Abstract:
A system and method for improving the durability and reliability of recording media used in hard drives is disclosed. A protective overcoat made by depositing a diamond like carbon (DLC) layer over a magnetic layer and then depleting a portion of the DLC protective layer of hydrogen before it is coated with a Perfluoropolyethers (PFPE) using an in-situ vapor lubrication technique. The portion of the DLC layer which is depleted can be data zone of the media so that the lubricant-bonding ratio is higher for the landing zone than it is for the data zone.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from U.S. provisional application Ser. No. 60/368,681, filed on Mar. 29, 2002 and incorporated herein by reference. This is a divisional of co-pending application Ser. No. 10/402,070 filed on Mar. 27, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to magnetic discs for use in computer disc drives, and, more particularly, to application of the lubricant layer over the magnetic disc  
         [0004]     2. Description of the Related Art  
         [0005]     Computer disc drives commonly use components made out of thin films to store information. Both the read-write element and the magnetic storage media of disc drives are typically made from thin films.  
         [0006]      FIG. 1A  is an illustration showing the layers of a conventional magnetic media structure including a substrate  105 , a seed layer  109 , a magnetic layer  113 , a diamond like carbon (DLC) protective layer  117 , and a lube layer  121 . The initial layer of the media structure is the substrate  105 , which is typically made of nickel-phosphorous plated aluminum or glass that has been textured. The seed layer  109 , typically made of chromium, is a thin film that is deposited onto the substrate  105  creating an interface of intermixed substrate  105  layer molecules and seed layer  109  molecules between the two. The magnetic layer  113 , typically made of a magnetic alloy containing cobalt (Co), platinum (Pt) and chromium (Cr), is a thin film deposited on top of the seed layer  109  creating a second interface of intermixed seed layer  109  molecules and magnetic layer  113  molecules between the two. The DLC protective layer  117 , typically made of carbon and hydrogen, is a thin film that is deposited on top of the magnetic layer  113  creating a third interface of intermixed magnetic layer  113  molecules and DLC protective layer  117  molecules between the two. Finally the lube layer  121 , which is a lubricant typically made of a polymer containing carbon (C) and fluorine (F) and oxygen (O), is deposited on top of the DLC protective layer  117  creating a fourth interface of intermixed DLC protective layer  117  molecules and lube layer  121  molecules.  
         [0007]     The durability and reliability of recording media is achieved primarily by the application of the DLC protective layer  117  and the lube layer  121 . The combination of the DLC protective layer  117  and lube layer  121  is referred to as a protective overcoat. The DLC protective layer  117  is typically an amorphous film called diamond like carbon (DLC), which contains carbon and hydrogen and exhibits properties between those of graphite and diamond. Thin layers of DLC are deposited on disks using conventional thin film deposition techniques such as ion beam deposition (IBD), plasma enhanced chemical vapor deposition (PECVD), magnetron sputtering, radio frequency sputtering or chemical vapor deposition (CVD). During the deposition process, adjusting sputtering gas mixtures of argon and hydrogen varies the concentrations of hydrogen found in the DLC. Since typical thicknesses of DLC protective layer  117 , are less than 100 Angstroms, lube layer  121  is deposited on top of the DLC protective layer  117 , for added protection, lubrication and enhanced disk drive reliability. Lube layer  121  further reduces wear of the disc due to contact with the magnetic head assembly.  
         [0008]     A typical lubricant used in lube layer  121  is Perfluoropolyethers (PFPEs), which are long chain polymers composed of repeat units of small perfluorinated aliphatic oxides such as perfluoroethylene oxide or perfluoropropylene oxide. As is well known in the art, PFPEs are used as lubricants because they provide excellent lubricity, wide liquid-phase temperature range, low vapor pressure, small temperature dependency of viscosity, high thermal stability, and low chemical reactivity. PFPEs also exhibit low surface tension, resistance to oxidation at high temperature, low toxicity, and moderately high solubility for oxygen. Several different PFPE polymers are available commercially, such as Fomblin Z (random copolymer of CF 2 CF 2 O and CF 2 O units) and Y (random copolymer of CF(CF 3 )CF 2 O and CF 2 O) including Z-DOL and AM 2001 from Montedison, Demnum (a homopolymer of CF 2 CF 2 CF 2 O) from Daikin, and Krytox (homopolymer of CF(CF 3 )CF 2 O).  
