PS-14 A 100 MHz Multi-layered High Performance Transducer Using Polyurea Thin Film

We have been investigating ultrasonic transducers using polyurea piezoelectric material, which is fabricated through vapor deposition process. To enhance the transducer performance, a multi-layered configuration is studied in this study. The fabrication process and the transducer design for the multi-layered structure are discussed. A special twin-vacuum-chamber is used for laminating the polyurea layers and the aluminum electrodes alternately. One chamber is for the vapor deposition polymerization of the polyurea layer, while the other is for the electron beam deposition of the aluminum electrode. Substrate of the transducer is moved between these chambers using belt conveyers without breaking the vacuum. We fabricate two-, three-, and four-layered transducers with 1.5-mum polyurea thin films. To evaluate the transducer performances, we measure the capacitances, the electrical admittances, the coupling factors, and the Q values. The capacitances at 1 kHz increase with the multilayer lamination. The electromechanical coupling coefficients also increase at the resonant frequencies of about 65 MHz and 100 MHz, whereas the Q values decrease. The pulse/echo measurements are conducted to determine the transmission and receiving characteristics of the transducers using a glass plate as a reflector. The results of the pulse/echo experiment show that the maximum amplitudes and the spectrum densities increase because of the multilayer lamination