This group of researchers found ways to compensate for the combined heating effect arising from the fact that the thermal relaxation time of the TES film is much longer than the period of the RF current.
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.