WO2015087252A1

WO2015087252A1 - Helical spring for mechanical timepieces

Info

Publication number: WO2015087252A1
Application number: PCT/IB2014/066756
Authority: WO
Inventors: Konrad Damasko
Original assignee: Damasko Gmbh
Priority date: 2013-12-11
Filing date: 2014-12-10
Publication date: 2015-06-18
Also published as: WO2015087252A4

Abstract

The invention discloses a helical spring (20) for a mechanical timepiece. The cross section (24) of the helical spring (20) comprises, along the height (h) of the helical spring (20), at least two regions (26_i,...,26_n), where i=1, ..., n, which are located one above the other and consist of a polycrystalline silicon. Each region (26_i) has formed at least two anchors (28_i,j) by virtue of crystals of the silicon dioxide (34) being grown into the boundary region (30), wherein each anchor (28_i,j) has a roughness (R_i,j), where j=1, ..., m. Each region (26_i) has arranged in it at least one anchor (28_i,j) which has the same roughness as another anchor (28_i-1,j',28_i+1,j') of an adjacent region (26_i). The invention also discloses a method for producing at least one functional element (8) for mechanical timepieces. Silicon particles or silicon crystals (1, 36) are distributed homogeneously, in respect of the size and orientation of the silicon particles or silicon crystals (1, 36), over the cross section (24) of the functional elements (8, 20).

Description

SPIRAL SPRING FOR MECHANICAL MOVEMENTS

Technical area

The invention relates to a coil spring for mechanical movements.

PRIOR ART A mechanical movement has as its central components a barrel with tension spring, gear train, escapement and oscillating system (balance). The barrel with tension spring provides the drive of the movement. The power is transmitted starting from the barrel via the gear train to the escape wheel, which represents a part of the escapement. The gear train drives the hands of the watch and translates the spring force stored in the tension spring into rotational motions of different speeds, indicating seconds, minutes, hours and so on.

The balance comprises a vibrating body, which is mounted pivotably about an axis of rotation by means of a balance shaft. Furthermore, a spiral spring is provided which, together with the mass of the oscillating body, forms the oscillatory and clocking system. Finally, the balance includes a device for regulating the speed, such as a back, with which the rocker characteristic of the coil spring changed and thus the desired correct gear of the clock can be adjusted. The exact course of the clock is based on the most even swinging back and forth of the coil spring to their equilibrium position. The armature intervenes alternately inhibiting and releasing in the escape wheel so that the movement always pulsates in the same time. However, without a steady supply of energy, the balance would stop moving. Therefore, the force coming from the barrel is continuously transmitted to the balance via the gear train. The escapement forwards the power via the escape wheel and the anchor to the balance wheel. Upon leaving its equilibrium position, the oscillating body of the balance causes biasing of the coil spring, creating a return torque that causes the coil spring, after release by the armature, to return to its equilibrium position. As a result, the oscillating body is given a certain amount of kinetic energy, which is why it oscillates beyond its equilibrium position until the counter-torque of the spiral spring stops it and forces it to swing back. The spiral spring thus regulates the oscillation period of the balance and thus the course of the clock.

A mechanical watch consists of a large number of smallest functional elements that must be precisely matched to each other and achieved with high accuracy in order to achieve high accuracy of the watch. Various methods for the production of functional elements, in particular also coil springs, for mechanical watches are known from the prior art.

Subsequently, silicon oxide or silicon dioxide is used as synonymous terms.

Si wafers (Si wafers) are used for the production of the functional elements or coil springs for mechanical watches. These Si wafers consist essentially of isotropic silicon particles, which can be produced in various ways. As a by-product of the production of silicon granules by means of fluidized bed process, the desired silicon particles with a diameter of 0.01 .mu.m to 10 .mu.m. In addition to the coarse-grained granules, these processes also produce very fine silicon powder whose particle sizes are in the desired range.

Silicon powder with particle sizes in the micrometer and sub-micron range can also be produced from silane gas by high-temperature pyrolysis, by the Siemens process, by hydrogen reduction processes using tetrachlorosilanes or by other chemical vapor deposition processes. From the silicon powder, a nanoparticle specimen is produced by means of a sintering process. For this purpose, international patent application WO 2010/097228 discloses spark plasma sintering. The German publication DE 1 1 2009 000 068 T5 of the international patent application WO 2009/155849 discloses the use of silicon powder with a grain diameter of 0, 1 pm to 1000 pm in cold isostatic or hot isostatic sintering process.

DE 10 2008 061 182 A1 discloses the production of spiral springs by laser cutting from the wear layer of a silicon wafer. EP 1 422 436 A1 discloses a method for producing spiral springs for the oscillatory system of mechanical clocks made of monocrystalline silicon.

EP 1 422 436 A1 discloses a method for producing spiral springs for the oscillatory system of mechanical clocks made of monocrystalline silicon.

DE 101 27 733 A1 discloses a method for producing helical or spiral springs made of crystalline, in particular monocrystalline silicon by a mechanical erosion machining.

DE 10 2008 029 429 A1 discloses a method for producing spiral springs for watch movements, in which the spiral springs are exposed by etching processes with the aid of etching masks made of a silicon starting material (Si wafers).

Finally, EP 2 201 428 A1 discloses a spiral spring which is produced by cutting or etching from a plate-shaped substrate obtained by epitaxial deposition of polycrystalline silicon. The epitaxial deposition of the polycrystalline silicon is carried out using a CVD method. The spiral springs obtained in this way have an excellent vibration behavior and thus cause a high accuracy of the movement. However, the manufacture of the coil springs frequently causes fractures and cracks in the springs, which results in a high scrap of material. The production of coil springs with excellent vibration behavior and at the same time the lowest possible material losses due to rejects is a central goal in the field of mechanical movements.

The thickness of the silicon oxide or silicon dioxide coating required for a given functional element in order to achieve optimum temperature compensation can easily be calculated by a person skilled in the art or simply determined experimentally. The calculated or determined layer thicknesses for the silicon oxide coating are available in tabular form. Customary coatings with thicknesses of 1 to 8 pm, more preferably 2 to 5 pm. The processes known from the prior art for applying a silicon oxide coating are all very time-consuming. Performing a thermal oxidation with oxygen to produce a conventional layer thickness of 3 to 8 pm at temperatures of about 1000 ° C usually takes 40 to 80 hours. It is therefore desirable that functional elements of a mechanical timepiece can be made such that they ideally show no temperature dependence in their movement behavior. In the event that the thermal oxidation of the spiral spring made of silicon is carried out by a CVD method, this takes place at temperatures and 1000 ° C.

In the following, another problem concerning the inhomogeneous vibration behavior due to inhomogeneous size distribution of the crystals in the spiral spring is described. It is a known disadvantage that the coil spring does not vibrate homogeneously in various subregions of the spiral spring or in subregions of a turn of the spiral spring or tends to twist. Another cause for this, in addition to the causes already mentioned above, are local differences in the bending stiffness of the spiral spring, which are caused by a different size distribution of the crystals in the spiral spring. This in turn causes different values for the modulus of elasticity (modulus of elasticity) over the cross section of the spiral spring on the basis of the known formula

Bending stiffness = (area moment of inertia I) ^* (modulus E) = I ^* E [Nmm ² ]. In this case, I is essentially dependent on the geometry or the cross section of the spiral spring, and E is essentially dependent on the orientation of the crystals in space or in the cross section of the spiral spring. When growing the silicon crystals (Si crystals) of the main body of the spiral spring, certain spatial directions (orientations) of these crystals are preferably formed, as FIG. 18 shows. The silicon crystals of the main body of the spiral, as shown in Fig. 18 (prior art) and Fig. 19 (invention), may be prepared by the methods known to those skilled in the art such as, for example, directed growth, for example epitaxy, crystallization or recrystallization or crystal growing. The crystals are simplified in some figures drawn as a rectangle or four, can be isotropic as well as anisotropic. Other methods for producing the crystals is spark plasma sintering or laser crystallization.

