Method for manufacturing mechanical resonators

Abstract

One aspect of the invention relates to a method 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.

Description

Technical field of the invention

[0001] The present invention relates to the field of manufacturing mechanical resonators, particularly in the watchmaking industry. More specifically, the invention concerns a method for manufacturing a batch of mechanical resonators in which a common structural characteristic, such as stiffness, falls within a predetermined range of values. Technological background

[0002] In the state of the art, it is known to use manufacturing processes for mechanical resonators such as watch balance springs in plates which employ engraving techniques such as laser engraving, plasma engraving, deep reactive ion etching (DRIE) or wet etching.

[0003] However, it is observed that the implementation of such processes classically results in a geometric dispersion between the watch spirals formed all according to the same pattern in the same plate.

[0004] To overcome these drawbacks, solutions are proposed in the state of the art, in particular in patents EP 3181938 and EP 3181939 which describe manufacturing processes for spirals.

[0005] In patent EP 3181938 the manufacturing process includes the following steps: a) a spiral is formed in dimensions larger than the dimensions required to obtain a spiral of predetermined stiffness, b) the stiffness of the spiral formed in step a) is determined by measuring the frequency of the spiral coupled with a balance wheel having a predetermined inertia, c) the thickness of material to be removed to obtain the spiral of predetermined stiffness is calculated and d) the calculated thickness of material is removed from the spiral formed in step a), steps b), c) and d) being able to be repeated to further improve the dimensional quality.

[0006] In patent EP 3181939, the manufacturing process includes the following steps: a) a spiral is formed in dimensions smaller than the dimensions required to obtain a spiral of predetermined stiffness, b) the stiffness of the spiral formed in step a) is determined by measuring the frequency of the spiral coupled with a balance wheel having a predetermined inertia, c) the thickness of material missing to obtain the spiral of predetermined stiffness is calculated and d) the spiral formed in step a) is modified to compensate for the thickness of material missing, steps b), c) and d) being able to be repeated to further improve the dimensional quality.

[0007] Such processes can be improved, in particular to limit platelet contamination that can occur during the measurement step they implement.

[0008] Under these conditions, it is understandable that there is a need to find solutions that will lead to such an improvement. Summary of the invention

[0009] One aim of the present invention is to propose a method for manufacturing a batch of mechanical resonators to meet the aforementioned needs.

[0010] Another goal is to improve the manufacturing accuracy of the batch of mechanical resonators whose structural characteristics, such as stiffness, have an average within a predetermined range of values.

[0011] The invention relates to a method for manufacturing a batch of mechanical resonators whose structural characteristics have an average within a predetermined range of values, said structural characteristic being common to each resonator in this batch, the method comprising the following steps: a) form in said plate mechanical resonators according to dimensions different from the dimensions required to obtain the batch of mechanical resonators whose structural characteristics are included in said predetermined range of values;b) forming in said plate at least one oscillating element in an opening provided in the plate, said element being made up of a trunk whose body is connected at a first end to a fixing part of a wall of said opening, and of two flexible arms connected at a second end of said trunk by means of a connecting part, said arms being parallel to an axis of symmetry of said trunk and extending in the direction of a part of said wall opposite the fixing part, the body of said trunk comprising a portion located between the first and second ends having an axial section which is less than the axial sections respectively of the first and second ends; c) determination of a value relating to the structural characteristic of said at least one oscillating element formed;d) calculate dimensional corrections to be applied to the formed resonators, based on the determined value relating to the structural characteristic; e) modify the dimensions of the formed resonators, based on the dimensional corrections calculated to obtain the batch of resonators whose structural characteristic values ​​are within the predetermined range of values.

[0012] In other embodiments: said forming step provides that the axial section is greater than an axial section of each of the arms; said forming step of the oscillating element provides that each arm is constructed according to a length adjustable according to a resonance measurement tolerance factor which is defined from at least one dimension of a flexible part of the resonator associated with said at least one oscillating element; said forming step of the oscillating element provides that one arm is constructed spaced from the other arm by a first distance and that the free end of each of these arms is spaced from the part opposite the fixing part by a second distance, said first distance being greater than said second distance; said forming step of the oscillating element provides that each arm is constructed with a thickness which is similar or substantially similar to that of a flexible part of each resonator formed in the plate;said oscillating element formation step provides for the construction of each arm with a free end made of material with an end element having a mass greater than the mass of the rest of the body of that arm; the end element has a cross-section which has a circular shape or a polygonal shape; said oscillating element formation step provides for the construction of the trunk body with a cross-section which is between 2 and 5 times smaller than the axial cross-sections respectively of the first and second ends; the formation steps of the mechanical resonators and of said at least one oscillating element are carried out by etching, in particular by deep reactive ion etching; the formation step each oscillating element is made in the wafer for at least one resonator of the batch of mechanical resonators; the formation step provides for the making in the wafer of a plurality of oscillating elements surrounding at least one resonator;The determination step includes a substep of estimating at least one resonance frequency of each oscillating element associated with at least one resonator in the batch of resonators; the determination step includes a substep of defining a structural characteristic of each oscillating element that is of the same nature as the structural characteristic common to each formed resonator, said substep being carried out from a processing unit connected to a device for modifying the formed resonators executing an algorithm for calculating this structural characteristic of each oscillating element on the basis of the estimated resonance frequency; the calculation step includes a substep of determining, from the determined value of the structural characteristic of each oscillating element, a thickness (e) of material to be added or removed from at least one dimension of each resonator associated with the oscillating element;The oscillating element is shaped like a tuning fork; the structural characteristic is a stiffness characteristic. Brief description of the figures

