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Curated by RSF Research Staff

Ultrafast nanoelectronics with new plasmon transducers

The future of electronic lays with nano-electronic circuits, photons and plasmons. Nano-electronic circuits provide the ability to control charge transport at the nanoscale. Photonic elements allow data processing and transportation speeds with a capacity exceeding 1000 times (> THz) that of electronic components. However, the relatively large wavelength of light requires optical components to be too large to compete in size with modern day nanoelectronics. This problem is solved by using plasmons and integrating them with nano-electronic circuits resulting in a true hybrid of optics and electronics at the nanoscale. The result is a combination of the small dimensions of nanoelectronics with the fast operating speed of optics via plasmonics.

Plasmon physics is intriguing and its understanding proved to be challenging. Their dynamic is highly responsive to a multitude of factors and linked to various quantum effects. Plasmons can be described as a collective excitation of electrons like ripples on the surface of a lake. The electronic fluid acts similarly of water thanks to the Pauli exclusion principle, which tends to keep the electrons out of each other's way.  Usually, plasmons results from the excitation of a light source, and most on-chip plasmon sources rely on the miniaturization of light sources using light-emitting diodes.

The left junction is the plasmon source and the right junction is the plasmon detector. Plasmons propagate via the plasmonic waveguide to the detector and modulate the tunnelling current that flows across the detector.

On-chip detection of plasmons by semiconductors relies on electron–hole pair generation. For practical applications of plasmonics in nanoelectronics, there is a need to generate and read out plasmonic signals by direct electrical means. A research team from Singapore demonstrated this is possible by coupling two metal–insulator–metal tunnel junctions to a single plasmonic waveguide. Doing so, they reported a lower limit of nearly 14% for the effective electron–plasmon coupling efficiency. This high efficiency was obtained because our devices are not limited by low photon outcoupling of on-chip electronic–plasmonic transducer.

In a recent report, the team led by Christian A. Nijhuis showed new progress with electronic–plasmonic transducers based on metal–insulator–metal tunnel junctions. They demonstrated that these junctions can be readily integrated into existing technologies, and they are promising for applications in on-chip integrated plasmonic circuits. These results showed these junctions are very promising for highfrequency optoelectronics. Although, researchers expect a possible to increase the cutoff frequency of the junction to the terahertz range. Considering that they believe that plasmonic–electronic transducers can find applications in many areas of research.

"This innovative transducer can directly convert electrical signals into plasmonic signals, and vice versa, in a single step. By bridging plasmonics and nanoscale electronics, we can potentially make chips run faster and reduce power losses. Our plasmonic-electronic transducer is about 10,000 times smaller than optical elements. We believe it can be readily integrated into existing technologies and can potentially be used in a wide range of applications in the future."

Associate Professor Christian Nijhuis from the Department of Chemistry at the NUS Faculty of Science.

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