Researchers Create Working Single-Atom Transistor

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A team of Australian and American researchers announced on Sunday that they had created a working transistor from a single phosphorus atom embedded precisely in a silicon crystal.
The transistor was completed by physicists at the University of New South Wales (UNSW), the University of Melbourne, and Purdue University, and according to a UNSW press release, this “remarkable feat of micro-engineering“¦ uses as its active component an individual phosphorus atom patterned between atomic-scale electrodes and electrostatic control gates.”
John Markoff of the New York Times reported in a February 19 article that the team believes they have laid the groundwork for what Markoff describes as a “futuristic quantum computer that might one day function in a nanoscale world and would be orders of magnitude smaller and quicker than today´s silicon-based machines.”
The reason, according to the Times reporter, is that traditional computers need to use transistors that have just two states, such as “on” and “off” or “0” and “1”. Quantum computers, on the other hand, are built from devices known as qubits that can represent more than one value at the same time, making it possible for large calculations to be completed more quickly.
That additional speed “might make it possible to factor large numbers more quickly than with conventional machines — thereby undermining modern data-scrambling systems that are the basis of electronic commerce and data privacy,” Markoff said. “Quantum computers might also make it possible to simulate molecular structures with great speed, an advance that holds promise for designing new drugs and other kinds of materials.”
According to the researchers, before now single-atom transistors had only been discovered by accident, but Michelle Simmons, Director of the UNSW’s ARC Centre for Quantum Computation and Communication and leader of the team, called the device “perfect” and said that this discovery marked “the first time anyone has shown control of a single atom in a substrate with this level of precise accuracy.”
The UNSW press release says that the tiny electrical device even has visible markers on its surface so that the physicists can connect metal contacts to it and apply a charge to it. Furthermore, Dr. Martin Fuechsel, lead author of a paper describing the device that has been published in the journal Nature Nanotechnology, said that the device is an exact match to predictions made by experts at Purdue University and the University of Melbourne.
“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,” the university’s press release said. “Using a lithographic process, they patterned phosphorus atoms into functional devices on the crystal then covered them with a non-reactive layer of hydrogen.”
“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,” it added. “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.”
CNET’s Martin LaMonica says that their findings prove that it could potentially be possible for experts to automate the process and manufacture these single-atom transistors. He adds that the work is one of a series of experiments to be conducted recently in order to fulfill what is known as Moore’s Law — a prediction which states that the number of transistors on a semiconductor doubles every year-and-a-half.
Purdue Electrical and Computer Engineering Professor Gerhard Klimeck told Markoff that the new study “shows that Moore´s Law can be scaled toward atomic scales in silicon,” while IBM physicist Andreas Heinrich told him that the research was, in Markoff’s words, “a significant step toward making a functioning quantum computing system.”
According to UNSW, “It is predicted that transistors will reach the single-atom level by about 2020 to keep pace with Moore’s Law,” while in a Purdue University press release, Klimeck called this discovery “the physical limit of Moore’s Law“¦ We can’t make it smaller than this.”

Image 2: This 3D perspective of an STM image shows a perfectly symmetrical single-atom transistor.

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