FR2865201A1 - Vertical comb-drive type electrostatic actuator for very large telescope, has two electrode sets moving with respect to each other, from rest to maximum positions, where sets partially and electrically overlap even in rest position - Google Patents

Abstract

The actuator has a set of electrodes (13) associated to a substrate (14) that holds a suspending beam (12). Another set of electrodes (10) moves with respect to the former set, from a rest position to a maximum position, along a direction perpendicular to a reference plane defined by an upper surface of the substrate. The two sets of electrode partially and electrically overlaps even in the rest position. Independent claims are also included for the following: (A) an actuating matrix including actuators (B) a deformable mirror including deformable membranes supporting a surface supported by an actuating medium (C) a method of fabricating an actuator.

Description

2865201 1

  TECHNIQUE FOR REALIZING HIGH STRUCTURES

SELF-ALIGNED TOPOLOGY

  DESCRIPTION TECHNICAL FIELD AND PRIOR ART

  The invention relates to Micro-Electro-Mechanical Systems (MEMS). More particularly, it describes a high-topology actuator, such as comb-drive actuators, based on a comb-shaped structure, as well as a manufacturing method.

  The invention also describes the production of an actuator or an actuator, in particular of the vertical comb-drive type, or of the vertical comb type, with a high form factor.

  Microstructures, in particular those machined in silicon, are used in a large number of applications such as sensors and actuators.

  More particularly, the large topology MEMS structures are useful for the actuators when the required force is important, but also for the adaptive optics, for wavefront correction, the bioMEMS, where high form factor channels are desired.

  The known devices and methods use different methods each posing problems of compatibility of the method with the electronic circuit associated with the electrodes and with different levels of complexity.

  A conventional approach for producing high-topology actuators is to use metal plating within patterns made in an X-ray or UV-sensitive resin (as described in US 2002/109894). However, this type of process leaves traces on the substrate, or wafer, which prevent a post-treatment.

  In addition, the use of metal layers 10 is highly critical in the case of subsequent annealing.

  Finally, the use of X-ray sources is not common in the microelectronics industry.

  Sacrificial layers were also used (as described in W00172631). It is then a matter of locally etching a sacrificial layer, or of depositing by PECVD the layer that will make it possible to produce the mobile electrode by etching.

  A sub-engraving allows to release the combs.

  The major disadvantage of this solution lies in the fact that the deposited layers are limited in thickness.

  Consequently, the stroke of the actuator, and therefore its performance, are limited.

  Another solution is to machine in dry etching trenches of substantial depth on a SOI double substrate (comprising 2 layers of buried oxide), in order to stop on an oxide barrier layer 2865201 3 (as described in FIG. US 2002/005976, and US 2003/073261).

  Then the buried oxide is locally underexposed to release the moving combs.

  These two steps preclude obtaining a high value form factor. The shape factor of a pattern is defined as the ratio height of this pattern. When holes of narrow section are engraved on a great depth, one loses in resolution (case of an engraving on slope, side not respected ...). This is all the more marked if engravings follow: if an engraving is done from a flat surface or an already engraved surface, the result is not the same.

  This is the problem of the techniques described in the US documents cited above: there is deep engraving and succession of several engravings.

  There is also a problem of making the connector, particularly because of the presence of an insulating layer (as in document W001 / 72631) or of the oxide layer (as in the US documents cited above), which requires a resumption of contact on the upper and lower faces of the actuator.

  SUMMARY OF THE INVENTION An electrostatic actuator according to the invention comprises a first set of electrodes associated with a support and a second set of electrodes, movable with respect to the first set and interdigitated, or arranged alternately, with respect to this first game, this section 2865201 4 second game being able to move from a first position, called rest, to a second position, or to a maximum position, between the electrodes of the first game, outside a plane of reference linked to the support or defined by the support, or according to a displacement having at least one component oriented perpendicularly to this reference plane.

  The invention relates to an electrostatic actuator with two sets of electrodes partially overlapping, or partially facing each other, even at rest, including electrically: the surrounding electrode conductive areas overlap or face each other, less partially.

  In the rest position, a portion of the electrodes of the second set is facing a portion of the electrodes of the first set, in planes perpendicular to the reference plane.

  The displacement of the second game can be done perpendicular to the reference plane or in a rotational movement along an axis parallel to the reference plane.

  Interdigit combs are surface variation actuators. The moving electrodes move relative to the fixed electrodes.

