According to Moore’s Law, the number of transistors on a integrated circuit doubles approximately every 2 years (18 months). Gordon E. Moore described his law in the 1965 paper ‘Cramming more components onto integrated circuits’ that was published in Electronics Magazine. Because of exponential growth over the last 48 years, this law has led to 24 doublings of the original number of transistors that could be placed on a circuit board. Moore’s law is now starting to buckle, because transistors based on semiconductors can only get so small.
“At the rate the current technology is progressing, in 10 or 20 years, they won’t be able to get any smaller,” said physicist Yoke Khin Yap of Michigan Technological University. Not only is the current technology starting to reach the mature phase of its growth (top of the S curve), but semiconductors also have another disadvantage: they waste an exorbitant amount of energy in the form of heat.
Over the last few decades, scientists have experimented with different materials, molecule designs, and semiconductor similar silicon. They have continued on Moore’s Law successfully, but Dr. Yap wanted to try something novel, something that might open the floodgates for a new age of electronics. ”The idea was to make a transistor using a nanoscale insulator with nanoscale metals on top,” he said. “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.”
Yap’s research team had figured out how to make a ‘virtual carpet’ of BNNTS, which happen to be insulators (that are highly resistant to electrical charge). By using a laser, the team placed quantum dots (QDs) of gold as small as three nanometers across on top of the BNNTs, forming QB-BNNTs.
When Yap and Oak Ridge National Laboratory (ORNL, an organization that Yap’s team collaborated with) fired electrons through both ends of the QB-BNNTs at room temperature, the electrons jumped with precision from gold dot to gold dot, by 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.”
Yap’s team had made a transistor without using a semiconductor. When sufficient voltage was applied, it switched to a conducting state, and when the voltage was low or turned off, it reverted to its natural state as an insulator. During this process there was no leakage. Meaning, no electrons from the gold dots escaped into the insulating BNNTs, allowing the tunneling channel to remain at a cool temperature, while silicon is subject to leakage, that waste energy and generates a lot of excess heat.
The method that separates Yap’s success to others who have tried to exploit quantum tunneling is that Yaps gold-and-nanotube device is submicroscopic size: one micron long and about 20 nanometers wide. Michigan Tech physicist John Jaszczak comments: “The gold islands have to be on the order of nanometers across to control the electrons at room temperature. If they are too big, too many electrons can flow.” In this case, smaller is truly better: “Working with nanotubes and quantum dots gets you to the scale you want for electronic devices.”
The channels can theoretically be miniaturized into virtually zero dimension when the distance between electrodes is reduced to a small fraction of a micron.
With Moore’s Law is coming to an end in the next 10 to 20 years, a new technology must raise to take its place to continue the technological development that has been seen in the last 50 years. In the future, we are going to see more scientists using quantum phenomena to overcome the traditional physical barriers that are starting to loom and threaten technological development. Yap’s method could continue Moore’s law along with creating more power-efficient devices that could go days without being charged.
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