Power/Performance Bits: April 13

Speedy data transfer; antiferromagnetic storage; sub-diffraction optical storage.


Speedy data transfer
Researchers from MIT, Intel, and Raytheon developed a new data transfer system that both boosts speeds and reduces energy use by taking elements from both traditional copper cables and fiber optics.

“There’s an explosion in the amount of information being shared between computer chips — cloud computing, the internet, big data. And a lot of this happens over conventional copper wire,” said Jack Holloway of Raytheon. He also noted the power requirements from dealing with heavy data loads: “There’s a fundamental tradeoff between the amount of energy burned and the rate of information exchanged.”

Instead of larger copper cables, the team used a conduit made of plastic polymer, making it lighter and potentially cheaper to manufacture than traditional copper cables. The polymer link is operated with sub-terahertz electromagnetic signals, which makes it more energy-efficient than copper in transmitting a high data load. The new link’s efficiency rivals that of fiber-optic, but Holloway noted that “It’s compatible directly with silicon chips, without any special manufacturing.” The team created low-cost chips to generate the high-frequency signals.

It sends signals over three different parallel channels, separated by frequency. The link’s total bandwidth is 105 gigabits per second, nearly an order of magnitude faster than a copper-based USB cable.

It’s also smaller: “The cross-sectional area of our cable is 0.4 millimeters by a quarter millimeter,” said Ruonan Han, associate professor in MIT’s Department of Electrical Engineering and Computer Science. “So, it’s super tiny, like a strand of hair.”

Han believes the polymer conduits can be made even faster by bundling them together. “Then the data rate will be off the charts. It could be one terabit per second, still at low cost.” The team sees data centers as potential adopters of the new cables, along with aerospace and automotive.

Antiferromagnetic storage
Researchers from the University of Basel, Helmholtz-Zentrum Institute of Ion Beam Physics and Materials Research, and Taras Shevchenko National University of Kyiv propose using antiferromagnetic materials for data storage.

The researchers focused on a single crystal of chromium(III) oxide (Cr2O3), in which the atoms are arranged in a regular crystal lattice with very few defects. “We can alter the single crystal in such a way as to create two areas (domains) in which the antiferromagnetic order has different orientations,” said Natascha Hedrich of Basel.

The two domains are separated by a domain wall. “Thanks to the high sensitivity and excellent resolution of our quantum sensors, we were able to experimentally demonstrate that the domain wall exhibits behavior similar to that of a soap bubble,” said Patrick Maletinsky, a professor at Basel.

The domain wall is elastic and has a tendency to minimize its surface energy, like a soap bubble. Its trajectory reflects the crystal’s antiferromagnetic material properties and can be predicted with a high degree of precision, which was confirmed by simulations.

The team was able to manipulate the trajectory of the domain wall by selectively structuring the surface of the crystal at the nanoscale, leaving behind tiny raised squares. These squares then alter the trajectory of the domain wall in the crystal in a controlled manner.

They could then use the orientation of the raised squares to direct the domain wall to one side of the square or the other. This is the fundamental principle behind the new data storage concept: if the domain wall runs to the “right” of a raised square, this could represent a value of 1, while having the domain wall to the “left” could represent a value of 0. Through localized heating with a laser, the trajectory of the domain wall can be repeatedly altered, making the storage medium reusable.

“Next, we plan to look at whether the domain walls can also be moved by means of electrical fields,” Maletinsky added. “This would make antiferromagnets suitable as a storage medium that is faster than conventional ferromagnetic systems, while consuming substantially less energy.”

Sub-diffraction optical storage
The amount of data the world generates is ever-increasing, making the search for high capacity storage more important. Researchers from the University of Shanghai for Science and Technology, RMIT University, and National University of Singapore propose a way to deliver higher capacity optical storage.

Optical disk storage capacity and the size of information bits has been limited by the diffractive nature of light. To overcome this, the researchers used earth-rich lanthanide-doped upconversion nanoparticles and graphene oxide flakes. The upconversion nanoparticles allow sub-diffraction nanoscale information bits to be written using low laser beam intensity, resulting in low energy consumption and a longer device lifespan. In addition, the continuous-wave lasers that are used are inexpensive, reducing operating costs compared to pulsed lasers.

They estimate the storage capacity of a 12-cm optical disk would be 700 TB, about 28,000 Blu-ray disks. The team said the technology also offers the potential for optical lithography of nanostructures in carbon-based chips for next-generation nanophotonic devices.

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