U.S. patent application number 14/025194 was filed with the patent office on 2014-01-09 for magneto-resistance effect device, and magnetic recorder.
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, Hiromi YUASA.
Application Number | 20140009854 14/025194 |
Document ID | / |
Family ID | 44065947 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140009854 |
Kind Code |
A1 |
FUJI; Yoshihiko ; et
al. |
January 9, 2014 |
MAGNETO-RESISTANCE EFFECT DEVICE, AND MAGNETIC RECORDER
Abstract
According to one embodiment, a magneto-resistance effect device
includes: a multilayer structure having 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; a function layer which is 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, the
function layer having oxide containing at least one element
selected from Zn, In, Sn and Cd, and at least one element selected
from Fe, Co and Ni; and a pair of electrodes for applying a current
perpendicularly to a film plane of the multilayer structure.
Inventors: |
FUJI; Yoshihiko;
(Kawasaki-shi, JP) ; FUKUZAWA; Hideaki;
(Kawasaki-shi, JP) ; YUASA; Hiromi; (Kawasaki-shi,
JP) ; HARA; Michiko; (Yokohama-shi, JP) ;
MURAKAMI; Shuichi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
TOKYO |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
TOKYO
JP
|
Family ID: |
44065947 |
Appl. No.: |
14/025194 |
Filed: |
September 12, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13481317 |
May 25, 2012 |
|
|
|
14025194 |
|
|
|
|
PCT/JP2009/006442 |
Nov 27, 2009 |
|
|
|
13481317 |
|
|
|
|
Current U.S.
Class: |
360/324 |
Current CPC
Class: |
G11B 5/398 20130101;
H01F 10/3259 20130101; H01L 43/12 20130101; B82Y 25/00 20130101;
G11B 5/3903 20130101; H01L 43/08 20130101; G11B 2005/3996 20130101;
G11B 5/39 20130101; H01L 43/10 20130101; H01F 10/3272 20130101;
G11B 5/3983 20130101; G11B 5/3906 20130101; G01R 33/093 20130101;
H01F 41/325 20130101 |
Class at
Publication: |
360/324 |
International
Class: |
G11B 5/39 20060101
G11B005/39 |
Claims
1. A magneto-resistance effect device comprising: a multilayer
structure comprising: a first magnetic layer; a second magnetic
layer; a spacer layer provided between the first magnetic layer and
the second magnetic layer; a function layer included in the
multilayer structure, the function layer having mixed oxide
containing at least one element selected from Zn, In, Sn and Cd,
and at least one element selected from Fe, Co and Ni, wherein
resistivity of the function layer is not higher than
5.times.10.sup.4 .mu..OMEGA.cm; and a pair of electrodes applying a
current perpendicular to a film plane of the multilayer
structure.
2. The device according to claim 1, wherein the mixed oxide
contains Zn and Fe.
3. The device according to claim 1, wherein film thickness of the
function layer is not smaller than 1 nm and not larger than 10
nm.
4. The device according to claim 1, wherein the product of a
sectional area perpendicular to a stacking direction of the
multilayer structure and resistance obtained from the pair of
electrodes when a current is applied perpendicularly to the film
plane of the multilayer structure is not larger than 1
.OMEGA..mu.m.sup.2.
5. The device according to claim 1, wherein the spacer layer
comprises: an insulating layer containing oxygen or nitrogen; and
current paths which punched though the insulating layer in a
direction perpendicular to a film plane of the spacer layer so that
a current can be applied in the spacer layer.
6. The device according to claim 1, wherein the function layer
further contains at least one element selected from Al, B, Ga, C,
Si, Ge and Sn.
7. The device according to claim 1, wherein the spacer layer
contains any one of Cu, Au and Ag.
8. The device according to claim 1, wherein the first magnetic
layer has a magnetization which is fixed, and the second magnetic
layer has a magnetization which is changeable.
9. A magnetic recorder comprising: a magnetic recording medium; a
magnetic recording head comprising a magneto-resistance effect
device comprising: a multilayer structure; a first magnetic layer;
a second magnetic layer; a spacer layer provided between the first
magnetic layer and the second magnetic layer; a function layer
included in the multilayer structure, the function layer having
mixed oxide containing at least one element selected from Zn, In,
Sn and Cd, and at least one element selected from Fe, Co and Ni,
wherein resistivity of the function layer is not higher than
5.times.10.sup.4 .mu..OMEGA.cm; a pair of electrodes applying a
current perpendicular to a film plane of the multilayer structure;
and a signal processing portion which performs signal
writing/reading into/from the magnetic recording medium by using
the magnetic recording head.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a Divisional of commonly owned U.S.
application Ser. No. 13/481,317, filed May 25, 2012 (now
abandoned), which is a Continuation application of PCT Application
No. PCT/JP2009/006442, filed Nov. 27, 2009, which is published
under PCT Article 21(2) in Japanese, the entire contents of which
are incorporated herein by reference.
FIELD
[0002] The present invention relates to a magneto-resistance effect
device, and a magnetic recorder using the same.
BACKGROUND ART
[0003] A magneto-resistance effect device having a thin-film spin
filter layer (SF) which is made of oxide or nitride and which is
inserted in each of ferromagnetic layers or in an interface between
each of the ferromagnetic layers and a nonmagnetic spacer layer has
been proposed in JP-A-2004-6589. This SF layer can increase the MR
(Magneto-Resistance) ratio because it has a spin filer effect in
inhibiting conduction of either up-spin electrons or down-spin
electrons.
BRIEF DESCRIPTION OF DRAWINGS
[0004] A general architecture that implements the various features
of the present invention will now be described with reference to
the drawings. The drawings and the associated descriptions are
provided to illustrate embodiments and not to limit the scope of
the present invention.
[0005] FIG. 1 is a view showing the configuration of a
magneto-resistance effect device according to a first embodiment of
the invention.
[0006] FIG. 2 is a view showing the configuration of an
undercoating layer.
[0007] FIG. 3 is a flow chart for explaining a method of
manufacturing the magneto-resistance effect device according to the
first embodiment.
[0008] FIG. 4 is a view showing the configuration of a
magneto-resistance effect device according to a first
modification.
[0009] FIG. 5 is a view showing the configuration of a
magneto-resistance effect device according to a second
modification.
[0010] FIG. 6 is a view showing the configuration of a
magneto-resistance effect device according to a third
modification.
[0011] FIG. 7 is a view showing the configuration of a
magneto-resistance effect device according to a fourth
modification.
[0012] FIG. 8 is a view showing the configuration of a
magneto-resistance effect device according to a fifth
modification.
[0013] FIG. 9 is a view showing the configuration of a
magneto-resistance effect device according to a sixth
modification.
[0014] FIG. 10 is a view showing a cross-sectional TEM image of the
magneto-resistance effect device.
[0015] FIG. 11 is a graph showing a result of three-dimensional
atom probe analysis of the magneto-resistance effect device.
[0016] FIG. 12A is a view showing the configuration of a
magnet-resistance effect device according to a second embodiment of
the invention.
[0017] FIG. 12B is a view showing the configuration of a
Current-confined-to-the-path layer.
[0018] FIG. 13 is a flow chart for explaining a method of
manufacturing the magnet-resistance effect device according to the
second embodiment.
[0019] FIG. 14 is a view showing the configuration of a
magneto-resistance effect device according to a seventh
modification.
[0020] FIG. 15 is a view showing the configuration of a
magneto-resistance effect device according to an eighth
modification.
[0021] FIG. 16 is a view showing the configuration of a
magneto-resistance effect device according to a ninth
modification.
[0022] FIG. 17 is a view showing the configuration of a
magneto-resistance effect device according to a tenth
modification.
[0023] FIG. 18 is a view showing the configuration of a
magneto-resistance effect device according to an eleventh
modification.
[0024] FIG. 19 is a view showing the configuration of a
magneto-resistance effect device according to a twelfth
modification.
[0025] FIG. 20 is a view showing the relations among the RA value
of each magneto-resistance effect device, the resistivity of each
function layer and the MR ratio.
[0026] FIG. 21 is a view showing the configuration of a magnetic
head according to a third embodiment.
[0027] FIG. 22 is a view showing the configuration of the magnetic
head.
[0028] FIG. 23 is a view showing the configuration of a magnetic
recorder according to a fourth embodiment.
[0029] FIG. 24 is a view showing the configuration of a head
slider.
[0030] FIGS. 25A and 25B are views showing the configuration of a
head stack assembly.
DETAILED DESCRIPTION
[0031] Embodiments of the invention will be described below with
reference to the drawings. In the drawings which will be described
later, parts given the same numerals represent the same parts and
duplicated description thereof will be omitted.
[0032] A CPP (Current Perpendicular to Plane)-GMR device including
a high-sensitive spin valve film using a giant magneto-resistance
(GMR) effect is assumed in the invention. The spin valve film is a
laminated film having a sandwich structure in which a nonmagnetic
spacer layer is sandwiched between two ferromagnetic layers. A
laminated film structure region exhibiting a resistance change is
also called sin-dependent scattering unit. The magnetization
direction of one (called "pin layer" or "magnetization pinned
layer") of the two ferromagnetic layers is fixed by an
antiferromagnetic layer or the like. The magnetization direction of
the other ferromagnetic layer (called "free layer" or
"magnetization free layer") can be changed by an external magnetic
field. In the spin valve film, a large magneto-resistance effect
can be obtained by change in relative angle between the
magnetization directions of the two ferromagnetic layers.
Incidentally, in the CPP-GMR device, a current is applied from a
direction perpendicular to the spin valve film plane.
First Embodiment
[0033] FIG. 1 is a view showing the configuration of a
magneto-resistance effect device 10 according to a first embodiment
of the invention.
[0034] The magneto-resistance effect device 10 according to this
embodiment has: a cap layer 19 which prevents the
magneto-resistance effect device 10 from deterioration such as
oxidation; a magnetization pinned layer (hereinafter referred to as
pin layer) 14 in which magnetization is fixed; a magnetization free
layer (hereinafter referred to as free layer) 18 which is provided
between the cap layer 19 and the pin layer 14 so that magnetization
rotates freely; an intermediate layer (hereinafter referred to as
spacer layer) 16 which is made of a nonmagnetic substance provided
between the pin layer 14 and the free layer 18; and a function
layer 21 which is provided between the spacer layer 16 and the free
layer 18 and which contains mixed oxide of at least one element of
Zn, In, Sn and Cd and at least one element of Fe, Co and Ni. The
cap layer 19, the free layer 18, the function layer 21, the spacer
layer 16 and the pin layer 14 are defined collectively here as a
multilayer structure.
[0035] The magneto-resistance effect device 10 further has: a pair
of electrodes 11 and 20 between which a current is applied
perpendicularly to a film plane of the multilayer structure a
pinning layer 13 which is provided between the electrode 11 and the
pin layer 14 and which is made of an antiferromagnetic substance
for fixing the magnetization direction of the pin layer 14; and an
undercoating layer 12 which is provided between the pinning layer
13 and the electrode 11.
[0036] The electrodes 11 and 20 are provided so that a current is
applied in a direction perpendicular to a film plane of the
magneto-resistance effect device 10. When a voltage is applied
between the electrodes 11 and 20, a current flows into the
magneto-resistance effect device 10 along the direction
perpendicular to the film plane.
[0037] Because this current flows, change of resistance caused by
the magneto-resistance effect can be detected so that magnetism can
be detected. Cu, Au, or the like which is relatively low in
electric resistance in order to apply a current to the
magneto-resistance effect device 10 is used as each of the
electrodes 11 and 20.
[0038] For example, the undercoating layer 12 is configured so that
a seed layer 12b is provided on a buffer layer 12a as shown in FIG.
2.
