Testing and Reliability
In ferroelectric random access memories (FeRAMs), the difference in the displacement charge between the two polarization states is fundamental to discriminate the binary states, ‘‘1’’ and ‘‘0’’. Therefore, the durability of the difference in the displacement charge and circuit techniques for sensing the difference are intimately related to the reliability of FeRAMs. In this chapter, we deal with electrical degradation phenomena in ferroelectric capacitors, such as resistance degradation, time-dependent dielectric breakdown (TDDB), ferroelectric fatigue, charge retention, and imprint, which affect the sensing of displacement charges from a memory cell all the way. In each topic, we refer to related testing techniques to characterize and qualify the performance and reliability of ferroelectric capacitors. These discussions include some fundamental considerations on aging mechanisms in ferroelectric capacitors, which may provide essential and meaningful feedback for materials, circuit design, and manufacturing process improvements.
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