Thin film programmable read-only memory having transposable input and

Abstract

A thin film programmable read-only memory is provided which comprises an X-Y matrix of conductors, the cross points of which are connected together by a switch element comprising a current-controlled negative differential resistance (CNDR) device in series with a semiconductor fuse. At low bias levels corresponding to read signals, the element behaves as a non-linear resistance. At large bias levels corresponding to write signals, the element will be driven to its negative differential resistance characteristic, the switching element becoming a permanent open circuit when the fuse blows. The symmetrical switching characteristics of the CNDR device allows the function of the X conductors (input or address lines) and Y conductors (output or word lines) to be transposed in that the address information can be applied to the Y lines, the output appearing at the X lines. In an alternate embodiment, a threshold switching (TS) device is utilized in place of the CNDR device. The current characteristics of the CNDR and TS devices are such that the fuse is blown rapidly and cleanly when the devices are appropriately biased.