Dielectric Multilayer Research Articles

Low-Loss Photonic Integrated Elements Based on Bound Bloch Surface Wave in the Continuum

A Bloch surface wave (BSW) confined at the surface of a truncated dielectric multilayer is a low-loss platform for chip-scale photonic integration. The guided BSW in a dielectric ridge is confined by the photonic band gap vertically, yet couples into the continuum modes of the multilayered substrate horizontally. We demonstrate that a low-loss BSW waveguide can be realized with the quasibound BSW modes in the continuum by engineering the geometric parameters, due to the destructive interference of multiple leakage channels in the multilayered substrate. In addition, a high-Q BSW resonator is obtained by optimizing the geometric parameter of the multilayered substrate, which provides an alternative way to realize ultrasmall resonators with a high-Q factor. The photonic integrated circuits on a low-loss BSW platform can be utilized for optical communications, enhancing light-matter interactions, and nonlinear optical applications.

Maximized Hole Trapping in a Polystyrene Transistor Dielectric from a Highly Branched Iminobis(aminoarene) Side Chain.

We synthesized highly branched and electron-donating side chain subunits and attached them to polystyrene (PS) used as a dielectric layer in a pentacene field-effect transistor. The influence of these groups on dielectric function, charge retention, and threshold voltage shifts (ΔVth) depending on their positions in dielectric multilayers was determined. We compared the observations made on an N-perphenylated iminobisaniline side chain with those from the same side chains modified with ZnO nanoparticles and with an adduct formed from tetracyanoethylene (TCNE). We also synthesized an analogue in which six methoxy groups are present instead of two amine nitrogens. At 6 mol % side chain, hopping transport was sufficient to cause shorting of the gate, while at 2 mol %, charge trapping was observable as transistor threshold voltage shifts (ΔVth). We created three types of devices: with the substituted PS layer as single-layer dielectric, on top of a cross-linked PS layer but in contact with the pentacene (bilayers), and sandwiched between two PS layers in trilayers. Especially large bias stress effects and ΔVth, larger than those in the case of the hexamethoxy and previously studied dimethoxy analogues, were observed in the second case, and the effects increased with the increasing electron-donating properties of the modified side chains. The highest ΔVth was consistent with a majority of the side chains stabilizing the trapped charge. Trilayer devices showed decreased charge storage capability compared to previous work in which we used less donating side chains but in higher concentrations. The ZnO and TCNE modifications resulted in slightly more and less negative ΔVth, respectively, when the side chain polystyrene was not in contact with the pentacene and isolated from the gate electrode. The results indicate a likely maximum combination of molecular charge stabilizing activity and side chain concentration that still allows gate dielectric function.

Lightweight, Ultra‐Wideband, and Polarization‐Insensitive Metamaterial Absorber Using a Multilayer Dielectric Structure for C‐ and X‐Band Applications

The design of a lightweight and ultra‐wideband absorber for C and X bands is still a challenge as the dimension of the absorber is relatively large in such a relatively low‐frequency band. Herein, an ultra‐wideband and lightweight metamaterial absorber (MMA) is presented for C‐ and X‐band applications. The unit cell of the proposed MMA consists of four copper sectors loaded by lumped resistors and a continuous copper ground plane, which is printed on two FR‐4 substrates. Furthermore, an airgap separating the FR‐4 layers is used as the active substrate medium of the MMA to achieve both ultra‐wideband absorption spectra and lightweight design. The MMA is investigated by simulation and measurement, showing that a good agreement is achieved. The result indicates that the absorptivity of the MMA under both transverse electric (TE) and transverse magnetic (TM) polarizations is greater than 90% in a wide range from 3.7 to 13.6 GHz for all polarization angles. Compared to other reported broadband absorbers, the proposed MMA shows an ultra‐wide absorption bandwidth and a lightweight design, which demonstrates a great potential for C‐and X‐band applications.

