Etched, Not Forged: How Semiconductor Fabrication Conquered the Mechanical Watch

A watchmaker forming a traditional hairspring works with a strip of Nivarox wire roughly 0.04 mm thick and 0.10 mm wide. Using tweezers and a coiling mandrel, the spring is wound into an Archimedean spiral about 10 mm across, then heat-treated, then adjusted by hand. Forming the terminal curve at the outer end requires bending a section of wire into a precise overcoil shape first described by Abraham-Louis Breguet around 1795. A skilled specialist can produce perhaps 15 finished springs in a working day.

On a silicon wafer, the same component is manufactured by exposing photoresist to ultraviolet light through a chrome mask, then etching the exposed silicon away with plasma. One 200 mm wafer yields hundreds of hairsprings in a single run, each identical to the others within a tolerance of roughly one micron. No tweezers. No heat treatment. No hand adjustment. Geometry that would take a metalworker hours to approximate is defined in the mask design and reproduced by chemistry and physics.

Between those two manufacturing methods sits a materials revolution that has quietly reshaped mechanical watchmaking over the past quarter century.

Why Metal Hairsprings Are a Problem

Nivarox is an iron-nickel alloy containing small amounts of chromium, molybdenum, tungsten, and beryllium. Developed by Swiss engineer Reinhard Straumann in the early 1930s as an improvement over the earlier Elinvar alloy, Nivarox solved the softness and damping issues that plagued iron-nickel springs. It became the industry standard. Today, Nivarox-FAR, a subsidiary of the Swatch Group, manufactures an estimated 95 percent of all hairsprings used in Swiss mechanical watches.

Nivarox is good. It is not perfect. Iron-nickel alloys are ferromagnetic. While a Nivarox spring does not retain magnetism permanently, it responds to external magnetic fields. Place a smartphone on a watch running a Nivarox hairspring and the rate can shift by seconds per day. Move the phone away and normal timekeeping resumes, but a watch passing through airport security, sitting near a laptop's speaker magnet, or resting on a wireless charger experiences repeated disturbances that accumulate.

Metal hairsprings also require lubrication at the pivot points of the escapement. Synthetic oils degrade over time, thicken in cold temperatures, and thin in heat. Service intervals of three to five years exist largely because lubricants eventually fail, not because the metal components themselves wear out. And despite Nivarox's thermoelastic compensation, rate stability degrades meaningfully below 0°C and above 40°C.

For 70 years, these were accepted tradeoffs. Every mechanical watch on earth lived with them.

Enter Element 14

Silicon is the second most abundant element in Earth's crust, after oxygen. In its pure crystalline form, it is a semiconductor with a density of 2.33 g/cm³, roughly one-third that of steel. It is completely non-magnetic. It has no internal friction worth measuring at oscillation frequencies used in watches. And it can be shaped into structures far more complex than any metalworking process can achieve.

In the semiconductor industry, single-crystal silicon wafers are the substrate on which every microprocessor is built. Fabricating transistors with gate lengths below 10 nanometers is routine. Watchmaking geometry, by comparison, is enormous. A hairspring is roughly 10 mm in diameter. A pallet fork is 3 mm long. By semiconductor standards, these are billboard-sized structures.

What silicon lacked, for watchmaking, was a way to compensate for temperature. Raw silicon has a thermoelastic coefficient roughly 15 times worse than Nivarox. Dr. Ludwig Oechslin at Ulysse Nardin discovered this firsthand in early 2002, when his experimental silicon hairsprings drifted 106 seconds over a temperature variation of 31°C. Unusable.

Claude Bourgeois and the team at CSEM (Centre Suisse d'Électronique et de Microtechnique) found the solution: grow a thin layer of silicon dioxide on the surface. SiO₂ has a thermoelastic coefficient that runs in the opposite direction to raw silicon. By controlling the oxide layer's thickness, the two effects cancel. A 0.5-micron coating, grown through thermal oxidation at roughly 1,100°C, produces a composite material whose frequency stability across the -10°C to +60°C range matches or beats the best Nivarox alloys.

