Low Dielectric Constant Research Articles

Harnessing Cu incorporation for achieving stable superior microwave dielectric properties in low permittivity MgSiO3-based ceramics through effective phase transition suppression

MgSiO3 ceramics with a low dielectric constant are highly promising for application in 5G communication due to their excellent performance and cost-effectiveness. However, the application remains constrained by phase transitions. This study aims to unlock their full potential by introducing Cu ions to mitigate phase transitions, thereby achieving stable and superior performance. Mg1-xCuxSiO3 (0 ≤ x ≤ 0.25) ceramics were synthesized by solid-state method, and the effects of Cu introduction on the crystal structure, phase constitution, microstructure and microwave dielectric properties were systematically investigated. Through XRD patterns and Rietveld refinement, it was found that when x = 0, both protoenstatite (PEN) and low-temperature clinoenstatite (CEN) phases coexist due to a phase transition from PEN to CEN. As x increases, the PEN phase dominance rises while the CEN phase diminishes, indicating that the addition of Cu ions inhibits the occurrence of phase transition. At x ≥ 0.2, only the orthoenstatite (OEN) phase was observed. SEM and EDS analyses revealed the beneficial impact of Cu introduction on sintering, yet excessive amounts can lead to abnormal grain growth, local segregation, and uneven distribution of Cu elements, thereby deteriorating microwave dielectric properties. The optimal microwave dielectric performance was achieved at x = 0.05: εr = 6.2, Qf = 93,600 GHz, τf = −33.7 ppm/°C. A one-year long-term comparative study revealed the stabilizing effect of Cu incorporation for obtaining stable excellent performance. These findings underscore the potential of introducing an appropriate amount of Cu to achieve stable and superior microwave dielectric properties in MgSiO3 ceramics, paving the way for practical applications in 5G communication.

High-strength low-k glass–ceramic composite covers for 6G communication mobile devices

Ceramic-based back covers are commercially utilized as a high-end option for the physical protection of mobile phones. Herein, an unprecedented composite structure consisting of a cordierite (2MgO.2Al2O35SiO2) glass–ceramic strengthened with yttria-stabilized zirconia (YSZ) fillers is introduced as a protective back cover, specifically for next-generation communication mobile phones additionally requiring a low dielectric constant at gigahertz frequencies. Crystallization sequence was rather complicated with the involvements of multiple crystalline phases, α- and μ-cordierite, tetragonal and monoclinic ZrO2, and ZrSiO4, depending on the glass and composite compositions. This unique approach effectively induced the best mechanical performance for the 10 wt% YSZ/glass–ceramic structure, despite the low sintering temperature of 1050 °C, with the highest Vickers hardness of ∼9.2 GPa and flexural strength of ∼196.8 MPa attained for the optimal composite. Although effective dielectric constant of the composites depended on the relative contents of the evolved crystalline phases, overall dielectric constant was kept low due to the utilization of cordierite glass as the main component.

Chemical, Structural, and Electrical Changes in Molecular Layer-Deposited Hafnicone Thin Films after Thermal Processing.

Post deposition annealing of molecular layer-deposited (MLD) hafnicone films was examined and compared to that of hafnium oxide atomic layer-deposited (ALD) films. Hafnicone films were deposited using tetrakis(dimethylamido)hafnium (TDMAH), and ethylene glycol and hafnia films were deposited using TDMAH and water at 120 °C. The changes in the properties of the as-deposited hafnicone films with annealing were probed by various techniques and then compared to the as-deposited and annealed ALD hafnia films. In situ X-ray reflectivity indicated a 70% decrease in thickness and ∼100% increase in density upon heating to 400 °C yet the density remained lower than that of hafnia control samples. The largest decreases in thickness of the hafnicone films were observed from 150 to 350 °C. In situ X-ray diffraction indicated an increase in the temperature required for crystallization in the hafnicone films (600 °C) relative to the hafnia films (350 °C). The changes in chemistry of the hafnicone films annealed with and without UV exposure were probed using Fourier transformed infrared spectroscopy and X-ray photoelectron spectroscopy with no significant differences attributed to the UV exposure. The hafnicone films exhibited lower dielectric constants than hafnia control samples over the entire temperature range examined. The CF4/O2 etch rate of the hafnicone films was comparable to the etch rate of hafnia films after annealing at 350 °C. The thermal conductivity of the hafnicone films initially decreased with thermal processing (up to 250 °C) and then increased (350 °C), likely due to porosity generation and subsequent densification, respectively. This work demonstrates that annealing MLD films is a promising strategy for generating thin films with a low density and relative permittivity.

