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 ${\rm NEP}\sim 4\times 10^{-17}\,{\rm W}/\sqrt{\rm Hz}$ for an input power of $\sim10^{-16}\,{\rm W}$, a response time of $τ_{th}\sim 200\, {\rm ns}$ and an integration time to obtain a Signal-to-Noise Ratio ${\rm SNR}=1$ of $τ_{\rm SNR=1}\sim 100\,μ{\rm s}$ for an input power $\sim 10^{-13}\,{\rm W}$. Therefore, the device shows promise for large-array cosmological experiment applications, also considering its advantages for fabrication and heat budget.
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.
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.
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.
We fabricate graphene-TiOx-aluminum tunnel junctions and characterize their radio frequency response. Below the superconducting critical temperature of aluminum and when biased within the superconducting gap, the devices show enhanced dynamic resistance which increases with decreasing temperature. Application of radio frequency radiation affects the dynamic resistance through electronic heating. The relation between the electron temperature rise and the absorbed radiation power is measured, from which the bolometric parameters, including heat conductance, noise equivalent power, and responsivity, are characterized.
We propose a passive single-photon detector based on the bipolar thermoelectric effect occurring in tunnel junctions between two different superconductors thanks to spontaneous electron–hole symmetry breaking. Our superconducting thermoelectric detector (STED) converts a finite temperature difference caused by the absorption of a single photon into an open circuit thermovoltage. Designed with feasible parameters, our STED is able to reveal single photons of frequency ranging from ∼15 GHz to ∼150 PHz depending on the chosen design and materials. In particular, this detector is expected to show values of the signal-to-noise ratio SNR∼15 at ν = 50 GHz when operated at a temperature of 10 mK. Interestingly, this device can be viewed as a digital single-photon detector, since it generates an almost constant voltage VS for the full operation energies. Our STED can reveal single photons in a frequency range wider than four decades with the possibility to discern the energy of the incident photon by measuring the time persistence of the generated thermovoltage. Its broadband operation suggests that our STED could find practical applications in several fields of quantum science and technology, such as quantum computing, telecommunications, optoelectronics, THz spectroscopy, and astro-particle physics.
Three types of composite superconductive bolometers are described in which the temperature-sensitive element is a superconducting film at the transition temperature, a superconductor–normal metal–superconductor Josephson junction, or a superconductor–insulator–normal metal quasiparticle tunneling junction. The temperature-sensitive element is evaporated onto a sapphire substrate on the reverse side of which is a bismuth film to absorb the submillimeter radiation. The noise limitations of each type of bolometer are calculated. The fabrication and measured performance of the transition-edge bolometer and the Josephson-junction bolometer are described. The best electrical (noise-equivalent power) NEP obtained with a transition-edge bolometer fabricated on a 4×4×0.005-mm sapphire substrate is (1.7±0.1) ×10−15 W Hz−1/2 at 2 Hz at an operating temperature of 1.27 K. This NEP is within a factor of 2 of the thermal noise limit. The effective absorptivity of the bismuth film is measured to be 0.47±0.05, and the corresponding detectivity D* is calculated to be (1.1±0.1) ×1014 cm W−1 Hz1/2. Suggestions are made for further improvements in sensitivity.
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.