U.S. patent number RE46,180 [Application Number 14/638,583] was granted by the patent office on 2016-10-18 for three axis magnetic field sensor.
This patent grant is currently assigned to EVERSPIN TECHNOLOGIES, INC.. The grantee listed for this patent is EVERSPIN TECHNOLOGIES, INC.. Invention is credited to Phillip Mather, Nicholas Rizzo, Jon Slaughter.
United States Patent |
RE46,180 |
Mather , et al. |
October 18, 2016 |
**Please see images for:
( Certificate of Correction ) ** |
Three axis magnetic field sensor
Abstract
Three bridge circuits (101, 111, 121), each include
magnetoresistive sensors coupled as a Wheatstone bridge (100) to
sense a magnetic field (160) in three orthogonal directions (110,
120, 130) that are set with a single pinning material deposition
and bulk wafer setting procedure. One of the three bridge circuits
(121) includes a first magnetoresistive sensor (141) comprising a
first sensing element (122) disposed on a pinned layer (126), the
first sensing element (122) having first and second edges and first
and second sides, and a first flux guide (132) disposed
non-parallel to the first side of the substrate and having an end
that is proximate to the first edge and on the first side of the
first sensing element (122). An optional second flux guide (136)
may be disposed non-parallel to the first side of the substrate and
having an end that is proximate to the second edge and the second
side of the first sensing element (122).
Inventors: |
Mather; Phillip (Phoenix,
AZ), Slaughter; Jon (Tempe, AZ), Rizzo; Nicholas
(Gilbert, AZ) |
Applicant: |
Name |
City |
State |
Country |
Type |
EVERSPIN TECHNOLOGIES, INC. |
Chandler |
AZ |
US |
|
|
Assignee: |
EVERSPIN TECHNOLOGIES, INC.
(Chandler, AZ)
|
Family
ID: |
43779581 |
Appl.
No.: |
14/638,583 |
Filed: |
March 4, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
12567496 |
Sep 25, 2009 |
8390283 |
Mar 5, 2013 |
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B82Y
25/00 (20130101); H01L 27/22 (20130101); G01R
33/093 (20130101); H01L 27/22 (20130101); B82Y
25/00 (20130101); H01L 43/08 (20130101); G01R
33/093 (20130101); H01L 43/08 (20130101) |
Current International
Class: |
G01R
33/02 (20060101); H01L 27/22 (20060101); G01R
33/00 (20060101); H01L 43/08 (20060101); G01R
33/09 (20060101); B82Y 25/00 (20110101) |
Field of
Search: |
;324/252,244,260 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
101221849 |
|
Jul 2008 |
|
CN |
|
0427171 |
|
May 1991 |
|
EP |
|
2006700 |
|
Dec 2008 |
|
EP |
|
2005-216390 |
|
Aug 2005 |
|
JP |
|
2008-525789 |
|
Jul 2008 |
|
JP |
|
2009-216390 |
|
Sep 2009 |
|
JP |
|
584735 |
|
Apr 2004 |
|
TW |
|
200604520 |
|
Feb 2006 |
|
TW |
|
WO 2008/148600 |
|
Dec 2008 |
|
WO |
|
WO 2009/048018 |
|
Apr 2009 |
|
WO |
|
Other References
International Search Report and Written Opinion issued in
corresponding International Application No. PCT/US2010/050398,
mailed Nov. 22, 2010 (8 pages). cited by applicant .
International Search Report on Patentability issued in
corresponding International Application No. PCT/US2010/050398,
mailed Apr. 5, 2012 (7 pages). cited by applicant.
|
Primary Examiner: Deb; Anjan K.
Attorney, Agent or Firm: Bookoff McAndrews, PLLC
Claims
The invention claimed is:
1. A ferromagnetic thin-film based magnetic field sensor
comprising: a substrate having a planar surface; .[.and.]. a first
magnetoresistive sensor comprising: a first sensing element having
.[.a.]. first .[.side.]. .Iadd.and second sides .Iaddend.lying
parallel to the planar surface of the substrate, .[.the first
sensing element having a second side opposed to the first side and
having.]. .Iadd.wherein the first side is defined by at least
.Iaddend.first and second opposed edges; and a first flux guide
comprising a soft ferromagnetic material.Iadd., a first flux guide
side, and a second flux guide side, wherein the second flux guide
side is orthogonal to the first flux guide side, the second flux
guide side is .Iaddend.disposed non-parallel to the first side of
the first sensing element.Iadd., .Iaddend.and .[.having.].
.Iadd.the second flux guide side includes .Iaddend.an end that is
proximate to the first edge and the first side of the first sensing
element.Iadd., wherein the first side of the first sensing element
extends in a first plane, the planar surface of the substrate
extends in a second plane parallel to the first plane, and the
first flux guide side extends in a third plane parallel to and
spaced apart from each of the first and second planes; and a second
magnetoresistive sensor comprising: a second sensing element having
first and second sides lying parallel to the planar surface of the
substrate, wherein the first side of the second sensing element
extends in the first plane, wherein the first magnetoresistive
sensor detects a magnetic field in a first direction orthogonal to
the planar surface, and the second magnetoresistive sensor detects
a magnetic field in a second direction parallel to the planar
surface.Iaddend..
.[.2. The ferromagnetic thin-film based magnetic field sensor of
claim 1 wherein the first magnetoresistive sensor further
comprises: a second flux guide comprising a soft ferromagnetic
material disposed non-parallel to the first side of the first
sensing element and having an end that is proximate to the second
edge and the second side of the first sensing element..].
.[.3. The ferromagnetic thin-film based magnetic field sensor of
claim 1 wherein the first magnetoresistive sensor comprises one of
an array of ferromagnetic thin-film based magnetic field
sensors..].
.[.4. The ferromagnetic thin-film based magnetic field sensor of
claim 1 wherein the first flux guide comprises a high aspect ratio
structure non-parallel to the first sense element..].
.[.5. The ferromagnetic thin-film based magnetic field sensor of
claim 1 wherein the first flux guide comprises a U shaped
element..].
.[.6. The ferromagnetic thin-film based magnetic field sensor of
claim 1 wherein the first flux guide includes a flared end..].
.[.7. The ferromagnetic thin-film based magnetic field sensor of
claim 1 further comprising a material disposed adjacent the first
flux guide and comprising one of the group consisting of a high
conductivity metal and a dielectric material..].
.[.8. The ferromagnetic thin-film based magnetic field sensor of
claim 1 wherein the first flux guide comprises a box shaped
structure..].
.[.9. The ferromagnetic thin-film based magnetic field sensor of
claim 1 wherein at least one of the first and second flux guides is
disposed substantially orthogonal to the plane of the
substrate..].
.[.10. The ferromagnetic thin-film based magnetic field sensor of
claim 1 wherein at least one of the first and second flux guides is
disposed at an angle of between 45 degrees and 90 degrees to the
plane of the substrate..].
11. The ferromagnetic thin-film based magnetic field sensor of
claim 1 .[.further comprising: a second magnetoresistive sensor
having a second sensing element for detecting a magnetic field in a
second direction orthogonal to the first direction; and.]..Iadd.,
wherein the magnetic field sensor further comprises:.Iaddend. a
third magnetoresistive sensor .[.having a third sensing element
orthogonal to the second sensing element for detecting.].
.Iadd.comprising: a third sensing element having first and second
sides lying parallel to the planar surface of the substrate,
wherein the first side of the third sensing element extends in the
first plane, and wherein the third magnetoresistive sensor detects
.Iaddend.a magnetic field in a third direction orthogonal to the
first and second directions, wherein the third .[.sensing element
is in a plane with the first and second sensing elements.].
.Iadd.direction is parallel to the planar surface.Iaddend..
12. The ferromagnetic thin-film based magnetic field sensor of
claim 11, wherein .Iadd.each of .Iaddend.the first, second, and
third .[.sensor.]. .Iadd.sensing .Iaddend.elements .[.each.].
comprise an imbalanced synthetic antiferromagnet formed with first
and second ferromagnetic layers separated by a spacer layer,
.[.where.]. .Iadd.wherein .Iaddend.the first and second
ferromagnetic layers have different magnetic moments.
