Are MIM WG-based plasmonic sensors practically realizable?
Semiconductors are significantly easier to microfabricate than metals
especially noble metals. With the use of sputtering or evaporation
methods, plasmonic metals may be deposited in vacuum environments.
Deposition rates are generally restricted to less than 1 nm/s to achieve
sufficient uniformity and quality. Due to the often-low necessary
plasmonics structure height, the modest deposition rate is not a major
issue. The electroplating process can produce faster growth rates, but
the surface quality may degrade, making it unsuitable for plasmon waves.
As there are few efficient ways to etch Cu, Ag, or Au, the pattern
transmission from the photoresist to metals is difficult for noble
metals. However, in Cl2-based settings, Al may be plasma
etched.
Plasmonic WGs are exceptionally lossy since they include metal, in
contrast to dielectric WGs where the propagation loss might be
negligible. Major ohmic losses that set a maximum propagation length
restriction on directed SP propagation. Various geometries have been
created employing arrays of nanosize dimension characteristics to
compensate for these losses. As plasmonic WGs, thin metal films with a
finite width embedded in a dielectric can be employed. Given that the
observed propagation length for operating with light with a wavelength
of 1550 nm is stated to be as long as 13.6 mm, this shape provides the
best propagation results for a surface plasmon-based WG. However, in
this plasmonic WG shape, the localization for both directions is on the
order of a few micrometers. One can narrow the wire’s width to achieve
subwavelength localization and then utilize SPs to direct light beneath
the nanowire.
In general, propagation loss and mode confinement reflect a trade-off in
any plasmonic WG. The propagation loss increases with decreasing mode
size. The modes carried by plasmonic WGs often have more complicated
geometries. Therefore, assessing the mode confinement of plasmonic WGs
is a difficult process. The definition of the mode region should rely on
the specific application, it has been considered and agreed upon. Energy
dissipation affects both plasmonic and electronic circuits. The SP
propagation length, over which the SPP intensity falls to 1/e of its
initial value, can be used to represent the propagation loss.Figure 3 presents the trade-off between the device sensitivity
and other major factors such as footprint, optical losses, and
fabrication complexities.