U.S. patent application number 15/199833 was filed with the patent office on 2018-01-04 for microwave assisted magnetic recording head having spin torque oscillator frequency detection.
The applicant listed for this patent is HGST Netherlands B.V.. Invention is credited to Keiichi Nagasaka, Susumu Okamura, Masashige Sato, Yo Sato.
Application Number | 20180005651 15/199833 |
Document ID | / |
Family ID | 60788922 |
Filed Date | 2018-01-04 |
United States Patent
Application |
20180005651 |
Kind Code |
A1 |
Sato; Masashige ; et
al. |
January 4, 2018 |
MICROWAVE ASSISTED MAGNETIC RECORDING HEAD HAVING SPIN TORQUE
OSCILLATOR FREQUENCY DETECTION
Abstract
A magnetic write head having a spin torque oscillator with a
magnetic field sensor for accurately determining magnetic field
oscillation frequency. The spin torque oscillator has one or more
tunnel junction (TMR) sensors formed at the side of the spin torque
oscillator. The TMR sensor advantageously detects a magnetic field
signal that is an additive signal of both fields from the spin
polarization layer and the magnetic field generation layer, thereby
providing efficient detection of magnetic field and associated
oscillation frequency.
Inventors: |
Sato; Masashige; (Atsugi,
JP) ; Okamura; Susumu; (Fujisawa, JP) ; Sato;
Yo; (Odawara, JP) ; Nagasaka; Keiichi;
(Isehara, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HGST Netherlands B.V. |
Amsterdam |
|
NL |
|
|
Family ID: |
60788922 |
Appl. No.: |
15/199833 |
Filed: |
June 30, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11B 5/3146 20130101;
G11B 5/3163 20130101; G11B 2005/0024 20130101; G11B 5/314
20130101 |
International
Class: |
G11B 5/39 20060101
G11B005/39 |
Claims
1. A magnetic write head, comprising: a spin torque oscillator
having a leading edge, a trailing edge and a side extending from
the leading edge to the trailing edge; and a magnetic sensor formed
at the side of the spin torque oscillator.
2. The magnetic write head as in claim 1, wherein the spin torque
oscillator further comprises a magnetic spin polarization layer, a
magnetic field generation layer, and a non-magnetic interlayer
located between the magnetic spin polarization layer and the
magnetic field generation layer.
3. The magnetic write head as in claim 1, wherein the magnetic
sensor includes a non-magnetic barrier layer, a magnetic layer and
a non-magnetic electrically conductive lead.
4. The magnetic write head as in claim 1, wherein the magnetic
sensor further includes a non-magnetic barrier layer formed on the
side of the spin torque oscillator, a magnetic layer formed on the
non-magnetic barrier layer, and a non-magnetic, electrically
conductive lead, wherein the non-magnetic barrier layer is located
between the magnetic layer and the spin torque oscillator and the
magnetic layer is located between the lead and the non-magnetic
barrier layer.
5. The magnetic write head as in claim 3, wherein the non-magnetic
barrier layer comprises Mg--O, and the magnetic layer comprises
Co--Fe--B.
6. The magnetic write head as in claim 3, wherein the non-magnetic,
electrically conductive lead is connected with circuitry for
measuring a change in electrical resistance of the non-magnetic
barrier layer.
7. The magnetic write head as in claim 3, wherein the non-magnetic,
electrically conductive lead is connected with circuitry for
measuring a voltage across the non-magnetic barrier layer and the
magnetic layer.
8. The magnetic write head as in claim 1, wherein the spin torque
oscillator and the magnetic sensor are both located between a
magnetic write pole and a trailing magnetic shield.
9. The magnetic write head as in claim 1, further comprising a
second magnetic sensor located at a second side of the spin torque
oscillator.
10. The magnetic write head as in claim 1, wherein the side of the
spin torque oscillator is a stripe height defining side located
opposite a media facing surface.
