Temperature Coefficient Of Capacitance Values Research Articles

Investigation of Structural, Dielectric, and Optical Behaviour of Dysprosium-Doped Barium Titanate Ceramics

The influence of Dysprosium (Dy) doping on the structure, dielectric and optical properties of the BaTiO3 system has been investigated in the manuscript. The solid-state reaction method was employed to prepare ceramics with compositions of Ba1−xDy2x/3TiO3 (x = 0.0, 0.01, 0.025, 0.05, 0.075, and 0.1). X-ray diffraction (XRD) structural analysis was carried out, showing complete dissemination of Dysprosium in the BaTiO3 lattice with a tetragonal symmetry. Close investigation of the XRD pattern revealed the existence of a small secondary phase above x ≥ 0.025. Microstructure was analyzed using scanning electron microscopy, showing that grain growth was suppressed by the incorporation of Dysprosium. Raman spectra further confirmed crystal symmetry and existence of a secondary phase for higher doping concentrations. Dielectric behavior was studied with variations of frequency and temperature. The temperature variant dielectric constant and dielectric loss represent a decrease of dielectric constant and loss with a rise in dysprosium content with a slight variation of transition temperature. Temperature coefficient of capacitance values for all compositions were calculated. The diffusivity parameter for all compositions was obtained using modified Curie-Weiss law and an enhancement in diffusivity was observed with increased dysprosium content. The optical behaviour of the doped samples was studied via UV–visible spectroscopy and the optical band gap was found to decrease with doping.

Resource efficient exploration of ternary phase space to develop multi-layer ceramic capacitors

We demonstrate a fast, efficient combinatorial method for the optimisation of materials for multi-layer ceramic capacitors (MLCCs). Experimentally gathered permittivity-temperature profiles for nine compositions spanning a solid solution are used as input, and with series mixing rules, binary and ternary permittivity contour maps are calculated based on individual layer thicknesses. These are converted into Temperature Coefficient of Capacitance (TCC) contour maps and an algorithm is then used to identify material combinations and individual thicknesses suitable for various MLCC classifications. These facilitate targeted experimentation and allowed experimental verification of the methodology. The approach highlights that binary systems can achieve X9 (R, S T and U). classification but the addition of a third complimentary material can facilitate a tighter TCC classification (X9P) with a wider tolerance in layer thicknesses, providing a better strategy for mass production of MLCCs. The room temperature permittivity (ƐRT) for combinations with similar TCC values can also be evaluated to ensure adequate ƐRT is achieved for commercial applications.

Structures and electric properties of cubic bismuth based pyrochlore thin films grown by pulsed laser deposition

The effects of cation substitution on the structure, dielectric properties, tunability, and temperature dependence of (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 (BZN) thin films were investigated. Four kinds of ceramic targets and thin films were prepared, which were (Bi1.5Zn0.1Ca0.4)(Zn0.5Nb1.5)O7 (BZNCa), (Bi1.5Zn0.5)(Nb0.5Ti1.5)O7 (BZNTi), (Bi1.5Sr0.5)(Sn1.5Nb0.5)O7 (BSSN) and (Bi1.5Sr0.5)(Zr1.5Nb0.5)O7 (BSZN). Thin films were deposited on Pt/TiO2/SiO2/Si(100) substrates at the substrate temperature of 650°C under an oxygen pressure of 10Pa by pulsed laser deposition. The resultant Bi-based thin films show a cubic pyrochlore structure. Meanwhile, the preferential orientation of the (111) plane is observed. Surface morphology features of the substituted thin films also show the difference. Compared with the pure BZN thin film, the dielectric constant of the BZNCa thin film slightly decreases. The temperature coefficient of capacitance (TCC) moves to the negative orientation TCC=−319ppm/°C. The dielectric constant of the BZNTi thin film significantly increases, reaching 229. At the same time, thin film still keeps the low loss tangent. However, the dielectric constants of the BSSN and BSZN thin films significantly decrease, dropping to 60 and 48, respectively. Furthermore the BSSN thin film exhibits the near zero temperature coefficient of +55ppm/°C. The BSZN thin film also shows the positive TCC value of +318ppm/°C. Moreover, BSSN and BSZN thin films show a near field independence (at low field).

