U.S. patent application number 16/250697 was filed with the patent office on 2020-07-23 for permanent magnet assisted magnetic recording.
The applicant listed for this patent is Headway Technologies, Inc.. Invention is credited to Yan Wu.
Application Number | 20200234728 16/250697 |
Document ID | / |
Family ID | 71125058 |
Filed Date | 2020-07-23 |
United States Patent
Application |
20200234728 |
Kind Code |
A1 |
Wu; Yan |
July 23, 2020 |
PERMANENT MAGNET ASSISTED MAGNETIC RECORDING
Abstract
A perpendicular magnetic recording writer is disclosed with a
permanent magnet (PM) formed within a write gap (WG) that is
between a main pole (MP) trailing side and a trailing shield. The
PM has a magnetization that is anti-parallel to a WG field
(H.sub.WG) when a transition is written thereby enhancing the MP
field on a magnetic bit, and generates a PM field that assists the
MP field. When H.sub.WG becomes saturated after the transition is
written and exceeds PM coercivity that is from 500 Oe to 8000 Oe,
PM magnetization flips to an opposite direction and reduces the MP
field thereby improving adjacent track erasure. The PM may be at
the air bearing surface (ABS) or recessed up to 50 nm from the ABS,
and has a down-track thickness less than the WG thickness, and a
cross-track width .ltoreq.to the track width of the MP trailing
side.
Inventors: |
Wu; Yan; (Cupertino,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Headway Technologies, Inc. |
Milpitas |
CA |
US |
|
|
Family ID: |
71125058 |
Appl. No.: |
16/250697 |
Filed: |
January 17, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11B 5/23 20130101; G11B
5/11 20130101; G11B 5/6082 20130101; G11B 5/4826 20130101; G11B
5/1278 20130101 |
International
Class: |
G11B 5/127 20060101
G11B005/127; G11B 5/60 20060101 G11B005/60; G11B 5/11 20060101
G11B005/11; G11B 5/48 20060101 G11B005/48; G11B 5/23 20060101
G11B005/23 |
Claims
1. A perpendicular magnetic recording (PMR) writer, comprising: (a)
a main pole (MP) with a MP tip having a leading side and a trailing
side, the leading side adjoins a leading gap at an air bearing
surface (ABS), and the trailing side has a track width (TW) and
adjoins a write gap (WG) at the ABS, and has a trailing edge formed
on a first plane that is orthogonal to the ABS; (b) a shield
structure comprising a first trailing shield (TS) on the write gap;
and (c) a permanent magnet (PM) formed within the WG and between
the MP tip and first TS wherein the PM has a cross-track width w
where w<TW, a down-track thickness that is less than a WG
thickness, and a backside that is less than a throat height of a
leading shield from the ABS, and the PM is configured with a
magnetization that is opposite to a WG field (H.sub.WG) at an onset
of writing a transition thereby enhancing a MP field, and the PM
magnetization flips to a direction parallel to H.sub.WG when
H.sub.WG exceeds a PM coercivity after the transition is
written.
2. The PMR writer of claim 1 wherein the PM has a front side at the
ABS, and the backside is at a height that is from 20 nm to 80 nm
from the ABS.
3-4. (canceled)
5. The PMR writer of claim 1 wherein the PM is one of Co, Fe, Ni,
CoPt, CoPd, FePt, or a multilayer structure with one or more of Co,
Fe, Ni, Pt, Pd, Ir, Ru, Cr, or alloys thereof.
6. The PMR writer of claim 1 wherein the PM is a polycrystalline
structure comprised of a CoPtCr--SiO.sub.2 or FePt--SiO.sub.2
composite.
7. The PMR writer of claim 1 wherein the PM coercivity is from 500
Oe to 8000 Oe.
8. The PMR writer of claim 1 wherein the PM has a top surface and a
bottom surface that are between the first TS and MP tip.
9. The PMR writer of claim 1 wherein the PM has a magnetic field
that assists the MP field during the process of writing a
transition on a magnetic bit proximate to the MP tip and PM.
10. The PMR writer of claim 1 further comprising: (a) a side gap
that contacts a side of the main pole formed between the trailing
side and leading side on each side of a center plane that bisects
the MP tip in a direction orthogonal to the ABS and the first
plane; (b) a side shield contacting each side gap; (c) the leading
shield adjoining a bottom surface of the leading gap at a second
plane that is parallel to the first plane, and contacting a bottom
surface of each side shield; and (d) a second trailing shield
formed on the first TS and on a top surface of each side shield at
the first plane thereby forming an all wrap around (AWA) shield
structure.
