A Resonant Cold-Electron Bolometer With a Kinetic Inductance Nanofilter

Abstract

A novel type of resonant cold-electron bolometer (RCEB) is proposed. In this sensor, the internal resonance is organized by the kinetic inductance of an ultrasmall NbN superconducting nanostrip and the capacitance of the nanoscale superconductor-insulator-normal (SIN) tunnel junction. The size of kinetic inductance is about 300 times smaller than the size of geometrical inductance of the same value. This reduction of size gives an opportunity to create nanofilters with a total size considerably smaller than the wavelength. This internal resonance acts as a bandpass filter (instead of external filters) with a bandwidth of 3%-50%, something needed for radioastronomy applications. The use of NbN as Andreev contact material against escaping hot quasiparticles provides a unique opportunity to create an optimal CEB with only one SIN junction and an Andreev SN contact for thermal protection, in contrast to a classical CEB with two SIN junctions. The problem of hot quasiparticles escaping over the Andreev barrier (Δ) for Al electrode is overcome here by creating a barrier higher than quantum energy Δ > hf to have working kinetic inductance. Replacing two SIN junctions by one junction, we could use this junction of half the area to keep the same capacitive coupling. Therefore, a single-junction RCEB would have four times less area of junctions (and volume of absorber) in comparison with a two-junction RCEB and should show better noise performance due to the proportionally decreased e-ph (electron-phonon) noise component. The RCEB can be effectively used to create multiband elements that are actual tasks in submillimeter astronomy due to the benefit that comes from its ability to use co-located data, and problems with the dramatic increase of the size of the focal plane.