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NEC, Toshiba develop key technologies for high-density MRAM

Posted: 22 Dec 2004 ?? ?Print Version ?Bookmark and Share

Keywords:mram? mtj?

NEC Corp. and Toshiba Corp. have announced two key advancements toward development of a magnetoresistive random access memory, a technology seen as key to the development of future generations of high performance mobile equipment. The companies revealed a cell design that halves power consumption during data writes and cuts writing errors, and a novel MRAM architecture with high speed characteristics and a performance that will support development of high-density devices.

According to NEC and Toshiba, they reduced write current by developing a new shape for the magnetic tunneling junction (MTJ) that stores information in the cell. The MTJ shape is similar to the standard rectangular shape, but with arc-shaped bulges on both sides, in the middle of the longer length. Seen from above, the outline of the shape resembles a coin placed on a rectangle. With this new design, write current is about half that of present MRAM, and writing errors are reduced, even if there is some fluctuation in the switching characteristics of each memory cell.

The companies have also developed a highly promising new cell architecture. Research to date has produced two basic proposals on MRAM cell structure. The first of these couples each cell with a transistor, which advances read times, but at a cost in increased cell size. The second, the cross point (CP) structure, removes the transistor from each individual cell, a move that reduces cell size, but read access time gets longer and read errors occur due to generation of sneak current, the tendency of current to be directed to the unselected cell. The companies have realized a high-speed CP cell structure that uses one transistor to control four cells. This achieves a cell that is the same size as a standard DRAM cell and conventional CP cell, and much smaller than an MRAM cell with transistor. The architecture also achieves a 250 nanosecond read time, four times faster than the conventional CP cell structure.





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