Low Relative Dielectric Constant Research Articles

Electric Field‐induced Orientation of Carbon Nanomaterials in Dispersions

AbstractCarbon nanomaterials (CNMs) exhibit excellent performance and potential application value in optical, electric, magnetic and thermal owing to their unique low dimensional structures, high specific surface areas and excellent electrical conductivities, however, the random orientation of CNMs in polymer dispersions negatively affects their optimal performances. Herein, the orientation of CNMs induced by an electric field in dispersions was investigated. The arrangement of carbon black, carbon nanotubes and graphite nanoplatelets in solvents under an electric field was characterized using a stereoscopic microscope. The effects of solvent type, nanomaterial concentration and electric field conditions on the orientation of the CNMs were systematically investigated. The results showed that the CNMs generally exhibited good electric field‐induced orientations in solvents with a low relative dielectric constant. The orientation structure resulting from using an appropriate CNMs concentration was relatively uniform and continuous. In particular, a more regular orientation structure was achieved upon applying an electric field (100 V/mm; 1000 Hz) for 30 s. Interestingly, well‐oriented CNMs in a solvent can also orient in polymer dispersions that are soluble in such a solvent. This extension of the orientation of CNMs from solvents to polymer dispersion systems provides a novel idea for preparing high‐performance composites.

Effect of CaF2 and Na2SiF6 nucleating agents on the crystallization behavior and properties of MgO-Al2O3-SiO2 glass-ceramics

MgO-Al2O3-SiO2 (MAS) glass-ceramics were prepared by melt and sintering method, and the effects of two kinds of nucleating agents CaF2 (labeled as C-group) and Na2SiF6 (labeled as N-group) on the crystallization kinetics mechanism, crystallization behavior, physical and chemical properties of MAS glass-ceramics were investigated. Herein, differential scanning calorimetry (DSC), X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM), density, corrosion resistance, dielectric properties, coefficient of thermal expansion (CTE) and other tests were carried out to evaluate the performance of both parent glass and glass-ceramics samples. The results show that the nucleating agent of CaF2 and Na2SiF6 exhibit a significant influence on the characteristic temperatures of Tg and Tp, and crystallization kinetics of MAS parent glass. The Tg of C-group parent glass are slightly higher than that of N-group parent glass. The Avrami parameter n value for N-group and C-group parent glass are 3.8 and 2.5, which suggesting the main crystal phase in N-group and C-group parent glass present three-dimensional and two-dimensional growth, respectively. However, the nucleating agent of CaF2 and Na2SiF6 present a negligible influence on the crystallization behavior, bulk density, acid resistance, CTE, dielectric constant and dielectric loss of MAS glass-ceramics. When the crystallization temperature increased from 900 to 1000 °C, the main crystal phase precipitated from the all these MAS glass-ceramics kept unchanged with α-cordierite phase (Mg2Al4Si5O18), and the grain size of these rod-like α-cordierite phase around 300–500 nm. All these two groups MAS glass-ceramics present low relative dielectric constant (εr), which is ranges from 1.32 to 2.40, and the εr of C-group glass-ceramics increases with increasing of the crystallization temperature. The MAS glass-ceramics samples also display low dielectric loss (tan δ), which is ranges from 0.42 × 10−2 to 4.93 × 10−2. This finding suggests the MAS glass-ceramics would be used as a potential candidate of dielectric materials for electronic devices, especially for high frequency applications.

Crystal structure and piezoelectric properties of lead-free epitaxial (K,Na)NbO3 thin films grown on Si substrates

Epitaxial growth of lead-free (K,Na)NbO3 (KNN) thin films on (001)SrRuO3/Pt/ZrO2/Si substrates was achieved by using RF magnetron sputtering. X-ray diffraction measurements revealed that lattice constants (a1 = 0.3987 nm, a2 = 0.3959 nm, a3 = 0.4011 nm) of epitaxial KNN thin films with a pseudo cubic system were close to KNN single crystals. Vertical piezoelectric force microscopy observation indicated that the spontaneous polarization Ps with a downward direction was dominant, and the epitaxial KNN thin films were naturally polarized. The epitaxial KNN thin films exhibited low relative dielectric constant (εr ∼ 267). In addition, piezoelectric coefficients |e31,f| showed a constant value of about 6.5 C m−2 with the increase in applied positive voltages. Relatively high converse |e31,f| values were obtained at low applied voltages due to an intrinsic piezoelectric effect. Therefore, the epitaxial KNN thin films might enable piezoelectric microelectromechanical systems driven at low applied voltages.