[0013] Other features and advantages of the invention will become more apparent upon reading the following description of a particular embodiment of the invention, given by way of simple illustrative and non-limiting example, and the accompanying figures, among which: there figure 1 is a schematic view of a plate comprising a set of mechanical resonators formed simultaneously, notably by engraving, all within this plate, according to embodiments of the invention; the figure 2A is a larger-scale view of an oscillating element shaped like a tuning fork, allowing the determination of a value for a characteristic common to mechanical resonators; this oscillating element, along with these resonators, is contained within the plate shown on the figure 1 , according to the embodiments of the invention; the figures 2B and 2C are variants of the oscillating element of the figure 2A whose free ends of the arms of this element comprise an end element having a mass greater than the mass of the rest of the body of this arm, according to the embodiments of the invention; the figure 3 is a schematic view of a section of a flexible part of the resonator manufactured using the process, the section having dimensions necessary to obtain the batch of mechanical resonators whose structural characteristics have an average within a predetermined range of values, according to embodiments of the invention; the figure 4 is a schematic view of a section of a flexible part of the resonator formed in the wafer using the process, the section having dimensions greater than the dimensions of the section of the manufactured flexible part of the resonator illustrated on the figure 3, according to embodiments of the invention; the figure 5 is a schematic view of a section of the flexible part of the resonator formed in the wafer using the process, the section having dimensions smaller than the dimensions of the section of the manufactured flexible part of the resonator illustrated on the figure 3 , according to embodiments of the invention, and the figure 6 is a flowchart relating to a manufacturing process for a batch of mechanical resonators whose structural characteristics have an average within a predetermined range of values, according to embodiments of the invention. Detailed description of the invention

[0014] There figure 6 shows a schematic representation of the manufacturing process for a batch of mechanical resonators 2a in a wafer 1 of material (in English " waferThis wafer 1 can be a single-crystal silicon wafer, but wafers made of other materials are also usable, for example, polycrystalline or amorphous silicon, other semiconductor materials, glass, ceramic, carbon, quartz, metal or alloy, or a composite comprising these materials. Single-crystal silicon, for its part, is relatively insensitive to magnetic fields and belongs to the cubic crystal class, whose coefficient of thermal expansion (alpha) is isotropic.

[0015] In this process, the mechanical resonator 2a, 2b, 2c is an elastically deformable component capable of being set in motion by oscillatory movements. In other words, this resonator 2a, 2b, 2c comprises a body consisting of a flexible part 3 and a connecting part that is rigid relative to this flexible part 3. This connecting part allows the resonator 2a, 2b, 2c to be fixed to an axis or shaft. Such a mechanical resonator 2a, 2b, 2c can be used in a watch, particularly in a mechanical regulator that regulates a mechanical watch movement. In the watch, the oscillations of such a resonator determine the rate of the movement. Many watches, for example, include a regulator with a balance spring as a resonator, mounted on the axis of a balance wheel and set into oscillation by means of an escapement. The natural frequency of the balance wheel-spring pair allows the watch to be regulated.Such a watch balance spring comprises an elastically flexible strand connected at one end to the ferrule and wound into a spiral to form several consecutive turns, the last of which is extended by a segment designed to be attached to a fixed balance bridge, for example, by means of a stud. This ferrule is intended to be secured to a pivoting arbor. Other known types of resonators are based, for example, on oscillating bars or other mechanical elements.

