Superconducting Microwave Resonator Arrays for Submillimeter/Far-Infrared Imaging

189 Pages·2012·15.57 MB·English

Superconducting Microwave Resonator Arrays for
Submillimeter/Far-Infrared Imaging
Thesis by
Omid Noroozian
In Partial Fulfillment of the Requirements
for the Degree of
Doctor of Philosophy
California Institute of Technology
Pasadena, California
2012
(Defended April 18, 2012)
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(cid:13)c 2012
Omid Noroozian
All Rights Reserved
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Dedicated to my family
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Acknowledgments
It has been a truly wonderful experience to have worked at the submillimeter astron-
omy research group at Caltech. During the past 5.5 years I have been very fortunate
to learn from some of the best scientists and engineers in the field of superconducting
photon detectors. My journey has been one of both professional and personal en-
lightenment - one which has deepened my appreciation for the beauty of science and
the methodology that has been behind mankind’s greatest discoveries. This journey
wouldnothavebeenpossiblewithoutthesupport, guidance, andencouragementfrom
my advisor, Professor Jonas Zmuidzinas. I would like to express my deepest gratitude
for the opportunity he gave me to explore my curiosity with freedom, whatever or
wherever it was, his patience in teaching me the intricate details of scientific inquiry,
and for being a guide to both my professional and personal life. It has been a great
pleasure to work with him.
I have had the privilege to work with and learn from many colleagues whose
help and support have been paramount to the completion of this thesis. I would
especiallyliketothankDr. PeterDayforhelpingmewithmeasurements, forusinghis
laboratory at JPL, and for his guidance and creative insight. The beautiful devices in
thisworkwereallfabricatedbyDr. HenryLeducatJPLforwhichIamverythankful.
I would also like to extend my special thanks to Dr. Byeong Ho Eom for assisting me
with many experiments at JPL. To Professor Sunil Golwala, I would like to express
my gratitude for all his help with my thesis work and proposals, creative flashes of
ideas, and support for my professional development. A special thank you goes to Dr.
Jiansong Gao who has been a close colleague, a friend, and was a wonderful office
mate from whom I learned some of the most elaborate details of our work. I would
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also like to extend special thanks to Ran Duan for being a great companion and office
mate, and for being there whenever I needed help.
I am indebted to all my current and former colleagues at the submillimeter as-
tronomy group at Caltech, including Anastasios Vayonakis, Dr. David Moore, Nicole
Czakon, Dr. Matt Hollister, Dr. Tom Downs, Dr. Loren Swenson, Dr. Chris McKen-
ney, Professor Ben Mazin, Dr. James Schlaerth, Dr. Jack Sayers, Dr. Matthew
Sumner, Dr. Roger O’Brient, and Dr. Jacob Kooi, for their support, for their in-
sightful discussions, and for providing a stimulating and fun group environment.
I would like to express my gratitude to my former advisor at Delft University
of Technology in the Netherlands, Professor Teun Klapwijk, for introducing me to
the field of superconducting photon detectors, and for being a role model for many
aspects of my professional career.
Apart from academic life, my time in Pasadena and Los Angeles has been enriched
by many valuable friendships. I would especially like to thank Pedram Khalili for his
unconditional friendship and support. He has been like a brother to me. I am also
grateful to my friends Ali Ayazi, Shahin Ayazi, Mohsen Mollazadeh, Ali Sajjadi,
Sara Haghayegh, Lillian Zeinalzadegan, Niloufar Safaei Nili, Younes Nouri, Raquel
Monje, Aaron Noell, Tom Bell, Christos Santis, Kaveh Pahlevan, Pablo Henonin,
Matt Shaw, Nuria Llombart, Juan Bueno, Ali Vakili, Sormeh Shadbakht, and many
others for bringing fun and joy to my life. I have many wonderful memories from our
adventures and trips.
Most important of all, this thesis is dedicated to my family. I owe my deepest
gratitude to them. To my father, Ebrahim, who has been the source of my encour-
agement and inspiration for studying science as far back in time as I can remember;
to my mother, Truus, whose unconditional love, support, and encouragement for my
decisions gave me the strength and boldness to pursuit my ambitions in life; to my
brother, Arman, and his fianc´ee, Saman, whose support, encouragement, and humor
kept me going; to my dearest wife, Azadeh, for her love, support, encouragement,
and patience during the final stages of my thesis; and to my wife’s parents, Elaheh
and Farhad, for their understanding and support - thank you!
