Spontaneous Polarization in an Ultrathin Improper-Ferroelectric/Dielectric Bilayer in a Capacitor Structure at Cryogenic Temperatures

To determine the effect of depolarization and the critical thickness in improper-ferroelectric hexagonal - ferrite thin films, we investigate the polarization switching of a ferroelectric/dielectric bilayer in capacitor structures at 20 K. Experimentally, we show that the spontaneous polarization persists throughout the stud- ied thickness range (3 to 80 unit cell), even with a thick (10-nm) dielectric layer, suggesting no practical thickness limit for applications. By fitting the effect of depolarization using the phenomenological the- ory, we show that the spontaneous polarization remains finite when the thickness of the ferroelectric layer approaches zero, providing a hint for the absence of critical thickness. We also find that the interfacial effects limit the multidomain formation and govern the polarization switching mechanisms.

Automated summary

Through experiments, we show that spontaneous polarization remains in a ferroelectric/dielectric bilayer thin film, even with a thick dielectric layer, suggesting no practical thickness limit. We also demonstrate that the spontaneous polarization persists even when the thickness of the ferroelectric layer approaches zero, hinting at the absence of a critical thickness. Additionally, interfacial effects limit multidomain formation and govern polarization switching mechanisms.