13. The ferromagnetic thin-film based magnetic field sensor of
claim 1 .[.further comprising:.]..Iadd., wherein .Iaddend.the first
magnetoresistive sensor .[.comprising:.]. .Iadd.further comprises
.Iaddend.a first pinned layer.[.; a.]..Iadd., wherein the
.Iaddend.second magnetoresistive sensor .[.comprising:.].
.Iadd.further comprises .Iaddend.a second pinned
layer.[.;.]..Iadd., .Iaddend.and .[.a.]. .Iadd.the .Iaddend.second
sensing element .Iadd.is .Iaddend.formed on the second pinned
layer.[.;.]..Iadd., and wherein the magnetic field sensor further
comprises: .Iaddend. a third magnetoresistive sensor comprising: a
third pinned layer; and a third sensing element formed on the third
pinned layer .[.and.]..Iadd., which is .Iaddend.orthogonal to
.Iadd.a pinned layer of .Iaddend.the second sensing
element.[.;.]..Iadd., wherein the third sensing element includes
first and second sides lying parallel to the planar surface of the
substrate, and wherein the first side of the third sensing element
extends in the first plane, and .Iaddend. wherein the second and
third pinned layers are oriented about 45 degrees to the first
pinned layer.
14. The ferromagnetic thin-film based magnetic field sensor of
claim .[.13.]. .Iadd.1, .Iaddend.wherein the first .[.magnetic
tunnel junction.]. .Iadd.magnetoresistive sensor .Iaddend.further
comprises: a second flux guide .Iadd.having a first flux guide side
and a second flux guide side, wherein the second flux guide side is
orthogonal to the first flux guide side, the second flux guide side
is .Iaddend.disposed non-parallel to the first side of the first
sensing element.Iadd., .Iaddend.and .[.having.]. an end .[.that.].
.Iadd.of the second flux guide side .Iaddend.is proximate to the
second edge and the second side of the first sensing element.Iadd.,
wherein the first flux guide side of the second flux guide is
disposed in a fourth plane parallel to and spaced apart from each
of the first, second, and third planes.Iaddend..
15. The ferromagnetic thin-film based magnetic field sensor of
claim 14.Iadd., .Iaddend.wherein the first and second flux guides
each comprise an aspect ratio greater than 10.
16. A ferromagnetic thin-film .Iadd.based .Iaddend.magnetic field
sensor comprising: a first bridge circuit comprising first, second,
third, and fourth magnetic tunnel junction sensors coupled as a
Wheatstone bridge for sensing a magnetic field orthogonal to
.[.the.]. .Iadd.a .Iaddend.plane of the sensors; the first magnetic
tunnel junction sensor comprising: a first reference layer; and a
first sensing element formed on the first reference layer, the
first sensing element having first and second edges and first and
second sides; and a first flux guide comprising a soft
ferromagnetic material disposed orthogonal to and spaced from the
first edge and the first side of the first sensing element; the
second magnetic tunnel junction sensor comprising: a second
reference layer; and a second sensing element formed on the second
reference layer, the second sensing element having first and second
edges and first and second sides; and a second flux guide
comprising a soft ferromagnetic material disposed orthogonal to and
spaced from the first edge and the first side of the second sensing
element; the third magnetic tunnel junction sensor comprising: a
third reference layer; and a third sensing element formed on the
third reference layer, the third sensing element having first and
second edges and first and second sides; and a third flux guide
comprising a soft ferromagnetic material disposed orthogonal to and
spaced from the first edge and the first side of the third sensing
element; the fourth magnetic tunnel junction sensor comprising: a
fourth reference layer; and a fourth sensing element formed on the
fourth reference layer, the fourth sensing element having first and
second edges and first and second sides; and a fourth flux guide
disposed orthogonal to and spaced from the first edge and the first
side of the fourth sensing element.
17. The ferromagnetic thin-film based magnetic field sensor of
claim 16.Iadd., .Iaddend.wherein the first, second, third, and
fourth magnetic tunnel junction sensors further comprise fifth,
sixth, seventh, and eighth flux guides disposed orthogonal to and
spaced from the second edge and the second side of the first,
second, third, and fourth sensing elements, respectively.
18. The ferromagnetic thin-film based magnetic field sensor of
claim 16.Iadd., .Iaddend.further comprising: a second bridge
circuit comprising fifth, sixth, seventh, and eighth magnetic
tunnel junction sensors coupled as a second Wheatstone bridge for
sensing a magnetic field in a second direction orthogonal to the
first direction; and a third bridge circuit comprising ninth,
tenth, eleventh, and twelfth magnetic tunnel junction sensors
coupled as a third Wheatstone bridge for sensing a magnetic field
in a third direction orthogonal to the first and second
directions.
.[.19. The ferromagnetic thin-film based magnetic field sensor of
claim 16 wherein each of the first, second, third, and fourth
sensors comprises an array of sense elements..].
.[.20. A method of testing the functionality and sensitivity of a
response of the Z axis of a ferromagnetic thin-film magnetic field
sensor including a substrate having a planar surface, and a first
magnetoresistive sensor comprising a sensing element having a first
side lying parallel to the planar surface of the substrate, the
sensing element having a second side opposed to the first side and
having first and second opposed edges, a first flux guide
comprising a soft ferromagnetic material disposed non-parallel to
the first side of the substrate and having an end that is proximate
to the first edge and the first side of the sensing element, and a
metal line formed adjacent contiguous to the flux guide, the method
comprising: applying a current through the metal line to provide a
magnetic field with a component parallel to the plane of the flux
guides..].
.[.21. The method of claim 20, further comprising: applying a
current pulse through the metal line to reset the flux guide domain
structure..].
.Iadd.22. The ferromagnetic thin-film based magnetic field sensor
of claim 14, wherein the first flux guide is disposed closer to the
first side of the first sensing element than the second side of the
first sensing element, and the second flux guide is disposed closer
to the second side of the first sensing element than the first side
of the first sensing element..Iaddend.
.Iadd.23. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein the first flux guide side includes a first
dimension and a second dimension longer than the first dimension,
the second flux guide side includes a third dimension and a fourth
dimension longer than the third dimension, and the third dimension
is orthogonal to the first dimension..Iaddend.
.Iadd.24. The ferromagnetic thin-film based magnetic field sensor
of claim 23, wherein the second dimension and the fourth dimension
are equal..Iaddend.
.Iadd.25. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein the first flux guide includes a width
dimension, a height dimension greater than the width dimension, and
a depth dimension greater than the height dimension..Iaddend.
.Iadd.26. The ferromagnetic thin-film based magnetic field sensor
of claim 25, wherein the second flux guide side is defined by the
height dimension and the depth dimension..Iaddend.
.Iadd.27. The ferromagnetic thin-film based magnetic field sensor
of claim 26, wherein the first flux guide side is defined by the
width dimension and the depth dimension..Iaddend.
.Iadd.28. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein the third plane is in between the first and
second planes..Iaddend.
.Iadd.29. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein the first plane is spaced apart from the second
plane..Iaddend.
.Iadd.30. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein the first flux guide side is closer to the
first side of the sensing element than the second side of the
sensing element..Iaddend.
.Iadd.31. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein an entirety of the first flux guide is
positioned closer to the first side of the first sensing element
than the second side of the first sensing element..Iaddend.
.Iadd.32. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein the end of the second flux guide side is closer
to the first side of the first sensing element than the second side
of the first sensing element..Iaddend.
.Iadd.33. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein the end of the second flux guide side is closer
to the first edge of the first sensing element than the second edge
of the first sensing element..Iaddend.
.Iadd.34. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein an entirety of the first flux guide includes a
one-piece construction..Iaddend.
.Iadd.35. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein the first flux guide is configured to guide a
magnetic field orthogonal to the first side of the first sensing
element into a plane parallel to the first side of the first
sensing element..Iaddend.
.Iadd.36. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein the first magnetoresistive sensor is formed
within a thickness of the substrate..Iaddend.