  In the prior art, the known 3D type actuators have electrode sets without electrical overlap areas. Thus, in document US 2002/5970 there is a mechanical but non-electric covering of the teeth of the combs, which requires large actuating voltages for moving from a rest position to a second position or to a maximum position .

  An actuator according to the invention, with two sets of electrodes partially overlapping from the electrical point of view, even at rest, overcomes this problem and therefore may have lower actuation voltages.

  An actuator according to the invention makes it possible to overcome the disadvantages of the methods described above, and in particular the problem of the form factor, the etching resolution, and the problem of the connection.

  In the invention, the double lithography mask eliminates the two successive etching steps of the prior art, which makes it possible to improve the performance in terms of form factor.

  In the invention, all the connector is on the rear face of the substrate.

  The support can be both a mechanical support of the first set of electrodes and a support for connection means of the electrodes.

  An actuator according to the invention may comprise a first and a second series of movable electrodes disposed on either side of a body movable in rotation about said axis of rotation.

  It may also comprise a first and a second series of fixed electrodes arranged at different heights relative to the reference plane, respectively on the side of the first and second sets of moving electrodes.

  The displacement of the second set of electrodes with respect to the first set of electrodes can be done in a translation movement along an axis, called the axis of symmetry, perpendicular to the reference plane.

  The electrodes of the first and second set of electrodes may be arranged radially with respect to said circular axis of symmetry.

  The electrodes of the second set of electrodes may be arranged on a circular support centered on the axis of symmetry.

  The support may be pyrex or silicon.

  In the case of a Pyrex support, at least the fixed electrodes may be connected to the support 15 by anodic welding.

  In the case of a silicon support, at least the fixed electrodes can be connected to the support by molecular bonding.

  The second set of electrodes or the axis of rotation can be connected to suspension beams. The beams can be connected to the support.

  The lower part facing the support, electrodes of the second set of electrodes may be located at a height h, relative to the lower part, facing the support, fixed electrodes.

  The invention also relates to an actuating die comprising a plurality of individual actuators as described above.

  The number of individual actuators may for example be between 1000 and 100,000.

  The invention also relates to a deformable mirror comprising a deformable membrane supporting a first reflecting surface and a second surface supported by an actuating die as above.

  A method according to the invention, for producing an actuator, using a substrate comprising a front face and a rear face, comprises the following steps: a) Engraving on the rear face of the substrate, to form teeth, b) Formation of connecting means, on a support, c) Sealing of the support and the rear face of the etched substrate, d) etching on the front face of the substrate, to release the actuator.

  The invention makes it possible to produce an actuator in the same substrate and to be limited only by the precision of the lithography.

  Advantageously, the backside engraving comprising two successive levels of lithography.

  An actuator according to the invention is therefore achievable by a manufacturing method using double-sided etching of the same substrate.

  Backside etching can make it possible to form teeth at different heights relative to the support.

  Step c) can be performed by anodic bonding or by molecular bonding.

  Step b) may comprise a deposit on said support, a metal layer, and then an insulating layer, and an etching of these layers to delimit tracks and connection areas.

  Prior to step a), it can be provided a deposit on both sides of said substrate, a protective layer.

  The structures can be made either in Pyrex, or in a solid silicon substrate, or in a substrate with buried etch stop layers. In the latter case, the process is the same, but instead of using a solid substrate, an SOI substrate is used with its stop layer which stops the etchings.

  The choice of substrate depends on the needs of the user and the criticality of the accuracy of the patterns of the final structure.

  An additional etching step makes it possible to form an axis of rotation of the actuator.

  It is possible to perform a double etching, on the front face (FAV) and on the rear face (FAR) of the substrate, using a set of at least two levels of masks for photolithography, which guarantees, depending on the machine used, a precision quasimicronique.

  This allows for very small spacings between the adjacent branches of the same comb and thus allows to obtain an actuator with a very good sensitivity.

  The invention also relates to the production of a substrate or a connector support which at the same time serves as mechanical support for the actuator.

  This support production technology is generic and can be used for any type of assembly where the structure is assembled with the substrate or the support on the rear face, and is released on the front face.

BRIEF DESCRIPTION OF THE DRAWINGS

  FIG. 1 represents a first embodiment of the invention, FIG. 2A represents a second embodiment of the invention, according to a circular structure; FIG. 2B represents a variant of the second embodiment of the invention; FIG. 2C represents a schematic view from above of a device according to the invention with a circular structure; FIG. 2D represents an enlargement of a portion of a device according to the invention in a circular structure; FIG. 3 represents a third embodiment of the invention; FIGS. 4A-4K represent steps of a method according to the invention; FIGS. 5A-5E represent steps of a method of producing a support; In accordance with the invention, FIGS. 6A-6K and 7A-7K show steps of a method for carrying out a method according to the invention; FIGS. 8A-8K represent steps of a process of real tion of a method according to the invention.

  DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS FIG. 1 represents a device according to the invention.

  This device, or microsystem, in the form of a comb, comprises an actuator, or an actuator.

  This comprises mobile electrodes 10 held by suspension beams 12.

  It also has fixed electrodes 13 serving as counter electrodes.

  The fixed electrodes alternate with the moving electrodes, conferring on the assembly the comb structure.

  The fixed electrodes are held on a support or substrate 14, for example Pyrex. In the illustrated example, this support, or substrate, holds the beams 12 of suspension.

  The device also comprises means 16 for electrical connection, for controlling the actuators 25 individually.

  This connection is preferably made on the support or substrate 14.

  It is prolonged, for the mobile electrodes, by connections made on the beams 12. The fixed electrodes 13 are preferably connected directly to the connection means made on the support 14.

  Both the moving electrodes and the electrodes fixed relative to the substrate are arranged in a plane perpendicular to a reference plane defined by the upper surface of the support or the substrate 14.

  In the rest position, an electrically conductive part of the electrodes, or of each electrode, of the second set is opposite one or faces an electrically conductive part of the electrodes or an electrode of the first play (partial electrical recovery condition).

  Since the two sets of electrodes overlap partially from the electrical point of view, even at rest, it is possible to have lower operating voltages than in the devices of the prior art.

  In addition, the mobile electrodes (those of the second set of electrodes) are, in the rest position, offset in a vertical direction with respect to the fixed electrodes (those of the first set of electrodes): the lower part of the moving electrodes, or the part of these electrodes facing the substrate or the support 14, is at a height h with respect to the reference plane, on which, in the example illustrated, the fixed electrodes rest. This height h is less than the height of the fixed electrodes 13 so that the partial recovery condition in the rest position is respected. This offset h makes it possible to have one operating deflection.

  In the activation position, the moving electrodes are flexibly displaced as shown in FIG. 1.

  Such a device makes it possible to orient a mirror, fixed for example on the upper parts of the moving electrodes.

  Another example of a device according to the invention is illustrated in FIG. 2A.

  In this device, with a circular structure, the fixed electrodes 20 are arranged radially with respect to an axis of symmetry 22. The movement of the moving electrodes is then vertical. They are mechanically connected to an outer circular support or, as in FIG. 2A, to a plurality of outer supports 24, each being in the form of an arc of a circle.

  These fixed electrodes 20 and their supports 24 are arranged on a support 25 on which, as in the previous embodiment, connecting means (not shown in the figure) are made.

  In Figure 2A, the fixed electrodes are not only on the periphery of the structure, there are also in the center (electrodes 20 ').

  The movable electrodes 30 are integral with a circular inner support 32, which can itself be connected to a central suspension stud 34.

  The latter is supported by suspension beams 36, themselves fixed on the support.

  An electrically conductive part of the moving electrodes (those of the second set of electrodes) is, in the rest position, approximately the same level as an electrically conductive part of the fixed electrodes (those of the first set of electrodes). electrodes). An offset in the vertical direction (or perpendicularly to the connection support) between the bottom of the fixed electrodes and that of the movable electrodes makes it possible to have an operating deflection.

  In this embodiment, a movable part of the actuator, fixed electrodes 20 and a connection support 25 are found.

  Again, this device uses two sets of electrodes partially overlapping from the electrical point of view, even at rest, which allows to have lower operating voltages than in the devices of the prior art.

  The support 25 is for example made in a pyrex substrate, which makes it possible to seal the support-actuator assembly by anodic welding.

  The connection means, for example the tracks and the pads, are preferably deposited directly on the pyrex in order to make contact with the silicon while ensuring the isolation between each pad.

  FIG. 2B represents a variant of this second embodiment of the invention. According to this variant, the fixed electrodes 27, of which only two are shown, are arranged projecting from a fixed electrode 29.

  The movable electrodes 31 are integral with a circular inner support 33, which can itself be connected to a suspension stud 35.

  The latter is supported by suspension beams 37, themselves fixed on the support.

  In this embodiment of FIGS. 2A-2B, the movement of the moving electrodes takes place along an axis XX '.

  FIG. 2C shows a schematic view from above of a device of the type of FIG. 2A, but with an additional stage of fixed and moving electrodes.

