U.S. patent application number 14/176989 was filed with the patent office on 2014-06-05 for method of manufacturing magnetoresistive element.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. The applicant listed for this patent is KABUSHIKI KAISHA TOSHIBA. Invention is credited to Yoshihiko FUJI, Hideaki FUKUZAWA, Michiko HARA, Shuichi MURAKAMI, Akihiko TAKEO, Hiromi YUASA.
Application Number | 20140153139 14/176989 |
Document ID | / |
Family ID | 45696973 |
Filed Date | 2014-06-05 |
United States Patent
Application |
20140153139 |
Kind Code |
A1 |
TAKEO; Akihiko ; et
al. |
June 5, 2014 |
METHOD OF MANUFACTURING MAGNETORESISTIVE ELEMENT
Abstract
According to one embodiment, a method of manufacturing a
magnetoresistive element includes a layered structure and a pair of
electrodes, the layered structure including a cap layer, a
magnetization pinned layer, a magnetization free layer, a spacer
layer and a functional layer provided in the magnetization pinned
layer, between the magnetization pinned layer and the spacer layer,
between the spacer layer and the magnetization free layer, in the
magnetization free layer, or between the magnetization free layer
and the cap layer and including an oxide, the method including
forming a film including a base material of the functional layer,
performing an oxidation treatment on the film using a gas
containing oxygen in a form of at least one selected from the group
consisting of molecule, ion, plasma and radical, and performing a
reduction treatment using a reducing gas on the film after the
oxidation treatment.
Inventors: |
TAKEO; Akihiko; (Tokyo,
JP) ; FUJI; Yoshihiko; (Kawasaki-shi, JP) ;
YUASA; Hiromi; (Kawasaki-shi, JP) ; HARA;
Michiko; (Yokohama-shi, JP) ; MURAKAMI; Shuichi;
(Tokyo, JP) ; FUKUZAWA; Hideaki; (Kawasaki-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
Tokyo |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
45696973 |
Appl. No.: |
14/176989 |
Filed: |
February 10, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13186389 |
Jul 19, 2011 |
8685491 |
|
|
14176989 |
|
|
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|
Current U.S.
Class: |
360/324.11 ;
427/128; 428/811.3 |
Current CPC
Class: |
H01F 10/3295 20130101;
H01F 10/3259 20130101; G11B 5/3983 20130101; H01L 43/12 20130101;
G01R 33/098 20130101; H01F 41/303 20130101; B82Y 40/00 20130101;
H01F 41/325 20130101; B82Y 25/00 20130101; H01F 10/3272 20130101;
G01R 33/093 20130101; Y10T 428/1129 20150115; G11B 5/3163 20130101;
G11B 5/3903 20130101 |
Class at
Publication: |
360/324.11 ;
428/811.3; 427/128 |
International
Class: |
G11B 5/39 20060101
G11B005/39 |
Claims
1. A magnetoresistive element manufactured by a method and
comprising a layered structure and a pair of electrodes allowing an
electric current to flow through the layered structure in a
thickness direction, the layered structure comprising: a cap layer;
a magnetization pinned layer; a magnetization free layer provided
between the cap layer and the magnetization pinned layer; a spacer
layer provided between the magnetization pinned layer and the
magnetization free layer; and a functional layer provided in the
magnetization pinned layer, between the magnetization pinned layer
and the spacer layer, between the spacer layer and the
magnetization free layer, in the magnetization free layer, or
between the magnetization free layer and the cap layer and
comprising an oxide containing at least one element selected from
the group consisting of Zn, In, Sn, and Cd and at least one element
selected from the group consisting of Fe, Co, and Ni; the method
comprising: forming a film comprising a base material of the
functional layer; performing an oxidation treatment on the film
using a gas containing oxygen in a form of at least one selected
from the group consisting of molecule, ion, plasma and radical; and
performing a reduction treatment using a reducing gas on the film
after the oxidation treatment.
2. A magnetic head assembly comprising: a suspension, the
magnetoresistive element of claim 1 mounted at one end of the
suspension, and an actuator arm connected to the other end of the
suspension.
3. A magnetic recording apparatus comprising: the magnetic head
assembly of claim 2 and a magnetic recording medium on which
information is to be recorded, the information on the magnetic
recording medium being read by the magnetoresistive element mounted
to the magnetic head assembly.
4. The magnetic recording apparatus of claim 3, wherein the
magnetoresistive elements are disposed in matrix.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of co-pending U.S. patent
application Ser. No. 13/186,389, filed Jul. 19, 2011, which is
based upon and claims the benefit of priority from Japanese Patent
Application No. 2010-196049, filed Sep. 1, 2010; the entire
contents of which are incorporated herein by reference.
FIELD
[0002] Embodiments described herein relate generally to a method of
manufacturing a magnetoresistive element, a magnetoresistive
element, a magnetic head assembly and a magnetic recording
apparatus.
BACKGROUND
[0003] Improvement of the quality of a magnetoresistive (MR)
element requires the increase of the MR ratio. For the purpose of
increasing the MR ratio, modification of the structure of
magnetoresistive elements and selection of the spacer layer
materials have been carried out. For example, a magnetoresistive
element including a thin spin-filter (SF) layer made of an oxide or
nitride within each ferromagnetic layer or between the
ferromagnetic layer and a non-magnetic spacer layer is proposed.
The SF layer has a spin-filter effect of inhibiting the passage of
upspin or downspin electrons, and thus increases the MR ratio.
Thus, magnetoresistive elements have undergone many improvements,
but are required to achieve further increase of the MR ratio.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] A general architecture that implements the various features
of the embodiments will now be described with reference to the
drawings. The drawings and the associated descriptions are provided
to illustrate the embodiments and not to limit the scope of the
invention.
[0005] FIG. 1 is a flowchart showing a part of a method of
manufacturing a magnetoresistive element according to one
embodiment;
[0006] FIG. 2 is a view showing the magnetoresistive element
according to the embodiment;
[0007] FIGS. 3A and 3B are views showing the magnetoresistive
element according to the embodiment;
[0008] FIG. 4 is a view showing a magnetoresistive element
according to a first modification example;
[0009] FIG. 5 is a view showing a magnetoresistive element
according to a second modification example;
[0010] FIG. 6 is a view showing a magnetoresistive element
according to a third modification example;
[0011] FIG. 7 is a view showing a magnetoresistive element
according to a forth modification example;
[0012] FIG. 8 is a view showing a magnetoresistive element
according to a fifth modification example;
[0013] FIG. 9 is a view showing a magnetoresistive element
according to a sixth modification example;
[0014] FIG. 10 is a view showing a magnetic head according to the
embodiment;
[0015] FIG. 11 is a view showing a magnetic head according to the
embodiment;
[0016] FIG. 12 is a view showing a magnetic recording apparatus
according to the embodiment;
[0017] FIG. 13 is a view showing a head slider according to the
embodiment;
[0018] FIGS. 14A and 14B are views showing a head stack assembly
according to the embodiment;
[0019] FIGS. 15A and 15B are views showing sections of
magnetoresistive elements;
[0020] FIGS. 16A and 16B are views showing elements contained in
layers of the magnetoresistive elements; and
[0021] FIG. 17 is a view showing results of X-ray diffraction
measurement.
DETAILED DESCRIPTION
[0022] Various embodiments will be described hereinafter with
reference to the accompanying drawings. In the drawings in the
following description, components having an identical reference
number are identical to each other, and overlapping description is
not repeated.
[0023] In general, according to one embodiment, a method of
manufacturing a magnetoresistive element comprises a layered
structure and a pair of electrodes allowing an electric current to
flow through the layered structure in a thickness direction, the
layered structure comprising a cap layer, a magnetization pinned
layer, a magnetization free layer provided between the cap layer
and the magnetization pinned layer, a spacer layer provided between
the magnetization pinned layer and the magnetization free layer and
a functional layer provided in the magnetization pinned layer,
between the magnetization pinned layer and the spacer layer,
between the spacer layer and the magnetization free layer, in the
magnetization free layer, or between the magnetization free layer
and the cap layer and comprising an oxide containing at least one
element selected from the group consisting of Zn, In, Sn, and Cd
and at least one element selected from the group consisting of Fe,
Co, and Ni, the method comprising forming a film comprising a base
material of the functional layer, performing an oxidation treatment
on the film using a gas containing oxygen in a form of at least one
selected from the group consisting of molecule, ion, plasma and
radical and performing a reduction treatment using a reducing gas
on the film after the oxidation treatment.
[0024] As a magnetoresistive element according to the embodiment, a
CPP-GMR (current-perpendicular-to-plane giant magnetoresistive)
element or a TMR (tunneling magnetoresistive) element including a
spin-valve film is conceived. A spin-valve film is a layered film
having a sandwich structure in which a nonmagnetic spacer layer is
sandwiched between two ferromagnetic layers, and a layered film
structure portion which causes a resistance change is also called a
spin-dependent scattering unit. A magnetization direction of one of
the two ferromagnetic layers (referred to as a "pinned layer" or
"magnetization pinned layer") is pinned by an antiferromagnetic
layer or the like. A magnetization direction of the other
ferromagnetic layer (referred to as a "free layer" or
"magnetization free layer") is changeable by an external magnetic
field. In the spin-valve film, a large magnetoresistive effect is
attained by a change in relative angle of the magnetization
directions of the two ferromagnetic layers. In the CPP-GMR element
and the TMR element, a current is caused to flow through the
spin-valve film in a thickness direction.
[0025] [Manufacturing Method]
[0026] A method of manufacturing a magnetoresistive element 10
according to the embodiment will be described.
[0027] FIG. 1 is a flowchart showing a part of the method of
manufacturing a magnetoresistive element according to the
embodiment. In the flowchart of FIG. 1, details of a process of
forming a functional layer 21 are particularly shown. It is
possible to manufacture the magnetoresistive element according to
the embodiment by sequentially forming layers.
[0028] Particularly, the formation of the functional layer 21
includes a first step S110, a second step S120, and a third step
S130. A film made from a base material of the functional layer is
formed in the first step S110; an oxidation treatment using a gas
containing oxygen in a form of at least one selected from the group
consisting of molecule, ion, plasma and radical is performed on the
film in the second step S120; and a reduction treatment using a
reducing gas is performed on the film after the oxidation treatment
in the third step S130. In contrast, in conventional manufacturing
methods, only the film formation and the oxidation treatment are
performed, and the reduction treatment is not performed.
[0029] In the present embodiment, the film formation method used in
manufacture of the element may be, for example, a sputtering method
such as DC magnetron sputtering or RF magnetron sputtering, ion
beam sputtering, vapor deposition, chemical vapor deposition (CVD),
or molecular beam epitaxy (MBE).
[0030] Hereinafter, details of the entire manufacturing method will
be described. As one example, a method of manufacturing a
magnetoresistive element shown in FIG. 2 according to the
embodiment will be described.
[0031] Firstly, the lower electrode 11 is formed on a substrate by
micromachining process. Subsequently, for example, Ta [1 nm]/Ru [2
nm] is formed as the underlayer 12 on the lower electrode 11. The
Ta corresponds to a buffer layer which reduces the roughness of the
lower electrode 11. The Ru layer corresponds to a seed layer which
controls the crystalline orientation and crystal grain size in the
spin valve film formed thereon.
[0032] Then, the pinning layer 13 is formed on the underlayer 12.
The material of the pinning layer 13 may be an antiferromagnetic
material such as PtMn, PdPtMn, IrMn, or RuRhMn.
[0033] The pinned layer 14 is formed on the pinning layer 13. The
pinned layer 14 may be, for example, a synthetic pinned layer made
of the lower pinned layer 141 (Co.sub.75Fe.sub.25 [3.2 nm]), the
magnetic coupling layer 142 (Ru), and the upper pinned layer 143
(Co.sub.50Fe.sub.50 [3 nm]).
[0034] Subsequently, a spacer layer 16 is formed on a pinned layer
14. As the spacer layer 16, a nonmagnetic metal layer containing at
least one element selected from Cu, Ag, and Au, a CCP spacer layer,
or a tunneling insulator is formed.
