PROCEEDINGS ARTICLE | August 25, 2017
Proc. SPIE. 10346, Plasmonics: Design, Materials, Fabrication, Characterization, and Applications XV
KEYWORDS: Plasmonics, Nanostructures, Refractive index, Multilayers, Defect detection, Optical properties, Reflection, Detector arrays, Optical alignment, Spiral phase plates
Plasmonic nanostructures are highly used for sensing purposes since they support plasmonic modes
which make them highly sensitive to the refractive index change of their surrounding medium.
Therefore, they can also be used to detect changes in optical properties of ultrathin layer films in a
multilayer plasmonic structure. Here, we investigate the changes in optical properties of ultrathin
films of macro structures consisting of STT-RAM layers. Among the highest sensitive plasmonic
structures, nanohole array has attracted many research interest because of its ease of fabrication,
small footprint, and simplified optical alignment. Hence it is more suitable for defect detection in
STT-RAM geometries. Moreover, the periodic nanohole pattern in the nanohole array structure
makes it possible to couple the light to the surface plasmon polariton (SPP) mode supported by the
structure. To assess the radiation damages and defects in STT-RAM cells we have designed a
multilayer nanohole array based on the layers used in STT-RAM structure, consisting 4nm-
Ta/1.5nm-CoFeB/2nm-MgO/1.5nm-CoFeB/4nm-Ta layers, all on a 300nm silver layer on top of a
PEC boundary. The nanoholes go through all the layers and become closed by the PEC boundary on
one side. The dimensions of the designed nanoholes are 313nm depth, 350nm diameter, and 700nm
period. Here, we consider the normal incidence of light and investigate zeroth-order reflection
coefficient to observe the resonance. Our simulation results show that a 10% change in refractive
index of the 2nm-thick MgO layer leads to about 122GHz shift in SPP resonance in reflection
pattern.
