Patent Application
20100021763
None.
Conventional magnetic recording media employ high magnetic anisotropy energy density (Ku) materials, often results in higher coercive force (Hc), to achieve better thermal decay in storage media for hard disk drive applications. One of the major adverse effects is the degradation of media writability and often leads to poor bit error rate (BER) performance. As coercivity increases, over write (OW) decreases. This problem is even more pronounced for media having an added mechanical texture utilized to achieve the high orientation.
The present invention demonstrates a unique approach to fabricate anti-ferromagnetic coupled (AFC) longitudinal media with a static coercivity above 5000 Oe, and a 2 dB improvement of OW over conventional media design. This invention provides magnetic recording media having different coercivity properties when writing information to the media, compared to the coercivity properties when the media is in storage. This magnetic media has the characteristic of being easy to write and hard to decay (“EWHD”). This media family can be characterized with a “kink” (i.e., a non-monotonicity) in the DC de-magnetized (DCD) curves.
As will be realized, this invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from this invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.
An electromagnetic converting portion (not shown) for recording/reproducing information is mounted on the magnetic head 13. The arm 15 has a bobbin portion for holding a driving coil (not shown). A voice coil motor 19 as a kind of linear motor is provided to the other end of the arm 15. The voice motor 19 has the driving coil wound on the bobbin portion of the arm 15 and a magnetic circuit (not shown). The magnetic circuit includes a permanent magnet and a counter yoke. The magnetic circuit opposes the driving coil to sandwich it. The arm 15 is swingably supported by ball bearings (not shown) provided at the upper and lower portions of a pivot portion 17. The ball bearings provided around the pivot portion 17 are held by a carriage portion (not shown).
A magnetic head support mechanism is controlled by a positioning servo driving system. The positioning servo driving system includes a feedback control circuit having a head position detection sensor (not shown), a power supply (not shown), and a controller (not shown). When a signal is supplied from the controller to the respective power supplies based on the detection result of the position of the magnetic head 13, the driving coil of the voice coil motor 19 and the piezoelectric element (not shown) of the head portion are driven.
Almost all the manufacturing of a disk media takes place in clean rooms where the amount of dust in the atmosphere is kept very low, and is strictly controlled and monitored. After one or more cleaning processes on a non-magnetic substrate, the substrate has an ultra-clean surface and is ready for the deposition of layers of magnetic media on the substrate. The apparatus for depositing all the layers needed for such media could be a static sputter system or a pass-by system, where all the layers except the lubricant are deposited sequentially inside a suitable vacuum environment.
Magnetic media structures are typically made to include a series of thin films deposited on top of aluminum substrates, ceramic substrates or glass substrates. A conventional magnetic media structure including a seed layer, under-layer, one or more magnetic layers and a protective layer. The glass substrate is typically a high quality glass having few defects
The seed layer is typically a thin film made of chromium based amorphous alloy such as CrTix (X<60), CoWy (Y<90) or B2 structure alloy such as NiAlz (Z=50), that forms the foundation for structures that are deposited on top of it. Under-layer, deposited on top of the seed layer, normally consists of a couple of Cr based BCC structural non-magnetic layers, such as Cr, and/or CrMoxTayMnz (X≦30, Y≦10, Z≦10). Magnetic layers, deposited on top of the under-layer, typically include a stack of several magnetic and non-magnetic layers. The magnetic layers are typically made out of magnetic alloys containing cobalt (Co), platinum (Pt) and chromium (Cr), whereas the non-magnetic layers are typically made out of metallic non-magnetic materials. Finally, a protective overcoat is a thin film typically made of carbon with hydrogen or nitrogen, which is deposited on top of the magnetic layers using conventional thin film deposition techniques
A conventional perpendicular recording disk medium, shown in
The increasing demands for higher areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr), magnetic remanence (Mr), coercivity squareness (S*), medium noise, i.e., signal-to-medium noise ratio (SMNR), and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements, particularly a high-density magnetic rigid disk medium for longitudinal and perpendicular recording. The magnetic anisotropy of longitudinal and perpendicular recording media makes the easily magnetized direction of the media located in the film plane and perpendicular to the film plane, respectively. The remanent magnetic moment of the magnetic media after magnetic recording or writing of longitudinal and perpendicular media is located in the film plane and perpendicular to the film plane, respectively.
The linear recording density can be increased by increasing the Hr of the magnetic recording medium, and by decreasing the medium noise, as by maintaining very fine magnetically non-coupled grains. Medium noise in thin films is a dominant factor restricting increased recording density of high-density magnetic hard disk drives, and is attributed primarily to inhomogeneous grain size and intergranular exchange coupling. Accordingly, in order to increase linear density, medium noise must be minimized by suitable microstructure control.