[0035] Subsequently, the functional layer 21 is formed on the
spacer layer 16.
[0036] More specifically, a metal layer of Fe.sub.50Co.sub.50 and
Zn is formed on an upper pinned layer 143 as the first step S110.
The metal layer made of Fe.sub.50Co.sub.50 and Zn may be a stack of
Fe.sub.50Co.sub.50 and Zn layers such as Fe.sub.50Co.sub.50/Zn,
Zn/Fe.sub.50Co.sub.50, or (Fe.sub.50Co.sub.50/Zn).times.2, or a
single layer of an alloy such as
Zn.sub.50(Fe.sub.50Co.sub.50).sub.50. As the first step S110, a
metal layer containing at least one element selected from the group
consisting of Zn, In, Sn, and Cd and at least one element selected
from the group consisting of Fe, Co, and Ni may be formed.
[0037] Next, as the second step S120, the oxidation treatment is
performed on the metal material containing Zn and
Fe.sub.50Co.sub.50. The oxidation treatment may use ion-assisted
oxidation (IAO), which is carried out by feeding oxygen to the
metal material layer under irradiation with rare gas ion beams or
plasma. In the ion-assisted oxidation treatment, oxygen gas ion
beams or plasma may be used. The energy assistance using ion beam
irradiation in the treatment of the metal material layer allows the
formation of a stable and uniform oxide layer as the functional
layer 21. In order to form the functional layer 21 having a single
layer structure, the formation and oxidation treatment of the
above-described metal material layer may be repeated several times.
In this case, instead of performing the film formation and
oxidation each only one-time in order to form the functional layer
21 having a predetermined thickness, it is more preferred that
formation of a thinner metal material layer and the oxidation
treatment thereof are repeated alternately. Alternatively, the
metal material layer containing Zn and Fe.sub.50Co.sub.50 may be
exposed to an oxygen atmosphere for natural oxidation. In order to
form a stable oxide, energy-assisted oxidation is preferred.
Alternatively, a stack of Zn and Fe.sub.50Co.sub.50 metal materials
is preferably oxidized under irradiation with an ion beam, thereby
forming the functional layer 21 made of uniformly mixed Zn with
Fe.sub.50Co.sub.50.
[0038] In the case of using an ion beam or plasma of a rare gas or
the like, a gas containing at least one selected from the group
consisting of argon, xenon, helium, neon, and krypton may be used
as the rare gas.
[0039] The energy assistance may use heat treatment in place of the
irradiation with an ion beam. In this case, for example, oxygen may
be fed to the formed metal material layer under heating at 100 to
300.degree. C.
[0040] The beam conditions for ion beam-assisted conversion
treatment for forming the functional layer 21 are described below.
When the formation of the functional layer 21 by conversion
treatment uses the above-described irradiation with rare gas ions
or plasma, the accelerating voltage V is preferably from 30 to 130
V, and the beam electric current Ib is preferably from 20 to 200
mA. These conditions are markedly milder in comparison with the
conditions for ion beam etching. The functional layer 21 may be
formed in the same manner using plasma such as RF plasma in place
of ion beams. The angle of incidence of the ion beam is changed as
appropriate from 0 to 80.degree., based on the definition that the
angle of the beam perpendicular to the layer surface is 0.degree.,
and that parallel to the layer surface is 90.degree.. The treatment
time of the process is preferably from 15 seconds to 1200 seconds,
and more preferably 30 seconds or more, from the viewpoint of
controllability. If the treatment time is too long, the
productivity of the magnetoresistive element deteriorates. From
these viewpoints, the treatment time is preferably from 30 seconds
to 600 seconds.
[0041] In the oxidation treatment using ions or plasma, the oxygen
exposure dose is preferably from 1.times.10.sup.3 to
1.times.10.sup.4 L [Langmiur, 1 L=1.times.10.sup.-6 Torr.times.sec]
for IAO, or from 3.times.10.sup.3 to 3.times.10.sup.4 L for natural
oxidation.
[0042] Next, as the third step, the reduction treatment using the
reducing gas is performed. As the reducing gas, a gas containing at
least one selected from the group consisting of argon, helium,
neon, krypton and xenon in a form of ion, plasma or radical and/or
at least one selected from the group consisting of hydrogen and
nitrogen in a form of molecule, ion, plasma or radical may be used.
Particularly, it is preferable to use the gas containing at least
one selected from the group consisting of argon, helium, neon,
krypton, xenon, hydrogen and nitrogen in a form of ion or plasma as
the reducing gas. It is further preferable to use the gas
containing argon in a form of ion or plasma as the reducing
gas.
[0043] By the reduction treatment, it is possible to adjust an
oxidation number of the film made from the base material after the
oxidation treatment. For example, in the case of using the oxide
containing Zn and Fe.sub.50Co.sub.50 as a functional layer, the
Zn--Fe oxide functional layer after the oxidation treatment is a
mixed oxide of Zn--Fe oxides having various crystal structures such
as (Fe--Co--Zn).sub.3O.sub.4, .alpha.-(Fe--Co--Zn).sub.2O.sub.3,
and .gamma.-(Fe--Co--Zn).sub.2O.sub.3. Though
(Fe--Co--Zn).sub.3O.sub.4 is a conductor and desirable oxide from
the viewpoint of attaining low resistivity,
.alpha.-(Fe--Co--Zn).sub.2O.sub.3 and
.gamma.-(Fe--Co--Zn).sub.2O.sub.3 are insulating oxides, and the
presence of .alpha.-(Fe--Co--Zn).sub.2O.sub.3 and
.gamma.-(Fe--Co--Zn).sub.2O.sub.3 entails an increase in
resistivity of the functional layer. In the manufacturing method
according to the embodiment, the reduction treatment using the
reducing gas is performed on the functional layer as the third
step, and oxidation numbers of .alpha.-(Fe--Co--Zn).sub.2O.sub.3,
.gamma.-(Fe--Co--Zn).sub.2O.sub.3, and the like are reduced for
conversion into (Fe--Co--Zn).sub.3O.sub.4, thereby giving a spin
filtering layer having low resistivity. Thus, it is possible to
realize a high MR change ratio due to a high spin filtering effect
attained by the suppression of occurrence of spin-flip.
[0044] In the third step, the reduction treatment may be performed
while heating the film made from the base material after the
oxidation treatment. For example, the reduction treatment may be
performed on the base material which is heated to 100.degree. C. to
300.degree. C. It is possible to more efficiently perform the
reduction treatment by the heating.
[0045] After the third step, at least one moisture elimination
treatment selected from the group consisting of irradiation with
argon ions, irradiation with argon plasma, and heating may be
performed as a fourth step. By means of the treatment, it is
possible to eliminate moisture produced during the reduction
treatment.
[0046] Also, when manufacturing the functional layer 21, the third
step and the fourth step may be repeated after finishing the first
step to the fourth step. By alternately repeating the elimination
of produced moisture and the reduction treatment, it is possible to
more efficiently reduce the film.
[0047] Further, a specific step may be repeated a plurality of
times in the aim of realizing good reduction in the case where
sufficient reduction is desired, a film thickness is too great, or
the like. For example, the first step, the second step, the third
step, and the fourth step may be repeated a plurality of times. In
this case, a series of treatments including the film formation, the
oxidation treatment, the reduction treatment, and the moisture
elimination is repeated a plurality of times. Alternatively, the
first step, the second step, and the third step may be repeated a
plurality of times. In this case, a series of treatments including
the film formation, the oxidation treatment, and the reduction
treatment is repeated a plurality of times, and, in the case of
performing the fourth step, the moisture elimination step is
performed lastly. Alternatively, the first step and the second step
may be repeated a plurality of times. In this case, after the film
formation and the oxidation treatment are performed alternately,
the reduction treatment is performed (and moisture elimination is
arbitrarily performed). As described above, it is preferable to
perform the film formation and the oxidation treatment repeatedly
and thereby form the film gradually rather than to form the whole
film at once by performing the film formation and the oxidation
treatment at once.
[0048] Particularly, beam conditions in the case of performing the
Ar ion beam irradiation in the above-described reduction treatment
will be described below. In the reduction treatment, when the
irradiation of the rare gas in a form of ion or plasma is used, an
acceleration voltage V may preferably be set to 30 to 130 V, and a
beam current Ib may preferably be set to 20 to 200 mA. These
conditions are considerably weak as compared to conditions for
performing ion beam etching. It is possible to form the functional
layer 21 in the same way by using plasma such as RF plasma in place
of the ion beam. An incident angle of the ion beam is appropriately
changed within a range of 0.degree. to 80.degree. when the
incidence which is vertical to a film surface is defined as
0.degree. and the incidence which is parallel to the film surface
is defined as 90.degree.. A treatment time of the step may
preferably be 15 to 1200 seconds, more preferably 30 seconds or
more from the viewpoints of controllability and the like. When the
treatment time is too long, productivity of the magnetoresistive
element is unpreferably degraded. The treatment time may preferably
be 30 to 600 seconds from these viewpoints.
[0049] Then, the free layer 18 is formed on the functional layer
21. The free layer 18 is, for example, Fe.sub.50Co.sub.50 [1
nm]/Ni.sub.85Fe.sub.15 [3.5 nm].
[0050] The cap layer 19 is formed on the free layer 18. The cap
layer 19 may be, for example, Cu [1 nm]/Ru [10 nm].
[0051] Thereafter, annealing treatment is carried out.
[0052] Finally, the upper electrode 20 for allowing electric
current to flow through the magnetoresistive element 10 in a
direction perpendicular to the magnetoresistive element 10 is
formed on the cap layer 19.
[0053] [Magnetoresistive Element]
Embodiment
[0054] FIG. 2 shows the magnetoresistive element 10 according to
the embodiment.
[0055] The magnetoresistive element 10 according to the present
embodiment includes a cap layer 19 which protects the
magnetoresistive element 10 from deterioration such as oxidation, a
magnetization pinned layer (hereinafter referred to as a pinned
layer) 14 in which magnetization has been fixed, a magnetization
free layer (hereinafter referred to as a free layer) 18 which is
provided between the cap layer 19 and the pinned layer 14, and in
which magnetization freely rotates, a spacer layer 16 provided
between the pinned layer 14 and the free layer 18, and a functional
layer 21 which is provided between the spacer layer 16 and the free
layer 18 and includes an oxide that includes at least one element
selected from the group consisting of Zn, In, Sn and Cd and at
least one element selected from the group consisting of Fe, Co and
Ni. The structure in which the components including the cap layer
19, the free layer 18, the functional layer 21, the spacer layer
16, and the pinned layer 14 are stacked is defined as a stack.
[0056] The magnetoresistive element 10 also includes a pair of
electrodes (lower electrode 11 and upper electrode 20) which allow
electric current to flow through the stack in a direction
perpendicular to the surface of the stack. These electrodes are in
contact with the outermost layers of the stack, respectively. The
electrode on the pinned layer 14 side of the stack is referred to
as the lower electrode 11, and the electrode on the free layer 18
side of the stack is referred to as the upper electrode 20.
Further, the magnetoresistive element 10 includes a pinning layer
13 which is provided between the lower electrode 11 and the pinned
layer 14, and is made of an antiferromagnetic substance for fixing
the magnetization direction of the pinned layer 14, and an
underlayer 12 provided between the pinning layer 13 and the lower
electrode 11.
[0057] The lower electrode 11 and the upper electrode 20 allow
electric current to flow through the magnetoresistive element 10 in
a direction perpendicular to the surface of the magnetoresistive
element 10. That is, when voltage is applied between the lower
electrode 11 and the upper electrode 20, an electric current flows
through the magnetoresistive element 10 perpendicularly to the
surface of the magnetoresistive element 10.
[0058] The passage of the electric current allows the detection of
the resistance change due to magnetoresistance, and thus allows the
detection of magnetism. The lower electrode 11 and the upper
electrode 20 are made of, for example, Cu, or Au having a
relatively small electrical resistance thereby allowing electric
current to flow through the magnetoresistive element 10.
[0059] The underlayer 12 has, for example, a structure in which a
buffer layer and a seed layer are stacked. The buffer layer is
positioned on the side of the lower electrode 11, and the seed
layer is positioned on the side of the pinning layer 13.
