Low Dielectric Properties Research Articles

Ultralow dielectric constant trifluorophenylvinyl-functionalized silica aerogels with excellent hydrophobicity and enhanced mechanical properties

Silica aerogels have low dielectric properties owing to their high porosity, however, their application in low dielectrics has been limited because of their low mechanical properties. To enhance their mechanical properties, silica aerogels were modified with low polarizable functional groups with low dielectric constants via covalent bonding in this study. In detail, the covalently bonded low-polarizability groups (i.e., CF3-phenyl with silica network) were synthesized and characterized by processing them into monoliths and thin films and characterizing their properties. The CF3-phenyl-functionalized silica aerogels showed an ultralow dielectric constant of 1.52. Meanwhile, Young's modulus of the CF3-phenyl-functionalized silica aerogels was 30% higher than pristine silica aerogels. Furthermore, the CF3-phenyl-functionalized silica aerogels were hydrophobic, which is crucial for achieving a low dielectric constant. Our work provides a simple approach for preparing silica aerogels with low dielectric constants, enhanced hydrophobicity, and improved mechanical properties.

Low dielectric loss and infrared emissivity coating with enhanced mechanical property by grafting modification of EPDM

Composite coating materials or structures with low infrared emissivity and high radar transmittance are in urgent need in practical applications, among which binder is one of the important factors affecting the mechanical properties, infrared and dielectric properties of coatings. Acrylic acid (AA) and maleic anhydride (MAH) were used as graft monomers to modify ethylene propylene diene monomer (EPDM) binder. Composite coating with low infrared emissivity and low dielectric properties was prepared by using modified EPDM as binder, floating aluminum (Al) powder and antistatic carbonaceous fiber (CF) as filler. The effects of the type and amount of modified monomer on the mechanical properties, infrared emissivity and dielectric properties of the binder and the composite coating were systematically studied. The results show that the tensile strength (σb) and elongation at break (e) of the composite coating can be increased by 32% and 18%, respectively, by appropriate grafting modification of the binder. The infrared emissivity and the dielectric properties of the composite coating has a slight change with the increase of graft monomer content. Grafting modification of the binder improves the compatibility, wettability and interfacial bonding between filler and binder, which remarkably enhanced the mechanical and comprehensive properties of the composite coating. The effect mechanism of grafting modification of AA and MAH is disclosed from the aspects of polarity, branching and crosslinking. This work increases the selection range of binders needed to prepare low infrared emissivity materials.

Low Dielectric Constant and Anisotropic Mechanical Properties of Dispenser‐Printed Polyetherimide Films Using Two‐Step Thermal Treatment

AbstractAlthough polyetherimide (PEI) has attracted attention owing to its good dielectric properties, superior mechanical properties, and thermal/chemical stabilities, there is still a lack of methodology to fabricate PEI films in desired shapes directly on devices. In this study, a dispenser printing method to fabricate sophisticated 2D PEI structures is introduced. As dispenser printing is a solution‐based process, PEI ink is prepared by dissolving PEI in N‐methyl pyrrolidone (NMP). The printing conditions are controlled by optimizing the pneumatic pressure and viscosity of the inks with various ratios of PEI and NMP, followed by a two‐step heat treatment to develop fine PEI films. The dielectric constant of the PEI film increases from 2.28 to 2.61 with the corresponding secondary heating time of 1–5 h, which is much lower than the theoretical value owing to the free volume and loosely entangled polymer chains generated from the shear forces in printing and solvent evaporation. Furthermore, the film exhibits anisotropic mechanical properties in different printing directions, stemming from the alignment effect of the polymer molecules. It is believed that the developed PEI films and the facile methodology can be diversely tuned to provide new insights into material utilization, further extending the application fields.

