Conventional Dielectric Materials Research Articles

Anisotropic dielectric dispersions and thermal behaviors in highly textured BN thin films for heat self-dissipating electronics

Mainstream high-k gate materials, such as SiO2, Al2O3, and HfZrO2, are in demand for modern electronics. However, these dielectrics possess lower thermal conductivity, significantly limiting thermal dissipation in electronic devices. Herein, we propose the utilization of complementary metal-oxide semiconductor- (CMOS) compatible high power impulse magnetron sputtering (HiPIMS) for the mass production of highly textured hexagonal boron nitride (h-BN) on (100)-, (110)-, and (111)-oriented SrTiO3 substrates. The as-prepared films exhibit distinct vertical alignments, as evidenced by HRTEM and FTIR analysis. Notably, the R value, ranging from 0.46 to 0.50, is associated with the stress in the film. Importantly, distinct anisotropies in thermal conductivity, dielectric constant, and optical band gap are observed. Furthermore, the values of thermal conductivity in these highly textured h-BN films are 4.5, 5.7, and 5.3 Wm−1K−1, which is almost three times larger than those of SiO2 (1.4 Wm−1K−1) and Al2O3 (1.35 Wm−1K−1), and even an order of magnitude larger than that of HfZrO2 (0.67 Wm−1K−1). The combination of excellent dielectric characteristics, favorable thermal conductivity, and superior stability over a broad temperature range makes this novel material outperform conventional dielectric gate materials in high-power electronics applications.

High Energy Density Achieved in Novel Lead-Free BiFeO3-CaTiO3 Ferroelectric Ceramics for High-Temperature Energy Storage Applications.

The development of high-performance electrostatic energy storage dielectrics is essential for various applications such as pulsed-power technologies, electric vehicles (EVs), electronic devices, and the high-temperature aviation sector. However, the usage of lead as a crucial component in conventional high-performance dielectric materials has raised severe environmental concerns. As a result of this, there is an urgent need to explore lead-free alternatives. Ferroelectric ceramics offer high energy density but lack stability at high temperatures. Here we present a lead-free (1 - x)BiFeO3-xCaTiO3 (x = 0.6, 0.7, and 0.8; BFO-CTO) ceramic capacitor with low dielectric loss, high thermal stability, and high energy density up to ∼200 °C. The introduction of CTO (x = 0.7) to the BFO matrix triggers a transition from the normal ferroelectrics to the relaxor ferroelectrics state, resulting in a high recoverable energy density of 1.18 J cm-3 at 190 °C with an ultrafast dielectric relaxation time of 44 μs. These results offer a promising, environmentally friendly, high-capacity ceramic capacitor material for high-frequency and high-temperature applications.

On the Working Mechanisms of Molecules-Based Van der Waals Dielectrics.

Sb2 O3 molecules offer unprecedented opportunities for the integration of a van der Waals (vdW) dielectric and a 2D vdW semiconductor. However, the working mechanisms underlying molecules-based vdW dielectrics remain unclear. Here, the working mechanisms of Sb2 O3 and two Sb2 O3 -like molecules (As2 O3 and Bi2 O3 ) as dielectrics are systematically investigated by combining first-principles calculations and gate leakage current theories. It is revealed that molecules-based vdW dielectrics have a considerable advantage over conventional dielectric materials: defects hardly affect their insulating properties. This shows that it is unnecessary to synthesize high-quality crystals in practical applications, which has been a long-standing challenge for conventional dielectric materials. Further analysis reveals that a large thermionic-emission current renders Sb2 O3 difficult to simultaneously satisfy the requirements of dielectric layers in p-MOS and n-MOS, which hinders its application for complementary metal-oxide-semiconductor (CMOS) devices. Remarkably, it is found that As2 O3 can serve as a dielectric for both p-MOS and n-MOS. This work not only lays a theoretical foundation for the application of molecules-based vdW dielectrics, but also offers an unprecedentedly competitive dielectric (i.e., As2 O3 ) for 2D vdW semiconductors-based CMOS devices, thus having profound implications for future semiconductor industry.