CSEM patented this method in November 2002 (European patent EP1422436B1). A consortium of Rolex, Patek Philippe, and the Swatch Group funded the research. Until the patent expired in November 2022, only consortium members and Ulysse Nardin (through a separate agreement) could legally produce thermocompensated silicon hairsprings.

How You Etch a Hairspring

Manufacturing a silicon hairspring uses Deep Reactive Ion Etching, or DRIE. Developed by Robert Bosch GmbH in the 1990s for MEMS (microelectromechanical systems) fabrication, DRIE alternates between two gases in rapid cycles. Sulfur hexafluoride (SF₆) plasma etches silicon isotropically. Octafluorocyclobutane (C₄F₈) deposits a thin polymer passivation layer on all surfaces, protecting the sidewalls. Each cycle removes a few microns of silicon in the vertical direction while the polymer prevents lateral erosion.

Hundreds of alternating etch-passivate cycles produce vertical walls with aspect ratios exceeding 20:1. For a hairspring roughly 50 microns thick, this means sidewalls that deviate less than 2.5 microns from perfectly vertical across the entire spiral. No metalworking process achieves comparable dimensional control on a curved structure this complex.

Before etching begins, the hairspring's geometry is defined in a photomask. Ultraviolet lithography transfers the pattern onto photoresist coating the wafer surface. Every hairspring on the wafer receives identical geometry, including the inner collet (the attachment point to the balance staff) and the outer stud attachment, both integrated into the single-piece structure. A metal hairspring requires the collet to be manufactured separately, fitted, and adjusted. Silicon eliminates that step entirely.

After etching and stripping the photoresist, the wafer enters a thermal oxidation furnace. At 1,100°C in an oxygen-rich atmosphere, a controlled SiO₂ layer grows on all exposed silicon surfaces. Quality control at this stage is critical: oxide thickness determines thermocompensation. Too thin and the spring runs fast in heat, slow in cold. Too thick and the compensation overshoots. Sigatec, the facility jointly owned by Ulysse Nardin, is one of a handful of companies worldwide with the process control to hold oxide thickness within specification across a full production wafer.

Twenty-Five Years in Five Movements

Silicon's arrival in watchmaking can be traced through five specific calibers, each representing a distinct engineering milestone.

2001: Ulysse Nardin Freak. Dr. Ludwig Oechslin and engineer Pierre Gygax placed silicon escape wheels in a movement with no dial, no hands, and no crown. It was the first production wristwatch to use any silicon component. Only the escape wheels were silicon; the hairspring was still Nivarox. Oechslin's collaboration with CSEM's André Perret on silicon hairsprings began shortly after, in autumn 2001.

2005: Patek Philippe ref. 5250. Released under the Advanced Research label, this annual calendar was the first watch with a Silinvar escape wheel. Patek later introduced the Spiromax silicon hairspring in 2006, making it the first brand to use silicon for both the escape wheel and the balance spring in production movements. By 2026, nearly every Patek Philippe caliber ships with a Spiromax spring.

2008: Omega Si14. Named for silicon's chemical symbol and atomic number, Omega's silicon hairspring was designed specifically for the Co-Axial escapement. Combined with a non-ferromagnetic balance and balance bridge, the Si14 spring made Omega movements resistant to magnetic fields up to 15,000 gauss, certified under the METAS Master Chronometer standard from 2015 onward. Omega was the first manufacturer to deploy silicon hairsprings across an entire production lineup.

2014: Rolex Syloxi. Introduced in Caliber 2236 for the Lady-Datejust, Rolex's silicon hairspring uses a patented geometry with variable blade width optimized through finite-element modeling. Unlike most competitors that adopted silicon to solve the magnetism problem, Rolex already had its Parachrom hairspring (a niobium-zirconium alloy, paramagnetic and ten times more shock-resistant than Nivarox). Rolex chose silicon for its chronometric benefits: isochronism that requires no terminal curve adjustment and consistency across production runs.

