MRAM cell having frustrated magnetic reservoirs

Details MRAM cell having frustrated magnetic reservoirs MRAM cell having frustrated magnetic reservoirs

2003-06-13

2004-10-19

Nguyen, Van Thu (Department: 2824)

Static information storage and retrieval

Systems using particular element

Magnetic thin film

C365S158000, C365S213000

Reexamination Certificate

active

06807092

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to memory devices. More specifically, the present invention relates to magnetoresistive random access memory (MRAM) devices.
2. Description of the Related Art
In a magneto-resistive random access memory (MRAM) device, a plurality of the memory cells (i.e., MRAM cells) is typically arranged in a cross-point array, wherein the MRAM cell is sandwiched at the intersection of a bit line and a word line. The bit lines and word lines are conductive lines facilitating selection of a given MRAM cell and read and write operations.
A MRAM cell generally comprises a magnetic structure known as a “magnetic tunnel junction” (MTJ). In the MRAM cell, information is stored in a form of a direction of magnetization in a magnetic layer of the MTJ. Such stored information may be preserved for long periods of time without use of sources of energy.
The MTJ generally comprises two magnetic layers of different coercivity that are separated by an insulating non-magnetic tunnel layer. The tunneling current depends on relative orientation of magnetization in these magnetic layers. In the MTJ, a memory state is characterized by the direction of magnetization of the magnetic layer having a lower coercivity than the other magnetic layer of the MTJ. The low coercivity layer is known as a “free magnetic layer”. To increase stability of the memory state, the free magnetic layer is generally elongated in the direction of magnetization.
Writing an information content (i.e., “0” or “1”) in the MRAM cell is accomplished by causing a magnetic material of the free magnetic layer to be magnetized in either one of two opposing directions, while the other layer permanently maintains its state of magnetization. Reading the information content of the MRAM cell is accomplished by sensing electrical resistance, which differs whether the magnetic layers of the MTJ are magnetized in the same or opposing directions. Magnetic fields used for programming the MRAM cell are created by passing currents through the bit and word lines (“write” operation) or through the lines and the MTJ (“read” operation). The write current of the MRAM cell is generally inversely proportional to anisotropy of a form factor of the free magnetic layer.
A value of the write current and stability of the information content (i.e., stability of the states of magnetization of the free magnetic layer) of the MRAM cell are among the most important characteristics of the MRAM device.
In the MRAM cell, the write current generally tends to increase as dimensions of the MRAM cell decrease. High-current electrical circuits occupy large areas of a MRAM chip and, as such, a high write current becomes a limitation for fabricating high-density MRAM devices. Additionally, the MRAM cell where a memory state depends on anisotropy of the form factor of the free magnetic layer has a narrow operational temperature range.
Therefore, there is a need in the art for an improved magnetoresistive random access memory (MRAM) cell having a low write current and a broad operational temperature range.
SUMMARY OF THE INVENTION
A magnetoresistive random access memory (MRAM) cell comprises a magnetic tunnel junction (MTJ) having frustrated (i.e., magnetized) magnetic reservoirs that are disposed oppositely along two edges of a free magnetic layer of the MTJ. The magnetic reservoirs are magnetized in the same direction and substantially orthogonally to the free magnetic layer of the MTJ. In one embodiment, the free magnetic layer comprises a centrally located region having a width that is smaller than the width of any other region of the layer.


REFERENCES:
patent: 6653703 (2003-11-01), Hosotani et al.
patent: 6704220 (2004-03-01), Leuschner
patent: 6744651 (2004-06-01), Tang

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