Method for manufacturing mechanical resonators

Abstract

One aspect of the invention relates to a method for manufacturing a set of mechanical resonators (2a) whose structural properties have an average value within a predetermined range, comprising the steps of: forming (20) mechanical resonators (2b, 2c) and at least one oscillating member (10a, 10b, 10c) in a substrate (1); based on the calculated dimension correction value, the dimensions of the formed resonators (2a) are modified (28) to obtain a set of resonators (2a) having structural characteristic values within a predetermined numerical range.

Description

(19) State Intellectual Property Office (12) Invention Patent Application (10) Application Publication Number (43) Application Publication Date (21) Application Number 202511847517.9 (22) Application Date 2025.12.09 (30) Priority Data 24219896.8 2024.12.13 EP (71) Applicant Nivallos-Fal GmbH Address Switzerland (72) Inventor G. Chasan P. Carson (74) Patent Agency Beijing Zhongzi Law Firm 11247 Patent Attorney Gao Meiyan Wu Peng (51) Int.Cl. H03H 9 / 24 (2006.01) H03H 3 / 00 (2006.01) G04B 17 / 20 (2006.01) (54) Invention Title: Method for Manufacturing Mechanical Resonators (57) Abstract: One aspect of the present invention relates to a method for manufacturing a set of mechanical resonators (2a) whose average structural characteristics are within a predetermined range, the method comprising the steps of: forming (20) mechanical resonators (2b, 2c) and at least one oscillating member (10a, 10b, 10c) in a substrate (1); modifying (28) the dimensions of the formed resonators (2a) based on a calculated size correction value to obtain a set of resonators (2a) whose structural characteristic values ​​are within a predetermined numerical range. Claims 2 pages, Description 10 pages, Drawings 4 pages, CN 122226009 A 2026.06.16 CN 1 22 22 60 09 A 1. A method for manufacturing a set of mechanical resonators (2a) having an average structural characteristic within a predetermined range, the structural characteristic being common to each mechanical resonator (2a) in the set of mechanical resonators (2a), the method comprising the steps of: a) step (20) forming mechanical resonators (2b, 2c) in a substrate (1), the size of the mechanical resonators (2b, 2c) being different from the size required to obtain the set of mechanical resonators (2a) with structural characteristics within the predetermined range; (b) Step (21) of forming at least one oscillating member (10a, 10b, 10c) in the substrate (1), wherein the at least one oscillating member (10a, 10b, 10c) is formed in the opening (9) of the substrate (1), and the oscillating member (10a, 10b, 10c) is composed of a main body (6) and two flexible arms (7, 8). The body of the main body (6) is connected at the first end (5a) to the fixing part (15) of the outer peripheral wall (13) of the opening (9). The two flexible arms are connected to the second end (5d) of the main body (6) through the connecting part (14). The two flexible arms (7, 8) are parallel to the axis of symmetry (A) of the main body (6) and face towards the main body.The portion (16) of the outer peripheral wall (13) opposite to the fixing part (15) extends, and the body of the main body (6) includes a portion between the first end (5a) and the second end (5d), the axial section (S4) of which is smaller than the axial section (S2) of the first end (5a) and the axial section (S1) of the second end (5d); c) Determining step (22), in which a value related to the structural characteristics of the formed at least one oscillating member (10a, 10b, 10c) is determined; d) Calculation step (26), in which a size correction value to be applied to the formed mechanical resonators (2b, 2c) is calculated based on the value determined for the structural characteristics; e) Modification step (28), in which the size of the formed mechanical resonators (2b, 2c) is modified based on the calculated size correction value to obtain the set of mechanical resonators (2a) with structural characteristic values ​​within a predetermined range. 2. The method according to claim 1, characterized in that, in step (21) of forming the oscillating members (10a, 10b, 10c), the axial cross section (S4) of the portion between the first end (5a) and the second end (5d) of the body of the main stem (6) is larger than the axial cross section (S3) of each of the flexible arms (7, 8). 3. The method according to any of the preceding claims, characterized in that, in step (21) of forming the oscillating members (10a, 10b, 10c), each of the flexible arms (7, 8) has a length (L) adjustable according to a resonance measurement tolerance factor defined by at least one dimension (E2, E3, H2, H3) of the flexible portion (3) of the mechanical resonator (2b, 2c) associated with the at least one oscillating member (10a, 10b, 10c). 4. The method according to any one of the preceding claims, characterized in that, in step (21) of forming the oscillating members (10a, 10b, 10c), one of the two flexible arms (7, 8) is spaced apart from the other flexible arm by a first distance (D1), and the free end (5b, 5c) of each of the flexible arms (7, 8) is spaced apart from the portion (16) opposite to the fixed portion (15) by a second distance (D2), wherein the first distance (D1) is greater than the second distance (D2). 5. The method according to any one of the preceding claims, characterized in that, in step (21) of forming the oscillating members (10a, 10b, 10c), the thickness (Er) of each of the flexible arms (7, 8) is equal to or substantially equal to the thickness of the flexible portion (3) of each mechanical resonator (2b, 2c) formed in the substrate (1).6. The method according to any one of the preceding claims, characterized in that, in step (21) of forming the oscillating members (10a, 10b, 10c), the free end (5b, 5c) of each of the flexible arms (7, 8) is integrally formed with the end member (11, 12), the mass of the end member being greater than the mass of the remaining portion of the body of the flexible arm (7, 8). 7. The method according to claim 6, characterized in that the end member (11, 12) has a circular or polygonal cross-section. Claims 1 / 2 page 2 CN 122226009 A 8. The method according to any one of the preceding claims, characterized in that, in step (21) of forming the oscillating members (10a, 10b, 10c), the axial section (S4) of the portion of the body of the main body (6) between the first end (5a) and the second end (5d) is 1 / 2 to 1 / 5 of the axial section (S2) of the first end (5a) and the axial section (S1) of the second end (5d), respectively. 9. The method according to any one of the preceding claims, characterized in that step (20) of forming the mechanical resonators (2b, 2c) and step (21) of forming at least one oscillating member (10a, 10b, 10c) are carried out by etching, particularly by deep reactive ion etching. 10. The method according to any one of the preceding claims, characterized in that step (21) of forming each oscillating member (10a, 10b, 10c) is carried out in the substrate (1) for at least one of the mechanical resonators (2b, 2c) in the group of mechanical resonators (2b, 2c). 11. The method according to any one of claims 1 to 9, characterized in that step (21) of forming the oscillating member (10a, 10b, 10c) is used to form a plurality of oscillating members (10a, 10b, 10c) around at least one mechanical resonator (2b, 2c) in the substrate (1). 12. The method according to any one of the preceding claims, characterized in that the determining step (22) includes an estimation sub-step (23), in which at least one resonant frequency is estimated for each oscillating member (10a, 10b, 10c) associated with at least one mechanical resonator (2b, 2c) in the group of mechanical resonators (2b, 2c). 13. The method according to any one of the preceding claims, characterized in that the determining step (22) includes a defining sub-step (25), in which a structural characteristic is defined for each oscillating member (10a, 10b, 10c) that is identical in nature to the structural characteristics common to each of the formed mechanical resonators (2b, 2c), the defining sub-step...(25) is executed by a processing unit connected to a device for modifying the formed mechanical resonators (2b, 2c), the processing unit executing an algorithm to calculate the structural characteristics of each oscillating member (10a, 10b, 10c) based on the estimated resonant frequency. 14. The method according to any one of the preceding claims, characterized in that the calculation step (26) includes a material thickness determination sub-step (27), in which the thickness (e) of material to be added to or removed from at least one dimension of each mechanical resonator (2b, 2c) associated with the oscillating member (10a, 10b, 10c) is determined based on the structural characteristic values ​​determined for each oscillating member (10a, 10b, 10c). 15. The method according to any one of the preceding claims, characterized in that the oscillating member (10) is in the shape of a tuning fork. 16. The method according to any one of the preceding claims, characterized in that the structural characteristics are stiffness characteristics. Claims 2 / 2 Page 3 CN 122226009 A Method for Manufacturing Mechanical Resonators Technical Field

