Circuit Josephson junction

Fig. 3. Scientist Donald L. Miller holds an integrated circuit chip comprising a high-resolution superconducting analog-to-digital converter. The one-square-cen timeter chip, known as a counting converter, holds promise as an unprecedented combination of high resolution and low power consumption, as needed in future air traffic control radar and infrared space-tracking applications. The 12-bit circuit (Josephson junction) has a resolution of 1 part in 40CK). (Westinghouse Electric Corporation)...

In the DC SQUID, two Josephson junctions are made in the loop, and a dc current is passed through the parallel circuit so formed. The voltage required to produce the current is then a function of the magnetic field trapped inside the loop. 

The circuit under consideration consists of a normal coherent conductor with conductance G in series with the Josephson junction(system) (Fig. 1). The system is biased with voltage source V k T/e. This assures that the normal conductor is in the shot noise regime. In addition, we inject extra current p that controls the slope of the Josephson washboard potential. 

The switching between states, a characteristic of Josephson junctions, is applicable to binary-based logic circuits there is no voltage across the junction for currents below the critical current 7C, but one appears for currents greater... 

The RF SQUID is based on the AC Josephson effect, uses only one Josephson junction, and is less sensitive than the DC SQUID, but is cheaper and easier to manufacture its SQUID is inductively coupled to a resonant tank circuit. Depending on the external magnetic field, as the SQUID operates in the resistive mode, the effective inductance of the tank circuit changes, thus changing the resonant frequency of the tank circuit. These frequency measurements can be easily done, and thus the losses that appear as the voltage across the load resistor in the circuit are a periodic function of the applied magnetic flux with a period of 0. 

Josephson junction A type of electronic circuit capable of switching at very high speeds when operated at temperatures approaching absolute zero. Composed of two superconductors that are separated by a thin nonsuperconducting layer in which electrons can cross through the insulating barrier, it was discovered by... 

The intrinsic sampler resolution is essentially determined by the ratio of current density to specific capacitance of a Josephson junction pulser contained in the sampling circuit. For picosecond resolution with existing helium temperature superconducting technologies, junction current densities are approaching 104 to 105 A/cm2. The upper end of this is at the limit that has presently been demonstrated for the YBaCuO superconductor itself at 77 K, so achieving such density in a junction will be a major challenge. 

Since the metal stripes are also conductors, a normal current can also be present once the potential is above (jAq. When the current supplied from an external source exceeds Jo, the current switches from a supercurrent to a normal current and a voltage now appears across the other end as shown in Figure 26.9. Thus the Josephson junction QJ) acts in the same manner as a transistor switch, except that the switching time is on the order of picoseconds—orders of magnitude faster than the fastest transistors. For this reason JJs are attractive for very high speed logic circuits. 

Active areas of Josephson junctions must be controlled with very high precision. A high-resolution lithography system is required to get a wide operating margin for a circuit with a small spread of the junction critical current. 

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M Aoyagi, H Nakagawa, I Kurosawa, S Takada. NbN/MgO/NbN Josephson junctions for integrated circuits. Jpn J Appl Phys 31 1778, 1992. 

M Aoyagi, A Shoji, S Kosaka, F Shinoki, H Nakagawa, S Takada, H Hayakawa. All niobium nitride Josephson junction with hydrogenated amorphous silicon barrier and its application to the logic circuit. Jpn J Appl Phys 23 L916, 1984. 

S Yano, Y Tarutani, H Mori, H Yamada, M Hirano, U Kawabe. Fabrication and characteristics of NbN-based Josephson junctions for logic LSI circuits. IEEE Trans Magn 23 1472, 1987. 

GL Kerber, IE Cooper, HW Fry, GR King, RS Morris, JW Spargo, AG Toth. An all refractory NbN Josephson junction medium scale integrated circuit process. J Appl Phys 68 4853, 1990. 

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