Dielectric Region Research Articles

A Dielectric Panel Design for RCS Reduction and EM Shielding

A novel dielectric panel structure that contains no metal layer or conductive compound is proposed for electromagnetic shielding and radar cross section (RCS) reduction uses. It is configured as a planar slab with periodically positioned holes. By choosing appropriate slab thickness, material properties, aperture-to-dielectric area ratio, and hole spacing, the holey panel can suppress reflection and transmission at the same time for plane wave incidences. It conceals back scattering features of targets behind and the panel-to-target distance is not necessarily a fixed number. A thorough analysis is provided to explain how this metalless, nonabsorptive, periodic structure reduces the reflection level by deforming the plane wave with the propagation delay difference between air and dielectric regions. Simulated and measured results of a prototype designed in the E-band indicate that it can provide more than 15 dB RCS reduction at the designated transmission suppressing frequency and the 10 dB reduction bandwidth is more than 20%.

Hybrid Surface Electric Field Volume Magnetic Field Integral Equations for Electromagnetic Analysis of Heterogeneous Dielectric Bodies With Embedded Electrically Conducting Structures

In this article, hybrid surface electric field volume magnetic field integral equations (SEVMIE) for electromagnetic analysis of heterogeneous dielectric bodies with embedded perfect electrical conductor (PEC) structures are presented. These are then solved using a quasi-exact vector moment method employing mixed order edge-based divergence conforming basis functions to expand the current on the PEC surface and node-based linear Lagrangian basis functions to expand the magnetic field within the dielectric region. For an incident plane wave scattered by the combined structure, this procedure results in a linear matrix equation for the surface currents and the volume magnetic fields. The method is demonstrated for three spherical test cases and the results compared to those obtained by a semi-analytic Mie series expansion. The performance is compared to that of the well-known volume surface integral equation (VSIE) method and found to provide more accurate results with approximately one-third the number of degrees of freedom. The method is then demonstrated on the scattering cross section calculation of a heterogeneous composite structure. This new method enables the efficient and accurate analysis of composite structures with large dielectric regions.

Enabling bottom-up nanoelectronics fabrication by selective sol–gel dielectric-on-dielectric deposition

Self-aligned patterning schemes for microelectronics fabrication require area-selective deposition processes. In this context, a sol–gel-based selective dielectric-on-dielectric deposition with respect to metal is reported. The selective deposition is achieved by first de-wetting a solution from the lyophobic surface areas and second ensuring uniform organosilicate polymer deposition during a droplet drying on the lyophilic surface regions. The de-wetting occurs when a critical volume for de-wetting is reached as a result of capillary solution draining. De-wetting from 1 µm wide lyophobic copper area separating lyophilic rectangular dielectric (SiO2) regions with a width as narrow as 4 µm is demonstrated. The subsequent solution drying results in a 200 nm thick dielectric film.

Dual-wide band plasmonic filter based on nanocomposite media

A dual, wide band pass metal–insulator–metal plasmonic filter based on nanocomposite media in the near-infrared band, 0.75 to 2.5 μm wavelength range, is proposed. Simulation results show that the pass bands can be adjusted to proper ranges by changing the size of the device and the relative permittivity of the dielectric region. Due to the importance of small structures in optical integration, we focused on tuning the transmitted bands by changing the dielectric relative permittivity. Realization of any desired relative permittivity for the dielectric region may be difficult using general dielectrics. In this way, the dielectric region is designed based on nanocomposite media, which no previous studies have focused on. Dielectric region is realized by a polymeric medium, poly-methyl-methacrylate, that consists of random distribution of guest spherical silver nanoparticles. The proper permittivity and consequently, the desired pass bands are obtained by changing the fill fraction of guest nanoparticles.

