Tokyo, Japan – To meet the need for nonvolatile memory devices with greater density as well as faster read and write performance in many mobile and embedded consumer devices, Fujitsu Ltd. is developing a new type of nonvolatile memory, resistive RAM (ReRAM).

It joins a number of companies who are actively investigating these new memory devices, which are expected to be commercially available by 2010, including Intel Corp., Samsung, Spansion Inc., and Nippon Telegraph and Telephone Corp. (NTT).

They are interested in ReRAMs because they offer a number of advantages over traditional novolatile memory devices such as flash, ferroelectric RAM, phase change RAM or magnetoresistive RAM including lower power consumption, faster data read time, and smaller cell size, as well as higher reliability.

What makes such ReRAMs even more attractive is the compatibility with the logic processes used in many of the advanced system on chip designs used in such applications. Where other NV memory devices require a different structure and a different set of fabrication processes, increasing cost, ReRAM arrays can be embedded in an SoC simply by the addition of two more masks to the production process used for the logic circuits on such ICs.

Although Fujitsu has already been mass producing d mass produced ferroelectric RAM (FeRAM) for use in memory cards, the former are more difficult to make at the new leading edge 45 to 65 nanometer fabrication technologies used in most next generation SoCs.

In Fujitsu's ReRAM, researchers used  a binary oxide TiO2 composed of two kinds of elements similar in structure to the Nitride oxide (NiO) used by Samsung Electronics Co., Ltd. and the copper dioxide (Cu2O) used by Spansion.

As in the other devices, binary operation makes use of the difference in resistance value of the material under different conditions.

A number of current paths (filaments) having a low resistance value are formed locally in a TiO2 film during the "Forming" process in which a large voltage is initially applied to a memory device. Due to the applied voltage, the positive

side is oxidized during the "Reset" process so that the resistance value is increased. During the "Set" process, the positive side of the filament is reduced by the interdevice “Joule” heat so as to decrease the resistance value again.

To learn more, go to www.fujitsu.com. 

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