Integrated Superconducting Transition-Edge-Sensor Energy Readout (ISTER)

We describe a million-pixel-scale multiplexed readout for superconducting Transition Edge Sensor (TES) microcalorimeters, using Rapid Single Flux Quantum (RSFQ) digital circuits. Depending on the application and the power dissipation requirements, the readout circuits may be either fabricated on the same wafer as the TES or integrated with the TES wafer using a multichip module, thereby integrating the TES and readout circuits. A data reduction scheme in the RSFQ circuits is described, using integrating counters to measure the TES pulse area. Power and clock requirements for measuring a large number of TES channels per readout line are discussed. Basic components of the ISTER readout circuit have been fabricated in the SFQ5ee process at MIT Lincoln Laboratory and operated at 4 K. The fabrication process has eight fully planarized Nb layers and one layer of Nb/Al-AlOx/Nb Josephson junctions with 100
$\mu$
A/
$\mu$
m
$^{2}$
critical current density. Simulations of a TES read out are performed to investigate possible limits on energy resolution using ISTER.