         [0009]     Lube layer  121  is typically applied evenly over the disc, as a thin film, by dipping the discs in a bath containing mixture of a few percent of PFPE in a solvent and gradually draining the mixture from the bath at a controlled rate. The solvent remaining on the disc evaporates and leaves behind a layer of lubricant less than 100 Angstroms. Recent advances have enabled the application of PFPE using an in-situ vapor deposition process that includes heating the PFPE with a heater in a vacuum lube process chamber. In this system, evaporation occurs in vacuum onto freshly deposited DLC protective layer  117  that has not been exposed to atmosphere, creating a thin uniform coating of PFPE lube layer  121 .  
         [0010]     Since it is known in the art that recording media with higher lubricant bonded ratio has better corrosion protection and that an in-situ vapor lubrication process enhances the bonding between lubricants and amorphous carbon, in-situ vapor lubrication has been used to lubricate amorphous carbon layers. In-situ vapor lubrication of recording media is the lubrication of the recording media immediately after the DLC protective layer  117  has been deposited over the magnetic layer  113  without exposing it to atmosphere.  
         [0011]      FIG. 1B  is a flow chart showing the typical steps used in an in-situ vapor lubrication process that deposits PFPE lubricant over a carbon layer. The process begins with step  150  by transferring a partially complete media with substrate  105 , seed layer  109 , and magnetic layer  113  into a vacuum chamber. The transferring process typically involves moving a disk, after depositing a magnetic layer on it, into a carbon deposition chamber without taking it out of vacuum. In step  155  an amorphous carbon layer is deposited over the partially complete media. Typically the amorphous carbon layer is diamond like carbon (DLC) that has been deposited by conventional sputter deposition techniques. Next in step  160 , the amorphous carbon is coated with a lube layer  121  of PFPE using an in-situ vapor lubrication process. Finally, in step  165  the lubed magnetic media is transferred to the next manufacturing operation.  
         [0012]     The same technology, however, works less effectively with a DLC protective layer  117 . When a DLC protective layer  117  is applied over the magnetic layer  115 , unpaired carbon electrons pair with hydrogen electrons and dangling carbon bonds are tied up, as illustrated in  FIG. 1C .  FIG. 1C  is an illustration showing the carbon bonds that are not tied up by other carbon atoms being tied up at the surface with hydrogen bonds. The termination of the carbon bonds on the surface by hydrogen effectively reduces the reactive sites. As a result, the bonding sites for lubricant molecules are reduced and therefore the lubricant bonded ratio decreases. This effect is particularly strong when lubricant is deposited in-situ after depositing the DLC protective layer  117 , as manifested by the poor adhesion of lube layer  121  to the DLC protective layer  117 . Because of this effect, IBD or PECVD processes, which produce DLC protective layer  117 , and in-situ vapor lubrication processes, which enhances bonding, have not been combined to achieve the maximum performance.  
         [0013]     The conflicting tribological requirements in the data zone (DZ) of a magnetic disc where information is stored and the landing zone (LZ) where a head takes-off and lands often require different lube designs in different zones. For example, bonded lube is more desirable in the DZ where flyability corrosion protection are the primary concerns, whereas sufficient mobile lube is essential in the LZ where wear durability is of greater importance. While the benefit of zone lubrication to satisfy both requirements has been recognized in the art, the known methods generally focus on post-lubrication treatments by either partial removal or by zone radiation. These additional steps could add considerable complexity to the disc manufacturing process. Particularly, in the case of in-situ vapor lubrication process, these post-lubrication treatments defeat the main benefit of the in-situ vapor lube process, i.e., simplicity and low cost.  