  According to one example, the combs 31 have the following geometrical characteristics: thickness e = 10 μm, length 1 = 100 μm, height h = 100 μm, distance between successive mobile electrodes: d = 10 μm.

  Identical or similar geometric characteristics may be retained for the fixed electrodes 27.

  FIG. 2D represents an enlargement of a portion of a device according to the invention, with a circular structure.

  In this 2D figure are indicated two cutting planes AA 'and BB' according to which a production method will be detailed below.

  Again, according to this embodiment, the structure is the comb-shaped, the movable electrodes alternating with the fixed electrodes.

  In the rest position, an electrically conductive portion of the electrodes, or each electrode, of the second set is opposite one or faces an electrically conductive part of the electrodes, or an electrode of the first play (partial electrical recovery condition).

  The two sets of electrodes partially overlapping from the electrical point of view, even at rest, make it possible to work with lower operating voltages.

  Another example of a device according to the invention is illustrated in FIG.

  In this device, the movable electrodes 40-1, 40-2 are movable about an axis of rotation 42 parallel to the plane of the support 44. This axis of rotation is embodied by an axis, of etched silicon, for example.

  A portion 46 of the fixed electrodes disposed on one side of the moving electrodes is disposed at a first height or distance h1 with respect to the support, while the other portion 48 is disposed at a second height or distance h2 with respect to the substrate, different from h1. In the example illustrated in Figure 3 h2 = 0, but we could also have non-zero h2. These distances h1 and h2 are measured between the bottom of the fixed electrodes and the support or substrate.

  The device according to this embodiment comprises a first series of fixed electrodes 46 opposite a first series 40-1 of moving electrodes, these two series of electrodes being arranged in the form of a comb 2865201 16 in a direction parallel to the axis of rotation 42.

  A second series of fixed electrodes 48 is arranged facing a second series 40-2 of moving electrodes, these two series of electrodes being also arranged in the form of a comb in a direction parallel to the axis of rotation 42 .

  The two sets of movable electrodes are attached to a body 43, also elongate in a direction defined by the axis of rotation 42 and movable about this axis.

  One could also have an embodiment with a single series of fixed electrodes (for example the electrodes 46) and a single series of moving electrodes (for example the electrodes 40-1) fixed to a body 43 rotating about an axis 42.

  In the example of FIG. 3, as well as the fixed electrodes, the mobile electrodes are, in the rest position, disposed on both sides of the body 43, at different heights relative to the support 44.

  At rest, the electrically conductive upper part of the electrodes of the first series of movable electrodes 40-1 is facing or facing the electrically conductive lower part of the first series of fixed electrodes. while the electrically conductive lower part of the electrodes of the second series of movable electrodes 40-2 is facing or facing the electrically conductive upper part of the first series of fixed electrodes 48 Other relative arrangements are possible at rest, but with respect to the electrical point of view.

  An actuator according to the invention, with two sets of electrodes partially overlapping from the electrical point of view, even at rest, makes it possible to work with lower operating voltages than in the devices of the prior art.

  When the device is activated, a rotation of the body 43 occurs around the axis 42, and the surface opposite each fixed electrode-mobile electrode pair decreases.

  The body 43 rotates any object attached to it, for example a mirror.

  A method of producing such a device implements a succession of dry etching steps from a substrate, for example solid silicon, or from an SOI substrate if it is desired to have a layer of stop engraving.

  Steps of a method according to the invention are as follows: 1) rear-face etching (FAR) of a substrate, preferably with two levels of masks, 2) deposition of tracks, or formation of connection means, on the support or the substrate, 3) Sealing of the connection support and the actuator, obtained by etching of the substrate, the sealing taking place on the rear face of the substrate, 4) Front face etching (FAV) of the substrate for release of the substrate. actuator.

  The production method differs from the state of the prior art in particular by its robustness: the technology has no critical step and ensures the result.

  On the other hand, this method, which is simpler than those of the prior art, makes it possible to obtain a better alignment accuracy of the actuator on the connector support, since the lithography is initially on a flat surface, and allows therefore to work on air gaps (separation distance between the pads, Figure 4K), lower (of the order of a few micrometers, for example between 3 and 10 pm, for example 5 pm).

  The sensitivity of the actuator, and therefore its performance, are significantly improved.

  A detailed example of a method of realization will now be given.

  In a first step (FIG. 4A), a substrate 100, for example made of silicon, is covered on the front face and on the rear face with two layers 102, 104 of oxide (SiO2).