[0039] The buffer layer 12a is a layer which relaxes surface
roughness of the electrode 11 so as to make crystallinity laminated
on the buffer layer 12a good. For example, Ta, Ti, V, W, Zr, Hf,
Cr, or alloys thereof can be used as the buffer layer 12a. It is
preferable that the film thickness of the buffer layer 12a is not
smaller than 1 nm and not larger than 10 nm. It is more preferable
that the film thickness of the buffer layer 12a is not smaller than
2 nm and not larger than 5 nm. If the buffer layer 12a is too thin,
the buffer effect is lost. On the other hand, if the buffer layer
12a is too thick, series resistance which does not contribute to
the MR ratio increases. Incidentally, when the seed layer 12b
formed on the buffer layer 12a has a buffer effect, it is
unnecessary to provide the buffer layer 12a. As a preferable
example, 3 nm-thick Ta can be formed.
[0040] The seed layer 12b is a layer for controlling the crystal
orientation and crystal gain size of a layer laminated on the seed
layer 12b. A metal or the like having an fcc structure
(face-centered cubic structure), an hcp structure (hexagonal
close-packed structure) or a bcc structure (body-centered cubic
structure) is preferred as the seed layer 12b.
[0041] For example, by using Ru having an hcp structure or NiFe
having an fcc structure as the seed layer 12b, the crystal
orientation of the spin valve film on the seed layer 12b can be
made as an fcc (111) orientation. When the pinning layer 13 is made
of IrMn, a good fcc (111) orientation can be achieved. When the
pinning layer 13 is made of PtMn, a regularized fct (111) structure
(face-centered tetragonal structure) can be obtained. When an fcc
metal is used as the free layer 18 and the pin layer 14, a good fcc
(111) orientation can be achieved. When a bcc metal is used as the
free layer 18 and the pin layer 14, a good bcc (110) orientation
can be achieved. To give full play to the function of the seed
layer 12b to improve the crystal orientation, the film thickness of
the seed layer 12b is set preferably to be not smaller than 1 nm
and not larger than 5 nm, and more preferably to be not smaller
than 1.5 nm and not larger than 3 nm. As a preferable example, 2
nm-thick Ru can be formed.
[0042] Besides Ru, an NiFe-base alloy (such as Ni.sub.xFe.sub.100-x
(x=90% to 50%, preferably, 75% to 85%) or
(Ni.sub.xFe.sub.100-x).sub.100-yX.sub.y (X=Cr, V, Nb, Hf, Zr, Mo)
obtained by adding a third element X to NiFe to nonmagnetize NiFe)
may be used as the seed layer 12b. The NiFe-base seed layer 12b is
relatively easy to obtain a good crystal orientation so that the
half-value width of a rocking curve can be set to be 3.degree. to
5.degree..
[0043] The seed layer 12b has not only the function of improving
the crystal orientation but also a function of controlling the
crystal grain size of the spin valve film. Specifically, the
crystal grain size of the spin valve film can be controlled to be
not smaller than 5 nm and not larger than 20 nm, so that a high MR
ratio can be achieved without causing variation in characteristic
even when the size of the magneto-resistance effect device becomes
small.
[0044] Incidentally, by setting the crystal grain size of the seed
layer 12b to be not smaller than 5 nm and not larger than 20 nm,
electron diffuse reflection and inelastic scattering sites due to
crystal grain boundaries can be reduced. To obtain this crystal
grain size, 2 nm-thick Ru is formed. In the case of
(Ni.sub.xFe.sub.100-x).sub.100-yZ.sub.y (Z=Cr, V, Nb, Hf, Zr, Mo),
it is preferable that a thickness of 2 nm is formed while a
composition y of the third element X is set to be about 0% to 30%
(inclusive of the case where y=0).
[0045] The crystal grain size of the spin valve film can be
discriminated based on the crystal grain size of a layer disposed
between the seed layer 12b and the spacer layer 16 (e.g. can be
determined based on a cross-sectional TEM or the like). For
example, when the pin layer 14 is a bottom type spin valve film
located as a layer under the spacer layer 16, it can be
discriminated based on the crystal grain size of the pinning layer
13 (antiferromagnetic layer) or the pin layer 14 (magnetization
pinned layer) formed on the seed layer 12b.
[0046] The pinning layer 13 has a function of giving unidirectional
anisotropy to the ferromagnetic layer serving as the pin layer 14
formed thereon to thereby fix magnetization. As the material of the
pinning layer 13, an antiferromagnetic material such as PtMn,
PdPtMn, IrMn or RuRhMn can be used. Of these, IrMn is favorable as
the material of a head supporting high recording density. Because
IrMn can give unidirectional anisotropy even when IrMn is thinner
in film thickness than PtMn, IrMn is suitable for forming a narrow
gap required for high density recording.
[0047] To give sufficiently intensive unidirectional anisotropy,
the film thickness of the pinning layer 13 is set suitably. When
the material of the pinning layer 13 is PtMn or PdPtMn, the film
thickness is set preferably to be not smaller than 8 nm and not
larger than 20 nm, and more preferably to be not smaller than 10 nm
and not larger than 15 nm. When the material of the pinning layer
13 is IrMn, the film thickness is set preferably to be not smaller
than 4 nm and not larger than 18 nm, and more preferably to be not
smaller than 5 nm and not larger than 15 nm because unidirectional
anisotropy can be given even when IrMn is thinner in film thickness
than PtMn or the like. As a preferable example, 7 nm-thick
Ir.sub.22Mn.sub.79 can be formed.
[0048] As the pinning layer 13, a hard magnetic layer may be used
in place of the antiferromagnetic 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%) or FePt (Pt=40% to 60%) can be used as the hard
magnetic layer. Because the hard magnetic layer (particularly,
CoPt) is relatively low in specific resistance, increase in series
resistance and resistance-area RA can be suppressed.
[0049] Here, the resistance-area RA means a product of a sectional
area perpendicular to the lamination direction of the laminated
film of the magneto-resistance effect device 10 and resistance
obtained from the pair of electrodes when a current is applied
perpendicularly to the film plane of the laminated film of the
magneto-resistance effect device 10.
[0050] The crystal orientation of the spin valve film or the
pinning layer 13 can be measured by X-ray diffraction. A good
orientation can be obtained when the half-value width of a rocking
curve at the fcc (111) peak of the spin valve film or the fct (111)
peak or bcc (110) peak of the pinning layer 13 (PtMn) is
3.5.degree. to 6.degree.. Incidentally, the dispersion angle of
this orientation can be discriminated based on diffraction spots
using cross-sectional TEM.
[0051] The pin layer 14 is configured so that a lower pin layer
141, a magnetic coupling layer 142 and an upper pin layer 143 are
laminated in this order in view from the pinning layer 13 side.
[0052] The pinning layer 13 and the lower pin layer 141 are
magnetically exchange-coupled to each other so that unidirectional
anisotropy is given. The lower pin layer 141 and the upper pin
layer 143 between which the magnetic coupling layer 142 is
sandwiched are coupled to each other so firmly that the
magnetization directions thereof are antiparallel to each
other.
[0053] For example, a Co.sub.xFe.sub.100-x alloy (x=0% to 100%), an
Ni.sub.xFe.sub.100-x alloy (x=0% to 100%) or a material obtained by
adding a nonmagnetic element thereto can be used as the material of
the lower pin layer 141. A single element such as Co, Fe or Ni or
an alloy thereof can be also used as the material of the lower pin
layer 141.
[0054] It is preferable that the film thickness of the lower pin
layer 141 is not smaller than 2 nm and not larger than 5 nm. This
is for the purpose of keeping unidirectional anisotropic magnetic
field intensity due to the pinning layer 13 high and keeping
antiferromagnetic coupling magnetic field intensity between the
lower pin layer 141 and the upper pin layer 143 through the
magnetic coupling layer 142 high.
[0055] If the lower pin layer 141 is too thin, the MR ratio is
reduced because the upper pin layer 143 giving an influence to the
MR ratio must be made thin. On the other hand, if the lower pin
layer 141 is too thick, it is difficult to obtain sufficient
unidirectional anisotropic magnetic field intensity necessary for
device operation.
[0056] In consideration of the magnetic film thickness (saturation
magnetization Bs.times.film thickness t (the product Bs-t)) of the
lower pin layer 141, it is preferable that the magnetic film
thickness of the lower pin layer 141 is substantially equal to the
magnetic film thickness of the upper pin layer 143. That is, it is
preferable that the magnetic film thickness of the upper pin layer
143 and the magnetic film thickness of the lower pin layer 141
correspond to each other.
[0057] For example, when the upper pin layer 143 is
(Fe.sub.50Co.sub.50 [1 nm]/Cu (0.25 nm)).times.2/Fe.sub.50Co.sub.50
[1 nm], the magnetic film thickness is 2.2 T.times.3 nm=6.6 T nm
because the saturation magnetization of Fe.sub.50Co.sub.50 in the
thin film is about 2.2 T. Because the saturation magnetization of
Co.sub.90Fe.sub.10 is about 1.8 T, the film thickness t of the
lower pin layer 141 giving a magnetic film thickness equal to the
above becomes 6.6 T nm/1.8 T=3.47 nm. Accordingly, in this case, it
is preferable that Co.sub.90Fe.sub.10 about 3.6 nm in film
thickness is used as the lower pin layer 141. When
Co.sub.75Fe.sub.25 is used as the lower pin layer 141, it is
preferable from the same calculation that the lower pin layer 141
has a film thickness of about 3.3 nm.
[0058] Here, `/` means that materials written in the left of `/`
are laminated successively. The description `Au/Cu/Ru` means that a
Cu layer is laminated on an Au layer and an Ru layer is laminated
on the Cu layer. In addition, `x2` means two layers. The
description `(Au/Cu).times.2` means that a Cu layer is laminated on
an Au layer, and an Au layer and a Cu layer are further laminated
on the Cu layer successively. In addition, `[ ]` means the film
thickness of the material.
[0059] The magnetic coupling layer 142 has a function of forming a
synthetic pin structure by bringing antiferromagnetic coupling to
the lower pin layer 141 and the upper pin layer 143 between which
the magnetic coupling layer 142 is sandwiched. Ru can be used as
the magnetic coupling layer 142. It is preferable that the film
thickness of the magnetic coupling layer 142 is not smaller than
0.8 nm and not larger than 1 nm. Incidentally, another material
than Ru may be used as the magnetic coupling layer 142 as long as
the material can bring sufficient antiferromagnetic coupling to the
lower pin layer 141 and the upper pin layer 143 between which the
magnetic coupling layer 142 is sandwiched. As the film thickness of
the magnetic coupling layer 142, a film thickness of 0.3 nm to 0.6
nm, both inclusively, corresponding to a first peak of RKKY
(Ruderman-Kittel-Kasuya-Yoshida) coupling may be used in place of a
film thickness of 0.8 nm to 1 nm, both inclusively, corresponding
to a second peak of RKKY coupling. Ru with a film thickness of 0.9
nm capable of obtaining characteristic of higher reliable coupling
stably can be taken here as an example.
[0060] The upper pin layer 143 is a magnetic layer directly
contributing to the MR effect. Both constituent material and film
thickness are important to obtain a large MR ratio. The magnetic
material located in an interface between the upper pin layer 143
and the spacer layer 16 is particularly important from the
viewpoint of contribution to spin-dependent interfacial scattering.
The spin-dependent interfacial scattering is a phenomenon that an
MR effect is exhibited in an interface between the spacer layer and
the free layer or the pin layer.
[0061] Fe.sub.50Co.sub.50 can be used as the upper pin layer 143.
Fe.sub.50Co.sub.50 is a magnetic material having a bcc structure.
