FRG: Epitaxial Heterostructures of PMN-PT Piezoelectric / SrRuO3 Conductive Oxide for Medical Ultrasound Transducer Applications

This FRG (Focused Research Group) project is a collaborative effort among researchers at Duke University, U. Michigan, Penn State U. and Argonne National Laboratory, as well as industry interactions with Boston Scientific, Endosonics, and Lucent Technologies. The objective of the project is the fabrication and characterization of epitaxial multilayer stacks of single crystal piezoelectric/ conductive oxide electrode heterostructures, and development of a new generation of high frequency transducer arrays for medical ultrasound imaging. Thin layers allow the stacks to be driven at higher fields thus taking advantage of the high saturation strain without increasing driving voltages. Thus, overall weight and volume of the transducer can be reduced and more easily integrated with other devices. A major challenge is in the synthesis/processing of materials in single crystal epitaxial films between metal electrodes, and to integrate them effectively for utilization in piezoelectric devices with advantages of yield, uniformity, low surface roughness, and performance associated with microelectronic technology. Specific research areas include: (1)synthesis, processing and characterization of single crystal films of piezoelectrics on single crystal conductive oxide electrodes; (2)examination of the microstructure in PMN-PT [Pb(Mg1/3Nb2/3)-PbTiO3)] thin films and atomic structure and local chemistry at PMN-PT/SrRuO3 interfaces using high resolution transmission electron microscopy; (3)fabrication and characterization of single crystal thick film transducers such as single pistons, 100 element arrays, and 192 element multilayer arrays; and (4)application and evaluation of the piezoelectric transducers for medical ultrasound imaging. High frequency transducers operate in the range from 10 MHz for breast imaging and intra-cardiac scanning to 40 MHz for intravascular applications and ophthalmic imaging to 100 MHz for ultrasound microscopy. The hypothesis is that more sensitive, broader bandwidth, less expensive transducers, including linear and multilayer arrays, can be developed using epitaxial films compared with conventional technologies.

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The project addresses basic research issues in a topical area of materials science and engineering having high potential technological/medical relevance. The research will contribute new knowledge at a fundamental level to important materials synthesis and fabrication aspects of electronic devices, and the basic materials science and engineering knowledge and understanding gained from the research is expected to contribute to improving the perform-ance capabilities of advanced ultrasound imaging devices for biomedical applications. An important feature of the interdisciplinary program is the integration of research and education through the training of students in a fundamentally and technologically significant area. This FRG project is co-supported by two ENG programs(BES/BME; CTS/FPH), an MPS program(DMR/EM), and the MPS OMA(Office of Multidisciplinary Activities).

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