Tomohito Hasegawa

Growth of Epitaxial KNbO3 Thick Films by Hydrothermal Method and Their Characterization

KNbO3 films were grown at 240 °C by the hydrothermal method using KOH and Nb2O5 as source materials. Film thickness increased with reaction time up to 3 h, however decreased for longer reaction times. A 16-µm-thick epitaxially grown KNbO3 film with {100}pc orientation were successfully grown on (100)cSrRuO3∥SrTiO3 substrate for 3 h. The relative dielectric constant and dielectric loss at 100 kHz were 415 and 8%, respectively. Clear hysteresis loops originating from ferroelectricity were observed and the remanent polarization was 20 µC/cm2 at the maximum applied electric field of 220 kV/cm. The effective longitudinal piezoelectric constant, d33eff, obtained using a laser Doppler velocimeter, was 86 pm/V.

Development of Small Ultrasonic Probe using Lead Zirconate Titanate Film Deposited by Hydrothermal Method

Miniature ultrasonic probes were developed by hydrothermally depositing lead zirconate titanate (PZT) polycrystalline films on a titanium (Ti) wire. The small ultrasound probes were fabricated using hydrothermally deposited PZT polycrystalline film on the end of a titanium wire with a diameter of 0.6 mm and a length of 50 mm. The performances of the prototype small ultrasound probes were measured. As a result, it was confirmed that the probe has a center frequency of 16 MHz, a fractional bandwidth of 70%, and a distance resolution of better than about 130 µm without using an acoustic matching layer. It was also found that the beam width was 0.55 mm for a distance of 4 mm between the string target and the miniature ultrasound probe.

Growth of Epitaxial 100-Oriented KNbO3?NaNbO3 Solid Solution Films on (100)cSrRuO3?(100)SrTiO3 by Hydrothermal Method and Their Characterization

Films of solid solution in KNbO3–NaNbO3 (KNN) were deposited at 240 °C on (100)cSrRuO3∥(100)SrTiO3 substrates by the hydrothermal method. (KxNa1-x)NbO3 films with x = 0–1.0 were synthesized by changing the fraction of KOH in a solution of KOH and NaOH. The x in (KxNa1-x)NbO3 continuously changed with the volume fraction of KOH, while the deposition amount strongly depended on x. Epitaxial films with 100 orientation were obtained in the entire composition range and their out-of-plane lattice spacing changed with x. All the films showed ferroelectricity and their remanent polarization became larger than what above x = 0.58.

Tissue imaging using the transmission of 100-MHz-range ultrasound through a fused quartz fiber

We have studied transmission methods of high-frequency ultrasonic waves through a thin fiber for direct observation of the microscopic image of the tissue. We reported previously that C-mode images of an artificial bone and an animal bone placed in water were obtained by reflection method using a fused quartz fiber as the probe. In this paper, we describe that the C-mode images of the tissue on the glass in water were obtained by penetration method.

Transmission of 100-MHz-range ultrasound through a fused quartz fiber

We have studied transmission methods of high-frequency ultrasonic waves through a thin fiber for direct observation of the microscopic image of the tissue. We reported that high frequency ultrasonic waves (70 - 175MHz) transmitted approximately 1.6mm in the acoustic coupling medium, and a C-mode image of a coin placed in water was obtained using a tapered fused quartz fiber as the probe. In this paper, we describe that the lateral resolution was improved by focusing ultrasonic-beams radiated from a fused quartz fiber, and the improved C-mode image of an animal bone was obtained.

Effect of Deposition Time on Film Thickness and Their Properties for Hydrothermally-Grown Epitaxial KNbO3 Thick Films

Deposition behavior and the crystal structure of the epitaxial KNbO3 films, grown at 240 °C on (100)cSrRrO3∥(100)SrTiO3 substrates using hydrothermal method, as well as their ferroelectric and piezoelectric properties were systematically investigated. Film deposition was detected to have begun after 2 h from the start, and the thickness increased with increasing the deposition time up to 4 h, but contrary decreased after 9 h due to the etching by KOH. X-ray diffraction (XRD) patterns of the films were basically the same regardless of the deposition time. However, the films deposited for 15 h introduces large amount of voids than those for 2 h. Ferroelectric and piezoelectric response of the films deposited for 2 and 15 h were measured to have similar film thickness, but the maximum applied electric field for the 2-h films was twice as that for the 15-h ones. The prototype ultrasonic transducer was fabricated using the KNbO3 films, which were deposited by hydrothermal method at 240 °C for 3 h, and proved to be able to transmit and receive ultrasonic signals above 90 MHz in degassed water.

