Microwave dielectric properties of SnO‐SnF₂‐P₂O₅ glass and its composite with alumina for ULTCC applications

Abstract Ultralow‐temperature sinterable alumina‐45SnF₂:25SnO:30P₂O₅ glass (Al₂O₃‐SSP glass) composite has been developed for microelectronic applications. The 45SnF₂:25SnO:30P₂O₅ glass prepared by melt quenching from 450°C has a low Tg of about 93°C. The SSP glass has εᵣ and tanδ of 20 and 0.007, respectively, at 1 MHz. In the microwave frequency range, it has εᵣ=16 and Qᵤ × f=990 GHz with τf=−290 ppm/°C at 6.2 GHz with coefficient of thermal expansion (CTE) value of 17.8 ppm/°C. A 30 wt.% Al₂O₃‐70 wt.% SSP composite was prepared by sintering at different temperatures from 150°C to 400°C. The crystalline phases and dielectric properties vary with sintering temperature. The alumina‐SSP composite sintered at 200°C has εᵣ=5.41 with a tanδ of 0.01 (1 MHz) and at microwave frequencies it has εᵣ=5.20 at 11 GHz with Qᵤ × f=5500 GHz with temperature coefficient of resonant frequency (τf)=−18 ppm/°C. The CTE and room‐temperature thermal conductivity of the composite sintered at 200°C are 8.7 ppm/°C and 0.47 W/m/K, respectively. The new composite has a low sintering temperature and is a possible candidate for ultralow‐temperature cofired ceramics applications

PVDF-SIC composite thick films an effective ESD composition for growing anti-static applications

Abstract Thin polyvinylidene fluoride-silicon carbide (PVDF-SiC) shielding composite films were prepared by a simple solution casting process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show the presence of both polymer and filler with no reaction between them. The coefficient of thermal expansion (CTE) and tensile strength of the composite exhibit a decreasing tendency, while that of conductivity and electromagnetic interference (EMI) shielding values increase with filler loading. The εr, and tanδ of the composites were also found to increase with filler loading in the frequency range of 8.2—18 GHz, which also influence the shielding behaviour of the composite. The high filler (60 vol.% of SiC) loaded composite of 1 mm thickness exhibits direct current (DC) conductivity of the order of 10-5 S/m indicating its potential for electrostatic discharge shielding applications. This is further confirmed from its EMI SE value of 12 dB, which corresponds 94% attenuation. The composite exhibits a partially reflecting and absorbing shielding nature, without any dominant shielding mechanism. The alternating current (AC) conductivity and skin depth value of the composites exhibit an inverse relationship with each other and influence the shielding thickness. The attenuating power of the PVDF-SiC composite with 60 volume % (vol.%) silicon carbide (SiC) changes from 84% to 99%, with an increase in sample thickness from 0.5 mm to 2 mm. Hence, thin and flexible paper-like EMI shield of PVDF-SiC composite can be easily prepared by simple, cost-effective approach for various shielding applications like electrostatic discharge shielding as well as EMI shielding

In situ polymerized polyaniline nanofiber-based functional cotton and nylon fabrics as millimeter-wave absorbers

Abstract Polyaniline nanofibers and their composite with graphite have been synthesized by a simple chemical polymerization method. Polyaniline nanofiber graphite composites with a thickness of 1 mm exhibit excellent electromagnetic interference (EMI) shielding of above 80 dB in the frequency range of 8.2–18 GHz. EMI shielding fabrics of 0.1 mm thickness based on polyaniline nanofibers and their composite have been developed by an in situ polymerization route. These fabrics combine the properties of polyaniline nanofibers as well as their composite and fabrics (cotton and nylon). The developed functional fabrics with 0.1 mm thickness exhibit EMI shielding effectiveness in the range of 11–15 dB in the 8.2–18 GHz frequency range. Optical and scanning electron microscopy studies indicate the uniform coating of the polyaniline nanofibers over the individual fibers and interweave regions. Thin and flexible shielding materials suitable for a broad range of millimeter-wave shielding applications have been developed using this simple and potentially profitable method

Graphite reinforced polyvinylidene fluoride composites an efficient and sustainable solution for electromagnetic pollution

