With an intense history that comprises more than a half-century of research, a Nobel Prize, and multiple attempts at practical applications, the story of negative differential resistance – or NDR – reads like a scientific mystery, a story that University of Alberta physicists have at last succeeded in unraveling.
This implies an opportunity to link the knowledge with current technology to generate cheaper, faster, and smaller electrical devices, a boon to the continued boom of the digital era.
NDR is a unique effect. We can think it by considering water being pushed through a hose. More pressure means a faster flow of water. Electrons in a wire act similarly, except voltage, is applied instead of pressure to augment flow. With water, increased pressure equals enhanced flow, but in special circumstances with electricity, there is sometimes a backward and counter-intuitive effect where flow reduced.
The foremost attempt at a practical application for NDR, the Esaki Diode named for invertor Japanese researcher Leo Esaki, was received in the 1950s with amazing excitement, some even proclaiming it to be more vital than the transistor. The work was awarded a Nobel award. Soon after it became clear that the mass production was too difficult, the once-heralded device was relegated to niche applications.
Substituting the NDR effect in a way that could be extensively deployed remained an enticing aim. Alternatives to the Esaki Diode were found, but those resisted bulk production. The advent of scanning tunneling microscopes in the 80s and the access they offer to nano-scale substance properties resulted in tantalizing NDR signatures from atom-scale structural irregularities in silicon. The excitement was re-kindled but proper comprehension and manufacturability remained elusive.
Fast forward to the present and a group of researchers led by Robert Wolkwow from the University of Alberta have now identified the precise atomic structure that results in NDR. Moreover, by estimating for the specific rules quantum mechanics enforces electron through a singular atom. Group members of Wolkwo, theoretical physicist Joseph Maciejko, have succeeded in estimating for the primary perplexing reduction in the present with increasing voltage. Such results direct towards the lucrative and practical applications in everyday electronics like computers and phones.
“It seems that if you can conveniently witness how to cheaply and neatly incorporate such NDR effect into on-going electronic transistors, you can prepare faster, smaller, and cheaper devices,” says Wolkwow. “The overall value of a hybrid transistor or NDR circuit has been identified for decades, but no one is aware of doing it cheaply or effectively enough to make it worthwhile.
“Over the years, individuals have introduced variants of the same atomic-scale effect. But, now one has able to solve the puzzle of the structure and its properties were never identified. But we now know exactly why all this occurs. We know exactly what constituents are required there for it to be regulated. We have defined the precise volume structure that gives rise to NDR, and luckily it is convenient to make,” concludes Wolkwow