.Iadd.37. The ferromagnetic thin-film based magnetic field sensor
of claim 1, further comprising: a third magnetoresistive sensor
including: a third sensing element having first and second sides
lying parallel to the planar surface of the substrate, wherein the
first side of the third sensing element extends in the first
plane..Iaddend.
.Iadd.38. The ferromagnetic thin-film based magnetic field sensor
of claim 1, wherein the soft ferromagnetic material includes nickel
iron..Iaddend.
.Iadd.39. The magnetic field sensor of claim 1, wherein an entirety
of the first flux guide is in between the planar surface and the
first sensing element..Iaddend.
.Iadd.40. A ferromagnetic thin-film based magnetic field sensor
comprising: a substrate having a planar surface; a first
magnetoresistive sensor comprising: a first sensing element having
first and second sides lying parallel to the planar surface of the
substrate, wherein the first side is defined by at least first and
second opposed edges; and a first flux guide comprising a high
permeability magnetic material, a first flux guide side, and a
second flux guide side, wherein the second flux guide side is
orthogonal to the first flux guide side, the second flux guide side
is disposed non-parallel to the first side of the first sensing
element, and the second flux guide side includes an end that is
proximate to the first edge and the first side of the first sensing
element, wherein the first side of the first sensing element
extends in a first plane, the planar surface of the substrate
extends in a second plane parallel to the first plane, and the
first flux guide side extends in a third plane parallel to and
spaced apart from each of the first and second planes; and a second
magnetoresistive sensor comprising: a second sensing element having
first and second sides lying parallel to the planar surface of the
substrate, wherein the first side of the second sensing element
extends in the first plane, wherein the first magnetoresistive
sensor detects a magnetic field in a first direction orthogonal to
the planar surface, and the second magnetoresistive sensor detects
a magnetic field in a second direction parallel to the planar
surface..Iaddend.
.Iadd.41. The ferromagnetic thin-film based magnetic field sensor
of claim 40, wherein the high permeability magnetic material
includes nickel iron..Iaddend.
.Iadd.42. The ferromagnetic thin-film based magnetic field sensor
of claim 40, further comprising: a third magnetoresistive sensor
comprising: a third sensing element having first and second sides
lying parallel to the planar surface of the substrate, wherein the
first side of the third sensing element extends in the first plane,
and wherein the third magnetoresistive sensor detects a magnetic
field in a third direction orthogonal to the first and second
directions..Iaddend.
.Iadd.43. The ferromagnetic thin-film based magnetic field sensor
of claim 42, wherein each of the first, second, and third sensing
elements comprise an imbalanced synthetic antiferromagnet formed
with first and second ferromagnetic layers separated by a spacer
layer, where the first and second ferromagnetic layers have
different magnetic moments..Iaddend.
.Iadd.44. The ferromagnetic thin-film based magnetic field sensor
of claim 40, wherein the first magnetoresistive sensor further
comprises a first pinned layer, wherein the second magnetoresistive
sensor further comprises a second pinned layer, and the second
sensing element is formed on the second pinned layer, and wherein
the magnetic field sensor further comprises: a third
magnetoresistive sensor comprising: a third pinned layer; and a
third sensing element formed on the third pinned layer, which is
orthogonal to a pinned layer of the second sensing element, wherein
the third sensing element includes first and second sides lying
parallel to the planar surface of the substrate, and wherein the
first side of the third sensing element extends in the first plane,
wherein the second and third pinned layers are oriented about 45
degrees to the first pinned layer..Iaddend.
.Iadd.45. The ferromagnetic thin-film based magnetic field sensor
of claim 40, wherein the first magnetoresistive sensor further
comprises: a second flux guide having a first flux guide side and a
second flux guide side, wherein the second flux guide side is
orthogonal to the first flux guide side, the second flux guide side
is disposed non-parallel to the first side of the first sensing
element, and an end of the second flux guide side is proximate to
the second edge and the second side of the first sensing element,
wherein the first flux guide side of the second flux guide extends
in a fourth plane parallel to and spaced apart from each of the
first, second, and third planes..Iaddend.
.Iadd.46. The ferromagnetic thin-film based magnetic field sensor
of claim 45, wherein the first and second flux guides each comprise
an aspect ratio greater than 10..Iaddend.
.Iadd.47. The ferromagnetic thin-film based magnetic field sensor
of claim 45, wherein the first flux guide is disposed closer to the
first side of the first sensing element than the second side of the
first sensing element, and the second flux guide is disposed closer
to the second side of the first sensing element than the first side
of the first sensing element..Iaddend.
.Iadd.48. The ferromagnetic thin-film based magnetic field sensor
of claim 40, wherein the first flux guide side includes a first
dimension and a second dimension longer than the first dimension,
the second flux guide side includes a third dimension longer than a
fourth dimension, wherein the third dimension is orthogonal to the
first dimension..Iaddend.
.Iadd.49. The ferromagnetic thin-film based magnetic field sensor
of claim 48, wherein the second dimension and the fourth dimension
are equal..Iaddend.
.Iadd.50. The ferromagnetic thin-film based magnetic field sensor
of claim 40, wherein the third plane is in between the first and
second planes..Iaddend.
.Iadd.51. A ferromagnetic thin-film based magnetic field sensor
comprising: a first bridge circuit comprising first, second, third,
and fourth magnetic tunnel junction sensors coupled as a Wheatstone
bridge for sensing a magnetic field orthogonal to a plane of the
sensors; the first magnetic tunnel junction sensor comprising: a
first reference layer; and a first sensing element formed on the
first reference layer, the first sensing element having first and
second edges and first and second sides; and a first flux guide
comprising a high permeability magnetic material disposed
orthogonal to and spaced from the first edge and the first side of
the first sensing element; the second magnetic tunnel junction
sensor comprising: a second reference layer; and a second sensing
element formed on the second reference layer, the second sensing
element having first and second edges and first and second sides;
and a second flux guide comprising a high permeability magnetic
material disposed orthogonal to and spaced from the first edge and
the first side of the second sensing element; the third magnetic
tunnel junction sensor comprising: a third reference layer; and a
third sensing element formed on the third reference layer, the
third sensing element having first and second edges and first and
second sides; and a third flux guide comprising a high permeability
magnetic material disposed orthogonal to and spaced from the first
edge and the first side of the third sensing element; the fourth
magnetic tunnel junction sensor comprising: a fourth reference
layer; and a fourth sensing element formed on the fourth reference
layer, the fourth sensing element having first and second edges and
first and second sides; and a fourth flux guide disposed orthogonal
to and spaced from the first edge and the first side of the fourth
sensing element..Iaddend.
.Iadd.52. The magnetic field sensor of claim 51, wherein the first,
second, third, and fourth magnetic tunnel junction sensors further
comprise fifth, sixth, seventh, and eighth flux guides disposed
orthogonal to and spaced from the second edge and the second side
of the first, second, third, and fourth sensing elements,
respectively..Iaddend.
.Iadd.53. The ferromagnetic thin-film based magnetic field sensor
of claim 51, further comprising: a second bridge circuit comprising
fifth, sixth, seventh, and eighth magnetic tunnel junction sensors
coupled as a second Wheatstone bridge for sensing a magnetic field
in a second direction orthogonal to the first direction; and a
third bridge circuit comprising ninth, tenth, eleventh, and twelfth
magnetic tunnel junction sensors coupled as a third Wheatstone
bridge for sensing a magnetic field in a third direction orthogonal
to the first and second directions..Iaddend.
.Iadd.54. The ferromagnetic thin-film based magnetic field sensor
of claim 53, wherein the second and third directions are parallel
to the plane of sensors..Iaddend.
