We wanted to learn more about the quite complex area. Firstly, we should clarify that of course there is a wide range of knowledge in physics, engineering and horology amongst our readers and fans, so we are:
1. Working on the basis that there’s no such thing as a stupid question
2. Assuming that many of us know little about this topic
What is silicon? Silicon is an element with the chemical symbol Si. It is a hard, brittle crystalline solid with a blue-grey metallic lustre and is defined as ‘metalloid’ which means it has properties between a metal and non-metal element. It has a crystalline structure, occurs naturally and is abundant (it’s found in sand). Its semi-conductor properties (meaning it is between a conductor & insulator) have made it essential in electronics and microchips.
How are its characteristics different to the metal parts it replaces?
The material used for our escapement wheel, anchor and hairspring is Silicon Oxide SiO2. Pure silicon has a rough surface structure making it unsuitable for use in watches. The oxidisation creates a smooth outer surface. SiO2 has a high tensile strength and is 75% lighter than steel. For watchmaking, these characteristics are significant as well as the fact that engineers can create shapes, which are not limited by what normal metal manufacturing techniques can achieve e.g. milling, stamping, turning etc. Lastly SiO2 escapement parts can be made at approximately 3 x higher tolerance (precision) than their metal equivalents. This combination makes the material so attractive.
How are the silicon parts made?
Firstly, the wafers are made by precisely slicing silicon ingots with a diamond wire. The silicon ingots are made by melting pure crystalline silicon into a vertical cylindrical form. During this ‘Czochralski’ process (after its Polish inventor, Jan Czochralski) precise amounts of oxygen are introduced to the silicon material. After cutting the wafers the surface is still rough, a finer surface is created by ‘lapping’. This is followed by chemical mechanical polishing (CMP) which finally achieves a sub-nanometre, virtually mirror-smooth surface. This thin wafer is then etched using the DRIE (Deep Reactive Ion Etching) process with the shape of the required component left after the wafer is masked.
How difficult is the manufacturing process? What are the key hurdles to overcome? This is one which like most industrial processes is heavily affected by volume. As a small, independent brand HORAGE is not churning out wafers day-in day out. Silicon wafers are produced inside a reactor with hundreds of etching passes required over each wafer. One example of the challenges of working with silicon is that the etching process doesn’t naturally produce perfect 90° vertical edges.
Do the designs of Silicon components differ from their traditional variants As mentioned previously, using silicon completely frees the movement designer from the restrictions of well-established metal production processes. A blessing and a curse – the freedom to achieve different forms requires the ability to think in a new and different way. For example: balance springs are traditionally formed of rolled steel wire. The material characteristics, production costs, manufacturing limits and component performance are all tried and tested with centuries of know how to lean into. Leaving this comfort zone is exciting and opens new opportunities but these also come with risks.
Looking at the pallet fork (or anchor) using silicon allows the designer to leave behind the traditional steel form fitted with 2 polished rubies and use a single silicon component (which is 10 x more expensive to make). This lighter part can be accelerated quicker and with less energy used. But fixing it (and the escape wheel) to a vertical metal axle brings a whole new layer of problems, which demand using new high-precision processes. The watchmakers must learn these processes, which are not commonly used or taught in education.
When did HORAGE start using silicon parts? HORAGE started using silicon escapement technology in our very first in-house callibre, the K1 which debuted in 2015. With a subtle irony, the silicon parts used in our timepieces are the only ones not made in Switzerland. Our partner isn’t so far away: located in the Black Forest in Southwest Germany. Luckily, the 1st parts we made with our German partner worked straight away – prototype K1 Nr. 01 is still running and we have yet to have a single movement returned with damaged silicon components (from impact for example).
Why don’t other watch brands or movement makers use silicon?
There are a multitude of reasons for this. Firstly, the Swiss watch making industry is characterised by traditionalism – it is almost logical for such a product as a mechanical watch to be made by traditionalists. Why change a product which is proven and works well? Secondly, a complex web of international patents covered using diverse types of silicon in different components. This restricted the use of the material for most brands outside of certain company holdings. Those unwilling to question this orthodoxy simply had to wait until the patents expired, which happened in 2022.
Will silicon feature in any other parts of the movement in the future? Silicon parts can achieve a remarkably high aspect ratio of 30:1 meaning that for example the vertical height of a part can be 30 times greater than its width. Some movement parts will never be produced in silicon, for example the main spring. This spring needs to create a significant amount of torque, and the material characteristics of silicon could not yield this energy. Certainly, other parts within the geartrain could be made in this material with the same benefits (and costs) described above. Product and process optimisation is never a job which is finished and shut away in a dark cellar! Our team are constantly striving to improve, learn from mistakes and make our in-house callibres better. Churning out designs penned 50 years ago or more is not a status quo we can ever be satisfied with – watch this space!
Thanks to Jonas, Pascal and Lenny for sharing their knowledge, we hoped you learned something new.
Were there questions about silicon which we missed? Post them in the comments!
What other topics should we dive into? Give us your ideas in the comments.
Thanks for the feedback! It's so good to get different perspectives and the aesthetic qualities of the material is not something we had really looked at yet. But we are always experimenting with new colours and textures for our dials.
Thanks for the breakdown on silicon Roger/Jonas/Lenny
My daughter recently was doing a project at school where the kids were asked to choose an element that they would be advocates for. I pushed her hard for silicon! Conductor and insulator? Metal and non metal? Computers and watches? How cool is silicon! Alas, she chose boring carbon (the boring element of life itself).
Knowing the Si advantages.. will we see silicon gear trains and a silicon handset from a watchmaker? I'd assume the lighter weight and lower need for lubricants is a benefit everywhere in a watch? The lower mass also suggests to me a better tolerance for shocks and vibration. Or would such a watch be cost prohibitive or not make sense for other reasons? (insane prices seldom seem to be a reason not to do something in watchmaking 😉)
Equally as interesting to me: silicon is also striking for it's aesthetics. I love seeing the flashing of a silicon escapement. Changing angles sometimes changes it's iridescent colors. Maybe a dial made from one of those circular wafers once it's polished up...? (Indices on the inside of the crystal if they can't be mounted on Si)