Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
2002-11-15
2004-08-03
Phan, Trong (Department: 2818)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S171000, C365S173000
Reexamination Certificate
active
06771534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to thermally-assisted magnetic writing and more particularly to current-induced heating in magnetic random access memory devices.
2. Description of the Related Art
The non-volatile memory chip market is today dominated by Flash technology. Unfortunately, Flash is very slow and has a very limited number of write cycles (about 10
6
) before failure, making it unsuitable as a replacement for volatile memories such as DRAM or SRAM. It is also believed to have limited scalability beyond the 65 nm technology node. Therefore, there is a need for a new type of non-volatile memory.
SUMMARY OF THE INVENTION
The invention provides a non-volatile magnetic random access memory (MRAM) device that has a stable magnetic electrode comprising of one or more layers, an oxide layer, and a free magnetic electrode comprising of one or more layers. When the oxide is used as a barrier, the stable and free magnetic electrodes are adjacent to the oxide. In the oxide design with holes, there can also be a nonmagnetic spacer metal between the two electrodes. The oxide layer is between the stable magnetic electrode and the free magnetic electrode. In the invention, a conductor is connected to a stable magnetic electrode. The oxide layer has a resistance at levels to allow sufficient power dissipation to occur to lower the magnetic anisotropy of the free magnetic electrode through current induced heating. Current-induced heating is used in combination with spin-transfer torque or a magnetic field to switch the free magnetic electrode. The stable magnetic electrode is thicker or has higher magnetic anisotropy than the free magnetic electrode.
In the invention, a transistor is used to control whether current passes between the free magnetic electrode and the stable magnetic electrode. The current induced heating only temporarily lowers the anisotropy until the free magnetic electrode is switched. The resistance and thermal properties of the oxide layer are optimized to temporarily reduce the anisotropy of the free magnetic electrode through the current-induced heating. A material selection for the free magnetic electrode is optimized to have an increased reduction in anisotropy for a small temperature change to allow the current density needed for switching to be reduced during writing. The invention provides a non-volatile MRAM memory device with a large number of read and write cycles, current-controlled switching, excellent scalability, ultra-fast switching speeds, very small bit cell, low voltage, low power, and optimal resistance for CMOS integration
The invention also provides a method of manufacturing a non-volatile magnetic random access memory (MRAM)device. The invention first forms a stable magnetic electrode. The invention then forms an oxide layer on the stable magnetic electrode and forms a free magnetic electrode on the oxide layer so that the oxide layer is between the stable magnetic electrode and the free magnetic electrode. The oxide layer is formed to have a resistance at levels to allow sufficient power dissipation to heat the free magnetic electrode to lower anisotropy of the free magnetic electrode through current induced heating. The heating can assist in switching the free magnetic electrode to write information in the MRAM device and can reduce the current density required to a value lower than that required in the absence of the heating. The forming of the stable magnetic electrode forms one or more layers. The heating current is spin-polarized and occurs at a level to allow spin-transfer-based writing to occur in the free magnetic electrode. The invention can form bit and word lines connected to the free magnetic electrode and the stable magnetic electrode. The heating current in combination with magnetic field from current passing through the bit and word lines switches the free magnetic electrode. The invention forms an oxide layer which has thermal properties. The resistance and thermal properties are optimized to temporarily reduce the anisotropy through the current-induced heating. A material selection for the free magnetic electrode is optimized to have an increased reduction in anisotropy for a small temperature change to allow a critical current density to be reducing during writing of the information.
REFERENCES:
patent: 5289410 (1994-02-01), Katti et al.
patent: 6174737 (2001-01-01), Durlam et al.
patent: 6340533 (2002-01-01), Ueno et al.
patent: 6545896 (2003-04-01), Munden et al.
Berthold, Esq. Thomas
International Business Machines - Corporation
McGinn & Gibb PLLC
Phan Trong
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