(Invited) Hybrid Wafer Bonding – The Fusion of Low Temperature Dielectric and Metal Bonding Technologies

There are two driving goals in wafer bonding. One is to use wafer bonding methods to engineer starting materials; to integrate silicon with any other material to enable hetero-device architectures. The second is to continually shrink device footprints by bonding layers of devices vertically. Low temperature wafer bonding combined with advances in CMP (chemical mechanical polishing), temporary bonding, and advanced metrology characterization tools are enabling researchers to achieve these goals. In particular, hybrid bonding, which enables simultaneous bonding of dielectric and metallic regions at an interface has produced extremely high-performance devices and miniaturization of display technologies. This talk will highlight the various requirements for hybrid bonding and critical specifications for implementing complex bonding methods.

Comparison of dielectric loss in titanium nitride and aluminum superconducting resonators

Lossy dielectrics are a significant source of decoherence in superconducting quantum circuits. In this report, we model and compare the dielectric loss in bulk and interfacial dielectrics in titanium nitride (TiN) and aluminum (Al) superconducting coplanar waveguide resonators. We fabricate isotropically trenched resonators to produce a series of device geometries that accentuate a specific dielectric region's contribution to the resonator quality factor. While each dielectric region contributes significantly to loss in TiN devices, the metal–air interface dominates the loss in the Al devices. Furthermore, we evaluate the quality factor of each TiN resonator geometry with and without a post-process hydrofluoric etch and find that it reduced losses from the substrate–air interface, thereby improving the quality factor.

Influence of the degree of spatial coherence on the Goos–Hänchen shifts for a three-dimensional Dirac semimetal

We study the behavior of Goos–Hänchen shift (GHS) using s- and p-polarized partial coherent beam incident on three-dimensional (3D) Dirac semimetal. By studying the real part of permittivity of 3D Dirac semimetal, we identify the dielectric, epsilon near zero (ENZ) metamaterial, and metallic regions for the incident wavelength. Interestingly, for s- and p-polarized partial coherent beam, we get a completely different behavior of GHS in the reflected beam in the dielectric and metallic regions. Some factors such as spatial coherence, the wavelength and spatial width of the incident beam, temperature, and thickness of 3D Dirac semimetal are discussed in the influence of GHS. We can have negative and positive GH shifts in these three regions of Dirac semimetal for s- and p-polarized partial coherent beam.

(Invited) Hybrid Wafer Bonding – The Fusion of Low Temperature Dielectric and Metal Bonding Technologies

There have typically been two pinnacle goals in wafer bonding. The first and ongoing goal is to use wafer bonding methods to engineer starting materials; to integrate silicon with any other material to enable hetero-device architectures. The second aspiration is to continually shrink device footprints by bonding layer upon layer of devices vertically. Low temperature wafer bonding combined with advances in CMP (chemical mechanical polishing), temporary bonding, and advanced metrology characterization tools are enabling researchers to achieve these dreams come true. In particular, hybrid bonding, which enables simultaneous bonding of dielectric and metallic regions at the bond interface has produced extremely high performance devices and miniaturization of display technologies. This talk will highlight the various requirements for hybrid bonding and critical specifications for implementing complex bonding methods.

Carrier density modulation and photocarrier transportation of graphene/InSb heterojunction middle-wavelength infrared photodetectors

The photoresponse mechanism of graphene/InSb heterojunction middle-wavelength infrared (MWIR) photodetectors was investigated. The devices comprised a graphene/InSb heterojunction as a carrier-injection region and an insulator region of graphene on tetraethyl orthosilicate (TEOS) for photogating. The MWIR photoresponse was significantly amplified with an increase in the graphene/TEOS cross-sectional area by covering the entire detector with graphene. The graphene-channel dependence of the MWIR photoresponse indicated that the graphene carrier density was modulated by photocarrier accumulation at the TEOS/InSb boundary, resulting in photogating. The dark current of the devices was suppressed by a decrease in the graphene/InSb carrier-injection region and the formation of the heterojunction using an n-type InSb substrate. The results indicate that photocarrier transportation was dominated by the formation of a Schottky barrier at the interface of the graphene/InSb heterojunction and a Fermi-level shift under bias application. The high-responsivity and low-dark-current photoresponse mechanism was attributed to the graphene/InSb heterojunction diode behavior and the photogating effect. The devices combining the aforementioned features had a noise equivalent power of 0.43 pW / Hz1/2. The results obtained in our study will contribute to the development of high-performance graphene-based IR image sensors.

