Role,effect, and influences of micro and nano‐fillers on various properties of polymer matrix composites for microelectronics: A review

Ever since the discovery of polymer composites, its potential has been anticipated for numerous applications in various fields such as microelectronics, automobiles, and industrial applications. In this paper, we review filler reinforced polymer composites for its enormous potential in microelectronic applications. The interface and compatibility between matrix and filler have a significant role in property alteration of a polymer nanocomposites. Ceramic reinforced polymeric nanocomposites are promising candidate dielectric materials for several micro‐ and nano‐electronic devices. Because of its synergistic effect like high thermal conductivity, low thermal expansion, and dielectric constant of ceramic fillers with the polymer matrix, the resultant nanocomposites have high dielectric breakdown strength. The thermal and dielectric properties are discussed in the view of filler alignment techniques and its effect on the composites. Furthermore, the effect of various surface modified filler materials in polymer matrix, concepts of network forming using filler, and benefits of filler alignment are also discussed in this work. As a whole, this review article addresses the overall view to novice researchers on various properties such as thermal and dielectric properties of polymer matrix composites and direction for future research to be carried out.     

颗粒填充聚合物高介电复合材料

颗粒填充聚合物高介电复合材料兼具聚合物材料的易加工、低损耗、耐击穿性能和陶瓷材料的高介电等性能,还可使金属材料具备介电性能,可以广泛应用于电气、电子行业。本文综述了非均匀体系介电理论研究的历史背景,以及陶瓷、金属颗粒填充聚合物高介电复合材料的组成、制备及介电性能的影响因素,并着重讨论了界面相在复合材料研究中的重要性,最后展望了发展方向。     

Structure and dielectric properties of a thermoplastic blend containing dispersed metal

In the present work broadband dielectric relaxation spectroscopy measurements were employed to investigate the dielectric properties of polymer composites. A polyethylene/polyoxymethylene (PE/POM) thermoplastic blend was used as a matrix, while the inclusions were iron (Fe) particles. For comparison, the two pure polymers- PE and POM- were used as a matrix, too. In the PE/POM-Fe composites, the polymer matrix is two-phase and the filler particles are localized only in the POM phase, resulting in an ordered distribution of the dispersed filler particles within the blend. In PE-Fe and POM-Fe composites, the filler spatial distribution is random. The behaviour of all the composites studied is described in terms of the percolation theory. The PE/POM-Fe composites, based on the PE/POM blend, demonstrate different electrical behaviour compared to that of POM-Fe and PE-Fe systems. The percolation threshold value of the PE/POM-Fe composites was found much lower than that of the other two systems. The results were related to the microstructure of the composites. A schematic model for the morphology of the composites studied has been proposed. This model explains the peculiar behaviour of the PE/POM-Fe composites by taking into account the ordered distribution of the filler particles in a binary polymer matrix. Optical microscopy photographs confirm this model.     

Structure-electrical properties relationships of polymer composites filled with Fe-powder

Structure-properties relationships of composite materials, consisting of a polymer matrix and metal inclusions, is very important for designing new materials with desirable properties. In the present work the electrical and dielectric properties of several composites, consisting of a polymer matrix and iron (Fe) particles as filler, were investigated. Broadband dielectric relaxation spectroscopy measurements were carried out. The electrical behaviour of the composites is described in terms of the percolation theory. Percolation threshold values were calculated and the values of the dielectric permittivity critical exponent were found in good agreement with the theoretical ones. The influence of using different polymer matrices on the physical properties of the composites was also of particular interest. The results were related to the microstructure of the composites and a schematic model was proposed.     

An Overview of Linear Dielectric Polymers and Their Nanocomposites for Energy Storage

As one of the most important energy storage devices, dielectric capacitors have attracted increasing attention because of their ultrahigh power density, which allows them to play a critical role in many high-power electrical systems. To date, four typical dielectric materials have been widely studied, including ferroelectrics, relaxor ferroelectrics, anti-ferroelectrics, and linear dielectrics. Among these materials, linear dielectric polymers are attractive due to their significant advantages in breakdown strength and efficiency. However, the practical application of linear dielectrics is usually severely hindered by their low energy density, which is caused by their relatively low dielectric constant. This review summarizes some typical studies on linear dielectric polymers and their nanocomposites, including linear dielectric polymer blends, ferroelectric/linear dielectric polymer blends, and linear polymer nanocomposites with various nanofillers. Moreover, through a detailed analysis of this research, we summarize several existing challenges and future perspectives in the research area of linear dielectric polymers, which may propel the development of linear dielectric polymers and realize their practical application.     