11. A magnetic data recording system, comprising: a housing; a
magnetic media held within the housing; an actuator mounted within
the housing; a slider connected with the actuator for movement
adjacent to a surface of the magnetic media; and a magnetic
recording head formed on the slider, the magnetic recording head
including: a spin torque oscillator having a leading edge, a
trailing edge and a side extending from the leading edge to the
trailing edge; and a magnetic sensor formed at the side of the spin
torque oscillator.
12. The magnetic data recording system as in claim 11, wherein the
spin torque oscillator further comprises a magnetic spin
polarization layer, a magnetic field generation layer, and a
non-magnetic interlayer located between the magnetic spin
polarization layer and the magnetic field generation layer.
13. The magnetic data recording system as in claim 11, wherein the
magnetic sensor includes a non-magnetic barrier layer, a magnetic
layer and a non-magnetic electrically conductive lead.
14. The magnetic data recording system as in claim 11, wherein the
magnetic sensor further includes a non-magnetic barrier layer
formed on the side of the spin torque oscillator, a magnetic layer
formed on the non-magnetic barrier layer, and a non-magnetic,
electrically conductive lead, wherein the non-magnetic barrier
layer is located between the magnetic layer and the spin torque
oscillator and the magnetic layer is located between the lead and
the non-magnetic barrier layer.
15. The magnetic data recording system as in claim 14, wherein the
non-magnetic barrier layer comprises Mg--O, and the magnetic layer
comprises Co--Fe--B.
16. The magnetic data recording system as in claim 13, wherein the
non-magnetic, electrically conductive lead is connected with
circuitry for measuring a change in electrical resistance of the
non-magnetic barrier layer.
17. The magnetic data recording system as in claim 13, wherein the
non-magnetic, electrically conductive lead is connected with
circuitry for measuring a voltage across the non-magnetic barrier
layer and the magnetic layer.
18. The magnetic data recording system as in claim 11, wherein the
spin torque oscillator and the magnetic sensor are both located
between a magnetic write pole and a trailing magnetic shield.
19. The magnetic data recording system as in claim 11, further
comprising a second magnetic sensor located at a second side of the
spin torque oscillator.
20. The magnetic data recording system as in claim 11, wherein the
side of the spin torque oscillator is a stripe height defining side
located opposite a media facing surface.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to magnetic data recording,
and more particularly to a magnetic write head having a magnetic
spin torque oscillator located between a magnetic write pole and a
magnetic trailing shield and having a structure for detecting the
magnetic oscillation frequency of the spin torque oscillator.
BACKGROUND
[0002] At the heart of a computer is an assembly that is referred
to as a magnetic disk drive. The magnetic disk drive includes a
rotating magnetic disk, write and read heads that are suspended by
a suspension arm adjacent to a surface of the rotating magnetic
disk and an actuator that swings the suspension arm to place the
read and write heads over selected tracks on the rotating disk. The
read and write heads are directly located on a slider that has an
air beating surface (ABS). The suspension arm biases the slider
into contact with the surface of the disk when the disk is not
rotating, but when the disk rotates air is swirled by the rotating
disk. When the slider rides on the air bearing, the write and read
heads are employed for writing magnetic impressions to and reading
magnetic impressions from the rotating disk. The write and read
heads are connected to processing circuitry that operates according
to a computer program to implement the writing and reading
functions.
[0003] The write head includes at least one coil, a write pole and
one or more return poles. When current flows through the coil, a
resulting magnetic field causes a magnetic flux to flow through the
coil, which results in a magnetic write field emitting from the tip
of the write pole. This magnetic field is sufficiently strong that
it locally magnetizes a portion of the adjacent magnetic media,
thereby recording a bit of data. The write field then, travels
through a magnetically soft under-layer of the magnetic medium to
return to the return pole of the write head.
