U.S. patent application number 11/772681 was filed with the patent office on 2008-01-17 for magnetic memory device and method for magnetic reading and writing.
Invention is credited to Santosh Kumar, Subodh Kumar, Divyanshu Verma.
Application Number | 20080013199 11/772681 |
Document ID | / |
Family ID | 33457262 |
Filed Date | 2008-01-17 |
United States Patent
Application |
20080013199 |
Kind Code |
A1 |
Kumar; Santosh ; et
al. |
January 17, 2008 |
Magnetic Memory Device and Method for Magnetic Reading and
Writing
Abstract
Disclosed herein are a magnetic memory device and method for
storing and retrieving data. The magnetic memory device includes a
read disk and a storage disk. The read disk comprises of an array
of read heads wherein the individual read head corresponds to a
storage element on the storage disk.
Inventors: |
Kumar; Santosh; (San Jose,
CA) ; Kumar; Subodh; (Glen Allen, VA) ; Verma;
Divyanshu; (Glen Allen, VA) |
Correspondence
Address: |
JAMES E. EAKIN
P.O. BOX 1250
MENLO PARK
CA
94025-4317
US
|
Family ID: |
33457262 |
Appl. No.: |
11/772681 |
Filed: |
July 2, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10725706 |
Dec 2, 2003 |
7239570 |
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11772681 |
Jul 2, 2007 |
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60471801 |
May 20, 2003 |
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Current U.S.
Class: |
360/63 ;
360/246.6; 360/324; 360/324.11; 360/324.12 |
Current CPC
Class: |
G11C 11/1659 20130101;
G11C 11/1673 20130101; G11C 11/14 20130101; G11C 11/1675 20130101;
B82Y 10/00 20130101; G11C 11/15 20130101; G11C 11/161 20130101 |
Class at
Publication: |
360/063 ;
360/246.6; 360/324; 360/324.11; 360/324.12 |
International
Class: |
G11B 15/12 20060101
G11B015/12 |
Claims
1. A magnetic mass storage memory device comprising: a) a read disk
having an array of read heads; b) a storage disk having an array of
magnetic storage elements wherein the read heads associate with a
corresponding storage element on the storage disk; and c) a control
circuit to select the desired storage element that controls an
orientation of a magnetic field of a corresponding read head.
2. The memory device according to claim 1, wherein the read head
comprising: a) a pinned layer; and b) a free layer.
3. The memory device according to claim 2, wherein the pinned layer
has a fixed magnetic orientation.
4. The memory device according to claim 3, wherein the free layer
has a variable magnetic orientation.
5. The memory device according to claim 4, wherein the storage
element comprising a second free layer.
6. The memory device according to claim 5, wherein the second free
layer has a variable magnetic orientation.
7. The memory device according to claim 6, wherein the magnetic
orientation of the first free layer is regulated by the magnetic
orientation of the second free layer.
8. The memory device according to claim 7, wherein a resistance of
the corresponding read head is indicative of a value stored
therein.
9. The memory device according to claim 8 wherein the read head is
an MR.
10. The memory device according to claim 8 wherein the read head is
a GMR.
11. The memory device according to claim 8 wherein the read head is
a CMR.
12. A magnetic mass storage memory device comprising: a) a read
disk having an array of read heads, each read head comprising a
plurality of magnetic layers; b) a storage disk having a plurality
of conductive lines with an array of magnetic storage elements
disposed between the conductive lines corresponding the read heads;
and c) a control circuit to select the desired storage element from
an array of storage elements such that a current through the
conductive lines will induce a magnetic field in the selected
storage element wherein the induced magnetic filed controls a
direction of a magnetic field of at least one layer in the
plurality of magnetic layers in the corresponding read head.
13. The memory device according to claim 12, wherein the plurality
of magnetic layers comprising: a) a pinned layer; and b) a free
layer.
14. The memory device according to claim 13, wherein a direction of
the magnetic field of the pinned layer is fixed.
