The effect of relative humidity, temperature and electrical field on leakage currents in piezo-ceramic actuators under dc bias

Abstract

A key advantage of piezo-ceramic technology is the extremely low power consumption that can be achieved compared to electromagnetic technology. However leakage currents through the ceramic limit the minimum power consumption achievable particularly when exposed to harsh environments. This paper presents a systematic study of temperature, humidity and electrical field on the electrical resistance of soft PZT ceramics under dc bias. Temperature–humidity bias testing methods are used to assess electrical resistance changes in soft PZT beams. Results show that changes in electrical resistance occur in two stages. The first stage shows little dielectric change and that its duration is dependent on the ambient relative humidity. The second stage is characterized by a much more rapid fall in ceramic resistance and is not as dependent on the relative humidity. Evidence is presented showing that the leakage currents are caused by an ionic migration process. Mathematical models are presented to describe the degradation process and to predict the onset of resistance. These models are shown to give good agreement with experimental results. The role of electrode materials and ceramic microstructure in the development of leakage currents is discussed.