[0004] A magnetoresistive sensor such as a Giant Magnetoresistive
(GMR) sensor, a Tunnel Junction Magnetoresistive (TMR) sensor or a
scissor type magnetoresistive sensor can be employed to read a
magnetic signal from the magnetic media. The magnetoresistive
sensor has an electrical resistance that changes in response to an
external magnetic field. This change in electrical resistance can
be detected by processing circuitry in order to read magnetic data
from the magnetic media.
SUMMARY
[0005] The present invention provides a magnetic write head for
microwave assisted magnetic recording. The magnetic write head
includes a spin torque oscillator having a leading edge, a trailing
edge and a side extending from the leading edge to the trailing
edge. The write head also includes a magnetic sensor formed at the
side of the spin torque oscillator.
[0006] The magnetic sensor formed at the side of the spin torque
oscillator advantageously detects magnetic field from the spin
torque oscillator in order to accurately determine the oscillation
frequency of the oscillating magnetic field produced by the spin
torque oscillator.
[0007] The spin torque oscillator can be formed with a magnetic
spin polarization layer, a magnetic field generation layer, and a
non-magnetic interlayer located between the spin polarization layer
and the magnetic field generation layer. The magnetic sensor formed
at the side of the spin torque oscillator advantageously detects
magnetic field from both the magnetic field generation layer and
also the magnetic spin polarization layer and does so in an
additive manner to produce a strong signal for accurately
determining the magnetic oscillation frequency of the field
generated by the spin torque oscillator.
[0008] The magnetic sensor formed at the side of the spin torque
oscillator can be in the form of a tunnel junction sensor,
including a non-magnetic barrier layer such as Mg--O formed at the
side of the spin torque oscillator, a magnetic layer such as
Co--Fe--B formed on the non-magnetic barrier layer, and an
electrically conductive lead layer formed on the magnetic
layer.
[0009] These and other features and advantages of the invention
will be apparent upon reading of the following detailed description
of the embodiments taken in conjunction with the figures in which
like reference numeral 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 side, cross-sectional, schematic view of a
magnetic read write head;
[0013] FIG. 3 is an enlarged view of a spin torque oscillator
structure for use with the write head of FIG. 2, as seen from the
media facing surface;
[0014] FIG. 4 is a side, cross sectional view of a spin torque
oscillator for use with the magnetic read write head of FIG. 2
according to an alternate embodiment; and
[0015] FIGS. 5-7 are views of a spin torque oscillator in various
intermediate stages of manufacture illustrating a method of
manufacturing a spin torque oscillator according to an
embodiment.
DETAILED DESCRIPTION
[0016] 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.
[0017] Referring now to FIG. 1, there is shown a disk drive 100.
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 may be in
the form of annular patterns of concentric data tracks (not shown)
on the magnetic disk 112.
[0018] 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 the slider 113 against
the disk surface 122. Each actuator arm 119 is attached to an
actuator means 127. The actuator cans 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 the
controller 129.
[0019] 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 the suspension 115 and supports the slider 113 off
and slightly above the disk surface by a small, substantially
constant spacing during normal operation.
[0020] 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, 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
the slider 113 to the desired data track on the media 112. Write
and read signals are communicated to and from write and read heads
121 by way of recording channel 125.
[0021] With reference to FIG. 2, a magnetic read/write head 200 can
include a read head 202 and a write head 204. The read head 202 can
include a read sensor 206 such as a giant magnetoresistive sensor
or tunnel junction sensor, which can be sandwiched between first
and second magnetic shields 208, 210. The space between the read
and write heads 202, 204 can be filled with a non-magnetic,
electrically insulating material 212, as can the space behind the
sensor 206 between the shields 208, 210.