  A mask 106 of resin is formed on the back face 104 (FIG. 4B) following which the oxide layer 104 is etched and the mask removed (FIG. 4C).

  A lithography mask 110, made of resin, is then formed, always on the back side (FIG. 4D), which makes it possible to engrave the substrate to a depth of between 1 μm and 100 μm. For example, the etching is a RIE (Reactiv Ion Etching) etching and the substrate is etched on 10 μm (FIG. 4E).

  An etched substrate is thus obtained with trenches 112 separated by teeth 114.

  Resin 110 is then removed (Figure 4F), leaving teeth 114-1, 114-2 covered with an oxide layer and teeth 114-3 exposed.

  An additional etching step on the rear face can then be performed (FIG. 4G) which makes it possible to increase the difference in levels between the teeth 114-1, 114-2 covered with an oxide layer and the teeth 114-3. naked, the latter being supergraded while the former are protected by the oxide layer.

  The actuator element 120 thus formed can be assembled with a support 122, for example by anodic welding. This support is prepared beforehand by forming layers 124 and 126 of connection. The preparation of these connections will be explained later.

  Because of the difference in levels obtained in the previous step, the teeth 114-3, etched more deeply, are not assembled with the support 122.

  A lithography step of the oxide layer 102 on the front face of the substrate can then be carried out and then etching this layer, for example by HF etching, which makes it possible to expose localized zones 1021, 102-2 of oxide protection device (FIG. 4I), above the teeth 114-3 supergraded on the rear face (FIG. 4G).

  Front-side etching is then performed of areas not located beneath these localized zones of oxide, thus releasing the top or the front face of the teeth 114-3 previously supergraded on the rear face (FIG. 4J).

  The different pads are then further secured by a layer 130 of substrate material.

  The actuator is completely released by etching on the front face of this layer 130 (FIG. 4K).

  There is thus obtained a device comprising moving electrodes 114-2 facing, even at rest, fixed electrodes 114-1, 114-3. Metallization can be performed, but the silicon can be sufficiently doped to provide conduction.

  In this way, a device is obtained with two sets of electrodes partially overlapping from the electrical point of view, even at rest, with the advantages, already explained, that this presents.

  It is thus possible to produce a device such as that of FIG. 1, the fixing beams 12 being formed by etching of the silicon substrate, masked appropriately during the etching step of FIG. 4K.

  A double engraving on the rear face, or a back-face engraving, and then a selective overgrafting on the same rear face, make it possible to define teeth or comb branches having the desired shape, and in particular neighboring branches facing each other, from the point of contact. electric view, even at rest.

  An actuator is thus obtained by etching a single substrate 100, another substrate or support being used for the connection means.

  FIGS. 5A-5E illustrate the preparation of the connections on a substrate 122. Layers 132 of conductive metal, for example chromium and gold, are

  deposited on this substrate, which is for example Pyrex (Figure 5A).

  This is followed by lithography and etching of these layers (FIG. 5B).

  An insulating layer 140, for example silicon nitride Si3N4, is then deposited (FIG. 5C), as well as a lithography mask 142 (FIG. 5D).

  The mask makes it possible to etch the layer 140, leaving metallic zones 124 protected by an insulating layer 126 (FIG. 5E).

  A substrate is thus obtained, provided with connection means, which can be assembled (FIG. 4H) with the actuator of FIG. 4G.

  Another detailed example of the method will now be given.

  This method makes it possible to produce a device such as that of FIGS. 2A2C.

  A first part of the method explains the embodiment of the actuator according to the section AA 'of FIG. 2D and a second part of the process explains the realization of the actuator according to the section BB' of this same 2D figure.

  These two parts can nevertheless be realized simultaneously.

  In a first step (FIG. 6A), a substrate 300, for example made of silicon, is covered with two protective insulation layers 302, 304 (Si3N4 2865201 22 for example) respectively on the front face and on the back face.

  A mask 306, 307 of resin is formed respectively on the protective layer 304 located on the rear face and on the protective layer 302 located on the front face (FIG. 6B), following which the protective layers 302, 304 are engraved, then the mask is removed (Figure 6C).

  A lithography mask 310, made of resin, is then formed, always on the back side (FIG. 6D), which makes it possible to engrave the substrate to a depth of between 10 μm and 100 μm. For example, the etching is a RIE (Reactiv Ion Etching) etching and the substrate is etched on 10 μm (FIG. 6E).

