Mechanical structure with one actuator and mechanical reinforcing agent as well as manufacturing method

Description

[0001] The invention generally relates to mechanical structures in which it is sought to transmit a deformation or a vibration mode to a mechanical element using an actuator and in particular an actuator produced using microelectronic techniques.

[0002] Such a problem is present in many areas of application such as those cited below in a non-exhaustive manner.

[0003] Today, various systems use actuators, for example, ceramic piezoelectric actuators (haptic panels, "inkjet" actuators, etc.). These ceramics must be placed individually on the final system and require high actuation voltages (typically 100 to 200V).

[0004] In parallel, the use of actuators deposited in thin layers by microelectronic processes makes it possible to collectively produce numerous systems by step sharing (a microelectronic step is carried out at the same time on all the systems present on the substrate), and thus makes it possible to reduce manufacturing costs. In addition, thin-film actuators make it possible to actuate electromechanical systems using low voltages (typically 10-20V). However, due to their low thickness and small dimensions, these actuators exhibit less deformation than that obtained with piezoelectric ceramics, and transmit less force or generate less displacement than ceramics.

[0005] An example of an application concerns the haptic interface. Currently, mobile phone manufacturers that have launched touchscreen mobiles are seeking to stand out by integrating a force feedback haptic interface on their devices. Thus, when a user slides their finger over an icon on the screen, they can feel a slight vibration coming from the mobile, a vibration intended to convey the impression of pressing a button. However, to date, haptic systems embedded in mobile phones, for example, have a limited haptic effect (simple vibration) and excessive power consumption.

[0006] Another example of an application for which it is interesting to amplify the deformation of an actuator is in areas where we are seeking to create a switch or a variable capacity.

[0007] This problem also arises when trying to create, for example, a MEMS speaker, using an actuator on a membrane. Actuating the membrane creates an acoustic pulse.

[0008] This same problem is also present in the field of photoacoustic imaging. In this case, the acoustic pulse, created by the displacement of air generated by the actuation of the membrane, is sent to a cell or an element to be "probed". The reflection of the acoustic wave can be recorded and analyzed for imaging.

[0009] We can also mention areas of application such as micro-pumps, which use the movement of a membrane to act as a micro-pump, for example to dispense insulin or any other medication.

[0010] Patent application publication US2010 / 090565 A1 describes a mechanical structure comprising: an elastic member; a piezoelectric actuator whose height can vary, located on the surface of a substrate; a mechanical transfer bar between said actuator and said elastic member; the transfer bar may comprise a notch.

[0011] In this general context, it remains interesting and necessary to be able to have small structures in which an effect introduced at the level of an actuator can be transmitted in an amplified manner to an element to which this actuator is coupled.

[0012] Therefore, the present invention relates to a mechanical structure as defined by claim 1.

[0013] According to a variant of the invention, the active substrate being oriented according to a first plane defined by two orthogonal axes X and Y, defined in an orthogonal reference frame (X, Y, Z), the trench is oriented according to a plane comprising an axis Z' making an angle θ with said axis Z, this angle possibly being zero.

[0014] According to a variant of the invention, said elementary structure comprises a stack of layers of which at least one layer comprises said trench.

[0015] According to a variant of the invention, the substrate having a surface oriented in a first plane defined by two orthogonal axes X and Y, said elementary structure comprises trenches distributed periodically along said first plane between said actuator and said substrate.

[0016] According to a variant of the invention, said structure comprises several actuators coupled to at least one elementary amplification structure, on said active substrate.

[0017] According to a variant of the invention, the actuator is a piezoelectric actuator.

[0018] According to a variant of the invention, the piezoelectric actuator comprises at least one layer of piezoelectric material which may be made of PZT, or AIN, or LNO, or BST.

[0019] According to a variant of the invention, the actuator comprises a thermal resistance which may comprise at least one layer of metal, adapted to ensure thermal actuation.

[0020] According to a variant of the invention, the actuator comprises at least one layer of magnetic material, making it possible to ensure magnetic actuation.

[0021] According to a variant of the invention, the active substrate is entirely or partly made of glass, or polymer, or silicon.

[0022] This substrate can be homogeneous (also called a “bulk” substrate) or heterogeneous, i.e. comprising a stack of layers.

[0023] According to a variant of the invention, the elementary structure comprises at least one part made of silicon.