[0016] This process therefore makes it possible to manufacture this batch of resonators 2a whose structural characteristics have an average within a predetermined range of values. In this process, this characteristic is common to all the resonators 2a in this batch. In other words, these resonators share the same structural characteristic. This structural characteristic can be a stiffness characteristic of this resonator 2a, and in particular of its flexible part 3. In this context, this process makes it possible to select this particular batch of resonators 2a from among a plurality of resonators formed in this wafer 1.To achieve this, the process helps establish an indicative map of the geometric dispersion between the dimensions of the resonators formed in the wafer, and therefore of the dispersion between their common structural characteristics. It also corrects the selected batch of resonators to ensure that their average structural characteristics fall within a predetermined range. This process aims to guarantee very high dimensional accuracy for the manufactured 2a resonators and, consequently, to ensure a more precise structural characteristic for these 2a resonators.

[0017] It should be noted that in a preferred embodiment of this process, the resonator 2a, 2b, 2c can be a watch balance spring, and the structural characteristic a stiffness of this spring, particularly of its blade. In this context, this process can then be a method for manufacturing a batch or set of watch balance springs 2a in the plate 1, whose average stiffnesses fall within a predetermined range.

[0018] With reference to the figure 1 A batch of mechanical resonators 2b, 2c is formed in the plate 1 of material. In this batch, each resonator 2b, 2c therefore comprises a flexible part 3 having a rigid connecting part allowing this resonator to be fixed on an axis or on a shaft.

[0019] In the context where this resonator 2b, 2c is a spiral, the latter includes a ferrule intended to be attached to a pivoting shaft.

[0020] Such a process is implemented by a system for manufacturing the batch of resonators 2a, 2b, 2c in the wafer 1. This system includes, in a non-exhaustive and non-limiting manner: a processing unit such as a computer, a device for forming resonators 2b, 2c and at least one oscillating element 10a, 10b, 10c in the wafer 1 and a device for modifying the resonators 2b, 2c formed in this wafer 1.

[0021] The device for forming resonators 2b, 2c and oscillating elements 10a, 10b, 10c is capable of implementing microfabrication technologies such as photolithography, machining, and etching processes in wafer 1. In particular, deep reactive ion etching, laser etching, chemical etching, or etching processes using a focused ion beam.

[0022] The device for modifying resonators 2b and 2c includes a module for determining structural characteristics and a module for dimensional correction of resonators 2b and 2c. This module for determining structural characteristics includes: a sub-module for driving / triggering a mechanical oscillation movement in the body of an oscillating element 10a, 10b, 10c around its stable equilibrium position; a sub-module for measuring a resonance frequency of the oscillating element 10a, 10b, 10c in mechanical oscillation movement.

[0023] Regarding the dimensional correction module for 2b, 2c resonators, it includes a sub-module for calculating a correction to be applied to 2b, 2c resonators and a sub-module for correcting these 2b, 2c resonators which implements technologies of oxidation and then deoxidation of these resonators, thermal oxidation, galvanic growth, physical vapor deposition, chemical vapor deposition, atomic layer deposition or any other additive process.

[0024] In this system, this processing unit is connected to the resonator-forming devices 2b, 2c and at least one oscillating element 10a, 10b, 10c in wafer 1, and to the modification of the formed resonators 2b, 2c. Such a processing unit comprises at least one processor and memory elements. This unit is capable of executing instructions for implementing a computer program designed, for example, to control these two devices. In particular, such a unit is capable of controlling the training and measurement sub-modules, as well as performing calculation / processing operations during which at least one algorithm, stored in the memory elements, is implemented. This algorithm may include a machine learning algorithm and / or mathematical formulas.This algorithm is capable of implementing a predictive model or a simulation model to determine the structural characteristic, in particular the stiffness, of at least one oscillating element 10a, 10b, 10c and the dimensional corrections to be made to the resonators 2b, 2c formed in the plate 1.

[0025] Such a process includes a forming step 20 in the plate 1 of the mechanical resonators 2b, 2c according to dimensions E2, E3, H2, H3 different from the dimensions E1, H1 required to obtain the batch of mechanical resonators 2a whose structural characteristics have an average within a predetermined range of values.

[0026] During this step 20, resonators 2b and 2c are formed in wafer 1. These resonators 2b and 2c are preferably formed simultaneously in wafer 1. The formation of these resonators 2b and 2c in wafer 1 is carried out by the formation device controlled by the system's processing unit. It should be noted that these resonators 2b and 2c preferably have similar geometries or form similar patterns.

[0027] With reference to Figures 1 , 4 and 5, these mechanical resonators 2b, 2c formed in this plate 1, have a flexible part 3 having sections 4b, 4c of dimensions E2, H2, E3, H3. The sections 4b, 4c of this flexible part 3 preferably have a polygonal shape like the blade of a spiral, they are then characterized by a height H1, H2, H3 and a thickness E1, E2, E3 of this section 4a, 4b, 4c - which are different from the dimensions E1, H1 required to obtain the batch of mechanical resonators 2a whose structural characteristics have the average within the predetermined range. In other words, the flexible part 3 of each resonator 2b, 2c can have a section 4b, 4c whose dimensions E2, H2, E3, H3 are greater or less than the dimensions E1, H1 required of the section 4a of this flexible part of the manufactured resonator 2a which allows to obtain a structural characteristic in the average within the predetermined range.

