U.S. patent application number 12/320669 was filed with the patent office on 2009-07-30 for magnetoresistive element and method of manufacturing the same.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Yoshihiko Fuji, Hideaki Fukuzawa, Shuichi Murakami, Hiromi Yuasa.
Application Number | 20090190264 12/320669 |
Document ID | / |
Family ID | 40898967 |
Filed Date | 2009-07-30 |
United States Patent
Application |
20090190264 |
Kind Code |
A1 |
Fukuzawa; Hideaki ; et
al. |
July 30, 2009 |
Magnetoresistive element and method of manufacturing the same
Abstract
A magnetoresistive element includes a magnetoresistive film
including a magnetization pinned layer, a magnetization free layer,
an intermediate layer arranged between the magnetization pinned
layer and the magnetization free layer, a cap layer arranged on the
magnetization pinned layer or on the magnetization free layer, and
a functional layer arranged in the magnetization pinned layer, in
the magnetization free layer, in the interface between the
magnetization pinned layer and the intermediate layer, in the
interface between the intermediate layer and the magnetization free
layer, or in the interface between the magnetization pinned layer
or the magnetization free layer and the cap layer, and a pair of
electrodes which pass a current perpendicularly to a plane of the
magnetoresistive film, in which the functional layer is formed of a
layer including nitrogen and a metal material containing 5 atomic %
or more of Fe.
Inventors: |
Fukuzawa; Hideaki;
(Kawasaki-shi, JP) ; Murakami; Shuichi;
(Fuchu-shi, JP) ; Yuasa; Hiromi; (Kawasaki-shi,
JP) ; Fuji; Yoshihiko; (Kawasaki-shi, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
40898967 |
Appl. No.: |
12/320669 |
Filed: |
January 30, 2009 |
Current U.S.
Class: |
360/246.4 ;
257/421; 257/E29.323; 427/130 |
Current CPC
Class: |
G11C 11/16 20130101;
H01L 43/10 20130101; H01L 43/12 20130101; G01R 33/093 20130101;
G01R 33/04 20130101; G11B 2005/3996 20130101; H01L 43/08 20130101;
G11C 11/161 20130101; G11C 11/1675 20130101; H01L 27/228 20130101;
B82Y 10/00 20130101; G11B 5/3906 20130101; G11C 11/1673 20130101;
B82Y 25/00 20130101 |
Class at
Publication: |
360/246.4 ;
427/130; 257/421; 257/E29.323 |
International
Class: |
G11B 5/48 20060101
G11B005/48; B05D 1/38 20060101 B05D001/38; H01L 29/82 20060101
H01L029/82 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2008 |
JP |
2008-019366 |
Claims
1. A magnetoresistive element comprising: a magnetoresistive film
comprising a magnetization pinned layer a magnetization direction
of which is substantially pinned in one direction, a magnetization
free layer a magnetization direction of which is varied depending
on an external magnetic field, an intermediate layer arranged
between the magnetization pinned layer and the magnetization free
layer, a cap layer arranged on the magnetization pinned layer or on
the magnetization free layer, and a functional layer arranged in
the magnetization pinned layer, in the magnetization free layer, in
the interface between the magnetization pinned layer and the
intermediate layer, in the interface between the intermediate layer
and the magnetization free layer, or in the interface between the
magnetization pinned layer or the magnetization free layer and the
cap layer; and a pair of electrodes which pass a current
perpendicularly to a plane of the magnetoresistive film, the
functional layer being formed of a layer comprising nitrogen and a
metal material containing 5 atomic % or more of Fe.
2. The magnetoresistive element according to claim 1, wherein the
functional layer has a crystalline orientation dispersion angle of
5 degrees or less.
3. The magnetoresistive element according to claim 1, wherein the
magnetization pinned layer or the magnetization free layer has a
crystalline orientation dispersion angle of 5 degrees or less.
4. The magnetoresistive element according to claim 1, wherein the
functional layer is formed of an alloy including Fe and Co.
5. The magnetoresistive element according to claim 1, wherein the
functional layer has a thickness from 0.3 nm to 5 nm.
6. The magnetoresistive element according to claim 1, wherein the
functional layer has a Fe content of 50 atomic % or more.
7. The magnetoresistive element according to claim 1, wherein the
intermediate layer is a metal layer comprising an element selected
from the group consisting of Au, Ag and Cu.
8. The magnetoresistive element according to claim 1, wherein the
intermediate layer comprises an insulating layer containing
nitrogen or oxygen and a current path penetrating the insulating
layer.
9. The magnetoresistive element according to claim 8, wherein the
current path comprises an element selected from the group
consisting of Au, Ag, Cu, Fe, Co and Ni.
10. The magnetoresistive element according to claim 8, wherein the
current path has a diameter of 1 nm or more and 7 nm or less.
11. A magnetoresistive element comprising: a magnetoresistive film
comprising a first magnetization free layer a magnetization
direction of which is varied depending on an external magnetic
field, a second magnetization free layer a magnetization direction
of which is varied depending on an external magnetic field, an
intermediate layer arranged between the first magnetization free
layer and the second magnetization free layer, and a functional
layer arranged in the first magnetization free layer, in the second
magnetization free layer, in the interface between the first
magnetization free layer and the intermediate layer, in the
interface between the intermediate layer and the second
magnetization free layer, or in the interface of the second
magnetization free layer opposite to the interface that is in
contact with the intermediate layer; and a pair of electrodes which
pass a current perpendicularly to a plane of the magnetoresistive
film, the functional layer being formed of a layer comprising
nitrogen and a metal material containing 5 atomic % or more of
Fe.
12. The magnetoresistive element according to claim 11, wherein the
functional layer has a crystalline orientation dispersion angle of
5 degrees or less.
13. The magnetoresistive element according to claim 11, wherein the
intermediate layer is a metal layer comprising an element selected
from the group consisting of Au, Ag and Cu.
14. The magnetoresistive element according to claim 11, wherein the
intermediate layer comprises an insulating layer containing
nitrogen or oxygen and a current path penetrating the insulating
layer.
15. A magnetic head gimbal assembly comprising the magnetoresistive
element of claim 1.
16. A magnetic recording apparatus comprising the magnetic head
gimbal assembly of claim 15.
17. A method of manufacturing a magnetoresistive element comprising
a magnetoresistive film including a functional layer arranged in a
magnetization pinned layer, in a magnetization free layer, in an
interface between the magnetization pinned layer and an
intermediate layer, in an interface between the intermediate layer
and the magnetization free layer, or in an interface between the
magnetization pinned layer or the magnetization free layer and a
cap layer, the method comprising: depositing a metal layer
containing 5 atomic % or more of Fe and exposing the metal layer to
a nitrogen atmosphere to form the functional layer; and repeating
the depositing step two or more times.
18. The method according to claim 17, wherein a thickness of the
functional layer in T nanometers and a number of times N, by which
the modules are repeated, satisfies the following formula:
N.gtoreq.(T/0.5).times.x, where x is a constant of 1 to 2, and
T.gtoreq.1.
19. The method according to claim 17, wherein a thickness of the
metal layer deposited in one module is 1 nm or less.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2008-019366,
filed Jan. 30, 2008, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a magnetoresistive element
which detects magnetism by passing a sense current in a direction
perpendicular to the plane of a magnetoresistive film, and a method
of manufacturing the same.
[0004] 2. Description of the Related Art
[0005] At present, magnetic recording apparatuses such as HDD (hard
disk drive) are used in applications of personal computers,
portable audio/video players, video cameras and car navigation
system. A further increase in recording capacity of HDD is desired
with the expansion of applications. For increasing recording
capacity without increasing the volume of HDD, further improvement
in recording density per unit area is needed.
[0006] The area of one bit recorded in a magnetic recording medium
is decreased with improvement in recording density. As a result, a
magnetic field signal from the recording medium becomes very weak
to make a conventional read head difficult to distinguish between
"0" and "1". Accordingly, a read head having high magnetic field
sensitivity is required with improvement in recording density.
[0007] The performance of magnetic devices, particularly magnetic
heads, has been drastically improved by using the giant
magnetoresistive effect (GMR) and tunneling magnetoresistive effect
(TMR). Particularly, application of a spin-valve film (SV film) to
magnetic heads and magnetic random access memories (MRAMs) has
brought about marked technical improvement in the field of magnetic
devices.
[0008] The "spin-valve film" is a stacked film called a
spin-dependent scattering unit having a structure in which a
nonmagnetic 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 antiferromagnetic
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
magnetoresistace change can be produced by a change of the relative
angle between the magnetization directions of the pinned layer and
the free layer.
[0009] Magnetoresistive elements using the spin-valve film include
CIP (current-in-plane)-GMR element, CPP
(current-perpendicular-to-plane)-GMR element, and TMR (tunneling
magnetoresistance) element. In the CIP-GMR element, a sense current
is conducted in parallel to the plane of the spin-valve film, and
in the CPP-GMR and TMR elements, a sense current is conducted in a
direction substantially perpendicular to the plane of the
spin-valve film. The trend of high recording density heads is
toward the system of conducting a sense current perpendicularly to
the plane.
[0010] Conventionally, there is known a magnetoresistive element
comprising a magnetoresistive film including a pinned layer, a free
layer, a spacer layer, and a thin film layer having an oxide,
nitride or oxynitride formed in the pinned layer, in the free
layer, in the interface between the pinned layer and the spacer
layer, or in the interface between the free layer and the spacer
layer, and a pair of electrodes that pass a sense current in a
direction approximately perpendicular to the plane of the
magnetoresistive film. See JP-A 2004-6589 (KOKAI). The thin film
layer is permeable preferentially to either up-spin electrons or
down-spin electrons, thus contributing to production of higher
magnetoresistive ratio (MR ratio). Such thin film layer is called a
spin filter layer (SF layer). Even if the SF layer is small in
thickness, the SF layer can generate a difference between up-spin
electron permeation and down-spin electron permeation and is thus
advantageous to narrower head gap.
[0011] However, it came to be found that the conventional spin
filter layer is insufficient in the difference between up-spin
electron permeation and down-spin electron permeation and there is
room to enable higher MR ratio.
BRIEF SUMMARY OF THE INVENTION
[0012] According to an aspect of the present invention, there is
provided a magnetoresistive element comprising:
[0013] a magnetoresistive film comprising a magnetization pinned
layer a magnetization direction of which is substantially pinned in
one direction, a magnetization free layer a magnetization direction
of which is varied depending on an external magnetic field, an
intermediate layer arranged between the magnetization pinned layer
and the magnetization free layer, a cap layer arranged on the
magnetization pinned layer or on the magnetization free layer, and
a functional layer arranged in the magnetization pinned layer, in
the magnetization free layer, in the interface between the
magnetization pinned layer and the intermediate layer, in the
interface between the intermediate layer and the magnetization free
layer, or in the interface between the magnetization pinned layer
or the magnetization free layer and the cap layer; and
[0014] a pair of electrodes which pass a current perpendicularly to
a plane of the magnetoresistive film,
[0015] the functional layer being formed of a layer comprising
nitrogen and a metal material containing 5 atomic % or more of
Fe.
