Static information storage and retrieval – Systems using particular element – Magnetic thin film
Reexamination Certificate
2002-07-29
2004-02-17
Le, Vu A. (Department: 2824)
Static information storage and retrieval
Systems using particular element
Magnetic thin film
C365S158000
Reexamination Certificate
active
06693826
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high density, non-volatile memory. One aspect of the invention pertains to on-chip magnetic memory elements (sometimes known as MRAM). However, the general invention is believed applicable to a variety of magnetic memory configurations. This could include conventional integrated memory that is electronically selected. But further, it could include moving or moveable memory such as hard drives, floppy discs, and the like, as will become apparent with reference to the specification herein. More particularly, the present invention relates to the detection of unstable states in magnetic memory that could result in erroneous memory operation, e.g. affect accuracy of the data read from memory or cause reduced reliability of the memory. MRAM possibly can have non-movable or moveable implementations, as has been suggested in the literature. See, e.g., L. Richard Carley, Gregory R. Ganger, and David F. Nagle, MEMS-Based Integrated-Circuit Mass-Storage Systems. in COMMUNICATIONS OF THE ACM, November 2000, Vol.43, No.11, which is incorporated by reference herein.
2. Problems with the Art
Many types of storage technologies exist today. One type of storage technology or memory is magneto-resistive RAM or MRAM. MRAM includes various implementations including giant magneto-resistance (GMR) embodiments. Other examples of MRAM include, but are not necessarily limited to AMR, CMR, and SDT or TMR embodiments. MRAM has many desirable properties including random accessibility, very short write times, density close to dynamic RAM, sizes scaleable with lithography, very little cost, radiation hardness, and non-volatility.
A variety of other memory configurations and implementations exist, as are well known in the art. These include what will be referred to as “moving memory”, to differentiate it from conventional integrated memory that is electronically selected. One example is a hard drive, having a disc or other magnetic storage media that moves past a read and/or write head. Alternatively, the term “moving memory” will also refer to configurations where a read and/or write head moves past a magnetic memory, or both move relative to each other. There are also implementations being developed that utilize magnetic material, without necessarily any partitioned or segregated structure, as a storage location for data.
The concept of magneto-resistance is that when ferro-magnetic materials are subjected to a magnetic field, the electrical resistance can change. This is generally known as the magnetoresistance effect and may be observed to occur in many types of both single and composite films of magnetic materials. What makes this effect useful in a magnetic memory is that the magnetic orientation, or relative magnetic orientations of multiple layers may be set by manufacturing or writing of data and then sensed by way of this predictable resistance change. This is useful in both “moving memory” where the sensing element may be shared over many memory bits and in MRAM, where there is effectively one sense element per storage element. One popular type of MRAM makes use of a giant magneto-resistance (GMR) resistor. Publicly available literature currently discloses several other types, including a variety of implementations of GMR techniques and what are known as AMR, CMR, and SDT or TMR configurations. For purposes of illustration and example, magnetic memory in the form of a GMR resistor will be primarily discussed herein, but it is to be understood that the concepts discussed have applicability to the variety of magnetic memory types available, discussed, or contemplated in the art. It is believed the invention will also have applicability to many, if not all, future implementations of magnetic memory using magnetoresistive properties.
One implementation of a GMR resistor uses a pair of magnetic thin films having the configuration shown in FIG.
1
. In
FIG. 1
, a GMR bit
10
is shown. The GMR bit
10
includes an upper layer
12
and a bottom layer
14
. The upper and bottom layers are magnetic layers and are typically composed at least in part of permalloy. The upper layer
12
is sometimes designated as M
1
and the lower layer
14
is sometimes designated as M
2
to denote that these are magnetic layers. Between these magnetic layers
12
and
14
is an inner layer
16
which is nonmagnetic, and for the GMR case, is a conductive film such as copper. The magnetic layers
12
and
14
typically have magnetic moments aligned along an axis set during manufacturing but for this case we consider to be aligned either to the “left” or to the “right.”
Examples of such magnetic devices, including GMR, tunneling devices, or other implementations, are described in the following publications and in the references cited in these publications, all of which are incorporated by reference herein:
(a) W. C. Black, Jr. and B. Das, “Programmable logic using giant-magnetoresistance and spin-dependent tunneling devices”,
Journal of Applied Physics
, Vol. 87, No. 9, Parts 2 and 3, May 1, 2000, pp. 6674-6679;
(b) R. Zhang, M. Hassoun, W. J. Black, Jr., B. Das, K. Wong, “Demonstration of A Four State Sensing Scheme For A Single Pseudo-Spin Valve GMR Bit”,
IEEE Transactions on Magnetics
, September 1999;
(c) W. C. Black, Jr. and M. Hassoun, U.S. Pat. No. 6,317,359, “Non-Volatile Magnetic Circuit”;
(d) W. C. Black, Jr., B. Das, M. Hassoun, U.S. Pat. No. 6,343,032, Non-Volatile Spin Dependent Tunnel Junction Circuit.
There are varieties of MRAM cells. For example, the bits may be of a “spin-valve” design where one of the layers is magnetically “pinned” in one direction or a “pseudo-spin-valve”, where both layers are free to rotate but where one of the layers usually requires a greater field to switch its orientation.
Both spin valve and the pseudo-spin-valve varieties of memories have been used with various sensing schemes including non-destructive read out (NDRO) schemes. The advantage of non-destructive read out being that the memory may be read without changing the state in the memory. The current that runs through the GMR bit
10
as shown in
FIG. 1
is commonly referred to as the sense current as it is used to determine or sense the state of the memory. The layer that runs either above, below or both above and below the GMR bit (shown in
FIG. 1
as reference numeral
20
) is commonly referred to as the word current as it is used to generate a controlled magnetic field to set the state of the memory during writing or produce a known magnetic field during reading. It should be noted that both sense and word line currents are important for setting the magnetic domains within the memory bit and this relationship is sometimes reflected in an “asteroid curve”. By proper circuit biasing it may be possible to take advantage of this curve by using sense and word line currents together for X-Y addressing purposes, but there may also be additional current lines in the vicinity of the bit used for unique addressing purposes (sometimes known as ‘digit’ lines).
Different types of sensing schemes are known in the art. These prior art sensing methods include sequential sensing and dummy sensing. In sequential sensing, usually a word current is changed sequentially (such as applied in opposite directions sequentially) through the same GMR device, and the measured difference in resistance is compared to determine the state. For some types of memories it may be advantageous to switch direction of the sense current, or both the sense and word currents. See illustration of
FIG. 2A.1
showing diagrammatically measuring R
1
by sending Iword (−ev) through the word line relative the GMR device 54, and then in
FIG. 2A.2
, measuring R
2
by sending Iword (+ev) through the word line. The memory states can be arbitrarily defined such that either or both layers may store data although one layer may also be used only for reading. The advantage of using one layer for reading is that non-destructive read-out schemes are easily implemented whereas use
Black, Jr. William C.
Zhang Ruili (Linda)
Iowa State University & Research Foundation, Inc.
McKee Voorhees & Sease, P.L.C.
LandOfFree
Magnetic memory sensing method and apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic memory sensing method and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic memory sensing method and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3294096