U.S. patent application number 10/676735 was filed with the patent office on 2005-03-31 for thin film media with a dual seed layer of rual/nialb.
Invention is credited to Doerner, Mary Frances, Tang, Kai, Xiao, Qi-Fan.
Application Number | 20050069730 10/676735 |
Document ID | / |
Family ID | 34218172 |
Filed Date | 2005-03-31 |
United States Patent
Application |
20050069730 |
Kind Code |
A1 |
Doerner, Mary Frances ; et
al. |
March 31, 2005 |
THIN FILM MEDIA WITH A DUAL SEED LAYER OF RUAL/NIALB
Abstract
A thin film structure for a magnetic thin film recording medium
including a dual seed layer of RuAl/NiAlB is disclosed. The use of
the RuAl/NiAlB structure provides reduced grain size, an increased
Mrt orientation ratio (OR), increased SNR and lower PW50 at higher
amplitude. The RuAl and NiAlB seed layers each have a B2
crystallographic structure. The RuAl/NiAlB dual seed layer can be
used to obtain an underlayer with a preferred in-plane orientation
of (200) and a cobalt alloy magnetic film with the preferred
in-plane orientation of (11.sup.-20).
Inventors: |
Doerner, Mary Frances;
(Santa Cruz, CA) ; Tang, Kai; (San Jose, CA)
; Xiao, Qi-Fan; (San Jose, CA) |
Correspondence
Address: |
Marlin Knight
Hoyt & Knight
PO Box 1320
Pioneer
CA
95666
US
|
Family ID: |
34218172 |
Appl. No.: |
10/676735 |
Filed: |
September 30, 2003 |
Current U.S.
Class: |
428/831 ;
360/135; G9B/5.288 |
Current CPC
Class: |
Y10T 428/12465 20150115;
B82Y 25/00 20130101; H01F 10/324 20130101; G11B 5/7379 20190501;
Y10T 428/12861 20150115; H01F 10/26 20130101; G11B 5/66 20130101;
G11B 5/656 20130101 |
Class at
Publication: |
428/694.00T ;
428/694.0TM; 360/135 |
International
Class: |
G11B 005/82; H01F
001/00 |
Claims
1. A magnetic thin film layer structure comprising: a layer of
RuAl; a layer of NiAlB epitaxially deposited on the layer of RuAl;
and a ferromagnetic layer structure deposited after the layer of
NiAlB.
2. The magnetic thin film layer structure of claim 1 wherein the
NiAlB has approximately from 2 to 5 atomic percent boron with the
remainder being generally divided between nickel and aluminum.
3. The magnetic thin film layer structure of claim 2 wherein NiAlB
has approximately 50 atomic percent nickel 48 atomic percent
aluminum and 2 atomic percent boron.
4. The magnetic thin film layer structure of claim 1 further
comprising a substrate and a pre-seed layer of CrTi deposited on
the substrate prior to the layer of RuAl.
5. The magnetic thin film layer structure of claim 5 wherein the
substrate is circumferentially textured glass.
6. The magnetic thin film layer structure of claim 1 further
comprising an underlayer of CrTi deposited on the layer of
NiAlB.
7. The magnetic thin film layer structure of claim 1 wherein the
ferromagnetic layer structure further comprises a magnetic layer
stack including a layer of CoCr and a layer of CoPtCrB separated by
a spacer layer.
8. The magnetic thin film layer structure of claim 7 wherein the
spacer layer is ruthenium.
9. A magnetic thin film disk comprising: an amorphous or
nanocrystalline pre-seed layer; a seed layer of RuAl with a B2
crystallographic structure deposited on the pre-seed layer; a seed
layer of NiAlB with a B2 crystallographic structure deposited on
the layer of RuAl, the NiAlB having approximately from 2 to 5
atomic percent boron with the remainder being generally divided
between nickel and aluminum; and a ferromagnetic layer structure
above the layer of NiAlB.
