All That Matters

A scanning tunnelling microscope image of a single-atom transistor during fabrication. The pink colours represent the areas where a single phosphorus atom (centre) as well as phosphorus source and drain contacts will be placed. The gate contacts that control the transistor action from the side are not visible here. Credit: Martin Fuechsle

When Gordon Moore made his observation in 1965 that the number of transistors integrated on a single silicon chip is doubling roughly every two years, the only logical end point for such a trend would be a transistor made from a single atom. This point has now been reached. Writing in Nature Nanotechnology, Michelle Simmons from the University of New South Wales in Sydney and colleagues report a single-atom transistor, the world’s smallest, on a silicon chip. The transistor is based on current flowing through a single atom of phosphorus embedded in a silicon wafer. […]

Intel's 3D tri-gate transistors have a feature size of only 22 nm. The thin structures are the silicon channels, the thicker ones are the gates and the contacts. Several gates can be used next to each other to enhance the efficiency of the switching. (c) Intel

Finally I am getting around to blog about the latest generation of transistors that Intel presented earlier this months. These transistors reach feature sizes of only 22 nanometres, down from 32 nm. To give you some perspective what this amazingly high integration means: 4,000 of those 22 nm structures fit across the width of a human hair, or similarly, 100 million of these transistors fit on the head of a pin.

Now how did they reduce transistor length scales down by almost a third? Well, even though Intel (and others) is in the business of shrinking transistor for more than 40 years, this time it’s a bit more than a mere scaling exercise. For the first time we have a commercial 3D transistor design on such a scale. In a typical ‘field-effect’ transistor, two electrical contacts are used to run an electric current through a silicon layer. The transistor is switched between an electrically conducting and an insulating state by a gate on top of the silicon. The voltage applied to that gate determines whether current can flow or not. Thereby the gate is able to set the digital ‘1’ and ‘0’ in a transistor.

A problem in shrinking transistors has been the fact that those three electric contacts need a certain minimum space of their own. Furthermore, as the gate has become smaller and smaller, it has been increasingly inefficient to switch the electric current in the silicon layer underneath. For smaller gates the electric fields from the gate just don’t reach that far down into the silicon layer. […]

The past year has been a great year for science with major advances in several areas. Too many exciting results to mention here. Instead, to reflect about the past year I have chosen a representative paper for each month of the year that I hope can serve as an example of the great science going on in a number of research fields. Of course, this is a highly subjective and personal collection, and indeed there might be others worth mentioning. But the aim was also to provide a balanced overview of the year that covers a variety of topics.

Of course, if you have an exciting paper to add, please feel free to use the comments section below to let us know!

Anyway, enough said, here are some of my highlights from the past year:

Simulations of electronic excitations in an iron-based superconductor. Image by Oak Ridge National Laboratory via flickr.

JANUARY – iron-based superconductors

Since they were discovered in 2008, iron-based superconductors, the pnictides, have been one of the hottest topics in condensed matter physics. Part of their appeal stems from the fact that they are based on iron, which is a magnetic element. Normally, magnets and superconductivity exclude each other.

The iron-based compounds have a similar crystal structure as the so-called cuprates, which are the materials with the highest superconducting temperatures known. The mechanism for these high-temperature superconductors is unknown, and studying the iron-based superconductors may also be relevant to the understanding of the cuprates.

This paper published in Science shows for the first time that the electrons in the iron-based superconductors show a periodic arrangement that is different to the periodicity of the atoms in the crystal. Similar observations have been made in the cuprates, and their understanding is considered important to the mechanism of high-temperature superconductivity.

Chuang, T., Allan, M., Lee, J., Xie, Y., Ni, N., Bud’ko, S., Boebinger, G., Canfield, P., & Davis, J. (2010). Nematic Electronic Structure in the “Parent” State of the Iron-Based Superconductor Ca(Fe1-xCox)2As2 Science, 327 (5962), 181-184 DOI: 10.1126/science.1181083

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