Thin Dielectric Layer Research Articles

Wideband High Gain Cylindrical Dielectric Resonator Antenna for X-Band Applications

Abstract In present work a wide band and high gain cylindrical dielectric resonator antenna working in X-band has been designed and validated experimentally. First the bandwidth of the antenna has been enhanced by placing the thin dielectric layer between antenna and feed network. Next gain of the antenna has been increased by placing a layer of high dielectric material at nearly λ/2 distance as superstrate. The proposed design with impedance bandwidth of 3 GHz and gain nearly 11dBi could be used in satellite communication and other wideband wireless applications operating in X-band.

Integrated dielectric-electrode layer for triboelectric nanogenerator based on Cu nanowire-Mesh hybrid electrode

Morphological engineering of nano- and micro-surface patterns has been considered as a key design element to achieve superior output performances in triboelectric energy harvesters. Most previous studies have focused on the surface engineering of dielectric materials rather than electrodes. In this study, a hierarchically three-dimensional (3D) copper nanowire-copper Mesh hybrid electrode (Cu NW-Cu Mesh) is reported for developing a high-performance and structurally reliable triboelectric nanogenerator (TENG). The hierarchical electrode has been embedded into a dielectric thin layer of polydimethylsiloxane (PDMS), resulting in an integrated dielectric-electrode layer that has much better structural reliability to repeatable impacts and inherits the roughened morphology of the Cu NW-Cu Mesh. The PDMS sealed Cu NW-Cu Mesh can be widely used in vertical contact-separation mode, single electrode mode, and wind-driven TENGs. Serially connected four hundred green LEDs can be lighted by free fall of a large size Cu NW-Cu Mesh based single electrode TENG. By tapping the large size TENG, a capacitor can be charged and used to power an electronic watch. The results indicate that the proposed integrated dielectric-electrode layer can be used as an effective mechanical energy harvester requiring both structural reliability and high output power under strong impacts due to large amplitude oscillations based on fluid-structure coupled dynamic instabilities.

Affordable Fabrication of Conductive Electrodes and Dielectric Films for a Paper-based Digital Microfluidic Chip.

In order to fabricate a digital microfluidic (DMF) chip, which requires a patterned array of electrodes coated with a dielectric film, we explored two simple methods: Ballpoint pen printing to generate the electrodes, and wrapping of a dielectric plastic film to coat the electrodes. For precise and programmable printing of the patterned electrodes, we used a digital plotter with a ballpoint pen filled with a silver nanoparticle (AgNP) ink. Instead of using conventional material deposition methods, such as chemical vapor deposition, printing, and spin coating, for fabricating the thin dielectric layer, we used a simple method in which we prepared a thin dielectric layer using pre-made linear, low-density polyethylene (LLDPE) plastic (17-μm thick) by simple wrapping. We then sealed it tightly with thin silicone oil layers so that it could be used as a DMF chip. Such a treated dielectric layer showed good electrowetting performance for a sessile drop without contact angle hysteresis under an applied voltage of less than 170 V. By using this straightforward fabrication method, we quickly and affordably fabricated a paper-based DMF chip and demonstrated the digital electrofluidic actuation and manipulation of drops.

Towards Accurate and Wideband <italic>In Vivo</italic> Measurement of Skin Dielectric Properties

In this paper, we first review the most common measurement methods, previously used, for assessing the complex permittivity of human skin, namely, open-ended coaxial and waveguide probe reflectometry methods. We then outline and emphasize their useful features and shortcomings that can adversely affect the measurements. Then, an approach utilizing an open-ended waveguide probe with an engineered ground plane and a thin dielectric layer in front of the aperture to prevent skin protrusion is proposed. This approach utilizes a full-wave electromagnetic model that accurately describes the interaction of a layered skin with this probe. Furthermore, comprehensive analyses were performed to investigate the important sources of modeling and measurement errors and their influences on the calculated skin complex permittivity. The results of these analyses have shown that the proposed method can achieve ~85% and ~95% calculation accuracy for skin relative (to free space) dielectric constant and relative dielectric loss factor, respectively. Finally, a series of in vivo measurement was performed in the Ka-band (26.5–40 GHz) on several different locations of three human subjects using this proposed method. In addition, it is demonstrated that the homogeneous skin model cannot be used for areas of the body where the stratum corneum (SC) layer is relatively thick (e.g., palm). Finally, the effect of a thick SC layer on the relative complex permittivity calculation was discussed, and a modified method to determine the relative complex permittivity of the layered skin was proposed and verified by simulations.

