Method of manufacturing magnetoresistive element, magnetoresistive element, magnetic head assembly and magnetic recording apparatus

Abstract
A method of manufacturing a magnetoresistive element includes forming a metal layer on a first ferromagnetic layer, oxidizing the metal layer to form an oxide layer in which unoxidized metal is remained and a magnetic conduction column penetrating the oxide layer in a thickness direction and including at least a part of constituent elements of the first ferromagnetic layer, annealing a resultant structure at a higher temperature than a temperature at which the oxide layer is formed to convert at least a part of a periphery of the magnetic conduction column into a magnetic oxide including a part of constituent elements of the oxide layer and at least a part of constituent elements of the magnetic conduction column, and forming a second ferromagnetic layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2008-249977, filed Sep. 29, 2008, the entire contents of which are incorporated herein by reference.


BACKGROUND OF THE INVENTION

1. Field of the Invention


The present invention relates to a method of manufacturing a magnetoresistive element having such a structure that a current is supplied in a direction perpendicular to the film plane, a magnetoresistive element manufactured by the method, a magnetic head assembly using the magnetoresistive element and magnetic recording apparatus using the magnetic head assembly.


2. Description of the Related Art


The performance of magnetic devices has been drastically improved by finding of the giant magnetoresistive effect (GMR) in a stacked structure of magnetic materials. In particular, since a spin-valve film (SV film) has a structure easily applicable to magnetic devices and efficiently exhibits the GMR effect, it has brought about marked technical improvement in the magnetic devices such as magnetic head assemblies and magnetic random access memories (MRAMs).


The “spin-valve film” has a structure in which a nonmagnetic metal spacer layer is sandwiched between two ferromagnetic layers. In the spin-valve film, the magnetization of one ferromagnetic layer (referred to as a “pinned layer” or “magnetization pinned layer”) is pinned by an anti-ferromagnetic layer or the like, whereas the magnetization of the other ferromagnetic layer (referred to as a “free layer” or “magnetization free layer”) is made rotatable in accordance with an external magnetic field. In the spin-valve film, a giant magnetoresistance change can be produced by a change of the relative angle between the magnetization directions of the pinned layer and the free layer.


Conventional spin-valve films are CIP (current-in-plane)-GMR element in which a sense current is supplied in parallel to the film plane. In recent years, TMR (tunneling magnetoresistance) elements and CPP (current-perpendicular-to-plane)-GMR elements, in which a sense current is supplied in a direction substantially perpendicular to the film plane, attract a great deal of attention because they exhibit a higher MR ratio than the CIP-GMR element.


On the other hand, there has been observed that a nanocontact between Ni wires exhibits a magnetoresistance effect with a high magnetoresistance change. See, Phys. Rev. Lett., 82, 2923 (1999).


Further, development of a magnetoresistive element in which the magnetic nanocontact is extended to a three-dimensional structure has been advanced. See, JP-A 2003-204095 (KOKAI). JP-A 2003-204095 (KOKAI) discloses, as a method of fabricating a nanocontact, more specifically as a method of forming a hole for the nanocontact, an electron beam (EB) irradiation process, a focused ion beam (FIB) irradiation process, atomic force microscope (AFM) technology and the like.


It is conceivable that the novel magnetoresistive effect described in the above documents may be derived from abrupt change of magnetization at the magnetic nanocontact. The abrupt change of magnetization at the magnetic nanocontact depends on a domain wall thickness or a domain wall width produced at the magnetic nanocontact. In other words, the abrupt change can be provided as the domain wall width is made narrower. In addition, since the domain wall width depends on a size of the magnetic nanocontact, it is preferable that the magnetic nanocontact has a small size. Further, it is preferable that the magnetic nanocontact or the domain wall has high purity of magnetic element. However, it is very difficult to form a magnetic nanocontact with a small size and high purity.


BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided a method of manufacturing a magnetoresistive element comprising: forming a metal layer on a first ferromagnetic layer; oxidizing the metal layer to form an oxide layer in which unoxidized metal is remained and a magnetic conduction column penetrating the oxide layer in a thickness direction and comprising at least a part of constituent elements of the first ferromagnetic layer; annealing a resultant structure at a higher temperature than a temperature at which the oxide layer is formed to convert at least a part of a periphery of the magnetic conduction column into a magnetic oxide comprising a part of constituent elements of the oxide layer and at least a part of constituent elements of the magnetic conduction column, so as to form the intermediate layer comprising the oxide layer, magnetic conduction column and magnetic oxide; and forming a second ferromagnetic layer on the intermediate layer. Also, there is provided a method of manufacturing a magnetoresistive element comprising: forming a metal layer on a first ferromagnetic layer; oxidizing the metal layer to form an oxide layer in which unoxidized metal is remained and a magnetic conduction column penetrating the oxide layer in a thickness direction and comprising at least a part of constituent elements of the first ferromagnetic layer; forming a second ferromagnetic layer; annealing resultant structure at a higher temperature than a temperature at which the oxide layer is formed to convert at least a part of a periphery of the magnetic conduction column into a magnetic oxide comprising a part of constituent elements of the oxide layer, at least a part of constituent elements of the magnetic conduction column and at least a part of constituent elements of the second ferromagnetic layer, so as to form the intermediate layer comprising the oxide layer, magnetic conduction column and magnetic oxide.


According to another aspect of the present invention, there is provided a magnetoresistive element comprising: a stacked film comprising first and second ferromagnetic layers a magnetization direction of one of which ferromagnetic layers is substantially pinned in a direction and a magnetization direction of the other of which ferromagnetic layers is varied depending on an external magnetic field, and an intermediate layer between the first and second ferromagnetic layers; and a pair of electrodes provided on a bottom and a top of the stacked film and configured to pass a current perpendicularly to a film plane of the stacked film, the intermediate layer comprising: an oxide layer; a magnetic conduction column penetrating the oxide layer in a thickness direction; and a magnetic oxide covering at least a part of a periphery of the magnetic conduction column and comprising a part of constituent elements of the oxide layer and at least a part of constituent elements of the magnetic conduction column.





BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING


FIG. 1 is a cross-sectional view of a magnetoresistive element according to an embodiment;



FIGS. 2A to 2C are cross-sectional views showing a method of manufacturing the magnetoresistive element shown in FIG. 1;



FIGS. 3A and 3B are cross-sectional views showing another method of manufacturing the magnetoresistive element shown in FIG. 1;



FIG. 4 is an exploded perspective view of a magnetic recording apparatus according to an embodiment with its top cover off;



FIG. 5 is a perspective view of a magnetic head stack assembly in the HDD in FIG. 4;



FIG. 6 is an exploded perspective view of the magnetic head stack assembly in FIG. 6;



FIG. 7 is a graph showing the relationship between the in-situ annealing temperature and MR ratio for the magnetoresistive element in Example 1; and



FIG. 8 is a graph showing the temperature dependence of the resistance change for the magnetoresistive element in Example 1.





DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the invention will be described with reference to the drawings.



FIG. 1 is a cross-sectional view of a magnetoresistive element according to an embodiment. The magnetoresistive element has a structure in which a stacked film is provided between a lower electrode (LE) 1 and an upper electrode (UE) 8.


In FIG. 1, the stacked film between the lower electrode (LE) 1 and the upper electrode (UE) 8 comprises an underlayer 2, an anti-ferromagnetic layer 3, a pinned layer (magnetization pinned layer) 4 as a first ferromagnetic layer, an intermediate layer 5, a free layer (magnetization pinned layer) 6 as a second ferromagnetic layer, and a protection layer 7.


The pinned layer 4 in FIG. 1 has a synthetic structure in which a lower pinned layer 4a and an upper pinned layer 4c are provided on the both sides of an anti-parallel coupling layer 4b. The intermediate layer 5 comprises an oxide layer 5a, a magnetic conduction column 5b penetrating the oxide layer 5a in a thickness direction, and a magnetic oxide 5c covering at least a part of the periphery of the magnetic conduction column 5b. The magnetic conduction column 5b comprises at least a part of constituent elements of the underlying first ferromagnetic layer (i.e., the pinned layer in this case) or at least a part of constituent elements of the second ferromagnetic layer (i.e., the free layer in this case). It should be note that the constituent element of the first ferromagnetic layer included in the magnetic conduction column 5b need not all the constituent elements but may be a part of the constituent elements. In addition, where a process is employed which comprises forming a metal layer on the first ferromagnetic layer, oxidizing the metal layer, forming a second ferromagnetic layer on the oxidized metal layer, and annealing the resultant structure at a higher temperature than the oxidation temperature, the magnetic conduction column 5b comprises a constituent element of the second ferromagnetic layer as well as a constituent element of the first ferromagnetic layer. It should be also note that the constituent element of the second ferromagnetic layer included in the magnetic conduction column 5b need not all the constituent elements but may be a part of the constituent elements. The magnetic oxide 5c comprises a part of constituent elements of the oxide layer 5a and at least a part of constituent elements of the magnetic conduction column 5b.


In FIG. 1, the pinned layer 4, intermediate layer 5 and free layer 6 constitute the spin-valve film.


In the magnetoresistive element, a sense current is supplied substantially perpendicular to the film plane of the stacked film via the lower electrode (LE) and upper electrode (UE), in other words, the element operates as a CPP (current-perpendicular-to-plane) magnetoresistive element.


A structure having an inverted stacked film can also be employed, in which the underlayer 2, free layer 6, intermediate layer 5, pinned layer 4 of a synthetic structure, anti-ferromagnetic layer 3 and protection layer 7 are stacked in this order from the lower electrode. In this case, the first ferromagnetic layer corresponds to the free layer 6, and the second ferromagnetic layer corresponds to the pinned layer 6 of synthetic structure.


Although the pinned layer 4 of synthetic structure is employed in FIG. 1, the pinned layer 4 may be a single-layered ferromagnetic layer. Although the single-layered free layer 4 is employed in FIG. 1, the pinned layer 4 may be of a stacked structure.


Hereinafter, each layer of the magnetoresistive element in FIG. 1 will be described in more detail.


The underlayer 2 may be a double-layered structure of a buffer layer and seed layer, for example. The buffer layer functions to alleviate roughness on the surface of the lower electrode (LE). The buffer layer may be formed of a material selected from the group consisting of Ta, Ti, W, Zr, Hf, Cr and an alloy thereof. The seed layer is a layer for controlling the crystalline orientation and the crystal grain size of the spin-valve film deposited thereon. The seed layer functions to control the crystalline orientation of the spin-valve film. The buffer layer may be formed of a material selected from the group consisting of Ru, (FexNi100-x)100-yXy, where X=Cr, V, Nb, Hf, Zr or Mo, 15<x<25, and 20<y<45, Cr and Cu. The underlayer 2 may be formed of either the buffer layer or seed layer.


The anti-ferromagnetic layer 3 functions to impart unidirectional anisotropy to the pinned layer 4 of synthetic structure and to fix the magnetization of the pinned layer. The anti-ferromagnetic layer 3 may be formed of an anti-ferromagnetic material such as PtMn, PdPtMn, IrMn and RuRhMn. In the case of using IrMn, it is preferable to set the Ir composition in IrMn above 22 at % in view of heat resistance.


The lower pinned layer 4a and upper pinned layer 4c in the pinned layer 4 may be formed of various types of magnetic materials such as Fe, Co, Ni, a FeCo alloy, a FeNi alloy, a FeCoNi alloy, and a CoFeB alloy. Also, a half metal-based material comprising Fe, Co, or Ni may be use for the upper pinned layer 4c in addition to the above materials. Further, a material prepared by adding a non-magnetic material to the above magnetic materials may be used. The anti-parallel coupling layer 4b has a function to anti-ferromagnetically couple the lower pinned layer 4a and upper pinned layer 4c and may be formed of a material such as Ru, Ir and Rh.


The oxide layer 5a in the intermediate layer 5 may be formed of an oxide comprising at least one element selected from the group consisting of Al, Mg, Li, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Se, Sr, Y, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Sb, Ba, Ka, Hf, Ta, W, Re, Pt, Hg, Pb, Bi, and lanthanoide elements. In addition, any material having a function of insulating a current may be appropriately used for the oxide layer 5a.


The magnetic conduction column 5b in the intermediate layer 5 functions as a path to pass a current perpendicularly to the film plane and as a contact to magentically contact the pinned layer 4a and free layer 6. The magnetic conduction column 5b may be formed of a ferromagnetic material such as Fe, Co, Ni and the alloy thereof which is a constituent element of the upper pinned layer 4c in the pinned layer 4 or the free layer 6.


