Ying-Chieh Lee

Effect of MgO Dopant on the Microstructure and Dielectric Properties of rf-Sputtered Ba0.5Sr0.5TiO3 Thin Films

MgO-doped Ba 0 . 5 Sr 0 . 5 TiO 3 (BST) thin films were synthesized by radio-frequency (rf) magnetron sputtering at substrate temperature 750°C using single-phase targets with different MgO contents ranging from 0 to 5 mol %. Microstructure, surface morphology, dielectric constant, and leakage current of the MgO-doped BST films were characterized to understand the influence of the MgO dopant on film properties. Polycrystalline and single-phase solid solution films with a dense microstructure were obtained in all deposition conditions. The electrical and dielectric properties of the BST-containing capacitors are both found to be improved significantly by doping MgO in the BST films. The leakage current density of the 5 mol % MgO-doped BST capacitors is nearly two orders of magnitude lower and the dielectric constant is about 45% times higher than that of the undoped BST capacitors. It is speculated that the increase in the dielectric constant is due to the formation of electric dipole Mg 2 - T i -V 2 + 0 complex resulting in an increase in the residual stress, whereas the improvement in the leakage properties is attributed to the oxygen vacancies by MgO doping, resulting in a reduced electron concentration in the materials.

Effects of dopant on the dielectric properties of CaZrO3 ceramic sintered in a reducing atmosphere

In this study, the influence of CaZrO3 doped with three dopants, SiO2, MnO, and Nb2O5, and then sintered in a reducing atmosphere on microstructure, phase formation, and electrical properties is investigated. SiO2 plays the role of sintering aid to enhance the density of CaZrO3 leading to better performance of electrical properties as a function of SiO2 content. MnO, and Nb2O5 were incorporated into the Zr-site of CaZrO3 to make stoichometric CaZrO3 into non-stoichiometric CaZrO3 with Zr excess resulting in the formation of a second phase, CaZr4O9, which has a lower dielectric constant (13) in comparison with that of the main phase of CaZrO3 (32). Thus, the dielectric constant of CaZrO3 doped with Nb2O5, or MnO is decreased markedly. In addition, Mn+2 incorporated into Zr-sites of CaZrO3 plays the role of acceptor, which compensates for the number of conduction electrons and contributes to better performance of electrical properties such as insulation resistance and tan δ. Conversely, Nb+5 incorporated into Zr-sites of CaZrO3 plays the role of donor and provides more conduction electrons, leading to poor performance of electrical properties.

A Study of Low-Temperature Sintering of (Ba0.6Sr0.4)(Ti0.94Cu0.06)O3 Ceramics with B2O3 Addition

The low-temperature sintering of (Ba0.6Sr0.4)(Ti0.94Cu0.06)O3 (BSTC) ceramics was investigated by conventional ceramics processing using a B2O3 sintering aid, and the dielectric properties and microstructures of the ceramics were examined. BSTC powders without B2O3 could not be fully densified at sintering temperatures lower than 1150°C. However, the addition of B2O3 markedly enhanced the sinterbility of BSTC powders, and the sintering temperature decreased from 1150 to 980°C. This may be due to the promotion of liquid-phase sintering. The 3 at.% B2O3-doped BSTC ceramics sintered at 980°C for 2 h exhibited a high density of 5.48 g/cm3. Transmission electron microscopy examination indicated that there are two kinds of secondary phases produced in BSTC ceramics during B2O3 addition; one is BaTi(BO3)2 with rhombohedral structure, and the other is Ba4Ti12O27 with monoclinic structure. The BSTC ceramics with 3 at.% B2O3 sintered at 980°C in air for 2 h exhibited a maximum permittivity, ϵ max = 1216, and a bulk density > 96% of theoretical density.

Relationship between microstructure and electrical properties of ZnO-based multilayer varistor

In this study, two types of ZnO-based multilayer varistor (MLV) with two different dielectric layers (12 and 24 µm), sintered from 900 to 1000 °C for 2 h were prepared to investigate the effects of microstructure such as the grain size and number of grain boundaries between two adjourn electrodes on electrical properties. The results show that the grain size linearly increases with sintering temperature, which results in an increase in the capacitance of ZnO-based MLVs. In contrast, the number of grain boundaries between two adjourn electrodes linearly decreases with sintering temperature associated with a decrease in breakdown voltage, leakage current and nonlinear coefficient of ZnO-based MLVs. The energy absorption capabilities determined from the peak current (PC) measurements of ZnO-based MLVs with sintering temperature are reported. The optimum peak currents of ZnO-based MLVs can be obtained by sintering at 950 °C.

