Electronic ink to transform devices

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Two researchers from the University of Cape Town (UCT) have used nanotechnology to create printable semiconductors, which can be applied to flexible surfaces at a low cost.

Professors David Britton and Margit H"arting, from the physics department at UCT, have produced silicon nanoparticle-based inks without the need for the usual high-temperature processing.

“We produced silicon nanoparticles with particular characteristics, which allow them to be turned into semiconducting ink,” explains Britton. Using a novel printing technique, they can print “electronic ink” on substrates like paper, which they say exhibits performance quality comparable to silicon thin film transistors.

Britton explains that semiconductor fabrication usually involves a highly complex procedure, whereby a crystal wafer has to go through several stages with different layers being deposited and etched away, all in an ultra-high vacuum using expensive and high-temperature processes.

“By looking at the basic science, we understand enough about nanoparticles to produce particles which don't require this high-temperature processing,” he notes. “We use novel printing processes to print directly onto any substrate,” explains H"arting, adding that the preferred material at the moment is paper. “With printing, what you see is what you get,” says Britton. He explains one can design a print and print it using different semiconductor inks.

According to Britton, their method of fabricating silicon nanoparticles is a lean process, using inexpensive material. It's also environmentally benign, notes Britton, as they use renewable substrates and non-toxic materials, which aren't harmful once they degrade.

“If you burn silicon, you get sand, and it's safe for landfills,” says H"arting, adding that because of the size range of these particles, they cannot penetrate the skin.

Infinite possibilities

Producing inks from silicon nanoparticles, say Britton and H"arting, presents a new way to produce electronic devices. This provides an opportunity for printed silicon to become the universal platform for disposable electronics, and could lead to a myriad of new product designs and applications, they explain.

“It could bring inexpensive, ubiquitous electronics in terms of intelligence in packaging, sensors for medical diagnostics, flexible displays and much more,” says Britton.

One application which could have a significant impact locally is using solar cells as charging units for portable electronics. “In an African context, a lot of people have cellphones, but don't have regular access to electricity,” explains H"arting. The researchers say these organic solar panels could be used in low-power devices for light household use in rural areas, without access to the electricity grid.

Other applications include low-resolution displays for cellphones and e-readers, disposable ticketing systems and smart packaging. “For example, you could have a shirt that monitors certain aspects of body functioning, and analyses the state of your health,” explains Britton.

It can also be used in simple medical patches, motion sensors in wallpaper, or logic in packaging data. “So a carton could tell you whether the milk is off instead of having a sell-by date.” A big application, according to Britton, will be newspapers, as a piece of paper would then have the ability to download information. ”It will bring the next generation of e-readers, where, instead of a case, your display will be a thick sheet of paper.”

H"arting adds the technology could result in boarding passes that display what time a traveller's baggage is on board or changes in gate numbers and updated flight information. “Or, you could have a parking ticket that tells you where your car is. It's about small things that help make our lives more convenient.”

Britton says: “These kinds of innovations are five to 10 years away, but all things are possible.”

Next steps

Their work has been funded by the Department of Science and Technology through the Innovation Fund. The team is also working in conjunction with the US Agency for International Development (USAID) on its programme for higher education development in Africa.

“This programme funds projects in Africa that build up capacity for research and development, as well as encourage entrepreneurship and innovation,” says Britton.

At the moment, Britton and H"arting are focusing on developing seed resources to tackle the commercial aspect of their solution. Britton says they're in talks with investors for certain applications involving simple circuitry and are working with industry, as the technology sits in the middle between the power and display components of a device.

Britton, who served as the second chair of the South African Nanotechnology Initiative, says, a few years ago, SA was probably five to 10 years behind most countries in terms of nanotechnology. “A very good decision was made to actually drive nanosciences and nanotechnology and towards the understanding of materials and systems,” notes H"arting.

Due to this push from government and by being imaginative in various fields of nanotechnology, Britton says SA managed to punch above its weight globally. “In terms of printable silicon, we're now probably five to 10 years ahead of international industry and academia,” he says.

Britton and H"arting are in the process of spinning out a company and in conjunction with USAID, hope to establish a centre based in Cape Town for innovation in nanosciences and technology.

In April, the researchers took the academic prize for their work in printable silicon at the printed electronics Europe conference, IDTechEx, held in Dresden.

For H"arting, it's stimulating working on systems with direct applications. “I love scientific work where you need real basic science to understand systems and implement it in applications.”

“The wonderful thing about working at the nanoscale,” adds Britton, “is this is where you observe changes at the fundamental, basic level.”

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