.Iadd.55. A ferromagnetic thin-film based magnetic field sensor
comprising: a substrate having a planar surface; a first
magnetoresistive sensor comprising: a first sensing element having
first and second sides lying parallel to the planar surface of the
substrate; and a first flux guide comprising a soft ferromagnetic
material, having a first flux guide side and a second flux guide
side, wherein the second flux guide side is orthogonal to the first
flux guide side, the second flux guide side is disposed
non-parallel to the first side of the first sensing element, and
the second flux guide side includes an end that is proximate to an
edge of the first side of the first sensing element; a second
magnetoresistive sensor comprising: a second sensing element having
first and second sides lying parallel to the planar surface of the
substrate; and a third magnetoresistive sensor comprising: a third
sensing element having first and second sides lying parallel to the
planar surface of the substrate, wherein the first magnetoresistive
sensor detects a magnetic field in a first direction, the second
magnetoresistive sensor detects a magnetic field in a second
direction orthogonal to the first direction, and the third
magnetoresistive sensor detects a magnetic field in a third
direction orthogonal to the first and second directions, wherein
the first direction is orthogonal to the planar surface, and the
second and third directions are parallel to the planar surface, and
wherein each of the first, second, and third sensing elements
includes a sense axis parallel to the planar surface..Iaddend.
.Iadd.56. The ferromagnetic thin-film based magnetic field sensor
of claim 55, wherein the first side of the first sensing element is
in a first plane, the planar surface of the substrate is in a
second plane parallel to the first plane, and the first flux guide
side is in a third plane parallel to and spaced apart from each of
the first and second planes, and wherein the third plane is in
between the first and second planes..Iaddend.
.Iadd.57. The ferromagnetic thin-film based magnetic field sensor
of claim 55, wherein an entirety of the first flux guide is
positioned closer to the first side of the first sensing element
than the second side of the first sensing element..Iaddend.
.Iadd.58. The ferromagnetic thin-film based magnetic field sensor
of claim 57, wherein the first magnetoresistive sensor further
comprises: a second flux guide positioned non-parallel to the first
side of the first sensing element, wherein an entirety of the
second flux guide is positioned closer to the second side of the
first sensing element than the first side of the first sensing
element..Iaddend.
.Iadd.59. The ferromagnetic thin-film based magnetic field sensor
of claim 55, wherein an entirety of the first flux guide is
positioned in between the first side of the first sensing element
and the planar surface of the substrate..Iaddend.
.Iadd.60. The ferromagnetic thin-film based magnetic field sensor
of claim 55, wherein the soft ferromagnetic material includes
nickel iron..Iaddend.
.Iadd.61. The ferromagnetic thin-film based magnetic field sensor
of claim 55, wherein the first flux guide is configured to guide a
magnetic field orthogonal to the first side of the first sensing
element into a plane parallel to the first side of the first
sensing element..Iaddend.
.Iadd.62. The ferromagnetic thin-film based magnetic field sensor
of claim 55, wherein the first magnetoresistive sensor is formed
within a thickness of the substrate..Iaddend.
.Iadd.63. The ferromagnetic thin-film based magnetic field sensor
of claim 55, wherein each of the first, second, and third sensing
elements includes an imbalanced synthetic antiferromagnet formed
with first and second ferromagnetic layers separated by a spacer
layer, where the first and second ferromagnetic layers have
different magnetic moments..Iaddend.
.Iadd.64. The ferromagnetic thin-film based magnetic field sensor
of claim 55, wherein an entirety of the first flux guide includes a
one-piece construction..Iaddend.
.Iadd.65. A ferromagnetic thin-film based magnetic field sensor
comprising: a substrate having a planar surface; a first
magnetoresistive sensor comprising: a first sensing element having
first and second sides lying parallel to the planar surface of the
substrate; and a first flux guide comprising a high permeability
magnetic material, having a first flux guide side and a second flux
guide side, wherein the second flux guide side is orthogonal to the
first flux guide side, the second flux guide side is disposed
non-parallel to the first side of the first sensing element, and
the second flux guide side includes an end that is proximate to an
edge of the first side of the first sensing element; a second
magnetoresistive sensor comprising: a second sensing element having
first and second sides lying parallel to the planar surface of the
substrate; and a third magnetoresistive sensor comprising: a third
sensing element having first and second sides lying parallel to the
planar surface of the substrate, wherein the first magnetoresistive
sensor detects a magnetic field in a first direction, the second
magnetoresistive sensor detects a magnetic field in a second
direction orthogonal to the first direction, and the third
magnetoresistive sensor detects a magnetic field in a third
direction orthogonal to the first and second directions, wherein
the first direction is orthogonal to the planar surface, and the
second and third directions are parallel to the planar surface, and
wherein each of the first, second, and third sensing elements
includes a sense axis parallel to the planar surface..Iaddend.
.Iadd.66. The ferromagnetic thin-film based magnetic field sensor
of claim 65, wherein the first side of the first sensing element is
in a first plane, the planar surface of the substrate is in a
second plane parallel to the first plane, and the first flux guide
side is in a third plane parallel to and spaced apart from each of
the first and second planes, and wherein the third plane is in
between the first and second planes..Iaddend.
.Iadd.67. The ferromagnetic thin-film based magnetic field sensor
of claim 65, wherein an entirety of the first flux guide is
positioned closer to the first side of the first sensing element
than the second side of the first sensing element..Iaddend.
.Iadd.68. The ferromagnetic thin-film based magnetic field sensor
of claim 67, wherein the first magnetoresistive sensor further
comprises: a second flux guide positioned non-parallel to the first
side of the first sensing element, wherein an entirety of the
second flux guide is positioned closer to the second side of the
first sensing element than the first side of the first sensing
element..Iaddend.
.Iadd.69. The ferromagnetic thin-film based magnetic field sensor
of claim 65, wherein an entirety of the first flux guide is
positioned in between the first side of the first sensing element
and the planar surface of the substrate..Iaddend.
.Iadd.70. The ferromagnetic thin-film based magnetic field sensor
of claim 65, wherein the high permeability magnetic material
includes nickel iron..Iaddend.
.Iadd.71. The ferromagnetic thin-film based magnetic field sensor
of claim 65, wherein the first flux guide is configured to guide a
magnetic field orthogonal to the first side of the first sensing
element into a plane parallel to the first side of the first
sensing element..Iaddend.
.Iadd.72. The ferromagnetic thin-film based magnetic field sensor
of claim 65, wherein the first magnetoresistive sensor is formed
within a thickness of the substrate..Iaddend.
Description
.Iadd.PRIORITY.Iaddend.
.Iadd.This application is a reissue application of U.S. Pat. No.
8,390,283 B2, which issued on Mar. 5, 2013, from U.S. patent
application Ser. No. 12/567,496, filed on Sep. 25, 2009, the entire
disclosure of which is expressly incorporated herein by
reference..Iaddend.
.Iadd.More than one reissue application has been filed for the
reissue of U.S. Pat. No. 8,390,283 B2. The reissue applications are
the present application, i.e., U.S. Reissue application Ser. No.
14/638,583, and U.S. Reissue application Ser. No. 15/165,600, which
is a continuation reissue application of the present
application..Iaddend.
FIELD
The present invention generally relates to the field of
magnetoelectronic devices and more particularly to CMOS-compatible
magnetoelectronic field sensors used to sense magnetic fields in
three orthogonal directions.
BACKGROUND
Sensors are widely used in modern systems to measure or detect
physical parameters, such as position, motion, force, acceleration,
temperature, pressure, etc. While a variety of different sensor
types exist for measuring these and other parameters, they all
suffer from various limitations. For example, inexpensive low field
sensors, such as those used in an electronic compass and other
similar magnetic sensing applications generally consist of
anisotropic magnetoresistance (AMR) based devices. In order to
arrive at the required sensitivity and reasonable resistances that
match well with CMOS, the sensing units of such sensors are
generally on the order of square millimeters in size. For mobile
applications, such AMR sensor configurations are costly, in terms
of expense, circuit area, and power consumption.
Other types of sensors, such as Hall effect sensors, giant
magnetoresistance (GMR) sensors, and magnetic tunnel junction (MTJ)
sensors, have been used to provide smaller profile sensors, but
such sensors have their own concerns, such as inadequate
sensitivity and being effected by temperature changes. To address
these concerns, MTJ sensors and GMR sensors have been employed in a
Wheatstone bridge structure to increase sensitivity and to
eliminate temperature dependent resistance changes. Many magnetic
sensing technologies are inherently responsive to one orientation
of applied field, to the exclusion of orthogonal axes. Indeed,
two-axis magnetic field sensors have been developed for electronic
compass applications to detect the earth's field direction by using
a Wheatstone bridge structure for each sense axis.