[0028] As we have mentioned, this wafer 1 is preferably made of doped or undoped silicon. This silicon can be monocrystalline, polycrystalline, or amorphous. Furthermore, this silicon can have the orientations {1,1,1}, {-1,1,1}, {1,-1,1}, {-1,-1,1}, for which the Young's model of silicon is most important.

[0029] It should be noted that during this training stage 20, the mechanical resonators 2b, 2c formed may have: dimensions E2, H2 greater than the dimensions E1, H1 required to obtain the batch of mechanical resonators 2a whose structural characteristics, such as stiffness, have the average within the predetermined range of values, i.e. a height H2 of the flexible part 3 and / or a thickness E2 of the flexible part 3 greater (s) than the height H1 and / or the thickness E1 (s) of the flexible part 3 of the mechanical resonators 2a whose structural characteristics, such as stiffness, have the average within the predetermined range;dimensions E3, H3 smaller than the dimensions E1, H1 required to obtain the batch of mechanical resonators 2a whose structural characteristics, such as stiffness, have the average within the predetermined range, i.e. a height H3 of the flexible part 3 and / or a thickness E3 of the flexible part 3 less than the height H1 and / or the thickness E1 of the flexible part 3 of the mechanical resonators 2a whose structural characteristics, such as stiffness, have the average within the predetermined range. ;

[0030] The process also includes a formation step 21 in the plate 1, of at least one oscillating element 10a, 10b, 10c provided with a trunk 6 and flexible arms / branches 7, 8, these arms 7, 8 being parallel to an axis of symmetry A of said trunk 6.

[0031] This step 21 is carried out in the same plate 1 comprising the formed mechanical resonators 2b, 2c and preferably simultaneously with the formation step 20 of these resonators 2b, 2c.

[0032] During this step 21, at least one oscillating element 10a, 10b, 10c is made in plate 1 for at least one resonator 2b, 2c from the set of mechanical resonators 2b, 2c. For example, an oscillating element 10a, 10b, 10c can be made for several resonators 2b, 2c arranged in its immediate vicinity or even for each resonator 2b, 2c. Alternatively, several oscillating elements 10a, 10b, 10c can be arranged in plate 1 around a single resonator 2b, 2c and in particular in the immediate vicinity of this resonator 2b, 2c.

[0033] During this step 21, this element 10a, 10b, 10c is constructed in an opening 9 made in this plate 1. Such an opening 9 is a through hole made in the thickness of the plate 1 which includes a peripheral wall 13. Such an opening 9 defines a space in which the oscillating element 10a, 10b 10c can freely execute a controlled mechanical oscillating movement.

[0034] As we have mentioned, this oscillating element 10a, 10b, 10c consists of a stem / bar 6 whose body, preferably straight, is connected at a first end 5a, also called the attachment end 5a, to the peripheral wall 13 of this opening 9 and in particular to a fixing portion 15 of this wall 13. This body of the stem 6 also includes a second end 5d having an axial section S1 which is substantially equal to or similar to an axial section S2 of the first end 5a. The body of this stem 6 includes a portion located between these first and second ends 5a, 5d which has an axial section S4 which is smaller than these axial sections S2, S1 of the first and second ends 5a, 5d respectively. It should be noted that this section S4 is preferably between 2 and 5 times smaller than these axial sections S2, S1.

[0035] This difference in sections allows the rigidity of the body of the trunk 6 to decrease at the level of this portion and to generate a difference between the modes where the arms 7, 8 are in phase and in antiphase when carrying out a measurement of the structural characteristic of the oscillating element 10a, 10b, 10c which is implemented within the framework of a determination step 22 of a relative value of this structural characteristic which will be described later.

[0036] Note that the in-phase mode corresponds to the mode where arms 7 and 8 oscillate in the same direction, simultaneously. In the antiphase mode, these arms 7 and 8 oscillate with a 180-degree phase shift. Both arms move in and out at the same time.

[0037] Furthermore, it should be noted that the difference in sections makes it possible to increase the rigidity of the body of the trunk 6 at the level of the first and second ends 5a, 5d in order to decouple the oscillation movement of the arms 7, 8 of the plate 1 during the performance of this measurement.

[0038] The body of this trunk 6 is preferably rigid with respect to the flexible arms 7, 8 included in this trunk 6. More precisely, the body of this trunk 6 is connected to these flexible arms 7, 8 at its second end 5d by means of a connecting part 14. These two arms 7, 8 extend in a straight line in this opening 9, being parallel to the axis of symmetry A, and this in the direction of a part 16 of said wall 13 opposite the fixing part 15. It should be noted that these arms 7, 8 can each have a thickness similar or substantially similar to that of the flexible part 3 of the resonator 2a, 2b.