Boosts charge utilization and enables high performance organic solar cells by marco- and micro- synergistic method

A ternary solar cell is a typical strategy that can well compensate light absorption and effectively regulate energy levels and the morphology of active layers. However, the commonly used active materials have low relative dielectric constant, which is one of the important limitations for improving the photovoltaic performance of organic solar cells (OSCs). In this work, an insulating polymer MPFM with high relative dielectric constant is introduced into the ternary active layers to improve the performance of OSCs by synergistic effect of macro light utilization and micro interface modulation. The introduction of MPFM not only strengthened the dielectric constant of bulk heterojunctions but also enhanced the degree of crystallinity and adhesivity, promoted the exciton separation, suppressed charge recombination, and significantly accelerated charge transport. As a result with the addition of MPFM, an outstanding efficiencies of 18.21% and 18.53% are achieved for devices based on PM6:Y6:PC71BM and PM6:BTP-eC9:PC71BM, respectively. These results indicated that constructing the micro-PIN junction by using MPFM is an effective strategy to further improve the photovoltaic performance of OSCs.

Sleeping Heart Monitoring Using Hydrogel-Textile Capacitive ECG Electrodes

In the application on sleeping heart monitoring by using capacitive electrocardiogram (cECG), a raw cECG signal with high quality is usually difficult to be obtained due to the low coupling capacitance composed of human skin, pajamas, bed sheet and sensing electrodes. This is mainly caused by a low relative dielectric constant of bed sheet and pajamas. In order to overcome this challenge, this study proposed a cECG system containing hydrogel-textile electrode for sleeping heart monitoring. The hydrogel layer was applied in an array pattern onto conductive textile to become a sensitive electrode in order to increase the coupling capacitance and lower the equivalent impedance as well, which was helpful to improve the quality of raw cECG signals. The reference electrode was linked to the circuit of the signal acquisition circuit to decrease the common-mode noises. The system incorporates eight membrane pressure sensors to capture the body’s sleep postures and detect the cECG signals from different sleep postures. The experimental results on tests with three different human sleep postures showed that the signal-noise ratio of the proposed system was close to the wet-electrode based ECG system. The sleeping heart monitoring experiments were conducted involving eight subjects with no constraint conditions through a period of two hours, the R-wave of the cECG signal was analyzed using RR interval extraction algorithms and the heart rate (HR) was calculated. The results showed that all subjects’ HRs during sleep state falls into a normal range, indicating that no signs of tachycardia and bradycardia can be observed.

Miniaturized Four-Arm Log-Periodic Toothed Antenna With Wide Bandwidth

An improved method of wideband performance is demonstrated by being applied to a miniaturized four-arm log-periodic toothed antenna with an integrated balun. The required minimum length of the integrated balun is reduced through the input impedance reduction structure on thin dielectrics with a low relative dielectric constant. In addition, destructive currents arising from the combination of the antenna structure and miniaturization structure are solved by modeling them as an equivalent circuit structure from an impedance perspective. The proposed antenna represents a voltage standing wave ratio of less than 2:1 in the 1.25&#x2013;18 GHz bandwidth range and has a realization gain of more than 2 dBi in the overall operating band with a diameter of 0.325 <inline-formula><tex-math notation="LaTeX">$\mathbf{\lambda}_{\mathbf {L}}$</tex-math></inline-formula>.

Design of Embroidery Antenna for Wearable Applications

The rapid growth of wearable devices has augmented the requirement for body centric wireless communication. In addition to this, to reduce the size of the device and its power consumption, it is also significant to develop a flexible antenna’s that may be incorporated for wearable applications. This paper presents the primary development of the wearable embroidery textile antenna for the wireless body area networks. The operating centre frequency ( fc ) of this wearable embroidery textile antenna is 2.40 GHz. Textile materials are used as the substrates as it has low relative permittivity and dielectric constant. A strip lines made up of conductive materials is used as radiating element. The nylon material used as a substrate material with a relative permittivity of 1.7 .The size of the antenna is very thin .The properties were analyzed for the proposed antenna.

