The structure of the new TMR element
The structure of the new TMR element
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Japanese researchers developed a tunnel magnetoresistance (TMR) element that has a low data writing current and a high data stability, which are necessary to increase the capacity of MRAM (magnetoresistive RAM).

The TMR element, which was developed by the Spintronics Research Group of the Nanoelectronics Research Institute of Japan's National Institute of Advanced Industrial Science and Technology (AIST), is expected to realize an MRAM with a capacity of more than 10 Gbits.

The group will announce the details of the TMR element at the 11th Joint MMM-Intermag Conference, an international academic conference on magnetic devices, which runs from Jan 18, 2010, in Washington, DC, the US.

The new TMR element is used as a memory element of spin torque transfer MRAMs, which write data by applying current to memory elements.

When the existing TMR elements of spin torque transfer MRAMs are miniaturized, there is a trade-off between data writing current and data stability. The magnetization of the free layer of a small TMR element is reversed due to thermal agitation, often causing data loss. When the thickness of the free layer is increased to solve this problem, the required data writing current becomes larger.

The research group solved the trade-off by using a free layer with a laminated structure where a nonmagnetic layer (Ru) is sandwiched by two ferromagnetic layers (CoFeB). The switched connection between the two ferromagnetic layers is controlled by changing the thickness of the nonmagnetic layer so that the magnetization directions of the ferromagnetic layers become the same. As a result, the resistance to thermal agitation was improved by five times, increasing the data writing current only by 80%.

This time, an in-plane magnetization film was employed for the free layer. But the data writing current is expected to be further reduced by using a perpendicular magnetization film, in which the magnetization direction is vertical to the laminated layers.

The research group said that it is possible to realize a 1-Gbit MRAM by using the TMR element with the in-plane magnetization film and a 10-Gbit MRAM by using the TMR element with the perpendicular magnetization film.