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Nanocrystal conductors using 'dirt-cheap material' promise massive 3-D storage

Rice researchers create 3-D memory chips that use only silicon -- no carbon

August 31, 2010 06:08 PM ET

Computerworld - Rice University announced today that scientists there have created the first two-terminal memory chips that use only silicon, extending the limits of miniaturization subject to Moore's Law.

The new technology places multiple layers of memory capacity on the same chip, creating what is referred to as a 3-D memory architecture.

According to a Rice University spokesman, the new memory technology will improve scalability by an order of magnitude compared to NAND flash technology available today. "The fact that they can do this in 3D makes makes it highly scalable," he said. "We've got memory that's made out of dirt-cheap material and it works."

In 2008, researchers at the university showed how electrical currents could repeatedly break and reconnect 10-nanometer strips of graphite, which could potentially boost flash memory capacity by many times. The Rice researchers said then that the new technology could withstand radiation and temperatures of 200 degrees Celsius that would cause solid-state disk memory to disintegrate.

At the time, the research team acknowledged that they weren't sure why their discovery worked so well. With the latest finding, the research team, including professors James Tour, Douglas Natelson and Lin Zhong, proved the circuit doesn't need the carbon to function, only silicon.

During the project, Jun Yao, a graduate student in Tour's lab, was able to confirm the hypothesis when he sandwiched an insulating layer of silicon oxide between semiconducting sheets of polycrystalline silicon that served as the top and bottom electrodes, Rice said.

Yao applied a charge to the electrodes, which created a conductive pathway by stripping oxygen atoms from the silicon oxide, forming a chain of nanometer-sized silicon crystals. Once formed, the chain can be repeatedly broken and reconnected by applying a pulse of varying voltage, the University said.

"It is more than 5 times denser than 20 nanometer flash ... without 3D stacking," Zhong said. "I would argue the nanowire-based solution is much more amenable to vertical stacking, which makes the technology very scalable as process technology improves. The density can be further doubled or tripled with two or three layers."

Unlike NAND flash memory, which is controlled by three terminals or wires, the new silicon memory requires two terminals, making it more viable for three-dimensional or stacked silicon arrays -- multiplying a chip's capacity. But like flash memory, chips made with silicon consume virtually no power while keeping data intact.

The nanocrystal wires are as small as 5 nanometers wide. A nanometer is one billionth of a meter.

"The beauty of it is its simplicity," said Tour, a professor of mechanical engineering and materials science and computer science, in a statement.

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