̽��ֱ�� of Cambridge - transistors

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

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Transistors

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̽��ֱ��next generation of computing

gm349 — Mon, 04 Jul 2011 08:01:04 +0000

Scientists have taken one step closer to the next generation of computers. Research from the Cavendish Laboratory, the ̽��ֱ�� of Cambridge’s Department of Physics, provides new insight into spintronics, which has been hailed as the successor to the transistor.

Spintronics, which exploits the electron’s tiny magnetic moment, or ‘spin’, could radically change computing due to its potential of high-speed, high-density and low-power consumption. ̽��ֱ��new research sheds light on how to make ‘spin’ more efficient.

For the past 50 years, progress in electronics has relied heavily on the downsizing of the transistor through the semiconductor industry in order to provide the technology for the small, powerful computers that are the basis of our modern information society. In a 1965 paper, Intel co-founder Gordon E. Moore described how the number of transistors that could be placed inexpensively on an integrated circuit had doubled every year between 1958 and 1965, predicting that the trend would continue for at least ten more years.

That prediction, now known as Moore’s Law, effectively described a trend that has continued ever since, but the end of that trend—the moment when transistors are as small as atoms, and cannot be shrunk any further—is expected as early as 2015. At the moment, researchers are seeking new concepts of electronics that sustain the growth of computing power.

Spintronics research attempts to develop a spin-based electronic technology that will replace the charge-based technology of semiconductors. Scientists have already begun to develop new spin-based electronics, beginning with the discovery in 1988 of giant magnetoresistance (GMR) effect. ̽��ֱ��discovery of GMR effect brought about a breakthrough in gigabyte hard disk drives and was also key in the development of portable electronic devices such as the iPod.

While conventional technology relies on harnessing the charge of electrons, the field of spintronics depends instead on the manipulation of electrons’ spin. One of the unique properties in spintronics is that spins can be transferred without the flow of electric charge currents. This is called “spin current” and unlike other concepts of harnessing electrons, the spin current can transfer information without generating heat in electric devices. ̽��ֱ��major remaining obstacle to a viable spin current technology is the difficulty of creating a volume of spin current large enough to support current and future electronic devices.

However, the new Cambridge researchers in close collaboration with Professor Sergej Demokritov group at the ̽��ֱ�� of Muenster, Germany, have, in part, addressed this issue. In order to create enhanced spin currents, the researchers used the collective motion of spins called spin waves (the wave property of spins). By bringing spin waves into interaction, they have demonstrated a new, more efficient way of generating spin current.

Dr Hidekazu Kurebayashi, from the Microelectronics Group at the Cavendish Laboratory, said: “You can find lots of different waves in nature, and one of the fascinating things is that waves often interact with each other. Likewise, there are a number of different interactions in spin waves. Our idea was to use such spin wave interactions for generating efficient spin currents.”

According to their findings, one of the spin wave interactions (called three-magnon splitting) generates spin current ten times more efficiently than using pre-interacting spin-waves. Additionally, the findings link the two major research fields in spintronics, namely the spin current and the spin wave interaction.

Dr Kurebayashi added: “I am grateful for the collegial and supportive environment at the Cavendish which makes the flexibility I have been afforded in my postdoc research. This allows me freedom to pursue my interest in spintronics outside of my normal research. I feel that Cambridge is the place where you are able to explore your ideas in an intellectually stimulating atmosphere."

̽��ֱ��research was published on Sunday 03 July in the journal Nature Materials.

Progress in electronics has relied heavily on reducing the size of the transistor to create small, powerful computers. Now spintronics, hailed as the successor to the transistor, looks set to transform the field.

You can find lots of different waves in nature, and one of the fascinating things is that waves often interact with each other. Likewise, there are a number of different interactions in spin waves. Our idea was to use such spin wave interactions for generating efficient spin currents.

Dr Hidekazu Kurebayashi, from the Microelectronics Group at the Cavendish Laboratory

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