Non-Thermal Absorption and Quantum Efficiency of SINIS Bolometer

Abstract

We study mechanisms of absorption in two essentially different types of superconductor-insulator-normal metalinsulator-superconductor (SINIS) bolometers with absorber directly placed on Si wafer and with absorber suspended above the substrate. The figure of merit for quantum photon absorption is quantum efficiency equal to the number of detected electrons for one photon. The efficiency of absorption is dramatically dependent on phonon losses to substrate and electrodes, and electron energy losses to electrodes through tunnel junctions. The maximum quantum efficiency can approach n=hf/kT=160 at f=350 GHz T=0.1 K, and current responsivity dI/dP=e/kT in quantum gain bolometer case, contrary to photon counter mode with quantum efficiency of n=1 and responsivity dI/dP=e/hf. In experiments, we approach intrinsic quantum efficiency up to n=80 electrons per photon in bolometer with suspended absorber, contrary to quantum efficiency of about one for absorber on the substrate. In the case of suspended Cu and Pd absorber, Kapitsa resistance protect from power leak to Al electrodes.

Arrays of Sub-Terahertz Cryogenic Metamaterial

“…KID sensors are more robust, but require rather complicated readout electronics. As reported in [4], the SINIS parameters of responsivity dV/dP ∼ = 10 9 V/W and NEP < 10 −16 W/Hz 1/2 can be improved by using microwave superconducting quantum interferometer (SQUID) readout electronics. Integrating SINIS detectors in a series or parallel matrices [5,6] improves the dynamic range and allows for their use in ground-based observatories with a background power load of tens of picowatts.…”

“…The most sensitive of these are superconducting detectors cooled down to sub-kelvin temperatures, which are the part of an integrated quasi-optical receiving system. The main competitors are transitionedge sensors (TESs) [1], kinetic inductance detectors (KIDs) [2,3], and superconductorinsulator-normal metal-insulator-superconductor (SINIS) detectors [4]. The main advantage of a TES is its high sensitivity, and the drawbacks are a narrow dynamic range, low speed, and a requirement of temperature stability.…”

Microwave SINIS Detectors

“…The development of quantum response theory [12] has made it possible to adequately describe processes at higher frequencies. A detailed experimental study of the transition from thermal absorption to quantum efficiency was carried out in [31] (schematic image of SINIS detector-see Figure 4). It was experimentally demonstrated that the thermal contact of the absorber and substrate could significantly reduce the responsivity.…”

“…The important conclusion drawn in [12,31] is that electron cooling does not lead to an increase in sensitivity. We analyzed the characteristic time constants of energy relaxation in different SINIS structures.…”

“…It was experimentally demonstrated that the thermal contact of the absorber and substrate could significantly reduce the responsivity. The important conclusion drawn in [12,31] is that electron cooling does not lead to an increase in sensitivity. We analyzed the characteristic time constants of energy relaxation in different SINIS structures.…”