[0060] The buffer layer reduces the effect of surface roughness of
the lower electrode 11, and improves the crystallinity in the layer
stacked on the buffer layer. The buffer layer may be made of, for
example, Ta, Ti, V, W, Zr, Hf, Cr, or an alloy thereof. The
thickness of the buffer layer is preferably 1 nm or more and 10 nm
or less, and more preferably 2 nm or more and 5 nm or less. If the
thickness of the buffer layer is too small, the buffer effect is
lost. On the other hand, if the thickness of the buffer layer is
too large, series resistance, which will not contribute to the MR
ratio, will increase. When the seed layer formed on the buffer
layer has a buffer effect, the buffer layer may not necessary. As a
preferred example, a Ta layer may be formed to have a thickness of
3 nm.
[0061] The seed layer controls the crystalline orientation and
crystal grain size in the layer stacked on the seed layer. The seed
layer is preferably made of a metal having a face-centered cubic
(fcc) structure, a hexagonal close-packed (hcp) structure, or a
body-centered cubic (bcc) structure.
[0062] For example, the seed layer may be made of Ru having a hcp
structure or NiFe having an fcc structure, such that the
crystalline orientation of the overlying spin-valve film has an fcc
(111) orientation. When the pinning layer 13 is made of IrMn, a
good fcc (111) orientation is achieved. When the pinning layer 13
is made of PtMn, a regulated face-centered tetragonal (fct) (111)
structure is obtained. When the free layer 18 and the pinned layer
14 are made of an fcc metal, a good fcc (111) orientation is
achieved. When the free layer 18 and the pinned layer 14 are made
of a bcc metal, a good bcc (110) orientation is achieved. The
thickness of the seed layer is preferably 1 nm or more and 5 nm or
less, and more preferably 1.5 nm or more and 3 nm or less, such
that the seed layer sufficiently improves the crystalline
orientation. As a preferred example, an Ru layer may be formed to
have a thickness of 2 nm.
[0063] Alternatively, the seed layer may be made of, in place of
Ru, a NiFe-based alloy (for example, 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]),
which has been prepared by adding a third element X to NiFe thereby
nonmagnetizing it, may be used. When an NiFe-based seed layer is
used, a good crystalline orientation is relatively easily obtained,
and a half width of the rocking curve within a range of 3 to
5.degree. can be achieved.
[0064] The seed layer improves the crystalline orientation, and
controls the crystal grain size in the spin-valve film. More
specifically, the seed layer adjusts the crystal grain size in the
spin-valve film from 5 nm or more and 20 nm or less, thereby
achieving a high MR ratio in spite of the decrease in the size of
the magnetoresistive element, without variation in the
properties.
[0065] When the crystal grain size in the seed layer is 5 nm or
more and 20 nm or less, diffused reflection of electrons and
inelastic scattering sites caused by crystal grain boundaries are
decreased. In order to achieve the crystal grain size, for example,
an Ru layer is formed to have a thickness of 2 nm. When the seed
layer is made of (Ni.sub.x Fe.sub.100-x).sub.100-yZ.sub.y (Z=Cr, V,
Nb, Hf, Zr, Mo), its thickness is preferably 2 nm, wherein the
ratio y of a third element X is from about 0 to 30% (including
y=0).
[0066] The crystal grain size in the spin-valve film may be
determined on the basis of the size of the crystal grains in the
layer interposed between the seed layer and the spacer layer 16
(for example, by cross-sectional TEM). For example, when the pinned
layer 14 is a bottom type spin-valve film underlying the spacer
layer 16, the crystal grain size in the spin-valve film may be
determined based on the crystal grain sizes in the pinning layer 13
(antiferromagnetic layer) or the pinned layer 14 (magnetization
pinned layer) formed on the seed layer.
[0067] 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 PtMn, PdPtMn,
IrMn and RuRhMn can be used. Among them, IrMn is advantageous for
application to heads adapted to high recording density. IrMn can
impart unidirectional anisotropy at a smaller thickness than PtMn
and is suitable for reducing a gap necessary for high density
recording.
[0068] 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 4 to 18 nm, more preferably 5 to 15
nm. A preferable example includes Ir.sub.22Mn.sub.78 of about 7 nm
in thickness.
[0069] 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
resistance-area product (RA).
[0070] The term "resistance-area product" refers to the product
obtained by multiplying the sectional area of the magnetoresistive
element 10 perpendicular to the stacking direction of the stacked
film by the resistance obtained between the pair of electrodes when
electric current is allowed to flow perpendicularly to the surface
of the stacked film of the magnetoresistive element 10.
[0071] The degree of crystalline orientation of the spin-valve film
and the pinning layer 13 may be determined by X-ray diffractometry.
When the half width of the rocking curve at the fcc (111) peak of
the spin-valve film, fct (111) peak or bcc (110) peak of the
pinning layer 13 (FtMn) is, for example, 3.5 to 6.degree., the
degree of crystalline orientation is considered to be sufficient.
This can also be assessed using the dispersion angle of the
diffraction spots obtained using cross-sectional TEM.
[0072] 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 in this order on the pinning layer 13.
[0073] The pinning layer 13 and the lower pinned layer 141 are
bonded together by magnetic exchange coupling so as to exhibit a
unidirectional anisotropy. The lower pinned layer 141 and the upper
pinned layer 143 sandwiching the magnetic coupling layer 142 are
strongly coupled such that the direction of magnetization are
anti-parallel to each other.
[0074] The lower pinned layer 141 may be made of, for example, a
Co.sub.xFe.sub.100-x alloy (x=0 to 100%), a Ni.sub.xFe.sub.100-x
alloy (x=0 to 100%), or any of these alloy further containing a
non-magnetic element. The lower pinned layer 141 may be made of a
single element such as Co, Fe or Ni, or an alloy of these elements.
Alternatively, a (Co.sub.xFe.sub.100-x).sub.100-YB.sub.X alloy (x=0
to 100%, x=0 to 30%) may be used. From the viewpoint of reducing
the variation in performance among elements each having the
magnetoresistive element of a small size, the use of an amorphous
alloy such as (Co.sub.xFe.sub.100-x).sub.100-YB.sub.X is
preferred.
[0075] The thickness of the lower pinned layer 141 is preferably
1.5 nm or more and 5 nm or less, thereby maintaining a high
magnetic field intensity of the unidirectional anisotropy exhibited
by the pinning layer 13 and a high magnetic field intensity for the
antiferromagnetic coupling between the lower pinned layer 141 and
the upper pinned layer 143 via the magnetic coupling layer 142.
[0076] If the thickness of the lower pinned layer 141 is too small,
the thickness of the upper pinned layer 143 which influences the MR
ratio must be decreased, which results in the decrease in the MR
ratio. On the other hand, if the thickness of the lower pinned
layer 141 is too large, sufficient unidirectional anisotropic
magnetic field enough for device operation is hard to obtain.
[0077] 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.
[0078] As an example, when the upper pinned layer 143 is
(Fe.sub.40Co.sub.40B.sub.20 [3 nm], the saturation magnetization of
the Fe.sub.50Co.sub.50 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.75Fe.sub.25 is approximately 2.1
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/2.1 T=3.15
nm. Therefore, it is desirable to use Co.sub.75Fe.sub.25 with a
thickness of approximately 3.2 nm.
[0079] The symbol `/` used later represents that the elements are
stacked in the order from the left of `/` to the right of `/`, so
that Au/Cu/Ru represents that a Cu layer is stacked on an Au layer,
and an Ru layer is stacked on the Cu layer. The symbol `.times.2`
represents two layers, so that (Au/Cu).times.2 represents that a Cu
layer is stacked on an Au layer, and another Au layer and another
Cu layer are stacked in this order on the Cu layer. The symbol `[
]` represents the thickness of the layer.
[0080] The magnetic coupling layer 142 allows an antiferromagnetic
coupling between the lower pinned layer 141 and the upper pinned
layer 143 sandwiching the magnetic coupling layer 142, thereby
forming a synthetic pinned structure. The magnetic coupling layer
142 may be made of Ru, and the thickness of the magnetic coupling
layer 142 is preferably 0.8 nm or more and 1 nm or less. The
material of the magnetic coupling layer 142 may be other than Ru,
as long as the material causes the antiferromagnetic coupling at a
sufficiently high intensity between the lower pinned layer 141 and
the upper pinned layer 143 sandwiching the magnetic coupling layer
142. The thickness of the magnetic coupling layer 142 may fall
within a range of 0.3 to 0.6 nm which corresponds to the first peak
of the Ruderman-Kittel-Kasuya-Yoshida (RKKY) coupling, instead of a
range of 0.8 nm to 1 nm which corresponds to the second peak of the
RKKY coupling. For example, Ru having a thickness of 0.9 nm may be
used, thereby stably forming a more reliable coupling and achieving
the function of the layer.
[0081] 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.
[0082] The upper pinned layer 143 may be made of
Fe.sub.50Co.sub.50. Fe.sub.50Co.sub.50 is a magnetic material
having a bcc structure. Since the material has a high
spin-dependent interface scattering effect, it achieves a high MR
ratio. Examples of FeCo alloys having a bcc structure include
Fe.sub.xCo.sub.100-x (x=30 to 100%), and Fe.sub.xCo.sub.100-x
containing an additional element. Among the materials,
Fe.sub.40Co.sub.60 to Fe.sub.80Co.sub.20 which offer sufficient
properties in all respects are examples to be readily used.
[0083] When the upper pinned layer 143 is made of a magnetic layer
having a bcc structure which readily achieves a high MR ratio, the
total thickness of the magnetic layer is preferably 1.5 nm or more,
thereby maintaining a stable bcc structure. The metal material used
to make a spin-valve film often has an fcc or fct structure, so
that only the upper pinned layer 143 may have a bcc structure.
Therefore, if the thickness of the upper pinned layer 143 is too
small, a stable bcc structure may be hard to maintain, which
results in a failure to achieve a high MR ratio.
[0084] Alternatively, the upper pinned layer 143 may be made of a
(Co.sub.xFe.sub.100-x).sub.100-YB.sub.x alloy (x=0 to 100%, x=0 to
30%). The amorphous alloy such as
(Co.sub.xFe.sub.100-x).sub.100-YB.sub.X is preferred from the
viewpoint of reducing the variation in performance among elements
due to the effects of crystal grains which cannot be ignored in
small magnetoresistive elements. In addition, the upper pinned
layer 143 made of the amorphous alloy is so flat that the tunnel
insulator formed on the upper pinned layer 143 is also flattened.
Flattening of the tunnel insulator reduces the frequency of defects
in the tunnel insulator, and thus is important for achieving a high
MR ratio with a low RA. In particular, when MgO is used as the
material of the tunnel insulator, the use of an amorphous alloy
such as (Co.sub.xFe.sub.100-x).sub.100-YB.sub.x increases the (100)
orientation of the MgO layer formed on the tunnel insulator. The
(100) orientation of the MgO layer is important for achieving a
high MR ratio. In addition, the
(Co.sub.xFe.sub.100-x).sub.100-YB.sub.x alloy is crystallized upon
annealing with the (100) plane of MgO as the template, and thus
achieves a good crystal lattice match between the MgO and
(Co.sub.xFe.sub.100-x).sub.100-YB.sub.x alloy. The good crystal
lattice match is important for achieving a high MR ratio.
[0085] In order to achieve a high MR ratio, the upper pinned layer
143 preferably has a large thickness. On the other hand, in order
to achieve a pinned magnetic field of high intensity, the thickness
is preferably small. Therefore, there is a trade-off relationship.
For example, when an FeCo alloy layer having a bcc structure is
used, a thickness of 1.5 nm or more is preferred, thereby
stabilizing the bee structure. Also when a CoFe alloy layer having
an fcc structure is used, a thickness of 1.5 nm or more is
preferred, thereby achieving a high MR ratio. On the other hand, in
order to achieve a pinned magnetic field of high intensity, the
upper pinned layer 143 preferably has a thickness of 5 nm or less,
and more preferably 4 nm or less. As described above, the thickness
of the upper pinned layer 143 is preferably 1.5 nm or more and 5 nm
or less, and more preferably 2.0 am or more and 4 nm or less.