[0001] This invention relates to the field of manufacturing mechanical resonators, particularly in the field of watchmaking. More specifically, this invention relates to a method for manufacturing a set of mechanical resonators, wherein structural characteristics common to these resonators, such as stiffness, are within a predetermined numerical range. Background Art

[0002] In the prior art, methods commonly used to manufacture mechanical resonators, such as watch hairsprings, in a substrate involve etching techniques such as laser etching, plasma etching, deep reactive ion etching (DRIE), or wet etching.

[0003] However, it has been found that using such methods often results in geometric deviations between all watch hairsprings formed on the same substrate with the same pattern.

[0004] To overcome these shortcomings, solutions have been proposed in the prior art, particularly patents EP 3181938 and EP 3181939, which describe methods for manufacturing hairsprings.

[0005] In patent EP3181938, the manufacturing method includes the following steps: a) forming a hairspring, the size of which is larger than the size required to obtain a hairspring with a predetermined stiffness; b) determining the stiffness of the hairspring formed in step a) by measuring the frequency of the hairspring connected to a balance wheel with a predetermined inertia; c) calculating the thickness of material to be removed to obtain a hairspring with a predetermined stiffness; and d) removing the calculated material thickness from the hairspring formed in step a), wherein steps b), c), and d) can be repeated to further improve dimensional accuracy.

[0006] In patent EP 3181939, the manufacturing method includes the following steps: a) forming a hairspring, the size of which is smaller than the size required to obtain a hairspring with a predetermined stiffness; b) determining the stiffness of the hairspring formed in step a) by measuring the frequency of the hairspring connected to a balance wheel with a predetermined inertia.The frequency is determined to determine the stiffness of the hairspring formed in step a); c) the material thickness missing to obtain a hairspring with a predetermined stiffness is calculated; d) the hairspring formed in step a) is modified to compensate for the missing material thickness, wherein steps b), c) and d) can be repeated to further improve dimensional accuracy.

[0007] Such methods can be improved, especially to limit substrate contamination that may occur during the measurement steps.

[0008] In this case, it is obvious that a solution that can bring about such improvement is needed. Summary of the Invention

[0009] The present invention aims to provide a method for manufacturing a set of mechanical resonators that meets the above requirements.

[0010] The present invention also aims to improve the manufacturing accuracy of multiple sets of mechanical resonators, wherein the average value of structural characteristics such as stiffness of the multiple sets of mechanical resonators is within a predetermined numerical range.

[0011] The present invention relates to a method for manufacturing a set of mechanical resonators, wherein the average value of the structural characteristics of the set of mechanical resonators is within a predetermined numerical range, the structural characteristics being common to each mechanical resonator in the set of mechanical resonators, the method comprising the following steps:

[0012] a) forming a mechanical resonator in a substrate, the size of the mechanical resonator being different from the size required to obtain the set of mechanical resonators with structural characteristics within the predetermined numerical range;

[0013] b) forming at least one oscillating member in the substrate, the at least one oscillating member being formed in an opening in the substrate, the oscillating member comprising a main body and two flexible arms, the body of the main body being described on page 1 / 10 of the specification, CN 122226009 A. A fixed portion is connected to the outer peripheral wall of the opening at one end. The two flexible arms are connected to the second end of the main body through a connecting portion. The two flexible arms extend parallel to the axis of symmetry of the main body and toward the portion of the outer peripheral wall opposite to the fixed portion. The body of the main body includes a portion between the first end and the second end, the axial section of which is smaller than the axial section of the first end and the axial section of the second end;

[0014] c) Determining step, in which a value related to the structural characteristics of the formed at least one oscillating member is determined;

[0015] d) Calculation step, in which a size correction value to be applied to the formed mechanical resonator is calculated based on the value determined for the structural characteristics;

[0016] e) Modification step, in which the size of the formed mechanical resonator is modified based on the calculated size correction value to obtain the set of mechanical resonators with structural characteristic values ​​within a predetermined range.

