Enhancement Of Dielectric Constant Research Articles

Synthesis and study of multiferroic properties of ZnFe2O4–BiFeO3 nanocomposites

Nanocomposites of xZnFe2O4–(1 − x)BiFeO3, x = 0.1, 0.2, 0.3, 0.4 have been prepared by sol–gel technique. The samples have been calcined at various temperatures ranging from 500 to 800 °C and then the effect of annealing temperature on dielectric and magnetic properties is studied. Transmission electron microscopy revealed the formation of powders of nano order size and the crystal size was found to be around 30 nm. The magnetic behavior is found to be strongly dependent upon concentration of Zn ferrite phase and annealing temperature. Enhancement of dielectric constant is observed for the samples with high ferrite concentration and antiferromagnetic Néel temperature is also evident for the samples with maximum ferrite concentration.

The dielectric properties and the relaxation phase transition of copper substituted [formula omitted] ferroelectric ceramics

The dielectric properties and the relaxation phase transition of Sr 1− x Cu x Bi 2Nb 2O 9 (SCBN) ferroelectric ceramics prepared by a solid-state process, with x ranging from 0.0 to 0.6, are reported. The microstructure of SrBi 2Nb 2O 9 (SBN) was clearly influenced by Cu 2+ substituting the Sr 2+ of SBN, as observed by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). An obvious enhancement in dielectric constant was observed and the frequency stability was enhanced for copper substituted SBN compared to SBN. At the same time, the sintering temperature of SBN was reduced significantly by approximately 80 ∘C because of the copper ions being introduced. The maximum dielectric constant peak broadened gradually with increasing copper content, indicating that the phase transition from a normal ferroelectric to a relaxor ferroelectric occurs in SBN.

Ge/GeO2 Interface Control with High Pressure Oxidation for Improving Electrical Characteristics

We have investigated High Pressure Oxidation (HPO) of Ge for improving Ge/GeO2 interface in terms of GeO desorption control. C-V characteristics in HPO-GeO2 MIS capacitors revealed the dramatic improvement with a very small hysteresis and frequency dispersion. Furthermore, the dielectric constant enhancement in GeO2 grown by HPO was observed. A sub-bandgap photo absorption was observed in GeO2 film grown by Atmospheric Pressure Oxidation (APO), while a sharp absorption edge at ~6 eV, corresponding to the bandgap of GeO2, was seen in the film by HPO. Based on the thermodynamic consideration, the effectiveness of HPO and low temperature oxygen annealing (LOA) in terms of the suppression of GeO desorption is discussed.

Synthesis, photoluminescence and dielectric properties of O-deficient SnO 2 nanowires

High-quality rutile SnO 2 nanowires were fabricated by a vapor-phase transport and condensation method assisted by carbothermal reduction. The composition and structure were investigated in detail. It is found that many oxygen vacancies exist in the single-crystalline rutile SnO 2 nanowires and can further influence the photoluminescence (PL) and dielectric property of the nanowires. The PL spectrum only exhibits a wide yellow emission centered at 570 nm and usual near band edge emission is not observed, which is ascribed to a large amount of ionized oxygen vacancies. The dielectric measurements indicate that the dielectric response of the SnO 2 nanowires is significantly enhanced in the low-frequency range. It is thought both the rotation direction polarization (RDP) and the space charge polarization (SCP) process induced by O vacancies and nanosize effects are the main reasons for the enhancement of relative dielectric constant ( ɛ r) of these SnO 2 nanowires.

Strain-induced effects on antiferromagnetic ordering and magnetocapacitance in orthorhombicHoMnO3 thin films

We investigated the magnetic and ferroelectric properties ofc-axis orientedorthorhombic phase HoMnO3 (o-HMO in Pbnm symmetry setting) thin films grown on Nb-dopedSrTiO3(001) substrates.The o-HMO films exhibit an antiferromagnetic ordering near 42 K, irrespective of theorientation of the applied field. However, an additional magnetic orderingoccurring around 35 K was observed when the field was applied along thec-axis ofo-HMO,which was absent when the field was applied in the ab-plane. The magnetocapacitance measured alongthe c-axis showed that although there is evidence of dielectric constant enhancement when thetemperature is below 35 K the expected abrupt change in dielectric constant appears at a muchlower temperature and reaches maximum around 13.5 K, indicating that the low-temperaturec-axis polarization might be related to the ordering of theHo3+ moment. The lattice constant analyses using x-ray diffraction and the observation of aslight magnetization hysteresis suggest that the weak second magnetic transition along thec-axis at 35 K might be more relevant to the strain-induced effect on antiferromagnetism.

