Hirotake Okino

Dependence of electrical properties of epitaxial Pb(Zr,Ti)O3 thick films on crystal orientation and Zr∕(Zr+Ti) ratio

Epitaxial Pb(Zr,Ti)O3(PZT) films, 1.5–2.0μm in thickness, with a Zr∕(Zr+Ti) ratio ranging from 0.20 to 0.75 were grown on (100)c-,(110)c-, and (111)c-oriented SrRuO3∕∕SrTiO3 substrates at 600 °C by metal-organic chemical vapor deposition (MOCVD). The effects the Zr∕(Zr+Ti) ratio had on the crystal structure, dielectric and ferroelectric properties, and piezoelectric response of these films with different crystal orientations were systematically investigated. We ascertained from x-ray-diffraction reciprocal-space-mapping analysis that (001)T-∕(100)T-∕(100)R-,(101)T-∕(110)T-∕(110)R-∕(101¯)R-, and (111)T-∕(111)R-∕(111¯)R-oriented films had epitaxially grown on the respective (100)c-,(110)c-, and (111)c-oriented SrRuO3∕∕SrTiO3 substrates. The constituent phase changed from a tetragonal single phase, a mixture phase of a tetragonal and rhombohedral, to a rhombohedral single phase with increasing Zr∕(Zr+Ti) ratio irrespective of the orientation of the substrates. However, the range of the Zr∕(Zr+Ti) ratio of th...

Domain structure and polarization properties of lanthanum-substituted bismuth titanate single crystals

Single crystals of bismuth titanate (BiT) and lanthanum-substituted BiT [Bi4−xLaxTi3O12 (BLT)] were grown by a self-flux method. BLT (x=0.85) showed a smaller remanent polarization (2Pr) along the a(b) axis of 41 μC/cm2 than 98 μC/cm2 for BiT, which mainly originates in its smaller ionic displacements along the a axis. Striped 90° domain walls as well as head-to-head and tail-to-tail 180° domain walls were observed for both crystals, and La substitution led to a marked decrease in the 90° domain width from 8.5 μm (BiT) to 2.5 μm for BLT (x=1.20). Piezoelectric-force microscope observations suggested that antiphase domain boundary (ADB) is present only for BLT and the ADB plays an important role in the formation of the 90° domain.

Crystal structure, electrical properties, and mechanical response of (100)-/(001)-oriented epitaxial Pb(Mg1∕3Nb2∕3)O3–PbTiO3 films grown on (100)cSrRuO3‖(100)SrTiO3 substrates by metal-organic chemical vapor deposition

Relaxor-type ferroelectric (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 (PMN-PT) films, 2–3μm in thickness, with a PbTiO3 content (x) ranging from 0 to 1 were grown on (100)cSrRuO3‖(100)SrTiO3 substrates at 650°C by metal-organic chemical vapor deposition. The effects the x value had on the crystal structure, dielectric and ferroelectric properties, and mechanical response of these films were systematically investigated. Epitaxial growth having (100)∕(001) orientation irrespective of x and the constituent phase change with x were ascertained from both x-ray diffraction reciprocal space mapping analysis and Raman spectroscopy. The constituent phase changed from a rhombohedral (pseudocubic) single phase, a mixture phase of rhombohedral (pseudocubic) and tetragonal phases, and a tetragonal single phase, with increasing x. The mixed phase region was found to exist at x=0.40–0.55, which was different from that reported for single crystals (x=0.31–0.35). The dependencies of relative dielectric constant and remanent polarizati...

Contact-Resonance Piezoresponse Force Microscope and Its Application to Domain Observation of Pb(Mg1/3Nb2/3)O3?PbTiO3 Single Crystals

The domain-structure images of (001) plates of Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) single crystals were successfully obtained in a vacuum using a contact-resonance piezoresponse force microscope (CR-PFM). During conventional PFM observations at sufficiently high temperature, the modulation voltages applied between the tip and the counter electrode induced polarization reversals and destroyed local domain structures under the tip. With the help of the contact-resonance mode, piezoresponse images could be obtained with a reduced amplitude of the modulation signal, that addressed the issue of the polarization reversals at high temperature. Using this CR-PFM, circular domains 30–100 nm in diameter were observed at temperatures above 175°C.

