Hafnium Films and Magnetic Shielding for TIME, A mm-Wavelength Spectrometer Array
Abstract
TIME is a mm-wavelength grating spectrometer array that will map fluctuations of the 157.7-μ m emission line of singly ionized carbon ([CII]) during the epoch of reionization (redshift z ∼ 5-9). Sixty transition-edge sensor (TES) bolometers populate the output arc of each of the 32 spectrometers, for a total of 1920 detectors. Each bolometer consists of gold absorber on a ∼ 3 × 3 mm silicon nitride micro-mesh suspended near the corners by 1 × 1 × 500 μ m silicon nitride legs targeting a photon-noise-dominated NEP ∼ 1 × 10^{-17} W/√{Hz}. Hafnium films are explored as a lower-T_c alternative to Ti (500 mK) for TIME TESs, allowing thicker support legs for improved yield. Hf T_c is shown to vary between 250 and 450 mK when varying the resident Ar pressure during deposition. Magnetic shielding designs and simulations are presented for the TIME first-stage SQUIDs. Total axial field suppression is predicted to be 5 × 10^7.
- Publication:
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Journal of Low Temperature Physics
- Pub Date:
- December 2018
- DOI:
- 10.1007/s10909-018-1906-3
- Bibcode:
- 2018JLTP..193..893H
- Keywords:
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- Spectrometers;
- Bolometers;
- Transition-edge sensors;
- Hafnium;
- Magnetic shielding