LAKE WALES Fla.—Everybody already knows that semiconductors are quickly approaching the atomic-level at under 5 nanometers, but most proposed solutions are based on variations-on-a-theme, such as going to a different "semiconductor" like graphene. Why not scrap semiconductors, instead, and use tunneling field effect transistors (TFETs)? The answer is that most materials require cryogenic cooling to make TFETs, according to Professor Yoke Khin Yap at Michigan Tech. Yap, however, has found a room-temperature solution using quantum-dot studded nanotubes.
Professor Yoke Khin Yap at Michigan Tech explains how his transistors switch on and off without semiconductors, as well as there potentially superior performance. (Source: Michigan Tech)
Michigan Tech (Michigan Technological University, Houghton) is not all the way there yet but does have a room-temperature tunneling FET proof-of-concept using iron quantum-dots aligned on boron-nitride nanotubes. Yip claims this solution can not only replace semiconductors but will be flexible enough to create super-small wearable technologies that will perform at levels beyond our wildest imaginations for semiconductors today.
Yap's lab is working toward ultra-small flexible electronics that eliminate semiconductors in favor of the more flexible capabilities of metallic quantum dots and isoelectronic crystals. According to Yap, iron quantum dots (QDs) decorating boron-nitride nanotubes (BNNTs) can use tunneling from quantum-dot to quantum-dot at ultra-low turn-on voltages, to switch the way that transistors do, but using a flexible low-power substrate with absolutely zero leakage current.
Iron quantum dots (yellow, above and grey, below) stud a boron-nitride nanotube, creating transistors without semiconductors by using quantum tunneling between dots when a voltage threshold is exceeded, thus turning-on the transistors without semiconductors. The electron can tunnel between quantum dots in a row, or an find its own path around a nanotube with randomly placed dots.
(Source: Michigan Tech, Sue Hill)
"We already know that the turn-on voltage for a typical QD-BNNT channel can be below 0.1 volts," Yap told EE Times. "But for the current proof of concept work, it is higher at (about 15 volts) due to the long channel length on our STM-TEM [scanning tunneling microscope-tunneling electron microscope] holder."
Using the STM-TEM Yap's team has observed the quantum tunneling in action on bendable nanotubes, which they say will be perfect for flexible wearables. In addition to having zero-leakage when "off," when "on" the channel current encounters zero resistance. Unlike an ordinary transistor channel, the electrons are merely tunneling from quantum dot to quantum dot, making devices based on them ultra-low power since almost no energy is lost as heat when the transistors is on or off.
Using a transmission electron microscope (TEM) the researchers observed quantum tunneling on bendable nanotubes--ac mat >>>Mmaterial could make wearable tech better. Credit: Mi‘‘]
(Source: Michigan Tech)
Yap's team has also observed the same action using gold quantum dots on BNNTs, using the same insulating boron-nitride nanotubes as the flexible tunneling channels. However, the iron quantum dots exert an averaging effect on the tunneling pathways--for randomly studded nanotubes--making their action more consistent and unaffected by bending.
"Iron has a higher melting point than gold and is more convenient to make a uniform distribution of quantum dots on BNNTs by annealing. We still can anneal gold quantum dots for the same purpose, but the current work chose to use iron for better distribution," Yap told us.