Patent Publication Number: US-2007120438-A1

Title: Electrostatic control device

Description:
TECHNICAL DOMAIN  
      The invention relates to an electrostatic actuation device with an improved mechanical performance.  
      “Zipping” type actuation is a particular electrostatic actuation in which a mobile electrode comes into contact with or is pressed into contact with an insulator separating it from a fixed electrode, this movement being done progressively and practically linearly with the applied voltage.  
      Documents 1 and 2, referenced at the end of this description, describe a simple zipping with a return mechanism, while documents 3 and 4 describe a double zipping.  
      In known devices, the electrostatic force is a force that only acts in one direction, in attraction between two electrodes. Zipping generates greater forces but it maintains this special feature.  
      This type of actuation can be achieved in a plane, provided that there is room for fixed electrodes to be placed on each side of the mobile electrode. However, it is sometime desirable to have electrodes only on one side of the mobile part, for example for overall size reasons.  
      However, for a displacement of the mobile electrode outside the plane, while it is particularly simple to integrate the first fixed electrode into a substrate (for example using the substrate itself as the fixed electrode), it is particularly complicated to make a second fixed electrode above the mobile electrode. This second electrode is a source of technological complexity, and in particular it generates optical or electrical losses.  
      Therefore, in general only electrodes fixed onto the substrate are used, and a different nature of opposite force is used, often purely mechanical (return force) as described in documents 1 or 2, either by using additional return arms, or using the return force of the zipping arms themselves.  
      Since the nature of the two forces is then different, they are many parameters to be controlled. Forces are more difficult to balance because they are not necessarily equal, and they do not depend on the same equations. Simulation is also more difficult to implement due to the large number of parameters and physical phenomena to be taken into account. Furthermore, the technology is more difficult to produce because the two forces require different materials or different geometries. For example, return arms are often thinner or their thicknesses are not the same as in zipping structures, and control of actuators is also more difficult.  
      Therefore, a common design has been an electrostatic actuation in a single direction, with return arms for the other direction.  
      Only one solution is available for displacement in the two opposite directions by zipping, and this is described in document 4. Displacement of an incompressible fluid between two cavities can deflect a membrane. This solution is expensive and the displacement is difficult to control.  
      Therefore the problem arises of finding a new type of electrostatic actuator that enables the use of zipping in two opposite directions.  
     PRESENTATION OF THE INVENTION  
      The invention relates to a zipping type actuation in two opposite directions.  
      The invention relates to an electrostatic actuation device comprising: 
          a so-called mobile electrode comprising at least one part free to move with respect to a substrate,     at least two electrodes fixed with respect to the substrate, located on the same side as the mobile electrode and each facing a part or an end of the mobile electrode,     means forming at least one pivot of at least one portion of the mobile electrode.        

      Thus, the two parts of an actuator can be controlled on each side of the pivot, with two zipping type forces of the same nature, and each of these two parts or a portion of each of these two parts can be brought into contact with the substrate or with a layer fixed with respect to the substrate, progressively as a function of the voltage.  
      The mobile electrode may bear on the pivot when one of the fixed electrodes attracts the part of the mobile electrode in front of which this fixed electrode is located, the other part of the mobile electrode possibly moving away from the substrate under the effect of mechanical return forces.  
      According to one variant, another purpose of the invention is an electrostatic actuation device comprising: 
          a part or membrane called the mobile or flexible part or membrane free to move with respect to a substrate, this part comprising at least two electrodes separated by an electrically insulating portion,     at least one electrode fixed with respect to the substrate, located on the same side of the mobile part and for which first and second parts are located facing one of the corresponding electrodes of the mobile part,     means forming at least one pivot of at least one portion of the mobile or flexible part or membrane.        

