Dielectric Constant Of Composite Films Research Articles

Preparation and properties of mesoporous SiO2/polyimide composite films

AbstractAlthough polyimide films have a low dielectric constant, with the advent of the 5G era, the dielectric properties of the material are required to be further improved. Therein, we prepared controlled hollow mesoporous SiO2 nanomicrospheres by the hard template method to make mesoporous low dielectric polyimide films. The composite membrane exhibits better thermal stability, mechanical properties, and hydrophobicity compared to the pure membrane. Hollow mesoporous SiO2 dispersed in polyimide can reduce the inhomogeneity of charge distribution between molecules and reduce the interaction between polar chemical bonds and aromatic rings, thus improving the dielectric properties of the whole film. The minimum dielectric constant of the composite films was 2.80 when the hollow mesoporous SiO2 was added at 1.0%. These results fully indicate that the addition of hollow mesoporous SiO2 is beneficial to the multifaceted performance of the polyimide films.Highlights Preparation of hollow mesoporous SiO2 microspheres by using different polystyrene microsphere solutions and TEOS ratios. Synthesis of composite films with different contents of hollow mesoporous SiO2 as functional fillers. The effect of hollow mesoporous SiO2 content on the mechanical properties and thermal stability of PI composite films was investigated. Addition of hollow mesoporous SiO2 reduces the dielectric constant of polyimide composite films.

A porous GO/PI coating prepared via breath figure method: Low dielectric constant with improved mechanical and water resistance properties

It is important to reduce dielectric constant while maintaining or improving water resistance and mechanical properties for the practical use of porous low-dielectric materials. Herein, a composite film in which GO and fluorinated PI (FPI) contained porous structure located on the surface of flat PI film was prepared by the simple breath figure method. The incorporation of GO/surfactant can break the design contradiction between low dielectric constant and high mechanical strength for porous structure, thereby realizing the synchronous promotion of dielectric and mechanical properties. Moreover, the water absorption of composite film was decreased significantly due to the synergy of fluorine atoms, porous structure and GO/surfactant, guarantee its high robustness to humid stress. The dielectric, water resistance and mechanical properties of the composite film could be regulated through varying the casting humidity and GO/surfactant content. A low dielectric constant of 2.3, water absorption of 0.6 % and high tensile strength of 122 MPa, with 31.11 % and 75.88 % of decrease and 26.99 % of increase compared to flat PI film was exhibited with the GO/surfactant loading of only 0.5 wt%. The dielectric constant of composite film is still below 2.5 after moisture treatment. These excellent properties facilitate the application of GO/PI composite film in microelectronics.

Relaxation processes and conduction behaviour in PVDF-TrFE and KNN-based composites

Polymer-ceramic composites have gained considerable attention in flexible electronic devices due to their uncommon features such as high dielectric constant, low conductivity, and good mechanical flexibility. The electrical and mechanical responses of various components (ceramic grain & grain boundary, polymer chains, and interface) need to be elucidated to rationally design high-performance polymer-ceramic composites. This paper provides a detailed analysis of dynamic mechanical and frequency-dependent dielectric behaviour with temperature to discern the various mechanisms responsible for the relaxations in the polyvinylidene fluoride-trifluoro ethylene/K0·5Na0·5NbO3–CaZn1/3Ta2/3O3 (PVDF-TrFE/KNN-1CZT) composite fabricated using solution casting technique. The FTIR spectra and x-ray diffraction patterns indicate the existence of the polar β-phase, confirming the ferroelectric nature of polymer films. The ferroelectric-paraelectric phase transition (TC ∼ 130 °C) of polymer film obtained from the DSC & DMA data was corroborated by the dielectric study. The introduction of ceramic fillers in polymer induces an additional relaxation in the 10 kHz to 1 MHz frequency range, owing to the ceramic-polymer interface formation, which is responsible for increment in the dielectric constant and storage capacity of the composites. The effective dielectric constant of the composite was modelled using the Maxwell-Garnet and Yamada models. The enhanced dielectric constant of composite films (εr ∼ 28) with the addition of dielectric filler qualifies these materials for flexible high-performance capacitive devices. Further, this study enables a better understanding of the various relaxation processes in the composite with dielectric fillers.