In current longitudinal magnetic recording media, high areal density and low noise are achieved by statistical averaging over several hundred weakly coupled ferromagnetic grains per bit cell. Continued scaling to smaller bit and grain sizes, however, may prompt spontaneous magnetization reversal processes when the stored energy per particle starts competing with thermal energy, thereby limiting the achievable areal density. Coercivity (Hc) is a measure of the magnetic field that is needed to reverse the direction of magnetization in a thin-film layer. A material's coercivity corresponds to its magnetic strength. The unit of measure for coercivity is an Oersted (Oe).
Conventional practice to achieve better thermal decay in storage media for hard disk drive applications has been to use high magnetic anisotropy energy density (Ku) materials, resulting in higher coercive force. A disadvantage of the conventional practice is the degradation of media writability, leading to poor bit-error-rate (BER) performance.
The present invention demonstrates a unique approach, by fabricating AFC longitudinal media with a static coercivity above 5000 Oe and a 2 dB improvement of OW over conventional media design. This invention provides magnetic recording media having different coercivity properties when writing information to the media, compared to the coercivity properties when the media is in storage. This magnetic media has the characteristic of being easy to write and hard to decay (“EWHD”). This media family can be characterized with a “kink” (i.e., a non-monotonicity) in the DC de-magnetized (DCD) curves.
The first layer overlying the substrate is an adhesion layer (25) of, e.g., amorphous Cr based alloy, for instance, CrTi, from 100 Å to 200 Å thick, capable of improving adhesion of seed layer (24).
Overlying the adhesion layer (25) is deposited the seed layer (24), which is typically a thin film made of structure materials having BCC or B2 crystal phases, that forms the foundation for structures that are deposited above it. Seed layer (24) also may be composed of amorphous or fine grain material. Typical composition for the seed layer (24) is B2 structure alloy NiAl or amorphous alloy CrWx (x≦90). Seed layer (24) is deposited using conventional thin film deposition techniques.
Overlying the seed layer (24) is deposited the first under-layer (21a) (“UL1”), which is chromium or a chromium-based alloy, such as Cr or CrMoxTayMnz (x≦30, y≦10, z≦10). The under-layer (21a) is typically deposited by a sputtering technique. Overlying the first under-layer (21a) is an optional second under-layer (21b) (“UL2”), also made of chromium or a chromium-based alloy, such as Cr or CrMoxTayMnz (x≦30, y≦10, z≦10). The chromium-based under-layer provides a magnetic recording media having superior magnetic property and microstructure, makes a good texture structure with Co-based magnetic layer deposited thereon and shows fine grain size distribution, high coercivity and high coercivity squaredness.
Overlying the second under-layer (21b) are the anti-ferromagnetically coupled (AFC) media layers with intermediate coupling strength, which produce a kink in the DCD curve. AFC media uses a thin layer of a material, typically ruthenium, to separate two magnetic layers on the surface of a magnetic recording disk. The AFC structure includes layers 22a, 26, 22b and 22c, which are described below in greater detail.
The first layer of the AFC structure is the stabilization layer (22a) (“ML1”), which is typically a compound of cobalt, such as CoCrxPtyBzXα (10≦x≦30, 5≦y≦20, 4≦z≦18, 0≦α≦5), in which “X” is an optional fifth element, for instance, Cu, Au, Ta, or V. The Co-based alloy magnetic layer is deposited by conventional techniques, and normally includes polycrystallites epitaxially grown on the under-layer (21b).
