Chin. Phys. B Vol. 24, No. 2 (2015) 028504
Mapping an on-chip terahertz antenna by a scanning
near-field probe and a fixed field-effect transistor
∗
L
¨
u Li(吕 利)
a)b)
, Sun Jian-Dong(孙建东)
a)†
, Roger A. Lewis
c)
, Sun Yun-Fei(孙云飞)
d)
,
Wu Dong-Min(吴东岷)
a)d)
, Cai Yong(蔡 勇)
a)
, and Qin Hua(秦 华)
a)‡
a)
Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123, China
b)
Graduate University of Chinese Academy of Sciences, Beijing 100049, China
c)
Institute for Superconducting and Electronic Materials and School of Physics, University of Wollongong, Wollongong, New South Wales 2522, Australia
d)
i-Lab, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123, China
(Received 16 August 2014; revised manuscript received 23 September 2014; published online 10 December 2014)
In the terahertz (THz) regime, the active region for a solid-state detector usually needs to be implemented accurately
in the near-field region of an on-chip antenna. Mapping of the near-field strength could allow for rapid verification and
optimization of new antenna/detector designs. Here, we report a proof-of-concept experiment in which the field mapping
is realized by a scanning metallic probe and a fixed AlGaN/GaN field-effect transistor. Experiment results agree well with
the electromagnetic-wave simulations. The results also suggest a field-effect THz detector combined with a probe tip could
serve as a high sensitivity THz near-field sensor.
Keywords: terahertz detector, terahertz antenna, near-field probe, high electron mobility transistor
PACS: 85.60.Gz, 72.80.Ey, 87.50.U–, 87.64.mt DOI: 10.1088/1674-1056/24/2/028504
1. Introduction
In the terahertz (THz, 1 THz = 10
12
Hz) portion of the
electromagnetic spectrum, many sensing applications, such as
security screening, near-field microscopy, and spectroscopy,
are being studied and developed.
[1]
Sensitive detectors are
one of the key elements for such applications.
[2]
In various
THz detectors, antennas are commonly applied to feed inci-
dent THz electromagnetic (EM) radiation into the active re-
gion of the detectors.
[3–9]
The efficiency of these antennas
is crucial for high sensitivity and is largely determined by
the near-field properties. The near-field distribution is usu-
ally obtained by performing a finite-element analysis of the
EM wave.
[10–13]
From the point of view of detector optimiza-
tion/development, it would be beneficial to experimentally ob-
tain the near-field distribution. In many THz near-field ex-
periments/applications, the near-field EM wave is transferred
by either a sharpened metallic probe tip or by a metallic pin-
hole aperture into the far field and detected therein.
[14–17]
In THz time-domain spectroscopy, a photoconductive detec-
tor has been integrated on a probe tip and serves as a direct
near field THz detector.
[18]
Here, we report our experiment on
imaging the near-field response of an antenna-coupled field-
effect-transistor (FET) THz detector by scanning the antennas
using a sharpened metallic tip. In the experiment, the scan-
ning metallic tip serves as a near-field coupler/agitator of the
antennas and the integrated FET detector reads out the THz
intensity. The experimental results are in good agreement
with a finite-difference time-domain (FDTD) simulation. This
method allows us to experimentally distinguish the most effec-
tive antenna blocks and provides direct guidance for the opti-
mization of antennas and detectors.
2. Experiment
The experimental setup is schematically shown in
Fig. 1(a), where the THz radiation from a backward wave os-
cillator (BWO) is collected, collimated, and focused by a pair
of off-axis parabolic mirrors (OAP#1 and OAP#2). The THz
frequency is set at f
0
= 875 GHz corresponding to a free-space
wavelength of λ
0
= 343 µm. The schematic zoom-in view of
the metallic probe scanning the detector surface is shown in
Fig. 1(b). The THz wave is polarized in direction x. The metal-
lic probe is glued on a piezoelectric vibrator which is driven by
a sinusoidal voltage with frequency 123 Hz and peak-to-peak
voltage 5 V. The probe tip vibrates in direction x and the vibra-
tion amplitude is δ x
p
≈ 1 µm. Accurate positioning and raster
scanning of the probe tip at a certain distance to the detector
surface are realized by mounting the piezoelectric vibrator on
a step-motorized XY Z stage. The probe is made of tungsten
and, as shown in Fig. 1(c), has a diameter of 500 µm. The
∗
Project partially supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX2-EW-705), China Postdoctoral
Science Foundation (Grant No. 2014M551678), Jiangsu Planned Projects for Postdoctoral Research Funds (Grant No. 1301054B), Instrument Developing
Project of the Chinese Academy of Sciences (Grant No. YZ201152), the National Natural Science Foundation of China (Grant No. 61271157), Suzhou Science
and Technology Project (Grant No. ZXG2012024), and the Chinese Academy of Sciences Visiting Professorship for Senior International Scientists (Grant
No. 2010T2J07).
†
Corresponding author. E-mail: dsun2008@sinano.ac.cn
‡
Corresponding author. E-mail: hqin2007@sinano.ac.cn
© 2015 Chinese Physical Society and IOP Publishing Ltd http://iopscience.iop.org/cpb http://cpb.iphy.ac.cn
028504-1