U.S. patent application number 14/178179 was filed with the patent office on 2015-08-13 for magnetic sensor having optimal free layer back edge shape and extended pinned layer.
This patent application is currently assigned to HGST NETHERLANDS B.V.. The applicant listed for this patent is HGST NETHERLANDS B.V.. Invention is credited to Katsumi Hoshino, Kouji Kataoka, Yukimasa Okada, Takashi Wagatsuma.
Application Number | 20150228297 14/178179 |
Document ID | / |
Family ID | 53719012 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150228297 |
Kind Code |
A1 |
Wagatsuma; Takashi ; et
al. |
August 13, 2015 |
MAGNETIC SENSOR HAVING OPTIMAL FREE LAYER BACK EDGE SHAPE AND
EXTENDED PINNED LAYER
Abstract
A magnetic read sensor having an extended pinned layer and
having a free layer structure with a back edge formed at an angle
for optimizing sensor performance and pinned layer pinning. The
magnetic free layer has a back edge that is formed at an angle of
between 6 and 10 degrees relative to a plane parallel with the air
bearing surface plane. The magnetic sensor can be formed by forming
the free layer stripe height with an ion milling that is performed
at an angle of 6 to 10 degrees relative to normal.
Inventors: |
Wagatsuma; Takashi;
(Odawara-shi, JP) ; Okada; Yukimasa; (Odawara-shi,
JP) ; Hoshino; Katsumi; (Odawara-shi, JP) ;
Kataoka; Kouji; (Odarawa-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HGST NETHERLANDS B.V. |
Amsterdam |
|
NL |
|
|
Assignee: |
HGST NETHERLANDS B.V.
Amsterdam
NL
|
Family ID: |
53719012 |
Appl. No.: |
14/178179 |
Filed: |
February 11, 2014 |
Current U.S.
Class: |
360/235.4 ;
204/192.34 |
Current CPC
Class: |
G11B 5/3929 20130101;
G11B 5/6082 20130101; G11B 5/398 20130101; G11B 2005/3996 20130101;
G11B 5/3909 20130101 |
International
Class: |
G11B 5/39 20060101
G11B005/39; G11B 5/60 20060101 G11B005/60 |
Claims
1. A magnetic sensor, comprising: a magnetic free layer structure
that extends from an air bearing surface to a first stripe height
as measured from the air bearing surface and having a back edge
opposite the air bearing surface that is formed at an angle of 6 to
10 degrees with respect to a plane parallel with the air bearing
surface; a magnetic pinned layer structure that extends beyond the
first stripe height; and a non-magnetic layer sandwiched between
the magnetic free layer structure and the magnetic pinned layer
structure.
2. The magnetic sensor as in claim 1, wherein the non-magnetic
layer is an electrically insulating barrier layer.
3. The magnetic sensor as in claim 1, wherein the non-magnetic
layer is an electrically conductive spacer layer.
4. The magnetic sensor as in claim 1, wherein the back edge of the
magnetic free layer structure has no re-deposited material formed
on it.
5. The magnetic sensor as in claim 1, wherein the pinned layer
structure further comprises first and second magnetic layers and a
non-magnetic anti-parallel coupling layer sandwiched
there-between.
6. The magnetic sensor as in claim 1, wherein the pinned layer
structure further comprises first and second magnetic layers, a
non-magnetic anti-parallel coupling layer sandwiched there-between,
the magnetic sensor further comprising a layer of
anti-ferromagnetic material exchange coupled with the first
magnetic layer.
7. (canceled)
8. The magnetic sensor as in claim 1, further comprising a
non-magnetic, electrically insulating fill layer in a region beyond
the first stripe height, the non-magnetic, electrically insulating
fill layer contacting the back edge of the magnetic free layer,
there being no re-deposited material between the non-magnetic,
electrically insulating fill layer and the back edge of the
magnetic free layer structure.