The modulus distribution has a direct effect on the flexural rigidity. At a bend of the spiral spring that spiral portion with a lower modulus of elasticity bends more strongly than one with a higher modulus of elasticity. If such an E-modulus difference within a turn of a coil spring, it tends to twisting.

Furthermore, as shown by the inhomogeneous distribution of the Si crystals shown in FIG. 18, an uncompensatable temperature drift can result, since the SiO ₂ coating required for compensating for the temperature drift is insufficient to compensate for the temperature drift. However, as already stated elsewhere, the temperature dependence of the movement behavior of the coil spring has a detrimental effect on the vibration behavior. As is known, an average layer thickness of the silicon dioxide coating is usually set for the compensation of the temperature drift. However, there may be regions of the spiral spring in which the local distribution of the Si crystals and their orientation is such that the direction-dependent temperature drift is so pronounced that an intended temperature compensation is insufficient. Presentation of the invention

The object of the invention is to provide a coil spring for mechanical movements with excellent vibration behavior. This object is achieved by a coil spring according to claim 1. Further advantageous aspects, details and embodiments of the invention will become apparent from the dependent claims, the description and the figures.

A spiral spring is known to include windings, wherein a cross section of a winding has a height and a width. At least one layer of silicon oxide is applied to a boundary region of the spiral spring. The cross section of the spiral spring comprises along its height at least two superposed regions of a silicon material. In this case, the respective silicon material comprises a plurality of regions of amorphous and / or polycrystalline and / or monocrystalline silicon.

Each region has formed at least two anchors by growing silicon oxide into the boundary region of the core of the coil spring. Each anchor has an individual roughness. The individual roughnesses of the anchors should ideally be the same, but naturally differ by the different growth behavior of the individual crystals of silicon oxide or silicon dioxide.

The spiral spring according to the invention for a mechanical movement is now characterized in that after the thermal oxidation by means of oxygen or a thermal CVD method for applying a Si0 ₂ - layer of the exposed Sprialfedern in each area at least one anchor, the same roughness as a has another anchor of an adjacent area. The greater the number of such anchors over adjacent regions having the same roughness, the easier the topology or roughness profile becomes over the entire height of the coil spring and the greater the likelihood of a comparatively low average roughness over all anchors of all regions of the coil spring , Such a spiral spring is correspondingly smooth and ensures an improved vibration behavior of the mechanical movement. The roughness, also known as the roughness depth, denotes the unevenness of the surface height of the anchors. For the quantitative characterization of the roughness, there are different calculation methods from the prior art, each of which takes into account different peculiarities of the surface of the anchors. The surface roughness can be influenced, inter alia, by the abovementioned production methods for the spiral spring, in which the surface of the spiral spring is polished, ground, lapped, honed, etched, vapor-deposited and / or oxidized or corroded.

The term roughness can furthermore designate a shape deviation of the third to fifth order in the case of technical surfaces in accordance with DIN 4760.

Especially in the production of coil springs for mechanical movements, the roughness is important. The roughness of the surfaces of the coil springs should be as small as possible. The roughness can be measured and determined with different measuring devices: by means of manual methods, for example by the Rugotest; using profile-based methods, such as stylus methods; and by means of area-based methods, for example by optically planar methods.

Parallelism or width variations of the oxide layer on the coil spring lead to deviations in the accuracy of accuracy in the event of temperature fluctuations. A fluctuation of 100nm leads to a deviation of 3 sec / day, with a temperature difference of 30 degrees Celsius. A width variation of an oxide layer on the spiral spring amounts to a maximum of 15%, preferably 10% and more preferably maximum. 5% / the total width of the oxide layer.

The above-described spiral spring according to the invention also overcomes a further disadvantage that, due to an inhomogeneous distribution of the roughness peaks, ie the tips of the armatures, inhomogeneous width fluctuations of the oxide layer along the height of the spiral spring arise along the height of the spiral spring. This adversely affects the vibration behavior. The inventive Instead, the spring has a homogeneous distribution of the roughness peaks, which promotes a uniform vibration behavior.

In one embodiment of the spiral spring according to the invention, the average roughness over the armatures of the regions assumes a maximum value from the interval 0.5 pm to 10.0 pm. The average roughness is preferably in the interval from 0.1 μm to 5.0 μm and more preferably in the interval from 0.3 μm to 3.0 μm.

It is also possible that in the coil spring, the average roughness over the anchors of the ranges in the interval from 0.001 pm to 2.0 pm.

The distribution of the individual roughnesses of the anchors of the areas should be minimal. The frequency with respect to the number of anchors of each area should be maximum.

As described above, there can be an uncompensatable temperature drift due to an inhomogeneous distribution of the Si crystals and their orientation across the cross section of the coil spring. In order to obtain a spiral spring which is independent of the temperature drift, according to the invention the cross section of the helical spring is constructed in such a way that the Si crystals are distributed essentially homogeneously with respect to their size and orientation over the cross section of the helical spring.

One possible method for producing at least one functional element for mechanical movements comprises the following steps:

Homogeneous distribution of silicon particles or silicon crystals over a respective cross section of the functional elements with regard to the size and the orientation of the silicon particles or silicon crystals;

Producing a solid by sintering the homogenized mixture of the substantially isotropic silicon particles;

Separating the at least one functional element by removing the material of the solid body surrounding the respective functional element. In addition to the sintering of the silicon particles or silicon crystals, other methods for producing a solid of silicon material are conceivable. For example, the solid can be prepared by sublimation, CVD, LPCVD, epitaxial deposition, etc. In one embodiment, the functional element is a spiral spring.

A homogeneous distribution of the silicon particles or Si crystals, preferably of amorphous and / or monocrystalline silicon particles or silicon crystals, over the cross section of the spiral spring is achieved for example by annealing. During tempering, in particular, a temperature T greater than or equal to 800 ° C. and a time duration t of tempering greater than or equal to 10 hours have proven to be advantageous. As a result, according to FIG. 19, a distribution of the Si crystals, which is much more homogeneous than that of FIG. 18, over the cross section of the spiral spring is obtained. In particular, as shown in FIG. 20, surfaces F1, F2, F3 have the same bending strength when a force F is exerted, thus ensuring substantially the same bending strength over the entire turn of the coil spring. This results in a homogeneous swing and torsion of the coil spring is avoided.

In further embodiments of the present invention provides a spiral spring for mechanical movements with a coincident with the vibration plane of the spiral spring coil spring plane E and a perpendicular to the spiral spring plane E, extending through the center of the spiral spring coil spring axis A available. The spiral spring is constructed in a direction parallel to the coil spring axis A of at least five layers, namely a first, outer layer of silicon oxide, at least a second layer of polycrystalline silicon and at least a fourth layer of polycrystalline silicon, wherein the second layer and the fourth layer consist of anisotropic silicon crystals, wherein the anisotropic silicon crystals have a diameter parallel to the spiral spring plane E of 10 nm to 1000 nm and a height parallel to the coil spring axis A from 2 pm to 50 pm, a third, between the second layer of polycrystalline silicon and the fourth layer of polycrystalline silicon arranged layer of polycrystalline silicon, wherein the third layer of substantially isotropic silicon crystals having a diameter of 10 nm to 1000 nm, and a fifth outer layer of silicon oxide.

The diameter of the anisotropic silicon crystals is 10nm to 30000nm and their height 500nm to 50pm. The diameter of the isotropic silicon crystals is 1 nm to 10000 nm.

As already mentioned, fractures and tearing of the springs often occur in the production of the spiral springs, which entails a high scrap of material. It can be assumed that these fractures are caused by stresses in the silicon substrate which build up during the epitaxial deposition of the polycrystalline silicon. Surprisingly, it has now been found that these stresses can be significantly reduced if the spiral spring has an intermediate layer of substantially isotropic silicon crystals, which is arranged between two layers of anisotropic silicon crystals. The construction of the spiral spring according to the invention of at least five layers is completed by two outer layers of silicon oxide, by which the sensitivity of the coil spring is reduced to temperature fluctuations. Thus, in its most general form, the present invention encompasses any type of spiral spring for mechanical movements in which at least two layers of anisotropic silicon crystals separated from one another by a layer of substantially isotropic silicon crystals are arranged between two outer layers of silicon oxide.

