Advances in the Fabrication of On-chip Superconducting Integral Field Units for CMB and Line-Intensity Astronomy

TL;DR

This paper presents new fabrication techniques for on-chip superconducting spectrometers, enabling larger, more efficient integral field units for detailed CMB and CIB studies, advancing observational capabilities.

Contribution

It introduces novel on-chip components and fabrication methods that improve polarization detection, reduce signal loss, and increase array yield for CMB and CIB spectroscopy.

Findings

Successful fabrication of a 14-spaxel integral field unit (IFU)

Enhanced polarization discrimination capabilities

Improved fabrication yield and reduced signal loss

Abstract

Studying the polarization and spectral distortion of the Cosmic Microwave Background (CMB) in tandem with intensity fluctuations of the Cosmic Infrared Background (CIB) allows us to verify our assumptions on cosmic inflation and investigate the dynamics and evolution of galaxy clusters in the last 10 billion years. Because of its broadband emission and being an all-sky extended source, observing the entire CMB in detail is a very time-consuming and expensive exercise. Fortunately, in the last few years, the on-chip superconducting spectrometer technology has moved out of the lab and into the telescope. With its compact size and background-limited sensitivity, this family of instruments is particularly well-suited for fast and large area observations in a relatively unexplored range of the electromagnetic spectrum. However, recent examples of this technology do not yet reach the requirements needed for large spectroscopic and polarimetric surveys of the CMB. We formulate several of these requirements and introduce novel on-chip components and fabrication techniques. We introduce a cross-over to enable distinguishing signal polarization, minimize signal loss by locally optimized lithography of a coplanar-waveguide (CPW), lower the spectral resolution of microstrip filters by deposition of a dielectric layer, and increase the yield of the spectrometer array by removing individual line shorts. These together have culminated in the successful fabrication of a fourteen-spaxel IFU.