U.S. patent application number 10/651634 was filed with the patent office on 2005-03-03 for magnetic thin film media with a bi-layer structure of crti/nip.
Invention is credited to Bian, Xiaoping, Doerner, Mary Frances, Mirzamaani, Mohammad S., Polcyn, Adam, Xiao, Qi-Fan.
Application Number | 20050048328 10/651634 |
Document ID | / |
Family ID | 34136634 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050048328 |
Kind Code |
A1 |
Bian, Xiaoping ; et
al. |
March 3, 2005 |
MAGNETIC THIN FILM MEDIA WITH A BI-LAYER STRUCTURE OF CRTI/NIP
Abstract
A thin film magnetic media structure with a bi-layer structure
of amorphous chromium titanium (CrTi) followed by an amorphous
layer of nickel phosphorus (NiP) is disclosed. After the NiP has
been deposited it is exposed to oxygen to form an oxidized surface.
Preferably the underlayer is deposited directly onto the oxidized
NiP surface. The bi-layer structure of CrTi/NiP promotes excellent
in-plane crystallographic orientation in the cobalt alloy magnetic
layer(s) and allows: an ultra-thin chromium underlayer to be used
which provides better control over grain size and distribution.
When the CrTi/NiP bi-layer structure is combined with a
circumferentially textured substrate, preferably glass, a high Mrt
orientation ratio (OR) results.
Inventors: |
Bian, Xiaoping; (San Jose,
CA) ; Doerner, Mary Frances; (Santa Cruz, CA)
; Mirzamaani, Mohammad S.; (San Jose, CA) ;
Polcyn, Adam; (San Jose, CA) ; Xiao, Qi-Fan;
(San Jose, CA) |
Correspondence
Address: |
Marlin Knight
Hoyt & Knight
PO Box 1320
Pioneer
CA
95666
US
|
Family ID: |
34136634 |
Appl. No.: |
10/651634 |
Filed: |
August 29, 2003 |
Current U.S.
Class: |
428/831 ;
428/611; 428/686; G9B/5.288 |
Current CPC
Class: |
G11B 5/73921 20190501;
Y10T 428/12861 20150115; Y10T 428/12986 20150115; Y10S 428/90
20130101; Y10T 428/12465 20150115; Y10T 428/12854 20150115; G11B
5/7369 20190501 |
Class at
Publication: |
428/694.0TS ;
428/611; 428/686; 428/065.3; 428/065.7 |
International
Class: |
B32B 003/02; G11B
005/64 |
Claims
1. A magnetic thin film storage medium comprising: a substrate; a
layer of amorphous CrTi deposited onto the substrate; a layer of
amorphous NiP deposited onto the layer of CrTi; at least one
underlayer over the layer of amorphous NIP; and at least one
magnetic layer over the underlayer.
2. The magnetic thin film storage medium of claim 1 wherein the
layer of amorphous NiP has an oxidized surface formed after the
layer of amorphous NiP was deposited.
3. The magnetic thin film storage medium of claim 2 wherein the
underlayer is chromium that is deposited onto the oxidized surface
of the layer of amorphous NiP.
4. The magnetic thin film storage medium of claim 1 wherein the
substrate is circumferentially textured glass.
5. The magnetic thin film storage medium of claim 1 wherein the
underlayer is chromium or an alloy of chromium.
6. The magnetic thin film storage medium of claim 1 wherein the
layer of amorphous CrTi is approximately from 45 to 55 at. %
titanium.
7. The magnetic thin film storage medium of claim 1 wherein the
layer of amorphous NiP is approximately from 15 to 25 at. %
phosphorus.
8. A disk drive comprising: a magnetic transducer including a read
and a write head; a spindle; and a magnetic thin film disk mounted
on the spindle, the magnetic thin film disk including a layer of
amorphous CrTi followed by a layer of amorphous NiP deposited onto
the layer of amorphous CrTi and at least one magnetic layer.
9. The disk drive of claim 8 wherein the layer of amorphous NiP has
an oxidized surface formed after the layer of amorphous NiP was
deposited
10. The disk drive of claim 9 wherein the underlayer is chromium or
a chromium alloy and is deposited onto the oxidized surface of the
layer of amorphous NiP.
