Self-focused ZnO transducers for ultrasonic biomicroscopy

A simple fabrication technique was developed to produce self-focused high frequency single element transducers with sputtered Zinc Oxide (ZnO) crystal films. The novelty of this technique lies in that the ZnO film can be sputtered directly onto a curved substrate. Two transducers were fabricated by sputtering an 18 μm thick ZnO layer on 2 and 3 mm diameter aluminum rods with ends shaped and polished to produce an f# equal to one. The aluminum rod served a dual purpose as the backing layer and positive electrode for the resultant transducers. A single 4 μm Parylene polymer matching layer was deposited on the transducers after housing and interconnect. The pulse-echo response for the 2 mm aperture transducer was centered at 109 MHz with a -6dB bandwidth of 43%. A 3 mm aperture transducer produced a 96 MHz echo response with a 52% bandwidth. The measured insertion loss for the 2 mm aperture was 45 dB and the 3 mm aperture was 42 dB. A wire phantom and adult zebrafish were imaged to show the capability of the transducers.