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

TIME is a mm-wavelength grating spectrometer array that will map fluctuations of the 157.7-$\mu m$ emission line of singly ionized carbon ([CII]) during the epoch of reionization (redshift z$\sim$ 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 $\sim$ 3 $\times$ 3 mm silicon nitride micro-mesh suspended near the corners by 1 $\times$ 1 $\times$ 500 $\mu$m silicon nitride legs targeting a photon-noise-dominated NEP $\sim 1\times {10}^{-17}W/\sqrt{Hz}$. 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 $5\times {10}^7$.