Application Note #145 Nanoscale Mapping of Permittivity and Conductivity with Scanning Microwave Impedance Microscopy

is an AFM-based technique for materials and device characterization. The reflected microwave signal from the tip-sample interface holds information of the electrodynamic properties of the sample surface underneath the tip apex. Detecting and processing of the reflectance in real time allows sMIM to directly access the permittivity and conductivity of materials. When an AFM-type sMIM probe is scanning across the sample surface, sMIM is capable of imaging variations in resistive (sMIM-R) and capacitive (sMIM-C) properties. This detection approach does not require making electrical contact between the sample and the substrate as sMIM is based on the capacitive coupling between the tip and the sample. By AC-biasing the sample or device under test, sMIM also provides carrier profiling (dC/dV) capability similar to traditional scanning capacitance microscopy (SCM). In the same way, it also uniquely offers mapping of nonlinear resistive properties (dR/dV). With both the sMIM and its AC-sample-bias modulated signals, sMIM is suitable for studying surfaces with complex composition or devices under test with a broad dynamic range, e.g., metallic, semiconducting, and insulating domains. As a near-field method, the resolution of sMIM is only limited by the tip radius of the probe, and it can easily achieve a lateral resolution of <30 nm for electrical mapping. Sub-aF sensitivity and high S/N ratios are realized by using waveguide tips with coaxial shielding. Having these unique capabilities, sMIM is superior to other AFM-based electrical modes for a broad range of applications. This application note provides an introduction of sMIM and its integration with Bruker’s versatile AFM platforms, such as the Dimension Icon® and Dimension EdgeTM AFMs. When combined with Bruker’s exclusive PeakForce Tapping® mode, it is possible to obtain sMIM results on delicate samples, such as carbon nanotubes. PeakForce Tapping (with PeakForce QNM®) additionally provides simultaneous mapping of other sample properties, including modulus and adhesion.