10. (canceled) The magnetic thin film disk of claim 9 wherein the
NiAlB has approximately from 2 to 5 atomic percent boron with the
remainder being generally divided between nickel and aluminum.
11. The magnetic thin film disk of claim 10 wherein the seed layer
of NiAlB has approximately 2 at. % boron.
12. The magnetic thin film disk of claim 9 further comprising a
substrate and wherein the pre-seed layer is CrTi deposited on the
substrate.
13. The magnetic thin film disk of claim 9 further comprising an
underlayer of CrTi deposited on the layer of NiAlB prior to the
ferromagnetic layer structure.
14. The magnetic thin film disk of claim 9 wherein the
ferromagnetic layer structure includes CoPtCrB and is preceded by a
spacer layer and a layer of CoCr forming a magnetic layer
stack.
15. A magnetic disk drive comprising: a magnetic transducer
including a read head and a write head; a suspension supporting the
magnetic transducer over a magnetic disk; and the magnetic disk
including a dual seed layer comprising a layer RuAl followed by a
layer of NiAlB epitaxially deposited onto the layer of RuAl.
16. The magnetic disk drive of claim 15 wherein the layer of NiAlB
has approximately from 2 to 5 atomic percent boron with the
remainder being generally divided between nickel and aluminum.
17. The magnetic disk drive of claim 16 wherein the layer of NiAlB
has approximately 50 atomic percent nickel, 48 atomic percent
aluminum and 2 atomic percent boron.
18. The magnetic disk drive of claim 15 wherein the magnetic disk
further comprises a circumferentially textured substrate and the
magnetic disk has an Mrt orientation ratio greater than one.
19. The magnetic disk drive of claim 15 wherein the magnetic disk
further comprises an underlayer of CrTi deposited on the layer of
NiAlB.
20. The magnetic disk drive of claim 15 wherein the magnetic disk
further comprises a magnetic layer stack deposited after the layer
of NiAlB including a layer of CoCr and a layer CoPtCrB separated by
a spacer layer.
Description
FIELD OF THE INVENTION
[0001] The invention relates to magnetic thin film media and
methods for their fabrication and more particularly to magnetic
thin film disks having a seed layer structure prior to an
underlayer.
BACKGROUND OF THE INVENTION
[0002] A typical prior art disk drive system 10 is illustrated in
FIG. 1. In operation the magnetic transducer 20 is supported by the
suspension 13 as it flies above the disk 16. The magnetic
transducer 20, usually called a "head" or "slider," is composed of
elements that perform the task of writing magnetic transitions (the
write head 23) and reading the magnetic transitions (the read head
12). The electrical signals to and from the read and write heads
12, 23 travel along conductive paths (leads) 14 which are attached
to or embedded in the suspension 13. The magnetic transducer 20 is
positioned over points at varying radial distances from the center
of the disk 16 to read and write circular tracks (not shown). The
disk 16 is attached to a spindle 18 that is driven by a spindle
motor 24 to rotate the disk 16. The disk 16 comprises a substrate
26 on which a plurality of thin films 21 are deposited. The thin
films 21 include ferromagnetic material in which the write head 23
records the magnetic transitions in which information is
encoded.
[0003] The conventional disk 16 consists of substrate 26 of AlMg
with an electroless coating of NiP which has been highly polished.
Glass is also commonly used for the substrate 26. The thin films 21
on the disk 16 typically include a chromium or chromium alloy
underlayer which is deposited on the substrate 26. The
ferromagnetic layer in the thin films is based on various alloys of
cobalt, nickel and iron. For example, a commonly used alloy is
CoPtCr. Additional elements such as tantalum and boron are often
used in the magnetic alloy. A protective overcoat layer is used to
improve wearability and corrosion. The three film disk described
above does not exhaust the possibilities. Various seed layers,
multiple underlayers and laminated magnetic films have all been
described in the prior art.
[0004] In particular, seed layers have been suggested for use with
nonmetallic substrate materials such as glass. Typically the seed
layer is a relatively thin layer which is the initial film
deposited on the substrate and is followed by the underlayer.