[0016] According to another aspect of the present invention, there
is provided a magnetoresistive element comprising:
[0017] a magnetoresistive film comprising a first magnetization
free layer a magnetization direction of which is varied depending
on an external magnetic field, a second magnetization free layer a
magnetization direction of which is varied depending on an external
magnetic field, an intermediate layer arranged between the first
magnetization free layer and the second magnetization free layer,
and a functional layer arranged in the first magnetization free
layer, in the second magnetization free layer, in the interface
between the first magnetization free layer and the intermediate
layer, in the interface between the intermediate layer and the
second magnetization free layer, or in the interface of the second
magnetization free layer opposite to the interface that is in
contact with the intermediate layer; and
[0018] a pair of electrodes which pass a current perpendicularly to
a plane of the magnetoresistive film,
[0019] the functional layer being formed of a layer comprising
nitrogen and a metal material containing 5 atomic % or more of
Fe.
[0020] According to still another aspect of the present invention,
there is provided a method of manufacturing a magnetoresistive
element comprising a magnetization pinned layer a magnetization
direction of which is substantially pinned in one direction, a
magnetization free layer a magnetization direction of which is
varied depending on an external magnetic field, an intermediate
layer arranged between the magnetization pinned layer and the
magnetization free layer, a cap layer arranged on the magnetization
pinned layer or on the magnetization free layer, and a functional
layer arranged in the magnetization pinned layer, in the
magnetization free layer, in the interface between the
magnetization pinned layer and the intermediate layer, in the
interface between the intermediate layer and the magnetization free
layer, or in the interface between the magnetization pinned layer
or the magnetization free layer and the cap layer, and a pair of
electrodes which pass a current perpendicularly to a plane of the
magnetoresistive film, the method comprising:
[0021] repeating two or more modules comprising depositing a metal
layer containing 5 atomic % or more of Fe and exposing the metal
layer to a nitrogen atmosphere to form the functional layer.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0022] FIGS. 1A and 1B are cross-sectional views of
magnetoresistive elements according to an embodiment of the present
invention;
[0023] FIGS. 2A and 2B are cross-sectional views of
magnetoresistive elements according to an embodiment of the present
invention;
[0024] FIGS. 3A and 3B are cross-sectional views of
magnetoresistive elements according to an embodiment of the present
invention;
[0025] FIGS. 4A to 4E are cross-sectional views showing a method of
manufacturing a magnetoresistive element according to an embodiment
of the present invention;
[0026] FIG. 5 is a view of an apparatus used in manufacturing a
magnetoresistive element according to an embodiment of the present
invention;
[0027] FIG. 6 is a view showing an example of a conversion
treatment chamber in FIG. 5;
[0028] FIG. 7 is a graph showing the area resistances (RA) and MR
ratios of the magnetoresistive elements in Examples 1 to 4 and
Comparative Example 1;
[0029] FIG. 8 is a graph showing the relationship between the Fe
concentration and MR ratio of a metal matrix before exposure to
nitrogen or oxygen;
[0030] FIG. 9 is a cross-sectional view of a magnetic head
according to an embodiment of the present invention;
[0031] FIG. 10 is a cross-sectional view of a magnetic head
according to an embodiment of the present invention;
[0032] FIG. 11 is a perspective view of a magnetic recording
apparatus according to an embodiment of the present invention;
[0033] FIG. 12 is a perspective view of a magnetic head gimbal
assembly according to an embodiment of the present invention;
[0034] FIG. 13 is a view showing an example of a matrix structure
of a magnetic memory according to an embodiment of the present
invention;
[0035] FIG. 14 is a view showing another example of a matrix
structure of a magnetic memory according to an embodiment of the
present invention;
[0036] FIG. 15 is a cross-sectional view showing a main part of the
magnetic memory according to the embodiment of the present
invention; and
[0037] FIG. 16 is a cross-sectional view taken along the A-A' line
in FIG. 15.
DETAILED DESCRIPTION OF THE INVENTION
[0038] The inventors found that a magnetoresistive element in a
system of passing a sense current perpendicularly to the plane
thereof can realize a high MR ratio by arranging a functional
layer, i.e., a spin filter layer or a SF layer, containing nitrogen
and a metal material containing 5% or more of Fe, in a
magnetization pinned layer, in a magnetization free layer, in the
interface between the magnetization pinned layer and an
intermediate layer, in the interface between the intermediate layer
and the magnetization free layer, or in the interface between the
magnetization pinned layer or the magnetization free layer and a
cap layer.
[0039] The inventors also found that the magnetoresistive element
realizing a high MR ratio as described above can be manufactured by
improving a method of forming the functional layer (SF layer).
[0040] In the conventional method, a metal layer is deposited on an
underlayer and then subjected to nitriding treatment to convert the
metal layer into a nitride or oxynitride, thereby forming an SF
layer. In this method, high conversion energy is not applied to
constituent atoms of the metal layer, and thus it is considered
that the metal layer is not converted into a nitride or oxynitride
over the whole thickness.
[0041] In the method of manufacturing a magnetoresistive element
according to an embodiment of the invention, the functional layer
(SF layer) is formed by repeating two or more modules each
comprising depositing a metal layer containing 5 atomic % or more
of Fe and exposing the metal layer to a nitrogen atmosphere. In
this case, a thin metal layer is subjected to nitriding treatment
where higher conversion energy can be applied to each of atoms of
the metal layer, and thus the metal layer can be converted into a
nitride over the whole thickness to improve the function of the SF
layer. The method of manufacturing the magnetoresistive element
will be described later in more detail with reference to FIG.
4.
[0042] Hereinafter, the magnetoresistive element according to an
embodiment of the invention will be described with reference to the
drawings. In this specification, all drawings are schematic
illustrations, and the sizes (thickness etc.) of each constituent
element and proportions among constituent elements are different
from actual ones.
[0043] Each of the magnetoresistive elements shown in FIGS. 1A and
1B, FIGS. 2A and 2B, and FIGS. 3A and 3B has a structure in which a
lower electrode 11, a magnetoresistive film SV and an upper
electrode 20 are stacked on a substrate (not shown).
[0044] FIGS. 1A and 1B are perspective views showing examples of a
magnetoresistive element having SF layer 21 arranged in a free
layer.
[0045] The magnetoresistive film SV in FIG. 1A has a structure in
which an underlayer 12, a pinning layer 13, a pinned layer 14, a
lower metal layer 15, a spacer layer 16, an upper metal layer 17, a
free layer 18 and a cap layer 19 are stacked. The pinned layer 14
has a structure in which a lower pinned layer 141, a magnetic
coupling layer 142 and an upper pinned layer 143 are stacked. The
spacer layer 16 has a current-confined path (CCP) structure
including an insulating layer 161 and current paths 162 penetrating
the insulating layer 161. The CCP structure including the lower
metal layer 15, the spacer layer 16 and the upper metal layer 17
may be assumed as a spacer layer in a broad sense. The free layer
18 has a structure in which a lower free layer 181, an SF layer 21
and an upper free layer 182 are stacked.
[0046] The magnetoresistive film SV in FIG. 1B has the same
structure as in FIG. 1A except that the spacer layer 16 is formed
of a metal layer, and the lower metal layer 15 and the upper metal
layer 17 are omitted.
[0047] FIGS. 2A and 2B are perspective views showing examples of a
magnetoresistive element having an SF layer 22 arranged in an upper
pinned layer. In FIG. 2A, a spacer layer 16 has a CCP structure. In
FIG. 2B, a spacer layer 16 is formed of a metal layer.
[0048] The magnetoresistive film SV in FIG. 2A has the same
structure as in FIG. 1A except that the upper pinned layer has a
structure in which a first upper pinned layer 144, an SF layer 22
and a second upper pinned layer 145 are stacked, and the free layer
18 is formed of a single magnetic layer.
[0049] The magnetoresistive film SV in FIG. 2B has the same
structure as in FIG. 2A except that the spacer layer 16 consists of
a metal layer, and the lower metal layer 15 and the upper metal
layer 17 are omitted.
[0050] FIGS. 3A and 3B are perspective views showing examples of a
magnetoresistive element having an SF layer 22 arranged in an upper
pinned layer and an SF layer 21 arranged in a free layer 18. In
FIG. 3A, a spacer layer 16 has a CCP structure. In FIG. 3B, a
spacer layer 16 is formed of a metal layer. The other structure is
the same as described with reference to FIGS. 1A and 1B and FIGS.
2A and 2B.
[0051] Hereinafter, components of the magnetoresistive element will
be described.
[0052] The lower electrode 11 and the upper electrode 20 are a pair
of electrodes for conducting a current in a direction perpendicular
to the spin valve film SV. Application of a voltage across the
lower electrode 11 and the upper electrode 20 passes a sense
current in the spin-valve film along a direction perpendicular to
the plane. Magnetism can be sensed by detecting a change in
resistance attributable to the magnetoresistive effect by
conducting the sense current. As the lower electrode 11, a metal
having relatively low electrical resistance, for example NiFe or
Cu, is used for conducting a current in the magnetoresistive
element.
[0053] The underlayer 12 functions as a buffer layer and a seed
layer, for example. The buffer layer is a layer for alleviating
roughness on the surface of the lower electrode 11. The seed layer
is a layer for controlling the crystalline orientation and the
crystal grain size of the spin-valve film deposited thereon.
[0054] As the buffer layer, Ta, Ti, W, Zr, Hf, Cr or an alloy
thereof can be used. The thickness of the buffer layer is
preferably approximately 2 nm to 10 nm, more preferably
approximately 3 nm to 5 nm. If the buffer layer is too thin, it
loses the buffer effect. On the other hand, if the buffer layer is
too thick, it increases series resistance that does not contribute
to an MR ratio. If the seed layer deposited on the buffer layer has
the buffer effect, the buffer layer need not necessarily be formed.
A preferable example of the buffer layer includes Ta of about 3 nm
in thickness.
[0055] The seed layer may be of any material as long as it is
possible to control the crystalline orientation of a layer to be
deposited thereon. As the seed layer, a metal layer or the like
having an fcc structure (face-centered cubic structure), hcp
structure (hexagonal close-packed structure) or bcc structure
(body-centered cubic structure) is preferable. For example, by
using Ru having the hcp structure or NiFe having the fcc structure
as the seed layer, the crystalline orientation of the spin-valve
film formed thereon can be fcc (111) orientation. Further, the
crystalline orientation of the pinning layer 13 such as IrMn can be
improved. Besides the materials described above, it is also
possible to employ Cr, Zr, Ti, Mo, Nb, W or alloys thereof. For
sufficiently exhibiting a function of improving crystalline
orientation, the thickness of the seed layer is preferably 1 to 5
nm, more preferably 1.5 to 3 nm. If the seed layer is too thin,
effects such as controlling the crystalline orientation will be
lost. On the other hand, if the seed layer is too thick, it leads
to increase in series resistance, and may further cause
irregularity of an interface of the spin-valve film. A preferable
example of the seed layer includes Ru of about 2 nm in
thickness.
