THIN FILM DIELECTRIC PROPERTIES CHARACTERIZATION BY SCANNING NEAR-FIELD MICROWAVE MICROSCOPY
Open AccessWe present a method for extracting high-spatial resolution dielectric constant data at microwave frequencies. A scanning near field microwave microscope probes samples with the data being acquired in the form of the frequency and quality factor shifts of a resonant cavity coupled to the sample. We find this technique is extremely sensitive to the behavior of the system in a small volume at the end of the scanning tip. In our experiments, the near field is confined to a 1 um region below the sample surface, Thus, We are able to observe the dielectric response with a spatial resolution as fine as 200 nm even with an 18 cm radiation wavelength. The theoretical part of the approach addressed here is to determine material parameters (in this case, the complex dielectric constant) from the measured shifts. Our approach is to apply cavity perturbation theory, which connects the shift in resonant frequency, to computations of the energy stored in the electromagnetic fields of the cavity and its surroundings in order to characterize the real part of the permittivity, and by applying a high frequency heat dissipation model to characterize the imaginary part of the permittivity. The electromagnetic fields are simulated with the finite element method (FEM) both in the quasi-static and high frequency modes. In this thesis, the details of the experiment and FEM calculation will be given. Examples of determining the dielectric properties in reduced dimensional thin-film materials will be presented.
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