低介电常数聚酰亚胺的研究进展

现代微电子工业要求层间绝缘材料具有较低的介电常数。该文介绍了几种降低聚酰亚胺介电常数的方法,包括含氟聚酰亚胺、聚酰亚胺无机杂化复合材料和聚酰亚胺多孔材料,其中最为有效的措施是将含氟取代基引入到聚酰亚胺分子结构中。     

Synthesis and characterization of novel adamantane‐based copoly(aryl ether ketone)s with low dielectric constants

A series of novel adamantane‐based copoly(aryl ether ketone)s (PAEK‐CF₃‐Ad) with low dielectric constants were prepared by post‐amidation of copoly(aryl ether ketone)s containing (3‐trifluoromethyl)phenyl and carboxyl groups with 4‐adamantylaniline. Compared with the preparation of adamantane‐containing poly(aryl ether ketone)s by direct polymerization of adamantyl‐substituted monomers, this side‐chain grafting method avoids various problems, such as high polymerization temperature and the difficult polymerization of adamantyl‐substituted monomers. The dielectric, thermal and mechanical properties of the synthesized PAEK‐CF₃‐Ad were characterized using a precision impedance analyzer, differential scanning calorimetry and thermogravimetric analysis, and a universal tester, respectively. The results indicate that PAEK‐CF₃‐Ad films exhibited low dielectric constants ranging from 2.33 to 2.65 at 1 MHz due to the introduction of the adamantyl groups. The synthesized PAEK‐CF₃‐Ad copolymers exhibited good thermal and mechanical properties. © 2013 Society of Chemical Industry     

Silacyclobutane-functionalized cyclosiloxanes as photoactive precursors for high thermal stability,low dielectric constant and low dielectric loss polymers

Low dielectric photoactive materials have significant potential as components in future microelectronics. Although a number of photosensitive groups have been used to construct photopatternable materials, it remains challenging to introduce these groups into polymer chains via facile yet controlled polymerization techniques. The present work demonstrates the synthesis of a new class of photoactive cyclosiloxane monomers having hybrid siloxane-carbosilane main chains. These compounds can be cured by applying ultraviolet radiation and heat to promote the reaction of the silacyclobutene units and form hyper-cross-linked cyclosiloxanes. The cured resins show high thermal stability (with T_5% values in the range of 460–550°C), low dielectric constants (2.36–2.76 at 10 MHz) and low dielectric losses (10⁻³ at 10 MHz). Thus, these polymers could possibly be used as high-performance dielectric materials.     

Fully aliphatic polyimides from adamantane‐based diamines for enhanced thermal stability,solubility, transparency,and low dielectric constant

We have synthesized a series of fully aliphatic polyimides (APIs) from bicyclo[2,2,2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BOCA) and various aliphatic diamines, including linear aliphatic, flexible alicyclic, and rigid adamantyl diamines. We performed the polymerization reactions using one‐step syntheses in m‐cresol at elevated temperatures without the isolation of poly(amic) acid. The chemical composition and structure of the polymers were characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectrometry. The characterization data are reported from analyses using gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), and wide‐angle X‐ray diffraction (WXAD) measurements. The polyimides are also subjected to solubility, solution viscosity, tensile strength, transparency, and dielectric constant measurements. The resultant polyimides possess well‐controlled molecular weight, reasonable intrinsic viscosity, good transparency, enhanced solubility, low dielectric constants, and high glass transition temperature, together with marginal thermal and mechanical stability. These properties were enhanced in copolyimides containing equimolar amounts of rigid and flexible moieties. These rigid‐rod APIs derived from the alicyclic dianhydride and aliphatic diamines are promising candidates as advanced materials for future applications in micro‐ and photoelectronic devices. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3316–3326, 2006     