[0056] Crystalline orientation of the spin-valve film and the
pinning layer 13 can be measured by X-ray diffraction. If half
value widths of rocking curves at an fcc (111) peak or bcc (110)
peak of the spin-valve film or an fcc (111) peak of the pinning
layer 13 (IrMn) is 3.5 degrees to 6 degrees, favorable crystalline
orientation can be obtained. The orientation dispersion angle can
also be determined from a diffraction spot using a cross-sectional
TEM.
[0057] As the seed layer, an NiFe-based alloy such as
Ni.sub.xFe.sub.100-x (x=90% to 50%, preferably 75% to 85%) or
(Ni.sub.xFe.sub.100-x).sub.100-yX.sub.y (X=Cr, V, Nb, Hf, Zr, Mo)
prepared by adding a third element X to NiFe so as to be made
nonmagnetic can also be used instead of Ru. With the NiFe-based
seed layer, a favorable crystalline orientation can be obtained
relatively easily, and the half value width of a rocking curve
measured in the same manner as described above can be 3 to 5
degrees.
[0058] The seed layer has not only the function to improve the
crystalline orientation but also the function to control the
crystal grain size in the layer formed thereon. The crystal grain
size in the layer formed on the seed layer can be determined by
cross-sectional TEM or the like. In the case of a bottom-type
spin-valve film where the pinned layer 14 is located lower than the
spacer layer 16, the crystal grain size of the pinning layer 13
(antiferromagnetic layer) or the pinned layer 14 (magnetization
pinned layer) formed on the seed layer is determined.
[0059] For a read head adapted to high density recording, an
element size is 100 nm or less, for example. When the ratio of the
crystal grain size to the element size is high and the number of
crystal grains per element area is low, dispersion of element
characteristics may be caused and thus a too large crystal grain
size is not so favorable. In particular, for the CCP-CPP element
having current paths, increasing the crystal grain size is not so
favorable. When the crystal grain size is too small, it is
generally made difficult to maintain a good crystalline
orientation. Accordingly, the crystal grain size of the spin-valve
film is preferably in the range of 5 to 40 nm, more preferably in
the range of 5 to 20 nm. When the crystal grain size is in this
range, a high MR ratio can be realized without dispersion of
characteristics even when the size of the magnetoresistive element
is reduced.
[0060] For attaining a crystal grain size in this range, Ru of
about 2 nm in thickness is preferably used as the seed layer. When
(Ni.sub.xFe.sub.100-x).sub.100-yX.sub.y (X=Cr, V, Nb, Hf, Zr, Mo)
is used as the seed layer, the composition y of the third element X
is preferably about 0 to 30%, including the case of y is 0%.
[0061] On the other hand, an element having a size of 100 nm or
more is used sometimes in application to MRAM etc., where a crystal
grain size as large as 40 nm or so may not be problematic. That is,
a large crystal grain size may be used in the seed layer. To
increase the crystal grain size to 40 nm or more, it is preferable
to use, as a material of the seed layer, an alloy containing a
large amount of Cr of about 35 to 45% based on NiFeCr and
exhibiting a boundary phase between fcc and bcc or an alloy having
a bcc structure.
[0062] The pinning layer 13 has a function of imparting
unidirectional anisotropy to a ferromagnetic layer serving as a
pinned layer 14 to be deposited thereon, thereby pinning
magnetization of the ferromagnetic layer. As the material of the
pinning layer 13, antiferromagnetic materials such as IrMn, PtMn,
PdPtMn and RuRhMn can be used. Among them, IrMn is advantageous for
application to heads adapted to high recording density. IrMn can
impart unidirectional anisotropy with a thinner film than PtMn and
is suitable for reducing a gap necessary for high density
recording.
[0063] In order to impart sufficiently intense unidirectional
anisotropy, the thickness of the pinning layer 13 is set
appropriately. When the material of the pinning layer 13 is PtMn or
PdPtMn, the thickness thereof is preferably approximately 8 to 20
nm, more preferably 10 to 15 nm. When the material of the pinning
layer 13 is IrMn, it is possible to impart unidirectional
anisotropy even with a thinner film than PtMn or the like, and the
thickness thereof is preferably 3 to 12 nm, more preferably 4 to 10
nm. A preferable example of the pinning layer includes IrMn of
about 7 nm in thickness.
[0064] As the pinning layer 13, a hard magnetic layer may be used
instead of the antiferromagnetic layer. As the hard magnetic layer,
for example, CoPt (Co=50 to 85%),
(Co.sub.xPt.sub.100-x).sub.100-yCr.sub.y (x=50 to 85%, y=0 to 40%),
FePt (Pt=40 to 60%) can be used. The hard magnetic layer,
particular CoPt, has relatively smaller specific resistance and is
thus capable of suppressing increase in series resistance and area
resistance RA.
[0065] A preferable example of the pinned layer 14 includes a
synthetic pinned layer constituted of a lower pinned layer 141 such
as Co.sub.90Fe.sub.10 [3.5 nm], a magnetic coupling layer 142 such
as Ru, and an upper pinned layer 143 such as (Fe.sub.50Co.sub.50 [1
nm]/Cu [0.25 nm]).times.2/Fe.sub.50Co.sub.50 [1 nm]. The pinning
layer 13 such as IrMn and the lower pinned layer 141 immediately
thereon are exchange-coupled so as to have unidirectional
anisotropy. The lower pinned layer 141 and the upper pinned layer
143 above and below the magnetic coupling layer 142 are strongly
magnetically coupled so that the magnetization directions thereof
are in antiparallel to each other.
[0066] For example, a Co.sub.xFe.sub.100-x alloy (x=0 to 100%) or
Ni.sub.xFe.sub.100-x alloy (x=0 to 100%), or alloys prepared by
adding a nonmagnetic element to the above alloys can be used as the
material of the lower pinned layer 141. A single element of Co, Fe,
Ni or an alloy thereof may be used as the material of the lower
pinned layer 141.
[0067] It is preferable that the magnetic thickness, i.e.,
(saturation magnetization Bs).times.(thickness t) or a product of
Bs with t of the lower pinned layer 141 is substantially equal to
the magnetic thickness of the upper pinned layer 143. Specifically,
it is preferable that the magnetic thickness of the upper pinned
layer 143 and the magnetic thickness of the lower pinned layer 141
correspond with each other. As an example, when the upper pinned
layer 143 is (Fe.sub.50Co.sub.50 [1 nm]/Cu [0.25
nm]).times.2/Fe.sub.50Co.sub.50 [1 nm], the saturation
magnetization of the FeCo in a thin film is approximately 2.2 T, so
that the magnetic thickness is 2.2 T.times.3 nm=6.6 T nm. Since the
saturation magnetization of Co.sub.90Fe.sub.10 is approximately 1.8
T, the thickness t of the lower pinned layer 141 which provides the
magnetic thickness equal to the above value is 6.6 T nm/1.8 T=3.66
nm. Therefore, it is desirable to use Co.sub.90 Fe.sub.10 with a
thickness of approximately 3.6 nm. When IrMn is used as the pinning
layer 13, the composition of the lower pinned layer 141 preferably
has a Fe concentration slightly higher than Co.sub.90Fe.sub.10.
Specifically, Co.sub.75Fe.sub.25 or the like is a preferable
example.
[0068] The thickness of the magnetic layer used for the lower
pinned layer 141 is preferably approximately 1.5 to 4 nm. It is
based on views of unidirectional anisotropy magnetic field
intensity by the pinning layer 13 such as IrMn and
antiferromagnetic coupling magnetic field intensity of the lower
pinned layer 141 and the upper pinned layer 143 via the magnetic
coupling layer 142 such as Ru. If the lower pinned layer 141 is too
thin, the MR ratio becomes small. On the other hand, if the lower
pinned layer 141 is too thick, it becomes difficult to obtain a
sufficient unidirectional anisotropy magnetic field necessary for
operating a device. A preferable example is a Co.sub.75Fe.sub.25
with a thickness of 3.6 nm.
[0069] The magnetic coupling layer 142 such as Ru has a function of
forming a synthetic pinned structure through antiferromagnetic
coupling between the upper and lower magnetic layers, i.e., lower
pinned layer 141 and upper pinned layer 143. The thickness of an Ru
layer as the magnetic coupling layer 142 is preferably 0.8 to 1 nm.
Note that any material other than Ru may be used as long as it
contributes to sufficient antiferromagnetic coupling between the
upper and lower magnetic layers. Instead of the thickness 0.8 to 1
nm corresponding to the second peak of RKKY
(Ruderman-Kittel-Kasuya-Yoshida) coupling, a thickness 0.3 to 0.6
nm corresponding to the first peak of the RKKY coupling can also be
used. An example is Ru of approximately 0.9 nm in thickness by
which stable characteristics can be obtained through more reliable
coupling.
[0070] A magnetic layer such as (Fe.sub.50Co.sub.50 [1 nm]/Cu [0.25
nm]).times.2/Fe.sub.50Co.sub.50 [1 nm] can be used as an example of
the upper pinned layer 143. The upper pinned layer 143 forms part
of a spin-dependent scattering unit. The upper pinned layer 143 is
a magnetic layer contributing directly to the MR effect, and its
constituent material and thickness are both important for obtaining
a high MR ratio. In particular, the magnetic material located at an
interface with the spacer layer 16 is important in terms of
contribution to spin-dependent interface scattering.
[0071] A magnetic material having the bcc structure, for example,
is preferably used as the upper pinned layer 143. When a magnetic
material having the bcc structure is used as the upper pinned layer
143, it provides a large spin-dependent interface scattering
effect, so that a high MR ratio can be realized. The FeCo-based
alloy having the bcc structure includes Fe.sub.xCo.sub.100-x (x=30
to 100%) and an alloy having an additive element added to
Fe.sub.xCo.sub.100-x. In particular, Fe.sub.40Co.sub.60 to
Fe.sub.60Co.sub.40 satisfying various characteristics, and
Fe.sub.50Co.sub.50 is a preferable material above all.
[0072] When the upper pinned layer 143 is formed of a magnetic
layer having the bcc structure with which a high MR ratio is easily
realized, the total thickness of this magnetic layer is preferably
1.5 nm or more. This is for keeping the bcc structure stable. Since
a metal material used in the spin-valve film often has the fcc or
fct structure, it is possible that only the upper pinned layer 143
may be in the bcc structure. Therefore, if the upper pinned layer
143 is too small in thickness, it becomes difficult to keep the bcc
structure stable, and the high MR ratio cannot be obtained. The
film of (Fe.sub.50Co.sub.50 [1 nm]/Cu [0.25
nm]).times.2/Fe.sub.50Co.sub.50 [1 nm], which is mentioned as an
example of the upper pinned layer 143, is constituted of FeCo with
a total thickness of 3 nm and Cu of 0.25 nm layered on every 1 nm
of FeCo, with the total thickness of 3.5 nm. On the other hand, the
thickness of the upper pinned layer 143 is preferably 5 nm or less.
This is for obtaining a large pinned magnetic field. In order to
achieve both the large pinned magnetic field and the stability of
the bcc structure, the thickness of the upper pinned layer 143
having the bcc structure is preferably about 2.0 to 4 nm.
