Nanoscale materials and device characterization via a scanning microwave microscope

Abstract

The vector network analyzer (VNA) architecture as it exists today has the ability to measure impedances close to the analyzer's own characteristic impedance (i.e., 50 ohms) with good precision up to 100GHz stimulus frequency. However, the measurement precision and resolution provided by a VNA drop by two orders of magnitude as impedance deviates from 50 ohms. We propose a solution that remedies the lack of measurement precision and resolution for large and small impedances when measured by a VNA. A new scanning microwave microscope (SMM) that utilizes a half-wavelength resonator in conjunction with a diplexer connected to a VNA to perform very sensitive capacitance measurements at the tip of a conductive atomic force microscope (AFM) is discussed. These measurements are achieved via transformation of the high impedance (i.e., the very small capacitance between the AFM tip/sample to the ground) to 50 ohms (i.e., the measurement system's characteristic impedance) using a half-wavelength resonator and diplexer.