Microsystems

The Microsystem concept was born at the end of the 1980s, in the United States, as a result of efforts at the University of California, Berkeley, to integrate sensors, signal processing and actuators on a single silicon chip. The integration of certain sensors with their signal processing had already been well explored for some years (thermal sensors, vision sensors, magnetic Hall sensors, etc.); what was new was the integration of electrostatic actuators in the form of rotary or linear motors. This concept very quickly aroused keen interest worldwide. Called MEMS (Micro Electro Mechanical Systems) in the USA, it became known as Micromachines in Japan and MST (Microsystèmes Technologies) in Europe. In France, the term Microsystème is used.

There are at least two reasons for this interest and the mobilization that followed:

• From the researcher's point of view, this concept poses new questions in terms of materials, technological compatibility and system design methodologies;

• from the engineer's point of view, the concept offers prospects for the integration and collective manufacture of new products which, thanks to their low cost, should rapidly penetrate markets held by more conventionally assembled products, and even open up new markets, if only because of the attractiveness of reduced dimensions.

In ten years, the situation has changed considerably. Numerous examples have been explored. The first generations of products have been marketed. Today, we can consider that feasibility has been established and that we are embarking on a second major phase of research and development of new products with a view to their industrialization.

This ten-year hindsight also allows us to better define the field of microsystems:

• microsystems are an extension of microelectronics, from which they borrow material (silicon) and basic technologies (photolithography, oxidation, implantation, diffusion, insulating and metallic layer deposition). They introduce new micromachining operations (volume micromachining, surface micromachining, deposition of sensory active layers);

• microsystems interface with numerous methods and technologies developed in other disciplines: micromechanics, micro-optics, chemistry and biochemistry, electromagnetics, etc., in a global, heterogeneous integration approach;

• Microsystems technologies combine the monolithic, all-silicon approach that forms the strategic basis, with hybrid assemblies that provide immediate, efficient solutions for system integration. This makes it easier to combine different technologies, solving only...