Interface engineering of HfO 2 -based ferroelectric devices for crystal phase control and enhanced ferroelectricity using atomic-layer-deposited ZrO 2 nucleation layers

Interface engineering is a key for high-performance HfO 2 -based ferroelectric devices. In this study, the fabrication techniques for HfO 2 -based thin films using atomic-layer-deposited ZrO 2 nucleation layers [atomic layer deposition (ALD)-ZrO 2 -NLs], which are inserted at ferroelectric/electrode interfaces, are systematically summarized. ALD-ZrO 2 -NLs were found to promote crystallization and formation of the ferroelectric orthorhombic (O) phase in HfO 2 -based films, resulting in superior ferroelectricity. This is attributed to two critical roles of ALD-ZrO 2 -NLs: providing a seed layer that induces epitaxial-like grain growth because of the high degree of lattice matching between the pre-crystallized ALD-ZrO 2 -NL and the O phase of HfO 2 , and acting as a stressor layer that induces tensile stress due to the difference in thermal expansion coefficients during annealing process. In addition, improved reliability and a low-temperature fabrication process for HfO 2 -based thin films are demonstrated using ALD-ZrO 2 -NLs. These findings suggest that interface engineering using ALD-ZrO 2 -NLs is a promising approach for fabricating next-generation HfO 2 -based ferroelectric devices.