We propose for the first time a method to crystallize 4.5 nm H$\mathrm{f}_{05} Z \mathrm{r}_{05}\mathrm{O}_{2}$ (HZO) in the ferroelectric orthorhombic phase (0-phase) by using a sub-nm InGaZnO (IGZO) seed layer. Atomic mismatch between IGZO and HZO layers introduces epitaxial strain, inducing ferroelectric phase crystallization even at thickness of 4.5 nm. HZO/IGZO achieved an EOT of 0.44 nm, coercive voltage of 0.51 V, and high endurance >10¹⁴. Hence, HZO/IGZO is a promising candidate for next generation high-k dielectric in DRAM capacitor applications.