Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Magnetic field
Reexamination Certificate
1998-02-27
2001-04-03
Fahmy, Wael (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Magnetic field
C257S295000, C257S424000, C365S001000, C365S007000, C365S008000, C365S050000, C365S055000, C365S065000, C365S158000, C365S170000, C365S171000, C365S173000, C365S232000
Reexamination Certificate
active
06211559
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to magnetic tunnel junctions in magnetic memory devices and more particularly to symmetric magnetic tunnel devices.
BACKGROUND OF THE INVENTION
A magnetic random access memory (MRAM) is a non-volatile memory which basically includes a magnetoresistive (MR) cell, a sense line, and a word line. The MRAM employs the MR effect to store memory states. Magnetic vectors in one or all of the layers of MR material are switched very quickly from one direction to an opposite direction when a magnetic field is applied to the MR cell over a certain threshold. According to the direction of the magnetic vectors in the MR cell, states are stored, and the MR cell maintains these states even without a magnetic field being applied.
The specific type of memory cell being addressed herein is commonly referred to as a magnetic tunneling cell or junction and uses multi-layer magnetoresistive materials (MR) and also utilizes dimensions below one micron, in order to increase density. In this type of cell a non-conductive layer is disposed between the multi-layers of magnetic material. The magnetization vectors are generally parallel to the length of the magnetic material instead of the width but sense current tunnels through the non-conducting layer from one layer of magnetic material to the other, rather than being conducted lengthwise by an intervening conductive layer.
The problem is that in most MR cells the MR ratio is relatively low (e.g. 10% or less) and, consequently, the cell signal (&Dgr;V), which is defined as the difference in bias voltage at a constant sense current between the two memory states, is low. As a result, reading or sensing the state stored in the MR cell can be relatively difficult. Some attempts have been made to increase the MR ratio of magnetic tunneling cells, which attempts still result in an MR ratio of less than 30%. See for example, U.S. Pat. No. 5,650,958, entitled “Magnetic Tunnel Junctions with Controlled Magnetic Response”, issued Jul. 22, 1997.
Accordingly, it is highly desirable to provide magnetic tunnel junctions or cells with increased cell signals and without increasing the magnetic field required for writing and reading.
It is a purpose of the present invention to provide a new and improved symmetric magnetic tunnel device with increased cell signal.
It is another purpose of the present invention to provide a new and improved symmetric magnetic tunnel device including an increased cell signal without changing the amount of magnetic field required for switching states.
It is a further purpose of the present invention to provide a new and improved symmetric magnetic tunnel device with increased cell signal while maintaining high speed and low power consumption.
SUMMARY OF THE INVENTION
The above problems and others are at least partially solved and the above purposes and others are realized in a symmetric magnetic tunnel device including a plurality of magnetic tunnel junctions each including a pinned magnetic layer, an insulating tunnel layer and a free magnetic layer stacked in parallel juxtaposition to allow tunneling of electrons through the insulating tunnel layer between the pinned and free magnetic layers. The plurality of magnetic tunnel junctions are positioned in parallel juxtaposition so as to form a continuous electron path through the plurality of magnetic tunnel junctions and to provide a cell signal across the plurality of magnetic tunnel junctions greater than the cell signal across each of the magnetic tunnel junctions individually.
In a preferred embodiment the plurality of magnetic tunnel junctions include two tunnel junctions which share a common free magnetic layer therebetween. Generally, the plurality of magnetic tunnel junctions includes a number of magnetic tunnel junctions determined by a total resistance across the plurality of magnetic tunnel junctions and a sense voltage required to produce a sense current through the plurality of magnetic tunnel junctions, wherein the sense voltage is less than a breakdown voltage for the plurality of magnetic tunnel junctions.
REFERENCES:
patent: 5640343 (1997-06-01), Gallagher et al.
patent: 5650958 (1997-07-01), Gallagher et al.
patent: 5729410 (1998-03-01), Fontana, Jr. et al.
patent: 5757056 (1998-05-01), Chui
patent: 5764567 (1998-06-01), Parkin
patent: 5768181 (1998-06-01), Zhu et al.
patent: 5792510 (1998-08-01), Farrow et al.
patent: 5793697 (1998-08-01), Scheuerlein
patent: 5801984 (1998-09-01), Parkin
patent: 5841692 (1998-11-01), Gallagher et al.
patent: 5930164 (1999-07-01), Zhu
Goronkin Herbert
Zhu Theodore
Fahmy Wael
Koch William E.
Motorola Inc.
Parsons Eugene A.
Warren Matthew E.
LandOfFree
Symmetric magnetic tunnel device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Symmetric magnetic tunnel device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Symmetric magnetic tunnel device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2484705