Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
2002-03-06
2003-06-03
Lebentritt, Michael S. (Department: 2824)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S171000
Reexamination Certificate
active
06574138
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
With regard to nonvolatile read/write memories, investigations are increasingly be made relating to memory cell configurations in which magnetoresistive elements are used for storing information.
Experts understand that a magnetoresistive element, also called a magnetoresistance element, is a structure that has at least two ferromagnetic layers and a non-magnetic layer arranged in between. Depending on the construction of the layer structure, a distinction is made between a GMR (Giant Magnetoresistance) element, a TMR (Tunneling Magnetoresistance) element and a CMR (Colossal Magnetoresistance) element (see S. Mengel, Technologieanalyse Magnetismus, Band 2, XMR-Technologien [Technology analysis magnetism, volume 2, XMR technologies], published by VDI Technologiezentrum Physikalische Technologien, August 1997).
The term GMR element is used for layer structures that have at least two ferromagnetic layers and a non-magnetic, conductive layer arranged in between and that exhibit the so-called GMR (Giant Magnetoresistance) effect. The GMR effect is understood to refer to the fact that the electrical resistance of a GMR element is dependent on whether the magnetizations in the two ferromagnetic layers are oriented parallel or anti-parallel to one another. The GMR effect is large in comparison with the so-called AMR (Anisotropic Magnetoresistance) effect. The AMR effect is understood to refer to the fact that the resistance in magnetized conductors is different parallel and perpendicular to the magnetization direction. The AMR effect is a bulk effect that occurs in ferromagnetic monolayers.
The term TMR element is used by experts for “Tunneling Magnetoresistance” layer structures that have at least two ferromagnetic layers and an insulating, non-magnetic layer arranged in between. In this case, the insulating layer is so thin that a tunneling current arises between the two ferromagnetic layers. These layer structures likewise exhibit a magnetoresistive effect brought about by a spin-polarized tunneling current through the insulating, non-magnetic layer arranged between the two ferromagnetic layers. In this case, too, the electrical resistance of the TMR element is dependent on whether the magnetizations in the two ferromagnetic layers are oriented parallel or anti-parallel to one another. In this case, the relative change in resistance is about 6 to 40% at room temperature.
It has been proposed (see, for example, D. D. Tang et al. IEDM 95, pages 997 to 999, J. M. Daughton, Thin Solid Films, Vol. 216 (1992), pages 162 to 168, Z. Wang et al, Journal of Magnetism and Magnetic Materials, Vol. 155 (1996), pages 161 to 163) to use GMR elements as memory elements in a memory cell configuration. The memory elements are connected in series using read lines. Word lines run transversely with respect to the read lines and are insulated both from the read lines and from the memory elements. Signals applied to the word lines cause a magnetic field as a result of the current flowing in each word line. This magnetic field, given sufficient strength, influences the magnetizations of the memory elements situated underneath. For writing information, x/y lines are used, which cross at the memory cell to be written to. Signals are applied to the x/y lines, and at the crossover point, these signals cause a magnetic field which is sufficient for the magnetization reversal. In this case, the magnetization direction is reversed in one of the two ferromagnetic layers. By contrast, the magnetization direction in the other of the two ferromagnetic layers remains unchanged. The magnetization direction in the last-mentioned ferromagnetic layer is fixed by using an adjacent antiferromagnetic layer that fixes the magnetization direction, or by increasing the switching threshold of the ferromagnetic layer through different material or different dimensioning, for example, a different layer thickness, in comparison with the first-mentioned ferromagnetic layer. For reading out the information, a pulsed signal is applied to the word line, and this pulsed signal switches the relevant memory cell back and forth between the two magnetization states. The current through the bit line is measured, from which the resistance of the corresponding memory element is determined.
U.S. Pat. No. 5,173,873 discloses a magnetoresistive memory cell configuration in which transistors are provided for selecting the memory cells that will be read.
U.S. Pat. No. 5,640,343 discloses a memory cell configuration in which TMR elements that are connected in series with a diode are used as memory elements. The diode serves for reading out the information of the individual memory cells.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a memory cell configuration having magnetoresistive elements and a method for operating the memory cell configuration which overcome the above-mentioned disadvantages of the prior art apparatus and methods of this general type.
In particular, it is an object of the invention to provide a memory cell configuration having magnetoresistive elements in which the stored information can be reliable read-out.
It is also an object of the invention to construct the memory cell configuration with a high packing density and with a low outlay on process engineering.
With the foregoing and other objects in view there is provided, in accordance with the invention, a memory cell configuration that includes: a signal line; and memory cells. Each one of the memory cells has two magnetoresistive elements. The two magnetoresistive elements of each one of the memory cells are magnetized to have different resistances. The signal line connects the two magnetoresistive elements of one of the memory cells in series to form an overall resistor with two ends. One of the two ends of the overall resistor is connected to a first voltage having a magnitude and a polarity. Another one of the two ends of the overall resistor is connected to a second voltage having a magnitude equal to the magnitude of the first voltage and a polarity opposite the polarity of the first voltage.
In accordance with an added feature of the invention, each one of the two magnetoresistive elements of each one of the memory cells is either a Giant Magnetoresistance element or a Tunneling Magnetoresistance element.
In accordance with an additional feature of the invention, the two magnetoresistive elements of one of the memory cells are configured adjacent to one another in a plane.
In accordance with another feature of the invention, there is provided a plurality of first lines running parallel to each other; and a plurality of second lines running parallel to each other. The plurality of the first lines and the plurality of the second lines cross each another. The two magnetoresistive elements of each one of the memory cells are connected between one of the plurality of the first lines and one of the plurality of the second lines. The two magnetoresistive elements of one of the memory cells are connected to different ones of the plurality of the first lines and to the same one of the plurality of the second lines.
In accordance with a further feature of the invention, each one of the two magnetoresistive elements of each one of the memory cells includes at least a first ferromagnetic layer element, a nonmagnetic layer element, and a second ferromagnetic layer element. The nonmagnetic layer element is configured between the first ferromagnetic layer element and the second ferromagnetic layer element. In each one of the memory cells, the first ferromagnetic layer element and the second ferromagnetic layer element of a first one of the two magnetoresistive elements have magnetizations that are oriented parallel to each other. In each one of the memory cells, the first ferromagnetic layer element and the second ferromagnetic layer element of a second one of the two magnetoresistive elements have magnetizations that are oriented anti-parallel to each other.
In accordance with a further
Miethaner Stefan
Schwarzl Siegfried
Infineon - Technologies AG
Lebentritt Michael S.
Mayback Gregory L.
Phung Anh
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