For example, Hall sensors are generally responsive to out-of-plane
field components normal to the substrate surface, while
magneto-resistive sensors are responsive to in-plane applied
magnetic fields. Utilizing these responsive axes, development of a
small footprint three axis sensing solution typically involves a
multi chip module with one or more chips positioned at orthogonal
angles to one another. For magnetoresistive sensors, the orthogonal
in-plane components may be achieved with careful sensor design, but
the out-of-plane response is commonly garnered through vertical
bonding or solder reflow to contact a secondary chip that has be
mounted vertically. As the size of the vertically bonded chip is
typically dominated by the pad pitch as determined from the
handling constraints, such a technique results in a large vertical
extent of the finished package, high die and assembly costs, and
makes chip scale packaging difficult and costly as through chip
vias must be incorporated.
Accordingly, a need exists for an improved design and fabrication
process for forming a single chip magnetic sensor that is
responsive an applied magnetic field in three dimensions. There is
also a need for a three-axis sensor that can be efficiently and
inexpensively constructed as an integrated circuit structure for
use in mobile applications. There is also a need for an improved
magnetic field sensor and fabrication to overcome the problems in
the art, such as outlined above. Furthermore, other desirable
features and characteristics of the present invention will become
apparent from the subsequent detailed description and the appended
claims, taken in conjunction with the accompanying drawings and
this background.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will hereinafter be described
in conjunction with the following drawing figures, wherein like
numerals denote like elements, and
FIG. 1 illustrates an electronic compass structure which uses
differential sensors formed from three bridge structures with MTJ
sensors in accordance with an exemplary embodiment;
FIG. 2 is a partial cross section of the Z axis bridge structure of
FIG. 1 in accordance with the exemplary embodiment;
FIG. 3 is a view of flux lines as calculated by finite element
simulation of two of the four magnetic tunnel junction sensors of
FIG. 2;
FIG. 4 is a partial cross section of the Z axis bridge structure of
FIG. 1 in accordance with another exemplary embodiment;
FIG. 5 is a partial cross section of the Z axis bridge structure of
FIG. 1 in accordance with yet another exemplary embodiment;
FIG. 6 is another shape of a flux guide as shown in FIG. 5;
FIG. 7 is yet another shape of the flux guide as shown in FIG.
5;
FIG. 8 is still another shape of the flux guide as shown in FIG. 5;
and
FIG. 9 is a graph illustrating the Z sensitivity expressed as a
percentage of the X sensitivity for a single (not differentially
wired) MTJ sense element as a function of the cladding to sensor
spacing.
It will be appreciated that for simplicity and clarity of
illustration, elements illustrated in the drawings have not
necessarily been drawn to scale. For example, the dimensions of
some of the elements are exaggerated relative to other elements for
purposes of promoting and improving clarity and understanding.
Further, where considered appropriate, reference numerals have been
repeated among the drawings to represent corresponding or analogous
elements.
SUMMARY
A ferromagnetic thin-film based magnetic field sensor includes a
first magnetoresistive sensor comprising a substrate having a
planar surface, and a first sensing element having a first side
lying parallel to the planar surface of the substrate, the first
sensing element having a second side opposed to the first side and
having first and second opposed edges; and a first flux guide
disposed non-parallel to the first side of the substrate and having
an end that is proximate to the first edge and the first side of
the first sensing element. An optional second flux guide may be
disposed non-parallel to the first side of the substrate and having
an end that is proximate to the second edge and the second side of
the first sensing element.
In another exemplary embodiment, a ferromagnetic thin-film based
magnetic field sensor includes first, second, and third
magnetoresistive sensors. The first magnetic tunnel junction sensor
includes a first pinned layer and a first sensing element formed on
the first pinned layer, the second magnetic tunnel junction sensor
includes a second pinned layer and a second sensing element formed
on the second pinned layer and orthogonal to the first sensing
element, and the third magnetic tunnel junction sensor includes a
third pinned layer and a third sensing element formed on the third
pinned layer, the third pinned layer disposed at about 45 degrees
to each of the first and second pinned layers, the third sensing
element having first and second edges and first and second sides. A
flux guide is disposed non-parallel to a planar surface of the
substrate and has an end that is proximate to the first edge and
the first side of the third sensing element.
DETAILED DESCRIPTION
The following detailed description is merely exemplary in nature
and is not intended to limit the invention or the application and
uses of the invention. Furthermore, there is no intention to be
bound by any theory presented in the preceding background or the
following detailed description.
Through the integration of high aspect ratio vertical bars (flux
guides) of a high permeability material, for example, nickel iron
(NiFe), whose ends terminate in close proximity to opposed edges
and opposite sides of a magnetic sense element, a portion of the Z
axis field can be brought into the XY plane. These flux guides
serve to capture magnetic flux from an applied field oriented in
the Z direction, and in so doing, bend the field lines in a
substantially horizontal manner near the ends of the flux guides.
Through asymmetric positioning of the flux guides, e.g., the flux
guide segment above the left edge of sense elements in two legs of
the four legs of a Wheatstone bridge, and the flux guide above the
right edge of sense elements in the other two legs, the horizontal
components may act in an opposite directions for the two pairs of
legs resulting in a strong differential signal. A field applied in
the X or Y direction will project equally on all four legs of the
bridge and hence be subtracted out and not contribute to the final
sensor signal. Separate bridges are included elsewhere on the
magnetic sensor chip for determining the X and Y components of the
magnetic signal, and in this manner, a field with components in all
three spatial orientations can be accurately determined by a single
chip magnetoresistive sensing module, for example, based on
magnetic tunnel junction (MTJ) sense elements. Finite Element
Method (FEM) simulations have shown that a pair of high aspect
ratio flux guides, e.g., 25 nm wide by 500 nm high and extending
several microns in the third direction, when optimally positioned
will provide a signal on an individual element that is about 80% of
the of the signal measured from an in plane (x axis) field of the
same strength. Additional signal may be obtained through closer
proximity of the flux guide to the sensor, increases in the flux
guide height, and additional shaping of the guide geometry. One
example is to add horizontal segments parallel to the sense element
which extend over the edges of the sense element. Other examples
are to form a U which is placed with the interior horizontal
segment aligned with the outer edge of the sense element, angled
termination of the vertical segments to extend the flux guide
partially in the plane of the sense element, and a similarly placed
box structure. These geometries serve to further enhance the
horizontal component of the guided flux and move it to a more
central region of the sensor. A structure with individual 25 nm
wide vertical bars utilized as flux guides is tolerant to overlay
errors and produces an apparent x to z field conversion (for a
differentially wired Wheatstone bridge) at the rate of 2.5% for a
misalignment of 85 nm (3 sigma) between a single flux guiding layer
and the sense layer.
The flux guiding layer may be formed from layers typically used in
the magnetic random access memory (MRAM) process flow, during which
bit and digit lines cladded with a high permeability magnetic
material (such as in typical magnetic memory devices), referred to
herein as a flux guide, are used to increase the field factors
present to reduce the current needed to switch the memory storage
element. In the sensor application, the same process flow may be
used with the optional additional step of sputtering out the bottom
of the digit line in order to remove any cladding present on the
trench's bottom. Modifications may be made to the process flow so
that the height and width of the cladding used for flux guiding are
at optimum values instead of the 500 nm and 25 nm, respectively
that are used in the exemplary process described above.