Good piezoelectricity of self-polarized thick epitaxial (K,Na)NbO3 films grown below the Curie temperature (240 °C) using a hydrothermal method

Using a hydrothermal method, (K0.88Na0.12)NbO3 films were deposited at 240 °C on (100) cSrRuO3//(100)SrTiO3 substrates. Moreover, without any poling treatment, direct and inverse transverse piezoelectric coefficients, e31,f, near 0 kV/cm were approximately −5.0 C/m2 for the as-deposited film. This value was nearly unchanged following the application of an electric field and poling treatment, suggesting that as-deposited films are almost in a fully self-polarized state without the application of an electric field. As-deposited films with a thickness of up to 22 μm showed constant piezoelectricity without any poling treatment. The films did not crack or peel because of substrates due to the small thermal strain originating from the low deposition temperature. The figures of merit (FOM) for the vibration energy harvester [FOM = e31,f2/(ε0εr)] and sensor [FOM = e31,f/(ε0εr)] were estimated to be good at 32.8 GPa and –5.9 GV/m, respectively, primarily because of the low relative dielectric constant of ∼110. Furthermore, the piezoelectric voltage coefficient g31 [= d31/(ε0εr)] was estimated and demonstrated a high value of 0.073 Vm/N.

Structure and microwave dielectric properties of a novel low-firing Ba1−xSrxCo2V2O8 ceramics

A low-firing BaCo2V2O8 ceramic was prepared by solid-state reaction and its microwave dielectric properties were reported for the first time. The sample calcined at 700 °C exhibited a low relative dielectric constant (er 16.7) and a high quality factor (Q(u) × f: 73,200 GHz), as well as a poor temperature coefficient of resonator frequency (τf − 41 ppm/°C). In order to obtain a near-zero τf value, Ba1−xSrxCo2V2O8 (x = 0–0.25) ceramics were synthesized by replacing Ba2+ with Sr2+ and the relationship between crystal structure and microwave dielectric properties were studied. The epsilon(r) decreased with the decrease of ionic polarization. The drop in the packing fraction worsened the Q(u) × f values. The varieties in τf values were considered to be closely related to A-site bond valence. Specimen (x = 0.25) fired at 730 °C possess superior microwave dielectric properties: er 14.6, Q(u) × f = 52,120 GHz and τf − 1.6 ppm/°C.

Synthesis and properties of AlN/MAS/Si3N4 ternary glass-ceramic composites with in-situ grown rod-like β-Si3N4 crystals

The AlN/MAS/Si3N4 ternary composites with in-situ grown rod-like β-Si3N4 were obtained by a two-step sintering process. The microstructure analysis, compositional investigation as well as properties characterization have been systematically performed. The AlN/MAS/Si3N4 ternary composites can be densified at 1650°C in nitrogen atmosphere. The in-situ grown rod-like β-Si3N4 grains are beneficial to the improvement of thermal, mechanical, and dielectric properties. The thermal conductivity of the composites was increased from 14.85 to 28.45W/(mK) by incorporating 25wt% α-Si3N4. The microstructural characterization shows that the in-situ growth of rod-like β-Si3N4 crystals leads to high thermal conductivity. The AlN/MAS/Si3N4 ternary composite with the highest thermal conductivity shows a low relative dielectric constant of 6.2, a low dielectric loss of 0.0017, a high bending strength of 325MPa, a high fracture toughness of 4.1MPam1/2, and a low thermal expansion coefficient (α25–300°C) of 5.11 × 10−6/K. This ternary composite with excellent comprehensive performance is expected to be used in high-performance electronic packaging materials.

ZnO thin film piezoelectric micromachined microphone with symmetric composite vibrating diaphragm

Residual stress is an important factor affecting the sensitivity of piezoelectric micromachined microphone. A symmetric composite vibrating diaphragm was adopted in the micro electro mechanical systems piezoelectric microphone to decrease the residual stress and improve the sensitivity of microphone in this paper. The ZnO film was selected as piezoelectric materials of microphone for its higher piezoelectric coefficient d31 and lower relative dielectric constant. The thickness optimization of piezoelectric film on square diaphragm is difficult to be fulfilled by analytic method. To optimize the thickness of ZnO films, the stress distribution in ZnO film was analyzed by finite element method and the average stress in different thickness of ZnO films was given. The ZnO films deposited using dc magnetron sputtering exhibits a densely packed structure with columnar crystallites preferentially oriented along (002) plane. The diaphragm of microphone fabricated by micromachining techniques is flat and no wrinkling at corners, and the sensitivity of microphone is higher than 1 mV Pa−1. These results indicate the diaphragm has lower residual stress.

