Programmable read-only memory formed with opposing PN diodes

A programmable read-only memory (PROM) in a semiconductor body containing a recessed electrically insulating region and an adjoining monocrystalline semiconducting region having an upper surface along which a group of PROM cells are laterally spearated from one another, each cell having a substantially horizontal first PN junction and a corresponding second PN junction that together form a pair of PN junction diodes connected to each other in an opposing configuration, the first PN junction for each cell lying in the semiconducting region and being formed by the upper boundary of a lower region of a first conductivity type in that cell, the edge of each first PN junction fully adjoining the insulating region, characterized in that:

• each second PN junction is substantially horizontal and lies in a corresponding substantially non-monocrystalline further region of the body downwardly adjoining the semiconducting region above the corresponding first PN junction, the edge of each second PN junction fully adjoining the insulating region which extends at least partly above the upper surface such that there is an intermediate region common to each pair of diodes between their PN junctions for which the portion of the boundary of the intermediate region extending between the edges of the PN junctions fully adjoins the insulating region;
• the PROM includes a plurality of more highly doped buried regions of the first conductivity type laterally spaced apart from one another, each associated with at least one of the lower regions, being upwardly continuous with each associated lower region, and adjoining the insulating region along the entire lower edge of the lateral periphery of each associated lower region;
• and
• the PROM further includes a like plurality of connective regions of the first conductivity type, each extending from a different one of the buried regions to the upper surface.