This material can achieve a large MR ratio because the
spin-dependent interfacial scattering effect is large. As an
FeCo-based alloy having a bcc structure, Fe.sub.xCo.sub.100-x
(x=30% to 100%) or a material obtained by adding an additive
element to Fe.sub.xCo.sub.100-x can be used. Among these,
Fe.sub.40Co.sub.60 to Fe.sub.80Co.sub.20 satisfying various
characteristics are examples of an easy-to-use material.
[0062] When the upper pin layer 143 is made of a magnetic layer
having a bcc structure easy to achieve a high MR ratio, it is
preferable that the total film thickness of this magnetic layer is
not smaller than 1.5 nm. This is for the purpose of keeping the bcc
structure stable. Because it is often that the metal material used
as the spin valve film has an fcc structure or an fct structure,
only the upper pin layer 143 may have a bcc structure. For this
reason, if the film thickness of the upper pin layer 143 is too
thin, it is difficult to keep the bcc structure stable so that a
high MR ratio cannot be obtained.
[0063] In such a case, a laminate of 1 nm-thick Fe.sub.50Co.sub.50,
0.25 nm-thick Cu, 1 nm-thick Fe.sub.50Co.sub.50, 0.25 nm-thick Cu
and 1 nm-thick Fe.sub.50Co.sub.50 can be used as the upper pin
layer 143.
[0064] In the upper pin layer 143 having such a laminate structure
in which magnetic layers (FeCo layers) and nonmagnetic layers (Cu
layers) are laminated alternately, the spin-dependent scattering
effect called spin-dependent bulk scattering effect can be improved
by the interposition of the Cu layers in the upper pin layer 143.
The spin-dependent bulk scattering effect is a phenomenon that an
MR effect is exhibited in the inside of the free layer or the pin
layer.
[0065] Although it is easy to obtain a large MR ratio when the film
thickness of the upper pin layer 143 is large, it is preferable
that the film thickness of the upper pin layer 143 is small enough
to obtain a large pin-fixing magnetic field. There is a trade-off
relation as to the film thickness of the upper pin layer 143. For
example, when an FeCo ally layer having a bcc structure is used, a
film thickness not smaller than 1.5 nm is preferred because it is
necessary to keep the bcc structure stable. When a CoFe alloy layer
having an fcc structure is used, a film thickness not smaller than
1.5 nm is still preferred to obtain a large MR ratio. On the other
hand, to obtain a large pin-fixing magnetic field, the film
thickness of the upper pin layer 143 is set preferably to be not
larger than 5 nm, and more preferably to be not larger than 4 nm.
As described above, the film thickness of the upper pin layer 143
is set preferably to be not smaller than 1.5 nm and not larger than
5 nm, and more preferably to be not smaller than 2.0 nm and not
larger than 4 nm.
[0066] In the upper pin layer 143, a Co.sub.90Fe.sub.10 alloy
having an fcc structure or Co or a Co ally having an hcp structure
which has been heretofore used widely in a magneto-resistance
effect device can be used in place of the magnetic material having
a bcc structure. A single metal such as Co, Fe or Ni, or an alloy
material containing any one of these elements can be used as the
upper pin layer 143. Examples of material advantageous to obtain a
large MR ratio as the magnetic material of the upper pin layer 143
are an FeCo alloy material having a bcc structure, a cobalt alloy
having a cobalt composition containing 50% or more of cobalt, and
an Ni composition containing 50% or more of Ni.
[0067] A Heusler magnetic alloy layer such as Co.sub.2MnGe,
Co.sub.2MnSi or Co.sub.2MnAl may be used as the upper pin layer
143.
[0068] The spacer layer 16 has a function of decoupling the
magnetic coupling of the pin layer 14 and the free layer 18. Any
element of Au, Ag and Cu can be used as the spacer layer 16. It is
preferable that the film thickness of the spacer layer 16 is not
smaller than 1.5 nm and not larger than 5 nm.
[0069] The free layer 18 is a layer having a ferromagnetic
substance in which the magnetization direction changes according to
an external magnetic field. For example, a double layer structure
of Co.sub.90Fe.sub.10 [1 nm]/Ni.sub.83Fe.sub.17 [3.5 nm] using CoFe
formed in an interface and NiFe can be used. Incidentally, when an
NiFe layer is not used, a single layer of Co.sub.90Fe.sub.10 [4 nm]
can be used. Alternatively, the free layer 18 made of a triple
layer structure of CoFe/NiFe/CoFe or the like may be used.
[0070] Co.sub.90Fe.sub.10 is preferred as the free layer 18 because
Co.sub.90Fe.sub.10 has stable soft magnetic characteristic among
CoFe alloys. When a CoFe alloy close to Co.sub.90Fe.sub.10 is used,
it is preferable that the film thickness is set to be not smaller
than 0.5 nm and not larger than 4 nm. Besides this,
Co.sub.xFe.sub.100-x (x=70% to 90%) may be used.
[0071] A laminate in which CoFe layers or Fe layers having a
thickness of 1 nm to 2 nm, both inclusively, and very thin Cu
layers having a thickness of 0.1 nm to 0.8 nm, both inclusively,
are laminated alternately may be used as the free layer 18.
[0072] An amorphous magnetic layer such as CoZrNb may be used as
part of the free layer 18. Incidentally, even when an amorphous
magnetic layer is used, it is necessary to use a magnetic layer
having a crystal structure in an interface with the spacer layer 16
giving a large influence on the MR ratio. As the structure of the
free layer 18, the following configuration can be provided in view
of the spacer layer 16 side. That is, as the structure of the free
layer 18, (1) only a crystal layer, (2) a laminate of a crystal
layer and an amorphous layer, (3) a laminate of a crystal layer, an
amorphous layer and a crystal layer, or the like, may be
considered. What is important here is that a crystal layer is
always in contact with an interface with the spacer layer 16 in any
one of (1) to (3).
[0073] The cap layer 19 has a function of protecting the spin valve
film. For example, the cap layer 19 can be formed as a plurality of
metal layers such as a double layer structure of a Cu layer and an
Ru layer (Cu [1 nm]/Ru [10 nm]). As the cap layer 19, an Ru/Cu
layer or the like containing Ru disposed on the free layer 18 side
may be used. In this case, it is preferable that the film thickness
of Ru is not smaller than 0.5 nm and not larger than 2 nm.
Particularly the thus configured cap layer 19 is preferable in the
case where the free layer 18 is made of NiFe. This is because Ru
and Ni are so immiscible that magnetostriction of an interfacial
mixing layer formed between the free layer 18 and the cap layer 19
can be reduced.
[0074] When the cap layer 19 is either Cu/Ru or Ru/Cu, it is
preferable that the film thickness of the Cu layer is not smaller
than 0.5 nm and not larger than 10 nm, and the film thickness of
the Ru layer can be set to be not smaller than 0.5 nm and not
larger than 5 nm. Because the specific resistance value of Ru is so
high that use of a too thick Ru layer is undesirable, it is
preferable that such a film thickness range is set.
[0075] As the cap layer 19, other metal layers may be provided in
place of the Cu layer and the Ru layer. The configuration of the
cap layer 19 is not particularly limited but another material may
be used as long as the material can serve as the cap for protecting
the spin valve layer. It is however necessary to pay attention
because the MR ratio or long-term reliability may vary according to
selection of the cap layer. Cu and Ru are examples of materials of
the cap layer preferred from these viewpoints.
[0076] The function layer 21 has a spin filter effect by which
transmission of up-spin electrons or down-spin electrons can be
controlled. The function layer 21 is characterized by containing
mixed oxide of at least one element of Zn, In, Sn and Cd and at
least one element of Fe, Co and Ni. Specifically, mixed oxide of
Fe.sub.50Co.sub.50 and Zn can be used. Incidentally, Zn is more
preferred because Zn among In, Sn and Cd belongs to the same
periodic group as Fe, Co and Ni so that Zn is easily magnetized to
stabilize magnetization of the function layer 21 when Zn is mixed
with Fe, Co and Ni as mixed oxide.
[0077] When these materials are used, a high spin filter effect and
reduction of spin-flip due to achievement of low resistivity can be
made consistent with each other so that the MR ratio of the
magneto-resistance effect device 10 can be improved.
[0078] Here, to achieve a low resistivity spin filtering layer, it
is effective that the spin filtering layer contains the
aforementioned oxide material containing Zn, In, Sn and 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. Although these oxide
semiconductors are semiconductors having a band gap of 3 eV or
higher, conduction electron density reaches about 10.sup.18
cm.sup.-1-10.sup.19 cm.sup.-3 because intrinsic defects such as
oxygen holes form a donor level when these oxide semiconductors are
slightly shifted to a reducing direction from the stoichiometric
composition. In the band structure of these conductive oxides, the
valence band is mainly formed from 2p orbits of oxygen atoms
whereas the conduction band is mainly formed from s orbits of metal
atoms. When the carrier density Fermi level increases to be higher
than 10.sup.18 cm.sup.-3, it reaches the conduction band to bring a
state called degeneracy. Such an oxide semiconductor is called
n-type degenerate semiconductor and has a sufficient concentration
and mobility of conduction electrons to achieve low
resistivity.
[0079] On the other hand, to achieve a spin filtering layer having
a high spin filter effect, it is effective that the spin filtering
layer contains oxide of Co, Fe and Ni having magnetism at room
temperature. An oxide material containing Zn, In, Sn and Cd
effective in achievement of low resistivity has no magnetism as
bulk characteristic. Although disclosure has been made in
JP-A-2004-6589 that even a nonmagnetic oxide material exhibits
magnetism to obtain a spin filter effect when a very thin oxide
layer is inserted in the free layer or the pin layer, the oxide
material may contain oxide of Co, Fe and Ni to exhibit magnetism
more easily to obtain a high spin filter effect without limitation
in film thickness of the oxide layer.
[0080] An additive element may be further added to the function
layer 21. There is a report that heat resistance is improved when
Al as an additive element is added to Zn oxide. Besides Al, B, Ga,
C, Si, Ge, Sn, or the like may be used as the additive element.
Although the mechanism to improve heat resistance is not entirely
clear, it is considered that the mechanism to improve heat
resistance is caused by change in carrier density because density
of oxygen holes formed in Zn oxide shifted to a reducing direction
from the stoichiometric composition is reduced by acceleration of
re-oxidation due to heat. As another reason of improvement of heat
resistance, these aforementioned elements are equivalent to Group
III or Group IV dopants which can suppress change of carrier
density in the function layer 21 and can further suppress change of
resistivity according to heat in order to prevent acceleration of
re-oxidation of Zn atoms due to heat.
[0081] It is preferable that the film thickness of the function
layer 21 is not smaller than 0.5 nm to obtain a sufficient spin
filtering effect. It is further preferable that the film thickness
of the function layer 21 is not smaller than 1 nm to obtain a more
uniform function layer 21 in consideration of dependence of the
device in terms of manufacturing. On the other hand, it is
preferable that the upper limit of the film thickness is not larger
than 10 nm from the viewpoint of preventing the read gap of the
reproduction head from being widened.
[0082] When the function layer 21 is formed in an interface between
the free layer 18 and the spacer layer 16, a soft magnetic film
more excellent in soft magnetic characteristic than a magnetic
compound can be used as the free layer 18 to improve magnetic field
responsiveness. The same rule can be applied to the case where the
function layer 21 is provided inside the free layer 18 or in an
interface between the free layer 18 and the cap layer 19 as shown
in a modification which will be described later. Single metals such
as Co, Fe and Ni or all alloy materials containing any one of these
elements can be used in the free layer 18. Particularly, as
described above, a double layer structure of Co.sub.90Fe.sub.10 [1
nm]/Ni.sub.83Fe.sub.17 [3.5 nm] using NiFe on CoFe formed in an
interface, a triple layer structure of CoFe/NiFe/CoFe etc., a
single layer of a Co--Fe alloy, or the like, can be used.
