High Εr Research Articles

Effects of oxygen pressure and Mn-doping on the electrical and dielectric properties of Bi5Nb3O15 thin film grown by pulsed laser deposition

Bi5Nb3O15 (B5N3) thin films grown at temperatures above 500 °C developed a crystalline B5N3 phase that decomposed into a BiNbO4 phase in the film grown at 700 °C, probably due to Bi2O3 evaporation. The leakage current density of the B5N3 film grown at 200 °C under an oxygen pressure (OP) of 100 mTorr was high at approximately 6.3 × 10−7 A cm−2 at 0.2 MV cm−1, with a small breakdown field of 0.24 MV cm−1 due to the presence of intrinsic oxygen vacancies. The electrical properties of the B5N3 films improved with increasing OP during the growth but the dielectric constant (εr) decreased. The Mn-doping also improved the electrical properties of the B5N3 films grown under low OP by producing doubly ionized oxygen vacancies, which decreased the number of the intrinsic oxygen vacancies. Furthermore, the Mn-doping increased the εr value of the B5N3 film, confirming the effectiveness of such doping in improving both the electrical and the dielectric properties of the B5N3 film. In particular, the 5.0 mol% Mn-doped B5N3 film grown at 200 °C under an OP of 100 mTorr exhibited a low leakage current density of 7.9 × 10−8 A cm−2 at 0.2 MV cm−1 and a large breakdown field of 0.4 MV cm−1 with a high εr of 64.

Microwave Dielectric Properties of ATe3O8 (A = Sn, Zr) Ceramics

ATe3O8 (A = Sn, Zr) ceramics were investigated as a promising dielectric materials for low temperature cofired ceramics (LTCC) applications. The ATe3O8 ceramics were synthesized using solid state reaction method by sintering in the temperature range 600 to 800 °C. The structure and microstructure of the ceramics were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. The dielectric properties of the ceramics were studied in the frequency range 4–6 GHz. The SnTe3O8 ceramic has a dielectric constant (εr) of 37.3, quality factor (Qu×f) of 9600 GHz, and temperature coefficient of resonant frequency (τf) of 223 ppm/°C, respectively. Ceramics with the composition 0.9TeO2–0.1SnTe3O8 has εr of 26.7, Qu×f of 10000 GHz, and a τf of 32 ppm/°C when sintered at 650 °C/2 h. ZrTe3O8 has relatively high εr of 67.5, Qu×f of 1800 GHz, and high positive τf of 362 ppm/°C.

Low Temperature Sintering Ba<sub>3</sub>Ti<sub>5</sub>Nb<sub>6</sub>O<sub>28</sub> Ceramics with Tunable Temperature Coefficient of Dielectric Constant

A middle permittivity dielectrics with the tunable temperature coefficient of dielectric constant (τε) in the BaO-TiO2-Nb2O5 system, Ba3Ti5Nb6O28, has been synthesized and characterized. The dielectric properties of Ba3Ti5Nb6O28 measured at 1MHz are as follows: dielectric constant (εr) ~38, dielectric loss (tanδ)<0.0002, temperature coefficient of dielectric constant (τε)~-22ppm/°C. The Ba3Ti5Nb6O28 phase satisfies the requirements of NP0 (MLCC) dielectrics, but the sintering temperature of the Ba3Ti5Nb6O28 phase (1250~1300°C) is too high to be co-fired with Ag or Cu electrodes. To lower the sintering temperature, an appropriate amount of ZnO-B2O3 frit (5~7wt.%) was added to the Ba3Ti5Nb6O28 phase and dense ceramics were obtained at the sintering temperature lower than 1000°C. Furthermore, the CaNb2O6 phase with the positive τε of 65ppm/°C was incorporated into the Ba3Ti5Nb6O28 phase to adjust the temperature coefficient of dielectric constant from negative to positive(-22~30ppm/°C). Near zero τε ceramics with high εr (38) and low tanδ (0.0002) were obtained at the composition of Ba3Ti5Nb6O28/ CaNb2O6/ ZB frit=76:17:7 wt.%.

