1. To: Helen Halaris
Program Coordinator
Massachusetts Space Grant Consortium of
National Aeronautics and Space Administration (NASA)
Massachusetts Institute of Technology
Bldg. 33, Room 208
77 Massachusetts Avenue
Cambridge, MA 02139
FINAL REPORT: MASSACHUSETTS SPACE GRANT CONSORTIUM FELLOWSHIP
Student Name: Chak S. Chan
Home Institution: Holyoke Community College (HCC)
Host Institution: University of Massachusetts at Amherst (UMass)
Department: Electrical and Computer Enginering (ECE)/Terahertz Laboratory
ECE Faculty Sponsor: Professor K. Sigfrid Yngvesson
September 2006
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2. NASA’s Massachusetts Space Grant Consortium Fellowship
Research Experience at the Terahertz Laboratory
Chak S. Chan
Division of Science Engineering and Math, Holyoke Community College
Holyoke, MA 01040; cchan512@hccdl.org; chakchan@ecs.umass.edu
Introduction
This report is a summary of the activities undertaken at the Terahertz Laboratory of the
Electrical and Computer Engineering (ECE) Department, University of Massachusetts
(UMass) at Amherst. I provided assistance and received training about different aspects
related to the design of terahertz heterodyne receivers. My work focused on learning
about two types of detectors, such as Hot Electron Bolometric (HEB) Mixers and Single-
Walled Carbon Nanotubes (SWCNT). Hot Electron Bolometric technology has become
the best technological choice to detect terahertz radiation in a heterodyne fashion (i.e.
converting the signal of interest into a low-frequency signal that can be processed with
microwave electronics); the main advantages of this technology are low intrinsic noise
and low local oscillator (LO) power requirements [1]. On the other hand, SWCNTs have
showed potential for sensitive detection in the terahertz regime [2].
Design experience
• 2-element array and 3D receiver packaging
I was responsible for the computer assisted design of a 2 by 1 element array block for the
National Institute of Standards and Technology (NIST). This receiver block is the
housing of an array that is used for high spatial resolution imaging and spectroscopy
measurements at terahertz frequencies. My main assignment was to use Autodesk
Inventor to make a full three-dimensional computer model of the prototype. The “mixer
block” was an extension of a previous design implemented by personnel of the Terahertz
laboratory [3]. The final deliverables for this task were 3D and 2D sketches of the block,
which were ultimately sent to a machine shop for fabrication. The prototype array will be
populated and tested during the Fall term of 2006, and I will continue to assist in this
process. An illustration of the design is shown in Figure 1.
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3. Figure 1. Three dimensional view of the 2-element focal plane assembly. The block was designed to have
interchangeable face plates to support either 1-element or 2-element operation.
HEB chip
IF output
(GPPO connector) IF
feedthrough
Figure 2. Three dimensional view of the 3D packaging scheme for a heterodyne receiver based on HEB
mixers and MMIC IF amplifiers.
I also used Autodesk Inventor to design a mixer block for an integrated receiver using
vertical IF interconnects. I was able to fulfill the required specifications based on device
and connector dimensions. This 3D package will host a printed circuit board (PCB) for
surface mount devices (SMD), two microwave transmission lines (microstrips), one
Microwave Monolithic Integrated Circuit (MMIC), one feedthrough for the IF output,
and several spring-loaded pins for IF grounding. The HEB chip is located on the plane
below the MMIC chip (Figure 2) and it’s contacted via a gold-plated bellows contact
spring soldered to the tip of the IF feedthrough. This is the first time a HEB mixer will
be integrated with an IF amplifier (MMIC) using vertical interconnects for the IF output.
The prototype will be tested during the Fall 2006.
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4. • Filter design and testing for Allan Variance measurements
A figure of merit of the HEB IF power stability is the Allan Variance. This is a statistical
measure of the output power fluctuations in the HEB detector, which is useful to quantify
various types of noise and drift in a sensitive receiver. According to a widely used
equation called the “Radiometric Equation”, the Allan Variance should change with the
bandwidth over which the measurement is taken. In order to verify this fact, different
low pass filters (LPF) were designed and fabricated. Each filter was designed to have a
different cutoff frequency (the frequency at which the magnitude of scattering parameter
S21 has dropped by 3 decibels (dB) with respect to the low frequency value).