[0083] When function layers 21 are formed in an interface between
the pin layer 14 and the spacer layer 16, inside the pin layer 14
and in an interface between the magnetic coupling layer 142 and the
pin layer 14, a material which can be more easily pinned in one
direction than the function layers 21 may be used as the upper pin
layer 143 to improve pin characteristic. Single metals such as Co,
Fe and Ni or all alloy materials containing any one of these
elements can be used as the material of the upper pin layer
143.
[0084] When function layers 21 are formed in an interface between
the free layer 18 and the spacer layer 16 and in an interface
between the pin layer 14 and the spacer layer 16, increase in the
MR ratio caused by increase in spin-dependent interfacial
scattering due to the spin filtering effect of the function layers
21 can be obtained. On the other hand, when function layers 21 are
formed inside the free layer 18, in an interface between the free
layer 18 and the cap layer 19, inside the pin layer 14 and in an
interface between the upper pin layer 143 and the magnetic coupling
layer 142, spin-dependent bulk scattering can be intensified by the
spin filtering effect of the function layers 21 so that the MR
ratio can be intensified.
[0085] A plurality of function layers 21 may be provided in the
free layer 18 or the pin layer 14. For example, when function
layers 21 are provided in an interface between the spacer layer 16
and the free layer 18 and inside the free layer 18, both
spin-dependent interfacial scattering and spin-dependent bulk
scattering can be intensified so that a high MR ratio can be
achieved. It is however necessary to suppress the number of
function layers 21 to be inserted to a suitable number because
occurrence of spin-flip is caused by increase in resistance when
the number to be inserted is too large. For example, about four
function layers 21 can be provided inside the free layer 18 or the
pin layer 14.
[0086] When a function layer 21 is formed in an interface between
the free layer 18 and the spacer layer 16 as shown in FIG. 1, the
function layer 21 contributes to spin-dependent interfacial
scattering as described above.
[0087] Incidentally, it is impossible to provide any function layer
21 inside the spacer layer 16. This is based on the following
reasons. The first reason is that when the function layer 21 is
provided inside the spacer layer 16, oxygen contained in the
function layer 21 is diffused in the spacer layer 16 to thereby
generate considerable spin-flip of conduction electrons passing
through the spacer layer 16 so that the conduction electrons
passing through the spacer layer 16 lose spin information. The
second reason is that simply free magnetization is generated to
inhibit conduction electrons passing through the spacer layer 16
because the function layer 21 is magnetically coupled neither to
the free layer 18 nor to the pin layer 14.
[0088] A method of manufacturing the magneto-resistance effect
device 10 according to this embodiment will be described below.
[0089] In this embodiment, a sputtering method such as DC magnetron
sputtering or RF magnetron sputtering, an ion beam sputtering
method, a vapor deposition method, a CVD (Chemical Vapor
Deposition) method, an MBE (Molecular Beam Epitaxy) method, or the
like, can be used as a forming method at the time of
manufacturing.
[0090] FIG. 3 is a flow chart for explaining a process of
manufacturing the magneto-resistance effect device 10.
[0091] In step S1, an electrode 11 is formed on a substrate (not
shown) by a microfabrication process in advance. Then, for example,
Ta [1 nm]/Ru [2 nm] as an undercoating layer 12 is formed on the
electrode 11. Ta is equivalent to the buffer layer 12a for relaxing
roughness of the lower electrode. Ru is equivalent to the seed
layer 12b for controlling the crystal orientation and crystal grain
size of the spin valve film formed thereon.
[0092] In step S12, a pinning layer 13 is formed on the
undercoating layer 12. An antiferromagnetic material such as PtMn,
PdPtMn, IrMn or RuRhMn can be used as the material of the pinning
layer 13.
[0093] In step S13, a pin layer 14 is formed on the pinning layer
13. The pin layer 14 can be provided as a synthetic pin layer, for
example, having a lower pin layer 141 (Co.sub.90Fe.sub.10 [4 nm]),
a magnetic coupling layer 142 (Ru), and an upper pin layer 143
(Co.sub.90Fe.sub.10 [4 nm]).
[0094] In step S14, a spacer layer 16 is formed on the pin layer
14.
[0095] The spacer layer 16 is made of any one metal of Au, Ag and
Cu.
[0096] In step S15, a function layer 21 is formed on the spacer
layer 16. Specifically, a metal layer of Fe.sub.50Co.sub.50 and Zn
is formed on the upper pin layer 143. Here, the metal layer of
Fe.sub.50Co.sub.50 and Zn may be provided as a laminate of an
Fe.sub.50Co.sub.50 layer and a Zn layer such as
Fe.sub.50Co.sub.50/Zn, Zn/Fe.sub.50Co.sub.50 or
(Fe.sub.50Co.sub.50/Zn).times.2 or may be provided as a single
layer of an alloy such as Zn.sub.50 (Fe.sub.50Co.sub.50).sub.50. A
metal material containing Zn and Fe.sub.50Co.sub.50 is oxidized to
form the function layer 21. This conversion process can use ion
assisted oxidation (IAO) which is performed in the presence of
supplied oxygen while irradiating a metal material layer with an
ion beam or plasma of rare gas or the like. In the aforementioned
ion assisted conversion process, oxygen gas may be ionized or
formed as plasma. By energy assist to the metal material layer due
to ion beam irradiation, a stable and uniform oxide layer can be
formed as the function layer 21. For formation of one function
layer 21, the aforementioned formation and conversion process of
the metal material layer may be repeated several times. In this
case, it is preferable that a function layer 21 having a
predetermined film thickness is not provided by one formation and
conversion process but the film thickness is divided so that a
conversion process is applied to a metal material layer having a
small film thickness. Natural oxidation to expose a metal material
layer containing Zn and Fe.sub.50Co.sub.50 to an oxygen atmosphere
may be used. To form stable oxide, an oxidation method using energy
assist is however preferred. When a metal material of Zn and
Fe.sub.50Co.sub.50 is provided as a laminate, it is preferable that
oxidation is made under ion beam irradiation in order to form a
function layer 21 of evenly mixed Zn and Fe.sub.50Co.sub.50.
[0097] Incidentally, besides ion beam irradiation, heating
treatment or the like may be performed as an energy assist method.
In this case, for example, oxygen may be supplied while a metal
material layer is heated at a temperature of 100.degree. C. to
300.degree. C. after the formation of the metal material layer.
[0098] Beam conditions in the case where an ion beam assisted
process is performed in a conversion process for forming a function
layer 21 will be described below. In the case where the
aforementioned rare gas is ionized or provided as plasma and
radiated when a function layer 21 is formed by a conversion
process, it is preferable that an acceleration voltage V thereof is
set to be 30V to 130V and a beam current Ib is set to be 20 mA to
200 mA. These conditions are remarkably weak conditions in
comparison with the condition for performing ion beam etching. Even
when plasma such as RF plasma is used in place of the ion beam, the
function layer 21 can be formed likewise. The incidence angle of
the ion beam is changed suitably in a range of 0.degree. to
80.degree. when the angle of incidence of the ion beam
perpendicular to the film plane is defined as 0.degree. and the
angle of incidence of the ion beam parallel to the film plane is
defined as 90.degree.. The processing time due to this process is
preferably 15 seconds to 1200 seconds and more preferably not
shorter than 30 seconds from the viewpoint of controllability or
the like. If the processing time is too long, productivity of the
magneto-resistance effect device decreases unfavorably. It is
preferable from these viewpoints that the processing time is 30
seconds to 600 seconds.
[0099] In an oxidation process using ion or plasma, oxygen exposure
of 1.times.10.sup.3 to 1.times.10.sup.4 L (1 L=1.times.10.sup.-6
Torr.times.sec) is preferred in the case of IAO. In the case of
natural oxidation, oxygen exposure of 3.times.10.sup.3 L to
3.times.10.sup.4 L is preferred.
[0100] In step S16, a free layer 18 is formed on the function layer
21. For example, Co.sub.90Fe.sub.10 [4 nm] is formed as the free
layer 18.
[0101] In step S17, a cap layer 19 is formed on the free layer 18.
For example, Cu [1 nm]/Ru [10 nm] is formed as the cap layer
19.
[0102] In step S18, an annealing process is performed.
[0103] Finally, an electrode 20 for applying a current
perpendicularly to the magneto-resistance effect device 10 is
formed on the cap layer 19.
(Modification 1)
[0104] FIG. 4 is a view showing a first modification of the
magneto-resistance effect device 10 according to the first
embodiment.
[0105] This modification is different from the first embodiment in
that the function layer 21 is provided inside the free layer 18.
The free layer 18 includes a first free layer 18a and a second free
layer 18b. Incidentally, the first free layer 18a is provided
between the spacer layer 16 and the function layer 21 while the
second free layer 18b is provided between the cap layer 19 and the
function layer 21.
[0106] For formation of the function layer 21 inside the free layer
18, the spacer layer 16, the function layer 21 and the second free
layer 18b are formed successively on the first free layer 18a.
[0107] When the function layer 21 is provided inside the free layer
18 in this manner, the function layer 21 contributes to
spin-dependent bulk scattering as described above. Because the
function layer 21 is magnetically coupled to the free layer 18 to
make the magnetization direction of the function layer 21 free
similarly to the free layer 18, the function layer 21 contributes
to improvement of the MR ratio of the magneto-resistance effect
device 10 without inhibition of the function of the free layer 18.
Moreover, because oxygen contained in the function layer 21 can be
restrained from being diffused into the spacer layer 16, occurrence
of spin-flip in the spacer layer 16 as caused by the presence of
any oxygen element in the spacer layer 16 can be suppressed so that
a high MR ratio can be obtained.
(Modification 2)
[0108] FIG. 5 is a view showing a second modification of the
magneto-resistance effect device 10 according to the first
embodiment.
[0109] This modification is different from the first embodiment in
that the function layer 21 is provided between the free layer 18
and the cap layer 19.
[0110] When the function layer 21 is provided between the free
layer 18 and the cap layer 19 in this manner, the function layer 21
contributes to spin-dependent bulk scattering as described above.
Because the function layer 21 is made of oxide, the function layer
21 can protect the magneto-resistance effect device 10 from
deterioration such as oxidation. Moreover, because oxygen contained
in the function layer 21 can be restrained from being diffused into
the spacer layer 16, occurrence of spin-flip in the spacer layer 16
as caused by the presence of any oxygen element in the spacer layer
16 can be suppressed so that a high MR ratio can be obtained.
(Modification 3)
[0111] FIG. 6 is a view showing a third modification of the
magneto-resistance effect device 10 according to the first
embodiment.
[0112] This modification is different from the first embodiment in
that the function layer 21 is provided between the pin layer 14 and
the spacer layer 16.
[0113] When the function layer 21 is provided between the pin layer
14 and the spacer layer 16 in this manner, the function layer 21
contributes to spin-dependent interfacial scattering as described
above. Because the function layer 21 is made of oxide so that the
function layer 21 can prevent the constituent material of the
spacer layer 16 and the constituent material of the pin layer 14
from being mixed with each other, the spacer layer 16 can make
conduction electrons pass through while suppressing spin-flip so
that the magnetization of the pin layer 14 can be fixed stably.
(Modification 4)
[0114] FIG. 7 is a view showing a fourth modification of the
magneto-resistance effect device 10 according to the first
embodiment.
[0115] This modification is different from the first embodiment in
that the function layer 21 is provided inside the upper pin layer
143.
[0116] When the function layer 21 is provided inside the upper pin
layer 143 in this manner, the function layer 21 contributes to
spin-dependent bulk scattering as described above. Because oxygen
contained in the function layer 21 is restrained from being
diffused into the spacer layer when the function layer 21 is
disposed in a position being not in contact with the spacer layer,
spin-flip in the spacer layer as caused by the presence of any
oxygen element in the spacer layer can be avoided so that a high MR
ratio can be obtained.