Improved dielectric properties of Al2O3-doped Pb0.6Ba0.4ZrO3 thin films for tunable microwave applications

The effect of doping Al2O3 on the Pb0.6Ba0.4ZrO3 thin films was investigated. With increasing Al2O3 content, the dielectric constant, tunability, and dissipation factor decrease while the figure of merit (FOM) increases. After doping with the optimal content of 1.5at.% Al2O3, the Pb0.6Ba0.4ZrO3 films have a dielectric constant of 190, a tunability of 30%, a dissipation factor of 0.0067, a FOM value of 49, and a temperature coefficient of capacitance value of 1.13×10−4. The loss mechanism is discussed in order to provide information, which could be useful for further improvement of the material performance.

Structural and Dielectric Properties of Ag(Nb0.8Ta0.2)1?xSbxO3(x?0.08) Ceramics

Sb2O5 were selected to substitute (Nb0.8Ta0.2)2O5 and the effects of Sb substitution on the dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics were studied. The perovskite Ag(Nb0.8Ta0.2)1−xSbxO3 ceramics showed no obvious change with x value being no more than 0.08, and the pseudoperovskite unit cell parameters a=c, b and monoclinic angle β decrease with Sb concentration increasing. The dielectric properties of Ag(Nb0.8Ta0.2)1−xSbxO3 ceramics were found to be affected greatly by the substitution of Sb for Nb/Ta. The ɛ value of Ag(Nb0.8Ta0.2)1−xSbxO3 ceramics sintered at their densified temperature increased from 480 to 825 with x from 0 to 0.08, the tan δ value decreased sharply from 0.0065 to 0.0023 (at 1 MHz) with x increasing from 0 to 0.04, and then kept a stable lower tan δ value ∼0.0024 with x to 0.08. The temperature coefficient of capacitance values continuously decreased from a positive value of 1450 ppm/°C for x=0 to a negative value of −38.52 ppm/°C for x=0.08.

The Dielectric Properties of Pb0.65Ba0.35ZrO3 Thin Films Applicable to Microwave Tunable Devices

Pb0.65Ba0.35ZrO3 (PBZ) thin films have been grown on MgO (001) substrates by pulsed-laser deposition (PLD). We have compared the structural and dielectric properties of PBZ films grown at various temperatures. A highly c-axis oriented PBZ film has been grown on a MgO (001) substrate at the deposition temperature of 550°C and has also shown the largest tunability among all the PBZ films in capacitance-voltage measurements. The tunability and dielectric loss of the PBZ film was 20% and 0.00959, respectively. In addition, we have compared the temperature coefficient of capacitance (TCC) of a PBZ film with that of a Ba0.5Sr0.5TiO3 (BST) film which is a well-known material applicable to tunable microwave devices. We have confirmed that TCC value of a PBZ thin film was three-times smaller than that of a BST thin film.

Low Sintering Temperature of CuO-Fluxed Ag(Nb, Ta)O3 Dielectric Ceramics

ABSTRACTSolid solutions in the Ag(NbxTa1−x)O3 (where 0 ≤ × ≤ 1) system exhibit excellent dielectric properties at microwave frequency including high dielectric constant (200<k<400), low loss (tanΔ ∼ 0.004) and a composition controlled temperature coefficient of capacitance (TCC). For Ta-rich and Nb-rich solid solutions, the TCC values are negative and positive, respectively, and two-phase mixtures provided an average TCC close to zero. Series, parallel, and logarithmic mixing rules were applied to predict dielectric constant and TCC of polyphase assemblages (45wt%Ag(Nb0.65Ta0.35)O3+55wt% Ag(Nb0.35Ta0.65)O3) yielded an average dielectric constant of 450 and a TCC of 180ppm/°C. Microstructure analysis revealed that a CuO-rich liquid remains at the grain boundary and transmission electron microscopy shows that the CuO resides at triple points. Ag(NbxTa1−x)O3 ceramics were successfully integrated into LTCC for embedded capacitors. The addition of CuO lowered the sintering temperature to below 900°C and a low TCC was maintained for fine grained microstructures.

Crystalline Phases and Dielectric Properties of Crystallized Glasses in the (Ca, Sr, Ba) O-Al2O3-SiO2-TiO2 System.