[0024] According to a variant of the invention, said structure comprises: an actuator which may comprise a piezoelectric layer; an elementary silicon structure; an active glass substrate.

[0025] According to a variant of the invention, the trench(es) have a width of between approximately 5 µm and 1000 µm and in the case of several trenches, they are spaced apart by a distance which can typically be between 5 µm and 1000 µm.

[0026] The invention also relates to a method for manufacturing a mechanical structure comprising a stack comprising an active substrate and at least one actuator adapted to generate vibrations at the level of said active substrate, said stack comprising an elementary structure for amplifying said vibrations: arranged between said actuator and said active substrate, the structure being adapted to transmit and amplify said vibrations and; comprising at least one trench, located between said actuator and said active substrate, characterized in that it comprises the following steps: the production of at least one actuator on the surface of an elementary substrate; an operation of bonding said elementary substrate on the actuator side, onto a temporary substrate; the production of at least one trench in said elementary substrate, on the face opposite to that comprising said actuator, the elementary substrate and said trench forming an elementary amplification structure; a bonding operation on the trench side of the elementary substrate comprising at least said trench, on the so-called active substrate, an operation of removing the temporary substrate to release the actuator.

[0027] According to a variant of the invention, the elementary substrate is entirely or partly made of silicon, the active substrate is entirely or partly made of glass and the actuator is entirely or partly made of piezoelectric material.

[0028] According to a variant of the invention, said method comprises: the deposition of at least one metal layer on the faces to be bonded respectively of the elementary substrate and of the active substrate; the bonding by thermocompression of said faces comprising said metal layers.

[0029] According to a variant of the invention, said method comprises an operation of thinning said elementary substrate from said face opposite that comprising said actuator, this step being carried out before the bonding step and before or after the creation of the trench.

[0030] According to a variant of the invention, the operation of bonding said temporary substrate is carried out with a polymer.

[0031] The invention will be better understood and other advantages will appear on reading the description which follows, given without limitation and thanks to the appended figures among which: there figure 1 illustrates an example of a mechanical structure according to the invention; the Figures 2a And 2b illustrate top views of mechanical structure respectively according to the known art using a full silicon wafer and a structure of the invention using a silicon wafer comprising trenches; the figure 3 schematizes the deformation under stress of a mechanical structure of the invention; the figure 4 illustrates the evolution of the deformation amplitude of a glass substrate in different configurations linked to different silicon substrate thickness / glass thickness ratios for an example of mechanical structure of the invention; the Figure 5illustrates an example of an application using the structure of the invention in a switch / interrupter or variable capacity type application. Figures 6a to 6g illustrate the different steps of an example of a method of manufacturing a mechanical structure of the present invention.

[0032] Generally speaking, the mechanical structure of the present invention comprises a substrate in which it is sought to transmit vibrations, an actuator generating said vibrations and an elementary amplification structure comprising at least one trench.

[0033] There figure 1 schematizes an example of a mechanical structure of the invention and highlights an active substrate 10 in which it is sought to propagate a vibration mode from an actuator 20 via an elementary amplification structure 30, comprising at least one, or even several Ti trenches, (two on the figure 1) the elementary structure 30 being secured to said substrate by means of, for example, a layer of glue 40.

[0034] In this example, the active substrate is oriented along a first plane defined by two orthogonal axes X and Y in an orthonormal frame (X, Y, Z). The trenches are oriented along a plane including a Z' axis coincident with the Z axis.

[0035] According to other possible configurations, the trenches could be oriented along planes including a Z' axis making a non-zero angle with the Z axis.

[0036] Typically, in different applications, the positioning of several actuators on the surface of a so-called active substrate is optimized in which we seek to propagate vibrating modes and preferably a mode centered on an optimal frequency.

[0037] The actuator 20, which may be piezoelectric, thermal or magnetic, may contract or expand. By bimetallic effect, due to the presence of the elementary structure 30 which connects it to the element to be deformed, the actuator generates a torque to the element to be deformed. This torque is amplified by the lever arm effect of the intermediate layer.

[0038] The Applicants carried out simulations to validate the concept of the present invention using Coventor finite element calculation software.

[0039] More specifically, the Applicants simulated the transmission of a vibration mode, which can be called "corrugated sheet", to a substrate by means of a thin-film actuator, which is of particular interest for haptic panel applications.