Development of bimorph vibrator using lead free BNT piezoelectric film deposited by hydrothermal method

PZT piezoelectric film synthesized hydrothermally has been studied actively in our laboratory. However, it is apprehended recently that PZT affects health and the environment, because PZT is chemical compound containing lead. Therefore, we tried to synthesize lead free BNT piezoelectric film on titanium substrate hydrothermally. The synthesized BNT films on titanium substrates were evaluated with SEM image, XRD pattern and EDS. We fabricated bimorph vibrators with synthesized lead free BNT film and evaluated their performances.

Evaluation of small ultrasonic probe using lead zirconate titanate poly-crystal film deposited by hydrothermal method

The present study evaluates the characteristics of a small ultrasound probe using PZT polycrystalline film deposited by a hydrothermal synthesis method. With the hydrothermal synthesis method, PZT film is deposited only on the titanium by reaction in the solution. Utilizing this feature, a PTZ polycrystalline film was deposited on the end face by a hydrothermal synthesis of a material with only its titanium wire end face exposed. This transducer was built into a small ultrasound probe and the characteristics were evaluated. As a result, we succeeded in the fabrication of a wideband ultrasound probe with a distance resolution of 32 µm, a frequency bandwidth of 50 MHz in the range of 25 to 74 MHz, and a fractional bandwidth of 99 %.

P1J-4 Evaluation of Small Ultrasonic Probe Using Lead Zirconate Titanate Film Deposited by Hydrothermal Method

Recently, our laboratory has explored the possibility of using lead zirconate titanate [PZT] polycrystalline film deposited hydrothermally on titanium substrate to fabricate a small actuator and ultrasound sensor. Hydrothermally deposited PZT polycrystalline films have piezoelectricity without a poling process, and it is easy to deposit PZT polycrystalline films on substrates that are tiny or complexly shaped. We confirmed that hydrothermally synthesized PZT polycrystalline films have wideband frequency characteristics with sensitivities in the megahertz band. It is thought that miniature ultrasound probes with wide- frequency band characteristics can be fabricated using hydrothermally synthesized PZT polycrystalline films. In our last report we assessed methods to produce a miniature ultrasound probe and transceiver characteristics. Here, the reception and transmission directivities of such a probe were measured at 5, 10, 15, and 20 MHz. The results showed that, except at 5 MHz, the theoretical and experimental values agreed. The difference at 5 MHz is attributed to the effect of the resonance frequency of the diameter direction.

P1M-2 Development of Miniature Ultrasonic Probe with PZT Film Deposited by Hydrothermal Method

Recently, the PZT poly-crystalline film deposited on titanium substrate by hydrothermal method has been studied actively for development of a small actuator and ultrasonic sensor in our laboratory. The PZT poly-crystalline films were deposited on a titanium substrate in KOH solution used as mineralizer which included Pb ion, Ti ion, and Zr ion under high temperature (about 150degC) and high pressure (about 4 kPa). We reported on the needle type miniature hydrophone and the ultrasonic transducer with hydrothermally synthesized PZT poly-crystalline films in 2005 IEEE International Ultrasonics Symposium in Rotterdam. It has confirmed that the hydrothermally synthesized PZT poly-crystalline films showed wide band frequency characteristics in MHz band of the sensitivities. It is thought that miniature ultrasonic probe with wide frequency band characteristics of sensitivities can be fabricated by using the hydrothermally synthesized PZT poly-crystalline films. The miniature ultrasonic probes were fabricated by hydrothermally deposited PZT poly-crystalline film on an end of the titanium wire with diameter of 0.6 mm and length of 50mm. The performances of trially fabricated ultrasound probes were measured. Ultrasonic imaging experiments using a target in water were performed with the trially fabricated ultrasonic probe with hydrothermally synthesized PZT films. As a result, it was confirmed that this probe has a center frequency of 16 MHz, a bandwidth of 80%, and distance resolution more than 80 micrometers. We will report about the structure and performance of the fabricated ultrasound probe with hydrothermally synthesized PZT poly-crystalline film and the results of imaging experiments under water