Akira Kawabata

Preparation of Zr-rich PZT and La-doped PbTiO3 thin films by RF magnetron sputtering and their properties for pyroelectric applications

Abstract Zr-rich PZT and La-doped PT films were fabricated on a PLT/Pt/Ti/SiO2/Si or Pt/Ti/SiO2/Si substrate by an RF planar magnetron sputtering equipment using powder targets with compositions of PbZr0 94Ti0.06O3, PbZr0.92Ti0.08O3 and Pb0.85La0.15 Ti0.96O3 with excess PbO of 20 mol%. The dielectric constants of PZT and PLT films showed anomalies at the transition temperatures of around 246 and 300°C, and their dielectric constants at room temperature were 350 and 1070, respectively. Significant pytroelectric currents were observed in both as-grown PZT and PLT films even without a poling treatment. The pyroelectric coefficients of those films were 10 and 30 nC/cm2K, respectively. Therefore, Zr-rich PZT and [111]-oriented PLT films sputtered on Pt/Ti/SiO2/Si substrates possess desirable properties for potential applications to pyroelectric devices.

Growth and properties of tungsten-bronze ferroelectric potassium lithium niobate single crystals

Abstract K3Li2Nb5O15 (KLN) single crystals have been grown by the rfheating Czochralski technique from a melt with the potassium and lithium enriched composition. The transparent and pale-yellow crystals showed very small optical absorption and the absorption edge at 378 nm. The dielectric constant ∼ T 33 showed a marked anomaly at the transition point of 420°C. Pyroelectric constant p at room temperature was determined as 80 μC/m2K. Further, the electro-optic constant rc was measured as about 40 × 10−12 m/V at a wavelength of 632.8 nm.

Design and Evaluation of Li2B4O7 Surface Acoustic Wave Filter

A 250 MHz Li2B4O7 surface acoustic wave (SAW) filter was successfully designed using a newly developed program for double-mode SAW (DMS) filters. The elastic, piezoelectric and dielectric constants of Li2B4O7 grown by the resistance-furnace heating Czochralski method were measured precisely to determine the accurete phase velocity and the electromechanical coupling coefficient of SAW. The mode coupling coefficients were determined as a function of the electrode thickness as well. These coefficients were introduced in the simulation program, and the SAW filter was designed. The DMS filter fabricated in this study had almost the same characteristics as those expected from the design.

Low-Temperature Sintering of Pb(Mg1/3Nb2/3)O3–PbTiO3 Ceramics with Addition of PbO–Bi2O3

The Low-temperature sintering has been examined in the preparation process of Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics. The sintering temperature could be reduced from 950° C to 800° C by addition of PbO–Bi2O3 as a lower-melting-point sintering aid. The dielectric constant of 16000 and loss tangent of 0.02 were obtained for Pb[(Mg1/3Nb2/3)0.95Ti0.05]O3 ceramics fired at 800° C with 2 mol% of PbO–Bi2O3. These low-temperature sintering dielectric materials are very promising for use in fabrication of printed thick-film capacitors.

Saw properties of Li2B4O7 crystals and their applications to acousto-optic waveguide modulators

Abstract Theoretical and experimental results have shown the potential usefulness of Li2B4O7 crystals for leaky SAW and acousto-optic applications. The shear leaky SAW has excited at (45°,90°,70°), whose SAW properties are vp of 3680m/s, k2 of 2.3% and TCD of 0. Further, k2 of the Rayleigh SAW was zero at this cut substrate, which gives no spurious response for the temperature compensated shear leaky SAW. The longitudinal leaky SAW with the fast vp of 6825m/s has been also observed at the (0°,45°,90°). Several amorphous thin films were successfully fabricated on the (110) LBO substrates by sputtering. Among them, the borate glass film has been a suitable material for acousto-optic applications because it has lower velocity and relatively larger index than those of LBO substrates

Dielectric Behaviors of γ-ray Irradiated Triglycine Sulfate

Triglycine sulfate crystals were subjected to gamma radiation from a Co60 source of intensity 2.27 x 105 r/hr. It is shown that the ferroelectric curie point shifts to lower temperature, and the maximum peak of dielectric constant decreases with increasing dosage. The dielectric loss tangent showed decrease for ferroelectric range and increase for paraelectric range. The crystal after irradiation reveals a biased double hysteresis loop as in the case of x radiation. The piezolectric property was remarkably affected for small dosages and tended to a constant value for large doses. (C.E.S.)

