The Simons Observatory is building both large (6 m) and small (0.5 m) aperture telescopes in the Atacama desert in Chile to observe the cosmic microwave background (CMB) radiation with unprecedented sensitivity. Simons Observatory telescopes in total will use over 60,000 transition edge sensor (TES) detectors spanning center frequencies between 27 and 285 GHz and operating near 100 mK. TES devices have been fabricated for the Simons Observatory by NIST, Berkeley, and HYPRES/SeeQC corporation. Iterations of these devices have been tested cryogenically in order to inform the fabrication of further devices, which will culminate in the final TES designs to be deployed in the field. The detailed design specifications have been independently iterated at each fabrication facility for particular detector frequencies.We present test results for prototype devices, with emphasis on NIST high frequency detectors. A dilution refrigerator was used to achieve the required temperatures. Measurements were made both with 4-lead resistance measurements and with a time domain Superconducting Quantum Interference Device (SQUID) multiplexer system. The SQUID readout measurements include analysis of current vs voltage (IV) curves at various temperatures, square wave bias step measurements, and detector noise measurements. Normal resistance, superconducting critical temperature, saturation power, thermal and natural time constants, and thermal properties of the devices are extracted from these measurements.

We report on the development of commercially fabricated multi-chroic antenna coupled Transition Edge Sensor (TES) bolometer arrays for Cosmic Microwave Background (CMB) polarimetry experiments. The orders of magnitude increase in detector count for next-generation CMB experiments requires a new approach in detector wafer production to increase fabrication throughput.We describe collaborative efforts with a commercial superconductor electronics fabrication facility (SeeQC, Inc.) to fabricate antenna coupled TES bolometer detectors. We have successfully fabricated an operational dual-polarization, dichroic sinuous antenna-coupled TES detector array on a 150 mm diameter wafer. The fabricated detector arrays have average yield of 95% and excellent uniformity across the wafer. Both RF characteristics and TES bolometer properties are suitable for CMB observations. We successfully fabricated different types of TES bolometers optimized for frequencymultiplexing readout, time-domain multiplexing readout, and microwave SQUID multiplexing readout. We also demonstrated high production throughput. We discuss the motivation, design considerations, fabrication processes, test results, and how industrial detector fabrication could be a path to fabricate hundreds of detector wafers for future CMB polarimetry experiments.

We implemented, optimized, and fully tested a superconducting Josephson junction fabrication process over multiple runs tailored for integrated digital circuits that are used for control and readout of superconducting qubits operating at millikelvin temperatures. This process was optimized for highly energy efficient rapid single flux quantum (ERSFQ) circuits with critical currents reduced by a factor of ∼10 as compared to those operated at 4.2 K. Specifically, it implemented Josephson junctions with 10 μA unit critical current fabricated with 10 μA/μm2 critical current density. In order to circumvent the substantial size increase in the SFQ circuit inductors, we employed an NbN high kinetic inductance layer with 8.5 pH/sq sheet inductance. Similarly, to maintain the small size of junction resistive shunts, we used a non-superconducting PdAu alloy with 4.0 Ω/sq sheet resistance. For integration with quantum circuits in a multi-chip module, 5 and 10 μm height bump processes were also optimized. To keep the fabrication process in check, we developed and thoroughly tested a comprehensive process control monitor chip set.

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