Research Bits: Feb. 22

Dense optical data storage; LEDs for power and data; carbon nanotube FETs for space.


Dense optical data storage
Researchers from the University of Southampton developed a laser writing method for producing high-density nanostructures in silica glass, which could be used for long-term, dense data storage.

“Individuals and organizations are generating ever-larger datasets, creating the desperate need for more efficient forms of data storage with a high capacity, low energy consumption and long lifetime,” said Yuhao Lei, a doctoral researcher at the University of Southampton. “While cloud-based systems are designed more for temporary data, we believe that 5D data storage in glass could be useful for longer-term data storage for national archives, museums, libraries or private organizations.”

The 5D refers to writing data that encompasses two optical dimensions plus three spatial dimensions. The new approach can write at speeds of 1,000,000 voxels per second, which is equivalent to recording about 230 kilobytes of data per second.

“This new approach improves the data writing speed to a practical level, so we can write tens of gigabytes of data in a reasonable time,” said Lei. “The highly localized, precision nanostructures enable a higher data capacity because more voxels can be written in a unit volume. In addition, using pulsed light reduces the energy needed for writing.”

The researchers used their new method to write 5 gigabytes of text data onto a silica glass disc about the size of a conventional compact disc with nearly 100% readout accuracy. Each voxel contained four bits of information, and every two voxels corresponded to a text character. With the writing density available from the method, the disc would be able to hold 500 terabytes of data. With upgrades to the system that allow parallel writing, the researchers said it should be feasible to write this amount of data in about 60 days.

The team is working to increase the writing speed and make the technology usable outside the laboratory. They also note that faster methods of reading data would be required for practical data storage.

And the writing method isn’t limited to storage applications. “The physical mechanism we use is generic,” said Lei. “Thus, we anticipate that this energy-efficient writing method could also be used for fast nanostructuring in transparent materials for applications in 3D integrated optics and microfluidics.”

LEDs for power and data
Researchers from IMDEA Networks Institute and Uppsala University suggest that IoT devices could operate and communicate without batteries.

The approach, which the researchers call PassiveLiFi, relies on using LEDs from which the IoT tag could harvest power through a solar panel. Additionally, data would be sent to the device by modulating the LEDs, called LiFi. The IoT tag then sends data by reflecting and modulating the RF signals present in the environment, called RF backscattering.

“Our work opens the door to long-range, battery-free Internet of Things applications retrofitting lighting infrastructure for communication, something that was not previously possible to achieve. It’s the result of three years of research; when we started, LiFi technology and RF backscattering were considered independent technologies, and we have shown that LiFi can solve the limitations of RF backscatter, and that LiFi can be applied to a new field, battery-free communication,” said Domenico Giustiniano, a research associate professor at IMDEA Networks.

“In PassiveLiFi, the LiFi transmitter sends a clock with varying frequency over the visible light channel that increases over time (up-chirp signal),” the researchers said. “Next, the tag receives these transmissions using low-power solar cell-based LiFi receiver and further modulates the signal based on the information to be transmitted.”

The IoT tag itself operates solely on energy harvested with its solar panel. It wakes when it receives a start frame delimiter from the LED LiFi transmitter. A nearby carrier wave generator is used to create the RF signal.

“Solar cells have been widely used to harvest energy. In this work, we go a step further and demonstrate that they can be used efficiently and simultaneously as both a source of power harvesting and as a communications receiver. Our solution solves the trade-off between the captured energy required by the IoT device and the desired data rate, allowing our system to operate without using batteries,” said Borja Genovés Guzmán, a post-doc researcher at IMDEA Networks.

In tests of the system, the team achieved communication with an RF receiver over a distance of 305 meters with an uplink power consumption of 3.8 W.

Carbon nanotube FETs for space
Researchers from MIT and US Air Force Research Laboratory propose using carbon nanotubes to improve radiation tolerance of electronics, an important metric for space applications.

The team sought to create a field-effect transistor to withstand high levels of radiation and build memory chips based on them. To do this, they deposited carbon nanotubes on a silicon wafer as the semiconducting layer in field-effect transistors. They also tested different transistor configurations with various levels of shielding, consisting of thin layers of hafnium oxide and titanium and platinum metal, around the semiconducting layer.

By placing shields both above and below the carbon nanotubes, the transistor’s electrical properties were protected against incoming radiation up to 10 Mrad, much higher than most silicon-based radiation-tolerant electronics can handle.

With a shield only placed beneath the carbon nanotubes, they were protected up to 2 Mrad, comparable to commercial silicon-based radiation-tolerant electronics.

In building the SRAM, the team used the bottom shield version to balance fabrication complexity with radiation robustness. The CNFET SRAM chips had a similar radiation threshold as silicon-based SRAM devices.

The researchers said that the results indicate that carbon nanotube field-effect transistors, especially double-shielded ones, could be a promising addition to next-generation electronics for space exploration.

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