15. The memory device according to claim 14, wherein the direction
of the magnetic field of the free layer is variable.
16. The memory device according to claim 15, wherein the storage
element comprising a second free layer.
17. The memory device according to claim 16, wherein a direction of
a magnetic field of the second free layer is regulated by a current
through the conducting lines.
18. A method for magnetic writing comprising the steps of: a)
selecting a storage element from an array of storage elements on a
storage disk by a control circuit; b) inducing a magnetic field in
the storage element by passing current through a plurality of
conducting lines around the storage element; and c) controlling the
magnetic field orientation of a layer in a corresponding read head
by the induced magnetic field.
19. The method according to claim 18 wherein the storage element
and the layer in the corresponding read head are magnetically
coupled.
20. The method according to claim 19, wherein the read head is a
GMR.
21. A method of magnetic reading on a storage device comprising the
steps of: a) selecting a magnetic storage element, from an array of
magnetic storage elements on a storage disk; b) passing current
through conducting lines surrounding the magnetic storage element;
c) inducing a magnetic field around the magnetic storage element by
the current through the conducting lines; d) setting the direction
of magnetization of a second free layer in the storage element and
d) controlling a direction of the magnetization of a free layer in
a corresponding read head from an array of read heads on a read
disk by the induced magnetic field; and e) measuring the resistance
of the corresponding read head.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. provisional
application Ser. No. 60/471,801, filed May 20, 2003 which is fully
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention pertains generally to memory storage
devices and particularly to magnetic memory storage devices.
BACKGROUND OF THE INVENTION
[0003] Within the field of memories, there is continuing interest
in finding ways to increase the storage density and speed. As the
personal use of small devices gain popularity, the memory of these
equipments has to be modified to match the function and design of
these small devices. Particularly, as more and more data needs to
be stored in the memory, the memory needs to have the capacity and
speed to handle such demand.
[0004] The discovery of new phenomena of magnetoresistive (MR) and
giantmagnetoresistive (GMR) effect provided a significant
advancement in the field of memory technology. This phenomena
demonstrated that resistance of multilayer thin film comprised of
ferromagnetic layers sandwiching a conducting layer can change
significantly depending on the direction of an external magnetic
field.
[0005] GMR is observed in magnetic metallic layered structures in
which it is possible to orient the magnetic moments of the
ferromagnetic layers relative to one another. One such type
magnetic metallic layered structure consists of a stack of four
magnetic thin films: a free magnetic layer, a nonmagnetic
conducting layer, a magnetic pinned layer and an exchange layer.
Magnetic orientation of the pinned layer is fixed and held in place
by the exchange layer. By applying an external magnetic field, the
magnetic orientation of the free layer may be changed with respect
to the magnetic orientation of the pinned layer. The change in the
magnetic orientation generates a significant change in the
resistance of the metallic layered structures. The resistance of
the structure determines the logical value to be stored
therein.
[0006] Currently this technology is predominantly used in the disk
drives. Disk drives use discs which are coated with a magnetizable
medium for storage of digital information in a plurality of
concentric data tracks. A track is a concentric set of magnetic
bits on the disk. A sector is a part of each track that is defined
with a magnetic marking and an ID number. A cylinder is group of
tracks with the same radius. In a typical magnetic disk drive, a
magnetic disk rotates at high speed and a read-write head uses air
pressure to "fly" over the top surface of the disk. The head
records information on the surface of the disk by impressing a
magnetic field on the disk. Information is read back using the head
by detecting magnetization of the disk surface. To access the disk
requires a sequence of steps. The total time required to complete
such sequence of steps is generally known as the access time.
Access time has two major components: seek time and rotational
latency. Seek time is the time needed for the read-write head to
move radially to the cylinder containing the desired sector.