[0086] The upper pinned layer 143 may be made of, in place of a
magnetic material having a bcc structure, a Co.sub.90Fe.sub.10
alloy having an fcc structure, or Co or a Co alloy having an hcp
structure, which are widely used in conventional magnetoresistive
elements. The upper pinned layer 143 may be made of a single metal
such as Co, Fe, or Ni, or an alloy material containing any of these
elements. As the magnetic material of the upper pinned layer 143,
an FeCo alloy material having a bcc structure, a cobalt alloy
containing 50% or more cobalt, or an Ni alloy containing 50% or
more Ni is advantageous in achieving a high MR ratio.
[0087] The upper pinned layer 143 may be a Heusler alloy layer such
as Co.sub.2MnGe, Co.sub.2MnSi, or Co.sub.2MnAl.
[0088] The spacer layer 16 decouples magnetic coupling between the
pinned layer 14 and a free layer 18. As the spacer layer 16, a
nonmagnetic metal layer, a CCP (current-confined-to-path) spacer
layer, or a tunneling insulator may be used.
[0089] In the case of using the nonmagnetic metal layer as the
spacer layer 16, any one of elements of Au, Ag, and Cu may be used.
A film thickness of the spacer layer 16 may preferably be 0.5 to 5
nm or less.
[0090] The case of using the CCP spacer layer as the spacer layer
16 will be described by using FIGS. 3A and 3B. As shown in FIG. 3A,
the CCP spacer layer is formed of a lower metal layer 15, a current
constriction layer 23, and an upper metal layer 17. Further, the
current constriction layer 23 comprises an insulating layer 25 and
a current path 24. The current path 24 allows a current to pass
therethrough.
[0091] The lower metal layer 15 is used for forming the current
path 24 and is a supply source of the current path 24. Also, when
the insulating layer 25 which is above the lower metal layer 15 is
formed, the lower metal layer 15 functions as a stopper layer which
suppresses oxidation of the upper pinned layer 143 positioned below
the lower metal layer 15.
[0092] In the case where a constituent material of the current path
24 is Cu, a constituent material of the lower metal layer 15 may
preferably be the same (Cu). In the case where the constituent
material of the current path 24 is a magnetic material, the
magnetic material may be the same as or different from a magnetic
material of the pinned layer 14. Au, Ag, or the like may be used as
the constituent material of the current path 24 in addition to
Cu.
[0093] The insulating layer 25 is formed of an oxide, a nitride, an
oxynitride, and the like. In order to exhibit the function as the
spacer layer, a thickness of the insulating layer 25 may preferably
be 1 to 3 nm, more preferably within a range of 1.5 to 2.5 nm.
[0094] Typical examples of a material to be used for the insulating
layer 25 include Al.sub.2O.sub.3 and those obtained by adding an
additive element to Al.sub.2O.sub.3. For example, Al.sub.2O.sub.3
having a film thickness of about 2 nm may be used. Examples of the
additive element include Ti, Hf, Mg, Zr, V, Mo, Si, Cr, Nb, Ta, W,
B, C, and the like. An amount of the additive element to be added
may appropriately be changed within a range of 0% to 50%.
[0095] For the insulating layer 25, Mg oxide, Zn oxide, Ti oxide,
Hf oxide, Mn oxide, Zr oxide, Cr oxide, Ta oxide, Nb oxide, Mo
oxide, Si oxide, V oxide, or the like may be used in place of the
Al oxide such as Al.sub.2O.sub.3. The above-described additive
elements may be used for the oxides, too. An amount of the additive
element to be added may appropriately be changed within a range of
about 0% to 50%.
[0096] For the insulating layer 25, a nitride or an oxynitride
based on Al, Si, Hf, Ti, Mg, Zr, V, Mo, Nb, Ta, W, B, or C may be
used in place of the oxide.
[0097] The current path 24 is the path (route) for allowing a
current to flow in a thickness direction of the current
constriction layer 23 and constricts the current. The current path
24 functions as a conductor which allows the current to pass in the
thickness direction of the insulating layer 25 and is formed of a
metal layer of Cu and the like, for example. Namely, the current
constriction layer 23 has a current constriction structure (CCP
structure), and it is possible to increase the MR change ratio by
the current constriction effect. A material to be used for forming
the current path 24 (CCP) may be Cu, Au, Ag, Ni, Co, Fe or an alloy
layer containing at least one of the elements. For example, the
current path 24 may be formed of an alloy layer containing Cu.
Also, an alloy layer of CuNi, CuCo, CuFe, or the like may be used.
Here, a composition having 50% or more of Cu is preferred for the
purposes of attaining the high MR change ratio and downsizing an
interlayer coupling field between the pinned layer 14 and the free
layer 18.
[0098] The current path 24 is a region in which contents of oxygen
and nitrogen are considerably lower than those of the insulating
layer 25 (content of oxygen or nitrogen in the insulating layer 25
is at least twice that of the current path 24) and is a crystal
phase. Since the crystal phase has lower resistance than an
amorphous phase, the crystal phase readily functions as the current
path 24.
[0099] The upper metal layer 17 functions as a barrier layer for
suppressing diffusion of oxygen and nitrogen from the current
constriction layer 23 into the free layer 18 as well as a seed
layer for promoting good crystal growth of the free layer 18. More
specifically, the upper metal layer 17 protects the free layer 18
formed thereon so that the free layer 18 is not oxidized or
nitrided by contacting the oxide, nitride, and oxynitride of the
current construction layer 23. Namely, the upper metal layer 17
restricts a direct contact between the oxygen in the oxide layer of
the current path 24 and the free layer 18. Also, the upper metal
layer 17 improves crystallinity of the free layer 18. For example,
though crystallinity of the metal layer formed on the insulating
layer 25 is deteriorated in the case where the material of the
insulating layer 25 is amorphous (Al.sub.2O.sub.3, for example), it
is possible to considerably improve the crystallinity of the free
layer 18 by disposing a extremely thin seed layer (Cu layer, for
example) which improves the crystallinity.
[0100] A material to be used for the upper metal layer 17 may
preferably be the same as the material (Cu, for example) of the
current path 24 of the current constriction layer 23. An increase
in interfacial resistance is caused in the case where the material
of the upper metal layer 17 is different from the material of the
current path 24, but the increase in interfacial resistance does
not occur when the materials are the same. In the case of using a
magnetic material for the constituent material of the current path
24, the magnetic material may be the same as or different from the
magnetic material of the free layer 18. As the constituent material
of the upper metal layer 17, Cu, Au, Ag, or the like may be
used.
[0101] In the case of using the tunneling insulator as the spacer
layer, a nonmagnetic oxide containing at least one element selected
the group consisting of Mg, Al, Ti, Zr, Hf, and Zn may be used.
Particularly, MgO is preferred from the viewpoints of attaining the
high MR change ratio since MgO causes a coherent spin-dependent
tunneling phenomenon. Also, a film thickness of the tunneling
insulator 16 may preferably be 1 nm or more and 4 nm or less.
[0102] The free layer 18 includes a ferromagnetic substance whose
magnetization direction is changed by the external magnetic field.
For example, the free layer 18 may have a two-layer structure of
Co.sub.90Fe.sub.10 [1 nm]/Ni.sub.93Fe.sub.17 [3.5 nm] obtained by
forming an NiFe layer and a CoFe layer in this order. When the NiFe
layer is not used, a single layer of Co.sub.90Fe.sub.10 [4 nm] may
be used. The free layer 18 may have a three-layer structure such as
CoFe/NiFe/CoFe.
[0103] Among CoFe alloys, Co.sub.90Fe.sub.10 having stable soft
magnetic properties is preferred as the material of the free layer
18. When a CoFe alloy having a composition close to that of the
Co.sub.90Fe.sub.10 is used, the thickness is preferably 0.5 nm or
more and 4 nm or less. A Co.sub.xFe.sub.100-x (x=70 to 90%) may be
used instead.
[0104] The free layer 18 may be a stack in which CoFe or Fe layers
having a thickness of 1 nm or more and 2 nm or less and very thin
Cu layers having a thickness of 0.1 nm or more and 0.8 nm or less
are stacked alternately.
[0105] The free layer 18 may includes an amorphous magnetic layer
such as a CoZrRb layer, as long as the free layer further includes
a magnetic layer having a crystal structure at its interface in
contact with the spacer layer 16, which gives a marked influence on
the MR ratio. The free layer 18 may have the following structures
when observing the spacer layer 16 side. More specifically, the
free layer 18 may be, for example, (1) a crystal layer alone, (2) a
stack of a crystal layer/an amorphous layer, (3) a stack of a
crystal layer/an amorphous layer/a crystal layer, etc. Here, it is
important that in all of the (1) to (3), a crystal layer is in
contact with the spacer layer 16.
[0106] 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 an Ru layer is placed on the side of the free layer 18 can
also be used. In this case, the thickness of the Ru layer is
preferably approximately 0.5 to 2 nm. The cap layer 19 of this
structure is desirable especially when the free layer 18 is made of
NiFe. This is because it can reduce magnetostriction in a mixed
interface layer formed between the free layer 18 and the cap layer
19 since Ru is insoluble with Ni.
[0107] 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.
[0108] 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. In these views, Cu
and Ru are desirable examples of a material for the cap layer.
[0109] The functional layer 21 has a spin-filter effect that allows
control of the permeation of upspin or downspin electrons. The
functional layer 21 includes an oxide made of at least one element
of Zn, In, Sn and Cd and at least one element of Fe, Co and Ni. For
example, a mixed oxide of Fe.sub.50Co.sub.50 and Zn may be used. Zn
is more preferred to In, Sn, and Cd, because Zn, Fe, Co, and Ni are
in the same period of the periodic table, so that the mixed oxide
of Zn with Fe, Co, or Ni is readily magnetized to stabilizes the
magnetization of the functional layer 21.
[0110] The use of these materials achieves a high spin-filter
effect and spin-flip reduction owing to a low resistivity, which
results in the increase of the MR ratio of the magnetoresistive
element 10.
[0111] In view of achieving a spin-filtering layer having a low
resistivity, it is effective that the spin-filtering layer includes
the above-described oxide material containing Zn, In, Sn, or Cd,
such as ZnO, In.sub.2O.sub.3, SnO.sub.2, ZnO, CdO,
CdIn.sub.2O.sub.4, Cd.sub.2SnO.sub.4, or Zn.sub.2SnO.sub.4.
[0112] One of the reasons why these oxide materials exhibit a low
resistivity is considered as follows. These oxide semiconductors
have a band gap of 3 eV or more. When the oxide semiconductors are
slightly reduced from the stoichiometry, an intrinsic defect such
as oxygen vacancy forms a donor level, so that the conduction
electron density reaches about 10.sup.18 to 10.sup.19 cm.sup.-3. In
the band structure of these conductive oxides, the valence band is
mainly offered by the 2p orbital of oxygen atoms, and the
conduction band is offered by the s orbital of metal atoms. When
the carrier density at the Fermi level exceeds 10.sup.18 cm.sup.-3,
the conduction band is reached, and a so-called degeneracy state
occurs. The oxide semiconductor is referred to as n-type degenerate
semiconductor which has sufficient concentration and mobility of
conduction electrons, and thus achieves a low resistivity. If any
oxide material does not fit in the theory, it may be used as long
as it exhibits a low resistivity.
[0113] On the other hand, in order to achieve a spin-filtering
layer having a high spin-filter effect, spin-filtering use of
spin-filtering layers containing Co, Fe, and Ni oxides having
magnetism at room temperature is effective. The oxide materials
containing Zn, In, Sn, and Cd, which are effective for achieving a
low resistivity, do not have magnetism in a bulk state. Jpn. Pat.
Appln. KOKAI Publication. No. 2004-6589 discloses that the
insertion of a very thin oxide layer into the free layer or pinned
layer of a non-magnetic oxide material develops magnetism therein,
and thus achieving a spin-filter effect. However, higher
spin-filter effects will be achieved by the addition of Co, Fe, and
Ni oxides which readily develop magnetism without limited by the
thickness of the oxide layer.
