̽��ֱ�� of Cambridge - Arokia Nathan

Engineers design ultralow power transistors that could function for years without a battery

sc604 — Thu, 20 Oct 2016 18:00:00 +0000

A newly-developed form of transistor opens up a range of new electronic applications including wearable or implantable devices by drastically reducing the amount of power used. Devices based on this type of ultralow power transistor, developed by engineers at the ̽��ֱ�� of Cambridge, could function for months or even years without a battery by ‘scavenging’ energy from their environment.

Using a similar principle to a computer in sleep mode, the new transistor harnesses a tiny ‘leakage’ of electrical current, known as a near-off-state current, for its operations. This leak, like water dripping from a faulty tap, is a characteristic of all transistors, but this is the first time that it has been effectively captured and used functionally. ̽��ֱ��results, reported in the journal Science, open up new avenues for system design for the Internet of Things, in which most of the things we interact with every day are connected to the Internet.

̽��ֱ��transistors can be produced at low temperatures and can be printed on almost any material, from glass and plastic to polyester and paper. They are based on a unique geometry which uses a ‘non-desirable’ characteristic, namely the point of contact between the metal and semiconducting components of a transistor, a so-called ‘Schottky barrier.’

“We’re challenging conventional perception of how a transistor should be,” said Professor Arokia Nathan of Cambridge’s Department of Engineering, the paper’s co-author. “We’ve found that these Schottky barriers, which most engineers try to avoid, actually have the ideal characteristics for the type of ultralow power applications we’re looking at, such as wearable or implantable electronics for health monitoring.”

̽��ֱ��new design gets around one of the main issues preventing the development of ultralow power transistors, namely the ability to produce them at very small sizes. As transistors get smaller, their two electrodes start to influence the behaviour of one another, and the voltages spread, meaning that below a certain size, transistors fail to function as desired. By changing the design of the transistors, the Cambridge researchers were able to use the Schottky barriers to keep the electrodes independent from one another, so that the transistors can be scaled down to very small geometries.

̽��ֱ��design also achieves a very high level of gain, or signal amplification. ̽��ֱ��transistor’s operating voltage is less than a volt, with power consumption below a billionth of a watt. This ultralow power consumption makes them most suitable for applications where function is more important than speed, which is the essence of the Internet of Things.

“If we were to draw energy from a typical AA battery based on this design, it would last for a billion years,” said Dr Sungsik Lee, the paper’s first author, also from the Department of Engineering. “Using the Schottky barrier allows us to keep the electrodes from interfering with each other in order to amplify the amplitude of the signal even at the state where the transistor is almost switched off.”

“This will bring about a new design model for ultralow power sensor interfaces and analogue signal processing in wearable and implantable devices, all of which are critical for the Internet of Things,” said Nathan.

“This is an ingenious transistor concept,” said Professor Gehan Amaratunga, Head of the Electronics, Power and Energy Conversion Group at Cambridge’s Engineering Department. “This type of ultra-low power operation is a pre-requisite for many of the new ubiquitous electronics applications, where what matters is function – in essence ‘intelligence’ – without the demand for speed. In such applications the possibility of having totally autonomous electronics now becomes a possibility. ̽��ֱ��system can rely on harvesting background energy from the environment for very long term operation, which is akin to organisms such as bacteria in biology.”

Reference:
S. Lee and A. Nathan, ‘Subthreshold Schottky-barrier thin film transistors with ultralow power and high intrinsic gain’. Science (2016). DOI: 10.1126/science.aah5035

A new design for transistors which operate on ‘scavenged’ energy from their environment could form the basis for devices which function for months or years without a battery, and could be used for wearable or implantable electronics.

If we were to draw energy from a typical AA battery based on this design, it would last for a billion years.

Sungsik Lee

Recklessstudios/Public Domain

Transistors

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Weaving electronics into the fabric of our physical world

bjb42 — Tue, 24 Jan 2012 09:45:59 +0000

̽��ֱ��potential applications for nanophotonics and nanoelectronics are truly startling, suggesting the brink of a revolution in human–machine interfaces that could turn science fiction into a reality. From interactive paper to clothing that generates energy and light-weight material with X-ray capabilities, weaving electronics into the building blocks of everyday materials will undoubtedly impact how we live in the future.