[0073] As the upper pinned layer 143, a Co.sub.90Fe.sub.10 alloy
having the fcc structure and a cobalt alloy having the hcp
structure, which are widely used in conventional magnetoresistive
elements, can be used in place of the magnetic material having the
bcc structure. As the upper pinned layer 143, single metals such as
Co, Fe and Ni or alloy materials containing any one of them can be
used. Magnetic materials for the upper pinned layer 143 include a
FeCo alloy material having the bcc structure, a cobalt alloy with a
cobalt concentration of 50% or more, and a nickel alloy with a Ni
concentration of 50% or more, when arranged in the order from the
most advantageous magnetic material for attaining a high MR
ratio.
[0074] The film of (Fe.sub.50Co.sub.50 [1 nm]/Cu [0.25
nm]).times.2/Fe.sub.50Co.sub.50 [1 nm] described as an example of
the upper pinned layer 143 has magnetic layers (FeCo layers) and
nonmagnetic layers (ultrathin Cu layers) stacked alternately. In
the upper pinned layer 143 having such a structure, a
spin-dependent scattering effect called a spin-dependent bulk
scattering effect can be improved by the ultrathin Cu layer.
[0075] The "spin-dependent bulk scattering effect" is used as a
term in pair with the "spin-dependent interface scattering effect".
The spin-dependent bulk scattering effect is a phenomenon that the
MR effect is exhibited inside a magnetic layer. The spin-dependent
interface scattering effect is a phenomenon that the MR effect is
exhibited at the interface between a spacer layer and a magnetic
layer.
[0076] As shown in FIGS. 2A and 2B, insertion of SF layer 22 into
the upper pinned layer has an effect of increasing the MR ratio.
The effect of increasing the MR ratio can be expected in both cases
where the spacer layer has a CCP structure as shown in FIG. 2A and
where the spacer layer is a metal layer as shown in FIG. 2B. The
material of SF layer 22 and the method of manufacturing the same
will be described later in detail in connection with arrangement of
SF layer 21 in the free layer, and thus their detailed description
is omitted here.
[0077] Hereinafter, improvement in the bulk scattering effect
attributable to use of the upper pinned layer having a layered
structure of magnetic and nonmagnetic layers will be described.
[0078] In the CPP-GMR element having the CCP structure as in FIG.
1A, a current is confined in the vicinity of the spacer layer, and
thus contribution of resistance in the vicinity of an interface of
the spacer layer is very large. That is, the ratio of the
resistance at the interface between the spacer layer 16 and the
magnetic layers, i.e., the pinned layer 14 and free layer 18, to
the resistance of the entire magnetoresistive element is large.
This shows that the contribution of the spin-dependent interface
scattering effect is very large in the CCP-CPP element and
therefore is important. That is, selection of the magnetic material
located at the interface of the spacer layer 16 has very important
meaning as compared to the case of a conventional CPP element. This
is the reason for using, as the upper pinned layer 143, the FeCo
alloy layer having the bcc structure with a large spin-dependent
interface scattering effect as described above.
[0079] However, use of a material with a large spin-dependent bulk
scattering effect is still important for obtaining a higher MR
ratio. For obtaining the spin-dependent bulk scattering effect, the
thickness of the ultrathin Cu layer is preferably 0.1 to 1 nm, more
preferably 0.2 to 0.5 nm. If the thickness of the Cu layer is too
thin, the effect of improving the spin-dependent bulk scattering
effect becomes weak. If the thickness of the Cu layer is too thick,
the spin-dependent bulk scattering effect may decrease, and
moreover the magnetic coupling of the upper and lower magnetic
layers with the non-magnetic Cu layers interposed therebetween
becomes weak, thereby making the characteristics of the pinned
layer 14 insufficient. For these reasons, Cu of 0.25 nm in
thickness is used in the preferable example of the upper pinned
layer.
[0080] For the material of the nonmagnetic layer between the
magnetic layers in the upper pinned layer 143, Hf, Zr, Ti or the
like may be used instead of Cu. When these ultrathin nonmagnetic
layers are inserted, the thickness thereof per one magnetic layer
such as FeCo is preferably 0.5 to 2 nm, more preferably
approximately 1 to 1.5 nm.
[0081] As the upper pinned layer 143, a layer made by alloying FeCo
and Cu may be used instead of the alternate layered structure of
the FeCo layer and the Cu layer. An example of such an FeCoCu alloy
is (Fe.sub.xCo.sub.100-x).sub.100-yCu.sub.y (x=about 30 to 100%,
y=about 3 to 15%), but another compositional range may be used.
Here, as an element to be added to FeCo, another element such as
Hf, Zr or Ti may be used instead of Cu.
[0082] For the upper pinned layer 143, a single layer film made of
Co, Fe, Ni or an alloy thereof may be used. For example, as the
upper pinned layer 143 with the simplest structure, a
Co.sub.90Fe.sub.10 single layer of 2 to 4 nm which has been used
widely may be used. To this material, another element may be
added.
[0083] The spacer layer 16 used is that of CCP structure having an
insulating layer 161 and current paths 162 penetrating the
insulating layer 161, or that of a metal layer or an all metal
layer.
[0084] First, the spacer layer, in a broad sense, of the CCP
structure will be described.
[0085] The lower metal layer 15 is a remaining layer after used as
a source for the current paths 162 and may not remain sometimes in
the final structure.
[0086] In the spacer layer of CCP structure, the insulating layer
161 is made of oxide, nitride, oxynitride or the like. As the
insulating layer 161, both that having an amorphous structure such
as Al.sub.2O.sub.3 and that having a crystal structure such as MgO
can be used. In order to exhibit the function as a spacer layer,
the thickness of the insulating layer 161 is preferably in the
range of 1 to 3.5 nm, more preferably 1.5 to 3 nm. It is preferable
that the current path has a diameter of 1 nm or more and 7 nm or
less in the upper surface of the intermediate layer. The area ratio
of the current path in the upper surface of the intermediate layer
varies the area resistance RA of the element. As the area ratio of
the current path becomes larger, the resistance against the current
flowing in the perpendicular direction to the film plane is
lowered, which reduces the area resistance RA. As the area ratio of
the current path becomes smaller, the resistance against the
current flowing in the perpendicular direction to the film plane is
raised, which increases the area resistance RA. In view of high
transmission rate, it is desirable to reduce the area resistance RA
as the recording density is raised, as described later.
[0087] A typical material used for the insulating layer 161
includes Al.sub.2O.sub.3 and Al.sub.2O.sub.3 to which an additive
element is added. By way of example, Al.sub.2O.sub.3 of about 2 nm
in thickness can be used. The additive element includes Ti, Hf, Mg,
Zr, V, Mo, Si, Cr, Nb, Ta, W, B, C, V, and the like. The addition
amount of the additive element can be varied appropriately in the
range of approximately 0 to 50%.
[0088] For the insulating layer 161, Ti oxide, Hf oxide, Mg oxide,
Zr oxide, Cr oxide, Ta oxide, Nb oxide, Mo oxide, Si oxide, and V
oxide can be used instead of the Al oxide such as Al.sub.2O.sub.3.
Also in the case of these oxides, the above materials can be used
as additive elements. The addition amount of the additive element
can be varied appropriately in the range of approximately 0 to
50%.
[0089] Instead of these oxides, nitrides or oxynitrides based on
Al, Si, Hf, Ti, Mg, Zr, V, Mo, Nb, Ta, W, B, and C as described
above may be used for the insulating layer 161.
[0090] The current paths 162 form confinement paths or routes for
passing a current perpendicularly to the plane of the spacer layer
16, and are formed of a metal such as Cu. When the spacer layer 16
uses a CCP structure, the MR ratio can be increased through the
current-confined effect. Materials of the current paths 162 include
Au, Ag, Al, Ni, Co, Fe, and an alloy including at least one of
these elements, besides Cu. Examples of Cu-containing alloys
include CuNi, CuCo, and CuFe. An alloy having a composition
containing 50% or more of Cu is preferably used to increase the MR
ratio and to reduce an interlayer coupling field (Hin) between the
pinned layer 14 and the free layer 18.
[0091] The current paths 162 are regions having significantly
smaller contents of oxygen and nitrogen, in which a difference in
the ratio of oxygen and nitrogen content is a half or less, as
compared with the insulating layer 161, and are generally in a
crystal phase. The crystal phase has lower resistance than an
amorphous phase and is thus preferable as the current paths
162.
[0092] The upper metal layer 17 constitutes a part of a spacer
layer in a broad sense. The upper metal layer 17 has a function as
a barrier layer for preventing the free layer 18 deposited thereon
from being oxidized upon contacting with oxides in the spacer layer
16, and a function of improving the crystallinity of the free layer
18. If the material of the insulating layer 161 is amorphous, for
example, as the case of Al.sub.2O.sub.3, the metal layer deposited
thereon has poor crystallinity. Thus, by arranging a layer which
makes fcc crystallinity favorable, for example, a Cu layer that may
be about 1 nm or less in thickness for the upper metal layer 17,
the crystallinity of the free layer 18 can be improved
significantly.
[0093] The upper metal layer 17 need not necessarily be provided
depending on the material of the spacer layer 16 or the material of
the free layer 18. The metal layer 17 on the spacer layer 16 can be
made unnecessary if degradation of crystallinity can be avoided by
optimization of anneal conditions, selection of the insulating
material in the spacer layer 16, and selection of the material in
the free layer 18.
[0094] In consideration of margin in manufacturing, it is
practically preferable to form the upper metal layer 17 on the
spacer layer 16 when the CCP structure is used. A preferable
example of the upper metal layer 17 includes Cu of about 0.5 nm in
thickness.
[0095] Instead of Cu, it is possible to use Au, Ag, or Ru as a
material for the upper metal layer 17. The material for the upper
metal layer 17 is preferably the same as that for the current paths
162 in the spacer layer 16. If different materials are used for the
upper metal layer 17 and for the current paths 162, the interface
resistance increases. However, this is prevented if the same
material is used for both components.
[0096] The thickness of the upper metal layer 17 is preferably 0 to
1 nm, more preferably 0.1 to 0.5 nm. The excessively large
thickness of the upper metal layer 17 extends a current confined by
the spacer layer 16 to make the current confined effect
insufficient, resulting in lowering of the MR ratio.
[0097] The spacer layer 16 need not necessarily have the CPP
structure, but it may be a metal layer (all-metal layer) not
containing the insulating layer. In this case, the spacer layer 16
may preferably be formed of a metal element selected from the group
consisting of Au, Ag, Cu, and Cr. The all-metal spacer layer may
preferably have a thickness from about 1.5 nm to 3 nm.
[0098] The free layer 18 is a layer containing a ferromagnetic
material whose magnetizing direction is varied by an external
magnetic field. For example, the magnetoresistive element in FIGS.
1A and 1B is provided with an SF layer 21 having a spin filter
effect, which is formed of a nitride of a metal material as a part
of the free layer 18 and can realize a higher MR ratio without
increasing the thickness. The metal material to be converted into
the SF layer of a nitride is a material containing 5 atomic % or
more of Fe and an element selected from the group consisting of Co,
Ni and B.