[0039] These two arms 7 and 8 have similar axial sections S3. Each axial section S3 is defined relative to the axis of symmetry B of each arm 7 and 8, which is parallel to the axis of symmetry A of the trunk body 6. In this configuration, the axial sections S1, S2, and S4 of the trunk body 6 are greater than the axial section S3 of each arm 7 and 8.

[0040] With reference to figures 6 And 2A to 2B During this step 21, arms 7 and 8 are constructed at: a first distance D1 from each other, this distance D1 being preferably greater than or substantially greater than or substantially similar to the inter-coil of the resonator 2b, 2c when it is a spring or a spiral, and a second distance D2 between a free end 5b, 5c of each of these arms 7, 8, and the part 16 opposite the fixing part 15 of the wall 13 of the opening 9 so that the oscillation of the arms 7, 8 cannot collide with the fixing part 15 of the wall 13 of the opening 9.

[0041] In this configuration, the first distance D1 is greater than the second distance D2.

[0042] It should be noted that these arms 7, 8 are constructed with a thickness Er which is preferably similar or substantially similar to the thickness E2, E3 of the flexible part 3 of each resonator 2b, 2c formed in the plate 1. In other words, when this flexible part 3 is the blade of the spiral, the thickness Er of each arm 7, 8 is then similar or substantially similar to the thickness E2, E3 of this flexible part 3. As an example, these arms 7, 8 can have a thickness Er between 10 and 60 µm, preferably 30 µm.

[0043] In this step 21, these arms 7, 8 are designed with a length L that can be adjusted according to the desired resonance measurement tolerance. This tolerance is defined based on at least one variation in the dimensions E2, E3, H2, H3 of the flexible section 3 of the resonator 2b, 2c associated with this oscillating element 10a, 10b, 10c. This tolerance has a value equal to a desired frequency range that allows for the measurement of a dimensional variation E2, E3, H2, H3 on the resonator 2b, 2c that results in a difference in the stiffness of this resonator that no longer requires correction. This value thus defines a measurement range within which fine / sensitive dimensional variations of the flexible section 3 of the formed resonator 2b, 2c are no longer necessarily detected. In other words, below this tolerance, no adjustment is necessary.This value is specifically adapted to the dimensions of this flexible part 3 of the resonator 2b,2c, in order to improve the sensitivity of the measurements and variations in etching thickness. As an example, the length L will be calculated so that a 10 Hz variation of the oscillating element allows for the measurement of a dimensional variation E2, E3 of the resonator of 10 nm.

[0044] During this step, the process of calculating the length L of the oscillating element 10a, 10b, 10c includes: define a dimension Er preferably similar or substantially similar to the thickness E2, E3 of the flexible part 3 of each resonator 2b, 2c formed in the plate 1; define a frequency variation measurable by the measurement system allowing accuracy on the measured frequency, between 2 and 10 times the measurement standard deviation; define the minimum dimensional variation of E2, E3, H2, H3 of the resonator 2b,2c that we wish to measure; calculate a length L of the arms 7, 8 between 1 mm and 2 mm, so that the measurement of frequency variation allows us to conclude on the dimensional variation of E2, E3, H2, H3 of the resonator 2b,2c.

[0045] It should be noted that the smaller the length L of the arms 7, 8, the higher the measured resonance frequency will be, and the relationship between adding or removing a uniform thickness of material on the oscillating element 10a, 10b, 10c and its resonance frequency will be sensitive.

[0046] In this step 21, it should be noted that the arrangement of the oscillating element 10a, 10b, 1c in this wafer 1 is preferably carried out so that its arms 7, 8 are positioned to maximize or minimize the Young's modulus, particularly when this wafer 1 is made of silicon. Indeed, since silicon is anisotropic, this arrangement avoids significant variability in the Young's modulus depending on the angle when determining structural characteristics such as stiffness. Furthermore, maximizing the Young's modulus is preferred to increase the accuracy of the correlation between stiffness and the measured frequency.

