High-frequency (50–100MHz) medical ultrasound transducer arrays produced by micromachining bulk PZT materials

This paper describes the development and characterization of a high frequency (65 MHz) ultrasound transducer array. The array was built using bulk PZT that was etched using an optimized chlorine-based plasma process. The median etch rate of 6 mum/hr yielded a good profile (sidewall) angle (>83⁰) and a reasonable processing time for etch depths up to 40 mum. A backing layer having an acoustic impedance of 6 MRayl together with a front-end matching layer of parylene yielded a transducer bandwidth of 40%. The impedance of the backing material will be increased to 20 MRayls in the near future, and this will increase the bandwidth to 70%. The two-way insertion loss and cross talk between adjacent channels at the center frequency are 26.5 dB and -25 dB, respectively.