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Group develops multi-layer cross-bar memories

Posted: 11 Aug 2009     Print Version  Bookmark and Share

Keywords:zinc-oxide diode  cross-bar architecture  memory cell 

Numonyx has joined a €2.95 million-project (about Rs.20.28 crore) to develop low-temperature zinc-oxide diodes for two-terminal memories based on cross-bar architectures. Such memories could be based on phase-change materials or on materials that change resistance through other mechanisms.

The diodes are needed to isolate individual memory cells and enable them to be read correctly in the cross-bar architecture. The European Union provided 1.86 million euro (about Rs.12.79 crore) of the total budget for the three-year VERSATILE project which ran from February 2006.

"The main point is not researching the memory cell itself but about the crossbar architecture and the diodes that are needed to build the crossbar devices," said Grazia Tallarida of the Laboratorio Nazionale MDM, near Milan, the coordinator of the project.

While a cross-bar array is potentially simple to make, ideally the memory array is laid down on top of other circuitry and that means that the temperature in the manufacturing process must be kept below 350°C. That rules out the use of silicon diodes, which need much higher temperatures in their fabrication.

Instead, the VERSATILE partners have designed a diode based on zinc oxide, a material not normally used in conventional CMOS technology, but which only needs processing temperatures of around 100 degrees.

The project involves research labs in Germany, Denmark and Poland as well as Italy. The industrial partner is Numonyx, a joint venture of Intel and STMicroelectronics set up in 2008 to exploit the market for non-volatile memory.

So far they have built a prototype array of 10,000 cells, each measuring 5µm across. Because of the low-temperature processing the approach would allow the crossbar architecture to be stacked, allowing a single chip to be built up with large storage capacities.

"What we are doing now, the last part of the project, is to demonstrate that this can be scaled down to a much smaller size," said Tallarida.

The team is currently fabricating an experimental 25-cell array with 100nm cells and will try an even smaller scale if it is successful.

VERSATILE complements another project, EMMA also funded by the European Union that has been developing materials for the memory cells themselves and supplied the nickel oxide cells used by VERSATILE.

Tallarida said she would like to pursue the idea of organic semiconductor diodes. "We think that there is also a need for an effort to push through the combination of organic and inorganic semiconductors. That could be interesting especially for low-cost or even disposable devices."

- Peter Clarke
EE Times Europe

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