Transistors – A Growing Problem
Transistors are arguably THE most important invention of the 20th century. Transistors replaced valves in electronics, allowing these devices to be made smaller, portable, and more energy efficient. They have also led to the invention of the integrated circuit, which has made modern life what it is today. Without transistors, we wouldn't have computing, the internet, or modern research techniques.
The transistor is arguably the most important invention of the 20th century
For devices to become more powerful, engineers have to squeeze as many transistors as possible onto integrated circuits. This usually results in attempts to shrink the size of transistors so that more can fit per unit area.
However, as a transistor's features are shrunk, effects that otherwise would be irrelevant become a problem. For example, the gate of a MOSFET needs to be electrically insulated from the source and drain regions for the device to function properly. If the gate is made too thin, then quantum tunneling can kick in, which results in a current flow between the gate and source/drain regions (which is very undesirable).
Another example would be the leakage current of transistors which, albeit small for individual transistors, can cause massive problems when a circuit contains one billion devices. This accumulated leakage current results in temperature rise, loss of efficiency, and energy loss which is problematic in a world where devices are becoming more portable.
Silicon is the black oil of technology. Image courtesy of Jack Spades [CC BY 2.0]
Efficiency, Portability, and Printable Electronics
A team of researchers from the University of Cambridge have created a special ultra-low power transistor that actually uses the undesirable effects of transistors to its advantage.
Firstly, the transistor operates in the leakage current region (near the cut-off region), which helps to reduce current draw.
Secondly, the Cambridge team changed the design of the transistor to take advantage of Schottky barriers between the electrodes. As the distance between transistor electrodes reduces, the leakage current and electrical noise increase, which effectively reduces the gain. The Schottky barrier helps to isolate the electrodes, increasing the gain of the transistor.
The research was published by two members of the Electrical Engineering department: Dr. Sungsik Lee and Dr. Arokia Nathan. Lee is a research associate and Nathan is a professor specializing in photonic systems and displays.
“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.” —Professor Arokia Nathan, University of Cambridge
The transistor, itself, operates on less than one volt while consuming less than a billionth of a watt. If scaled up on an integrated circuit, this could result in extremely efficient portable devices with longer battery life. Lee has been quoted as claiming that this design could allow an AA battery to supply power for a billion years.
On top of all of these advantages, the newly developed transistor has one extra property that could revolutionize how technology is integrated into modern life: It can be printed onto nearly all materials including polyester, glass, and paper.
Printed electronics is a growing industry with examples including the Optomecs Aerosol system and Pulse Electronics' 3D conductive printing. Indium-Gallium-Zinc oxide transistors could allow for implantation of electronics into environments such as flexible displays, clothing, and even inside living tissue.
Cross section of the Indium-Gallium-Zinc Oxide transistor. Image credit Sungsik Lee and Arokia Nathan / Science
With the continual rise in power demand from modern devices, it won't be long before Moore's law begins to break down. It is developments like the low-power transistor that will help to shape the future of semiconductors and provide hardware that can meet the technological requirements that are yet to come.
Read more about the research in Science.