The magnetic oxide 5c in the intermediate layer 5 comprises a part of constituent elements of the oxide layer 5a and at least a part of constituent elements of the magnetic conduction column 5b. Although FIG. 1 shows that the magnetic oxide 5c covers the entire periphery of the magnetic conduction column 5b, the magnetic oxide 5c needs not always to cover the entire periphery and it suffices to cover a part of the periphery. However, it is preferable that the magnetic oxide 5c covers the entire periphery of the magnetic conduction column 5b in order to reduce the size of the magnetic conduction column 5b more effectively.


The free layer (magnetization free layer) 6 may be formed of a ferromagnetic material, a magnetization direction of which is varied depending on an external magnetic field, such as Fe, Co, Ni, a FeCo alloy and a FeNi alloy. Also, a half metal-based material comprising Fe, Co, or Ni may be use for the free layer 6 in addition to the above materials. Further, a material prepared by adding a non-magnetic material to the above magnetic materials may be used. Although FIG. 1 shows that the free layer 6 is a single-layered film, the free layer 6 may be of a stacked structure including plurality of layers as described above. It is not necessary that the pinned layer and free layer have the same constituent elements and composition ratio of alloy.


The protection layer 7 has a function of protecting the spin valve film. The protection layer 7 may be a single layer, a multilayer or a stacked film comprising an element selected from the group consisting of Ti, V, Cr, Co, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au, Si, Al, Pt, Ni, Co, Re, V and an alloy thereof. For example, the protection layer 7 may be formed of a double-layered film of Cu/Ru or a triple-layered film of Cu/Ta/Ru.


When a magnetic field having an opposite direction to the magnetization direction of the upper pinned layer 4a is applied to the free layer 6 and the magnetization direction of the free layer 6 is directed to the direction of the above magnetic field, the magnetization directions of the upper pinned layer 4a and free layer 6 are made anti-parallel to each other. In this case, since the magnetic conduction column 5b is sandwiched between two ferromagnetic layers, i.e., the upper pinned layer 4a and free layer 6, a domain wall is produced in the magnetic conduction column 5b. In the magnetoresistive element according to the embodiment, the magnetic conduction column 5b has a narrow domain wall width, and thus, a steep magnetization change can be provided in the magnetic conduction column 5b.


Next, a method of manufacturing a magnetoresistive element shown in FIG. 1 will be described with reference to FIGS. 2A to 2C.


(1) Formation of the Lower Electrode (LE) 1, Underlayer 2 and Ferromagnetic Layer:


The lower electrode 1 is formed on a substrate (not shown) by a fine-processing technology. The underlyer 2 and ferromagnetic layer 3 are deposited in this order on the lower electrode 1.


(2) Formation of the Pinned Layer 4 of Synthetic Structure:


The lower pinned layer 4a, anti-parallel coupling layer 4b, and upper pinned layer 4c are deposited in this order on the ferromagnetic layer 3.


(3) Formation of the Intermediate Layer 5:


As shown in FIG. 2A, a metal layer 9 made of a metal such as Al to be converted into the oxide layer is deposited on the upper pinned layer 4c.


As shown in FIG. 2B, the metal layer (Al) 9 is oxidized by natural exposure, an ion-assisted method, a RF plasma method, an ion-beam method or a radical method by which the oxide layer 5a and the magnetic conduction column 5b penetrating the oxide layer 5a in the thickness direction and comprising at least a part of constituent elements of the upper pinned layer 4c are formed. At this time, it is not necessary to heat the substrate, and the oxidation can be performed at room temperature.


In the embodiment, the oxidation conditions are made more moderate compared to proper or excessive oxidation conditions under which the entire metal layer (Al) 9 is oxidized, and thus, unoxidized metal (Al) 9a is made remained in the oxide layer 5a. The more moderate oxidation conditions compared to proper or excessive oxidation conditions can be attained by reducing the oxygen flow rate, reducing the oxygen pressure, or shortening the oxidation time. The quantity of the remaining unoxidized metal can be changed by adjusting the above conditions and by adjusting the thickness of the metal layer (Al) 9.


Also, the oxide layer 5a in which unoxidized metal (Al) 9a is remained may be subjected to a RF plasma method or an ion-beam method to form the magnetic conduction column 5b.


As shown in FIG. 2C, after the oxide layer 5a in which unoxidized metal (Al) 9a is remained and the magnetic conduction column 5b are formed, the resultant structure is annealed in vacuum at a higher temperature than the oxidation temperature, where the process is referred to as in-situ annealing herein, such that a part of the periphery of the magnetic conduction column 5b is converted, thereby to form the magnetic oxide 5c comprising a part of constituent elements of the oxide layer 5a and at least a part of constituent elements of the magnetic conduction column 5b. Thus, the intermediate layer 5 comprising the oxide layer 5a, magnetic conduction column 5b and magnetic oxide 5c is formed.


In the case where Fe50Co50, for example, is used for the material of the upper pinned layer 4c, FeCo, Fe, Co, FeCo-oxide and the like are present in the magnetic conduction column 5b at the end of the oxidation and a supplemental process performed if necessary for forming the magnetic conduction column 5b. When the annealing is performed in this state, the FeCo-oxide is react with the unoxidized metal (Al) to produce FeAl-oxide and Co through reduction. As a result, the magnetic conduction column 5b is highly purified in a composition mainly comprised of Co and the FeAl-oxide covers at least a part of the periphery of the magnetic conduction column 5b and reduces the size of magnetic conduction column 5b. The annealing temperature is set at a higher temperature than the oxidation temperature so as to cause above reaction. The upper limits of the annealing conditions are determined in a range of temperature and time where no diffusion is caused at the interfaces of the layers. The temperature at which the diffusion is caused at the interfaces of the layers is not specifically determined because it depends on a degree of mixing at the interfaces of the layers after deposition and surface irregularity.


It should be noted that the material of the upper pinned layer 4c is preferably made of an alloy comprising Fe which is easily oxidized and Co or Ni which is hard to be oxidized like the above example.


