Permalloy film NDRO memory

Abstract

A thin magnetic film NDRO storage cell has been developed for very high-speed word-organized memories. The storage cell contains two 500-A, 15-mil-square Permalloy film elements with a read and sense line between them. One film element is deposited on a metallic ground plane, so that the read line and its image in the ground plane are coupled to the readout film and decoupled from the storage film. A 3-ns-wide 300-mA read pulse with a 1-ns rise time yields a 4- to 6-mV output signal. Two methods of coincident current writing were investigated. One with the word and digit lines outside the storage cell required 500-mA word current, 80-mA digit current, and a read after write pulse. Writing takes 50 ns and the storage cell will tolerate coincident word and digit disturb currents of 50 and 100 mA, respectively. The other method uses the read and sense lines between the films as word and digit lines. Word currents of 300 mA and digit currents of 50 mA are required to write. The disturb margins are greater, and read after write pulse is not required. Because the eddy currents in the ground plane must decay, writing takes 3 μs. A 512-word, 40-digit test plane has been built and partially populated to determine problems in building a large array. The characteristic impedances and effects of attenuation and delay have been observed. In particular, the output signals are reduced one half because of attenuation and the difference in signal propagation time in the two directions on the sense line.