2017: Zenith Defy Lab. Guy Sémon, then head of the LVMH Watch Division's R&D institute, replaced the entire oscillating system with a single silicon component. No separate balance wheel. No separate hairspring. No separate lever or escape wheel. One monolithic silicon flexure, 0.5 mm thick, oscillates at 15 Hz (108,000 vibrations per hour), roughly four times the frequency of a standard 4 Hz movement. Accuracy: plus or minus 0.3 seconds per day. Power reserve: 60 hours, despite the extreme frequency. Position-dependent rate variation: effectively zero, because the flexure has no pivots.

What Silicon Cannot Do

Silicon is brittle. Drop a silicon hairspring on a hard surface and it shatters. A metal spring bends, deforms, and can often be re-formed. Silicon offers no such forgiveness. Shock protection systems like Incabloc and KIF, designed around the elastic deformation of metal pivots, work differently with silicon components that flex rather than bend.

Repairability is the more consequential limitation. A traditional watchmaker can replace a broken Nivarox hairspring with aftermarket or new-old-stock wire, coiling and adjusting it on the bench. Replacing a silicon hairspring requires a factory-original component produced on the same photomask with the same oxide specification. If the manufacturer discontinues the caliber and stops producing spare parts, no independent watchmaker can fabricate a replacement. Fifty years from now, servicing a silicon-equipped movement will require either manufacturer support or a compatible stockpile of original parts.

Watchmaking traditionalists raise this concern frequently, and it is valid. But the same argument applied to quartz movements in the 1970s, and the industry adapted. It also applies to any proprietary alloy. Rolex's Parachrom hairspring cannot be replicated by an independent workshop any more easily than a Spiromax silicon spring. Manufacturing exclusivity is not unique to silicon; it is a feature of any advanced material.

After the Patent Wall Fell

When European patent EP1422436B1 expired on November 25, 2022, the thermocompensated silicon hairspring became available to any manufacturer willing to invest in the fabrication infrastructure. Before that date, the technology appeared almost exclusively in watches priced above $5,000. Tissot's Ballade, fitted with a silicon hairspring from Swatch Group's internal supply at around $1,000, was the notable exception.

Since 2022, smaller independent manufacturers and movement suppliers have begun incorporating silicon components. Miyota (a Citizen subsidiary), Sellita, and several Chinese movement makers have announced or shipped calibers with silicon escape wheels. Full silicon hairsprings remain harder to produce, because the thermocompensation oxide step demands precise process control, but the barrier is now capital expenditure rather than intellectual property.

Within a decade, silicon hairsprings may become as standard as synthetic rubies. A component that once signaled a $10,000+ Swiss watch could appear in a $500 Japanese automatic. For the end user, this means watches that hold their rate better near magnets, keep time more consistently across temperature swings, and need less frequent lubrication service at the escapement.

Two Manufacturing Philosophies, One Wrist

A modern Patek Philippe Nautilus contains both philosophies in one movement. Bridges are finished with Geneva stripes applied on a lathe, one pass at a time. Screw heads are chamfered by hand under a microscope. Bevels are polished with a boxwood lap dressed in diamond paste, consuming minutes per edge. All of this artisanal labor sits alongside a Spiromax hairspring that was photolithographically defined, plasma-etched from a silicon wafer, and thermally oxidized in a semiconductor-grade furnace.

No one involved sees a contradiction. Craftsmanship defines the movement's appearance. Silicon defines its performance. Both disciplines serve the same goal: a better watch.

Christiaan Huygens published his balance spring design in 1675. For 326 years, every improvement to that concept involved better alloys, better forming techniques, better heat treatments of metal. In 2001, Ulysse Nardin placed a silicon escape wheel in the Freak and the industry split from a single material lineage into two. Metal and semiconductor. Forge and foundry. Mandrel and photomask. Both still making springs that oscillate at frequencies Huygens would recognize. One of them produces those springs hundreds at a time, identical to the micron, on a wafer the size of a dinner plate.