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Transition edge sensor (TES) is a sensitive low temperature photon detector and is a promising tool for chemical state analysis, astronomical X-ray observation and radioactive isotope analysis. It transforms photon energy into heat through an absorber. The resistance of a superconducting film changes dramatically with the temperature of the film at the superconducting transition edge, and thus by measuring the variation in the current flowing through the film, one can deduce precisely the energy of the incident photons. We developed a TES microcalorimeter using proximately coupled Mo and Au films. In this talk, I will present the fabrication process, the measurements of the electrothermal parameters and the noise characterizations of the micro-calorimeter. Using a 55Fe radioactive X-ray source, we characterized the detector responses to incident photons at various working points. The best instrumental energy resolution achieved was 4.13 eV @ 5.9 keV, which agrees well with the estimation from noise spectrum.
The readout of TES relies on low noise current amplifiers that should have low impedance, high bandwidth and can work under extremely low temperature. Superconducting quantum interference devices (SQUIDs) are the best-suited amplifiers for TES. We designed and fabricated various frontend SQUIDs and amp SQUID series array (SSA). We achieved a noise floor better than 10 pA/Hz1/2. In addition, many applications require TES array with a large number of pixels. To reduce the thermal loads brought by cables connecting room temperature electronics and low temperature detectors/amplifiers, a multiplexed readout technique is needed. We are developing a time-division multiplexed (TDM) readout system for TES array. The proto-type system uses a single-stage SQUID readout scheme. The basic multiplexing unit is composed of a SSA amplifier in parallel with a SQUID-based superconducting/normal switch. I will present the architecture of our TDM system and also some preliminary characterizations of the SSA amplifier and the switch.
Bo Gao received his bachelor degree in physics from Fudan University in 1999. He received engineer diploma from Ecole Polytechnique (Palaiseau) in 2002. He entered the joint Ph.D program of Ecole Normale Superieure (Paris)/University Paris VI, and received his Ph.D degree in 2006. He conducted postdoctoral research in Delft University of Technology and Max-Planck institute for solid state research over the following years. His main research interest was electron transport in low dimensional materials, such as carbon nanotubes, organic molecules and topological insulators. In 2012, He joined Shanghai institute of microsystem and information technology, Chinese Academy of Sciences. In 2015, he changed his research direction to superconducting electronics and worked in Stanford University as a visiting scholar from 2015 to 2016. He focuses on the development of transition edge sensor micro-calorimeter and SQUIDbased readout techniques for low temperature detectors.