Recent progress in plasmonic colour filters for image sensor and multispectral applications

Abstract

Using nanostructured thin metal films as colour filters offers several important advantages, in particular high tunability across the entire visible spectrum and some of the infrared region, and also compatibility with conventional CMOS processes. Since 2003, the field of plasmonic colour filters has evolved rapidly and several different designs and materials, or combination of materials, have been proposed and studied. In this paper we present a simulation study for a singlestep lithographically patterned multilayer structure able to provide competitive transmission efficiencies above 40% and contemporary FWHM of the order of 30 nm across the visible spectrum. The total thickness of the proposed filters is less than 200 nm and is constant for every wavelength, unlike e.g. resonant cavity-based filters such as Fabry-Perot that require a variable stack of several layers according to the working frequency, and their passband characteristics are entirely controlled by changing the lithographic pattern. It will also be shown that a key to obtaining narrow-band optical response lies in the dielectric environment of a nanostructure and that it is not necessary to have a symmetric structure to ensure good coupling between the SPPs at the top and bottom interfaces. Moreover, an analytical method to evaluate the periodicity, given a specific structure and a desirable working wavelength, will be proposed and its accuracy demonstrated. This method conveniently eliminate the need to optimize the design of a filter numerically, i.e. by running several time-consuming simulations with different periodicities.

Exploitation of Magnetic Dipole Resonances in Metal–Insulator–Metal Plasmonic Nanostructures to Selectively Filter Visible Light

“…Moreover, the addition of a second top thin metallic layer in the MIM structure (from configuration (iii) to (ii)) greatly reduces the transmission efficiency of the second broad peak at longer wavelengths -which is almost of the same magnitude as the first narrower resonance in configuration (iii) -and strongly compromises the passband characteristics of the filter, causing optical colour cross-talk in particular between the blue and red part of the visible spectrum. 31 Previous studies 10,32 have demonstrated that when the propagation constant of SPPs, k SPP , (Equation (1)) matches the reciprocal vectors G ij given by the periodicity of the array (Equation (2)) minima in transmission appear, ascribed to the spectral location of Wood-Rayleigh anomalies. The transmission maxima, or EOT peaks, appear then red-shifted in wavelength.…”

“…Figure a presents the schematic top view (i) and cross-section (ii) of the proposed MIM architecture, in comparison with the cross sections (iii) and (iv) , of two previously reported configurations based on periodic hexagonal nanohole arrays. Their transmission characteristics have been simulated (see Methods for details) and the results are presented in Figure b.…”

“…A significant improvement in bandwidth results from the increase in refractive index (RI) of the hole filling material (from configuration (iv) to (iii) and (ii)). Moreover, the addition of a second top thin metallic layer in the MIM structure (from configuration (iii) to (ii)) greatly reduces the transmission efficiency of the second broad peak at longer wavelengths, which is almost of the same magnitude as the first narrower resonance in configuration (iii) and strongly compromises the passband characteristics of the filter, causing optical color cross-talk in particular between the blue and red part of the visible spectrum …”

Longwave infrared multispectral image sensor system using aluminum-germanium plasmonic filter arrays

“…Hole array periodicity is varied to tune the SP resonance wavelength causing spectral shifts in the corresponding spectral curves. Recently, plasmonic lters composed of periodic microhole arrays in noble metals like gold (Au), and silver (Ag) are demonstrated by exploiting SSP resonance [21][22][23]. Jang et al further demonstrated spectral imaging with a square array of micron-sized holes in Au lm on gallium arsenide dielectric as an SSP structure [24].…”

LWIR multispectral imaging using plasmonic filters integrated on a single thermal image sensor

“…These filters manipulate light in a promising way to create imaging technologies with accurate color representation. While nanostructured plasmonic hole arrays have been widely used as color filters in CMOS image sensors operating within the visible range of 400-700 nm [12][13][14][15], a fully-functional thermal multispectral camera with plasmonic hole array has not yet been reported to the best of our knowledge. Such next-generation thermal imaging sensors could have significant implications in the fields of multispectral imaging and spectroscopy with a wide range of applications such as surveillance, medical imaging, and non-destructive investigation.…”