Fire safe epoxy composite with low dielectric properties from a combination of fluoro-phosphonium salt, melamine and copper hydroxystannate

A phosphorus-fluorine containing compound tetraphenylphosphine hexafluorophosphate (Ph4PPF6) was synthesized by one-step method and characterized by FTIR, NMR, SEM, and EDX. Epoxy resin (EP) cured with an aliphatic hardener and Ph4PPF6 as a multifunctional additive were fabricated. The combined effects of Ph4PPF6 with melamine (MEL) and copper hydroxystannate (CuHS) on the fire safety, thermal stability, smoke toxicity and dielectric performances of EP were investigated. It is found that EP containing 2 wt% P (from Ph4PPF6) combined with 10 wt% MEL (sample EP 2P 10M) and EP with 2 wt% P from Ph4PPF6 combined with 5 wt% MEL, 5 wt% CuHS (sample EP 2P 5M5C) pass V0 classification in UL-94 VB tests. The cone calorimetric tests on these composites reveal that the peak heat release rate of sample EP 2P 5M5C is reduced by 64.2% in comparison to pure EP. The toxic gases including HF, CO, HCN are reduced to different extent when MEL and CuHS used as co-additives. The dielectric loss of sample EP 2P 10M is reduced by 26.3% in comparison to pure EP.

In-situ growth of porous Cu3(BTC)2 on cellulose nanofibrils for ultra-low dielectric films with high flexibility

The design of flexible polymeric films with internal porous structures has received increasing attention in low dielectric applications. The highly porous metal-organic frameworks (MOFs) of [Cu3(BTC)2]n (BTC=benzene-1,3,5-tricarboxylate) were introduced into aramid nanofibers (ANF) matrix by using carboxylated cellulose nanofibrils (CNF) as carriers to obtain strong, flexible, and ultra-low dielectric films. The well-dispersed “flowers-branch” like [email protected] through in-situ growth of CuBTC on CNF surface endowed the ANF/[email protected] films with excellent thermal stability, mechanical integrity and low dielectric properties. Besides, the flexible dielectric films exhibited superior ultraviolet (UV) resistance, lower coefficient of thermal expansion (4.28×10−5 °C − 1) and increased water contact angle (83.81°). More interestingly, the removal of guest molecules from the ANF/[email protected] films according to the vacuum heat treatment (VHT) process significantly improved their dielectric response. The specific surface areas of the composite films after VHT increased obviously, and the dielectric constant and dielectric loss tangent decreased to the expected 1.8–2.2 and 0.001–0.03 at 100 MHz, respectively. Consequently, such designable ultra-low dielectric films with high flexibility play an incredible significance in applications of microelectronics under large deformation conditions, especially in flexible/wearable devices at the arrival of 5 G era.

Boosting exciton dissociation by regulating dielectric constant in covalent organic framework for photocatalysis

Polymer semiconductor photocatalysts usually suffer from the high exciton binding energy because of the low dielectric constant. Herein, two crystalline polymer photocatalyst prototypes, neutral covalent organic framework (COF) and ionic covalent organic framework ( i COF), were employed to investigate the exciton effect. After polarization by the ionic sites with high dipole moment, the i COF endows a greatly increased dielectric constant to reach the low exciton binding energy of 23 meV, below the thermal energy under room temperature ( k B T, 26 meV). Thus, enhanced generation, separation, and transport of photogenerated charge carriers over the i COF catalyst resulted in a hydrogen peroxide production rate of 10.01 mmol g -1 h -1 in the photocatalytic oxygen reduction coupling with water oxidation reaction, which is almost 7 times higher than the neutral COF under identical conditions. This work demonstrates a promising way to tune the dielectric properties of polymer photocatalysts in order to regulate the exciton effect and related photocatalytic behavior. • Highly crystalline i COF was obtained in a microwave-assisted solvothermal route • The highly polar ionic sites enhanced the dielectric constant of the COF matrix • Low exciton binding energy was reached to allow spontaneous exciton dissociation • Rapid H 2 O 2 production was observed under visible-light irradiation in pure water Photocatalytic production of high-energy chemicals such as H 2 O 2 plays an essential role in seeking sustainable energy. Organic polymeric semiconductors that can be prepared from the earth’s abundant elements are preferential photocatalysts with advantages such as tunability. Nonetheless, the inherent low dielectric properties of organic polymers result in high exciton binding energies that inhibit the spontaneous exciton dissociation and thus restrict photocatalytic activity. Herein, we demonstrated that polarizing the covalent organic framework by integration of ionic moieties, fabricating i COF, can greatly increase the dielectric constant and thus reduce the exciton binding energy down to k B T (26 meV). The spontaneous exciton dissociation was obtained, accelerating the separation and transport of photogenerated carriers and thus a high H 2 O 2 production rate. This work opens a new avenue to boost the efficiency of organic semiconductors for solar-fuel production. The high polarization of the ionic sites greatly increases the dielectric constant of the COF matrix and thus reduces the exciton binding energy, effectively accelerating the H 2 O 2 production rate under visible-light irradiation.

