Ultrasonic transducers employing a ZnO/Pyrex-glass membrane on a Si substrate

The authors propose a ZnO/Pyrex-glass membrane structure for developing low-loss, spurious-free, wide-bandwidth underwater ultrasonic transducers in the VHF and UHF ranges. Since Pyrex-glass possesses a small acoustic impedance, it behaves as an effective acoustic matching layer between the ZnO film and water. Theoretical analysis suggested that high-performance transducers can be realized by properly determining the thickness ratio of the Pyrex-glass film relative to the ZnO film. It was experimentally shown that the ZnO/Pyrex-glass membrane transducer successfully radiates and detects ultrasonic waves at the fundamental frequency of 155 MHz with a relative -3 dB bandwidth of 11.1% and a minimum transduction loss of 4.3 dB, which are in good agreement with the theoretical calculation