In order to achieve a constant oscillation behavior of the coil spring and thus a high and as constant as possible accuracy of the movement, namely the Rückholkonstante the spiral spring must be as constant as possible. In order to minimize the temperature dependence of the return constant, in the case of spiral springs made of silicon, the fact is utilized that silicon oxide has a temperature coefficient of the modulus of elasticity opposite to the silicon. By coating a silicon spiral spring with a coating of silicon oxide, the temperature dependence of the modulus of elasticity of the spiral spring and thus the temperature dependence of the return constant C can be minimized. As a result, the sensitivity of the coil spring to temperature fluctuations can be minimized.

The thickness of the silicon oxide coating required for a given cross-section of the coil spring to achieve optimum temperature compensation can be readily calculated by one skilled in the art or simply determined experimentally. The calculated or determined layer thicknesses for the silicon oxide coating are available in tabular form. Common are coatings with thicknesses of 2 to 8 pm.

Preferably, the coil spring is constructed in a direction parallel to the spiral spring axis A of at least five layers, namely a first layer of silicon oxide, a second layer of polycrystalline silicon disposed on the first layer of silicon oxide, wherein the second layer consists of anisotropic silicon crystals, wherein the anisotropic silicon crystals have a diameter parallel to the spiral spring plane E of 10 nm to 3000 nm, preferably 10 nm to 1000 nm, and a height parallel to the coil spring axis A of 2 pm to 500nm, preferably 2 pm to 50 pm, a third polycrystalline silicon layer disposed on the second polycrystalline silicon layer, the third layer consisting of substantially isotropic silicon crystals having a diameter of 1 nm to 1000 nm, preferably 10 nm to 1000 nm, one on the third layer Polycrystalline silicon arranged fourth layer of polycrystalline silicon, wherein the fourth layer consists of anisotropic silicon crystals, the anisotropic silicon crystals having a diameter parallel to the spiral spring plane E of 10 nm to 3000 nm, preferably 10 nm to 1000 nm, and a height parallel to the coil spring axis A from 2 m to 500 nm, preferred 2 pm to 50 pm, and a fifth layer of silicon oxide disposed on the fourth layer of polycrystalline silicon.

In this embodiment, in the method for producing the spiral spring described in more detail below, the two outer layers of silicon oxide are formed with complete dissolution of the outer layers of substantially isotropic silicon crystals present before the oxidation. In the finished Spiral spring then stand the two outer layers of silicon oxide in direct contact with each one layer of anisotropic silicon crystals.

Also preferred is a helical spring which is constructed in a direction parallel to the spiral spring axis A of at least six layers, namely a first, outer layer of silicon oxide, a sixth, arranged on the first layer of silicon oxide layer of polycrystalline silicon, wherein the sixth layer consists of substantially isotropic silicon crystals with a diameter of 10 nm to 1000 nm, arranged on the sixth layer of polycrystalline silicon second layer of polycrystalline silicon, wherein the second layer consists of anisotropic silicon crystals, wherein the anisotropic silicon crystals a diameter parallel to the spiral spring plane E of 10 nm to 1000 nm and a height parallel to the coil spring axis A from 2 pm to 50 pm have a third, arranged on the second layer of polycrystalline silicon layer of polycrystalline silicon, wherein the third layer of We - essential isotropic Silicon crystals having a diameter of 10 nm to 1000 nm, a fourth layer of polycrystalline silicon disposed on the third layer of polycrystalline silicon, wherein the fourth layer consists of anisotropic silicon crystals, wherein the anisotropic silicon crystals have a diameter parallel to Spiral spring plane E of 10 nm to 1000 nm and a height parallel to the coil spring axis A from 2 pm to 50 pm, and arranged on the fourth layer of polycrystalline silicon fifth, outer layer of silicon oxide.

In this embodiment, only one of the two outer layers of silicon oxide with complete dissolution of the present before the oxidation outer layer of substantially isotropic silicon crystals is formed in the method described below in more detail for the preparation of the coil spring. During the formation of the further outer layers of silicon oxide, in the course of the oxidation no complete dissolution of the outer layer of essentially isotropic silicon crystals present before the oxidation takes place. In the finished spiral spring, one of the two outer layers of silicon oxide is in direct contact Contact with a layer of anisotropic silicon crystals and the other outer layer of silicon oxide is in direct contact with a layer of substantially isotropic silicon crystals, which then again followed by a layer of anisotropic silicon crystals. According to a further preferred embodiment, the spiral spring is constructed in a direction parallel to the coil spring axis A of at least seven layers, namely a first, outer layer of silicon oxide, a sixth, arranged on the first layer of silicon oxide layer of polycrystalline silicon, wherein the sixth layer consists of substantially isotropic silicon crystals with a diameter of 10 nm to 1000 nm, arranged on the sixth layer of polycrystalline silicon second layer of polycrystalline silicon, wherein the second layer consists of anisotropic silicon crystals, wherein the anisotropic silicon crystals a diameter parallel to the spiral spring plane E of 10 nm to 1000 nm and a height parallel to the coil spring axis A from 2 pm to 50 pm, a third, arranged on the second layer of polycrystalline silicon layer of polycrystalline silicon, wherein the third layer of the Substantially isotropic silicon crystals having a diameter of 10 nm to 1000 nm, a arranged on the third layer of polycrystalline silicon fourth layer of polycrystalline silicon, wherein the fourth layer consists of anisotropic silicon crystals, wherein the anisotropic silicon crystals have a diameter parallel to the spiral spring plane E of 10 nm to 1000 nm and a height parallel to the coil spring axis A of 2 pm to 50 pm, a seventh, arranged on the fourth layer of polycrystalline silicon layer of polycrystalline silicon, wherein the seventh layer of substantially isotropic silicon crystals having a diameter of 10 nm to 1000 nm, a fifth, outer layer of silicon oxide disposed on the seventh layer of polycrystalline silicon.

In this embodiment, in the method for producing the spiral spring described in more detail below, the two outer layers of silicon oxide are only partially dissolved by the outer layer present before the oxidation Layers of essentially isotropic silicon crystals are formed. During the formation of the two outer layers of silicon oxide, in the course of the oxidation no complete dissolution of the outer layers of substantially isotropic silicon crystals present before the oxidation takes place. In the finished coil spring, both outer layers of silicon oxide are then in direct contact with a layer of essentially isotropic silicon crystals, which are then each followed by a layer of anisotropic silicon crystals.

The spiral spring preferably has at least one further layer consisting essentially of isotropic silicon crystals in one direction parallel to the spiral spring axis A and at least one further layer consisting of anisotropic silicon crystals, wherein the further layer consisting essentially of isotropic silicon crystals is arranged between two layers consisting of anisotropic silicon crystals and the further layer consisting of anisotropic silicon crystals is arranged between two layers consisting of essentially isotropic silicon crystals. The second intermediate layer of essentially isotropic silicon crystals provided according to this embodiment further reduces the stresses in the silicon substrate and reduces damage during the production process.

According to a further preferred embodiment of the present invention, the spiral spring in a direction parallel to the spiral spring axis A n further consisting of substantially isotropic silicon crystals layers and n further consisting of anisotropic silicon crystals layers, each further consists of substantially isotropic silicon crystals Crystalline layer is disposed between two layers consisting of anisotropic silicon crystals and each further consisting of anisotropic silicon crystals layer between two consisting of substantially isotropic silicon crystals layers is arranged, where n is a natural number from the interval [1; 200] is; preferably, n is selected from the interval [1; 20]. Further intermediate layers of essentially isotropic silicon crystals additionally increase the stresses in the silicon substrate. lely reduced and damage during the manufacturing process practically reduced to zero.

