Thin-film circuits - Traditional thin films

The main ambiguity attached to thin-film technology is contained in its name, namely the notion of thin versus thick film. Is the notion of thickness sufficient to distinguish one from the other? Certainly not, as the various authors are so divided on the subject. I prefer the notions of electrical and physical properties, deposited materials and deposition processes.

Thin films have been used for many decades in a wide range of applications. The oldest and still most widespread are probably optical applications. Metallurgy and photography have also used thin films, but the most modern applications now include chemistry, biochemistry and medicine, around sensors of all kinds, from gases to DNA (biochips).

As early as the 1960s, the need to integrate electronic functions led to the use of thin-film technology for the very first integrated circuits - hybrid integrated circuits or HICs - in competition with monolithic silicon integration technologies.

At the beginning of the 1980s, thick-film technologies replaced the former, which were handicapped by their production costs and certain technical difficulties in producing multilayers. Only very specific applications, such as high-precision networks, microwave circuits and certain sensors, remained in thin-film.

The concept of the "multichip module" (MCM) appeared around 1985 and, thanks to a number of technical innovations, gave a new lease of life to thin films, which found in these applications the opportunity to fully exploit their integration capabilities (see the following article). ).

But history only repeats itself. Monolithic integration is constantly evolving and gaining ground on heterolithic integration, pushing it to evolve in its turn. If MCMs are today's (heterolithic) answer to the limitations encountered by (monolithic) ASICs, then (heterolithic) SOPs will be tomorrow's answer to the (monolithic) SOCs that are trying to take the place of MCMs today. It's certain that thin-film electronics will play a more important role than ever in SOPs, which are super-hybrids combining high-density electrical and optical interconnections, active and passive components, cooling devices and, why not, electromechanical microsystems.