Versatile Landscape of Low-k Polyimide: Theories, Synthesis, Synergistic Properties, and Industrial Integration

The development of microelectronics and large-scale intelligence nowadays promotes the integration, miniaturization, and multifunctionality of electronic and devices but also leads to the increment of signal transmission delays, crosstalk, and energy consumption. The exploitation of materials with low permittivity (low-k) is crucial for realizing innovations in microelectronics. However, due to the high permittivity of conventional interlayer dielectric material (k ∼ 4.0), it is difficult to meet the demands of current microelectronic technology development (k < 3.0). Organic dielectric materials have attracted much attention because of their relatively low permittivity owing to their low material density and low single bond polarization. Polyimide (PI) exhibits better application potential based on its well permittivity tunability (k = 1.1-3.2), high thermal stability (>500 °C), and mechanical property (modulus of elasticity up to 3.0-4.0 GPa). In this review, based on the synergistic relationship of dielectric parameters of materials, the development of nearly 20 years on low-k PI is thoroughly summarized. Moreover, process strategies for modifying low-k PI at the molecular level, multiphase recombination, and interface engineering are discussed exhaustively. The industrial application, technological challenges, and future development of low-k PI are also analyzed, which will provide meaningful guidance for the design and practical application of multifunctional low-k materials.

A Review of Polyolefin-Insulation Materials in High Voltage Transmission; From Electronic Structures to Final Products

This review focuses on the use of polyolefins in high-voltage direct-current (HVDC) cables and capacitors. A short description of the latest evolution and current use of HVDC cables and capacitors is first provided, followed by the basics of electric insulation and capacitor functions. Methods to determine dielectric properties are described, including charge transport, space charges, resistivity, dielectric loss, and breakdown strength. The semicrystalline structure of polyethylene and isotactic polypropylene is described, and the way it relates to the dielectric properties is discussed. A significant part of the review is devoted to describing the state of art of the modeling and prediction of electric or dielectric properties of polyolefins with consideration of both atomistic and continuum approaches. Furthermore, the effects of the purity of the materials and the presence of nanoparticles are presented, and the review ends with the sustainability aspects of these materials. In summary, the effective use of modeling in combination with experimental work is described as an important route toward understanding and designing the next generations of materials for electrical insulation in high-voltage transmission.

The Recent Advances of Polymer-POSS Nanocomposites With Low Dielectric Constant

This study provides a comprehensive overview of the preparation methods for polyhedral oligomeric silsesquioxane (POSS) monomers and polymer/POSS nanocomposites. It focuses on the latest advancements in using POSS to design polymer nanocomposites with reduced dielectric constants. The study emphasizes exploring the potential of POSS, either alone or in combination with other materials, to decrease the dielectric constant and dielectric loss of various polymers, including polyimides, bismaleimide resins, poly(aryl ether)s, polybenzoxazines, benzocyclobutene resins, polyolefins, cyanate ester resins, and epoxy resins. In addition, the research investigates the impact of incorporating POSS on improving the thermal properties, mechanical properties, surface properties, and other aspects of these polymers. The entire study is divided into two parts, discussing systematically the role of POSS in reducing dielectric constants during the preparation of POSS composites using both physical blending and chemical synthesis methods. The goal of this research is to provide valuable strategies for designing a new generation of low dielectric constant materials suitable for large-scale integrated circuits in the semiconductor materials domain.

Dielectric Properties of Benzocyclobutene-Based Resin: A Molecular Dynamics Study

Benzocyclobutene (BCB)-based resins have garnered considerable attention because of their remarkable dielectric properties and thermal stability. However, in molecular dynamics (MD) simulations, progress in BCB-based resin research has yet to keep pace with experimental advancements, resulting in a shortage of theoretical underpinnings at the molecular level. This study focuses on a novel homopolymer, poly(2-(4-benzocyclobutenyl)-divinylbenzene(DVB-S-BCB)), and devises an interactive methodology suitable for BCB-based resins. We implemented a Python script for the joint relaxation method to construct a three-dimensional model of the cured polymer using MadeA and LAMMPS. We conducted MD simulations to investigate how the cross-linking degree and resin molecular weight influence the dielectric properties of the cured polymer. Furthermore, we analyzed the thermodynamic properties through simulation. The results illustrate that augmenting the cross-linking degree and resin molecular weight results in a higher cross-linking density and reduced free volume, thereby increasing the dielectric constant of the resin. The cross-link density does not increase indefinitely with molecular weight, and after a certain threshold is reached, it cannot have a significant effect on the dielectric constant. The degree of cross-linking exerts a more pronounced impact on the dielectric constant than the molecular weight of the resin. In addition, the simulation results denote the excellent thermodynamic properties of the cured polymer. This study also examines the dielectric and thermodynamic properties of the resin samples that were experimentally prepared. The obtained data successfully confirm the reliability of the simulation results. This study offers novel insights for future simulation research on benzocyclobutene-based resins. Additionally, it provides theoretical support for exploring experimental work on low-dielectric materials in the electronic field.

