Light-based memory chip is the first ever to store data permanently

September 22, 2015

The world's first entirely light-based memory chip to store data permanently has been developed by material scientists at Oxford University and University of Münster in collaboration with scientists at Karlsruhe and Exeter. The device, which makes use of materials used in CDs and DVDs, could help dramatically improve the speed of modern computing.

Today's computers are held back by the relatively slow transmission of electronic data between the processor and the . "There's no point using faster processors if the limiting factor is the shuttling of information to-and-from the memory—the so-called von-Neumann bottleneck," explains Professor Harish Bhaskaran, the Oxford engineer who led the research along with Professor Wolfram Pernice from the University of Münster. "But we think using light can significantly speed this up."

Simply bridging the processor-memory gap with photons isn't efficient, though, because of the need to convert them back into electronic signals at each end. Instead, memory and processing capabilities would need be light-based too. Researchers have tried to create this kind of photonic memory before, but the results have always been volatile, requiring power in order to store data. For many applications—such as computer disk drives—it's essential to be able to store data indefinitely, with or without power.

Now, an international team of researchers—including researchers from Oxford University's Department of Materials, the University of Münster, the Karlsruhe Institute of Technology and the University of Exeter—has produced the world's first all-photonic nonvolatile memory chip. The new device uses the phase-change material Ge2Sb2Te5 (GST)—the same as that used in rewritable CDs and DVDs—to store data. This material can be made to assume an amorphous state, like glass, or a crystalline state, like a metal, by using either electrical or optical pulses. In a paper published in Nature Photonics, the researchers describe the device they've created, which uses a small section of GST on top of a silicon nitride ridge, known as a waveguide, to carry light.

The team has shown that intense pulses of light sent through the waveguide can carefully change the state of the GST. An intense pulse causes it to momentarily melt and quickly cool, causing it to assume an amorphous structure; a slightly less-intense pulse can put it into an .

Later, when light with much lower intensity is sent through the waveguide, the difference in the state of the GST affects how much light is transmitted. The team can measure that difference to identify its state—and in turn read off the presence of information in the device as a 1 or 0. "This is the first ever truly non-volatile integrated optical memory device to be created," explains Clarendon Scholar and DPhil student Carlos Ríos, one of two lead authors of the paper along with Matthias Stegmaier. "And we've achieved it using established materials that are known for their long-term data retention—GST remains in the state that it's placed in for decades."

By sending different wavelengths of light through the waveguide at the same time—a technique referred to as wavelength multiplexing—the team also showed that they could use a single pulse to write and read to the memory at the same time. "In theory, that means we could read and write to thousands of bits at once, providing virtually unlimited bandwidth," explains Professor Wolfram Pernice of the University of Munster.

The researchers have also found that different intensities of strong pulses can accurately and repeatedly create different mixtures of amorphous and crystalline structure within the GST. When lower intensity pulses were sent through the waveguide to read the contents of the device, they were also able to detect the subtle differences in transmitted light, allowing them to reliably write and read off eight different levels of state composition—from entirely crystalline to completely amorphous. This multi-state capability could provide memory units with more than the usual binary information of 0 and 1, allowing a single bits of memory to store several states or even perform calculations themselves instead of at the processor.

"This is a completely new kind of functionality using proven existing materials," explains Professor Bhaskaran. "These optical bits can be written with frequencies of up to one gigahertz and could provide huge bandwidths. This is the kind of ultra-fast data storage that modern computing needs."

Now, the team is working on a number of projects that aim to make use of the new technology. They're particularly interested in developing a new kind of electro-optical interconnect, which will allow the to directly interface with other components using light, rather than electrical signals.

Explore further: Study demonstrates rapid control of phase-changes in resonantly bonded materials

More information: "Integrated all-photonic non-volatile multi-level memory," Nature Photonics (2015) DOI: 10.1038/nphoton.2015.182

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1.2 / 5 (5) Sep 22, 2015
Well who would have guessed that the material used for CD-R's could be used for optical memory and read with a laser?? Another years grant money well spent.
1 / 5 (2) Sep 22, 2015
This news is just like "Forever young" news report on the work of Vas(ant) Narasimhan, The Global Head of Norvatis pharmaceuticals!
Humanity making big strides.
1 / 5 (2) Sep 22, 2015
Well who would have guessed that the material used for CD-R's could be used for optical memory and read with a laser?? Another years grant money well spent.

It really makes me very angry when they publish B.S Research on useless findings such as Chimps making stones to use as weapons etc., etc., wasting public money.
Who does that? Find those NAMES. You will be really surprised!
That's being too nice to them.
4.2 / 5 (10) Sep 22, 2015
It never ceases to amaze how the trolls flock to articles they don't understand.
It also never ceases to amaze how the trolls also don't understand how science works.
It's not all grand schemes.
Most of the time it's just putting small pieces of knowledge together to come up with the new: And that is exactly what they wrote:
... —has produced the world's first all-photonic nonvolatile memory chip.

No one has done this before and it is an essential step towards an all-photonic computer.

Without anyone doing stuff like this you would never get any advances in technology. So instead of griping you should be glad someone did it...because sure as hell none of you trolls would contribute anything to science - no matter how much money was thrown at you.
1 / 5 (1) Sep 22, 2015
anti....: I understood it perfectly.
They have taken the insides of a CD-R drive, including the disc, and replicated it as a single bit of memory on an optical bench.
There is no novel memory material nor new writing/reading methodology. The epitaxial SiN waveguides are the most recent (~7 years) addition.
If they had used multi-spectral holography to create high data density on their 'chip' I would have been impressed.

But this is the sort of project they give to an undergraduate to keep them busy for a single term, and practise their paper writing skills. This paper will never be cited by anyone else.
not rated yet Sep 22, 2015
What's the endurance of a single bit?

I remember my RW discs had 1000 erases. In practice they started breaking down after 10 and became unreadable after a few years.
4 / 5 (4) Sep 22, 2015
anti....: I understood it perfectly

Doesn't look like it. Certainly looks like you didn't read the last four paragraphs which detail some things they did which are not the ususal "CD RW" tech.
3 / 5 (2) Sep 22, 2015
The latter paragraphs are the "spin" they put in papers to make them sound more important than they are. Where impressive figures like 'multiple wavelengths' (i.e 2) cam indeed write and read at the same time. Their 1GHz figure means that a high speed high power 1nS pulse can write a 1 ( but not a zero as Amorphous cycling is faster than re-crystallisation). They will also have also conveniently forgotten the >>1ns time to cool/set before the next write cycle can be attempted. Their Multi-level 3 bit cell may possibly be unique to this material but it has been done on phase change memory elsewhere.
3 / 5 (2) Sep 22, 2015
Since when was calling people names a serious solution to any real problem that life faces?

5 / 5 (1) Nov 02, 2015
Well who would have guessed that the material used for CD-R's could be used for optical memory and read with a laser?? Another years grant money well spent.

EyeNStein. You're SO wrong, how dare you even using a nickname like that?.
They have taken the insiders of a CD inlcuding the disk? Did you read the paper? It is an evanescent coupling from a photonic circuit what switches the material. There is no disk. Writing/reading is completely new (or you think the reviewers of such journals are stupid?) and, if it was that easy, why no one did it before? A clue, it was very easy to crystallize but no one was able to amorphize all-optically and on an integrated circuit - the whole erasing protocol is a great discovery. So much, for the future of technology, that in the News and Views of Nature Photonics, they dedicated a full paper to this called: "Optical memory: Phase-change memory".
(BOOM! first citation already)

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