Domain Orientation Imaging of PbTiO3 Single Crystals by Vertical and Lateral Piezoresponse Force Microscopy

Four kinds of domain structures (180° c-c, 180° a-a, 90° a-a and 90° a-c domains) on grown surfaces of PbTiO3 single crystals were imaged successfully using vertical and lateral piezoresponse force microscopy (PFM). Domain orientations (i.e., polarization vector distributions) at the surface of each domain structure are presented. These domain images are compared with simultaneously observed surface topographic images decorated by an acid etching treatment.

Double-layer type microwave absorber made of magnetic-dielectric composite material

Abstract Changing the combination of 2nd layer in a double-layer type microwave absorber, the matching frequency (8.10–10.88 GHz), maximum reflection loss and matching thickness at the matching frequency could be systematically controlled and compared with those of single-layer type microwave absorber.

Dielectric and Magnetic Properties of a Titanium Oxide and Carbonyl Iron Composite Material and Application as a Microwave Absorber

A microwave absorber for use in an electronic toll collection (ETC) device, having a central frequency of 5.8 GHz, is fabricated using a composite of dielectric (titanium oxide, TiO2) and magnetic (carbonyl iron, Fe(CO)5) materials. The reflection loss in free space, using a circularly polarized wave, was -20 dB or more around a central frequency of 5.8 GHz at incident angles of up to 60°, which satisfy the necessary conditions for ETC use.

Electrical Properties of Highly Strained Epitaxial Pb(Zr,Ti)O3 Thin Films on MgO(100)

The film thickness (20–200 nm) dependence of the crystalline structure, lattice parameters and electrical properties of highly strained Pb(Zr,Ti)O3 (PZT) thin films on MgO(100) was investigated. The PZT films were practically c-axis orientation. As the film thickness decreased ( 40 nm) films exhibited a certain amount of remanent polarization in the in-plane direction, implying the formation of a-domains. The relationship between electrical properties and the inner strain is discussed.

PbTiO3 content dependence of crystal structure and electrical properties of (100)-/(001)-oriented epitaxial Pb(Mg1∕3Nb2∕3)O3-PbTiO3 films grown by metalorganic chemical vapor deposition

PbTiO3 content (x) dependencies of the crystal structure, and dielectric and piezoelectric properties were investigated for epitaxial (1−x)Pb(Mg1∕3Nb2∕3)O3-xPbTiO3[PMN-PT] films, 2–3μm in thickness, grown on (100)cSrRuO3∕∕(100)SrTiO3 substrates. (100)-/(001)-oriented epitaxial films with the x ranging from 0 to 1 were successfully grown at 650 °C by metalorganic chemical vapor deposition irrespective of x. The constituent phase changed from a rhombohedral (pseudocubic) single phase, a mixture phase of rhombohedral (pseudocubic) and tetragonal phases, and a tetragonal single phase with increasing x. The film with the mixture phase was formed when x=0.40–0.55, which was different from that reported for single crystals. The dependence of relative dielectric constant on x was maximum at the mixed phase region, which was similar to the case of a PMN-PT sintered body, but the magnitude of these dependencies was relatively lower than the reported one for the single crystals and sintered bodies. The longitudinal ...

Thermally Stimulated Current and Polarization Fatigue in Pb(Zr,Ti)O3 Thin Films

In order to clarify the origin of the polarization fatigue phenomena, charge traps in ferroelectric Pb(Zr,Ti)O3 (PZT) thin films were measured using the thermally stimulated current (TSC) technique. For polarization fatigued Pt/PZT/Pt/SiO2/Si(100) capacitors, a peak of TSC was observed, and the trap density estimated from the TSC data increased as switching cycles increased. Activation energy and density of the charge traps were estimated to be 0.7–0.8 eV and on the order of 1018 cm-3, respectively. It was also observed that degradation of remanent polarization of PZT was improved by the TSC measurement process. On the other hand, no TSC peak was observed for fatigue free Ir/PZT/Ir/IrO2/SiO2/Si(100) capacitors. From these results, it was suggested that the main origin of the polarization fatigue phenomena was the domain pinning caused by trapped charge carriers injected by polarization reversal.