[0040] In this context, the simulations were carried out with an optimization of positioning of several actuators 20 as illustrated in Figure 2a. Two rows of three actuators are arranged on the surface of an intermediate silicon structure 30, in order to transfer a vibration mode to a glass slab. The vibration mode, called "corrugated sheet" is also influenced by the dimensions of the actuators (their width and length).

[0041] The following different cases were simulated on the basis of a PZT (Lead Titanium Zirconate) based actuator and on a glass slab type substrate. 1) PZT / glass: this could correspond to an ideal case but which is currently difficult to envisage from a technological point of view given the constraints of realization of the high-performance PZT thin layer on glass, in particular due to the high temperatures induced by the shaping of the PZT; 2) PZT / Gold / glass: it was therefore considered to use an intermediate layer of gold, corresponding from a technological point of view to a transfer of the PZT actuator on a glass slab after removal of the silicon substrate which was used to produce the PZT; 3) PZT / Si 10µm / Gold / glass: it was also considered a transfer of the PZT actuator on a glass slab after thinning of the silicon substrate which could be used to produce the PZT, the intermediate layer between the PZT and the glass being a gold / silicon bilayer;4) PZT / Si 100µm / Gold / Glass: it was also considered to transfer the PZT actuator onto a glass slab after less significant thinning than in the previous case, of the silicon substrate which could be used to produce the PZT, the intermediate layer between the PZT and the glass therefore being a gold / silicon bilayer.;

[0042] The materials cited above are indicative, essentially enabling the difference in transmission of the mode to the substrate capable of deforming under the action of the thin-layer actuator to be highlighted when an intermediate structure is present.

[0043] The intermediate structure can thus be made up of one or more layers of various materials. It has a mechanical role allowing the actuator to be bonded and transferred to the vibrating element. It can be made up of a layer of gold, oxide, or silicon. It can also be made up, in a non-limiting manner, of a multi-layer gold / silicon or oxide / silicon or oxide / gold / silicon stack.

[0044] The Applicants thus obtained the following simulation results summarized in Table 1 below: PZT / glass PZT / Gold / Glass PZT / Si 10µm / Gold / glass PZT / Si 100µm / Gold / Glass Mode frequency 20.898 KHz 20.898 KHz 21.102 KHz 21.918 KHz Vibration amplitude 45 µm 28 µm 18 µm 16 µm

[0045] Vibration amplitudes were simulated with arbitrary damping in air under -30V.

[0046] These results are relative and not absolute; to obtain absolute amplitudes, it would be advisable to first extract a damping coefficient from the measurement. More precisely, a simulation is carried out by introducing a damping coefficient which is adjusted so that the simulation gives a result in good agreement with the measurement carried out on a manufactured device.

[0047] It appears that the presence of a gold layer significantly reduces the vibration amplitude of the panel compared to the ideal PZT / glass case. The Applicants have also observed that the presence of a gold layer induces the appearance of parasitic modes.

[0048] By keeping 10µm or 100µm of silicon, the vibration amplitude is even more damped (because the presence of silicon induces an increase in the overall rigidity of the system), and parasitic modes appear even more, to the point of making obtaining the final mode very uncertain.

[0049] From these simulations, the Applicants studied the effect of introducing trenches into an intermediate silicon structure, making it possible to cause the lever arm effect, in a configuration illustrated in Figure 2b which schematizes Ti trenches made in the amplifier structure 30.

[0050] The lever arm effect is represented schematically in figure 3 . The actuator 20, which may be piezoelectric, thermal or magnetic, may contract or expand. By bimetallic effect, due to the presence of the intermediate amplification structure 30 which connects it to the element to be deformed 10, the actuator generates a torque, transmitted to the element to be deformed. This torque is amplified by the lever arm effect of the intermediate layer 30.

[0051] Thus, by using the elementary structure of the invention, with trenches, it becomes possible to promote the deformation to be transmitted to the element to be deformed or the desired mode and even increase its amplitude compared to the case of the mode obtained with the presence of the same layer of silicon without trenches as shown in Table 2 below: Table 2 PZT / Glass PZT / Gold / ver re PZT / Si 10µm / Gold / glass PZT / Si 100µm / Gold / Glass PZT / Si sliced ​​10 µm / gold / Glass Mode frequency 20.898 KHz 20.898 KHz 21.102 KHz 21.918 KHz 20.898 KHz Vibration amplitude 45 µm 28 µm 18 µm 16 µm 25 µm

[0052] Thus, by introducing trenches into the silicon structure, we benefit from the presence of silicon under the actuator rather than suffering from it. The silicon trenches act as a lever arm by amplifying the amplitude of the mode (25µm with the trenches in the silicon compared to 18µm for the same thickness of silicon without trenches). The trenches also act as a “filter” by favoring the desired mode. Indeed, the Applicants observed that the desired mode was preserved by eliminating parasitic modes.

