Multi-breakdown model for explaining the formation and growth of black spots in PZT capacitor under DC bias

•The black spots formed in PZT during the electrical degradation process have been observed through various microscopes.•The black spot areas are with different grain arrangement and thicker grain boundaries as the bulk ceramic.•Energy released from each electrical breakdown event is not enough for forming a certain size of black spot as observed.•A multi-breakdown model has been proposed for explaining the mechanisms of the black spots formation and growth.

Lead zirconate titanate (PZT) is widely used in various electro-mechanical devices because of its piezoelectric function. In some of its applications, the piezo ceramic will be subjected to a DC bias. The applied DC bias will stress the PZT ceramic and can undergo an electrical degradation process. This electrical degradation process demonstrates itself as resistance decreases and leakage current increases. Therefore, the electrical degradation phenomenon can severely impact on device performance and reliability. It has been found that, accompany this electrical breakdown process, black spots will appear in the ceramic body. In this paper, the formation and growth of the black spots in a PZT capacitor under DC bias is investigated. The black spot area is further characterized with various analytical methods. Based on previous research, a multi-breakdown model is proposed for explaining the mechanism of black spot growth.