9. A method for manufacturing a magnetic read sensor, comprising:
depositing a magnetic pinned layer structure; depositing a
non-magnetic layer over the magnetic pinned layer structure;
depositing a magnetic free layer structure over the non-magnetic
layer; forming a mask over the magnetic free layer structure, the
mask having a back edge that is located a desired distance from an
air bearing surface plane so as to define a first stripe height;
performing an ion milling to remove portions of the magnetic free
layer that are not protected by the first mask, the ion milling
being performed at an angle of 6 to 10 degrees relative to normal
so as to form the magnetic free layer with a back edge that defines
an angle of 6 to 10 degrees relative to the air bearing surface
plane.
10. The method as in claim 9 wherein the ion milling is terminated
before removing the non-magnetic layer.
11. The method as in claim 9 wherein the ion milling is terminated
before removing any of the magnetic pinned layer structure.
12. The method as in claim 9 wherein the mask is a bi-layer mask
having an overhanging portion at its back edge.
13. The method as in claim 9 wherein the mask is a first mask and
the ion milling is a first ion milling, the method further
comprising: after performing the first ion milling, depositing a
magnetic fill layer; removing the first mask; forming a second mask
having a back edge located a distance from the air bearing surface
plane so as to define a second stripe height that is longer than
the first stripe height; and performing a second ion milling
sufficiently to remove at least some of the magnetic pinned layer
structure.
14. The method as in claim 13, wherein the ion milling is performed
completely through the pinned layer structure.
15. The method as in claim 13 wherein the second mask is a bi-layer
mask having an overhanging portion at its back edge.
16. The method as in claim 13, further comprising: after performing
the second ion milling, depositing a second non-magnetic,
electrically insulating fill layer; and removing the second
mask.
17. The method as in claim 13 wherein the magnetic pinned layer
structure is deposited over a first magnetic shield, and wherein
the second ion milling is performed until the magnetic shield has
been reached.
18. The method as in claim 9 wherein the ion milling is terminated
upon reaching the non-magnetic layer.
19. The method as in claim 9 wherein the ion milling is terminated
immediately upon reaching the non-magnetic layer.
20. The method as in claim 9 further comprising after depositing
the non-magnetic, electrically insulating fill layer, performing a
chemical mechanical polishing.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to magnetic data recording and
more particularly to a magnetic read head having an extended pinned
layer structure and a free layer having a back edge formed at an
angle for optimized sensor performance and stability.
BACKGROUND OF THE INVENTION
[0002] In recent years, as information technology has developed,
interest has focused on the greater processing speeds of central
processing units (CPU), as well as the increase in storage capacity
of storage devices. Among these developments, magnetic disk storage
devices are most often used as large capacity storage devices, and
research is being performed into further increases in their speed
and data density.
[0003] Magnetic read heads that use magnetoresistive (MR) effect
elements are used for reading the information on the magnetic disks
of magnetic disk storage devices. Magnetoresistive effect elements
normally have a structure in which an antiferromagnetic layer, a
pinned layer, a non-magnetic intermediate layer, a free layer, and
a cap layer are stacked in that order. Due to the effect of the
magnetic disk information magnetic field, the magnetization
direction of the free layer is changed with relative to the
magnetization direction of the pinned layer, whose magnetic force
direction is fixed by the antiferromagnetic layer, and this changes
the overall resistance of the magnetoresistive effect element. The
electrical resistance across the magnetoresistive effect element is
proportional to the relative directions of magnetization of the
free and pinned layers. Therefore, as the relative orientation of
magnetization of the free and pinned layers changes, the resulting
change in electrical resistance can be detected as a magnetic
signal.
[0004] The known formats of magnetoresistive effect elements
include the current-in-plane (CIP) format in which current flows
parallel to the film surfaces of the magnetoresistive effect
element, the current perpendicular to plane (CPP) format in which
the current flows perpendicular to the film surfaces, the giant
magnetoresistive (GMR) format and the tunnelling magnetoresistive
(TMR) format. As a result of the high density recording capacity in
recent years, the CPP-GMR format and the TMR format have become the
main formats used.