Sensitivity analysis of the electrostatic interaction between the atomic force microscopy probe and a thin dielectric film with 3D-localized charge cloud

Recent experimental studies have demonstrated that the Electrostatic Force Distance Curve (EFDC) can be used for space charge probing in thin dielectric layers. Experiments highlight that this method seems to be sensitive to charge localization. However, the relative contributions of charge distribution parameters (density, lateral/in-depth spreading) remain unknown. The aim of this paper is to determine the contribution of each charge distribution parameters to EFDC. To reach this aim, we have developed an electrostatic and an electromechanical model to simulate EFDC over a charge cloud trapped in a thin dielectric layer. Hence, the EFDC sensitivity to charge localization could be investigated through the shape parameters of the charge cloud and by extracting the respective contributions from the atomic force microscopy tip and the cantilever.

Methodology for the design of a multi-functional device with switchable absorption and polarization conversion modes by graphene and metallic metasurfaces

A methodology to design a multi-functional device (MFD) with switchable absorption and polarization conversion (PC) modes is proposed in this research. The methodology combines graphene absorbing metasurface (GAM) and polarization conversion metasurface (PCM) in one component. The key point is that the absorbing metasurface (AM) should be made completely by conductivity tunable material, such as graphene. The PCM can be constructed by fine metal. A prototype is designed to verify the designing methodology by stacking a layer of gold pattern PCM and two layers of GAM with fishnet shape patterns. In the PC mode, the chemical potentials of the two GAMs are µc1 = µc2 = 0 eV, then, the graphene layers act as thin dielectric layers, which can be treated as transparency. Thus, the PCM plays a leading role in the performances of the whole structure. Therefore, a linear polarized incidence is rotated by 90° in the 2.10-3.13 THz (39.5% at 2.61 THz) with polarization conversion ratio (PCR) larger than 90%. In the absorption mode with µc1 = 0.5 eV and µc2 = 0.8 eV, the GAMs have strong surface plasmon-polaritons (SPPs), and they concentrate most of the incident power, which makes the GAMs dominate roles of the whole structure. Therefore, the incident power is dissipated in the GAMs, and the absorption rate is larger than 90% in the 1.30-3.01 THz (79.5% at 2.15 THz). The absorption band for absorption rate larger than 70% is 1.19-3.90 THz (106.7% at 2.54 THz). The design methodology is useful for the designing of components with switchable absorption and PC modes.

Field-enhanced nanofocusing of radially polarized light by a tapered hybrid plasmonic waveguide with periodic grooves.

This study reports the field-enhanced nanofocusing of radially polarized light by tapered hybrid plasmonic waveguide (THPW) with periodic grooves. The THPW consists of a conical high-index dielectric cone, a sandwiched low-index dielectric thin layer, and a metal cladding. The axially symmetric 3D finite element method is used to investigate the nanofocusing effect. Under radially polarized illumination at 632.8nm, strongly enhanced nanofocusing occurs. The hybrid plasmonic structure effectively reduces the energy loss and improves the field enhancement nearly 554 times. Furthermore, periodic grooves are constructed on the metallic surface of the THPW, satisfying the phase-matching condition, and they couple the light energy from the inside to the outside. Finally, an optimized nanofocusing performance with field enhancement of approximately 1810 times is obtained. The results offer an important reference for designing related photonic devices, and the proposed scheme could be potentially exploited in the application of light-matter interactions.

A novel microsensor for measuring thermal conductivity of fluid based on three omega method.