[0017] In other embodiments:

[0018] - In the step of forming the oscillating member, the first end and the second end of the body of the main body are made toThe axial cross section of the portion between them is larger than the axial cross section of each of the flexible arms;

[0019] - In the step of forming the oscillation member, each of the flexible arms has a length that can be adjusted according to a resonance measurement tolerance factor defined by at least one dimension of the flexible portion of the mechanical resonator associated with the at least one oscillation member;

[0020] - In the step of forming the oscillation member, one of the two flexible arms is spaced apart from the other flexible arm by a first distance, and the free end of each of the flexible arms is spaced apart from the portion opposite to the fixed portion by a second distance, the first distance being greater than the second distance;

[0021] - In the step of forming the oscillation member, the thickness of each of the flexible arms is equal to or substantially equal to the thickness of the flexible portion of each mechanical resonator formed in the substrate;

[0022] - In the step of forming the oscillation member, the free end of each of the flexible arms is integrally formed with an end member, the mass of which is greater than the mass of the rest of the body of the flexible arm;

[0023] - The end member has a circular or polygonal cross section;

[0024] - In the step of forming the oscillating member, the axial cross-section of the portion of the main body between the first end and the second end is 1 / 2 to 1 / 5 of the axial cross-section of the first end and the axial cross-section of the second end, respectively;

[0025] - The steps of forming the mechanical resonator and forming at least one oscillating member are carried out by etching, particularly by deep reactive ion etching;

[0026] - The step of forming each oscillating member is carried out in the substrate for at least one mechanical resonator in the group of mechanical resonators;

[0027] - The step of forming the oscillating member is used to form a plurality of oscillating members around at least one mechanical resonator in the substrate;

[0028] - The determining step includes an estimation sub-step in which at least one resonant frequency is estimated for each oscillating member associated with at least one mechanical resonator in the group of mechanical resonators;

[0029] - The determining step includes a definition sub-step in which structural characteristics are defined for each oscillating member, the structural characteristics being the same as those common to each formed mechanical resonator. This definition sub-step is executed by a processing unit connected to a device for modifying the formed mechanical resonators. The processing unit executes an algorithm to calculate the structural characteristics of each oscillating member based on the estimated resonant frequency.

[0030] - The calculation step includes a material thickness determining sub-step, in which the material thickness determining sub-step determines the mechanical resonator to be associated with each oscillating member based on the structural characteristic values ​​determined for each oscillating member.The thickness of material added to or removed from at least one dimension;

[0031] - The oscillating member is in the shape of a tuning fork;

[0032] - The structural characteristic is a stiffness characteristic.

[0033] Other features and advantages of the invention will become apparent from the description of specific embodiments of the invention provided with reference to the accompanying drawings, which are illustrative and not limiting examples only, wherein:

[0034] FIG1 is a schematic diagram of a substrate according to an embodiment of the invention, the substrate comprising a set of mechanical resonators, all of which have been simultaneously formed, particularly by etching, in the substrate;

[0035] FIG2A is an enlarged view of an oscillating member in the form of a tuning fork according to an embodiment of the invention, the oscillating member being capable of determining common characteristic values ​​of the mechanical resonators, the oscillating member and its resonators being contained in the substrate shown in FIG1;

[0036] FIG2B and FIG2C are variations of the oscillating member in FIG2A according to an embodiment of the invention, wherein the free end of the flexible arm of the oscillating member includes an end member, the mass of which is greater than the mass of the rest of the flexible arm;

[0037] FIG3 is a schematic cross-sectional view of the flexible portion of a resonator manufactured using the method according to an embodiment of the invention, the dimensions of which are necessary to ensure that the average value of the structural characteristics of the set of mechanical resonators is within a predetermined range;

[0038] Figure 4 is a schematic cross-sectional view of a flexible portion of a resonator formed in a substrate using the method according to an embodiment of the present invention. The size of this cross-section is larger than the size of the cross-section of the resonator shown in Figure 3.

[0039] Figure 5 is a schematic cross-sectional view of a flexible portion of a resonator formed in a substrate using the method according to an embodiment of the present invention. The size of this cross-section is smaller than the size of the cross-section of the resonator shown in Figure 3.

[0040] Figure 6 is a flowchart relating to a method for manufacturing a set of mechanical resonators according to an embodiment of the present invention, wherein the average value of the structural characteristics of the set of mechanical resonators is within a predetermined numerical range. Detailed Description

[0041] Figure 6 shows a schematic diagram of a method for manufacturing a set of mechanical resonators 2a on a substrate 1 (referred to as a "wafer") formed of a material. The substrate 1 may be a monocrystalline silicon substrate, but may also be a substrate made of other materials, such as polycrystalline silicon, amorphous silicon, other semiconductor materials, glass, ceramics, carbon, quartz, metals, alloys, or composite materials containing these materials. However, monocrystalline silicon is relatively insensitive to magnetic fields and is a cubic crystal with an isotropic coefficient of thermal expansion (α).

[0042] In this method, the mechanical resonators 2a, 2b, and 2c are elastically deformable components capable of being driven by oscillating motion. In other words, the mechanical resonators 2a, 2b, and 2c include a body composed of a flexible portion 3 and a connecting portion that is rigid relative to the flexible portion 3, the connecting portion allowing the mechanical resonators 2a, 2b, and 2c to be fixed to a shaft or spindle. This mechanical resonator...Vibrators 2a, 2b, and 2c can be used in watches, especially in the mechanical regulators of mechanical watch movements. In watches, the oscillation of such mechanical resonators determines the timekeeping error of the movement. For example, many watches include a regulator that includes a hairspring as a mechanical resonator, which is mounted on the balance wheel shaft and oscillates via an escapement. The natural frequency of the hairspring-balance wheel mechanism regulates the watch's speed. The hairspring includes an elastic flexible band that is connected at one end to an inner stud and is wound in a spiral to form multiple consecutive turns, with the last turn extending into an attachment section for attachment, for example, to a fixed balance bridge via an outer stud. The inner stud is designed to be fixed to a pivot. Other known types of resonators are illustrated on page 3 / 10 of the specification, 6 CN 122226009 A, such as those based on an oscillating rod or other mechanical components.

[0043] Therefore, this method is capable of producing a set of mechanical resonators 2a whose average structural characteristics are within a predetermined range. In this method, the structural characteristic is common to all mechanical resonators 2a in the group of mechanical resonators. In other words, these mechanical resonators have the same structural characteristics. The structural characteristic can be the stiffness characteristic of the mechanical resonator 2a, especially the stiffness characteristic of its flexible part 3. In this case, the method makes it possible to select the specific group of mechanical resonators 2a from the plurality of mechanical resonators formed in the substrate 1. To this end, the method helps to generate a mapping map that indicates the geometric dispersion between the dimensions of the plurality of mechanical resonators formed in the substrate, thereby indicating the dispersion between their common structural characteristics, and by correcting the selected group of mechanical resonators, the average value of their structural characteristics is within a predetermined numerical range. This method aims to ensure that the manufactured mechanical resonators 2a have extremely high dimensional accuracy, while at the same time ensuring that these mechanical resonators 2a have more accurate structural characteristics.

