Online proceedings - EDA Publishing Association

interaction with the underlying materials. By analyzing the
reflected microwave signals, the electrical properties of
underlying materials can be evaluated. In this paper, some
special samples with different thickness of dielectric films
which plays the role of oxide layer created on the material
surface were fabricated, and the measurement of electrical
properties of materials under the oxide layer by the M-AFM
was investigated in details.
11-13
May 2011, Aix-en-Provence, France
A
Microwave generator
Tunable
short
Measurement system
Attenuator
Multiplier
Magic
tee
II.
EXPERIMENTAL PROCEDURE
A. Probe Fabrication
To restrain the attenuation of microwave propagating in
the probe, a non-doped GaAs wafer was used as the substrate
of the probe. Wet etching was used to fabricate the probe
because it is possible to obtain the desired structure by
causing a side etching under the etching mask. The
fabrication method and process of the M-AFM probe have
been studied in details by Ju et al. [10,11].
Topography
B
Tip
Ag film
Laser
Microwave
image
Cantilever
SiO oxide layer
2
Silicon substrate
Detector
Probe holder
AFM
Fig. 2. Schematic diagram of the M-AFM measurement
system.
The images of the cantilever and tip of M-AFM probe
were taken by scanning electron microscopy (SEM), as
shown in Fig. 1. Fig. 1A shows the forepart of cantilever, a
sharp tip with a height of 7 μm was formed at the front of the
cantilever. As shown in Fig. 1B, a nano-slit was introduced
across the cantilever through the center of the tip by focus ion
beam (FIB) fabrication. The width of the nano-slit is
approximately 100 nm.
Fig. 1. SEM images, A: the cantilever of M-AFM probe; B:
a nano-slit across the probe tip introduced by FIB
fabrication.
B. Microwave Measurement System
The measurements in this paper were carried out by a
compact microwave instrument which is composed of an
amplifier, a magic-Tee, an attenuator, a tunable short, and a
diode detector [13], as shown in Fig. 2. Fig. 2A shows the
flow chart of the operating microwave signals for
measurements. The microwave signals working at a
frequency f=94 GHz, which was generated by a microwave
generator. Then the microwave signals were separated into
two branches by the magic-Tee. One branch signal was sent
to the M-AFM probe to sense the samples and then the
reflected signal was received by the probe tip, as shown in
Fig. 2B. Another branch signal was sent to the attenuator and
then to the tunable-short to form a reference signal with a
constant phase difference and a similar amplitude comparing
with the reflected signal from the sample. The reference
signal was determined by setting the output voltage of the
detector to be a definite value when the M-AFM was set in
air without the approaching, and this was carried out by
adjusting the attenuator and the tunable-short. The reflected
signal and the reference signal were finally synthesized by
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