Broadband dielectric microwave microscopy on $\mu$m length scales

TL;DR

This paper introduces a broadband microwave near-field microscope capable of imaging dielectric properties at micron scales across a wide frequency range, enabling detailed impedance analysis of materials.

Contribution

The work presents a novel broadband microwave microscopy technique using a transmission line resonator, allowing frequency-dependent imaging of dielectric and resistive properties at micron resolution.

Findings

Imaging of dielectric properties on BSTO thin films from 1.3 GHz to 17.4 GHz.

Electrostatic approximation fails above ~10 GHz, requiring full-wave analysis.

Microscope functions as a spatially-resolved impedance analyzer.

Abstract

We demonstrate that a near-field microwave microscope based on a transmission line resonator allows imaging in a substantially wide range of frequencies, so that the microscope properties approach those of a spatially-resolved impedance analyzer. In the case of an electric probe, the broadband imaging can be used in a direct fashion to separate contributions from capacitive and resistive properties of a sample at length scales on the order of one micron. Using a microwave near-field microscope based on a transmission line resonator we imaged the local dielectric properties of a Focused Ion Beam (FIB) milled structure on a high-dielectric-constant Ba_{0.6}Sr_{0.4}TiO_3 (BSTO) thin film in the frequency range from 1.3 GHz to 17.4 GHz. The electrostatic approximation breaks down already at frequencies above ~10 GHz for the probe geometry used, and a full-wave analysis is necessary to obtain qualitative information from the images.