Study on properties of low dielectric loss resin matrix

Allyl phenyl compounds, allyl epoxy resins, and epoxy acrylate resins are adapted to copolymerize with bismaleimide (BMI) resins and to modify mechanical properties and processing properties. Reaction activity, physical properties, mechanical properties, dielectric properties, and thermal stability were investigated. Impact strength and flexural strength of modified BMI resin are increased about twice and 42% than that of pure BMI resin, respectively. Fracture elongation is from 1.6 to 2.3%. The fracture surfaces of the broken specimens are examined by scanning electron microscopy (SEM). As a result, modified BMI resins put up typical toughness rupture. The modified BMI resins possess excellent dielectric properties, and dielectric constant and dielectric loss almost hold the line with increasing epoxy concentration. When the test frequency scope is from 1 to 20 GHz, the dielectric constant and dielectric loss of modified BMI resins is 3.05–3.12 and 0.0089–0.012, respectively. The modified BMI resins still possess fine properties after hydrothermal aging. After 100 h in boiling water, the reservation ratios of both the impact strength and flexural strength of modified system exceeded 90%, and the water absorption and heat distortion temperature (HDT) is 2.6% and 235°C, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 315–319, 2006     

Synthesis and properties of aromatic polyimides based on ether-sulfone-diamines

Two diamine monomers, 4,4′-[sulfonylbis(1,4-phenyleneoxy)]dianiline (III _a ) and 4,4′-[sulfonylbis(2,6-dimethyl-l,4-phenyleneoxy)]dianiline (III _b ), were prepared by an aromatic nucleophilic substitution of 4,4′-sulfonyldiphenol (I _a ) and 4,4′-sulfonylbis(2,6-dimethylphenol) (I _b ) with p-chloronitrobenzene in the presence of potassium carbonate, followed by hydrazine catalytic reduction of the intermediate dinitro compounds. The diamines III _a and III _b were used as monomers with various aromatic tetracarboxylic dianhydrides (IV _a–f ) to synthesize polyimides. The polymerization was conducted in two steps via the formation of a poly(amic acid) precursor followed by thermal cyclodehydration. The poly(amic acid)s had inherent viscosities above 0.87 and up to 2.56 dL/g. Most poly(amic acid)s could be coated and thermodehydrated into flexible and transparent polyimide films. The polyimides derived from the dianhydrides containing-O-and-SO₂-or-C(CF₃)₂-bridging groups between the phthalic anhydride units were soluble in some organic solvents such as N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF). The glass transition temperatures (T_g) of the polyimides were in the range from 254 to 300 °C. The methyl-substituted polyimides exhibited slightly higher solubility and higher T_g compared to the corresponding unsubstituted polyimides. Thermogravimetric analysis (TG) showed that the polyimides containing methyl substitutents started to lose weight around 450 °C and the unsubstituted ones started to lose weight around 550 °C.     

Epoxy/benzoxazinyl POSS nanocomposite resin with low dielectric constant and excellent thermal stability

Benzoxazinyl modified polyhedral oligomeric silsesquioxane (BZPOSS) is successfully synthesized and used to prepare nanocomposites with bisphenol A type epoxy resin (E51). The differential scanning calorimetry results showed the curing peak temperature of E51/BZPOSS blend decrease to 242°C, suggesting the high catalytic activity of BZPOSS to the polymerization of E51. The scanning electron microscope micrographs of poly(E51/BZPOSS)s and silicon element distribution maps given by EDS both demonstrated homogeneous dispersion of BZPOSS. Dielectric properties tests confirmed the dielectric constant can be reduced by the introduction of BZPOSS, which is attributed to the nano-pores from the cage structure of POSS. When 20 wt% BZPOSS was added, the dielectric constant decreased to 2.28 at 1 MHz. Meanwhile, DMA and TGA results indicated the thermal stability and heat resistance of poly(E51/BZPOSS)s at high temperature increased with the increase of BZPOSS, which is due to the increase of the crosslinking density and the change of crosslinking structure of copolymer.     

Dependence of the dielectric constant on the fluorine content and porosity of polyimides

The trend toward miniaturization in integrated circuit fabrication demands good interlayer dielectric materials. This need can be met by polyimide (PI), which has extreme thermal and chemical stability and, most importantly, a low dielectric constant. Four porous PIs with symmetrically substituted fluorine contents were synthesized. Different porosity levels were achieved with a sol–gel technique through the incorporation of 10 or 20% tetraethyl orthosilicate into the polymer matrix and then acid etching. Their dielectric constants were correlated with the fluorine contents and porosity levels. High porosity levels and higher fluorine contents induced substantial decreases in the PI dielectric constants (2.4–2.7). The resultant values were within the applicable range for dielectric materials in integrated circuits. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polyimide hollow glass microspheres composite films with low dielectric constant and excellent thermal performance

