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-mm emission line of singly ionized carbon ([CII]) during the epoch of reionization (redshift z similar to 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 similar to 3 x 3 mm silicon nitride micro-mesh suspended near the corners by 1 x 1 x 500 mu m silicon nitride legs targeting a photon-noise-dominated NEP similar to 1 x 10-(17) W/root 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 x 10(7).