[0005] As magnetoresitive effect elements become smaller, the
magnetic stability of the sensor becomes worse. For example, the
reduced area between the pinned layer and the AFM layer reduces the
exchange coupling between these layer and, therefore, reduces the
pinning strength of the sensor. Japanese Unexamined Patent
Application Publication No. 2007-220154 discloses a step structure
for the top surface of the pinned layer of a junction end portion
in the height direction of a TMR element, wherein the pinned layer
extends further from the air bearing surface than the free layer.
This can increase the area of the pinned layer for improved pinning
strength. However, such a design that incorporates an extended
pinned layer presents its own challenges with regard to
manufacturability and sensor performance.
SUMMARY OF THE INVENTION
[0006] The present invention provides a magnetic sensor, that
includes a magnetic free layer structure that extends from an air
bearing surface to a first stripe height measured from the air
bearing surface and that has a back edge opposite the air bearing
surface that is formed at an angle of 6 to 10 degrees with respect
to a plane parallel with the air bearing surface. The sensor also
has a magnetic pinned layer structure that extends beyond the first
stripe height, and a non-magnetic layer sandwiched between the
magnetic free layer structure and the magnetic pinned layer
structure.
[0007] The magnetic sensor can be formed by a method that includes
depositing a magnetic pinned layer structure, depositing a
non-magnetic layer over the magnetic pinned layer structure and
depositing a magnetic free layer structure over the non-magnetic
layer. A mask is formed over the magnetic free layer structure, the
mask having a back edge that is located a desired distance from an
air bearing surface plane so as to define a first stripe height. An
ion milling is then performed to remove portions of the magnetic
free layer that are not protected by the first mask, the ion
milling being performed at an angle of 6 to 10 degrees relative to
normal so as to form the magnetic free layer with a back edge that
defines an angle of 6 to 10 degrees relative to the air bearing
surface plane.
[0008] Forming the back edge of the free layer with an angle of
between 6 and 10 degrees optimizes sensor free sensor performance
as well as pinned layer stability. If the back edge angle is less
than 6 degrees the pinned layer may be damaged by the ion milling
used to form the free layer back edge, and the strength of pinning
of the magnetization of the pinned layer can suffer. On the other
hand, if the angle is greater than 10 degrees the performance of
the sensor (MR ratio) decreases. Forming the back edge of the free
layer with a back edge angle of 6-10 degrees avoids both of these
problems, thereby optimizing sensor performance and robustness.
[0009] These and other features and advantages of the invention
will be apparent upon reading of the following detailed description
of preferred embodiments taken in conjunction with the figures in
which like reference numerals indicate like elements
throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] For a fuller understanding of the nature and advantages of
this invention, as well as the preferred mode of use, reference
should be made to the following detailed description read in
conjunction with the accompanying drawings which are not to
scale.
[0011] FIG. 1 is a schematic illustration of a disk drive system in
which the invention might be embodied;
[0012] FIG. 2 is an ABS view of a slider illustrating the location
of a magnetic head thereon;
[0013] FIG. 3 is an air bearing surface view of a magnetic read
sensor;
[0014] FIG. 4 is a side cross sectional view of the sensor of FIG.
3 as seen from line 4-4 of FIG. 3;
[0015] FIGS. 5-12 are views of a magnetic sensor in various
intermediate stages of manufacture, illustrating a method of
manufacturing a magnetic sensor;
[0016] FIG. 13 is a graph illustrating a relationship between free
layer back edge angle and MR ratio; and
[0017] FIG. 14 is a graph illustrating a relationship between free
layer back edge angel and magnetic resonance frequency.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The following description is of the best embodiments
presently contemplated for carrying out this invention. This
description is made for the purpose of illustrating the general
principles of this invention and is not meant to limit the
inventive concepts claimed herein.