Regression Analysis of the Dielectric and Morphological Properties for Porous Nanohydroxyapatite/Starch Composites: A Correlative Study.

This paper aims to investigate the dielectric properties, i.e., dielectric constant (ε′), dielectric loss factor (ε″), dielectric tangent loss (tan δ), electrical conductivity (σ), and penetration depth (Dp), of the porous nanohydroxyapatite/starch composites in the function of starch proportion, pore size, and porosity over a broad band frequency range of 5 MHz–12 GHz. The porous nanohydroxyapatite/starch composites were fabricated using different starch proportions ranging from 30 to 90 wt%. The results reveal that the dielectric properties and the microstructural features of the porous nanohydroxyapatite/starch composites can be enhanced by the increment in the starch proportion. Nevertheless, the composite with 80 wt% of starch proportion exhibit low dielectric properties (ε′, ε″, tan δ, and σ) and a high penetration depth because of its highly interconnected porous microstructures. The dielectric properties of the porous nanohydroxyapatite/starch composites are highly dependent on starch proportion, average pore size, and porosity. The regression models are developed to express the dielectric properties of the porous nanohydroxyapatite/starch composites (R2 > 0.96) in the function of starch proportion, pore size, and porosity from 1 to 11 GHz. This dielectric study can facilitate the assessment of bone scaffold design in bone tissue engineering applications.

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Preparation and performance of low‐dielectric benzocyclobutene resins containing dicyclopentadiene

AbstractLow‐dielectric‐constant polymer materials are widely used in the electronic industry owing to their unique characteristics. Benzocyclobutene (BCB) resin is one such material with excellent dielectric properties and thermal stabilities. In this work, a novel BCB‐functionalized monomer (DCPDNO‐BCB) was synthesized from 2,6‐dimethyl phenol‐DCPD novolac (DCPDNO) and 4‐Bromobenzocyclobutene through Ullmann coupling. The structure of DCPDNO‐BCB was characterized by 1H NMR, 13C NMR, and ESI‐MS, and poly(DCPDNO‐BCB), obtained by ring‐opening and subsequent Diels–Alder reaction at the appropriate temperature, was found to exhibit low dielectric properties (k = 2.53 at 10 MHz), low water absorption, high thermal stability (Td5 = 430°C), and good film flatness.

A novel UV-curable epoxy resin modified with cholic acid for high-frequency dielectric packaging

With the development of high-frequency communication technology, higher requirements are put forward to solder resist resin called dielectric ink that is applied to electric chips as coating, which needs high heat resistance and low dielectric properties. In this paper, different from general solder-resistance resin, cholic acid instead of acrylic acid was using to react with epoxy resin because of its unique configuration and multiple reactive sites (hydroxyl groups), after that, one mole carboxyl group would introduce four mole hydroxyl groups. All the hydroxyl groups were reacted with 1,2,5,6-Tetrahydrophthalic anhydride to produce four mole double bonds and four mole carboxyl groups. In order to adjust the acid value and increase the content of double bond of mixture, 1, 2, 3 and 4 mol glycidyl methacrylate were introduced to react with carboxyl groups. It was found that this kind of new UV-light-sensitive solid resist resin have high glass transition temperature (the highest is 144 °C), high double-bond conversion (68%) and low dielectric constant (the lowest is 2.51). Depending on above features, it is promising of the resin that can be applied for light-curing inks in high-frequency electronic packaging which requires better thermal and dielectric properties nowadays.

Low temperature sintering and dielectric properties of LaAlO3–BaSnO3-based microwave dielectrics

ABSTRACT LaAlO3–BaSnO3 ceramics as a new microwave dielectric material were investigated in terms of optimum synthesis conditions and thereby the relative density, microstructure, solid-solution state, and dielectric properties with the addition of various sintering aids at different sintering temperatures. The dielectric properties of 0.9LaAlO3–0.1BaSnO3 (LA-0.1BS) were strongly influenced by relative density, microstructure, chemical ordering, and mixing rule of the dielectric constant. Densification of the LA-0.1BS ceramics was improved from 82.3 to 96.13% with an average grain size of around 1.9 µm at reduced sintering temperature by 250°C. The LA-0.1BS ceramics sintered with 3 mol% of Bi2O3–SiO2 (BS) showed dielectric constant (ϵr) ∼21.18 with associated dielectric loss (tan δ) ∼0.00824 and Q × f ∼1213.59 (10 GHz) which could be achieved at low sintering temperature of 1400–1450°C.

