| We have been studied hydrophones using PZT poly-crystalline films deposited by hydrothermal method. The PZT poly-crystalline films have piezoelectricity without polling process and it is easy to form the PZT film on Ti substrate with extremely small size by hydrothermal method. The hydrophone is used for performance evaluation of medical ultrasound equipment such as ultrasound diagnostic equipment. Therefore, improvement of hydrophone's performance is important for human safety. We reported the manufacturing and the receiving sensitivity of the miniature needle type hydrophone using hydrothermally synthesized PZT poly-crystalline films at 2005 IEEE International Ultrasonics Symposium. However, the PZT poly-crystalline films of hydrophones have a problem of pinholes in the deposited PZT poly-crystalline films. Therefore, characteristics of hydrothermally synthesized PZT films were decreased. Consequently, we attempted the improvement of characteristics of the PZT poly-crystalline films on the Ti substrate by surface modification of Ti substrate using anodic oxidation. Anodic oxidation is that metal surface is oxidized by electrolysis in acid solution. At first, Ti substrate surface was pretreated using anodic oxidation. Then, the PZT poly-crystalline films were formed on the Ti substrate in the KOH solution with Pb ion, Ti ion and Zr ion under high temperature about 160 degrees centigrade and high pressure about 0.6 MPa. As the results, characteristics of the PZT poly-crystalline films on the anodized Ti substrate were improved. Density, young's modulus and dielectric breakdown voltage of PZT films on Ti substrate with pretreatment were increased compared with PZT films on Ti substrate without pretreatment. Characteristics of PZT poly-crystalline films were improved by surface modification of Ti substrate using anodic oxidation. |