SILICON

Table of main properties of silicon

Property	Typical Value	Remarks
Density	~2.33 g/cm³	Low
Young’s modulus (E)	~130–185 GPa	High (anisotropic)
Tensile strength	~150–700 MPa	Depends on structure and defects
Hardness (HV)	~700–1200 HV	Very high
Thermal conductivity	~120–150 W/m·K	High
Electrical conductivity	Semiconductor	Depends on doping
Thermal expansion	~2.5–3 ×10⁻⁶ /K	Very low
Melting point	~1414 °C
Magnetism	No	Non-magnetic
Corrosion resistance	Excellent	Forms stable oxide layer
Machinability	Not machinable (brittle)	Produced by etching (DRIE, etc.)

Silicon belongs to the family of metalloids. It is a semiconductor material derived from the microelectronics industry, introduced into watchmaking in the early 2000s. It is now widely used for the production of critical components, particularly in the regulating organ (hairsprings) and the escapement.

Its shaping relies on microfabrication processes, notably DRIE etching (Deep Reactive Ion Etching), which enables extremely precise and highly repeatable geometries. Silicon stands out above all for its exceptional physical properties, particularly suited to modern watchmaking requirements.

Main Properties

Silicon exhibits a set of unique properties:

Non-magnetic material
Very low density (~2.3 g/cm³)
High Young’s modulus (~130–190 GPa depending on crystal orientation)
Excellent wear resistance
Very low thermal expansion coefficient (~2.5 ×10⁻⁶ /K)
No lubrication required (low friction coefficient)
Very high achievable geometric precision

These properties make it particularly suitable for components subjected to dynamic stresses.

Silicon used in watchmaking is monocrystalline, which gives it:

High homogeneity
No internal defects
Directional mechanical properties (anisotropy)

Unlike metals, silicon is:

Brittle (fragile)
Non-ductile
Insensitive to plastic deformation

It therefore cannot be deformed or reworked after fabrication.

Silicon can be surface-modified to enhance certain properties:

Thermal oxidation → formation of a SiO₂ layer
Coatings (e.g., vapor phase depositions, nitrides)
Passivation → improved stability

These treatments make it possible to:

Reduce friction
Improve resistance
Stabilize performance

Silicon is primarily used for:

Its properties enable:

Reduced friction

Improved frequency stability
Elimination of lubrication
Insensitivity to magnetic fields

Advantages

Non-magnetic
Very lightweight
Excellent thermal stability
High manufacturing precision
No lubrication required
High wear resistance
Enables innovative and complex component geometries
Allows extremely high precision and repeatability
Reduced production costs

Limitations

Brittleness (fragile material)
No plastic deformation possible
No possibility of traditional adjustment or finishing (timing, escapement adjusting)
Dependence on advanced and costly industrial processes
Non-repairable