(Modification 5)
[0117] FIG. 8 is a view showing a fifth modification of the
magneto-resistance effect device 10 according to the first
embodiment.
[0118] This modification is different from the first embodiment in
that the function layer 21 is provided between the upper pin layer
143 and the magnetic coupling layer 142.
[0119] When the function layer 21 is provided between the upper pin
layer 143 and the magnetic coupling layer 142 in this manner, the
function layer 21 contributes to spin-dependent bulk scattering as
described above. Because oxygen contained in the function layer 21
is restrained from being diffused into the spacer layer when the
function layer 21 is disposed in a position being not in contact
with the spacer layer, spin-flip in the spacer layer as caused by
the presence of any oxygen element in the spacer layer can be
avoided so that a high MR ratio can be obtained.
(Modification 6)
[0120] FIG. 9 is a view showing a sixth modification of the
magneto-resistance effect device 10 according to the first
embodiment.
[0121] This modification is different from the first embodiment in
that a second function layer 22 is further provided between the
spacer layer 16 and the free layer 18 in addition to the function
layer 21 provided between the upper pin layer 143 and the spacer
layer 16.
[0122] Incidentally, since the configuration of the function layer
21 is the same as that of the function layer 22, description
thereof will be omitted.
[0123] When the second function layer 22 is further provided
between the spacer layer 16 and the free layer 18 in addition to
the function layer 21 provided between the upper pin layer 143 and
the spacer layer 16 in this manner, an effect as the sum of spin
filtering effects of the two function layers can be obtained so
that a high MR ratio can be obtained in comparison with the case
where one function layer is used.
[0124] Incidentally, because the magnet-resistance effect devices
10 according to the modifications 1 to 6 can be produced by use of
the method of manufacturing the magnet-resistance effect device 10
described in the first embodiment, description about the method of
manufacturing the magneto-resistance effect devices 10 according to
the modifications 1 to 6 will be omitted.
EXAMPLES
[0125] Magneto-resistance effect devices 10 according to the first
embodiment and the modifications 1 to 6 were produced and
perpendicular current conduction was performed between the
electrodes 11 and 20 to thereby evaluate the RA values of the
magneto-resistance effect devices 10 and the MR ratios of the
magneto-resistance effect devices 10.
Example 1
[0126] A magneto-resistance effect device 10 according to the first
embodiment was produced and the RA value and MR ratio thereof were
evaluated. That is, a structure in which the function layer 21 was
provided between the spacer layer 16 and the free layer 18 as shown
in FIG. 1 was produced.
[0127] As for the method of producing the function layer 21, 2
nm-thick Fe.sub.50Co.sub.50 was formed on the spacer layer 16 of
Cu, and 0.6 nm-thick Zn was formed thereon. Then, this
Fe.sub.50Co.sub.50 and Zn were converted into oxide of Zn and
Fe.sub.50Co.sub.50 (hereinafter described as
Zn--Fe.sub.50Co.sub.50-O) by IAO to thereby form the function layer
21. On this occasion, the film thickness of the function layer 21
was 3 nm. On this occasion, oxygen exposure used in IAO was used as
3.0.times.10.sup.4 Langmiur. Then, 2 nm-thick Fe.sub.50Co.sub.50
was formed on the function layer 21 to thereby form the free layer
18. Finally, an annealing process was performed at 280.degree. C.
for 5 hours so that electrodes 11 and 20 were formed.
[0128] Incidentally, because the method of forming the function
layer is the same in the following examples, description thereof
will be omitted.
[0129] The configuration of the magneto-resistance effect device 10
formed in this example will be shown below.
[0130] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0131] Pinning Layer 13: Ir.sub.22Mn.sub.7 [7 nm]
[0132] Pin Layer 14: Co.sub.90Fe.sub.10 [4.4 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [4 nm]
[0133] Spacer Layer 16: Cu [3 nm]
[0134] Function Layer 21: Zn--Fe.sub.50Co.sub.50--O [3 nm]
[0135] Free Layer 18: Fe.sub.50Co.sub.50 [2 nm]
[0136] FIG. 10 is a view showing a cross-sectional TEM image of the
magneto-resistance effect device 10 according to this example. It
can be confirmed that the function layer 21 is formed evenly in an
interface between the spacer layer 16 and the free layer 18.
[0137] FIG. 11 is a graph showing a result of element proxygram
analysis in a film thickness direction of the magneto-resistance
effect device 10 according to this example using a
three-dimensional atom probe.
[0138] In a place corresponding to the function layer 21, peaks of
Zn, ZnO, FeO and CoO are entirely in agreement, so that it can be
known that an oxide layer of entirely mixed Zn and
Fe.sub.50Co.sub.50 is formed.
[0139] Incidentally, in any magneto-resistance effect device
according to the invention, it could be confirmed from the TEM
image and three-dimensional atom probe analysis that the function
layer was formed.
[0140] The RA of the magneto-resistance effect device 10 according
to this example was 0.16 .OMEGA.m.sup.2, and the MR ratio thereof
was 3.5%.
Example 2
[0141] A magneto-resistance effect device 10 according to
Modification 1 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 21
was provided inside the free layer 18 as shown in FIG. 4 was
produced.
[0142] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0143] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0144] Pin Layer 14: Co.sub.90Fe.sub.10 [4.4 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [4 nm]
[0145] Spacer Layer 16: Cu [3 nm]
[0146] Free Layer 18A: Fe.sub.50Co.sub.50 [1 nm]
[0147] Function Layer 21; Zn--Fe.sub.50Co.sub.50--O [3 nm]
[0148] Free Layer 18B: Fe.sub.50Co.sub.50 [1 nm]
[0149] The RA of the magneto-resistance effect device 10 according
to this example was 0.18 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 3%.
Example 3
[0150] A magneto-resistance effect device 10 according to
Modification 2 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 21
was provided between the cap layer 19 and the free layer 18 as
shown in FIG. 5 was produced.
[0151] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0152] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0153] Pin Layer 14: Co.sub.90Fe.sub.10 [4.4 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [4 nm]
[0154] Spacer Layer 16: Cu [3 nm]
[0155] Free Layer 18: Fe.sub.50Co.sub.50 [2 nm]
[0156] Function Layer 21: Zn--Fe.sub.50Co.sub.50--O [3 nm]
[0157] The RA of the magneto-resistance effect device 10 according
to this example was 0.18 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 2.5%.
Example 4
[0158] A magneto-resistance effect device 10 according to
Modification 3 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 21
was provided between the spacer layer 16 and the upper pin layer
143 as shown in FIG. 6 was produced.
[0159] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0160] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0161] Pin Layer 14: Co.sub.90Fe.sub.10 [4.4 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [2 nm]
[0162] Function Layer 21: Zn--Fe.sub.50Co.sub.50-O [3 nm]
[0163] Spacer Layer 16: Cu [3 nm]
[0164] Free Layer 18: Fe.sub.50Co.sub.50 [4 nm]
[0165] The RA of the magneto-resistance effect device 10 according
to this example was 0.2 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 2.5%.
Example 5
[0166] A magneto-resistance effect device 10 according to
Modification 4 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 21
was provided inside the upper pin layer 143 as shown in FIG. 7 was
produced.
[0167] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0168] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0169] Pin Layer 14: Co.sub.90Fe.sub.10 [4.4 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [1 nm]
[0170] Function Layer 21: Zn--Fe.sub.50Co.sub.50--O [3 nm]
[0171] Pin Layer 143B: Fe.sub.50Co.sub.50 [1 nm]
[0172] Spacer Layer 16: Cu [3 nm]
[0173] Free Layer 18: Fe.sub.50Co.sub.50 [4 nm]
[0174] The RA of the magneto-resistance effect device 10 according
to this example was 0.2 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 2.8%.
Example 6
[0175] A magneto-resistance effect device 10 according to
Modification 5 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 21
was provided between the upper pin layer 143 and the magnetic
coupling layer 142 as shown in FIG. 8 was produced.
[0176] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0177] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0178] Pin Layer 14: Co.sub.90Fe.sub.10 [4.4 nm]/Ru [0.9 nm]
[0179] Function Layer 21: Zn--Fe.sub.50Co.sub.50-O [3 nm]
[0180] Pin Layer 143B: Fe.sub.50Co.sub.50 [2 nm]
[0181] Spacer Layer 16: Cu [3 nm]
[0182] Free Layer 18: Fe.sub.50Co.sub.50 [4 nm]
[0183] The RA of the magneto-resistance effect device 10 according
to this example was 0.20 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 2.5%.
Example 7
[0184] A magneto-resistance effect device 10 according to
Modification 6 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 22
was provided between the free layer 18 and the spacer layer 16 and
the function layer 21 was provided between the spacer layer 16 and
the upper pin layer 143 as shown in FIG. 9 was produced.
[0185] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0186] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0187] Pin Layer 14: Co.sub.90Fe.sub.10 [4.4 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [2 nm]
[0188] Function Layer 21: Zn--Fe.sub.50Co.sub.50--O [3 nm]
[0189] Spacer Layer 16: Cu [3 nm]
[0190] Function Layer 22: Zn--Fe.sub.50Co.sub.50-O [3 nm]
[0191] Free Layer 18: Fe.sub.50Co.sub.50 [2 nm]
[0192] The RA of the magneto-resistance effect device 10 according
to this example was 0.2.OMEGA..mu.m.sup.2, and the MR ratio thereof
was 4.2%.
Comparative Example 1
[0193] A magneto-resistance effect device using no function layer
was produced and the RA value and MR ratio thereof were
evaluated.
[0194] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0195] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0196] Pin Layer 14: Co.sub.90Fe.sub.10 [4.4 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [4 nm]
[0197] Spacer Layer 16: Cu [3 nm]
[0198] Free Layer 18: Fe.sub.50Co.sub.50 [4 nm]
[0199] The RA of the magneto-resistance effect device 10 according
to this example was 0.08 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 1.5%.
[0200] Each of the MR ratios of the magneto-resistance effect
devices 10 according to Examples 1 to 7 exhibits a larger value
than the MR ratio in Comparative Example 1. It can be known that
the MR ratio can be improved when any one of the magneto-resistance
effect devices 10 according to the first embodiment and
Modifications 1 to 6 is used.
[0201] As for the reason why the MR ratio is improved, it is
considered that the function layer can make a high spin filter
effect and reduction of spin-flip due to achievement of low
resistivity consistent with each other. Because the spin filtering
layer of oxide is apt to be a high resistivity material, resistance
is apt to be high. Generally, when electrons pass through a high
resistance layer, spin-flip by which spin information is lost
occurs easily. When spin-flip occurs, the MR ratio decreases. When
spin-flip is reduced in the spin filtering layer of oxide, there is
further room for increasing the MR ratio.
Second Embodiment
[0202] FIG. 12A is a view showing the configuration of a
magnet-resistance effect device 10 according to a second embodiment
of the invention.
[0203] The magnet-resistance effect device 10 according to this
embodiment is different from the magnet-resistance effect device 10
according to the first embodiment in that a
Current-confined-to-the-path layer 23 sandwiched between an upper
electrode 17 and a lower electrode 15 is provided between the upper
pin layer 143 and the cap layer 19. That is, the spacer layer 16
according to the first embodiment is equivalent to the
Current-confined-to-the-path layer 23, and the
Current-confined-to-the-path layer 23 is sandwiched between the
upper electrode 17 and the lower electrode 15. Incidentally, the
Current-confined-to-the-path layer 23 is equivalent to the spacer
layer 16 as a constituent member of the magneto-resistance effect
device 10 according to the first embodiment but different from the
spacer layer 16 in that current paths 24 are formed in the
Current-confined-to-the-path layer 23.
[0204] FIG. 12B is a view showing the configuration of the
Current-confined-to-the-path layer 23.