Rotational latency is the additional time waiting for the disk to
rotate the desired sector to the disk head. The access time is a
sum of the seek time and the rotational latency time. The disk
drives available today has an access time of 14 ms and this is too
long for the future demand. The speed of the disk drive is
negatively impacted by such long access time.
[0007] Spindle motors are generally used to rotate the disk at high
speeds. A read-write head carried by a head slider is positioned
over a track on the surface of the disk to write data to or read
data from the track. The head slider is supported by a movable
actuator which is controlled to position the read-write head
carried by the head slider to a location with respect to the disk
while the disk is rotating. However this arrangement using spindle
motors are known to have problems. Even minor vibrations or bumps
can cause the disk drive to crash. Mechanical constraints are
limiting the function of the disk drive. Moreover, as the disk
drives are being produced with increasing track densities and
decreasing access time, the feedback control systems in modern disc
drives must move the sliders to the correct position in a very
short period of time. Seek errors may occur if the slider is not
moved to the correct position.
[0008] As can be seen there is a clear need in the industry to have
disk drives with shorter access time and without the mechanical
constraints.
[0009] Meanwhile, a magnetic memory device known as
Magnetoresistive Random Access Memory (MRAM) has been developed on
an Integrated Circuit (IC) chip. This type of memory device
generally includes conductive lines positioned perpendicular to one
another. Each conductive lines act as either write or a bit line. A
magnetic stack is placed where the two conductive lines cross. An
electrical current flowing through one of the conductive line
induces a magnetic field around that conductive line. A different
current flowing through the other conductive line induces another
magnetic field around the second conductive line. The induced
magnetic fields align or realign the magnetic dipoles in the
magnetic stack. The resistance of the magnetic stack determines the
logical value to be stored therein.
[0010] For the MRAM the transistor logic circuits are embedded in
the IC chip itself. As a a result of having transistor logic
circuit in close proximity with the magnetic stack, the magnetic
field interferes with the functions of the logic circuit. The
magnetic field interference with the control circuits also makes it
difficult to integrate MRAM various devices. Moreover, the amount
of memory available through the use of an MRAM is only in the range
of 1 Mbit. This amount of memory is not suitable for most
applications. Also, since the MRAM is basically an IC chip it is
not adaptable to other types of fabrications especially into memory
devices like a disk drive.
[0011] While MRAMs provide a non-volatile memory it is not suitable
for most of the present day applications due to its small amount of
memory and inability to integrate, small amount of memory.
[0012] As can be seen there is clear need in the industry to have a
memory device that is fast with a large memory and is durable.
SUMMARY OF THE INVENTION
[0013] It is accordingly an object of the invention to provide a
memory storage device that overcomes the above mentioned
disadvantages of the prior art devices of this general type.
[0014] One aspect of the invention includes a magnetic memory
storage device having a read disk and a storage disk. The read disk
includes of an array of read heads. The storage disk comprises of
an array of magnetic storage elements. The magnetic storage
elements are disposed between a plurality of conducting lines. The
individual read head on the disk has a corresponding storage
element on the storage disk.
[0015] The individual read head includes two layers. The first
layer includes a pinned layer and a first free layer. The magnetic
field of the pinned layer fixed. The magnetic field orientation of
the free layer may vary depending on other variables.
[0016] The writing operation involves passing current through the
conducting lines on the storage disk. The current through
conducting lines will induce a magnetic field around the storage
element. The storage element includes a second free layer. The
direction of magnetization of second free layer may vary.
Accordingly, the induced magnetic field fixes the direction of the
magnetization of the second free layer. The direction of
magnetization of the second free layer determines the value to be
stored.
[0017] The reading and writing operation in the memory storage
device is performed and controlled by different circuits. For
reading, a control circuit selects a read head from the array of
read heads on the read disk to perform the reading. The second free
layer of the corresponding storage element in the storage disk
controls the direction of the magnetization of the first free
layer. The resistance value of the read head depends on the
magnetic direction of the pinned layer and the free layer. As the
direction of the first free layer is controlled by the second free
layer of the storage element, the direction of the first free layer
depends on the stored value of the storage element. By measuring
the resistance of the read head the stored value may be
determined.