(4) Formation of the Free Layer 6, Protection Layer 7 and Upper Electrode (UE) 8:


The free layer 6 is deposited on the intermediate layer 5, and then the protection layer 7 and the upper electrode (UE) 8 are deposited in this order on the free layer 6. In such a manner, the magnetoresistive element can be provided.


(5) Annealing in a Magnetic Field:


The resultant magnetoresistive element is annealed in a magnetic field by which the magnetization direction of the pinned layer 4 is pinned.


Although FIGS. 2A to 2C show the case where the first ferromagnetic is a pinned layer, processes similar to those described above will be used in the case where the first ferromagnetic is a free layer. It is needless to say that the magnetic conduction column 5b in this case comprises a part of constituent elements of the free layer.


The above describes the case where the intermediate layer 5 is formed prior to deposition of the free layer. Hereinafter, the case where the intermediate layer 5 is formed after the free layer is deposited will be described with reference to FIGS. 3A and 3B.


The processes of (1) and (2) are the same as the above processes.


(3′) Formation of the Intermediate Layer 5 and Free Layer 6:


Like FIG. 2A, a metal layer 9 made of a metal such as Al to be converted into the oxide layer is deposited on the upper pinned layer 4c. Like FIG. 2B, the metal layer (Al) 9 is oxidized by natural exposure, an ion-assisted method, a RF plasma method, an ion-beam method or a radical method by which the oxide layer 5a and the magnetic conduction column 5b penetrating the oxide layer 5a in the thickness direction and comprising at least a part of constituent elements of the upper pinned layer 4c are formed. At this time, it is not necessary to heat the substrate, and the oxidation can be performed at room temperature.


In the embodiment, the oxidation conditions are made more moderate compared to proper or excessive oxidation conditions under which the entire metal layer (Al) 9 is oxidized, and thus, unoxidized metal (Al) 9a is made remained in the oxide layer 5a. The more moderate oxidation conditions compared to proper or excessive oxidation conditions can be attained by reducing the oxygen flow rate, reducing the oxygen pressure, or shortening the oxidation time. The quantity of the remaining unoxidized metal can be changed by adjusting the above conditions and by adjusting the thickness of the metal layer (Al) 9.


Also, the oxide layer 5a in which unoxidized metal (Al) 9a is remained may be subjected to a RF plasma method or an ion-beam method to form the magnetic conduction column 5b.


Then, as shown in FIG. 3A, the free layer 6 is deposited on the oxide layer 5a, in which unoxidized metal (Al) 9a is remained, and the magnetic conduction column 5b.


As shown in FIG. 3B, after the free layer 6 is formed, the resultant structure is annealed in vacuum at a higher temperature than the oxidation temperature to convert a part of the periphery of the magnetic conduction column 5b (in-situ annealing), thereby to form the magnetic oxide 5c comprising a part of constituent elements of the oxide layer 5a and at least a part of constituent elements of the magnetic conduction column 5b. Thus, the intermediate layer 5 comprising the oxide layer 5a, magnetic conduction column 5b and magnetic oxide 5c is formed. In this case, the constituent elements of the magnetic conduction column 5b may be mainly comprised of the constituent elements of the free layer or may be the constituent elements of the upper pinned layer mixed with the constituent elements of the free layer.


In the case where Fe50Co50, for example, is used for the material of the upper pinned layer 4c, FeCo, Fe, Co, FeCo-oxide and the like are present in the magnetic conduction column 5b at the end of the oxidation, a supplemental process performed if necessary for forming the magnetic conduction column 5b and the deposition of the Fe50Co50 free layer. When the annealing is performed in this state, the FeCo-oxide is react with the unoxidized metal (Al) with the Fe element supplied from the free layer to produce FeAl-oxide and Co through reduction. As a result, the magnetic conduction column 5b is highly purified in a composition mainly comprised of Co and the FeAl-oxide covers at least a part of the periphery of the magnetic conduction column 5b and reduces the size of magnetic conduction column 5b. The annealing temperature is set at a higher temperature than the oxidation temperature so as to cause above reaction. The upper limits of the annealing conditions are determined in a range of temperature and time where no diffusion is caused at the interfaces of the layers. The temperature at which the diffusion is caused at the interfaces of the layers is not specifically determined because it depends on a degree of mixing at the interfaces of the layers after deposition and surface irregularity.


It should be noted that the material of the upper pinned layer 4c or free layer 6 is preferably made of an alloy comprising Fe which is easily oxidized and Co or Ni which is hard to be oxidized like the above example.


(4′) Formation of the Protection Layer 7 and Upper Electrode (UE) 8:


The protection layer 7 and the upper electrode (UE) 8 are deposited in this order on the free layer 6. In such a manner, the magnetoresistive element can be provided.


(5) Annealing in a Magnetic Field:


The resultant magnetoresistive element is annealed in a magnetic field by which the magnetization direction of the pinned layer 4 is pinned.


Although FIGS. 3A and 3B show the case where the first ferromagnetic is a pinned layer, processes similar to those described above will be used in the case where the first ferromagnetic is a free layer. The magnetic conduction column 5b in this case comprises both the constituent elements of the free layer and pinned layer or a part of constituent elements of the pinned free layer.


A magnetic head assembly and an HDD using the above magnetoresistive element will now be described.



FIG. 4 is a perspective view showing the internal structure of the HDD with its top cover off. As shown in FIG. 4, the HDD is provided with a housing 10. The housing 10 includes a base 12 in the form of an open-topped rectangular box and a top cover 14, which is fastened to the base with screws 11 so as to close the top opening of the base. The base 12 includes a rectangular bottom wall 12a and a sidewall 12b set up along the peripheral edge of the bottom wall.


The housing 10 contains one magnetic disk 16 for use as a recording medium and a spindle motor 18 as a drive section that supports and rotates the magnetic disk. The spindle motor 18 is located on the bottom wall 12a. The housing 10 has a size large enough to accommodate a plurality of, e.g., two, magnetic disks, and the spindle motor 18 is configured to support and drive two magnetic disks.