Tuning the Effective Fine Structure Constant in Graphene: Opposing Effects of Dielectric Screening on Short- and Long-Range Potential Scattering

We reduce the dimensionless interaction strength alpha in graphene by adding a water overlayer in ultrahigh vacuum, thereby increasing dielectric screening. The mobility limited by long-range impurity scattering is increased over 30%, due to the background dielectric constant enhancement leading to a reduced interaction of electrons with charged impurities. However, the carrier-density-independent conductivity due to short-range impurities is decreased by almost 40%, due to reduced screening of the impurity potential by conduction electrons. The minimum conductivity is nearly unchanged, due to canceling contributions from the electron-hole puddle density and long-range impurity mobility. Experimental data are compared with theoretical predictions with excellent agreement.

Evaluation of layer properties of effective parameters of metallic rod metamaterials in GHz frequencies

In this paper, analytical modeling and numerical simulation of the complex effective dielectric, magnetic constants and refractive index of a metallic rod metamaterial in microwave frequency range are presented. Analytical modeling has been done using modified mathematical models of the complex dielectric and magnetic constants obtained for rod metamaterial structure. Numerical simulation of the above-mentioned parameters has been made using S-parameters obtained with the help of finite-difference time-domain (FDTD) calculations. The numerical simulation has been carried out for different thickness of rods. Remarkable coincidence between analytical and numerical results was found. The effective dielectric constant enhancement of the considered composite has been obtained. Recommendations for the practical application of considered metamaterial structure for designing patch antennas have been discussed.

Effects of nitrogen atom doping on optical properties and dielectric constant of HfO2 gate oxides

The effect of nitrogen atom doping on the optical properties and dielectric constant of HfO2 films has been systematically investigated. Spectroscopic ellipsometry was employed to investigate the optical properties of nitrogen incorporated HfO2 films. The values of average oscillator strength and average oscillator position extracted from spectroscopic ellipsometry demonstrated that nitrogen incorporation could influence the dipole oscillator strength and oscillator position of HfO2. A physical model of dipole structures was proposed to verify the enhancement of dielectric constant of HfO2 films by nitrogen incorporation.

Development of electrical properties in lead-free bismuth sodium lanthanum titanate–barium titanate ceramic near the morphotropic phase boundary

Abstract The near morphotropic phase boundary (MPB) of lead-free piezoelectric ceramics based on bismuth sodium lanthanum titanate (Bi 0.487 Na 0.487 La 0.017 TiO 3 :BNLT) and barium titanate (BaTiO 3 :BT) was carefully investigated by a modified two step mixed-oxide method. In this case the BNLT and BT powders were produced separately using calcination temperatures of 900 °C and 1200 °C, respectively. After that they were mixed with the desired compositions of (1 − x )BNLT– x BT, where x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10. Then the powders were pressed and subsequently sintered at various temperatures to obtain the maximum density under each condition. It was found that the BT addition has a significant effect on grain growth inhibition of the BNLT–BT ceramics and this in turn gave rise to an enhancement in dielectric constant ( e r ) of the corresponding ceramics. The piezoelectric coefficient ( d 33 ) was also improved greatly to about 130 pC/N in the 0.96BNLT–0.04BT ceramic sample sintered at 1125 °C. This offered an opportunity to obtain a good candidate for replacing the lead-based piezoelectrics.

Optical and dielectric properties of junctionlike CdS nanocomposites embedded in polymer matrix

CdS nanocomposites have been grown in a polymer (polyvinyl alcohol) matrix using a simple chemical bath deposition process. Transmission electron micrographs of nanocomposites grown at different solution temperatures revealed the formation of isolated as well as junctionlike structures. X-ray and selected area electron diffraction patterns show that the nanocomposites are polycrystalline with cubic CdS phase. Optical band gaps of nanocomposite films are found to decrease (3.26–2.86eV) with the increase in bath temperature from 70to90°C. Photoluminescence spectra show strong green emission attributed to the Cd2+ or Cd+ ion-related recombination via moderately deep trap states. The nanocomposites show an enormous enhancement of dielectric constant in polyvinyl alcohol matrix over a frequency range of 40Hz–10MHz.

