# Shielded cantilever with on-chip interferometer circuit for THz scanning probe impedance microscopy

## TL;DR

This paper presents a THz near field cantilever with an on-chip interferometer that enables sensitive, quantitative impedance measurements and topography imaging, advancing THz scanning probe microscopy technology.

## Contribution

Introduction of a microstrip-based THz cantilever with an on-chip interferometer for enhanced sensitivity and impedance measurement in near field microscopy.

## Key findings

- Sensitivity below 0.25 fF demonstrated.
- Distinct reflection coefficient changes observed with different samples.
- Enables topography imaging in AFM mode.

## Abstract

We have realized a microstrip based THz near field cantilever which enables quantitative measurements of the impedance of the probe tip at THz frequencies (0.3 THz). A key feature is the on-chip balanced hybrid coupler which serves as an interferometer for passive signal cancellation to increase the readout circuit sensitivity despite extreme impedance mismatch at the tip. We observe distinct changes in the reflection coefficient of the tip when brought into contact with different dielectric (Si, SrTiO3) and metallic samples (Au). By comparing to finite element simulations we determine the sensitivity of our THz probe to be well below 0.25 fF. The cantilever further allows for topography imaging in a conventional atomic force microscope mode. Our THz cantilever removes several critical technology challenges and thus enables a shielded cantilever based THz near field microscope.