Preferably, the first and / or the fifth layer of silicon oxide has a thickness parallel to the spiral spring axis A of 2 pm to 8 pm. By a thickness of the silicon oxide layer of 2 pm to 8 pm, the temperature dependence of the elastic modulus of the spiral spring and thus the temperature dependence of the return constant C can be minimized.

Particularly preferably, the layers consisting of essentially isotropic silicon crystals have a layer thickness parallel to the spiral spring axis A of 20 nm to 5 μm. A layer thickness of 20 nm to 5 pm has been found to be ideal in terms of reducing stresses in the silicon substrate.

According to a further preferred embodiment, the layers consisting of anisotropic silicon crystals have a layer thickness parallel to the spiral spring axis A of 2 μm to 150 μm. A layer thickness of 2 μm to 150 μm has proven to be outstandingly suitable for preventing stresses in the material and for achieving an excellent vibration behavior of the spiral spring.

Particularly preferably, the anisotropic silicon crystals have a diameter parallel to the spiral spring plane E of 20 nm to 500 nm and a height parallel to the coil spring axis A of 5 m to 20 pm. Crystals with the dimensions mentioned have proven to be excellent for preventing stresses in the material and for achieving excellent vibration behavior of the coil spring. As will be described below in connection with the method according to the invention, it will not be difficult for a person skilled in the art to control the process parameters in the context of a CVD deposition in such a way that crystals grow in the desired dimensioning.

According to another preferred embodiment of the present invention, the substantially isotropic silicon crystals have a diameter of 20 nm to 400 nm, preferably 50 nm to 100 nm. By intermediate layers, which are composed of substantially isotropic silicon crystals with a diameter of 20 nm to 400 nm, preferably 50 nm to 100 nm, stresses in the silicon substrate are particularly greatly reduced. The area of a cutting plane of the spiral spring containing the spiral spring axis A is preferably from 0.001 mm ² to 0.01 mm ² and / or the height of the spiral spring parallel to the spiral spring axis A is from 0.05 mm to 0.3 mm. By a cross-sectional area and / or a height in the mentioned order of magnitude, particularly good properties with respect to the vibration behavior result. The present invention also includes a method of making a helical spring for mechanical timepieces comprising the steps of providing a silicon wafer, wherein the silicon wafer comprises a sacrificial layer of silicon dioxide, performing an LPCVD method of forming a first sacrificial layer disposed on the silicon dioxide sacrificial layer A layer of polycrystalline silicon, wherein the first layer consists of substantially isotropic silicon crystals having a diameter of 10 nm to 1000 nm, performing a CVD method for forming a second layer of polycrystalline silicon disposed on the first layer of polycrystalline silicon, wherein the second layer consists of anisotropic silicon crystals, wherein the anisotropic silicon crystals have a diameter parallel to the spiral spring plane E of 10 nm to 1000 nm and a height parallel to the coil spring axis A of 2 pm to 50 pm, performing an LPCVD method to the training a third, arranged on the second layer of polycrystalline silicon layer of polycrystalline silicon, wherein the third layer consists of substantially isotropic silicon crystals having a diameter of 10 nm to 1000 nm, performing a CVD method for forming one on the third Layer of polycrystalline silicon arranged fourth layer of polycrystalline silicon, wherein the fourth layer consists of anisotropic silicon crystals, wherein the anisotropic silicon crystals have a diameter parallel to the spiral spring plane E of 10 nm to 1000 nm and a height parallel to the coil spring axis A of 2 pm to 50 pm, implementation an LPCVD method for forming a fifth layer of polycrystalline silicon disposed on the fourth polycrystalline silicon layer, the fifth layer consisting of substantially isotropic silicon crystals having a diameter of 10 nm to 1000 nm, structuring the coil spring by a material-removing layer Etching or cutting method, detaching the coil spring from the silicon wafer by dissolving the sacrificial layer of silicon dioxide by means of an etching process, performing an oxidation to produce a silicon oxide surface coating of the spiral spring comprising at least a sixth and a seventh layer of silicon oxide, wherein the formation of the 6th layer of silicon oxide with dissolution of at least a portion of the first consisting of substantially isotropic silicon crystals layer and the formation of the seventh layer of silicon oxide with dissolution of at least a portion of the fifth in Wese natural isotropic silicon crystal layer exists. In principle, the process parameters for carrying out a low-pressure chemical vapor deposition (LPCVD) process, as well as the process parameters for carrying out a chemical vapor deposition (CVD) process for the removal of carbon from the gas phase, are known to the person skilled in the art. By varying the pressure and temperature in the respective reactor chamber, the speed and type of deposition of the carbon and thus the crystal formation on the silicon dioxide sacrificial layer of the silicon wafer can be controlled.

The structuring of the spiral spring takes place by a person skilled in the known per se material-removing etching or cutting process. The material removal can be carried out, for example, by means of an etching process with the aid of photomasks.

Subsequently, the spiral spring is detached from the silicon wafer by dissolving the sacrificial layer of silicon dioxide by means of an etching process. Chemical etching processes using, for example, hydrofluoric acid are well known to those skilled in the art. The oxidation carried out after detachment of the spiral spring from the silicon wafer takes place according to a method familiar to the person skilled in the art. Thus, for example, a thermal oxidation can be carried out at elevated temperatures. Since the oxidation is carried out after the detachment of the coil spring from the silicon wafer, the coil spring is accessible from all sides, whereby an outer silica surface coating is formed. In the course of the formation of the silicon oxide layer, the first and fifth layers consisting of essentially isotropic silicon crystals which are initially formed by the method according to the invention are at least partially oxidized and thus at least partially dissolved as a layer of polycrystalline silicon or at least partially into one Layer of silicon oxide converted.

If the oxidation is carried out after the detachment of the spiral spring from the silicon wafer for a longer period of time, a complete dissolution of the initially formed first and / or fifth layers consisting of essentially isotropic silicon crystals takes place. One or both of the layers are thereby converted into layers of silicon oxide.

The LPCVD process is preferably carried out for a period in which a layer of polycrystalline silicon with a thickness parallel to the spiral spring axis A of from 0.2 μm to 1 μm is formed. With LPCVD process relatively low Schichtabscheideraten of about 20 nm / min are connected. The preferred layer thicknesses of 0.2 μm to 1 μm in the context of the present invention can thus be achieved within acceptable process times.

The CVD method is preferably carried out for a period of time in which a layer of polycrystalline silicon having a thickness parallel to the spiral spring axis A of 2 pm to 150 pm is formed. With the process parameters preferred in the context of the present invention, layer deposition rates of 1 μm / min to 5 μm / min are achieved in CVD methods. In the context of the present invention preferred layer thicknesses of 2 m to 150 m can thus be achieved within acceptable process times.

According to a further preferred embodiment of the present invention, the oxidation is carried out after the detachment of the coil spring from the silicon wafer for a period in which a layer of silicon oxide with a thickness parallel to the coil spring axis A from 2 pm to 8 pm is formed. By a thickness of the silicon oxide layer of 2 pm to 8 pm, the temperature dependence of the elastic modulus of the coil spring and thus the temperature dependence of the return constant C can be minimized. Preferably, the CVD process is carried out at a process temperature between 600 ° C and 1200 ° C, more preferably between 960 ° C and 1060 ° C. At the mentioned process temperatures, layers of polycrystalline silicon are formed, which are composed of anisotropic silicon crystals with a diameter parallel to the spiral spring plane E of 10 nm to 1000 nm and a height parallel to the coil spring axis A from 2 pm to 50 pm. These have excellent properties with respect to the prevention of stress and to achieve excellent vibration behavior of the coil spring.