Abstract Graphite flakes reinforced polyvinylidene fluoride (PVDF) composites were prepared and investigated the influence of DC (Direct Current), AC (Alternating Current) conductivity, sample thickness as well as presence of conductive layer on its electromagnetic interference (EMI) shielding effect. The graphite incorporated PVDF composite with sample thickness of 1 mm exhibit good shielding properties of about 55–57 dB in the frequency range of 8.2–18 GHz for highest filler loading. These composites exhibit absorption as the primary mechanism for EMI shielding. Addition of graphite decreases the coefficient of thermal expansion (CTE) and improved the mechanical properties. The EMI shielding effect improved with increase in sample thickness and by incorporating a conductive layer to the graphite flake composite. The graphite flake based composites are found to be lightweight, thin and good EMI shielding materials that can be tuned to wide range of shielding applications

Microwave dielectric properties of low-temperature sinterable α-MoO3

Abstract The α-MoO3 ceramics were prepared by uniaxial pressing and sintering of MoO3 powder at 650 °C and their structure, microstructure, densification and sintering and microwave dielectric properties were investigated. The sintering temperature of α-MoO3 was optimized based on the best densification and microwave dielectric properties. After sintering at 650 °C the relative permittivity was found to be 6.6 and the quality factor was 41,000 GHz at 11.3 GHz. The full-width half-maximum of the A1g Raman mode of bulk α-MoO3 at different sintering temperatures correlated well with the Qf values. Moreover, the sintered samples showed a temperature coefficient of the resonant frequency of −25 ppm/°C in the temperature range from −40 to 85 °C and they exhibited a very low coefficient of thermal expansion of ±4 ppm/°C. These microwave dielectric properties of α-MoO3 will be of great benefit in future MoO3 based materials and their applications

Can zinc aluminate-titania composite be an alternative for alumina as microelectronic substrate?

Abstract Alumina, thanks to its superior thermal and dielectric properties, has been the leading substrate over several decades, for power and microelectronics circuits. However, alumina lacks thermal stability since its temperature coefficient of resonant frequency (τf) is far from zero (−60 ppmK⁻¹). The present paper explores the potentiality of a ceramic composite 0.83ZnAl₂O₄-0.17TiO₂ (in moles, abbreviated as ZAT) substrates for electronic applications over other commercially-used alumina-based substrates and synthesized using a non-aqueous tape casting method. The present substrate has τf of + 3.9 ppmK⁻¹ and is a valuable addition to the group of thermo-stable substrates. The ZAT substrate shows a high thermal conductivity of 31.3 Wm⁻¹K⁻¹ (thermal conductivity of alumina is about 24.5 Wm⁻¹K⁻¹), along with promising mechanical, electrical and microwave dielectric properties comparable to that of alumina-based commercial substrates. Furthermore, the newly-developed substrate material shows exceptionally good thermal stability of dielectric constant, which cannot be met with any of the alumina-based HTCC substrates

Ultra-low sintering temperature ceramic composites of CuMoO₄ through Ag₂O addition for microwave applications

Abstract The present paper presents ceramic composites with ultralow sintering temperature of 500 °C and densification of 96% by adding small amount (0.5, 1 and 2 wt%) of Ag₂O to CuMoO₄ by simple mixing method. The effect of Ag₂O addition on the structure, microstructure, sintering and thermal as well as microwave dielectric properties of CuMoO4 is also studied. The reduction in the sintering temperature is due to the formation of trace amount (1.4%) of copper silver molybdate (Cu₂Ag₂(MoO₄)₃) as observed from Rietveld refinement analysis as well as backscattered SEM image. Doping has very little influence on the structure and coefficient of thermal expansion that is about 4.7–5.2 ppm/°C. The composites sintered at 500 °C exhibit relative permittivity of about 8–9, quality factor (Qf) of 26000–37000 GHz at 12 GHz, temperature coefficient of resonant frequency of −31–33 ppm/°C and are compatible with Al electrode. The present work results in obtaining well-densified ultralow temperature cofired ceramic composites at low sintering temperature without much structural change and good thermal properties but with different dielectric properties by small doping. These composites can be used as low cost candidates for wide range of microwave applications like multilayer packages and substrates owing to the low energy required during processing and hence can pave way to the advancement of electronic materials

A new design approach for a hybrid monopole to achieve increased ultrawide bandwidth

Abstract A design approach has been explored and successfully demonstrated to achieve an improved gain of a hybrid monopole maintaining its optimum achievable bandwidth. This challenge has been resolved based on the knowledge acquired in earlier investigations. A three-segment composite dielectric ring resonator (DRR) has been designed and fabricated. This, along with a vertical monopole, promises about 137% (5.4:1) matching bandwidth with consistent monopolelike radiation and 6–10-dBi gain over the entire band. Two sets of customized prototypes have been realized and experimentally validated to furnish the predicted characteristics in transmit and receive modes, both in frequency and time domain