A method and apparatus are subsequently described in more detail
for providing multi-axis pinning on a bulk wafer which may be used
to form an integrated circuit sensor with different reference
layers having three different pinning directions, two of which are
substantially orthogonal that are set with a single pinning
material deposition and bulk wafer setting procedure. As a
preliminary step, a stack of one or more layers of ferromagnetic
and antiferromagnetic materials are etched into shaped reference
layers having a two-dimensional shape with a high aspect ratio,
where the shape provides a distinction for the desired
magnetization direction for each reference layer. Depending on the
materials and techniques used, the final magnetization direction
may be oriented along the short axis or the long axis of the shaped
layer. For example, if the pinned layer is formed with a slightly
imbalanced synthetic anti-ferromagnet (SAF) patterned into
micron-scale dimensions, the magnetization will direct along the
short axis. As will be appreciated by those skilled in the art, the
SAF embodiment provides a number of benefits related to the use of
pinned-SAF reference layers in magnetoelectronic devices. In other
embodiments, by controlling the thicknesses of the pinned and fixed
layers and the in-plane spatial extent of the patterned structure,
the final magnetization may be directed along the long axis. Using
shape anisotropy, different magnetization directions are induced in
the reference layers by heating in the presence of an orienting
field that is aligned between the desired magnetization directions
for the reference layers. In selected embodiments, the reference
layers are heated sufficiently to reduce the material component of
the anisotropy and allow the shape and external field to dominate
the magnetization direction. In this manner, once the orienting
field is removed, the shape anisotropy directs the magnetization in
the desired direction. Upon removing the orienting field, the
magnetizations of the reference layers relax to follow the shape of
the reference layers so as to induce a magnetization that is
aligned along the desired axis of the shaped reference layer. An
optional compensating field may be applied to help induce
orthogonality, and the reference layers are then heated to above
the phase transition temperature of the antiferromagnetic pinning
layers. For example, if two reference layers are shaped to have
longer dimensions which are perpendicular to one another, then the
induced magnetizations for the two reference layers will be close
to being perpendicular to one another.
Various illustrative embodiments of the present invention will now
be described in detail with reference to the accompanying figures.
While various details are set forth in the following description,
it will be appreciated that the present invention may be practiced
without these specific details, and that numerous
implementation-specific decisions may be made to the invention
described herein to achieve the device designer's specific goals,
such as compliance with process technology or design-related
constraints, which will vary from one implementation to another.
While such a development effort might be complex and
time-consuming, it would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure. In addition, selected aspects are depicted with
reference to simplified cross sectional drawings without including
every device feature or geometry in order to avoid limiting or
obscuring the present invention. It is also noted that, throughout
this detailed description, conventional techniques and features
related to magnetic sensor design and operation, Magnetoresistive
Random Access Memory (MRAM) design, MRAM operation, semiconductor
device fabrication, and other aspects of the integrated circuit
devices may not be described in detail herein. While certain
materials will be formed and removed to fabricate the integrated
circuit sensors as part of an existing MRAM fabrication process,
the specific procedures for forming or removing such materials are
not detailed below since such details are well known and not
considered necessary to teach one skilled in the art of how to make
or use the present invention. Furthermore, the circuit/component
layouts and configurations shown in the various figures contained
herein are intended to represent exemplary embodiments of the
invention. It should be noted that many alternative or additional
circuit/component layouts may be present in a practical
embodiment.
FIG. 1 shows a magnetic field sensor 100 formed with first, second,
and third differential sensors 101, 111, 121 for detecting the
component directions of an applied field along a first axis 120
(e.g., the y-axis direction), a second axis 110 (e.g., the x-axis
direction), and a third axis 130 (e.g., the z-axis direction),
respectively. The z-axis direction is represented as a dot and
cross-hairs as going either into or out of the page on which FIG. 1
is situated. Exemplary embodiments of the first and second sensors
101, 111 are described in detail in U.S. patent application Ser.
No. 12/433,679. As depicted herein, each sensor 101, 111, 121 is
formed with unshielded sense elements that are connected in a
bridge configuration. Thus, the first sensor 101 is formed from the
connection of a plurality of sense elements 102-105 in a bridge
configuration over a corresponding plurality of pinned layers
106-109, where each of the pinned layers 106-109 is magnetized in
the x-axis direction. In similar fashion, the second sensor 111 is
formed from the connection of a plurality of sense elements 112-115
in a bridge configuration over a corresponding plurality of pinned
layers 116-119 that are each magnetized in the y-axis direction
that is perpendicular to the magnetization direction of the pinned
layers 106-109. Furthermore, the third sensor 121 in the same plane
as the first and second sensors 101, 111 is formed from the
connection of a plurality of sense elements 122-125 in a bridge
configuration over a corresponding plurality of pinned layers
126-129 that are each magnetized in the xy-axis direction that is
at 45 degrees to the magnetization direction of the pinned layers
106-109 and 116-119. In the depicted bridge configuration 101, the
sense elements 102, 104 are formed to have a first easy axis
magnetization direction and the sense elements 103, 105 are formed
to have a second easy axis magnetization direction, where the first
and second easy axis magnetization directions are orthogonal with
respect to one another and are oriented to differ equally from the
magnetization direction of the pinned layers 106-109. As for the
second bridge configuration 111, the sense elements 112, 114 have a
first easy axis magnetization direction that is orthogonal to the
second easy axis magnetization direction for the sense elements
113, 115 so that the first and second easy axis magnetization
directions are oriented to differ equally from the magnetization
direction of the pinned layers 116-119. In the third bridge
configuration 121, the sense elements 122 123,124, and 125 all have
an easy axis magnetization direction that is orthogonal to the
pinned magnetization direction of the pinned layers 126, 127, 128,
and 129. The third bridge configuration 121 further includes flux
guides 132-135 positioned adjacent to the right edge of sense
elements 122-125, and flux guides 136-139 positioned adjacent to
the left edge of sense elements 122-125, respectively. Flux guides
132,137, 134, and 139 are positioned above sense elements 122-125,
and flux guides 136, 133, 138, and 135 are positioned below sense
elements 122-125. The positioning of these flux guides 132-139 is
subsequently described in more detail in FIG. 2. In the depicted
sensors 101, 111, 121 there is no shielding required for the sense
elements, nor are any special reference elements required. In an
exemplary embodiment, this is achieved by referencing each active
sense element (e.g., 102, 104) with another active sense element
(e.g., 103, 105) using shape anisotropy techniques to establish the
easy magnetic axes of the referenced sense elements to be deflected
from each other by 90 degrees for the x and y sensors, and
referencing a sense element that responds in an opposite manner to
an applied field in the Z direction for the Z sensor. The Z sensor
referencing will be described in more detail below. The
configuration shown in FIG. 1 is not required to harvest the
benefits of the third sensor 121 structure described in more detail
in FIG. 2, and is only given as an example.
By positioning the first and second sensors 101, 111 to be
orthogonally aligned, each with the sense element orientations
deflected equally from the sensor's pinning direction and
orthogonal to one another in each sensor, the sensors can detect
the component directions of an applied field along the first and
second axes. Flux guides 132-139 are positioned in sensor 121 above
and below the opposite edges of the elements 122-125, in an
asymmetrical manner between legs 141, 143 and legs 142, 144. As
flux guides 132, 134 are placed above the sense elements 122, 124,
the magnetic flux from the Z field may be guided by the flux guides
132 and 134 into the xy plane along the right side and cause the
magnetization of sense elements 122 and 124 to rotate in a first
direction towards a higher resistance. Similarly, the magnetic flux
from the Z field may be guided by the flux guides 133 and 135 into
the xy plane along the right side of the sense element and cause
the magnetization of sense elements 123 and 125 to rotate in a
second direction, opposite from the first direction towards a lower
resistance, as these flux guides are located below the sense
elements 123, 125. Thus, the sensor 121 can detect the component
directions of an applied field along the third axis. Although in
the preferred embodiment, the flux guides are in a plane orthogonal
to the plane of the field sensor, the flux guides will still
function if the angle they make with the sensor is not exactly 90
degrees. In other embodiments, the angle between the flux guide and
the field sensor could be in a range from 45 degrees to 135
degrees, with the exact angle chosen depending on other factors
such as on the ease of fabrication.
As seen from the foregoing, a magnetic field sensor may be formed
from differential sensors 101, 111, 121 which use unshielded sense
elements 102-105, 112-115, and sense elements 122-125 with guided
magnetic flux connected in a bridge configuration over respective
pinned, or reference, layers 106-109, 116-119, and 126-129 to
detect the presence and direction of an applied magnetic field.
With this configuration, the magnetic field sensor provides good
sensitivity, and also provides the temperature compensating
properties of a bridge configuration.