[0099] As shown in FIGS. 2A and 2B, the SF layer 22 may be arranged
in the upper pinned layer, and as shown in FIGS. 3A and 3B, the SF
layer 21 may be arranged in the free layer 18 and also the SF layer
22 may be arranged in the upper pinned layer. A plurality of SF
layers may be arranged in the free layer or in the pinned layer.
Alternatively, the SF layer may be arranged in the interface
between the pinned layer 14 and the spacer layer 16, in the
interface between the spacer layer 16 and the free layer 18, or in
the interface between the free layer 18 and the cap layer 19.
[0100] The cap layer 19 has a function of protecting the spin valve
film. The cap layer 19 can be a plurality of metal layers, for
example, a two-layer structure of a Cu layer and an Ru layer (Cu [1
nm]/Ru [10 nm]). Further, as the cap layer 19, a Ru/Cu layer in
which Ru is arranged on the side of the free layer 18 can also be
used. In this case, the thickness of Ru is preferably approximately
0.5 to 2 nm. The cap layer 19 of this structure is desirable
especially when the free layer 18 is constituted of NiFe. This is
because it can reduce magnetostriction in an interface mixing layer
formed between the free layer 18 and the cap layer 19 since Ru is
insoluble with Ni.
[0101] When the cap layer 19 is either of Cu/Ru or Ru/Cu, the
thickness of the Cu layer is preferably approximately 0.5 to 10 nm,
and the thickness of the Ru layer is preferably approximately 0.5
to 5 nm. Since Ru has a high specific resistance value, use of an
excessively thick Ru layer is not favorable.
[0102] As the cap layer 19, a metal layer other than the Cu layer
or Ru layer may be provided. For the cap layer 19, another material
may be used as long as it can protect the spin-valve film. However,
selection of a cap layer may change the MR ratio or the long-term
reliability, and therefore care must be taken. Also in these views,
Cu and Ru are desirable examples of a material for the cap
layer.
[0103] For the upper electrode 20, a material with low electrical
resistance, for example, Cu, Au or NiFe can be used.
[0104] Then, the method of manufacturing a magnetoresistive element
according to an embodiment of the invention will be described.
FIGS. 4A to 4E are cross-sectional views showing steps for forming
an SF layer 21 on a lower free layer 181 in manufacturing the
magnetoresistive element of FIG. 1B.
[0105] As shown in FIG. 4A, a first metal layer 211 to be converted
into an SF layer 21 is deposited on the lower free layer 181. The
first metal layer 211 is made of a metal material containing 5
atomic % or more of Fe.
[0106] As shown in FIG. 4B, the first metal layer 211 is subjected
to conversion treatment and formed into a converted layer 211'
containing nitrogen. The converted layer 211' serves as a part of
SF layer 21. In this conversion treatment, conversion into the
desired converted layer is not feasible by mere exposure of the
surface of the metal layer 211 to a nitrogen atmosphere. Conversion
treatment should be carried out while atoms of the metal layer are
supplied with kinetic energy by ion beam in a nitrogen atmosphere.
In such treatment, energy assist is exerted on atoms of the metal
layer. Conversion treatment uniform in the depth direction can be
performed by depositing a first metal layer 211 in a small
thickness.
[0107] As shown in FIG. 4C, a second metal layer 212 to be
converted into an SF layer 21 is deposited on the converted layer
211'. The second metal layer 212 also is formed of a metal material
containing 5 atomic % or more of Fe.
[0108] As shown in FIG. 4D, the second metal layer 212 is subjected
to conversion treatment in the same manner as in FIG. 4B, to form a
converted layer 212' containing nitrogen. At this time, not only
the conversion of the second metal layer 212 but also the
conversion of the underlying converted layer 211' and of the lower
free layer 181 may proceed. Since the energy of nitride formation
varies depending on metal material, the depth to which the
conversion proceeds depends considerably on the composition and
crystal structure of the metal material.
[0109] Further, the SF layer 21 is formed by performing modules
each including metal layer deposition and conversion treatment
necessary times repeatedly that vary depending on the thickness of
the SF layer 21 to be finally formed.
[0110] Thereafter, an upper free layer 182 is deposited as shown in
FIG. 4E. A free layer 18 containing the lower free layer 181, the
SF layer 21 and the upper free layer 182 is formed in this manner.
As described above, if the conversion treatment has proceeded such
that the lower free layer 181 is influenced, clear distinction
between the SF layer 21 and the lower free layer 181 may have
disappeared. This case is equivalent to formation of the SF layer
21 in the interface between the spacer layer 16 and the free layer
18 which includes only the upper free layer 182 in this case.
[0111] When the SF layer made of a nitride is to be formed, the
number of times N, by which the module each including metal layer
deposition and conversion treatment is repeated when the thickness
of the completed SF layer is T nanometers, is determined by the
following formula:
N.gtoreq.(T/0.5).times.x (1),
where x is a constant of 1 to 2, and T.gtoreq.1.
[0112] The number of times N is varied depending on the thickness
of the completed SF layer made of a nitride, and determined
according to the formula (I) above, to perform a series of
manufacturing steps. The energy of nitride formation is so high
that when a metal layer to be converted into SF layer is deposited
to a thickness of greater than 1 nm and subjected to nitriding
treatment, a thin nitride layer is merely formed and fails to
exhibit the desired effect as the SF layer, thus decreasing an
effect of improving an MR ratio. Accordingly, the thickness of the
metal layer deposited in one module is preferably 1 nm or less.
[0113] Particularly as shown in FIGS. 2A and 2B, pinning
characteristics (Hua) of the pinned layer are preferably prevented
from being reduced when the SF layer 22 is arranged in the upper
pinned layer 143. In this case, the formation of SF layer by
subjecting a ferromagnetic metal layer selected from Ni, Fe, Co and
an alloy thereof to conversion treatment is preferable in that Hua
is hardly reduced. Also, it is desirable that two ferromagnetic
layers sandwiching the SF layer 22 are ferromagnetically coupled
with each other.
[0114] If a ferromagnetic metal layer is subjected to conversion
treatment to form the SF layer when the SF layer is to be arranged
in the free layer, exchange coupling between magnetic moments in
the ferromagnetic material is exerted, thereby ferromagnetically
coupling the whole of the free layer to cause simultaneous
magnetization rotation. Accordingly, a low coercivity (Hc) that is
one of the requirements of the free layer can be realized with good
controllability.
[0115] The thickness of the completed SF layer 21 made of a nitride
is preferably about 0.2 nm to 10 nm, more preferably about 0.3 to 5
nm. The area resistance of a nitride material known as an
insulating layer is increased with increase in thickness, and thus
the SF layer 21 having a thickness near to 10 nm is not practical
in manufacturing a magnetoresistive element for low resistant
head.
[0116] To form a more uniform SF layer, a gas such as argon, xenon,
helium, neon or krypton may be made into ion or plasma for the
purpose of assisting atomic migration energy, and such ion or
plasma atmosphere may be supplied with a nitrogen gas or the like
to generate an ion and plasma with which the surface of the metal
layer is irradiated for conversion treatment.
[0117] In formation of SF layer, it is conceivable to use natural
nitriding by mere exposure of the metal layer to a nitrogen gas
atmosphere instead of the ion beam-assisted nitriding described
above, but for formation of a uniform SF layer, it is preferable to
deposit divided metal layers each having a small thickness
determined according to the formula (I).
[0118] The area resistance RA of the magnetoresistive element
including the SF layer is preferably 0.5 .OMEGA..mu.m.sup.2 or
less, specifically 0.05 .OMEGA.m.sup.2 to 0.3
.OMEGA..mu.m.sup.2.
[0119] Hereinafter, beam conditions for forming the SF layer will
be described. When a rare gas is made into ion or plasma as
described above in forming the SF layer by nitriding treatment, it
is preferable that the acceleration voltage V is set at +30 to 130V
and the beam current Ib at 20 to 200 mA. These conditions are
extremely weaker than those for performing ion beam etching. In
place of ion beam, plasma such as RF plasma can be similarly used
to form the SF layer. The incident angle of the ion beam can be
varied between 0 to 80.degree. where the incident angle is defined
to be 0.degree. when the beam is perpendicular to the plane upon
incidence and to be 90.degree. when the beam is parallel to the
plane upon incidence. The treatment time for this step is
preferably 15 to 180 seconds and more preferably 30 seconds or more
in terms of controllability and the like. A too long time is not
preferable because productivity for CPP elements is reduced. From
these viewpoints, the treatment time is most preferably 30 to 180
seconds.
[0120] In the case of nitriding treatment with ion or plasma, the
amount of nitrogen exposure is preferably 1,000 to 10,000,000 L (1
L=1.times.10.sup.-6 Torr.times.sec).
[0121] By using the above-described appropriate conditions in each
of the steps in FIG. 4, the SF layer giving good characteristics
can be realized.
[0122] The first metal layer 211 and the second metal layer 212
deposited in the divided manner in FIGS. 4A and 4C may be made of
the same material or different materials. Generally, the same
material is often used, but use of the same material is not always
necessary.
[0123] FIG. 5 is a schematic view showing a deposition apparatus
used for manufacturing the magnetoresistive element according to an
embodiment of the invention. As shown in FIG. 5, a load lock
chamber 51, a pre-cleaning chamber 52, a first metal deposition
chamber (MC1) 53, a second metal deposition chamber (MC2) 54, and a
conversion treatment chamber 60 are provided via vacuum valves
respectively with a transfer chamber (TC) 50 located in the center.
In this deposition apparatus, a substrate can be transferred in
vacuum between respective chambers connected via the vacuum valves,
so that the surface of the substrate is kept clean.
[0124] The metal deposition chambers 53, 54 have multiple (5 to 10)
targets. Examples of the deposition method include sputtering such
as DC magnetron sputtering and RF magnetron sputtering, ion beam
sputtering, vacuum evaporation, CVD (chemical vapor deposition),
MBE (molecular beam epitaxy), and the like. In the conversion
treatment, a chamber having an ion beam mechanism, an RF plasma
mechanism or a heating mechanism can be used and should be
separated from the metal deposition chamber.
[0125] The ultimate degree of vacuum in the vacuum chamber is
typically in the order of 10.sup.-9 Torr, and a degree of vacuum in
first half of 10.sup.-8 Torr is also acceptable. Specifically, the
ultimate degree of vacuum in the metal deposition chamber is
preferably 1.times.10.sup.-8 Torr or lower and is generally in the
range of about 5.times.10.sup.-10 to 5.times.10.sup.-9 Torr. The
ultimate degree of vacuum in the transfer chamber 50 is in the
order of 10.sup.-9 Torr. The ultimate degree of vacuum in the
conversion treatment chamber 60 is desirably 8.times.10.sup.-8 Torr
or less.
[0126] Deposition of a metal layer to be converted into the SF
layer is conducted in either the metal deposition chamber 53 or 54.
The conversion treatment is carried out in the conversion treatment
chamber 60. After deposition of a metal layer, the substrate is
transferred via the transfer chamber 50 to the conversion treatment
chamber 60 where the substrate is subjected to conversion
treatment. Thereafter, the substrate is transferred to either the
metal deposition chamber 53 or 54 where a second metal layer is
deposited, and the substrate is transferred again via the transfer
chamber 50 to the conversion treatment chamber 60 where the
substrate is subjected to conversion treatment.
