OMT-Coupled CMB Detector Development at Argonne

Future cosmic microwave background (CMB) experiments will deploy increasing numbers of superconducting detectors with requirements for increased sensitivity and reduced systematics. We report on the ongoing development of OMT-coupled CMB detectors at Argonne National Laboratory. Key areas of development include bolometers with dual Transition Edge Sensors (TES) for easier lab characterization, a hybrid SiN membrane fabrication process, a chemical vapor deposition (CVD) SiN dielectric process, and a new pixel design for improved compatibility with large scale fabrication. These developments enhance our ability to fabricate large-scale (150 mm diameter wafers) detector arrays with the performance necessary for future CMB experiments.

I. Introduction

The cosmic microwave background provides a unique window on the state of the universe 300 k years after the Big Bang. The CMB can be used to study a rich variety of fundamental questions about our universe including searching for the signature of inflation and determining the effective number of neutrinos [1]. It also provides a means of identifying galaxy clusters and studying large scale structure in the universe. In order to characterize the CMB, highly sensitive detectors are required to measure the small perturbations in CMB temperature and polarization over a range of frequencies (30 GHz to 300 GHz for ground-based experiments). Over the past several decades, the detectors used in CMB experiments have evolved in both sensitivity and scale, eventually reaching the point at which ground-based experiments are background limited, i.e. the dominant source of noise is from the photon background. Having reached these sensitivity levels, the path to further increasing experimental sensitivity is through increasing total detector counts and reducing experimental systematics.