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Abstract
Superconductingmicrowaveresonatorshavethepotentialtorevolutionizesubmillime-
ter and far-infrared astronomy, and with it our understanding of the universe. The
field of low-temperature detector technology has reached a point where extremely
sensitive devices like transition-edge sensors are now capable of detecting radiation
limited by the background noise of the universe. However, the size of these detector
arrays are limited to only a few thousand pixels. This is because of the cost and
complexity of fabricating large-scale arrays of these detectors that can reach up to 10
lithographic levels on chip, and the complicated SQUID-based multiplexing circuitry
and wiring for readout of each detector. In order to make substantial progress, next-
generation ground-based telescopes such as CCAT or future space telescopes require
focalplaneswithlarge-scaledetectorarraysof104–106 pixels. Arraysusingmicrowave
kinetic inductance detectors (MKID) are a potential solution. These arrays can be
easily made with a single layer of superconducting metal film deposited on a silicon
substrate and pattered using conventional optical lithography. Furthermore, MKIDs
are inherently multiplexable in the frequency domain, allowing ∼ 103 detectors to be
read out using a single coaxial transmission line and cryogenic amplifier, drastically
reducing cost and complexity.
An MKID uses the change in the microwave surface impedance of a supercon-
ducting thin-film microresonator to detect photons. Absorption of photons in the
superconductor breaks Cooper pairs into quasiparticles, changing the complex sur-
face impedance, which results in a perturbation of resonator frequency and quality
factor. For excitation and readout, the resonator is weakly coupled to a transmission
line. The complex amplitude of a microwave probe signal tuned on-resonance and
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transmitted on the feedline past the resonator is perturbed as photons are absorbed
in the superconductor. The perturbation can be detected using a cryogenic amplifier
and subsequent homodyne mixing at room temperature. In an array of MKIDs, all
the resonators are coupled to a shared feedline and are tuned to slightly different fre-
quencies. They can be read out simultaneously using a comb of frequencies generated
and measured using digital techniques.
This thesis documents an effort to demonstrate the basic operation of ∼ 256 pixel
arrays of lumped-element MKIDs made from superconducting TiN on silicon. The
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resonators are designed and simulated for optimum operation. Various properties of
the resonators and arrays are measured and compared to theoretical expectations. A
particularly exciting observation is the extremely high quality factors (∼ 3×107) of
ourTiN resonatorswhichisessentialforultra-highsensitivity. Thearraysaretightly
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packed both in space and in frequency which is desirable for larger full-size arrays.
However, this can cause a serious problem in terms of microwave crosstalk between
neighboring pixels. We show that by properly designing the resonator geometry,
crosstalk can be eliminated; this is supported by our measurement results. We also
tackle the problem of excess frequency noise in MKIDs. Intrinsic noise in the form
of an excess resonance frequency jitter exists in planar superconducting resonators
that are made on dielectric substrates. We conclusively show that this noise is due
to fluctuations of the resonator capacitance. In turn, the capacitance fluctuations
are thought to be driven by two-level system (TLS) fluctuators in a thin layer on
the surface of the device. With a modified resonator design we demonstrate with
measurements that this noise can be substantially reduced. An optimized version of
this resonator was designed for the multiwavelength submillimeter kinetic inductance
camera (MUSIC) instrument for the Caltech Submillimeter Observatory.