11. A head gimbal assembly (HGA), comprising: (a) a slider on which
the PMR writer of claim 1 is formed; and (b) a suspension that has
a flexure to which the slider is joined, a load beam with one end
connected to the flexure, and a base plate connected to the other
end of the load beam.
12. A magnetic recording apparatus, comprising: (a) the HGA of
claim 11; (b) a magnetic recording medium positioned opposite to
the slider; (c) a spindle motor that rotates and drives the
magnetic recording medium; and (d) a device that supports the
slider, and that positions the slider relative to the magnetic
recording medium.
13-28. (canceled)
29. The PMR writer of claim 1 wherein the PM has a front side that
is recessed a distance greater than 0 nm but less than or equal to
50 nm from the ABS.
30. The PMR writer of claim 29 wherein the PM has a backside that
is at a height from 20 nm to 80 nm from the PM front side.
Description
RELATED PATENT APPLICATIONS
[0001] This application is related to the following: U.S. Pat. No.
10,014,021; and Docket # HT17-045, Ser. No. 16/037,197, filing date
7/17/18; assigned to a common assignee and herein incorporated by
reference in their entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to a design for a
perpendicular magnetic recording (PMR) writer wherein a permanent
magnet (PM) having a magnetization opposite to that of the WG field
is inserted in the write gap (WG), and generates a magnetic field
that enhances the main pole (MP) field on the magnetic medium at
the start of writing a transition, but PM magnetization flips to an
opposite direction when the WG field increases beyond the
coercivity of the PM after the transition is written thereby
reducing the MP field and improving adjacent track erasure
(ATE).
BACKGROUND
[0003] As the data areal density in hard disk drive (HDD)
increases, critical dimensions in the write heads are required to
be made in smaller sizes in order to be able to write small media
bits. However, as the main pole dimensions (track width and
down-track thickness) shrink, its writability degrades. To improve
writability, new technology is being developed that assists writing
by either increasing the effective write field generated by the
heads or by heating up the media to lower the coercivity in the
media near the area when the transition is written. Two approaches
currently being investigated are heat assisted magnetic recording
(HAMR), and microwave assisted magnetic recording (MAMR), that is
described by J-G. Zhu et al. in "Microwave Assisted Magnetic
Recording", IEEE Trans. Magn., vol. 44, pp. 125-131 (2008).
Although MAMR has been in development for a number of years, it is
not shown enough promise to be introduced into any products yet. In
particular, a difficult challenge is to find a spin torque
oscillator (STO) film that is thin enough to fit into the small
write gap required for state of the art products while providing a
high magnetic moment in the oscillation layer to generate a
sufficient radio-frequency (RF) field for the microwave assist
effect.
[0004] Spin transfer (spin torque oscillator or STO) devices are
based on a spin-transfer effect that arises from the spin dependent
electron transport properties of ferromagnetic-non-magnetic
spacer-ferromagnetic multilayers. When a spin-polarized current
passes through a magnetic multilayer in a CPP (current
perpendicular to plane) configuration, the magnetic moment of
electrons incident on a ferromagnetic layer interacts with magnetic
moments of the ferromagnetic layer near the interface between the
ferromagnetic and non-magnetic spacer. Through this interaction,
the electrons transfer a portion of their angular momentum to the
ferromagnetic layer. As a result, spin-polarized current can switch
the magnetization direction of the ferromagnetic layer if the
current density is sufficiently high.
[0005] In a PMR writer, the main pole generates a large local
magnetic field to change the magnetization direction of the medium
in proximity to the writer. By switching the direction of the field
using a switching current that drives the writer, one can write a
plurality of media bits on a magnetic recording medium. A new
"assist" technology is needed to controllably boost or reduce the
MP field on the magnetic medium, and that does not rely on
generating a RF field or providing a heating mechanism since MAMR
and HAMR have not reached a point of maturity that enables
large-scale manufacturing and incorporation into actual
devices.
SUMMARY
[0006] One objective of the present disclosure is to provide an
improved PMR writer that is configured to enhance the MP field on a
magnetic medium during the writing of a transition, and then
reduces the MP field after a transition is written.
[0007] A second objective of the present disclosure is to provide a
method of forming the PMR writer according to the first
objective.
[0008] According to a first embodiment of the present disclosure,
these objectives are achieved with a permanent magnet (PM) formed
in a write gap (WG) and having a front side at the ABS, a
cross-track width that is less than or equal to the track width of
the MP trailing side, and a down-track thickness less than the WG
thickness. The PM height is preferably less than or equal to that
of the throat height of the magnetic trailing shield. A center
plane that is orthogonal to the ABS bisects the PM at the ABS, and
also bisects the MP trailing and leading sides. The PM has a
magnetization opposing the WG field at the start of a transition.
