Abstract:
A method and apparatus for forming a thin film magnetic recording media, the method comprises generating magnetic nanoclusters from a target of magnetic material, crystallizing the magnetic nanoclusters, and depositing the magnetic nanoclusters onto a substrate to form a thin film of magnetic particles thereon. The magnetic nanoclusters are deposited onto the substrate after crystallized and therefore after the deposition. The apparatus comprises a first chamber, a second chamber connected to the first chamber, and a third chamber connected to the second chamber. The first chamber has a source for generating magnetic nanoclusters. The second chamber is to receive the magnetic nanoclusters and crystallize the magnetic nanocluster. The third chamber is to receive the crystallized magnetic nanoclusters from the second chamber and deposit the crystallized magnetic nanoclusters onto the substrate positioned therein.

Description:
RELATED APPLICATIONS 
     This application claims priority to Singapore Application Serial No. 200300519-6, filed Feb. 11, 2003, the contents of which are incorporated herein by reference in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to magnetic recording media. In particular, it relates to thin film magnetic recording media for data storage devices. 
     BACKGROUND OF THE INVENTION 
     The rapid development of computer and information technology has resulted in great demand for high capacity storage devices. Currently, these storage devices are being pushed to their limits by applications as diverse as digital video editing and genomics. Therefore, the data storage industry is continually under pressure to increase the capacity of data storage devices. One of the primary methods to increase capacity is to increase the recording density of the magnetic recording media in most storage devices. To achieve an ultra-high recording density of, for example, about 100 Gbits/inch 2  or higher, magnetic recording media are required to possess a low remnant-thickness product (Mrδ), a high coercivity (Hc) as well as a high signal-to-media noise (S/Nm). 
     In a conventional magnetic recording media, such as a Cobalt (Co) based alloy, non-magnetic elements such as Chromium (Cr) and/or Boron (B) are incorporated into the thin film magnetic recording media to reduce the grain size as well as to reduce the intergranular coupling effect of the magnetic particles in the recording media. The result is a magnetic recording medium having a grain size of about 8–12 nanometers (nm) with a distribution width of about 20% or more. In this context, the term “distribution width” denotes the Full Width at Half Maximum (FWHM) height of the grain size distribution. 
     In order to obtain a high S/N m  magnetic recording media, the grain size and their distribution width as well as the intergranular coupling between the magnetic gains must be properly controlled to further scale down. 
     Reduction of grain size for Co-based alloy recording media is limited by the thermal-instability of the magnetic grains or particles, commonly referred to as the “superparamagnetism” effect. Attempts to overcome this limitation are illustrated in “Effect Of Magnetic Anisotropy Distribution In Longitudinal Thin Film Media” by Hee et al (J. Appl. Phys., Volume 87, 5535–5537, 2000) and U.S. Pat. No. 6,183,606 to Kuo et al. The Hee article discloses a method using highly oriented media to allow further reduction of the grain size. In contrast, the Kuo patent uses L1 0  ordered FePt or CoPt material to form longitudinal or perpendicular magnetic recording media with very small magnetically stable grains. 
     While the above methods provide possibilities to obtain magnetically stabled grains with further reduced size in a first place, in the subsequent post-deposition annealing process, a high temperature, for example 600° C. or above, is to apply to the substrate in order to obtain recording media with an appropriate crystallized structure or with chemically ordered L1 0  FePt or CoPt. Unfortunately, this high temperature annealing process also increases gain size from about 10 nanometers nm) to about 3 nm in the deposited thin film, which eventually reduces the recording density. In addition, no solution is provided by these methods to control the grain distribution width. Due to the larger grain size and their wide distribution width, these films have presented rather poor recording properties, in particular a very low S/N m . Moreover, the high-temperature annealing process is not compatible with existing magnetic recording media fabrication process and materials. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide a method and apparatus for forming thin film magnetic recording media with higher recording density by virtue of the reduced grain size and distribution width. The present invention also provides a thin film magnetic recording medium formed accordingly. The present invention successfully eliminates the post annealing process necessary for the conventional methods as the deposition is done after the magnetic particles are crystallized, therefore avoids the grain growth after the formation of the thin film magnetic recording media by heating up the substrate for annealing purpose. According to the present invention the magnetic easy axis of the magnetic particles are finely controlled during the deposition process and further, the magnetic particles are well isolated from each other either before or during the deposition process. 
     In accordance with a first aspect of the present invention, there is provided a method for forming a thin film magnetic recording media, the method comprises generating magnetic nanoclusters from a target of magnetic material, crystallizing the magnetic nanoclusters, and depositing the magnetic nanoclusters onto a substrate to form a thin film of magnetic particles hereon. The magnetic nanoclusters are deposited onto the substrate after crystallized and therefore after the deposition, it is unnecessary to heat up the substrate. 
     In accordance with a second aspect of the present invention, there is provided an apparatus for forming a thin film magnetic recording media onto a substrate. The apparatus comprises a first chamber, a second chamber connected to the first chamber, and a third chamber connected to the second chamber. The first chamber has a source for generating magnetic nanoclusters. The second chamber is to receive the magnetic nanoclusters and crystallize the magnetic nanoclusters. The third chamber is to receive the crystallized magnetic nanoclusters from the second chamber and deposit the crystallized magnetic nanoclusters onto the substrate positioned therein. 
     In accordance with a third aspect of the present invention, there is provided a thin film magnetic recording medium, the medium comprises a non-magnetic substrate and a magnetic thin film layer disposed on the substrate. The magnetic thin film layer comprises magnetic particles isolated by a non-magnetic material, and the magnetic particles are formed on the substrate after crystallized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an enlarged cross sectional view showing a thin film magnetic recording medium according to one embodiment of the present invention. 
         FIG. 1B  is an enlarged cross sectional view showing a thin film magnetic recording medium according to another embodiment of the present invention. 
         FIG. 2A  is an enlarged top view showing a parallel magnetization orientation of the magnetic nanoparticles formed according to one embodiment of the present invention. 
         FIG. 2B  is an enlarged top view showing a circumferential magnetization orientation of the magnetic nanoparticles formed according to another embodiment of the present invention. 
         FIGS. 3A and 3B  are enlarged cross sectional views showing perpendicular magnetization orientations of the magnetic nanoparticles formed according to the present invention. 
         FIG. 4  is a schematic diagram showing an apparatus for forming magnetic thin film onto a substrate according to one embodiment of the present invention. 
         FIGS. 5A ,  5 B and  5 C are schematic diagrams showing various configurations of the magnetic field according to the present invention. 
         FIG. 6  is a schematic diagram showing an apparatus for forming magnetic thin film onto a substrate according to another embodiment of the present invention. 
         FIG. 7  is a schematic diagram showing an apparatus for forming magnetic thin film onto a substrate according to a further embodiment of the present invention. 
         FIG. 8  is a flow chart showing a method for forming magnetic thin film onto a substrate according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1A  illustrates a thin film magnetic recording medium formed according to one embodiment of the present invention. The thin film magnetic recording medium  100  comprises a substrate  110 , a thin film magnetic layer  120  deposited onto the substrate  110  and a protective overcoating  130  deposited on the thin film magnetic layer  120 . The substrate  110  may be formed of a non-magnetic material such as silicon, glass, or aluminum alloy. The thin film magnetic layer  120  comprises a plurality of magnetic particles  122 . Examples of magnetic materials that may be used to form magnetic particles  122  include Co, Fe, Ni, Sm, Pt, Cr, Ta, Nd, Pd, Gd, B, N, C, P, Ti, W, Mo, Ag, Ru, Au, Nb, Pb, Dy, a binary alloy of aforesaid elements, a ternary alloy of said elements, an oxide of Fe further comprising at least one of the said elements other than Fe, barium ferrite and strontium ferrite, carbide and nitride of the said elements. The preferred magnetic materials are, for example, CoPt, FePt or CoPd. 
     The magnetic particles  122  are encapsulated by non-magnetic material  124   a . The magnetic particles  122  are oriented with its magnetic easy axis  126  aligned parallel to a surface  114  of the substrate  110 . In  FIG. 1B , the magnetic particles  122  are disposed on the substrate  110  simultaneously with a non-magnetic material  124   b , such that the magnetic particles  122  are dispersed within the non-magnetic material  124   b . It should be appreciated that the intergranular coupling effect of the magnetic particles isolated by the non-magnetic material  124   a  ( FIG. 1) and 124   b  ( FIG. 2 ) in the above structure can be effectively reduced. 
