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Design of Antenna-Coupled Lumped-Element Titanium Nitride KIDs for LongWavelength Multi-Band Continuum Imaging


Ji, Chenguang (2015) Design of Antenna-Coupled Lumped-Element Titanium Nitride KIDs for LongWavelength Multi-Band Continuum Imaging. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9W66HQ7.


Many applications in cosmology and astrophysics at millimeter wavelengths including CMB polarization, studies of galaxy clusters using the Sunyaev-Zeldovich effect (SZE), and studies of star formation at high redshift and in our local universe and our galaxy, require large-format arrays of millimeter-wave detectors. Feedhorn and phased-array antenna architectures for receiving mm-wave light present numerous advantages for control of systematics, for simultaneous coverage of both polarizations and/or multiple spectral bands, and for preserving the coherent nature of the incoming light. This enables the application of many traditional "RF" structures such as hybrids, switches, and lumped-element or microstrip band-defining filters.

Simultaneously, kinetic inductance detectors (KIDs) using high-resistivity materials like titanium nitride are an attractive sensor option for large-format arrays because they are highly multiplexable and because they can have sensitivities reaching the condition of background-limited detection. A KID is a LC resonator. Its inductance includes the geometric inductance and kinetic inductance of the inductor in the superconducting phase. A photon absorbed by the superconductor breaks a Cooper pair into normal-state electrons and perturbs its kinetic inductance, rendering it a detector of light. The responsivity of KID is given by the fractional frequency shift of the LC resonator per unit optical power.

However, coupling these types of optical reception elements to KIDs is a challenge because of the impedance mismatch between the microstrip transmission line exiting these architectures and the high resistivity of titanium nitride. Mitigating direct absorption of light through free space coupling to the inductor of KID is another challenge. We present a detailed titanium nitride KID design that addresses these challenges. The KID inductor is capacitively coupled to the microstrip in such a way as to form a lossy termination without creating an impedance mismatch. A parallel plate capacitor design mitigates direct absorption, uses hydrogenated amorphous silicon, and yields acceptable noise. We show that the optimized design can yield expected sensitivities very close to the fundamental limit for a long wavelength imager (LWCam) that covers six spectral bands from 90 to 400 GHz for SZE studies.

Excess phase (frequency) noise has been observed in KID and is very likely caused by two-level systems (TLS) in dielectric materials. The TLS hypothesis is supported by the measured dependence of the noise on resonator internal power and temperature. However, there is still a lack of a unified microscopic theory which can quantitatively model the properties of the TLS noise. In this thesis we derive the noise power spectral density due to the coupling of TLS with phonon bath based on an existing model and compare the theoretical predictions about power and temperature dependences with experimental data. We discuss the limitation of such a model and propose the direction for future study.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:sensors, low-temperature detectors, bolometers, submillimeter-wave and millimeter-wave receivers and detectors, kinetic inductance detectors, radio telescopes and instrumentation
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Golwala, Sunil
Group:Astronomy Department
Thesis Committee:
  • Golwala, Sunil (chair)
  • Goddard, William A., III
  • Johnson, William L.
  • Rutledge, David B.
  • Zmuidzinas, Jonas
Defense Date:18 May 2015
Non-Caltech Author Email:jcg051987 (AT)
Record Number:CaltechTHESIS:05282015-121920930
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8896
Deposited By: Chenguang Ji
Deposited On:28 May 2015 23:57
Last Modified:10 Mar 2020 19:19

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