EFFECT OF RARE-EARTH (RE = La, Nd, Ce AND Gd) DOPING ON THE PIEZOELECTRIC of PZT(52:48) CERAMICS

The purpose of this research is to study the effect of doping some rare earth ions into PZT(52:48) ceramics. The ferroelectric Pb ( Zr x Ti 1-x) O 3 ceramics are well-known as piezoelectric materials for electro-mechanical transducers such as ultrasonic generator, electronic buzzer, and stress sensor, etc. The highest piezoelectric coupling coefficients as well as maximum permittivity are located near the morphotropic phase boundary (MPB). The region of phase transition between the tetragonal and rhombohedral structures in the Pb ( Zr x Ti 1-x) O 3 ceramic shows very adoptable piezoelectric characteristics due to the phase coexistence phenomena, and exhibits a sensitivity of properties to the preparation method, the composition, the firing temperatures and the kinds of additives. The purpose of this research is to study the effect of doping La , Nd , Ce and Gd into Pb ( Zr 0.52 Ti 0.48) O 3 ceramics prepared by solid state reaction. The properties include microstructure, physical properties, dielectric constant (εr) and piezoelectric properties (kp and Qm) of undoped and La , Nd , Ce and Gd doped PZT ceramics. Several effects, such as firing temperature, grain size and dopants, on the properties of PZT were also studied. The undoped PZT ceramics with Zr/Ti at 52/48 indicated the highest εr=1969 and kp= 0.381 for La doping. Doping with La , Nd , Ce and Gd led to an improvement in the εr but a reduced Qm value. The optimum values of electric properties were found in PZT (52/48) doped La with 10.0 mol% sintered at 1200°C for 2 h.

Microstructures and Dielectric Properties of CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub> Polycrystalline Ceramics

We report important factors affecting the dielectric properties of CaCu3Ti4O12 (CCTO) polycrystalline ceramics prepared by the conventional solid-state ceramic process. The relative dielectric constants (εr) up to several thousands (~ 3,000 at 1 kHz) were gradually increased with increasing the sintered density of samples in the case that no exaggerated grain growth occurred. An abrupt increase in εr values were, however, accompanied by the formation of abnormally grown large grains, and thus with increasing the population of abnormally grown grains, which could be achieved by a prolonged sintering at 1060°C, the εr values were remarkably increased from several thousands to ~105. Optimally processed CCTO sample exhibited a very high εr of ~ 90,000 at 1 kHz.

Preparation and Microwave Dielectric Properties of (1-x)Ca<sub>2/5</sub>Sm<sub>2/5</sub>TiO<sub>3</sub> -x Li<sub>1/2</sub>Nd<sub>1/2</sub>TiO<sub>3</sub> Ceramics

(1-x) Ca2/5Sm2/5TiO3-x Li1/2Nd1/2TiO3 (CSLNT) ceramics, suitable for use in resonators or filters at microwave frequency, have a high εr and a low temperature coefficient of resonant frequency. The effects of calcinations on the microwave dielectric properties of CSLNT were studied. The CSLNT (x = 0.3) ceramics sintered at 1300oC for 3 h showed microwave properties with εr of 92, Qf of 5060 GHz and τf of 7.5 ppm/oC. The microwave dielectric properties of CSLNT (x = 0.3) ceramics were also improved by soft chemistry methods such as citric acid gel route and ethylenediaminetetraacetic acid (EDTA) chelating method. The excellent microwave properties with εr = 96, Qf = 6290 GHz and τf = 6 ppm/oC were obtained by EDTA chelating method for CSLNT (x = 0.3) ceramics.

