Characterisation of thin layers of parylene at high frequency using PZT thick film resonators

High frequency electrical impedance measurements on PZT thick film structures were used to characterise thin layers of parylene for acoustic matching applications. The parylene properties (i.e. longitudinal wave velocity and acoustic impedance) were obtained in a realistic configuration for transducer applications. The measured parylene properties were compatible with medical imaging requirements, in particular for high frequency, since the deposited thickness can be controlled with high accuracy (around 1 μm). The mean longitudinal wave velocity was measured at 2135 ms−1 and corresponding acoustic impedance was 2.75 MRa. Three high frequency single element transducers were simulated to show that using parylene as a matching layer is a good trade-off between transducer performance and the technical process.