In this work, microwave characterization of magnetic materials using the scanning microwave microscopy (SMM) technique is presented. The capabilities of the SMM are employed for analyzing and imaging local magnetic properties of the materials under test at the nanoscale. The analyses are performed by acquiring both amplitude and phase of the reflected microwave signal. The changes in the reflection coefficient S-11 are related to the local properties of the material under investigation, and the changes in its magnetic properties have been studied as a function of an external DC magnetic bias. Yttrium iron garnet (YIG) films deposited by RF sputtering and grown by liquid phase epitaxial (LPE) on gadolinium gallium garnet (GGG) substrates and permalloy samples have been characterized. An equivalent electromagnetic transmission line model is discussed for the quantitative analysis of the local magnetic properties. We also observed the hysteretic behavior of the reflection coefficient S11 with an external bias field. The imaging and spectroscopy analysis on the experimental results are evidently indicating the possibilities of measuring local changes in the intrinsic magnetic properties on the surface of the material. (C) 2016 Elsevier B.V. All rights reserved.

The capability of scanning microwave microscopy for calibrated sub-surface and non-contact capacitance imaging of silicon (Si) samples is quantitatively studied at broadband frequencies ranging from 1 to 20 GHz. Calibrated capacitance images of flat Si test samples with varying dopant density (10-10 atoms cm) and covered with dielectric thin films of SiO (100-400 nm thickness) are measured to demonstrate the sensitivity of scanning microwave microscopy (SMM) for sub-surface imaging. Using standard SMM imaging conditions the dopant areas could still be sensed under a 400 nm thick oxide layer. Non-contact SMM imaging in lift-mode and constant height mode is quantitatively demonstrated on a 50 nm thick SiO test pad. The differences between non-contact and contact mode capacitances are studied with respect to the main parameters influencing the imaging contrast, namely the probe tip diameter and the tip-sample distance. Finite element modelling was used to further analyse the influence of the tip radius and the tip-sample distance on the SMM sensitivity. The understanding of how the two key parameters determine the SMM sensitivity and quantitative capacitances represents an important step towards its routine application for non-contact and sub-surface imaging.

We showed the capability of the SMM to measure calibrated capacitances and dopant densities on the nanoscale. In particular we have shown a noise level of 1 aF for capacitance measurements and a dynamic range of 10E14-10E20 atoms/cm3 for dopant profiling. The sensitivity for the dopant profiling varies with respect to the dopant density; overall we have a relative accuracy of 20% on both capacitance and dopant profiling measurement. Furthermore we were able to show a lateral resolution of 10 nm using standard electrical conductive cantilevers and semiconductor samples. There is upside potential along all the performance parameters in case they are required for the future VSMM project: the sensitivity of the capacitance measurement can potentially be improved to the sub-aF using standard PNA averaging capabilities while improved lateral resolution below 10 nm is envisioned using sharpened AFM tips. We tested the general useability of the capacitance calibration samples from MC2 including reproducibility, cleaning of dirt adhered to the gold caps, stability of the native oxide, the gluing of samples to steel plates for magnetic mounting etc. Overall the performance of the calibration samples is properly shown and verified by a large amount of test experiments. The MC2 calibration samples can be used for the further work in the VSMM project regarding SMM capacitance calibration, and the current SMM delivers enough sensitivity for the project objectives in terms of capacitance measurements and lateral resolution.

We have designed and fabricated a toolbox to perform S21 (transmission) measurements by using the Agilent 5600 LS AFM (SMM). In this type of measurement, an additional microwave emitter is located below the sample and the nano-scale probe of the SMM system (the tip) is located on the sample surface (or in close proximity) working as receiver of the transmitted wave. This set up allows to study the electromagnetic properties of the material under test obtained through the measurement of the S21 parameter by means of a two port VNA setup. Advanced microwave modelling software is used to study the measurement sensitivity, dynamic range, and other system characteristics like sub-surface depth resolution.