Terahertz metamaterials on free-standing highly-flexible polyimide substrates

Abstract

We have fabricated resonant terahertz metamaterials on free standing polyimide substrates. The low-loss polyimide substrates can be as thin as 5.5 µm yielding robust large-area metamaterials which are easily wrapped into cylinders with a radius of a few millimeters. Our results provide a path forward for creating multi-layer non-planar metamaterials at terahertz frequencies. PACS numbers:The advent of metamaterial composites has given rise to numerous electromagnetic functionalities previously unimagined. This includes negative refractive index, superlensing, cloaking, and quite generally, the fabrication of metamaterials which have been designed using coordinate transformation approaches [1,2,3, 4,5]. Many of these ideas were initially implemented at microwave frequencies where fabrication of multilayer composites has become increasingly sophisticated during the past several years. This has resulted in dramatically reduced times from conceptualization and electromagnetic simulation to, ultimately, fabrication and characterization. However, the fabrication of subwavelength unit cells becomes increasingly challenging in moving from the microwave to visible region of the electromagnetic spectrum though important progress has been made [6,7,8,9]. To date, the majority of this work has been on planar composites. At terahertz (THz) frequencies and above, creating multiple unit cell structures in the direction of propagation and taking full advantage of coordinate transformation MM design to realize non-planar MM composites requires the development of new fabrication strategies.The far-infrared, or terahertz, is a promising region to investigate novel approaches to metamaterials fabrication. First, the unit cells are on the order of tens of microns which is amenable to novel microfabrication approaches. Second, and perhaps of greater importance, there is a strong technological impetus to create sources, detectors, and components at terahertz frequencies to realize the unique potential of THz radiation [10,11,12,13]. Metamaterials are expected to play an important role in this regard as evidenced by recent demonstrations of MM-based modulators and frequency tunable filters [14,15,16]. An important step in the progression of functional THz MM composites is the fabrication of multilayer structures. For example, a strongly resonant THz MM absorber consisting of two layers spaced by approximately six microns [24] was recently demon- * Electronic address: xinz@bu.edu † Electronic address: raveritt@physics.bu.edu strated (see also [17] for the microwave perfect absorber). The entire structure, however, was on top of a thick GaAs supporting substrate. There has also been other work at THz frequencies using polymer spin-coating based techniques to fabricate metamaterials, but the focus of this work was not on ultrathin flexible substrates [18,19]. FIG. 1: (Color) Photographs of the free standing electric metamaterials fabricated on polyimide substrate. The thin samples naturally roll up into a cylinder unless supported on a fra...

Single-layer terahertz metamaterials with bulk optical constants

“…A thin polyimide film, although well characterized by optical constants 28 , is highly flexible, mechanically weak and not self supporting. In the single layer case the as measured films surface is slightly modulated resulting in undesirable effects.…”

“…For the last layer, a 25µm thick layer of polyimide was coated on top. In the final step, the entire multilayer sample, encapsulated in polyimide, was peeled off the silicon substrate, thus yielding a free-standing metamaterial multilayer structure embedded within the host dielectric material 28 .…”

Terahertz Sensing Application by Using Fractal Geometries of Split-Ring Resonators

“…In [22,23], the direct write technique called proton beam writing (PBW) was used to fabricated high aspect ratio SRRs. In [24,25], MTMs were fabricated on ultra-thin silicon nitride substrates. Both of the methods have been proven to have the ability to enhance the sensitivity.…”

Realization of Variable Three‐Dimensional Terahertz Metamaterial Tubes for Passive Resonance Tunability

“…[ 16 ] In recent research, fl exible PEN fi lms were used as substrates to construct metamaterials for resonance enhancement and broadband resonance. [17][18][19] This kind of thin fl exible metamaterial can make metamaterials into non-planar form, allowing more potential designs and applications than the metamaterials made on rigid substrates.…”