Imprint was observed for fatigued PZT (Zr/Ti = 53/47) capacitors which were subjected to a thermal cycle (at 80°C for a period of time). It was also observed for capacitors whose top electrode was defined by ion milling. In addition, capacitors with an asymmetric multilayered structure showed severe imprint problems. Based on the above observations, imprinting was categorized as:
1) Intrinsic imprint which is caused by inherent conditions such as device structure, configuration, and material composition.
2) Extrinsic imprint which is generated by external sources such as electrical stress, thermal stress, time, and processing.
Imprint mechanisms were discussed for each imprinting category. Most importantly, based on partial switching, a new memory logic was suggested. It is shown that stable imprinting may be useful for low density FRAM applications when the proposed new memory logic is applied. Reliability of the new logic was also shown to be significantly better than conventional operation.