[0127] FIG. 6 shows an example of the conversion treatment chamber
60 in FIG. 5. The conversion treatment chamber 60 uses an ion beam.
As shown in FIG. 6, the conversion treatment chamber 60 is
evacuated by a vacuum pump 61, and a reaction gas whose flow rate
is controlled by a mass flow controller (MFC) 63 is introduced into
the conversion treatment chamber 60 through a conduit 62. An ion
source 70 is provided in the conversion treatment chamber 60. Types
of the ion source include an inductive coupled plasma (ICP) type, a
capacitive coupled plasma type, an electron-cyclotron resonance
(ECR) type, and a Kauffman type. A substrate holder 80 is arranged
opposite to the ion source 70, and a substrate 1 is arranged
thereon.
[0128] Three grids 71, 72, and 73 are provided at an ion emission
port of the ion source 70 to adjust ion acceleration. A neutralizer
74 is provided outside the ion source 70 to neutralize ions. The
substrate holder 80 is supported so as to be freely tilted. The
angle at which ions are incident on the substrate 1 can be varied
over a wide range. A typical incident angle ranges between
15.degree. to 60.degree..
[0129] In the conversion treatment chamber 60, energy assist for
the conversion treatment with ion can be performed by irradiating
the substrate 1 with an ion beam such as Ar, and the metal layer
can be converted into SF layer by irradiating the substrate 1 with
an ion beam such as Ar while supplying the chamber 60 with a
reaction gas from the conduit 62.
[0130] An RF plasma chamber or the like may be used as the
conversion treatment chamber. Anyway, conversion treatment shall be
conducted in a chamber wherein an ion or plasma can be generated to
give energy in the conversion treatment.
[0131] As a means of giving energy, heat treatment may be
conducted. In this case, heat treatment at a temperature of 100 to
300.degree. C. for several tens of seconds to a few minutes, for
example, may be conducted.
[0132] Hereinafter, the method of manufacturing the
magnetoresistive element shown in FIGS. 1A and 1B will be described
entirely.
[0133] (1) Formation of the Underlayer 12
[0134] The lower electrode 11 is formed in advance on the substrate
(not shown) by a micro-fabrication process. As the underlayer 12,
for example Ta [5 nm]/Ru [2 nm] is deposited on the lower electrode
11. Ta is a buffer layer for alleviating roughness on the surface
of the lower electrode. Ru is a seed layer for controlling the
crystalline orientation and crystal grain size of the spin-valve
film deposited thereon.
[0135] (2) Formation of the Pinning Layer 13
[0136] The pinning layer 13 is deposited on the underlayer 12. As a
material of the pinning layer 13, an antiferromagnetic material
such as PtMn, PdPtMn, IrMn or RuRhMn can be used.
[0137] (3) Formation of the Pinned Layer 14
[0138] The pinned layer 14 is formed on the pinning layer 13. The
pinned layer 14 can be a synthetic pinned layer of a lower pinned
layer 141 (Co.sub.90Fe.sub.10), a magnetic coupling layer 142 (Ru),
and an upper pinned layer 143 (Co.sub.90Fe.sub.10), for
example.
[0139] (4) Formation of the Spacer Layer
[0140] Next, the spacer layer is formed. The spacer layer may be
one which has a CCP structure as shown in FIG. 1A, or may be a
metal layer as shown in FIG. 1B.
[0141] The spacer layer having a CCP structure can be formed by a
method disclosed in, for example, JP-A 2006-54257 (KOKAI). The
spacer layer made of a metal layer can be formed by depositing Cu,
Au, Ag, Cr or Mn in the metal deposition chamber.
[0142] (5) Formation of the Free Layer
[0143] Then, the free layer 18 including the SF layer 21 is formed
according to the method described with reference to FIGS. 4A to
4E.
[0144] (6) Formation of the Cap Layer 19 and Upper Electrode 20
[0145] As the cap layer 19, Cu [1 nm] and Ru [10 nm], for example,
are deposited on the free layer 18. On the cap layer 19, the upper
electrode 20 for conducting a current perpendicularly to the
spin-valve film is formed.
EXAMPLES
Example 1
[0146] The magnetoresistive element shown in FIG. 1B was prepared
in this example. The structure of the magnetoresistive element in
Example 1 is as follows:
Lower electrode 11 Underlayer 12: Ta [1 nm]/Ru [2 nm] Pinning layer
13: Ir.sub.22Mn.sub.78 [7 nm] Pinned layer 14: Co.sub.90Fe.sub.10
[4 nm]/Ru [0.85 nm]/Co.sub.90Fe.sub.10 [4 nm] Spacer layer (all
metal) 16: Cu [3 nm] Lower free layer 181: Co.sub.90Fe.sub.10 [2
nm] SF layer 21: (nitride of Fe.sub.80Co.sub.20 [0.4 nm]).times.5
layers prepared by the method in FIGS. 4A to 4E Upper free layer
182: Co.sub.90Fe.sub.10 [2 nm] Cap layer 19 Upper electrode 20.
[0147] Now, a method of forming the free layer including the SF
layer after the layers to the spacer layer 16 are deposited will be
described. When the free layer including the SF layer is formed as
in this example, a magnetic layer having half the thickness of the
usual free layer is deposited and then the SF layer 21 is formed
thereon. In this example, Co.sub.90Fe.sub.10 of 2 nm in thickness
was deposited as the lower free layer 181.
[0148] Then, in the step of FIG. 4A, Fe.sub.80Co.sub.20 of 0.4 nm
in thickness was deposited as the first metal layer 211 to be
converted into the SF layer. In the step of FIG. 4B, the conversion
treatment was conducted in the following manner. While the surface
of the metal layer is irradiated with an Ar ion beam, nitrogen gas
was flowed into the conversion treatment chamber. The accelerating
conditions for Ar ion beam was set to 60V. In this manner, a first
ultrathin nitride layer 211' was formed. The flow of nitrogen gas
was stopped, and the substrate was transferred to the metal
deposition chamber. In the step of FIG. 4C, Fe.sub.80Co.sub.20 of
0.4 nm in thickness was deposited again as the second metal layer
212 to be converted into the SF layer. In the step of FIG. 4D, the
second metal layer 212 was subjected to conversion treatment. The
conditions for this conversion treatment were the same as the
nitriding conditions in FIG. 4B. In this manner, a second ultrathin
nitride layer 212' was formed. The processes of such metal-layer
deposition and nitriding treatment were repeated 5 times in total,
whereby the SF layer 21 made of a nitride layer of
Fe.sub.80Co.sub.20 having a final thickness of 2 nm was formed.
[0149] After formation of the SF layer 21 was completed, the
substrate was transferred to the metal deposition chamber, and the
upper free layer and the cap layer were deposited. Because the CPP
element to be produced has a final layer structure by heat
treatment conducted after deposition of all layers, the CPP element
may not have the final layer structure during the stage of film
deposition. Actually, the heat treatment conducted after deposition
of films to the cap layer also shows the energy assist effect. This
heat treatment was carried out at 280.degree. C. for 4 hours.
Example 2
[0150] A magnetoresistive element was prepared in the same manner
as in Example 1 except that (nitride of Co.sub.64Fe.sub.16B.sub.20
[0.4 nm]).times.5 layers prepared by the method in FIGS. 4A to 4E
was used as the SF layer 21.
Example 3
[0151] A magnetoresistive element was prepared in the same manner
as in Example 1 except that (nitride layer of Fe.sub.50Co.sub.50
[0.4 nm]).times.5 layers prepared by the method in FIGS. 4A to 4E
was used as SF layer 21.
Example 4
[0152] A magnetoresistive element was prepared in the same manner
as in Example 1 except that (nitride layer of Ni.sub.95Fe.sub.5
[0.4 nm]).times.5 layers prepared by the method in FIGS. 4A to 4E
was used as SF layer 21.
Comparative Example 1
[0153] A magnetoresistive element having a free layer 18 consisting
of Co.sub.90Fe.sub.10 of 4 nm in thickness and not including an SF
layer was prepared in Comparative Example 1. The structure of the
magnetoresistive element in Comparative Example 1 is as
follows:
Lower electrode 11 Underlayer 12: Ta [1 nm]/Ru [2 nm] Pinning layer
13: Ir.sub.22Mn.sub.78 [7 nm] Pinned layer 14: Co.sub.90Fe.sub.10
[4 nm]/Ru [0.85 nm]/Co.sub.90Fe.sub.10 [4 nm] Spacer layer (all
metal) 16: Cu [3 nm] Free layer 18: Co.sub.90Fe.sub.10 [4 nm] Cap
layer 19 Upper electrode 20.
Comparative Example 2
[0154] A magnetoresistive element was prepared in the same manner
as in Example 1 except that a 1-nm Fe.sub.80Co.sub.20 oxide layer
was used as the SF layer 21.
[0155] Characteristics of the thus prepared magnetoresistive
elements in Examples 1 to 4 and Comparative Examples 1 and 2 were
evaluated. The area resistance and MR ratio of each element were
measured by passing a current from the pinned layer 14 to the free
layer 18 where the flow of electrons is from the free layer 18 to
the pinned layer 14. When a current is passed from the free layer
18 to the pinned layer 14 where the flow of electrons is from the
pinned layer 14 to the free layer 18, the noise by spin transfer
torque effect is increased. Therefore, the current is passed
preferably from the pinned layer 14 to the free layer 18 as
described above to reduce the spin transfer noise.
[0156] FIG. 7 shows the area resistances (RA) and MR ratios of the
magnetoresistive elements in Examples 1 to 4 and Comparative
Examples 1 and 2. In the element in Comparative Example 1, RA is
about 0.08 .OMEGA..mu.m.sup.2, and MR ratio is about 0.8%. In the
element in Example 1, RA is 0.1 .OMEGA..mu.m.sup.2, and MR ratio is
1.1%. The elements in Examples 2 to 4 also showed improvements in
area resistance (RA) and MR ratio as compared with those of the
element in Comparative Example 1. That is, even when a magnetic
element hardly forming a nitride was used as a matrix, an increase
in MR ratio could be recognized in all the Examples by improving
the formation method. The magnetoresistive element showing the
maximum increase in MR ratio was one using, as the matrix,
Fe.sub.80Co.sub.20 having the maximum Fe content. That is, a layer
containing nitrogen and a metal material with a higher content of
Fe was found to show a higher effect of increasing the MR ratio. A
layer containing nitrogen and a metal material with a Fe content of
5 atomic % or more is found to be effective.
[0157] In the element in Comparative Example 2, RA is 0.14
.OMEGA..mu.m.sup.2, and MR ratio is 0.8%, and thus the area
resistance RA only was increased, and an increase in MR ratio was
not recognized. That is, the sample exposed not to a nitrogen
atmosphere but to an oxygen atmosphere showed an increase in RA
only, but did not produce an increase in MR ratio. When the
material, even with a high content of Fe, is not a nitride but an
oxide, an increase in area resistance RA only is observed, and an
increase in MR ratio is hardly achieved. An increase in area
resistance is not preferable in application to magnetic heads.