[0018] These and other objects, features, and advantages of the
present invention will become more apparent upon reading the
following detailed description in conjunction with the accompanying
drawings.
DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic top view of a storage disk 100.
[0020] FIG. 2 is schematic bottom view of a read disk 200.
[0021] FIG. 3a is a schematic top view of storage cell 300.
[0022] FIG. 3b is a schematic cross sectional view of a storage
cell 300 shown in FIG. 3a.
[0023] FIG. 4 shows a cross sectional view of structure 400 having
read head 402 and storage disk 406.
[0024] FIG. 5a shows a cross sectional view of a read head 500.
[0025] FIG. 5b shows a cross sectional view of a storage element
403.
[0026] FIG. 5c shows a cross sectional view of a storage cell unit
520 having a read disk and a storage element.
DETAILED DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 shows a schematic top views of a storage disk 100.
The storage disk 100 comprises of a plurality of conducting lines
102. Disposed between the conducting lines are an array magnetic
storage elements 104. A control circuit (not shown) will select a
particular storage element from the array of magnetic storage
elements. A current through the conducting lines will induce a
magnetic filed and it magnetizes the selected storage element. The
magnetic storage elements have a single axis of magnetization. The
direction of the magnetization is fixed by the induced magnetic
field and the direction of magnetization is interpreted as a binary
1 or 0.
[0028] Each of the magnetic storage element is capable of storing
at least one bit of data. Each magnetic storage element 104 is
exchangely isolated from other storage elements in the array.
However the storage elements 104 are strongly exchange coupled
within the array of storage elements that enable them to function
as a large single magnetic unit. It is understood that the magnetic
storage elements shown in FIG. 1 are not drawn to scale. Each
magnetic storage element are essentially the same size and has a
single magnetic domain.
[0029] FIG. 2 is a schematic bottom view of a read disk 200. The
read disk 200 comprises of an array of read heads 204. Even this
figure is not drawn to scale. Each one of the read heads on the
read disk correspond to a storage element on the storage disk. The
resistance of the read head depends on the direction of the
magnetization of the corresponding storage element on the storage
disk in FIG. 1. The resistance of the read head 200 determines the
logical value to be stored therein.
[0030] The reading and writing process in this embodiment of the
invention is accomplished by two different circuits. Writing is
done by the storage disk and its controlling circuits and reading
is done by the read head and its controlling circuits. The read
heads may be an MR, GMR, or CMR. Separating the circuits to
accomplish reading and writing provides a lot more control over the
circuit. Also, by having corresponding heads for each storage
element the seek and latency time associated with the disk drives
are virtually eliminated. It is understood that even though here we
are showing a one to one mapping between the storage elements and
the read heads that is not a necessity. Several storage elements
may be mapped to a single read head.
[0031] It should be appreciated that the current design avoids the
need for mechanical components like spindle motor and servo. As a
result, this memory storage device is not limited by the mechanical
capabilities. Another unique feature of the invention is that the
disks are not required to spin at high speeds thus providing
reliability and making it immune from crashes. Also, this design is
more durable as the present embodiment virtually eliminates the
dependence on mechanical components in turn it is less susceptible
to damage from shock or vibration.
[0032] The present invention keeps the control circuits to select
the desired storage element during write operation and the read
head during read operation are external to the read disk and the
storage disk. This allows the active circuit elements to be kept
away from the magnetic material and this will prevent leakage and
bit to bit interference.
[0033] FIG. 3a is top view of an individual storage cell 300 on a
storage disk (not shown) similar to the one shown in FIG. 1. The
cell 300 includes conductive lines 302. A magnetic storage element
304 disposed between the conductive lines. A current through the
conductive lines will induce a magnetic field around the storage
element. This in turn will magnetize the storage element. The
magnetic storage element has a single axis of magnetization. The
direction of the magnetization is interpreted as a binary 1 or 0.