[0044] It should be noted that in a preferred embodiment of the method, the mechanical resonators 2a, 2b, 2c can be a clock spring, and its structural characteristic can be the stiffness of the spring, especially the stiffness of its strip. In this case, the method can then be a method for manufacturing a set of clockwork springs 2a or a component of clockwork springs 2a in a substrate 1, wherein the average stiffness of each spring is within a predetermined range.

[0045] Referring to FIG1, a set of mechanical resonators 2a is formed in a substrate 1. In this set of mechanical resonators, each mechanical resonator 2a includes a flexible portion 3 and a rigid connecting portion for fixing the mechanical resonator to a shaft or spindle.

[0046] In the case where the mechanical resonator is a clockwork spring, the clockwork spring includes an inner stud for fixing it to a pivoting spindle.

[0047] This method is used in a system for manufacturing a set of mechanical resonators 2a, 2b, 2c in a substrate 1. The system includes, but is not limited to, a system for manufacturing a set of mechanical resonators 2a, 2b, 2c in a substrate 1.The invention may be exhaustive or not limited to: a processing unit (e.g., a computer), means for forming mechanical resonators 2b, 2c and at least one oscillation member 10a, 10b, 10c in a substrate 1, and means for modifying the mechanical resonators 2b, 2c formed in the substrate 1.

[0048] The means for forming the mechanical resonators 2b, 2c and the oscillation members 10a, 10b, 10c can be used to implement microfabrication techniques in the substrate 1, such as photolithography, machining, and etching methods. In particular, methods such as deep reactive ion etching, laser etching, chemical etching, or etching using a focused ion beam can be employed.

[0049] The means for modifying the mechanical resonators 2b, 2c includes a module for determining the structural characteristics of the mechanical resonators 2b, 2c and a module for correcting the dimensions of the mechanical resonators 2b, 2c. The module for determining structural characteristics includes:

[0050] - a driving submodule for driving / releasing the mechanical oscillating motion of the bodies of the oscillating members 10a, 10b, 10c about their stable equilibrium positions;

[0051] - a measuring submodule for measuring the resonant frequency of the oscillating members 10a, 10b, 10c in the mechanical oscillating motion.

[0052] Regarding the size correction module for the mechanical resonators 2b, 2c, it includes a calculation submodule for calculating the corrections required for the mechanical resonators 2b, 2c and a correction submodule for correcting these mechanical resonators 2b, 2c using techniques that oxidize and then deoxidize these mechanical resonators, including thermal oxidation, electroplating growth, physical vapor deposition, chemical vapor deposition, atomic layer deposition, or any other additive process.

[0053] In this system, the processing unit is connected to the means for forming the mechanical resonators 2b, 2c and at least one oscillating member 10a, 10b, 10c in the substrate 1 and means for modifying the formed mechanical resonators 2b, 2c. Such a processing unit includes at least a processor and a storage element. The processing unit is capable of executing computer program instructions, for example, designed to guide / control both devices. Specifically, the processing unit ensures guidance / control of the drive submodule and the measurement submodule, and ensures computational / processing operations in which at least one algorithm stored in the storage element is executed. The algorithm may include machine learning algorithms and / or mathematical formulas. The algorithm is capable of using predictive or simulation models to determine the structural characteristics, particularly the stiffness, of at least one oscillating component 10a, 10b, 10c, and to determine dimensional correction values ​​for the mechanical resonators 2b, 2c formed in the substrate 1.

[0054] The method includes a step 20 of forming the mechanical resonators 2b, 2c, in which dimensions E2, E3, H2, H3 are...Mechanical resonators 2b and 2c are formed in substrate 1, and their dimensions E2, E3, H2, H3 are different from the dimensions E1, H1 required for a group of mechanical resonators 2a to obtain a set of mechanical resonators whose average structural characteristics are within a predetermined range.

[0055] In this step 20, mechanical resonators 2b and 2c are formed in substrate 1. Preferably, these mechanical resonators 2b and 2c are formed simultaneously in substrate 1. The formation of these mechanical resonators 2b and 2c in substrate 1 is performed by a forming apparatus controlled by the processing unit of the system. It should be noted that these mechanical resonators 2b and 2c preferably have similar geometries or form similar structures.

[0056] Referring to Figures 1, 4, and 5, these mechanical resonators 2b and 2c formed in substrate 1 have a flexible portion 3, which has cross sections 4b and 4c, respectively, having dimensions E2, H2 and E3, H3. The cross sections 4b and 4c of the flexible portion 3 preferably have a polygonal shape similar to a hairspring strip, and are characterized in that the heights H2 and H3 and the thicknesses E2 and E3 of the cross sections 4b and 4c are different from the dimensions E1 and H1 required for a group of mechanical resonators 2a to obtain an average value of their structural characteristics within a predetermined range. In other words, the dimensions E2, H2, E3, and H3 of the cross sections 4b and 4c of the flexible portion 3 of each mechanical resonator 2b and 2c can be greater than or less than the dimensions E1 and H1 required for the cross sections 4a of the flexible portion of the manufactured mechanical resonator 2a to obtain an average value of its structural characteristics within a predetermined range.

[0057] As described above, the substrate 1 is preferably made of doped or undoped silicon. The silicon can be monocrystalline silicon, polycrystalline silicon, or amorphous silicon. Furthermore, the silicon can have orientations {1,1,1}, {-1,1,1}, {1,-1,1}, {-1,-1,1}, where orientation is most important for the Young's modulus of silicon.

[0058] It should be noted that during step 20, the formed mechanical resonators 2b and 2c may have:

[0059] - Dimensions E2 and H2, which are greater than the dimensions E1 and H1 required for a group of mechanical resonators 2a to obtain a set of mechanical resonators 2a with an average value of structural characteristics such as stiffness within a predetermined range, that is, the height H2 and / or the thickness E2 of the flexible portion 3 are greater than the height H1 and / or the thickness E1 of the flexible portion 3 of the mechanical resonator 2a with an average value of structural characteristics such as stiffness within a predetermined range;

[0060] - Dimensions E3 and H3, which are less than the dimensions E1 and H1 required for a group of mechanical resonators 2a to obtain a set of mechanical resonators 2a with an average value of structural characteristics such as stiffness within a predetermined range, that is, the height H3 and / or the thickness E3 of the flexible portion 3 are less than the height H1 and / or the thickness E1 of the flexible portion 3 of the mechanical resonator 2a with an average value of structural characteristics such as stiffness within a predetermined range.