A novel microsensor has been designed for the measurement of thermal conductivity of fluids based on the three omega (3ω) method. First, we theoretically analyzed the heat conduction using the 3ω method to demonstrate the mechanism of the microsensor to measure the thermal conductivity of a fluid. For the main structure of the microsensor, a heater was supported by the thin dielectric layers. In order to obtain the optimal parameters, we used the finite element method to simulate the working condition of the microsensor. In the simulation model, the effects of the thicknesses of the heater and dielectric layers on the thermal conductivity λ of the fluid were analyzed. The simulation results confirmed the validity and accuracy of conventional analytical calculations. Based on the simulation and theoretical calculation, a microsensor was optimally designed and fabricated to measure the thermal conductivity of fluids. Experimental data are consistent with those reported in the literature and demonstrate that the proposed sensor is effective for measuring thermal conductivity of fluids, including conductive ones.

Selection of dielectric material for producing diffuse dielectric barrier discharge plasma at atmospheric pressure

Abstract We report the effect of dielectric layer and its selection criterion to produce diffuse dielectric barrier discharge plasma at atmospheric pressure. The dielectric barriers over electrodes are used to prevent glow-to-arc transition by limiting growth of discharge current. We have analyzed the dielectric properties such as secondary electron emission, dielectric constant, dielectric thickness etc in order to get better power efficiency at breakdown. It is observed that a thin dielectric layer with high dielectric constant is suitable for lowering the breakdown voltage. During one of our experiments, planar-surface discharge plasma was produced with the use of epoxy resin dielectric-covered stripe electrodes. High-voltage high frequency signal was applied between the electrodes to produce the discharge. It is observed that the discharge remain stable & uniform in our parametric range. However, after prolonged discharge operation, degradation of dielectric layer was observed in the form of powder formation over the dielectric insulation. SEM analysis reveals that the powder contains individual as well as cluster of particles of micrometer size dimension. Such micro-particle formation may be useful for some material and biomedical applications, however in other way degraded dielectric would lead to spark formation in plasma. In this context, theoretical and experimental analysis of our results is presented in this paper.

Усиление терагерцового излучения высокодобротными резонансными плазмонами в двухслойной периодической структуре на основе графена в режиме антикроссинга плазмонных мод

AbstractThe spectrum of amplification of terahertz radiation in a structured active graphene bilayer consisting of two identical periodic graphene microribbon arrays separated by a thin dielectric barrier layer is theoretically investigated. The system supports optical and acoustic plasmon modes. The resonant frequencies of the optical and acoustic modes change oppositely with the dielectric-layer thickness, which allows plasmon-mode anticrossing. It is shown that the investigated graphene structure is characterized by a strong plasmon response and giant terahertz-radiation amplification at plasma resonance frequencies in the vicinity of the anticrossing between the optical and acoustic plasmon modes at room temperature.

Electroless Grafting of Polymer Insulation Layers in Through-Silicon Vias

A through-silicon via (TSV) with a polymeric insulation layer is promising in three-dimensional packaging technology because of its outstanding electrical properties. In this study, we present an electroless grafting method to realize the fabrication of a thin insulation layer in high aspect ratio TSVs. The proposed method is based on the polymerization of a vinyl monomer and an aryl diazonium salt on a silicon surface. Both poly(acrylic acid) and poly(methyl methacrylate) insulation layers were successfully prepared in TSVs to demonstrate the feasibility of the proposed method to fabricate hydrophilic and hydrophobic layers. The resulting polymer insulation layer exhibited high step coverage and superior dielectric properties. The electroless grafting method is a novel synthesis route to prepare polymeric insulation layers with outstanding dielectric properties in high aspect ratio TSVs.

Ordered Array of Metal Particles on Semishell Separated with Ultrathin Oxide: Fabrication and SERS Properties

Metal particles in gap cavities provide an interesting system to achieve hybrid local surface plasmon modes for local field enhancement. Here, we demonstrate a relatively simple method to fabricate Ag nanoparticles positioned on Ag semishells separated by a thin (~5 nm) dielectric layer. The obtained structure can provide strong local electric field enhancement for surface-enhanced Raman scattering (SERS). The fabrication of the ordered array structure was realized by nanosphere self-assembly, atomic layer deposition, and metal thin-film dewetting. Numerical simulation proved that, compared to the conventional metal semishell arrays, the additional Ag particles introduce extra hot spots particularly in the valley regions between adjacent Ag semishells. As a result, the SERS enhancement factor of the metal semishell-based plasmonic structure could be further improved by an order of magnitude. The developed novel plasmonic structure also shows good potential for application in plasmon-enhanced solar water-splitting devices.

