1/2013

Electronics without current: the future of nanoelectronics

Tapio Niemi, Donlad Lupo and Mircea Guina

Professors Tapio Niemi (left), Donald Lupo and Mircea Guina and their research groups
are exploring paths toward a completely new way of designing smaller, faster and more
energy-efficient logic circuits. The group headed by Professors Nikolai Tkachenko
and Helge Lemmetyinen is also involved.

The power consumption of and waste heat produced by integrated circuits are problems that face both laptop users and high-performance data centres. If researchers at TUT succeed in their quest to develop a circuit that consumes no current, the need for energy-intensive cooling systems will be drastically reduced.

Researchers at Tampere University of Technology have launched a cross-disciplinary project entitled "PhotonicQCA" that combines expertise in organic chemistry, semiconductor growth and nanofabrication. They are exploring paths towards a completely new way of designing logic circuits that consume no current and can be written and read with light.

The researchers are exploring a radically new approach for designing and making logic circuits by integrating photosensitive organic molecules into tiny particles of semiconductor material called quantum dots. This visionary technology will hopefully enable the development of circuits that are smaller, faster and more energy-efficient than any other circuit that is currently available or even on the horizon.

"As far as we can tell, no one has ever tried anything like this before. It'll be a huge breakthrough if we succeed," says project coordinator, Professor Donald Lupo from the Department of Electronics at Tampere University of Technology.

Diverse expertise required

Researchers at the Optoelectronics Research Centre (ORC) of TUT are developing a technology platform for the logic circuit made up of quantum dots.

Researchers at the Department of Chemistry and Bioengineering are looking into ways of bridging the gap between nanoscale and macroscale, i.e. how data is written and read, by using organic molecules that serve as go-betweens. Researchers at the Department of Electronics bring their expertise in novel architectures to the project.

"The circuit we're developing will be made up of cells that each contain four quantum dots and are arranged in a series like dominos. The result will be a circuit that is capable of performing the same logical operations as a conventional circuit," says Professor Tapio Niemi from ORC.

When light of the right wavelength shines on a photosensitive molecule attached to a quantum dot, the molecule absorbs a photon and injects a charge into the dot. Due to repulsive electric force and the quantum mechanical tunnelling, the injected electron causes an electron already present in another dot within the cell to move to the opposite corner of the cell. Likewise, the position of the charges in one cell affects the position of the charges in the next cell.

Current is simply the flow of electrons in a particular direction. This new type of logic circuit consumes no current, because the only movement occurs when a single electron travels from one quantum dot to another. When no charge flows from one cell to the next, no net current exists.

Quantum dots

The photo depicts two quantum dots grown on nanoimprint lithography
patterned wafers. The distance between the dots is 300 nanometres.

Challenges ahead

Several challenges must be overcome before the theoretical understanding of this complex and sensitive phenomenon can be put into practice.

According to Tapio Niemi, the basic components of the logic circuit already exist and researchers are able to control and measure the properties of individual quantum dots, provided that they are sufficiently spaced apart.

"We know how to grow quantum dots on a substrate, but the difficult part is placing them close to each other and at precise locations on the surface. We're looking to solve this problem by using different nanopatterning methods," says Niemi.

"One of the key objectives of the project is the development of hybrid structures that combine semiconductors and organic materials," says Professor Helge Lemmetyinen.

"The Photochemistry Research Group has extensive experience of conducting research on photoactive molecules. We've applied this expertise to develop solar cells and know the principles governing the assembly of photoactive molecules inside out. Hybrid structures will open up whole new avenues for exploring and discovering nanophotonic phenomena."

 

Ground-breaking research idea

  • With a total budget of two million euros, PhotonicsQCA is TUT's largest nanophotonics project to date.
  • The Academy of Finland has granted the project 1.6 million euros under the "Programmable Materials" funding scheme.
  • The four-year project is coordinated by Professor Donald Lupo from the Department of Electronics. The research groups headed by Professors Mircea Guina and Tapio Niemi at the Optoelectronics Research Centre and Professors Helge Lemmetyinen and Professor Nikolai Tkachenko at the Department of Chemistry and Bioengineering are also involved.

 

Text: Martti Tammisto
Photo: Petri Laitinen


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