Micromachining of High-Quality PMN–PT/Epoxy 1–3 Composite for High-Frequency (>30 MHz) Ultrasonic Transducer Applications

Fabricating PMN–PT composites, the core component of high-frequency (> 30 MHz) transducers, remains challenging due to their poor machinability and ultrasmall kerfs. This urgent problem is significantly impeding the development of PMN–PT ultrasonic transducers for use in clinical research, biomedical sciences, and nondestructive testing (NDT). In this study, high-quality PMN–0.3PT/epoxy 1–3 composites at 30 and 50 MHz were manufactured using a modified picosecond (1.5 ps) laser technique. Their performance was thoroughly analyzed, which was comparable to that with low-stress dry plasma etching. There were fewer microcracks around PMN–PT pillars. The minimum kerf was less than
$4.5 ~\mu \text{m}$
, and the highest aspect ratio was larger than 7.5. The microdomain morphology and hysteresis loops of PMN–PT pillars further confirmed that composites still maintained excellent piezoelectric performance and suffered fewer damages during laser cutting. The characterization results exhibited a large electromechanical coupling (>0.77), a high dielectric constant (>1600), and a relatively low acoustic impedance (< 17 Mrayls). The ultrasonic transducers with center frequencies of 30 and 50 MHz were designed and prototyped to validate the performance of composites. The transducers showed broad bandwidth (>80%), high two-way insertion loss (IL) (>−23 dB), and imaging resolution superior to
$40 ~\mu \text{m}$
. Finally, the C-scan experiments of IC chips were also used to further illustrate the applicability of transducers. These encouraging results further demonstrated that ultrafast laser technology will bring more accessible and affordable methods for fabricating high-frequency PMN–PT composite transducers with excellent performance.