Effect of Inner Electrode on Electrical Properties of (Zn,Mg)TiO3-Based Multilayer Ceramic Capacitor

In this study, different proportions of silver–palladium alloy used as an inner electrode are adopted to fabricate (Zn,Mg)TiO3-based multilayer ceramic capacitors. Effects of sintering temperature, and measuring frequency on the dielectric properties of the samples with different proportions of the Pd–Ag inner electrode are investigated. The continuity of the inner electrode and the proportion of Pd–Ag of the inner electrode of samples sintered at different temperatures play important roles in determining the dielectric properties.

Characterization of ZnO-Based Multilayer Varistor Sintered by Hot-Press Sintering

To attain the homogeneous microstructure of ZnO-based multilayer varistors (MLVs), hot-press sintering is conducted. To determine the effect of hot-press sintering on the microstructure, the dielectric and varistor properties of ZnO-based MLVs were investigated and compared with those of ZnO-based MLVs fabricated by free sintering. In hot-press sintering, the average grain size and the distribution of grain size of a ZnO-based MLVs are both reduced. The results show that the leakage current and nonlinear coefficient ( α) of ZnO-based MLVs can be improved. The increase in nonlinear coefficient ( α) is directly related to the inhibition of grain growth of ZnO grains when hot-press sintering is performed instead of free sintering. Note that the energy absorption capabilities in terms of peak current (PC) measurements of ZnO-based MLVs are remarkably improved due to the homogeneity of microstructure when hot-press sintering is conducted.

Investigation of dielectric properties of BaZr(BO3)2 ceramics

The effects of 3Zn-B2O3, B2O3 and flux additions on the microwave dielectric properties and the microstructures of Ba2Ti9O20-based ceramics have been investigated in our previous study. BaZr(BO3)2 phase existed in the Ba2Ti9O20-based ceramics, and could affect the microwave dielectric properties when the formation of the BaZr(BO3)2 phase is enhanced. In order to understand well the effect of the BaZr(BO3)2 phase on the dielectric properties of Ba2Ti9O20-based ceramics, the BaZr(BO3)2 composition was synthesized by conventional solid-state methods from individual BaCO3, ZrO2 and B2O3 powders. X-ray diffraction (XRD) results show the presence of the mainly crystalline phase, BaZr(BO3)2, and the minor phases are BaZrO3 and ZrO2 in the sintered ceramics. Scanning electron microscopy images show that the BaZr(BO3)2 grain prefers to develop oriented dendrite microstructures. Plots of dielectric loss versus sintering temperatures show a linearity, and ranges from 0.85 (at 1080°C) to 0.08 (at 1250°C). However, the dielectric constant does not increase with increasing sintering temperature, and its value is maintained at 11–13.

Mn-Doped BaO–(Nd0.7,Sm0.3)2O3–4TiO2 Ceramic Sintered in a Reducing Atmosphere

The effect of MnCO3 doping from 0 to 55 mol % into BaO–(Nd0.7Sm0.3)2O3–4TiO2 (BNST) sintered in a reducing atmosphere on the phase transformation, microstructure and electrical properties was studied. The variation of d-spacing with Mn content can be divided into three regimes in this study. In regime (I), 0 to 5 mol % Mn-doped BNST, the d-spacing decreases successively until 5 mol % which is the maximum solubility, because Mn+3 is incorporated into Ti+4-sites of BNST. In regime (II), 5 to 42 mol % Mn-doped BNST, the d-spacing remains constant and Mn2O3 is precipitated because the amount of MnCO3 doped is more than the solubility. In regime (III), 43 to 55 mol % Mn-doped BNST, the d-spacing is the same as BNST without MnCO3 doping. Heavily doping MnCO3 into BNST gives rise to two parallel reactions, forming two ternary systems, BaO–(Nd,Sm)2O3–TiO2 and BaO–(Nd,Sm)2O3–Mn2O3. Mn-doped BNST sintered in a reducing atmosphere is in a semiconducing state in regimes (I) and (II), because the concentration of free electron is higher than that of the acceptors. In contrast, Mn-doped BNST in regime (III) sintered in a reducing atmosphere is in an insulating state because the concentration of the acceptors is higher than that of liberated free electron.