According to another preferred embodiment, the CVD process is carried out at a process pressure of between 2.7-10 ³ Pa and 13.3-10 ³ Pa. In the process pressures mentioned, layers of polycrystalline silicon are formed, which are made up of anisotropic silicon crystals having a diameter parallel to the spiral spring plane E of 10 nm to 1000 nm and a height parallel to the spiral spring axis A of 2 pm to 50 pm. These have excellent properties in terms of preventing stress and achieving excellent vibratory behavior of the coil spring.

Particularly preferably, the LPCVD process and / or the CVD process is carried out using silane or dichlorosilane as the process gas. When using these process gases, the desired layers form within relatively short process times. The CVD process is preferably carried out with an increased gas flow compared to the LPCVD process, an increased process pressure and an elevated process temperature. By the mentioned change of the process parameters, the formation of the desired different layers can be controlled. Preferably, the CVD method is carried out at process parameters that lead to the deposition of a layer thickness of 1 pm to 5 pm per minute. The preferred layer thicknesses of from 2 μm to 150 μm in the context of the present invention can thus be achieved within acceptable process times.

The present invention also includes a helical spring for a mechanical watch, wherein the helical spring is made according to one of the methods described above.

In addition, the present invention includes a mechanical watch with one of the coil springs described above.

As already described above, the functional elements of a mechanical timepiece should ideally show no temperature dependence in their motion behavior. To minimize the temperature dependence of the movement behavior of functional elements made of silicon, the fact is exploited that silicon oxide has a temperature coefficient of the modulus of elasticity opposite to the silicon. By coating a functional element made of silicon with a coating of silicon oxide or silicon dioxide and the penetration of silicon oxide or silicon dioxide into the functional element, the sensitivity of the functional element to temperature fluctuations can be reduced to a minimum.

On the functional element, a surface coating of silicon oxide or silicon dioxide is produced by a thermal oxidation and in the functional element a plurality of armatures are likewise formed by the thermal oxidation. The anchors penetrate into the material of the functional element and provide for a temperature dependence of the movement behavior of the functional element. The substantially isotropic silicon particles preferably have a diameter of 0.03 pm to 1 pm. The solids formed in the solid pores preferably have a diameter of 0.01 m to 0.3 pm.

The solid produced by sintering has a density of at least 95% and preferably at least 99% of the density of crystalline silicon.

Due to the interplay of the size of the silicon particles used and the size of the pores formed in the solid after sintering, functional elements are obtained whose silicon oxide surface coating and also the formation of the anchors are produced in a significantly reduced reaction time. This results in a further improved mechanical stability while minimizing the temperature dependence of the movement behavior.

The process according to the invention has a significantly reduced expenditure of time for the production of the silicon oxide surface coating. Through the use of essentially isotropic silicon particles, with the properties described above, the pores with the properties described above form during sintering.

In the formation of the silicon oxide surface coating, the oxidation of the silicon can proceed more rapidly due to the pores also located on the surface, since a larger surface area of the silicon particles present in the solid body is accessible for the oxidation. Thus, anchors in the functional element are formed by the thermal oxidation such that the anchors of silicon oxide extend at least partially into a second layer of silicon particles.

For example, by coating a silicon spiral spring with a coating of silicon oxide, the temperature dependence of the modulus of elasticity of the coil spring and thus the temperature dependence of the return constant C can be minimized. As a result, the sensitivity of the coil spring to temperature fluctuations can be minimized. With progressing oxidation, the silicon oxide anchors are formed in the material of the functional element, which protrude into the functional element into the second or third layer of silicon particles. Surprisingly, it has been found that these silicon oxide anchors impart a significantly improved mechanical stability to the functional element.

This increased mechanical stability occurs in addition to the known minimization of the temperature dependence of the movement behavior of the functional element caused by a silicon oxide surface coating.

The silicon particles obtained in the abovementioned processes have a "substantially isotropic" form. The term "substantially isotropic" in the context of the present invention means particles which have no clearly defined preferred direction. The silicon particles do not have an ideal isotropic shape because they are not formed as spheres but have slight irregularities such as edges and small, flat surfaces. The diameter of a substantially isotropic silicon particle is understood to mean the maximum diameter of the silicon particle.

The isostatic pressing method provided according to the invention is based on the physical law that the pressure in liquids and gases propagates uniformly on all sides and generates forces on the applied surfaces which are directly proportional to these surfaces. In the method according to the invention, a mold filled with silicon particles is introduced into the pressure vessel of a press plant. The pressure acting on all sides of the mold via the liquid in the pressure vessel uniformly compresses the enclosed silicon powder. The binders used are preferably polyvinyl alcohol, polyvinyl butyral, polyethylene glycol and mixtures thereof. These binders have been found to be particularly suitable for use in the manufacture of functional elements for mechanical watches. According to a preferred embodiment of the present invention, silicon particles and binder in a weight ratio of silicon particles to binder of 100: 0, 1 to 100: 3 are used. Particular preference is given to using silicon particles and binders in a weight ratio of silicon particles to binder of from 100: 0.2 to 100: 2, and particularly preferably in a weight ratio of from 100: 0.5 to 100: 1. The said preferred amounts of binder are on the one hand large enough to provide a sufficient connection of the silicon particles in the Homogenisierungsschritts, and on the other hand low enough to be removed easily after the compression step from the solid can.

Ethanol is particularly preferably added to the binder before mixing with the silicon particles, in particular preferably in a weight ratio of ethanol to silicon particles of about 5: 1.

M ischen of Si l silicon particles and B ittel preferably carried out by spraying the binder on the silicon particles.

Particularly good results can be achieved if the homogenization of the mixture of silicon particles and binder by milling in a ball mill for a period of 2 to 24 hours. Particularly preferably, the milling takes place in the ball mill with simultaneous vacuum degassing. Of particular importance for the formation of the desired pores has the step of compacting the homogenized mixture of silicon particles and binder to a solid. As a result of the application of cold isostatic or hot isostatic pressing, the pressure is uniformly applied to the silicon powder from all directions. The hot isostatic pressing also improves the structure of the forming silicon solid by heating.

In principle, a hot isostatic pressing at 10 to 800 MPa and 30 ° C to 1400 ° C can be performed. Excellent properties of the functional elements arise when compacting at a temperature of 600 ° C to 1400 ° C or at a pressure of 100 to 300 MPa. Particularly preferably, the compression is carried out at a temperature of 600 ° C to 1400 ° C and at a pressure of 100 to 300 MPa.

Preferably, the homogenized mixture of silicon particles and binder is preheated prior to the densification step at a temperature of 100 ° C to 120 ° C. The compression is preferably carried out for a period of 2 to 4 hours.

The functional elements produced have particularly good properties if the solid produced by the compacting step has pores with a maximum diameter of 0.001 μm to 1 μm.

From the silicon solid body, the functional element is separated by removal of the material surrounding the functional element in the manner known to those skilled in the art. The material removal is preferably carried out by etching or cutting. The etching is particularly preferably carried out by a dry etching process, the cutting is particularly preferably carried out by laser cutting. The methods mentioned are known from the prior art, which is why their use in the context of the method according to the invention is not a problem for the person skilled in the art.

Preferably, the silica surface coating is produced by thermal oxidation. In this case, oxygen acts on the functional element at elevated temperature. By the duration of the oxidation, the thickness of the silicon oxide surface coating can be controlled. The precise parameters of thermal oxidation to form a silica surface coating are well known in the art. Their finding for a specific oxidation process is therefore no problem for the person skilled in the art. In principle, any type of functional element for mechanical watches can be produced by the method according to the invention. The functional elements are preferably a helical spring, a toothed wheel, a gear wheel, an escape wheel, an armature, a riff free or a shaft. Special advantages ben in the production of a coil spring for mechanical watches, since a particularly high mechanical stability and a particularly temperature-independent vibration behavior are required for this functional element.

The functional element according to the invention is characterized in that a solid produced from isotropic silicon particles by isostatic compaction has formed a multiplicity of pores having a maximum diameter of 0.001 μm to 1 μm. The functional element carries a silicon oxide surface coating on the functional element. Furthermore, a plurality of silicon oxide anchors are formed in the solid body, which extend in the solid state of the functional element at least up to a second layer of silicon particles. The pores formed in the solid body preferably have a diameter of 0.01 μm to 0.3 μm.