[0114] The functional layer 21 may further contain an additional
element. It is reported that the addition of Al to a Zn oxide
improves the heat resistance. Examples of the additional element
other than Al include B, Ga, In, C, Si, Ge and Sn. The mechanism of
the improvement of heat resistance is not completely evident, but
is presumed to be as follows. That is, the heat-accelerated
reoxidation decreases the density of the oxygen vacancy in the Zn
oxide produced by slight reduction from the stoichiometry and thus
changes the carrier density. As other reason for the improvement of
the heat resistance, it is presumed that the above-described
elements, which correspond to the dopants of Group III or IV,
prevent the acceleration of reoxidation of Zn atom due to heat,
thus the change in the carrier density in the functional layer 21
and the resistivity change caused by heat are minimized.
[0115] The thickness of the functional layer 21 is preferably 0.5
nm or more thereby achieving a sufficient spin-filtering effect. In
order to obtain a higher uniformity of the functional layer 21, in
consideration of the dependence on the manufacturing equipment, the
thickness is more preferably 1 nm or more. On the other hand, the
upper limit of the thickness is preferably 10 nm or less from the
viewpoint of preventing the increase of the read-gap of the
reproducing head.
Modification Example
[0116] A position on which the functional layer 21 is to be
provided is not limited to the embodiment shown in FIG. 2 (that is,
between the free layer 18 and the spacer layer 16). For example,
the functional layer 21 may be inserted into various positions as
shown in FIGS. 4 to 9. The modification examples will be described
below.
[0117] (Modification 1)
[0118] FIG. 4 shows a first modification of the magnetoresistive
element 10 according to the embodiment.
[0119] The present modification is different from the embodiment in
that a functional layer 21 is provided within a free layer 18. The
free layer 18 includes a first free layer 18a and a second free
layer 18b. The first free layer 18a is provided between a spacer
layer 16 and the functional layer 21, and the second free layer 18b
is provided between a cap layer 19 and the functional layer 21.
[0120] When the functional layer 21 is formed within the free layer
18, the spacer layer 16, the functional layer 21, and the second
free layer 18b are formed on the first free layer 18a in this
order.
[0121] In this manner, even when the functional layer 21 is
provided within the free layer 18, the functional layer 21
contributes to spin filtering effect as described above. In
addition, the functional layer 21 forms a magnetic coupling with
the free layer 18, so that its magnetization direction is unfixed
like in the free layer 18, and thus contributes to the increase of
the MR ratio of the magnetoresistive element 10, without inhibiting
the function of the free layer 18. In addition, dispersion of
oxygen contained in the functional layer 21 into the spacer layer
16 is reduced, so that the occurrence of spin-flip in the spacer
layer 16 caused by the elemental oxygen in the spacer layer 16 is
prevented, whereby a high MR ratio is achieved.
[0122] (Modification 2)
[0123] FIG. 5 shows a second modification of the magnetoresistive
element 10 according to the embodiment.
[0124] The present modification is different from the embodiment in
that a functional layer 21 is provided between a free layer 18 and
a cap layer 19.
[0125] In this manner, even when the functional layer 21 is
provided between the free layer 18 and the cap layer 19, as
described above, the functional layer 21 contributes to spin
filtering effect. In addition, since the functional layer 21 is
made of an oxide, it protects the magnetoresistive element 10 from
deterioration such as oxidation. Further, dispersion of oxygen
contained in the functional layer 21 into a spacer layer 16 is
reduced, so that the occurrence of spin-flip in the spacer layer 16
caused by the elemental oxygen in the spacer layer 16 is prevented,
whereby a high MR ratio is achieved.
[0126] (Modification 3)
[0127] FIG. 6 shows a third modification of the magnetoresistive
element 10 according to the embodiment.
[0128] The present modification is different from the embodiment in
that a functional layer 21 is provided between a pinned layer 14
and a spacer layer 16.
[0129] In this manner, when the functional layer 21 is provided
between the pinned layer 14 and the spacer layer 16, the functional
layer 21 contributes to spin-dependent tunneling as described
above. In addition, since the functional layer 21 is made of an
oxide, it prevents mixing of the material of the spacer layer 16
with the material of the pinned layer 14. As a result of this, the
spacer layer 16 allows conduction electrons to pass therethrough
while preventing spin-flip, and stably fixes the magnetization of
the pinned layer 14.
[0130] (Modification 4)
[0131] FIG. 7 shows a fourth modification of the magnetoresistive
element 10 according to the embodiment.
[0132] The present modification is different from the embodiment in
that a functional layer 21 is provided within an upper pinned layer
143.
[0133] In this manner, even when the functional layer 21 is
provided within the upper pinned layer 143, as described above, the
functional layer 21 contributes to spin filtering effect. In
addition, when the functional layer 21 is arranged at a position
not in contact with a tunneling insulator, dispersion of oxygen
contained in the functional layer 21 into the tunneling insulator
is reduced, so that the occurrence of spin-flip in the tunneling
insulator caused by the oxygen element in the tunneling insulator
is prevented, whereby a high MR ratio is achieved.
[0134] (Modification 5)
[0135] FIG. 8 shows a fifth modification of the magnetoresistive
element 10 according to the embodiment.
[0136] The present modification is different from the embodiment in
that a functional layer 21 is provided between an upper pinned
layer 143 and a magnetic coupling layer 142.
[0137] In this manner, even when the functional layer 21 is
provided between the upper pinned layer 143 and the magnetic
coupling layer 142, the functional layer 21 contributes to spin
filtering effect as described above. When the functional layer 21
is arranged at a position not in contact with the spacer layer,
dispersion of oxygen contained in the functional layer 21 into a
spacer layer is reduced, so that the occurrence of spin-flip in the
spacer layer caused by the oxygen element in the spacer layer is
prevented, whereby a high MR ratio is achieved.
[0138] (Modification 6)
[0139] FIG. 9 shows a sixth modification of the magnetoresistive
element 10 according to the embodiment.
[0140] The present modification is different from the embodiment in
that a functional layer 21 is provided between an upper pinned
layer 143 and a spacer layer 16, and that a second functional layer
22 is provided between a spacer layer 16 and a free layer 18.
[0141] The composition of the functional layer 21 is the same as
that of the functional layer 22, so that the explanation thereof is
not repeated here.
[0142] In this manner, a synergistic spin-filtering effect of the
two functional layers is achieved by forming the functional layer
21 and the second functional layer 22 between the upper pinned
layer 143 and the spacer layer 16, and between the spacer layer 16
and the free layer 18, respectively. As a result of this, a higher
MR ratio is achieved in comparison with the case using a single
functional layer.
[0143] The magnetoresistive elements 10 according to Modifications
1 to 6 may be manufactured using the method for manufacturing the
magnetoresistive element 10 described in the embodiment, so that
the explanations of the methods for making the magnetoresistive
elements 10 according to Modifications 1 to 6 are not repeated
here.
[0144] [Magnetic Head]
[0145] Hereinafter, a magnetic head using the magnetoresistive
element 10 according to the embodiment will be described.
[0146] FIGS. 10 and 11 are sectional views showing the magnetic
head into which the magnetoresistive element 10 according to the
embodiment is incorporated. FIG. 10 is a cross-sectional view of
the magnetoresistive element 10, cut almost parallel to an air
bearing surface facing a magnetic recording medium (not shown).
FIG. 11 is a cross-sectional view of the magnetoresistive element
10, cut perpendicular to the surface facing the medium.
[0147] The magnetic head shown in FIGS. 10 and 11 has a so-called
hard abutted structure. The lower electrode 11 and the upper
electrode 20 are provided under and over the magnetoresistive
element 10, respectively. In FIG. 10, bias magnetic field
application films 41 and insulating films 42 are stacked on the
both sides of the magnetoresistive element 10. As shown in FIG. 11,
a protective layer 43 is provided on the air bearing surface of the
magnetoresistive element 10.
[0148] A sense current for the magnetoresistive element 10 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 element
10, respectively. Further, the pair of bias magnetic field
application films 41, which are provided on the both sides of the
magnetoresistive element 10, applies a bias magnetic field to the
magnetoresistive element 10. The bias magnetic field controls the
magnetic anisotropy of the free layer 18 in the magnetoresistive
element 10 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.
[0149] Since the S/N ratio of the magnetoresistive film is
improved, the application of the magnetoresistive element 10 to a
magnetic head enables sensitive magnetic reproduction.
[0150] [Magnetic Recording Apparatus and Magnetic Head
Assembly]
[0151] A magnetic recording apparatus and a magnetic head assembly
including the magnetoresistive element 10 according to the present
embodiment are described below.
[0152] FIG. 12 is a perspective view of the magnetic recording
apparatus according to the present embodiment.
[0153] As shown in FIG. 12, a magnetic recording apparatus 310
according to the present embodiment is of a type using a rotary
actuator. A magnetic recording medium 230 is installed on a spindle
330 and rotated in a medium moving direction 270 by a motor (not
shown) which responds to control signals from a drive controller
(not shown). The magnetic recording apparatus 310 may include a
plurality of magnetic recording mediums 230.
[0154] As shown in FIG. 13, a head slider 280 which records and
reproduces the information on the magnetic recording medium 230
includes a magnetic head 140 provided with the magnetoresistive
element 10. The head slider 280 is made of, for example,
Al.sub.2O.sub.3/TiC, and configured to relatively move above the
magnetic recording medium 230 such as a magnetic disk while
floating thereover or in contact therewith.
[0155] The head slider 280 is attached to the tip of a thin
film-shaped suspension 350. The magnetic head 140 is provided near
the tip of the head slider 280.
[0156] When the magnetic recording medium 230 is rotated, the
pressing pressure applied by the suspension 350 matches with the
pressure developed on the air bearing surface of the head slider
280. The air bearing surface of the head slider 280 is kept away
from the surface of the magnetic recording medium 230 at a
predetermined floating height. The head slider 280 may be of
"in-contact type" which contacts with the magnetic recording medium
230.
[0157] The suspension 350 is connected to one end of an actuator
arm 360 which includes a bobbin part supporting a driving coil (not
shown). A voice coil motor 370, which is a kind of linear motor, is
provided at the other end of the actuator arm 360. The voice coil
motor 370 may include a magnetic circuit including the driving coil
(not shown), which is wound around the bobbin part of the actuator
arm 360, and a permanent magnet and a counter yoke which are
provided to face each other so as to sandwich the driving coil.
[0158] The actuator arm 360 is held by ball bearings (not shown)
provided at the top and bottom of a pivot 380, and is configured to
be swingably slide by the voice coil motor 370. This allows free
moving of the magnetic head 140 to any position on the magnetic
recording medium 230.
[0159] FIG. 14A shows a head stack assembly 390 as a portion of the
magnetic recording apparatus 310 according to the present
embodiment.
[0160] FIG. 14B is a perspective view showing a magnetic head
assembly (head gimbal assembly [HGA]) 400 as a portion of the head
stack assembly 390.
[0161] As shown in FIG. 14A, the head stack assembly 390 includes
the pivot 380, a head gimbal assembly 400 extending from the pivot
380, and a support frame 420 which extends from the pivot 380 in a
direction opposite to the head gimbal assembly 400 and supports a
coil 410 of the voice coil motor.
[0162] As shown in FIG. 14B, the head gimbal assembly 400 includes
the actuator arm 360 extending from the pivot 380, and the
suspension 350 extending from the actuator arm 360.
[0163] The head slider 280 including a magnetic recording head 140,
which has been described in the second embodiment, is provided at
the tip of the suspension 350.
[0164] The magnetic head assembly (head gimbal assembly [HGA]) 400
according to the present embodiment includes the magnetic recording
head 140 described in the second embodiment, the head slider 280
including the magnetic recording head 140, the suspension 350
equipped with the head slider 280 at one end thereof, and the
actuator arm 360 connected to the other end of the suspension
350.