Fabrication of High-Efficiency Piezoelectric Energy Harvesters of Epitaxial Pb(Zr,Ti)O3 Thin Films by Laser Lift-off

Abstract We fabricated piezoelectric vibration energy harvesters of c-axis-oriented epitaxial Pb(Zr,Ti)O3 (PZT) thin films on stainless steel (SS304) cantilevers in an effort to improve their power-generation efficiency and toughness. Using radio-frequency magnetron sputtering, we deposited the epitaxial PZT thin films on the MgO substrates, and then transferred the PZT films onto microfabricated SS304 cantilevers using laser lift-off (LLO). LLO did not degrade the transferred epitaxial PZT thin films, which exhibited a high piezoelectric coefficient (e 31,f =–4.8 C/m2) and a low relative dielectric constant (ε r=340), comparable to those of the original PZT thin film on MgO. At a resonance frequency of 143 Hz, the energy harvesters generated large output power of 1.8 μW at an acceleration of 1.0 m/s2, and the output power reached a maximum of 49 μW at an acceleration of 7.5 m/s2.

High mobility thin-film transistor with solution-processed hafnium-oxide dielectric and zinc-indium-tin-oxide semiconductor

In this paper, bottom-gate-top-contact structured thin-film transistors (TFTs) are fabricated by solution-processing of hafnium oxide (HfO2) dielectrics and zinc-indium-tin-oxide (ZITO) semiconductors. Solution-processed HfO2 films are annealed at different temperatures, and the 500℃ annealed HfO2 dielectrics can exhibit optimizing film properties such as smooth surfaces (the RMS value of HfO2 films is less than 1 nm), low leakage current density (1.25×10-7 A/cm2 at 1 MV/cm), high transmittance (above 80% at the wavelength ranging from 400 to 800 nm) and high relative dielectric constant (about 12). The smooth surface of HfO2 dielectrics is attributed to the decreased charge trapping states at the interface between the HfO2 dielectrics and ZITO semiconductors, and thus improves the device electrical performance and stability. Hence, TFT devices of HfO2 dielectrics annealed at 500℃ show a high saturated field effect mobility of more than 100 cm2·V-1·s-1 a low threshold voltage of -0.5 V, an on-to-off current ratio of 5×106 and a small subthreshold swing of 105 mV/dec. An almost negligible threshold voltage shift is observed under a positive bias stress for 1000 s, indicating the excellent stability of HfO2 TFT devices.

Solution based prompt inorganic condensation and atomic layer deposition of Al2O3 films: A side-by-side comparison

A comparison was made of Al2O3 films deposited on Si via prompt inorganic condensation (PIC) and atomic layer deposition (ALD). Current–voltage measurements as a function of annealing temperature indicate that the solution-processed PIC films, annealed at 500 °C, exhibit lower leakage and roughly equivalent breakdown strength in comparison to ALD films. PIC films are less dense than as-deposited ALD films and capacitance–voltage measurements indicate a lower relative dielectric constant. On the basis of x-ray photoelectron spectroscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopy, it is found that the 500 °C anneal results in the formation of a ∼6 nm thick interfacial SiO2 layer at the Si interface. This SiO2 interfacial layer significantly affects the electrical performance of PIC Al2O3 films deposited on Si.

A compact tapered slot antenna for ultrawideband applications

An elliptically tapered slot antenna fed by a tapered microstrip line ended with a sector-shaped tuning stub for ultrawideband operations is presented. The antenna is printed on a circuit board with a low relative dielectric constant of 2.65. A T-shaped shorting strip is used to improve directional radiation performance. The antenna achieves a measured impedance bandwidth from 3.25 to 12 GHz with the gain in the end-fire direction up to 5.5 dB and a compact size of 27 × 40 × 0.5 mm3. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:295–299, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27319

Enhanced thermal conductivity of low-temperature sintered borosilicate glass–AlN composites with β-Si3N4 whiskers