         [0014]     Therefore what is needed is a system and method which overcomes these problems and makes it possible to apply a lubricant to a carbon overcoat using an in-situ vapor lubrication process that results in a reliable final overcoat with desirable properties. Desirable properties include a resulting lubricant that is bonded to the carbon overcoat more strongly at the data zone than at the landing zone.  
       SUMMARY OF THE INVENTION  
       [0015]     This limitation is overcome by depleting hydrogen from the diamond like carbon layer at the data zone while leaving the landing zone alone. Depleting hydrogen from the diamond like carbon layer prior to the application of the lube layer enhances the bond between the diamond like carbon protective layer and the lube layer. Therefore depleting hydrogen from the diamond like carbon layer at the data zone while leaving the landing zone alone enhances the bond between the diamond like carbon layer and the lube at the data zone without effecting the existing bond between the diamond like carbon layer and lubricant at the landing zone.  
         [0016]     Depletion of hydrogen in the data zone activates the surface of the DLC protective layer  117 , in the data zone, by creating unpaired electrons in the DLC that are ready to react. The unpaired electrons create a strong bond between the DLC protective layer  117  and the lube layer  121 .  
         [0017]     The data zone of the DLC protective layer  117  is depleted of hydrogen by bombarding the data zone with argon ions. The hydrogen atoms are ejected from the surface of the data zone DLC protective layer  117  when the accelerated argon ions collide with them.  
         [0018]     These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.  
     
    
     BRIEF DESCRIPTION OF THE INVENTION  
       [0019]      FIG. 1A  is a block diagram showing a prior art conventional magnetic media structure;  
         [0020]      FIG. 1B  is a flowchart illustrating the prior art method of using in-situ vapor lubrication on a carbon layer;  
         [0021]      FIG. 1C  is an illustration of a prior art DLC protective layer ready to be lubed;  
         [0022]      FIG. 2  is an illustration of a DLC protective layer, with the landing zone being Hydrogen Depleted DLC (HDDLC), ready for in-situ vapor lubrication, in accordance with an embodiment of the invention;  
         [0023]      FIG. 3  is a block diagram showing the HDDLC layer  200  in a magnetic media environment;  
         [0024]      FIG. 4  is a flowchart showing the preferred method of depositing the protective overcoat including the HDDLC layer  200  and the lube layer  121 ;  
         [0025]      FIG. 5  is a block diagram showing a thin film deposition system used to deposit the magnetic media structure  300 ; and  
         [0026]      FIG. 6  is an illustration showing details of surface modifier  520  of system  500  of  FIG. 5 .  
         [0027]      FIG. 7  is a bar graph comparing the percentage of bonded lubricant, which is deposited using vapor deposition and dipping, on hydrogenated carbon that has been activated with argon ions.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     The invention provides a system and method for protecting magnetic media.  
         [0029]      FIG. 2  is an illustration of a partially hydrogen depleted DLC (HDDLC) layer  200 , with the data zone, landing zone and transition zone clearly demarcated, ready for in-situ vapor lubrication, in accordance with one embodiment of the invention. The data zone, which is shown to be hydrogen depleted, is the portion of the magnetic media from where data is recorded and retrieved. The landing zone, which is shown not to be hydrogen depleted, is the portion of the magnetic media where the head comes to rest when the magnetic media stops spinning. The transition zone, which is shown to be partially hydrogen depleted, is the region of the magnetic media separating the landing zone from the data zone where the data zone transitions into the landing zone. The HDDLC layer  200  includes a plurality of carbon atoms  210 , a plurality of hydrogen atoms  220 , a plurality of carbon-hydrogen bonds  230 , a plurality of carbon-carbon bonds  240  and a plurality of free dangling carbon bonds  250 .  
         [0030]     The free dangling carbon bonds  250  are created by bombarding a portion, corresponding to the data zone, of the DLC protective layer  117  with charged ions as is furthered described with reference to  FIG. 4  below. This bombardment process converts the DLC protective layer  117  into a more reactive HDDLC layer  200  by creating free dangling bonds  250  in the data zone. This increases the bonding between the hydrogen depleted portion of the HDDLC  200  layer and the lubricant that is deposited over the entire HDDLC layer  200  with an in-situ vapor lube process as is described with reference to  FIG. 4  below.  