Materials proposed for use as seed layers include chromium,
titanium, tantalum, Ni3P, MgO, carbon, tungsten, AlN, FeAl, RuAl
and NiAl. In U.S. Pat. No. 5,789,056 to Bian, et al., the use of a
CrTi seed layer is described. The underlayers mentioned are Cr, CrV
and CrTi.
[0005] In U.S. Pat. No. 6,010,795 to Chen, et al. a magnetic
recording medium is described which has a surface oxidized seed
layer (such as NiP), a Cr-containing sub-underlayer, a NiAl or FeAl
underlayer and a Cr-containing intermediate layer on the NiAl or
FeAl underlayer. The underlayer is said to have a (200)
crystallographic orientation.
[0006] A MgO seed layer is disclosed in U.S. Pat. No. 5,800,931 to
Lee, et al. A B2 structure underlayer, preferably NiAl or FeAl., is
used along with an optional thin Cr or Cr alloy intermediate layer
between the underlayer and the magnetic layer.
[0007] In published U.S. application Ser. No. 20010024742, Bian, et
al. described a RuAl seed layer deposited directly onto a pre-seed
layer and an optional layer of NiAl following the RuAl. This double
layer configuration could result in cost savings by reducing the
amount of Ru required to form the seed layer. Ru is an expensive
element so a reduction in the required quantity of Ru reduces the
costs. In the double layer structure the RuAl seed layer
establishes the grain size and orientation and the subsequently
deposited NiAl follows the established patterns.
[0008] Continued improvement in the magnetic recording properties
is needed to further increase the areal recording density for
magnetic media.
SUMMARY OF THE INVENTION
[0009] The applicants disclose a magnetic thin film recording
medium including a dual seed layer of RuAl/NiAlB. The use of the
RuAl/NiAlB structure provides reduced grain size, increased Mrt
orientation ratio (OR), increased SNR and lower PW50 at higher
amplitude. The RuAl and NiAlB seed layers each have a B2
crystallographic structure. The RuAl/NiAlB dual seed layer can be
used to obtain an underlayer with a preferred in-plane orientation
of (200) and a cobalt alloy magnetic film with the preferred
in-plane orientation of (11.sup.-20).
BRIEF DESCRIPTION OF THE FIGURES
[0010] FIG. 1 is a symbolic illustration of the prior art showing
the relationships between the head and associated components in a
disk drive.
[0011] FIG. 2 is an illustration of a preferred embodiment layer
structure for a magnetic thin film disk according to the
invention.
DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED
EMBODIMENTS
[0012] Reference is made to FIG. 2 to illustrate the thin film
layers in a preferred embodiment of a magnetic film disk 16
including the dual seed layer of the invention. The dual seed layer
of the invention is preferably used with a pre-seed layer. The
pre-seed layer is sputter deposited directly onto the substrate
surface 26 which may be glass or any other appropriate material or
surface. The preferred pre-seed layer 31 is an amorphous or
nanocrystalline layer of CrTi alloy, with CrTi.sub.50 being even
more preferred. Amorphous or nanocrystalline AlTa, CrTa or AlTi can
also be considered as preferred materials for use as a pre-seed
layer 31. The use of a pre-seed layer of CrTi, CrTa, AlTa or AlTi
improves grain size, grain distribution, in-plane crystallographic
orientation, coercivity and SNR.
[0013] The dual seed layer of the invention includes a crystalline
layer of RuAl 32A followed by a crystalline layer of NiAlB 32B. The
RuAl layer grows as a B2 crystallographic structure on the
amorphous pre-seed layer. The NiAlB epitaxially follows as a B2
crystallographic structure. The addition of boron to NiAl reduces
the grain size of the NiAlB layer and this reduced grain can be
maintained through the subsequent crystalline layers. The preferred
composition includes from 2 to 5 at. % boron, with nickel and
aluminum being approximately equal, but several atomic percentage
points difference between the nickel and aluminum are acceptable.