Aspects of structural, optical properties, and relaxation in (BiFeO3 or NaTiO3)–PMMA: Hybrid films for dielectric applications

Perovskite–polymer hybrids are fascinating materials combining improved physical properties with a flexibility that make them very suitable for electric and optoelectronic devices and applications. In the present work, nano-sized BiFeO3 and NaTiO3 were mixed with polymethyl methacrylate (PMMA) by solution casting to obtain transparent nanocomposite films. The structural properties, interactions between the film constituents as well as film thickness were evaluated by using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy combined with energy–dispersive spectroscopy. The composite films were nonporous of semicrystalline nature. The NaTiO3 interacted strongly with PMMA molecules than BiFeO3. Nano-filler incorporation narrowed the optical bandgap significantly while maintaining a reasonably high transmittance. The dielectric constant of composite films was higher than that of pure polymer maintaining a low dielectric loss. The effect of these perovskites on the dielectric modulus, relaxation, and ac conductivity were discussed. The prepared composites are suitable for integral thin film capacitors, electric stress control devices, and bio-engineering systems.

Preparation of polyimide/BaTiO3‐nanocrystal hybrid thin films and their dielectric property

High dielectric constant is highly desirable in capacitors and memory devices. In this work, oleic acid (OA)‐capped BaTiO3 nanocrystals were synthesized by a two‐phase approach. Polyimide (PI)/BaTiO3‐nanocrystal composite thin films with high dielectric constant have been successfully fabricated. The morphologies and dielectric properties of the hybrid films were exploited. The results showed that BaTiO3 nanocrystals can be uniformly dispersed in the PI thin films owing to the surface modification of OA‐capped BaTiO3 nanocrystals. It was found that the dielectric constant of composite film varies with the volume fraction of BaTiO3 nanocrystals and sintering temperatures and reaches a maximum value of 44.1, which is around 13 times higher than that of pristine PI thin film (3.2). These results demonstrated that PI/BaTiO3‐nanocrystal composite films have considerable application potential in microelectronic fields.

Preparation of polyarylene ether nitriles/fullerene composites with low dielectric constant by cosolvent evaporation

Fullerenes are widely used to reduce the dielectric constant of composites due to their special hollow cage structure. However, the main challenge for the realization of its material potential application is to improve the interfacial compatibility between the polymer matrix and fullerenes. Here we report a pure physical method of cosolvent evaporation to prepare polyarylene ether nitriles (PEN) composite films with well-defined monodisperse clusters of fullerenes for manufacturing flexible printed circuit boards. The presence of fullerenes is proven to be crucial to decrease the dielectric constant of composite films. The film with 3 wt% fullerenes loading possesses the lowest dielectric constant of 2.65 at 1 MHz, and its service life is detected as 3.3 years by Flynn–Wall–Ozawa method. Additionally, when the composite films used in flexible copper clad laminate (FCCL), the 180° peeling strength between the resin and copper foil is 6.91 N cm−1. Therefore, this PEN/fullerene composite provides potential application for the preparation of FCCL.

A study on the structure and properties of poly(vinylidene fluoride)/graphite micro-sheet composite films

In this paper, poly(vinylidene fluoride)-based dielectric composite films with graphite micro-sheet as fillers were prepared by solution casting method. Graphite micro-sheet was first heated to thermal expansion and was then allowed to experience the surface chemical etching (hydroxyl modification) to improve its’ surface hydroxyl contents. This hydroxyl-modified graphite micro-sheet was added to the poly(vinylidene fluoride) matrix to prepare the poly(vinylidene fluoride)/graphite micro-sheet composite films. The microstructures, crystallization, thermodynamic stabilities and dielectric properties of the composite films were tested, and the effects of graphite microchip on the structures and properties of the films were analyzed. Scanning electron microscope results showed that the prepared graphite sheets were well dispersed in poly(vinylidene fluoride) matrix. X-ray powder diffraction spectrum indicated that the introduction of graphite micro-sheets has little effect on the phases’ change of poly(vinylidene fluoride) films. Thermal analysis showed that the addition of graphite micro-sheets slightly decreased the thermal stability of the composite films. Broadband dielectric spectroscopy test results showed that with the increase of the content of graphite micro-sheet, the dielectric constant of the composite films increased continuously. The dielectric constant of composite films increases as high as 6.5 × 105 under 100 Hz test frequency at the case of graphite micro-sheets’ content is 6 wt%. The results also indicated that the highest breakdown field strength of this composite film is 0.63 kV/mm and its specific energy storage is 2.07 J/cm3 which is over 120 times than that of pure poly(vinylidene fluoride) film.