Effective plasma frequency in tunable THz reflectors based on graphene and phosphorene

In this work, we show that a THz reflector made of a phosphorene (graphene)–dielectric multilayer can be analyzed through a simple effective plasma frequency model. We obtain the cutoff frequency, marking the beginning of the transmission region in terms of the effective plasma frequency, which depends on structural parameters of the multilayer and, more importantly, on the carrier density of phosphorene (graphene) layers. This implies that the cutoff frequency can be varied when considering carrier density tuning. We also show that the frequency regime, where cutoff frequency is obtained by carrier density tuning, goes through a wide range in the THz domain (3–25 THz), making the design of tunable reflectors in these frequencies possible through electrical doping. We numerically analyze the cutoff frequency as a function of carrier density and optical thickness of the multilayer, finding that the cutoff frequency and carrier density of phosphorene (graphene) have a very simple quadratic (quartic) relation. Our analysis allows us to obtain ranges where the effective analytical model fits better with the cutoff frequency computed from photonic bands for the multilayer periodic structure.

The Effect of Si Surface Flattening Process on the MISFET With High-k HfNx Multilayer Gate Dielectrics

Metal-insulator-semiconductor field-effect transistors (MISFETs) with high-k HfN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> multilayer gate dielectrics fabricated with Si surface flattening process were investigated. The Si surface flattening process was carried out by Ar/1.0%H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> annealing for 30 min. A higher I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> on</sub> / I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> off</sub> current ratio was obtained by increasing the number of HfN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> gate dielectric layers while its characteristics such as drain current, saturation mobility and subthreshold swing (SS) are not markedly degraded. This is attributed to the thicker gate dielectrics. Furthermore, it is found that these characteristics are found to be effectively improved by Si surface flattening process.

Study of a Composite Consisting of Metal Nanoparticles in a Dielectric Matrix and Multilayer Bandpass Filters Based on It

Study of a Composite Consisting of Metal Nanoparticles in a Dielectric Matrix and Multilayer Bandpass Filters Based on It

Progress in Advanced Properties of Electrowetting Displays.

Electrowetting display (EWD) has promising prospects in the electronic paper industry due to it having superior characteristics, such as the ability to provide a comfortable reading experience and quick response. However, in real applications, there are also problems related to dielectric deterioration, excess power consumption, optical instability and narrow color gamut etc. This paper reviewed the existing challenges and recent progress made in terms of improving the optical performance and reliability of EWD. First, the principle of electrowetting applied in small and confined configurations is introduced and the cause of the failure of the dielectric layer is analyzed. Then, the function of the pixel structures is described to avoid display defects. Next, electric signal modulations are compared in terms of achieving good image quality and optical stability. Lastly, the methods are presented for color panel realization. It was concluded that multi-layer dielectrics, three-dimensional pixel structures, proper electric frequency-and-amplitude modulation and an RGB color panel are expected to resolve the current limitations and contribute to designing advanced reflective displays.

A Selective Solar Absorber for Unconcentrated Solar Thermal Panels

A new Selective Solar Absorber, designed to improve the Sun-to-thermal conversion efficiency at mid temperatures in high vacuum flat thermal collectors, is presented. Efficiency has been evaluated by using analytical formulas and a numerical thermal model. Both results have been experimentally validated using a commercial absorber in a custom experimental set-up. The optimization procedure aimed at obtaining Selective Solar Absorber is presented and discussed in the case of a metal dielectric multilayer based on Cr2O3 and Ti. The importance of adopting a real spectral emissivity curve to estimate high thermal efficiency at high temperatures in a selective solar absorber is outlined. Optimized absorber multilayers can be 10% more efficient than the commercial alternative at 250 °C operating temperatures, reaching 400 °C stagnation temperature without Sun concentration confirming that high vacuum flat thermal collectors can give important contribution to the energy transition from fossil fuels to renewable energy for efficient heat production.

Measurement and control of optical nonlinearities in dispersive dielectric multilayers.

