A Superconducting - Normal metal - Superconducting junction (SNS junction) may exhibit a Low Voltage Negative Differential Resistance (LVNDR) effect over part of its Current Voltage Characteristic (CVC). As the LVNDR effect is stable against a bias voltage at this CVC range, it should be possible to combine a SNS junction with conventional electronic circuits to obtain electronic devices such as mixers, amplifiers and oscillators. Making use of this remarkable effect, we show tliat an amplifier may be feasible by assembling a simple voltage divider made up of a SNS junction in series witli a resistor. The amplifier circuit includes an adjustable DC voltage supply (the bias voltage) and an AC signal source with a given voltage. The SNS junction is connected in series with a resistor R. Choosing values of the load resistance R approximately equal to the module of the negative differential resistance (dV/dI), at the bias voltage, we may obtain large gains in this amplifier device. In order to get an oscillator, the SNS junction should be connected to a RLC tank circuit with a bias voltage adjusted in the range of the LVNDR region of its CVC. A power output of the order of one microwatt may be easily obtained.
A Superconducting - Normal metal - Superconducting junction (SNS junction) may exhibit a Low Voltage Negative Differential Resistance (LVNDR) effect over part of its Current Voltage Characteristic (CVC). As the LVNDR effect is stable against a bias voltage at this CVC range, it should be possible to combine a SNS junction with conventional electronic circuits to obtain electronic devices such as mixers, amplifiers and oscillators. Making use of this remarkable effect, we show tliat an amplifier may be feasible by assembling a simple voltage divider made up of a SNS junction in series witli a resistor. The amplifier circuit includes an adjustable DC voltage supply (the bias voltage) and an AC signal source with a given voltage. The SNS junction is connected in series with a resistor R. Choosing values of the load resistance R approximately equal to the module of the negative differential resistance (dV/dI), at the bias voltage, we may obtain large gains in this amplifier device. In order to get an oscillator, the SNS junction should be connected to a RLC tank circuit with a bias voltage adjusted in the range of the LVNDR region of its CVC. A power output of the order of one microwatt may be easily obtained.
We report signal amplification and harmonic multiplication processes based on the nonlinear current-voltage characteristics (CVC) displayed by superconductor-normal metal-superconductor (SNS) junctions. Such junctions may exhibit a negative differential resistance at low voltages, the so called low-voltage-negative-differential-resistance (LVNDR) effect. This effect is due to the quantum mechanical multiple Andreev reflection mechanism in very clean systems and is stable against a bias voltage. Therefore, it is in principle possible to use these junctions as an active element in a variety of circuit applications such as oscillators, amplifiers or mixers, in the microwave and millimeter-wave range.
The current carried by the bound quasi-particles in the N region of a mesoscopic SNS junction has dc and cosine components. The dc current component is carried by the pair charge (-2e) transferred by a couple of Andreev reflections at both of the NS interfaces. The pair-charge transfers decrease due to reduction of the allowed number, 2/spl Delta//V, of Andreev reflections when the voltage, V, increases. Therefore, the low-voltage negative-differential-resistance is observed on the I-V curves of mesoscopic SNS junction, when the junction is driven by the low impedance voltage-bias source. The supercurrent carried by the quasi-particle in the N-region is sensitive to the external high-frequency fields. In a mixer experiment using the nano-meter SNS junctions of NbN, prominent IF signal peaks are observed at low bias voltage. Each IF signal peak corresponds to the negative differential resistance region at low bias voltage.
We propose new designs for millimeter-wave heterodyne detectors using the negative differential resistance of SNS junctions. The SNS junction may be used as the local oscillator in conventional receivers or a single SNS junction may be simultaneously used as the local oscillator and as the mixer itself, taking advantage of the nonlinearity of the current-voltage characteristic (CVC) of the junction. We calculate CVC curves for high-Tc SNS junctions (YBCO-SNS junctions), which are expressed as a function of T/Tc and other parameters.
It has been shown recently that the current-voltage characteristic of a metallic (non-tunneling) Josephson junction could exhibit a negative differential resistance at low voltages, as a predictable and reproducible effect. This letter shows an alternative procedure to generate non-Josephson microwaves (in the cm and mm range) taking advantage of this effect. It is shown that, instead of obtaining harmonic oscillations with the AC Josephson effect, it is possible to generate microwaves using the averaged IVC (current-voltage characteristics) of a SNS junction (a Josephson junction which exhibits no tunneling and has no hysteresis in the IVC).
We design a millimeter-wave heterodyne receiver using Superconductor-Normal metal-Superconductor (SNS) junction. We simulate its Current-Voltage Characteristics (CVC) as a function of its relevant physical parameters. Performing computer simulations, we use the negative derivative range of its CVC to calculate the conversion gain and reflectivity coefficients of the proposed device. These parameters show that it should be possible to increase the sensitivity of the SNS mixer and a reflection parametric amplifier may be feasible.
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.