Single-atom transistor: small, smaller, as small as it gets

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In many areas of our lives these days, bigger is always seen as better. However, this isn’t the case when it comes to electronics. Here, what would normally be classed as tiny is seen as gargantuan.

For years now, engineers at the University of Michigan and IBM have been battling it out to see who can build the world’s smallest computer. It seems that last month, Michigan pulled slightly ahead of IBM. The edge length of its fully functional computer is a mere 0.3 millimeters. Only in February of this year, IBM had a slight lead, having produced a device the size of a grain of salt.

Scientists from the Karlsruhe Institute of Technology (KIT), on the other hand, have already reached the lowest limit of miniaturization. Their single-atom transistor can switch an electrical current by means of the controlled repositioning of one single atom. As such, it could make a sizable contribution to improving the energy efficiency of information technology in the future because the quantum electronic element enables switching energies smaller than those of conventional silicon technology by a factor of 10,000. When you consider that USB sticks costing only a few euros already contain several billion transistors, the potential becomes very clear.

Single-atom transistor at room temperature

Professor Dr. Thomas Schimmel from KIT has been working on atomic-scale transistors for just under 15 years. This shows just how drawn out research projects in these scale ranges can be. The basic design has not changed though: two tiny metal contacts leave a gap the width of a metal atom. By means of an electrical control pulse, a single silver atom is placed into the gap and hence closes the electrical circuit. Reversing the process opens the electric circuit again.

The world’s smallest transistor can therefore switch an electrical current by means of the controlled and reversible relocation of one single atom. Unlike conventional quantum electronic components, it doesn’t require extremely low temperatures near absolute zero (zero Kelvin) of minus 273 degrees Celsius in order to do this. It can actually function at room temperature, which will be hugely beneficial in terms of future applications.

The researchers at KIT came up with an entirely new technical approach for the single-atom transistor whereby the transistor is made entirely of metal and has no semiconductors. This means extremely low electrical voltages and hence extremely low energy consumption.

Until now, the single-atom transistor depended on a liquid electrolyte. It now also works for the first time ever in a quasi-solid electrolyte. The gel electrolyte created as a result of the gelation of an aqueous silver electrolyte with pyrogenic silica combines the advantages of a solid with the electrochemical properties of a liquid and hence improves both safety and the handling of the single-atom transistor.

Original publication:
Fangqing Xie, Andreas Peukert, Thorsten Bender, Christian Obermair, Florian Wertz, Philipp Schmieder, and Thomas Schimmel: Quasi-Solid-State Single-Atom Transistors. Advanced Materials. Adv. Mater. 2018, 30, 1801225. DOI: 10.1002/adma.201801225
The scientists present the transistor in the journal Advanced Materials (DOI: 10.1002/adma.201801225).


Discover more about Transistors in Halls A4/B4–5/C3–6.


Single-atom transistor (Image: Group of Professor Thomas Schimmel/KIT)

The single-atom transistor that works in a gel electrolyte reaches the limit of miniaturization. (Image: Group of Professor Thomas Schimmel/KIT).