Modeling the Effect of Material Viscoelasticity on the Dielectric Permittivity of Deformed Elastomers

Elastomers, as a typical category of soft dielectrics, have shown great potential for developing stretchable electronics and soft transducers. However, the performance of dielectric elastomers (DEs) is susceptible to the dielectric permittivity of the material, whether as insulators or actuators. On the other hand, experiments suggest that the material viscoelasticity significantly influences the dielectric permittivity of DEs. Based on the theory of finite-deformation viscoelasticity, this work adopts the Brillouin function to develop a modeling framework to examine the effect of material viscoelasticity on the dielectric permittivity for the first time. A comparison of the data fitting results between the models with and without consideration of the material viscoelasticity is presented. Simulation results also reveal that the viscous network of the elastomer exerts a mitigation effect on the decrease in the dielectric permittivity when the material is deformed. Furthermore, it is found that the loading rate is a key parameter that strongly affects the dielectric permittivity, mainly through the inelastic deformation.

Amorphous Poly (Aryl Ether Ketones) Containing Methylene Groups with Excellent Thermal Resistance, Dielectric Properties and Mechanical Performance

Low-dielectric constant polymers are widely used in various microelectronic materials. With the development of 5G communication technology, there is an urgent need for polymer materials with low dielectric constant at high frequency, good thermal resistance, and mechanical properties. In this study, four novel poly (aryl ether ketone) (PAEK) containing different numbers of methylene groups were synthesized via nucleophilic polycondensation reaction. At 10 GHz, these polymer films exhibit excellent dielectric properties with dielectric constants as low as 2.76. The relationship between the dielectric constant and the number of methylene groups is illustrated by constructing the amorphous accumulation cell model. In addition, methylene groups provided the polymer with favorable mechanical performance, including Young's modulus in the range of 2.17-2.21 GPa, the tensile strength from 82.0 to 88.5 MPa and the elongation at the break achieved 7.94%, respectively. Simultaneously, the polymer maintains good thermal resistance with a glass transition temperature (Tg) reaching 216 °C. The result indicates that the obtained novel PAEK is potentially valuable in the field of high-frequency communications.

Recent Progress of Low Dielectric and High-Performance Polybenzoxazine-Based Composites

With the rapid advancement of intelligent electronics, big data platforms, and other cutting-edge technologies, traditional low dielectric polymer matrix composites are no longer sufficient to satisfy the application requirements of high-end electronic information materials, particularly in the realm of high integration and high-frequency, high-speed electronic communication device manufacturing. Consequently, resin-based composites with exceptional low dielectric properties have garnered unprecedented attention. In recent years, benzoxazine-based composites have piqued the interest of scholars in the fields of high-temperature-resistant, low dielectric electronic materials due to their remarkable attributes such as high strength, high modulus, high heat resistance, low curing shrinkage, low thermal expansion coefficient, and excellent flame retardancy. This article focuses on the design and development of modification of polybenzoxazine based on low dielectric polybenzoxazine modification methods. Studies on manufacturing polybenzoxazine co-polymers and benzoxazine-based nanocomposites have also been reviewed.

Design and Synthesis of Low Dielectric Poly(aryl ether ketone) from Incorporation Bulky Fluorene Groups and Regular Hydroquinone Structure

To decrease the dipole polarization rate and reduce the dielectric constant of poly(aryl ether ketone) (PAEK) resin, 1,4-di(4-fluorobenzoyl) cyclohexane (DFBCH), a weakly polarizing cyclohexane-based monomer, was designed and synthesized as the primary reactant. The bulky fluorene group was incorporated to increase the free volume of the resin, further reducing the dielectric constant. Additionally, hydroquinone with a symmetric and regular structure was utilized to enhance the molecular chain's regularity and reduce dipole relaxation, further lowering the resin's dielectric constant and dielectric loss. The PFQEKs series resins exhibited excellent thermal stability with glass transition temperature (Tg) ranging from 222 to 239 °C and 5% weight loss (Td5%) ranging from 458 to 463 °C, with different monomer ratios. As the hydroquinone content increased, the dielectric constant (Dk) and dielectric loss (Df) of the resin decreased significantly, with Dk ranging from 2.92 to 2.77 and Df ranging from 0.011 to 0.008 at 10 GHz.