[0165] The suspension 350 includes leads (not shown) for reading
and writing signals, for heater for controlling the floating
height, and for STO10. The leads are electrically connected to the
electrodes of the magnetic recording head 140 included in the head
slider 280. Electrode pads (not shown) are provided in the head
gimbal assembly 400. In the present embodiment, eight electrode
pads are provided; two electrode pads for the coil of a main
magnetic pole 200, two electrode pads for a magnetic reproducing
element 190, two electrode pads for dynamic flying height (DFH),
and two electrode pads for STO10.
[0166] A signal processor 385 (not shown) is provided on the back
of the magnetic recording apparatus 310 shown in FIG. 12. The
signal processor 385 reads and writes signals to the magnetic
recording medium 230 using the magnetic recording head 140. The
input and output lines of the signal processor 385 are connected to
the electrode pads of the head gimbal assembly 400, and
electrically coupled with the magnetic recording head 140.
[0167] The magnetic recording apparatus 310 according to the
present embodiment includes the magnetic recording medium 230, the
magnetic recording head 140, a moving unit which can move the
opposing magnetic recording medium 230 and magnetic recording head
140 in a relative manner while keeping them away or in contact with
each other, a position controller which places the magnetic
recording head 140 to a predetermined recording position on the
magnetic recording medium 230, and the signal processor 385 which
reads and writes signals on the magnetic recording medium 230 using
the magnetic recording head 140.
[0168] As the magnetic recording medium 230, the above-described
magnetic recording medium 230 is used. The above-described moving
unit may include the head slider 280. The above-described position
controller may include the head gimbal assembly 400.
[0169] The magnetic recording apparatus 310 includes the magnetic
recording medium 230, the head gimbal assembly 400, and the signal
processor 385 which reads and writes signals on the magnetic
recording medium 230 using the magnetic recording head 140 included
in the head gimbal assembly 400.
[0170] Based on the above-described magnetic head and magnetic
recording apparatus as the embodiments, any magnetoresistive
elements, magnetic heads, magnetic recording apparatuses, and
magnetic memories, which may be appropriately modified by those
skilled in the art, may also includes the magnetoresistive element
according to the above embodiment.
[0171] In the above embodiments, although the magnetoresistive
element 10 of bottom type is described, the magnetoresistive
element 10 of top type, in which the pinned layer 14 is formed
above the spacer layer 16, will achieve the effect of the above
embodiments.
EXAMPLES
Example 1
[0172] A magnetoresistive element was manufactured in accordance
with the manufacturing method according to the embodiment, and
performance thereof was investigated.
[0173] The magnetoresistive element shown in FIG. 2 was
manufactured. More specifically, the magnetoresistive element in
which the functional layer 21 is provided between the spacer layer
16 and the free layer 18 was manufactured. Details of the layers
are s follows.
[0174] Underlayer 12: Ta [1 nm]/Ru [2 nm]
[0175] Pinning layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0176] Pinned layer 14: Co.sub.75Fe.sub.25 [4 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [4 nm]
[0177] Nonmagnetic spacer layer 16: Cu [3 nm]
[0178] Functional layer 21: Zn--Fe.sub.50Co.sub.50--O [2 nm]
[0179] Free layer 18: Fe.sub.50Co.sub.50 [3 nm]
[0180] Magnetoresistive elements were manufactured in accordance
with the method shown in FIG. 1. Particularly, the functional layer
21 was manufactured as described below. As the first step,
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm] was formed as a base material
of the functional layer 21. Next, as the second step, a surface of
the layer of Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm] described above
was converted into Zn--Fe.sub.50Co.sub.50--O [2 nm] by ion beam
oxidation (IAO), plasma oxidation, or natural oxidation. In
Examples, a reduction treatment using Ar plasma, ion, or radical as
the reducing gas was performed after the oxidation treatment. In
contrast, the reduction treatment was not performed in Comparative
Examples. Details of each of the treatments are shown in the
Tables.
[0181] An MR change ratio and areal resistance RA of each of the
manufactured magnetoresistive elements are measured. The MR change
ratios and the areal resistance RA were measured by a direct
current four-terminal method.
[0182] The manufactured magnetoresistive elements and measurement
results thereof are summarized in Tables 1-1 to 1-3 shown
below.
TABLE-US-00001 TABLE 1-1 Oxidation Reduction MR change RA treatment
treatment Details of manufacturing process ratio [%]
[.OMEGA..mu.m.sup.2] REF None None Fe.sub.50Co.sub.50 [1 nm]
(without functional layer) 1.5 0.07 Comparative IAO None
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 5.4 0.25 Example 1-1 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL) Example 1-1 IAO Ar plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6
nm]/ 9.4 0.20 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (RF plasma: 40 W, Ar gas) Example 1-2
IAO Ar ion Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 9.0 0.21 IAO
(beam voltage: 60 V, beam current: 60 mA/ oxygen exposure degree:
1.5 KL)/ ORT (beam voltage: 60 V, beam current: 60 mA, Ar gas)
Example 1-3 IAO Ar radical Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/
8.5 0.21 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (microwave power: 100 W, Ar gas)
[0183] Shown in Table 1-1 are Comparative Example 1-1 and Examples
1-1 to 1-3. Oxidation by IAO was performed on each of the
magnetoresistive elements, and reductions by Ar plasma, ion, and
radical were further performed on the magnetoresistive elements of
Examples. "REF" in the Table is a reference sample which is a
magnetoresistive element of a spin-valve structure which does not
include any functional layer.
[0184] As shown in Table 1-1, the high MR change ratio was
exhibited in the case of performing the reduction treatment by
using Ar (Examples 1-1 to 1-3) as compared to the case of not
providing any functional layer (REF) and the case of not performing
the reduction treatment (Comparative Example 1-1). Also,
Comparative Example 1-1 exhibited the higher MR change ratio than
REF. However, the increase in MR change ratio of each of Examples
1-1 to 1-3 with respect to REF is much greater than that of
Comparative Example 1-1.
[0185] The reasons for the great increase in MR change ratio which
is enabled by the reduction treatment are considered as follows.
The difference between the functional layer formation according to
Examples and the conventional functional layer formation is the
irradiation with the reducing gas (oxygen reduction treatment
[ORT]) which is performed on the film which is oxidized by natural
oxidation, IAO or plasma oxidation in Examples. In the conventional
functional layer formation, trivalent (which is an insulating
valence) .alpha.-(FeCoZN).sub.2O.sub.3 or
.gamma.-(FeCoZN).sub.2O.sub.3 is formed in FeCoZn mixed oxides to
entail resistivity of the functional layer. Since the increase in
resistance of the functional layer promotes occurrence of the
spin-flip in the functional layer, it is difficult to attain a
satisfactory increase in MR change ratio by the spin filtering
effect. In contrast, since it is possible to reduce
.alpha.-(FeCoZN).sub.2O.sub.3 and .gamma.-(FeCoZN).sub.2O.sub.3 in
the functional layer by the irradiation with the reducing gas, it
is possible to form the spin filtering layer having the low
resistivity. As a result, it is possible to obtain the
magnetoresistive elements having the high MR change ratio by the
spin filtering effect by suppressing the occurrence ratio of the
spin-flip as in Examples.
[0186] For more detailed analysis, a section of each of the
magnetoresistive elements of Comparative Example 1-1 and Example
1-1 was imaged to investigate a minute structure thereof. Results
of cross-sectional TEM (transmission election microscopy) analysis
are shown in FIGS. 15A and 15B. Shown in FIG. 15A is the section of
Comparative Example 1-1, and shown in FIG. 15B is the section of
Example 1-1. A film thickness of the functional layer of each of
Comparative Example 1-1 and Example 1-1 was 1.8 nm. From the
results, it is confirmed that etching of the functional layer is
not caused by the Ar plasma irradiation. In view of the above, it
is confirmed that the increase in MR change ratio is enabled by ORT
even in the case where the film thickness of the functional layer
is not changed.
[0187] Further, elements contained in the each layer of Comparative
Example 1-1 and Example 1-1 were analyzed. Results of analysis by
using a three-dimensional atomic probe are shown in FIGS. 16A and
16B. Shown in FIG. 16A are the results of Comparative Example 1-1,
and shown in FIG. 16B are the results of Example 1-1. From FIG.
16A, it is apparent that an oxygen content in the functional layer
of Comparative Example 1-1 is about 20 atomic. In contrast, it is
apparent that an oxygen content in the functional layer of
Comparative Example 1-1 is about 10 atomic %. Namely, it is
confirmed the oxygen content in the functional layer is reduced by
the reduction treatment. Since it is confirmed by the
cross-sectional TEM images shown in FIGS. 15A and 15B that the film
thickness of the functional layer is not reduced by ORT, it is
confirmed that the functional layer is reduced by ORT in view of
the results using the three-dimensional atomic probe shown in FIGS.
16A and 16B.
[0188] Further, in order to evaluate crystallinity of the
functional layers of Comparative Example 1-1 and Example 1-1, model
films each consisting of 30 layers of the functional layer were
prepared, and X-ray diffraction measurements of the model films
were performed.
[0189] Underlayer: Ta [5 nm]/Cu [5 nm]
[0190] Functional layer: (Zn--Fe.sub.50Co.sub.50--O [2
nm]).times.30 layers
[0191] Two functional layers as the model films described above
were prepared in the same way as in Comparative Example 1-1 and
Example 1-1 to be compared to each other. Results of the X-ray
diffraction measurements are shown in FIG. 17. A broken line (a)
indicates the result of the sample prepared by the same
manufacturing method as that of Comparative Example 1-1, and a
solid line (b) indicates the result of the sample prepared by the
same manufacturing method as that of Example 1-1. From FIG. 17, it
is confirmed that (311) diffraction peak intensity near
2.theta.=36.degree. of a spinel structure attributable to the
Zn--Fe.sub.50Co.sub.50--O layer of Example 1-1 is increased to
about three times that of Comparative Example 1-1. From the
results, it is confirmed that the reduction treatment using Ar
plasma attains not only the effect of adjusting the oxidation
number of the functional layer 21 but also an effect of improving
crystallinity of the functional layer 21. Since the improvement in
crystallinity of the functional layer 21 contributes to a reduction
of defect in the functional layer 21 and is capable of reducing
scattering which does not depend on spin during electron
conduction, the crystallinity improvement is favorable from the
viewpoint of attaining the high MR change ratio.
TABLE-US-00002 TABLE 1-2 Oxidation Reduction MR change RA treatment
treatment Details of manufacturing process ratio [%]
[.OMEGA..mu.m.sup.2] REF None None Fe.sub.50Co.sub.50 [1 nm]
(without functional layer) 1.5 0.07 Comparative IAO None
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 5.4 0.25 Example 1-1 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL) Comparative Plasma None Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6
nm]/ 5.0 0.25 Example 1-2 oxidation Plasma oxidation (RF plasma: 20
W, oxygen exposure degree: 1.5 KL) Comparative Natural None
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 4.0 0.20 Example 1-3
oxidation Natural oxidation (oxygen exposure degree: 200 KL)
Example 1-1 IAO Ar plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/
9.4 0.20 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (RF plasma: 40 W, Ar gas) Example 1-4
Plasma Ar plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 9.0 0.22
oxidation Plasma oxidation (RF plasma: 20 W, oxygen exposure
degree: 1.5 KL)/ ORT (RF plasma: 40 W, Ar gas) Example 1-5 Natural
Ar plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 7.5 0.18 oxidation
Natural oxidation (oxygen exposure degree: 200 KL)/ ORT (RF plasma:
40 W, Ar gas)
[0192] Shown in Table 1-2 are Comparative Examples 1-1 to 1-3 and
Examples 1-1, 1-4, and 1-5. The oxidation treatment by IAO was
performed on Comparative Example 1-1 and Example 1-1; the oxidation
treatment by plasma oxidation treatment was performed on
Comparative Example 1-2 and Example 1-4; and the oxidation by
natural oxidation was performed on Comparative Example 1-3 and
Example 1-5. Also, the reduction treatment using Ar plasma was
performed on Examples 1-1, 1-4, and 1-5 after the oxidation
treatments. "REF" in the Table is a reference sample which is a
magnetoresistive element of a spin-valve structure which does not
include any functional layer.