[0019] Referring now to FIG. 1, there is shown a disk drive 100
embodying this invention. The disk drive 100 includes a housing
101. At least one rotatable magnetic disk 112 is supported on a
spindle 114 and rotated by a disk drive motor 118. The magnetic
recording on each disk is in the form of annular patterns of
concentric data tracks (not shown) on the magnetic disk 112.
[0020] At least one slider 113 is positioned near the magnetic disk
112, each slider 113 supporting one or more magnetic head
assemblies 121. As the magnetic disk rotates, slider 113 moves in
and out over the disk surface 122 so that the magnetic head
assembly 121 can access different tracks of the magnetic disk where
desired data are written. Each slider 113 is attached to an
actuator arm 119 by way of a suspension 115. The suspension 115
provides a slight spring force which biases slider 113 against the
disk surface 122. Each actuator arm 119 is attached to an actuator
means 127. The actuator means 127 as shown in FIG. 1 may be a voice
coil motor (VCM). The VCM comprises a coil movable within a fixed
magnetic field, the direction and speed of the coil movements being
controlled by the motor current signals supplied by controller
129.
[0021] During operation of the disk storage system, the rotation of
the magnetic disk 112 generates an air bearing between the slider
113 and the disk surface 122 which exerts an upward force or lift
on the slider. The air bearing thus counter-balances the slight
spring force of suspension 115 and supports slider 113 off and
slightly above the disk surface by a small, substantially constant
spacing during normal operation.
[0022] The various components of the disk storage system are
controlled in operation by control signals generated by control
unit 129, such as access control signals and internal clock
signals. Typically, the control unit 129 comprises logic control
circuits, storage means and a microprocessor. The control unit 129
generates control signals to control various system operations such
as drive motor control signals on line 123 and head position and
seek control signals on line 128. The control signals on line 128
provide the desired current profiles to optimally move and position
slider 113 to the desired data track on disk 112. Write and read
signals are communicated to and from write and read heads 121 by
way of recording channel 125.
[0023] With reference to FIG. 2, the orientation of the magnetic
head 121 in a slider 113 can be seen in more detail. FIG. 2 is an
ABS view of the slider 113, and as can be seen the magnetic head
including an inductive write head and a read sensor, is located at
a trailing edge of the slider. The above description of a typical
magnetic disk storage system and the accompanying illustration of
FIG. 1 are for representation purposes only. It should be apparent
that disk storage systems may contain a large number of disks and
actuators, and each actuator may support a number of sliders.
[0024] FIG. 3 shows a view of a magnetic read head 300 according to
a possible embodiment of the invention as viewed from the air
bearing surface. FIG. 3 shows a magnetic read sensor, 300 that
includes a sensor stack 302 that is sandwiched between first and
second magnetic shields 304, 306. The magnetic shields 304, 306 can
be constructed of an electrically conductive, magnetic material
such as NiFe so that they can function as electrical leads for
supplying a sense current to the sensor stack 302.
[0025] The sensor stack 302 can include a magnetic pinned layer
structure 308, a magnetic free layer structure 310 and a
non-magnetic barrier or spacer layer 312, sandwiched between the
magnetic pinned layer structure 308 and magnetic free layer
structure 310. If the sensor 300 is a giant magnetoresistive (GMR)
sensor, then the layer 312 can be a non-magnetic, electrically
conductive material such as Cu or AgSn. If the sensor 300 is a
tunnel junction magnetic sensor (TMR), then the layer 312 can be a
non-magnetic, electrically insulating layer such as MgO.
[0026] The pinned layer structure can be an anti-parallel pinned
structure including a first magnetic layer (AP1) 314, a second
pinned layer (AP2) 316 and a non-magnetic, anti-parallel coupling
layer such as Ru 318 sandwiched between the first and second
magnetic layers (AP1 and AP2 layers) 314, 316. The first magnetic
layer 314 can be exchange coupled with a layer of antiferromagnetic
material AFM layer 320, which can be a material such as IrMn or
PtMn. This exchange coupling can be used to pin the magnetization
of the first magnetic layer 314 in a first direction perpendicular
to the air bearing surface as indicated by arrow head symbol 322.
