MEMS | ARTICLE
MEMS ARE A WATCH’S BEST FRIEND Aurélie Pezous | Michel Despont, CSEM Neuchâtel, Switzerland
<< Figure 1: Examples of hybrid watch parts made by wafer-level bonding. Si wheel-Au pinion (left); balance with integrated inertial Au proof mass (centre); balance-spiral (right). >>
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ilicon, as a lightweight material with excellent mechanical proprieties, has been combined with the high precision of today’s MEMS technology to open new perspectives in the
manufacturing of watch components. For more than a decade, CSEM has invested in the micro machining of micro mechanical structures particularly to serve the increasing demands of watchmakers for ever more complex parts. This has led to a complete offering from R&D to pre-volume and small-volume manufacturing, and to reliability studies for more highly performing and sophisticated watches, but also simply for the pleasure of beautiful designs.
Between Tradition and High Technology
It might seem strange to think about mechanical watches as high- tech devices. They were invented centuries ago and little has changed in the way they operate. Moreover, tradition is at the heart of the mechanical-watch industry, an industry which targets the more luxury segment of the wristwatch market. Customers are looking for aestheticism but also seek to own a piece of history. However, today even a masterpiece full of tradition needs to operate smoothly and precisely and require as little maintenance as possible. Hence, watchmakers are continuously seeking to optimise the operation of the watch movement to make it more precise, less subject to wear, more resistant to shock, or less in need of lubricants. The use of materials with better mechanical and tribological proprieties along with machining technology that gives
better surface finishing is a continuous quest. In this way, new metal alloys have been introduced and more precise fine-machining techniques have been used for the manufacturing of watch movements. However, such innovations are rather incremental steps that have had little impact on the performance of mechanical watches.
In the eighties, a new research field emerged from the technologies developed by the micro electronics industry: technologies called MEMS. Micro electronics technology uses mainly silicon substrates processed in a batch manner and relies on precise definition of shapes by photolithography and further processing to form complex and high-density electronic circuitry at a low cost. If, in micro electronics, silicon is used for the advantages offered by its semiconductor proprieties, in MEMS its outstanding mechanical proprieties are equally important. Silicon is light, hard, and offers excellent elasticity and tribological proprieties. Moreover, an important aspect for watches, it does not magnetise and has a small thermal expansion coefficient. But a watch part is rather thick by micro electronic technology standards and specific micro fabrication technology needed to be invented to transfer shapes from a mask of some micro meters to several hundreds of micro meters of silicon. A technique called deep reactive ion etching (DRIE) has become the standard etching technology for high-aspect-ratio structuration of silicon and is widely used for MEMS technology. It brings with it an unmatched freedom in design flexibility and accuracy in the micro meter range. In this way, it has opened a new field of exploration for
28 | commercial micro manufacturing international Vol 7 No.1
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