The world might still be 20 years from the end of Moore's Law, but the hunt for technologies to replace semiconductors is going on right now. A group from Michigan Technological University is offering one such alternative: a quantum tunnelling transistor that operates at room temperature.
The culmination of work begun in 2007, their demonstration has been published in Advanced Materials, here (abstract).
Moore's famous observation (the number of transistors on an IC doubles roughly every two years) is one day going to run into two physical constraints: the feature size of the transistor, and its ability to dissipate heat.
Quantum properties are seen as a promising replacement for semiconductors on both scores: transistors can be built at the single-atom scale, and they don't have the same heat dissipation issues. However, most quantum effect transistors need to function at cryogenic temperatures.
That makes room temperature operation an important goal for development – and that's what the MTU group, led by MTU physicist Yoke Khin Yap, is claiming.
Their quantum transistor is fabricating by placing gold quantum dots on boron nitride nanotubes. The three-nanometre gold dots were placed using lasers, while the nanotubes both provide insulation between the dots, and confine the dots.
Working with Oak Ridge National Laboratory, the MTU group then applied a voltage electrodes at both ends at room temperature, and observed electrons tunnelling from dot-to-dot.
However, that tunnelling only happened with enough voltage: below the critical voltage, electrons don't get enough energy to make the jump between dots – making the device a quantum transistor that doesn't need semiconducting material.
As fellow physicist John Jaszczak, who developed the theoretical framework for Yap's work, explains in the university's announcement, the device has to be about one micron long and 20 nanometres wide to operate.
“The gold islands have to be on the order of nanometers across to control the electrons at room temperature,” Jaszczak said. “If they are too big, too many electrons can flow. Working with nanotubes and quantum dots gets you to the scale you want for electronic devices.” ®