The present invention also includes a mechanical watch having a functional element formed according to the invention. All of the above-mentioned preferred embodiments may individually or in combination with other preferred embodiments further develop the coil spring according to the invention.

Brief description of the drawings

The invention will be explained in more detail below with reference to exemplary embodiments in conjunction with the drawings. The proportions in the figures do not always correspond to the actual size ratios, as some shapes are simplified and other shapes are shown enlarged in relation to other elements for ease of illustration. In the figures show

Fig. 1 is a perspective view of an embodiment of a coil spring used in a mechanical timepiece;

Figure 2 is a Schamtischen view of a cross section through a turn of the coil spring. Fig. 3 is an enlarged view of the Queschnitts by the coil spring, wherein on a Ausenfläche a layer of silicon dioxide is applied;

Fig. 4 is a schematic detail view of an armature extending from the layer of silicon dioxide into the core of silicon; Fig. 5 is another schematic representation of a section through the coil spring wherein the silicon core of the coil spring is constructed in its crystalline structure according to a first embodiment;

Fig. 6 is another schematic representation of a section through the coil spring, which is constructed according to a further embodiment; FIG. 7 is a plan view of a Si wafer produced by a sintering process in which the coil springs have already been produced by etching or cutting; FIG.

FIG. 8 is a detail view of the area marked A in FIG. 7; FIG.

Fig. 9 is a schematic partial view of a vertical section, wherein two opposite side surfaces of the coil spring are shown; 10 to 13, 15 shots with an electronic scanning microscope of a section of the edge region of a turn of a spiral spring, wherein the plan view is shown on the height h of the coil spring;

Figure 14 is a perspective view with an electronic scanning microscope of a portion of a turn of the coil spring; FIG. 16 shows various micrographs of a silicon-oxide-wound spiral spring produced from polycrystalline silicon;

FIG. 17 shows various micrographs of a coil spring made of monocrystalline silicon and coated with silicon oxide; Figure 18 is a schematic view of a cross section of a coil spring in which the silicon crystals are not homogenized and increase in size with increasing height of the coil spring;

Figure 19 is a schematic view of a cross section of a coil spring in which the silicon crystals are homogenized by a special process and thus have a widely homogeneous size distribution along the height of the coil spring; and

Figure 20 is a perspective view of a portion of the coil spring to illustrate the resulting due to the invention bending stiffness. Ways to carry out the invention

Figure 1 shows a perspective view of a coil spring 20 for mechanical movements. The spiral spring 20 has a spiral spring plane E which coincides with the oscillation plane of the spiral spring 20 and a spiral spring axis A which extends perpendicular to the spiral spring plane E through the oscillation center of the spiral spring 20. For non-rotatable connection with a balance shaft (not shown), the coil spring 20 has an inner coil spring attachment portion S. The outer spring holding point H of the coil spring 20 serves for the fixed connection of the spiral spring with a circuit board or a bearing plate. The coil spring 20 has a plurality of turns 22. Figure 2 shows a plan view of a cross section 24 through a turn 22 of the coil spring 20. In the embodiment shown here, each of the turns 22 of the coil spring 20 consists of a core 25 and a sheath 27, which consists of a layer 34 of silicon dioxide. The layer 34 of silicon dioxide is carried by each of the side surfaces 30 of each turn 22 of the coil spring 20. The layer 34 of silicon dioxide is generated by thermal odidation of the coil spring 20. After the thermal oxidation (with oxygen or a suitable CVD method) results for the coil spring 20, a height h and a width b of the windings 22 of the coil spring 20th Figure 3 shows a section through the coil spring 20 of Figure 1, according to an alternative embodiment. The coil spring 20 carries on an outer side a layer 34 of silicon dioxide. This can be achieved by suitable masking measures. The coil spring 20 comprises windings 22 (see FIG. 1), wherein a cross-section 24 of a winding 22 has a height h and a width b. At least one layer 34 of silicon dioxide is applied to a boundary region 31. The cross-section 24 along the height h comprises at least two superimposed discrete regions 26 _! , 26 _n , i = 1, n, of a silicon material. The silicon material of the regions 2Q i = 1, n, comprises amorphous and / or polycrystalline and / or monocrystalline silicon 2, 3, 4, 8, 9, 1 1, 12, 13, 14. Each region 26, has at least two Anchor 28 _{u formed} by growing crystals of silicon dioxide 34 in the boundary region 31. The anchors are formed in the process of thermal oxidation (with oxygen or a suitable CVD method) of silicon material of the existing coil spring 20. Each armature 28 _u has an individual roughness R _u , j = 1, ..., m.

According to the invention, at least one armature 28 _{u is} arranged in each region 26, which has the same roughness as another armature 28 _{Μ, Γ} and / or 28 _{i + 1, r of} an adjacent region 26, ie R _u , = R _ii , and / or R _u , = R, + _{! ,,} '.

An E-module may be used in areas 26 _! , 26 ₂ , ..., 26 _n vary by a maximum of 2% to a maximum of 3%. The modulus of elasticity is measured on the total modulus of elasticity of the considered cross-section 24 of the coil spring 20. To calculate the effective modulus of elasticity z. In the case of polysilicon, for example, epitaxial deposition processes or directional growth preferentially form crystal orientations or textures, preferably <1 10> and <1 1 1> and The textures <100>, <21 1> or <331> may also be present, however, because of the different e-moduli of the textures, a homogeneous distribution of the textures over the cross-section 24 of the spiral spring is to be aimed at. There must be at least two different textures in the regions 26 _!, 26 ₂ ,..., 26 _{n in} order to ensure a largely sufficient homogeneity of the cross section 24 of the spiral spring 20. In FIGS. 3 and 4, the crystals are shown in simplified form as rectangles or rectangles, but they may be both isotropic and anisotropic, as shown for example in FIGS. 5 or 6.

The finished outer surface 39 of the winding 22 of the spiral spring 20 corresponds to the outer surface of the finished at least one layer 34 made of silicon dioxide, ie after completion of the separation process of the spiral spring 20 from the carrier (silicon wafer 10) and after completion of the oxidation process to produce the at least one Layer 34 of silicon dioxide (see, for example, Figures 5 to 9 and the description thereof). For reasons of simplified illustration, only one single layer 34 of silicon dioxide 34 is shown in FIG. 3, but more than one layer 34 of silicon dioxide can be applied to the silicon material.

FIG. 4 shows a detailed view of an armature 28 _{u of} a region 26, according to FIG. 3. The armature 28 _u has an individual roughness R _u which does not generally coincide exactly with the mean roughness R over all armatures 28 of all regions 26 - roughness R runs along a center line 32 through all the anchors of all areas.

The illustrations of FIGS. 6 and 6 each show a section through a turn 22 of the spiral spring 20 of FIG. 1, wherein the spiral spring axis A is a component of the cutting plane and thus the cutting plane is perpendicular to the spiral spring plane E. The thicknesses of the individual layers are not reproduced to scale in FIGS. 5 and 6, so that it is not possible to deduce from the thickness of the one layer illustrated in the drawing to the thickness of another layer.

FIG. 6 shows a state of the coil spring 20 during the manufacturing process. The serving as a carrier silicon wafer 10 is provided in the representation shown in Figure 6 with a sacrificial layer 10.1 made of silicon dioxide. By means of an LPCVD method, a 0.4 pm thick first layer 1 1 made of polycrystalline silicon is deposited on the sacrificial layer 10. This first layer 1 1 consists of essentially isotropic silicon crystals 9, which in the exemplary embodiment shown have a diameter of 100 nm to 400 nm. The LPCVD procedure is carried out with silane as the process gas at a pressure of 0.6-10 ³ Pa and a temperature of 1000 ° C. Due to the deposition rate of about 200 nm / min, the first layer 1 1 builds up within about 2 minutes.