However, the PM magnetization flips to a direction substantially
parallel to the WG field (H.sub.WG) after a transition is written
and H.sub.WG becomes saturated. As a result, the PM magnetic field
enhances the MP field during a transition but reduces the MP field
after the transition is written thereby improving direct current
(DC) field ATE. Moreover, PM coercivity is sufficient so that PM
magnetization will retain its flipped direction at the beginning of
the next transition and once again will be anti-parallel to
H.sub.WG to provide an assist effect to the MP field when writing
the next transition.
[0009] Preferably, PM coercivity is in the range of 500 Oe to 8000
Oe, and the PM is made of CoPt, CoPd, FePt, or a multilayer
structure with one or more of Co, Fe, Ni, Pt, Pd, or alloys
thereof. In other embodiments, the PM is a CoPtCr--SiO.sub.2 or
FePt--SiO.sub.2 composite.
[0010] According to a second embodiment, the PM is part of a spin
flipping element having a front side at the ABS, and with the same
thickness and width requirements as the PM in the first embodiment.
The spin flipping element is formed closer to the first trailing
shield (TS) with the addition of a spacer layer underneath the PM.
The spacer layer may be Ta, Ru, W, Pt, Ir, Cu, Au, Pd, Ag, Cr, Al,
or Ti, or a multilayer made by these elements.
[0011] Again, PM magnetization opposes H.sub.WG at the start of a
transition but flips to a direction parallel to H.sub.WG when
H.sub.WG exceeds the PM coercivity. Moreover, a current l.sub.b of
sufficient magnitude may be applied across the PM during a
transition to help control the PM magnetization flipping with the
spin torque effect. The mechanism for PM flipping is spin torque
applied to the PM magnetization from either the first TS or MP tip
depending on the direction of I.sub.b. PM magnetization will retain
its flipped direction (for the next transition) once the applied
current is removed because of sufficient PM coercivity as described
previously.
[0012] In other embodiments, the PM of the first embodiment (or
spin flipping element containing a PM in the second embodiment) is
recessed to have the front side at a first height (h1) from the
ABS, and a backside at a second height (h2) where h2>h1. Thus,
the position of the PM in the WG may be adjusted to provide the
best field gain and field gradient gain to enable improved writing
of transitions. Accordingly, PM thickness may be significantly
larger than in previous embodiments because of a greater distance
between the main pole and trailing shield at heights including h1
and h2, but PM down-track thickness is still less than the WG
thickness at h1 and h2. PM magnetic field assist during a
transition depends on h1, H.sub.WG magnitude, and the size (volume)
of the PM.
[0013] A method of forming a PM in a write gap is also described. A
conventional process flow is followed to provide a MP with a MP tip
adjoined on each side by a side gap and on a bottom surface
(leading side) with a leading gap. A side shield contacts an outer
side of each side gap, and a leading shield contacts a bottom
surface of the leading gap and bottom surfaces of the side gaps.
The main pole may have a tapered trailing side with a front edge at
a first plane at the ABS where the first plane also comprises a top
surface of each side gap and each side shield. According to one
embodiment, a full film PM layer with or without an additional WG
layer with total thickness equal to the desired final WG are
sequentially deposited on the MP trailing side and on top surfaces
of the side gaps and side shields. Then, a first photoresist layer
is coated on the stack with the PM layer and optional WG layer.
Using a photo mask and conventional photo process, the first
photoresist layer is patterned to form a photoresist island having
a cross-track width and height that corresponds to the desired
width (w) and height of the PM. The photoresist island shape is
transferred through the PM layer with an ion beam etch (IBE) or
reactive ion etch (RIE). Additional WG material is refilled on
areas that are etched away to form a WG covering beyond the island
shape, and then any remaining photoresist is removed. Next, the
first TS layer and a second photoresist layer are sequentially
formed on the WG top surface. The second photoresist layer is
patterned to form a second photoresist island having a width (w1)
and height corresponding to the desired width and height of the
first TS where w1>w. Subsequently, the second photoresist island
shape is etch transferred through the WG and first TS layer and
stops on the side shields to form a WG side that is coplanar with a
first TS side on each side of the center plane. Thereafter, a
second TS layer is deposited on the side shields and on the first
TS top surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a perspective view of a head arm assembly of the
present disclosure.
[0015] FIG. 2 is side view of a head stack assembly of the present
disclosure.
[0016] FIG. 3 is a plan view of a magnetic recording apparatus of
the present disclosure.
[0017] FIG. 4 is a down-track cross-sectional view of a combined
read-write head with leading and trailing loop pathways for
magnetic flux return to the main pole according to an embodiment of
the present disclosure.
