We have investigated dielectric properties of several bismuth-based ceramics at microwave frequencies. BiNbO4 ceramics containing CuO and V2O5, had a high Q value of Q=4260 (at 4.3 GHz), ε=43, and τf=+38 ppm/°C. In the Bi2O3-CaO-Nb2O5 system, Bi18Ca8Nb12O65 composition had a high dielectric constant of ε=59, Q=610 (at 3.7 GHz), and τf=+24 ppm/°C. The crystal structure of this composition is considered to be an ordered structure based on the body center tetragonal cell (a=0.377, c=0.542 nm). Furthermore, by substituting Zn for Ca, ε increased and τf changed to negative values. In the composition of 45.75BiO3/2-21.75(Ca0.725Zn0.275)O-32.5NbO5/2, excellent properties of ε=79, Q=360 (at 3.3 GHz), and τf=+1 ppm/°C were obtained. As all the above ceramics can be sintered below 950°C, they are applicable to multilayer microwave devices with Ag inner conductors.

We have investigated microwave dielectric properties and crystal structures of Ca(B3+ 1/2B1/2 ′5+)O3 (B: Al, Cr, Mn, Fe; B′: Nb, Ta) and Ca(B2+ 1/3B2/3 ′5+)O3 (B: Mg, Ca, Co, Ni, Cu, Zn; B′: Nb, Ta) perovskite ceramics. Compared with well-known Ba-based perovskite dielectrics, the Ca-based complex perovskite dielectrics had lower relative permittivities (ε r ), lower Q values, and larger negative temperature coefficients of resonant frequencies (τ f ). Ca(Mg1/3Ta2/3)O3 had the highest Q value (Q f=78000 GHz) in this investigation. All Ca(B1/2B1/2 ′)O3 had perovskite structures similar to CaTiO3 with a unit cell including four simple perovskite cells. Ca(B1/3B2/3 ′)O3 with a small B ion such as Ni had the same structure Ca(B1/2B1/2 ′)O3. Ca(B1/3B2/3 ′)O3, however, had perovskite structures with larger unit cells than CaTiO3 when B ions had larger ionic radii.

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We examined sintering additives for alumina. When using CuO-TiO2-Nb2O5 additive, dense sintered alumina was obtained by firing at 1000°C or below, even though additive content was at most 10 mass%. It is considered that the formation of mixed oxide consists of CuO, TiO2 and Nb2O5 has an important role for low temperature sintering of alumina. Thermal conductivity of the above sample was 15 W/mK, which was the highest value yet reported within LTCC (Low Temperature Co-fired Ceramics) materials.

We studied the dielectric properties of Al 2 O 3 -MgO-ReO x (Re: rare earth) systems in the microwave region and found that the magnetoplumbite phases in the MgO-poor regions of MgReAl 11 O 19 (Re: La ∼ Tb) compositions had positive TCF (temperature coefficient of resonance frequency) values in spite of having low dielectric constants of under 20. By mixing a lead-free glass with the above system, a novel LTCC (which we term an AMSG) was obtained that was characterized by a low dielectric constant (<10), a near zero TCF, and high bending strength. When firing these AMSG green sheets inserted between HTCC alumina or magnesia green sheets that cannot be sintered at the AMSG sintering temperature, the AMSG sheets were seen to shrink not in the x-y directions but in the z direction due to the constraining effects of the HTCC layers. The obtained non-shrinkage substrate had precise dimensions and a high degree of flatness. The AMSG and the non-shrinking techniques have potential for application to integrated RF modules in mobile communications equipment.