Separation of Near Interface Regions From Central Bulk in a Ferroelectric Thin Film

Abstract

The fabrication and operation of a ferroelectric thin film capacitor may change the electric properties of the material layers next to the top and bottom electrodes through various processes, such as chemical reaction and diffusion. The existence of these near interface regions (NIRs) can have significant effect on the device performance and imposes a limit on the minimum thickness of a functional film. It is of both basic and practical interest to separate the NIRs from the central bulk region (CBR) of a film and characterize the related thickness and resistivity. Based on the understanding that the NIRs should be the same for the films of the same composition under the same process conditions, we developed a method to separate the NIRs from the CBR. Using sol-gel fabricated PLZT films with different metal contacts, Pt and Ir, as an example, we demonstrate how to quantify the thickness of the NIRs and the CBR resistivity. The experimental data show good agreement with the model. Our results reveal that (1) the thickness of the NIRs can be a considerable portion of the total film thickness; (2) the total thickness of the NIRs depends only on the electrode material in use; (3) the CBR resistivity depends only on the impurity doping level. The fact that the NIR is much narrower when Pt electrodes are used instead of Ir, and that the NIR resistivity is always considerably lower than the CBR, suggest that NIRs is probably originated from material non-stoichiometry/defects rather than the band bending at the metal/insulator interfaces.