U.S. patent application number 09/734114 was filed with the patent office on 2002-06-13 for multi-stage thermoelectric microcoolers for cooling write coils and gmr sensors in magnetic heads for disk drives.
This patent application is currently assigned to IBM Corporation. Invention is credited to Ghoshal, Uttam Shyamalindu.
Application Number | 20020071223 09/734114 |
Document ID | / |
Family ID | 24950365 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020071223 |
Kind Code |
A1 |
Ghoshal, Uttam Shyamalindu |
June 13, 2002 |
Multi-stage thermoelectric microcoolers for cooling write coils and
GMR sensors in magnetic heads for disk drives
Abstract
An improved read/write head for use in computer hard drives is
provided. In one embodiment, the read/write head includes a first
and second thermally conducting plates and a first and second
stages of microcoolers. The second thermally conducting plate is
thermally coupled to a read sensor of the read/write head. The
second microcooler includes a hot plate and a cold plate, wherein
the cold plate extends proximate the read sensor so as to cool the
sensor to ambient or below temperatures. The first thermally
conducting plate extends between the write coil and the read sensor
in the read/write head and is thermally coupled to the hot plate of
the second microcooler. The hot plate of the first microcooler is
thermally coupled to one or more heat dissipation elements.
Inventors: |
Ghoshal, Uttam Shyamalindu;
(Austin, TX) |
Correspondence
Address: |
Duke W. Yee
Carstens, Yee & Cahoon, LLP
P. O. Box 802334
Dallas
TX
75380
US
|
Assignee: |
IBM Corporation
|
Family ID: |
24950365 |
Appl. No.: |
09/734114 |
Filed: |
December 11, 2000 |
Current U.S.
Class: |
360/317 ;
360/128; G9B/5.034; G9B/5.143 |
Current CPC
Class: |
B82Y 25/00 20130101;
G11B 5/40 20130101; B82Y 10/00 20130101; G11B 5/3967 20130101; G11B
5/10 20130101; G11B 2005/3996 20130101; G11B 2005/001 20130101 |
Class at
Publication: |
360/317 ;
360/128 |
International
Class: |
G11B 005/39; G11B
005/10 |
Claims
What is claimed is:
1. A read/write head for a magnetic storage device, comprising: a
first thermally conducting plate situated between a write coil and
a read sensor in the read/write head; a first microcooler
comprising a hot plate and a cold plate, wherein the cold plate is
thermally coupled to the first thermally conducting plate and the
hot plate is thermally coupled to one or more heat dissipation
elements; a second thermally conducting plate thermally coupled to
the read sensor of the read/write head; and a second microcooler
comprising a hot plate and a cold plate, wherein the cold plate is
thermally coupled to the second thermally conducting plate and the
hot plate is coupled to the cold plate of the first
microcooler.
2. The read/write head as recited in claim 1, wherein the heat
dissipation elements comprise posts.
3. The read/write head as recited in claim 1, wherein the heat
dissipation elements comprise fins.
4. The read/write head as recited in claim 1, wherein the heat
dissipation elements include copper.
5. The read/write head as recited in claim 1, wherein the first
thermally conducting plate includes electrically conducting
materials and is patterned to reduce eddy currents.
6. The read/write head as recited in claim 5, wherein the
electrically conducting materials include copper.
7. The read/write head as recited in claim 5, wherein the
electrically conducting materials include tungsten.
8. A disk drive with a high performance head, comprising: a
rotating magnetic storage medium; a head positioning apparatus
operable to selectively locate a read/write head proximate selected
positions on the rotating magnetic storage medium; and a head
cooler integral to said read/write head, wherein the head cooler
includes: a first thermally conducting plate situated between a
write coil and a read sensor in the read/write head; a first
microcooler comprising a hot plate and a cold plate, wherein the
cold plate is thermally coupled to the first thermally conducting
plate and the hot plate is thermally coupled to one or more heat
dissipation elements; a second thermally conducting plate thermally
coupled to the read sensor of the read/write head; and a second
microcooler comprising a hot plate and a cold plate, wherein the
cold plate is thermally coupled to the second thermally conducting
plate and the hot plate is coupled to the cold plate of the first
microcooler.