Reflectance properties of polymer-stabilised cholesteric liquid crystals cells with cholesteryl compounds of different functionality

In this paper, we describe the synthesis of cholesteryl compounds of different functionality. A series of polymer-stabilised cholesteric liquid crystal (PSCLC) cells are prepared by photo-polymerisation of a cholesteric liquid crystal (Ch-LC) mixture containing a non-reactive liquid crystal, a nematic diacrylate and the above cholesteryl compounds. The effect of cholesteryl compound functionality on the morphology and the reflectance properties of PSCLC cells is evaluated, as are parameters such as the polymerisation temperature. The results indicate that the higher functional cholesteryl compound is more effective for broadening the reflection band of the Ch-LC composites, which is speculated to be a result of the pitch differences in the local network environment. Scanning electron microscopy is used to examine the morphologies of the polymer network of the PSCLC cells. We have found that the morphologies of the polymer network are determined by the functionality of the cholesteryl compounds as well as polymerisation temperature, which further influence the reflectance properties of the composites.     

Swift heavy ion induced modification in dielectric and microhardness properties of polymer composites

Polymer composites with different concentrations of organometallics (ferric oxalate) dispersed PMMA were prepared. PMMA was synthesized by solution polymerization technique. These films were irradiated with 120 MeV Ni¹⁰⁺ ions in the fluence range 10¹¹-5 × 10¹² ions/cm². The radiation induced modifications in dielectric properties, microhardness, structural changes and surface morphology of polymer composite films have been investigated at different concentrations of filler and ion-fluences. It was observed that electrical conductivity and hardness of the films increase with the concentration of the filler and also with the fluence. The dielectric constant (?) obeys the Universal law given by ?αfⁿ⁻¹. The dielectric constant/loss is observed to change significantly due to irradiation. This suggests that ion beam irradiation promotes the metal to polymer bonding and convert polymeric structure into hydrogen depleted carbon network. This makes the composites more conductive and harder. Surface morphology of the films has been studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The average surface roughness is observed to increase after irradiation as revealed by AFM studies. The SEM images show the blisters type of phenomenon on the surface due to ion beam irradiation.     

A calculation scheme for estimation of dielectric loss factors in polymers

For the quantitative estimation of dielectric loss tangent tanδ in linear and network polymers, the calculation scheme based on the Debye theory is proposed. The calculation is performed for both polar and nonpolar dielectrics in a wide frequency interval ranging from 10² to 10⁶ Hz. This calculation requires knowledge of only the chemical structure of a repeating unit in a linear polymer or a repeating fragment in a polymer network. Experiments on the estimation of frequency dependences of tanδ are conducted for polymer networks based on poly(urethanes) and poly(isocyanurates) of different compositions. A fair correlation between calculation and experimental data is obtained. It has been shown that tanδ tends to change with the increasing content of bulky isocyanurate network junctions that are responsible for the specific behavior of the system under the action of alternating mechanical and electric fields.     

The acquirement of desirable dielectric properties of carbon nanofiber composites based on the controlled crystallization

This study focused on uncovering the relationship among nanofiller, crystallization behavior, and dielectric property of polymer composites. The effects of carbon nanofibers (CNFs) and heat treatment on the crystalline structures and dielectric properties of the semi‐crystalline polymers were analyzed by using high density polyethylene (HDPE) as a matrix, which is a representative of non‐polar polymer and contains only one crystal structure. The experimental results showed that the degree of crystallinity, size distribution of crystallity, and relative amount of different crystal planes in the HDPE matrix were changing due to the addition of CNFs. With the increase of CNF loading, the dielectric constant, dielectric loss and AC conductivity of the HDPE composites were increased, presenting a typical percolation characteristic, and the dependence of the dielectric constant on frequency became more obvious. All kinds of electronic transmission, polarization effect, and relaxation behaviors in CNF/HDPE composite system were deeply analyzed. After heat treatment, the degree of crystallinity of HDPE composites was decreased with the enhanced cooling rate. For the CNF/HDPE composites with nanofiller content slightly higher than the percolation threshold, the significant increase of the dielectric constant and the dramatical reduction of the dielectric loss over a wide frequency range were realized simultaneously through rapid cooling treatment. The research indicated that a general commercial polymer material with excellent dielectric properties, which exhibited a high dielectric constant and a low dielectric loss, can be obtained by a simple technical approach different from traditional fabrication method of threshold composites.     

