New transistor design could run for years without batteries

Printable on any fabric at low temperature and requiring less than one nanowatt of power

The University of Cambridge claims to have developed a new ultra-low power transistor design that could run for months or even years at a time on what it calls "scavenged energy". The design is being touted for use in wearable devices 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," claimed Dr Sungsik Lee, one of the authors of the research paper revealing the development and a member of the University of Cambridge's Department of Engineering.

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. The transistors can be produced at low temperatures and can be printed on almost any material, from glass and plastic to polyester and paper," claims the university.

It continues: "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'."

The indium-gallium-zinc-oxide thin-film transistors can operate with less than one nanowatt of power and at switching voltages of less than one volt, according to Science magazine, which adds that the "devices work by changing the height of the so-called ‘Schottky barrier' formed between the semiconductor gate material and the metal drain contact".

"We're challenging conventional perception of how a transistor should be," said Professor Arokia Nathan of Cambridge's Department of Engineering, co-author of the research paper published in Science.

"We've 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 also gets around the challenge of building ultra-low power transistors small enough as well.

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 properly. Using the Schottky barrier helps keep the electrodes apart, so that the transistors can be scaled down.