( 1 − x ) Ba Ti O 3 − x ( Na 0.5 K 0.5 ) Nb O 3 ceramics for multilayer ceramic capacitors

( 1 − x ) Ba Ti O 3 − x ( Na 0.5 K 0.5 ) Nb O 3 ceramics with 0.0⩽x⩽0.08 formed a homogeneous solid solution. As (Na0.5K0.5)NbO3 (NKN) was added, the Curie temperature of the BaTiO3 (BT) ceramics decreased and specimens became a relaxor as x exceeded 0.04. The grain size of the BT ceramics decreased with increasing NKN. The average grain size was approximately 0.4μm at x=0.06. The dielectric constant (εr) of the specimen increased with increasing NKN and high εr of 7402 with low dielectric loss of <1.0% was observed for the 0.94BT-0.06NKN ceramic. Therefore, the 0.94BT-0.06NKN ceramic is proposed as a promising candidate material for thin multilayer ceramic capacitors with high capacitance.

Rare-earth scandate single- and multi-layer thin films as alternative gate oxides for microelectronic applications

Thin films of rare-earth scandates (RE ScO3) as well as multi-layers of scandates and titanates have been prepared using pulsed laser deposition. Epitaxial films were grown on SrRuO3/SrTiO3(100) as well as amorphous films on silicon substrates. The epitaxial films are investigated to measure the physical properties of the crystalline material. Electrical measurements (CV, leakage current) show for example high ϵr>20 for the scandates and ϵr>35 for the epitaxial and amorphous multi-layer films. A diffusion of the new materials into silicon is not observed.

Material characterization of a high‐dielectric‐constant polymer–ceramic composite for embedded capacitor for RF applications

AbstractEmbedded capacitor technology can improve electrical performance and reduce assembly cost compared with traditional discrete capacitor technology. Polymer–ceramic composites have been of great interest as embedded capacitor materials because they combine the processability of polymers with the desired electrical properties of ceramics. We have developed a novel nanostructure polymer–ceramic composite with a very high dielectric constant (εr ≈ 150, a new record for the highest reported εr value of a nanocomposite) in a previous work. RF applications of embedded capacitors require that the insulating material have a high εr at a high frequency (in the gigahertz range), low leakage current, high breakdown voltage, and high reliability. A set of electrical tests were conducted in this study to characterize the electrical properties of the novel high‐εr polymer–ceramic nanocomposite developed in‐ house. The results show that this material had a fairly high εr in the RF range, low electrical leakage, and high breakdown voltage. An 85°C/85% thermal humidity aging test was been performed, and it showed that this novel high‐K material had good reliability. An embedded capacitor prototype with a capacitance density of 35 nF/cm2 was manufactured with this nanocomposite with spin‐coating technology. This novel nanocomposite can be used for the integral capacitors for RF applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2228–2231, 2004

Microwave Dielectric Characteristics of Ca[(Li1/3Nb2/3)1-xZrx]O3-δ Ceramics

The microwave dielectric characteristics of Ca[(Li1/3Nb2/3)1-xZrx]O3-δ ceramics were investigated. The microwave dielectric properties of Ca(Li1/3Nb2/3)O3-δ sintered at 1150°C exhibit a the dielectric constant (εr) of 29.6, a Q·f0 of 40000 GHz, and a temperature coefficient of resonant frequency (τf) of -21 ppm/°C. To control of the τf of Ca(Li1/3Nb2/3)O3-δ, Zr4+ was substituted for [Li1/3Nb2/3]3.67+. As the Zr content increased, the εr slightly increased and the τf shifted to positive and then negative value. However, the Q·f0 initially increased and then continuously decreased. A new composition having high Q·f0 (≈36300 GHz), high εr (≈30), stable τf (≈-5 ppm/°C), and relatively low sintering temperature (1150°C) was developed and the relationship between microstructure and microwave dielectric characteristics was investigated.

