A novel type of the zero-biased thermo-electric bolometer (TEB) is proposed. The bolometer is based on a Charge-to-Voltage Converter (CVC) with a Superconductor- Insulator-Normal (SIN) Tunnel Junction and a superconducting absorber. The absorption of photons in the absorber leads to excitation of quasiparticles with some fraction of charge imbalance, tunneling through the SIN junction and generation of voltage. The thermoelectric voltage is determined by accumulation of tunneling charge in an external capacitance. Conversion efficiency is very high and voltage values comparable with a superconducting gap are easily achieved. The zero-biased CVC-TEB can be effectively used for creation of an array of bolometers.
A novel type of the zero-biased thermo-electric bolometer (TEB) is proposed. The bolometer is based on a Charge-to-Voltage Converter (CVC) with a Superconductor- Insulator-Normal (SIN) Tunnel Junction and a superconducting absorber. The absorption of photons in the absorber leads to excitation of quasiparticles with some fraction of charge imbalance, tunneling through the SIN junction and generation of voltage. The thermoelectric voltage is determined by accumulation of tunneling charge in an external capacitance. Conversion efficiency is very high and voltage values comparable with a superconducting gap are easily achieved. The zero-biased CVC-TEB can be effectively used for creation of an array of bolometers.
A novel concept of the parallel/series array of Cold-Electron Bolometers (CEB) with Superconductor-Insulator-Normal (SIN) Tunnel Junctions has been proposed for matching with JFET readout. The current-biased CEBs are connected in series for DC and in parallel for HF signal. A signal is concentrated to the absorber through the capacitance of tunnel junctions and additional capacitance for coupling of superconducting islands. Due to dividing power between CEBs in the array and increasing responsivity, the noise matching could be effectively optimized and the photon Noise Equivalent Power could be easily achieved at 300 mK with a room temperature JFET readout.
We design a superconducting thermoelectric bolometer made of a Graphene-Insulator-Superconductor tunnel junction. Our detector has the advantage of being passive, as it directly transduces input power to a voltage without the need to modulate an external bias. We characterize the device via numerical simulation of the full nonlinear thermal dynamical model of the junction, considering heating of both sides of the junction. While estimating noise contributions, we found novel expressions due to the temperatures of both sides being different than the bath temperature. Numerical simulations show a Noise Equivalent Power NEP∼4×10−17W/Hz for an input power of ∼10−16W, a response time of τth∼200ns and an integration time to obtain a Signal-to-Noise Ratio SNR=1 of τSNR=1∼100μs for an input power ∼10−13W. Therefore, the device shows promise for large-array cosmological experiment applications, also considering its advantages for fabrication and heat budget.
A novel concept of the optimal Cold-Electron Bolometer (CEB) with a Superconductor-Insulator-Normal (SIN) Tunnel Junction and Andreev SN contact has been proposed. This concept has been developed to improve noise properties of the CEB by increasing current responsivity for SQUID readout (in voltage-biased mode) in comparison with classical CEB concept comprising two SIN tunnel junctions. In this configuration the power of incoming signal is not split between two series junctions and the current response of a single junction is twice larger in comparison with double junction structure. The signal is concentrated from antenna to an absorber through capacitance of the tunnel junction from one side and Andreev contact from another side. HF matching is realized by resistance of a normal metal absorber that is independent on tunnel junction parameters. The volume of a normal metal is partly squeezed due to proximity effect of a superconducting electrode from the Andreev contact that also increases efficiency of the electron cooling. The concept is based on direct electron cooling of the absorber by SIN tunnel junction that serves as negative electrothermal feedback for the signal. Noise properties are considerably improved by decreasing the electron temperature. Ultimate performance of the CEB is determined by optical load converted to shot noise of the signal readout. The goal is to achieve noise-equivalent power (NEP) of the CEB with standard SQUID readout less than photon noise. Ultimate NEP better than photon noise can be achieved practically in wide range of power loads from 0.1 fW (SPICA) to 30 pW (OLIMPO, CLOVER, PILOT). Applicability of the CEB to post-Herschel space missions looks very promising.
We introduce a zero-bias superconducting voltage amplifier that harvests energy from a thermal gradient by exploiting negative differential resistance (NDR) in an asymmetric tunnel junction. The device is based on an asymmetric superconductor-insulator-superconductor (SIS) junction with an energy-gap ratio of Δ1/Δ2=0.5, connected in series with a load resistor. Owing to the superconducting bipolar thermoelectric effect, the current-voltage characteristic of the junction exhibits a region of NDR, in which the net current flows opposite to the applied voltage. This mechanism enables voltage amplification in the absence of any external electrical bias, relying solely on the temperature difference between the electrodes (TH≃1 K, TB≃20 mK). Numerical simulations predict a voltage gain of 20 dB, a 1 dB compression point at an input amplitude of 2 μV, and a total harmonic distortion below −50 dB. The input-referred noise is approximately 1 nV/Hz, with an associated thermal load on the order of nanowatts. The frequency response is broadband from near DC, with a −3 dB cutoff around 180 MHz, set by the RC time constant of the junction. Using Al-, Al-Cu-, and AlOx-based technologies, the amplifier is compatible with conventional superconducting circuit fabrication processes. These findings demonstrate that thermoelectric superconducting junctions can deliver bias-free voltage amplification from near DC up to about 200 MHz, making them promising candidates for transition-edge sensor readout, quantum circuit instrumentation, and low-frequency cryogenic signal processing.
The Cold-Electron Bolometer (CEB) is an ultrasensitive device designed for the detection of cosmic microwave background radiation. The key to its sensitivity is the electron cooling of the absorber by the superconductor-insulator-normal metal (SIN) tunnel junction. At a voltage near and below the superconducting gap, the electrons in the absorber are cooled well below the phonon temperature of the normal metal. This translates to the enhanced sensitivity of the CEB. This thesis describes the work we have done on the optimization of electron cooling of the normal metal absorber, and our measurement of the sensitivity of the CEB. We have optimized the electron cooling of the absorber by SIN tunnel junctions. The best electron cooling was achieved when normal metal traps were added in proximity to the superconducting electrodes in addition to the advanced geometry of the superconducting electrodes. With these modifications, we have decreased the electron temperature by 198 mK. With just the advanced geometry, the electron temperature drop was 129 mK. With just a simple geometry, the drop in temperature was 56 mK.The noise equivalent power (NEP) of the CEB was also measured at 100 mK to be at the level of 10^-18 W/Hz^1/2 at 1 kHz. The NEP was obtained by measuring the noise of the CEB, and then dividing that by its power responsivity, dV/dP. The main limitation in our measurements was the noise component from the amplifier. Finally, we have made measurements on the temperature sensitivity of the SIN tunnel junctions. We have compared the sensitivity between single and ten SIN junctions in series and found that it increases proportionally to the number of junctions. The best temperature responsivity obtained for 10 junctions was approximately 15 μV/mK. Using such thermometer, we have been able to measure the temperature stability of the Oxford Instruments cryogenfree refrigerator to be plus/minus 250 μK for a period of 8 hours. The resolution of the thermometer was measured to be plus/minus100 μK, limited by the noise due to the amplifier. The current and future works are also discussed. These include: a CEB array designed to distribute the total power load, improving further the sensitivity; a one-thousand SIN tunnel junction series thermometer in order to realize and understand the fundamental limitation of such a device; a superconducting cold-electron bolometer (SCEB) for high background power loads; and different read-out systems including an on-chip quasiparticle amplifier (QPA).