Advanced Four-Layered Josephson Junctions for Digital Applications

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 characteristicsevenfarabove4.3 K, appealing properties for programmable Josephson voltage standard applications.