9. The drive as recited in claim 8, wherein the first stage
microcooler comprises a thermoelectric cooler.
10. The drive as recited in claim 8, wherein the second stage
microcooler comprises a thermoelectric cooler.
11. The drive as recited in claim 8, wherein the first cold plate
includes electrically conducting materials.
12. The drive as recited in claim 11, wherein the electrically
conducting materials include copper.
13. The drive as recited in claim 11, wherein the electrically
conducting materials include tungsten.
14. The drive as recited in claim 8, wherein the heat dissipation
elements include posts.
15. The drive as recited in claim 8, wherein the heat dissipation
elements include fins.
16. The drive as recited in claim 8, wherein the heat dissipation
elements comprise copper.
Description
CROSS REFERENCE TO RELATED PATENTS
[0001] The present application is related to U.S. Pat. No.
6,105,381 entitled "METHOD AND APPARATUS FOR COOLING GMR HEADS FOR
MAGNETIC HARD DISKS" issued Aug. 22, 2000 and to U.S. patent
application Ser. No. ______ (IBM Docket No. AUS990827US1) entitled
"THERMOELECTRIC MICROCOOLERS FOR COOLING WRITE COILS AND GMR
SENSORS IN MAGNETIC HEADS FOR DISK DRIVES" filed even date
herewith. The contents of the above mentioned commonly assigned
U.S. Patent and co-pending U.S. Patent Application are hereby
incorporated herein by reference for all purposes.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates generally to data storage
devices within data processing systems and more particularly to a
method and apparatus for alleviating elevated temperatures within
the read/write head of a hard disk type data storage devices.
[0004] 2. Description of Related Art
[0005] The requirement for high density magnetic storage of data on
hard disk drives has been increasing steadily for the past several
years. Hard disk drives include magnetic heads for reading and
writing data to the hard disk. The heads include write coils and
sensors for reading data from the disks. For purposes of the
ensuing description of the assembly including the write coil and
yoke will be referred to as the "write coil" and the assembly
including the magnetoresistive sensor situated between magnetic
shields will be referred to as the "read sensor"
[0006] Miniaturization of magnetoresistive (MR) sensors for disk
drives in the early 1990's allowed disk drive products to maximize
storage capacity with a minimum number of components. Fewer
components result in lower costs, higher reliability, and lower
power requirements for the hard disk drives.
[0007] MR sensors are used for the read element of a read/write
head. MR sensors read magnetically encoded information from the
magnetic medium of the disk by detecting magnetic flux stored in
the magnetic medium of the disk. As storage capacity of disk drives
has increased, the storage bit has gotten smaller and its magnetic
field has correspondingly become weaker. MR heads are more
sensitive to weaker magnetic fields than are the inductive read
coils used in earlier disk drives. Thus, the move away from
inductive read coils and to MR sensors for use in disk drives.
[0008] As discussed above, MR sensors are known to be useful in
reading data with a sensitivity exceeding that of inductive or
other thin film sensors. However, the development of Giant
Magnetoresistive (GMR) sensors (also referred to as GMR head chips)
has greatly increased the sensitivity and the ability to read
densely packed data. Thus, although the storage capacity for MR
disks is expected to eventually reach 5 gigabits per square inch of
surface disk drive (Gbits/sq.in.), the storage capacity of GMR
disks is expected to exceed 100 Gbits/sq.in.
[0009] The GMR effect utilizes a spacer layer of a non-magnetic
metal between two magnetic metals. The non-magnetic metal is chosen
to ensure that coupling between magnetic layers is weak. GMR disk
drive read sensors operate at low magnetic flux intensities. When
the magnetic alignment of the magnetic layers is parallel, the GMR
sensor resistance is relatively low. When the magnetic alignment of
the layers is anti-parallel, the resistance is relatively high.
Heat generated in the read/write head together with heat from other
components within the disk drive materially affects the operating
temperature of the GMR read sensor in the head.
