On the concept of an optimal hot-electron bolometer with NIS tunnel junctions

Abstract

Optimization of the hot-electron bolometer with a normal metal–insulator–superconductor (NIS) tunnel junction as a temperature sensor has been done theoretically. The responsivity and the noise equivalent power (NEP) of the bolometer are obtained numerically for typical experimental parameters. We demonstrate that electron cooling by the NIS junction, which serves as a thermometer, can improve the sensitivity of the device. This effect is especially useful in the presence of a finite power load. Optimization of the hot-electron bolometer in the presence of a finite power load is discussed. It has been shown that the optimal regime can be realized when thermal conductance through the tunnel junctions is larger than the electron–phonon conductance. The electron–phonon noise is negligible and the NEP is determined mainly by the noise of the NIS junctions because of practically full transference of power of the incoming signal to a readout amplifier through the junctions.