Printable cross-linked polymer blend dielectrics. Design strategies, synthesis, microstructures, and electrical properties, with organic field-effect transistors as testbeds

We report here the synthesis and dielectric properties of optimized, cross-linked polymer blend (CPB) dielectrics for application in organic field-effect transistors (OFETs). Novel silane cross-linking reagents enable the synthesis of CPB films having excellent quality and tunable thickness (from 10 to approximately 500 nm), fabricated both by spin-coating and gravure-printing. Silane reagents of the formula X 3Si-R-SiX 3 (R = -C 6H 12- and X = Cl, OAc, NMe 2, OMe, or R = -C 2H 4-O-C 2H 4- and X = OAc) exhibit tunable reactivity with hydroxyl-containing substrates. Dielectric films fabricated by blending X 3Si-R-SiX 3 with poly(4-vinyl)phenol (PVP) require very low-curing temperatures ( approximately 110 degrees C) and adhere tenaciously to a variety of FET gate contact materials such as n (+)-Si, ITO, and Al. The CPB dielectrics exhibit excellent insulating properties (leakage current densities of 10 (-7) approximately 10 (-8) A cm (-2) at 2.0 MV/cm) and tunable capacitance values (from 5 to approximately 350 nF cm (-2)). CPB film quality is correlated with the PVP-cross-linking reagent reactivity. OFETs are fabricated with both p- and n-type organic semiconductors using the CPB dielectrics function at low operating voltages. The morphology and microstructure of representative semiconductor films grown on the CPB dielectrics is also investigated and is correlated with OFET device performance.     

Enabling Polymer Single Crystals to Be High-Performance Dielectric

Semicrystalline polymer dielectrics (SPDs) are highly sought-after state-of-the-art dielectric materials. As the disorder in SPDs degrades their electrical properties, homogeneously ordered SPDs are desired. However, complex crystallization behaviors of polymers make such homogeneity elusive. Polymer lamellar single crystals (PLSCs), the most regularly-ordered form of SPDs possible under mild crystallizing conditions, are ideal platforms for understanding and developing high-performance dielectric materials. Here, a typical and widely used SPD, polyethylene (PE) is selected as the model material. We successfully obtained, large, uniform, and high-quality PE PLSCs and devised a non-destructive strategy to construct PE PLSC-based vertical capacitors. These nanometer-thick capacitors exhibit exceptional dielectric properties, with a high breakdown strength of 6.95 MV/cm and a low dielectric constant of 2.14±0.07, that outperform the properties of any existing neat PE. This work provides novel insights into exploring the performance possibility of ordered SPDs and reveals the PLSCs as potential high-performance dielectric materials.     

Correlation between dielectric/organic interface properties and key electrical parameters in PPV-based OFETs

We report on the influence of the dielectric/organic interface properties on the electrical characteristics of field-effect transistors based on polyphenylenevinylene derivatives. Through a systematic investigation of the most common dielectric surface treatments, a direct correlation of their effect on the field-effect electrical parameters, such as charge carrier mobility, On/Off current ratio, threshold voltage, and current hysteresis, has been established. It is found that the presence of OH groups at the dielectric surface, already known to act as carrier traps for electrons, decreases the hole mobility whereas it does not substantially affect the other electrical characteristics. The treatment of silicon dioxide surfaces with gas phase molecules such as octadecyltrichlorosilane and hexamethyldisilazane leads to an improvement in hole mobility as well as to a decrease in current hysteresis. The effects of a dielectric polymer layer spin coated onto silicon dioxide substrates before deposition of the semiconductor polymer can be related not only to the OH groups density but also to the interaction between the dielectric and the semiconductor molecules. Specifically, the elimination of the OH groups produces the same effect observed with hexamethyldisilazane. The hole mobility values obtained with hexamethyldisilazane and polymer dielectrics are the highest reported to date for PPV-based field-effect transistors.     

Study of dielectric properties of styrene-acrylonitrile graphite sheets composites in low and high frequency region

Conducting polymer composites should have a high dielectric constant and a high dissipation factor in the low and high frequency regions if they are to be used in charge storing devices, decoupling capacitors and electromagnetic interference shielding applications. Currently, extensive research is being carried out to enhance the dielectric constants of graphite-polymer, ceramic powder-polymer, metal powder-polymer and nanotube-polymer composites in the low frequency region. In this paper, we present the dielectric properties of styrene-acrylonitrile (SAN)-graphite sheets (GS) composites in the low and high frequency ranges. SAN-GS composites were prepared by the mixing process and by the hot compression mold technique. The composites showed a high dielectric constant and a high dissipation factor in the low and radio frequency region. Furthermore, the EMI shielding properties of these composites are evaluated in the radio frequency range. The conductivity and the dielectric constant of the SAN/GS composites increased with the addition of GS composites, and followed the power law model of percolation theory. The dielectric constant and the dissipation factor of the composites were analyzed according to the low and high frequency region.     