Performance of MOS Capacitor with Different Dielectric Material Simulated Using Silvaco TCAD Tools

Metal oxide semiconductor (MOS) capacitor is a trilayer device that comprises of metal, dielectric, and semiconductor layer. The advancement of MOS technology has greatly give huge improvement to MOS devices which lead to scaling down the MOS devices. The reduction of dielectric thickness of conventional dielectric material has coming to an end, therefore as alternative new material with high mobility carrier is suggested to overcome the problem. The objectives of this work are to study the performance of MOS capacitor. Two parameters were varied, first the semiconductor material which is silicon (Si), germanium (Ge) and silicon germanium (SiGe) and second is the dielectric material that is silicon dioxide (SiO2) and silicon nitride (Si3N4). The performance of the MOS capacitor is evaluated based on the capacitance-voltage (C-V) and current-voltage (I-V) characteristics. Silvaco TCAD tool were use as as simulation tool for the method of investigation. Result shown that the performance of the MOS capacitor increased when Ge and SiGe were used as semiconductor material and Si3N4 as dielectric layer. It can see that with VT of 4.15 V for MOS with Ge and 4.28 V for MOS with SiGe. For the C-V properties Cmax value for both devices are F and F, respectively. The results show that there is around 100% increment in capacitance value when Ge is used as semiconductor layer but there is no increment or decrement in capacitance value when SiGe is used. Based on the obtained results, Ge is chosen as the best semiconductor material.

Ultrahigh Energy Storage in 2D High-κ Perovskites

Dielectric capacitors have greater power densities than batteries, and, unlike batteries, they do not utilize chemical reactions during cycling. Thus, they can become ideal, safe energy storage devices. However, dielectric capacitors yield rather low energy densities compared with other energy storage devices such as batteries and supercapacitors. Here, we present a rational approach for designing ultrahigh energy storage capacitors using two-dimensional (2D) high-κ dielectric perovskites (Ca2Nam-3NbmO3m+1; m = 3-6). Individual Ca2Nam-3NbmO3m+1 nanosheets exhibit an ultrahigh dielectric strength (638-1195 MV m-1) even in the monolayer form, which exceeds those of conventional dielectric materials. Multilayer stacked nanosheet capacitors exhibit ultrahigh energy densities (174-272 J cm-3), high efficiencies (>90%), excellent reliability (>107 cycles), and temperature stability (-50-300 °C); the maximum energy density is much higher than those of conventional dielectric materials and even comparable to those of lithium-ion batteries. Enhancing the energy density may make dielectric capacitors more competitive with batteries.

A new perception to the spectroscopic, dielectric and impedance behavior of graphene oxide

The present study explores the synthesis of graphene oxide (GO) using Hummer’s method followed by a characterization that uses XRD, FTIR, Raman spectroscopy, UV, zeta potential, dielectric, and impedance study. The study of XRD, FTIR, UV, and Raman spectra revealed the presence of polar functional groups containing oxygen and structural deformity induced in GO. The nature of the surface charge, hydrodynamic diameter, and stability of graphite and GO in colloidal solution was ascertained from the zeta potentiometer. Raman spectra and zeta potential showed the presence of defects. The dielectric study of GO pellets with variation in frequency (1 Hz to 1 MHz) revealed the large dielectric constant of GO (∼105 at 26 °C and 1 Hz), which is comparable to conventional perovskite titanates dielectric materials. Both Lydanne–Sachs–Teller (LST) and Debye’s models of dielectric relaxation were taken into account while explaining the findings of giant dielectric constant in GO. Various mechanisms such as the presence of polar groups, Dirac fermions, and surface plasmon resonance have been discussed to explain the giant dielectric constant and its subsequent variation with frequency. The frequency dependence impedance and dielectric spectra were fitted using origin software to analyze poly dispersive nature and departure from Debye’s relaxation with an appraisal of static dielectric constant, static resistance, optical dielectric constant, optical resistance, mean relaxation time, and spreading factor. Nyquist plot was exploited to study the conductivity behavior of the GO by measuring grain capacitance, grain resistance, grain boundary capacitance, grain boundary resistance, and electrode resistance as well as capacitance. An equivalent electrical circuit was proposed for the measured data and it was correlated with the experimental findings. The findings suggest that synthesized GO pellets can be used for replacing perovskite materials and ferroelectric materials in high-performance electronic devices and energy storage devices such as supercapacitors.

