Characterizing reliability of multilayer PZT actuators
Stephanie A. Hooker
Many new applications are emerging for piezoelectric ceramics including adaptive structures, active-flow-control devices, and vibration and noise suppression systems. Additionally, there are opportunities to use these devices in the biomedical field for miniature pumps, ultrasonic surgical tools, micro-needle arrays, and nanorobotics. In each of these instances, actuator stability is critical, representing a significant challenge for piezoelectric ceramic materials. In particular, the properties of lead zirconate titanate (PZT) have been found to degrade, often significantly, during continuous operation due to a combination of domain pinning, relaxation of interfacial stress, and, in the worst cases, micro-crack formation. This degradation, referred to as actuator fatigue, can be even more pronounced when high voltages are used to achieve maximum displacement or more complex actuator designs are required. For example, multilayer actuators, such as co-fired stacks, are important for many emerging applications and are now being produced with very small physical dimensions, lowering power requirements. However, multilayer components may be highly susceptible to long-term fatigue due to the large number of interfaces involved in their configuration. In this work, we report a method for rapidly characterizing the reliability of multilayer PZT actuators by monitoring degradation in switching polarization over time. To verify this approach, a series of miniature (3 mm x 3 mm x 2 mm) multilayer actuators were characterized over 1 million cumulative cycles. These actuators were produced commercially from soft PZT materials, and the sintering temperature was varied to tailor the ceramic microstructure and performance characteristics. Evaluation of cyclic polarization degradation was found to be an effective method for illuminating differences among the different actuators tested, as well as serving to predict their long-term resistance to fatigue.