[0061] The method further includes a step 21 of forming at least one oscillating member 10a, 10b, 10c, in which at least one oscillating member 10a, 10b, 10c is formed in a substrate 1, the oscillating member comprising a main body 6 and flexible arms / branches 7, 8, the flexible arms / branches 7, 8 being parallel to the axis of symmetry A of the main body 6.

[0062] Step 21 is performed on the same substrate 1 including the formed mechanical resonators 2b, 2c, preferably simultaneously with step 20 of forming these mechanical resonators 2b, 2c.

[0063] In step 21, at least one oscillating member 10a, 10b, 10c is fabricated in the substrate 1 for at least one of the group of mechanical resonators 2b, 2c. For example, oscillating members 10a, 10b, 10c can be fabricated for multiple mechanical resonators 2b, 2c arranged adjacent to each other or for each mechanical resonator 2b, 2c. Alternatively, multiple oscillating components 10a, 10b, 10c can be arranged around a single mechanical resonator 2b, 2c in the substrate 1, particularly in the immediate vicinity of the mechanical resonators 2b, 2c.

[0064] In step 21, the oscillating components 10a, 10b, 10c are constructed in an opening 9 in the substrate 1. The opening 9 is a through-hole formed within the thickness of the substrate 1, and includes an outer peripheral wall 13. The opening 9 defines a space in which the oscillating components 10a, 10b, 10c can freely perform guided / controlled mechanical oscillating motion.

[0065] As described above, the oscillating components 10a, 10b, and 10c include a main body / shaft portion 6, which includes a preferably straight body. A first end 5a (also referred to as an attachment end 5a) of the main body is connected to the outer peripheral wall 13 of the opening 9, and in particular to a fixing portion 15 connected to the outer peripheral wall 13. The body of the main body 6 also includes a second end 5d, the axial section S1 of which is equal to or substantially equal to the axial section S2 of the first end 5a. The body of the main body 6 includes a portion between the first end 5a and the second end 5d, which has an axial section S4 that is smaller than the axial section S2 of the first end 5a and the axial section S1 of the second end 5d, respectively. It should be noted that the axial section S4 is preferably 1 / 2 to 1 / 5 of these axial sections S2 and S1.

[0066] The difference in axial cross-section can reduce the stiffness of the main body 6 in that part, and when measuring the structural characteristics of the oscillating members 10a, 10b, 10c, a difference arises between the in-phase and out-of-phase modes of the flexible arms 7 and 8, which is used to determine the relative value of this structural characteristic in step 22 described below.

[0067] It should be noted that the in-phase mode corresponds to the mode in which the flexible arms 7 and 8 oscillate simultaneously in the same direction.In the anti-phase mode, the oscillation phase difference between flexible arms 7 and 8 is 180 degrees. Both flexible arms move inward and outward simultaneously.

[0068] Furthermore, it should be noted that the difference in axial cross-section increases the stiffness of the main body 6 at the first end 5a and the second end 5d, so as to decouple the oscillating motion of the flexible arms 7 and 8 of the substrate 1 during this measurement.

[0069] The main body 6 is preferably rigid relative to the flexible arms 7 and 8. More specifically, the main body 6 is connected to these flexible arms 7 and 8 at its second end 5d by means of a connecting portion 14. The two flexible arms 7 and 8 extend in a straight line within the opening 9 parallel to the axis of symmetry A and toward the portion 16 of the outer peripheral wall 13 opposite to the fixing portion 15. It should be noted that the thickness of these flexible arms 7 and 8 can be equal to or substantially equal to the thickness of the flexible portion 3 of the mechanical resonators 2a and 2b.

[0070] The axial cross-sections S3 of the two flexible arms 7 and 8 are similar. Each axial section S3 is defined relative to the axis of symmetry B of its respective flexible arm 7, 8, which is parallel to the axis of symmetry A of the main body 6. In this configuration, the axial sections S1, S2, S4 of the main body 6 are larger than the axial sections S3 of each flexible arm 7, 8.

[0071] Referring to Figures 6 and Figures 2A to 2B, in this step 21, the flexible arms 7, 8 are designed such that:

[0072] - they are spaced apart from each other by a first distance D1, which is preferably greater than or significantly greater than or substantially equal to the inter-turn distance of the mechanical resonators 2b, 2c (when the mechanical resonators 2b, 2c are springs or more specifically hairsprings), and

[0073] - the free ends 5b, 5c of each of these flexible arms 7, 8 are spaced apart from the portion 16 opposite to the fixed portion 15 of the outer peripheral wall 13 of the opening 9 by a second distance D2, such that the oscillation of the flexible arms 7, 8 will not collide with this portion 16 of the outer peripheral wall 13 of the opening 9.

[0074] In this configuration, the first distance D1 is greater than the second distance D2.

[0075] It should be noted that the thickness Er of these flexible arms 7, 8 is preferably designed to be equal to or substantially equal to the thickness E2, E3 of the flexible portion 3 of each mechanical resonator 2b, 2c formed in the substrate 1. In other words, when the flexible portion 3 is a strip of a hairspring, the thickness Er of each flexible arm 7, 8 is equal to or substantially equal to the thickness E2, E3 of the flexible portion 3. For example, the thickness Er of these flexible arms 7, 8 may be between 10µm and 60µm, preferably 30µm.

[0076] In this step 21, these flexible arms 7, 8 are given a length L, which can be adjusted according to the required resonance measurement tolerance. This tolerance is based on the flexible portion 3 of the mechanical resonator 2b, 2c associated with the oscillating member 10a, 10b, 10c.The tolerance is defined by at least one deviation of dimensions E2, E3, H2, H3. The value of this tolerance is equal to a frequency range in which the dimensional changes E2, E3, H2, H3 measured on the mechanical resonators 2b, 2c no longer require correction for stiffness differences. This value thus defines a measurement range in which it is no longer necessary to determine the fine / sensitive dimensional changes of the flexible portion 3 of the formed mechanical resonators 2b, 2c. In other words, no adjustment is required below this tolerance. (Specification 6 / 10, page 9, CN 122226009 A) This value is specifically adapted to the dimensions of the flexible portion 3 of the mechanical resonators 2b, 2c to improve measurement sensitivity and the sensitivity to detection of etching thickness changes. For example, the length L is calculated such that when the frequency change of the oscillating element is 10Hz, a 10nm dimensional change E2, E3 of the mechanical resonator can be measured.