11. The disk drive of claim 9 wherein the substrate is
circumferentially textured glass.
12. The disk drive of claim 9 wherein the layer of amorphous CrTi
is approximately from 45 to 55 at. % titanium.
13. The disk drive of claim 9 wherein the layer of amorphous NiP is
approximately from 15 to 25 at. % phosphorus.
14. A method of fabricating a magnetic thin film storage medium
comprising the steps of: depositing a thin film of CrTi on a
substrate; and depositing a thin film of NiP onto the thin film of
CrTi.
15. The method of claim 14 further comprising the step of oxidizing
an exposed surface of the thin film of NiP.
16. The method of claim 15 further comprising the step of
depositing a thin film chromium underlayer onto the thin film of
amorphous NiP.
17. The method of claim 15 wherein the substrate is
circumferentially textured glass.
18. The method of claim 15 further comprising the step of
depositing a thin film chromium alloy underlayer onto the thin film
of amorphous NiP.
19. The method of claim 15 wherein the thin film of CrTi is
approximately from 45 to 55 at. % titanium.
20. The method of claim 15 wherein the thin film of NIP is
approximately from 15 to 25 at. % phosphorus.
Description
FIELD OF THE INVENTION
[0001] The invention relates to magnetic thin film media and
methods for their fabrication and more particularly to materials
for use in magnetic thin film disks prior to an underlayer.
BACKGROUND OF THE INVENTION
[0002] A typical prior art head and disk 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.
Historically the substrate was AlMg with an amorphous NiP surface
film deposited by wet electroless plating. The AlMg/NiP disk was
considered to be the substrate on which thin films were vacuum
deposited to form the layers of the magnetic media.
[0003] One embodiment of the thin films 21 typically used with a
glass substrate includes an amorphous initial thin film which is
called a pre-seed layer and is followed by a crystalline seed
layer. Typically both the pre-seed layer and seed layer are
relatively thin layers. In U.S. Pat. No. 5,789,056 to Bian, et al.,
the use of a crystalline CrTi seed layer is described. Following
the seed layer is typically a chromium or chromium alloy underlayer
such as Cr, CrV and CrTi. One or more ferromagnetic layers based on
various alloys of cobalt follow the underlayer. For example, a
commonly used alloy is CoPtCr. Additional elements such as tantalum
and boron are also often used in the magnetic alloy. A protective
overcoat layer is used to improve wearability and corrosion
resistance. The disk embodiment described above is one of many
possibilities. For example, multiple seed layers, multiple
underlayers and multiple magnetic layers have all been proposed in
the prior art.
[0004] U.S. Pat. No. 6,593,009 issued to Bian, et al. on Jul. 15,
2003 describes a thin film magnetic media structure comprising a
pre-seed layer CrTi which presents an amorphous or nanocrystalline
structure. In the following text the term amorphous will be used to
include nanocrystalline. The preferred seed layer is said to be
RuAl. The use of the CrTi/RuAl bi-layer structure provides superior
adhesion to the substrate and resistance to scratching, as well as,
excellent coercivity and signal-to-noise ratio (SNR) and reduced
cost over the prior art.
[0005] U.S. Pat. No. 6,567,236 to Doemer, et al., describes a
preferred embodiment of a layer structure as: an amorphous pre-seed
layer of CrTi, a seed layer of RuAl, a crystalline underlayer of
CrTi, a bottom ferromagnetic layer of CoCr, an antiferromagnetic
coupling/spacer layer of Ru; and a top ferromagnetic structure
including: a thin first sublayer of CoCr, CoCrB or CoPtCrB, and a
thicker second sublayer of CoPtCrB with a lower moment than the
first sublayer.
[0006] U.S. Pat. No. 5,879,783 to Chang, et al., describes the use
of a NiP seed layer which is sputtered deposited on a glass or
glass-ceramic substrate, and the surface is roughened by oxidation.
