Engineers at the University of Cambridge have developed an ultralow power transistor that could function for months or even years without a battery. The transistors scavenge energy from their environment, thereby drastically reducing the amount of power used. A range of new electronic applications including implantable or wearable devices could benefit from this new development.

The new transistor uses a near off state current for its operations. This is a small ‘leakage’ of electrical current, which is more commonly used by computers in sleep mode. This is the first time that this leak has been effectively captured and used functionally, although it is a characteristic of all transistors. In an article in the journal Science, the research team explain that this opens up new avenues for system design for the Internet of Things. The Internet of Things is a concept in which most of the things we interact with daily are connected to the Internet.

The transistors can be printed on almost any material from paper and polyester to plastic and glass, and are produced at low temperatures. Based on a unique geometry, they use a non-desirable characteristic – the so-called Schottky barrier – that is formed by the point of contact between the semiconducting and metal components of a transistor.

Professor Arokia Nathan of Cambridge’s Department of Engineering, the paper’s co-author, notes that the study challenges conventional perception of how a transistor should behave as most engineers try to avoid the Schottky barriers. The team found that these Schottky barriers actually have the perfect characteristics for the type of ultralow power applications they’re looking at, such as electronics that can be worn or implanted for health monitoring.

The new design solves one of the key issues preventing the development of ultralow power transistors, namely the capability to manufacture them at very small sizes. A transistor’s two electrodes start to influence the behavior of one another as they become smaller. As the voltages spread, transistors fail to function as wanted below a certain size. The Cambridge team were able to use the Schottky barriers to keep the electrodes autonomous from one another by changing the design of the transistors. This allowed them to scale down the transistors to very small geometries.

A very high level of signal amplification or gain is achieved by the design. The transistors’ power consumption is less than a billionth of a watt and they have an operating voltage of less than one volt. This extremely low power consumption makes them suitable for applications where speed is less important than function, which is the essence required by the Internet of Things.

Dr Sungsik Lee from the Department of Engineering and the paper’s first author notes that drawing energy from a typical AA battery based on this design, it would last for a billion years. He adds that the use of the Schottky barrier allows them to keep the electrodes from interfering with each other. This amplifies the amplitude of the signal even at the state where the transistor is nearly switched off.

Nathan believes that this will bring about a new design model for ultralow power analogue signal processing and sensor interfaces in implantable and wearable devices. All of these are critical for the Internet of Things.

Professor Gehan Amaratunga, Head of the Electronics, Power and Energy Conversion Group at Cambridge’s Engineering Department describes the device as an ingenious transistor concept. This type of ultra-low power operation is a requirement for many of the new universal electronics applications, where function, rather than the demand for speed, matters. The possibility of having autonomous electronics now becomes a possibility in such applications. The system harvesting background energy from the environment for long-term operations is similar to the functioning of organisms, such as bacteria, in biology.

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