Probing charge traps at the 2D semiconductor/dielectric interface.

The family of 2-dimensional (2D) semiconductors is a subject of intensive scientific research due to their potential in next-generation electronics. While offering many unique properties like atomic thickness and chemically inert surfaces, the integration of 2D semiconductors with conventional dielectric materials is challenging. The charge traps at the semiconductor/dielectric interface are among many issues to be addressed before these materials can be of industrial relevance. Conventional electrical characterization methods remain inadequate to quantify the traps at the 2D semiconductor/dielectric interface since the estimations of the density of interface traps, Dit, by different techniques may yield more than an order-of-magnitude discrepancy, even when extracted from the same device. Therefore, the challenge to quantify Dit at the 2D semiconductor/dielectric interface is about finding an accurate and reliable measurement method. In this review, we discuss characterization techniques which have been used to study the 2D semiconductor/dielectric interface. Specifically, we discuss the methods based on small-signal AC measurements, subthreshold slope measurements and low-frequency noise measurements. While these approaches were developed for silicon-based technology, 2D semiconductor devices possess a set of unique challenges requiring a careful re-evaluation when using these characterization techniques. We examine the conventional methods based on their efficacy and accuracy in differentiating various types of trap states and provide guidance to find an appropriate method for charge trap analysis and estimation of Dit at 2D semiconductor/dielectric interfaces.

Ultralow Loss and High Tunability in a Non‐perovskite Relaxor Ferroelectric

AbstractDielectric ceramics are fundamental for electronic systems, including energy storages, microwave applications, ultrasonics, and sensors. Relaxor ferroelectrics show superb performance among dielectrics due to their high efficiency and energy density by the nature of nanodomains. Here, a novel non‐perovskite relaxor ferroelectric, Bi6Ti5WO22, with ultralow loss, ≈10−3, highly tunable permittivity, ≈2200 at room temperature with 40% tunability and the superparaelectric region at room temperature is presented. The actual crystal structure and the nanodomains of Bi6Ti5WO22 are demonstrat Various‐temperature neutron powder diffraction and in situ high‐resolution transmission‐electron‐microscopy illustrate the twinning effect, subtle structure change and micro‐strain in the material influenced by temperature, manifesting the actual crystal structure of Bi6Ti5WO22. Compared with dielectric loss of BaTiO3‐based dielectric tunable materials, the loss of Bi6Ti5WO22 is more than an order of magnitude lower, which makes it exhibit a figure of merit (≈240), much higher than that of conventional dielectric tunable materials (< 100), endorse the material great potential for direct applications. The present research offers a strategy for discovering novel relaxor ferroelectrics and a highly desirable material for fabricating energy storage capacitors, microwave dielectrics, and ultrasonics.

A Renewed Focus on Surface Chemistry for Advanced Logic-Node Epitaxial Growth Processes

Increased CMOS logic and memory scaling has forced chip architectures into 3D design spaces such as finFET, GAA, nanosheet, etc. These applications require epitaxial structures to be grown in complicated and restrictive geometries which are composed of an increasingly different range of materials. Epi growth selectivity to conventional dielectric materials such as SiO2 and SiNx as well as less conventional materials like SiOxN1-x, Al2O3, and SiOCN must be maintained as usual. However changing demands on epi doping levels and thermal budgets places a large burden on conventional selectivity approaches, which most-often rely on higher HCl partial pressures or HCl etch-back steps. Cl2 etch-back processes have also been used in limited cases as an alternative to HCl, but apart from that, new selective epi growth technology has become somewhat stagnant.The 3D nature of advanced logic architectures means that epi must also be grown on multiple crystal surface orientations like the (100), (110), and (111). For epitaxial growth processes, which by-definition are highly sensitive to the starting surface structure, this represents unique challenges to epitaxial engineers. New approaches to achieve orientation selective growth is now also paramount. Each surface orientation can have different growth rates, etch rates, and dopant incorporation efficiencies which can result in undesirable morphology, defects, and inhomogeneous chemical compositions. Depending on the application the growth rate may need to be maximized on one surface and minimized on another, for example to facilitate “bottom-up” growth from the (100) surface. In other instances, the growth rates may need to be matched as closely as possible, for example to achieve symmetric “diamond-shaped” epi-growth on a Si fin.These issues are at a fundamental level related to surface chemical interactions and finding new solutions will require a molecular-level understanding. In this work we present a fundamental chemical view of these challenges using both theoretical (density functional theory) calculations and in-situ surface analytical results. We analyze the reactive sites on dielectric surfaces and how various deposition precursors interact with these sites. Based on these results we will discuss alternative and/or novel routes to achieving selective epitaxial growth. We apply similar methods to analyzing the structure and reactivity of the Si (100), (110), and (111) surfaces and how deposition precursor molecules react on each surface. Our results reveal why changing Si surface orientations can result in such varied reactivity and ultimately in differing growth and etching rates. We similarly use these results to suggest methods for controlling facet/plane selective epitaxy and/or etching. Central to both dielectric and facet selectivity is precursor engineering, which entails designing new molecules to customize their reactivity (or lack of reactivity) toward specific dielectric surfaces or surface orientations. Figure 1