[0022] The write head 204 can include a magnetic write pole 214 and
a magnetic return pole 216, both of which can extend to a media
facing surface MFS. The magnetic return pole 216 can be connected
with the magnetic write pole 214 by a magnetic back gap layer 218
and a magnetic shaping layer 220. The magnetic shaping layer 220
helps to channel magnetic flux to the tip of the magnetic write
pole 214. The write head 204 can also include a trailing magnetic
shield 222 formed near the trailing edge of the write pole 214 at
the media facing surface MFS. The trailing magnetic shield 222 can
be connected with the back portion of the write head 204 by a
trailing magnetic return pole 224.
[0023] The write head 204 also includes a non-magnetic,
electrically conductive write coil 226 (shown in cross section in
FIG. 2) that can pass above and below the write pole 214. The write
coil 226 can be embedded in a non-magnetic, electrically insulating
material such as alumina 228. When an electrical current flows
through the write coils 226, a magnetic field is generated. This
causes a magnetic flux to flow through the write pole 214. The
resulting write field travels from the tip of the write pole 214 to
a magnetic media (not shown in FIG. 2) and then travels back
through the return pole 216. Because the return pole 216 has a
larger cross section at the media facing surface NHS than does the
write pole 214 the return of the magnetic write field to the return
pole 216 does not erase the previously recorded bit of data.
[0024] As demands for increased data density require ever smaller
magnetic bit sizes, the magnetic bits recorded to a recording media
become inherently, magnetically unstable. In order to make the
recorded magnetic bits more stable, the magnetic media can be
designed to have an increased magnetic anisotropy, and or magnetic
coercivity. This however makes the media harder to record to,
especially with the smaller write pole required to record the
smaller magnetic bit.
[0025] One way to overcome this challenge is to generate an
oscillating magnetic field just at or adjacent to the location of
the write pole. This oscillating magnetic field temporarily reduces
the magnetic anisotropy of the magnetic media, making it easier to
record to. To this end, as shown in FIG. 2 a magnetic oscillator
such as a spin torque oscillator 230 can be employed. The spin
torque oscillator 230 can be located between the write pole 214 and
the trailing magnetic shield 222. The spin torque oscillator 230
generates an oscillating magnetic field that moves in a
precessional manner as indicated by arrow 308.
[0026] A current source 234 can be provided to supply an electrical
current to flow through the spin torque oscillator 230. The current
source 234 can be connected with the magnetic write head 204 so
that current flows between the write pole 214 and the trailing
shield 222 through the spin torque oscillator 230. This current
causes the spin torque oscillator to generate the oscillating
magnetic field 308. An electrically insulating layer 235 can be
provided at the back of the write head 204 to prevent this
electrical current from being shunted through the back portion of
the write head 204.
[0027] FIG. 3 shows an enlarged view of the spin torque oscillator
230 according to one embodiment. The spin torque oscillator 230
includes two magnetic layers 302, 304 separated by a non-magnetic
interlayer 306 located between the magnetic layers 302, 304. The
first magnetic layer 302 is a spin polarization layer, and the
second magnetic layer 304 is a magnetic field generation layer.
When a current flows through the spin torque oscillator as
indicated by arrow i, in a direction perpendicular to the layers
302, 304, 306, the electrons flowing through the spin polarization
layer 302 become spin polarized due to the magnetization of the
spin polarization layer 302. When these spin polarized electrons
flow from the spin polarization layer 302, through the interlayer
306 to the field generation layer 304, they impart a spin torque on
the field generation layer 304. This spin torque causes the
magnetization of the field generation layer 304 to oscillate as
indicated by arrow 308. The magnetic oscillation 308 of the field
generation layer 304 can impart an oscillation 314 in the spin
polarization layer 302 as a result of magnetostatic coupling
between the magnetic layers 302, 304. In addition to the layers
302, 304, 306, the spin torque oscillator 230 may also include a
seed layer 310 to promote a desired grain structure in the above
formed layers 302, 304, 306 and may also include a capping layer
312 at the end opposite the seed layer 310.
[0028] An important design parameter for magnetic recording systems
that employ spin torque oscillators is the frequency of the
magnetic oscillation of the spin torque oscillation. A magnetic
media has an optimal magnetic frequency oscillation range for
promoting the writing of magnetic data to the magnetic media.