Anti-parallel coupling between the first and second magnetic layers
314, 316 pins the magnetization of the second magnetic layer 316 in
a second direction that is perpendicular to the air bearing surface
and anti-parallel with the first direction, as indicated by arrow
tail symbol 324.
[0027] The magnetic free layer 310 has a magnetization that is
generally oriented parallel with the air bearing surface as
indicated by arrow 326, but that is free to move in response to an
external magnetic field. The magnetization 326 can be biased by
magnetic bias structures 328, 330 at either side of the sensor
stack. The bias structures 328, 330 can be hard or soft bias
structures, and can be separated from the sensor stack and from the
bottom shield 304 by a thin insulation layer 332 such as
alumina.
[0028] The sensor stack 302 can also include a seed layer 334 at
its bottom. The seed layer can be provided to initiate a desired
grain growth in the above formed layers. In addition, the sensor
stack 302 can include a non-magnetic, electrically conductive
capping layer 336 at its top, above the free layer 310. The capping
layer 336 can be used to protect the free layer 310 from damage or
corrosion during manufacture of the sensor 300.
[0029] FIG. 4 is a side, cross sectional view as seen from line 4-4
of FIG. 3. In FIG. 4 it can be seen that the free layer structure
310 extends to a first stripe height SH1 as measured from the air
bearing surface ABS. The pinned layer structure 308 extends to a
second stripe height SH2, also measured from the air bearing
surface, the second stripe height SH2 being longer than the first
stripe height SH1. The first stripe height SH1 defines the
effective, magnetic stripe height of the sensor. However, the
extended stripe height SH2 of the pinned layer structure improves
pinning strength of the pinned layer structure 308. As sensor size
becomes smaller in order to provide increased data density,
maintaining strong pinning of the pinned layer structure becomes
more difficult. Extending the pinned 308 layer as shown improves
this pinning strength, thereby allowing for the production of a
very small, high resolution magnetic sensor that is also reliable
and robust. Extending the pinned layer structure 308 as shown in
FIG. 4 improves pinning in multiple ways. First the area of
exchange coupling between the magnetic layer 314 and the AFM layer
320 is increased. Also, the extended shape of the magnetic layers
314, 316 provides a shape enhanced magnetic anisotropy that also
improves pinning.
[0030] As can be seen in FIG. 4, the free layer 310 has a back edge
402 that defines an angle 404 with respect to a plane that is
parallel with the air bearing surface ABS. The inventors have
discovered that the magnitude of this angle 404 has a significant
effect on sensor performance. If the angle 404 is too small, there
is a risk of damage to the pinned layer structure during an ion
milling process used to define the stripe height SH1 of the free
layer 310 (this ion milling will be discussed below). Therefore, if
this angle 404 is too small, the magnetic resonance frequency of
the pinned layer 308 suffers and pinning strength is thereby
reduced. This can result in a loss of pinning which can lead to
catastrophic failure of the magnetic sensor 300.
[0031] On the other hand if the angle 404 is too large, magnetic
performance of the sensor 300 (more specifically the MR ratio)
suffers. If the angle 404 becomes too large, the variation in the
direction of the magnetization 326 (FIG. 3) increases, and the MR
ratio is degraded. Therefore, optimal sensor performance can be
achieved by ensuring that the angle 404 is between 6 and 10
degrees. A method for forming the sensor 300 with such an angle 404
is described herein below.
[0032] FIGS. 5-12 show a magnetic sensor in various intermediate
stages of manufacture in order to illustrate a method of
manufacturing a magnetic sensor having a desired free layer back
edge configuration. With reference now to FIG. 5 a bottom shield
502 is formed having a smooth planar upper surface. A series of
sensor layers 500 is deposited over the shield 502. The series of
sensor layers 500 can include a seed layer 504, a pinned layer
structure 506 a non-magnetic spacer or barrier layer 508, a
magnetic free layer 510 and a capping layer 512. The pinned layer
structure, while being shown as a single layer for purposes of
simplicity in FIG. 5, can include multiple layers such as the
layers 320, 314, 316, 318 of FIGS. 3 and 4. In FIG. 5, the location
of an air bearing surface plane is indicated by the dashed line
denoted as ABS.