Ternary WSe2@CNTs/Co3O4 nanocomposites for highly efficient multi-band microwave absorption

The ideal electromagnetic (EM) absorption material requires high efficiency, broadband absorption, lightweight and multi-band absorption. Conventional dielectric materials have limitations in microwave absorption due to the single attenuation mechanism. Introducing magnetic materials is an effective strategy to improve the microwave attenuation capability of absorbers. In this work, the novel ternary WSe2@CNTs/Co3O4 nanocomposites with efficient multi-band EM absorption capabilities were fabricated, its minimum reflection loss (RL) can reach up to −54.09 dB and the effective bandwidth (BW) of RL < −10 dB can reach 4.64 GHz. Meanwhile, the BW can be effectively tuned by optimizing the content of Co3O4 and thickness of absorbers to achieve multiband absorption.

Stress engineered SU-8 dielectric-microbridge based polymer MEMS Pirani gauge for broad range hermetic characterization

The paper introduces a SU-8 dielectric µ-bridge based polymer microelectromechanical systems (MEMS) Pirani gauge which can be employed for hermetic characterization of packaged electronic sensors. The µ-bridge structure is adopted due to its simplicity in fabrication and lower footprint, which makes it feasible for heterogeneous integration. Further, the integration of SU-8 polymer with the active thermistor offers superior thermal isolation from the substrate and extends the dynamic range. Before fabricating the actual device, the SU-8 based µ-bridge is optimized for stress-free release. A stress engineering is performed and thermal processing of SU-8 is optimized. The measurement results reveal that the removal of quenching from the baking steps leads to the successful fabrication of freely suspended µ-bridge with SU-8 polymer as a structural layer. A quantitative comparison of the proposed gauge is established by comparing the gauge performance with conventional dielectric materials like silicon dioxide (SiO2), silicon nitride (Si3N4), and aluminum oxide (Al2O3). The fabricated SU-8 polymer-based MEMS Pirani gauge with a 40 µm × 7 µm footprint can be used for hermetic characterization from 30 Pa to 105 Pa and is an ideal candidate for heterogeneous integration.

Dynamically tunable second-harmonic generation using hybrid nanostructures incorporating phase-change chalcogenides

Abstract Nonlinear metasurfaces with high conversion efficiencies have been vastly investigated. However, strong dynamic tunability of such devices is limited in conventional passive plasmonic and dielectric material platforms. Germanium antimony telluride (GST) is a promising phase-change chalcogenide for the reconfiguration of metamaterials due to strong nonvolatile changes of the real and imaginary parts of the refraction index through amorphous-crystalline phase change. The orderly structured GST has an even higher potential in tunable second-harmonic generation (SHG) with a non-centrosymmetric crystal structure at the crystalline phase, while the amorphous phase of GST does not exhibit bulk second-order nonlinearity. Here, we experimentally demonstrate SHG switches by actively controlling the crystalline phase of GST for a GST-based hybrid metasurface featuring a gap-surface plasmon resonance, and a quarter-wave asymmetric Fabry–Perot (F–P) cavity incorporating GST. We obtain SHG switches with modulation depths as high as ∼ 20 dB for the wavelengths at the on-state resonance. We also demonstrate the feasibility of multi-level SHG modulation by leveraging three controlled GST phases, i.e., amorphous, semi-crystalline, and crystalline, for the gap-surface plasmon hybrid device, which features stronger light–matter interaction and has higher resonant SHG efficiencies than the asymmetric F–P cavity device at respective GST phases. This research reveals that GST-based dynamic SHG switches can be potentially employed in practical applications, such as microscopy, optical communication, and photonic computing in the nonlinear regime.

