System Bits: July 15

Rice University researchers use porous silicon oxide to reduce forming voltage and improve manufacturability; scientists at Oxford University have developed a way to create pixels just a few hundred nanometres wide, which could pave the way for super high-resolution, low-energy thin, flexible displays.

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Silicon oxide memories
Thanks to a refinement that will allow manufacturers to fabricate devices at room temperature with conventional production methods, Rice University’s silicon oxide technology for high-density, next-generation computer memory is one step closer to mass production.

Rice’s silicon oxide memories are a type of two-terminal, “resistive random-access memory” (RRAM) technology and were first discovered 5 years ago and are believed to be superior to all other two-terminal unipolar resistive memories by almost every metric, the researchers said.

The devices use silicon oxide — the most studied material on Earth. As such, the underlying physics are both well-understood and easy to implement in existing fabrication facilities. The researchers began work on their breakthrough RRAM technology more than five years ago with the basic concept behind the devices being the insertion of a dielectric material — one that won’t normally conduct electricity — between two wires. When a sufficiently high voltage is applied across the wires, a narrow conduction path can be formed through the dielectric material.

This illustration depicts the rewriteable crystalline filament pathway in Rice University's porous silicon oxide RRAM memory devices. (Source: Rice University)

This illustration depicts the rewriteable crystalline filament pathway in Rice University’s porous silicon oxide RRAM memory devices. (Source: Rice University)

RRAM is under development worldwide and expected to supplant flash memory technology in the marketplace within a few years because it is faster than flash and can pack far more information into less space. For example, manufacturers have announced plans for RRAM prototype chips that will be capable of storing about one terabyte of data on a device the size of a postage stamp — more than 50 times the data density of current flash memory technology, the researchers added.

‘Nano-pixels’ for thin, flexible high-res displays
A team of researchers led by Oxford University have made a discovery that could make it possible to create pixels just a few hundred nanometers across which may pave the way for very high-resolution and low-energy thin, flexible displays for applications including ‘smart’ glasses, synthetic retinas and foldable screens.

The team explored the link between the electrical and optical properties of phase change materials – materials that can change from an amorphous to a crystalline state – and found that by sandwiching a 7nm-thick layer of a phase change material (GST) between two layers of a transparent electrode, they could use a tiny current to ‘draw’ images within the sandwich ‘stack.’

Still images were first created using an atomic force microscope but the team went on to demonstrate that such tiny ‘stacks’ can be turned into prototype pixel-like devices. These ‘nano-pixels’ – just 300 by 300 nm in size – can be electrically switched ‘on and off’ at will, creating the colored dots that would form the building blocks of an extremely high-resolution display technology.

The phase change material used was the alloy Ge2Sb2Te5 (Germanium-Antimony-Tellurium or GST) sandwiched between electrode layers made of indium tin oxide (ITO).