[0053] The above-mentioned layers, constituting the mechanical structure of the invention, are only given as examples and the present invention can be generalized to other piezoelectric materials than PZT and to other types of actuators than piezoelectric actuators.

[0054] So the piezoelectric material can be PZT, AIN, LNO, BST or other.

[0055] The actuator can be thermal (same principle diagram as the piezoelectric, the actuator is in this case a thermal resistance, typically a metal like aluminum or gold...) or magnetic (in this case the actuator is a magnetic material).

[0056] The so-called active substrate can be made of glass, polymer or other.

[0057] The amplifying structure may include intermediate layers which may be made of oxide, silicon, polysilicon, gold, etc.

[0058] Trenches can be provided only in the silicon because this solution is easily achievable technologically. However, through trenches going from the so-called active substrate to the actuator are possible.

[0059] The thicknesses of the materials in the amplifier structure can typically be between a hundred nanometers and a few microns, or even a few tens of microns.

[0060] Typically, the amplification structure can be made of silicon, the glue layer being metallic, for example gold.

[0061] The Applicants also highlighted that there could be an optimal thickness of the amplifying structure.

[0062] To do this, he performed various FEM simulations using Coventor to find the optimum silicon substrate thickness. The silicon substrate used to support the production of PZT thin-film actuators must be thinned. As shown in figure 4 , an optimum exists, and a remaining silicon thickness of the order of 40 to 60µm seems to allow the greatest deformation of the substrate.

[0063] This value is linked to the thickness and nature of the glass substrate that were used in simulation, namely 700µm, but the methodology can be transcribed for other dimensions and other materials.

[0064] The Applicants have thus established a curve relating to the displacement of the substrate, illustrated by the amplitude of the vibration mode of interest as a function of the ratio of the thicknesses: thinned silicon / active glass substrate. The optimum is thus found to be around 0.08.

[0065] Similarly, the Applicants highlighted that the distribution of the trenches and their sizing in the amplifying structure made it possible to increase the amplification phenomenon.

[0066] Trenches that are too thin and / or too close together will not significantly reduce the rigidity induced by silicon, while very wide and very distant trenches, which greatly reduce rigidity, lead to technological problems such as poor bonding. It is therefore necessary to find the best compromise between these two effects.

[0067] The Applicants have highlighted the good performance obtained with trenches of 5 to 1000 µm and spaced at a distance which can typically be between 5 and 1000 µm and more particularly with trenches having a width of 300 µm and spaced at 400 µm.

[0068] It should be noted that the silicon layer can be fully sliced ​​(trenches through the thickness of the silicon) or partially sliced ​​as shown in the following Table 3. Table 3 Case Outflow trenches Partial trenches (10µm of Si remaining) Partial trenches (20µm of Si remaining) Substrate deformation amplitude (finite element simulation with -30V applied to the piezoelectric material 140 µm 50 µm 15 µm Main stress (main stress, relative comparison) 630 380 250

[0069] It appears that if we lose in the efficiency of amplification of the mechanical movement by the use of partial trenches (the amplitude of deformation of the substrate goes from 140 to 50 then 15µm), we can greatly reduce the stress generated in the actuator by the deformation of the substrate (main stress going from 630 to 380 then 250). This reduction in stress can increase the reliability of the system.

[0070] We therefore favor open trenches leading to greater amplification. First example of application using the structure of the invention: the haptic panel.

[0071] Generally speaking, a haptic panel works by an air blade effect, created on the surface of the panel by the latter's vibration. This vibration is generated by piezoelectric actuators glued or deposited and engraved on the plate.

[0072] For a good haptic effect, it is necessary to obtain a vibration amplitude of typically around 1µm in the “corrugated sheet” mode.

[0073] Due to its high piezoelectric coefficient, PZT is an excellent candidate for producing an actuator to obtain integrated haptic panels, presenting good performances, using low actuation voltages, in particular compared to other piezoelectric materials such as LNO or AIN.