Lanthanum substitution effect on the structural, optical, and dielectrical properties of nanocrystalline BaFe2O4 ferrites

The effects of varying the amount of lanthanum infusion on the barium ferrite characteristics were investigated in this study. An orthorhombic structure formed as a majority phase and traces of barium lanthanum iron oxide as segregated phases in the ferrites composites. The optical bandgap energy values of the BaLaxFe2−xO4 nanoferrites were 3.50–3.72 eV. SEM confirmed that the prepared nanoferrites had spherical morphology with size of 66.50–81.50 nm. The dielectric parameters of BaLaxFe2−xO4 nanoferrites were studied in the specified spectrum, which revealed the La doped barium nanoferrites had a low dielectric constant and conductivity properties compared to the barium nanoferrites. The saturation magnetization (60.03–25.98 emu g−1) and coercivity (454.85–80.65 Oe) of the prepared nanoferrites were improved due to an effect of La3+ ions. Accordingly, the observed optical bandgap energy, dielectric constant, and magnetism could be employed in high-frequency magneto-optoelectronic systems.

Flexible boron nitride composite membranes with high thermal conductivity, low dielectric constant and facile mass production

With the ever-increasing development of 5G technology, high signal propagation loss and high heating flux in miniaturizing devices bring about simultaneous and urgent requirement for thermal management materials with insulating, flexible, highly thermal conductive and low dielectric properties. However, these properties are not easy to simultaneous implement due to the phonon scattering and interfacial polarization, bringing a negative impact on working efficiency and service life of high-power electronics and portable devices. Herein, the flexible boron nitride composite membranes with high thermal conductivity, low dielectric constant and facile mass production was successfully prepared by coating directional forming and vacuum pressure technology. The directional arrangement of 2D boron nitride nanosheets (BNNS) in boron nitride-enhanced heat spreaders (BNHS) made the heat diffuse along in-plane direction and effectively improve the TC as high as 81.49 Wm−1K−1. In addition, the BNHS had a series of advantages of good electric insulation (the order of 1013 Ω cm), low dielectric constant (ϵ＜3) and low dielectric loss in the frequency range of 1 MHz–1 GHz. The BNHS also exhibited excellent flexibility (bending 20,000 times), high thermal stability and low water absorption. Distinguishing from electroconductive and heat-conducting graphite or graphene films, such superior BNHS with electric insulation but high TC and low dielectric constant will carve a distinctive path in the application of thermal management materials, such as RF antenna, filter, resonator and wireless charger.

Green polymer synthesis and low dielectric properties obtained by oxidative polymerization of thymol with CuCl-2-(p-tolyl)pyridine catalyst

Polymerization of thymol (2-isopropyl-5-methylphenol) was conducted using a bulky copper catalyst (CuCl-2-(p-tolyl)pyridine) in toluene under dioxygen atmosphere to give the corresponding 1,4-coupled polythymol (PPETh) with the Mn up to 22.7 kDa in moderate yield. The OH absorption in the IR spectrum disappeared almost completely and the presence of only nine signals in the 13C NMR spectrum clearly indicated the satisfactory formation of the expected linear PPETh. The PPETh exhibited good solubility in tetrahydrofuran, N,N-dimethylformamide, 1,4-dioxane, and CHCl3 (well-known for preparing industrial PPE26 from oxidative polymerization of 2,6-dimethylphenol), and good thermostability (Td5 in N2 of 410 °C). PPETh was mixed with PPE26 and the tough films were successfully prepared by the hot-press method in the weight fraction of PPETh up to 60%. TMA and DMA were performed to evaluate the Tg and the CTE of the films at 179–222 °C and 82–130 ppm/K, respectively. The dielectric properties were measured using a cavity resonator, in which the relative permittivity ranged from 2.28 (PPETh60%) to 2.46 (PPE26), and the dissipation factor from 0.00173 (PPE26) to 0.00495 (PPETh60%) at 10 GHz. The bulky isopropyl substituent gave to the PPETh polymer good solubility and insulating property with maintained thermal stability.