[0193] As shown in Table 1-2, it is apparent that it is possible to
greatly increase the MR change ratio by performing the reduction
treatment after the oxidation treatment in the case where IAO, the
plasma oxidation, or the natural oxidation is performed as the
oxidation treatment.
TABLE-US-00003 TABLE 1-3 Oxidation Reduction MR change RA treatment
treatment Details of manufacturing process ratio [%]
[.OMEGA..mu.m.sup.2] REF None None Fe.sub.50Co.sub.50 [1 nm]
(without functional layer) 1.5 0.07 Comparative IAO None
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 5.4 0.25 Example 1-1 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL) Example 1-6 IAO Ar plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6
nm]/ 7.4 0.25 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (RF plasma: 10 W, Ar gas) Example 1-7
IAO Ar plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 8.5 0.23 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL)/ ORT (RF plasma: 20 W, Ar gas) Example 1-1 IAO Ar plasma
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 9.4 0.20 IAO (beam voltage:
60 V, beam current: 60 mA, oxygen exposure degree: 1.5 KL)/ ORT (RF
plasma: 40 W, Ar gas) Example 1-8 IAO Ar plasma Fe.sub.50Co.sub.50
[1 nm]/Zn [0.6 nm]/ 9.3 0.22 IAO (beam voltage: 60 V, beam current:
60 mA, oxygen exposure degree: 2 KL)/ ORT (RF plasma: 60 W, Ar gas)
Example 1-9 IAO Ar plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/
9.3 0.21 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 2.5 KL)/ ORT (RF plasma: 80 W, Ar gas) Example
1-10 IAO Ar plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 9.3 0.20
IAO (beam voltage: 60 V, beam current: 60 mA, oxygen exposure
degree: 3 KL)/ ORT (RF plasma: 100 W, Ar gas) Example 1-11 IAO Ar
plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 7.5 0.17 IAO (beam
voltage: 60 V, beam current: 60 mA, oxygen exposure degree: 3 KL)/
ORT (RF plasma: 120 W, Ar gas)
[0194] Shown in Table 1-3 are Comparative Example 1-1 and Examples
1-1 and 1-6 to 1-11. Comparative Example 1-1 is a magnetoresistive
element obtained by not performing any reduction treatment after
the oxidation treatment. Examples 1-1 and 1-6 to 1-11 are
magnetoresistive elements which were manufactured by performing the
reduction treatment using Ar plasma after the oxidation treatment
and changing the high-frequency bias for producing plasma within a
range of 10 to 120 W. "REF" in the Table is a reference sample
which is a magnetoresistive element of a spin-valve structure which
does not include any functional layer.
[0195] As shown in Table 1-3, the MR change ratio is increased as
compared to REF and Comparative Example 1-1 in the case where the
reduction treatment is performed (Examples 1-1 and 1-6 to 1-11),
and the increase is prominent in the case where the high-frequency
bias is within the range of 20 to 100 W or less. Particularly, the
highest MR change ratio is exhibited in the case where the
high-frequency bias is 40 W (Example 1-1).
Example 2
[0196] Magnetoresistive elements were manufactured in accordance
with the manufacturing method according to the embodiment, and
performances thereof were investigated.
[0197] The magnetoresistive elements were manufactured in the same
way as in Example 1 except for using He in place of Ar for the
reduction treatment. An MR change ratio and an areal resistance RA
of each of the manufactured magnetoresistive elements were measured
in the same way as in Example 1.
[0198] The manufactured magnetoresistive elements and results of
the measurements are shown in Table 2 below.
TABLE-US-00004 TABLE 2 Oxidation Reduction MR change RA treatment
treatment Details of manufacturing process ratio [%]
[.OMEGA..mu.m.sup.2] REF None None Fe.sub.50Co.sub.50 [1 nm]
(without functional layer) 1.5 0.07 Comparative IAO None
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 5.4 0.25 Example 2-1 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL) Example 2-1 IAO He plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6
nm]/ 8.0 0.23 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (RF plasma: 40 W, He gas) Example 2-2
IAO He ion Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 7.5 0.22 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL)/ ORT (beam voltage: 60 V, beam current: 60 mA, He gas)
Example 2-3 IAO He radical Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/
7.5 0.22 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (microwave power: 100 W, He gas)
[0199] Shown in Table 2 are Comparative Example 2-1 and Examples
2-1 to 2-3. Oxidation by IAO was performed on each of the
magnetoresistive elements, and reductions using He plasma, ion, and
radical were further performed on the magnetoresistive elements of
Examples. "REF" in the Table is a reference sample which is a
magnetoresistive element of a spin-valve structure which does not
include any functional layer.
[0200] As shown in Table 2, it is confirmed that Examples 2-1 to
2-3 exhibits the high MR change ratio as compared to REF and
Comparative Example 2-1 even in the case where the element used for
the reduction treatment is changed to He.
[0201] Also, magnetoresistive elements were manufactured in
accordance with Example 2-1 by changing the oxidation treatment to
plasma oxidation and natural oxidation, and each of the
thus-manufactured magnetoresistive elements exhibited a high MR
change ratio as in Example 2-1.
Example 3
[0202] Magnetoresistive elements were manufactured in accordance
with the manufacturing method according to the embodiment, and
performances thereof were investigated.
[0203] The magnetoresistive elements were manufactured in the same
way as in Example 1 except for using Ne in place of Ar for the
reduction treatment. An MR change ratio and an areal resistance RA
of each of the manufactured magnetoresistive elements were measured
in the same way as in Example 1.
[0204] The manufactured magnetoresistive elements and results of
the measurements are shown in Table 3 below.
TABLE-US-00005 TABLE 3 Oxidation Reduction MR change RA treatment
treatment Details of manufacturing process ratio [%]
[.OMEGA..mu.m.sup.2] REF None None Fe.sub.50Co.sub.50 [1 nm]
(without functional layer) 1.5 0.07 Comparative IAO None
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 5.4 0.25 Example 3-1 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL) Example 3-1 IAO Ne plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6
nm]/ 7.8 0.24 IAO (beam voltage: 60 V, beam current: 60 mA/ oxygen
exposure degree: 1.5 KL)/ ORT (RF plasma: 40 W, Ne gas) Example 3-2
IAO Ne ion Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 7.6 0.21 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL)/ ORT (beam voltage: 60 V, beam current: 60 mA, Ne gas)
Example 3-3 IAO Ne radical Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/
7.5 0.20 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (microwave power: 100 W, Ne gas)
[0205] Shown in Table 3 are Comparative Example 3-1 and Examples
3-1 to 3-3. Oxidation by IAO was performed on each of the
magnetoresistive elements, and reductions using Ne plasma, ion, and
radical were further performed on the magnetoresistive elements of
Examples. "REF" in the Table is a reference sample which is a
magnetoresistive element of a spin-valve structure which does not
include any functional layer.
[0206] As shown in Table 3, it is confirmed that Examples 3-1 to
3-3 exhibits the high MR change ratio as compared to REF and
Comparative Example 3-1 even in the case where the element used for
the reduction treatment is changed to Ne.
[0207] Also, magnetoresistive elements were manufactured in
accordance with Example 3-1 by changing the oxidation treatment to
plasma oxidation or natural oxidation, and each of the
thus-manufactured magnetoresistive elements exhibited a high MR
change ratio as in Example 3-1.
Example 4
[0208] Magnetoresistive elements were manufactured in accordance
with the manufacturing method according to the embodiment, and
performances thereof were investigated.
[0209] The magnetoresistive elements were manufactured in the same
way as in Example 1 except for using Kr in place of Ar for the
reduction treatment. An MR change ratio and an areal resistance RA
of each of the manufactured magnetoresistive elements were measured
in the same way as in Example 1.
[0210] The manufactured magnetoresistive elements and results of
the measurements are shown in Table 4 below.
TABLE-US-00006 TABLE 4 Oxidation Reduction MR change RA treatment
treatment Details of manufacturing process ratio [%]
[.OMEGA..mu.m.sup.2] REF None None Fe.sub.50Co.sub.50 [1 nm]
(without functional layer) 1.5 0.07 Comparative IAO None
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 5.4 0.25 Example 4-1 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL) Example 4-1 IAO Kr plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6
nm]/ 8.1 0.22 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (RF plasma: 40 W, Kr gas) Example 4-2
IAO Kr ion Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 8.1 0.23 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL)/ ORT (beam voltage: 60 V, beam current: 60 mA, Kr gas)
Example 4-3 IAO Kr radical Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/
7.8 0.22 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (microwave power: 100 W, Kr gas)
[0211] Shown in Table 4 are Comparative Example 4-1 and Examples
4-1 to 4-3. Oxidation by IAO was performed on each of the
magnetoresistive elements, and reductions using Ne plasma, ion, and
radical were further performed on the magnetoresistive elements of
Examples. "REF" in the Table is a reference sample which is a
magnetoresistive element of a spin-valve structure which does not
include any functional layer.
[0212] As shown in Table 4, it is confirmed that Examples 4-1 to
4-3 exhibit the high MR change ratio as compared to REF and
Comparative Example 4-1 even in the case where the element used for
the reduction treatment is changed to Kr.
[0213] Also, magnetoresistive elements were manufactured in
accordance with Example 4-1 by changing the oxidation treatment to
plasma oxidation or natural oxidation, and each of the
thus-manufactured magnetoresistive elements exhibited a high MR
change ratio as in Example 4-1.
Example 5
[0214] Magnetoresistive elements were manufactured in accordance
with the manufacturing method according to the embodiment, and
performances thereof were investigated.
[0215] The magnetoresistive elements were manufactured in the same
way as in Example 1 except for using Xe in place of Ar for the
reduction treatment. An MR change ratio and an areal resistance RA
of each of the manufactured magnetoresistive elements were measured
in the same way as in Example 1.
[0216] The manufactured magnetoresistive elements and results of
the measurements are shown in Table 5 below.
TABLE-US-00007 TABLE 5 Oxidation Reduction MR change RA treatment
treatment Details of manufacturing process ratio [%]
[.OMEGA..mu.m.sup.2] REF None None Fe.sub.50Co.sub.50 [1 nm]
(without functional layer) 1.5 0.07 Comparative IAO None
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 5.4 0.25 Example 5-1 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL) Example 5-1 IAO Xe plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6
nm]/ 8.8 0.23 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (RF plasma: 40 W, Xe gas) Example 5-2
IAO Xe ion Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 8.5 0.21 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL)/ ORT (beam voltage: 60 V, beam current: 60 mA, Xe gas)
Example 5-3 IAO Xe radical Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/
8.2 0.20 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (microwave power: 100 W, Xe gas)
[0217] Shown in Table 5 are Comparative Example 5-1 and Examples
5-1 to 5-3. Oxidation by IAO was performed on each of the
magnetoresistive elements, and reductions using Xe plasma, ion, and
radical were further performed on the magnetoresistive elements of
Examples. "REF" in the Table is a reference sample which is a
magnetoresistive element of a spin-valve structure which does not
include any functional layer.
[0218] As shown in Table 5, it is confirmed that Examples 5-1 to
5-3 exhibit the high MR change ratio as compared to REF and
Comparative Example 5-1 even in the case where the element used for
the reduction treatment is changed to Xe.
[0219] Also, magnetoresistive elements were manufactured in
accordance with Example 5-1 by changing the oxidation treatment to
plasma oxidation or natural oxidation, and each of the
thus-manufactured magnetoresistive elements exhibited a high MR
change ratio as in Example 5-1.
Example 6
[0220] Magnetoresistive elements were manufactured in accordance
with the manufacturing method according to the embodiment, and
performances thereof were investigated.
[0221] The magnetoresistive elements were manufactured in the same
way as in Example 1 except for using hydrogen in place of Ar for
the reduction treatment. An MR change ratio and an areal resistance
RA of each of the manufactured magnetoresistive elements were
measured in the same way as in Example 1.
[0222] The manufactured magnetoresistive elements and results of
the measurements are shown in Table 6 below.