Ultrastable 3D Heterogeneous Integration via N-Heterocyclic Carbene Self-Assembled Nanolayers.

The commercialization of 3D heterogeneous integration through hybrid bonding has accelerated, and accordingly, Cu-polymer bonding has gained significant attention as a means of overcoming the limitations of conventional Cu-SiO2 hybrid bonding, offering high compatibility with other fabrication processes. Polymers offer robust bonding strength and a low dielectric constant, enabling high-speed signal transmission with high reliability, but suffer from low thermomechanical stability. Thermomechanical stability of polymers was not achieved previously because of thermal degradation and unstable anchoring. To overcome these limitations, wafer-scale Cu-polymer bonding via N-heterocyclic carbene (NHC) nanolayers was presented for 3D heterogeneous integration, affording ultrastable packing density, crystallinity, and thermal properties. NHC nanolayers were deposited on copper electrodes via electrochemical deposition, and wafer-scale 3D heterogeneous integration was achieved by adhesive bonding at 170 °C for 1 min. Ultrastable conductivity and thermomechanical properties were observed by the spatial mapping of conductivity, work function, and force-distance curves. With regard to the characterization of NHC nanolayers, low-temperature bonding, robust corrosion inhibition, enhanced electrical conductivity, back-end-of-line process compatibility, and fabrication process reduction, NHC Cu/polymer bonding provides versatile advances in 3D heterogeneous integration, indicating that NHC Cu/polymer bonding can be utilized as a platform for future 3D vertical chip architectures.

New type of UV cured low dielectric naphthalene resin: Structure-activity relationship of different substitution sites

UV-curing low dielectric materials exhibit wide applications in the field of additive manufacturing of electronic packaging, owing to their environmental protection, good thermal stability, low dielectric constant (Dk), and dielectric loss (Df). Wherein, one-step UV curing realizes process simplification of low dielectric materials gradually sparked widespread research. In this work, a series of novel naphthalene-based low dielectric materials were prepared for one-step UV curing. The double bond conversion rate of resins exceeds 90 % in a short time and the resins perform exceptional dielectric properties (Dk < 2.8, Df < 0.009, 110 MHz), high thermal stability (T5% > 270 °C), and hydrophobicity (water contact angle > 95°). Notably, 1,6-naphthalene dimethacrylate/Trihydroxymethylbutyl trimethylacrylate (1,6-NEA/TMPTA) suggests lowest dielectric performance (Dk = 2.19, Df = 0.005) with significant thermal stability (Tg = 190 °C, T5% = 367.4 °C) because the π-π conjugation of the asymmetric structure of 1,6-NEA, which allows for a greater variety of stacking patterns and increases the effective collisions between the reactive sites of the photosensitive monomer and the reactive diluent. This work has revealed the structure-activity relationship between the substituents on naphthalene derivatives and their photochemical properties, providing a novel methodology for the development of low dielectric electronic packaging materials through additive manufacturing techniques.

A comprehensive enhancement of the optical, mechanical, low dielectric, and flame-retardant characteristics of epoxy resin by the incorporation of multifunctional additive

Epoxy resin is widely utilized but faces the drawback of flammability. However, adding flame retardants often results in the compromise of other properties, such as mechanical and optical characteristics. In this study, a phosphorus-nitrogen multifunctional flame retardant named DPVPI was successfully synthesized. The resulting epoxy resin containing DPVPI demonstrated good transparency and low dielectric constant. Furthermore, the unique structure of DPVPI led to additional enhancements in the mechanical properties of EP composite. The tensile strength of EP composite was increased by 33 %, and the impact strength was improved from 13.61 kJ/m² to 25.74 kJ/m². Remarkably, the composites with Only 4wt% DPVPI can achieve a V-0 rating in the UL-94 test and the maximum limiting oxygen index (LOI) of it reached 32.6 %. The cone calorimeter test showed that the peak heat release of the composites with a 5 wt% addition decreased by 35 %, the total smoke release decreased by 37 %, and the char yield doubled. This research presents a novel strategy for subsequent synthesis endeavors about multifunctional flame retardants.

Reduced subthreshold swing in a vertical tunnel FET using a low-work-function live metal strip and a low-k material at the drain.

In this research paper, a vertical tunnel field-effect transistor (TFET) structure containing a live metal strip and a material with low dielectric constant is designed, and its performance metrics are analyzed in detail. Low-k SiO2 is incorporated in the channel-drain region. A live molybdenum metal strip with low work function is placed in a high-k HfO2 layer in the source-channel region. The device is examined by the parameters I off, subthreshold swing, threshold voltage, and I on/I off ratio. The introduction of a live metal strip in the dielectric layer closer to the source-channel interface results in a minimum subthreshold slope and a good I on/I off ratio. The low-k material at the drain reduces the gate-to-drain capacitance. Both the SiO2 layer and the live metal strip show excellent leakage current reduction to 1.4 × 10-17 A/μm. The design provides a subthreshold swing of 5 mV/decade, which is an excellent improvement in TFETs, an on-current of 1.00 × 10-5 A/μm, an I on/I off ratio of 7.14 × 1011, and a threshold voltage of 0.28 V.

Frequency-Dependent Dielectric Permittivity and Water Permeability in Ordered Mesoporous Silica-Grafted Fluorinated Polyimides.

Polymers with a low dielectric constant (Dk) are promising materials for high-speed communication networks, which demand exceptional thermal stability, ultralow Dk and dissipation factor, and minimum moisture absorption. In this paper, we prepared a series of novel low-Dk polyimide films containing an MCM-41-type amino-functionalized mesoporous silica (AMS) via in situ polymerization and subsequent thermal imidization and investigated their morphologies, thermal properties, frequency-dependent dielectric behaviors, and water permeabilities. Incorporating 6 wt.% AMS reduced the Dk at 1 MHz from 2.91 of the pristine fluorinated polyimide (FPI) to 2.67 of the AMS-grafted FPI (FPI-g-AMS), attributed to the free volume and low polarizability of fluorine moieties in the backbone and the incorporation of air voids within the mesoporous AMS particles. The FPI-g-AMS films presented a stable dissipation factor across a wide frequency range. Introducing a silane coupling agent increased the hydrophobicity of AMS surfaces, which inhibited the approaching of the water molecules, avoiding the hydrolysis of Si-O-Si bonds of the AMS pore walls. The increased tortuosity caused by the AMS particles also reduced water permeability. All the FPI-g-AMS films displayed excellent thermooxidative/thermomechanical stability, including a high 5% weight loss temperature (>531 °C), char residue at 800 °C (>51%), and glass transition temperature (>300 °C).

Effect of Inorganic Fillers on Electrical and Mechanical Properties of Ceramizable Silicone Rubber.

Ceramizable silicone rubber (CSR) composed of silicone rubber matrix and inorganic fillers can be transformed into a dense flame-retardant ceramic upon encountering high temperatures or flames. Conventionally, CSR can be sintered into a dense ceramic at temperatures above 1000 °C, which is higher than the melting point of a copper conductor used in a power cable. In this study, the vulcanization process and mass ratio of inorganic fillers of CSR were studied to lower its ceramization temperature to 950 °C. The electrical and mechanical properties of CSRs and their ceramic bulks were studied with various ratios of wollastonite and muscovite. It was found that the CSR samples could be successfully fabricated using a two-step vulcanization technique (at 120 °C and 150 °C, respectively). As a high ratio of muscovite filler was introduced into the CSR, the sample presented a high dc electrical resistivity of 6.713 × 1014 Ω·cm, and a low dielectric constant of 4.3 and dielectric loss of 0.025 at 50 Hz. After the thermal sintering (at 950 °C for 1 h) of the CSR sample with a high ratio of muscovite, the ceramic sample exhibits a dense microstructure without any pores. The ceramic also demonstrates excellent insulating properties, with a volume resistivity of 8.69 × 1011 Ω·cm, and a low dielectric loss of 0.01 at 50 Hz. Meanwhile, the three-point bending strength of the ceramic sample reaches a value of 110.03 MPa. This study provides a potential route to fabricate CSR used for fire-resistant cables.

Freezing of Water Solvation Dynamics in Nanoconfinement by Reverse Micelles at Room Temperature.

Much attention has recently been paid to anomalously low dielectric constants of nanoconfined water between two slabs at room temperature (Fumagalli et al. Science, 2018, 360, 1339). These low values imply that the dipole rotation of the interfacial water on the slab is completely suppressed. Such freezing has so far been observed for water confined between solids. In contrast, it remains unclear whether this holds for water in soft confinement, which is omnipresent naturally and artificially. Here, we address this question using encapsulated reverse micelles with a dye molecule, allowing us to study water sandwiched between the surfactant and dye molecules in solution. Moreover, we examine the solvation related to the dielectric property of water, which is reorientational motion in the hydration layer of the dye molecule, by persistent hole-burning spectroscopy. We first show that the dye molecule is surrounded by water without contact with the surfactant and that the dye molecule has two or three hydration layers on average. We next demonstrate that the solvation dynamics is frozen below the water droplet size of ∼4 nm, whereas they become liquid-like when the RM size is further increased. The average gap distance (∼1.5 nm) for freezing the solvation agrees with the gap distance with no rotational water motions between slabs. Our findings may have biological relevance, providing a new aspect for understanding biological function in cells.

Study on plasma-polymerized 1-(trimethylsilyl)pyrrolidine films deposited by plasma-enhanced chemical vapor deposition for use as a Cu diffusion barrier in multilevel metallization process

As integration continues in the modern semiconductor industry, copper (Cu) is used for metal lines and low dielectric constant (low-k) films are used for intermetal dielectrics (IMD) to reduce signal delays occurring in device interconnects. A diffusion barrier is essential between the Cu metal lines and the IMD to prevent Cu diffusion, and silicon carbon-nitride (SiCN) films with relatively low dielectric constants are being widely studied. In this study, SiCN films deposited from 1-(trimethylsilyl)pyrrolidine (TSPD) precursor by plasma-enhanced chemical vapor deposition (PECVD) were investigated for use as a Cu diffusion barrier in multilevel metallization process. This plasma-polymerized TSPD (ppTSPD) monolayer film as SiCN was deposited in plasma powers ranging from 15 to 30 W. The electrical properties of ppTSPD were measured and the chemical properties were analyzed by Fourier-transform infrared spectroscopy (FTIR). The dielectric constant increased with increased plasma power. The lowest dielectric constant of 3.70 and leakage current density at 1 MV/cm of 2.27×10−8 A/cm2 were found for ppTSPD film deposited at 15 W. To verify the Cu diffusion barrier characteristics of the ppTSPD films, a ppTSPD/ppOMCTS bilayer was introduced by using plasma-polymerized octamethylcyclotetrasiloxane (ppOMCTS) as porous low-k SiCOH films. The time-dependent dielectric breakdown (TDDB) characteristic was enhanced around five times than ppOMCTS monolayer used as a reference. The ppTSPD was suggested for fabricating SiCN films for use as a Cu diffusion barrier in multilevel metallization process.

Linear and nonlinear optical properties of hybrid Polyaniline/CoFe2O4 nanocomposites: Electrochemical synthesis, characterization, and analysis

This study presents a focused investigation and comprehensive analysis of the synthesis of hybrid Polyaniline/Cobalt ferrite (PANI/CoFe2O4) nanocomposites using an optimized electrochemical polymerization method. CoFe2O4 nanoparticles (NPs) were incorporated into the PANI matrix at varying concentrations (3, 6, and 12 wt%). The research examined the newly synthesized hybrid nanocomposites in terms of their structure, dielectric properties, and both linear and nonlinear optical properties. As a result of the Williamson-Hall method, the average crystallite size varied between 45 and 99 nm. Initially, adding a small quantity of NPs decreased the nanocomposite size, but further additions increased it due to aggregation. The Tauc plot showed a gradual increase in the energy band gap of the films as the concentration of CoFe2O4 NPs increased up to 12 wt%. This trend showed stronger absorption bands and higher coefficients, indicating improved light absorption compared to pure PANI films. Dielectric properties, including dielectric constants (ɛr, ɛi) and dielectric loss (tan δ), were examined as a function of frequency. The experimental results indicated that PANI/CoFe2O4 exhibited lower dielectric constants than bare PANI. Concentration-dependent optical properties, such as electronic transition excitation energies, dispersion energies, and optical conductivity, were also investigated. These properties were modeled using a single oscillator based on the Wemple-DiDomenico (WDD) approach. The study revealed a reduction in key optical parameters—linear susceptibility, nonlinear third-order susceptibility, and nonlinear refractive index—as nanoparticle content increased. Conversely, increasing concentrations of CoFe2O4 NPs led to a significant increase in the ratio of free carriers to effective mass (N/m٭), from 3.89 × 10³⁶ to 4.04 × 10³⁶ m⁻³ kg⁻1. Additionally, the electrical conductivity of both PANI and PANI/CoFe2O4 nanocomposites exhibited temperature-dependent improvement, reaching maximum values. The observed findings indicate that hybrid PANI-CoFe2O4 nanocomposites possess enhanced properties, highlighting their promising potential as active materials for a broad range of optoelectronic applications.

Phase structural characteristics and microwave dielectric properties of Ge-doped cordierite-based ceramics

The cordierite-based ceramics, Mg2Al4(Si1-xGex)5O18(MASG-x (x = 0, 0.1, 0.2, and 0.3) was successfully synthesized with Ge-substitution for Si, and subsequent analysis was conducted on their phase structural characteristics and microwave dielectric properties. Ge4+ substitution was discovered to be a key property-dependent factor. The analysis of phase fractions demonstrated the coexistence of orthorhombic and hexagonal phases in varying proportions across all compositions. Specifically, the hexagonal phase was identified as the predominant phase in Ge-substituted samples, reaching an optimal fraction of around 66.62% for MASG-0.2 and slightly decreasing to 63.45% for MASG-0.3. The correlation between the maximum quality factor (Qf)values and the hexagonal phase fraction exhibited strong consistency, thus playing a substantial role in explaining the origin of high Qf due to the related high symmetry structure of the hexagonal phase. An optimal Qf∼107,555 GHz and low dielectric constant (εr<5) was achieved by the MASG-0.2 sample sintered at 1380 °C.

Tunable microware dielectric properties of high-entropy (Mg1/2Zn1/2)0.4+xLi0.4(Co1/2Ni1/2)0.4-xAl2O4 ceramics with low loss

In present study, high-entropy (Mg1/2Zn1/2)0.4+xLi0.4(Co1/2Ni1/2)0.4–xAl2O4 (x = 0.00–0.40) ceramics were fabricated via the solid-state reaction approach. The high-entropy ceramics exhibited a spinel structure with short-range local disorder and long-range structural order. The reduction of Co2+ and Ni2+ content suppress the damping behavior of atomic vibrations, promoting the structural ordering and contributing to higher quality factor (Q×f). The x = 0.35 sample with sintering at 1550 °C exhibited great microwave dielectric properties: a low dielectric constant (εr) of 7.92, a high-quality factor of 135,525 GHz, and a temperature coefficient of resonance frequency (τf) of −49 × 10−6 °C−1. The εr value was jointly dominated by both polarizability and relative density. The Q×f value was primarily connected to relative density, atomic vibrations, and the degree of covalency. The τf value was highly associated with the bond strength. These findings demonstrate the effectiveness of adopting high-entropy composition design for significantly improving microwave dielectric properties.

Control of sulfur number in sulfur-containing compounds: The effect of base type, equivalent of the base, and reaction solvent in synthesizing linear sulfur

Abstract Since the properties of sulfur-containing compounds depend on the sulfur number contained in the compound, it is desirable to develop a method to control the sulfur number. A common method for synthesizing sulfur-containing compounds is to mix sulfur with a base to form linear sulfur, which is then reacted with an organic compound to obtain a sulfur-containing compound. In this study, we systematically investigated the relationship between the type of base, equivalent amount of the base, and the reaction solvent and the sulfur number in the resulting sulfur-containing compound. The sulfur number of sulfur-containing compounds prepared in water was controlled by the equivalent ratio of elemental sulfur (S8) and base. Sulfur-containing compound with high sulfur values was obtained using solvents with low dielectric constants and with lower base equivalents compared to S8.

Ultrahigh Heat/Fire-Resistant, Mechanically Robust, and Closed-Loop Chemical Recyclable Polycarbonate Enabled by Facile Bond Dissociation Energy Modulation.

Plastics serve as an essential foundation in contemporary society. Nevertheless, meeting the rigorous performance demands in advanced applications and addressing their end-of-life disposal are two critical challenges that persist. Here, an innovative and facile method is introduced for the design and scalable production of polycarbonate, a key engineering plastic, simultaneously achieving high performance and closed-loop chemical recyclability. The bisphenol framework of polycarbonate is strategically adjusted from the low-bond-dissociation-energy bisphenol A to high-bond-dissociation-energy 4,4'-dihydroxydiphenyl, in combination with the incorporation of polysiloxane segments. As expected, the enhanced bond dissociation energy endows the polycarbonate with an extremely high glow-wire flammability index surpassing 1025°C, a 0.8mm UL-94V-0 rating, a high LOI value of 39.2%, and more than 50% reduction of heat and smoke release. Furthermore, the π-π stacking interactions within biphenyl structures resulted in a significant enhancement of mechanical strength by as more as 37.7%, and also played a positive role in achieving a lower dielectric constant. Significantly, the copolymer exhibited outstanding closed-loop chemical recyclability, allowing for facile depolymerization into bisphenol monomers and the repolymerized copolymer retains its high heat and fire resistance. This work provides a novel insight in the design of high-performance and closed-loop chemical recyclable polymeric materials.

Essential oil-derived robust and heat-resistant polybenzoxazine-POSS composites as low dielectric matrixes

Polybenzoxazines (PBozs) are regarded as prime candidates as low dielectric matrixes. However, the fabrication of high-performance PBozs that combines low dielectric property with high thermal stability using sustainable resources as the starting raw materials remains a significant challenge. In this work, we constructed a novel main-chain benzoxazine (Boz) oligomer from natural essential oil-derived compounds (eugenol and p-menthane diamine) to fulfill the principles of green chemistry. To enhance their low dielectric properties, polar C-Si unit on the main-chain and cellular structure of polyoctahedral silsesquioxanes (POSS) as the cross-linkers were introduced in PBoz-POSS composites. The obtained composites demonstrated excellent thermal stability, mechanical property, and with remarkable low dielectric constants. Coupled with their exceptional hydrophobicity and heat resistance, these materials are promising matrixes for low dielectric application in contemporary electronic industries.

Low-κ, low CTE, high-temperature epoxy resin with high storage modulus based on spirobisindane for high-frequency electronic circuit field