[0205] The Current-confined-to-the-path layer 23 is made of an
insulating layer 25. Current paths 24 through which a current
passes are formed in the insulating layer 25.
[0206] Description about the same configuration as that described
in the first embodiment will be omitted here.
[0207] A lower metal layer 15 is used for forming the current paths
24 in the Current-confined-to-the-path layer 23. The lower metal
layer 15 has also a function of suppressing oxidation of the upper
pin layer 143 located under the lower metal layer 15 when the
insulating layer 23 forming the Current-confined-to-the-path layer
25 is formed. A metal such as Cu, Au or Ag can be used as the lower
metal layer 15.
[0208] The Current-confined-to-the-path layer 23 has a function of
magnetically decoupling the pin layer 14 and the free layer 18 from
each other, and also a function of making a current pass through
the current paths 24 between the pin layer 14 and the free layer
18.
[0209] The insulating layer 25 forming the
Current-confined-to-the-path layer 23 is made of oxide, nitride,
oxynitride, or the like. Specifically, Ti oxide, Hf oxide, Mn
oxide, Zr oxide, Cr oxide, Ta oxide, Nb oxide, Mo oxide, Si oxide,
V oxide, etc. or nitride or oxynitride having Al, Si, Hf, Ti, Mg,
Zr, V, Mo, Nb, Ta, W, B or C as a base can be used. As a typical
material, Al.sub.2O.sub.3 and a material obtained by adding an
additive element thereto can be used. Examples of the additive
element are Ti, Hf, Mg, Zr, V, Mo, Si, Cr, Nb, Ta, W, B, C, etc. As
for the amounts of these additive elements to be added, each
additive element in a range of 0% to 50% can be added to the
insulating layer 25.
[0210] The current paths 24 forming the
Current-confined-to-the-path layer 23 have a function of making a
current pass through perpendicularly to the film plane of the
magneto-resistance effect device 10 to thereby narrow the current.
Accordingly, the MR ratio of the magneto-resistance effect device
10 can be improved. As the current paths 24, Cu, Au, Ag, Ni, Co, Fe
or an alloy containing at least one of these elements can be used.
Specifically, AlCu, CuNi, CuCo, CuFe, or the like, can be used.
Here, to reduce an interlayer coupling field (Hin) between the pin
layer 14 and the free layer 18, it is preferable that the Cu
content is not smaller than 50% when an alloy containing Cu is
used.
[0211] When FeCo having an fcc structure or a bcc structure is used
as the insulating layer 25 in the case where the current paths 24
are made from a material containing Cu in this manner, the MR ratio
may be further improved. Specifically, Fe.sub.xCo.sub.100-x (x=30%
to 100%) or a material obtained by adding an additive element such
as Ti, Hf, Mg, Zr, V, Mo, Si, Cr, Nb, Ta, W, B or C thereto can be
used. Co.sub.50Fe.sub.50 [1 nm]/Ni.sub.85Fe.sub.15 [3.5 nm] can be
used.
[0212] Although it is preferable that the same material is used as
the material of the current paths 24 and the material of the lower
metal layer 15, the material of the current paths 24 may be
different from the material of the lower metal layer 15 when the
constituent material of the current paths 24 is a magnetic
material.
[0213] Incidentally, it is preferable from the viewpoint of
magnetic decoupling that the film thickness of the
Current-confined-to-the-path layer 23 is not smaller than 1 nm and
not larger than 3 nm, and it is more preferable that the film
thickness of the Current-confined-to-the-path layer 23 is not
smaller than 1.5 nm and not larger than 2.5 nm.
[0214] The upper metal layer 17 serves as a barrier layer for
restraining oxygen and nitrogen forming the
Current-confined-to-the-path layer 23 from being diffused into the
free layer 18, and also as a seed layer for improving the
crystallinity of the free layer 18. Specifically, the upper metal
layer 17 is provided so that the free layer 18 formed on the upper
metal layer 17 suppresses oxidation or nitriding of the insulating
layer 25 forming the Current-confined-to-the-path layer 23.
[0215] It is preferable that the material of the upper metal layer
17 is the same as the material of the current paths 24 forming the
Current-confined-to-the-path layer 23. This is because increase in
interfacial resistance is suppressed when the material of the upper
metal layer 17 is the same as the material of the current paths 24
though increase in interfacial resistance is caused when the two
materials are different from each other. Incidentally, when the
constituent material of the current paths 24 is a magnetic
material, the material may be the same as the magnetic material of
the free layer or may be different from the magnetic material of
the free layer. As the constituent material of the upper metal
layer 17, Cu, Au, Ag or the like can be used. When the insulating
layer 25 forming the Current-confined-to-the-path layer 23 is made
of amorphous Al.sub.2O.sub.3, the crystallinity of the upper metal
layer 17 formed on the Current-confined-to-the-path layer 23
becomes poor but the crystallinity of the free layer 18 can be made
good when a very thin seed layer of Cu or the like with a thickness
of about 0.25 nm is provided between the
Current-confined-to-the-path layer 23 and the upper metal layer
17.
[0216] A method of manufacturing the magneto-resistance effect
device 10 according to this embodiment will be described below with
reference to a flow chart shown in FIG. 13.
[0217] Step S114 shown in FIG. 13 is different from the method of
manufacturing the magneto-resistance effect device 10 described in
the first embodiment with reference to FIG. 3. Since the other
steps S11 to S13 and S15 to S18 are the same as those in the method
of manufacturing the magneto-resistance effect device 10 according
to the first embodiment, description thereof will be omitted.
[0218] In step S114, an insulating layer 25 having current paths 24
is formed on the upper pin layer 143. Description will be made here
in the case where the Current-confined-to-the-path layer 23
including the current paths 24 made of Cu is formed in the
insulating layer 25 made of Al.sub.2O.sub.3 having an amorphous
structure, by way of example.
[0219] First, after a lower metal layer 15 of Cu is formed, a metal
layer of AlCu is formed on the lower metal layer 15.
[0220] Then, the metal layer is irradiated with an ion beam of rare
gas such as Ar, Xe, Kr or He to perform preprocessing. This
processing is called PIT (Pre-ion Treatment). As a result of the
PIT, a part of the lower metal layer 15 is sucked up and forcibly
enters the metal layer.
[0221] Then, while the metal layer is irradiated with an ion beam
of rare gas such as Ar, Xe, Kr or He, oxidizing gas such as O.sub.2
is supplied to oxidize the metal layer. By this oxidation, the
metal layer is converted into the insulating layer 25 of
Al.sub.2O.sub.3, and the current paths 24 piercing the insulating
layer 25 are formed so that the Current-confined-to-the-path layer
23 can be formed. This method is called IAO (Ion Assisted
Oxidation). This is a process using an oxidation energy difference
that Al is easily oxidizable but Cu is hardly oxidizable.
(Modification 7)
[0222] FIG. 14 is a view showing a seventh modification of the
magneto-resistance effect device 10 according to the second
embodiment.
[0223] This modification is different from the second embodiment in
that the function layer 21 is provided inside the free layer 18.
That is, the free layer 18 includes a first free layer 18a and a
second free layer 18b. Incidentally, the first free layer 18a is
provided between the upper metal layer 17 and the function layer
21, and the second free layer 18b is provided between the cap layer
19 and the function layer 21.
[0224] When the function layer 21 is provided inside the free layer
18 in this manner, the function layer 21 contributes to
spin-dependent bulk scattering as described above. Because oxygen
contained in the function layer 21 is restrained from being
diffused into the metal paths of the Current-confined-to-the-path
layer 23 when the function layer 21 is disposed in a position being
not in contact with the spacer layer, increase in resistivity of
the metal paths as caused by the presence of any oxygen element in
the Current-confined-to-the-path layer 23 can be avoided so that a
high MR ratio can be obtained. Incidentally, because the
magnetization direction of the function layer 21 is free in the
same manner as in Modification 1, the function layer 21 contributes
to improvement in the MR ratio of the magneto-resistance effect
device 10 without inhibition of the function of the free layer
18.
(Modification 8)
[0225] FIG. 15 is a view showing an eighth modification of the
magneto-resistance effect device 10 according to the second
embodiment.
[0226] This modification is different from the second embodiment in
that the function layer 21 is provided between the free layer 18
and the cap layer 19.
[0227] When the function layer 21 is provided between the free
layer 18 and the cap layer 19 in this manner, the function layer 21
contributes to spin-dependent bulk scattering as described above.
Because oxygen contained in the function layer 21 is restrained
from being diffused into the metal paths of the
Current-confined-to-the-path layer 23 when the function layer 21 is
disposed in a position being not in contact with the metal layer
15, the Current-confined-to-the-path layer 23 and the metal layer
17, increase in resistivity of the metal paths as caused by the
presence of any oxygen element in the Current-confined-to-the-path
layer 23 can be avoided so that a high MR ratio can be obtained.
Moreover, the function layer 21 can prevent the magneto-resistance
effect device 10 from deterioration such as oxidation.
(Modification 9)
[0228] FIG. 16 is a view showing a ninth modification of the
magneto-resistance effect device 10 according to the second
embodiment.
[0229] This modification is different from the second embodiment in
that the function layer 21 is provided between the upper pin layer
143 and the lower metal layer 15.
[0230] When the function layer 21 is provided between the upper pin
layer 143 and the lower metal layer 15 in this manner, the function
layer 21 contributes to spin-dependent interfacial scattering as
described above. Moreover, because the function layer 21 can
prevent the constituent material of the metal layer 15 and the
constituent material of the upper pin layer 143 from being mixed
with each other, the constituent material of the upper pin layer
143 is hardly mixed in the metal paths forming the
Current-confined-to-the-path layer 23. As a result, conduction
electrons can pass through the Current-confined-to-the-path layer
23 while spin-flip is suppressed, so that the magnetization of the
upper pin layer 143 can be fixed stably.
(Modification 10)
[0231] FIG. 17 is a view showing a tenth modification of the
magneto-resistance effect device 10 according to the second
embodiment.
[0232] This modification is different from the second embodiment in
that the function layer 21 is provided inside the upper pin layer
143.
[0233] When the function layer 21 is provided inside the upper pin
layer 143 in this manner, the function layer 21 contributes to
spin-dependent bulk scattering as described above. Because oxygen
contained in the function layer 21 is restrained from being
diffused into the metal paths of the Current-confined-to-the-path
layer 23 when the function layer 21 is disposed in a position being
not in contact with the metal layer 15, the
Current-confined-to-the-path layer 23 and the metal layer 17,
increase in resistivity of the metal paths as caused by the
presence of any oxygen element in the Current-confined-to-the-path
layer 23 can be avoided so that a high MR ratio can be
obtained.
(Modification 11)
[0234] FIG. 18 is a view showing an eleventh modification of the
magneto-resistance effect device 10 according to the second
embodiment.
[0235] This modification is different from the second embodiment in
that the function layer 21 is provided between the upper pin layer
143 and the magnetic coupling layer 142.
[0236] When the function layer 21 is provided between the upper pin
layer 143 and the magnetic coupling layer 142 in this manner, the
function layer 21 contributes to spin-dependent bulk scattering as
described above. Because oxygen contained in the function layer 21
is restrained from being diffused into the metal paths of the
Current-confined-to-the-path layer 23 when the function layer 21 is
disposed in a position being not in contact with the metal layer
15, the Current-confined-to-the-path layer 23 and the metal layer
17, increase in resistivity of the metal paths as caused by the
presence of any oxygen element in the Current-confined-to-the-path
layer 23 can be avoided so that a high MR ratio can be
obtained.
(Modification 12)
[0237] FIG. 19 is a view showing a twelfth modification of the
magneto-resistance effect device 10 according to the second
embodiment.
