SILICON
Extraction and Refinement
Silicon is the element with atomic number 14, symbolised as Si. It belongs to the family of metalloids. After oxygen, it is the second most abundant element in the Earth’s crust, constituting 27.72% of its mass. In 2023, the leading silicon-producing countries were China (accounting for 80% of global production), Russia, and Brazil*.
In its natural state, silicon does not exist as a pure substance. It is found in the form of silicon dioxide (SiO2), which is extracted from mineral or even biogenic ores. Various chemical methods are used to isolate relatively pure silicon. The Czochralski process, known as “crystal pulling”, is a monocrystalline growth technique developed in 1916, which is still used today to produce the purest form of silicon.
Monocrystalline Silicon and DRIE Etching
Components of a watch movement (typically escapement components and balance springs) are manufactured using monocrystalline silicon produced through the Czochralski method. This method yields cylindrical ingots, 2 meters long with a diameter ranging from 20 to 45 cm. These ingots are then sliced into disks, known as wafers. The components are cut from the wafers using the same method employed in the production of integrated circuits: DRIE etching.
Unique Properties
Monocrystalline silicon possesses particularly interesting characteristics. It is hard and three times lighter than steel (2.33 g/cm³). It is elastic, has a very low coefficient of thermal expansion, and is amagnetic. Additionally, silicon-made escapements do not require lubrication.
Silicon was discovered in the early 19th century, and since then, its refining methods have continuously improved.
Silicon carbide (SiC) was reportedly discovered accidentally in 1824 and was commercialised in 1890 under the name carborundum, a term familiar to watchmakers. As the watchmaking industry became more industrialised and standardised, cutting tools used in horology (such as chisels, milling cutters, and drills) were often made from silicon carbide or alloys containing it.
Silicon experienced its true breakthrough with the fastest technological advancement in human history: integrated circuits. In 1955, the first silicon integrated circuit was produced using DRIE etching. Since then, integrated circuits have continuously decreased in size and cost while their performance has increased.
It wasn’t until 2006 that silicon began to be used in the manufacturing of watch components, produced using the same method as in electronics. The mechanical and physical properties of silicon have led to a rapid revolution in the production of escapements and balance springs. Its production method (DRIE etching) allows for both small and large series production at competitive costs. Long-term reproducibility is guaranteed with absolute dimensional accuracy, without tool wear or machine drift. Moreover, this process offers a design freedom that no other production method can provide.
Machining tools used in horology are sometimes made from or contain silicon carbide.
Monocrystalline silicon and the DRIE etching method are primarily applied to the production of movement components, particularly in the escapement. This method is predominantly used to manufacture silicon escape wheels, anchors, and balance springs. However, many other components can also be produced from this material using the same technique. Currently, the thickness of components is limited to 1-1.20mm. The DRIE etching process cuts the component’s contour, which means that only two distinct vertical planes can appear in the component’s design.