Citation
Wandui, Albert Kamau (2025) Thermal Kinetic Inductance Detectors (TKIDs) for Cosmic Microwave Background (CMB) Polarimetry. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/hw92-qd36. https://resolver.caltech.edu/CaltechTHESIS:05232024-191504825
Abstract
The modern era of precision cosmology has been driven by advances in detector technology and observing techniques. Observational cosmology is experiencing a rapid growth in detector numbers. New architectures are emerging for low-loading applications such as far-infrared spectroscopy, ultra-sensitive low-threshold sensors for particle astrophysics, and dark matter investigations. Current millimeter-wave observatories use kilo-pixel arrays of detectors to measure the polarization of the Cosmic Microwave Background (CMB). There is a strong push within the CMB community to deploy new experiments with hundreds of thousands of detectors to achieve novel scientific outcomes. However, for over a decade, CMB detectors have been limited by background noise, where fluctuations in the photon flux incident on the camera overshadow internal detector noise. As a result, improving instrument sensitivity now requires increasing the number of pixels. This focal plane size and detector density increase significantly complicates integration and readout. Thermal Kinetic Inductance Detectors (TKIDs) are an innovative solution for scaling up detector counts, offering high sensitivity and ease of multiplexing. TKIDs are narrow-bandwidth superconducting resonators that can be multiplexed and read out using a single transmission line via microwave frequency division multiplexing. In this thesis, I present the design, development, and laboratory characterization of a TKID polarimeter for CMB studies at 150 GHz with a 25% bandwidth. I provide a detailed physical model of TKID operation and readout, accurately predicting detector noise and responsivity. Three generations of prototype detectors were developed and tested, leading to the final tile design. The first generation demonstrated the feasibility of fabricating TKIDs with internal noise low enough for background-limited performance given the expected optical loading on our telescope. The second generation validated the scalability of the initial design to larger arrays and was crucial for refining fabrication processes, cosmic ray susceptibility testing, and readout development. The third generation integrated the tested detector design with a polarization-sensitive planar phased-array antenna. This required precise fabrication of sub-micron microstrip lines and an in-depth understanding of both the antenna and detector fabrication processes. We show that antenna-coupled TKIDs achieve end-to-end optical efficiency comparable to existing Transition Edge Sensor (TES) detectors and exhibit smooth Gaussian antenna beams matching the design spectral response. Our efforts culminate in the design of a 64-pixel dual-polarization TKID array, intended for CMB observations in a telescope observing from the South Pole. This camera will be the first demonstration of TKIDs in the millimeter-wave regime, advancing the technology for future cosmological and astrophysical applications. I present results from in-lab dark and optical testing of the TKID focal plane, along with design methodologies, electromagnetic simulations, and fabrication procedures for achieving high-yield, uniform TKID arrays.
| Item Type: | Thesis (Dissertation (Ph.D.)) | |||||||||||||||
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| Subject Keywords: | superconducting detectors, CMB, polarimetry, TKIDs, Kinetic Inductance Detectors, bolometers, | |||||||||||||||
| Degree Grantor: | California Institute of Technology | |||||||||||||||
| Division: | Physics, Mathematics and Astronomy | |||||||||||||||
| Major Option: | Physics | |||||||||||||||
| Thesis Availability: | Not set | |||||||||||||||
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| Defense Date: | 3 June 2024 | |||||||||||||||
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| Record Number: | CaltechTHESIS:05232024-191504825 | |||||||||||||||
| Persistent URL: | https://resolver.caltech.edu/CaltechTHESIS:05232024-191504825 | |||||||||||||||
| DOI: | 10.7907/hw92-qd36 | |||||||||||||||
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| Default Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | |||||||||||||||
| ID Code: | 16419 | |||||||||||||||
| Collection: | CaltechTHESIS | |||||||||||||||
| Deposited By: | Albert Wandui | |||||||||||||||
| Deposited On: | 04 Sep 2024 16:30 | |||||||||||||||
| Last Modified: | 04 Sep 2024 16:30 |
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