Permittivity enhancement of aluminum oxide thin films with the addition of silver nanoparticles

Multilayer reactive electron-beam evaporation of thin aluminum oxide layers with embedded silver nanoparticles (Ag-nps) has been used to create a dielectric thin film with an enhanced permittivity. The results show a frequency dependent increase of the dielectric constant κ. Overall stack κ of the control sample was found to be 7.7–7.4 in the 1kHz–1MHz range. This is in comparison with κ=16.7–13.0 over the same frequency range in the sample with Ag-nps. Capacitance-voltage and conductance-voltage measurements indicate the presence of charge capture resulting from the Ag-nps. The authors attribute this dielectric constant enhancement to dipole and space charge polarization mechanisms.

Enhancement of dielectric constant in HfO2 thin films by the addition of Al2O3

Hf O 2 films with an enhanced dielectric constant, prepared through phase transition engineering by the addition of Al2O3, were deposited by plasma-enhanced atomic layer deposition adopting a supercycle concept. After an annealing step at 700°C, the tetragonal phase, which is a high-temperature phase of HfO2, was stabilized completely at room temperature and the crystallographic direction was changed to the preferred (002) orientation. As a result, Hf aluminate film with a (002)-oriented tetragonal phase had a dielectric constant of 47, approximately twice as large as the reported value of HfO2 film with a monoclinic phase.

Enhanced Dielectric Constant of HfO2 and Al2O3 Thin-Films with Silver Nanoparticles

Through an electron beam evaporation process, silver nanoparticles (Ag-nps) were introduced into dielectric thin-films. Silver incorporation into the oxide films resulted in a distribution of insulating Ag-nps at a density of ~10^12 particles/cm^2. For these samples, an enhancement of about two fold in dielectric constant was observed in both Al2O3 and HfO2. We attribute the dielectric constant enhancement to the polarizability of metallic nanoparticles. The dipole moment of the Ag-nps increased the stack dielectric constant in a frequency dependent manner. Because of the inherent relaxation frequency of the Ag-np dipoles and space-charge polarization, the dielectric constant was more strongly enhanced at lower frequencies (down to 100 Hz) relative to higher frequencies (up to 1 MHz). Gate leakage currents remained comparable between the control and nanocomposite samples. The Ag-nps also produced a memory effect. Potential applications of these Ag-np based films in CMOS devices are discussed.

Dielectric constant enhancement due to Si incorporation into HfO2

The authors investigated the dielectric constant change of Hf(1−x)SixO2 film as functions of Si concentration and annealing temperature. As a result, the dielectric constant of Hf(1−x)SixO2 was increased when doped with a small amount of Si after 800°C annealing. The authors revealed that the dielectric constant enhancement of Hf(1−x)SixO2 films is related to the phase transformation from the monoclinic to the tetragonal phase of HfO2. By using the Clausius-Mossotti relation, it is concluded that the dielectric constant enhancement through the structural phase transformation is derived from the molar volume shrinkage rather than the molar polarizability increase.

High-frequency magnetic and dielectric properties of a three-phase composite of nickel, Co2Z ferrite, and polymer

A three-phase, double-percolating composite with Co2Z ferrite particles and nickel particles embedded in a poly(vinylidene fluoride) matrix was prepared by using a simple low-temperature hot-pressing technique. The large ferrite particles in the composite not only act as the magnetic phase but also present as a high volume fraction discrete (nonpercolating) phase, confining polymer and metallic particles into a continuous double-percolating structure of low volume fraction. With the addition of a small number of magnetic nickel particles, a large enhancement in both initial permeability and dielectric constant of the three-phase composite was observed. This can be explained by effective medium approach and percolation theory. The three-phase composite showed both frequency-independent inductive and capacitive properties in the high-frequency range up to ∼500MHz. Such a multifunctional magnetic-electric three-phase composite could be used in high-frequency communications and electromagnetic interference filters not only as an inductor but also as a capacitor.