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Contents
Acknowledgments iv
Abstract vi
1 Introduction 1
1.1 Scientific motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Submillimeter/far-IR astronomy . . . . . . . . . . . . . . . . . 1
1.1.2 Detector technology . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Microwave kinetic inductance detectors . . . . . . . . . . . . . . . . . 6
2 Principles of kinetic inductance detectors 9
2.1 Principle of detection . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.1 Surface impedance and complex conductivity of superconductors 9
2.1.2 Quasiparticle lifetime . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 Resonator circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3 Resonator response . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.4 Resonator sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4.1 Photon noise limited condition . . . . . . . . . . . . . . . . . . 26
3 Two-level system (TLS) noise reduction for MKIDs 28
3.1 Introduction to two-level systems . . . . . . . . . . . . . . . . . . . . 29
3.2 Resonator loss from TLS . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.3 Resonator frequency noise from TLS . . . . . . . . . . . . . . . . . . 33
3.4 A microwave resonator design for reduced TLS noise . . . . . . . . . 35
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3.4.1 Device details . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.4.2 Some design considerations . . . . . . . . . . . . . . . . . . . . 40
3.5 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.5.1 Low-temperature resonance frequencies and quality factors . . 41
3.5.2 Temperature sweep . . . . . . . . . . . . . . . . . . . . . . . . 43
3.5.3 Noise measurement technique and data analysis . . . . . . . . 48
3.5.4 Noise results and discussion . . . . . . . . . . . . . . . . . . . 50
3.5.5 Dark NEP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.6 IDC resonators for the multiwavelength submillimeter kinetic induc-
tance camera (MUSIC) . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.7 Chapter summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4 Submillimeter/far-infrared imaging arrays using TiN MKIDs 59
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4.1 MKID resonator types . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.2 Lumped-element kinetic inductance detectors . . . . . . . . . . . . . 65
4.2.1 Radiation coupling method . . . . . . . . . . . . . . . . . . . 65
4.2.2 Analytical approximations for capacitance and inductance . . 68
4.3 Approximate analytical design of a lumped-element resonator . . . . 70
4.3.1 Inductor meander . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.3.2 Interdigitated capacitor . . . . . . . . . . . . . . . . . . . . . . 72
4.3.3 Resonance frequency . . . . . . . . . . . . . . . . . . . . . . . 73
4.3.4 Coupling quality factor and feedline . . . . . . . . . . . . . . . 73
4.3.5 Electromagnetic simulations . . . . . . . . . . . . . . . . . . . 76
4.4 Resonator and array designs . . . . . . . . . . . . . . . . . . . . . . . 79
4.4.1 Design A (“meander”) . . . . . . . . . . . . . . . . . . . . . . 79
4.4.2 Design B (“spiral”) . . . . . . . . . . . . . . . . . . . . . . . . 82
4.4.3 Fabrication method . . . . . . . . . . . . . . . . . . . . . . . . 87
4.5 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.5.1 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.5.2 Design A measurements . . . . . . . . . . . . . . . . . . . . . 88
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4.5.2.1 Film T measurement . . . . . . . . . . . . . . . . . 88
c
4.5.2.2 Low-temperature resonance frequencies and quality
factors . . . . . . . . . . . . . . . . . . . . . . . . . . 88
4.5.2.3 Bath temperature sweep . . . . . . . . . . . . . . . . 89
4.5.2.4 Black-body response . . . . . . . . . . . . . . . . . . 93
4.5.3 Design B measurements . . . . . . . . . . . . . . . . . . . . . 94
4.5.3.1 Film T measurement . . . . . . . . . . . . . . . . . 94
c
4.5.3.2 Low-temperature resonance frequencies and quality
factors . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.5.3.3 Bath temperature sweep . . . . . . . . . . . . . . . . 96
4.5.3.4 Black-body response . . . . . . . . . . . . . . . . . . 96
4.6 Material-dependent sensitivity in MKIDs . . . . . . . . . . . . . . . . 104
4.6.1 TiN film fabrication . . . . . . . . . . . . . . . . . . . . . . . 105
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4.6.2 Film properties and advantages of TiN resonators . . . . . . 106
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4.7 Chapter summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
5 Crosstalk reduction for superconducting microwave resonator ar-
rays 111
5.1 Coupled resonators model . . . . . . . . . . . . . . . . . . . . . . . . 112
5.2 Calculation of coupling elements from δf . . . . . . . . . . . . . . 116
split
5.3 Simulation of coupled pixels . . . . . . . . . . . . . . . . . . . . . . . 119
5.4 Full array circuit model and simulation . . . . . . . . . . . . . . . . . 122
5.4.1 Array eigenfrequencies . . . . . . . . . . . . . . . . . . . . . . 124
5.4.2 Array eigenvectors . . . . . . . . . . . . . . . . . . . . . . . . 128
5.4.3 Array eigenfrequency quality factors . . . . . . . . . . . . . . 132
5.5 Pixel crosstalk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
5.5.1 Crosstalk simulation . . . . . . . . . . . . . . . . . . . . . . . 139
5.6 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
5.6.1 Measurement setup . . . . . . . . . . . . . . . . . . . . . . . . 143
5.6.2 Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143