Dielectrics for Terahertz Metasurfaces: Material Selection and Fabrication Techniques

Abstract

on distinctive spectral signatures resulting from vibrational modes of covalent and hydrogen bonds. [8,[13][14][15][16] The focus on this spectrally rich region is attributed to the highly coherent and nonionizing nature of terahertz radiation, wide unallocated frequency bands, distinctive wavelengths, and their penetration through a significant depth of dielectric materials. Terahertz technology is geared toward realizing devices that can efficiently manipulate the phase, amplitude, and polarization of terahertz radiations for the above-mentioned myriad of applications.However, progress in this domain is held back by low terahertz power available from compact sources, high free-space path loss, and limited choice of materials that exhibit less absorption of terahertz waves. [17] Owing to the fact that natural materials demonstrate weak wave-matter interaction at terahertz frequencies, terahertz devices with engineered subwavelength resonant metallic inclusions on dielectric spacers have been realized, to interact strongly with an incident electromagnetic wave.In the past, metamaterials have been a promising route to building terahertz devices. These devices have in essence been engineered as 3D resonating elements that effectively manipulate both permittivity and permeability of an effective medium to couple to free space. The underlining disadvantage of these structures is the difficulty involved in the fabrication of 3D geometrical structures using standard semiconductor fabrication techniques. Standard fabrication techniques are generally amenable to 2D design with extrusion of these structures into thickness (the third, vertical dimension). Moreover, the choice and availability of dielectric materials and metals that provide sufficient interaction while retaining device efficiency has proved challenging. [13,[18][19][20] Recently, effective manipulation of electromagnetic wave has been widely demonstrated with 2D metasurfaces, which were originally employed as building blocks for 3D metamaterials. In these lower-dimension designs, effective manipulation of terahertz waves for various applications is achieved by carefully designing sub-wavelength resonant structures as is evident in published review articles. [21,22] Metasurfaces present high degree of compactness that enhances radiation efficiency. Additionally, the planar form factor of metasurfaces enables Manipulation of terahertz radiation opens new opportunities that underpin application areas in communication, security, material sensing, and characterization. Metasurfaces employed for terahertz manipulation of phase, amplitude, or polarization of terahertz waves have limitations in radiation efficiency which is attributed to losses in the materials constituting the devices. Metallic resonators-based terahertz devices suffer from high ohmic losses, while dielectric substrates and spacers with high relative permittivity and loss tangent also reduce bandwidth and efficiency. To overcome these issues, a proper choice of low loss and low relative permittivi...

All‐Dielectric Metamaterial Fabrication Techniques

“…Basically, all‐dielectric metamaterials are composed of polymers, dielectrics, ferrites, or composite materials. [ 20–22 ] The unusual electromagnetic properties of all‐dielectric metamaterials not only derive from their artificial structure, but also originate directly from the materials, revealing an approach to designing metamaterials with more freedom. [ 23 ]…”

Metagrating-Based Terahertz Polarization Beam Splitter Designed by Simplified Modal Method

“…Over the past decades, terahertz (THz) waves are finding a growing number of applications in communications [1][2][3], security check [4], imaging [5], pharmaceutical quality control [6], and other fields because of their particular location in the electromagnetic spectrum [7][8][9][10][11]. As a result, functional devices for THz waves like polarization beam splitters (PBSs) are highly needed.…”

A 1-bit High-Gain Flexible Metasurface Reflectarray for Terahertz Application

“…Therefore, it is usually replaced by Gold at THz. Similarly, dielectric substrates used at RF and mmWave frequencies are also replaced by materials with low loss tangent at THz [5]. The first use of reflectarray in the THz range was demonstrated in [6].…”