Electrical and optical properties of a bolometer with a suspended absorber and tunneling-current thermometers

Abstract

We have developed a bolometer with a suspended normal-metal absorber connected to superconducting leads via tunneling barriers. Such an absorber has reduced heat losses to the substrate, which greatly increases the responsivity of the bolometer to over 109 V/W at 75 mK when measured by dc Joule heating of the absorber. For high-frequency experiments, the bolometers have been integrated in planar twin-slot and log-periodic antennas. At 300 GHz and 100 mK, the bolometer demonstrates the voltage and current response of 3 × 108 V/W and 1.1 × 104 A/W, respectively, corresponding to the quantum efficiency of ∼15 electrons per photon. An effective thermalization of electrons in the absorber favors the high quantum efficiency. We also report on how the in-plane- and transverse magnetic fields influence the device characteristics.