         [0031]      FIG. 3  is a block diagram showing the HDDLC layer  200  in a magnetic media environment  300  including a substrate  105 , a seed layer  109 , a magnetic layer  113 , a lube layer  121 , and a hydrogen depleted region  310 . The hydrogen-depleted region  310  is the same region as the data zone region discussed with reference to  FIG. 2 , above. HDDLC layer  200  protects magnetic media from wear and tear as does DLC protective layer  117  except that it has been modified so that the lube layer  121  adheres to the data zone, which corresponds to the hydrogen depleted region  310 , much better than it otherwise would, providing improved protection.  
         [0032]      FIG. 4  is a flow chart showing the preferred steps used to make a protective overcoat including an HDDLC layer  200  and in-situ lubed layer  121 . Protective overcoats typically include a hard layer such as DLC and a lubrication layer. The process begins with step  405  by transferring a partially complete media having substrate  105 , seed layer  109 , and magnetic layer  113  into a vacuum chamber. The transferring process typically involves moving a disk, after depositing a magnetic layer on it, into a carbon deposition chamber without taking it out of vacuum.  
         [0033]     Next in step  410 , a DLC protective layer  117  containing carbon and hydrogen is deposited onto the substrate. The deposition process can be done by various thin film deposition techniques including ion beam deposition (IBD), plasma enhanced chemical vapor deposition (PECVD), magnetron sputtering, radio frequency sputtering, or chemical vapor deposition (CVD). In one embodiment, the DLC protective layer  117  is prepared by ion beam deposition using a work gas is C 2 H 2 . The energy per C atom is 90 eV.  
         [0034]     Next in step  415 , the DLC protective layer  117  is masked so that only a portion of it will be hydrogen depleted. The masking can be done by placing a shield in front of the portions of the DLC protective layer that will not be hydrogen depleted, as is further discussed with reference to  FIG. 6  below. The masking is typically done by covering the entire media except in places that are to be hydrogen deleted. For example, placing a shield in front of the magnetic media in all places except the data zone will mask the media so that only the data zone is hydrogen depleted in the subsequent step  420 .  
         [0035]     In step  420 , the masked DLC protective layer  117  is exposed to argon ions (Ar + ), from an argon ion plasma, which depletes the unmasked areas of the DLC protective layer  117  of hydrogen atoms. Exposing includes bombarding the DLC protective layer  117  with ions that are accelerated by an electric field as well as allowing atoms, molecules or ions to randomly strike the DLC protective layer  117  in the absence of an electric field. As Ar +  ions bombard the DLC protective layer  117 , hydrogen atoms are ejected, reducing the number of hydrogen atoms left on the DLC protective layer  117 , creating an HDDLC layer  200 . The depletion of hydrogen activates the DLC by making it a reactive carbon. The HDDLC is reactive because carbon atoms that were once bonded to hydrogen atoms now have unpaired electrons available for bonding. Although, the preferred process of removing hydrogen atoms from the DLC layer  117  is the mechanical process of Ar +  ion bombardment, other processes including chemical processes can be used.  
         [0036]     Step  420  can be done in the same chamber as that in which the DLC protective layer  117  is deposited or it can be done in a different chamber. If step  420  is performed in a second vacuum chamber then the partially complete media is transferred to a second chamber after the DLC protective layer  117  is deposited. The transferring process is done under vacuum or in an inert environment such as argon. The application of the mask in step  415  can be done in the DLC deposition chamber, the transfer process or the argon bombardment chamber.  