[0010] As GMR sensors allow extremely high data densities on disk
drives, a stable sensor temperature is essential to accurate read
operations in high track density hard disk drives. It is well known
that the signal to noise ratio of GMR read sensors increases with a
decrease in temperature. Various methods of cooling hard disk drive
components are known and include forced air, cooling fins, and heat
pipes. Generally, the cooling methods have been limited to
attaching materials or structures that have high thermal
conductivities to transfer heat away from the head. However, due to
space limitations and ambient conditions, means for cooling,
whether to ambient or subambient temperatures, are generally not
available to the GMR read sensor.
[0011] As the requirements for the GMR read sensors have been
increasing over the years, the requirements for the write coils
within the disk drives have also been increasing. New disk drives
require fast field reversal during the write operation. This
requirement for fast field reversal during the write operation
implies larger write currents. Also, as the storage densities
increase, the media coercivity has to increase to avoid thermal
instability and the superparamagnetic limit. This reinforces the
need for even larger write currents. However, large write currents
increase the Joule heating in the coil such that the coil
temperatures are 40 to 80 degrees Celsius above ambient
temperatures. However, for optimal operation, the write coils need
to be kept near ambient temperatures. Furthermore, since the write
coil is immediately adjacent the GMR read sensor in the head, the
heating and elevated temperatures are shared by the GMR read
sensor.
[0012] Therefore, it would desirable to have a method and apparatus
for cooling the GMR read sensor and the write coils in the heads of
hard disk drives that would be practical and fit within the
structure of the head without requiring serious structural changes
to the hard disk drive. Cooling GMR read sensors would
significantly enhance magnetic sensing capacity of the GMR read
sensors during the read operation and increase performance of the
write coils during a write operation. It would also be desirable to
provide a practical method for cooling the heads to subambient
temperatures that would allow the utilization of GMR materials that
have significantly higher sensitivities.
SUMMARY OF THE INVENTION
[0013] The present invention provides an improved read/write head
for use in computer hard drives. In one embodiment, the read/write
head includes a first and second thermally conducting plates and a
first and second stages of microcoolers. The second thermally
conducting plate is thermally coupled to a read sensor of the
read/write head. The second microcooler includes a hot plate and a
cold plate, wherein the cold plate extends proximate the read
sensor so as to cool the sensor to ambient or below temperatures.
The first thermally conducting plate extends between the write coil
and the read sensor in the read/write head and is thermally coupled
to the hot plate of the second microcooler. The hot plate of the
first microcooler is thermally coupled to one or more heat
dissipation elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The novel features believed characteristic of the invention
are set forth in the appended claims. The invention itself,
however, as well as a preferred mode of use, further objectives and
advantages thereof, will best be understood by reference to the
following detailed description of an illustrative embodiment when
read in conjunction with the accompanying drawings, wherein:
[0015] FIG. 1 depicts a cut-away, top plan view of a data storage
system in accordance with the present invention;
[0016] FIG. 2 depicts a high-level conceptual diagram of a
Thermoelectric Cooling (TEC) device;
[0017] FIG. 3 depicts a planar view of a read/write head with cold
plate using single stage thermoelectric microcoolers in accordance
with the present invention;
[0018] FIG. 4 depicts a planar view of a read/write head with cold
plate using selectively acting two stage thermoelectric coolers in
accordance with the present invention; and
[0019] FIG. 5 depicts a conceptual diagram of a two stage
thermoelectric cooler in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] With reference now to the figures, and in particular with
reference to FIG. 1, a cut-away, top plan view of a hard disk data
storage system is depicted in accordance with the present
invention. Data storage system 100 includes a housing 101
containing at least one rotatable data storage disk 102 supported
on a spindle 105 and rotated by a drive motor (not shown).
Typically, a data storage system will comprise a plurality of disks
and a slider 106 with a read/write head 104 for each disk. As an
example, in a magnetic disk storage device, each data storage disk
102 has the capability of receiving and retaining data, through the
use of a magnetic recording medium formed on at least one disk
surface 103, where the magnetic recording medium is arranged in an
annular pattern of multiple concentric data tracks 108. Though only
a few data tracks 108 are shown, it is known that the number of
tracks varies according to at least the recording medium and the
read/write head 104. At least one slider 106, including one or more
read/write heads 104 is positioned over data storage disk 102.