[0238] This modification is different from the second embodiment in
that a second function layer 22 is further provided between the
upper metal layer 17 and the free layer 18 in addition to the
function layer 21 provided between the upper pin layer 143 and the
lower metal layer 15.
[0239] When the second function layer 22 is further provided
between the upper metal layer 17 and the free layer 18 in addition
to the function layer 21 provided between the upper pin layer 143
and the lower metal layer 15 in this manner, an effect as the sum
of spin filtering effects of the two function layers can be
obtained so that a high MR ratio can be obtained in comparison with
the case where one function layer is used.
[0240] Incidentally, because the magnet-resistance effect devices
10 according to the aforementioned modifications 7 to 12 can be
produced by use of the methods of manufacturing the
magnet-resistance effect devices 10 described in the first and
second embodiments, description about the method of manufacturing
the magneto-resistance effect devices 10 according to the
modifications 7 to 12 will be omitted.
Examples
[0241] Magneto-resistance effect devices 10 according to the second
embodiment and the modifications 7 to 12 were produced and
perpendicular current conduction was performed between the
electrodes 11 and 20 so that the RA values and MR ratios of the
magneto-resistance effect devices 10 were evaluated.
Example 8
[0242] A magneto-resistance effect device 10 according to the
second embodiment was produced and the RA value and MR ratio
thereof were evaluated. That is, a structure in which the function
layer 21 was provided between the free layer 18 and the metal layer
17 as shown in FIG. 12A was produced.
[0243] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0244] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0245] Pin Layer 14: Co.sub.75Fe.sub.25 [3.9 nm]/Ru [0.9
nm])/Fe.sub.50Co.sub.50 [1.8 nm]/Cu [0.25 nm]/Fe.sub.50Co.sub.50
[1.8 nm]
[0246] Metal Layer 15: Cu (0.6 nm)
[0247] Current-confined-to-the-path layer 23: Insulating Layer 161
of Al.sub.2O.sub.3 and Current Paths 162 of Cu
[0248] Metal Layer 17: Cu [0.4 nm]
[0249] Function Layer 21: Zn--Fe.sub.50Co.sub.50--O [2 nm]
[0250] Free Layer 18: Ni.sub.83Fe.sub.17 [3.5 nm]
[0251] The RA of the magneto-resistance effect device 10 according
to this example was 0.3 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 15%.
Example 9
[0252] A magneto-resistance effect device 10 according to
Modification 7 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 21
was provided inside the free layer 18 as shown in FIG. 14 was
produced.
[0253] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0254] Pinning Layer 13: Ir.sub.22Mn.sub.7 [7 nm]
[0255] Pin Layer 14: Co.sub.75Fe.sub.25 [3.9 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [1.8 nm]/Cu [0.25 nm]/Fe.sub.50Co.sub.50
[1.8 nm]
[0256] Metal Layer 15: Cu [0.6 nm]
[0257] Current-confined-to-the-path layer 23: Insulating Layer 161
of Al.sub.2O.sub.3 and Current Paths 162 of Cu
[0258] Metal Layer 17: Cu [0.4 nm]
[0259] Free Layer 18A: Fe.sub.50C.sub.50 [1 nm]
[0260] Function Layer 21: Zn--Fe.sub.50Co.sub.50-O [1 nm]
[0261] Free Layer 18: Ni.sub.83Fe.sub.17 [3.5 nm]
[0262] The RA of the magneto-resistance effect device 10 according
to this example was 0.33 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 14.5%.
Example 10
[0263] A magneto-resistance effect device 10 according to
Modification 8 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 21
was provided between the cap layer 19 and the free layer 18 as
shown in FIG. 15 was produced.
[0264] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0265] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0266] Pin Layer 14: Co.sub.75Fe.sub.25 [3.9 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [1.8 nm]/Cu [0.25 nm]/Fe.sub.50Co.sub.50
[1.8 nm]
[0267] Metal Layer 15: Cu [0.6 nm]
[0268] Current-confined-to-the-path layer 23: Insulating Layer 161
of Al.sub.2O.sub.3 and Current Paths 162 of Cu
[0269] Metal Layer 17: Cu [0.4 nm]
[0270] Free Layer 18: Fe.sub.50Co.sub.50 [1 nm]/Ni.sub.83Fe.sub.17
[3.5 nm]
[0271] Function Layer 21: Zn--Fe.sub.0.5Co.sub.50--O [1 nm]
[0272] The RA of the magneto-resistance effect device 10 according
to this example was 0.30 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 14%.
Example 11
[0273] A magneto-resistance effect device 10 according to
Modification 9 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 21
was provided between the metal layer 15 and the upper pin layer 143
as shown in FIG. 16 was produced.
[0274] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0275] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0276] Pin Layer 14: Co.sub.75Fe.sub.25 [3.9 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [1.8 nm]/Cu [0.25 nm]
[0277] Function Layer 21: Zn--Fe.sub.50Co.sub.50--O [2 nm]
[0278] Metal Layer 15: Cu [0.6 nm]
[0279] Current-confined-to-the-path layer 23: Insulating Layer 161
of Al.sub.2O.sub.3 and Current Paths 162 of Cu
[0280] Metal Layer 17: Cu [0.4 nm]
[0281] Free Layer 18: Fe.sub.50Co.sub.50 [2 nm]/Ni.sub.83Fe.sub.17
[3.5 nm]
[0282] The RA of the magneto-resistance effect device 10 according
to this example was 0.350 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 14.5%.
Example 12
[0283] A magneto-resistance effect device 10 according to
Modification 10 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 21
was provided inside the upper pin layer 143 as shown in FIG. 17 was
produced.
[0284] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0285] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0286] Pin Layer 14: Co.sub.75Fe.sub.25 [3.9 nm]/Ru [0.9
nm]/Fe50Co50 [1.8 nm]/Cu [0.25 nm]
[0287] Function Layer 21; Zn--Fe.sub.50Co.sub.50--O [1 nm]
[0288] Pin Layer 143B: Fe.sub.50Co.sub.50 [1 nm]
[0289] Metal Layer 15: Cu [0.6 nm]
[0290] Current-confined-to-the-path layer 23: Insulating Layer 161
of Al.sub.2O.sub.3 and Current Paths 162 of Cu
[0291] Metal Layer 17: Cu [0.4 nm]
[0292] Free Layer 18: Fe.sub.50Co.sub.50 [2 nm]/Ni.sub.83Fe.sub.17
[3.5 nm]
[0293] The RA of the magneto-resistance effect device 10 according
to this example was 0.3 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 14.5%.
Example 13
[0294] A magneto-resistance effect device 10 according to
Modification 11 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 21
was provided between the upper pin layer 143 and the magnetic
coupling layer 142 as shown in FIG. 18 was produced.
[0295] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0296] Pinning Layer 13: Ir.sub.22Mn.sub.7 [7 nm]
[0297] Pin Layer 14: Co.sub.75Fe.sub.25 [3.9 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [1 nm]
[0298] Function Layer 21: Zn--Fe.sub.50Co.sub.50--O [1 nm]
[0299] Pin Layer 1438: Cu [0.25 nm]/Fe.sub.50Co.sub.50 [1.8 nm]
[0300] Metal Layer 15: Cu [0.6 nm]
[0301] Current-confined-to-the-path layer 23: Insulating Layer 161
of Al.sub.2O.sub.3 and Current Paths 162 of Cu
[0302] Metal Layer 17: Cu [0.4 nm]
[0303] Free Layer 18: Fe.sub.50Co.sub.50 [2 nm]/Ni.sub.83Fe.sub.17
[3.5 nm]
[0304] The RA of the magneto-resistance effect device 10 according
to this example was 0.31 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 13.8%.
Example 14
[0305] A magneto-resistance effect device 10 according to
Modification 12 was produced and the RA value and MR ratio thereof
were evaluated. That is, a structure in which the function layer 21
was provided between the free layer 18 and the metal layer 17, and
the function layer 22 is provided between the metal layer 15 and
the upper pin layer 143 as shown in FIG. 19 was produced.
[0306] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0307] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0308] Pin Layer 14: Co.sub.75Fe.sub.25 [3.9 nm]/Ru [(0.9
nm]/Fe.sub.50Co.sub.50 [1.8 nm]/Cu [0.25 nm]
[0309] Function Layer 21: Zn--Fe.sub.50Co.sub.50-O [2 nm]
[0310] Metal Layer 15: Cu [0.6 nm]
[0311] Current-confined-to-the-path layer 23: Insulating Layer 161
of Al.sub.2O.sub.3 and Current Paths 162 of Cu
[0312] Metal Layer 17: Cu [0.4 nm]
[0313] Function Layer 21: Zn--Fe.sub.50Co.sub.50--O [2 nm]
[0314] Free Layer 18: Ni.sub.83Fe.sub.17 [3.5 nm]
[0315] The RA of the magneto-resistance effect device 10 according
to this example was 0.45 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 16%.
Comparative Example 2
[0316] A magneto-resistance effect device using no function layer
was produced and the RA value and MR ratio thereof were evaluated.
This magneto-resistance effect device is different from the
magneto-resistance effect device according to Comparative Example 1
in that the spacer layer has an insulating layer sandwiched between
two metal layers and current paths piercing the insulating
layer.
[0317] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0318] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0319] Pin Layer 14: Co.sub.50Fe.sub.25 [3.9 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [1.8 nm]/Cu [0.25 nm]/Fe.sub.50Co.sub.50
[1.8 nm]
[0320] Function Layer 21: Zn--Fe.sub.50Co.sub.50-O [2 nm]
[0321] Metal Layer 15: Cu [0.6 nm]
[0322] Current-confined-to-the-path layer 23: Insulating Layer 161
of Al.sub.2O.sub.3 and Current Paths 162 of Cu
[0323] Metal Layer 17: Cu [0.4 nm]
[0324] Free Layer 18: Fe.sub.50Co.sub.50 [2 nm]/Ni.sub.83Fe.sub.17
[3.5 nm]
[0325] The RA of the magneto-resistance effect device 10 according
to this example was 0.28 .OMEGA..mu.m.sup.2, and the MR ratio
thereof was 12.5%.
[0326] It was confirmed that each of the MR ratios of the
magneto-resistance effect devices 10 according to Examples 8 to 14
exhibits a larger value than the MR ratio in Comparative Example 2.
The MR ratio can be improved when any one of the magneto-resistance
effect devices 10 according to the second embodiment and
Modifications 7 to 12 is used.
Examples 15 to 17 and Comparative Examples 2 and 3
[0327] As for the magneto-resistance effect device 10 shown in FIG.
1 as described in the first embodiment, oxygen exposure was changed
so that the RA value of the magneto-resistance effect device and
resistivity of the function layer forming the magneto-resistance
effect device were changed. Further, the influence of the RA value
of the magneto-resistance effect device and the resistivity of the
function layer on the MR ratio was examined.
[0328] The magneto-resistance effect device 10 according to this
example includes: a multilayer structure having a cap layer 19
which prevents the magneto-resistance effect device 10 from
deterioration such as oxidation, a pin layer 14 in which
magnetization is fixed, a free layer 18 which is provided between
the cap layer 19 and the pin layer 14 so that magnetization rotates
freely, a spacer layer 16 made of a nonmagnetic substance provided
between the pin layer 14 and the free layer 18, and a function
layer 21 provided between the spacer layer 16 and the free layer 18
and containing mixed oxide of any one element of Zn, In, Sn and Cd
and any one element of Fe, Co and Ni; a pair of electrodes 11 and
20 for applying a current perpendicularly to a film plane of the
multilayer structure; a pinning layer 13 provided between the
electrode 11 and the pin layer 14 and made of an antiferromagnetic
substance for fixing the magnetization direction of the pin layer;
and an undercoating layer 12 provided between the pinning layer 13
and the electrode 11.