       FIGS. 2A and 2B  show two examples of the highly oriented alignment of magnetic easy axis of the magnetic particles in the magnetic thin film for longitudinal recording media.  FIG. 2A  shows that the magnetic easy axes  226   a  of the magnetic particles  222  are parallel to the surface of the substrate  210 .  FIG. 2B  shows that the magnetic easy axes  226   a  of the magnetic particles  222  are parallel to the surface of the substrate  210  and are circumferentially aligned. 
       FIG. 3A  illustrates a thin film magnetic recording medium formed according to another embodiment of the present invention. The thin film magnetic recording medium  300  comprises a substrate  310 , a thin film magnetic layer  320  deposited onto the substrate  110  and a protective overcoating  330  deposited on the thin film magnetic layer  120 . The substrate  110  may be formed of a non-magnetic material made of, for example, a silicon wafer, glass or aluminum alloy. The thin film magnetic layer  320  includes a plurality of magnetic particles  322  comprising magnetic material, such as Co, Fe, Ni, Sm, Pt, Cr, Ta, Nd, Pd, Gd, B, N, C, P, Ti, W, Mo, Ag, Ru, Au, Nb, Pb, Dy, a binary alloy of aforesaid elements, a ternary alloy of said elements, an oxide of Fe further comprising at least one of the said elements other than Fe, barium ferrite and strontium ferrite, carbide and nitride of the said elements. 
     The magnetic particles  322  are encapsulated by a layer of non-magnetic material  324   a  according to the method illustrated below, and with its magnetic easy axis  326  aligned perpendicular to the surface  314  of the substrate  310 . In  FIG. 3B , the magnetic particles  322  are disposed on the substrate  310  simultaneously with a non-magnetic material  324   b  such that the magnetic particles  322  are dispersed within the non-magnetic material  324   b.    
     As shown in  FIG. 4 , an apparatus for forming magnetic thin film onto a substrate according to one embodiment of the present invention comprises a cluster-forming chamber  410 , a healing chamber  420 , an encapsulation chamber  429  and a deposition chamber  430 . The cluster-forming chamber  410  comprises a target  416  made of a magnetic material selected from, for example, Co, Fe, Ni, Sm, Pt, Cr, Ta, Nd, Pd, Gd, B, N, C, P, Ti, W, Mo, Ag, Ru, Au, Nb, Pb, Dy, a binary alloy of aforesaid elements, a ternary alloy of said elements, an oxide of Fe further comprising at least one of the said elements other than Fe, barium ferrite and strontium ferrite, carbide and nitride of the said elements. The cluster-forming chamber  410  comprises a power unit  412  connected to an anode  413  and the target  416  (which is used as a cathode). The cluster-forming chamber  410  also includes a first conduit  411  for supplying a first gas, such as argon (Ar) and a second conduit  415  for supplying a second gas such as helium (He). The Ar serves as both sputtering gas and aggregation gas while the He is used to control the cluster size and initial distribution width due to its high heat-transfer ability. A liquid nitrogen cooling unit  414  is also provided for promoting the formation of the cluster with desired size. Examples of the power unit  412  are a direct current (DC) or radio frequency (RF) power supply. The cluster-forming chamber  410  preferably operates at a working pressure in a range of about 0.1 Torr to 1 Torr. which is higher than that of the conventional sputtering pressure. The purpose of using a pressure for sputtering in this level is to provide more collision chance of the particle and to form large particle. The parameters of controlling the particle size include gas pressure, gas flow rate, ratio of Ar and He. A diaphragm  417  is provided at one end of the nitrogen cooling unit. Another diaphragm  418  is provided to connect the cluster-forming chamber  410  and the heating chamber  420 . 
     Pumping systems  433 ,  434 , and  435  are provided for adjusting the pressure of the cluster-forming chamber  410 , the encapsulation chamber  429  and the deposition chamber  430 . The pressure of the deposition chamber  430  is maintained at a level lower than the pressure of the other two chambers to enable cluster transportation from the cluster-forming chamber  410  to the deposition chamber  430 . The pressure range of the cluster-forming chamber  410 , the encapsulation chamber  429  and the deposition chamber  430  can be set to about 0.1–1 Torr, 10 −4  Torr, and 10 −6  Torr, respectively. 