[0074] Since haptic panels are used in particular on smartphones or tablet PCs, it is necessary to use a transparent vibrating panel, which cannot therefore be made of silicon.

[0075] Since direct deposition of PZT material on glass is not compatible with the high crystallization temperatures required for PZT deposited by the sol-gel method, it is also necessary to use an intermediate structure, as explained previously.

[0076] In this context, the present invention is of major interest in that it makes it possible, through the use of a necessary intermediate structure, to make it an amplifier of transmitted vibration modes.

[0077] For such an embodiment, a variant of the present invention consists of transferring the PZT actuators produced on silicon onto a glass wafer.

[0078] To do this, PZT actuator strips made on silicon serving as an elementary substrate can be cut and fixed on a temporary substrate hereinafter called a temporary handle allowing the silicon substrate to be partially thinned or removed, then the actuator strips to be transferred and fixed on the glass slabs by metal-metal thermocompression, for example: gold-gold. Second example of application using the structure of the invention: Switch or variable capacity.

[0079] There Figure 5thus illustrates an example in which the deformation of an actuator 20 is amplified, via an amplification structure 30 comprising Ti trenches, said deformation being able to be transmitted and amplified to a beam for example 10, to produce a switch or a variable capacitance, equipped with a clean contact or a mobile electrode 50, opposite a fixed contact or electrode 60. This fixed contact or electrode is on a mechanical support on which the switch or the variable capacitance has been mounted or produced. In particular, this mechanical support can be a silicon substrate. In this case, it is a question of deforming a double-embedded or simply embedded beam under the effect of a voltage applied to the actuator. The deformation of the beam is amplified to more quickly cause contact between the mobile element and the fixed contact, or to increase the difference in capacitance between the two electrodes facing each other.

[0080] Other examples can also be mentioned such as: those using a membrane and in particular: ∘ a loudspeaker using a MEMS component comprising a membrane, activated by an actuator, the actuation of the membrane making it possible to produce an acoustic pulse; ∘ a micro pump using the displacement of a membrane for example to dispense insulin or any other medication; a device for photoacoustic imaging. In this case the acoustic pulse, created by the displacement of the air generated by the actuation of the membrane, is sent to a cell or an element to be "probed". The reflection of the acoustic wave can be recorded and analyzed for imaging; an electromechanical resonator serving as a time base. In this case the actuator must cause a vibration mode at a given frequency. This frequency serves as a time reference for electronics such as that managing mobile phones.The greater the vibration, the more distinct it will be from the surrounding electronic noise, and the more effectively it will be used by the electronics. In the case of the invention, it is possible to amplify the vibration, and therefore increase the signal-to-noise ratio in order to increase the quality of the electromechanical resonator. Example of a method for manufacturing a mechanical structure of the invention comprising at least several piezoelectric actuators and which can advantageously be used in a haptic panel.

[0081] The main steps of the process are illustrated using the Figures 6a to 6g .

[0082] According to a first step illustrated in Figure 6a , piezoelectric actuators 20 are produced on the surface of an elementary silicon substrate 30 intended to serve as an elementary amplification structure, comprising at least one layer of piezoelectric material between electrodes.

[0083] According to a second step illustrated in Figure 6b, a temporary handle 80 is bonded using a glue 70. The temporary handle can be a substrate which can be made of any type of material, the glue layer 70 can be made of polymer, which can be made fluid by heating.

[0084] According to a third step illustrated in Figure 6c , an operation of thinning the substrate 30 is carried out (for example by chemical-mechanical polishing).

[0085] According to a fourth step illustrated in figure 6d , a metal deposit 41, for example in gold, is made on the rear face of the substrate 30, said metal deposit being intended for bonding an active substrate (such as a glass slab, for example).

[0086] According to a fifth step illustrated in Figure 6e , Ti trenches are produced by etching, in said substrate 30 and in the adhesive layer 41, from the rear face. The areas to be etched are previously defined by a photolithography step.

[0087] According to a sixth step illustrated in Figure 6f , an active substrate 10 is bonded in which it is sought to propagate vibrations, previously covered with a metal layer 42. Bonding can be carried out by thermocompression after bringing the two layers 41 and 42 into contact.

[0088] According to a seventh step illustrated in figure 6g , said temporary handle 80 is detached and a step of releasing the bonding layer 70 (partially as shown or totally) at said actuators 20 is also carried out. The bonding layer may be partially removed or totally removed as advantageously for polymer bonding.

