Dependence of Ferroelectricity on Film Thickness in Nano-Scale Pb(Zr,Ti)O₃ Thin Films

Abstract

We present the dependence of the ferroelectric polarization on the film thickness. Below the film thickness of 21 nm, Pb metallic phase was formed at grain boundary and the pervoskite phase disappeared. As the film thickness decreased, the intensity of phonon modes decreased and the compressive stress in the Pb(Zr,Ti)O₃ thin film, which had tetragonal and rhombohedral structures, increased. The remnant polarization decreased from 6 μ C/cm² to 2.5 μ C/cm², while the coercive field increased from 50 kV/cm to 150 kV/cm, with the decrease in film thickness from 152 nm to 32 nm. The suppression of ferroelectricity resulted from the crystallinity degradation observed using X-ray photoelectron spectroscopy (XPS) and Raman analysis and size effect derived from the residual compressive stress evaluated using a laser reflectance method. The Pb/(Zr+Ti) ratio would be the important factor determining the crystal structure in PZT thin films, especially nano-scale PZT films.

Keywords:

• PZT
• film thickness
• stress
• Raman spectra

ACKNOWLEdGMENT

This work was supported by the Ministry of Education (Brain Korea 21), the Ministry of Science and Technology (21C Frontier R&D program), the Institute of Information Technology Assessment (IITA) and Samsung Electronics, Korea.