Hafnium Films and Magnetic Shielding for TIME, A mm-Wavelength Spectrometer Array

• DOI: 10.1007/s10909-018-1906-3
• Publication Date: 2018-04-06T22:07:06Z
• Authors: J. Hunacek; J. Bock; C. M. Bradford; V. Butler; T.-C. Chang; Y.-T. Cheng; A. Cooray; A. Crites; C. Frez; S. Hailey-Dunsheath; B. Hoscheit; D. W. Kim; C.-T. Li; D. Marrone; L. Moncelsi; E. Shirokoff; B. Steinbach; G. Sun; I. Trumper; A. Turner; B. Uzgil; A. Weber; M. Zemcov
• Keywords: Transition edge sensor

TIME is a mm-wavelength grating spectrometer array that will map fluctuations of the 157.7-μm 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 μm 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.