Comparative performances of piezoceramics and crystal SAW filters

Morgan´s analysis of a SAW transducer is used to examine the theoretical performances of a 25 MHz SAW filter, with one apodized transducer, as a function of electromechanical characteristics of the piezoelectric substrate. For three piezoelectric materials, i.e. a lead zirconate titanate ceramic, a modified lead titanate ceramic (MPT) and a Y+128° cut lithium niobate single crystal, the effect of the material dielectric and electromechanical properties on the insertion losses of the filter are discussed. These theoretical calculations are experimentally verified for each material. For the ceramics, the effect of a hot isostatic press post sintering process on the performances of the device are also studied. Both theoretical and experimental results show that a high permittivity leads to low insertion losses