The pursuit of smaller and smaller transistors is about to hit a major roadblock. Soon, they will reach their minimal operational size, but physicist Yoke Khin Yap may have stumbled upon a solution.
Transistors are like electronic switches: two conductors are separated by a gap, over which a semi-conductor is drawn. When in the “off” state, the semi-conductor acts as an insulator and no current passes through, but when in the “on” state, a voltage is applied to the semi-conductor, turning it into a conductor which allows the current to flow. Since it’s invention, the transistor has been getting smaller and smaller by minimizing the gap between the two conductors. This allows for more transistors on a chip, more data operations per chip, and ultimately more computing power for the computer it’s used in. A consumer level CPU today has around two billion transistors. Moore’s law states that the number of transistors on a chip will double every 18 months, or to say it in a different way; the size (gap) of a transistor shrinks by half every 18 months.
“At the rate the current technology is progressing, in 10 or 20 years, they won’t be able to get any smaller,” says physicist Yoke Khin Yap of Michigan Technological University. At that point, the gap in the transistors will be so small that quantum physical effects will allow the current to jump through the insulating gap between the two conductors. To solve the problem, more and more scientists have been looking into various materials which may optimize the gap, but all of them have involved semi-conductors like silicon. Prof. Yap has a different idea altogether.
Yoke Khin Yap
“The idea was to make a transistor using a nanoscale insulator with nanoscale metals on top,” he explains. “In principle, you could get a piece of plastic and spread a handful of metal powders on top to make the devices, if you do it right. But we were trying to create it in nanoscale, so we chose a nanoscale insulator, boron nitride nanotubes, or BNNTs for the substrate.” His plan is to make carpets of BNNTs, which are electrically resistant insulators, and use lasers to graft 3nm dots of gold to their surface. The BNNT material is perfect for this job because of their controllable and very uniform shape. When Yap and his team, in collaboration with Oak Ridge National Laboratory, applied electrodes to both ends of the BNNT, they observed that the electrons jumped from gold dot to gold dot, a phenomenon known as quantum tunneling. “Imagine that the nanotubes are a river, with an electrode on each bank. Now imagine some very tiny stepping stones across the river,” said Yap. “The electrons hopped between the gold stepping stones. The stones are so small, you can only get one electron on the stone at a time. Every electron is passing the same way, so the device is always stable.”
Artist’s depiction of the gold-hopping electrons
In other words, Yap had created a replacement for the traditional semi-conductor. When a sufficiently high voltage is applied, the electrons move from one end to the other, but when the voltage is low, or off, the material becomes an insulator. Unlike traditional transistors, the BNNT material also wastes less electricity, making them more efficient and cooler. “Theoretically, these tunneling channels can be miniaturized into virtually zero dimension when the distance between electrodes is reduced to a small fraction of a micron,” said Yap, who has filed for an international patent on the technology.