Subsequently, gas flow, process pressure and process temperature are increased, and using silane as a process gas, a CVD process is performed. At a process pressure of 5.7 - 10 ³ Pa and a process temperature of 1060 ° C, a deposition rate of about 2 pm per minute sets. Within 20 minutes, a second layer 12 of polycrystalline silicon arranged on the first layer 1 1 of polycrystalline silicon is formed with a thickness parallel to the spiral axis A of 40 μm. The second layer 12 of polycrystalline silicon is made of anisotropic silicon crystals 8, wherein the anisotropic silicon crystals 8 in the illustrated embodiment has a diameter parallel to the spiral spring plane E of 50 nm to 100 nm and a height parallel to the coil spring axis A from 5 pm to 30 pm exhibit. Subsequently, the parameters gas flow, process pressure and process temperature are set to the values for the method described above in connection with the formation of the first layer 11 and an LPCVD method for forming a third 13, arranged on the second 12 layer of polycrystalline silicon 0, 4 m thick layer of polycrystalline silicon performed. This third layer 13 in turn consists of substantially isotropic silicon crystals 9 with a diameter of 100 nm to 400 nm.

Subsequently, gas flow, process pressure and process temperature are increased again, and using silane as the process gas another CVD process is performed. At a process pressure of 5.7 - 10 ³ Pa and a process temperature of 1060 ° C, a deposition rate of about 2 pm per minute sets. Within 20 minutes, a fourth polycrystalline silicon layer 14 disposed on the third polycrystalline silicon layer 13 is formed with a thickness parallel to the coil spring axis A of 40 μm. The fourth layer 14 of polycrystalline silicon likewise consists of anisotropic silicon crystals 8, wherein the anisotropic silicon crystals 8 in the illustrated embodiment have a diameter. have parallel to the spiral spring plane E from 50 nm to 100 nm and a height parallel to the coil spring axis A of 5 pm to 30 pm.

After this process step, the spiral spring connected to the silicon wafer 10 has the shape shown in FIG. Subsequently, the structuring of the spiral spring takes place successively by a material-removing chemical etching process with the aid of photomasks, the detachment of the spiral spring from the silicon wafer 10 by dissolving the sacrificial layer 10.1 made of silicon dioxide by means of a chemical etching process, and the implementation of a thermal oxidation (with oxygen or a suitable CVD method) to produce a layer 34 of silicon oxide. The thermal oxidation (with oxygen or a suitable CVD method) is carried out for a correspondingly selected time period so that a first 1 and a fifth 5 layer 34 of silicon oxide with a layer thickness of about 2.5 μm are formed. In the course of the formation of the first layer 34 made of silicon oxide, the first, consisting of substantially isotropic silicon crystals layer 1 1 dissolves completely. By the silicon oxide surface coating, a minimization of the temperature dependence of the vibration behavior of the coil spring 20 is achieved.

An inventive embodiment of the coil spring 20 for mechanical movements is shown in FIG. The spiral spring is constructed in a direction parallel to the spiral spring axis A of five layers 1, 2, 3, 4, 5, namely a 2.5 pm thick, first layer 1 of silicon oxide, one arranged on the first layer 1 of silicon oxide, 40th m thick, second layer 2 of polycrystalline silicon, wherein the second layer 2 consists of anisotropic silicon crystals 8, wherein the anisotropic silicon crystals 8 have a diameter parallel to the spiral spring plane E of 50 nm to 100 nm and a height parallel to the spiral spring axis A from 5 pm to 30 pm, a 0.4 pm thick third, arranged on the second layer 2 of polycrystalline silicon layer 3 of polycrystalline silicon, wherein the third layer 3 of substantially isotropic silicon crystals 9 having a diameter of 100 nm to 400 nm, one on the third layer 3rd made of polycrystalline silicon, 40 pm thick, the fourth layer 4 of polycrystalline silicon, wherein the fourth layer 4 of anisotropic silicon crystals 8, wherein the anisotropic silicon crystals 8 have a diameter parallel to the spiral spring plane E of 50 nm to 100 nm and a Have height parallel to the spiral spring axis A from 5 pm to 30 pm, a arranged on the fourth layer 4 of polycrystalline silicon, 2.5 pm thick, fifth layer 5 of silicon oxide.

The coil spring shown can be manufactured with minimal loss through fractures and cracks of consistently excellent quality. Although the following description refers to a coil spring as a functional element, this should not be construed as limiting the invention.

FIG. 7 shows a plan view of an Si wafer 10 produced by a sintering process, in which the spiral springs 20 have already been produced and exposed by etching or cutting. In the method for producing the Si wafer 10, essentially isotropic silicon particles 40 (see FIG. 9) with a diameter of between 0.03 μm and 1 μm were used as a by-product in the production of silicon granules with the aid of a fluidized bed Procedures were incurred. The binder used was polyvinyl alcohol. The mixture of silicon particles 40 and binder in the ratio of 100: 0.75 was carried out by spraying a Binder ittel / ethanol mixture on the silicon particles 40. The mixture thus produced was prepared by milling in a ball mill for a period of Homogenized for 12 hours with simultaneous vacuum degassing.

After introducing the homogenized mixture of silicon particles 40 and binder into a mold (not shown), the homogenized mixture was sintered to a solid. In the case where the sintering is a hot isostatic compaction, this is carried out at a temperature of 1000 ° C and a pressure of 250 MPa for 3 hours. The produced solid or Si wafer 6 has pores 2 (see FIG. 9) with a maximum diameter P of 0.001 μΓΠ to 1 m. The solid produced by the densification of the homogenized mixture of silicon particles 1 and binder preferably has a density of at least 95%, preferably at least 99%, of the density of crystalline silicon. The binder was removed by evacuation from the solid produced in this way. The separation of the binder is preferably carried out by evacuation or by purging with an inert gas. Simultaneously with the separation of the binder, the silicon solid formed is cooled to room temperature.

FIG. 8 shows a detailed view of the region of the Si wafer 10 labeled A in FIG. 6. It is obvious to a person skilled in the art that the material of the spiral spring 20 can be different. The separation of the coil spring 20 is preferably carried out by a dry etching, whereby the surrounding the coil spring 20 material 21 is removed.

The silicon particles 40 illustrated as spheres in an idealized manner in FIG. 9 each have an average diameter D of between 0.03 μm and 1 μm. It is a schematic partial view of a vertical section shown, wherein two opposite side surfaces 30 of the coil spring 20 are shown in part. Between the individual silicon particles 40, the pores 42 can be seen, which have formed due to the sintering process. The pores 42 have a maximum diameter P of 0.001 pm to 1 pm, preferably 0.01 pm to 0.3 pm. The solid (Si wafer 10) produced by compacting a homogenized mixture of silicon particles 1 and the binder polyvinyl alcohol has a density of at least 95%, preferably at least 99%, of the density of crystalline silicon. Depending on the choice of the size distribution of the silicon particles 40, the density of the sintered solid body can correspond to up to 99.9% of the density of crystalline silicon.

The layer 34 on the silicon surface is formed in the course of the treatment of the Si wafer 10. In the course of the formation of the layer 34 on the silicon surface, a plurality of anchors 44 of silicon oxide or silicon dioxide are formed. within the Si wafer 10, which have the material properties described above. The individual silicon particles 1 arrange themselves during the compaction in layers 45 _! , 45 ₂ , .., 4 5 _n . Due to the size distribution of the silicon particles 40 and the size distribution of the pores 42 in the Si wafer 10, the layers 45 _! , 45 ₂ , .., 45 _n are shown only schematically. The size distribution of the pores 42 in the Si wafer 10 and the treatment parameters in the furnace in the production of the layer 34 on the silicon surface cause the largest proportion of the anchor 44 of silicon oxide at least until the second layer 45 ₂ and 45 _{n -} i extends from silicon particles 40th The spiral spring thus produced has excellent properties in terms of temperature behavior and excellent mechanical stability.