Preparation of Zr-RICH Pb(ZrxTi1-x)O3 thin films and their properties

Abstract An RF planar magnetron sputtering equipment with three cathodes was used to fabricate Zr-rich PZT thin films on PLT/Pt/Ti/SiO2/Si substrates using a multi-target. The multi-target consisted of PbO and metal titanate pellets on a zirconium metal plate. The optimum sputtering conditions were a gas content of Ar:O2 = 8:2 Sccm, gas pressure of 5 × 10×3 Torr, RF power of 100 W and substrate temperatures of 630–660°C. Polycrystalline Zr-rich PZT thin films have been successfully grown onto platinum film substrates, although the crystal structures of films were sensitive to the substrate temperature. The temperature dependence of the dielectric constant, tan δ and pyroelectric current of the PZT films were measured. Significant peak for the pyroelectric current was observed at the transition temperature of about 90°C from a low temperature to high temperature rhombohedral ferroelectric phases in as-grown PZT films without a poling treatment. Therefore, Zr-rich PZT films sputtered on PLT/Pt/Ti/SiO2/Si su...

Low-Temperature Mixed Sintering of Pb(Zr1-xTix)O3–Pb(Zn1/3Nb2/3)O3 Ceramics and Their Pyroelectric Properties

Low-temperature mixed sintering in the preparation process of Pb(Zr 1-x Ti x )O 3 -Pb(Zn 1/3 Nb 2/3 )O 3 ceramics has been examined. Dense composite ceramics having z = 0.02, 0.03 and 0.04 with fine grains were obtained at firing temperatures from 900°C to 950°C by adding PbO as a lower-melting-point sintering aid. The pyroelectric coefficient of this mixed sintered ceramic fired at 900°C was above 60 nC/(cm 2 .K) in the temperature range of 15°C to 50°C. These low-temperature mixed sintering pyroelectric materials are very promising for use in the fabrication of highly sensitive infrared detectors.

Crystal growth of BaTiO/sub 3/ by the TSSG method and its thermal poling

BaTiO/sub 3/ single crystals were grown by using the TSSG technique. The seeding process was the most important point in the growth. The dielectric constant was resonant at the cubic-tetragonal transition at T/sub c/=131/spl deg/C. A thermal poling process was developed in this work. Samples with two parallel or one polished surfaces (/spl plusmn/c) were heated to 1100/spl deg/C, held for 3 hours and then cooled to room temperature. After the thermal poling, an electrical field of about 1 kV/cm was applied along the c direction at a temperature near Tc for 10 hours in order to obtain single-domain BaTiO/sub 3/ crystals.

Preparation and properties of [111]-oriented PLT films by RF magnetron

[111]-oriented PLT films have been successfully grown onto platinum film substrates by the rf-magnetron sputtering method using Pb enriched PLT (85/15) powder targets. The sputtering conditions for growing [111]-oriented films were investigated. Crystallographic identifications of the films were made by the X-ray measurements. Dielectric, ferroelectric and pyroelectric properties of these films were measured. The dielectric constant of the highly [111]-oriented PLT film showed an anomaly at the transition point of around 300 degree(s)C and its value at room temperature was large as 1070, indicating that the PLT thin film with La rich composition is also available for the DRAM because of its large dielectric constant. The D-E hysteresis loops measurement has been carried out using the Sawyer-Tower circuit at 60 Hz. The asymmetric hysteresis loops were observed. The Pr and Ec were 8.5 (mu) C/cm2 and 78 kV/cm, respectively. The pyroelectric coefficient of this film was determined as 30nC/cm2K even without a poling treatment. [111]-oriented PLT films sputtered on Pt/Ti/silicon substrates possess desirable properties for potential applications to pyroelectric and memory devices.