Liquid crystals stabilized by polymer networks

This review is devoted to the characteristics of a new class of polymer composites, dispersions of chemical polymer networks in LCs. Photopolymerization of various bifunctional monomers in the medium of LCs leads to the formation of a polymer network that stabilizes the structure of crystals. Methods for the preparation of the above composites, their structure, morphology, and optical characteristic are reviewed, and areas of practical application of such materials are described.     

Dielectric,magnetic and mechanical properties of ferrite composites

The dielectric and magnetic properties of carbonyl—iron (CI) and nickel zinc ferrite polymer composites were studied with respect to the ferrite particulate content and microwave frequency. From the experimental data and using empirical models that relate the composite dielectric and magnetic properties, the respective dielectric and magnetic properties of the neat fillers were estimated. The tensile properties of the particulate composites comprising CI were shown to follow qualitatively Mooney's equation for the elastic modulus. The tensile strength of an elastomeric polyurethane and PVC composites containing CI increased with particulate content, while the elongation to break decreased with filler content. SEM micrographs of tensile fracture surfaces indicated that somewhat better adhesion is obtained in the case of the polyurethane-based composites compared to the PVC ones.     

Improving breakdown strength and energy storage efficiency of poly(vinylidene fluoride-co-chlorotrifluoroethylene) and polyurea blend films by double layer structure design

All-organic composites are widely used in energy storage application due to the high breakdown strength performance, but the improvement of energy storage was limited by the relatively low dielectric constant. Therefore, to satisfy the high demands of dielectric materials, energy storage properties of polymer composites should be further enhanced. In this article, poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) and polyurea (PUA), which are known as high dielectric ferroelectric material and linearly high energy storage efficiency material respectively, are composited through double layer (DL) casting method for the first time. The properties of DL structured composite film is contrasted with solution blending structure especially in energy storage efficiency, and the results demonstrate that DL structure design can make great use of advantages of two materials and also can avoid the influence of phase separation between P(VDF-CTFE) and PUA efficiently. Moreover, high breakdown strength (6180 kV/cm) and high energy storage efficiency (77%) of DL composites can be realized simultaneously by incorporating PUA as an insulating layer, and the mechanism is discussed in detail. This work provides an effective route to improve the energy storage properties of polymer dielectric materials and shows great application potential.     

The enhancement of the oxidation resistance of carbonyl iron by polyaniline coating and consequent changes in electromagnetic properties

In order to enhance the stability of commercially unmodified processed carbonyl iron (CI) and to prevent corrosion, CI powders were coated with polyaniline (PANI) by using surfactant-stabilized PANI colloids in chloroform. PANI coats the individual particles with a film of a few micrometres thickness. Electromagnetic properties, as well as thermal and storage stability, of polymer composites filled with pristine and PANI-coated CI have been studied. The PANI overlayer has negligible influence on the magnetic and dielectric spectra of CI-filled polymer composites at ambient temperature. However, the temperature-frequency study of complex permittivity demonstrated that the composites containing PANI-coated CI powders are characterized by temperature-independent dielectric spectra, whereas the complex permittivity of polymer composites with pristine powders drastically decreased at elevated temperature. Additionally, the thermogravimetric analysis of pristine and PANI-coated CI powders in air has shown improvement in the stability. PANI overlayer prevents the oxidation of particles and acts as corrosion protection of CI.     

A Facile Photo-cross-linking Method for Polymer Gate Dielectrics and Their Applications in Fully Solution Processed Low Voltage Organic Field-effect Transistors on Plastic Substrate

A simple and effective photochemical method was developed for cross-linking of polymer gate dielectrics.Laborious synthetic processes for functionalizing polymer dielectrics with photo-cross-linkable groups were avoided.The photo-cross-linker,BBP-4,was added into host polymers by simple solution blending process,which was capable of abstracting hydrogen atoms from polymers containing active C―H groups upon exposure to ultraviolet(UV) radiation.The cross-linking can be completed with a relatively long wavelength UV light(365 nm).The approach has been applied to methacrylate and styrenic polymers such as commercial poly(methylmethacrylate)(PMMA),poly(iso-butylmethacrylate)(Pi BMA) and poly(4-methylstyrene)(PMS).The cross-linked networks enhanced dielectric properties and solvent resistance of the thin films.The bottom-gate organic field-effect transistors(OFETs) through all solution processes on plastic substrate were fabricated.The OFET devices showed low voltage operation and steep subthreshold swing at relatively small gate dielectric capacitance.     

低介电常数介质薄膜的研究进展

用低介电常数介质薄膜作金属线间和层间介质可以降低超大规模集成电路(ULSI) 的互连延迟、串扰和能耗。从介质极化的原理出发,揭示了开发低介电常数介质薄膜的可能途径;综述了低介电常数介质薄膜的制备方法、结构与性能表征、工艺兼容性等领域的最新进展。