Hiroshi Kagata

Low-Fire Bismuth-Based Dielectric Ceramics for Microwave Use

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), e=43, and τf=+38 ppm/°C. In the Bi2O3-CaO-Nb2O5 system, Bi18Ca8Nb12O65 composition had a high dielectric constant of e=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, e 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 e=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.

Dielectric properties of (PbCa)(MeNb)O3 at microwave frequencies

We have investigated the dielectric properties up to microwave frequencies of ceramics represented as (Pb1-xCax)-(MemNb1-m)O3 where Me is selected from Li, Na, Mg, Zn, Ni, Co, Fe, Y, Yb, Al and Cr. High Q values and small temperature coefficients of resonant frequency were obtained in (PbCa)(Mg1/3Nb2/3)O3, (PbCa)(Ni1/3Nb2/3)O3 and (PbCa)-(Fe1/2Nb1/2)O3 with perovskite structure. These dielectric constants and the Q values for a near-zero temperature coefficient are er=73 with Q=1330, er=59 with Q=1700 and er=91 with Q=1650, respectively. The other ceramics with smaller amounts of perovskite phase had degraded characteristics, i.e., low Q values or large temperature coefficients. In lead- and calcium-based perovskite, it seems that the high dielectric constant occurs due to Pb content in A-sites and smaller average ion radius in B-sites.

Dielectric Properties of Pb-Based Perovskite Substituted by Ti for B-site at Microwave Frequencies

Substitutions of B-sites by Ti in several Pb-based perovskite ceramics that had high relative permittivities (er), high Q values, and small temperature coefficients of resonant frequency (τf) were studied in order to control er and τf independently. It was found that relative permittivities with near-zero τf in (Pb, Ca)(Zr, Ti)O3, (Pb, Ca){(Fe1/2Nb1/2), Ti}O3, and (Pb, Ca){(Mg1/3Nb2/3), Ti}O3 systems could be controlled in the er regions lower than 105, 95, and 70, respectively. All these systems had sufficiently high Q values. They are applicable to resonant devices for mobile communications.

Dielectric properties of lead alkaline-earth zirconate at microwave frequencies

Dielectric properties of alkaline-earth-substituted PbZrO3 ceramics up to microwave frequencies were investigated. Although there were no preferable characteristics in the Ba- or Sr-substituted system, the ceramics in a (PbCa)ZrO3 system showed not only high dielectric constants in the range of 100 to 118, but also high Q values of 1000 to 1150 and small temperature coefficients of resonant frequency of 0 to 30 ppm/ °C. The crystal structure of the Ca-substituted ceramics was also investigated by X-ray powder diffraction. The structure changed from PbZrO3-type orthorhombic to CaZrO3-type orthorhombic through cubic and rhombohedral with increasing Ca substitution. Coaxial dielectric resonators made of the selected above material had Q values in the range of 430 to 450 at the 900 MHz band.

A very small dielectric planar filter for portable telephones

A high-performance dielectric filter 4.5 mm*3.2 mm*2.0 mm in size has been developed. It has two planar resonators and is made of high-permittivity multilayer ceramic in the Bi-Ca-Nb-O system. The transmission characteristic of the planar filter is found to have a distinctive attenuation pole feature. The behavior of the attenuation pole is explained by the relation between even-odd mode impedances and an equivalent expression with lumped elements.<<ETX>>

A first practical model of very small and low insertion loss laminated duplexer using LTCC suitable for W-CDMA portable telephones

A laminated duplexer using Low Temperature Co-fired Ceramics (LTCC) has been developed for the first time practically. The technologies of reducing the insertion loss are explained. They include the new ceramic-lamination process and the filter circuit design. The inner electrodes for the resonators are thicken by the state-of-art ceramic lamination process. The design of a laminated band elimination filter is also studied. As the result, its size is reduced by 30% comparing to a conventional mono block duplexer, while the performances are almost the same. It is very suitable for the next generation W-CDMA portable telephones.

Maltilayer Ceramic Capacitor with Copper Electrode

Dielectric material of (PbaCab){(Mg1/3Nb2/3)Ti(Ni1/2W1/2)}O2+a+b, where a+b>1, has been investigated. This composition has been proved to be fired under low oxygen partial pressure of less than 10-1 Pa with high resistivity. To make multilayer ceramic capacitor, the dielectric material was co-fired with copper electrode in an atmosphere of intermediate oxygen pressure. The obtained capacitor met to Z5U specification and had low dissipation factor and small change of capacitance under a d.c. bias voltage.

Crystal Structure Refinement of (Pb1-xCax)ZrO3 by the Rietvelt Method

Superlattice structures in rhombohedral perovskite (Pb 1-x Ca x )ZrO 3 , which has high dielectric constant with small temperature coefficient and high Q value at microwave frequencies, were refined by the X-ray Rietvelt powder profile analysis. The superlattice structure is caused by slight displacement of lead and zirconium ions from the ideal perovskite sites, together with twisting and deformation of oxygen octahedra. The Q value of (PbCa)ZrO 3 at microwave frequencies has no relation to the formation of the superlattice structures, as indicated by the absence of cation ordering

Analysis of Metal–Insulator–Metal Structure and Its Application to Sensor

In this paper, analysis and design method of a metal-insulator-metal (MIM) structure is introduced. When an electromagnetic wave enters an MIM structure, a surface plasmon is excited on both metals. In this case, an electromagnetic-field standing wave by the surface plasmon used as a wave source is generated in the insulator. This electromagnetic-field standing wave has various modes depending on the thickness of the insulator. In this paper, we establish by calculation, 3-D simulation, and measurement that a plasmon resonant wave can be controlled by changing the thickness of the insulator. We propose a sensor with an MIM structure that exploits this phenomenon. If the insulator of the MIM structure comprises air, the target solution can be injected into the insulator by capillary action, and the MIM structure is thus used as a sensor. This is because the wavelength of the electromagnetic-field standing wave in the insulator is made shorter in proportion to the refractive index of the target solution. We have confirmed this fact by calculation, 3-D simulations, and measurement. Our measurements show good agreement with the calculations and 3-D simulations, indicating that our MIM sensor is able to detect differences in refractive index of the order of 0.7%.

The Power Generation Characteristics and Durability of a Vibration Power Generation Device using Piezoelectric Thick Film Formed Directly by Screen Printing on a Stainless Steel Substrate

This paper presents a small, high-performance and novel device that generates power from vibrations, made using screen-printing to form a piezoelectric thick film directly on a stainless steel substrate. This simple and cheap method realizes a 20 – 40 μm-thick piezoelectric film, otherwise difficult to achieve using thin-film techniques or ceramic sintering, on a stainless steel substrate. A maximum output power of 1.1 mW was recorded with acceleration of 0.1 G0p (0.98 ms−2) applied at a resonance frequency of 24 Hz. We also evaluated the durability of the device by repeatedly striking the tip of the element. Output power exceeding 100 mW under damped resonant vibration was generated at the instant of striking, with approximately 0.9 mJ of power measured per single damped vibration. No deterioration was seen in the integrity of the stainless steel substrate or the piezoelectric thick film after over 10 million strikes.