The bridge circuits 101, 111, 121 may be manufactured as part of an
existing MRAM or thin-film sensor manufacturing process with only
minor adjustments to control the magnetic orientation of the
various sensor layers and cross section of the flux guiding
structures. Each of the pinned layers 106-109, 116-119, and 126-129
may be formed with one or more lower ferromagnetic layers, and each
of the sense elements 102-105, 112-125, 122-125 may be formed with
one or more upper ferromagnetic layers. An insulating tunneling
dielectric layer (not shown) may be disposed between the sense
elements 102-105, 112-125, 122-125 and the pinned layers 106-109,
116-119, and 126-129. The pinned and sense electrodes are desirably
magnetic materials whose magnetization direction can be aligned.
Suitable electrode materials and arrangements of the materials into
structures commonly used for electrodes of magnetoresistive random
access memory (MRAM) devices and other magnetic tunnel junction
(MTJ) sensor devices are well known in the art. For example, pinned
layers 106-109, 116-119, and 126-129 may be formed with one or more
layers of ferromagnetic and antiferromagnetic materials to a
combined thickness in the range 10 to 1000 .ANG., and in selected
embodiments in the range 250 to 350 .ANG.. In an exemplary
implementation, each of the pinned layers 106-109, 116-119, and
126-129 is formed with a single ferromagnetic layer and an
underlying anti-ferromagnetic pinning layer. In another exemplary
implementation, each pinned layer 106-109, 116-119, and 126-129
includes a synthetic anti-ferromagnetic stack component (e.g., a
stack of CF (Cobalt Iron), Ruthenium (Ru) and CFB) which is 20 to
80 .ANG. thick, and an underlying anti-ferromagnetic pinning layer
that is approximately 200 .ANG. thick. The lower anti-ferromagnetic
pinning materials may be re-settable materials, such as IrMn,
though other materials, such as PtMn, can be used which are not
readily re-set at reasonable temperatures. As formed, the pinned
layers 106-109, 116-119, and 126-129 function as a fixed or pinned
magnetic layer when the direction of its magnetization is pinned in
one direction that does not change during normal operating
conditions. As disclosed herein, the heating qualities of the
materials used to pin the pinned layers 106-109, 116-119, and
126-129 can change the fabrication sequence used to form these
layers.
One of each of the sense elements 102-105, 112-125, 122-125 and one
of each of the pinned layers 106-109, 116-119, 126-129 form a
magnetic tunnel junction (MTJ) sensor. For example, for bridge
circuit 121, sense element 122 and pinned layer 126 form an MTJ
sensor 141. Likewise, sense element 123 and pinned layer 127 form
an MTJ sensor 142, sense element 124 and pinned layer 128 form an
MTJ sensor 143, and sense element 125 and pinned layer 129 form an
MTJ sensor 144.
The pinned layers 106-109, 116-119, and 126-129 may be formed with
a single patterned ferromagnetic layer having a magnetization
direction (indicated by the arrow) that aligns along the long-axis
of the patterned reference layer(s). However, in other embodiments,
the pinned reference layer may be implemented with a synthetic
anti-ferromagnetic (SAF) layer which is used to align the
magnetization of the pinned reference layer along the short axis of
the patterned reference layer(s). As will be appreciated, the SAF
layer may be implemented in combination with an underlying
anti-ferromagnetic pinning layer, though with SAF structures with
appropriate geometry and materials that provide sufficiently strong
magnetization, the underlying anti-ferromagnetic pinning layer may
not be required, thereby providing a simpler fabrication process
with cost savings.
The sense elements 102-105, 112-125, 122-125 may be formed with one
or more layers of ferromagnetic materials to a thickness in the
range 10 to 5000 .ANG., and in selected embodiments in the range 10
to 60 .ANG.. The upper ferromagnetic materials may be magnetically
soft materials, such as NiFe, CoFe, Fe, CFB and the like. In each
MTJ sensor, the sense elements 102-105, 112-125, 122-125 function
as a sense layer or free magnetic layer because the direction of
their magnetization can be deflected by the presence of an external
applied field, such as the Earth's magnetic field. As finally
formed, sense elements 102-105, 112-125, 122-125 may be formed with
a single ferromagnetic layer having a magnetization direction
(indicated with the arrows) that aligns along the long-axis of the
patterned shapes.
The pinned layers 106-109, 116-119, 126-129 and sense elements
102-105, 112-125, 122-125 may be formed to have different magnetic
properties. For example, the pinned layers 106-109, 116-119,
126-129 may be formed with an anti-ferromagnetic film exchange
layer coupled to a ferromagnetic film to form layers with a high
coercive force and offset hysteresis curves so that their
magnetization direction will be pinned in one direction, and hence
substantially unaffected by an externally applied magnetic field.
In contrast, the sense elements 102-105, 112-125, 122-125 may be
formed with a magnetically soft material to provide different
magnetization directions having a comparatively low anisotropy and
coercive force so that the magnetization direction of the sense
electrode may be altered by an externally applied magnetic field.
In selected embodiments, the strength of the pinning field is about
two orders of magnitude larger than the anisotropy field of the
sense electrodes, although different ratios may be used by
adjusting the respective magnetic properties of the electrodes
using well known techniques to vary their composition.
The pinned layers 106-109, 116-119, 126-129 in the MTJ sensors are
formed to have a shape determined magnetization direction in the
plane of the pinned layers 106-109, 116-119, 126-129 (identified by
the vector arrows for each sensor bridge labeled "Pinning
direction" in FIG. 1). As described herein, the magnetization
direction for the pinned layers 106-109, 116-119, 126-129 may be
obtained using shape anisotropy of the pinned electrodes, in which
case the shapes of the pinned layers 106-109, 116-119, 126-129 may
each be longer in the pinning direction for a single pinned layer.
Alternatively, for a pinned SAF structure, the reference and pinned
layers may be shorter along the pinning direction. In particular,
the magnetization direction for the pinned layers 106-109, 116-119,
126-129 may be obtained by first heating the shaped pinned layers
106-109, 116-119, 126-129 in the presence of a orienting magnetic
field which is oriented non-orthogonally to the axis of longest
orientation for the shaped pinned layers 106-109, 116-119, 126-129
such that the applied orienting field includes a field component in
the direction of the desired pinning direction for the pinned
layers 106-109, 116-119, 126-129. The magnetization directions of
the pinned layers are aligned, at least temporarily, in a
predetermined direction. However, by appropriately heating the
pinned layers during this treatment and removing the orienting
field without reducing the heat, the magnetization of the pinned
layers relaxes along the desired axis of orientation for the shaped
pinned pinned layers 106-109, 116-119, 126-129. Once the
magnetization relaxes, the pinned layers can be annealed and/or
cooled so that the magnetic field direction of the pinned electrode
layers is set in the desired direction for the shaped pinned layers
106-109, 116-119, 126-129.
The exemplary embodiments described herein may be fabricated using
known lithographic processes as follows. The fabrication of
integrated circuits, microelectronic devices, micro electro
mechanical devices, microfluidic devices, and photonic devices
involves the creation of several layers of materials that interact
in some fashion. One or more of these layers may be patterned so
various regions of the layer have different electrical or other
characteristics, which may be interconnected within the layer or to
other layers to create electrical components and circuits. These
regions may be created by selectively introducing or removing
various materials. The patterns that define such regions are often
created by lithographic processes. For example, a layer of
photoresist material is applied onto a layer overlying a wafer
substrate. A photomask (containing clear and opaque areas) is used
to selectively expose this photoresist material by a form of
radiation, such as ultraviolet light, electrons, or x-rays. Either
the photoresist material exposed to the radiation, or that not
exposed to the radiation, is removed by the application of a
developer. An etch may then be applied to the layer not protected
by the remaining resist, and when the resist is removed, the layer
overlying the substrate is patterned. Alternatively, an additive
process could also be used, e.g., building a structure using the
photoresist as a template.