[0047] In illustrated variants on the figures 2B and 2C, the formation step 21 of the oscillating element 10a, 10b, 10c provides for the construction of each arm 7, 8 with a free end 5b, 5c made of material with an end element 11 having a mass greater than the mass of the rest of the body of this arm 7, 8. On the figure 2B , the end element 11 has a cross-section that is in the shape of a polygon and on the figure 2C This section of the end element 12 has a circular shape. This end element 11, 12 allows the resonant frequency of the arms 7, 8 to be reduced while maintaining good sensitivity between the engraving thickness Er and this frequency. In this context, the calculation process for the length of the oscillating element 10a, 10b, 10c: define a dimension Er preferably similar or substantially similar to the thickness E2, E3, H2, H3 of the flexible part 3 of each resonator 2b, 2c formed in the plate 1; define a frequency variation measurable by the measurement system allowing accuracy on the measured frequency, between 2 and 10 times the measurement standard deviation, this frequency variation can be for example 10hz; define the minimum dimensional variation of E2, E3, H2, H3 of the resonator 2b,2c that we wish to measure, this variation can be for example 10nm for a measurable frequency variation of 10hz; calculate a length L of the arms 7, 8 between 1 mm and 2 mm, so that the measurement of frequency variation allows us to conclude on the dimensional variation of E2, E3, H2, H3 of the resonator 2b,2c; calculate the dimensions of the end of the arms in order to reduce the measurement frequency into a reasonable range for the measurement system.

[0048] Advantageously, these end elements 11, 12 offer a larger surface area than that of the arms 7, 8, which makes it easier to measure the resonance frequency of this oscillation element 10b, 10c.

[0049] We understand that the oscillating element 10a, 10b, 10c constructed during this training step 21 has a general shape of a tuning fork or is a tuning fork.

[0050] This oscillating element 10a, 10b, 10c allows for optimal decoupling of the fixed effect at resonant frequencies. Indeed, during harmonic excitations, the fixed element has a significant effect on the resonant frequency. In the case of this oscillating element 10a, 10b, 10c, there is substantial decoupling between this fixed element and the resonant frequency of the arms 7, 8. The correlation between the resonant frequency and the structural characteristic, such as stiffness, becomes independent of the quality of the fixed element engraving.

[0051] Furthermore, such an oscillating element 10a, 10b, 10c is configured so that its structural characteristic can be easily determined from the structural characteristic determination module of the resonator modification device. It should be noted that such an oscillating element 10a, 10b, 10c is configured to vibrate at a stable frequency despite changes in certain parameters related, in particular, to the mounting and the manufacturing process. This stable frequency varies according to one or more structural parameters / characteristics of this oscillating element 10a, 10b, 10c. In the present embodiment, the structural characteristic of the oscillating element 10a, 10b, 10c that significantly affects the resonant frequency is preferably the thickness of the arms Er. Other characteristics besides the thickness of the arms Er can be used, such as: stiffness, arm height h.In the actual process, a frequency is measured, and a dimension is deduced from it under the engraving mask (arm thickness = arm values ​​on the DRIE mask - dimension under the engraving). The tuning fork stiffness is not obtained directly. Then, from this deduced thickness (dimension under the engraving mask), the balance spring stiffness is calculated, and the necessary adjustments are then made.

[0052] The process subsequently includes a step 22 for determining the structural characteristic of at least one oscillating element 10a, 10b, 10c associated with at least one resonator 2b, 2c formed in the plate 1. Such a step 22 includes a substep 23 for estimating at least one resonance frequency of said at least one oscillating element 10a, 10b, 10c. During this substep 23, said at least one oscillating element 10a, 10b, 10c is subjected to a mechanical oscillation around its stable equilibrium position. During this oscillation, the resonance frequency of this oscillating element 10a, 10b, 10c is then determined during a measurement phase 24.

[0053] This measurement phase 24 is implemented by the measurement sub-module of the structural characteristics determination module for the resonator modification device 2b, 2c. In variants of the oscillating element 10b, 10c equipped with arms 7, 8, each comprising an end element 11, 12, the measurement sub-module includes a velocimeter that can be focused on these end elements 11, 12 of the arms 7, 8 performing oscillatory movements. Thus, in this configuration, this measurement can be carried out out of plane, the velocimeter axis being orthogonal to the plane of the wafer.

[0054] It should be noted that when several oscillating elements 10a, 10b, 10c are associated with a single resonator 2a, 2c, the resonance frequencies of all these oscillating elements 10a, 10b, 10c are measured, and an average of these frequencies is then calculated to correspond to the resonance frequency relative to this combination of oscillating elements 10a, 10b, 10c. Alternatively, the measured resonance frequency of this combination can be a resonance frequency of a single one of its oscillating elements 10a, 10b, 10c or a resonance frequency of a sample of its oscillating elements 10a, 10b, 10c.

[0055] Once the resonant frequency is estimated, this step 22 includes a substep 25 defining the structural characteristic such as the stiffness of said at least one oscillating element 10a, 10b, 10c. During substep 25, the processing unit executes the algorithm for calculating this structural characteristic from the estimated resonant frequency of said at least one oscillating element 10a, 10b, 10c.

