Micromachining of bulk piezoelectric substrates for fabrication of high frequency, broadband piezoelectric composite transducers is reported in this paper. A deep reactive ion etching process was developed for bulk PMN-PT single crystal etching with an aspect ratio of >8. A piezoelectric composite with a resonance of 75 MHz was fabricated and the electromechanical coupling coefficient was measured to be 0.67. A 75 MHz piezoelectric composite transducer was prototyped and pulse echo experiments showed that the transducer bandwidth is about 80 - 90% and the sensitivity was significantly improved (>10 dB gain) relative to a commercial 75 MHz transducer. The developed HF piezoelectric composite transducers hold promise for medical ultrasound imaging, ultrasound NDE, and other novel sensors for biological, medical and industrial process monitoring.