Slider 106 is suspended from an actuator arm (not shown) by a
suspension (also not shown) and the radial position of slider 106
with respect to data tracks 108 of data storage disk 102, is
controlled by a voice coil motor (not shown).
[0021] During operation of data storage system 100, the rotation of
data storage disk 102 generates an air bearing between head 104 and
disk surface 103. The air bearing counterbalances a slight
downward-biased spring force of the suspension and supports head
104 above disk surface 103 by a small, substantially constant
spacing. As disk 102 is rotated by the drive motor, slider 106 is
moved radially in and out in response to the movement of the
actuator arm by the voice coil motor, permitting read/write head
104 to read and write data from and to the concentric tracks 108.
Though only one read/write head 104 and slider 106 assembly is
shown, it is well known that a plurality of sliders 106 may be
employed to access a plurality of disks 102, stacked one atop the
other on spindle 105.
[0022] The temperature of read/write head 104 may rise during
operation of data storage drive 100 due to previously discussed
magnetic field changes and ambient conditions in data storage
system 100. The primary contributor of heat is the write coil.
Magnetic instability may arise in read/write head 104 due to
increasing read/write head 104 temperatures. Higher temperature
increases the Johnson voltage noise of the read sensor and
decreases the net signal to noise capability of the read
sensor.
[0023] According to the present invention, a thermoelectric
microcooler, is mounted on the read/write head 104 and thermally
coupled to a cold plate situated between the write coil and the
read sensor to provide active heat transfer of the energy
dissipated by the write coil. Also, the microcooler device may
utilize a separate power source or the same power source as the
read/write head 104. Though Peltier effect thermoelectric cooling
(TEC) devices are used to cool many heat producing components such
as, for example, blood analyzers, lasers, and microprocessors, lack
of efficiency and size has limited their applications.
[0024] With reference to FIG. 2, a high-level block diagram of a
generic TEC device 200 is depicted. Thermoelectric cooling, a well
known principle, is based on the Peltier effect, by which DC
current from power source 202 is applied across two dissimilar
materials causing heat to be absorbed at the junction of the two
dissimilar materials. A typical thermoelectric cooling device
utilizes p-type semiconductor 204 and n-type semiconductor 206
sandwiched between poor electrical conductors 208 that have good
heat conducting properties. N-type semiconductor 206 has an excess
of electrons, while p-type semiconductor 204 has a deficit of
electrons. As electrons move from p-type semiconductor 204 to
n-type semiconductor 206 via electrical conductor 210, heat energy
is transferred from cold plate 212 to hot plate 216.
[0025] With reference now to FIG. 3, a schematic diagram of a
read/write head 300 for a disk drive is depicted in accordance with
the present invention. The read/write head 300 includes a read
sensor 308, bond pads 392-397, and a cold plate 302. The cold plate
302 is situated between the GMR read sensor and the write coil of
read/write head 300. The relative position of the actual coils is
depicted at 312, while the relative position of the magnetic
shields is depicted at 310. Their functions and locations are well
known. In one embodiment, cold plate 302 includes a patterned ring
of copper (Cu) or tungsten (W). Given that cold plate 302 is
electrically conducting, as is depicted in the present example,
then cold plate 302 should be patterned with radial grooves 311 to
electrically segment the cold plate such that eddy currents are
suppressed. Thereby the coupling effects of the magnetic field
produced by the are minimized.
[0026] In one embodiment, the read/write head 300 includes two
thermoelectric microcoolers 356 and 357 thermally coupled to cold
plate 302 and on the hot side to copper posts 320. Heat is thereby
transferred from the cold plate, lying between the write coil and
read sensor, to the disk drive interior ambient. Microcoolers
356-357 are fabricated using an electrodeposition method, which is
a low temperature post-processing step after the head fabrication.
More information regarding the fabrication of microcoolers is
available in U.S. patent application Ser. No. 09/498,826 filed on
Feb. 4, 2000 which is hereby incorporated by reference for all
purposes.
