Patent GB-986157-A (GB)
Title: Superconductive in-line gating devices and circuits
IPC: G11C11/44
Filed: 1962-07-19
Abstract: 986,157. Super-conductor devices. INTERNATIONAL BUSINESS MACHINES CORPORATION. July 19, 1962 [Aug. 23, 1961], No. 27732/62. Heading H1K. [Also in Division H3] A super-conductor gating device comprises a gated conductor and a control conductor arranged so that the magnetic field of the control conductor acts in one portion of the gated conductor in one sense and in another portion in the opposite sense, relative to the direction of current flow in the gated conductor. Fig. 1 shows the basic structure of an in-line cryatron which is utilized in the invention. Current flowing in control conductors 14 and 16 sets up a magnetic field to control the conduction state of gated conductor 12, the thickness of which is appreciably greater than the penetration depth. The gate portion 12A of the gate conductor is made of soft superconductive material such as tin or indium and the remainder of the gated conductor and the control conductors are made of hard superconductor such as lead. The conductors are thin and closely spaced so that currents in 14 and 16 are equally effective and the results is determined by their algebraic sum. If the control and gated conductors are of the same width, the critical gate current (i.e. the current at which the gate becomes resistive due to its own heating effect) is increased if the control of currents flow in the opposite direction (antiparallel) to the gate current but is decreased if the control currents flow in the same direction (parallel) at the gate current. The characteristic of critical gate current against control current is thus asymmetrical and this can be used to provide a current gain by employing a bias current in one control conductor and a control current in the other. If the width of the control conductor(s) is increased this allows a higher critical valve for the gate current and the control current-gate current characteristic becomes symmetrical. If alternatively, the gate conductor width is reduced the characteristic is again symmetrical but the critical valve of gate current is reduced. Fig. 7 shows an in line cryatron according to the invention in which the net inductive coupling between control and gated conductors is zero. This is due to the figure of eight formation of the control conductor whereby control and gate currents flow in the same direction in adjacent cryatron portions 50A and 52A and in opposite directions in the similar adjacent portions 50B and 52B. The gated conductor 50 is narrower than the control conductor 52 so that in this embodiment the direction of the control current is immaterial for gate control purposes and both soft portions 50A, 50B of the gated conductor will go resistive at the same time. A narrow gate conductor facilitates high-resistance outputs which reduces the tendency for " heat latching " i.e. for the conductor to remain resistive due to its own I<SP>2</SP>R heat. The gated and control conductors may be interchanged. In a further embodiment (Fig. 9 not shown) the gated and control conductors are of the same width and only one of the operative portions (70B) of the gated conductor is made of soft superconductive material; this cryatron portion (70B, 72B) thus resembles Fig. 1 and can be used to provide current gain while the other portion (70A, 72A) acts as a dummy cryatron (i.e. it always remains superconductive) while providing the compensating inductive effect. Other arrangements are described in which parallel feed or centre feed of gated or control conductors is used to provide the non- inductive arrangement, including one example (Fig. 12), in which a current in a superconductive shield, which is the image current of the control current is used in conjunction with a portion of the gated conductor to form a cryatron. Fig. 13 shows devices according to the invention used to form a bi-stable switch with two superconductive paths 112, 114 in parallel across a current source I 1 . Each path has a superconductive gate, 125 and 135, of the type shown in Fig. 9 except that gate and control are interchanged and an additional control conductor 123, 133 is used to supply a bias control current I 2 . Since the bias current is continuous there is no need to form the conductors 123, 133 in figure of eight or other shape to eliminate inductive coupling. The conductors are placed above a superconductive shield 118 and holes 124, 134 in the shield provide inductance chokes to prevent penetration of L.F. signals into conductors 123 and 133. Switching is accomplished by energizing the appropriate one of the control conductors, 122 or 132, to drive the corresponding portion of its gated conductor resistive and so switch the current into the other path. A further cryatron device 145 is used for reading out. The control conductor of this cryatron lies in circuit 114 and both portions 140A, 140B of the adjacent gated conductor are made of soft superconductive material. The presence of current in arm 114 is thus indicated by the fact that gated conductor 140 is in the resistive state. Specifications 935,209 and 971,306 are referred to.