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Magic MRAM Cells

IP.com Disclosure Number: IPCOM000019664D
Publication Date: 2003-Sep-24
Document File: 4 page(s) / 2M

Publishing Venue

The IP.com Prior Art Database

Related People

Daniel Braun: AUTHOR [+2]

Abstract

MRAM cells store information in the direction of the magnetization of a soft magnetic layer. In MRAM cell arrays, the cells interact and therefore the required writing field of a given field is shifted by an amount depending on the information stored in neighboring cells. This problem is solved to a large degree in the present invention by 1.) adjusting cell size and cell pitch in such a way that from the most important first layer of cells around a given one (containing 8 cells) to good approximation only 5 different field values arise. Cells/arrays adjusted in this way will be called magic cells. 2.) by measuring the information content of the 4 nearest neighbors before writing a cell and adapting the write current correspondingly to one of the 5 different values The invention therefore allows to reliably write a given cell even in dense arrays, where the interaction problem is expected to become worse with increasing integration density; and it allows to do so with only 5 predefined write current add-ons instead of 9, as one would have from the nearest neighbors for non-magic MRAM cells.

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Magic MRAM cells

         Daniel Braun (Infineon Technologies)

         Yu Lu (IBM)

ABSTRACT

MRAM cells store information in the direction of the magnetization of a soft magnetic layer. In MRAM cell arrays, the cells interact and therefore the required writing field of a given field is shifted by an amount depending on the information stored in neighboring cells. This problem is solved to a large degree in the present invention by

1.)           adjusting cell size and cell pitch in such a way that from the most important first layer of cells around a given one (containing 8 cells) to good approximation only 5 different field values arise. Cells/arrays adjusted in this way will be called magic cells.

2.)           by measuring the information content of the 4 nearest neighbors before writing a cell and adapting the write current correspondingly to one of the 5 different values

The invention therefore allows to reliably write a given cell even in dense arrays, where the interaction problem is expected to become worse with increasing integration density; and it allows to do so with only 5 predefined write current add-ons instead of 9, as one would have from the nearest neighbors for non-magic MRAM cells.

DECRIPTION OF INVENTION

In a magnetic RAM (MRAM) information is stored in the magnetization pattern of a magnetic layer. Typically, patterns are chosen in which the magnetization of a given MRAM cell may point in positive or negative easy axis direction of the cell, corresponding to stored values 0 or 1. Due to its magnetization, each MRAM cell creates a stray field which is seen by neighboring cells, and which influences the neighboring cells’ behavior under writing. For writing an MRAM cell, a certain critical magnetic field must be applied in the easy direction (which may depend on a simultaneously applied hard axis field), the field pointing in the direction to which one wants to switch the magnetization. In the state of the art writing scheme which selects a cell by applying fields from orthogonal world lines (WL) and bit lines (BL) the field range that may be applied for writing is severely limited by the requirement that none of the so-called half selected cells on the WL or the BL which are not addressed should switch. It is therefore advantageous to use as small writing currents as possible, and making use of the fi...