Near-field Scanning Microwave Microscopy (NSMM) techniques experimented with a remarkable development as they are cutting-edge tools, devoted to the characterization of materials, especially semiconductor structures and even superconductors. These methods provide possibilities to characterize the surface and sub-surface of materials, offering measurements in a non-contact, non-invasive and, the most important, non-destructive way.
The NSMM technique comprises a coaxial microwave resonant cavity connected to a vector network analyzer (VNA). A sharp tip extending from the inner conductor of the coaxial cavity resonator is fed by a microwave source to form a near field probe in order to analyze the sample to be tested. The distance between the probe tip and the surface or substrate of the sample is kept constant while the entire sample to be analyzed is "scanned". Changes in the resonance frequency of the coaxial cavity resonator and reflection, or transmission coefficients respectively are measured and recorded using a computing system. These parameters are dependent on the local electrodynamics properties of the sample to be analyzed. By plotting these measured quantities with respect to the probe tip position, a complex conductivity that can be investigated and a dielectric map providing information about the properties of the sample can be obtained.