A mask programmable read only memory device comprises a plurality of memory cell blocks each having a plurality of first series combinations of memory transistors and a plurality of second series combinations of memory transistors, and each of the memory transistors is operative in either enhancement...http://www.google.de/patents/US5429968?utm_source=gb-gplus-sharePatent US5429968 - Method of forming a mask programmable read only memory device with multi-level memory cell array
