Enhanced dielectric constant resolution of thin insulating films by electrostatic force microscopy

Abstract

Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in: Abstract: Electrostatic Force Microscopy has been shown to be a useful tool to determine the dielectric constant of insulating films of nanometer thicknesses that play a key role in many electrical, optical and biological phenomena. Previous approaches make use of simple analytical formulae to analyse the experimental data for thin insulating films deposited directly on a metallic substrate. Here we show that the sensitivity of the EFM signal to changes in the dielectric constant of the thin film can be enhanced by using dielectric substrates with low dielectric constants. We present detailed numerical calculations of the tipsample electrostatic interaction in the following set-up: the insulating thin film, a dielectric substrate (or spacing layer) of known low dielectric constant and a metallic electrode. The EFM sensitivity to the dielectric constant increases with the thickness of the spacing layer and saturates for thicknesses above 100-300 nm, when it is close to that of an infinite medium.

A Model for the Characterization of the Polarizability of Thin Films Independently of the Thickness of the Film

“…Both the metallic and Air/vacuum limits correspond to a tip over a metallic sample with different tip-sample distances (D and D+h respectively). The behaviour of the force is well known for metallic samples 21 . Taken into account these previous results and the boundary conditions of a dielectric plate, a simple expression can be deduced for the electrostatic force:…”

Influence of the Substrate and Tip Shape on the Characterization of Thin Films by Electrostatic Force Microscopy

“…[9] In the case of thin films, it has been also shown that the substrate thickness and dielectric constant are key parameters for a quantitative characterization. [10] Some effects like the detection of effective ultrahigh dielectric constants due, for example, to the presence of certain conductivity in the thin film can be also present. [11] In the EFM setup proposed in this article, there are at least three layers that could modify the magnitude and behaviour of the electrostatic force.…”

“…The details of this method, including a three layers thin film sample have been described elsewhere 10 and only a brief description is given here. Basically, the GICM can be understood by a method that includes the sample and tip shape in two steps.…”

Finite Conductivity Effects in Electrostatic Force Microscopy on Thin Dielectric Films: A Theoretical Model

“…These technical improvements have been especially relevant in the characterization of thin films [7][8][9][10]. Most of the previous work has been focused on perfectly insulating dielectrics [11], but the possible effect of a small conductivity on the EFM signal has not been addressed before (i.e., previously, every layer included in the sample was only characterized by the thickness and dielectric constant). The conductivity, even with small values, is very important in the characterization of thin films in air ambient conditions where water and molecular adsorption and water condensation [12][13][14] can be detected as a finite surface conductivity due to the ions added on the otherwise insulating sample.…”