Therefore, in order to maximize writing efficiency, the magnetic
oscillation frequency of the spin torque oscillator is preferably
matched to the magnetic media of the magnetic recording system.
[0029] However, previously there has not been an effective way to
measure the oscillation frequency of the spin torque oscillator.
Measuring the voltage across the spin torque oscillator in a
direction perpendicular to the layers 302, 304, 306 does not
provide an effective measure of the magnetic field oscillation
frequency. This voltage change is a factor of the relative angles
of the oscillations 308, 314 and they combine in a subtractive,
rather than additive manner, resulting in a weak signal.
Furthermore, use of a conventional field sensor, such as a sensor
wire located adjacent to the spin torque oscillator 230 also fails
to provide an effective measure of oscillation frequency. This is
because spin torque oscillators operate at very high frequencies at
which conventional magnetic field sensors saturate.
[0030] Therefore, in order to accommodate this long felt, but unmet
need, the write head is provided with tunnel junction magnetic
sensors 316 formed at the sides of (or behind the spin torque
oscillator 230. The tunnel junction magnetic sensor 316 can be at
one side, or can be at both sides of the sensor as shown. As shown
in FIG. 3, the magnetic tunnel junction sensor 316 includes a
non-magnetic barrier layer 318, a magnetic layer 320 and a
non-magnetic, electrically conductive side lead 322. The side lead
322 is electrically insulated from the shield 222 by an
electrically insulating layer 325, which may be a material such as
alumina.
[0031] The non-magnetic barrier layer 318 can be a material such as
Mg--O, and as shown in FIG. 3, the non-magnetic barrier layer 318
can be thicker over the write pole 214 and thinner along the side
of the spin torque oscillator 230. The thicker barrier layer 214
over the write pole 214 will prevent current shunting to the write
pole 214, and the barrier layer 318 should be thin enough along the
side of the spin torque oscillator 230 to allow quantum tunneling
of charge carriers there-through in a manner similar to a standard
tunnel junction magnetic sensor as might be used to read a magnetic
signal from a magnetic media. The magnetic layer 320 can be
constructed of Co--Fe--B, and the side leads 322 can be constructed
of an electrically conductive material such as Cu or Au.
[0032] As a result of spin tunneling of electrons through the
barrier layer 318, the electrical resistance between the spin
torque oscillator 230 and the lead 322 will vary depending upon the
relative directions of magnetizations of the magnetic layers 302,
304 and the magnetic layer 320 of the tunnel junction sensor.
Therefore, because the magnetization 308, 314 of the magnetic
layers 302, 304 are oscillating as described above, the resistance
across the harrier layer will 318 will vary with the magnetic
oscillations 308, 314. What's more, this variation in electrical
resistance will be additive for both the magnetic oscillations 314,
308. By measuring the electrical resistance between the spin torque
oscillator 230 and the lead 322, the frequency of the oscillations
308, 314 can be efficiently and reliably measured. The lead 322
effectively forms a third electrical terminal, in addition to those
provided by the write pole 214 and trailing shield 222. The lead
322 and either or both of the write pole 214 and/or trailing shield
222 can be connected with circuitry 324 that can apply a voltage
between the spin torque oscillator 230 and the lead 322. The
circuitry 324 can measure the change in resistance across the
layers 318, 320 and can also determine the frequency of the
electrical resistance change. Therefore, the frequency of magnetic
oscillation produced by the spin torque oscillator 230 can be
accurately measured.
