PZT Epitaxial Thick Film for Ultrasonic Transducer at Frequencies below 100 MHz

The frequency range of 20-100 MHz ultrasonics are promising for photoacoustic imaging, which is useful to observe blood in vivo at high resolution. However, PVDF, which is generally used for transducers in this range does not exhibit high piezoelectricity (electromechanical coUpiing coefficient \pmb{k}-{\mathbf{t}^{2}}=4\%). On the other hand, our group previously reported high \pmb{k}-{\mathbf{t}}^{2} of the PZT family epitaxial thin films above 100 MHz (28.1% for PTO and 17.6% for PZT). In order to achieve lower frequency operation, thicker film is one of the approaches. In this study, we report sputter PZT epitaxial thicker film (16.0 \boldsymbol{\mu} \mathbf{m}) high efficient (\pmb{k}-{\mathbf{t}}^{2}=26.0\%) transducer whose thickness extensional mode resonant frequency is 89 MHz.