[0018] FIG. 5 is an ABS view of an all wrap around (AWA) shield
structure surrounding a main pole according to a prior art design
used by the inventors.
[0019] FIG. 6A is an ABS view of a PMR writer having a permanent
magnet (PM) formed within a write gap between a trailing side of a
main pole and a trailing shield structure according to a first
embodiment of the present disclosure.
[0020] FIG. 6B is a down-track cross-sectional view of the MP,
leading shield, and trailing shield structure of the PMR writer in
FIG. 6A.
[0021] FIG. 7 is an illustration of PM magnetization, and PM
magnetic field magnitude at a distance 15 nm below the center of
the PM of the first embodiment.
[0022] FIG. 8 is a plot showing the PM magnetic field of a 40
nm.times.40 nm.times.5.5 nm PM with Ms=2 Tesla in a perpendicular
direction and longitudinal direction at a distance 15 nm below the
PM center according to the first embodiment.
[0023] FIG. 9A is an ABS view of a PMR writer having a permanent
magnet (PM) formed between a spin polarization preserving layer and
a non-spin polarization preserving layer, and within a write gap
according to a second embodiment of the present disclosure.
[0024] FIG. 9B is a down-track cross-sectional view of the MP,
leading shield, and trailing shield structure of the PMR writer in
FIG. 9A.
[0025] FIG. 10A is a down-track cross-sectional view of a PMR
writer wherein a spin flipping element containing a permanent
magnet in the write gap is recessed from the ABS according to a
third embodiment of the present disclosure.
[0026] FIG. 10B is a down-track cross-sectional view of a PMR
writer wherein a permanent magnet in the write gap is recessed from
the ABS according to a fourth embodiment of the present
disclosure.
[0027] FIG. 11 is an ABS view of the PMR writer in the first
embodiment wherein the PM magnetization is oriented anti-parallel
to the write gap field.
[0028] FIG. 12 is an ABS view of the PMR writer in FIG. 11 after
the write gap field (H.sub.WG2) is saturated and causes PM
magnetization to flip to a direction substantially parallel to
H.sub.WG2 according to an embodiment of the present disclosure.
[0029] FIG. 13 is an ABS view of the PMR writer of the second
embodiment after a current of sufficient magnitude is applied to
flip PM magnetization to a direction opposite to H.sub.WG2.
[0030] FIGS. 14-18 show ABS views of a sequence of steps that are
used to form a PM within a WG and having a thickness less than the
WG thickness according to an embodiment of the present
disclosure.
DETAILED DESCRIPTION
[0031] The present disclosure is a PMR writer structure wherein a
permanent magnet (PM) is formed within a write gap and generates a
magnetic field that enhances the MP field during a write process at
the start of a transition, and where PM magnetization flips to an
opposite direction that is parallel to the WG field (H.sub.WG) when
H.sub.WG increases beyond the PM coercivity after the transition is
written thereby reducing the MP field on the magnetic medium to
improve ATE. The PMR writer is not limited to the structure shown
in the exemplary embodiments, and may have other designs for the
leading loop and trailing loop pathways for magnetic flux return,
other coil designs and different schemes for the leading shield and
trailing shield structures, for example. In the drawings, the
y-axis is in a cross-track direction, the z-axis is in a down-track
direction, and the x-axis is in a direction orthogonal to the ABS
and towards a back end of the PMR writer. Thickness refers to a
down-track distance, width is a cross-track distance, and height is
a distance from the ABS in the x-axis direction. The terms
"flipping" and "switching" may be used interchangeably when
referring to changing a magnetization direction in the PM
layer.
[0032] The term "behind" refers to an x-axis position of one
structural feature with respect to another. For example, component
B formed behind (or beyond) component or plane A means that B is at
a greater height from the ABS than A. A "front side" of a layer is
a side facing the ABS, and a backside or backend faces away from
the ABS. The terms "above" and "below" refer to a down-track (DT)
position of one layer with respect to another layer or plane.
[0033] Referring to FIG. 1, a head gimbal assembly (HGA) 100
includes a magnetic recording head 1 comprised of a slider and a
PMR writer structure formed thereon, and a suspension 103 that
elastically supports the magnetic recording head. The suspension
has a plate spring-like load beam 222 formed with stainless steel,
a flexure 104 provided at one end portion of the load beam, and a
base plate 224 provided at the other end portion of the load beam.
The slider portion of the magnetic recording head is joined to the
flexure, which gives an appropriate degree of freedom to the
magnetic recording head. A gimbal part (not shown) for maintaining
a posture of the magnetic recording head at a steady level is
provided in a portion of the flexure to which the slider is
mounted.