[0033] FIG. 4 illustrates an alternate embodiment and shows a cross
sectional view along a plane that is perpendicular to the media
facing surface MFS. FIG. 4 shows a tunnel junction sensor 316
located at the back edge (stripe height) of the spin torque
oscillator 230. The structure of the tunnel junction sensor 316 can
be similar to that described above, having a non-magnetic
electrically insulating barrier layer 318, magnetic layer 320 and
an electrically conductive lead 322. Again, the layer 322 is
electrically insulated from the lead 222 by an electrically
insulating layer 325. It should also be pointed out that, the
tunnel junction sensor 316 formed at the back edge of the spin
torque oscillator 230 can be in lieu of those formed at the sides
as described above with reference to FIG. 3. Or, alternatively, the
back edge tunnel junction sensor 316 can be in addition to those
formed at the sides so as to form a tunnel junction sensor 316 that
wraps around the sides and back edge of the spin torque
oscillator.
[0034] The above described side formed tunnel junction sensors 316
provide a way of producing a strong signal for determining the
frequency of the magnetic oscillation of the magnetizations 308,
314 produced by the spin torque oscillator 230. If a signal were
measured across the spin torque oscillator 230 in a direction
perpendicular to the planes of the layers 302, 304, 306
(essentially using the spin torque oscillator 230 as a giant
magnetoresistive (GMR) sensor) the signal would be subtractive,
with the signal resulting from oscillation 314 being subtracted
from the signal resulting from oscillation 308. The resulting
signal would, therefore, be very week and ineffective. On the other
hand, using the side tunnel junction sensors 316, the signals from
the magnetizations 308, 314 are additive rather than subtractive,
resulting in a very strong effective signal.
[0035] The side tunnel junction sensors 316 can be used to
determine the actual oscillation frequency of the spin torque
oscillator 230 early in the manufacture process. In this way, if
the frequency is not within a desired range, the head can be
scrapped without unnecessary further manufacturing. In addition,
the use of the side tunnel junction sensors 316 can be used to
determine the oscillation frequency during manufacture, and the
various manufactured heads can be grouped by oscillation frequency
to be later matched up with magnetic media most suitable for use in
that frequency range. This can further reduce waste by allowing the
head use to be optimized while avoiding the need to scrap heads or
entire magnetic recording systems.
[0036] FIGS. 5-7 illustrate a magnetic spin torque oscillator in
various intermediate stages of manufacture in order to illustrate a
method of manufacturing a magnetic write head such as those
described above. With reference to FIG. 5, the magnetic layers of
the spin torque oscillator are deposited over the magnetic write
pole 214. These layers can include: a seed layer 310; a first
magnetic layer 302 deposited over the seed layer 310; a
non-magnetic intermediate layer 306 deposited over the first
magnetic layer 302; a second magnetic layer 304 deposited over the
non-magnetic intermediate layer; and a capping layer 312 deposited
over the second magnetic layer 304. A mask 502 is formed over these
layers, the mask being configured to define a width and/or stripe
height of the spin torque oscillator.
[0037] With reference to FIG. 6, a material removal process such as
ion milling is performed to remove portions of the layers 310, 302,
306, 304, 312 that are not protected by the mask 502. A
non-magnetic, electrically insulating barrier layer such as Mg--O
318 is then deposited. The barrier layer 318 is deposited in such a
manner as to have a thickness at the sides of the layers 302, 306,
304 that allows it to function as a barrier layer and to be thicker
over the write pole 214 so as to prevent current shunting through
the write pole 214. Then, a magnetic layer 320 such as CoFeB is
deposited over the barrier layer 318, and an electrically
conductive lead 322 such as Cu or Au is deposited over the magnetic
layer 320. An electrically insulating layer 325 is deposited over
the lead material 322, and can be a material such as alumina. Then,
with reference to FIG. 7, a mask lift-off process and/or chemical
mechanical polishing is performed to remove the mask 502 (FIG. 6)
and planarize the surface. The insulating layer 325 is deposited at
a level and thickness such that it will remain after the mask
removal and/or chemical mechanical polishing.
[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 inventions
should not be limited by any of the above-described exemplary
embodiments, but should be defined only in accordance with the
following Maims and their equivalents.
* * * * *