Broadband Ultrasonic Array Transducer From Multilayer Piezoelectric Ceramic With Lowered Co-Firing Temperature

Increasing array transducer bandwidth (BW) and signal-to-noise ratio (SNR) is a critical issue for producing a high-quality medical ultrasound image. However, array elements with small size tend to have poor sensitivity due to a much higher impedance compared with the electrical impedance of the transmitter and receiver circuit. Implementation of multilayer ceramic (MLC) is an effective way of reducing impedance, and thus, with a potential for improving SNR for an ultrasonic probe. In this work, we fabricated multilayer piezoelectric ceramic with a composition of 0.1Pb(Ni_1/3Nb_2/3)O₃-0.35Pb(Zn_1/3Nb_2/3)O₃-0.15Pb(Mg_1/3Nb_2/3)O₃-0.1PbZrO₃-0.3PbTiO₃-4mol% excess NiO (PNN-PZN-PMN-PZ-PT), by a roll to roll tape casting process and co-fired with 90Ag/10Pd electrode at a low temperature of 950 °C. Using five-layer MLC (5L-MLC) as obtained, we designed and demonstrated a 5 MHz 32-element array transducer for ultrasonic and photoacoustic imaging. The five-layer transducer element exhibited a BW of 87% at -6 dB, substantially higher than 62% for single-layer ceramic (SLC) element. In addition, the insertion loss was improved by 16.2 dB over the SLC element with an external impedance of 50 Ω . Both the experimental results and theoretical analysis showed that our array transducer made of the PNN-PZN-PMN-PZ-PT MLC is promising for acquiring high-quality ultrasonic and photoacoustic images.