Towards an ideal high-κ HfO₂-ZrO₂-based dielectric

The existence of a morphotropic phase boundary (MPB) inside HfO₂-ZrO₂ solid solution thin films has been predicted; if it exists, it provides a new path toward an ideal silicon-compatible dielectric. Herein, we investigate the structural evolution along with the dielectric and ferroelectric behaviors of differently designed HfO₂-ZrO₂ thin films to engineer the density of the MPB inside the film structure and consequently, enhance the dielectric properties. Polarization vs. electric field (P-E) measurements of Hf_0.25Zr_0.75O₂ thin films reveal ferroelectric (FE)-antiferroelectric (AFE) characteristics. For this composition, the dielectric constant ε_r is higher than those of FE Hf_0.5Zr_0.5O₂ and AFE ZrO₂ thin films; the difference is attributed to the formation of the MPB. To increase the density of the MPB and subsequently the dielectric properties, 10 nm Hf_0.5Zr_0.5O₂ (FE)/ZrO₂ (AFE) nanolaminates were prepared with different lamina thicknesses t_L. The coexistence of FE and AFE properties was confirmed by structural characterization studies and P-E measurements. The thinnest layered nanolaminate (t_L = 6 Å) showed the strongest dielectric constant ε_r∼ 60 under a small signal ac electric field of ∼50 kV cm^-1; this is the highest ε_r so far observed in HfO₂-ZrO₂ thin films. This behavior was attributed to the formation of an MPB near FE/AFE interfaces. The new design provides a promising approach to achieve an ideal high-κ CMOS-compatible device for the current electronic industry.