TABLE-US-00008 TABLE 6 Oxidation Reduction MR change RA treatment
treatment Details of manufacturing process ratio [%]
[.OMEGA..mu.m.sup.2] REF None None Fe.sub.50Co.sub.50 [1 nm]
(without functional layer) 1.5 0.07 Comparative IAO None
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 5.4 0.25 Example 6-1 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL) Example 6-1 IAO H molecule Fe.sub.50Co.sub.50 [1 nm]/Zn
[0.6 nm]/ 6.5 0.24 IAO (beam voltage: 60 V, beam current: 60 mA,
oxygen exposure degree: 1.5 KL)/ ORT (H molecule exposure degree:
200 KL) Example 6-2 IAO H plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6
nm]/ 6.8 0.22 IAO (beam voltage: 60 V, beam current: 60 mA/ oxygen
exposure degree: 1.5 KL)/ ORT (RF plasma: 40 W, H.sub.2 gas)
Example 6-3 IAO H ion Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 7.0
0.21 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen exposure
degree: 1.5 KL)/ ORT (beam voltage: 60 V, beam current: 60 mA,
H.sub.2 gas) Example 6-4 IAO H radical Fe.sub.50Co.sub.50 [1 nm]/Zn
[0.6 nm]/ 6.8 0.22 IAO (beam voltage: 60 V, beam current: 60 mA,
oxygen exposure degree: 1.5 KL)/ ORT (microwave power: 100 W,
H.sub.2 gas)
[0223] Shown in Table 6 are Comparative Example 6-1 and Examples
6-1 to 6-4. Oxidation by IAO was performed on each of the
magnetoresistive elements, and reductions using hydrogen molecule,
plasma, ion, or radical were further performed on the
magnetoresistive elements of Examples. "REF" in the Table is a
reference sample which is a magnetoresistive element of a
spin-valve structure which does not include any functional
layer.
[0224] As shown in Table 6, it is confirmed that Examples 6-1 to
6-4 exhibit the high MR change ratio as compared to REF and
Comparative Example 6-1 even in the case where the element used for
the reduction treatment is changed to hydrogen.
[0225] Also, magnetoresistive elements were manufactured in
accordance with Example 6-1 by changing the oxidation treatment to
plasma oxidation or natural oxidation, and each, of the
thus-manufactured magnetoresistive elements exhibited a high MR
change ratio as in Example 6-1.
Example 7
[0226] Magnetoresistive elements were manufactured in accordance
with the manufacturing method according to the embodiment, and
performances thereof were investigated.
[0227] The magnetoresistive elements were manufactured in the same
way as in Example 1 except for using nitrogen in place of Ar for
the reduction treatment. An MR change ratio and an areal resistance
RA of each of the manufactured magnetoresistive elements were
measured in the same way as in Example 1.
[0228] The manufactured magnetoresistive elements and results of
the measurements are shown in Table 7 below.
TABLE-US-00009 TABLE 7 Oxidation Reduction MR change RA treatment
treatment Details of manufacturing process ratio [%]
[.OMEGA..mu.m.sup.2] REF None None Fe.sub.50Co.sub.50 [1 nm]
(without functional layer) 1.5 0.07 Comparative IAO None
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 5.4 0.25 Example 7-1 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL) Example 7-1 IAO N molecule Fe.sub.50Co.sub.50 [1 nm]/Zn
[0.6 nm]/ 5.8 0.25 IAO (beam voltage: 60 V, beam current: 60 mA,
oxygen exposure degree: 1.5 KL)/ ORT (N molecule exposure degree:
200 KL) Example 7-2 IAO N plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6
nm]/ 6.5 0.23 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (RF plasma: 40 W, N.sub.2 gas)
Example 7-3 IAO N ion Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 6.3
0.22 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen exposure
degree: 1.5 KL)/ ORT (beam voltage: 60 V, beam current: 60 mA,
N.sub.2 gas) Example 7-4 IAO N radical Fe.sub.50Co.sub.50 [1 nm]/Zn
[0.6 nm]/ 6.0 0.22 IAO (beam voltage: 60 V, beam current: 60 mA,
oxygen exposure degree: 1.5 KL)/ ORT (microwave power: 100 W,
N.sub.2 gas)
[0229] Shown in Table 7 are Comparative Example 7-1 and Examples
7-1 to 7-4. Oxidation by IAO was performed on each of the
magnetoresistive elements, and reductions using nitrogen molecule,
plasma, ion, or radical were further performed on the
magnetoresistive elements of Examples. "REF" in the Table is a
reference sample which is a magnetoresistive element of a
spin-valve structure which does not include any functional
layer.
[0230] As shown in Table 7, it is confirmed that Examples 7-1 to
7-4 exhibit the high MR change ratio as compared to REF and
Comparative Example 7-1 even in the case where the element used for
the reduction treatment is changed to N.
[0231] Also, magnetoresistive elements were manufactured in
accordance with Example 7-1 by changing the oxidation treatment to
plasma oxidation or natural oxidation, and each of the
thus-manufactured magnetoresistive elements exhibited a high MR
change ratio as in Example 7-1.
Example 8
[0232] Magnetoresistive elements were manufactured in accordance
with the manufacturing method according to the embodiment, and
performances thereof were investigated.
[0233] The magnetoresistive elements were manufactured in the same
way as in Example 1 except for using hydrogen in place of Ar for
the reduction treatment. Further, a water elimination step using Ar
gas was performed after the reduction treatments. An MR change
ratio and an areal resistance RA of each of the manufactured
magnetoresistive elements were measured in the same way as in
Example 1.
[0234] The manufactured magnetoresistive elements and results of
the measurements are shown in Table 8 below.
TABLE-US-00010 TABLE 8 Water Oxidation Reduction elimination MR
change RA treatment treatment treatment Details of manufacturing
process ratio [%] [.OMEGA..mu.m.sup.2] REF None None None
Fe.sub.50Co.sub.50 [1 nm] (without functional layer) 1.5 0.07
Comparative IAO None None Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/
5.4 0.25 Example 8-1 IAO (beam voltage: 60 V, beam current: 60 mA,
oxygen exposure degree: 1.5 KL) Example IAO H plasma None
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 6.8 0.22 8-1 IAO (beam
voltage: 60 V, beam current: 60 mA, oxygen exposure degree: 1.5
KL)/ ORT (RF plasma: 40 W, H.sub.2 gas) Example IAO H plasma Ar ion
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 9.0 0.22 8-2 IAO (beam
voltage: 60 V, beam current: 60 mA, oxygen exposure degree: 1.5
KL)/ ORT (RF plasma: 40 W, H.sub.2 gas)/ water elimination step
(beam voltage: 60 V, beam current: 60 mA, Ar gas) Example IAO H
plasma Ar plasma Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 9.3 0.22
8-3 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen exposure
degree: 1.5 KL)/ ORT (RF plasma: 40 W, H.sub.2 gas)/ water
elimination step (RF plasma: 40 W, Ar gas) Example IAO H plasma Ar
radical Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]/ 8.8 0.22 8-4 IAO
(beam voltage: 60 V, beam current: 60 mA, oxygen exposure degree:
1.5 KL)/ ORT (RF plasma: 40 W, H.sub.2 gas)/ water elimination step
(microwave power: 100 W, Ar gas)
[0235] Shown in Table 8 are Comparative Example 8-1 and Examples
8-1 to 8-4. Oxidation by IAO was performed on each of the
magnetoresistive elements, and reductions using hydrogen plasma was
further performed on the magnetoresistive elements of Examples. The
water elimination treatments using Ar ion, plasma, or radial were
performed on Examples 8-2 to 8-4. "REF" in the Table is a reference
sample which is a magnetoresistive element of a spin-valve
structure which does not include any functional layer.
[0236] As shown in Table 8, it is confirmed that Examples 8-2 to
8-4 exhibit the high MR change ratio as compared to REF and
Comparative Example 8-1 even in the case where the water
elimination treatment is performed after the reduction
treatment.
[0237] Further, it is confirmed that Examples 8-2 to 8-4 exhibit
the higher MR change ratio as compared to Example 8-1 for which the
water elimination treatment was not performed.
Example 9
[0238] Magnetoresistive elements were manufactured in accordance
with the manufacturing method according to the embodiment, and
performance thereof was investigated.
[0239] The magnetoresistive elements were manufactured in the same
way as in Example 1 except for using Fe [1 nm]/Zn [0.6 nm] as the
base metal layer of the functional layer in place of
Fe.sub.50Co.sub.50 [1 nm]/Zn [0.6 nm]. An MR change ratio and areal
resistance RA of each of the manufactured magnetoresistive elements
were measured in the same way as in Example 1.
[0240] The manufactured magnetoresistive elements and results of
the measurement are summarized in Table 9 shown below.
TABLE-US-00011 TABLE 9 Oxidation Reduction MR change RA treatment
treatment Details of manufacturing process ratio [%]
[.OMEGA..mu.m.sup.2] REF None None Fe.sub.50Co.sub.50 [1 nm]
(without functional layer) 1.5 0.07 Comparative IAO None Fe [1
nm]/Zn [0.6 nm]/ 5.4 0.27 Example 9-1 IAO (beam voltage: 60 V, beam
current: 60 mA, oxygen exposure degree: 1.5 KL) Example 9-1 IAO Ar
plasma Fe [1 nm]/Zn [0.6 nm]/ 10.0 0.21 IAO (beam voltage: 60 V,
beam current: 60 mA, oxygen exposure degree: 1.5 KL)/ ORT (RF
plasma: 40 W, Ar gas) Example 9-2 IAO Ar ion Fe [1 nm]/Zn [0.6 nm]/
9.3 0.22 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen
exposure degree: 1.5 KL)/ ORT (beam voltage: 60 V, beam current: 60
mA, Ar gas) Example 9-3 IAO Ar radical Fe [1 nm]/Zn [0.6 nm]/ 9.0
0.22 IAO (beam voltage: 60 V, beam current: 60 mA, oxygen exposure
degree: 1.5 KL)/ ORT (microwave power: 100 W, Ar gas)
[0241] Shown in Table 9 are Comparative Example 9-1 and Examples
9-1 to 9-3. Oxidation by IAO was performed on each of the
magnetoresistive elements, and reductions by Ar plasma, ion, and
radical were further performed on the magnetoresistive elements of
Examples. "REF" in the Table is a reference sample which is a
magnetoresistive element of a spin-valve structure which does not
include any functional layer.
[0242] As shown in Table 9, the high MR change ratio was exhibited
in the case by performing the reduction treatment by using Ar
(Examples 9-1 to 9-3) as compared to the case of not providing any
functional layer (REF) and the case of not performing the reduction
treatment (Comparative Example 9-1). Also, Comparative Example 9-1
exhibited the higher MR change ratio than REF. However, the
increase in MR change ratio of each of Examples 9-1 to 9-3 with
respect to REF is much greater than that of Comparative Example
9-1.
[0243] By Example 9, it is confirmed that the improvement in the MR
change ratio is attained by employing the reduction treatment even
in the case of using Fe [1 nm]/Zn [0.6 nm] as the base metal layer
of the functional layer in place of Fe.sub.50Co.sub.50 [1 nm]/Zn
[0.6 nm]. As the base metal layer of the functional layer, a metal
layer obtained by combining at least one element selected from the
group consisting of Zn, In, Sn, and Cd and at least one element
selected from the group consisting of Fe, Co, and Ni may be used in
addition to the above-described combination of Fe, Co, and Zn, and
it is possible to attain the improvement in MR change ratio by
preparing the functional layer by employing the oxidation treatment
and the reduction treatment as in Examples.
[0244] (Modification Example of Spacer Layer)
[0245] Magnetoresistive elements were manufactured in the same way
as in the above-described Examples by using a metal spacer layer
(Ag or Au) or a tunneling insulator (MgO, Al.sub.2O.sub.3, or
TiO.sub.2), and an MR change ratio and areal resistance of each of
the magnetoresistive elements were analyzed in the same way.
[0246] As a result, it is confirmed that it is possible to greatly
change the MR change ratio as compared to the case of not providing
any functional layer and the case of performing oxidation treatment
and not performing any reduction treatment.
[0247] The various modules of the systems described herein can be
implemented as software applications, hardware and/or software
modules, or components on one or more computers, such as servers.
While the various modules are illustrated separately, they may
share some or all of the same underlying logic or code.
[0248] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *