Power/Performance Bits: Feb. 25

Thinner, flexible touchscreens
Researchers from RMIT University, University of New South Wales, and Monash University developed a thin, flexible electronic material for touchscreens. The material is 100 times thinner than current touchscreen materials.

The new screens are still based on indium-tin oxide (ITO), a common touchscreen material. However, a liquid metal printing approach was used. An indium-tin alloy is heated to 200C, where it becomes liquid, and then rolled over a surface to print off nano-thin sheets of indium tin oxide.

These 2D nanosheets have the same chemical make-up as standard ITO but a different crystal structure, giving them new mechanical and optical properties. As well as being fully flexible, the new type of ITO absorbs just 0.7% of light, compared with the 5-10% of standard conductive glass. To make it more electronically conductive, you just add more layers.

“We’ve taken an old material and transformed it from the inside to create a new version that’s supremely thin and flexible,” said Torben Daeneke, an Australian Research Council DECRA Fellow at RMIT. “You can bend it, you can twist it, and you could make it far more cheaply and efficiently that the slow and expensive way that we currently manufacture touchscreens. Turning it two-dimensional also makes it more transparent, so it lets through more light. This means a cell phone with a touchscreen made of our material would use less power, extending the battery life by roughly 10%.”

The ultra-thin and ultra-flexible electronic material could be printed and rolled out like newspaper, for the touchscreens of the future. (Credit: RMIT University)

The nano-thin sheets are readily compatible with existing electronic technologies. The flexibility of the material means it could potentially be manufactured through roll-to-roll (R2R) processing just like a newspaper.

“The beauty is that our approach doesn’t require expensive or specialized equipment – it could even be done in a home kitchen,” Daeneke said. “We’ve shown its possible to create printable, cheaper electronics using ingredients you could buy from a hardware store, printing onto plastics to make touchscreens of the future.”

The research team created a working touchscreen with the new material as a proof-of-concept and have applied for a patent for the technology. They see possibilities for other optoelectronic applications, like LEDs and smart windows.

Encapsulating 2D materials
Researchers at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Columbia University, and the National Institute for Materials Science in Japan created a way to integrate indium selenide (InSe) and gallium selenide (GaSe) with other electronic components without degrading.

The 2D semiconductors show promise for various applications in areas such as high-frequency electronics, optoelectronics and sensor technology. These materials can be made into flake-like films only 5 to 10 atomic layers thick which can be used to produce electronic components of extremely small dimensions. However, they degrade when exposed to air during manufacturing.

“We managed to make encapsulated transistors based on indium selenide and gallium selenide,” said Artur Erbe, head of the Transport in Nanostructures group at HZDR’s Institute of Ion Beam Physics and Materials Research. “The encapsulation technique protects the sensitive layers from external impacts and preserves its performance.” For encapsulation, the scientists used hexagonal boron nitride (hBN), which is both inert and can be formed into a thin layer.

During encapsulation, the 2D flakes are arranged between two layers of hexagonal boron nitride and thus completely enclosed. The upper hBN layer is responsible for outward insulation, the lower one for maintaining distance to the substrate.

Applying external contacts to the semiconductors posed a problem, however, as evaporative deposition using a photomask meant the delicate materials could get degraded. Instead, the team used a lithography-free contacting technique involving metal electrodes made of palladium and gold embedded in hBN foil. This means the encapsulation and the electric contact with the 2D layer underneath can be achieved concurrently.

“In order to produce the contacts, the desired electrode pattern is etched onto the hBN layer so that the holes created can be filled with palladium and gold by means of electron beam evaporation,” said Himani Arora, a doctoral candidate of physics at HZDR. “Then you laminate the hBN foil with the electrodes onto the 2D flake.” When there are several contacts on an hBN wafer, contact with several circuits can be made and measured. For later application, the components will be stacked in layers.

The team says the encapsulation technique is easy to apply to other complex 2D materials and successfully protected against decomposition and degradation for long-term quality and stability.

Stealthy optical encryption
Researchers at Ben-Gurion University (BGU) developed an all-optical ‘stealth’ encryption technology they say will be significantly more secure and private for highly-sensitive cloud and data center network transmission.

The team used standard optical equipment to make the fiber-optic light transmission invisible or stealthy.

Instead of using one color of the light spectrum to send one large data stream, this method spreads the transmission across many colors in the optical spectrum bandwidth (1,000x wider than digital) and intentionally creates multiple weaker data streams that are hidden under noise and elude detection. Weaker encrypted data can be transmitted under a stronger inherent noise level which cannot be detected.

The solution also employs a commercially available phase mask, which changes the phase of each wavelength. That process also appears as noise but destroys the coherence, or ability to recompile the data without the correct encryption key. The optical phase mask cannot be recorded offline, so the data is destroyed if a hacker tries to decode it, the team said.

“Basically, the innovative breakthrough is that if you can’t detect it, you can’t steal it,” said Dan Sadot, Chairman of the Cathedra for Electro-optics at BGU. “Because an eavesdropper can neither read the data or even detect the existence of the transmitted signal, our optical stealth transmission provides the highest level of privacy and security for sensitive data applications.”

The optical encryption method has been patented, and BGN Technologies, the technology transfer company of Ben-Gurion University, is working to introduce it commercially.

Applications include high-speed communication and sensitive transmission of financial, medical or social media-related information, said Zafrir Levy, Senior Vice President, Exact Sciences & Engineering, BGN Technologies. “In fact, with this novel method, an eavesdropper will require years to break the encryption key. BGN is now seeking an industry partner to implement and commercialize this game-changing technology.”