Because area resistance RA is desirably lower, it was found that
the nitride is more desirable than the oxide.
[0158] The results of MR ratio plotted against the Fe is
concentration of the metal matrix before exposure to nitrogen or
oxygen are shown in FIG. 8. As can be seen from FIG. 8, in the
sample exposed to the nitrogen atmosphere an increase in MR ratio
could be recognized when the Fe content of the metal matrix before
exposure to a nitrogen atmosphere is 5 atomic % or more. On the
other hand, the sample even with a Fe content of 5 atomic % or more
was not recognized to produce an increase in MR ratio when it was
exposed to an oxygen atmosphere. That is, the sample having a Fe
content of 5 atomic % or more and exposed to nitrogen was found to
produce an increase in MR ratio without increasing the area
resistance RA.
[0159] When a cross-sectional transmission electron microscopic
(cross-sectional TEM) image of the element in Example 1 was
measured, it was found that the crystalline orientation plane of
the spacer layer 16 and the crystalline orientation plane of the
lower free layer 181 are different from each other at their
interface as the boundary between the crystalline orientation
planes. The portion corresponding to the lower free layer and the
portion corresponding to the SF layer of (nitride of
Fe.sub.80Co.sub.20 [0.4 nm]).times.5 layers were found to have the
same crystalline orientation plane. The crystalline orientation
plane of these portions and the crystalline orientation plane of
the portion corresponding to the upper free layer thereon were
different from each other.
[0160] The cross-sectional TEM image was subjected to fast Fourier
transformation (FFT) to give reciprocal lattice spots of
crystalline orientation planes. Reciprocal lattice spots of the
spacer layer 16 and reciprocal lattice spots of the SF layer 21
(and the lower free layer 181) were superimposed with a spot in the
[001] direction as the center. It was found that the crystalline
orientation planes of the spacer layer 16 and SF layer 21, which
were considered equivalent with almost the same distance between
the central spot and the reciprocal lattice spot, were inclined to
each other at an angle of about 60.degree..
[0161] On the other hand, the presence of the interface in which
the crystalline orientation planes of two layers were inclined to
each other as in Example 1 was not recognized in Examples 2 to 4
and Comparative Example 1.
[0162] The foregoing result can be explained as follows. When the
process of metal-layer deposition and nitride treatment is repeated
5 times to form the SF layer, the thickness of the metal layer is
sufficiently small per layer (0.4 nm in this case). When the thin
metal layer is subjected to nitriding treatment with ion or plasma,
sufficient energy is supplied to constituent atoms of the metal
layer. Accordingly, the metal layer is converted certainly into a
nitride film over the whole thickness, to show an excellent spin
filter function. When a metal layer with a high content of Fe is
subjected to nitriding treatment, the crystalline orientation plane
of the SF layer (and the lower free layer) and that of the
underlying spacer layer are inclined to each other to impart
additional effect, thereby showing a further excellent spin filter
function. Accordingly, it is estimated that the area resistance
(RA) and MR ratio in Example 1 were higher than in Examples 2 to 4,
as shown in FIG. 7. Therefore, the nitride film containing 5 atomic
% or more of Fe is preferable as the SF layer. Further, the results
of the Examples show that the nitride film containing 50 atomic %
or more of Fe is more preferable.
Example 5
[0163] The magnetoresistive element shown in FIG. 2B was prepared
by using the following materials:
Lower electrode 11 Underlayer 12: Ta [1 nm]/Ru [2 nm] Pinning layer
13: Ir.sub.22Mn.sub.78 [7 nm] Lower pinned layer 141:
Co.sub.90Fe.sub.10 [4 nm] Antiferromagnetic coupling layer 142: Ru
[0.85 nm] First upper pinned layer 144: Co.sub.90Fe.sub.10 [2 nm]
SF layer 21: Nitride layer in any of Examples 1 to 4 Second upper
pinned layer 145: Co.sub.90Fe.sub.10 [2 nm] Spacer layer (all
metal) 16: Cu [3 nm] Free layer 18: Co.sub.90Fe.sub.10 [4 nm] Cap
layer 19: Cu [1 nm]/Ru [10 nm] Upper electrode 20.
Example 6
[0164] The magnetoresistive element shown in FIG. 2A was prepared
by using the following materials:
Lower electrode 11 Underlayer 12: Ta [1 nm]/Ru [2 nm] Pinning layer
13: Ir.sub.22Mn.sub.78 [7 nm] Lower pinned layer 141:
Co.sub.90Fe.sub.10 [4 nm] Antiferromagnetic coupling layer 142: Ru
[0.85 nm] First upper pinned layer 144: Co.sub.90Fe.sub.10 [2 nm]
SF layer 21: Nitride layer in any of Examples 1 to 4 Second upper
pinned layer 145: Co.sub.90Fe.sub.10 [2 nm] Spacer layer (CCP-NOL)
16: Al.sub.2O.sub.3 insulating layer 161 and Cu current paths 162
Free layer 18: Co.sub.90Fe.sub.10 [4 nm] Cap layer 19: Cu [1 nm]/Ru
[10 nm] Upper electrode 20.
Example 7
[0165] The magnetoresistive element shown in FIG. 1A was prepared
by using the following materials:
Lower electrode 11 Underlayer 12: Ta [1 nm]/Ru [2 nm] Pinning layer
13: Ir.sub.22Mn.sub.78 [7 nm] Pinned layer 14: Co.sub.90Fe.sub.10
[4 nm]/Ru [0.85 nm]/Co.sub.90Fe.sub.10 [4 nm] Spacer layer
(CCP-NOL) 16: Al.sub.2O.sub.3 insulating layer 161 and Cu current
paths 162 Lower free layer 181: Co.sub.90Fe.sub.10 [2 nm] SF layer
21: Nitride layer in any of Examples 1 to 4 Upper free layer 182:
Co.sub.90Fe.sub.10 [2 nm] Cap layer 19: Cu [1 nm]/Ru [10 nm] Upper
electrode 20.
Example 8
[0166] The magnetoresistive element shown in FIG. 3B was prepared
by using the following materials:
Lower electrode 11 Underlayer 12: Ta [1 nm]/Ru [2 nm] Pinning layer
13: Ir.sub.22Mn.sub.78 [7 nm] Lower pinned layer 141:
Co.sub.90Fe.sub.10 [4 nm] Antiferromagnetic coupling layer 142: Ru
[0.85 nm] First upper pinned layer 144: Co.sub.90Fe.sub.10 [2 nm]
SF layer 22: Nitride layer in any of Examples 1 to 4 Second upper
pinned layer 145: Co.sub.90Fe.sub.10 [2 nm] Spacer layer (all
metal) 16: Cu [3 nm] Lower free layer 181: Co.sub.90Fe.sub.10 [2
nm] SF layer 21: Nitride layer in any of Examples 1 to 4 Upper free
layer 182: Co.sub.90Fe.sub.10 [2 nm] Cap layer 19: Cu [1 nm]/Ru [10
nm] Upper electrode 20.
Example 9
[0167] The magnetoresistive element shown in FIG. 3A was prepared
by using the following materials:
Lower electrode 11 Underlayer 12: Ta [1 nm]/Ru [2 nm] Pinning layer
13: Ir.sub.22Mn.sub.78 [7 nm] Lower pinned layer 141:
Co.sub.90Fe.sub.10 [4 nm] Antiferromagnetic coupling layer 142: Ru
[0.85 nm] First upper pinned layer 144: Co.sub.90Fe.sub.10 [2 nm]
SF layer 22: Nitride layer in any of Examples 1 to 4 Second upper
pinned layer 145: Co.sub.90Fe.sub.10 [2 nm] Spacer layer (CCP-NOL)
16: Al.sub.2O.sub.3 insulating layer 161 and Cu current paths 162
Lower free layer 181: Co.sub.90Fe.sub.10 [2 nm] SF layer 21:
Nitride layer in any of Examples 1 to 4 Upper free layer 182:
Co.sub.90Fe.sub.10 [2 nm] Cap layer 19: Cu [1 nm]/Ru [10 nm] Upper
electrode 20.
[0168] These magnetoresistive elements in Examples 5 to 9 can also
achieve the same effect as that of the magnetoresistive elements in
Examples 1 to 4.
[0169] (Application of the Magnetoresistive Element)
[0170] Application of the magnetoresistive element according to the
embodiments of the present invention will be described below.
[0171] In the embodiments of the present invention, the element
resistance RA of the CPP element is preferably set to 0.3
.OMEGA..mu.m.sup.2 or less, more preferably 0.15 .OMEGA..mu.m.sup.2
or less, from the viewpoint of compatibility with higher density.
The element resistance RA is calculated by multiplying the
resistance R of the CPP element by the effective area A of a
conductive part of the spin-valve film. In this case, the element
resistance R can be directly measured. On the other hand, the
effective area A of the conductive part of the spin-valve film has
a value dependent on the element structure. Accordingly, attention
must be paid to determination of the effective area A.
[0172] For example, if the entire spin-valve film is patterned as
an effectively sensing part, the effective area A is the area of
the entire spin-valve film. In this case, the area of the spin
valve film is preferably set to 0.04 .mu.m.sup.2 or less.
[0173] If a lower electrode 11 or an upper electrode 20 having a
smaller area than the spin-valve film is formed in contact with the
spin-valve film, the effective area A of the spin-valve film is the
area of the lower electrode 11 or upper electrode 20. If the lower
electrode 11 and upper electrode 20 have different areas, the area
of the smaller electrode is the effective area A of the spin-valve
film. In this case, the area of the smaller electrode is set to
0.04 .mu.m.sup.2 or less so as to set an appropriate element
resistance.
[0174] The smallest area of the spin-valve film is that of a part
where the film is in contact with the upper electrode 20, and thus
the width of this part is considered as the track width Tw. The
smallest height of the spin-valve film is also that of a part where
the film is in contact with the upper electrode 20, and thus the
height of this part is considered as the height length D. In this
case, the effective area A of the spin-valve film is determined as:
A=Tw.times.D.
[0175] In the magnetoresistive element according to the embodiment
of the present invention, the resistance R between the electrodes
can be set to 100.OMEGA. or less. The resistance R is a resistance
value measured for example between two electrode pads in a read
head installed to the tip of a head gimbal assembly (HGA).
[0176] The magnetoresistive element according to the embodiment of
the present invention desirably has an fcc (111) orientation
property if the pinned layer 14 or free layer 18 has the fcc
structure. The magnetoresistive element desirably has a bcc (110)
orientation property if the pinned layer 14 or free layer 18 has
the bcc structure. The magnetoresistive element desirably has an
hcp (001) or hcp (110) orientation property if the pinned layer 14
or free layer 18 has the hcp structure.
[0177] The crystalline orientation property of the magnetoresistive
element according to the embodiment of the present invention
preferably has a dispersion angle of 5.0 degrees or less, more
preferably 3.5 degrees or less, still more preferably 3.0 degrees
or less. This value is obtained by measuring a half value width of
a rocking curve at a peak position obtained by .theta.-2.theta.
measurement in X-ray diffraction. This value can be detected as a
dispersion angle of a nano-diffraction spot in a cross section of
element.
