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Scientists create precise single-atom transistors

Posted: 23 Feb 2012 ?? ?Print Version ?Bookmark and Share

Keywords:single-atom transistor? quantum computers? silicon chip?

Physicists from the University of New South Wales (UNSW) have developed a working transistor made of a single atom placed precisely in a silicon crystal. The transistor uses as its active component an individual phosphorus atom patterned between atomic-scale electrodes and electrostatic control gates.

According to the scientists involved in the project, this unprecedented atomic accuracy may yield the elementary building block for a future quantum computer with unparalleled computational efficiency.

Before, single-atom transistors were only realized by chance. Researchers had to either search through many devices or tune multiatom devices to isolate one that works.

"This is the first time anyone has shown control of a single atom in a substrate with this level of precise accuracy," said Michelle Simmons, group leader and director of the ARC Center for Quantum Computation and Communication Technology at UNSW.

The microscopic device has tiny visible markers etched onto its surface, making it possible for the researchers to connect metal contacts and apply a voltage, said research fellow and lead author Martin Fuechsle from UNSW.

"Our group has proved that it is really possible to position one phosphorus atom in a silicon environmentexactly as we need itwith near-atomic precision, and at the same time register gates," Fuechsle said.

According to Fuechsle, the device's electronic characteristics exactly match theoretical predictions undertaken with Gerhard Klimeck's group at Purdue University in the U.S. and Hollenberg's group at the University of Melbourne, the joint authors on the paper.

The UNSW team used a scanning tunneling microscope (STM) to see and manipulate atoms at the surface of the crystal inside an ultra-high vacuum chamber. Using a lithographic process, they patterned phosphorus atoms into functional devices on the crystal then covered them with a non-reactive layer of hydrogen.

Single atom transistor

A 3D perspective on an STM image showing a perfectly symmetrical single-atom transistor.

Hydrogen atoms were removed selectively in precisely defined regions with the super-fine metal tip of the STM. A controlled chemical reaction then incorporated phosphorus atoms into the silicon surface.

Finally, the structure was encapsulated with a silicon layer and the device contacted electrically using an intricate system of alignment markers on the silicon chip to align metallic connects. The electronic properties of the device were in excellent agreement with theoretical predictions for a single phosphorus atom transistor.

Keeping pace with Moore's Law, it was predicted that transistor will reach the single-atom level by 2020, describing the on-going trend in computer hardware that sees the number of chip components double every 18 months.

This new development in the technology, made well ahead of schedule, may provide valuable insights to manufacturers into how devices will behave once they reach the atomic unit, Simmons concluded.





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