[0034] HGA 100 is mounted on an arm 230 formed in the head arm
assembly 103. The arm moves the magnetic recording head 1 in the
cross-track direction y of the magnetic recording medium 140. One
end of the arm is mounted on a base plate 224. A coil 231 that is a
portion of a voice coil motor is mounted on the other end of the
arm. A bearing part 233 is provided in the intermediate portion of
arm 230. The arm is rotatably supported using a shaft 234 mounted
to the bearing part 233. Arm 230 may be driven by changing the
magnetic flux in the voice coil. Next, a side view of a head stack
assembly (FIG. 2) and a plan view of a magnetic recording apparatus
(FIG. 3) wherein the magnetic recording head 1 is incorporated are
depicted. The head stack assembly 250 is a member to which a first
HGA 100-1 and second HGA 100-2 are mounted to arms 230-1, 230-2,
respectively, on carriage 251. A HGA is mounted on each arm at
intervals so as to be aligned in the perpendicular direction
(orthogonal to magnetic medium 140). The coil portion (231 in FIG.
1) of the voice coil motor is mounted at the opposite side of each
arm in carriage 251. The voice coil motor has a permanent magnet
263 arranged at an opposite position across the coil 231.
[0035] With reference to FIG. 3, the head stack assembly 250 is
incorporated in a magnetic recording apparatus 260. The magnetic
recording apparatus has a plurality of magnetic media 140 mounted
to spindle motor 261. For every magnetic recording medium, there
are two magnetic recording heads arranged opposite one another
across the magnetic recording medium. The head stack assembly and
voice coil motor actuator correspond to a positioning device, and
support the magnetic recording heads, and position the magnetic
recording heads relative to the magnetic recording medium. The
magnetic recording heads are moved in a cross-track of the magnetic
recording medium by the actuator. The magnetic recording head
records information into the magnetic recording media with a PMR
writer element (not shown) and reproduces the information recorded
in the magnetic recording media by a magnetoresistive (MR) sensor
element (not shown).
[0036] Referring to FIG. 4, magnetic recording head 1 comprises a
combined read-write head. The down-track cross-sectional view is
taken along a center plane (44-44 in FIG. 5) formed orthogonal to
the ABS 30-30, and that bisects the main pole layer 14. The read
head is formed on a substrate 81 that may be comprised of AlTiC
(alumina+TiC) with an overlying insulation layer 82 that is made of
a dielectric material such as alumina. The substrate is typically
part of a slider formed in an array of sliders on a wafer. After
the combined read head/write head is fabricated, the wafer is
sliced to form rows of sliders. Each row is typically lapped to
afford an ABS before dicing to fabricate individual sliders that
are used in a magnetic recording device. A bottom shield 84 is
formed on insulation layer 82.
[0037] A magnetoresistive (MR) element also known as MR sensor 86
is formed on bottom shield 84 at the ABS 30-30 and typically
includes a plurality of layers (not shown) including a tunnel
barrier formed between a pinned layer and a free layer where the
free layer has a magnetization (not shown) that rotates in the
presence of an applied magnetic field to a position that is between
being parallel or antiparallel to the pinned layer magnetization,
which resulted in a change in the resistance. This resistance is
measured to give an indication of the magnetic field near the read
element. Insulation layer 85 adjoins the backside of the MR sensor,
and insulation layer 83 contacts the backsides of the bottom shield
and top shield 87. The top shield is formed on the MR sensor. An
insulation layer 88 and a top shield (S2B) layer 89 are
sequentially formed on the top magnetic shield. Note that the S2B
layer 89 may serve as a flux return path (RTP) in the write head
portion of the combined read/write head. Thus, the portion of the
combined read/write head structure formed below layer 89 in FIG. 4
is typically considered as the read head. In other embodiments (not
shown), the read head may have a dual reader design with two MR
sensors, or a multiple reader design with multiple MR sensors.
[0038] The present disclosure anticipates that various
configurations of a write head may be employed with the read head
portion. In the exemplary embodiment, magnetic flux 70 in main pole
(MP) layer 14 is generated with flowing a current through bucking
coil 80b and driving coil 80d that are below and above the main
pole layer, respectively, and are connected by interconnect 51.
Magnetic flux 70 exits the main pole layer at pole tip 14p at the
ABS 30-30 and is used to write a plurality of bits on magnetic
media 140. Magnetic flux 70b returns to the main pole through a
trailing loop comprised of trailing shields 17, 18, PP3 shield 26,
and top yoke 18x. There is also a leading return loop for magnetic
flux 70a that includes leading shield 11, leading shield connector
(LSC) 33, S2C 32, return path 89, and back gap connection (BGC) 62.
