IEE Review. Semiconductor memories

The paper reviews the evolution of semiconductor memories from the early 1960s to the present day. It includes descriptions and comparisons of the principal types of memory presently available, followed by a survey of the main semiconductor technologies used in the fabrication of VLSI memories. Typical cell designs are first presented, starting with basic electrical designs and proceeding to show how these may be implemented as layouts for a practical chip. The fabrication steps required to realise such cells within a memory chip are described. The design and organisation of complete memories is then discussed; the design of the principal types of read-only memories, read/write memories, content-addressable memories and serial memories being included. The remainder of the paper deals with the important topic of specification and timing requirements of memories; followed by a general review of different types of semiconductor memory, both from the applications point of view and as a comparison of their principal characteristics with those using alternative fabrication technologies. Finally, there is brief projection of future developments. The paper is written throughout primarily from the technological rather than the applications viewpoint.