was first reported by N Chekurov et al in their article "The fabrication of silicon nanostructures by local gallium implantation and cryogenic deep reactive ion etching". Precision Machinery DRIE has enabled the use of silicon mechanical components in high-end wristwatches. According to an engineer at Cartier, “There is no limit to geometric shapes with DRIE,”. With DRIE it is possible to obtain an aspect ratio of 30 or more, meaning that a surface can be etched with a vertical-walled trench 30 times deeper than its width. This has allowed for silicon components to be substituted for some parts which are usually made of steel, such as the hairspring. Silicon is lighter and harder than steel, which carries benefits but makes the manufacturing process more challenging. References See also Reactive-ion etching Microelectromechanical systems Semiconductor device fabrication Microtechnology Etching (microfabrication)