The magnetic core may also comprise a bottom yoke 35 below the main
pole layer. Dielectric layers 10, 11, 13, 36-39, and 47-49 are
employed as insulation layers around magnetic and electrical
components. A protection layer 27 covers the PP3 trailing shield
and is made of an insulating material such as alumina. Above the
protection layer and recessed a certain distance u from the ABS
30-30 is an optional cover layer 29 that is preferably comprised of
a low coefficient of thermal expansion (CTE) material such as SiC.
Overcoat layer 28 is formed as the uppermost layer in the write
head.
[0039] Referring to FIG. 5, a MP with MP tip 14p having a track
width TW, trailing side 14t1, leading side 14b1, and two sides 14s
formed equidistant from a center plane 44-44 is shown with an AWA
shield structure that is known to the inventors. Write gap 16 with
thickness t is on the MP trailing side, and there are side gaps 15
adjoining each MP side, and a leading gap 13 below the MP leading
side. The trailing shield structure comprises a first trailing
shield (TS) with a high magnetic saturation value from 19 kiloGauss
(kG) to 24 kG, and with a front portion 17a on the write gap. The
trailing shield structure also includes a second TS 18 formed on
the first TS top surface 17t and sides 17s, on write gap sides 16s,
and on a top surface of the side shields 12 at plane 41-41. Plane
41-41 includes the trailing edge of the MP trailing side at the
ABS. Side shields contact a top surface of the leading shield 11 at
plane 42-42 that is parallel to plane 41-41 and includes the MP
leading side at the ABS.
[0040] According to a first embodiment of the present disclosure
illustrated in FIG. 6A, the PMR writer structure in FIG. 5 is
modified with insertion of a PM 20 in the write gap 16. The PM has
a thickness s between a top surface 20t and a bottom surface 20b
thereof where s is preferably less than the WG thickness. Thus, a
portion of the WG is formed above and below the PM such that PM top
and bottom surfaces are separated from first TS 17 and MP tip 14p,
respectively. Moreover, the PM is bisected by center plane 44-44
and has a width w where w<TW. Far sides 60, 61 of the shield
structure are shown on opposing sides of the center plane.
[0041] A key feature is that the PM has a coercivity that is in a
range of 500 Oe to 8000 Oe so that when the PMR writer is writing a
transition on a magnetic medium (not shown), PM magnetization 20m
will be aligned substantially in the opposite down-track direction
as the WG field (H.sub.WG1) in FIG. 11, but will flip to a
direction parallel to the WG field after the transition is written
when the WG field (H.sub.WG2) becomes saturated and exceeds PM
coercivity as indicated in FIG. 12.
[0042] Furthermore, PM magnetization will retain the flipped
direction at the beginning of next transition, and once again is
anti-parallel to the WG field that will be opposite to the
direction of H.sub.WG1 in the previous transition. MP magnetization
14m that is proximate to MP trailing side 14t1 and first TS
magnetization 17m that is proximate to first TS bottom surface 17n
are also aligned parallel to H.sub.WG1 and H.sub.WG2, respectively,
in FIG. 11 and FIG. 12.
[0043] As explained in related application Ser. No. 16/037,197,
when a magnetization in a magnetic layer within the WG is opposed
to the WG field, there is increased reluctance in the WG that
causes the MP field to be enhanced. In the present disclosure,
there is a further advantage when writing a transition in that the
PM also has a magnetic field (see simulation in FIG. 7) that
assists the MP field on a magnetic medium. Thus, PM magnetization
not only opposes H.sub.WG (H.sub.WG1 in FIG. 11) and thereby
enhances the MP field, but the PM field provides an assist in
writing a transition on a magnetic bit. Another important feature
is that after the transition when H.sub.WG (H.sub.WG2 in FIG. 12)
exceeds PM coercivity and causes PM magnetization to flip, the PM
magnetic field and PM magnetization are both reversed and serve to
reduce the MP field to minimize ATE.
[0044] In some embodiments, the PM is made of CoPt, CoPd, FePt, or
a multilayer structure with one or more of Co, Fe, Ni, Pt, Pd, Ir,
Ru, Cr or alloys thereof. In other embodiments, the PM is a
CoPtCr--SiO.sub.2 or FePt--SiO.sub.2 composite that is formed by
sputter depositing a CoPtCr--SiO.sub.2 or FePt--SiO.sub.2 target,
and has a polycrystalline structure typical of the material used in
commercial PMR media.
[0045] The down track cross-sectional view at center plane 44-44 in
FIG. 6A is illustrated in FIG. 6B. MP leading side 14b1 is tapered
and connects with MP bottom surface 14b2 that is aligned orthogonal
to the ABS 30-30, and formed on dielectric layer 39. According to a
leading shield (LS) design disclosed in related U.S. Pat. No.