The housing 10 further contains magnetic heads 17, head stack assembly (HSA) 22, voice coil motor (VCM) 24, ramp load mechanism 25, latch mechanism 26, and board unit 21. The magnetic heads 17 record and reproduce information to and from the magnetic disk 16. The HSA 22 supports the heads 17 for movement with respect to the disk 16. The VCM 24 swings and positions the HSA 22. The ramp load mechanism 25 holds the magnetic heads in a retracted position at a distance from the magnetic disk when the heads are moved to the outermost periphery of the disk. The latch mechanism 26 holds the HSA in its retracted position when the HDD is jolted. The board unit 21 includes a preamplifier and the like. A printed circuit board (not shown) is screwed to the outer surface of the bottom wall 12a of the base 12. The circuit board controls the operations of the spindle motor 18, VCM 24, and magnetic heads through the board unit 21. A circulation filter 23 is disposed on the sidewall of the base 12 and situated outside the magnetic disk 16. The filter 23 captures dust that is produced in the housing when any moving part is operated.


The magnetic disk 16 is formed with a diameter of, for example, 65 mm (2.5 inches) and has magnetic recording layers on its upper and lower surfaces, respectively. The disk 16 is coaxially fitted on a hub (not shown) of the spindle motor 18 and clamped and fixed on the hub by a clamp spring 27. Thus, the disk 16 is supported parallel to the bottom wall 12a of the base 12. The disk 16 is rotated at a predetermined speed of, for example, 5,400 or 7,200 rpm by the spindle motor 18.



FIG. 5 is a perspective view showing the HSA 22, and FIG. 6 is an exploded perspective view of the HSA. As shown in FIGS. 5 and 6, the HSA 22 is provided with a rotatable bearing portion 28, two head gimbal assemblies (HGAs) 30 extending from the bearing portion, a spacer ring 44 laminated between the HGAs, and a dummy spacer 50.


The bearing portion 28 is situated apart from the center of rotation of the magnetic disk 16 along the length of the base 12 and near the outer peripheral edge of the disk. The bearing portion 28 includes a pivot 32 set up on the bottom wall 12a of the base 12 and a cylindrical sleeve 36 coaxially supported for rotation on the pivot by a bearing 34. An annular flange 37 is formed on the upper end of the sleeve 36, while a thread portion 38 is formed on the outer periphery of its lower end portion. The sleeve 36 of the bearing portion 28 is formed with such a size, or an axial length in this case, that four HGAs at the most, for example, and spacers between adjacent pairs of HGAs can be mounted in a stack.


Since the magnetic disk 16 is set to be one in number in the present embodiment, the bearing portion 28 is provided with two HGAs 30, the number of which is smaller than four, the maximum mountable number, by two. Each HGA includes an arm 40 extending from the bearing portion 28, a suspension 42 extending from the arm, and the magnetic head 17 supported on an extended end of the suspension by a gimbal portion.


The arm 40 is a thin flat plate formed by laminating, for example, stainless steel, aluminum, and stainless steel layers to one another. A circular through hole 41 is formed on one end or proximal end of the arm 40. The suspension 42 is formed of an elongated leaf spring, and its proximal end is fixed to the distal end of the arm 40 by spot welding or adhesive bonding and extends from the arm. The suspension 42 and the arm 40 may be formed integrally of the same material.


The magnetic head 17 includes a substantially rectangular slider and a write head and a CPP-GMR read head formed on the slider and is fixed to the gimbal portion formed on the distal end portion of the suspension 42. Further, the magnetic head 17 includes four electrodes (not shown). A relay flexible printed circuit board (a relay FPC, not shown) is set on the arm 40 and the suspension 42. The magnetic head 17 is electrically connected to a main FPC 21b through the relay FPC.


The spacer ring 44 is formed of aluminum or the like having a predetermined thickness and a predetermined outer diameter. A plastic support frame 46 is molded integrally with the spacer ring 44 and extends outward from the spacer ring. A voice coil 47 of the VCM 24 is fixed to the support frame 46.


The dummy spacer 50 includes an annular spacer body 52 and a balancing portion 54 extending from the spacer body and is integrally formed of a metal such as stainless steel. The outer diameter of the spacer body 52 is equal to that of the spacer ring 44. More specifically, the outer diameter of that part of the spacer body 52 which contacts the arm 40 is equal to that of that part of the spacer ring 44 which contacts the arm. Further, a thickness T1 of the spacer body 52 is equal to the sum of those of the arms of the smaller number of HGAs than the maximum, that is, the two arms, and the spacer ring arranged between these arms.


The dummy spacer 50, the two HGAs 30, and the spacer ring 44 are fitted on the sleeve 36 of the bearing portion 28 that is passed through the bore of the spacer body 52, the through hole 41 of the arm 40, and the bore of the spacer ring, and are stacked on the flange 37 along the axis of the sleeve. The spacer body 52 of the dummy spacer 50 and the spacer ring 44 are fitted on the sleeve 36 in such a manner that they are sandwiched between the flange 37 and one of the arms 40 and between the two arms 40, respectively. Further, an annular washer 56 is fitted on the lower end portion of the sleeve 36.


The dummy spacer 50, two arms 40, spacer ring 44, and washer 56 that are fitted on the sleeve 36 are sandwiched between the flange 37 and a nut 58, which is threadedly fitted on the thread portion 38 of the sleeve 36, and are fixedly held on the outer periphery of the sleeve.


The two arms 40 are individually located on predetermined positions with respect to the circumference of the sleeve 36 and extend in the same direction from the sleeve. Thus, the two HGAs can be swung integrally with the sleeve 36 and extend parallel to the surfaces of the magnetic disk 16 so as to face each other with predetermined spacing. Further, the support frame 46 that is integral with the spacer ring 44 extends in the opposite direction to the arms 40 from the bearing portion 28. Two pin-like terminals 60 protrude from the support frame 46 and are electrically connected to the voice coil 47 through a wire (not shown) that is embedded in the frame 46.


EXAMPLES
Example 1

In this example, a magnetoresistive element was manufactured as described below.


First, respective layers from the underlayer 2 to the upper pinned layer 4 were formed on the lower electrode (LE) 1 using the flowing materials.

  • Underlayer 2: Ta [5 nm]/Ru [2 nm],
  • Anti-ferromagnetic layer 3: IrMn [7 nm],
  • Lower pinned layer 4a: Co90Fe10 [3.3 nm],
  • Anti-parallel coupling layer 4b: Ru [0.9 nm],
  • Upper pinned layer 4c: Fe50Co50 [2.5 nm].