[0077] In this step, the process of calculating the length L of the oscillating components 10a, 10b, and 10c includes:

[0078] - Defining the dimension Er, which is preferably equal to or substantially equal to the thickness E2 and E3 of the flexible portion 3 of each mechanical resonator 2b and 2c formed in the substrate 1;

[0079] - Defining the frequency variation that can be measured by the measurement system, thereby allowing for accurate frequency measurement, wherein the frequency variation is 2 to 10 times the standard deviation of the measurement;

[0080] - Defining the minimum dimensional variation of E2, E3, H2, and H3 of the mechanical resonators 2b and 2c to be measured;

[0081] - Calculating the length L of the flexible arms 7 and 8, which is between 1 mm and 2 mm, such that the measurement of the frequency variation can lead to conclusions about the dimensional variation of E2, E3, H2, and H3 of the mechanical resonators 2b and 2c.

[0082] It should be noted that the shorter the length L of the flexible arms 7 and 8, the higher the measured resonant frequency, and the more sensitive the ratio between the addition or removal of uniformly thick material on the oscillating components 10a, 10b, and 10c and their resonant frequency becomes.

[0083] In this step 21, it should be noted that the oscillating components 10a, 10b, and 10c are preferably arranged in the substrate 1 such that the positions of their flexible arms 7 and 8 allow the Young's modulus to reach its maximum or minimum value, especially when the substrate 1 is made of silicon. In fact, due to the anisotropy of silicon, this arrangement can avoid significant changes in the Young's modulus due to the angle used to determine structural characteristics such as stiffness. Furthermore, the maximum Young's modulus should be given priority to improve the accuracy of the correlation between stiffness and the measured frequency.

[0084] In the variants shown in Figures 2B and 2C, step 21 of forming the oscillating members 10a, 10b, 10c causes the free ends 5b, 5c of each flexible arm 7, 8 to be integrally formed with the end member 11, the mass of which is greater than the rest of the flexible arm 7, 8.The quality of the component. In Figure 2B, end member 11 has a polygonal cross-section; while in Figure 2C, end member 12 has a circular cross-section. These end members 11 and 12 allow for a reduction in the resonant frequency of the flexible arms 7 and 8, while maintaining good sensitivity between the etch thickness Er and this frequency. In this case, the process of calculating the lengths of the oscillating components 10a, 10b, and 10c includes:

[0085] - Defining a dimension Er, which is preferably equal to or substantially equal to the thicknesses E2, E3, H2, and H3 of the flexible portion 3 of each mechanical resonator 2b and 2c formed in the substrate 1;

[0086] - Defining a frequency variation that can be measured by a measurement system, thereby allowing for accurate frequency measurement, wherein the frequency variation is between 2 and 10 times the standard deviation of the measurement; for example, the frequency variation may be 10 Hz;

[0087] - Defining the minimum dimensional variation of E2, E3, H2, and H3 of the mechanical resonators 2b and 2c to be measured; for example, for a measurable frequency variation of 10 Hz, the minimum dimensional variation may be 10 nm;

[0088] - Calculating the length L of the flexible arms 7 and 8, which is between 1 mm and 2 mm, such that the measurement of the frequency variation can lead to conclusions regarding the dimensional variations of E2, E3, H2, and H3 of the mechanical resonators 2b and 2c;

[0089] - Calculate the dimensions of the flexible arm ends to reduce the measurement frequency to a reasonable range for the measurement system.

[0090] Advantageously, these end members 11, 12 provide a larger surface area than the flexible arms 7, 8, which makes it easier to measure the resonant frequency of the oscillating members 10b, 10c.

[0091] It should be understood that the oscillating members 10a, 10b, 10c designed during step 21 have a general shape of a tuning fork or are themselves tuning forks.

[0092] The oscillating members 10a, 10b, and 10c achieve optimal decoupling of the fixed-end effect from the resonant frequency. In fact, the fixed end has a significant influence on the resonant frequency during harmonic excitation. For the oscillating members 10a, 10b, and 10c, there is a clear decoupling between the fixed end and the resonant frequency of the flexible arms 7 and 8. The correlation between the resonant frequency and structural characteristics such as stiffness is no longer related to the etching quality of the fixed end.

[0093] Furthermore, these oscillating components 10a, 10b, and 10c are configured such that their structural characteristics can be easily determined by the structural characteristic determination module in the mechanical resonator modification device. It should be noted that these oscillating components 10a, 10b, and 10c are configured to vibrate at a stable frequency even if certain parameters change, particularly those related to the fixed end and manufacturing process. The change in this stable frequency depends only on one or more parameters / structural characteristics of the oscillating components 10a, 10b, and 10c. In this embodimentIn the example, the structural characteristic of the oscillating members 10a, 10b, 10c that can significantly change the resonant frequency is preferably the thickness Er of the flexible arm. In addition to the thickness Er of the flexible arm, other characteristics, such as stiffness and the height h of the flexible arm, can also be used. In actual operation, the frequency is first measured, and then the dimension under the etch mask is derived from it (arm thickness = arm dimension on the DRIE mask - etched dimension). The stiffness of the tuning fork cannot be obtained directly. Therefore, after the thickness (the dimension under the etch mask) is inferred, the stiffness of the hairspring can be calculated so that necessary adjustments can be made.

[0094] The method then includes a determination step 22, in which the structural characteristics of at least one oscillating member 10a, 10b, 10c associated with at least one mechanical resonator 2b, 2c formed in the substrate 1 are determined. The determination step 22 includes an estimation sub-step 23, in which at least one resonant frequency of at least one oscillating member 10a, 10b, 10c is estimated. In the estimation sub-step 23, the at least one oscillating member 10a, 10b, 10c is mechanically oscillating about its stable equilibrium position. During this movement, in the measurement phase 24, the resonant frequency of the oscillating member 10a, 10b, 10c is determined.

[0095] This measurement phase 24 is implemented by the measurement sub-module of the structural characteristic determination module in the modification device of the mechanical resonators 2b, 2c. In a variant of the oscillating member 10b, 10c having flexible arms 7, 8 (each flexible arm including end members 11, 12), the measurement sub-module includes a velocimeter that can be focused on the end members 11, 12 of the flexible arms 7, 8 that are oscillating. In this configuration, measurements can be performed out of plane, with the velocimeter axis perpendicular to the wafer plane.