Dispersive dielectric multilayer mirrors, high-dispersion chirped mirrors in particular, are widely used in modern ultrafast optics to manipulate spectral chirps of ultrashort laser pulses. Dispersive mirrors are routinely designed for dispersion compensation in ultrafast lasers and are assumed to be linear optical components. In this work, we report the experimental characterization of an unexpectedly strong nonlinear response in these chirped mirrors. At modest peak intensities <2 TW/cm2-well below the known laser-induced damage threshold of these dielectric structures-we observed a strong reflectivity decrease, local heating, transient spectral modifications, and time-dependent absorption of the incident pulse. Through computational analysis, we found that the incident laser field can be enhanced by an order of magnitude in the dielectric layers of the structure. The field enhancement leads to a wavelength-dependent nonlinear absorption, that shows no signs of cumulative damage before catastrophic failure. The nonlinear absorption is not a simply two-photon process but instead is likely mediated by defects that facilitate two-photon absorption. To mitigate this issue, we designed and fabricated a dispersive multilayer design that strategically suppresses the field enhancement in the high-index layers, shifting the high-field regions to the larger-bandgap, low-index layers. This strategy significantly increases the maximum peak intensity that the mirror can sustain. However, our finding of an onset of nonlinear absorption even at 'modest' fluence and peak intensity has significant implications for numerous past published experimental works employing dispersive mirrors. Additionally, our results will guide future ultrafast experimental work and ultrafast laser design.

Research on the spin Hall effect of light for nonlinear multilayer dielectrics and its bistable and nonreciprocal features

In this paper, by utilizing the transfer matrix method, a structure composed of one-dimensional (1D) periodic multilayer dielectrics, InSb, and nonlinear material is proposed to investigate the behavior of the spin Hall effect of light (SHEL) and its nonreciprocity and bistable features. The results demonstrate that, as the light intensity increases, the reflection coefficients under both TM and TE waves have a bistable phenomenon, and the points of both horizontal and vertical displacements are consistent with the regions where reflection is close to 0. Furthermore, to make our study complete, the thicknesses of the nonlinear and InSb layers are adjusted to study the effects on the performance of SHEL, and it can be found that, with the escalation of the thicknesses of the nonlinear and InSb layers, all the points of displacements are shifting to the direction of the angle. Besides, all parameters demonstrate the phenomenon of nonreciprocity. This research supplies meaningful guidelines for some optical instruments, such as light intensity sensors.

Computational Failure Analysis of Resistive RAM Used as a Synapse in a Convolutional Neural Network for Image Classification

Abstract Various NVM technologies are being explored for neuromorphic system realization, including resistive RAM, ferroelectric RAM, phase change RAM, spin transfer torque RAM, and NAND flash. This article discusses the potential of RRAM for such applications and evaluates key performance and reliability metrics in the context of neural network image classification. The authors conclude that the accuracy-power tradeoff may be further improved using alternative material stacks and multi-layer dielectrics so as to achieve better control of the oxygen vacancy or metallic filamentation process that governs RRAM switching characteristics.

Electric Field and DC Breakdown Voltage of Multi-layer Dielectrics in Parallel-Plane Geometry

In this paper, the electric field, space charge and temperature distributions across a double layered dielectric are investigated under DC voltage. The dissimilarity of material properties of different layers, the effect of electric field and temperature dependent conductivity are found to play critical role in the electro-thermal problem of multi-dielectrics. At the interface, Maxwell-Wagner polarization is incorporated for electric field and interfacial charge, while temperature is considered as a continuous function of space inside the material. The current continuity equation, thermal continuity equation and Poisson's equation are simultaneously solved using numerical methods in parallel-plane electrode geometry. The electric field distribution, temperature distribution, space charge distribution and thermal breakdown limits are obtained at various boundary temperatures for different thickness proportions of layers.

