Semiconductor memories

Like integrated circuit technologies, semiconductor memories use silicon as their starting material. They represent a privileged field in which progress in advanced integration is immediately felt. They represented the first applications of complex integrated circuits (LSI Large Scale Integration, 1,000 gates per integrated circuit), and will continue to be vehicles of choice for demonstrating the feasibility of highly complex integrated circuits, and as technology tractor components.

The key advantages of silicon integrated circuit technology are :

• the use of collective manufacturing operations, which reduce manufacturing costs and have in the past made these memories price-competitive with magnetic solutions (cores); the trend towards greater integration also means lower system costs (power supplies, buildings, operating costs, etc.);

• the production of circuits using very clean technological operations, sometimes under vacuum (such as metallization), leading to improved reliability of components and therefore of systems, which is becoming essential for highly complex assemblies;

• high speed performance (e.g. read access time) compared with magnetic solutions, especially since performance generally improves as the level of integration increases (parasitic capacitances are reduced by decreasing component dimensions);

• the reciprocal knock-on effect linked to the existence of logic IC production, which in any case contributes to improving the quality of the starting material, the technology and the design tools, thus making the corresponding technologies more efficient, whatever the market share taken by a particular field of application.

In addition, the vast amount of research carried out on semiconductors in general has led to the discovery of new physical effects that enable us to overcome the limitations of semiconductor memories compared with magnetic memories (hard disks, magnetic tapes, etc.) in certain fields. One example is the non-volatile retention of information in an EPROM structure.