Polyadenylation of Histone H3.1 mRNA Promotes Cell Transformation by Displacing H3.3 from Gene Regulatory Elements.

SummaryReplication-dependent canonical histone messenger RNAs (mRNAs) do not terminate with a poly(A) tail at the 3′ end. We previously demonstrated that exposure to arsenic, an environmental carcinogen, induces polyadenylation of canonical histone H3.1 mRNA, causing transformation of human cells in vitro. Here we report that polyadenylation of H3.1 mRNA increases H3.1 protein, resulting in displacement of histone variant H3.3 at active promoters, enhancers, and insulator regions, leading to transcriptional deregulation, G2/M cell-cycle arrest, chromosome aneuploidy, and aberrations. In support of these observations, knocking down the expression of H3.3 induced cell transformation, whereas ectopic expression of H3.3 attenuated arsenic-induced cell transformation. Notably, arsenic exposure also resulted in displacement of H3.3 from active promoters, enhancers, and insulator regions. These data suggest that H3.3 displacement might be central to carcinogenesis caused by polyadenylation of H3.1 mRNA upon arsenic exposure. Our findings illustrate the importance of proper histone stoichiometry in maintaining genome integrity.

Behaviour of Poynting vector for dielectric-metal-dielectric optical waveguides and applications

In this paper, we derive analytical expressions for the spatial evolution of the instantaneous Poynting vector for the transverse magnetic (TM) surface plasmon (SP) modes of a symmetric planar dielectric-metal-dielectric optical waveguide. We discuss the behaviour of the Poynting vector in the metal film due to the optical absorption of electromagnetic waves propagating through the medium to excite the surface plasmons in a resonant manner in the metal film at the interface. This optical absorption of the electromagnetic waves results in a finite propagation length of SP modes. We derive an analytical formula for the penetration depth of the instantaneous Poynting vector in the dielectric cladding regions and show that it is different as compared to the penetration depth of the average Poynting vector. We utilize this analytical formula to calculate the optimum thickness of the affinity layer in a graphene-based surface plasmon resonance (SPR) biosensor and analyze its performance in terms of sensitivity and Figure-of-Merit. We also show that our analytical formula can be used to calculate the optimum thickness of a thin high-index dielectric layer which is added to any conventional SPR based sensor to enhance its sensitivity. The optimum thickness thus calculated correlates closely with the experimental results that have been published previously. The analysis done in this paper can also be utilized in calculating the separation between any two adjacent waveguides/optical films which are coupled together evanescently, such as directional couplers and TE/TM polarisers.

Phase-Gradient Metasurfaces Based on Local Fabry–Pérot Resonances

In this work, we present a new mechanism for designing phase-gradient metasurfaces (PGMs) to control an electromagnetic wavefront with high efficiency. Specifically, we design a transmission-type PGM, formed by a periodic subwavelength metallic slit array filled with identical dielectrics of different heights. It is found that when Fabry–Pérot (FP) resonances occur locally inside the dielectric regions, in addition to the common phenomenon of complete transmission, the transmitted phase differences between two adjacent slits are exactly the same, being a nonzero constant. These local FP resonances ensure total phase shift across a supercell, fully covering a range of 0 to 2π, satisfying the design requirements of PGMs. Further research reveals that, due to local FP resonances, there is a one-to-one correspondence between the phase difference and the permittivity of the filled dielectric. A similar approach can be extended to the reflection-type case and other wavefront transformations, creating new opportunities for wave manipulation.