Preparation and properties of PVDF composite films modified with organic ferroelectric croconic acid

ABSTRACTPoly(vinylidene fluoride) (PVDF) composite films modified with croconic acid were prepared and characterized by XRD, FTIR, TG, DSC, SEM, dielectric and ferroelectric test. The influence of loading content of croconic acid upon the structure, crystallinity, thermal stability, dielectric and ferroelectric properties of the modified PVDF films are investigated. The introduction of croconic acid could slightly improve the crystallinity of composite films. The dielectric constants of composite films could be two times larger than that of neat PVDF. The Ps value of PVDF composite film is lower than that of croconic acid, but is larger than that of pure PVDF.

Overall improvement in dielectric and mechanical properties of porous graphene fluoroxide/polyimide nanocomposite films via bubble-stretching approach

Low dielectric constant is desired for polyimide to be used in microelectronic industry. In the present study, a series of porous graphene fluoroxide/polyimide (GFO/pPI) nanocomposite films with improved dielectric and mechanical properties were fabricated. Polyethylene glycol (PEG) was introduced into the system to play the roles of an intercalator in exfoliation of graphite fluoroxide and a blowing agent in preparation of porous structure. The in-situ bubble-stretching, resulting from PEG decomposition during the thermal imidization, not only hindered the agglomeration of GFO nanosheets, but also generated micro-pores in PI matrix. Both the porous structure and the GFO nanosheets significantly decreased the dielectric constant of composite films, and the load transfer between GFO and PI matrix efficiently improved the mechanical properties of composite films. A very low dielectric constant of 2.29 as well as high tensile modulus of 4.43GPa and tensile strength of 159MPa was obtained for the composite film with the GFO loading of only 0.30wt%. In addition, the glass transition temperature of GFO/pPI films was increased from 355°C to 388°C, and the coefficient of linear thermal expansion of GFO/pPI films was decreased from 48.7ppm/K to 24.9ppm/K.

Enhanced dielectric properties in polyvinyl alcohol – Multiwall carbon nanotube composites

Here we report the study of direct current (DC) and alternate current (AC) electrical transport properties and current–voltage (I–V) characteristic of Polyvinyl Alcohol – Multiwall Carbon nanotube (PVA–MWCNT) composites, prepared by an in-situ chemical oxidative preparation technique, within temperature range 300 K ≤ T ≤ 423 K and in the frequency range 150 Hz ≤ f ≤ 2 MHz. The DC conductivity gives the presence of two different activation energies at two different temperature regions. It is observed that the dielectric constant of composite film is higher in comparison to pure PVA film and is well-fitted with modified Cole–Cole equation. The presence of hydroxyl group affects the relaxation phenomenon of composite film. The frequency variation of AC conductivity follows the power law (fS) and is found to follow correlated barrier hopping (CBH) model. The imaginary part of electric modulus shows non-Debye type asymmetric behaviour. The current – voltage characteristic has been analysed by the concept of back to back Schottky diode.

The relationship between processing and performances of polyarylene ether nitriles terminated with phthalonitrile/trifunctional phthalonitrile composites

A novel series of polyarylene ether nitriles terminated with phthalonitrile/trifunctional phthalonitrile (PEN-Ph/TPh) composite films were prepared via solution casting method. The effects of concentration of TPh and prepolymerization treatment as well as curing treatment on the performance of the PEN-Ph/TPh composite films were studied systematically. SEM images shows that the morphology of the composites transformed from phase separated state to homogeneous phase through the prepolymerization and curing treatment, due to the crosslinking reaction between the TPh and the PEN-Ph matrix resin. Moreover, the formation of phthalocyanine rings and triazine rings through crosslinking reaction resulted in the favorable enhancement of thermal, mechanical, and dielectric properties of the PEN-Ph/TPh composites. The glass transition temperature (T g ) of films were promoted from 197 °C to 248 °C and the temperature corresponding to 5 % weight loss (T 5%) increased by 20 °C. The mechanical testing results showed that the tensile strength was enhanced by 30 %, from 92 MPa to 119 MPa. Furthermore, the dielectric constant of composite films increased because the phthalocyanine rings formed via crosslinking reaction and the maximum value reached to 5.40 at 1 KHz.