An epsilon-near-zero-based Dallenbach absorber

We report a theoretical analysis of total absorption conditions in a structure consisting of a lossy coating layer on top of a metal substrate, which is known as a Dallenbach absorber. All possible combinations of complex refractive indices of the coating material and thicknesses of the coating layer providing complete absorption are described for the case of normal incidence of a plane wave. The resulting solution space allows Dallenbach absorbers to be designed both with the use of conventional lossy dielectric or semiconductor materials having a refractive index greater than unity and with the use of epsilon-near-zero (ENZ) materials. Simple analytical relations are obtained for the total absorption conditions in ENZ materials. For coatings with different values of the refractive index, we present a comparative analysis of the angular dependences of the absorption coefficient and the profiles of the electromagnetic field distribution. The design of an indium-tin oxide (ITO) coating on an aluminum substrate is presented by the example of an ENZ-based Dallenbach absorber. It is shown that by varying the concentration of free carriers in ITO in the range 1019 − 1021 cm−3, the total absorption can be achieved at any wavelength in the range of approximately 1–10 μm.

Deep Well Trapping of Hot Carriers in a Hexagonal Boron Nitride Coating of Polymer Dielectrics.

Polymer dielectrics can be cost-effective alternatives to conventional inorganic dielectric materials, but their practical application is critically hindered by their breakdown under high electric fields driven by excited hot charge carriers. Using a joint experiment-simulation approach, we show that a 2D nanocoating of hexagonal boron nitride (hBN) mitigates the damage done by hot carriers, thereby increasing the breakdown strength. Surface potential decay and dielectric breakdown measurements of hBN-coated Kapton show the carrier-trapping effect in the hBN nanocoating, which leads to an increased breakdown strength. Nonadiabatic quantum molecular dynamics simulations demonstrate that hBN layers at the polymer-electrode interfaces can trap hot carriers, elucidating the observed increase in the breakdown field. The trapping of hot carriers is due to a deep potential well formed in the hBN layers at the polymer-electrode interface. Searching for materials with similar deep well potential profiles could lead to a computationally efficient way to design good polymer coatings that can mitigate breakdown.

The transverse electric plasmonic modes in a negative refractive index black phosphorene waveguide structure

We consider the transverse electric (TE) plasmonic modes supported by black phosphorene (BP) in a parallel waveguide structure with left-handed material (LHM) instead of the conventional right-handed dielectric material. The existence condition of the TE BP surface plasmon polariton (SPP) is . When an electric field is polarized along one of the two orthogonal crystal axes, the anisotropic symmetric and anti-symmetric plasmonic modes depend on the incident optical energy, the chemical potential, and the distance between two BP sheets can be observed. The symmetric mode has a more extensive effective refractive index, which possesses stronger field confinement. With a decreasing distance d between two BP sheets, the coupling strength between the two separate BPSPP waves increases. When d is small enough, the anti-symmetric mode root does not exist. LHMs can be used to realize a TE BPSPP mode to enhance the localization of the BPSPP, which is a practical method in optoelectronic devices based on black phosphorene.

Exceptional points in a topological waveguide-cavity coupled system

Exceptional points (EPs) as branch singularities describe peculiar degeneracies of non-Hermitian systems, widely studied in topological and non-topological optical architectures with introducing gain or loss technically. This work focuses on the EPs in a topological waveguide (TW)-cavity coupled structure, where there is no need to introduce practical gain or loss. The topological cavity contains two degenerate counter-propagation topological whispering gallery modes, whose coupling with the TW leads to the effective gain and loss, responsible for the EP. Such a photonic architecture is designed practically by crystal-symmetry-protected topological photonic insulators based on air rods in conventional dielectric materials. The relevant EP reveals the breaking of the parity-time symmetry, reflected by the change of the transmission-dip number in the optical transmission spectra of the system. Achieving EPs in topological photonic systems possibly opens a new avenue toward robust optical devices with exceptional-point-based unique properties and functionalities.