Microwave dielectric properties of MO–La2O3–TiO2 (M = Ca, Sr, Ba) ceramics

Single-phase polycrystalline ceramics in the MO–La2O3–TiO2 (M = Ca, Sr, Ba) system, such as cation-deficient hexagonal perovskites CaLa4Ti4O15, SrLa4Ti4O15, BaLa4Ti4O15, and Ca2La4Ti5O18 and the orthorhombic phases CaLa4Ti5O17 and CaLa8Ti9O31, were prepared through the solid-state ceramic route. The phases and structure of the ceramics were analyzed through x-ray diffraction and scanning electron microscopy. The microwave dielectric properties of the ceramics were studied using a network analyzer. The investigated ceramics show high εr in the range 42 to 54, high quality factors with Q ×f in the range 16,222 to 50,215 GHz, and low Tf in the range –25 to +6 ppm / °C. These high dielectric constant materials with high Q × f up to 50,215 GHz are suitable for applications where narrow bandwidth and extremely low insertion loss is necessary, especially at frequencies around 1.9 GHz.

Effect of starting powder-size of BaTiO3 on relaxor behavior in 0.85BaTiO3-0.15KNbO3

KNbO3 had been found to be an effective additive to BaTiO3 normal ferroelectrics to realize lead-free relaxor. This paper discussed the influence of starting powder-size of BT on ferroelectric properties of 0.85BaTiO3-0.15KNbO3 relaxor. The ferroelectric properties of fine-powder derived sample are in accordance with the result that has been reported and display the highest ϵr ’ maximum in the ϵr ’-T relationship. In coarser powder derived samples, ϵr ’ is lower with a fluctuation of ϵr ’ in lower frequencies as 100Hz to 1000Hz. It is also found that Tm shift to lower temperatures with the increase of starting powder size of BaTiO3. In fine-powder derived sample, DC bias properties behave like that in lead-based relaxors. At temperature near Tm DC bias dependence of ϵr ’ also displayed a maximum with frequency dispersion but with quite lower corresponding bias field level.

Characteristics and Applications of Sr-Modified Ferroelectric Pb(Zr,Ti)O3 Thin Films

AbstractWe have investigated the structural and electrical properties of Sr-modified Pb(Zr,Ti)O3, i.e., (Pb1-xSrx)(Zr0.53Ti0.47)O3 (PSZT), thin films. Sol-gel derived PSZT films were deposited by spin casting onto Pt/Ti/SiO2/Si substrates. Ferroelectric perovskite phases were found for all specimens (x ≤ 0.6), which implied the successful substitution of Sr for Pb. The values of dielectric constant (εr) as well as remanent polarization (Pr) of PSZT capacitors decreases monotonically with increasing Sr for x ≥ 0.1. PSZT (x=0.4) thin film was found to be applicable to high permittivity films for high density dynamic random access memories, whose Pr and εr are 5 μC/cm2 and 350, respectively, and leakage current density is low as 1×10−7 A/cm2 at a electric field of 100 kV/cm. In this paper, we also discuss the characteristics of Sr-modified PbTiO3 thin films.

Solid materials with high dielectric constants for hyperthermia applications

The manufacture of solid components with high permittivities εr of 1–100 and differing conductivities s` of 0–1.0 S/m has practical significance for fabricating applicators and phantoms in radiofrequency hyperthermia. For this purpose, various plastics (resins, polyurethane and silicone) were combined with additives (graphite and metal powder) and tested to assess their radiofrequency and mechanical characteristics and to identify manufacturing problems. Most of the plastics could be made highly dielectric and conductive by adding graphite in the range of muscle tissue (i.e. εr ≈ 80, s` ≈ 0.8 S/m). However, there are major differences between the materials with respect to mechanical behaviour, durability, feasibility of manufacture, and reproducibility. Manufacturing water-equivaent plastics (low conductivity s` < 0.05 S/m and εr value of 70–80) is particuarly difficult. A less filled polyester resin in which concentration of brass powder can achieve an εr value of up to 100 at low conductivity proved to be the only suitable medium. Such a plastic can be used for future applicator designs. Other materials of interest include plastics equivalent to lossy media (e.g. s` = 0.45–0.55 S/m, εr = 70–80), fat-equivalent plastics (polyurethane with graphite) and higher dielectric flexible plastics (silicone with brass powder).