Preparation and properties of silicon nitride-phosphate composites for application in microwave furnace

Si3N4 ceramic is one of the most promising microwave metallurgy furnace materials because of the outstanding mechanical, relatively low dielectric properties and excellent thermal shock resistance. However, the difficult sintering of Si3N4 ceramics extremely restrict their large-scale application in the field of refractories for microwave metallurgy. In this work, silicon nitride-phosphate ceramics were fabricated by introducing aluminum phosphate or chromium phosphate aluminum into Si3N4 ceramics at 1500 °C. The effect of the amount of aluminum phosphate and chromium phosphate aluminum on sintering performance and dielectric properties was investigated. The results showed that the addition of aluminum phosphate or chromium phosphate aluminum could promote sintering, and the mechanical and dielectric properties of Si3N4 ceramics were efficiently improved. The Si3N4-aluminum phosphate composites exhibited better sintering performance (higher density and mechanical property) than that of Si3N4-chromium phosphate aluminum composites. Meanwhile, the dielectric constant and dielectric loss of Si3N4-chromium phosphate aluminum composites were better than Si3N4-chromium phosphate aluminum composites.

Polyhedral oligosilsesquioxane-modified boron nitride enhances the mechanical properties of polyimide nanocomposites.

A novel high-strength polyimide (PI) nanocomposite film was designed and constructed by the copolymerization of epoxidized polyhedral oligomeric silsesquioxane-modified hexagonal boron nitride and polyamic acid (PAA). The composite filler (EPPOSS@Gh-BN) was composed of silane coupling agent KH550 modified hexagonal boron nitride (Gh-BN) and epoxidized polyhedral oligomeric silsesquioxanes (EPPOSS), which improved not only the dispersion of the h-BN but also the effective interfacial stress transfer, leading to an enhanced mechanical strength of the resultant PI nanocomposite film of 114 MPa even with a slight EPPOSS@Gh-BN loading of 0.30 wt%, and the storage modulus was increased by more than 30% to 4 GPa compared to pure PI. Meanwhile, the PI/EPPOSS@Gh-BN nanocomposite has better heat transfer performance, higher hydrophobicity, lower dielectric properties, and higher heat stability than pure PI, and is therefore expected to provide an ideal platform for the development of highly flexible electronics in the future.

UV-curable low dielectric siloxane-benzocyclobutene resins via introducing carbosilane groups

• New UV-curable low dielectric siloxane-benzocyclobutene oligomers ( SBCOs ) on the basis of carbosilane groups were prepared. • The oligomeric SBCOs have a UV/thermally dual crosslinked structure. • Cured siloxane-benzocyclobutene resins exhibited high thermostability, mechanical strength, and low dielectric properties. Low dielectric UV-curable resins are compatible with photolithography and 3D printing technique, and have great potential for use in inter-layered packaging and antenna. However, it is still a challenge to construct photoactive structure which combines low dielectric properties. In the present work, we propose a new type of low dielectric UV-curable resins by employing photoactive silacyclobutene groups. This low dielectric resins were prepared by UV/thermally curing of siloxane-benzocyclobutene oligomers (SBCOs). Oligomeric SBCOs were prepared by the simple hydrolysis-polycondensation of 1,1-dichlorosilacyclobutane followed by termination of the benzocyclobutene groups. In this way, silaycyclobutene and benzocyclobutene groups were simultaneously introduced into the resins to enable UV and thermally curing of SBCOs. The molecular weight of SBCOs were tuned by the ratio of 1,1-dichlorosilacyclobutane and benzocyclobutene-containing monomer. The cured siloxane-benzocyclobutene resins were thermostable, mechanically strong, and had low dielectric properties.

