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Keysight Technologies
Scanning Microwave Microscope Mode
Application Note
Introduction
Measuring electromagnetic properties of materials can provide insight into
applications in many areas of science and technology, and increasingly, these
properties need to be evaluated at the nanometer scale. Since electromagnetic
properties, such as the dielectric constant, are ultimately related to a material's
molecular structure, correlating the detailed physical structure of a material with
its electromagnetic properties is frequently more valuable than the knowledge of
either alone.
Scanning Microwave Microscope (SMM) Mode is a new Scanning Probe Microscope
(SPM) that combines the electromagnetic measurement capabilities of a microwave
vector network analyzer (VNA) with the nanometer-resolution and Angstrom-scale
positioning capabilities of an Atomic Force Microscope (AFM).
The Keysight Technologies, Inc. VNAs are mature, highly sophisticated
characterization instruments that make extremely accurate, calibrated
measurements of complex-valued ratios on electromagnetic signals.
The ratios are and
The incident signal is generated and controlled inside the VNA; as a result, the
ratios R and T are not merely relative, but referenced to the well-known, accurately
quantiied incident signal.
This measurement capability, delivered to the apex of an AFM tip makes the SMM
the only SPM in its class, enabling calibrated, traceable measurements of electrical
properties such as impedance and capacitance, with the high spatial resolution that
is the hallmark of a well-designed, well-constructed AFM.
Microwave Vector Network Analyzer
The SMM uses Keysight's VNA microwave vector network analyzer (Figure 1).1
Like all network analyzers, this VNA is a stimulus-response instrument, optimized
for accurate and repeatable measurement of the response of a network or a
device under test (DUT) to a known stimulus signal. This is in contradistinction
to instruments such as the spectrum analyzer, which are usually conigured as
a receiver (only) of an unknown signal, and which do not include a source for a
stimulus to be applied to the DUT.
A VNA has two operational modes: transmission and relection. In the relection
(alternatively, transmission) mode, the VNA measures the magnitude and phase
characteristics of the DUT by comparing the signal that relects off (alternatively,
transmits through) the device with the stimulus signal.2 Each mode enables
measurement of several useful parameters. In the relection mode, the VNA can
measure (among other things) the impedance of the DUT.3 Scanning Impedance
Figure 1. Keysight's VNA microwave vector
Microscopy is a major application of the SMM. network analyzer (top) and 5500 AFM (bottom).
03 | Keysight | Scanning Microwave Microscope Mode