[0089] Typically when a bonding polymer has been used, this latter operation can be carried out by raising the temperature (by any heat source) making said polymer malleable and therefore making it possible to separate the temporary substrate called a handle from the entire mechanical structure of the invention which has been produced.

Claims

1. A mechanical structure comprising a stack containing an active substrate (10) and at least one actuator (20) adapted to generate vibrations at said active substrate, said stack comprising an elementary structure for amplifying said vibrations (30): - arranged between said actuator (20) and said active substrate (10), the structure being adapted to transmit and amplify said vibrations and; - comprising at least one trench (Ti) located between said actuator (20) and said active substrate (10); characterised in that said trench (Ti) opens at least on said active substrate (10).

2. The mechanical structure according to claim 1, characterised in that said elementary structure comprises a stack of layers, at least one layer of which comprises said trench.

3. The mechanical structure according to one of claim 1 or 2, characterised in that the substrate has a surface which is oriented in a first plane defined by two orthogonal axes X and Y, said elementary structure comprises trenches (Ti) that are distributed periodically along said first plane between said actuator and said substrate.

4. The mechanical structure according to one of claims 1 to 3, characterised in that it comprises multiple actuators coupled with at least one elementary amplification structure, on said active substrate.

5. The mechanical structure according to one of claims 1 to 4, characterised in that the actuator is a piezoelectric actuator.

6. The mechanical structure according to claim 5, characterised in that the piezoelectric actuator comprises at least one layer of piezoelectric material that may be made of PZT, AIN, LNO or BST.

7. The mechanical structure according to one of claims 1 to 4, characterised in that the actuator comprises a thermal resistor that may comprise at least one metal layer, adapted to carry out a thermal actuation.

8. The mechanical structure according to one of claims 1 to 4, characterised in that the actuator comprises at least one layer made of magnetic material, allowing a magnetic actuation to be carried out.

9. The mechanical structure according to one of claims 1 to 8, characterised in that the active substrate is entirely or partly made of glass, polymer, or silicon.

10. The mechanical structure according to one of claims 1 to 9, characterised in that the elementary structure comprises at least one portion made of silicon.

11. The mechanical structure according to claims 5 and 10, characterised in that it comprises: - an actuator that may comprise a piezoelectric layer; - an elementary structure made of silicon; - an active substrate made of glass.

12. The mechanical structure according to claim 11, characterised in that the width of the trench or trenches is between approximately 5 µm and 1000 µm and, in the case of multiple trenches, said trenches are spaced apart by a distance that may typically be between 5 µm and 1000 µm.

13. A method for manufacturing a mechanical structure comprising a stack containing an active substrate (10) and at least one actuator (20) adapted to generate vibrations at said active substrate, said stack comprising an elementary structure for amplifying said vibrations (30): - arranged between said actuator (20) and said active substrate (10), the structure being adapted to transmit and amplify said vibrations and; - comprising at least one trench (Ti) located between said actuator (20) and said active substrate (10), the method comprising the following steps: - producing at least one actuator (20) on the surface of an elementary substrate (30); - an operation of bonding said elementary substrate, on the actuator side, to a temporary substrate (80); - producing at least one trench (Ti) in said elementary substrate, at the face opposite that containing said actuator, the elementary substrate and said trench forming an elementary amplification structure; - an operation of bonding, on the trench side, said elementary substrate comprising at least said trench to the so-called active substrate; - an operation of removing the temporary substrate to free the actuator.

14. The manufacturing method according to claim 13, characterised in that the elementary substrate is entirely or partly made of silicon, the active substrate is entirely or partly made of glass and the actuator is entirely or partly made of piezoelectric material.

15. The manufacturing method according to claim 13 or 14, characterised in that the bonding operation comprises: - the deposition of at least one metal layer on the faces to be bonded of the elementary substrate and of the active substrate, respectively; - bonding, by means of thermocompression, said faces containing said metal layers.

16. The manufacturing method according to one of claims 13 to 15, characterised in that it comprises an operation of thinning said elementary substrate from said face opposite that containing said actuator, this step being carried out before the bonding step and before or after producing the trench.

17. The manufacturing method according to one of claims 13 to 16, characterised in that the operation of bonding said temporary substrate is carried out using a polymer.