Modeling of electromagnetic behavior of composite thin layers using genetic algorithm

In this paper, a new hybrid model is presented using the high frequency electromagnetic simulator for several binary mixtures where the load is in the lossless and thin film form with a permittivity of (ϵ́ = 100, 200, 300, and 400) and for various thickness values in a range of 10μm to 250μm. This model operates in a variety of frequencies from 8.2 GHz to 12.4 GHz. The effective permittivity of composites is evaluated using Nicholson Ross Weir (NRW) algorithm in a rectangular waveguide. The implementation of NRW algorithm is conducted on various samples simulated in order to estimate the dielectric composite behavior. Furthermore, a genetic algorithm methodology (GA) is employed for the optimization of filling factors of the proposed model by Wiener law. The obtained results show a good agreement with Mosallaei model, which ensure the validity of our proposed model based on GA for characterizing the electromagnetic behavior of dielectric thin layers.

Dielectric surrounding decimates eigenmodes of microdisk optical resonators

We performed a numerical study of optical whispering gallery modes in microdisk resonators modified via their embedding in a homogeneous dielectric surrounding or covering with a thin dielectric layer. Mode spectra and electromagnetic field distributions were calculated through the solution of the Helmholtz equation using COMSOL Multiphysics environment. It is shown that the modification results in the decimation of the resonator modes.

Au-SiO2-Si hybrid plasmonic waveguide micro-ring resonator sensor

A refractive index sensor based on straight silicon waveguide and a hybrid plasmonic micro-ring resonator of radius 1 µm is presented. The hybrid waveguide is made up of a Metal-Insulator-Silicon structure, where the electric field is significantly enhanced in the thin insulator layer. The micro-ring design is optimized where silicon micro-ring waveguide width and a total height of the structure is 400 nm and 220 nm, respectively. The transmission spectrum and electric field distribution of this sensor structure are simulated using Finite Element Method (FEM). Despite the small size of hybrid micro-ring resonator and sensing medium, the sensitivity is relatively high as compared to conventional dielectric micro-ring resonator sensors. The resonance shift of Δλ = 27 nm is obtained for Δn = 0.15 and yields the best sensitivity of 180 nm/RIU in the near infrared range.

Frequency-Dependent MNL-FDTD Scheme for Wideband Analysis of Printed Circuit Boards With Debye Dispersive Media

A semiimplicit and frequency-dependent 3-D finite-difference time-domain (FDTD) scheme with relaxed numerical stability was presented for wideband analysis of multilayer printed circuit boards (PCBs) with thin conductive and dielectric layers. This new scheme is formulated by directionally and magnetically introducing the Newmark-beta method into the conventional FDTD explicit scheme based on the recursive convolution ( RC ) approach for the so-called extended Debye model with an effective dc conductivity. No dependence of mesh step in the normal direction to the PCB layers is included in its stable condition. Interestingly, the presented semiimplicit scheme can be reduced to the RC -based explicit FDTD when the Newmark parameter is chosen as zero. The scheme was carefully verified in applications to rectangular power-bus structures, an irregular power-bus structure with decoupling capacitors and multilayer PCBs with planar electromagnetic bandgap structures. It was demonstrated in these test problems that the calculation time was reduced by a factor of 1/4–1/30 in comparison with the explicit scheme, while maintaining the same level of accuracy.

Resistive switching at the high quality metal/insulator interface in Fe3O4/SiO2/α-FeSi2/Si stacking structure