Figure 3a shows the layout of three different filters designed in microstrip technology for
different cutoff frequencies: 1 GHz, 2 GHz, and 5 GHz. In order to complete this design,
the first step was to perform hand calculations from the equations given in the classic
textbook by Pozar [5]. Later, I used the CAD tool Microwave Office to simulate the
specific geometry and verify that the design would perform according to specifications. I
then exported the file to AutoCAD for further processing. A PCB milling machine was
used to fabricate the filters on Duroid (Teflon). A photograph showing the different
fabricated filters is presented in Figure 3b.
+
(a)
1 GHz
2 GHz
5 GHz
(b)
Figure 3. Filters for Allan Variance measurements: (a) AutoCAD’s layout; (b) photographs. The frequency
to the left of each filter denotes its cut-off frequency.
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5. • Design of a Bias Tee Circuit and Amplifier Input Matching Network Circuit
I designed a “bias tee” circuit, which is intended to bias the HEB device with the
appropriate voltages and currents, without affecting its performance at the IF frequency
band of interest. The Bias Tee is to allow DC current to flow into the Mixer and to
prevent AC current (higher frequency) from causing interference. On the other hand, the
Matching Network allows transforming of impedance from the HEB (on the right side),
before the power passes onto MMIC IF amplifier. The layout of these circuits is shown in
Figure 4.
Figure 4. “Bias tee” and amplifier matching network.
General HEB experiment’s assistance
• Cryogenics
I gained significant experience as to the operation and general use of a cryogenic
refrigerator (also called Dewar, after the person who invented this type of cryogenic
vessel). I learned how to properly cool this apparatus and the safety measures for the
proper handling of cryogenic liquids (Nitrogen and Helium) required to bring its inside
temperature down to 4K. This cryostat was used to enable our superconducting samples
to be cooled in order to perform “noise temperature” measurements. The noise
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6. temperature is a way to quantify the sensitivity of these superconducting mixers. Figure 5
shows the laboratory setup used for performing these measurements
Figure 5: Laboratory setup for measuring HEB noise temperature.
Figure 6. Performing a LN2 pre-cooling operation.
• Microscope operation
I practiced soldering MMIC circuits and resistors (size 2x1 mm or less) assisted by a high
magnification optical microscope. I also soldered SMA launchers for the filters
fabricated (as described earlier) before testing them on a vector network analyzer.
• Far Infrared (FIR) laser operation
With guidance from the graduate students, I was able to understand the basic operation of
a CO2 laser pumped FIR laser and other optical components used for device HEB
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7. characterization. The laser works as the local oscillator (LO) source for the
superconducting mixers. The laser can be tuned to a different frequency (line) by
changing the gas in the FIR tube. After finishing tuning the CO2 laser to our targeted
wavelength (line), I was able to confidently change to a different laser line in order to
obtain CW radiation at the different wavelengths. My part of the research required
caution and precision.
Figure 7. FIR Laser system.
• Basic assistance on Carbon Nanotube Technology (CNT) experiment
In the Terahertz Lab at UMass, we are not only conducting research at the terahertz
frequency region using HEB/MMIC but also SWNTs. The testing procedure is
somewhat similar to HEB/MMIC, except that so far it has been done for much lower
frequencies (up to 5 GHz). I assisted setting up the experimental apparatus for measuring
the direct detection response of several nano-tube samples fabricated on-site. As a result
of my involvement in CNT’s experiments, I was made a co-author of a research poster. I
also participated in the presentation of our poster at the Center for Hierarchical
Manufacturing (CHM) for the Fall 2006 first annual meeting. CHM Meeting and the
Semiconductor Research Corporation Nanomaufacturing Review are organized by the
new Nanotechnology Center at UMass Amherst, National Science Foundation (NSF) [2].
