Advancing Transition-Edge Sensor Bolometer Microfabrication Processes for Astronomical and Quantum Applications

Abstract: The transition-edge sensor (TES) bolometer has been established as an enabling technology for current generation astronomical instruments detecting ultra-low radiation signals across the electromagnetic spectrum. Arrays of TES bolometers have led to ground-breaking Cosmic Microwave Background (CMB) polarimetry experiments and potential future far-infrared (FIR) space science. Co-fabricating TESs with transmon qubits or tunnel junctions expands their utility into active energy removal and/or active cooling of quantum circuits.

For each of these application areas, this presentation will focus on microfabrication process advancements developed at the National Institute of Standards and Technology (NIST) to enhance sensor performance, scalability, and versatility. For large-scale CMB experiments, including for SPT-3G+, establishing a repeatable, high-yield process is critical to deliver the thousands of TES bolometers per array across dozens to hundreds of wafers. Process metrology, quality control throughout fabrication, and the use of witness wafers will be discussed. Future FIR space observatories have strict noise requirements (<1^e-19 W/rt-Hz). Controlling and understanding thin-film stress, material heat capacity, and plasma etch roughness is essential to realize ultralow-noise, direct-absorption TES bolometers with coherent 1D phonon-engineered low-thermal-conductance legs.

Finally, co-fabricating disparate devices on a shared substrate requires demonstrating that neither fabrication process degrades the performance of the other. Achieving this relies on systematically evaluating each fabrication step to confirm that TES integration introduces negligible microwave loss and preserves high qubit coherence. Together, these microfabrication advancements expand the capabilities and optimize the performance of TESs across both astronomy and quantum computing.