THIN-FILM ZNO ULTRASONIC TRANSDUCER ARRAYS FOR OPERATION AT 100 MHZ

Thin-film ZnO ultrasonic transducer arrays for operation at 100 MHz were developed and evaluated. Epitaxial, high acoustic quality ZnO film layers of 10 mum thickness could be produced by sputter deposition on well (111)-oriented gold films with chromium sublayers evaporated on (0001) sapphire. Using a photoresist etching mask of the desired pattern, the upper Au/Cr electrode and subsequent ZnO film were etched to form grooves separating the multi-layered film into array elements with a 100 mum pitch. It was found that the ultrasound beam in the azimuth plane for a 32-element array could be electronically focused in the 100 MHz range to obtain a half-amplitude width of 60 mum at the focal depth in water. This value reasonably agrees with the theoretically calculated value.