“Temperature-stable, corrosion-resistant, lightweight and highly flexible”
As the regulating heart of a mechanical movement, the hairspring plays a decisive role in timekeeping precision. Steadily refined over the centuries, this delicate component has been undergoing a revolution of its own for the past 20 years: the use of silicon. With its exceptional robustness, reliability and longevity, the silicon hairspring is shaping up to be the solution of the future. We explain the secret and the fascinating story behind this modern innovation.
The hairspring – the heartbeat of the movement
The history of the hairspring dates back to 1675, when the Dutch physicist Christiaan Huygens was working to optimize the balance and hairspring system. He realized that a steady beat for the timekeeping mechanism was only possible with a flexible spiral spring: it slows the oscillation of the balance wheel, pulls it back and lets it swing out in the opposite direction. A system as ingenious as it is essential, and its basic principle can still be found in every mechanical movement today.
Over the following centuries, Huygens’ invention inspired numerous watchmakers to improve the hairspring. With success: while Abraham Louis Breguet increased precision in 1796 by bending up the outermost coil (the “Breguet overcoil”), the French mathematician Eduard Phillips managed to calculate the perfect curve 60 years later. When the Swiss engineer Reinhard Straumann finally discovered the novel alloy “Nivarox” in 1931, the story of the hairspring seemed to have reached a happy ending – precision and reliability were higher than ever before. For a full 70 years, Straumann’s innovation would remain the ultimate in the world of hairsprings.
Research and breakthrough: the road to the silicon hairspring
But by 2001 at the latest, when Ulysse Nardin presented two silicon escape wheels in its Freak collection, a new era of mechanical watchmaking was dawning. At first, competitors were reserved. However, when the luxury brand launched the first balance spring made of the new material shortly afterward, the major players went into a state of shock: Patek Philippe, Rolex and the Swatch Group joined forces to fund research into the silicon hairspring.
A breakthrough was needed. To speed up the process, the powerful alliance brought in not only the Swiss Center for Electronics and Microtechnology (CSEM) but also the Institute of Microtechnology at the University of Neuchâtel. This concentrated effort soon faced a major challenge. Just like ordinary metals, the semimetal silicon is sensitive to temperature fluctuations: heat causes it to expand, cold causes it to contract. A circumstance that is incompatible with the delicate structure of a hairspring. Fortunately, the Swiss alliance’s diligent search led to an elegant solution: a thin layer of silicon oxide gives the component significantly greater temperature resistance and reliability.
In 2006, the technology went into series production in the Patek Philippe 5350, followed by its gradual introduction in the renowned Co-Axial calibers from Omega. Today, silicon hairsprings have conquered every price range, and you can get started for just a few hundred euros with the Powermatic 80 caliber from Tissot.
Overwhelming: the wealth of advantages
Regardless of price range, these modern hairsprings offer a number of decisive advantages over conventional versions. The monocrystalline form of silicon used has a crystal structure similar to that of diamond, making the material roughly 60 percent harder and 70 percent lighter than steel. Also distinguished by its corrosion resistance and resistance to magnetic fields, the material boasts excellent elasticity – the perfect prerequisite for use in wafer-thin hairsprings.
Speaking of wafer-thin: with conventional hairsprings, severe shocks often lead to disastrous deformation. Because the silicon hairspring can withstand forces up to five times greater, it dramatically reduces the likelihood of such deformation. Incidentally, other movement components such as the pallet fork and escape wheel also benefit from the material, since its extremely smooth surface makes it possible to do without oils that age over time.
Cutting-edge and sophisticated: the manufacturing process
The silicon hairspring can only play to its strengths if it is manufactured with one hundred percent accuracy. The process consists of several steps, starting with a so-called silicon wafer: a disc roughly 15 centimeters across from which around 600 hairsprings are later etched. The first step is photolithography, in which a thin photoresist is applied to the wafer. This resist protects the material during the subsequent “deep reactive ion etching” treatment, in which corrosive gases remove material down to the target height of around one millimeter. A special acid is used to separate the extremely thin wafer from its carrier without damage. While still attached to the wafer, the tiny hairsprings are then measured by random sampling, after which oxidation takes place to create the temperature resistance mentioned above.
Just how incredibly delicate these steps are is illustrated by the thickness of the oxide layer: a mere 0.003 millimeters. All in all, three weeks pass before the silicon hairspring can be separated from the wafer and then fitted into the caliber. Three weeks in which a wide range of chemical processes were used to create a fascinating result. For years, probably even decades, this tiny component will ensure high precision on its wearer’s wrist – whether in the Tissot Powermatic 80, a Co-Axial Omega or an exclusive Patek Philippe. In this way, the little hairspring impressively demonstrates why our passion for mechanical masterpieces runs so deep.