         [0037]     In the preferred embodiment, the rate at which hydrogen atoms are removed from the DLC protective layer  117  can be adjusted by changing parameters such as voltages, pressures, flow rates, and temperatures. Voltage controls the electric field acting on the Ar +  ions and consequently the force with which Ar +  ions bombard the DLC protective layer  117 . Bombarding occurs when the ions are accelerated towards the DLC protective layer  117 , because of the electric field acting on the Ar +  ions, and collide with the DLC protective layer  117 . Pressure and flow rates control physical properties of the plasma such as the number of Ar +  ions available to bombard the DLC protective layer  117 . Temperature controls the kinetic energy at the surface of the DLC protective layer  117  and consequently the amount of energy that must be imparted to the surface to remove hydrogen atoms.  
         [0038]     In the preferred embodiment the plasma is made out of ionized argon. Argon is used in the preferred embodiment because it is inert and readily available. However, other inert gases such as helium (He), neon (Ne), krypton (Kr) or xenon (Xe) can also be used to make up the plasma of charged ions, which bombard the DLC protective layer  117  and remove hydrogen atoms from it. In one embodiment, step  415  is done immediately after deposition where Ar gas is introduced into the process chamber at a flow rate of 10 sccm. The argon is ionized, in the plasma, and accelerated causing the argon ions to bombard the unmasked portions of the DLC films. The duration for this process is 0.5 seconds.  
         [0039]     Noble gases are preferred because they are inert and do not chemically react with the DLC protective layer  117 . This enables the removal hydrogen atoms from the DLC protective layer  117  by the mechanical process of bombardment. The invention, however, is not limited to only using noble gases because this process can be carried out using non-noble gases which do not chemically react with the DLC protective layer  117 . Additionally, this invention is not limited to the removal of hydrogen atoms from the DLC protective layer  117  by mechanical means only. Other methods such as heating the DLC protective layer  117  or chemically reacting another substance with the DLC protective layer  117  can be used to remove hydrogen atoms from the DLC protective layer  117 .  
         [0040]     Next in step  425 , an in-situ vapor deposition technique is used to apply a lubricant onto a partially completed media completing the protective overcoat. In the preferred embodiment PFPE is applied to the partially completed media using an in-situ vapor deposition process that includes heating the lubricant with a heater in a vacuum lube process chamber. In this embodiment, evaporation of PFPE occurs in a vacuum onto HDDLC  200  after the DLC protective layer  117  has been deposited and a portion of its surface depleted of hydrogen  310  by exposing it to ionized argon without exposing the HDDLC  200  to atmosphere. The portion of the DLC surface depleted of hydrogen  310 , which corresponds to the data zone in this application, bonds stronger to the lubricant than the portion of the DLC surface that has not been depleted of hydrogen, which in this application corresponds to the landing zone.  
         [0041]     Finally in step  430  the lubed magnetic media is transferred to the next manufacturing operation.  
         [0042]     Although the preferred steps used to make a protective overcoat are described in reference to a DLC protective layer  117  and lube layer  121 , those skilled in the art will recognize that the same steps can be used to deposit any two layers, wherein the bonding between the two layers is improved or where it is desirable to provide areas of differential bond strength. For example, a first layer, which can be metallic, insulating, semi-conducting or semi-metallic, can be deposited as described with reference to step  410 . The first layer can then be masked in step  415  so that only the portions of the first layer that are to be activated are uncovered and the remaining portions of the first layer are covered. The first layer is then activated as described with reference to step  420 . After the first layer is activated, a second layer, which can also be metallic, insulating, semi-conducting or semi-metallic, can be deposited as described with reference to step  425 . The combination of the first layer and second layer can then be transferred to the next manufacturing operation as described in step  425 .  
         [0043]      FIG. 5  represents a multilayer thin film deposition system  500  equipped with an in-situ DLC deposition system, a carbon surface modifying system and a vapor lube system. System  500  preferably includes a loader  510 , a DLC depositor  515 , a surface modifier  520 , a vapor luber  525 , an unloader  530 , a controller  535 , a power system  540 , a pumping system  545  and a gas flow system  550 .  