Small footprint symmetrical graphene hybrid plasmonic waveguides for high-speed broadband optical modulation

In this work, nanowire-based symmetrical graphene hybrid plasmonic waveguides for possible broadband optical modulation have been proposed. The full-vectorial finite element method has been employed to analyze the modal properties and modulation characteristics of the proposed structures. The fundamental supermode supported by these geometries is evolved from a near-field coupling between metallic and dielectric nanowires. Here, the strong optical capacitance effect in the low-index dielectric gap region has been exploited to enhance light–graphene interaction in the subwavelength device size. Thus, the optical absorption of graphene significantly increases. Therefore, the structures even with their small footprints offer a very high extinction ratio and small energy consumption per bit (as low as 0.9 fJ/bit), simultaneously with appreciably high modulation bandwidth at the telecommunication wavelength. A substantially small variation of modulation performance for a broad range of operation wavelength and gap widths suggest their broadband operability. Furthermore, the modulation performance has been studied incorporating the optical anisotropy of graphene. Thus, the proposed waveguides show a good promise in high-speed broadband optical modulation.

Shrinking the surface plasmon

AbstractSurface plasmons at an interface between dielectric and metal regions can in theory be made arbitrarily compact normal to the interface by introducing extreme anisotropy in the material parameters. We propose a metamaterial structure comprising a square array of gold cylinders and tune the filling factor to achieve the material parameters we seek. Theory is compared to a simulation wherein the unit cell dimensions of the metamaterial are shown to be the limiting factor in the degree of localisation achieved.

Synthesis, mesomorphic and dielectric properties of new bent-core liquid crystal with a terminal lactate group

The synthesis, liquid crystalline properties and dielectric properties of a new bent-core compound (DBOB) composed of terephthalate based rod-like units with a O-dodecyl lactate group substituted at one side as well as n-octyloxy located at other terminal are presented. The liquid crystalline properties have been investigated by polarizing optical microscopy, differential scanning calorimetry and electro-optical studies. The dielectric parameters and phase regions of DBOB, which exhibits an enantiotropic non-polar SmA phase between 156 and 100 °C as well as SmA phase with a ferroelectric polar response at lower temperatures than 100 °C, have been carried out by impedance spectroscopy at different temperatures. The dielectric relaxation mechanisms have been analyzed by Cole-Cole plots. The Debye distribution parameters and activation energies have also been determined.

Analytical model of a novel double gate metal-infused stacked gate-oxide tunnel field-effect transistor (TFET) for low power and high-speed performance

Abstract In this work, an innovative structure of a novel double gate tunnel field-effect transistor (TFET) is proposed with a channel length of 20 nm.The gate dielectric regions have been renovated by inserting metal strips and using stacked gate-oxide concept. The device exhibits suppressed ambipolar current, excellent subthreshold swing and good ION/IOFF ratio. The proposed structure proves to be a promising candidate for high speed applications as it shows lesser gate-capacitance than conventional stacked-oxide gate structure. The surface potential and electric field have been modelled considering the depletion regions, using 2-D Poisson's equation with appropriate boundary conditions, based on parabolic potential approximation. A semi-empirical method has been utilized to incorporate the effect of mobile charges on the device characteristics. A physics-based model for charge and terminal capacitances has been derived, following the potential model. The drain current model is able to accurately predict the ambipolar current as well as the effects of drain voltage in saturation region. Proper optimization of the device structure has been performed to derive the best desired electrical characteristics. SILVACO ATLAS simulation data have been used to validate the analytical results of the proposed structure, thereby corroborating the precision of the present analytical model. Finally, an inverter circuit has been designed in CADENCE circuit-simulation environment to justify the usage of our device in low power and high speed digital circuit applications.