  After removal of the resin 310 (FIG. 6F), a substrate etched with a trench 312, open on the rear face, separating a tooth 314 from the remainder 315 of the substrate is obtained. The tooth is still protected by a remaining portion 305 of the protective layer 304 initially formed on the rear face, but not the rest of the substrate, the complementary portion of the protective layer having been eliminated during the step of FIG. 6C.

  An additional etching step (for example RIE) on the rear face can then be performed (FIG. 6G) which makes it possible to increase the difference in levels between the tooth 314 covered with its protective layer 305 and the remainder 315 of the substrate, which the last being etched while the tooth 314 is protected by said protective layer. This step at the same time makes it possible to reduce the area, above the trench 312, which connects the tooth 314 to the rest of the substrate.

  The actuator element 320 thus formed can be assembled with a support 322, for example by anodic welding. This support is prepared beforehand by forming layers 124 and 126 of connection. The preparation of these connections has already been explained above.

  Because of the difference in levels obtained in the previous step, only the tooth 314, etched less deeply, is assembled with the support 322.

  A step of etching, for example RIE, of the substrate on the front face can then be performed, which makes it possible to disengage a comb 324 that is not bonded to the support 322, whereas the tooth 314 remains linked to this support (FIG. 61).

  According to section BB ', the process is as follows (FIGS. 7A-7I).

  In a first step (FIG. 7A), the substrate 300 is covered by the two protective insulating layers 302, 304 (for example Si3N4) respectively at the front and at the rear.

  The masks 306, 307 of resin are formed, as explained above with reference to FIG. 6B, respectively on the protective layer 304 located on the rear face and on the protective layer 302 located on the front face (FIG. following which the protective layers 302, 304 are etched and the mask removed (Figure 7C).

  The lithography mask 310, made of resin, is then formed, still in the rear face (FIG. 2865201 24 7D), which makes it possible to etch the substrate on the back face to a depth of between 10 μm and 100 μm. For example, the etching is a RIE (Reactiv Ion Etching) etching and the substrate is etched on 10 μm (FIG. 7E).

  After removal of the resin 310 (FIGS. 7E and 7F), an etched substrate is obtained with trenches 312-1, 312-2, 312-3 open on the rear face, separating teeth 314-1, 314-2, 314. -3. Some teeth 314 - 2 are still protected by a remaining portion of the protective layer 304 initially formed on the rear face, but not the other teeth 314-1, 314-3, the complementary portion of the protective layer having been eliminated during the step of Figure 7C.

  An additional etching step (for example RIE) on the rear face, or a step of selective overgrading of the rear face, can then be performed (FIG. 7G) which makes it possible to increase the difference h of levels between the teeth 314-2. covered with the protective layer and the other teeth 314-1, 314-3, the latter being etched while the teeth 314-2 are protected by the protective layer.

  The actuator element 320 thus formed can be assembled with the support 322, for example by anodic welding (FIG. 7H). As already explained above, this support was previously prepared by forming the connection layers 124 and 126. The preparation of these connections has already been explained above.

  Due to the difference in levels obtained in the previous step, only the teeth 314-2, etched less deeply, are assembled with the support 322.

  A step of etching, for example RIE, of the substrate on the front face can then be performed, which makes it possible to disengage the teeth 314-1, 314-3, which have been etched more deeply on the rear face and which form the comb 324, not bound to the support 322, while the teeth 314-2 remain connected to this support (Figure 71).

  It is thus possible to produce a device such as that of FIGS. 2A-2C, the outer elements 24, 32 of support being formed by etching of the silicon substrate, masked appropriately during the etching step of FIGS. 6K and 7K.

  The process is then performed radially (for the steps of FIGS. 6A-6I) and with symmetry about an axis (for the steps of FIGS. 7A-7I).

  Another detailed example of a method of realization will now be given in conjunction with FIGS. 8A-8K.

  This method makes it possible to produce a device 25 such as that of FIG.

  The steps of this process are similar to the previous ones, with an extra level for engraving the axis of rotation.

  In a first step (FIG. 8A), a substrate 400, for example made of silicon, is covered front and rear face with two layers 402, 404 of oxide (SiO 2).

  A mask 406, 407 of resin is formed on the back face and on the front face (FIG. 8B) following which the oxide layer 404 is etched on the back face (FIG. 8C).

  A lithography mask 410, made of resin, is then formed, on the rear face, to complete the mask 406 (FIG. 8D), which makes it possible to etch the substrate deeply (FIG. 8E). For example, the etching is an RIE (Reactiv Ion Etching) etching and the substrate is etched on for example 20 μm.

  This gives a substrate etched with trenches 412.

