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.