The Simons Observatory: Production-level Fabrication of the Mid- and Ultra-High-Frequency Wafers

TL;DR

The paper reports on the development of a reliable, production-level fabrication process for the mid- and ultra-high-frequency detector wafers used in the Simons Observatory's cosmic microwave background instrumentation, achieving high yield and timely delivery.

Contribution

It introduces a comprehensive fabrication framework for SO detector arrays, including process monitoring and metrology, enabling scalable production of high-performance wafers.

Findings

Nearly 100 superconducting focal plane components delivered

88% of detector wafers met integration criteria

Channel yield exceeded 95%

Abstract

The Simons Observatory (SO) is a cosmic microwave background instrumentation suite in the Atacama Desert of Chile. More than 65,000 polarization-sensitive transition-edge sensor (TES) bolometers will be fielded in the frequency range spanning 27 to 280 GHz, with three separate dichroic designs. The mid-frequency 90/150 GHz and ultra-high-frequency 220/280 GHz detector arrays, fabricated at NIST, account for 39 of 49 total detector modules and implement the feedhorn-fed orthomode transducer (OMT)-coupled TES bolometer architecture. A robust production-level fabrication framework for these detector arrays and the monolithic DC/RF routing wafers has been developed, which includes single device prototyping, process monitoring techniques, in-process metrology, and cryogenic measurements of critical film properties. Application of this framework has resulted in timely delivery of nearly 100 total superconducting focal plane components to SO with 88% of detector wafers meeting nominal criteria for integration into a detector module: a channel yield > 95% and Tc in the targeted range.