Superconducting circuit

The fabrication of logic elements using such devices allows in principle the construction of a large capacity, compact, high-speed computer [50], Major problems with the technology are that large fan-out ratios are difficult to achieve and that superconducting circuits have a very low inherent impedance and so are difficult to couple with conventional elements at room temperature. 

In spite of the usually low cooling efficiencies (see the exercise above), recent experiments have demonstrated an anti-Stokes cooling from room temperature to 77 K within a certain internal volume of Yb + doped fluorochloride and fluoride glasses under high photon irradiances (Fernandez et ai, 2000). Future practical applications of optical cooling of solids include cooling systems for spacecraft electronics and detectors, as well as for superconductive circuits. 

Recently CMP of an interlevel dielectric SiO, deposited using evaporation techniques, was carried out for superconducting circuits. "CMP of the interlevel dielectric film allows the junction area to be greatly reduced, thereby increasing the speeds of operation of the circuits, by eliminating the need to open vias to make contact to the top electrode. ITie key to the success was in (a) the precise control to terminate the CMP within 200 nm after reaching the endpoint and (b) the ability to planarize a few hundred-micron-wide features. 

A unique feature of the book is its emphasis on applications. These include mechanical vibrations, lasers, biological rhythms, superconducting circuits, insect outbreaks, chemical oscillators, genetic control systems, chaotic waterwheels, and even a technique for using chaos to send secret messages. In each case, the scientific background is explained at an elementary level and closely integrated with the mathematical theory. 

Superconducting circuits for microelectronic applications usually represent a more or less complex structure consisting of connecting lines, active or passive... 

Current control in most superconducting circuits is achieved by the cryotron, which makes use of the resistance parameter for this purpose. However, since, by their very nature, cryogenic circuits are basically devoid of all resistance, inductance is often used to effect a desired current distribution. This is accomplished by designing the branches of a network with certain relative inductances an applied circuit current then splits among the branches in inverse proportion to the inductances. 

The dc current required for support can be trapped in a superconducting circuit, eliminating support power. 

The dc power supply is turned off and the current continues to flow through the circuit formed by A and B. The current in the superconducting loop is measured by using the readout coil. When the current in the superconducting circuit is destroyed, it induces an instantaneous current in the readout coil which can be read on a galvanometer. 

One solution to this difficulty, which is finding considerable application, uses a transformer located in the cryostat. Low currents efficiently conducted into the cryostat are stepped up in magnitude as needed. In superconducting circuits where no steady loss of power is involved, a normal transformer with suitable modification performs quite satisfactorily as a dc device. The above restriction of zero power loss is enforced by the environment so that it constitutes no real limitation to the transformer. Thedc transformer affords a method of obtaining currents of hundreds and even thousands of amperes at cryogenic temperatures. These currents are easily controlled through the primary circuit resistance located externally. When operated in a dc manner there are no losses associated with the transformer core. It is the purpose of this paper to briefly outline the operating principle of a dc transformer and to illustrate several applications. 

Equation (5) takes on a fundamental aspect for superconducting circuits. It states that the net linked flux for a superconducting circuit is constant regardless of the current in that circuit. 

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