Next, an Al film [0.9 nm] as the metal layer 9 to be converted into the oxide layer was deposited on the upper pinned layer 4c. After the deposition of the Al film [0.9 nm], Ar ions were applied to the surface of the Al film while introducing oxygen in the chamber at room temperature. After introducing oxygen was stopped, Ar ions were further applied to the surface of the Al film. In such a manner, the oxide layer 5a and the magnetic conduction column 5b penetrating the oxide layer 5a in the thickness direction and comprising at least a part of constituent elements of the upper pinned layer 4c were formed.


The oxidation conditions in this process were lower oxygen exposure conditions with a reduced oxygen flow rate or a shortened oxidation time compared to proper (or excessive) oxidation conditions for oxidizing the entire metal layer (Al) 9, and thus, the Al film was not oxidized entirely.


Another sample was prepared in such a manner that a structure was provided by stopping the processes at this stage and the protection layer was deposited on the oxide layer. The test sample was analyzed by X-ray photoelectron spectroscopy (XPS), with a result that unoxidized Al was remained in the oxide layer 5a.


Then, the resultant structure was annealed at 200 to 300° C. for 30 minutes (in-situ annealing) to form the magnetic oxide 5c comprising a part of constituent elements of the oxide layer 5a and at least a part of constituent elements of the magnetic conduction column 5b so as to cover a part of the magnetic conduction column 5b, by which the intermediate layer 5 comprising the oxide layer 5a, magnetic conduction column 5b and magnetic oxide 5c was formed.


Further, the free layer 6 and protection layer 7 were formed using the following materials, respectively, and then the upper electrode (UE) 8 was formed.

  • Free layer 6: Fe50Co50 [2.5 nm],
  • Protection layer 7: Cu [1 nm]/Ta [2 nm]/Ru [15 nm].


The resultant magnetoresistive element was annealed in a magnetic field at 290° C. for approximately one hour in order to fix the magnetization direction of the pinned layer 4.



FIG. 7 is a graph showing the relationship between the in-situ annealing temperature and MR ratio with respect to several magnetoresistive elements manufactured in Example 1. FIG. 7 shows that the magnetoresistive elements in Example 1 exhibited improved MR ratio as the in-situ annealing temperature was raised in the range of 200 to 300° C.


Further, the following experiment was performed to confirm the presence of magnetic oxide in the resultant magnetoresistive element. The magnetoresistive element was examined for the temperature dependence of the resistance change in the case where the element was cooled to 15 K while applying a field of +10 kOe in such a direction as to reverse the magnetization of the upper pinned layer in the pinned layer of the lower pinned layer, Ru layer and upper pinned layer and in the case where the element was cooled to 15 K at zero field, respectively. FIG. 8 shows the temperature dependence of the resistance change, dR(T)/dR(300 K).


As shown in FIG. 8, in the case where the magnetoresistive element was cooled to 15 K while applying a field of +10 kOe, the resistance change was decreased abruptly at approximately 150 K. This means that a magnetic oxide with a magnetic transition point at approximately 150 K exists in the magnetoresistive element. In this Example, a magnetoresistive ratio of 50% or more was obtained for an area resistance (RA) of 0.3 Ωμm2.


Although the above Example describes the case where the in-situ annealing was performed prior to the deposition of the free layer, the similar result to the above Example was also obtained in the case where the in-situ annealing was performed after the deposition of the free layer. In the case where the in-situ annealing is performed after the deposition of the free layer, a free layer in a stacked structure of Fe50Co50/Co90Fe10 may be used.


Further, another magnetoresistive element was manufactured using the following materials:

  • Underlayer 2: Ta [5 nm]/Ru [2 nm],
  • Anti-ferromagnetic layer 3: IrMn [7 nm],
  • Lower pinned layer 4a: Co90Fe10 [3.3 nm],
  • Anti-parallel coupling layer 4b: Ru [0.9 nm],
  • Upper pinned layer 4c: Fe50Co50 [2.5 nm],
  • Metal layer 9: Al [1.5 nm],
  • Free layer 6: Fe50Co50 [0.3 nm]/Cu [0.3 nm]/Fe50Co50 [4.7 nm],
  • Protection layer 7: Cu [1 nm]/Ta [2 nm]/Ru [15 nm].


The resultant magnetoresistive element exhibited similar results to those of the Example described above.


Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims
  • 1. A method of manufacturing a magnetoresistive element comprising: forming a metal layer on a first ferromagnetic layer;oxidizing the metal layer at a temperature to form an oxide layer in which unoxidized metal remains and a magnetic conduction column penetrating the oxide layer in a thickness direction and comprising at least a part of constituent elements of the first ferromagnetic layer;annealing a resultant structure at a higher temperature than the temperature at which the oxide layer is formed to convert at least a part of a periphery of the magnetic conduction column into a magnetic oxide comprising a part of constituent elements of the oxide layer and at least a part of constituent elements of the magnetic conduction column; andforming a second ferromagnetic layer.
  • 2. The method according to claim 1, wherein oxidizing the metal layer to form the oxide layer and the magnetic conduction column comprises applying an ion beam or RF plasma of a rare gas to the metal layer while supplying an oxidizing gas.
  • 3. The method according to claim 1, wherein oxidizing the metal layer to form the oxide layer and the magnetic conduction column comprises applying an ion beam or RF plasma of a rare gas to the metal layer while supplying an oxidizing gas and further comprising applying the ion beam or RF plasma of the rare gas to the oxidized metal layer without supplying the oxidizing gas.
  • 4. A magnetoresistive element comprising: a stacked film comprising first and second ferromagnetic layers, a magnetization direction of one of which ferromagnetic layers is substantially pinned in a direction and a magnetization direction of the other of which ferromagnetic layers is varied depending on an external magnetic field, and an intermediate layer between the first and second ferromagnetic layers; anda pair of electrodes provided on a bottom and a top of the stacked film and configured to pass a current perpendicularly to a film plane of the stacked film,the intermediate layer comprising: an oxide layer; a magnetic conduction column penetrating the oxide layer in a thickness direction; and a magnetic oxide covering at least a part of a periphery of the magnetic conduction column and comprising a part of constituent elements of the oxide layer and at least a part of constituent elements of the magnetic conduction column.
  • 5. The magnetoresistive element according to claim 4, wherein the first and second ferromagnetic layers comprise at least one element selected from the group consisting of Fe, Co and Ni.
  • 6. The magnetoresistive element according to claim 4, wherein the oxide layer comprises Al as a metal element.
  • 7. A magnetic head assembly comprising the magnetoresistive element according to claim 4.
  • 8. A magnetic recording apparatus comprising a magnetic recording medium and the magnetic head assembly according to claim 7.
  • 9. The method according to claim 1, wherein the magnetic oxide covers the periphery of the magnetic conduction column.
  • 10. The magnetoresistive element according to claim 4, wherein the magnetic oxide covers the periphery of the magnetic conduction column.
Priority Claims (1)
Number Date Country Kind
2008-249977 Sep 2008 JP national
US Referenced Citations (170)
Number Name Date Kind
5304975 Saito et al. Apr 1994 A
5313186 Schuhl et al. May 1994 A
5448515 Fukami et al. Sep 1995 A
5459687 Sakakima et al. Oct 1995 A
5549978 Iwasaki et al. Aug 1996 A
5668688 Dykes et al. Sep 1997 A
5715121 Sakakima et al. Feb 1998 A
5768181 Zhu et al. Jun 1998 A
5768183 Zhu et al. Jun 1998 A
5777542 Ohsawa et al. Jul 1998 A
5900324 Moroishi et al. May 1999 A
5923504 Araki et al. Jul 1999 A
5936402 Schep et al. Aug 1999 A
5949622 Kamiguchi et al. Sep 1999 A
5962080 Tan et al. Oct 1999 A
6002553 Stearns et al. Dec 1999 A
6013365 Dieny et al. Jan 2000 A
6016241 Coffey et al. Jan 2000 A
6033584 Ngo et al. Mar 2000 A
6074743 Araki et al. Jun 2000 A
6096434 Yano et al. Aug 2000 A
6114056 Inomata et al. Sep 2000 A
6117569 Lin et al. Sep 2000 A
6127045 Gill Oct 2000 A
6132892 Yoshikawa et al. Oct 2000 A
6159593 Iwasaki et al. Dec 2000 A
6205008 Gijs et al. Mar 2001 B1
6219275 Nishimura Apr 2001 B1
6275363 Gill Aug 2001 B1
6303218 Kamiguchi et al. Oct 2001 B1
6313973 Fuke et al. Nov 2001 B1
6330137 Knapp et al. Dec 2001 B1
6340533 Ueno et al. Jan 2002 B1
6348274 Kamiguchi et al. Feb 2002 B1
6353318 Sin et al. Mar 2002 B1
6368706 Iwasaki et al. Apr 2002 B1
6400537 Sakakima et al. Jun 2002 B2
6452763 Gill Sep 2002 B1
6469926 Chen Oct 2002 B1
6473275 Gill Oct 2002 B1
6495275 Kamiguchi et al. Dec 2002 B2
6517896 Horng et al. Feb 2003 B1
6519123 Sugawara et al. Feb 2003 B1
6522507 Horng et al. Feb 2003 B1
6556390 Mao et al. Apr 2003 B1
6567246 Sakakima et al. May 2003 B1
6603642 Arki et al. Aug 2003 B1
6636391 Watanabe et al. Oct 2003 B2
6674615 Hayashi Jan 2004 B2
6686068 Carey et al. Feb 2004 B2
6690163 Hoshiya et al. Feb 2004 B1
6710984 Yuasa et al. Mar 2004 B1
6720036 Tsunekawa et al. Apr 2004 B2
6759120 Jangill et al. Jul 2004 B2
6767655 Hiramoto et al. Jul 2004 B2
6770382 Chang et al. Aug 2004 B1
6853520 Fukuzawa et al. Feb 2005 B2
6882509 Chang et al. Apr 2005 B2
6903907 Hasegawa Jun 2005 B2
6905780 Yuasa et al. Jun 2005 B2
6929957 Min et al. Aug 2005 B2
6937446 Kamiguchi et al. Aug 2005 B2
6937447 Okuno et al. Aug 2005 B2
7038893 Koui et al. May 2006 B2
7046489 Kamiguchi et al. May 2006 B2
