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New memory materials could boost storage density

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Scientists at Rice University have created a solid-state memory technology that enables high-density storage, while simultaneously reducing energy consumption.

A schematic shows the layered structure of tantalum oxide, multilayer graphene and platinum used for a new type of memory developed at Rice University.

It comprises a layered structure of tantalum, nanoporous tantalum oxide and multilayer graphene between two platinum electrodes. The researchers claim that the design – details of which are published online in the American Chemical Society journal Nano Letters - could allow for crossbar array memories that store up to 162 gigabits (around 20 GB).

“This is a new way to make ultradense, nonvolatile computer memory,” said James Tour, professor of materials science, nanoengineering and computer science at Rice University.

While current flash technology requires three electrodes per circuit, the device developed by the team at Rice needs just two. According to Tour, it uses 100 times less energy than current devices.

“This tantalum memory is based on two-terminal systems, so it’s all set for 3D memory stacks,” he said. “And it doesn’t even need diodes or selectors, making it one of the easiest ultradense memories to construct. This will be a real competitor for the growing memory demands in high-definition video storage and server arrays.”

Electron microscope image of the memory device.

Electron microscope image of the memory device.

During development, the researchers found the tantalum oxide gradually loses oxygen ions, changing from an oxygen-rich, nanoporous semiconductor at the top, to oxygen-poor at the bottom. Where the oxygen disappears completely, it becomes pure tantalum.

“The exchange of contact barriers causes the bipolar switching,” explained lead-author Gunuk Wang, a former postdoctoral researcher at Rice who is now based in Korea.

The researchers claim the tantalum oxide memories can be fabricated at room temperature, and that the control voltage that writes and rewrites the bits is adjustable, allowing for a wide range of switching characteristics.

According to Wang, some hurdles remain before the device can be commercialised, including a method for controlling the size of the nanopores, and fabricating a dense enough crossbar device to address individual bits.