Takahiro Takada

Structure and Dielectric Properties of (Ca1-xNd2x/3)TiO3

(Ca1-x Nd2x /3)TiO3 sintered samples are fabricated with 0x1 and the crystal structure and dielectric properties are investigated. It is shown that (Ca1-x Nd2x /3)TiO3 has an orthorhombic GdFeO3-type structure for 0x0.69 and an La2/3TiO3-type double-layered perovskite structure for 0.78x0.93. High e and high fQ values are obtained for the GdFeO3 phase of (Ca1-x Nd2x /3)TiO3, e.g., e=108 and fQ=17200 GHz for x=0.39. On the other hand, for the La2/3TiO3 phase, e is between 80 and 100 and fQ is below 1000 GHz.

Synthesis and microwave dielectric properties of xRe2O3-yB2O3 (Re = La, Nd, Sm, Dy, Ho and Y) compounds

The microstructure, crystal structure and microwave dielectric properties of xRe2O3-yB2O3 (Re = La, Nd, Sm, Dy, Ho and Y) were studied. Sintering temperature was increased while decreasing Re ion radius. The only compound well-sintered with porosity <1% was LaBO3 which had the highest fQ = 53000 GHz and dielectric constant (er) = 12.5 at 1200°C. With increases in A-site ion radii from Y to La, er increased from 5 to 12.5. The microstructure of LaBO3 ceramics was significantly different from that of other ReBO3 ceramics as seen by scanning electron microscope (SEM) and this will be effective for obtaining superior dielectric properties. (La1-xNdx)BO3 compounds were successfully synthesized and their microwave dielectric properties were also investigated.

Synthesis and Microwave Dielectric Properties of La2O3–xB2O3-Based Melt Mixtures for Low-Temperature Cofired Ceramics

La2O3–xB2O3-based melts were fabricated. Two kinds of melts, crystalline at x=2 and amorphous at x=3 with ZnO additions, were obtained. The microwave dielectric properties and microstructure of the ceramics prepared from the melts and calcined La2O3–B2O3 were investigated. Several mixtures of 50 wt % melts and 50 wt % calcined powder were fireable around 900°C, which was a low firing temperature for cofiring with a low-loss conductor. Among them, the dielectric properties for a fired mixture of 50 wt % La2O3–2B2O3–0.5ZnO melt and 50 wt % calcined powder showed an fQ value of about 30000 GHz and er=9–10 at 13 GHz. 5 wt % crystalline additives fired at 925°C, which have the same composition as the host ceramic material, increased fQ to 63000 GHz. The mixtures of 20–80 wt % crystalline melt and 80–20 wt % amorphous melt were also sinterable below 900°C. The best dielectric properties, fQ=72000 GHz and er=8 at 13 GHz, with low firing temperatures were exhibited when the mixing ratio was 20 wt % crystalline melt and 80 wt % amorphous melt. The green sheet, which contained two kinds of melts, could be cofired with Ag at 900°C.

Microwave dielectric properties of mixed phase ceramics, Ba(Zn1/3Ta2/3)O3–xCaTiO3 and xMgTiO3–yCaTiO3–z(Nd2O3,wTiO2)

The effect of different chemical compositions on the microwave dielectric properties of Ba(Zn1/3Ta2/3)O3–xCaTiO3 and xMgTiO3–yCaTiO3–z(Nd2O3,wTiO2) was studied. High fQ dielectrics were designed by optimizing composition and firing conditions. Adding up to 1 mol % CaTiO3 to Ba(Zn1/3Ta2/3)O3 increased εr from 25 to 30 at a firing temperature of 1450 °C, and produced very high fQ values of more than 100 000 GHz at a firing temperature of 1550 °C. EPMA and XRD suggested that ceramics based on Ba(Zn1/3Ta2/3)O3 with CaTiO3 had mixed phases of Ba(Zn1/3Ta2/3)O3 and Ca–Ti–Zn–O. Addition of CaTiO3 increased the Ba(Zn1/3Ta2/3)O3 peak observed in XRD and decreased the Ba3Ta2O8 peak. Prolonged sintering of Ba(Zn1/3Ta2/3)O3 with CaTiO3 increased the fQ value but kept εr constant. 0.5MgTiO3–0.5CaTiO3–z(Nd2O3,wTiO2) showed a high dielectric constant εr>40 and fQ>20 000 GHz. When w=1, τf decreased linearly with z around 0 ppm/ °C in 0.5MgTiO3–0.5CaTiO3–z(Nd2O3,TiO2) (0.25≤z≤0.5). X-ray and EDX analysis revealed a mixed phase matrix of MgTiO3 and (Ca1−αNd2α/3)TiβO3. It was concluded that εr of the high fQ materials Ba(Zn1/3Ta2/3)O3–xCaTiO3 and xMgTiO3–yCaTiO3–z(Nd2O3,wTiO2) would be increased by varying their chemical compositions, x, y, z, and w, and that their fQ value would be improved by appropriate choices of heating temperature and time.

Novel Low Temperature Co-Fired Ceramic Material System Composed of Dielectrics with Different Dielectric Constants

We found that the co-firing low temperature co-fired ceramic (LTCC) materials of different dielectric constants (er) with Cu wiring is achievable using a novel, original design. It was confirmed that the dielectric characteristics of the dielectrics designed in this study are very suitable for the use of the dielectrics in electronic components such as filters mounted in high-speed radio communication equipment. The dielectric constants of the lower- and higher-dielectric-coefficient materials were 8.1 and 44.5, respectively, which are sufficiently effective for downsizing LTCC components. Observing the co-fired interface, it was confirmed that excellent co-firing conditions resulted in no mechanical defects such as delamination or cracks. On the basis of the results of wavelength dispersive X-ray spectrometry (WDX) and X-ray diffractometry (XRD), it was confirmed that co-firing with minimal interdiffusion was realized using the same glass for both dielectrics. It is concluded that the materials developed are good for co-firing in terms of the mechanical defects and interdiffusion that appear in them.

Novel Glass-free LTCC Material co-fired with Cupper-Electrodes

Abstract Low Temperature Co-fired Ceramics (LTCC) have excellent high-frequency characteristics and have widely been used for microwave electronic components. By lowering the sintering temperature of the ceramics used as insulating layers, LTCC was co-fired with a high-conductivity wiring conductor, such as Cu or Ag. LTCC substrate has been expected as one of the most promising technologies to realize miniaturization of RF circuits in the field of wireless communications. There is no limitation to demand for further downsizing of RF circuits, suppression of electric loss and high mechanical strength of the substrate. However, conventional LTCC materials for substrates contain glass frit which causes defects, such as pores or cracks, and low mechanical strength. In this work, we have developed a novel LTCC material system BaO-Al2O3-SiO2-MnO-TiO2, without any glass frits. The material was co-fired with cupper electrodes, which have low resistivity and show less diffusion than silver in LTCC, under a low-oxy...