MR) sensor  107  is formed. The MR sensor  107  may be an anisotropic magnetoresistive (AMR) sensor, canted current sensor, spin valve (SV) sensor, giant magnetoresistive (GMR) sensor, or other known sensor, the details of which are known in the art and omitted here for conciseness. After the MR sensor  107  has been defined a back gap  110  and second read gap  112  of nonmagnetic material such as alumina are formed, optionally at the same time. A first pole layer  115  of magnetically permeable material such as permalloy that also serves as a shield for the sensor  107  is then formed. A nonmagnetic, electrically insulating write gap  118  of material such as alumina is formed on the pole layer, and a conductive coil  120  is formed on the write gap  118 , the coil surrounded by nonmagnetic, electrically insulating material  122  such as baked photoresist. A second pole layer  125  of magnetically permeable material is then formed, and a protective coating  127  of alumina, DLC or other materials is conventionally formed. The substrate and thin film layers are then diced along line  130  and other lines, not shown, forming perhaps thousands of heads from a single wafer  100 . 
     A portion of an individual head  150  having a transducer  152  formed by the above process is shown in FIG.  7 . The head  150  has been rotated to expose cut surface  130  and is held in a row along with other diced heads for forming air-bearing or media-facing surfaces. Surface  130  for the row of heads is lapped or polished while a transfer tool monitors resistance of sensors such as MR sensor  107  for an indication of when lapping has been optimized. After lapping and cleaning, a platter containing rows of heads may be moved to an apparatus such as shown in FIG. 3 or FIG.  5 . Initially, the head surfaces such as surface  130  may be cleaned by neutral atom bombardment, as described above regarding FIGS. 3 and 5, during rotation at various angles. A dense, hard, essentially defect-free overcoat  155  of SiC is then formed on the cleaned surface  130  by IBS in combination with neutral atom bombardment, as described above. The SiC coating may have a thickness in a range between about 8 Å to 60 Å, and demonstrates excellent resistance to corrosion and wear, as well as low stiction. Stiction may also be favorably affected by interaction of a media-facing surface  160  formed by the SiC coating  155  with a disk coating made of a different material, such as conventional DLC. Alternatively and as described above, the SiC coating may provide a dense, hard adhesion layer for a DLC or ta-C overcoat, not shown in this figure. 
     After formation of the hard overcoat  155  containing SiC on surface  130 , head  150  may be shaped by masking and ion beam or reactive ion etching, for example, into surface patterns known to be favorable for high speed, closely-spaced interaction with a disk, for instance. FIG. 8 illustrates a media-facing side of the head  150  of FIG. 7 after such masking and etching. The transducer  152  is visible through the SiC coating near a trailing end  163  of the media-facing surface  160  of the head. The media-facing or air-bearing surface (ABS)  160  has a raised center rail  166  and a pair of side rails  170  and  172 . The transducer  152  is located near a trailing end of the center rail  166 . A step  175  is located near a front end  177  of the head  150 . Recessed areas  180  and  182  are located between the rails, providing stability of the head at various speeds. 
     In FIG. 9 a portion of a disk  200  of the present invention is shown. The disk  200  includes a wafer substrate  202  that may be made of glass, SiC, aluminum, or any of a number of other materials known to be used for this purpose. The substrate may or may not be roughened or patterned, as is known, in the art, and is covered with an underlayer  205  that may provide adhesion and a desired structure for a media layer  210  formed on the underlayer. The media layer  210  may be a conventional cobalt (Co) based alloy, which may include elements such as chromium (Cr), platinum (Pt) and tantalum (Ta), for instance. Although a single media layer  210  is shown for conciseness, layer  210  may actually represent several layers as is known, and may be designed for longitudinal or perpendicular data storage. The underlayer  205  may include Cr, nickel aluminum (NiAl), magnesium oxide (MgO) or other materials known in the art, and may be formed of more than one layer. Atop the media layer  210  a thin layer  212  of SiC is formed according to the present invention, creating a dense, hard surface  215  for the disk  200 . The layer  212  may be formed in an apparatus including elements such as represented in FIGS. 3 and 5. Formation of layer  212  may begin with a cleaning step of bombardment by neutral atoms, followed by neutral atom beam assisted IBS of SiC. Layer  212  may have a thickness in a range between about 8 Å to 50 Å and demonstrates excellent resistance to corrosion and wear, as well as low stiction. Alternatively and as described above, the SiC layer  212  may provide a dense, hard adhesion layer for an ultrathin DLC or ta-C surface layer, not shown in this figure. 
     FIG. 10 shows the head  150  of FIGS. 7 and 8 in operation with the disk  200  of FIG. 9, such as within a disk drive. The disk is moving relative to the head in a direction shown by arrow  220 , while the head may be positioned over a single concentric data track of the disk or may be sweeping across the disk in a direction into or out of the paper of this cross-sectional drawing. The disk may be rotating at various speeds known in the art, so that the relative speed in the direction of arrow  220  may range between a few meters per second and well over ten meters per second. A layer of air or other ambient gas accompanies the rapidly spinning disk surface  215  and interacts with the ABS  160  of the head  150 , causing the head in this embodiment to levitate slightly from the disk. In other embodiments, the head maybe designed to operate in occasional, frequent or continuous physical contact with the disk. The head surface  160  is separated from the disk surface  215  by a physical spacing (H p ) that may range between several hundred angstroms and zero, with a preferred spacing of between about two hundred angstroms and about fifty angstroms. A lubricant including perfluorocarbon molecules or other known materials may be distributed on the disk surface  215  beneath the head. 
     A magnetic separation (H m ) between the media and the head is a significant factor in performance characteristics of the drive, affecting resolution of the head in both reading and writing magnetic signals on the disk. The magnetic separation H m  is measured from the top of the media layer  210  to the bottom of the transducer  152 , and includes any physical spacing H p  as well as the thickness of any head overcoat  155  and media overcoat  212 . The thickness of the head overcoat  155  and media overcoat  212  thus become increasingly important determinants of the magnetic spacing (H m ) as the physical spacing (H p ) is reduced. The achievement of hard, dense, corrosion resistant overcoats of SiC having a thickness as low as several angstroms without the need for an adhesion layer can dramatically decrease the magnetic separation H m  and dramatically increase storage capacity of the drive. 
     Alternatively, as described above, the hard, dense, corrosion resistant SiC can form an adhesion layer for an ultrathin DLC or ta-C overcoat on both the head and disk. While this approach may increase the minimum thickness of the solid layers separating the transducer  152  and media layer  210 , it affords employment of hard carbon surfaces that are becoming conventional in head-disk interfaces. Due to the hardness, density and corrosion resistance of the SiC interlayers, both the SiC and carbon layers can be made extremely thin, forming in essence an ultrathin double overcoat. Such an ultrathin double overcoat can instead be used in other embodiments on only one of the head or disk interface surfaces, with the other interface surface having a hard, dense, corrosion resistant SiC overcoat of the present invention. Any of these embodiments may help to lower stiction at the interface, as the intermolecular attraction between disparate surfaces of SiC and C may be less than that between two surfaces of C. 
     Although we have focused on teaching the preferred embodiments, other embodiments and modifications of this invention will be apparent to persons of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.