Low-impedance shielded tip piezoresistive probe enables portable Microwave Impedance Microscopy

We present new scanning probes suitable for Microwave Impedance Microscopy measurements on any scanning platform using a piezoactuator. We 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 nanometer vertical resolution for samples or setups where laser detection is not feasible or desirable. MIM is a scanning probe technique that utilizes the interaction of a GHz electrical signal with a sample and yields a conductivity map of the sample at the nanoscale. Our new design exhibits vertical displacement resolution of 3.5 nm in a measurement bandwidth from 1 Hz to 10 kHz. The capacitance between shield and inner conductors measured with an impedance analyzer is 9.5 pF and the trace resistance is 32 Ω. We have demonstrated sample location and topographic scanning capabilities using the self-sensing piezoresistor.