Referring to FIG. 2 and in accordance with an exemplary embodiment
of the present invention, the structure of the MTJ devices 141-144
of the third bridge circuit 121 include the pinned layers 126-129,
the sense elements 122-125, and the flux guides 132-139, all formed
within the dielectric material 140. The flux guide 136 is
positioned adjacent a line 145 and has an end positioned below an
edge of the sensor element 122. The flux guides 133 and 138 are
positioned on opposed sides of a line 146 and have ends positioned
below edges of the sensor elements 123 and 124, respectively. The
flux guide 135 is positioned adjacent a line 147 and has an end
positioned below an edge of the sensor element 125. The flux guides
132 and 137 are spaced apart by an upper line 148 and have ends
positioned above edges of the sensor elements 122 and 123,
respectively, and the flux guides 134 and 139 are spaced apart by
an upper line 149 and have ends positioned above edges of the
sensor elements 134 and 139, respectively. The lines 145-149, are
preferably copper, but in some embodiments may be a dielectric. A
metal stabilization line 150 is positioned above the MTJ devices
141-144 for providing a stabilization field to the sense elements.
The ends of the flux guides may be brought as close as possible to
the sensor elements, with a preferable spacing of less than or
equal to 250 nm between the two. The sense elements are brought as
close as possible for the tightest density array, preferably less
than 2.5 um apart.
FIG. 3 is a view of flux lines as calculated by finite element
simulation of MTJ devices 141, 142 of FIG. 2 with a magnetic field
in the z direction imparted upon the sense elements 122-123. FEM
modeling shows the resultant magnetic flux lines 160, exhibiting a
component in the plane of the sensor. MTJ device 141 is represented
by flux guides 132 and 136 on opposed ends of the sensing element
122. MTJ device 142 is represented by flux guides 133 and 137 on
opposed ends of the sensing element 123. Stated otherwise, sensing
element 122 extends from flux guides 132 and 136, and sensing
element 123 extends from flux guides 133 and 137. The magnetic
field 160 in the Z-axis 130 produces an asymmetric response in the
sensing elements 122, 123 along the X-axis 120 as indicated by the
arrows 170. In this manner, for a field 160 in the Z direction 130
directed towards the bottom of the page, the magnetization of sense
element 122 rotates away from the pinning direction (and to higher
resistance) of the pinned layer 126, while the magnetization of
sense element 123 rotates towards the pinning direction (and to
lower resistance) of pinned layer 127. For a field in the X
direction 120, both elements 122, 123 show induced magnetization in
the same direction (towards higher or lower resistance). Therefore,
by wiring MTJ elements 141, 142 in a Wheatstone bridge for
differential measurement and subtracting the resistances of MTJ
devices 141, 142, the X field response is eliminated and twice the
Z field response is measured.
Referring again to FIG. 2, in the case of an exposure to a large
magnetic field which may induce magnetization disturbances and
domain structure in the flux guides 132-139, a large current pulse
may be introduced along metal lines 145-149 to reset the flux guide
domain structure.
In another exemplary embodiment (shown in FIG. 4), each of the
cladded lines 145-149 are divided into two independent metal lines,
and additional non-flux guiding cladding (161-168 and 191-198) is
placed in between these two metal lines at the interior edges. For
sensor 141, the flux guide 161 on the left edge of the left metal
line, 148 guides Z field flux into the sense element 122 to its
left, and the flux guide 192 on the right most edge of the right
metal line 145 guides Z field flux into the sense element 122 on
its right. Sensors 142-144 function similarly, with the cladded
edge of the metal line adjacent to each sense element serving the
active flux guiding function. As these lines are separated, a
current may be made to pass through cladded lines 145, 146, 182 and
183 into the page, and 181, 147, 148, and 149 out of the page to
create a magnetic field along the cladded line edges with a Z
component pointing in a consistent direction (down in this
example). These current orientations can serve to create a magnetic
field with a strong component in the Z direction, which, through a
calibration for the geometry can serve as a self test for the
functionality and sensitivity of the Z axis response.
Another exemplary embodiment (see FIG. 5) includes extensions
152-159 integrally formed with the flux guides 132-139. The
extensions 152-159 extend along the same axis as the sensor
elements 122-125 and accentuate the horizontal component of the
flux guide and move the horizontal component more to the center of
the appropriate sense element 122-125.
While various exemplary embodiments have been shown for the flux
guides, including the vertical elements 132-139 of FIG. 2, and the
"L" shaped flux guides including extensions 152-159 of FIG. 5,
other exemplary embodiments may be used for both upper and lower
flux guides, such as box shaped or "U" shaped flux guides. In the
"U" shaped structure (FIG. 6), a horizontal NiFe segment 171
connects the two vertical segments 161, 162 along the bottom metal
line, while in the box shaped structure (FIG. 7), a horizontal
segment 172 connects the two vertical segments both above the metal
line as well. A horizontal segment helps to couple the magnetic
structure of the two vertical segments, increasing the field
conversion factor by 10-20% over that of two isolated vertical flux
guides. Two horizontal segments of the box like structure provide
better coupling and increase the field conversion factor by twenty
to forty percent over a simple vertical flux guide. Additionally,
the vertical segments of the "U" shaped structure of FIG. 6 may be
flared 173, 174 (FIG. 8) out so that the region near the sense
element edge has a horizontal component. Similar to the L shaped
guides, the flared segments guide the magnetic flux so that there
is a component directly in the plane of the magnetic sensor to
further amplify the field conversion factor. However, care must be
taken that the overlay is not too great or the magnetic flux will
be shielded from the sensor.
FIG. 9 is a graph showing the Z/X sensitivity ratio versus the
cladding/sensor spacing for a 25 nm wide, 500 nm tall vertical
segments placed above and below the sense element. The Z/X
sensitivity increases, to about 75 percent, as the cladding is
brought to 25 nanometers of distance. Additional factors may be
gained through cross sectional changes such as those highlighted
above, or through aspect ratio improvements in the flux guide, for
example, making the guide taller and increasing the aspect ratio
will linearly increase the Z/X sensitivity ratio. Therefore, it is
important to bring the flux guide as close as possible to the sense
element, and increase its aspect ratio as much as is possible
without adversely impacting the magnetic microstructure.
Although the described exemplary embodiments disclosed herein are
directed to various sensor structures and methods for making same,
the present invention is not necessarily limited to the exemplary
embodiments which illustrate inventive aspects of the present
invention that are applicable to a wide variety of semiconductor
processes and/or devices. Thus, the particular embodiments
disclosed above are illustrative only and should not be taken as
limitations upon the present invention, as the invention may be
modified and practiced in different but equivalent manners apparent
to those skilled in the art having the benefit of the teachings
herein. For example, the relative positions of the sense and
pinning layers in a sensor structure may be reversed so that the
pinning layer is on top and the sense layer is below. Also the
sense layers and the pinning layers may be formed with different
materials than those disclosed. Moreover, the thickness of the
described layers may deviate from the disclosed thickness values.
Accordingly, the foregoing description is not intended to limit the
invention to the particular form set forth, but on the contrary, is
intended to cover such alternatives, modifications and equivalents
as may be included within the spirit and scope of the invention as
defined by the appended claims so that those skilled in the art
should understand that they can make various changes, substitutions
and alterations without departing from the spirit and scope of the
invention in its broadest form.
Benefits, other advantages, and solutions to problems have been
described above with regard to specific embodiments. However, the
benefits, advantages, solutions to problems, and any element(s)
that may cause any benefit, advantage, or solution to occur or
become more pronounced are not to be construed as a critical,
required, or essential feature or element of any or all the claims.
As used herein, the terms "comprises," "comprising," or any other
variation thereof, are intended to cover a non-exclusive inclusion,
such that a process, method, article, or apparatus that comprises a
list of elements does not include only those elements but may
include other elements not expressly listed or inherent to such
process, method, article, or apparatus.
While at least one exemplary embodiment has been presented in the
foregoing detailed description, it should be appreciated that a
vast number of variations exist. It should also be appreciated that
the exemplary embodiment or exemplary embodiments are only
examples, and are not intended to limit the scope, applicability,
or configuration of the invention in any way. Rather, the foregoing
detailed description will provide those skilled in the art with a
convenient road map for implementing an exemplary embodiment of the
invention, it being understood that various changes may be made in
the function and arrangement of elements described in an exemplary
embodiment without departing from the scope of the invention as set
forth in the appended claims.
* * * * *