Physics of failure modes in accelerometers utilizing single crystal piezoelectric materials

For over forty years, the lead zirconate – lead titanate system (PZT) has been the industrial standard of sensing materials for piezoelectric accelerometers. This ceramic has established a reliability benchmark given the uniformity of its electromechanical properties, the negligible dependence of these properties on temperature and pre-stress, and the ability to manufacture the sensing element cost-effectively into a myriad of geometries. Today, revolutionary advances in the growth of single crystal piezoelectric materials have spawned the evolution of novel sensor designs. With piezoelectric coefficients exceeding 2000 pC/N, and electromechanical coupling factors above 90%, single crystals of Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ [PMNT] and Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃ [PZNT] have the potential of superseding PZT ceramics in certain critical applications.; This dissertation reports the first results of the design, development and performance characterization for an accelerometer utilizing bulk, single crystal piezoelectric materials. Numerous prototypes, developed in the compression and flexural-mode design configurations, exhibit charge sensitivities that exceed that of their PZT-counterparts by a factor of greater than three times. The introduction of accelerometer prototypes employing single crystal piezoelectric material is an important advancement for the sensor industry.; Root-cause failure processes were identified and subsequently used as a reliability enhancement tool to prevent device failures through robust design and manufacturing practices. Crystal machining techniques were analyzed in which a scanning electron microscope was used to inspect the crystal surface for defects. Inhomogeneity in the piezoelectric properties over the surface of the crystal was quantified and recognized as a major obstacle to commercialization. Measurements were made on the material's fracture toughness and electromechanical properties over a wide temperature range. Effects of aging and mechanical cycling were also studied.; The identification of these failure modes was the basis from which to develop optimal design guidelines specific to the single crystal piezoelectric material. Integral to this analysis was assessing the reliability of single crystal piezoelectric materials vis-à-vis ceramic PZT. The knowledge garnered from this research now serves as the cornerstone from which to develop a new-generation vibration sensor.