High-temperature BaTiO3-based ternary dielectric multilayers for energy storage applications with high efficiency

High-temperature BaTiO3-based ceramic capacitors have broad application prospects in energy storage devices. However, energy density and efficiency of BaTiO3-based ceramic capacitors are bottleneck challenges that limit the applications of ceramic capacitors in the vast of industrial applications. To address this issue, it needs to design novel BaTiO3-based ceramics to elevate the breakdown strength, energy density and efficiency of capacitors. Here, high performance BaTiO3-based ceramics with breakdown strength of 290 kV cm−1, discharge energy density is more than 2.4 J cm−3, energy storage efficiency is achieve 91.5% are achieved in novel ternary system 0.88BaTiO3-0.12(1-x)Bi(Li0.5Nb0.5)O3-0.12xBi(Mg0.5Ti0.5)O3 (BT-BLN-BMT) (0.2 ≤ x ≤ 0.8) lead-free ceramic. Moreover, 0.88BT-0.12(1-x)BLN-0.12xBMT (x = 0.6) multilayer ceramics capacitors effectively increased breakdown strength and energy density values are more than 500 kV cm−1 and 4.42 J cm−3, improved by 488% and 1373% compared with only 85 kV cm−1 and 0.3 J cm−3 for the pure BaTiO3. It maintains high thermal stability in the temperature range from 25 °C to 150 °C. All these results have clearly collaborated the promising future of this novel BaTiO3-based ceramics in energy storage applications in the future.

Bilayer polymer dielectric systems for high response NO2 gas sensors

In this study, the effects of bilayer polymer dielectric systems on the characteristic of nitrogen dioxide (NO2) gas sensors and organic field effect transistor (OFET) were investigated. Different bilayer polymer dielectrics were obtained by depositing polymethyl methacrylate (PMMA) films on monolayer polystyrene (PS), polyvinyl pyrrolidone (PVP), or PMMA films by spin coating. The responsivity of PS/PMMA-based sensors to 30 ppm NO2 gas is up to 7633%, which is 35.7% higher than that of PMMA/PMMA-based sensors. Meanwhile, the sensitivity to NO2 gas has increased from the lowest 191%/ppm to 265%/ppm. The copper phthalocyanine (CuPc) film on PS/PMMA dielectric layer is induced to form more gaps between the rod domains, which are favorable to the gas interaction. The response mechanism was proposed that the equivalent three-dimensional sensing films caused by multi-layer polymer dielectrics play a significant role in the remarkable increase of gas response.

Impact of Window Penetration Loss on Building Entry Loss From 3.5 to 24 GHz

We investigated the impact of window penetration loss (WinPL) on the frequency dependence of building entry loss (BEL) from 3.5 to 24 GHz. The WinPL characteristics of an ideal double-glazed glass and an actual double-glazed window were simulated and measured on-site, respectively, and both results showed almost the same oscillatory characteristics with respect to the frequency changes that occurred due to the impedance oscillation of the double glass-like multilayer dielectrics. Two BEL measurement scenarios were examined to analyze the frequency dependence of BEL in a traditional office building with double-glazed windows identical to those analyzed in the on-site WinPL measurements. The experiments included a complex propagation route (the first scenario) from the facade of the building to the corridors through windows and offices and a simple propagation route (the second scenario) through only windows lateral to the building. The two main findings are (i) BEL showed strong frequency-dependent behavior regardless of the propagation route and (ii) the WinPL characteristics of the outer double-glazed window were the main contributors to the frequency dependence of BEL.

Tuning of Laser Damage Threshold by Adjusting Field Zones in Multilayer Dielectric Coatings

Tuning of Laser Damage Threshold by Adjusting Field Zones in Multilayer Dielectric Coatings

A bidirectional threshold switching selector with a symmetric multilayer structure

Selectors have been proposed as a highly effective tool for suppressing substantial leakage currents without sacrificing the high density of resistive random-access memory (RRAM) crossbar arrays. Among various selector types, the programmable metallization cell (PMC) selector is promising due to its simple structure and high selectivity. In this work, we demonstrate a new PMC selector that exhibits bidirectional threshold switching behavior by implementing symmetric multilayer dielectrics. The proposed Ag/SiTe/HfO$_{2}$/SiTe/Ag selector device has a low off current ($ 10^{5}$), and low threshold voltage variation ($<$ 0.05). Upon connection to a bipolar RRAM cell via a wire, the proposed selector successfully suppresses the leakage current of an unselected device below the threshold voltage.