In U.S. Pat. No. 6,596,419 to Chen, et al., a magnetic recording
medium is described that includes a seed layer comprising a
material selected from the group consisting of oxidized NiP (NiPOx)
and CrTi. The thickness of the seed layer is said to be about 4 nm
to 6 nm. It is stated that the CrTi and NiPOx seed layers enhance
the development of CoTi/Cr(200) and Co(11.0) crystallographic
orientation, and help to reduce grain size of CoTi/Cr-alloy
underlayers.
[0007] The preferred orientation (PO) of the various crystalline
materials forming the layers on the disk, as discussed herein, is
not necessarily an exclusive orientation which may be found in the
material, but is merely the most prominent orientation. When the Cr
underlayer is sputter deposited at a sufficiently elevated
temperature on a NiP-coated AlMg substrate a [200] PO is usually
formed. This PO promotes the epitaxial growth of [11-20] PO of the
hexagonal close-packed (hcp) cobalt (Co) alloy, and thereby
improves the magnetic performance of the disk. The [11-20] PO
refers to a film of hexagonal structure whose (11-20) planes are
predominantly parallel to the surface of the film. Likewise the
[10-10] PO refers to a film of hexagonal structure whose (10-10)
planes are predominantly parallel to the surface of the film. The
[10-10] PO can be epitaxially grown on an appropriate underlayer
with a PO of [112].
[0008] One technique used in the prior art to improve magnetic
recording performance on thin film disks is circumferential
polishing to create a pattern of fine "scratches" (circumferential
texture) which are generally oriented along tracks (concentric
circles) on the disk surface. The scale of the texture of
commercial thin film disks is microscopic with a peak-to-valley of
less than 5 nm typically. A 5 nm texture appears mirror-like to the
untrained eye. Special polishing equipment is necessary to achieve
circumferential texture this fine. The topography of the surface on
which a thin film is deposited can have a significant effect on the
way the film nucleates and grows and also upon its characteristics.
So called circumferential texture on magnetic disks has been
commonly used to influence the inplane magnetic anisotropy for a
wide range of magnetic alloys. For longitudinal recording it is
sometimes useful to have a higher coercivity (Hc) and Mrt in the
circumferential direction than in the radial direction. The ratio
of the circumferential Hc to the radial Hc is called the coercivity
orientation ratio (OR). Similarly the ratio of the circumferential
Mrt to the radial Mrt is called the Mrt orientation ratio (OR).
Current disks typically use hexagonal close packed (hcp) cobalt
alloys and most (but not all) circumferentially textured disks have
an Hc or Mrt OR>1.
SUMMARY OF THE INVENTION
[0009] The applicants disclose a thin film magnetic media structure
with a bi-layer structure of amorphous chromium titanium (CrTi)
followed by an amorphous layer of nickel phosphorus (NiP) deposited
prior to the underlayer. After the NiP has been deposited it is
preferably exposed to oxygen to form an oxidized surface.
Preferably the underlayer is deposited directly onto the oxidized
NiP surface. The bi-layer structure of CrTi/NiP promotes excellent
in-plane crystallographic orientation in the cobalt alloy magnetic
layer(s) and allows an ultra-thin chromium underlayer to be used
which provides better control over grain size and distribution.
When the CrTi/NiP bi-layer structure is combined with a
circumferentially textured disk, preferably glass, a high Mrt
orientation ratio (OR) results.
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 thin film layer stack for a
magnetic thin film disk embodying the CrTi/NiP bi-layer structure
of the invention.
[0012] FIG. 3 is an illustration of an embodiment of a magnetic
thin film layer structure for use in the layer stack of FIG. 2.
DETAILED OF THE INVENTION
[0013] For longitudinal media on glass or other nonmetallic
substrates, it is important to maximize the c-axis in-plane
crystallographic orientation and maintain the orientation ratio.
Some seed layer materials contribute to good in-plane c-axis
orientation when used on smooth or randomly polished substrates,
but turn out not to be satisfactory for used on circumferential
textured substrates because they produce a much lower orientation
ratio (OR). The bi-layer structure described herein is composed of
two amorphous or nanocrystalline layers. The structure is
particularly suited to use on circumferentially textured substrates
since it helps achieve a good in-plane c-axis orientation, as well
as, a high orientation ratio.