[0056] The process subsequently includes a calculation step 26 of a dimensional correction to be applied to each resonator 2b, 2c of the set of mechanical resonators based on the structural characteristic determined for its associated system 3. During this step 26, a quantification of the dimensional correction to be applied to resonator 2b, 2c is then determined.

[0057] To do this, this step 26 includes a sub-step of determination 27, from this determined structural characteristic, of a thickness e of material to be added or removed from at least one dimension of the resonator 2b, 2c of the batch of mechanical resonators formed during the formation step 20 to obtain the batch of mechanical resonators 2a whose structural characteristics have the average within the predetermined range of values.

[0058] This dimensional correction effectively corresponds to a thickness e of material to be removed or added to the resonator 2b, 2c in order to vary at least one of its dimensions E2, H2, E3, H3, namely: only the height H2, H3 of the flexible part 3, or only the thickness E2, E3 of the flexible part 3, or both this height H2, H3 and this thickness E2, E3.

[0059] This dimensional correction can be made on one or more distinct lengths of the flexible part 3 or on the entire length of the flexible part 3 of this resonator 2b, 2c.

[0060] Such a sub-step 27 thus allows, by determining the dimensional correction, to participate in shaping a geometry of this resonator 2b, 2c which will give it a value of the structural characteristic which will be within the predetermined range of value.

[0061] The process then includes a modification step 28 of the dimensions E2, E3, H2, H3 of the mechanical resonators 2b, 2c from a dimensional correction calculated to obtain the batch of mechanical resonators 2a whose structural characteristics have the average within the predetermined range of values.

[0062] In this context, if the dimensions E2, H2 of the resonators 2b are greater than the dimensions E1, H1 required to obtain the batch of mechanical resonators 2a whose average structural characteristics fall within the predetermined range of values, then this step 28 includes a substep of material removal 29 based on the calculated thickness e of material to be removed. Such removal can then be carried out during an oxidation and then deoxidation process of these resonators 2b, a process well known in the prior art. This substep 29 aims to reduce the dimensions of the section 4b of the flexible part 3 of this resonator 2b over a given length or over the entire length of this flexible part 3.

[0063] When the dimensions E3, H3 of the resonators 2c are smaller than the dimensions E1, H1 required to obtain the batch of mechanical resonators 2a whose average structural characteristics fall within the predetermined range, this step 28 then includes a substep 30 for adding material based on the calculated thickness e of material to be added. Such material addition can then be carried out using well-known prior art processes such as thermal oxidation, galvanic growth, physical vapor deposition, chemical vapor deposition, atomic layer deposition, or any other additive process. This substep 30 aims to increase the dimensions E3, H3 of the cross-section 4c of the flexible part 3 of this resonator 2c over a given length or over the entire length of this flexible part 3.

[0064] Thus such a process makes it possible to correct with great precision provided by the said reference stiffness indication systems, the dimensional errors of resonators manufactured by such processes implementing photolithography and / or DRIE engraving technologies. Nomenclature

[0065] 1. Plate comprising at least one resonator 2a. Manufactured mechanical resonator 2b. Mechanical resonator formed in the plate with a cross-section larger than that of the manufactured resonator 2c. Resonator formed in the plate with a cross-section smaller than that of the manufactured resonator 3. Flexible part of the mechanical resonator 4a. Manufactured resonator cross-section 4b. Formed resonator cross-section larger than that of the manufactured resonator cross-section 4c. Formed resonator cross-section smaller than that of the manufactured resonator cross-section 5a. Attachment end of the oscillating element 5b, 5c. Free end of the oscillating element 6. Rod / Trunk of the oscillating element 7. First flexible arm of the oscillating element 8. Second flexible arm of the oscillating element 9. Opening in which the oscillating element is arranged 10. Oscillating element 11.12. End element of section having the shape of a polygonal 13. End element of section having a circular shape 14. Peripheral wall of the opening 15. Part connecting the arms to the trunk of the oscillating element 16. Part fixing in the wall of the opening of the oscillating element 17. Part of said wall opposite the fixing part.