Figures 10 to 13, 15 show images with an electronic scanning microscope of a section of the edge region of a turn of a spiral spring, wherein the plan view is shown on the height h of the coil spring. FIG. 10 shows an enlarged detail of FIG. 11, and FIG. 12 shows an enlarged detail of FIG. 13.

FIGS. 10 and 11 show, with respect to a first sample, a section of the cross-section 24 of a winding 22 of a first spiral spring, wherein the roughness on the finished outer surface 39 of the winding 22 of the first spiral spring is comparatively large. (The finished outer surface 39 also corresponds to the side surface 16 in FIG. 9.)

FIGS. 12 and 13 show, with respect to a second sample, a section of the cross section 24 of a winding 22 of another second spiral spring, the roughness on the finished outer surface 39 of the winding 22 of the second spiral spring of FIGS. 12 and 13 in comparison with FIGS. 10 and 1 1 is small.

The finished outer surface 39 of the winding 22 of the respective spiral spring corresponds to the outer surface of the respective finished at least one layer of silicon dioxide 34, ie after completion of the separation process of the respective coil spring from the carrier, for example from the silicon wafer 10, and after completion of the oxidation process for producing the at least one layer of silicon dioxide 34 (cf., for example, FIGS. 5 to 9 and the description thereof).

In the embodiments relating to FIGS. 3 and 4, the roughness or roughness depth R of the material of the transition or boundary region 30 to the at least one oxide layer, in particular silicon dioxide layer 34, is considered. This material can be, for example, amorphous and / or polycrystalline and / or monocrystalline silicon, for example layers 2, 4, 12, 14 of anisotropic silicon crystals, layers 3, 11, 13 of substantially isotropic silicon (-5) crystals, respectively anisotropic silicon crystals 8 and isotropic silicon crystals 9, respectively. However, there is also a direct relationship between on the one hand the roughness depth of the output surface 38 for applying the at least one layer of silicon dioxide 34, thus for example the etched silicon side surface 38 according to FIG. 6, and on the other hand the finished outer surface 39 of the grown oxide layer 34 10 to 13 and already described above, have the resulting from the two different finished samples with respect to the first coil spring 20 (see Figure 10 and 1 1) and the second coil spring 20 (see Figures 12 and 13) Outside surfaces 39 greatly different roughness. The comparatively large roughness on the finished outer surface 39 of the winding 22 of the first coil spring 20 according to FIGS. 10 and 11 has the disadvantage that with the associated component or functional element 8 or spiral spring 20 with ever greater roughness the stability also decreases and the risk of breakage increases, as previously described in detail at various points.

A roughness R _{z of} the output surface 38 in the amount of 0.001 pm to 3 pm, preferably from 0.01 pm to 2 pm, has proven to be ideal with respect to the reduction of stresses in the finished coil spring 20. For this purpose, the surface roughness R _{z of} the finished outer surface 39 should be 0.001 m to 2 pm.

Figure 14 shows a perspective view with an electronic scanning microscope of a portion of a winding 22 of the coil spring. FIG. 16 shows various micrographs of a coil spring made of polycrystalline silicon and coated with silicon oxide.

FIG. 17 shows various microscopic photographs of a spiral spring produced from monocrystalline silicon 36 and coated with silicon dioxide 34. FIG. 18 shows a schematic view of a cross section of a spiral spring 20, in which the silicon crystals 36 are not homogenized and increase in size as the height h of the spiral spring 20 increases.

FIG. 19 shows a schematic view of a cross section of a spiral spring 20, in which the silicon crystals 36 are homogenized by a special process, for example annealing, as described above and thus have a largely homogeneous size distribution along the height h of the spiral spring 20.

Figure 20 is a perspective view of a portion of the coil spring 20 illustrating the bending stiffness resulting from the invention, as previously described.

LIST OF REFERENCE NUMBERS

1 first layer of silicon oxide

2 second layer of anisotropic silicon crystals

3 third layer of essentially isotropic silicon-5 crystals

4 fourth layer of anisotropic silicon crystals

5 fifth layer of silicon oxide

8 anisotropic silicon crystals

9 isotropic silicon crystals

10 silicon wafers

10.1 sacrificial layer of silicon dioxide

1 1 first layer of substantially isotropic silicon crystals

12 second layer of anisotropic silicon crystals

13 third layer of substantially isotropic silicon crystals 14 fourth layer of anisotropic silicon crystals

20 spiral spring

21 surrounding material

22 turn

24 cross section

25 core

26 area

27 serving

28 anchor made of silicon dioxide

30 side surface

31 border area

32 midline

34 layer of silicon dioxide

36 crystal (silicon material)

38 output surface

39 finished outer surface

40 silicon particles 42 pores

44 anchors

45 !, 45 ₂ , ..., 45 _n layers

A spiral spring axis

b Width of the spiral spring

E spiral spring plane

F force

F1. F2. F3 area

S Spiral spring attachment section h Height of the spiral spring

H spring breakpoint

R roughness (roughness)

ß angle

Claims

claims

Comprising a spiral spring (20) for a mechanical movement

Windings (22), wherein a cross section (24) of a winding (22) of the spiral spring

(20) has a height (h) and a width (b), and

a layer (34) of silicon dioxide is deposited on at least one of the side surfaces (30),

wherein the cross section (24) along the height (h) at least two superimposed regions (26, 26, 26 _n ), i = 1, n, from a silicon material comprises, and

each region (26,) has formed at least two anchors (28, 10) formed by growing the layer (34) of silicon dioxide in a boundary region (31), each anchor (28,) having a roughness (R,.) , j = 1, m, has,

characterized in that

in each region (26,) at least one armature (28,.) is formed, which has the same roughness as another armature (28, _.1 , 28, _{+ 1} ..) of an adjacent region (26,).

Spiral spring (20) according to claim 1, wherein the average roughness (R) over the armature (28, _j ) of the regions (26, 26, 26 _n ) is a maximum in the interval of 0.5pm to 10.0 m, preferably in the interval from 0, 1 pm to 5.0 pm, and more preferably in the interval from 0.3pm to 3.0pm.

A coil spring (20) according to claim 1, wherein the average roughness (R) across the anchors (28 _,. ) Of the regions (26, 26, 26 _n ) is in the interval 0.001 pm to 2.0 pm.

Spiral spring (20) according to one of the preceding claims, wherein a width variation of an oxide layer on the coil spring at most 15%, preferably 10% and more preferably maximum. 5% / the total width of the oxide layer is.

5. spiral spring (20) according to any one of the preceding claims, wherein the distribution of the roughness (R,.) Via the armature (28,,) of the areas (26 _!, ..., 2ß _n ) is minimal.

6. coil spring (20) according to one of the preceding claims, wherein the frequency with respect to the number of anchors (28, _j ) of each region (26, 26, 26 _n ) is maximum.

7. spiral spring (20) according to one of the preceding claims, wherein an E-modulus of the regions (26, 26, 26 _n ) varies by a maximum of 2% to 3% based on a total modulus of the considered cross section of the coil spring. 8. spiral spring (20) according to any one of the preceding claims, wherein in each of the regions (26, 26, 26 _n ) at least two different textures are present.

9. spiral spring (20) according to any one of the preceding claims, wherein the respective silicon material of the regions (26, 26, 26 _n ), i = 1, n, amorphous and / or polycrystalline and / or monocrystalline silicon (2, 3, 4 , 8, 9, 11, 12, 13, 14).

10. spiral spring (20) according to one of the preceding claims, wherein a roughness R _{z of} an output surface (38) for applying the at least one layer of silicon dioxide (34) between 0.03 pm to 3 pm and preferably 0.01 pm to 2 pm, wherein a roughness R _{z of} a finished outer surface (39) is between 0.001 m to 2 pm.

11. Mechanical watch with a spiral spring (20) according to one of the preceding claims.