Effect of practical layered dielectric loads on SAR patterns from dual concentric conductor microstrip antennas

Radiation patterns of 2 and 4 cm square Dual Concentric Conductor (DCC) microstrip antennas were studied theoretically with Finite Difference Time Domain (FDTD) analysis and compared with experimental measurements of power deposition (SAR) in layered lossy dielectric loads. Single and array configurations were investigated with 915 MHz excitation applied across either one, two or four sides, or four corners of the square apertures. FDTD simulations were carried out for realistic models of a muscle tissue load coupled to the DCC antennas with a 5 mm thick bolus of either distilled water or low loss Silicone Oil. This study characterizes the effect on SAR of adding three additional thin dielectric layers which are necessary for clinical use of the applicator. These layers consist of a 0.1 mm thick dielectric coating on the array surface to provide electrical isolation of DCC apertures, and 0.15 mm thick plastic layers above and below the bolus to contain the liquid. Experimental measurements of SAR in a plane 1 cm deep in muscle phantom agree well with theoretical FDTD simulations in the multi-layered tissue models. These studies reveal significant changes in SAR for applicator configurations involving low dielectric constant (εr) layers on either side of a high εr water bolus layer. Prominent changes include a broadening and centring of the SAR under each aperture as well as increased SAR penetration in muscle. No significant differences are noted between the simple and complete load configurations for the low εr Silicone Oil bolus. Both theoretical and measured data demonstrate relatively uniform SAR distributions with 50% of maximum SAR extending to the perimeter of single and multi-aperture array configurations of DCC applicators when using a thin 5 mm water or Silicone Oil bolus.

Evaluation of an empirical radar backscatter model for predicting backscatter characteristics of geologic units at Pisgah Volcanic Field, California

Comparison of radar backscatter coefficients (σ°, in dB), calculated by using the empirical model of Oh et al. [1992], to σ° extracted from AIRSAR data of four geologic units at Pisgah shows that the model predicts measured σ°vv and σ°hv to within ±3 dB. The model predicts higher σ°hh than those observed. For smooth surfaces (rms height=s, s&lt;8 cm), model results depend strongly on the accuracy of the surface measurements ( s and dielectric constant, ϵr). For rougher surfaces, the model is less dependent on the accuracy of surface characterizations. The model may be inverted to estimate s from measured σ° for surfaces with ks&lt;3 (k = wavenumber, or 2π/λ, where λ = radar wavelength). Model inversion for a pahoehoe unit at 30° to 50° incidence angles (θ) resulted in an estimate of s to within &lt;1 cm of the measured 3 cm. The inability of the model to estimate accurately σ°hh and the anomalously high nadir Fresnel reflection coefficients (Γo) and ϵr required in the model inversion may both be due to ∼equal co‐polarized ratios (σ°hh/σ°vv=p∼1) of the soils used to derive the model. For effective application to many geologic surfaces, for which p&lt;1 is often observed at θ&gt;30°, the model will require modification to include surfaces with non‐unity σ°hh/σ°vv.

Microwave Characteristics of TiO2-Bi2O3 Dielectric Resonator

The microwave characteristics of the binary-system TiO2-Bi2O3 ceramics, which is widely known to exhibit a comparatively high dielectric constant in the lower-frequency band, are investigated from a new standpoint. It is shown in this article that the composition of 0.919TiO2-0.081Bi2O3 has a high dielectric constant (εr=80), high Q (1800 at 5 GHz) and low temperature coefficient of resonant frequency (τf=+21 ppm/°C). From the X-ray diffraction and X-ray microanalysis, it is indicated that the crystal structure of this material is composed of two phases, TiO2 and Bi2Ti4O11, which possess a high εr with a negative temperature coefficient and a high εr with a positive temperature coefficient, respectively. The measurements of linear thermal expansion and temperature coefficient of capacitance are also carried out in order to study the behavior of temperature compensation in this system.

Electric-monopole antenna using a dielectric ring resonator

A dielectric ring resonator antenna structure which radiates like an electric monopole is reported. The use of high εr resonator material leads to small antenna height. Experiments show that the proposed antenna configuration is potentially useful for constructing small and compact ‘electric-monopole’ antennas.