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Conventional Josephson metal-insulator-metal devices are inherently underdamped and exhibit hysteretic current-voltage response due to a very high subgap resistance compared to that in the normal state. At the same time, overdamped junctions with single-valued characteristics are needed for most superconducting digital applications. The usual way to overcome the hysteretic behavior is to place an external low-resistance normal-metal shunt in parallel with each junction. Unfortunately, such solution results in a considerable complication of the circuitry design and introduces parasitic inductance through the junction. This paper provides a concise overview of some generic approaches that have been proposed in order to realize internal shunting in Josephson heterostructures with a barrier that itself contains the desired resistive component. The main attention is paid to self-shunted devices with local weak-link transmission probabilities that are so strongly disordered in the interface plane that transmission probabilities are tiny for the main part of the transition region between two super-conducting electrodes, while a small part of the interface is well transparent. We discuss the possibility of realizing a universal bimodal distribution function and emphasize advantages of such junctions that can be considered as a new class of self-shunted Josephson devices promising for practical applications in superconducting electronics operating at 4.2 K. [ABSTRACT FROM AUTHOR]

Abstract: An interesting feature of Superconductor–Normal metal–Superconductor Josephson junctions for digital applications is due to their non-hysteretic current–voltage characteristics in a broad temperature range below T c. This allows to design Single-Flux-Quantum (SFQ) cells without the need of external shunts. Two advantages can be drawn from this property: first the SFQ cells can be more compact which leads to a more integrated solution towards nano-devices and more complex circuits; second the absence of electrical parasitic elements associated with the wiring of resistors external to the Josephson junctions increases the performance of SFQ circuits, in particular regarding the ultimate speed of operation. For this purpose Superconductor–Normal metal–Insulator–Superconductor Nb/Al–AlO x /Nb Josephson junctions have been recently developed at INRiM with aluminum layer thicknesses between 30 and 100nm. They exhibit non-hysteretic current–voltage characteristics with I c R n values higher than 0.5mV in a broad temperature range and optimal Stewart McCumber parameters at 4.2K for RSFQ applications. The main features of obtained SNIS junctions regarding digital applications are presented. [Copyright &y& Elsevier]

Abstract: The overdamped Nb/Al-AlOx/Nb superconductor-normal metal-insulator-superconductor SNIS Josephson junctions recently developed at INRIM exhibit high values of critical current density and characteristic voltage, making these devices appealing both for metrology and digital electronics. High current densities could allow reduction of junction size, increasing the integration level. In this work authors present first results concerning the realization of sub-μm SNIS including a nanolithographic technique (Electron Beam Lithography, EBL) into the conventional process, to reduce junction dimensions. Fabrication and electrical parameters have been evaluated considering the scaling of the areas of junctions, furthermore RF and temperature behaviour have been studied. [Copyright &y& Elsevier]

Abstract: Device-modeling physics of four-layered Nb/Al-ultra-thin AlO x barrier-Nb Josephson structures is discussed, empha sizing practical applications. The temperature effect on the minigap induced in a proximized Al layer and that on a critical voltage across the SNIS junction is numerically simulated. The McCumber-Stewart parameter is found to decreasefromabout2at1.7Ktovalues nearunityat4.2K, becauseofthe temperature suppressedsubgap resistance.Due to the single-valued current-voltage dependence and comparatively high critical voltage values, the overdamped SNIS junctionshave demonstrated well-developed rf-induced featuresinthe current-voltage characteristicsevenfarabove4.3K, appealing properties for programmable Josephson voltage standard applications. [Copyright &y& Elsevier]

Abstract: Superconducting tunnel junctions (STJ) are promising high-resolution radiation detectors because of their larger energy resolution with respect to conventional Si-based detectors. We have developed a fabrication process for Nb/Al–AlO x /Nb STJ devices which produces junctions with subgap currents below 50pA at 300mK, a factor of 10−6 less than the subgap current at 4.2K. We report the details of the fabrication process and preliminary results on X-ray measurements at 300mK with a 5mC 55Fe source. [Copyright &y& Elsevier]

The temperature dependence of the quantized voltage steps near the superconducting transition temperature of Nb/Al–AlOx/Nb overdamped Josephson junctions irradiated at 75 GHz has been studied. These junctions can switch between the hysteretic and nonhysteretic regime either by varying a fabrication parameter or, as shown in the present paper, by changing the junction operating temperature. Due to the high values of JC and VC up to 75 kA/cm2 and 0.5 mV at 4.2 K, respectively, and to the moderate temperature dependence of these parameters, the height of the first rf-induced step was larger than 1 mA at T=6–8 K, corresponding to 0.7–0.9T/TC on a junction of 5×5 μm2. The flatness at the nanovolt level of this step demonstrates the feasibility of programable or ac voltage standards operating in a cryocooler setup. [ABSTRACT FROM AUTHOR]