High-temperature thermosetting resin with low dielectric constant (κ), low thermal expansion coefficient (CTE), and high modulus are drawing more and more attention from scientists and engineers in the field of the high-frequency circuit, 5G and 6G communication networks to improve the signal transmission speed. Epoxy resin, as one of the important thermosetting resin members, possesses excellent properties such as heat resistance, cohesiveness, and reactivity. However, Epoxy resin was usually mixed with different inorganic fillers to meet the above requirements, especially to decrease the κ and CTE. In this work, a new class of spirobisindane epoxy resin monomer (TSDEP) was synthesized by a classic two-step method based on 3,3,3′,3′-tetramethyl-1,1′-spirobisindane-6,6′-diol (TSD). Due to the highly distorted rigid structure of TSD, the movement of the TSDEP molecular segment is subject to more restrictions after being cured, and the free volume will increase. After cured by 4,4′-diamino diphenyl sulfone (DDS), the TSDEP/DDS resin exhibited many desirable physical properties, e.g., low dielectric constant (∼3.45, 1 MHz), low dielectric loss (∼0.025, 1 MHz), low coefficient of thermal expansion (CTE, 72 ppm/ °C, 35–150 °C), high glass transition temperature (Tg > 241 °C) and high thermal stability (Td5%∼400 °C). Furthermore, TSDEP/DDS exhibited excellent mechanical rigidity with a storage modulus of ∼ 3.1 GPa. Compared with TSDEP/DDS, 4-methylhexahydrophthalic anhydride (MHHPA) cured TSDEP system showed lower κ (∼3.09) and dielectric loss (0.015) due to weaker polar ester groups instead of more polar hydroxy groups.

Microcellular long-chain branched polyphenylene oxide (PPO) with excellent comprehensive properties and comprehensive analysis of its dielectric properties

High-frequency and high-speed communications impose stringent requirements on low-dielectric materials with exceptional comprehensive properties. The development of dielectric materials with low dielectric constants and low dielectric dissipation factors holds significant value in reducing interconnect delay, power consumption, and crosstalk in high-frequency communication. In this study, polyphenylene oxide (PPO), known for its excellent properties, was chosen as the base material. Modified PPO with a long-chain branched structure was prepared using the multi-epoxy modifier ADR-4468. The increase in molecular weight and the formation of a long-chain branched structure improved the thermal stability, flexural properties, and foamability of PPO. Introduction of low-dielectric air into the material was achieved through supercritical CO2 foaming, resulting in a series of microcellular PPO foams exhibiting low dielectric properties (with a dielectric constant as low as 1.12 and a dielectric dissipation factor as low as 0.000636). Concurrently, the dielectric properties of microcellular PPO foams were examined at 10 GHz, revealing that the foam’s dielectric properties were minimally impacted by the properties of the raw materials. Based on water absorption analysis, an improved equation for calculating the dielectric dissipation factor was proposed, comprehensively analyzing the influencing factors on the foam’s dielectric dissipation factor. The study unveiled that water absorption significantly affects the foam’s dielectric dissipation factor, and under high expansion ratios, water absorption’s impact on the dielectric dissipation factor exceeds that of air introduction. These microcellular PPO foams, possessing excellent comprehensive properties and low dielectric characteristics, hold promise for applications in the realm of high-frequency and high-speed communications.

Effect of boron nitride content on mechanical、dielectric and thermal shock resistance properties of Si3N4-BN-MAS composites

Achieving an optimal balance between mechanical properties, dielectric properties, and thermal shock resistance presents a significant challenge in the development of advanced ceramics. This study investigates Si3N4-BN composite materials, prepared by hot-press sintering with magnesium aluminum silicate (MAS) as the sintering additive, to assess the impact of varying hexagonal boron nitride (h-BN) content on their mechanical and dielectric properties, as well as their thermal shock resistance. At an h-BN content of 20 wt%, the BN layers act as a toughening phase through a pull-out mechanism, minimally impacting the composite's density. This composition results in superior fracture toughness (7.4 MPa m1/2), high strength (598 MPa), low dielectric constants (∼6.8), and dielectric loss (∼7.4 × 10−3). Notably, after a thermal shock at 1000 °C, the composite exhibits a peak residual strength of 621 MPa, surpassing its initial strength. This enhanced performance is attributed to the formation of a dense Mg–Al–Si–B–O oxide glass layer on the surface during thermal shock, which not only repairs surface defects but also induces compressive stress. The development of the Si3N4-BN-MAS composite, with its outstanding comprehensive performance, marks a significant advancement for materials used in high-temperature wave transmission applications.