MEMS | ARTICLE
mechanical watches. Situated in the heartland of the Swiss watchmaking industry, CSEM has naturally played, and continues to play, a key role in the research and development of technology for silicon-based watch parts.
CSEM’s MEMS Technology for Watches
Thanks to CSEM’s dedicated micro fabrication processes and its reliability and testing laboratory, the centre tackled fundamental challenges such as surface tribology and the behaviour of silicon parts exposed to shock and vibration, including the investigation of coatings and surface treatments for improving performance in a watch’s operating environment. CSEM also developed new fabrication technologies to integrate new functionalities and manufacture more complex parts. One such technology — hybridisation — allows multi-level silicon micro parts to be formed to address the drawback, inherent to micro fabrication technology, of being limited to extruding only two-dimensional shapes. Typically, hybridisation takes place by wafer-level bonding to maintain accuracy and batch- manufacturing capability. To make multi- level components, each level is fabricated separately on a wafer before all are aligned and bonded together. Different bonding technologies are used depending on the device in question. These include gold-silicon eutectic bonding, gold-gold thermo-compression bonding, and silicon-silicon fusion bonding. Moreover, adding thick galvanic deposition, hybridisation makes possible the creation of silicon micro parts into which other materials are integrated. For example, gold micro structures are, making use of the substance’s high density, integrated to serve as an inertial proof mass or, making use of its ductility, pressfit on an axis for final assembly in a watch. Finally, hybridisation could be used to manufacture high-accuracy, preassembled modules hence avoiding fastidious and less precise assembly steps and the problems associated with them which include surface damage and chipping. Examples of hybrid subassemblies are shown in figure 1 and an example of a Si wheel-Au pinion sub- assembly pressfitted on an axis is shown in figure 2.
Continued on page 30 29 | commercial micro manufacturing international Vol 7 No.1
The use of materials with better mechanical and tribological properties along with machining technology which gives better surface finishing is a continuous quest.
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