[0033] With reference to FIG. 6 a mask 602 is formed over the
sensor layers. The mask 602 is preferably a bi-layer mask having an
overhanging portion 602 as shown, and has a back edge 604 that is
located a desired distance from the air bearing surface plane ABS
so as to define a first stripe height, as will be seen.
[0034] With reference now to FIG. 7, an ion milling process is
performed to remove portions of the capping layer 512 and magnetic
free layer 510 that are not protected by the mask 602. The ion
milling is terminated when the barrier/spacer layer 508 is reached,
thereby leaving the pinned layer 506 extending beyond the free
layer 510. More preferably, the ion milling is terminated
immediately before the spacer/barrier layer 508 has been reached,
so that even though the angle 702 of the back edge of the free
layer 510 is between 6 and 10 degrees there is no possibility of
shunting due to re-deposition of material from the ion milling
process. The ion milling is performed in such a manner as to form a
back edge 702 of the magnetic free layer 510 that defines an angle
704 that is 6 to 10 degrees with respect to the ABS plane. In other
words, the angle 704 is 80 to 84 degrees with respect to the plane
of the as deposited layers 504, 506, 508, 510, 512. To achieve this
effect, the ion milling is preferably performed at an angle 706
that is 6-10 degrees with respect to normal. Performing the ion
milling in this manner minimizes the re-deposition of material on
the back edge 702 of the sensor 510 and on the barrier/spacer layer
508 or pinned layer 506.
[0035] With reference now to FIG. 8 a non-magnetic, electrically
insulating fill layer such as alumina 802 is deposited to at least
the level of the capping layer 512. The fill layer 802 can be
deposited by a process such as sputter deposition. Then, the mask
602 is removed. The mask 602 can be removed by a chemical liftoff
process or other suitable process. The bi-layer shape of the mask
602 allows the liftoff chemicals to reach the mask 602, thereby
facilitating removal of the mask 602. An optional chemical
mechanical polishing process may also be performed to planarize the
structure, leaving a structure with a smooth planar surface as
shown in FIG. 9.
[0036] With reference to FIG. 10, another mask 1002 is formed over
the sensor material 500 and fill layer 802. This mask has a back
edge 1004 that is located so as to define a back edge of the pinned
layer, or second stripe height, as will be seen. A second ion
milling can then be performed. The second ion milling can be
performed until the bottom shield 502 has been reached, leaving a
structure as shown in FIG. 11. Then, a second process of fill layer
deposition, mask liftoff and optional chemical mechanical polishing
can be performed, leaving a structure as shown in FIG. 12 with a
second fill layer 1202.
[0037] FIGS. 13 and 14 show graphs that help to illustrate the
advantages of forming a sensor with the desired back edge angle 404
described above with reference to FIG. 4. With particular reference
to FIG. 13 it can be seen that the sensor performance (MR ratio)
remains substantially constant until the free layer back edge angel
reaches about 10 degrees. At this point the sensor performance
drops off linearly with increasing free layer back edge angle. On
the other hand, with reference to FIG. 14 it can be seen that the
pinning strength as determined by magnetic resonance frequency of
the pinned layer structure 308 (FIGS. 3 and 4) increases until the
free layer back edge angle reaches 10 degrees. Therefore, it can be
seen that an optimal balance of pinning robustness and sensor
performance can be achieved when the free layer back edge angle is
maintained at between 6 and 10 degrees.
[0038] While various embodiments have been described above, it
should be understood that they have been presented by way of
example only and not limitation. Other embodiments falling within
the scope of the invention may also become apparent to those
skilled in the art. Thus, the breadth and scope of the invention
should not be limited by any of the above-described exemplary
embodiments, but should be defined only in accordance with the
following claims and their equivalents.
* * * * *