The Single-Atom Transistor
The single-atom transistor was fabricated by placing an atom of phosphorus (P) on the surface of a silicon (Si) sample. Researchers accomplished this by using using phosphine (PH3) as the source of phosphorus. The phosphine molecule was adsorbed (the process by which a dissolved solid substance sticks to a surface) onto the surface of the silicon sample. Researchers heated the system at 350oC, which caused the phosphine to dissociate, or break up. One of the single resulting atoms of phosphorus was then incorporated into the silicon sample, by substituting and ejecting an atom of silicon.
For this system to work as a transistor, however, the positioning of the phosphorus into the silicon structure had to be accomplished with the maximum accuracy. Researchers used an advanced microscopic technique called Scanning Tunnelling Microscopy (STM), in lithography mode. This method allowed them to place the phosphorus atom between 5 silicon atoms, with an atomic precision, corresponding to ± 3.8×10-10 m (3.8 Å).
Dr. Martin Fuechsle, leading author of this research, explained the importance of this point:
“To be able to use this system, we should be able to control exactly the position where the phosphorus atom is. In the past, other single atom transistors were made, but the uncertainty in the atom positions was too big, about 10 nm (10-9 m). In our work, we can control the position at atomic level; phosphorus replaces exactly a silicon atom in the lattice.”
When the scientists performed tests on transistors fabricated by this method, the tests showed that the system works properly but, at present, only at very low temperatures (just above -273oC, the absolute zero temperature).
Nanotechnology and Electronics: A Technological Breakthrough
Commenting on the importance of these results, Dr. Fuechsle said:
“The device is not ready yet for practical and commercial applications; many parameters have to be improved and optimized.
What we achieved, however, is very important. It is the first time that a functional electronic element was created with a single atom exactly positioned in a silicon crystal; this really is a technological breakthrough.
Furthermore, these findings are also important from a scientific point of view: in fact, they allow us to study how the electronic components behave when they get smaller and smaller. This could lead us to more interesting discoveries.”
This video details the findings of Dr. Fuechsle and his coworkers.
M. Fuechsle et al. A single-atom transistor. (2012). Nature Nanotechnology. doi:10.1038/nnano.2012.21. Accessed February 22, 2012.
G.E. Moore. Cramming more components into integrated circuits. (1965). Electronics. Accessed February 22, 2012.
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