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Microwave near-field scanning microscope
F. Sakran, M. Abu-Teir, A. Copty, M.Golosovsky and D. Davidov
Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, Israel
Introduction
We present the development of a novel near-field scanning
microwave microscope based on a dielectric resonator. This
probe allows local characterization of conducting and insulating
films. Our probe has proved the capability of contactless
mapping of local thickness, conductivity, and spatially-resolved
Electron Spin Resonance (ESR). As the probe is also polarization
sensitive, it allows locally mapping the Hall Effect of
semiconductors and the magnetization of ferromagnetic thin
films. Recently, we designed various probes operating in the
frequency range 4-26 GHz with high quality factor, very good
sensitivity and high spatial resolution of micron and sub-micron.
Our probe also allows the integration of an optical path to the
sample deeming it suitable for optically detected magnetic
resonance and other optical-microwave measurements.
Microwave scanning probes for local characterization of conducting and
insulating films attract considerable interest since they are contactless,
versatile, and provide high spatial resolution. Recently several microwave
scanning probes have been developed, namely coaxial tip [1], slot aperture
[2], and dielectric resonator [3].
In our work, there are two important requirements: spatial resolution and
sensitivity. In order to achieve high spatial resolution, one needs to use
small aperture radiators for near-field scanning. The combination of the
dielectric resonator and small aperture, which we report here, provide a
highly efficient and sensitive microwave scanning probe.
We have developed a variety of Near-Field Scanning Microwave
Microscopes working in the 4-26 GHz frequency range [4]. Our probes
already proved their efficiency of measuring thickness of conducting layers
in the range of 0.1-1 μm mostly applicable to the semiconductor industry.
Our near-field microscope allows measurement of the (a) Hall effect [5] (b)
Ferromagnetic Resonance (FMR) and (c) Magnetoresistance of magnetic
thin films with micron spatial resolution. Moreover, our probe can perform
localized electron spin resonance (ESR) measurements [6].
(a)
Our Microwave Near-Field Scanning
Microscope based on dielectric resonator
and narrow slit. (a) The 9 GHz probe
design, (b) The actual probe, (c) the
probe’s resonance as measured by a
Network Vector Analyzer. The probe
transmit more than 90% of the incident
microwave power.
0
coaxial
connector
sapphire resonator
coax-to
waveguide
adaptor
slit
sapphire
transducer
air-gap
tuning screw
SMA connector
(c)
-10
Reflection (dB)
Abstract
Probe design
-20
(b)
-30
-40
-50
-60
8.865
8.870
8.875
8.880
8.885
8.890
(Frequency (GHz))
Results
b) Hall effect:
a) Conductivity/Thickness of thin conducting films:
c) Electron Spin Resonance (ESR) :
S12   xy  R0 H  Re M
Reflectivi ty 
Z0 - is the impedance of free space;
Zs - is the effective surface impedance;
Thick films:
Z s  f 0 
f - is the measurement frequency
0 - is the free space permeabili ty
 - is the resistivity
Thin films:
h  gH
Zs  Z 0
2Z
1 s
Zs  Z0
Z0
Zs 

d
d - is the film thickness.
S12 is the microwave reflectivity
measured at port 2.
g – is the g-factor
ρxy is the Hall resistivity
μB - is the Bohr magneton
H is the magnetic field
H – is the magnetic field
M is the magnetization.
ν – is the resonant
frequency of the probe
The first term here, RoH,
represents the ordinary Hall
effect.
h – is plank constant
The second term ReH represaents
the Extra ordinary Hall effect.
Measurement Setup
Measurement Setup
(a) Probe design and (b) measurement setup.
300
150
100
3
7
4
S 12 (x10 )
6
2
Ni
0
d=30nm
0
increasing field
decreasing field
4
80 nm
-50
0
4
4
S 12 (x10 )
-0.5
1
0.1
0.2
0.3
 H(T)

100
-100
3
0
0.1
0.2
8.45
8.46
8.47
8.48
30 nm
1
0
0.3
0
10 nm
0
0.1
0.2
 H(T)
)
The reflectivity Vs. film sheet resistance.
The inset shows the a Q factor Vs. sheet
resistance.
8.44
Frequency (GHz)
p-Si
-1
8.43
2
0
Near-field reflectivity (S11) of thin silver
films of different thickness d.
Note the increase of S11 upon increasing
film thickness.
50
200
1
0.5
5
S12 ( x 10 )
Ni
1.5
n-Si
0.3
0.4
 H(T)

Contactless measurement of the Hall
effect in Si wafers on a metal
substrate.
-100
Microwave Hall effect in ferromagnetic Ni
Fig.5 M.
Abu-Teir
et al.
films. (Extraordinary
Hall
effect)
-200
2990
1
3000
3010
3020
Magnetic Field (G)
0.15
Probe
Local ESR signal from a 120- μm-thick DPPH layer measured by a 9 GHz
probe. The inset shows the ESR signal (using a different DPPH sample)
obtained via a frequency sweep and a field modulation.
2” Si wafer
S
N Permanent
Magnet
XYZ
stage
0.1
North pole up
0.5
0.096
0.094
0
NdFeB magnet
0
μ 0 H (T)
0.05
S12 (x 104)
Magnitude (a.u.)
0.098
10 mm
0.092
-0.05
-0.5
0.09
South pole up
-0.1
0.088
0
100
200
300
400
500
600
-1
Distance (microns)
-0.15
-15
-10
-5
0
5
10
15
X (mm)
Probe spatial resolution: X-scan over 0.1 mm chromium strips. The resonator
includes slot width of 60 µm. Higher resolution can be obtained by narrowing the slit
width.
Mapping of the perpendicular magnetic field of a NdFeB permanent
magnet. The solid curve yields the calculated field of the magnet.
Spatially-resolved ESR signal from four DPPH grains. An XY-scan, at fixed
magnetic field and at fixed frequency, over four small grains of DPPH. We
observe four clearly defined ‘‘hills,’’ corresponding to the four DPPH grains. the
inset shows the optical image of the sample.
Conclusions :
References :
[1] C. Gao and X. –D. Xiang, Rev. Sci. Instrum. 69, 3846 (1998)
1. Contactless measurements of conductivity/thickness of thin conducting films in the range 0.1- 1μm.
[2] M. Golosovsky and D. Davidov, Appl. Phys. Lett. 68, 1579 (1996)
[3] J. Gallop, L. Hao, and F. Abbas, Physica C 282-287, 1579 (1997)
2. Local, sensitive and contactless Hall effect in semiconductors and magnetization of thin ferromagnetic films.
Possibility for low temperature measurements.
3. Our ESR spectrometer is local, sensitive, contactless and non limited to sample size. The sensitivity of our
present probe is already better than the sensitivity of a conventional ESR spectrometer.
[4] Abu-Teir M, Golosovsky M, Davidov D, Near-field scanning microwave probe based on a
dielectric resonator,REV. SCI. INSTRUM. 72 (4): 2073-2079 APR 2001
[5] Abu-Teir M, Sakran F, Golosovsky M, Local contactless measurement of the ordinary and
extraordinary Hall effect using near-field microwave microscopy APPL PHYS LETT 80 (10): 17761778 MAR 11 2002
[6] Sakran F, Copty A, Golosovsky M, Electron spin resonance microscopic surface imaging using
a microwave scanning probe APPL PHYS LETT 82 (9): 1479-1481 MAR 3 2003