         [0044]     Loader  510  and unloader  530  represent conventional load locks that allow substrates to be transferred into and out of a vacuum chamber without venting the entire vacuum system. DLC depositor  515  represents a conventional thin film deposition chamber used to deposit the DLC protective layer  117 . DLC depositor  515  can use ion beam deposition (IBD), plasma enhanced chemical vapor deposition (PECVD), magnetron sputtering, radio frequency sputtering or chemical vapor deposition (CVD) techniques to deposit the DLC protective layer  117 . Surface modifier  520  is used to deplete a portion of the top surface of the DLC protective layer  117  of hydrogen, creating HDDLC layer  200  as is further discussed with reference to  FIG. 4  above. Although surface modifier  520  is shown separate from DLC depositor  515  and vapor luber  525 , surface modifier  520  can be incorporated into DLC depositor  515  or vapor luber  525 .  
         [0045]     Vapor luber  525  represents a conventional vapor lubing system used to deposit the lube layer  121  onto the HDDLC layer  200 . Controller  535  is the software and hardware that controls the operation of system  500 . Power system  540  represents power supplies used to power the system  500  and include power supplies for heaters, conveyers, DC magnetrons, rf sources. Pumping system  545  represents all pumps and valves used to evacuate the vacuum chambers including mechanical pumps, turbo pumps, cryogenic pumps and gate valves. Gas flow system  550  represents the gas delivery equipment such as mass flow controllers, valves, piping and pressure gauges.  
         [0046]      FIG. 6  is an illustration showing surface modifier  520  depleting hydrogen atoms from a portion of the top surface of the DLC protective layer  117 . In one embodiment, surface modifier  520  includes a vacuum chamber  605 , an argon ion plasma  610 , argon ions (Ar + )  615 , a first voltage V 1    620 , a second voltage V 2    625 , a stage  630 , and a mask  635  depleting hydrogen atoms from a portion of the top surface of the DLC protective layer  117  of a partially completed media.  
         [0047]     After depositing the DLC protective layer  117 , as discussed with reference to  FIG. 1B , a portion of the top surface of the DLC protective layer  117  is exposed to an argon ion plasma  610  consisting of (Ar + ) ions  615 . In step  415 , the partially complete media is moved to a grounded vacuum chamber  605  that is maintained at process pressures ranging from 10 −3  torr to 10 −2  torr. Power supplies such as the Advanced Energy MDX series manufactured by Advanced Energy of Fort Collins, Colo., USA are used to maintain the DLC protective layer  117  and the mask  635  at a first voltage V 1    615  and the argon ion plasma at a second voltage V 2    625 . The voltage difference between the plasma and the DLC protective layer  117  and the mask  635  creates an electric field  630  that accelerates the Ar +  ions towards the DLC protective layer  117  and mask  635 . The actual trajectory  635  of the argon ions depends on many factors including the initial velocity of the ions and the configuration of the electric field, which is determined by the first voltage  620  and the second voltage  625 .  
         [0048]     In this embodiment, the purpose of the mask  635  is to block the ions  615  from bombarding the DLC layer  117  at the areas where the mask  635  is located. In other embodiments where the activation of the DLC surface is done by chemical means purpose of the mask  635  is to prevent the activating chemicals from reacting with the surface at positions where the mask is located.  
         [0049]      FIG. 7  is a graph showing the lubricant-bonding ratio with and without Argon sputtering for both lubricants applied using a vapor lube techniques and a dipping techniques. For lubricant applied using vapor lubrication techniques the bonding ratio increases from about 72% to about 90% by activating the surface with positive argon ions. Similarly, for lubricant applied using dipping techniques the bonding ratio increases from about 49% to about 54% by activating the surface with positive argon ions. In both cases the data suggests that bombarding the surface of the DLC with positive argon ions makes the surface more reactive and increases the lubricant-bonding ratio between the DLC surface and the lubricant.  
         [0050]     It will also be recognized by those skilled in the art that, while the invention has been described above in terms of preferred embodiments, it is not limited thereto. Various features and aspects of the above-described invention may be used individually or jointly. Further, although the invention has been described in the context of its implementation in a particular environment and for particular applications, those skilled in the art will recognize that its usefulness is not limited thereto and that the present invention can be utilized in any number of environments and implementations.