[0096] It should be noted that when multiple oscillating elements 10a, 10b, 10c are associated with a single mechanical resonator 2a, 2c, the resonant frequencies of all these oscillating elements 10a, 10b, 10c are measured, and then the average of these frequencies is calculated to correspond to the resonant frequency associated with the combination of oscillating elements 10a, 10b, 10c. Alternatively, the measured resonant frequency of the combination may be the resonant frequency of only one of its oscillating elements 10a, 10b, 10c, or it may be the resonant frequency of a sample of its oscillating elements 10a, 10b, 10c.

[0097] Once the resonant frequencies have been estimated, step 22 includes a definition sub-step 25 in which a structural characteristic, such as stiffness, of the at least one oscillating element 10a, 10b, 10c is defined. In this definition sub-step 25, the processing unit executes an algorithm for calculating the structural characteristic based on the estimated resonant frequencies of the at least one oscillating element 10a, 10b, 10c.

[0098] Then, the method includes a calculation step 26, in which the structural characteristics determined for the relevant system 3 are used to perform calculations.The calculation step 26 calculates the dimensional correction value to be applied to each mechanical resonator 2b, 2c in the group of mechanical resonators. In calculation step 26, the dimensional correction amount to be applied to mechanical resonators 2b, 2c is determined.

[0099] To this end, calculation step 26 includes a material thickness determination sub-step 27, in which, based on the determined structural characteristics, the thickness e of the material to be added to or removed from at least one dimension of the mechanical resonators 2b, 2c formed in step 20 is determined to obtain a group of mechanical resonators 2a whose average structural characteristics are within a predetermined numerical range.

[0100] This dimensional correction actually corresponds to the thickness e of the material removed from or added to the mechanical resonators 2b and 2c, so as to change at least one of their dimensions E2, H2, E3, and H3, namely:

[0101] - only the heights H2 and H3 of the flexible portion 3, or

[0102] - only the thicknesses E2 and E3 of the flexible portion 3, or specification page 8 / 10 11 CN 122226009 A

[0103] - both the heights H2 and H3 and the thicknesses E2 and E3.

[0104] This dimensional correction can be performed on a single segment or multiple segments of the flexible portion 3 of the mechanical resonators 2b and 2c, or on the entire length of the flexible portion 3.

[0105] Therefore, by determining the dimensional correction value, the material thickness determination sub-step 27 can participate in forming the geometry of the mechanical resonators 2b and 2c so that their structural characteristic values ​​are within a predetermined range.

[0106] The method then includes a modification step 28, in which the dimensions E2, E3, H2, H3 of the mechanical resonators 2b and 2c are modified based on the calculated dimension correction values ​​to obtain a set of mechanical resonators 2a whose average structural characteristics are within a predetermined range.

[0107] In this case, if the dimensions E2, H2 of the mechanical resonator 2b are greater than the dimensions E1, H1 required to bring the average structural characteristics of the set of mechanical resonators 2a within the predetermined range, the modification step 28 includes a sub-step 29, in which material is removed according to the calculated thickness e of the material to be removed. The material removal can be carried out using a process known in the art of oxidation followed by deoxidation for these mechanical resonators 2b. The purpose of this sub-step 29 is to reduce the dimension of the cross section 4b of the flexible portion 3 of the mechanical resonator 2b over a given length or the entire length of the flexible portion 3.

[0108] If the dimensions E3 and H3 of the mechanical resonator 2c are smaller than the dimensions E1 and H1 required to bring the average structural characteristics of the group of mechanical resonators 2a within a predetermined range, then modification step 28 includes sub-step 30, in which material is added according to the calculated thickness e of the material to be added. The material can be added using methods known in the art, such as thermal...Oxidation, electroplating growth, physical vapor deposition, chemical vapor deposition, atomic layer deposition, or any other additive process. The purpose of this sub-step 30 is to increase the dimensions E3, H3 of the cross-section 4c of the flexible portion 3 of the mechanical resonator 2c over a given length or the entire length of the flexible portion 3.

[0109] Therefore, this method can utilize the high precision provided by the reference stiffness indication system to correct dimensional errors in resonators manufactured using methods such as photolithography and / or DRIE technology.

[0110] Terminology

[0111] 1. A substrate including at least one mechanical resonator

[0112] 2a. A manufactured mechanical resonator

[0113] 2b. A mechanical resonator formed in a substrate and having a cross-sectional dimension larger than that of the manufactured mechanical resonator

[0114] 2c. A mechanical resonator formed in a substrate and having a cross-sectional dimension smaller than that of the manufactured mechanical resonator

[0115] 3. A flexible portion of a mechanical resonator

[0116] 4a. A cross-section of a manufactured mechanical resonator

[0117] 4b. A cross-section of a mechanical resonator with a dimension larger than that of the manufactured mechanical resonator

[0118] 4c. A cross-section of a mechanical resonator with a dimension smaller than that of the manufactured mechanical resonator

[0119] 5a. An attachment end of an oscillating member

[0120] 5b, 5c. A free end of an oscillating member

[0121] 6. A main body / shaft portion of an oscillating member

[0122] 7. 8. First flexible arm of the oscillating member

[0123] 9. Second flexible arm of the oscillating member

[0124] 10. Opening of the oscillating member arranged therein

[0125] 11. Description of the oscillating member, 9 / 10 pages, 12 CN 122226009 A

[0126] 12. End member with polygonal cross section

[0127] 13. End member with circular cross section

[0128] 14. Outer peripheral wall of the opening

[0129] 15. Connecting part that connects the flexible arm to the main body of the oscillating member

[0130] 16. Fixing part on the outer peripheral wall of the opening of the oscillating member

[0131] 17. The portion of the outer peripheral wall opposite to the fixing part. Specification page 10 / 10 13 CN 122226009 A Figure 1 Figure 2A Specification drawing page 1 / 4 14 CN 122226009 A Figure 2B Figure 2C Specification drawing page 2 / 4 15 CN 122226009 A Figure 3 Figure 4 Figure 5 Specification drawing page 3 / 4 16 CN 122226009 A Figure 6 Specification drawing page 4 / 4 17 CN 122226009 A One aspect of the invention relates to amethod for manufacturing a batch of mechanical resonators (2a) whose structural characteristics have an average within a predetermined range of values, the method comprising a step of forming in the wafer (1) the mechanical resonators (2b, 2c) and at least one oscillating element (10a, 10b, 10c) as well as a step of modifying (28) the dimensions of the resonators (2a) formed, from the dimensional corrections calculated for obtaining the batch of resonators (2a) whose structural characteristics are within the predetermined range of values.