     At the start of the process, energized argon gas ions (Ar+) are accelerated towards the target  416  to eject atoms  421  from the target  16  upon impact. The ejected atoms  421  are then decelerated by collision with the argon gas (Ar+) and start to agglomerate to form clusters. The liquid nitrogen cooling unit  414  and helium supplied from the conduit  415  aid in cooling the ejected atoms  421  to form a set of clusters  422 . 
     After being exposed to the noble gases (Ar+), the clusters  422  then move through the diaphragm  417  and agglomerate together to form a set of larger clusters  423 , which continue move onwards to the heating chamber  420  through diaphragm  418 , and further form final clusters  424  in the heating chamber  420 . The clusters  424  may consist of several hundred magnetic atoms up to several million magnetic atoms, which are loosely bonded with each other. In the process atoms are agglomerated together to form clusters and more atoms are attached to the boundary portions of the clusters continuously. As a result, the clusters will be formed with larger sized agglomerates located at the center portion and with relatively smaller sized agglomerates locates at the boundary portion. Upon passing through the diaphragm  418 , smaller sized agglomerates located at the boundary portions of the clusters  423  can be trimmed off by the diaphragm. As a result, the clusters  424  passing through the diaphragm will have the smaller sized agglomerates removed. Therefore, clusters with a distribution width smaller than that of the clusters  423  before the diaphragm  418  can be obtained. In this embodiment, the dimension of the clusters  424  is in a range of about 1 nm to 20 nm and a distribution width of about 10% or less. 
     It should be appreciated according to the above illustration that various parameters may be adjusted to control the dimension and distribution width including the pressure of the cluster-forming chamber  410 , the sputtering rate of the target materials, the ratio of the helium to other noble gases, the distance between the target  416  and the diaphragm  417  and the size of the diaphragms  417  and  418 , etc. 
     The apparatus further comprises a number of heaters  419  for heating the gas-phase clusters  424  to a temperature of about 900° C. to achieve crystallization Examples of the heaters  419  include a resistance furnace heater or a lamp heater. After heating, the clusters  424  are converted into crystallized magnetic nanoclusters  425  with a desired crystalline structure for data storage purpose. 
     The magnetic nanoclusters  425  are then moved to the encapsulation chamber  429 . A surfactant  427  is then supplied to the encapsulation chamber by a spray nozzle  428 , such as a nebuliser. The surfactant is preferably a material which can be absorbed by the magnetic nanocrystals  425  to form encapsulated magnetic nanocrystals  426 . The surfactant  427  may be selected from a group of organic materials, including fatty acids, alkyl thiols, alkyl diulfides, alkyl nitriles and alkyl isonitiles, which is an end group that is attracted to the magnetic nanocrystals  425 . The surfactant may also be a methylene having a chain 8 to 12 units long, which provides steric repulsion to prevent the magnetic nanocrystals  425  from adhering to the substrate in the subsequent deposition process. The term “8 to 12 units long” denotes that for polymer materials, its structure is chain-like, for example “8 unit” refer to the chain structure of C—C—C—C—C—C—C—C (C means carbon, other bonds of carbon bond to the function group such as hydrogen, —OH etc.) 
     The encapsulated magnetic nanocrystals  426  are then transported into the deposition chamber  430  to be deposited onto the substrate  431 . As illustrated above, because the magnetic nanocrystals  425  are crystallize before reaching the substrate  431 , the magnetic nanocrystals  425  are usually a single domain. Because the energy of the magnetic nanocrystals  425  is very low, the encapsulated magnetic nanocrystals  426  will remain intact after deposition onto the substrate. 
     An external magnetic field  432  is provided adjacent to the substrate  431 , which forms a relatively uniform magnetic field direction as illustrated in  FIG. 4 . When the encapsulated magnetic nanoclusters  426  reach the substrate  431  they will be aligned by following the direction of the magnetic field  432  whilst depositing on the substrate  431 . The magnetic thin firm can then be formed with highly oriented magnetic easy axis along a predetermined direction controlled by the magnetic field  432 . 