Nowadays, polyimide (PI) with low dielectric constant is expected to be widely applied in microelectronics. For this reason, hollow glass microspheres (HGM) modified by silane coupling agent KH-550 (K-HGM), a series of HGM/PI and K-HGM/PI composite films with excellent thermal performance, hydrophobic and low dielectric constant were fabricated by in situ polymerization. The effect of HGM/K-HGM content on the properties of composite films was studied. The superior heat resistance of HGM can improve the thermal performance of composite films. Due to silane coupling agent KH-550, K-HGM exhibits a good interfacial compatibility with PI matrix and forms an interfacial adhesion region. With the HGM loading of 6%, comparing with pure PI films, the glass transition temperatures (T_g) of composite films were dramatically increased by 32.3°C. Especially, the low dielectric constant of 2.21 and dielectric loss of 0.0059 at 1 MHz were obtained for the PI/K-HGM composite film with addition of 8 wt%. Thus, PI/K-HGM composite films show more excellent performance. The current work provides a promising solution for fabrication of PI with low dielectric constant and superior thermal performance that may be applied in microelectronics industry.     

High and temperature-stable dielectric constants in PNb9O25 ceramic

PNb₉O₂₅ ceramic was prepared using a sparking plasma sintering (SPS) method. Microstructure, dielectric and electrical properties of the ceramic were investigated. Dense ceramic was obtained, and the ceramic exhibited a high dielectric constant (>1000) and a low dielectric loss (∼2%) in the investigated frequency range of 100 Hz-100 kHz at room temperature. Dielectric relaxations with strong frequency dispersion occurred at temperatures higher than 250°C, which were due to oxygen vacancies. A highly stable capacitance (< 10% deviation) over a wide temperature range of –30°C to –200°C was obtained. The ceramic also showed a relatively high electrical conductivity (>4 × 10⁻⁸ S/cm) with an activation energy of approximately 0.9 eV in the temperature range of >200°C.     

Inclusion of covalent triazine framework into fluorinated polyimides to obtain composites with low dielectric constant

Polyimides possess good mechanical properties, favorable dielectric properties, and chemical inertness, which enabled them to find applications in microelectronic industries. The dielectric constant of the polyimides varies between 2.5 and 4, which is rather high for such applications. Hence, synthesizing polyimides with still lower dielectric constant has become one of the critical research confronts. As the properties of a terpolyimides (TPI) could be altered as per the requirement, it was synthesized by combining the dianhydrides 3,3′,4,4′-biphenyldianhydride, 3,3′,4,4′-oxydiphthalicdianhydride, and 4,4′-(hexafluoroisopropylidene) with a diamine 4,4′-(hexafluoroisopropylidene)dianiline or 2,2-bis[4-(4-amino phenoxy)phenyl]hexafluoropropane. As porous covalent triazine framework (CTF-1) is capable of capturing much air within its pores and interfacial voids, it was combined with the TPI matrix in different loadings to obtain CTF-1/TPI composite films with low dielectric constant. The composites exhibited high thermal stability, as their thermal decomposition occurred above 520°C. The tensile properties and the dielectric constant of the composites declined with the raise in CTF-1 loading up to 4%. The decrease in dielectric constant is essentially due to the incorporation of air voids (dielectric constant of air ~1) in the TPI matrix due to the inclusion of porous CTF-1.     

Structural effects of pendant groups on thermal and electrical properties of polyimides

Two series of aromatic polyimides containing various‐sized alkyl side groups were synthesized by thermal imidization of the poly(amic acid)s prepared from the polyaddition of benzophenonetetracarboxylic dianhydride and hexafluoro‐isopropylidene bis(phthalic anhydride) with 4,4′‐methylenedianiline, 4,4′‐methylene‐bis(2,6‐dimethylaniline), 4,4′‐methylene‐bis(2,6‐diethylaniline), and 4,4′‐methylene‐bis(2,6‐diisopropylaniline). The extent to which alkyl substitutes affect the thermal properties of polyimides was examined by differential scanning calorimetry, thermomechanical analyzer, and thermogravimetric analysis techniques. The analytical results demonstrated that the incorporation of alkyl moieties causes a moderate increase in the coefficient of thermal expansion and a slight decrease in thermal stability. Notably, all polymers had a decomposition temperature exceeding 500°C. The glass transition temperature increases markedly when hydrogen atoms at ortho positions on aniline rings are replaced with methyl groups, but decreases with growing alkyl side group size. The dielectric measurements show that the polymer possessing a large alkyl side group would have the lower dielectric value. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4672–4678, 2006     