Dielectric constant enhancement in a silicone elastomer filled with lead magnesium niobate–lead titanate

Lead magnesium niobate–lead titanate (PMN–PT) ferroelectric powder was used to develop a particulated composite based on a silicone elastomer matrix, with improved dielectric permittivity. The filler was characterised by X-ray diffraction and scanning electron microscopy. Complex dielectric permittivity (10–10 8 Hz) and tensile mechanical properties (elastic modulus and ultimate stress) of composites at various filler contents (up to 30% by vol.) were compared with those of the neat silicone elastomer. Both the dielectric constant and loss factor regularly increased with the filler content. The elastic modulus increased with a lower rate than that of the dielectric constant. Even though the addition of filler resulted in a detriment of both toughness, ultimate stress and elongation at break, a good stretchability was still retained, as elongation ratios greater than 3 were possible at the highest filler content. Several dielectric models were compared to the experimental data and the best match was achieved by the Bruggeman model, which can be used as a predictive rule for different volume contents of filler.

Enhancement of Electric Field inside Metallodielectric Metamaterial

A metallodielectric metamaterial have been investigated by using FDTD (Finite Difference Time Domain) method and fabricated with a resin based rapid prototyping machine. It was composed of 7 layers of parallel periodic copper wires embedded in resin. The metallodielectric metamaterial shows a different near field distribution with direction of incident electric field E that causes different electromagnetic (EM) properties. In particular, when incident electric field E is vertical to the wires inside resin, we observe enhacement of electric field in the vicinity of the embedded metal wires according to the incident direction of electirc field E as compared with dielectirc wihout metal wires. The enhanced electric field by the embedded metal wire is responsible for the enhancement of effective dielectric constant.

Inorganic Oxide Core, Polymer Shell Nanocomposite as a High K Gate Dielectric for Flexible Electronics Applications

Organic/inorganic core shell nanoparticles have been synthesized using high K TiO(2) as the core nanoparticle, and polystyrene as the shell. This material is easy to process and forms transparent continuous thin films, which exhibit a dielectric constant enhancement of over 3 times that of bulk polystyrene. This new dielectric material has been incorporated into capacitors and thin film transistors (TFTs). Mobilities approaching 0.2 cm(2)/V.s have been measured for pentacene TFTs incorporating the new TiO(2) polystyrene nanostructured gate dielectric, indicating good surface properties for pentacene film growth. This novel strategy for generating high K flexible gate dielectrics will be of value in improving organic and flexible electronic device performance.

Dielectric and ferroelectric characteristics of 0.7PZT–0.3PZN ceramics substituted with Sr

Lead zirconate titanate–lead zinc niobate (PZT–PZN) ceramics with compositions close to the morphotropic phase boundary were investigated as a function of Sr doping. The powders were prepared using the columbite-(wolframite) precursor method. Dielectric and ferroelectric properties of the as-sintered and annealed samples were measured. The results showed that with increasing Sr concentration dielectric constant versus temperature curves become gradually broader. Sr doping has been shown to produce a linear reduction in the transition temperature (Tm) (294.1−12.7x °C) with concentration (x). The maximum value of the dielectric constant decreased and the degree of diffuse phase transition was enhanced with Sr doping. However, the results indicated that the degree of disorder in Sr-modified PZT–PZN was further improved by thermal annealing. After thermal annealing at 900°C for 48 h a strong enhancement of dielectric constant (εr) and remanent polarization (Pr) was observed.

DIELECTRIC PROPERTY OF LaAlO3 THIN FILMS DOPED WITH MAGNETIC Co AND Co3O4 CLUSTERS

The thin films of Co -doped and Co3O4-doped dielectric LaAlO3 (LAO) by co-ablation of magnetic metal Co and dielectric LAO on Pt – Ti – SiO2 – Si substrates have been prepared by pulsed laser deposition. A significant enhancement of dielectric constant of LAO upon doping of Co and cobalt oxide clusters is observed. Furthermore, modulation of the dielectric constant of the thin films by applying a magnetic field is verified, obviously due to the ferromagnetism of Co metal and Co oxide clusters embedded in the LAO thin films. A series of microstructural and dielectric characterizations on the as-prepared thin films have been performed and the mechanism underlying the dielectric enhancement upon the doping of Co and Co3O4 clusters is discussed.