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Magnetoresistive random access memory (MRAM)

A magnetoresistive random access memory (MRAM) is a non-volatile memory device using magnetic elements having magnetoresistance effects in a memory cell. The magnetoresistive random access memory (MRAM) has been developed as a next generation memory device capable of replacing a conventional dynamic random access memory (DRAM) in which it has a fast data write speed but data stored inside is erased once an electric power is off, and a flash memory having a data write speed 1,000 times slower than the DRAM. A magnetoresistance effect is a phenomenon that occurs when a magnetic field is applied to a ferromagnetic material, electric resistance changes in accordance with the direction of magnetization of the ferromagnetic material. The MRAM has a plurality of memory cells. Each memory cell is a multilayered structure in which two layers of magnetic material are separated by a layer of non-magnetic metallic conducting material. Each memory cell comprises a memory element (e.g., a giant magnetoresistance (GMR) element or a magnetic tunnel junction (MTJ) element) in electrical communication with a transistor through an interconnect stack. An MTJ element has a structure formed by sandwiching an insulating film by two magnetic films having conductivity. Two states are created depending on whether the spin directions in the two magnetic films that sandwich the insulating film are parallel or anti-parallel. In each memory cell of an MRAM, an MTJ element serving as an information storage element is formed at the interconnection between a bit line and a word line. In a data write mode, a current is supplied to each of a selected bit line and a selected word line. Data is written in the MTJ element of the selected cell located at the intersection between the selected bit line and the selected word line by a composed magnetic filed generated by the currents. An MRAM using a tunneling magnetoresistance effect (TMR) in a magnetic tunnel junction has a sandwich structure in which an insulating layer (tunnel barrier layer) is inserted between two ferromagnetic layers (MTJ).


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