[0329] The structure of the magneto-resistance effect device 10
produced according to this example will be described as
follows.
[0330] Undercoating Layer 12: Ta [1 nm]/Ru [2 nm]
[0331] Pinning Layer 13: Ir.sub.22Mn.sub.78 [7 nm]
[0332] Pin Layer 14: Co.sub.90Fe.sub.10 [4.4 nm]/Ru [0.9
nm]/Fe.sub.50Co.sub.50 [4 nm]
[0333] Spacer Layer 16: Cu [3 nm]
[0334] Function Layer 21: Zn--Fe.sub.50Co.sub.50--O [2 nm]
[0335] Free Layer 18: Fe.sub.50Co.sub.50 [3 nm]
[0336] As for the method of producing the function layer, 1
nm-thick Fe.sub.50Co.sub.50 was formed on a spacer layer of Cu, and
0.6 nm-thick Zn was formed thereon. Then, this Fe.sub.50Co.sub.50
and Zn were converted into oxide of Zn and Fe.sub.50Co.sub.50
(hereinafter referred to as Zn--Fe.sub.50Co.sub.50--O) by IAO to
thereby form a function layer. Oxygen exposure used in IAO was
changed. On this occasion, the oxygen exposure was set to be
1.2.times.10.sup.4 Langmiur in Example 15, 1.5.times.10.sup.4
Langmiur in Example 16, and 1.8.times.10.sup.4 Langmiur in Example
17. The oxygen exposure was set to be 3.0.times.10.sup.4 Langmiur
in Comparative Example 3. Incidentally, in Examples 1 to 14, the
film thickness of the function layer was so large that the oxygen
exposure was set to be a little higher than Examples 15 to 17.
[0337] FIG. 20 is a view showing results of the MR ratio of the
function layer when oxygen exposure used in IAO was changed to
thereby change the RA value of the magneto-resistance effect device
and the resistivity of the function layer made of
Zn--Fe.sub.50Co.sub.50--O. Incidentally, a result (corresponding to
Comparative Example 2) of measurement of a magneto-resistance
effect device having no function layer is also shown for
reference.
[0338] The resistivity .rho..sub.Zn--FeCo--O of the function layer
was calculated according to the following expression 1 when the
resistivity of the function layer is .rho..sub.Zn--Fe50Co50-O, the
film thickness of the function layer is t.sub.Zn--FeCo--O, and the
increasing amount of areal resistance of the magneto-resistance
effect device due to the provision of the function layer is
.DELTA.RA.sub.Zn--FeCo--O.
[ Numeral 1 ] .rho. Zn - Fe 50 Co 50 - O = .DELTA. R A Zn - Fe 50
Co 50 - O t Zn - Fe 50 Co 50 - O ( Expression 1 ) ##EQU00001##
[0339] When the film thickness of the function layer was obtained
from a cross-sectional TEM observation image, the film thickness of
the function layer according to any one of Examples 15, 16 and 17
and Comparative Example 3 was 2 nm. Incidentally, the value of
.DELTA.RA uses a difference between the RA value of the
magneto-resistance effect device not provided with any function
layer (Comparative Example 2 in FIG. 20) and the RA value of the
magneto-resistance effect device provided with the function
layer.
[0340] It can be known from FIG. 20 that the MR ratio is improved
when the resistivity of the function layer is not higher than
5.times.10.sup.4 .mu..OMEGA.cm. It can be also known that the MR
ratio is improved when the RA value of the magneto-resistance
effect device is not higher than 1 .mu..OMEGA.cm.
[0341] It can be considered that the aforementioned results are
obtained because spin-flip inside the function layer 21 can be
suppressed when the function layer 21 of low resistivity is
produced by use of an appropriate oxygen exposure.
Third Embodiment
[0342] A magnetic head using a magneto-resistance effect device 10
according to this embodiment will be described below.
[0343] FIGS. 21 and 22 are views showing a state where a
magneto-resistance effect device 10 according to this embodiment is
incorporated in a magnetic head. FIG. 21 is a sectional view of the
magneto-resistance effect device 10 taken in a direction
substantially parallel to a medium facing surface which faces a
magnetic recording medium (not shown). FIG. 22 is a sectional view
of the magneto-resistance effect device 10 taken in a direction
perpendicular to the medium facing surface ABS.
[0344] The magnetic head illustrated in FIGS. 21 and 22 has a
so-called hard abutted structure. Electrodes 11 and 20 are provided
on upper and lower sides of the magneto-resistance effect device
10, respectively. In FIG. 21, a laminate of a bias magnetic field
application film 41 and an insulating film 42 is provided on each
of opposite sides of the magneto-resistance effect device 10. As
shown in FIG. 22, a protective layer 43 is provided on the medium
facing surface of the magneto-resistance effect device 10.
[0345] A sense current for the magneto-resistance effect device 10
is poured in a direction substantially perpendicular to the film
plane by the electrodes 11 and 20 on the upper and lower sides, as
represented by the arrow A. A bias magnetic field is applied to the
magneto-resistance effect device 10 by the pair of bias magnetic
field application films 41 provided on the left and right. When
magnetic anisotropy of the free layer 18 of the magneto-resistance
effect device 10 is controlled by this bias magnetic field to form
a single domain, the domain structure thereof can be stabilized so
that Burkhausen noise caused by movement of a domain wall can be
suppressed.
[0346] Because the S/N ratio of the magneto-resistance effect film
10 is improved, high-sensitive magnetic reproduction can be made
when the magneto-resistance effect device 10 is applied to the
magnetic head.
Fourth Embodiment
[0347] A magnetic recorder and a magnetic head assembly using a
magneto-resistance effect device 10 according to this embodiment
will be described below.
[0348] FIG. 23 is a perspective view showing the magnetic recorder
according to this embodiment.
[0349] As shown in FIG. 23, the magnetic recorder 310 according to
this embodiment is an apparatus of the type using a rotary
actuator. A magnetic recording medium 230 is provided on a spindle
motor 330 so that the magnetic recording medium 230 is rotated in a
direction of a medium moving direction 270 by a motor (not shown)
responding to a control signal given from a drive control portion
(not shown). The magnetic recorder 310 may be provided with a
plurality of magnetic recording media 230.
[0350] As for each head slider 280 which performs recording and
reproducing of information stored in the magnetic recording medium
230, a magnetic head 140 having a magneto-resistance effect device
10 is provided in the head slider 280, as shown in FIG. 24. The
head slider 280 is made of Al.sub.2O.sub.3/TiC or the like,
designed so that the head slider 280 can move relatively while
floating up from the magnetic recording medium 230 such as a
magnetic disk or being in contact with the magnetic recording
medium 230, and having an air inflow side 290 and an air outflow
side 300.
[0351] The head slider 280 is attached to a front end of a
thin-film suspension 350. The head slider 280 is formed so that the
magnetic head 140 is provided near a front end of the head slider
280.
[0352] When the magnetic recording medium 230 rotates, a pressure
caused by each suspension 350 is balanced with a pressure generated
in the medium facing surface (ABS) of each head slider 280. The
medium facing surface of the head slider 280 is retained with a
predetermined floating amount from a surface of the magnetic
recording medium 230. There may be provided a "contact traveling
type" in which the head slider 280 is in contact with the magnetic
recording medium 230.
[0353] The suspension 350 is connected to one end of an actuator
arm 360 having a bobbin portion, etc. for holding 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 driving coil (not shown) wound up on
the bobbin portion of the actuator arm 360, and a magnetic circuit
having a permanent magnet and a counter yoke provided oppositely so
that the driving coil is put therebetween.
[0354] The actuator arm 360 is retained by a ball bearing (not
shown) provided in two places on upper and lower sides of a bearing
portion 380 so that the actuator arm 360 can be slid and rotated
freely by the voice coil motor 370. As a result, the magnetic head
140 can be moved to any position of the magnetic recording medium
230.
[0355] FIG. 25A shows a head stack assembly 390 which forms a part
of the magnetic recorder 310 according to this embodiment.
[0356] FIG. 25B is a perspective view showing magnetic head
assemblies (head gimbal assemblies (HGA)) 400 which are a part of
the head stack assembly 390.
[0357] As shown in FIG. 25A, the head stack assembly 390 has a
bearing portion 380, the head gimbal assemblies 400 extending from
the bearing portion 380, and a support frame 420 extending from the
bearing portion 380 in a direction opposite to the head gimbal
assemblies 400 and supporting a coil 410 of a voice coil motor.
[0358] As shown in FIG. 25B, each head gimbal assembly 400 has an
actuator arm 360 extending from the bearing portion 380, and a
suspension 350 extending from the actuator arm 360.
[0359] A head slider 280 having a magnetic recording head 140 as
described in the second embodiment is provided at a front end of
each suspension 350.
[0360] The magnetic head assembly (head gimbal assembly (HGA)) 400
according to this embodiment has a magnetic recording head 140
described in the second embodiment, a head slider 280 provided with
the magnetic recording head 140, a suspension 350 having one end
where the head slider 280 is mounted, and an actuator arm 360
connected to the other end of the suspension 350.
[0361] The suspension 350 has lead wires (not shown) for signal
writing and reading, for heater for floating amount adjustment and
for STO10. The lead wires are electrically connected to respective
electrodes of the magnetic recording head 140 incorporated in the
head slider 280. Electrode pads (not shown) are provided in the
head gimbal assembly 400. In this embodiment, eight electrode pads
are provided. Two electrode pads are provided for coil of main
magnetic poles 200, two electrode pads are provided for a magnetic
reproducing device 190, two electrode pads are provided for DFH
(dynamic flying height), and two electrode pads are provided for
STO10.
[0362] A signal processing portion 385 (not shown) is provided on
the back (in the drawing) of the magnetic recorder 310 shown in
FIG. 23. The signal processing portion 385 performs signal
writing/reading into/from the magnetic recording medium 230 by
using the magnetic recording heads 140. Input/output lines of the
signal processing portion 385 are connected to the electrode pads
of the head gimbal assemblies 400 and electrically connected to the
magnetic recording heads 140.
[0363] The magnetic recorder 310 according to this embodiment has a
magnetic recording medium 230, magnetic recording heads 140, a
movable portion which can move relatively while making the magnetic
recording medium 230 and each of the magnetic recording heads 140
be separated from each other or be in contact with each other in a
state where the magnetic recording medium 230 and the magnetic
recording head 140 confront each other, a position control portion
which aligns the magnetic recording heads 140 with a predetermined
recording position of the magnetic recording medium 230, and a
signal processing portion 385 which performs writing/reading
into/from the magnetic recording medium 230 by using the magnetic
recording heads 140.
[0364] A magnetic recording medium 230 is used as the
aforementioned magnetic recording medium 230. The aforementioned
movable portion can include the head sliders 280. The
aforementioned position control portion can include the head gimbal
assemblies 400.
[0365] The magnetic recorder 310 has a magnetic recording medium
230, head gimbal assemblies 400, and a signal processing portion
385 which performs signal writing/reading into/from the magnetic
recording medium 230 by using the magnetic recording heads 140
mounted in the head gimbal assemblies 400.
[0366] The magneto-resistance effect device according to the
invention can be used also in all magneto-resistance effect
devices, magnetic heads, magnetic recorders and magnetic memories
which can be implemented with a design changed suitably by those
skilled in the art based on the aforementioned magnetic heads and
magnetic recorders according to the embodiments of the
invention.
[0367] Although the bottom type magneto-resistance effect device 10
has been described in the embodiments of the invention, the effect
of the invention can be obtained even in a top type
magneto-resistance effect device 10 in which the pin layer 14 is
formed above the spacer layer 16.
[0368] 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
methods and systems described herein may be embodied in a variety
of other forms; furthermore, various omissions, substitutions and
changes in the form of the methods and systems 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.
* * * * *