Broadband dielectric spectroscopy of La0.65Sr0.35MnO3@TiO2 core–shell nanocomposites

Core–shell composites of ferromagnetic conducting nanoparticles La0.65Sr0.35MnO3 (LSMO) embedded in an insulating matrix of TiO2 (LSMO@TiO2) have been processed, structurally and magnetically characterized, and their DC magnetoresistivity and complex dielectric response measured and fitted from Hz up to the infrared (IR) range (1014 Hz). XRD indicates that the TiO2 shells are amorphous. Modelling of the IR spectra using standard models based on the effective medium approximation has it confirmed and has characterized the effective phonon modes of the LSMO nanoceramics and LSMO@TiO2 composite. Modelling of the lower-frequency spectra has shown that TiO2 shell thicknesses are rather non-uniform down to thin nm values, which leads to giant low-frequency permittivity values and non-negligible free-carrier tunnelling among the LSMO cores. Two main dielectric dispersion regions were observed and shown to be due to the inhomogeneous conductivity—the one occuring in the 1011–1012 Hz range relates to nonmagnetic less-conducting dead layers on the surface of LSMO nanocrystallites and the broad second one below the 1010 Hz range is due to the non-uniform thicknesses of the dielectric TiO2 shells. In the IR range, effective phonon modes of the LSMO nanoceramics and LSMO@TiO2 composite were characterized from the reflectivity spectra.

BCS-BEC crossover in a (t2g)4 excitonic magnet

The condensation of spin-orbit-induced excitons in $(t_{2g})^4$ electronic systems is attracting considerable attention. In the large Hubbard U limit, antiferromagnetism was proposed to emerge from the Bose-Einstein Condensation (BEC) of triplons ($J_{\textrm{eff}} = 1$). In this publication, we show that even for the weak and intermediate U regimes, the spin-orbit exciton condensation is possible leading also to staggered magnetic order. The canonical electron-hole excitations (excitons) transform into local triplon excitations at large U , and this BEC strong coupling regime is smoothly connected to the intermediate U excitonic insulator region. We solved the degenerate three-orbital Hubbard model with spin-orbit coupling ($\lambda$) in one-dimensional geometry using the Density Matrix Renormalization Group, while in two-dimensional square clusters we use the Hartree-Fock approximation (HFA). Employing these techniques, we provide the full $\lambda$ vs U phase diagrams for both one- and two- dimensional lattices. Our main result is that at the intermediate Hubbard U region of our focus, increasing $\lambda$ at fixed U the system transitions from an incommensurate spin-density-wave metal to a Bardeen-Cooper-Schrieffer (BCS) excitonic insulator, with coherence length r coh of O(a) and O(10a) in 1d and 2d, respectively, with a the lattice spacing. Further increasing $\lambda$, the system eventually crosses over to the BEC limit (with r coh << a).

Performance Investigation of Pentacene Based Organic Double Gate Field Effect Transistor and its Application as an Ultrasensitive Biosensor

In this paper, the electrical performance of double gate organic field effect transistor (DG-OFET) are thoroughly investigated and feasibility of the device as an efficient biosensor is comprehensively assessed. The introduced device provides better gate control over the channel, yielding better charge injection properties from source to channel and providing higher on-state current in comparison with single gate devices. The susceptibility of fundamental electrical parameters with respect to the variation of design parameters is thoroughly calculated. In particular, standard deviation and average value of main electrical parameters signify that metal gate workfunction, channel thickness and gate oxide thickness are fundamental design measures that may modify the device efficiency. The insensitivity of off-state current to the change of channel length and drain bias confirms feasibility of the device in nanoscale regime. Next, a nano cavity is embedded in the gate insulator region for accumulation of biomolecules. The immobilization of molecules with different dielectric constants in the gate insulator hollow alters the gate capacitance and results in the drain current deviation with respect to the air- filled cavity condition. It is shown that by the occupancy of whole volume of the nanogap, a maximum range of on-state current variation can be achieved.

Phase Diagram and Mechanism of Superconductivity in Strongly Correlated Electrons

We investigate the phase diagram of two-dimensional (2D) Hubbard model by employing the optimization variational Monte Carlo method. The 2D Hubbard model is the most simple electronic model for cuprate high-temperature superconductors. The phase diagram consists of three regions; they are antiferromagnetic insulator region, superconducting region, and the coexistent region of superconductivity and antiferromagnetism. The phase diagram obtained by numerical calculations well agrees with the experimental phase diagram for high-temperature cuprates.