̽��ֱ��Electrical Division in the Department of Engineering is leading the charge for Cambridge, both in terms of fundamental research and application within industry. While research is of course essential, of almost equal importance in fields like nanoelectronics is showing real world application, demonstrating the potential of technology to industry through prototyping, and encouraging investment from around the world.

To aid this approach, the ̽��ֱ�� has recently recruited Professor Arokia Nathan from ̽��ֱ�� College London (UCL) to a new Chair of Photonic Systems and Displays. Nathan, a world leader in the development of display technology, will work between the three primary groups in the Electrical Engineering Division (electronic materials, photonics and energy), acting as a conduit and catalyst for ideas and research.

“For me this is a fantastic opportunity to collaborate with researchers at the top of their game, working on this idea of systems that can integrate functionality such as communications and energy into materials to enhance everyday life,” he explained. One of his primary visions for Cambridge is the foundation of a new Design Centre to demonstrate the potential of this technology to industry through prototyping and to encourage investment from around the world.

Initially, Professor Nathan and colleagues within the Division will be developing electronic systems that can be seamlessly layered on to a material or substrate, such as plastic or polyester, with embedded transistors and sensors for transmitting and receiving information. While at UCL, Nathan and a team of collaborators from CENIMAT/FCTUNL, Portugal demonstrated the first inverter and other circuit building blocks on a piece of paper, representing the first step towards animated images and videos on magazine pages.

Power is a vital question for these processes to address. “If a magazine has electronic displays as an integral part of a page, then it’s got to cover its own power,” says Nathan. “Solar energy will be a major focus of the work. I can see it becoming commonplace for clothing to have embedded electronics that generate energy from solar and even body heat, essentially doubling as a battery that can be charging your phone as it’s in your pocket.

This could be coupled with what’s known as ‘green broadcasting’, to build a picture of an individual self-powering their portable electronics as they are out and about. “These portable devices which otherwise lay idle could be sending out information at very low bit rates without using much energy. It could always be active – this is where our photonics group has expertise,” says Nathan. “It’s easy to see how these technologies might appeal to major industry, from clothing manufacturers to publishers, and certainly the military.”

Nanowires will be a key area of investigation for Nathan in the coming years. These structures have an extraordinary length-to-width ratio, only a few nanometres in diameter, and a much greater capacity in terms of speed. “Uniformly dispersed over large areas, the wires could result in millions of transistors on a single sheet of A4 for example,” says Nathan.

“While it hasn’t been done yet, we will be working on this in an attempt to match the speeds of a Pentium-like chip, scaled to A4. Pentium chips cost 10 dollars per centimetre squared, while a nano thin film transistor could cost as little as 10 cents per centimetre squared, a much cheaper alternative.”

Industries such as biomedicine could also benefit hugely from this interlacing of nano-electronics into materials. “You could foresee a time when you can take the X-ray to the patient rather than vice-versa,” says Nathan. “Patients might lie on a surface woven with electronics, so that data can be broadcast straight from the material. You couldn’t do this with Pentium-like chips because of yield and cost issues.”

“With these non-conventional materials you have a great deal of freedom. We believe this approach to circuitry in substrates will lead to the creation of smart substances, and once you start thinking about the possible applications, it’s hard to stop: surgeon’s gloves with smart skin, walls of a house that store energy and generate large-scale displays, magazines with interactive video in the pages, devices that dissolve the toxins in water, bio-interfaces in mobile phones with diagnostic capabilities, clothing that generates energy – the possibilities are endless!”

̽��ֱ��integration of electronics with materials opens up a world of possibilities, the surface of which is just being scratched. Professor Arokia Nathan has joined the ̽��ֱ�� to take up a new Chair in Engineering, where he will be exploring the application of research that allows us to glimpse a world rivalling our wildest dreams of the future.

We believe this approach to circuitry in substrates will lead to the creation of smart substances, and once you start thinking about the possible applications, it’s hard to stop.

Arokia Nathan

CORE-Materials from Flickr

Aligned carbon nanotubes, coated with a conducting polymer

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