10,014,021, the LS top surface may have a notch such that a first
portion 11t1 of the LS top surface is substantially parallel to the
tapered MP leading side and extends from the ABS to a throat height
(TH). A second portion 11t2 of the LS top surface is also
substantially parallel to the tapered MP leading side but is a
greater distance therefrom and is connected to first portion 11t1
by LS side 11s that is parallel to the ABS. LS backside 11e is at
height c from the ABS while LS front side 11f is at the ABS. This
LS design enables improvement in overwrite, bit error rate, and
tracks per inch capability (TPI) capability compared with a LS top
surface not having a notch.
[0046] The MP trailing side 14t1 is also tapered and connects with
MP top surface 14t2 that is parallel to the MP bottom surface.
Dielectric layer 47 adjoins the MP top surface and backsides 17e,
18e of first TS 17 and second TS 18, respectively, at height k.
Typically, k>c. First TS comprises a front portion 17a that is
substantially parallel to the MP tapered trailing side and has a
front side 17f at the ABS, and comprises a back portion 17b that is
parallel to the MP top surface. PM 20 has height (h) from the ABS
that is from 20 nm to 80 nm. Preferably, h<k and less than the
throat height (TH) of the bottom yoke. It should be understood that
other leading shield and trailing shield designs are compatible
with the PM feature of the present disclosure. Thus, the
embodiments of the present disclosure are not limited to the LS and
TS shield designs depicted herein.
[0047] Referring to FIG. 7, modeling of a PM 20 with magnetization
20m substantially in a down-track (z-axis) direction is depicted
and shows magnetic field orientation and magnitude for PM magnetic
field (H.sub.20) at 15 nm below the PM bottom position where a
magnetic medium is typically located during a write process. Arrows
pointing substantially in the down (-x axis) direction are
locations where the PM magnetic field assists the MP field (not
shown). The center of the magnetic bit (not shown) being written to
is proximate to point P.
[0048] FIG. 8 shows a plot of magnetic field as a function of
location in the down-track (z-axis) direction represented by curve
90, and in the perpendicular (x-axis) direction represented by
curve 91 at 15 nm below the PM bottom surface. The PM has a width
of 40 nm, height of 40 nm, and thickness of 5.5 nm, and a
saturation magnetization (Ms)=2 Tesla.
[0049] Referring to FIG. 9A, a second embodiment of the present
disclosure is depicted wherein a PM is formed within a spin
flipping element hereinafter called flipping element 22 within
write gap 16. The flipping element has a thickness t preferably
from 5 nm to 30 nm that is equal to the write gap thickness, and a
width w that is preferably less than or equal to the track width TW
of the MP tapered trailing side 14t1 at the ABS. The PM 20 is
selected from the same materials as in the first embodiment. The
flipping element has a stack wherein a non-spin polarization
preserving layer 21, the PM, and spin polarization preserving layer
19 are sequentially formed on the MP tapered trailing side, and the
spin polarization preserving layer contacts the first TS 17a. The
non-spin polarization preserving layer is typically a metal
conductor such as Ta, W, Pt, Ru, Ti, or Pd, and the spin
polarization preserving layer is also a conductive layer and is
preferably comprised of Cu, Ag, Au, AI, or Cr, or an alloy
thereof.
[0050] Similar to the first embodiment (FIG. 11), PM magnetization
20m is substantially anti-parallel to the WG field H.sub.WG1 and to
MP magnetization 14m at MP trailing side 14t1, and anti-parallel to
first TS and second TS magnetizations 17m, 18m, respectively, when
writing a transition. However, as depicted in FIG. 13, when a
current I.sub.b of sufficient magnitude is applied in a direction
parallel to saturated WG field H.sub.WG2, magnetization 20m will
maintain the direction that is anti-parallel to H.sub.WG2 for a
longer time than without the current I.sub.b before eventually
flipping at sufficiently high H.sub.WG2. In preferred embodiments,
I.sub.b has a current density in a range of 1.times.10.sup.-7 to
1.times.10.sup.-9 Amp/cm.sup.2. In order for the flipping element
to have acceptable reliability, the magnitude of current I.sub.b
must be maintained as low as possible since excessive current may
cause degradation of one or more layers 19-21 due to
electromigration and/or excessive local heating. In addition, it is
preferred that I.sub.b is not so large such that the magnetization
of PM 20 is still aligned in the direction that is parallel to the
gap field at the end of writing the current bit.