  The resin 410 is then removed from the back face (FIG. 8E).

  An additional etching step on the rear face can then be performed (FIG. 8F) which makes it possible to deepen or overgraze the trench 412 and to selectively etch zones 413 of the rear face. The engraving depth of this step is, for example, 150 μm.

  Areas 414-1, 414-2 remain protected by the mask 406: they are not etched.

  The actuator element 420 thus formed can be assembled with a support 422, for example by anodic welding, after removal of the mask 406 and the oxide remaining on the rear face (FIG. 8G).

  The support 422 is previously prepared by forming connection layers. The preparation of these connections has been explained above, in connection with FIGS. 5A-5E.

  Because of the previous etching steps, the zones 413, 412 are not assembled with the support 422.

  A lithography step of the oxide layer 402 on the front face of the substrate can then be performed (FIG. 8H), forming a mask 409 intended to allow the etching of the future axis of rotation (axis 42 of FIG. 3).

  Then there is etching, for example reactive ion etching on about 5 of the layer 402 (Figure 8I), releasing a pad 429 of the same layer.

  A lithography 430 is then carried out on the front face of the device (FIG. 8J), which will then make it possible to produce the teeth of the mobile part 43 (FIG. 3).

  By etching, for example of reactive ionic type, the body 43 of the device is thus formed, its axis 42, its lateral electrodes (not visible in FIG. 8K, but visible in FIG. 3), and the fixed electrodes 46 and 48 ( Figure 3).

  A device is thus obtained comprising mobile electrodes facing, even at rest, fixed electrodes, as illustrated in FIG. 3. It is possible to perform a metallization, but the silicon can be sufficiently doped to ensure the conduction.

  In this way, a device is obtained with two sets of electrodes partially overlapping from the electrical point of view, even at rest, with the advantages, already explained, that this presents.

  A double engraving on the rear face, or a back-face engraving, and then a selective overgrafting on the same rear face, make it possible to define teeth or comb branches having the desired shape, and in particular neighboring branches facing each other, from the point of contact. electric view, even at rest.

  An actuator is thus obtained by etching a single substrate 400, another substrate or support being used for the connection means.

  A method of producing an actuator according to the invention thus implements a monolithic machining of a single substrate, for example solid silicon.

  By using different levels of masks, it is possible to obtain a different topography on each face.

  The masks may consist of oxide layers (SiO2 for example) or resin. This makes it possible to avoid resin deposition on one side with a pronounced relief.

  In a first step, the so-called rear face is etched in at least two levels (for example three) in order to obtain the teeth of the counter-electrode comb, the teeth forming mobile electrodes and those forming fixed electrodes.

  After removal of the protective layer on the rear face (for example by deoxidation), the substrate can be assembled with a connecting means support.

  The example of a pyrex support has been given above, but it may also be a silicon support on which will have been made connection vias of the electrodes.

  In the latter case, the joining technique may be molecular bonding.

  The assembly, as well as the suspension beams, can be released by etching on the front face.

  Furthermore, the movable and fixed parts of the actuator being already vis-à-vis at rest, the boot voltage is even lower.

  This generic technology makes it possible to obtain actuators working either in translation, or in rotation, or by twisting suspension arms.

  For this we can do an axial symmetry to improve the results.

  An actuator of this type can be used to translate mirrors into adaptive optics applications, or to rotate them for scanner systems, as in Figure 3.

  An actuator according to the invention is applicable to any type of electrostatic actuator and in particular to those used in adaptive optics, such as deformable mirrors, especially those that can be inserted into large VLT type telescopes.

  An actuator according to the invention also makes it possible to produce optical multiplexers / de-multiplexers.

  An actuator according to the invention can also be applied in the field of sensors.

  This type of actuator can also allow the realization of an actuation matrix with several actuators juxtaposed. It may even be a matrix with a very large number of actuators, for example in the number of between 100 or 1000 and 100,000, for example with a pitch between actuators of between 500 μm and 1.5 mm, for example approximately 1 mm. .

  The pitch between adjacent branches of the comb may be about 10 μm, or between 1 μm and 15 μm or 20 μm.

  The stroke of an isolated actuator can be between +1 pm and + 10 pm, for example +5 pm.

  Integrated into a matrix system (for example a mirror), two neighboring actuators will have their race shortened, especially since the mirror will be rigid.