Hyperbranched-polysiloxane-based hyperbranched polyimide films with low dielectric permittivity and high mechanical and thermal properties

A series of hyperbranched polysiloxane (HBPSi)-based hyperbranched polyimide (HBPI) films with low dielectric permittivity and multiple branched structures are fabricated by copolymerizing 2,4,6-triaminopyrimidine (TAP) with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, 4,4′-diaminodiphenyl ether, and HBPSi via the two-step polymerization method. The dielectric permittivity of HBPSi hyperbranched polyimide films decreases with increasing TAP fraction, namely, from 3.28 for sample PI-1 to 2.80 for PI-4, mainly owing to the enlarged free volume created by the incorporation of multiple branched structures. Moreover, HBPSi HBPI possesses desirable solubility and good mechanical properties and thermal stability. PI-4 not only has low dielectric permittivity (2.80, 1 MHz), excellent solubility (soluble in several common organic solvents), and remarkable thermal properties (glass-transition temperature of 273 °C, 5% weight loss temperature of 498 °C in N₂ and 486 °C in O₂), but it also demonstrates admirable mechanical properties with a tensile strength of 103 MPa, elongation at break of 7.3%, and a tensile modulus of 2.16 GPa. HBPSi HBPI might have potential applications in interlayer dielectrics and other microelectronics fields. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47771.     

Mechanical and Thermal Performances of Roselle Fiber-Reinforced Thermoplastic Polyurethane Composites

The aim of this paper is to present research findings on the measurements of mechanical, morphological, and thermal properties of Roselle fiber-reinforced thermoplastic polyurethane composites. The Roselle fiber/thermoplastic polyurethane composites were prepared with fibers of different sizes such as 125?µm and lower, 125–300 and 300–425?µm by internal mixer and hot press at 170°C. The results show that mechanical properties (tensile, flexural, and impact properties) of the composites were improved with the increase in fiber sizes. The highest tensile (10.45?MPa), flexural strength (6.93?MPa), and impact strength (20.22 kJ/m²) was obtained from composites with 300–425?µm fiber size of Roselle fiber/thermoplastic polyurethane composites. Morphological properties of dispersion fiber and tensile fracture surfaces were studied using scanning electron microscope. Thermal properties of the composites were studied using thermogravimetric analyses and results showed that the thermal decomposition effect was almost similar for all compositions.     

Phosphorus‐containing polyhedral oligomeric silsesquioxane/polyimides hybrid materials with low dielectric constant and low coefficients of thermal expansion

Novel phosphorus‐containing polyhedral oligomeric silsesquioxane (POSS)/polyimides (PI) hybrid materials with low dielectric constant and low linear coefficients of thermal expansion (CTE) were prepared and characterized. The POSS/PI hybrid materials were synthesized with octa(aminopropyl)silsesquioxane (OAPS) and a series of phosphorus‐containing polyamide acids(PAA). The PAAs were synthesized with bis(4‐aminophenoxy) phenyl phosphine oxide (BAPPO), 4,4’‐diaminodiphenyl ether (ODA) and 3,3',4,4'‐biphenyl tetracarboxylic diandhydride (BPDA). The structures and properties of the hybrid materials were characterized. And the effect of the phosphorus‐containing structure on the POSS/PI hybrid materials was discussed. The dielectric constants and CTE of the hybrid materials were remarkably lower than that of the unmodified POSS/PI films. The lowest values of dielectric constant and CTE could achieve as low as 2.64 (1 MHz) and 27.45 ppm/K. Besides, the hybrid materials also had excellent thermal properties. The highest 5% weight loss temperature of the hybrid materials was as high as 580°C under air. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42611.     

Adhesive and Thermo-Mechanical Behavior of Phosphorus-Containing Thermoplastic Polyimides

Recently some papers were published, where criticism of current theories of adhesion had been given.^1,2,3 As a most general theory the rheological theory of adhesion has been proposed, or the theory of mechanical deformation of adhesive joints. This conception should be very useful if only it could give any reasonable clue to understanding of the cause of interfacial adhesion.     