Millimeter-wave free-space dielectric characterization

Millimeter wave technologies have widespread applications, for which dielectric permittivity is a fundamental parameter. The non-resonant free-space measurement techniques for dielectric permittivity using vector network analysis in the millimeter wave range are reviewed. An introductory look at the applications, significance, and properties of dielectric permittivity in the millimeter wave range is addressed first. The principal aspects of free-space millimeter wave measurement methods are then discussed, by assessing a variety of systems, theoretical models, extraction algorithms and calibration methods. In addition to conventional solid dielectric materials, the measurement of artificial metamaterials, liquid, and gaseous-phased samples are separately investigated. The pros of free-space material extraction methods are then compared with resonance and transmission line methods, and their future perspective is presented in the concluding part.

Design of broadband all-dielectric valley photonic crystals at telecommunication wavelength

Topological photonic crystals (TPC) can effectively suppress the backscattering from defects and achieve unidirectional transmission with high forward transmittance, thus becoming a promising candidate in integrated photonic chip applications. Among different TPCs, the valley photonic crystals (VPCs) based on quantum valley Hall effect (QVHE) originating from valley-dependent spin-split bulk bands, can achieve spin-dependent unidirectional transmission at telecommunication wavelength with conventional dielectric material, such as silicon, which can be readily fabricated by current CMOS nanofabrication techniques. Therefore, VPCs recently attract broad attention. Generally, a large working bandwidth is preferred in optical communications and information processing, which should be as large as possible. Currently, the maximum working bandwidth of VPCs at telecommunication wavelength is limited to about 130 nm. Based on theoretical analysis and numerical simulation, a triangular lattice VPC composed of all-dielectric silicon-based triangular air holes is proposed, and the working bandwidth at 1550 nm is further extended to 229 nm. By combining two mirror-inversed VPCs, we observe the valley–spin locking behavior results in selective net spin flow inside bulk VPCs to achieve unidirectional transmission with a high forward transmittance up to 0.97. Moreover, the intensity distributions of the incident light show neglectable scattering loss at the sharp edge of the zigzag and Ω shape waveguides, confirming the achievement of scattering immune propagation. The designed VPCs not only offer a possibility to expand the working bandwidth, but also can be applied to device applications in integrated photonics and information processing using spin-dependent transportation.

THE EFFECT OF FREQUENCY VARIATION ON DIELECTRIC CONSTANT OF RAPHIA HOOKERI

This work sought to investigate the effect of varying the frequency of an applied electric field on the dielectric constant of raphia hookeri. The aim of the work was to ascertain the suitability of using the sample for engineering applications. It was revealed, from the recorded results, that the dielectric constant of the sample decays exponentially with frequency. Also, greater degree of polarisation was observed with decrease in frequency. Again, as a good thermal insulator, it was revealed that the values of the sample’s dielectric constant compared favourably with those of commonly used conventional dielectric materials. Thus, it is obvious that if put into production cycle, the sample can serve as a low-cost and environmentally friendly material suitable for engineering applications within audio frequency range. This will, in turn, help to provide raw material for electronic industry and also improve the economy.

A Novel Method for Backward Wave Cancellation of Traveling Wave Tube Amplifier Using Ferrite Material

This article presents a novel dielectric support for RF circuits of helix traveling wave tubes (TWTs) for the backward wave cancellation. RF circuit comprised two sections: the first section is a conventional dielectric material and the second section is a ferrite rod which replaces the dielectric support. Considering nonreciprocal electromagnetic property of ferrites, the proposed solution acts as a one-way tunable bandstop filter which only affects the propagating waves in one direction. By tuning this filter in the backward wave frequency, the backward wave can be suppressed without any effect on the forward wave. The electromagnetic characteristics and hot test behavior of ferrite-added slow wave structure (SWS) are observed through the numerical simulations. The proposed structure successfully damps the backward wave oscillation and higher gain is achieved in comparison with conventional TWTs.