High frequency ultrasound imaging has many clinical applications because of its improved image resolution. It is gaining acceptance as a clinical tool for the examination of the anterior segment of the eye, skin and intravascular imaging. Its development has pushed the limits of ultrasonic imaging technology, giving diagnostic quality information about microscopic structures in living tissue. One of the technical challenges for high frequency imaging is the fabrication of transducers with piezoelectric elements of a thickness of only a few tens of micrometers. It is very difficult and time consuming to lap down the ceramic to very thin elements and to dice very small elements in the fabrication of high frequency single element transducers and arrays. Piezoelectric thick-film technology is an alternative solution with a low cost. With NIH SBIR Phase I funding support, we have proven in Phase I that 20-40 urn thick PZT film can be deposited via a novel sol-gel drop-on process, with relatively high dielectric constant (typical er=780). In the post Phase I research, thick PZT film transducers were designed using a PiezoCAD model and fabricated from thick PZT film with one matching layer. The central frequency of the transducer was 40 MHz. The bandwidth at -6 dB was approximately 75%. In proposed Phase II research and development, the sol-gel drop-on PZT thick film technology will be further optimized towards application in high frequency medical imaging. For device design, it is difficult to match both acoustic impedance and electric impedance and other requirement. During Phase II, we will address this problem by developing PZT film with adjustable dielectric constant in the range of 1000 to 3000. Five-element prototype linear arrays with frequency of 50-100 MHz will be designed and fabricated using PZT thick films under different substrates. The thickness to width aspect ratio will be adjusted to avoid undesirable lateral resonance. As a supplier for sol-gel precursors and nano powders, Chemat will production develop PZT fine powder and PZT nanocomposite thick film precursor and market sol-gel drop-on thick PZT film high frequency ultrasonic transducer. This innovation may impact high frequency medical imaging market, since lapping down ceramics to a few tens micrometers is very difficult and time consuming. Success of this project provides an alternative solution for fabrication of high frequency single element transducers and array with scale-up capability and low cost. ? ? ?
