Gold Ground Plane Research Articles

Broadband, high-efficiency, arbitrary focusing lens by a holographic dielectric meta-reflectarray

In this paper, a metalens based on the dielectric meta-reflectarray consisting of silicon nanorods in combination with a gold ground plane is proposed to realize an arbitrary focusing lens. We have demonstrated that the meta-reflectarray is served as a half-waveplate with near-unity reflectance and over 98% polarization conversion efficiency over a wavelength range from 1.5 to 1.6 μm for circularly polarized light incidences. We have also demonstrated that single spot and four-spaced spots focusing with more than 96% diffraction efficiency over 100 nm bandwidth can be realized by this metalens in the near infrared band just by controlling the reflection phases. The spatial phase distributions of the corresponding designed metalens can be determined via a computer-generated hologram method. Meanwhile, the desired phase can be simply obtained by modulating the orientation of the silicon nanorods. The proposed approach demonstrates a high-performance solution for creating low-cost and lightweight beam-shaping and beam-focusing devices at telecommunication wavelengths.

Reflective gradient metasurfaces for polarization-independent light focusing at normal or oblique incidence

Reflective gradient metasurfaces are reported as flat, ultra-thin light focusers using a cross-resonator array with spatially varied geometric parameters atop a continuous gold ground plane spaced by a layer of SiO2. The sub-wavelength cross-shaped building element offers polarization-independent performance and full 2π phase tuning range by varying its width and length, which is explained by an analytical model based on harmonically oscillating dipole antenna. With a radial phase gradient, a metasurface is demonstrated to function as a parabolic reflector at 1.47 μm wavelength with the measured efficiency of 44%. In addition, by elaborately engineering the planar distribution of different building elements, another two focusing reflectors are designed and experimentally verified to anomalously reflect and concentrate light along normal direction but with oblique incident angles of 30° and 60°, respectively.

Metasurface Broadband Solar Absorber.

We demonstrate a broadband, polarization independent, wide-angle absorber based on a metallic metasurface architecture, which accomplishes greater than 90% absorptance in the visible and near-infrared range of the solar spectrum, and exhibits low absorptivity (emissivity) at mid- and far-infrared wavelengths. The complex unit cell of the metasurface solar absorber consists of eight pairs of gold nano-resonators that are separated from a gold ground plane by a thin silicon dioxide spacer. Our experimental measurements reveal high-performance absorption over a wide range of incidence angles for both s- and p-polarizations. We also investigate numerically the frequency-dependent field and current distributions to elucidate how the absorption occurs within the metasurface structure.

Graphene-Based Tunable Polarization Insensitive Dual-Band Metamaterial Absorber at Mid-Infrared Frequencies**Supported by the National Natural Science Foundation of China under Grant No 61001018, the Natural Science Foundation of Shandong Province under Grant No ZR2012FM011, the Shandong-Provincial Higher Educational Science and Technology Program under Grant No J11LG20, the Qingdao City Innovative Leading Talent Plan under Grant No 13-CX-25, the THz Science and

A graphene-based tunable dual-band metamaterial absorber which is polarization insensitive is numerically proposed at mid-infrared frequencies. In numerical simulation the metamaterial absorber exhibits two absorption peaks at the resonance wavelengths of 6.246 μm and 6.837 μm when the Fermi level of graphene is fixed at 0.6 eV. Absorption spectra at different Fermi levels of graphene are displayed and tuning functions are discussed in detail. Both the resonance wavelengths of the absorber blue shift with the increase in Fermi level of graphene. Moreover, the surface current distributions on the gold resonator and ground plane at the two resonance wavelengths are simulated to deeply understand the physical mechanism of resonance absorption.

Constructing Dual Band Metamaterial Absorbers at Mid-Infrared by Employing Multi-Resonant Structures

In this paper, we present two metamaterial absorbers (MMA) at mid-infrared using multi-resonant structures. The dual band MMAs employ the typical metal/dielectric/metal structure with 80 nm gold ground plane at the bottom, 190 nm SiO2 dielectric spacer in the middle and periodic gold patterns on top. The top resonant structure in MMA1 consists of a gold cross resonator ringed by four gold split-ring resonators (SRR) at the ends of the cross, while in the unit cell of MMA2, gold SRRs are placed at the four quadrants of the cross resonator. MMA1 shows two absorption peaks of 90.3% and 88.4% at 4.17μm and 4.86μm respectively, and the absorption peaks of MMA2 are observed to be 72.4% at 3.90μm and 48.0% at 5.66μm.

