High frequency ultrasound is needed for high resolution imaging applications in dermatology, ophthalmology, intravascular imaging, and laproscopy. The purpose of the proposed effort will be to develop a novel lithography-based micromachining method for single crystal piezoelectrics in order to fabricate 2-2 and 1-3 composite transducers capable of operating at frequencies from 20 MHz to greater than 50 MHz. Single crystal piezoelectrics have considerably higher piezoelectric coefficients and electromechanical coupling factors than PZT ceramics, and as a result they are being used to fabricate ultrasound transducers with unprecedented bandwidth and sensitivity. Application of single crystal piezoelectrics to high frequency transducers is expected to result in devices with much larger depths of field, limits on which are a significant draw back for existing high frequency transducers. In addition use of single cyrstals, as opposed to ceramic, allows fabrication by lithography based micromachining methods. Thus, very fine featured crystal-polymer composite transducers can be easily fabricated at reasonable cost. In this program both wet etching and reactive ion etching will be investigated as methods for micromaching 2-2 and 1-3 crystal-polymer composite structures for ultrasound transducers. The resulting transducers are expected to have bandwidths in excess of 100% with sensitivities even better than current ceramic transducers operated below 20 MHz. This would be an unprecedented advance for high frequency ultrasound imaging and would lead to greatly improved diagnostic capability in applications ranging form early stage glaucoma detection to biopsy or melanoma tumor histology.