Claims (19)

31 CLAIMS   An electrostatic actuator comprising: a first set of electrodes (13, 20, 20 ', 27, 46, 48), associated with a support (14, 25, 44), and 31, 40-1, 40 -2), inter-digitized bya second set of electrodes (10, 30, movable relative to the first set and related to this first set, said second set being said to be capable of resting, to move from a first position, to a second position, or at a maximum position, between the electrodes of the first game, in at least one direction perpendicular to a reference plane defined by the support, a part of the electrodes of the second game being, in the rest position, facing a part of the electrodes of the first game.   2. An actuator according to claim 1, the displacement of the second set of electrodes (10, 30, 31) relative to the first set of electrodes (13, 20, 20 ', 27) being perpendicular to the reference plane.   The actuator of claim 1, moving the second set of electrodes (40-1, 40-2) relative to the first set of electrodes (46, 48) in a rotational manner about a axis (42) parallel to the reference plane.   An actuator according to claim 3, having first and second sets of movable electrodes (40-1, 40-2) disposed on the one hand and a second one on a body (43) rotatable about said rotation axis (42).   5. An actuator according to claim 4, comprising a first and a second series of fixed electrodes (46, 48) arranged at different heights (h1, h2) with respect to the reference plane, respectively on the side of the first and the second set of moving electrodes (40-1, 40-2).   6. Actuator according to claim 1, the displacement of the second set of electrodes (30, 31) relative to the first set of electrodes (20, 20 ', 27) being in a translation movement along an axis. (22, 34, 35), said circular axis of symmetry, perpendicular to the reference plane.   7. An actuator according to claim 6, the electrodes (20, 20 ', 27, 30, 31) of the first and second set of electrodes being arranged radially relative to said axis (22, 34, 35) of circular symmetry.   8. Actuator according to claim 7, the electrodes of the second set of electrodes being arranged on a circular support (32, 33) centered on the axis of symmetry.   9. An actuator according to one of claims 1 to 8, the support (14, 25, 44) being a mechanical support of the first set of electrodes and a support for connection means (16) of the electrodes.   An actuator according to claim 9, the support being pyrex or silicon.   11. An actuator according to claim 10, the support being Pyrex and at least the fixed electrodes being connected to the support by anodic welding.   12. Actuator according to claim 10, the support being made of silicon and the electrodes being bonded by molecular bonding.   13. Actuator according to one of claims 1 to 12, the second set of electrodes (10, 30, 31) or the axis of rotation (22, 34, 35, 42) being connected to beams (12, 36). , 37) suspension.   14. An actuator according to claim 13, the beams being connected to the support (14, 25, 44).   15. Actuator according to one of claims 1 to 14, the lower portion facing the support, the electrodes of the second set of electrodes being located at a height h, relative to the lower part, facing the support, fixed electrodes.   2865201 34 16. Actuation matrix comprising a plurality of individual actuators according to at least one of claims 1 to 15.   17. Actuation matrix according to claim 16, the number of individual actuators being between 1000 and 100,000.   18. Deformable mirror comprising a deformable membrane supporting a first reflecting surface and a second surface supported by an actuating die according to claim 16 or 17.   19. A method of producing an actuator, using a substrate (100, 300, 400) comprising a front face and a rear face, this method comprising the following steps: a) etching on the rear face of the substrate ( 100, 300, 400) for forming teeth (114-1, 114-2, 114-3, 314, 314-1, 314-2, 314-3, 324), b) forming connection means (124), , 126), on a support (122, 322, 422), c) Sealing the support and the rear face of the etched substrate, d) Engraving on the front face of the substrate (100, 300, 400), to release the actuator.   20. The method of claim 19, the backside etching having at least two successive levels of lithography.   The method of claim 19 or 20, the backside engraving for forming teeth at different heights relative to the support.   22. Method according to one of claims 19 to 21, step c) being carried out by anodic bonding or molecular bonding.   23. Method according to one of claims 19 to 22, step b) comprising a deposit on said support, a metal layer (132), and an insulating layer (140), and an etching of these layers for delineating tracks and connection areas (124, 126).   24. Method according to one of claims 19 to 23, comprising, prior to step a), a deposit on both sides of said substrate, a layer (102, 104, 302, 304, 402, 404). protection.   25. Method according to one of claims 19 to 24, the support on which are formed the connection means being Pyrex.   26. Method according to one of claims 19 to 24, the support on which are formed the connection means being made of silicon.   27. Method according to one of claims 19 to 24, the support on which are formed the connecting means 2865201 36 being a substrate with buried etch stop layers.   28. Process according to one of the claims   19 to 24, further comprising an additional etching step to form an axis of rotation (42) of the actuator.