Fe3O4-based films composed of ubiquitous elements are promising for resistive switching. In general, the disadvantage of this film is the low Off/On resistance ratio. We achieved the highest resistance ratio in a Fe3O4-based stacking structure including a thin SiO2 layer with a high quality interface. For fabrication of the stacking structure, Fe oxide films were epitaxially grown on the intentionally formed α-FeSi2 layers on Si substrates, where the high quality epitaxial interfaces were formed owing to the α-FeSi2 layer role: blocking of Si atom diffusion from the substrate through the interface. The high quality Fe3O4/α-FeSi2 interfaces were oxidized by the low O2 pressure annealing process to succeed in inserting thin SiO2 layers at the interfaces. The resulting stacking structure of the Fe3O4 film/SiO2 layer/α-FeSi2 layer showed the resistive switching behavior with the resistance ratio of ∼140 which is the highest value of Fe3O4 materials. This high value comes from much higher resistance in the high resistive state because the stacking structure has a thin SiO2 insulator layer with high quality interfaces without defects working as leakage sites. This means overcoming the disadvantage of conventional Fe3O4-based films, low resistance ratio, and demonstrates the possibility of realization for rare-metal-free resistance random access memory.

Dynamically switchable polarization-independent and broadband metasurface perfect absorber in the visible and near-infrared spectra regime

Abstract An electrically tunable absorber in the visible (Vis) and near-infrared (NIR) regime is theoretically investigated. The absorber is composed of aluminum (Al)-indium tin oxide (ITO) composite square pillars on top of thin dielectric layer and Al substrate. Significant tuning of absorption with modulation ratio of 86% can be achieved. The modulation ratio above 75% can be maintained from 1427 to 1795 nm and over 90% absorbance at the NIR regime from 1500 to 1800 nm can also be achieved. The symmetry of the absorber eliminates the polarization dependence and the near unity absorption efficiency can be maintained by incidence angles up to 70°. The presented method will enhance the functionality of absorber and has the potential for the applications that require active control over light absorption.

Investigation of temperature dependent negative capacitance in the forward bias C-V characteristics of (Au/Ti)/Al2O3/n-GaAs Schottky barrier diodes (SBDs)

In this study, a metal-insulator-semiconductor (MIS) type Schottky barrier diodes (SBDs) were fabricated by growing a thin Al2O3 insulator layer between Au/Ti and n-GaAs using atomic layer deposition (ALD) method. The effect of temperature and voltage on interface states (Nss) and series resistance (Rs) of the (Au/Ti)/Al2O3/n-GaAs (MIS) type Schottky barrier diodes (SBDs) was investigated using the capacitance/conductance-voltage (C/(G/ω)-V) data measured in wide range of temperature (200–380 K) and voltage ( ± 5 V). It was found that C and G/ω are strongly dependent on temperature and voltage. The value of C in the forward bias region reaches to maximum and then becomes negative. This negative capacitance (NC) behavior of this SBD is observed for each temperature level. Also, capacitance-current (C-I) and conductance-current (G/ω-I) plots were drawn to explain the NC behavior. The negative value of C in the accumulation region corresponds to the maximum value of G/ω. Such behavior of C can be explained by the loss of interface charges located at (Al2O3)/n-GaAs interface because of impact ionization process, the existence of surface states (Nss), series resistance (Rs) and interfacial of (Al2O3) oxide layer.Therefore, the voltage dependent profiles of Rs and Nss were obtained using Nicollian-Brews and Hill-Colleman methods for enough high forward biases as a function of temperature at various positive bias voltages. The changes in Rs and Nss values were attributed to restructure and reordering of the carriers under temperature and voltage effects.

VSIE-Based Domain Decomposition Method With Simplified Prism Vector Basis Functions for Planar Thin Dielectric-Conductor Composite Objects

A nonoverlapping and nonconforming volume-sur-face integral equation (VSIE) domain decomposition method (DDM) using simplified prism vector (SPV) basis functions is presented for complex electrically large composite planar thin dielectric-perfect electric conductor objects. Compared with the recently developed SPV-based VSIE, this scheme considerably accelerates the convergence of iterative solutions by an effective preconditioner resulted from the DDM. Moreover, this DDM does not require imposing continuity conditions at the interfaces between adjacent subdomains, and the use of discontinuous Galerkin approach allows the nonconforming volume discretizations. Due to the nonconforming nature, subdomains can be built up separately, resulting in a flexible and convenient geometrical modeling. For composite subdomains involving thin dielectric layers, the full/half SPV basis is applied so that, in comparison with the generally used Schaubert–Wilton–Glisson basis, the number of unknowns is remarkably reduced. Several numerical examples are reported to illustrate the efficiency and fast convergence of this scheme.