Claims

1. A method for manufacturing a set of mechanical resonators (2a) having an average structural characteristic within a predetermined range, said structural characteristic being common to each of the mechanical resonators (2a) in the set, said method comprising the following steps: a) Step (20) of forming mechanical resonators (2b, 2c) in substrate (1), wherein the size of the mechanical resonators (2b, 2c) is different from the size required to obtain the set of mechanical resonators (2a) with structural characteristics within the predetermined numerical range; (b) Step (21) of forming at least one oscillating member (10a, 10b, 10c) in the substrate (1), wherein the at least one oscillating member (10a, 10b, 10c) is formed in the opening (9) of the substrate (1), and the oscillating member (10a, 10b, 10c) is composed of a main body (6) and two flexible arms (7, 8), wherein the body of the main body (6) is connected at the first end (5a) to the fixing part (15) of the outer peripheral wall (13) of the opening (9), and the two flexible arms are connected by a connecting... The connecting part (14) is connected to the second end (5d) of the main body (6). The two flexible arms (7, 8) extend parallel to the axis of symmetry (A) of the main body (6) and toward the portion (16) of the outer peripheral wall (13) opposite to the fixed part (15). The body of the main body (6) includes a portion between the first end (5a) and the second end (5d), the axial section (S4) of which is smaller than the axial section (S2) of the first end (5a) and the axial section (S1) of the second end (5d). c) Determine step (22), in which a value related to the structural characteristics of the formed at least one oscillating member (10a, 10b, 10c) is determined; d) Calculation step (26), in which the size correction values ​​to be applied to the formed mechanical resonators (2b, 2c) are calculated based on the values ​​determined for the structural characteristics; e) Modification step (28), in which the dimensions of the formed mechanical resonators (2b, 2c) are modified based on the calculated dimension correction values ​​to obtain the set of mechanical resonators (2a) with structural characteristic values ​​within a predetermined range.

2. The method according to claim 1, characterized in that, In step (21) of forming the oscillating members (10a, 10b, 10c), the axial section (S4) of the portion between the first end (5a) and the second end (5d) of the body of the main stem (6) is made larger than the axial section (S3) of each of the flexible arms (7, 8).

3. The method according to any one of the preceding claims, characterized in that, In step (21) of forming the oscillating components (10a, 10b, 10c), each of the flexible arms (7, 8) is given a length (L) that can be adjusted according to a resonance measurement tolerance factor defined by at least one dimension (E2, E3, H2, H3) of the flexible portion (3) of the mechanical resonator (2b, 2c) associated with the at least one oscillating component (10a, 10b, 10c).

4. The method according to any one of the preceding claims, characterized in that, In step (21) of forming the oscillating member (10a, 10b, 10c), one of the two flexible arms (7, 8) is spaced apart from the other flexible arm by a first distance (D1), and the free end (5b, 5c) of each of the flexible arms (7, 8) is spaced apart from the portion (16) opposite to the fixed part (15) by a second distance (D2), wherein the first distance (D1) is greater than the second distance (D2).

5. The method according to any one of the preceding claims, characterized in that, In step (21) of forming the oscillating components (10a, 10b, 10c), the thickness (Er) of each of the flexible arms (7, 8) is made equal to or substantially equal to the thickness of the flexible portion (3) of each mechanical resonator (2b, 2c) formed in the substrate (1).

6. The method according to any one of the preceding claims, characterized in that, In step (21) of forming the oscillating components (10a, 10b, 10c), the free end (5b, 5c) of each of the flexible arms (7, 8) is integrally formed with the end member (11, 12), the mass of which is greater than the mass of the rest of the body of the flexible arm (7, 8).

7. The method according to claim 6, characterized in that, The end members (11, 12) have a circular or polygonal cross-section.

8. The method according to any one of the preceding claims, characterized in that, In step (21) of forming the oscillating member (10a, 10b, 10c), the axial section (S4) of the portion of the main body (6) between the first end (5a) and the second end (5d) is 1 / 2 to 1 / 5 of the axial section (S2) of the first end (5a) and the axial section (S1) of the second end (5d), respectively.

9. The method according to any one of the preceding claims, characterized in that, The steps (20) of forming the mechanical resonator (2b, 2c) and (21) of forming at least one oscillating element (10a, 10b, 10c) are carried out by etching, particularly by deep reactive ion etching.

10. The method according to any one of the preceding claims, characterized in that, Step (21) of forming each oscillating element (10a, 10b, 10c) is carried out in the substrate (1) for at least one of the mechanical resonators (2b, 2c) in the group of mechanical resonators (2b, 2c).

11. The method according to any one of claims 1 to 9, characterized in that, Step (21) of forming oscillating members (10a, 10b, 10c) is used to form a plurality of oscillating members (10a, 10b, 10c) around at least one mechanical resonator (2b, 2c) in the substrate (1).

12. The method according to any one of the preceding claims, characterized in that, The determining step (22) includes an estimation sub-step (23), in which at least one resonant frequency is estimated for each oscillating element (10a, 10b, 10c) associated with at least one mechanical resonator (2b, 2c) in the group of mechanical resonators (2b, 2c).

13. The method according to any one of the preceding claims, characterized in that, The determining step (22) includes a defining sub-step (25) in which a structural characteristic is defined for each oscillating element (10a, 10b, 10c) that is the same as the structural characteristic shared by each of the formed mechanical resonators (2b, 2c). The defining sub-step (25) is performed by a processing unit connected to a device for modifying the formed mechanical resonators (2b, 2c). The processing unit executes an algorithm to calculate the structural characteristic of each oscillating element (10a, 10b, 10c) based on the estimated resonant frequency.

14. The method according to any one of the preceding claims, characterized in that, The calculation step (26) includes a material thickness determination sub-step (27), in which the thickness (e) of the material to be added to or removed from at least one dimension of each mechanical resonator (2b, 2c) associated with each oscillating member (10a, 10b, 10c) is determined based on the structural characteristic values ​​determined for each oscillating member (10a, 10b, 10c).

15. The method according to any one of the preceding claims, characterized in that, The oscillating component (10) is in the shape of a tuning fork.

16. The method according to any one of the preceding claims, characterized in that, The structural characteristic mentioned is stiffness characteristic.

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