According to Moore’s law, which states that the number of transistors that can be placed on an integrated circuit doubles every two years, the size of our transistors will need to have shrunk to a single atom by 2020. In a massive leap into the future, researchers at the University of New South Wales, Purdue University and the University of Melbourne have created a controllable transistor engineered from a single phosphorus atom. This is not only important for the future of traditional computing, but also provides a scalable foundation to explore the possibilities of quantum computing.
The transistor, which is made from a single phosphorous-31 isotope placed on a base of silicon crystal and is under one nanometer across, represents the physical limit of Moore’s law. It just isn’t possible to make a transistor smaller than this, but with Intel’s current manufacturing process managing to place 2.3-billion transistors 32 nanometers apart this represents an order of magnitude much smaller than anything we are creating commercially today.
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Actually, this transistor is not really the first one-atom transistor ever to be created. Ten years ago, Cornell University demonstrated a working single-atom transistor made from a cobalt atom. The problem with single-atom transistors has been that up until now we haven’t had the precision required to be able to place a single atom within a silicon case so that the devices can be manufactured reliably. In fact, the margin of error for placing the atom in the correct place has been about 10 nanometers, which is pretty big when dealing with atoms that are about 0.1 nanometers in size. This latest research provides a reliable way to actually position the atom with exact precision so that we can easily scale up the number of transistors in the circuit to create functional processors.
Critically, the researchers were able to confirm that electrodes within the silicon actually made contact with the transistor and that they were able to successfully change the quantum states of the atom, providing the foundation for a transistor which needs to be able to switch between two different states in order to function. While that’s great news for the future of conventional computing, there are a few drawbacks. The first is that the technique used to manufacture the transistor made use of Scanning Tunneling Microscopy within an ultra-high vacuum chamber, an expensive process that is not likely to make its way into the fabs in a hurry. There’s also the problem of temperature. In order to work, a single-atom transistor has to be kept very cold, at least as cold as liquid nitrogen, or -196 Celsius.
Gerhard Klimeck, who directed the Purdue group that ran the simulations, says “The atom sits in a well or channel, and for it to operate as a transistor the electrons must stay in that channel. At higher temperatures, the electrons move more and go outside of the channel. For this atom to act like a metal you have to contain the electrons within the channel. If someone develops a technique to contain the electrons, this technique could be used to build a computer that would work at room temperature. But this is a fundamental question for this technology.”
So, maybe atomic sized transistors are still realistically around 20 years away when it comes to any form of commercial viability. Nonetheless, the development is genuinely exciting and if we’re willing to put conventional computing on one side, the idea that we may finally have the potential to build a computer that can ultimately control electrons and thereby quantum information, or qubits, means that we are one step closer to realizing quantum computing. Certainly, this is the view held by Michelle Simmons, group leader and director of the ARC Centre for Quantum Computation and Communication at the University of New South Wales.
“This is a beautiful demonstration of controlling matter at the atomic scale to make a real device,” Simmons says. “Fifty years ago when the first transistor was developed, no one could have predicted the role that computers would play in our society today. As we transition to atomic-scale devices, we are now entering a new paradigm where quantum mechanics promises a similar technological disruption. It is the promise of this future technology that makes this present development so exciting.”
