Low-impedance shielded tip piezoresistive probe enables portable microwave impedance microscopy

New scanning probes suitable for microwave impedance microscopy (MIM) measurements on any scanning platform using a piezoactuator are presented. The authors microfabricated piezoresistive cantilevers integrated with low-impedance, electrically shielded transmission lines to enable simultaneous topographical and electrical scanning probe microscopy. The probes provide topography feedback with nanometre vertical resolution for samples or setups where laser detection is not feasible or desirable. MIM is a scanning probe technique that uses the interaction of a gigahertz electrical signal with a sample, and yields a conductivity map of the sample at the nanoscale. The proposed design exhibits vertical displacement resolution of 3.5 nm in a measurement bandwidth from 1 to 10 kHz. The capacitance between shield and inner conductors measured with an impedance analyser is 9.5 pF and the trace resistance is 32 . Sample location and topographic scanning capabilities using the self-sensing piezoresistor are demonstrated.