Claims

1. A method for manufacturing a batch of mechanical resonators (2a) whose structural characteristics have an average within a predetermined range of values, said structural characteristic being common to each resonator (2a) of this batch, the method comprising the following steps: a) forming (20) in said wafer (1) mechanical resonators (2b, 2c) according to dimensions different from the dimensions required to obtain the batch of mechanical resonators (2a) whose structural characteristics are within said predetermined range of values;(b) form (21) in said plate (1) at least one oscillating element (10a, 10b, 10c) in an opening (9) provided in the plate (1), said element (10a, 10b, 10c) being made up of a trunk (6) the body of which is connected at a first end (5a) to a fixing portion (15) of a wall (13) of this opening (9), and of two flexible arms (7, 8) connected at a second end (5d) of said trunk (6) by means of a connecting portion (14), said arms (7, 8) being parallel to an axis of symmetry (A) of said trunk (6) and extending in the direction of a portion (16) of said wall (13) opposite the fixing portion (15), the body of said trunk (6) comprising a portion located between the first and second ends (5a, 5d) having a axial section (S4) which is less than axial sections (S2, S1) respectively of the first and second ends (5a, 5d);(c) determination (22) of a value relating to the structural characteristic of said at least one oscillating element (10a, 10b, 10c) formed; (d) calculation (26) of dimensional corrections to be applied to the resonators (2b, 2c) formed, from the determined value relating to the structural characteristic; (e) modification (28) of the dimensions of the resonators (2b, 2c) formed, from the dimensional corrections calculated to obtain the batch of resonators (2a) whose structural characteristic values ​​are within the predetermined range of values.

2. Method according to the preceding claim, wherein said forming step (21) provides that the axial section (S4) is greater than an axial section (S3) of each of the arms (7, 8).

3. A method according to any one of the preceding claims, wherein said oscillating element (10a, 10b, 10c) formation step (21) provides for the construction of each arm (7, 8) according to a length (L) adjustable according to a resonance measurement tolerance factor which is defined from at least one dimension (E2, E3, H2, H3) of a flexible part (3) of the resonator (2b, 2c) associated with said at least one oscillating element (10a, 10b, 10c).

4. A method according to any one of the preceding claims, wherein said oscillating element (10a, 10b, 10c) formation step (21) provides for the construction of an arm (7) spaced from the other arm (8) by a first distance (D1) and a free end (5b, 5c) of each of these arms (7, 8) which is spaced from the part (16) opposite the fixing part (15) by a second distance (D2), said first distance (D1) being greater than said second distance (D2).

5. A method according to any one of the preceding claims, wherein said oscillating element (10a, 10b, 10c) formation step (21) provides for the construction of each arm (7, 8) with a thickness (Er) which is similar or substantially similar to that of a flexible part (3) of each resonator (2b, 2c) formed in the plate (1).

6. A method according to any one of the preceding claims, wherein said oscillating element (10a, 10b, 10c) formation step (21) provides for the construction of each arm (7, 8) with a free end (5b, 5c) made of material with an end element (11, 12) having a mass greater than the mass of the rest of the body of that arm (7, 8).

7. Method according to the preceding claim, wherein the end element (11, 12) has a cross-section which has a circular shape or a polygonal shape.

8. A method according to any one of the preceding claims, wherein said oscillating element (10a, 10b, 10c) formation step (21) provides for the construction of the trunk body (6) with the section (S4) which is between 2 and 5 times smaller than the axial sections (S2, S1) respectively of the first and second ends (5a, 5d).

9. A method according to any one of the preceding claims, wherein the formation steps (20, 21) of the mechanical resonators (2b, 2c) and of said at least one oscillating element (10a, 10b, 10c) are carried out by etching, in particular by deep reactive ion etching.

10. Method according to any one of the preceding claims, wherein in the forming step (21) each oscillating element (10a, 10b, 10c) is made in the wafer (1) for at least one resonator (2b, 2c) of the batch of mechanical resonators (2b, 2c).

11. Method according to any one of claims 1 to 9, wherein the formation step (21) provides for the creation in the plate (1) of a plurality of oscillating elements (10a, 10b, 10c) surrounding at least one resonator (2b, 2c).

12. A method according to any one of the preceding claims, wherein the determination step (22) includes a substep of estimating (23) at least one resonance frequency of each oscillating element (10a, 10b, 10c) associated with at least one resonator (2b, 2c) of the set of resonators (2b, 2c).

13. A method according to the preceding claim, wherein the determination step (22) comprises a substep defining (25) a structural characteristic of each oscillating element (10a, 10b, 10c) which is of the same nature as the structural characteristic common to each resonator (2b, 2c) formed, said substep (25) being carried out from a processing unit connected to a device for modifying the resonators (2b, 2c) formed executing an algorithm for calculating this structural characteristic of each oscillating element (10a, 10b, 10c) on the basis of the estimated resonance frequency.

14. A method according to any one of the preceding claims, wherein the calculation step (26) includes a substep of determining (27) from the determined value of the structural characteristic of each oscillating element (10a, 10b, 10c), a thickness (e) of material to be added or removed from at least one dimension of each resonator (2b, 2c) associated with the oscillating element (10a, 10b, 10c).

15. A method according to any one of the preceding claims, wherein the oscillating element (10) has the shape of a tuning fork.

16. A method according to any one of the preceding claims, wherein the structural characteristic is a stiffness characteristic.

Images