       FIGS. 5A and 5B  show alternative configurations of a magnetic field adjacent to a substrate for aligning the orientation of the magnetic particles. In  FIG. 5A , two permanent magnets or electromagnets  537   a  and  537   b  are placed underneath a substrate  531 . The north magnetic pole of magnet  537   a  and the south magnetic pole of magnet  537   b  are placed adjacent to the substrate  530  to generate a magnetic field  520 . The magnetic field  520  aligns the magnetic particles along a direction parallel to the top surface  531   a  of the substrate  531  during deposition. In addition, the substrate  531  and the magnets  537   a ,  537   b  may be rotated during the deposition process to achieve uniformity of the magnetic thin film deposition. 
     As shown in  FIG. 5B  a circumferentially-oriented magnetic field  540  may be obtained by passing through an electrical wire  538  through the center of the substrate  531 . The magnetic field  540  aligns the magnetic clusters during deposition along a direction parallel to and circumferential with respect to the a top surface  531   a  of the substrate  531 . 
     As shown in  FIG. 5C , a magnetic field  560  with a direction perpendicular to a top surface  531   a  of the substrate  531  may be obtained by placing a solenoid,  539  around the substrate  531 . The solenoid aligns the magnetic particles during deposition along a direction perpendicular to the substrate surface. It should be appreciated that magnetic thin films having different magnetic orientations may be obtained by applying an appropriate magnetic field adjacent to the substrate. 
       FIG. 6  shows an apparatus for forming magnetic thin film onto a substrate according to another embodiment of the present invention. The apparatus comprises a cluster-forming chamber  610 , a heating chamber  620 , an encapsulation chamber  629 , and a deposition chamber  630 . In this embodiment, the encapsulation chamber  629  is coupled between the cluster-forming chamber  610  and the heating chamber  620 . 
     The loosely bonded magnetic nanoclusters  624  formed by the cluster-forming chamber  610  are transported into the encapsulation chamber  629 . A spray of organic solvent or surfactant  627  are supplied by the nozzle  628  into the encapsulation chamber  629  to mix with the magnetic nanoclusters  624  to form the encapsulated nanoclusters  625 . 
     The encapsulates nanoclusters  625  are transported into the heating chamber  620  thereafter. The encapsulated nanoclusters  624   a  are heated by the heaters  619  to a temperature of about 900° C. to form crystalized magnetic nanoclusters  626 . At the same time, the organic materials encapsulating the nanoclusters will be carbonized by the heating process, therefore the crystallized magnetic nanoclusters  626  are encapsulated with a layer of amorphous carbon. The encapsulated magnetic nanoclusters are then deposited onto the substrate  631  located in the deposition chamber  630 . 
       FIG. 7  shows an apparatus for forming magnetic thin film onto a substrate according to a further embodiment of the present invention. The apparatus comprises a cluster-forming chamber  710 , a heating chamber  720  and a deposition chamber  730 . In this embodiment, the loosely bonded magnetic nanoclusters  724  are formed in the cluster-forming chamber  710 , and transported into the heating chamber  720 . 
     After heating in the heating chamber  720 , the loosely bonded nanoclusters  724  become close-packed and crystallized magnetic nanoclusters  725 . The magnetic nanoclusters  725  are then transported into the deposition chamber  730  to be deposited onto substrate  731 . At the same time, non-magnetic materials are also deposited onto the substrate  731  by a source  736 . Examples of non-magnetic materials that may be used include C, SiO 2 , Si 3 N 4  BN and/Dr carbon hydrogenate polymer. 
       FIG. 8  shows a method  800  for forming a thin film magnetic recording media according to the present invention. In a first block  802 , magnetic nanocluster are generated from a target. In a next block  804 , the magnetic nanoclusters are heated to a crystallization temperature, whereby the magnetic nanoclusters are crystallized so that to process necessary properties for data storage purpose. Thereafter in a further block  806 , the crystallized magnetic nanoclusters mixed up with a non-magnetic material. The non-magnetic material encapsulate the crystallized magnetic nanoclusters and therefore, the intergranular coupling effect of the magnetic particles will be reduced. In a next block  808 , the encapsulated magnetic nanoclusters are disposed onto a substrate to form solid-phase magnetic particles. 
     It should be appreciated that according to the above method, since the desired crystalline structure are obtained before deposition, the substrate after the magnetic nanoclusters deposited thereon needs not be heated up for annealing purpose. Accordingly, the grain growth by the post-deposition annealing is successfully eliminated.