Tip–sample distance control for near-field scanning microwave microscopes

Abstract

We demonstrate a near-field scanning microwave microscope (NSMM) which uses a tuning fork shear-force feedback method to control the distance between tip and sample. This distance control method is independent of local microwave characteristics. The probe tip for the NSMM is attached to one prong of a quartz tuning fork and directly coupled to a high-quality microstrip resonator with a dielectric resonator at an operating frequency of f=4.5–5.5 GHz. The amplitude of the tuning fork was used as a distance control parameter in the feedback system. To demonstrate the ability of the distance regulation system, we present topographic images of an uneven conducting metal sample and compare the height response and the NSMM image.