GB1438005A - Superconducting memory cell - Google Patents

Abstract

1438005 Superconductive devices INTERNATIONAL BUSINESS MACHINES CORP 8 Aug 1973 [29 Sept 1972] 37570/73 Heading H3X A superconductive storage cell for use in a storage matrix comprises two branches 11, 12, Fig. 1, forming a loop, with a Josephson device 13 in one branch and the loop inductance primarily concentrated in the other branch, the loop current being switched from one direction to the other, or alternatively changed in magnitude, by coincidence of currents I w , I c in a word line 14 connected to the loop and a digit line 16 coupled to the Josephson device. An essential requirement for loop current switching is that the condition is met, i mo being the maximum Josephson current at zero magnetic field, L the loop inductance and # o the magnetic flux quanta capable of being trapped in the loop. Construction of a cell is shown in Figs. 3A and 3B in which a common Pb ground plane 30 supports, with interleaved insulating SiO or SiO 2 films, a loop 11, 12 formed by a superconducting layer 32 and a digit line 16 formed by a superconducting Pb layer 35. The Josephson device in branch 11 consists of two overlapping superconducting layers 32a and 32b of InPb and Pb respectively, the layers being separated by a thin PbO film 33. Suitable dimensions are given. A matrix of such cells with the word and digit lines 55 1 -55 3 and 54 1 -54 3 serially connected in rows and columns is shown in Fig. 5, cell selection by coincident currents being effected in the normal manner from an address register 51 through decoders 52, 53 and current drivers X 1 -X 3 , Y 1 -Y 3 . Reading is effected either by an induced voltage in a sense line due to flux change when the loop current reverses or changes, or by using a further Josephson junction which is influenced by the loop magnetic field.