The effects of β-Si3N4 whiskers on the thermal conductivity of low-temperature sintered borosilicate glass–AlN composites were systematically investigated. The thermal conductivity of borosilicate glass–AlN ceramic composite was increased from 11.9 to 18.8 W/m K by incorporating 14 vol% β-Si3N4 whiskers, and high flexural strength up to 226 MPa were achieved along with low relative dielectric constant of 6.5 and dielectric loss of 0.16% at 1 MHz. Microstructure characterization and percolation model analysis indicated that thermal percolation network formation in the ceramic composites led to the high thermal conductivity. The crystallization of the borosilicate microcrystal glass also contributed to the enhancement of thermal conductivity. Such ceramic composites with low sintering temperature and high thermal conductivity might be a promising material for electronic packaging applications.

Thermal conductivity of low-temperature sintered calcium aluminosilicate glass–silicon nitride whisker composites

A new type of low temperature co-fired ceramic (LTCC) composite, comprising β-Si3N4 whiskers and calcium aluminosilicate (CAS) glass, is introduced in this paper. We show that the CAS–Si3N4 composite can be densified at 775–850 °C in air. The effect of β-Si3N4 whiskers incorporation on the thermal conductivity of this relatively low-temperature sintered CAS–Si3N4 composite is investigated. The thermal conductivity of the CAS glass is increased from 1.6 to 7.9 W/mK after adding 35 vol% of β-Si3N4 whiskers. Microstructure characterization and percolation model analysis indicate that the likely cause of increased thermal conductivity of the ceramic composites is the formation of thermal percolation networks. The crystallization of the CAS glass also contributes to the enhancement of thermal conductivity. The sample with the highest thermal conductivity shows a low relative dielectric constant of 7.1 and a dielectric loss of 0.006 at 1 MHz. Such a ceramic composite with excellent thermal and dielectric properties is a promising LTCC substrate material.

MINIATURIZED ULTRAWIDEBAND WIDE SLOT ANTENNA WITH DUAL BAND-NOTCHES AND ELIMINATING SPURIOUS STOP BAND

A wide slot antenna fed by a microstrip line ended with a hexagonal tuning stub and its variation with dual band-notched function for ultrawideband operations are presented. The fundamental conflguration is a rectangular slot on a printed circuit board with a low relative dielectric constant of 2.65. Three tuning stubs are employed at the edges of the slot to ensure the impedance matching. This original antenna achieves an operation bandwidth from 3.1 to 11.5GHz with a stable gain performance and a very compact size of 22mm £ 22mm £ 0.5mm. By etching a C-shaped slit and a Hilbert fractal curve slit on the original antenna without retuning, band-notched characteristics in the 3.40{3.69GHz WiMAX band and the 5.15{5.825GHz WLAN band can be realized, respectively. A rectangular patch is added to eliminate the spurious notched band around 10.5GHz.

Design and Analysis of Rectangular and U Slotted Patch for Satellite Communication

paper presents Microstrip antenna in the application for a satellite band microwave communication system for super high frequency (SHF), at a frequency range of 4.0 Ghz - 6.0Ghz. Currently, most security, research and education platforms are equipped with SHF communication systems. For their operational requirements, a design study is needed for the development of a light weight, low volume, low profile antenna. Hence, in this paper, bandwidth enhancement techniques such as, use of various substrate with low relative dielectric constant (Ɛ r), size of antenna as well as U slotted patch antenna with coaxial probe feed technique are discussed and explained using optimization program in java and the genetic algorithm is developed. IndexTerms-- Microstrip antenna, communication, dielectric constant, frequency, bandwidth, java program, algorithm,Optimization program, genetic algorithm, SHF, U slot.

Design and Analysis of Rectangular and U Slotted Microstrip Patch using Optimization Program in Java for UHF Applications

paper presents Microstrip antenna in the application for a military band short range radio communication system ultra high frequency(UHF), at a frequency range of 1Ghz - 1.5Ghz. Currently, most military aviation platforms are equipped with UHF communication system for their operational requirements, a design studies in the development for a lightweight, low volume, low profile. Hence, in this paper, bandwidth enhancement techniques such as use of various substrate with low relative dielectric constant (Ɛ r), size of antenna as well as U slotted patch antenna with coaxial probe feed technique are discussed and explained using optimization program in java and the genetic algorithm is developed.