Enhanced transmission induced by embedded graphene in periodic, quasiperiodic, and random photonic crystals

The study of photonic crystals, artificial materials whose dielectric properties can be tailored according to the stacking of their constituents, remains an attractive research field, and it is the basis of photonic devices based on the generation, processing, and storage of photons. In this paper, we employ a transfer-matrix treatment to study the propagation of light waves in periodic, quasiperiodic (Fibonacci, Octonacci, and Dodecanacci), and random dielectric multilayers with graphene embedded. The structures considered here are composed of two building blocks, silicon dioxide (building block A = S i O 2 ) and titanium dioxide (building block B = T i O 2 ). We calculate their transmission spectra as a function of incident angle θ and reduced frequency Ω . Our main goal is to investigate the enhancement of the transmission due to the presence of graphene. In particular, we show that bandgap regions become passband regions when graphene is embedded in the optical multilayers. More specifically, for a range of the incident angle θ and reduced frequency Ω , the PCs with graphene embedded display an unexpected property: the electromagnetic radiation is transmitted mainly through the multilayers and not reflected or absorbed as expected for large structures.

Evaluating the Accuracy of Reconstruction of the Electrical and Geometric Parameters of Multilayer Dielectric Coatings by a Multifrequency Radio-Wave Method for Slow Surface Electromagnetic Waves

One of the most important problems in the diagnostics of multilayer dielectric materials and coatings is the development of methods for quantitative interpretation of the results of monitoring the electrical and geometric parameters of these materials. Results are presented from a study of the potential informativeness of a multifrequency radio-wave method for slow surface electromagnetic waves for reconstruction of the electrical and geometric parameters of multilayer dielectric coatings. A simulation model is shown for evaluating the accuracy of reconstructing the electrical and geometric parameters of multilayer dielectric coatings. The model takes into account the electrical and geometric parameters of the coating, the level of noise in the measurement data, and the measurement bandwidth. Simulation modeling and experimental test data for the reconstruction of the relative dielectric constants and thicknesses of one- and two-layer equal-thickness dielectric coatings based on polymethyl methacrylate, ftoroplast (teflon) F-4D, and RO3010 for different values of the mean square deviation of the noise level in the measured attenuation coefficients for the field of a slow surface electromagnetic wave. The accuracy of the reconstruction of the geometric and electrical parameters of the layers is found to decrease as the number of estimated parameters and the noise level increase, as well as when the dielectric constant and thickness of the layers are reduced. Experimental data confirm the adequacy of the simulation model developed here. This model can be used for a specific measurement complex employing a multifrequency radio-wave technique for slow surface electromagnetic waves to estimate quantitatively the potential possible accuracy of reconstructing the geometric and electrical parameters of multilayer dielectric materials and coatings. A simulation model and experimental study of a multilayer dielectric coating show that for a measurement bandwidth of 1 GHz the errors in estimating the dielectric constants and thicknesses of the layers do not exceed 10% with a confidence coefficient of 0.95 for a mean square deviation of 0.003–0.004 in the noise level.

Tunable Ultra‐High Q‐Factor and Figure of Merit based on Fano Resonance in Graphene–Dielectric Multilayer Corrugated Structure

AbstractHigh‐performance sensors have been a focus of the nanophotonics in recent years owing to their great potential for use in medical diagnosis and environmental remediation. Particularly, the sensing properties based on graphene have attracted intensive interest. Yet, low quality‐factor (Q‐factor) and figure of merit (FOM) have limited significant device performance. Here, a graphene–dielectric–graphene corrugated structure is proposed, the simulations show that by introducing the graphene the Q‐factor becomes tunable and can be significantly improved. The transmission and reflection spectra exhibit asymmetric Fano resonance with ultra‐narrow width that depends on the Fermi energy and modulation amplitude. Based on the high Q‐factor of the structure, the sensing properties of the structure are exploited when introducing sensing medium. For the shallow grating modulation, ultra‐high FOM is obtained. The proposed structure based on graphene has a promising potential for designing and fabricating novel refractive index sensors.