FIG. 3b is the cross sectional view of the storage cell 300 shown
in FIG. 3a. FIG. 3b shows the conductive lines 302 and magnetic
storage element 304 disposed between the conductive lines.
[0034] FIG. 4 shows a cross sectional view of a magnetic storage
device 400. The device include a read disk 402 and a storage disk
406. The read disk has read heads 404. The storage disk 406 has
magnetic storage elements 408 disposed between conductive lines
(not shown). A current through the conductive lines (not shown)
will induce a magnetic field. This in turn will magnetize the
storage element. The magnetic storage element 408 has a single axis
of magnetization. The direction of the magnetization is interpreted
as a binary 1 or 0. Depending on the value stored in the storage
element i.e. 1 or 0 the resistance of the read head 304 is changed.
Reading is done by measuring the resistance of the read head.
[0035] FIG. 5a shows a cross sectional view of a read head 500. The
read head includes a pinned layer 502 and a first free layer 504.
The direction of the magnetization in the pinned layer 502 is
fixed. The direction of the magnetization of the first free layer
504 may vary. FIG. 5b shows a cross sectional view of a storage
element 503. The storage element has a second free layer 506. The
direction of the magnetization of the second free layer controls
the direction of magnetization of the first free layer 504 in the
read head 500. FIG. 5c shows a magnetic unit cell 520 in the
magnetic storage device (not shown). The magnetic unit cell 520
includes read head 500 of FIG. 5a and a storage element 503 of FIG.
5b. The read head 500 and the storage element 503 are separated by
an optional conductive layer 508 on the read head. The conductive
layer 508 acts as a router to make connection with the control
circuit. It is fabricated from paramagnetic material such as
tantalum. The pinned layer 502 and the first free layer 504 of the
read head 500 makes up the MR, GMR or the CMR.
[0036] The method of writing is done by passing current through
conductive lines (not shown) surrounding the storage element 503
which induces a magnetic field. The induced magnetic field
magnetizes the second free layer 506 of the storage element 503.
The direction of the magnetization of the second free layer depends
on the logical value to be written. The second free layer 506 and
the first free layer 504 are magnetically coupled thus the
direction of the magnetization of the second free layer 506
determines the direction of magnetization in the first free layer
504. If the direction of the magnetization of the first free layer
504 and the pinned layer 502 are in the same direction the
resistance will be low. If the direction of the magnetization of
the magnetization of the first free layer 504 and the pinned layer
502 are in the opposite direction the resistance would be high.
Accordingly if the resistance is low the value read will be 1 and
if the resistance is high the value read will be a logical zero.
The method of reading is done by measuring the resistance of the
first free layer 504 and the pinned layer 502.
[0037] Even though the description shows a read disk and a storage
disk, it is understood that the devices need not circular like a
disk. It can take any shape as it is not an integrated circuit (IC)
chip. This can be adapted into other types of devices such as a
cell phone, personal digital assistant (PDA), video games, MP3s
etc. It can be used for mass storage of digital data. The memory of
the storage device described herein varies from mega bit to the
giga bit range depending on application. The memory storage device
can be integrated virtually into any device because the active
circuit elements are separated from the magnetic elements. Since
the memory storage device is not an IC chip it can be made to the
fit the shape of the device into which it would be incorporated
into.
[0038] Additional advantages include higher amount of current
through the conducting lines as the area used for storage may range
from 1 square centimeter to several hundred square centimeter. Also
the number of conducting lines, around the storage element, through
which the desired current would pass, to magnetize the free layer,
in the storage element, may be adjusted according to the amount of
current needed for magnetization.
[0039] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification rather than limitation, and it is
understood that various changes may be made without departing from
the spirit and scope of the invention.
* * * * *