Overlying the stabilization layer (22a) is the anti-ferromagnetic coupling spacing layer (26) (“AFCL”), which is typically a compound including RuXy, in which “X” is optional; if “X” is present, it may be for instance, Cr, Mo, Ti, etc., and with 0≦y≦40. The AFCL is designed to be strong enough to ensure that the magnetization of layers 22a, 22b are antiparallel in the remanent state. The AFCL maintains stability of the media with reductions in the magnetic remanence times film thickness (Mrt) ratios in between the magnetic layers. In general, the exchange coupling oscillates from ferromagnetic to anti-ferromagnetic with certain coupling/spacer film thickness, the preferred thickness being about 6˜8 Å. Preferably, the thickness of the ruthenium coupling/spacer layer 26 is selected to correspond with the first antiferromagnetic peak in the oscillation for the particular thin film structure shown in
Overlying the AFC spacing layer (26) is the middle magnetic layer (22b) (“ML2”), which is typically a compound of cobalt, such as CoCrxPtyBzXα (8≦x≦28, 5≦y≦20, 4≦z≦18, 0≦α≦5), in which “X” is an optional fifth element, for instance, Cu, Au, Ta, V, etc.). Overlying ML2 (22b) is the top magnetic layer (22c) (“ML3”), which is typically a compound of cobalt, such as CoCrxPtyBzXα (4≦x≦20, 5≦y≦20, 4≦z≦18, 0≦α≦8), in which “X” is an optional fifth element, for instance, Cu, Au, Ta, V, etc. ML3 acts as a protective overcoat. ML2 or ML3 may be optional, but media performance will decrease without ML2 or ML3. ML1, ML2, and/or ML3 may be identical among themselves, but such composition of ML1-ML3 would not produce the preferred media performance. The ML1 ratio, defined as Mrt1/(Mrt1+Mrt2)*100%, may vary between >0% and 100%. The magnetic layers are typically deposited by sputtering techniques.
Optionally, an inner enhanced layer may be provided between the AFC spacing layer 26 and layer 22b.
Conventional practices also include bonding a lubricant topcoat (not shown) to ML3 (22c), e.g., a perfluoropolyether material, typically deposited by dipping or spraying.
The antiferromagnetic coupling strength can be adjusted during the sputtering process by spacer thickness and sputtering process.
The antiferromagnetic spacing layer is sputtered under conditions, which are quite different from the traditional process setting for sputtered magnetic media in at least three ways. First, conventional sputtering uses a sputtering power density of 0.10 kW, but the present invention uses a sputtering power density in a range of approximately 0.40 kW to 1.00 kW, thereby increasing the Ru sputtering power density by a factor of from 4 to 10. The resulting Ru film will be denser and the layer surface will be smoother, compared to an Ru film made with a sputtering power density outside these limits. Second, conventional sputtering uses a process delay time of 0.5 seconds, but the present invention uses a process delay time of approximately 3.6 seconds or more, thereby increasing the process delay time by a factor of ≧7. The process delay time includes sputter process cycle time, disk station to station transfer time, and Ru sputter duration time. Third, the process gas flow rate for the conventional process is 15 standard cubic centimeters per minute (sccm), but the present invention uses a process gas flow rate of approximately 36 sccm or more, thereby increasing the sputtering process Ar gas flow rate and the resulting sputtering pressure by a factor of ≧2. The Ar gas flow rate may be 40 sccm or more.
In the lab test results described below, the following acronyms may be used:
Applicants have produced disks having compositions falling within the ranges identified above, and have studied the magnetic writing and decay properties of the magnetic recording materials so produced. The materials and their properties are given below in Table 1. In the discussion that follows, “KuV/kbT” is a thermal stability factor; “Ku” is the magnetic anisotropy energy density; “kb” is Boltzmann's constant; T is a temperature measured in absolute degrees Kelvin; and “V” is a volume of the magnetic particle. The lab tests are summarized in Table 1:
Table 1 shows the parametric testing result of three separate compositions of the invented media, labeled “Invented C1,” “Invented C2” and “Invented C3.” Comparison is shown to three reference compositions of conventional media, labeled “Ref1,” “Ref2” and “Ref3.” All media including the three reference disks have the alloy compositions given in Table 2.
It can be seen that the invented media has very high Hc (around 5000 Oe), but the OW is comparable to that of the conventional media with much lower Hc (Ref3), and much better than those with high Hc (Ref1 and Ref2). The BER performance of the invented media is comparable or better to that of conventional media.
In addition, the thermal amplitude decay of the invented media was improved by 0.5% per decade (Table 3). Table 3 also shows that the invented media has lower dynamic coercivity and larger KuV/kbT, resulted from Sharrock fits. VSM measurement in
Jex is the interlayer exchange coupling energy.
The above description is presented to enable a person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the preferred embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, this invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
This application discloses several numerical range limitations. Persons skilled in the art would recognize that the numerical ranges disclosed inherently support any range within the disclosed numerical ranges even though a precise range limitation is not stated verbatim in the specification because this invention can be practiced throughout the disclosed numerical ranges. A holding to the contrary would “let form triumph over substance” and allow the written description requirement to eviscerate claims that might be narrowed during prosecution simply because the applicants broadly disclose in this application but then might narrow their claims during prosecution. Where the term “plurality” is used, that term shall be construed to include the quantity of one, unless otherwise stated. The entire disclosure of the patents and publications referred in this application are hereby incorporated herein by reference. Finally, the implementations described above and other implementations are within the scope of the following claims.