[0178] Although depending on the material for the antiferromagnetic
film, the lattice spacing of the antiferromagnetic film is
generally different from that of the pinned layer 14, spacer layer
16, and free layer 18. Consequently, the orientation dispersion
angle can be separately calculated for each layer. For example, the
lattice spacing of platinum manganese (PtMn) is often different
from that of the pinned layer 14, spacer layer 16, and free layer
18. Since the platinum manganese (PtMn) is made in a relatively
thick film, it is a suitable material for measuring dispersion in
crystalline orientation. For the pinned layer 14, spacer layer 16,
and free layer 18, the pinned layer 14 and the free layer 18 may
have different crystal structures such as the bcc and fcc
structures. Consequently, the pinned layer 14 and the free layer 18
have different dispersion angles.
[0179] (Another Magnetoresistive Element)
[0180] The spin-filtering element according to the present
invention can be applied not only the typical spin-valve type
magnetoresistive element having a pinned layer as described above
but also a dual-free type magnetoresistive element in which both
the lower and upper magnetic layers sandwiching the spacer layer
are formed of the free layer, respectively, and no pinned layer is
included (Hou et al., Pub. No. US 2005/0088789-A1).
[0181] Even in this case, the effect of improving the MR ratio by
the spin-filtering film according to the present invention can also
be attained, and the spin-filtering film is applicable to the
dual-free type magnetoresistive element as it is. The
spin-filtering layer may be arranged in the first magnetization
free layer, in the second magnetization free layer, in the
interface between the first magnetization free layer and the
intermediate layer, in the interface between the intermediate layer
and the second magnetization free layer, or in the interface of the
second magnetization free layer opposite to the interface that is
in contact with the intermediate layer. When two spin-filtering
layers according to the present invention are provided, two
spin-filtering layers may be arranged in one free layer or in two
free layers.
[0182] (Magnetic Head)
[0183] FIG. 9 shows the magnetoresistive element according to the
embodiment of the present invention which is incorporated in a
magnetic head. FIG. 9 is a cross-sectional view of the
magnetoresistive element taken along a direction substantially
parallel to the air bearing surface facing a magnetic recording
media (not shown). FIG. 10 is a cross-sectional view of the
magnetoresistive element taken along a direction perpendicular to
the air bearing surface (ABS).
[0184] The magnetic head shown in FIG. 9 has a so-called hard
abutted structure. The lower electrode 11 and the upper electrode
20 are provided under and over the magnetoresistive film SV,
respectively. In FIG. 9, bias magnetic field application films 41
and insulating films 42 are stacked on the both sides of the
magnetoresistive film. As shown in FIG. 10, a protective layer 43
is provided in the air bearing surface of the magnetoresistive
film.
[0185] A sense current for the magnetoresistive film is supplied by
the lower electrode 11 and the upper electrode 20 perpendicularly
to the plane as shown by arrow A, the electrodes 11 and 20 being
arranged under and over the magnetoresistive film. Further, the
pair of bias magnetic field application films 41, 41, provided on
the both sides of the magnetoresistive film, applies a bias
magnetic field to the magnetoresistive film. The bias magnetic
field controls the magnetic anisotropy of the free layer 18 in the
magnetoresistive film to make the free layer 18 into a single
domain. This stabilizes the domain structure of the free layer. It
is thus possible to suppress Barkhausen noise associated with
movement of magnetic domain walls. The present invention improves
the S/N ratio of the magnetoresistive film. Accordingly, the
application of the present invention to a magnetic head enables
sensitive magnetic reproduction.
[0186] (Hard Disk and Head Gimbal Assembly)
[0187] The magnetic head shown in FIG. 10 may be incorporated in a
read/write integrated magnetic head assembly, which can then be
mounted in a magnetic recording apparatus. FIG. 11 is a perspective
view schematically showing the configuration of a major portion of
such a magnetic recording apparatus. A magnetic recording apparatus
150 according to the embodiment is of a type using a rotary
actuator. In this figure, a magnetic disk 200 is installed on a
spindle 152. The magnetic disk 200 is rotated in the direction of
arrow A by a motor (not shown) that responds to control signals
from a drive controller (not shown). The magnetic recording
apparatus 150 according to the embodiment of the present invention
may comprise a plurality of magnetic disks 200.
[0188] A head slider 153 is attached to the tip of a suspension 154
of the thin film to read from and write to the magnetic disk 200.
The head slider 153 has a magnetic head mounted near the tip
thereof and including the magnetoresistive element according to any
of the above embodiments.
[0189] When the magnetic disk 200 rotates, the air bearing surface
(ABS) of head slider 153 is held so as to float on the surface of
the magnetic disk 200 by a predetermined height. Alternatively, the
head slider 153 may be of a so-called in-contact type contacting to
the magnetic disk 200.
[0190] The suspension 154 is connected to one end of an actuator
arm 155. A voice coil motor 156, a kind of linear motor, is
provided on the other end of the actuator arm 155. The voice coil
motor 156 is formed of a magnetic circuit including a driving coil
(not shown) wound around a bobbin and a permanent magnet and a
counter yoke arranged opposite to each other so as to sandwich the
coil therebetween.
[0191] The actuator arm 155 is held by ball bearings (not shown)
provided at two vertical positions of the spindle 157. The actuator
arm 155 can be rotatably slid by the voice coil motor 156.
[0192] FIG. 12 is an enlarged perspective view of a part of the
head gimbal assembly including tip end side of the actuator arm
155, which is viewed from the disk. The assembly 160 has the
actuator arm 155, and the suspension 154 is connected to one end of
the actuator arm 155. The head slider 153 is attached to the tip of
the suspension 154, and the head slider 153 comprises a magnetic
head including the magnetoresistive element according to any of the
above embodiments. The suspension 154 has leads 164 used to write
and read signals. The leads 164 are electrically connected to
respective electrodes in the magnetic head incorporated in the head
slider 153. Reference numeral 165 in the figure denotes electrode
pads of the assembly 160.
[0193] The present invention comprises the magnetic head including
the magnetoresistive element according to any of the above
embodiments of the present invention. This makes it possible to
reliably read information magnetically recorded on the magnetic
disk 200 at a recording density higher than that in the prior
art.
[0194] (Magnetic Memory)
[0195] A magnetic memory using the magnetoresistive element
according to an embodiment of the present invention will now be
described. The magnetoresistive element according to the embodiment
of the present invention can be used to realize a magnetic memory
such as a magnetic random access memory (MRAM) in which memory
cells are arrayed in a matrix.
[0196] FIG. 13 is a diagram showing an example of the matrix
configuration of a magnetic memory according to an embodiment of
the present invention. This figure shows the circuit configuration
in which memory cells are arrayed. The magnetic memory comprises a
column decoder 350 and a row decoder 351 to select one bit in the
array. A bit line 334 and a word line 332 are used to turn on and
uniquely select a switching transistor 330. Detection by a sense
amplifier 352 enables reading of the bit information recorded in
the magnetic recording layer (free layer) in the magnetoresistive
film. To write bit information, a write current is passed through a
particular word line 323 and a particular bit line 322 to generate
a magnetic field to be applied.
[0197] FIG. 14 is a diagram showing another example of the matrix
configuration of a magnetic memory according to an embodiment of
the present invention. In this case, one of bit lines 322 is
selected by a decoder 361, while one of the word lines 334 is
selected by a decoder 360; the bit lines 322 and the word lines 334
are arrayed in a matrix. Thus, a particular memory cell in the
array is selected. Each memory cell has a structure in which the
magnetoresistive film SV and a diode D are connected in series.
Here, the diode D serves to prevent a sense current from bypassing
in the memory cells other than the selected magnetoresistive film
SV. A write operation is performed by using a magnetic field
generated by passing a write current through each of a particular
bit line 322 and a particular word line 323.
[0198] FIG. 15 is a cross-sectional view showing a major portion of
a magnetic memory according to an embodiment of the present
invention. FIG. 16 is a cross-sectional view taken along the line
A-A' in FIG. 15. The structure shown in these figures corresponds
to a memory cell for one bit included in the magnetic memory shown
in FIG. 13 or 14. The memory cell has a storage element 311 and an
address selecting transistor 312.
[0199] The storage element 311 has the magnetoresistive film SV and
a pair of wires 322 and 324 connected to the magnetoresistive film
SV.
[0200] On the other hand, the address-selecting transistor 312 is
provided with a transistor 330 connected to the magnetoresistive
film through vias 326 and buried wires 328. The transistor 330
performs a switching operation in accordance with a voltage applied
to a gate 332 to controllably open and close the current paths
between the magnetoresistive film SV and a wire 334.
[0201] A write wire 323 is provided below the magnetoresistive film
SV in a direction orthogonal to the wire 322. The write wires 322
and 323 can be made of, for example, aluminum (Al), copper (Cu),
tungsten (W), tantalum (Ta), or an alloy containing any one of
these elements.
[0202] In the memory cell thus constituted, to write bit
information to the magnetoresistive film SV, a write pulse current
is passed through the wires 322 and 323 to induce a synthetic
magnetic field. The synthetic magnetic field is applied to
appropriately reverse the magnetization of the recording layer of
the magnetoresistive film.
[0203] Further, to read bit information, a sense current is passed
through the wire 322, the magnetoresistive film SV including the
magnetic recording layer, and the lower electrode 324. Then, the
resistance value or a change in resistance value of the
magnetoresistive film SV is measured.
[0204] The magnetic memory according to the embodiment of the
present invention uses the magnetoresistive element according to
any of the above embodiments. Consequently, even with a reduction
in cell size, the magnetic domains in the recording layer are
surely controlled to allow write and read operations to be reliably
performed.
Other Embodiments
[0205] The embodiment of the present invention is not limited to
the above described embodiment, and can be extended and varied. The
extended and varied embodiments are also within the technical scope
of the present invention. For the specific structure of the
magnetoresistive film as well as the shapes and materials of the
electrodes, bias application film, insulating film, and the like,
those skilled in the art can similarly implement the present
invention to produce similar effects by making appropriate
selections from the corresponding well-known ranges. For example,
when the magnetoresistive element is applied to a read head, the
detection resolution of the read head can be defined by providing
magnetic shields on both sides of the element.
[0206] Further, the present invention can be applied to a magnetic
head or magnetic recording apparatus based on a perpendicular
magnetic recording system as well as a longitudinal magnetic
recording system. Moreover, the magnetic recording apparatus
according to the present invention may be a so-called a rigid type
constantly provided with particular recording media or a so-called
removable type that allows recording media to be exchanged.
[0207] The scope of the present invention also includes all the
magnetoresistive elements, magnetic heads, magnetic recording
apparatuses, and magnetic memories that can be implemented by those
skilled in the art by appropriately changing the designs of the
above magnetic heads and magnetic recording apparatuses described
above, based on the embodiments of the present invention. For
example, the magnetoresistive element according to an embodiment of
the invention can be used in all HDD compatible with high recording
density and can be applied to the recording apparatus such as
personal computers, portable audio/video players, car navigation
system and video cameras for civilian applications.
* * * * *