[0027] In the prior art, a simple cooling plate of copper placed
proximate the write coil and read sensor is thermally connected to
copper posts without an intervening active cooling device. Thus, in
the prior art, the read/write head write coil and adjacent read
sensor were always at a temperature well above the disk drive
interior ambient. The inclusion of the thermoelectric coolers
356-357 allows the write coils and read sensor of read/write head
300 to be actively cooled to a temperature than in the prior art.
Since the permeability of the yoke of the write coil and the signal
to noise performance of the read sensor are sensitive to
temperature, the use of microcoolers 356-357 in read/write head 300
greatly improves multiple aspects of the read/write head 308
performance. Also, since most of the heat is generated by the write
coils, the shape and location of cold plate 311 should align with
the write coils.
[0028] The plurality of copper posts 320 may be constructed from
other material that is a good conductor of heat. Alternatively,
posts 320 may be replaced by fins.
[0029] With reference now to FIG. 4, a planar view of a read/write
head 400 with two stage microcoolers is depicted in accordance with
the present invention. In this embodiment, in addition to stage one
microcoolers 356 and 357 as depicted in FIG. 3, stage two
microcoolers 362-364 have also been included in the read/write head
400. In all other regards, the read/write head 400 is similar to
read/write head 300 in FIG. 3. By using a two stage microcooler,
the GMR read sensor 308 may be cooled to a point beyond that
possible with the use of a single stage microcooler in further
recognition of the temperature sensitivity exhibited by read sensor
308.
[0030] The cold plate 306 is thermally coupled to thermoelectric
coolers 356-357 which are each in turn thermally coupled to posts
320. The cold plate of second stage thermoelectric microcoolers
362-364 is thermally coupled to arm 366, which is constructed from
a thermally conductive material, such as, for example, copper,
extends beneath but in close thermal proximity to GMR read sensor
308. The hot plate of second stage microcoolers 362-364 is
thermally coupled to cold plate 306. Thus, the read sensor 308 is
cooled to an even lower temperature than the write coils cold
plate, and possibly event to subambient levels.
[0031] Because the read head generates much less heat than do the
write coils, the second stage microcoolers 362-364 do not need to
be as large as the first stage microcoolers 356-357. For similar
reasons, arm 366, which serves as the cold plate for second stage
microcoolers 362-364 does not need to be as large as cold plate
306.
[0032] Also, because the physical size of the read/write head
elements depicted in FIGS. 3 and 4 are determined by the bond pads,
which require much more room than is necessary to implement the
basic write coils and read sensor, the cold plates and microcoolers
may be included in the read/write head without materially
increasing the size of the read/write head.
[0033] With reference now to FIG. 5, a schematic diagram of a two
stage thermoelectric cooler is depicted in accordance with the
present invention. Two stage thermoelectric cooler 500 may be
implemented as, for example, stage one microcooler 356 and stage
two microcooler 364 in FIG. 4. Two stage microcooler 500 includes a
first stage microcooler comprising p-type impurity thermoelectric
material elements 502 and 504 and n-type impurity thermoelectric
material elements 506 and 508. Two stage microcooler 500 also
includes a second stage comprising p-type impurity thermoelectric
material element 510 and n-type impurity thermoelectric material
element 512.
[0034] A current I.sub.0 is connected by conductor to
thermoelectric material elements 502 and 504. The current I.sub.0
is split into I.sub.1 and I.sub.2. Current I.sub.2 passes through
thermoelectric material element 504 and through region
thermoelectric element 506. Current I.sub.2 passes through
thermoelectric material elements 502, 510, 512, and 508. The cold
plate for the first stage microcooler is between the first stage
and the second stage and is the hot plate for the second stage
microcooler.
[0035] The description of the present invention has been presented
for purposes of illustration and description, and is not intended
to be exhaustive or limited to the invention in the form disclosed.
Many modifications and variations will be apparent to those of
ordinary skill in the art. The embodiment was chosen and described
in order to best explain the principles of the invention, the
practical application, and to enable others of ordinary skill in
the art to understand the invention for various embodiments with
various modifications as are suited to the particular use
contemplated.
* * * * *