Adhesive and Thermo-Mechanical Behavior of Phosphorus-Containing Thermoplastic Polyimides

Thermally stable, soluble and amorphous bis(m-aminophenoxy) triphenylphosphine oxide (m-BAPPO) based polyimides were synthesized in controlled high molecular weight via solution imidization. Several dianhydrides were used to establish chemical-structure-physical property behavior. The m-BAPPO based polyimides were characterized by several techniques, including intrinsic viscosity, thermal analysis, single lap shear adhesive bond strength and thermo-mechanical behavior. The resulting phosphorus-containing polyimides were demonstrated to be thermally stable via dynamic TGA in air up to 500°C and showed 10 ∼ 20% char yield at 750°C, suggesting improved fire resistance. In addition, these polyimides showed good tensile modulus, ductile stress-strain behavior and excellent adhesion to a Ti-6A1-4V substrate, as determined by single lap shear tests. The rheological behavior was investigated by using a parallel plate type viscometer which confirmed that the materials were true thermoplastics. Tailoring the polyimides with the non-reactive phthalimide end group inhibited crosslinking and chain extension and, hence, was essential for the observed good processibility.     

Composition design and properties investigation of BPDA/PDA/TFDB co-polyimide films with low dielectric permittivity

Aiming at fabricating the polyimide (PI) films with low permittivity and excellent comprehensive properties, 2,2′-bis-(trifluoromethyl)-4,4′-diaminobiphenyl was incorporated into the polyimide backbone composed of 3,3′,4,4′-biphenyltetracarboxylic dianhydride and p-phenylenediamine. The introduction of trifluoromethyl ( CF₃) groups led to a substantial reduction of the PI's permittivity (3.42–2.96). Meanwhile, as-prepared co-PI films showed excellent mechanical performance (217.13–238.20 MPa for strength and 3.49–4.90 GPa for modulus), as well as good thermal stability (high glass transition temperature over 354 °C, whereas low thermal expansion coefficient below 10 ppm/K). Structure–property relationship of the PI samples was further established through molecular simulations (MS), which suggested the crucial effects of polarizability per unit volume (α/V_vdw) and free volume on PI permittivity. The computational results were highly consistent with the experimental findings, meaning that MS technique is of guiding importance in copolymer design. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47989.     

Low-fired fluoride microwave dielectric ceramics with low dielectric loss

Low-fired fluoride microwave dielectric ceramics (LiF, CaF₂, SrF₂ and BaF₂) were prepared through a simple one-step sintering process. Fluoride ceramics, especially LiF, which had the lowest sintering temperature of 800?°C, could be well sintered below 1050?°C. Rietveld refinement results showed that LiF, CaF₂, SrF₂ and BaF₂ ceramics crystallized into a cubic structure with space group Fm-3m. The relative permittivity (ε_r), quality factor (Q?×?f) and temperature coefficient of the resonant frequency (τ_f) of the fluoride ceramics were closely related to relative density, the ionic polarizability of the primitive unit cell, the packing fraction and the bond valence. In this series of low-permittivity fluoride ceramics, LiF, CaF₂ and BaF₂ could be co-fired with Ag powders, and LiF ceramic exhibited the highest Q×f value of 73880?GHz, which is comparable to those of traditional oxide microwave dielectric ceramics.     

Structure–property relationship of polyimides based on pyromellitic dianhydride and short‐chain aliphatic diamines for dielectric material applications

Most polyolefins that are used for dielectric materials exhibit a low dielectric constant and operating temperatures up to 70°C. Polyimides offer a means to a higher dielectric constant material by the introduction of a polar group in the polymer backbone and are thermally stable at temperatures exceeding 250°C. A common dianhydride, pyromellitic dianhydride (PMDA), is reacted with various short‐chain diamines to produce polymers with high imide density. Homopolymers and copolymers synthesized had dielectric constants ranging from 3.96 to 6.57. These materials exhibit a dielectric constant twice that of biaxially oriented polypropylene and therefore a twofold increase in capacitance as well as maintaining low dissipation factors that are acceptable for this application. The experimental dielectric constants of these materials are also compared to density functional theory calculations and exhibit a close relationship. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1276‐1280, 2013