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April 01, 2009

Singapore has made computer memory devices using graphene


Ones and zeros: By depositing a ferroelectric material on top of graphene, researchers have coaxed graphene into holding on to two different levels of electrical conductivity, which could serve as bits 1 and 0 in computer memory.
Credit: Barbaros Özyilmaz, National University of Singapore


MIT TEchnology Review reports that researchers at the National University of Singapore have made computer memory devices using graphene based on the well understood ferroelectric effect. This is the first step toward memory that could be much denser and faster than the magnetic memory used in today's hard drives. The researchers have made hundreds of prototype graphene memory devices, and they work reliably, according to Barbaros Özyilmaz, the physics professor who led the work presented at a recent American Physical Society meeting in Pittsburgh.

The new memory idea is "thrilling because it's very simple," says Andre Geim, professor of physics at the University of Manchester, UK, who first isolated graphene sheets from graphite. "Ferroelectrics are well known. It's also known that an electric field changes graphene's resistivity by a factor of typically 10. [Özyilmaz] combines those two very well-known facts."

Graphene memory would have significant advantages over today's magnetic memory. Bits could be read 30 times faster because electrons move through graphene quickly. Plus, the memory could be denser. Bit areas on hard disks are currently a few tens of nanometers across. At densities of 1 terabit per square inch, they will be about 25 nanometers across, too small to hold their magnetization direction. With graphene, bits could shrink to 10 nanometers or even smaller. In fact, the memory devices would work better with smaller graphene areas. Stanford University researchers have shown that cutting graphene into ribbons a few nanometers wide enhances the difference between its two conductivity states.


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The unique linear energy band dispersion and its purely 2D crystalline structure have made graphene a rising star not only for fundamental research but also for nanoscale device applications. Here we demonstrate a novel non-volatile memory device using a combination of graphene and a ferroelectric thin film. The binary information, i.e. ``1'' and ``0'', is represented by the high and low resistance states of the graphene working channels and is switched by the polarization directions of the ferroelectric thin film. A highly reproducible resistance change exceeding 300\% is achieved in our graphene-ferroelectric hybrid devices under ambient conditions. The experimental observations are explained by the electrostatic doping of graphene by the remnant electrical field at the ferroelectric/graphene interface.


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