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Toshiba develops new MRAM device which opens the way to giga-bits capacity

06 November, 2007


World's first perpendicular magnetic anisotropy MTJ device

Tokyo--Toshiba Corporation today announced important breakthroughs in key technologies for magnetoresistive random access memory (MRAM), a promising, next-generation semiconductor memory device. The company has successfully fabricated a MRAM memory cell integrating the new technologies and verified its stable performance. Full details of the new technologies were presented today at the 52nd Magnetism and Magnetic Materials Conference in Tampa, Florida, USA which is being held from November 5th to 9th.

MRAM is a highly anticipated next-generation non-volatile semiconductor memory device that offers fast random write/access speeds, enhances endurance in operation with very low power consumption. MRAM can theoretically achieve high level integration as the memory cell structure is relatively simple.
In making these major advances, Toshiba applied and proved the spin transfer switching and perpendicular magnetic anisotropy (PMA) technologies in a magnetic tunnel junction, which is a key component in the memory cell.

Spin transfer switching uses the properties of electron spin to invert magnetization and writes data at very low power levels. It is widely regarded as a major candidate among next-generation principles for new memory devices. PMA aligns magnetization in the magnetic layer perpendicularly, either upward or downward, rather than horizontally as in in-plane shape anisotropy layers. The technology is being increasingly used to enhance for storage capacity for high-density hard disc drives (HDDs), and Toshiba has successfully applied it to a semiconductor memory device. With PMA data write operation and magnetic switching can be achieved at a low energy level. Toshiba also overcame the hurdle of achieving the required precision in the interface process and significantly cutting write power consumption.

In order to realize a miniature memory cell based on PMA, Toshiba optimized the materials and device structure of the new MRAM. Close observation of performance confirms stable operation (see the diagram for full explanation of structure).

Toshiba will further enhance development toward establishing fundamental technologies within the coming years.

Development of the new MRAM technologies was partly supported by grants from Japan's New Energy and Industrial Technology Development Organization (NEDO).

Outline of Development

(1) Cell Structure
Cell structure

A material with perpendicular magnetic anisotropy, which is used for recording media and a type of cobalt-iron, is employed in the magnetic layer, with magnesium oxide in the insulating layer and cobalt-iron-boron in the interface layers.

(2) Operational Results
Operational Results

Figure 1
Resistance versus voltage pulses: Shows device resistance characteristics after voltage pulses are applied to perform write operation. The switching between high and low resistive states is clearly seen at the voltage threshold in both the positive and negative directions.
   
Figure 2
  Resistance versus DC magnetic field: Device resistance characteristics when the magnetic field is applied perpendicular to layers. The high and low resistive states are clearly observed, and are produced by the magnetization direction in the free layer with reference to the reference layer.

(3) Major characteristics and specifications of MRAM device

Major characteristics and specifications of MRAM device

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