Access structure for high density read only memory

Abstract

A high density read only memory structure is arranged to have the decoders and selectors which are used to access the read only memory arrays in a layer which is above and/or below the read only memory array layers. Note that by layer it is meant a substantially planar structure with some thickness in which the circuitry that makes up particular functionality resides. Thus, the inefficient two-dimensional structure of the prior art is folded over to create a compact read only memory device with a three-dimensional structure. Connection of the decoders to the rows is not limited to the ends of the rows, but instead may be made at any point along the rows. Similarly, connection of the selectors to the columns is not limited to the ends of the columns, but instead may be made at any point along the columns. Advantageously, additional circuitry is not required on the periphery of the memory array, so that a smaller overall memory device is achieved. In addition, in order to reduce cross talk when reading the memory array with a low impedance amplifier, the memory is addressed using a single active row, and, it is read only one column at a time.