Collin S. Meierbachtol

Metamaterial-inspired absorbers for Terahertz packaging applications

In this paper, thin metamaterial-inspired structures are investigated for wide-band absorption of stray signals for THz packages. The absorber itself consists of a low-index, low-loss dielectric sandwiched between a patterned, two-dimensionally periodic, thin metallic layer, and a metal backing. Numerical simulations were performed using both the finite element (FEM) and finite-difference time domain (FDTD) numerical methods. Design, fabrication and tests were carried out for absorbers having center frequencies of 0.2 THz and 0.4 THz. Ultra-wide bandwidth and strong absorption were obtained by taking advantage of skin-effect losses in metamaterial structures, and through multi-stacking of these structures. Absorbers having high absorption coefficients and bandwidth (> 1THz) can easily be fabricated using the approach demonstrated in this paper. Two measurement approaches are applied to characterize these structures, details of which are presented in this paper.

Surface plasmon-assisted terahertz imaging array

In this paper, a spoof surface plasmon assisted antenna is paired with a metamaterial enhanced bolometer structure in the formation of a THz focal plane array pixel. The antenna element focuses the electromagnetic wave onto the bolometer element and the bolometer detects this incident power through resistance change. Numerical analysis was performed in order to simulate the plasmonic structure at 0.1 and 0.3 THz. This system was then fabricated and detailed measurements were carried out. This system shows high sensitivity at the desired operating frequency. The performance of the spoof plasmon antenna is favorable when considering the same size of the aperture without exciting plasmonic modes.

Planar surface plasmonic structures for terahertz circuits and sensors

This paper presents planar metal patterned structures that support surface plasmon polaritons (SPPs) like propagation mode. Four unit cells, each having a solid ground plane, were designed that support SPPs. To optimize return loss, these structures were first simulated as infinitely periodic in two dimensions. These were then further optimized by designing waveguide structures. Using multi-band unit cell designs, THz circuits (transmission line and power splitter) were fabricated and tested. A new approach to probe these planar plasmonic devices is presented using wide band THz dielectric probes. Measured results of THz circuits match closely with simulation results. It is also shown through simulations that these structures can be used in the design of THz chemical and biological sensors.

A NOVEL SUBWAVELENGTH MICROBOLOMETER FOR TERAHERTZ SENSING

A subwavelength aperture-microbolometer sensor was simulated using a finite-difference time domain (FDTD) numerical method. The system consisted of a focusing bullseye grating with a central subwavelength aperture. A thin vanadium oxide sensing layer was suspended behind the aperture for sensing purposes, backed by a thin layer of silicon dioxide. The maximum electric field across the vanadium oxide was measured as a function of incident field. Total noise equivalent power (NEP) was estimated to be 180 pW/√Hz at a frequency of 0.665 THz, comparable to similar current micro sensors. The formation of surface plasmonics greatly increases its sensitivity to particular incident wavelengths. This fact, along with its compact size, make this system a promising candidate for numerous low-cost, small-scale terahertz sensing applications.

Self-consistent convective fluid model for moderate pressure microwave plasma-assisted chemical vapor deposition reactors

Microwave plasma-assisted chemical vapor deposition (PACVD) reactors are used for the production of high quality diamond films. Microwave PACVD systems have traditionally been operated at pressures between 10 and 150 Torr, resulting in diamond growth rates of up to 5 um/hr.

Enhanced bandwidth “bull's eye” antenna using corrugated metalized plastic

This paper presents a plastic, surface plasmon (SP) enhanced bullseye antenna for millimeter wave and terahertz (THz) frequency range. A low refractive index plastic layer is used to confine incident electromagnetic energy to the structure. A metal grating layer focuses the incident wave through a subwavelength aperture via SP. The electromagnetic propagation characteristics were simulated and analyzed using both FDTD and commercial FEM software tools. The structure was also fabricated, and experimental data will be presented at the time of the conference.

Plasmonic waveguide coupling at terahertz frequencies

Two approaches for coupling terahertz radiation to surface plasmonic waveguides are proposed and simulated. The first approach utilizes a rectangular waveguide with a tapered plasmonic feed, which allows for the gradual confinement of terahertz waves into a plasmonic structure. The second method employs a ribbon dielectric waveguide, which edge couples terahertz radiation onto a surface plasmonic structure. Coupling designs are presented along with simulation results.

Self-consistent modeling of higher pressure Microwave PACVD reactors

Self-consistent simulation of Microwave PACVD reactors at higher pressures is challenging as it involves coupling many different physical phenomena that are highly nonlinear. This paper presents a solution for these problems. Two major components of the simulation include a finite-difference frequency domain (FDFD) electromagnetic model, and a steady-state convective plasma flow model. These two components are run concurrently while converging toward a single, self-consistent solution. To our knowledge, this is the first model to describe in detail the various physical, chemical, and thermal processes occurring during Microwave PACVD diamond film growth at higher pressures (up to 40% atmosphere). Detailed results and comparisons with experimental data will be presented at the conference.

Computational modeling of moderate pressure microwave plasma-assisted chemical vapor deposition reactors

Summary form only given. Microwave plasma-assisted chemical vapor deposition (PACVD) reactors have been used extensively for the growth of diamond films. The design geometric features of these reactors vary to enable control and shaping of the electromagnetic fields and plasma discharge. In particular, the design and tuning of various geometric parameters is known to affect not only the electromagnetic field structure, but also the plasma shape during operation. For example, the positioning of the substrate height is known to greatly affect the plasma characteristics when changed as little as a few millimeters. In the past, empirical experience has often guided decisions for changing these physical parameters during design and operation. A more detailed numerical study of these effects related to the geometry and the interaction of the microwave fields and plasma discharge is required. This study may also lead to more efficient reactor designs and ultimately faster deposition rates.

Modeling of convective plasma flow in high pressure microwave PACVD diamond reactors

Summary form only given. Microwave plasma-assisted chemical vapor deposition (PACVD) reactors have been used extensively for the growth of synthetic diamond. Simulations of such reactors have been developed in order to aid in the testing of new designs and parameters. Since this type of diamond growth has historically been carried out at relatively low pressures (less than 100 Torr), the plasma transport properties have been approximated as purely diffusive. However, recent experiments citing numerous advantages of growing at higher pressures (100-300 Torr) have suggested this approximation to be insufficient. Thus, a more advanced transport model accurately predicting complex convective plasma flows is required. This paper details a self-consistent multi-physics model that simulates microwave PCAVD diamond reactors at higher pressures of 100-300 Torr. As with previous simulations, a finite-difference electromagnetic simulation is coupled to a plasma fluid model, converging on a self-consistent solution. However, this new simulation includes a time-dependent fluid flow plasma model which includes diffusion, conduction, and convection processes. Moreover, a reactor geometry temperature profile model is also inserted into the solution scheme. The absorbed power within the plasma is passed to the plasma model, while the neutral species temperature, and electron temperature and density are converted to conductivity and passed to the electromagnetic simulation. This process is iterated until a stable solution is achieved. Numerical results of electromagnetic power distribution, species concentration, temperature profiles, and temporal solution convergence will be presented. These results will also be compared to selected experimental data.