Today, much hope rests on superconducting bolometers based on transition-edge sensing (TES) for radio-astronomy applications, as they can operate with noise equivalent power (NEP) below 10-19 W/Hz0.5. When TES acts as a thermometric device, there is an increase of the heated volume/mass over the volume/mass of the thermometer that is limiting sensitivity of the TES-based bolometric devices. In contrast, an antenna-coupled TES directly dissipates the time-dependent signal current from the feeding antenna. In doing so, it performs Joule heating within the tiny volume of its own electron gas.
A challenge still remains in creating a reliable readout for the imaging array. Although the frequency-division-multiplexing (FDM) method has been suggested, it suffers from the restricted instantaneous bandwidth of even the best SQUID-sensors. One alternative proposed is to replace the SQUID amplifiers with a semiconductor high-frequency cooled amplifier.
Inspired by the need to improve FDM in TES imaging arrays, this idea was turned into prototypes by the following: Artyom A. Kuzmin from the Moscow Institute of Physics and Technology; Sergey V. Shitov from the V.A. Kotel’nikov Institute of Radioengineering and Electronics; and Alexander Scheuring, Johannes M. Meckbach, Konstantin S. Il’in, Stefan Wuensch, Michael Siegel, and Alexey V. Ustinov from Germany’s Karlsruhe Institute of Technology. With their approach, one 10-GHz amplifier serves an array of more than 1000 detectors.
Essentially, they implement an antenna-coupled TES as a load for a high-Q resonator, which is weakly coupled to a transmission line. For a submicron-size TES absorber made of Ti, NEP as low as 2 x 10-19/Hz0.5 is estimated at an ambient temperature of 300 mK. That NEP is limited by the amplifier’s 3 K noise temperature. The team developed and tested prototype TES devices made of Niobium (Nb) beyond 4.5 K. NEP of roughly 1.5 x 10-15 W/Hz0.5 is estimated for these devices. See “TES Bolometers with High-Frequency Readout Circuit,” IEEE Transactions On Terahertz Science and Technology, Jan. 2013, p. 25.