Toshiba Develops Fundamental Technology for Gbit-class STT-MRAM

Jul 6, 2011
Jyunichi Oshita, Nikkei Electronics
A cross-sectional image of the MTJ device developed by Toshiba
A cross-sectional image of the MTJ device developed by Toshiba
[Click to enlarge image]

Toshiba Corp developed a perpendicular magnetization-type magnetic tunnel junction (MTJ) device that has excellent properties and is a basic element to realize a gigabit-class spin torque transfer MRAM (STT-MRAM).

Its rewriting current density, which determines data writing electricity, is 5 x 105Acm-2, which is 1/6 that of the company's existing products. And its magnetic resistance (MR), which determines data reading margin, is 200%, which was drastically improved from the 15% of the existing products.

"We will shift from the development of elemental technologies to the development of products using the latest research results," Toshiba said.

Toshiba plans to commercialize a gigabit-class STT-MRAM within three or four years, expecting that it will be used as non-volatile memory for random access data, which are frequently rewritten and read out.

Specifically, it is expected to be used as the cache memories of HDDs and SSDs and to replace part of the DRAMs and low- and medium-speed SRAMs in smartphones, notebook computers and other mobile devices. By replacing the main memories or cache memories of devices with STT-MRAMs, it becomes possible to realize a "normally off" operation, Toshiba said.

It has been difficult to realize a low rewriting current density and a high MR ratio at the same time with traditional perpendicular magnetization-type MTJ devices because there is a trade-off between rewriting current density and MR ratio. This time, Toshiba solved this problem by using materials that are based on cobalt (Co) and iron (Fe), which are prone to magnetization reversal, for the recording (free) layer, which is one of the two ferromagnetic electrodes constituting an MTJ device.

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