Engineers at the University of Cambridge have created a new design for transistors that can operate on ‘scavenged’ energy from their environment. This new technology might form the basis for devices which could function for months (or years) without needing a recharging.
Future devices based on these ultra-low power transistor might function for months or even years without a battery by ‘scavenging’ energy from their environment. The technology opens up a whole range of electronic applications including wearable and implantable devices which could be completely revolutionised by reducing the amount of power used.
The transistors operate on a similar principle to a computer in sleep mode. By harnessing a tiny ‘leakage’ of electrical current (known as a near-off-state current) it is able to operate for long periods of time by ‘refilling’ itself.
The transistor itself is made from glass and plastic to polyester and paper and can be produced at low temperatures. The design itself is fascinating – based on a unique geometry which uses a ‘non-desirable’ characteristic (this is the point of contact between the metal and semiconducting part of a transistor – known as the ‘Schottky barrier’).
Professor Arokia Nathan, one of the paper’s authors, explained that the team had “found that these Schottky barriers, which most engineers try to avoid, actually have the ideal characteristics for the type of ultra low power applications we’re looking at, such as wearable or implantable electronics for health monitoring”.
The design is ground-breaking because the team were able to produce them at very small sizes. This has traditionally been a problem because as transistors become smaller their electrodes start to influence each other and voltages spread out stopping them functioning as they should.
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Changing the fundamentals of the design, the team at Cambridge were able to make use of the Schottky barrier to keep each transistors electrodes independent from one another. Allowing them to scale the transistors down to incredibly small sizes and allows for high levels of ‘gain’ (signal amplification). This means that operating voltage for each transistor is less than a single volt and total consumption is a billionth of a watt.
Dr Sungsik Lee, the paper’s lead author, explained that if the team were to “draw energy from a typical AA battery based on this design, it would last for a billion years“.
There is plenty of reasons to be excited about the impact this new design might have. Professor Gehan Amaratunga, Head of the Electronics, Power and Energy Conversion Group said that the team had demonstrated an “ingenious transistor concept” and “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. The 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.”.
While commercial applications might still be some way off the team hope this technology will open up new avenues for system design for the Internet of Things.
The team reported their findings in the journal Science: 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