Mid-Infrared Tunable Dual-Frequency Cross Polarization Converters Using Graphene-Based L-Shaped Nanoslot Array

In this paper, we proposed a novel dual-frequency cross polarization converter that can simultaneously work at two frequencies in the reflection mode, which is constructed of an L-shaped perforated graphene sheet printed on a dielectric material backed by a gold ground plane. For the normal incidence, the optical rotation at these two working frequencies originates from the simultaneous excitation of both eigenmodes that are characterized as the results of the localized surface plasmon resonances. Moreover, by merely varying the Fermi energy of the graphene, both working frequencies can be tuned within a large frequency range, which suggests numerous potential optical applications.

Theoretical and Experimental Demonstrations of a Dual-Band Metamaterial Absorber at Mid-Infrared

We present the design, fabrication, and physical interpretation of an infrared dual-band metamaterial absorber. The unit cell of the metamaterial absorber consists of a cross resonator ringed by four split-ring resonators spaced a distance above a gold ground plane with a dielectric layer of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The absorber shows two absorption peaks of 90.3% and 88.4% at 4.17 μm and 4.86 μm, respectively. The multireflection interference theory is applied to explain the absorption mechanism with the gold ground plane described by Drude model, and the theoretical calculation agrees well with the simulations and experiments. In addition, the designed absorber is insensitive to incident angle and polarization direction in a broad range, which are highly favorable features in practical applications.

Broadband metamaterial absorber at mid-infrared using multiplexed cross resonators

In this paper, we theoretically and experimentally demonstrate broadband metamaterial absorbers that work in the mid-infrared regime. In the absorbers, two or four gold cross resonators with different sizes are multiplexed in a unit cell on SiO(2) spacing layer on top of gold ground plane. Compared with the single cross resonator absorbers with a Q factor of 6.39, the developed absorber with two cross resonators multiplexed reduces the Q factor to 3.78. When four different cross resonators are integrated, the Q factor drops to as low as 1.85, and the bandwidth almost covers the full mid-infrared regime from 3 μm to 5 μm with absorbance higher than 50%.

Infrared perfect absorber based on nanowire metamaterial cavities

An infrared perfect absorber based on a gold nanowire metamaterial cavities array on a gold ground plane is designed. The metamaterial made of gold nanowires embedded in an alumina host exhibits an effective permittivity with strong anisotropy, which supports cavity resonant modes of both electric dipole and magnetic dipole. The impedance of the cavity modes matches the incident plane wave in free space, leading to nearly perfect light absorption. The incident optical energy is efficiently converted into heat so that the local temperature of the absorber will increase. Results show that the designed absorber is polarization-insensitive and nearly omnidirectional for the incident angle.

Design and fabrication of a gold electroplated electromagnetic and electrostatic hybrid MEMS relay

This paper reports on a gold electroplated hybrid microrelay that combines the advantages offered by electromagnetic and electrostatic actuation mechanisms. The microrelay design achieves signal by out-of-plane motion of a contact cross-bar fabricated on a diaphragm fixed at both ends to short the isolated input and output contacts. Major factors influencing the design approach include low contact resistance in the closed state, high signal isolation in the open state, latching upon loss of power, and fabrication robustness and cost. The MEMS device is surface micromachined with structures fabricated by electroplating gold through photoresist masks. Experimental results show that 95% of the devices can be actuated and ≈50% of them pass signal. The average contact resistance is about 170mΩ and the system isolation is 70dB at 20MHz when a gold ground plane is added.

