Continuous capacitance–voltage spectroscopy mapping for scanning microwave microscopy

A new method, scanning sawtooth capacitance spectroscopy (SSCS), is proposed to measure a map of capacitance/voltage curves (C–V) by applying a low frequency voltage sawtooth signal (20–100 Hz) to the AFM tip while scanning. For this a scanning microwave microscope (SMM) is used to acquire calibrated capacitance data in the high frequency range of 1–20 GHz. While the capacitance is acquired pixel by pixel, the applied voltage signal is recorded as well, and each pixel of the capacitance is assigned the corresponding voltage value. Assuming the voltage variable is smooth over time, adjacent pixels within a scan line will have similar voltage values and a small sequence of neighboring pixels can be combined into a virtual C–V spectroscopy curve. With standard SMM operation parameters roughly 26,000 C–V curves can be acquired within few minutes data acquisition time. The method is demonstrated for n-type and p-type silicon semiconductor samples and can be applied to other samples including new materials and bio-membranes.