PZT Thick Films Deposited by Improved Hydrothermal Method for Thickness Mode Ultrasonic Transducer
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PZT Thick Films Deposited by Improved Hydrothermal Method for Thickness Mode Ultrasonic Transducer Mutsuo Ishikawa1 Minoru Kurosawa1 Naoki Katsura Shinichi Takeuchi Faculty of Engineering Toin University of Yokohama, 1 Interdisciplinary Graduate School of Science and Engineering Tokyo Institute of Technology, Kurosawa lab. Department of Advanced Applied Electronics,Department of Intelligent and Mechanical Engineering 4259 Nagatutamati, Midori-ku, Yokohama, Kanagawa 226-8502, Japan ABSTRACT The purpose of this study was to improve deposition rate of the hydrothermal method for lead zirconate titanate (PZT) thick film on titanium substrate. We developed a high-speed rotaion substrate holder at a tangential velocity of about 0.8m/s in autoclave. A titanium substrate was fixed by the holder on the surface of a stirring bar. For the film deposition, powder of TiO2 was used instead of the liquid TiCl4. The deposition rate on titanium substrate was improved up to 7µm/24h. Piezoelectric constant d31 of the hydrothermal PZT film was -2.6× 10-11 V/m. This result was lower than that of PZT ceramics. However, this hydrothermal method obtained thick film and this film was confirmed to be polycrystalline PZT analyses of XRD and SEM. In addition, performance of thickness mode vibration of hydrothermal PZT 50µm thick film was investigated by radiating in water. The phase velocity of dilatational wave of the thickness mode vibration of the hydrothermal PZT film was 1800m/s and the electromechanical coupling factor was 47%. INTRODUCTION Lead Zirconate Titanate (PZT) is a promising ferroelectrics material with a variety of functional application such as micro actuators, ultrasonic transducers and others. There are a lot of studies on fabrication of PZT films by the sol-gel１), the chemical vapor deposition2) , the sputtering3), the aerosol deposition4) , the hydrothermal method5) , etc. Among these techniques, hydrothermal method has attracted considerable interest. This is because the hydrothermal method is available to deposit on concave and convex surface of titanium substrate, reaction temperature is less than 200℃, poling process and annealing process are not required, deposition over 10µm thick is available, peel-strength was 20MPa and over. This deposition process was utilized to fabricate novel application reports, such as a micro ultrasonic motor6), a touch prove sensor7), a tuning type vibrator8), and fluidic device9). The device application achieved in parallel with improvement of deposition process5-13). These literatures reported characteristic of films with changing the process conditions such as temperature, reaction time, etc. However, it was difficult to prepare thick film more than 20µm by the hydrothermal method. The hydrothermal process is performed in an autoclave. In the previous deposition process, a base material was placed in the solution statically6-8), or stirring speed was slow as it controlled for occurrence of turbulent flow in autoclave. We developed, however, a high-speed rotation substrate hol
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