Phosphorus-Containing Flame-Retardant Benzocyclobutylene Composites with High Thermal Stability and Low CTE

As a component of printed circuit substrate, copper clad laminate (CCL) needs to meet the performance requirements of heat resistance, flame retardancy, and low coefficient of thermal expansion (CTE), which, respectively, affects the stability, safety, and processability of terminal electronic products. In this paper, benzocyclobutylene (BCB)-functionalized phosphorus-oxygen flame retardant composites were prepared through introducing the BCB groups, and the performance was researched by thermogravimetric analysis, microcombustion calorimetry, and thermomechanical analysis. The research results show that these phosphorus oxide compounds containing BCB groups show good thermal stability and low total heat release (THR) after thermal curing, and the more BCB groups on the phosphorus oxide monomers, the better the thermal stability and flame retardancy of cured resins. The T_d5 and THR of the composite (M3) are as high as 443 °C and 23.1 kJ/g, respectively. In addition, the CTE of M3 is as low as 16.71 ppm/°C. Introduction of BCB groups which can be crosslinked through heat to improve the thermal stability, flame retardancy, and reduced CTE of traditional organophosphorus flame retardant materials. These materials are expected to be good candidates for CCL substrates for electronic circuits.

Polyimide/crown ether composite film with low dielectric constant and low dielectric loss for high signal transmission

Dielectric properties of polyimide (PI) are constrained by its inherent molecular structure and inter-chain packing capacities. The compromised dielectric properties of PI, however, could be rescued by introducing trifluoromethyl and forming a host-guest inclusion complex with the introduction of crown ethers (CEs). Herein, we report PI/crown ether composite films as a communication substrate that could be applied under high frequency circumstances. In this work, three kinds of bisphenol A-containing diamine (2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(2-methyl-4-aminophenoxy)phenyl]propane, and 2,2-bis[4-(2-trifluoro methyl-4-aminophenoxy)phenyl]propane) are synthesized and polymerized with 4,4'-(hexafluoroisopropylidene)diphthalic anhydride to prepare low-dielectric PI films by means of thermal imidization. Crown ethers are introduced into the PI with different mass fractions to obtain three series of PI films. Following the combination of trifluoromethyl into the molecular chain of PI, high frequency dielectric loss of modified PI films can be effectively reduced. The properties of these materials (especially the dielectric properties) are thoroughly explored by crown ether addition. The results show that the crown ether addition process can offer crown ethers with increased free volume of PI matrix, thus allowing them to generate a special necklace-like supramolecular structure, which makes the crown ether disperse more uniformly in the PI matrix, resulting in improved dielectric properties. Importantly, the dielectric constant and dielectric loss of the composite films at high frequencies are remarkably reduced to 2.33 and 0.00337, respectively. Therefore, these composite films are expected to find extensive use as a 5G communication substrate at high frequencies in the future.

Non-Coplanar Diphenyl Fluorene and Weakly Polarized Cyclohexyl Can Effectively Improve the Solubility and Reduce the Dielectric Constant of Poly (Aryl Ether Ketone) Resin

With the rapid development of high-frequency communication and large-scale integrated circuits, insulating dielectric materials require a low dielectric constant and dielectric loss. Poly (aryl ether ketone) resins (PAEK) have garnered considerable attention as an intriguing class of engineering thermoplastics possessing excellent chemical and thermal properties. However, the high permittivity of PAEK becomes an obstacle to its application in the field of high-frequency communication and large-scale integrated circuits. Therefore, reducing the dielectric constant and dielectric loss of PAEK while maintaining its excellent performance is critical to expanding the PAEK applications mentioned above. This study synthesized a series of poly (aryl ether ketone) resins that are low dielectric, highly thermally resistant, and soluble, containing cyclohexyl and diphenyl fluorene. The effects of cyclohexyl contents on the properties of a PAEK resin were studied systematically. The results showed that weakly-polarized cyclohexyl could reduce the molecular polarization of PAEK, resulting in low permittivity and high transmittance. The permittivity of PAEK is 2.95-3.26@10GHz, and the transmittance is 65-85%. In addition, the resin has excellent solubility and can be dissolved in NMP, DMF, DMAc, and other solvents at room temperature. Furthermore, cyclohexyl provided PAEK with excellent thermal properties, including a glass transition temperature of 239-245 °C and a 5% thermogravimetric temperature, under a nitrogen atmosphere of 469-534 °C. This makes it a promising candidate for use in high-frequency communications and large-scale integrated circuits.

High-Dielectric PVP@PANI/PDMS Composites Fabricated via an Electric Field-Assisted Approach

Polymer-based composite films with multiple properties, such as low dielectric loss tangent, high dielectric constant, and low cost are promising materials in the area of electronics and electric industries. In this study, flexible dielectric films were fabricated via an electric field-assisted method. Polyaniline (PANI) was modified by polyvinylpyrrolidone (PVP) to form a core–shell structure to serve as functional particles and silicone rubber polydimethylsiloxane (PDMS) served as the matrix. The dielectric constant of the composites prepared under electric fields was improved by the micro-structures formed by external electric fields. With the addition of 2.5 wt% PVP@PANI, the dielectric constant could be significantly enhanced, up to 23; the dielectric loss tangent is only 1, which is lower than that of the aligned PANI samples. This new processing technology provides important insights for aligning fillers in polymer matrix to form composites with enhanced dielectric properties.