Submicron scaling of HBTs

The variation of heterojunction bipolar transistor (HBT) bandwidth with scaling is reviewed. High bandwidths are obtained by thinning the base and collector layers, increasing emitter current density, decreasing emitter contact resistivity, and reducing the emitter and collector junction widths. In mesa HBTs, minimum dimensions required for the base contact impose a minimum width for the collector junction, frustrating device scaling. Narrow collector junctions can be obtained by using substrate transfer or collector-undercut processes or, if contact resistivity is greatly reduced, by reducing the width of the base ohmic contacts in a mesa structure. HBTs with submicron collector junctions exhibit extremely high f/sub max/ and high gains in mm-wave ICs. Transferred-substrate HBTs have obtained 21 dB unilateral power gain at 100 GHz. If extrapolated at -20 dB/decade, the power gain cutoff frequency f/sub max/ is 1.1 THz. f/sub max/ will be less than 1 THz if unmodeled electron transport physics produce a >20 dB/decade variation in power gain at frequencies above 110 GHz. Transferred-substrate HBTs have obtained 295 GHz f/sub T/. The substrate transfer process provides microstrip interconnects on a low-/spl epsiv//sub r/ polymer dielectric with a electroplated gold ground plane. Important wiring parasitics, including wiring capacitance, and ground via inductance are substantially reduced. Demonstrated ICs include lumped and distributed amplifiers with bandwidths to 85 GHz and per-stage gain-bandwidth products over 400 GHz, and master-slave latches operating at 75 GHz.

Ciliary microactuator array for scanning electron microscope positioning stage

The performance of a ciliary microactuator array as a positioning stage inside a scanning electron microscope is described. Such arrays are attractive because they can provide micron scale positioning resolution with direct electronic control within the sample chamber. The present array uses thermal actuation of a polyimide bimorph to produce long-travel deflection of each cilium and electrostatic actuation to provide a low-power hold-down mode. Each cell in the array consists of four orthogonally oriented cilia which, with proper drive signals, can produce object motion along any direction within the plane of the array. Adapting this array for use inside a scanning electron microscope (SEM) requires only a small mounting block and a modest multiconductor feedthrough. Improved thermal isolation within the vacuum chamber of the SEM drastically reduces the electrical input power requirements over those in air, while still allowing full positioning resolution. The addition of a gold ground plane coating to the array eliminates charging problems by the electron beam and reduces electrical interference from the drive signals.

Electrical-transport properties and microwave device performance of sputtered TlCaBaCuO superconducting thin films

Tl-Ca-Ba-Cu-O high-temperature superconducting thin films were deposited on lanthanum aluminate substrates, by rf magnetron sputtering and postannealing methods. A reproducible fabrication process with low-resistance metal contacts has been established for high-Tc and high-Jc TlCaBaCuO thin films after patterning using standard microelectronic photolithography and wet chemical etching techniques. Low-resistance gold contacts on TlCaBaCuO thin films were obtained by annealing in an oxygen flow of 1 l/min followed by a slow furnace cooling. Specific contact resistivity was approximately 10−10 Ω cm2 below 77 K. High transition temperatures as high as 100 K, and current density at zero magnetic field greater than 105 A/cm2 are routinely obtained in 0.3–0.5 μm TlCaBaCuO thin films. The morphology studies of the films using scanning electron microscopy show the correlation between Jc and the microstructure of the films. Films with featureless morphology have larger zero-field transport currents. The microwave properties of TlCaBaCuO thin films were investigated by designing, fabricating, and characterizing microstrip ring resonators with a fundamental resonance frequency of 12 GHz on 10-mil-thick lanthanum aluminate (LaAlO3) substrates. Ring resonators with a superconducting ground plane of 0.3 μm thickness and a gold ground plane of 1 μm thickness were fabricated and characterized in the temperature range of 60–95 K. Typical unloaded quality factors Q for the ring resonators at 12 GHz were above 1500 at 65 K, compared to an unloaded Q of 370 for a gold ring resonator. A surface resistance as low as 1.5 mΩ at 12 GHz and 77 K was obtained in 0.3 μm TlCaBaCuO thin films using the ring resonator Q measurements. Typical values of penetration depth at 0 K in the TlCaBaCuO thin films were determined to be between 7000 and 8000 Å using the temperature variation of resonance frequency measurements.