Preparation of polyimide/BaTiO3/Ag nanocomposite films via in situ technique and study of their dielectric behavior

Triphase polyimide nanocomposite films were fabricated using barium titanate (BaTiO3) with high dielectric constant and silver (Ag) with high conductivity as fillers. In situ method was utilized to obtain the homogeneous dispersion of nanoparticles. The in situ polymerization of polyimide precursor-poly(amic acid) was performed in the presence of BaTiO3 particles. Silver compound 1,1,1-trifluoro-2,4-pentadionato silver(I) was added into the BaTiO3 containing poly(amic acid) solution to achieve silver nanoparticles via in situ self metallization technique. The thermally induced reduction converted silver (I) to metallic silver with concomitant imidization of poly(amic acid) to polyimide. Both BaTiO3 and silver nanoparticles were uniformly dispersed in the polyimide substrate. The dependence of dielectric behavior on the BaTiO3 and Ag contents was studied. The incorporation of small amount of silver nanoparticles greatly increased dielectric constant of composite films.

Preparation and dielectric properties of surface modified TiO2/PEN composite films with high thermal stability and flexibility

A series of surface modified titanium dioxide (TiO2)/polyarylene ether nitriles (PEN) composite films with different modified TiO2 contents were prepared by solution casting method combined with ultrasonic dispersion technology. TiO2 particles were successfully surface modified by PEN–COOH polymer previously, which was confirmed by transmission electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. Besides, SEM images of composite films revealed that the interfacial adhesion between surface modified TiO2 particles and the PEN matrix was effectively improved because of their common cyano groups and similar structure units. Furthermore, thermal, mechanical and dielectric characterizations showed that the composite films possess excellent thermal properties and flexibility as well as good dielectric properties, their glass transition temperatures were as high as 223 °C and the initial decomposition temperatures were all above 480 °C. In addition, it was found that the tensile strength of modified TiO2/PEN composites was better than raw TiO2/PEN composites. More importantly, the dielectric constant of composite films increases linearly with increment of the surface modified TiO2 particles content. When the mass fraction of modified TiO2 particles reached 40 %, the dielectric constant of the composite film increased to 7.9 (1 kHz), while the dielectric loss is just 0.028 (1 kHz).

Green dielectric materials composed of natural graphite minerals and biodegradable polymer

Polymeric nanocomposites are a promising dielectric due to their low cost, easy processability and flexibility but most polymers are difficult to treat and recycle leading to “white pollution”. Here, we report an eco-friendly “green” dielectric material made from natural graphite minerals and biodegradable poly(butylene succinate) synthesized by solution casting and hot pressing. Dielectric constant of resulting composite films agreed quite well with percolation theory and a low percolation threshold fc = 5.98% was obtained due to a high aspect ratio of natural graphite minerals. Composite films possessed a high dielectric constant of 113, around 28 times higher than that of pristine PBS (103) when volume fraction reached 5.5%. Furthermore, dynamic mechanical properties of composite films can be improved at the same time. Dielectric constant of composite films can be greatly improved by incorporating natural graphite minerals while mechanical flexibility can be maintained to be as good as that of pure polymer matrix.

Effects of additive elements on improvement of the dielectric properties of Ta2O5 films formed by metalorganic decomposition

Ta 2 O 5 -based composite thin films formed by metalorganic decomposition have been investigated with respect to their dielectric properties. The dielectric and insulating properties of composite (1−x)Ta2O5−xTiO2 and (1−x)Ta2O5−xWO3 thin films are found to be improved compared to those of pure Ta2O5 thin films. In particular, thin films with x=0.08 composition of additive TiO2 or WO3 to Ta2O5 exhibited superior dielectric and insulating properties. The maximum dielectric constant and charge storage density of composite films are about 20 and 53.6 fC/μm2, respectively, higher than those of pure Ta2O5 films (about 13 and 34.5 fC/μm2). The temperature coefficient of the dielectric constant of composite films dramatically decreases from 65 ppm/°C for pure Ta2O5 to less than 11 ppm/°C. The leakage current density of composite films is lower than 1×10−9 A/cm2 up to an applied electric field of 3 MV/cm. The dominant conduction is Poole–Frenkel conduction in the films according to the measurement temperature dependence of the I−V characteristics.