7116529 Yoshikawa et al. Oct 2006 B2
7163755 Hiramoto et al. Jan 2007 B2
7177121 Kojima et al. Feb 2007 B2
7196877 Yoshikawa et al. Mar 2007 B2
7218484 Hashimoto et al. May 2007 B2
7223485 Yuasa et al. May 2007 B2
7240419 Okuno et al. Jul 2007 B2
7301733 Fukuzawa et al. Nov 2007 B1
7304825 Funayama et al. Dec 2007 B2
7331100 Li et al. Feb 2008 B2
7372672 Nishiyama May 2008 B2
7379278 Koui et al. May 2008 B2
7390529 Li et al. Jun 2008 B2
7476414 Fukuzawa et al. Jan 2009 B2
7514117 Fukuzawa et al. Apr 2009 B2
7522390 Yuasa et al. Apr 2009 B2
7525776 Fukuzawa et al. Apr 2009 B2
7602592 Fukuzawa et al. Oct 2009 B2
7610674 Zhang et al. Nov 2009 B2
7776387 Fuji et al. Aug 2010 B2
7785662 Fuji et al. Aug 2010 B2
20010005300 Hayashi Jun 2001 A1
20010009063 Saito et al. Jul 2001 A1
20010014000 Tanaka et al. Aug 2001 A1
20010040781 Tanaka et al. Nov 2001 A1
20020048127 Fukuzawa et al. Apr 2002 A1
20020048128 Kamiguchi et al. Apr 2002 A1
20020051380 Kamiguchi et al. May 2002 A1
20020054461 Fujiwara et al. May 2002 A1
20020058158 Odagawa et al. May 2002 A1
20020073785 Prakash et al. Jun 2002 A1
20020114974 Carey et al. Aug 2002 A1
20020135935 Covington Sep 2002 A1
20020145835 Suzuki et al. Oct 2002 A1
20020150791 Yuasa et al. Oct 2002 A1
20020159201 Li et al. Oct 2002 A1
20020191355 Hiramoto et al. Dec 2002 A1
20030011463 Iwasaki et al. Jan 2003 A1
20030026049 Gill Feb 2003 A1
20030035256 Hayashi et al. Feb 2003 A1
20030049389 Tsunekawa et al. Mar 2003 A1
20030053269 Nishiyama Mar 2003 A1
20030099868 Tanahashi et al. May 2003 A1
20030104249 Okuno et al. Jun 2003 A1
20030123200 Nagasaka et al. Jul 2003 A1
20030128481 Seyama et al. Jul 2003 A1
20030156360 Kawawake et al. Aug 2003 A1
20040021990 Koui et al. Feb 2004 A1
20040121185 Fukuzawa et al. Jun 2004 A1
20040137645 Hu et al. Jul 2004 A1
20040150922 Kagami et al. Aug 2004 A1
20040169963 Okuno et al. Sep 2004 A1
20040201929 Hashimoto et al. Oct 2004 A1
20040206619 Pinarbasi Oct 2004 A1
20040246631 Dieny et al. Dec 2004 A1
20050042478 Okuno et al. Feb 2005 A1
20050068855 Morikawa et al. Mar 2005 A1
20050073778 Hasegawa et al. Apr 2005 A1
20050094317 Funayama May 2005 A1
20050094322 Fukuzawa et al. May 2005 A1
20050094327 Okuno et al. May 2005 A1
20050141148 Aikawa et al. Jun 2005 A1
20050276998 Sato Dec 2005 A1
20060002184 Hong et al. Jan 2006 A1
20060018057 Huai Jan 2006 A1
20060034022 Fukuzawa et al. Feb 2006 A1
20060050444 Fukuzawa et al. Mar 2006 A1
20060098353 Fukuzawa et al. May 2006 A1
20060114620 Sbiaa et al. Jun 2006 A1
20060164764 Kamiguchi et al. Jul 2006 A1
20070070556 Zhang et al. Mar 2007 A1
20070081276 Fukuzawa et al. Apr 2007 A1
20070092639 Fuji et al. Apr 2007 A1
20070159733 Hashimoto et al. Jul 2007 A1
20070172690 Kim et al. Jul 2007 A1
20070188936 Zhang et al. Aug 2007 A1
20070188937 Carey et al. Aug 2007 A1
20070202249 Yuasa et al. Aug 2007 A1
20070253122 Fukuzawa et al. Nov 2007 A1
20070259213 Hashimoto et al. Nov 2007 A1
20080005891 Yuasa et al. Jan 2008 A1
20080008909 Fuji et al. Jan 2008 A1
20080013218 Fuke et al. Jan 2008 A1
20080062577 Fukuzawa et al. Mar 2008 A1
20080068764 Fukuzawa et al. Mar 2008 A1
20080080098 Fuke et al. Apr 2008 A1
20080102315 Fukuzawa et al. May 2008 A1
20080192388 Zhang et al. Aug 2008 A1
20080204944 Aikawa et al. Aug 2008 A1
20080239590 Fuke et al. Oct 2008 A1
20080278864 Zhang et al. Nov 2008 A1
20090059441 Zhang et al. Mar 2009 A1
20090061105 Fukuzawa et al. Mar 2009 A1
20090091864 Carey et al. Apr 2009 A1
20090091865 Zhang et al. Apr 2009 A1
20090104475 Fuji et al. Apr 2009 A1
20090109581 Fukuzawa et al. Apr 2009 A1
20090141408 Fukuzawa et al. Jun 2009 A1
20090162698 Fukuzawa et al. Jun 2009 A1
20090225477 Fukuzawa et al. Sep 2009 A1
20100037453 Zhang et al. Feb 2010 A1
20100091412 Yuasa et al. Apr 2010 A1
20100091414 Yuasa et al. Apr 2010 A1
20100091415 Yuasa et al. Apr 2010 A1
20100092803 Yuasa et al. Apr 2010 A1
Foreign Referenced Citations (64)
Number Date Country
1431651 Jul 2003 CN
1183517 Jan 2005 CN
1746980 Mar 2006 CN
0 687 917 Dec 1995 EP
0 877 398 Nov 1998 EP
1 328 027 Jul 2003 EP
1 400 957 Mar 2004 EP
1 548 762 Jun 2005 EP
1 607 941 Dec 2005 EP
1 626 393 Feb 2006 EP
2 390 168 Dec 2003 GB
08-049063 Feb 1996 JP
09-116212 May 1997 JP
09-306733 Nov 1997 JP
10-173252 Jun 1998 JP
10-324969 Dec 1998 JP
11-121832 Apr 1999 JP
11-154609 Jun 1999 JP
11-238923 Aug 1999 JP
11-296820 Oct 1999 JP
2000-137906 May 2000 JP
2000-156530 Jun 2000 JP
2000-188435 Jul 2000 JP
2000-215414 Aug 2000 JP
2000-228004 Aug 2000 JP
2000-293982 Oct 2000 JP
2001-094173 Apr 2001 JP
2001-143227 May 2001 JP
2001-176027 Jun 2001 JP
2001-229511 Aug 2001 JP
2001-237471 Aug 2001 JP
2001-358380 Dec 2001 JP
2002-076473 Mar 2002 JP
2002-124721 Apr 2002 JP
2002-150512 May 2002 JP
2002-204010 Jul 2002 JP
2002-208744 Jul 2002 JP
2003-086866 Mar 2003 JP
2003-110168 Apr 2003 JP
2003-152243 May 2003 JP
2003-204095 Jul 2003 JP
2004-006589 Jan 2004 JP
2004-153248 May 2004 JP
2004-214234 Jul 2004 JP
2005-097693 Apr 2005 JP
2005-136309 May 2005 JP
2005-166896 Jun 2005 JP
2005-339784 Dec 2005 JP
2005-353236 Dec 2005 JP
2006-019743 Jan 2006 JP
2006-049426 Feb 2006 JP
2006-054257 Feb 2006 JP
2006-114610 Apr 2006 JP
2006-135253 May 2006 JP
2006-319343 Nov 2006 JP
2007-221135 Aug 2007 JP
10-0302029 Jun 2001 KR
2001-0081971 Aug 2001 KR
2002-0015295 Feb 2002 KR
10-2005-0027159 Mar 2005 KR
10-2005-0118649 Dec 2005 KR
10-2006-0050327 May 2006 KR
9747982 Dec 1997 WO
03032338 Apr 2003 WO
Related Publications (1)
Number Date Country
20100079918 A1 Apr 2010 US