Effects of mechanical tolerances on the Kinetic Inductance Detector (KID) arrays for the Terahertz Intensity Mapper

The Terahertz Intensity Mapper (TIM) aims to investigate the trends in star formation within dust-obscured, star-forming galaxies during the peak of cosmic star formation by measuring the redshifted 157.7 μm line of singly ionized carbon ([CII]). To perform this measurement, TIM utilizes two R ∼ 250 long-slit grating spectrometers that span the wavelength range of 240-420 μm. Each spectrometer is equipped with a focal plane unit housing four wafer-sized arrays (“quadrants”) of horn-coupled aluminum kinetic inductance detectors (KIDs). TIM’s hornblock design incorporates ∼ 80 bosses per quadrant, which serve as support beams to maintain a 50 μm distance between the hornblock and detector wafer to minimize optical cross-talk between detectors without jeopardizing their performance. However, the air gap created by these bosses introduces challenges that could be impacting the resonance frequencies of our KIDs. While initial designs aimed for a uniform 50-μm boss height, measurements revealed non-uniformity across quadrant-scale hornblocks. To understand the impact of the non-uniformity of the bosses on resonance frequencies, we compare variation in boss heights on two quadrant-scale hornblocks to the frequency shifts observed when measuring one TIM KID quadrant in either housing structure. We measure boss height variations across various housing structures, which determine the air gaps between the housing structures and detector quadrant. We find that while all structures are non-uniform in boss heights, the true hornblock demonstrates the least variation. We measure frequency scatter of one TIM detector quadrant when housed in the different structures, showing a fractional frequency scatter of ∼ 10^(−3). Furthermore, we show qualitative agreement between the variation in air gaps due to non-uniform boss heights measured on the housing structures and the frequency scatter of the quadrant.