Investigation of Imprint in FE-HfO₂ and Its Recovery

Ferroelectric (FE)-HfO 2 -based FETs (FEFETs) are one of the most promising candidates for emerging memories. However, the FE material suffers from a unique reliability phenomenon known as imprint: the coercive voltage shifts during data retention, which has been regarded as a major issue for memory operation, while the mechanism causing it is still under research. In this article, imprint and its recovery in FE-HfO 2 are investigated in detail by comprehensive electrical measurements to reveal its underlying mechanism including the cause of asymmetric coercive voltage shifts. The recovery measurements clarify that domain switching is indispensable for the recovery from imprint. The subloop imprint effect shows that imprint and its recovery must be independent for each domain. In addition, switching time measurements and corresponding fitting results with the nucleation-limited-switching (NLS) model strongly indicate that imprint is caused by domain-seeds-pinning. Based on these results, we conclude that charge trapping and detrapping affecting activation barriers for domain switching, accompanied by domain switching, is responsible for imprint and its recovery.