[0051] In FIG. 9B, a down-track cross-sectional view at plane 44-44
in FIG. 9A is illustrated. Flipping element 22 and the PM therein
(not shown) extend from the ABS 30-30 to a height h of 20 nm to 80
nm. MP 14, LS 11, and TS 17 retain the structural features
described earlier with respect to the first embodiment in FIG.
6B.
[0052] Referring to FIG. 10A, a third embodiment of the present
disclosure is illustrated from a down-track cross-sectional view.
In the exemplary embodiment, the flipping element 22 comprised of
PM 20 is retained from the second embodiment but a front side 22f
thereof is recessed at height b that is >0 nm but .ltoreq.50 nm
from ABS 30-30. The flipping element has a height d of 20 nm to 80
nm between the front side 22f and backside 22e thereof. In this
case, at least a portion of the flipping element may be at a height
greater than TH.
[0053] Alternatively, in FIG. 10B, a fourth embodiment is shown
where the first embodiment is modified to form a recessed PM 20
with a front side 20f that is >0 nm but .ltoreq.50 nm from ABS
30-30. Preferably, the recessed PM has a height d of 20 nm to 80 nm
between the PM front side and the backside 20e. It is believed that
a recessed PM (or as a recessed PM layer in a flipping element)
offers flexibility in optimizing field gain (MP field and H.sub.20
in FIG. 7) and field gradient gain thereby optimizing the writing
of transitions.
[0054] The present disclosure also encompasses a method of
fabricating a PMR writer with an AWA shield structure around a MP,
and where a PM 20 is formed in a write gap 16 between the MP tip
14p and the first TS 17a at the ABS. From a perspective at the
eventual ABS in FIG. 14, leading shield 11 is plated first on a
substrate and then side shield (SS) layer 12 is plated using
conventional methods. All layers (not shown) below LS 11 are formed
by well known processes and are not described herein. A
conventional sequence of steps is used to form an opening (not
shown) in the SS layer that exposes sides 12s and LS top surface
11t. Thereafter, a gap layer comprised of side gaps 15 and leading
gap 13 is conformally deposited to partially fill the opening.
Then, the MP layer including MP 14p is deposited on the side gaps
and leading gap to fill the opening. A CMP process may be performed
to generate a MP trailing side 14t1 that is coplanar with side
shield top surfaces 12t and side gap top surfaces 15t at plane
41-41. A well known process may be employed to form a taper (not
shown) on the MP trailing side.
[0055] Referring to FIG. 15, a first WG layer 16a, PM layer 20 with
thickness s, and second WG layer 16b are sequentially deposited on
top surfaces of side shields 12, side gaps 15 and MP tapered
trailing side 14t1. A first photoresist layer is coated on the
second WG layer, and is patternwise exposed via a photo mask and
developed to form photoresist island 54 that is bisected by center
plane 44-44 and has sides 54s separated by width w. Portions of WG
top surface 16t are uncovered by opening 55 on each side of the
center plane.
[0056] Referring to FIG. 16, openings 55 are etch transferred
through exposed portions of the second WG layer 16b, PM layer 20,
and first WG layer 16a using a RIE or IBE process that stops at
plane 41-41 and thereby forms PM 20 having width w and thickness s
on first WG layer 16a. A third write gap layer 16c is then
deposited on side gaps 15, and side shields 12 before the
photoresist is removed. Hereinafter, WG 16 is shown as the
combination of WG layers 16a-16c.
[0057] In FIG. 17, the partially formed writer with PM in FIG. 16
is shown after first TS 17 with a Ms preferably from 19 kG to 24 kG
is deposited on WG 16. Then, a second photoresist is coated on the
first TS and is patternwise exposed using a photo mask and
developed to form a second photoresist island 56 that is bisected
by center plane 44-44 and has a width w1 between sides 56s where
w1>w. Openings 57 on each side of the second photoresist island
expose a portion of first TS top surface 17t.
[0058] FIG. 18 depicts the partially formed PMR writer in FIG. 17
after a RIE or IBE process is employed to transfer opening 57
through exposed portions of first TS 17 and WG 16 and stops on a
top surface of side shields 12 (at plane 41-41) on each side of the
center plane 44-44. Then, the second TS 18 with a Ms of 10 kG to 19
kG is deposited on the side shields and first TS top surface 17t.
Subsequently, conventional steps known to those skilled in the art
are followed to complete the trailing shield structure and form a
PMR writer as shown in FIG. 4. Note that a lapping process is the
final step in forming an ABS at plane 30-30.
[0059] While the present disclosure has been particularly shown and
described with reference to, the preferred embodiments thereof, it
will be understood by those skilled in the art that various changes
in form and details may be made without departing from the spirit
and scope of this disclosure.
* * * * *