The relationship between crystallized phases and dielectric properties of crystallized glasses in the (Ca, Sr, Ba)O-Al2O3-SiO2-TiO2 system was investigated. Powder sample of 0.386(Ca0.189, Sr0.518, Ba0.293)O⋅0.094Al2O3⋅0.520SiO2⋅0.121TiO2 glass (sample Ti-G) was used for this study and powder samples of 0.386(Ca0.189, Sr0.518, Ba0.293)O⋅0.094Al2O3⋅0.520SiO2 glass (sample G) and mixture of sample G with 0.121TiO2 (sample G/Ti) were used to obtain reference data. These powders were pressed in disks and sintered at 850, 900 and 950°C for 2h. Crystalline phases of (Ca, Sr, Ba)Al2Si2O8 (AS) and (Ca, Sr, Ba)2TiSi2O8 (TS) precipitated in sample Ti-G and only AS phase precipitated in sample G at 950°C. Dielectric constant and temperature coefficient of capacitance (TCC) were measured for each sintered sample. The TCC values of the samples Ti-G and G (sintered at 950°C) were negative and positive values, respectively. These experimental results clearly show that the negative TCC value of sintered Ti-G samples is mainly due to the presence of TS phase. The dielectric constant and the TCC of the TS phase, estimated by empirical equations involving the rule of mixture, were 13.2 and -241ppm/°C, respectively.

Multilayer capacitor ceramics in the PMN-PT-BT system: effect of MgO and 4PbO·B 2 O 3 additions

Coexistence of pyrochlore phase is one of the major problems in the preparation of lead magnesium niobate (PMN) based perovskites as it leads to deterioration of the dielectric and piezoelectric properties. Although the columbite precursor method substantially reduces the formation of pyrochlore phase, the success of this process depends on various process conditions such as reactivity of MgO, level of mixing or grinding, control of PbO volatility and reversibility of the reaction. Compositions in the system (1−x)[(1−y)PMN yPT]x BT (where PT = PbTiO3 and BT = BaTiO3) were prepared by the columbite route. Results show that addition of excess MgO and 4PbO·B2O3 glass before sintering not only eliminates the pyrochlore phase completely but also produces a series of ceramics with low firing temperature, very high dielectric constant, low dissipation factor, high d.c. resistivity and extremely low temperature coefficient of capacitance (TCC). The unusually low TCC values make these high K dielectrics suitable for application in multilayer ceramic capacitors having EIA specifications Y5P, Y5R and Y5S.

Lead Perovskite Relaxor-Based Low-Loss Ceramic Dielectric for High-Voltage Ceramic Capacitors

A low-loss ceramic dielectric with a less than 0.1% dissipation factor at 100 kHz, based on a modified lead zinc niobate relaxor, has been fabricated by shifting the ferroelectric transition temperature (Tc) to below -55°C. This dielectric has a high dielectric constant (K), ranging from 250 to 2000. The temperature coefficient of capacitance (TCC) locates at the middle area between values for temperature compensation dielectric and values for high-K dielectric. Even at 150°C, high insulation resistance, more than 5×1013 Ωcm, was also retained. Moreover, a typical composition with K=530 revealed that the dielectric has a high breakdown voltage of 95 kV per 10 mm of thickness and a TCC value of -2900 ppm/°C. Accordingly, this dielectric has proven useful for high-voltage ceramic capacitors.

Preparation and Properties of Sputtered Hafnium and Anodic HfO2 Films

Hafnium films sputtered at high voltages (4 kV) had a density of 98% of the bulk, specific resistivities as low as 50 µmhm‐cm and TCR as high as 1580 ppm/°C. Films with a density of 50% of that of the bulk, a specific resistivity of 815 µohm‐cm, and TCR of 800 ppm/°C were obtained at the lower sputtering voltages (1.5 kV). High‐ and low‐density films had Hall coefficients of and , respectively. All the sputtered films had the same hexagonal close‐packed structure as the bulk material, although the high‐ and low‐density films had different preferred orientation. The oxide density, anodization constant, and dielectric constant for hafnium oxide were found to be 7.9 g/cm3, 20 Aå/V, and 18, respectively. The anodized hafnium oxide had a monoclinic polycrystalline structure with some preferred orientation, or (001) plus . Test capacitors with anodic oxides formed to 100V at 1 mA/cm2 had capacitance density values of 0.085 µf/cm2, dissipation factors below 0.01 at 1 kHz, and a frequency dependence of capacitance of ±1% in the range of 0.1–100 kHz relative to the 1 kHz value. Temperature coefficient of capacitance values varied from 300 to 600 ppm/°C.