Single crystal piezoelectrics: a revolutionary development for transducers

Lead-based single crystal relaxor ferroelectrics have been developed with fundamental properties that in theory should dramatically enhance the bandwidth and sensitivity-bandwidth product for ultrasound transducers. High sensitivity array elements with fractional bandwidths of over 120% have been modeled using the properties measured for single crystal resonators. Single element transducers and arrays have been built with performance that is significantly better than that for arrays built with PZT ceramic. Not all of the properties are better than PZT. The crystals usually have a low coercive field and can be depoled at relatively low temperatures. Also, there are significant challenges to using the materials effectively. These include: learning to repeatably grow large crystals with uniform properties, reducing crystal cost, improving adhesion to single crystals, and developing array processes that create the small resonators required without damaging them. This paper reviews the unique features of single crystals and reports that all of the obstacles except for cost effective growth of high quality crystals have been effectively addressed. We argue that single crystals will displace ceramics for high performance array applications. The critical questions are: when, at what development cost, to what array cost, and to what level of array performance.