GB935208A - Improvements in and relating to superconductive circuit elements - Google Patents

Abstract

935,208. Semi-conductor devices. INTERNATIONAL BUSINESS MACHINES CORPORATION. April 29, 1960 [April 29, 1959], No. 15183/60. Class 37. [Also in Group XXXIX] In a circuit in which a superconductive element is supported close to a superconductive shield, the shield is connected to the conductor to provide a return path for current passed through the conductor. Fig. 1 shows a simple form of the invention in which an insulating base 14 carries an evaporated layer 24 of hard superconducting material, an evaporated layer of insulating material 26 and evaporated control and gate conductors 10, 12 separated by insulating material 28. The portion of gate conductor 12 which is crossed by the control conductor 10 is relatively " soft." Both control and gate conductors are connected at 12a and 10a to the shield layer. A current from source 30 flows in the control conductor and returns through the shield in a path immediately below. This control current controls the resistivity of the gate conductor 12 and hence the current flowing from source 32 through the gate conductor and back through the shield. The effect of the shield is to reduce the inductance of the conductors forming the shield by making the current flow in these conductors more uniform to raise the Silsbee current for the gate. Where there is no connection between the circuit and the shield this is achieved by induced shield currents. These currents which are believed to return along the edge of the shield may reach, when there are of several circuits, too high a density at this point and may cause coupling between adjacent circuits. The connection to the shield ensures that the currents return immediately beneath the conductors through the path of minimum inductance. Fig. 2 shows an arrangement in which either of gates 52 or 54 is made resistive according as the control point is applied from source 70 or 76 to the appropriate control conductors 62, 64. These conductors are joined to the shield through holes 75, 80 in the insulating layer 60. Fig. 3 shows a number of bi-stable circuits connected in series each operating one of a pair of utilization circuits. The narrowed portion of each conductor represents a control conductor and the shaded portion a gate conductor. The current in the bi-stable circuits 98, 110 is finally connected to the shield at 124 returning to output terminal 126. Initially, a control signal may be applied to either of control conductors 134 or 136 at terminals 130 or 132, the return path of this control signal being through the shield to terminal 142. One of the arms, say 100, of bistable circuit 98 becomes resistive and current flows in the other 102. This makes gate conductor 144 resistive so that source 149 feeds gate conductor 146 and the utilization circuit connected to it. The current in branch 102 makes branch 108 of the next bi-stable circuit resistive so that current flows in 106. This in turn causes source 171 to feed the circuit connected to conductor 162. All the utilization circuit currents return through the shield as does the current which finally leaves the bi-stable circuit at 122. The bi-stable circuits are isolated from each other by holes in the shield such as 103a, 111a which act as chokes. The arrangement shown in Fig. 4 is provided with a shield 188 below and 194 above the gate conductors. Any of four utilization circuits 203a-203d may be energized by signals applied to any pair of terminals 230, 232, 234, 236. If, for example, signals are applied to terminals 230, 236, conductors 238, 250 become resistive. As a result parallel conductors 212 and 218 become resistive so that current flows in inductors 210, 220. If current is used to make conductors 202a, 202c and 202d resistive so that 202b conducts. The circuit is then from source 201 through 202b, conductors 210 and 220 and back through both shields at point 226. The return path for all the control conductors is through both top and bottom shields, connections being made at 242, 244, 252, 254 and 256. Tin and lead are suggested as superconductor materials. Specifications 862,178 and 935,207 are referred to.