Fabrication of a piezoelectric array for use in a dual frequency hybrid piezoelectric—CMUT probe

Wideband transducers are highly preferable for medical ultrasound imaging. Dual-frequency transducers have been developed to enlarge the operating bandwidth by separating transmission and reception. A novel dual-frequency transducer design, comprising a hybrid configuration of a partly epoxy-filled kerf piezoelectric array and a capacitive micromachined ultrasound transducer (CMUT) array, has been proposed. This work studied the fabrication feasibility such hybrid transducer, including both fabrication of the partly epoxy-filled piezoelectric array and lamination of inactive CMUTs to this array to mimic the hybrid transducer. The bonding properties of piezoelectric elements on a flexible printed circuit board were characterized through both mechanical and electrical methods. The adhesion strength of elements to the flexible printed circuit board demonstrates robustness, with a peel strength reaching up to 2.7 N/mm. Additionally, the contact resistance of an element to the board is negligibly small, approximately 0.11 Ω. Four prototype arrays, each consisting of 80 elements with air-filled kerfs, were successfully fabricated, achieving a yield ratio up to 100%. The lamination process was successfully performed, resulting in a shear strength above 4.2 MPa and maintaining an epoxy fill less than 30% in the kerfs.