Modeling of a Cantilever-Based Near-Field Scanning Microwave Microscope

TL;DR

This paper models and characterizes a scalable, cantilever-based near-field scanning microwave microscope using finite-element analysis, enabling high-sensitivity measurements of small impedance changes at microwave frequencies.

Contribution

It introduces a detailed modeling approach for a microwave nanoprobe with separated excitation and sensing electrodes, including finite-element and transmission line analysis, for improved sensitivity and characterization.

Findings

Achieved sensitivity below 1 atto-Farad for capacitance changes

Demonstrated electrical and topographical imaging modes

Validated the model with experiments on semiconductor samples

Abstract

We present a detailed modeling and characterization of our scalable microwave nanoprobe, which is a micro-fabricated cantilever-based scanning microwave probe with separated excitation and sensing electrodes. Using finite-element analysis, the tip-sample interaction is modeled as small impedance changes between the tip electrode and the ground at our working frequencies near 1GHz. The equivalent lumped elements of the cantilever can be determined by transmission line simulation of the matching network, which routes the cantilever signals to 50 Ohm feed lines. In the microwave electronics, the background common-mode signal is cancelled before the amplifier stage so that high sensitivity (below 1 atto-Farad capacitance changes) is obtained. Experimental characterization of the microwave probes was performed on ion-implanted Si wafers and patterned semiconductor samples. Pure electrical or topographical signals can be realized using different reflection modes of the probe.