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8. Conclusion
With this superior opportunity, I was able to learn, work, and participate in the research
conducted at the Terahertz Laboratory of UMass Amherst. Through continuing
instruction, I learned the usage of several computer assisted design (CAD) tools such as
Autodesk Inventor and AutoCAD, MatLab, Mathematica, and Microwave Office.
Under specific guidelines and specifications, I designed a compact block to house a 2 x 1
element array using an as well as a HEB down-converter with vertical IF interconnects
(3D packaging technology). I got exposure to the operation of a CO2 laser pumped FIR
LASER system. I am able to operate the FIR laser system, including the change of the
laser wavelength (line).
I was able to learn the basic use of general microwave laboratory equipment such as
power meters, network analyzers, dc-supplies, etc. I learned about cryogenic testing of
superconducting devices, including the proper handling of cryogenic liquids used for
cooling a laboratory-grade cryostat (cooling refrigerator for micro- and nano-devices).
My summer at the Terahertz Lab of UMass Amherst was a unique life experience. At the
beginning of my fellowship’s journey, I entered the lab as a child who fell into the
unpredictably magical world of engineering; by the end of my fellowship’s period,
although I still have many unsolved questions, I do have clearer and broader perspectives
of what engineering and research are like. Moreover, I realize an important relationship
between engineering and scientific discoveries; after this residential summer research, I
feel even more motivated to pursue engineering and/or a scientific career in the future.
Acknowledgements
The National Aeronautics and Space Administration (NASA)’s Massachusetts Space
Grant Consortium Fellowship 2006 supported this learning experience. It was through
this fellowship that I had chance to learn about aerospace-related technology.
I am truly grateful to Professor K. S. Yngvesson, who was my sponsor in the Terahertz
Laboratory of UMass Amherst. Without his permission and guidance, I would not have
been able to receive valuable knowledge of microwave engineering and terahertz
technology. I thank him for his support and tremendous help.
I appreciate the opportunity to have met my instructor F. Rodriguez-Morales, who not
only introduced me into the Terahertz Laboratory, but also provided me with constant
lectures, trainings, advice, and supervision through this advanced learning experience.
I would like to thank Professor M. Dolan at Department of Geoscience in UMass
Amherst, who brought the NASA’s Space Grant Consortium Fellowship information to
me. Especially, I would like to thank Professor S. Dolan at HCC, who is an advisor of
the International Student Organization (ISO) and encouraged me to apply for this
fellowship.
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9. Lastly, I thank all the graduate students and the THz Lab’s research engineer, who taught
and helped me, and for creating a great friendly atmosphere.
References
[1] K. Yngvesson, C. Musante, M. Ji, F. Rodriguez, Y. Zhuang, E. Gerecht, M.
Coulombe, Dickinson, T. Goyette, J. Waldman, C. K. Walker, A. Stark, and A. Lane.
Terahertz Receiver with NbN HEB Device (Trend) – A Low-Noise Receiver User
Instrument for AST/RO at the South Pole. In Proceeding: 12th
International Symposium
on Space Terahertz Technology, San Diego CA, Feb 2001.
[2] Application of Metallic Carbon Nanotube as Detectors for Microwave and Terahertz
Radiation. Fernando Rodriguez-Morales, Richard Zannoni, J. Nicholson, M. Fischetti,
Kan Fu, Alexander de Geofroy, Chak Chan, Stephan Adams, and Sigfrid Yngvesson.
Poster presented at the first annual meeting of the Center for Hierarchical Manufacturing,
University of Massachusetts, Amherst, Sep 2006.
[3] ] F. Rodriguez-Morales, S. Yngvesson, R. Zannoni, E. Gerecht, D.Gu, N. Wadefalk, and
J.Nicholson, Development of Integrated HEB/MMIC Receivers for Near-Range Terahertz
Imaging. IEEE Trans. Microw. Theory Tech. Vol. 54, No. 6, Jun. 2006, pp. 2301- 2311.
[4] F. Rodriguez-Morales. Impedance and Bandwidth Characterization of NbN Hot
Electron Bolometric Mixers. Master’s thesis, University of Massachusetts Amherst,
USA, 2003.
[5] D. Pozar. Microwave Engineering (second edition). John Wiley & Sons Inc. 1998.
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