Analysis of bolometer operation near the superconducting transition edge using microwave readout

The results of pioneering experiments on using a new method of microwave recording the bolometric response from a metal film near its superconducting transition edge are analyzed. Experiments are carried out at 4.5 K using a thin-film niobium absorber with a critical temperature of 6.7 K. The validity of the adopted electrodynamic model is confirmed. The chip contains a miniature antenna tuned to approximately 600 GHz and integrated into a planar resonator with a frequency of 6 GHz, which is weakly coupled with a pump line. Based on the experimental and model data, the presence of electrothermal feedback is shown, stability criteria are found, and I–V characteristics at microwaves are obtained. Bulk experimental samples with an absorber measuring 5 $\mu$m $\times$ 2.5 $\mu$m $\times$ 15 nm are fabricated with optical photolithography. At an amplifier channel noise of 3 K, the optical sensitivity of a prototype receiver can be expected at a level of 10–15 W/Hz$^{1/2}$.