Enhanced toughness and lowered dielectric loss of reactive POSS modified bismaleimide resin as well as the silica fiber reinforced composites

AbstractInherent brittleness is the most weakness of bismaleimide resin, which adversely affects the performance and application of the terminal fiber reinforced bismaleimide composites. In this study, polyhedral oligomeric silsesquioxane (POSS) with glycidyl group (G‐POSS) and methacryloxy propyl group (MA‐POSS) are utilized to toughen diallyl bisphenol‐A/N, N′‐4,4′‐diphenylmethane bismaleimide (BD resin) to obtain hybrid resins named BDGP and BDMP. The results of hybrid resins show that the two series hybrid resins perform higher toughness, strength, water resistance as well as lower dielectric constant and loss comparing with pristine BD resin, and BDMP perform better than BDGP due to that MA‐POSS can react with BD resin while G‐POSS cannot. In specific, the BDMP3 in which 3 wt% MA‐POSS is added performs the highest impact strength of 19.0 KJ/m2, increased by 102.1% comparing with pristine BD resin, and it also performs the lowest dielectric constant of 3.04 as well as lowest dielectric loss of 0.006 at 1 MHz. In addition, the silica fiber reinforced BDMP composites (SF/BDMP) are fabricated, and the results show that the bending strength and interlaminar shear strength of SF/BDMP3 composite are enhanced to 290.2 and 32.5 MPa, 32.0% and 38.4% higher than those of SF/BD composite, and the corresponding dielectric loss (0.025) at 8.2 GHz is reduced by 45.9%. This research displays that reactive POSS can improve the toughness and reduce the dielectric loss of resin, which is benefit to obtain a high performance and functional resin‐based composites with excellent mechanical properties and low dielectric properties.

Low-dielectric styrene resins with high mechanical strength and good (re)processability via constructing imine-crosslinked network and introducing small amount of amino molecules

• By introducing free amine compound (dodecylamine, DDA), styrene resins exhibited good (re)processability, while preserving low dielectric constant at 2.71 and the high mechanical strength 52 MPa. • We found for the first time that the incorporation of small amount of amino compound (dodecylamine, DDA) resulted in the great increase of (re)processability owing to the formation of imine moieties with relatively high free degree. • As compared with most of current (re)processable polymers, PS-imine exhibited advantageous trade-off between reprocessability and mechanical performance. Materials used in circuit boards need to be recyclable in order to decrease resource waste and mitigate environmental pollution. However, it is challenging to prepare resins with high mechanical strength while preserving their good reprocessing and low dielectric property. In this study, an adaptable imine crosslinking network (imine-CAN) was constructed and a free amine compound (dodecylamine, DDA) was introduced to obtain styrene resins exhibited good (re)processability even at a high crosslinking density. The resin has a low dielectric constant of 2.71 and high mechanical strength of 52 MPa. Moreover, after reprocessing three times, the dielectric constants of the PS-imines remained constant and 94% mechanical strength was recovered. Further investigation indicated that the (re)processability and decrosslinking at high temperatures were regulated by incorporating different amounts of DDA. PS-imines showed superior mechanical and reprocessing performance compared to most current reprocessable resins. These new vitrimers could be potential candidates for use in recyclable circuit boards.

(Invited) Boron Carbon Nitride (BCN) Thin Films for Low-k Interdielectric Layer Applications

New forms of carbon have gathered attention for many years for advanced technological development as well as to address environmental concerns. Carbon when combined with other elements enhances its structural diversity. This enhancement in structural diversity has been the fundamental step towards progress of carbon-based materials for an extensive range of applications. Particularly, compounds in the boron-carbon-nitrogen (BCN) phase diagram such as diamond (C), cubic boron nitride (c-BN) and boron carbide (B4C) exhibit interesting properties owing to their covalent bonding, short bond lengths, low atomic mass [1]. As graphite is semi-metallic and h-BN is insulating, hybrid BCN materials between graphite and h-BN exhibits excellent semiconducting properties. BCN materials are known to combine unique properties of B4C and BN, and the properties are tunable based on the composition and structure. These properties assigns BCN materials with low dielectric constant along with excellent thermal and mechanical strength [2].BCN compounds gathered interest due to their low dielectric properties, which is the primary pursuit of semiconductor industry during the past few decades. What makes BCN materials prominent is not only the fact that it is possible to tune their properties, but also distinct composition exhibits unique property. BCN materials can be synthesized using various techniques such as chemical vapor deposition (CVD), magnetron sputtering, pulsed laser deposition (PLD). This talk will focus on the thin film growth of BCN films by RF sputtering technique. Influence of synthesis methods and its process parameters on the electrical properties and elemental composition of BCN materials will be discussed.