Nanoinspection of Dielectric and Polarization Properties at Inner and Outer Interfaces in PZT Thin Films

Abstract

We report on novel approaches using scanning force methods [i.e. piezoresponse force microscopy (PFM), Kelvin probe force microscopy (KPFM) and pull-off force spectroscopy (PFS)] in order to deduce the local dielectric and polarization properties of PZT thin films both at outer and inner interfaces with < 50 nm lateral resolution. We show that the polarization profile into the depth of the PZT sample varies dramatically being built up at the bottom Pt electrode over a transition layer of more than 200 nm in thickness. Also this interfacial area shows a different relaxation behavior upon switching. The results are explained both in the view of negatively charged defects pinned at the PZT/Pt interface as well as the possible variation in the local dielectric properties across the film thickness. Investigating the latter made the quantitative deduction of values such as the effective dielectric polarization P _z ,the deposited charge density σ, and the surface dielectric constant ε _surface in thin ferroelectric PZT films necessary. We illustrate that such measurements in fact are possible on the nanometer scale revealing quantitative data when combining PFM and PFS.