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Memory and Storage

Rice Researchers Develop Novel Memory, Grow Graphene One Atom at a Time

18 July 2013

Rice University researchers have built a 1-kilobit rewritable silicon oxide device with diodes that eliminate data-corrupting crosstalk. Separately, the researchers have synthesized graphene nanoribbons on metal from the bottom up — atom by atom.

The proof of concept memory chip is based on an earlier discovery that when electricity passes through a layer of silicon oxide, it strips away oxygen molecules and creates a channel of pure metallic phase silicon that is less than five nanometers wide. Normal operating voltages can repeatedly break and “heal” the channel, which can be read as either a “1” or “0” depending on whether it is broken or intact.

The circuits require only two terminals instead of three, as in most memory chips and show promise for stacking in three-dimensional arrays.

The device sandwiches the active silicon oxide between layers of palladium. The silicon-palladium rests upon a thin layer of aluminum that combines with a base layer of p-doped silicon to act as a diode. The 32 x 32-bit test arrays are a little more than a micrometer deep with crossbar line widths of 10 to 100 micrometers for testing purposes.

The Boeing Corp. and the Air Force Office of Scientific Research funded the work. A rudimentary version of the chip is undergoing reliability tests aboard the International Space Station.

In the graphene research instead of growing it in the usual manner in a hot furnace by chemical vapor deposition researchers found that the entire edge of a fast-growing sheet of graphene becomes a nucleation site when hydrogenated. The edge lets carbon atoms get under the graphene skin, where they start a new sheet.

According to the researchers, they were able to change relative pressures of the growth environment of hydrogen versus carbon and get entirely new structures, dramatically different from regular graphene.

The width of the resultant graphene rings, which range from 10 to 450 nanometers, also affects their electronic properties, so finding a way to control it will be one focus of continued research.

“if we can consistently make 10-nanometer ribbons, we can begin to gate them and turn them into low-voltage transistors,” said Rice Chemist James Tour.

They may also be suitable for lithium storage for advanced lithium ion batteries, he said.



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