Ultrasonic sensors that use piezoelectric thin films as sensing
elements have been extensively studied for various applications
[5–10]. These devices are usually fabricated on Si wafers using
a standard integrated circuit (IC) process and a micromachining
process. In addition, the fabrication of ultrasonic sensors
on Si substrates permits integration with signal processing circuits
such as preamplifiers and impedance-matching circuits. In
our previous work, we have reported that ultrasonic transducers
constructed using epitaxial PZT thin films grown on epitaxial
Pt/-Al2O3/Si were able to transmit and receive ultrasonic waves
[11]. Here, we report the preparation of epitaxial multi-layer
structures that are suitable for sensor fabrication on Si substrates,
and we evaluate the sensitivity of these ultrasonic sensors to provide
details of the first reported use of epitaxial PZT films on
SrRuO3/Pt/-Al2O3/Si structures.