This illustration shows two tunnel junctions
coupled together by a plasmonic waveguide in the center. When a voltage is
applied to the source junction, tunneling electrons excite surface plasmons,
which propagate along the plasmonic waveguide and modulate the tunneling
current at the detector junction. Inset: A light emission image of tunnel
junctions, showing plasmons scattering from the end of the plasmonic waveguide.
© 2018
Du Wei, National University of Singapore
Photonic and electronic devices could soon be
successfully integrated thanks to new transducers developed by a team of
Singaporean researchers that can generate, manipulate and read small packets of
energy called surface plasmon polaritons (SPPs).
Photonic devices, which use light rather than electric
charges to carry information, can operate thousands of times faster than
conventional electronics, although they tend to be large and difficult to
integrate with microchips.
The team of researchers led by Hong-Son Chu at the A*STAR Institute of High Performance Computing and Christian Nijhuis at the National University of Singapore believe that SPPs, electromagnetic surface waves that exist at the interface of two materials, could be used to seamlessly link photonic devices and electronics.
“SPPs essentially contain light confined to dimensions
smaller than its wavelength, and they function like photonic elements, carrying
information at high speeds,” says Chu. “However, the SPPs offer the best of
both worlds because they have the operational speed of optical elements as well
as a small size suitable for nano-electronics applications. We have developed
the first on-chip electronic-plasmonic transducers that operate at optical
frequencies, and we achieved an electron-to-SPP conversion efficiency of more
than 10 per cent.”
Most existing plasmonic devices require light sources
such as LEDs to generate SPPs. This indirect method is quite slow. Chu and
co-workers realized it would be much faster to produce SPPs by direct electrical
means, so they designed transducers comprising aluminum and gold electrodes, separated by a two nanometer-thick layer of aluminum oxide that acts as an
insulating ‘quantum tunneling’ barrier. Electrons that make the quantum leap
across this gap will either generate or detect SPPs.
By joining two transducers with a plasmonic waveguide,
so that one acted as a source and another as detector (see image), the
researchers observed about 1 in 7 of the tunneling electrons coupling to a
SPP. Although the reasons for this high tunneling rate are uncertain, Chu and
co-workers suggest that SPPs at the junctions might induce an oscillating
electric field, which changes the effective size of the tunneling gap and
therefore the number of electrons that can cross the gap and interact with SPPs.
“By doing away with the need for light sources and
detectors, devices based on this mechanism would be intrinsically fast,” says
Chu. “Our work has attracted interest from research communities and industries,
with potential applications in three-dimensional integrated circuits and high
bandwidth memory devices. For example, there is a need for small, high-speed
interconnectors to improve processing speeds.”
The
A*STAR-affiliated researchers contributing to this research are from the Institute
of High Performance Computing.