[0014] Reference is made to FIG. 2 illustrate the thin film layers
in a magnetic film disk 16 embodying the invention. In the
embodiment shown in FIG. 2 the substrate 26 is preferably glass,
but can be any other appropriate material. Even more preferably the
substrate is circumferentially textured glass. The CrTi layer 31 is
vacuum deposited directly onto the substrate surface 26. The NiP
layer 32 is vacuum deposited onto the CrTi layer 31. These layers
are preferably deposited at room temperature and without substrate
voltage bias. The CrTi layer and NiP layers will be referred to
collectively as the CrTi/NiP bi-layer structure. After the NiP
layer has been vacuum deposited, the surface of the NiP is oxidized
by supplying oxygen gas into the deposition chamber or by breaking
vacuum and exposing the surface to the atmosphere. After the NiP
surface has been oxidized the underlayer 33 is vacuum deposited
directly onto NiP. The underlayer is preferably chromium, but can
also be a chromium alloy. The bi-layer structure of the invention
allows the underlayer 33 to be kept very thin. The advantage of
having an ultra-thin underlayer is that control over the grain size
and distribution is improved. In general, the thinner the
underlayer, the smaller the spread in grain sizes. The magnetic
layer structure 34 is followed by a protective overcoat layer
35.
[0015] The preferred range for the combined thickness of the
CrTi/NiP bi-layer structure and the underlayer is from 60 to 150
anstroms. As an illustration, one embodiment of the invention has a
20 angstrom CrTi layer, a 45 angstrom NiP layer and a 40 angstrom
chromium underlayer for a combined thickness of 105 angstroms. This
is to be compared with an embodiment from the U.S. Pat. No.
6,593,009 issued to Bian, et al. of 200 angstroms CrTi, 60
angstroms RuAl and 60 angstroms of a CrTi underlayer.
[0016] The bi-layer structure of the invention can be used with a
wide range of magnetic layer structures 34. The magnetic layer
structure 34 can be a single magnetic layer or it can comprise a
combination of multiple magnetic layers, spacer layers, onset
layers, etc. as are known in the art. An antiferromagnetically
coupled magnetic layer stack can also be used. FIG. 3 illustrates a
particular embodiment of the magnetic layer structure 34 that can
be used with the bi-layer structure of the invention. The functions
of the onset layer 41 are described in the prior art. In this
embodiment CrMo is preferred. The lower magnetic layer 42 is
preferably CoCr. The spacer layer 43 is preferably ruthenium. The
upper magnetic layer 44 is preferably CoPtCrB.
[0017] In an experiment magnetic disks were prepared using NiP as a
sole seed layer and the CrTi/NiP bi-layer structure of the
invention. The underlayer was chromium and magnetic layer
structures were as described above. The substrates were
circumferentially textured glass. The measured results are given in
Table 1.
1 TABLE 1 Cr(200) Co(11-20) Mrt Rocking Curve Rocking Curve Seed
Mrt Hc OR tangential radial tangential radial CrTi/NiP 0.35 4100
2.0 6.6 12.9 6.0 10.4 NiP 0.36 3900 1.5 7.3 13.3 6.8 11.4
[0018] The Mrt orientation ratio (OR) was 1.5 for the NiP seed, but
the CrTi/NiP of the invention yielded an Mrt OR 2.0. The higher OR
is desirable. The FWHM rocking curve measurements relate to the
distribution of the crystallographic orientations. Lower values
indicate a smaller (better) distribution of orientations. The
CrTi/NiP bi-layer structure yielded smaller rocking curve values
for both the Cr(200) orientation and the Co(11-20) orientation.
[0019] The preferred compositional range for the CrTi layer is
limited by the requirement that it remain amorphous; therefore,
approximately from 45 to 55 at. % titanium should be used with 50
at. % being preferred. The preferred compositional range for NiP
layer is from 15 to 25 at. % phosphorus which must likewise remain
amorphous. NiP with 19 at. % phosphorus is particularly preferred.
The atomic percent compositions are given without regard for the
small amounts of contamination that invariably exist in sputtered
thin films as is well known to those skilled in the art.
[0020] The invention has been described with respect to particular
embodiments, but other uses and applications for the seed layer
structure of the invention will be apparent to those skilled in the
art.
* * * * *