Imec has fabricated electrical sources of
surface plasmons, based on integrating light emitting diodes with metal-insulator-metal
(MIM) waveguides. These sources, together with earlier work demonstrating plasmon
detectors, are a prerequisite for making an interface between electronics and
plasmonic circuits. This will lead the way to fully integrated plasmonic biosensing.
Simulated (left) and experimental (right) coupling of the light emitted by a light-emitting diode (LED) into a MIM waveguide. The left figure shows the electric field profile that results of the coupling of a dipole emitter placed near a subwavelength slit in the bottom layer of the MIM waveguide. The emitted light couples efficiently to the plasmon waveguide mode and results in a standing wave pattern between two slits in the waveguide. This is also measured experimentally, as shown in the spectrally resolved output in the right figure for different lengths between the slits.
Metal-based nanophotonics (plasmonics) is a field concerned with manipulating
and focusing light on nanoscale structures that are much smaller than conventional
optic components. Plasmonic technology, today still in an experimental stage,
has the potential to be used in future applications such as nanoscale optical
interconnects for high performance computer chips, highly efficient thin-film
solar cells, and extremely sensitive (bio)molecular sensors.
On the nanoscale, incoming light results in surface plasmon polaritons (SPPs),
charge density oscillations at metal-dielectric interfaces. These have proven
to be excellent markers for biochemical events, because they strongly enhance
the local field near metal surfaces or nanostructures, and thus also the specific
change induced by the presence of even ultrasmall quantities of biomolecules.
Such a detection technique based on surface plasmon resonance (SPR) on thin
gold films has already been successfully commercialized. But this technique
still uses large external light sources and detectors.
The state of the art in plasmonic waveguides has already been pushed forward
substantially during the past years, demonstrating both plasmon propagation
in low-loss long-range plasmon waveguides and highly confined plasmon propagation
in e.g. metal-dielectric-metal waveguides. However, in order to incorporate
such waveguides in realistic integrated circuits, they need to interface with
fast and efficient electronics. But to do so, we’d need integrated electrical
SPP sources and SPP detectors.
In recent publications in Nano Letters (De Vlaminck, Van Dorpe et al, 2007)
and Nature Photonics (Neutens, Van Dorpe et al, 2009), imec has demonstrated
the feasibility of efficient integrated detectors of surface plasmons. We have
now extended this to integrated electrical sources of surface plasmons based
on integrating light emitting diodes with metal-insulator-metal (MIM) waveguides.
The strong measured polarization dependence, the experimentally obtained influence
of the waveguide length, the measured spectral response are all in line with
theoretical expectations. Also surface plasmon polariton interference inside
the waveguide is experimentally observed, which allowed us to reliably extract
information about the wavelength and confinement of the propagating plasmons
(illustrated in the figure). The realization of this building block completes
the toolset that is needed to construct truly integrated electrically driven
plasmonic circuits and hence paves the way for the integration of nanoscale
plasmonic circuitry and integrated plasmonic biosensing.
This work has been published in the highly ranked journal Nano Letters: Neutens
et al, Nano Lett. 2010, 10, 1429–1432.