An even more preferred composition is NiAl.sub.48B.sub.2. RuAl
tends to be more expensive than NiAlB, so one advantage of the
bi-layer is that the RuAl layer can be kept very thin saving on the
high cost of RuAl.
[0014] One or more underlayers 33 follow the NiAlB layer 32B.
Underlayers are commonly chromium alloys. The preferred underlayer
is CrTi and even more preferred is an underlayer of CrTi.sub.20.
The chromium based underlayer 33 can also be kept very thin when
CrTi is used.
[0015] It is known that the cobalt alloy magnetic films may be
grown with the in-plane preferred orientations of (10.sup.-10) or
(11.sup.-20) by first depositing an underlayer with a (112) or
(200) preferred orientations respectively. The RuAl seed layer with
a B2 crystallographic structure has been used alone to obtain an
underlayer with a preferred in-plane orientation of (200) and a
cobalt alloy magnetic film with the preferred in-plane orientation
of (11.sup.-20). The addition of the NiAlB does not change this
epitaxy when used following RuAl. However, NiAlB used without RuAl
will tend to produce a (10.sup.-10) which is undesirable for media
with a target orientation ratio greater one. The preferred
embodiment disk structure uses a circumferentially textured
substrate and has an orientation ratio greater than one.
[0016] FIG. 2 shows a magnetic layer stack 34 following the
underlayer 33. A protective overcoat 35 is the final layer. The
magnetic layer stack 34 can include any of a large variety of
single or multiple layers at least one of which must be
ferromagnetic. Examples of commonly used ferromagnetic alloys are
CoPtCr, CoPtCrTa and CoPtCrB. Laminated magnetic layers and
antiferromagnetically coupled magnetic layers can be used along
with the seed bi-layer of the invention. An onset layer can also be
used. The preferred embodiment uses a magnetic layer stack 34 of
CoCr/spacer/CoPtCrB. An even more preferred embodiment uses a
magnetic layer stack 34 of
CoCr.sub.10/Ru/CoPt.sub.12Cr.sub.18B.sub.8.
[0017] Experimental data on the magnetic performance for selected
experimental disks is presented in table 1. The preferred
NiAl.sub.48B.sub.2 alloy and the most preferred materials and
compositions given above were used for the other layers. Disk 3
used RuAl with no other seed layer to show the benefit of adding
the NiAlB layer.
1TABLE 1 RuAI NiAIB thick- thick- DC SNR ness ness Mrt SNR @310KBPI
PW50 LFTAA Disk (nm) (nm) OR (dB) (Db) (nm) (mv) 1 5.7 8.6 1.43
33.9 29.3 101.5 1.193 2 8.6 5.7 1.39 34.1 29.3 101.3 1.186 3 17.2 0
1.27 33.7 29.1 101.9 1.162
[0018] The disks with the RuAl/NiAlB seed bi-layer of the invention
had significantly higher Mrt OR than did the RuAl disk. The SNR is
increased and PW50 is lower at higher amplitude.
[0019] The total thickness of the seed bi-layer only needs to be
sufficient to establish good crystallographic orientation. The
upper limit on the thickness will be determined by the tendency of
the grain size to increase with thickness. The NiAlB layer can be
thicker than the RuAl. Table 2 shows the Mrt orientation ratio (OR)
for four different thicknesses of RuAl used with a constant NiAlB
layer of 8.6 nm. Mrt OR increases slightly with decrease of RuAl
thickness.
2 TABLE 2 RuAI thickness (nm) Mrt OR 1.7 1.45 2.3 1.46 4.8 1.43 8.3
1.40
[0020] The atomic percent compositions given above are given
without regard for the small amounts of contamination that
invariably exist in thin films as is well known to those skilled in
the art. The invention has been described with respect to
particular embodiments, but other uses and applications for the
bilayer structure comprising a RuAl/NiAlB will be apparent to those
skilled in the art.
* * * * *