Miniaturized 6 MHz phased-array ultrasound probe based on lead-free doped BaTiO₃ piezoceramics

For many years, piezoelectric PZT-based materials for medical imaging have an exemption in the RoHS Directive that may not be reconducted in the future. Commercially and production-compatible products for substitution are still rare on the market. BaTiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> is a well-known lead-free composition that is a good candidate to allow an upscaling of the fabrication, compared to KNN compositions which have good potential performances for ultrasound imaging probe but have volatile compounds leading to an unstable manufacturing process.In this work, synthesis of cobalt-calcium-niobium codoped barium titanate (Co, Ca, Nb BaTiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>) powder has been optimized to scale up the production, and to obtain pre-industrial batches (up to 50 kg). Green ceramics are shaped by uni-axial pressing of atomized powder, debinded and sintered to obtain pellets that could have been processed to be implemented in a miniaturized 6 MHz ultrasound phased-array.A complete characterization of ceramics was also realized to demonstrate the good reproducibility of the manufacturing process. Moreover, a modeling method based on a genetic algorithm was used to get the whole piezoelectric dataset of the co-doped BaTiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> material. A 1-3 piezocomposite was designed and fabricated by the Dice and Fill Method (DFM) and used to manufacture a 64 elements array with a pitch of 200 µm and an elevation of 2 mm in order to obtain the ultrasound phased-array. Electroacoustic measurements of the complete transducer were compared with the same PZT-based transducer. It showed quite comparable results for the pulse-echo duration and corresponding bandwidth even if sensitivity for the lead-free transducer is lower than the PZT based one.