|Here, graphene is used as crossbar terminals, Rice University researchers are following through on research that shows silicon oxide, one of the most common materials on Earth, can be used as a reliable computer memory. The memories are flexible and transparent and can be built in 3D configurations. (Credit: Jun Yao/Rice University)|
Houston, TX--Researchers at Rice University are designing transparent, two-terminal, 3D computer memories on flexible sheets that show promise for head-up displays and electronics. The technique is based on the switching properties of silicon oxide (SiOx) and the use of indium tin oxide (ITO) or graphene as the electrodes.1
Led by chemist James Tour and physicist Douglas Natelson, the Rice team is making highly transparent, nonvolatile resistive memory devices based on the revelation that SiOx itself can be a switch. A voltage run across a thin sheet of SiOx strips oxygen atoms away from a channel 5 nm wide, turning it into conductive silicon. With lower voltages, the channel can then be broken and repaired repeatedly, over thousands of cycles.
That channel can be read as a "1" or a "0," making it a switch. At a 5 nm feature size, it shows promise to extend Moore's Law, which predicted computer circuitry will double in power every two years. Current state-of-the-art electronics are made with 22 nm circuits.
The research details memories that are 95% transparent and made of SiOx and crossbar graphene (or ITO) terminals on flexible plastic. The Rice lab is making its devices with a working yield of about 80%, "which is pretty good for a nonindustrial lab," says Tour. "When you get these ideas into industries' hands, they really sharpen it up from there."
Manufacturers who have been able to fit millions of bits on small devices like flash memories now find themselves bumping against the physical limits of their current architectures, which require three terminals for each bit. But the Rice unit, requiring only two terminals, makes it far less complicated. It means arrays of two-terminal memories can be stacked in 3D configurations, vastly increasing the amount of information a memory chip might hold. Tour said his lab has also seen promise for making multistate memories that would further increase their capacity.
The marriage of silicon and graphene would extend the long-recognized utility of the first and prove the value of the second. Tour noted the devices not only show potential for radiation-hardened devices -- several built at Rice are now being evaluated at the International Space Station -- but also withstand heat up to about 700°C. That means they can be mounted directly atop integrated processors with no ill effects.