A piezoelectric element for an automatic frequency control circuit. The element includes a balance spring formed of a piezoelectric crystal strip, a first electrode connected to the automatic control circuit, and disposed on at least a first side of the strip, and a second electrode connected to the automatic control circuit and disposed on at least a second side of the strip. The first and second electrodes are placed on one portion or over the entire length of the balance spring in a predetermined angular distribution.

A process for fabricating a hairspring having a final stiffness includes the steps of fabricating a hairspring to thickened dimensions, and determining the initial stiffness of the hairspring formed in order to remove the volume of material to obtain the hairspring having the dimensions required for said final stiffness.

Disclosed is a method including the following steps: a) providing a substrate including a first silicon layer, a second silicon layer and an intermediate silicon oxide layer therebetween; b) etching the first silicon layer in order to form the timepiece components therein; c) releasing from the substrate a wafer formed by at least all or part of the etched, first silicon layer and including the timepiece components; d) thermally oxidizing and then deoxidizing the timepiece components; e) forming by thermal oxidation or deposition a silicon oxide layer on the timepiece components; f) detaching the timepiece components from the wafer.

A spiral timepiece spring with a two-phase structure, made of a niobium and titanium alloy, and method for manufacturing this spring, including producing a binary alloy containing niobium and titanium, with niobium: the remainder to 100%; titanium between 45.0% and 48.0% by mass of the total, traces of components among O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, of between 0 and 1600 ppm by mass of the total individually, and less than 0.3% by mass combined; applying deformations alternated with heat treatments until a two-phase microstructure is obtained including a solid solution of niobium with -phase titanium and a solid solution of niobium with -phase titanium, the -phase titanium content being greater than 10% by volume, with an elastic limit higher than 1000 MPa, and a modulus of elasticity higher than 60 GPa and less than 80 GPa; wire drawing to obtain wire able to be calendered; calendering or winding.

A spiral timepiece spring with a two-phase structure, made of a niobium and titanium alloy, and method for manufacturing this spring, including: producing a binary alloy containing niobium and titanium, with: niobium: the remainder to 100%; titanium: strictly greater than 60% and less than or equal to 85% by mass of the total, traces of components from among O, H, C, Fe, Ta, N, Ni, Si, Cu, Al; applying deformations alternated with heat treatments until a two-phase microstructure is obtained comprising a solid solution of niobium with -phase titanium and a solid solution of niobium with -phase titanium, the -phase titanium content being greater than 10% by volume, wire drawing to obtain wire able to be calendered; calendering or insertion into a ring to form a mainspring, in a double clef shape before it is wound for the first time, or winding to form a balance spring.

Disclosed is a method including the following steps: a) providing a substrate including a first silicon layer, a second silicon layer and an intermediate silicon oxide layer therebetween; b) etching the first silicon layer in order to form the timepiece components therein; c) releasing from the substrate a wafer formed by at least all or part of the etched, first silicon layer and including the timepiece components; d) thermally oxidizing and then deoxidizing the timepiece components; e) forming by thermal oxidation or deposition a silicon oxide layer on the timepiece components; f) detaching the timepiece components from the wafer.

A method for producing a thermocompensated and coloured coil spring including the steps of forming a first layer of silicon oxide on at least one face of the core and on at least one other face of the core, the first layer having a thickness equal to a fraction of the thickness required for achieving thermal compensation, removing the first layer from at least one face of the core, forming a second layer of silicon oxide on at least one face of the core and on at least one other face of the core, the second layer having a thickness equal to the remaining fraction of the thickness required for achieving thermal compensation which is lower than or equal to 1 m for giving at least one face of the core a colour as a result of the interference effect.

A balance spring for an oscillator of a timepiece, wherein it comprises a component part, in particular at least a coil or a portion of a coil, provided with heavily doped silicon having an ion density greater than or equal to 10.sup.18 at/cm.sup.3, in order to permit the thermo-compensation of the oscillator.

Disclosed is a support member for supporting a wafer during a heat treatment of the wafer. The support member includes a support plate and spacers and retaining elements carried by the support plate. The spacers serve to maintain a gap between the support plate and the wafer. The retaining elements serve to prevent the wafer from moving horizontally. The support plate may be made of silicon, quartz or silicon carbide. The spacers and the retaining elements may be fixed to the support plate by bayonet-type connections.

A spiral spring is configured to equip a balance of a horological movement. The spiral spring is made of an alloy consisting of: Nb, Ti and at least one element selected from V and Ta, optionally at least one element selected from Zr and Hf, optionally at least one element selected from W and Mo, possible traces of other elements selected from O, H, C, Fe, N, Ni, Si, Cu, Al, with the following weight percentages: a total content of Nb, V and Ta comprised between 40 and 85%, a total content of Ti, Zr and Hf comprised between 15 and 55%, a content for W and Mo respectively comprised between 0 and 2.5%, a content for each of the elements selected from O, H, C, Fe, N, Ni, Si, Cu, Al between 0 and 1600 ppm with the sum of the traces less than or equal to 0.3% by weight.