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Characterization and Improvement of the Thermal Stability of TES Bolometers


Sonka, Rita Frances (2018) Characterization and Improvement of the Thermal Stability of TES Bolometers. Senior thesis (Major), California Institute of Technology. doi:10.7907/4v3d-7k67.


The successful detection and characterization of the B-modes in the Cosmic Microwave Background (CMB) would dramatically illuminate the physics of the inflationary era. The Observational Cosmology Group is iterating on bolometers in an attempt to detect this signal. The previous detector design became unstable in parts of its transition when adjusted for 220/270 GHz frequencies, limiting its use.

We study the mechanism of instability in these transition edge sensor (TES) bolometers used for ground based observations of the Cosmic Microwave Background (CMB) at 270GHz. The instability limits the range of useful operating resistances of the TES down to ≈50% of the TES normal resistance (R_n), and due to variations in detector properties and optical loading within a column of multiplexed detectors, limits the effective on sky yield to ≈67 %.

Through comparison of 7 new detector thermal capacity designs and measurements of the electrical impedance of the detectors, we show the instability is due to the increased bolometer leg G for higher-frequency detection inducing decoupling of the palladium-gold heat capacity from the thermistor. We demonstrate experimentally that the limiting thermal resistance is due to the small cross sectional area of the silicon nitride bolometer island, and so is easily fixed by layering palladium-gold over an oxide protected TES. The resulting detectors can be biased down to a resistance ≈10% of Rn, improving the effective on-sky yield to ≈93%.

We also investigate a possibly related, unexpected slope in the Aluminum calibration TES transition and determine that it is not due to phase separation, even accounting for the science TES thermal instability.

Item Type:Thesis (Senior thesis (Major))
Subject Keywords:TES; Transition Edge Sensor; CMB; Cosmic Microwave Background; B modes; Thermal Stability; IV curve; PR curve;
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Minor Option:Computer Science
Awards:D.S. Kothari Prize in Physics, 2018
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Bock, James J. (advisor)
  • Steinbach, Bryan A. (advisor)
Group:Astronomy Department
Thesis Committee:
  • Stone, Edward C. (chair)
  • Libbrecht, Kenneth George
  • Frautschi, Steven C.
  • Politzer, Hugh David
  • Refael, Gil
Defense Date:22 May 2018
Funding AgencyGrant Number
Record Number:CaltechTHESIS:07182018-144446266
Persistent URL:
Related URLs:
URLURL TypeDescription in-development paper on part of the thesis work.
Sonka, Rita Frances0000-0002-1187-9781
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11125
Deposited By: Rita Sonka
Deposited On:18 Jul 2018 22:55
Last Modified:10 Mar 2020 18:42

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