A high-quality superconducting resonator with a microbridge of hafnium film for use in a circuit for readout a terahertz-band imaging array with frequency division multiplexing is demonstrated experimentally. The variability of the impedance of the bridge at a frequency of 1.5 GHz, which is a key factor in the control of the quality of the resonator, is studied. The bridge, having a thickness of about 50 nm, a critical temperature T _ C ≈ 380 mK, and a plan size of 2.5 × 2.5 μm, was connected as a load of a resonator made of niobium film with a thickness of about 100 nm ( T _ C ~ 9 K). It is shown that the bridge smoothly changes its impedance proportionally to the bias power in the entire temperature range. The effective thermal insulation of the bridge was measured in a dilution cryostat at temperatures of 50–300 mK. Thermal conductivity G of the bridge was calculated and found to be ~4 × 10^–13 W/K, which gives an estimate of the sensitivity of the structure in the bolometric mode NEP ≈ 8 × 10^–19 W/Hz^1/2 at a temperature of 150 mK.
The concept of an active superconducting terahertz detector for array applications is based on the combination of an RFTES bolometer and a microwave preamplifier based on a DC SQUID within the common integrated circuit providing the maximum, theoretically possible, signal transmission from the sensor to the amplifier. The problems associated with the design and positioning of the amplifier, that restrict the functionality and sensitivity of the ultra-low temperature detector, are considered. For the first time, a method for connecting a SQUID amplifier to an RFTES bolometer using the principle of partial loads of a resonator has been proposed and analyzed. The presented electromagnetic model of the active detector is suitable for optimization of RFTES, MKID and other detectors using high-Q superconducting planar resonators.
The device operates at temperatures <300 mK and comprises a hafnium microbridge and a superconducting aluminum tunnel junction both integrated into a common coplanar waveguide. The microbridge is a thermodynamic source and operates as an optical blackbody at frequencies 600–700 GHz. The coplanar terminal is the blackbody output in the 1–2 GHz frequency range. The microbridge temperature can be set in the range of 0.4–9 K and calibrated using the shot noise of the tunnel junction. Activation and temperature modulation of each of the sources can be performed independently using a direct current which transit them from the superconducting to the normal state with characteristic times <0.1 ms and heating power <1 μW.
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