      The flexible part or membrane may bear on the pivot when one of the fixed electrodes attracts one of the electrodes of the mobile or flexible part or membrane, the other mobile electrode being free to move away from the substrate under the effect of mechanical return forces.  
      The electrode or the mobile part may be free to move along a direction approximately perpendicular to the substrate or a main plane of this substrate.  
      An insulating layer located on the substrate or on the mobile membrane can be used to separate the fixed electrodes and the mobile electrode or part.  
      The part or mobile membrane or the mobile electrode may be connected by a pad to a membrane located above the actuator or on the other side of the actuator from the substrate.  
      The pivot is used to keep at least one point of the electrode or the membrane or the mobile part at a distance of for example between 50 nm and 20 μm from the substrate. For example, it comprises at least one pad fixed with respect to the substrate, or according to another example, at least one arm placed on one side of the mobile part of the mobile electrode or the mobile membrane. Advantageously, it comprises two arms located on each side, the system then being symmetrical.  
      A load may be placed on the mobile or flexible membrane, laterally offset from the means forming the pivot. This load may thus have an amplitude greater than the height of the means forming the pivot. The amplitude of a point on the membrane laterally offset from the means forming the pivot is greater than the height of these means. For example, the means forming the pivot are arranged asymmetrically between two fixed electrodes or non-centred with respect between these fixed electrodes, and the amplitude of a point on the central part of the flexible electrode or membrane is greater than the amplitude of the means forming the pivot.  
      The mobile part of the mobile electrode or membrane may form an elbow, which enables a large movement.  
      A non-linear movement of a load located on the mobile part may be compensated by a structure comprising four fixed electrodes arranged in pairs facing each other, the mobile electrode or membrane comprising two mobile parts arranged crosswise.  
      The ends of the mobile electrode or membrane may be free or may comprise at least one fixed or embedded part, that may be fixed onto or into the substrate or an insulating layer. In one example, magnetic means fixed with respect to the substrate cooperate with magnetic means of the mobile electrode or membrane to maintain the ends of the electrode or the membrane in a fixed position with respect to the substrate.  
      According to one embodiment, the mobile electrode or membrane comprises at least two mobile parts, for example parallel to each other, each being free at one of its ends, a fixed electrode facing each mobile part. The free end of each mobile part has good flexibility, greater than the flexibility of a point located between the ends of the mobile electrode or membrane if these ends were fixed. These free ends make it possible to come into contact above the fixed electrode using low voltages.  
      For example, the mobile electrode or membrane comprises three mobile parts and there are three fixed electrodes, each located facing a part of the mobile electrode.  
      The mobile parts of the mobile electrode or membrane may be approximately elongated along one direction, at least two fixed electrodes being offset from each other in this direction. Depending on the variants, the mobile parts may be positioned at an acute angle or with lateral offsets, which provides mechanical stability in the plane of the substrate.  
      An element of electrical contact may be fixed on the mobile part to make a contactor. This is used to create a contact between two tracks or conducting areas in a given position of the mobile electrode or membrane. A variable capacitor may also be formed by a fixed armature and a mobile armature, for which the distance from the mobile armature is defined by the voltages applied to the actuator.  
      According to one variant, the mobile electrode or membrane, the fixed electrodes and the pivot are made approximately in a plane on the surface of the substrate.  
      Furthermore, the mobile electrode or membrane may comprise magnetic elements or means, or may be partially magnetic itself and may cooperate with magnetic elements or means fixed with respect to the substrate. This assembly of magnetic elements makes the system stable. At least two stable positions can be made in this way.  
      Preferably, the relative difference between the electrostatic force and the magnetic forces involved during a contact is at least 10%.  
      Mechanical return forces are preferably less than or very much less than the electrostatic force and the magnetic forces involved during a contact, for example at least 10 times less.  
      An actuation device according to the invention is useful for various applications, and particularly actuation systems with means forming a support for an optical component or an optical component itself.  
      The invention also relates to a process for making a device according to the invention, comprising: 
          production of a first substrate comprising one or two fixed electrodes with respect to the substrate,     production of means forming a pivot and a mobile electrode or membrane, comprising at least two electrodes separated by an insulating portion, this electrode or this membrane being free to move with respect to the substrate.        

      The mobile electrode or membrane may be made on a sacrificial layer formed or deposited on the substrate, then eliminated after formation of the membrane or the mobile electrode.  
      It may also be made on the surface of a second substrate subsequently assembled with the first substrate.  
      The mobile electrode or membrane is then removed from the surface of the second substrate by thinning the second substrate.  
      For example, the means forming the pivot are formed on the first substrate.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIGS. 1A  to  2 B show variants of a first embodiment of the invention,  
       FIG. 3  shows another embodiment of the invention with a membrane connected to the contactors,  
       FIGS. 4A-4B  show two other embodiments of the invention, the ends of the mobile electrode being embedded or held in place by magnetic means,  
       FIG. 5  shows an embodiment in the plane or on the surface of a substrate,  
       FIGS. 6 and 7  show two other embodiments of the invention, with actuator forming an elbow or a cross,  
       FIGS. 8A-8E  show variants of an actuator with three mobile parts,  
       FIGS. 9A-11C  are examples of actuators with electrical contact and/or magnetic means,  
       FIGS. 12A-12B  are manufacturing steps of a device according to the invention,  
       FIGS. 13A-14B  explain variants of devices according to the invention,  
       FIGS. 15A-15B  show another type of device according to the invention that can be used as a micro-mirror or micro-lens,  
       FIGS. 16A-17B  show variants of a device according to the invention that can be used as a micro-mirror or micro-lens,  
       FIGS. 18A-18L  are manufacturing steps of a device according to the invention,  
       FIG. 19  shows another embodiment of a device according to the invention,  
       FIGS. 20A-20G  show manufacturing steps of another type of a device according to the invention,  
       FIGS. 21A-21E  show other manufacturing steps of another type of a device according to the invention,  
       FIGS. 22A-22C  diagrammatically show operation of a device according to the invention,  
       FIGS. 23 and 24  show other aspects of a device according to the invention. 
    
    
     DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS  
       FIG. 1A  shows an example of a device according to the invention.  
      A fixed electrode  12 ,  14  is located facing each end of a mobile or flexible structure or electrode  10 , or a mobile or flexible membrane, one point of which is supported on a stop or a pad or a pivot  18 , in a laterally offset position (along the XX′ direction) with respect to the position  16  of a load, for example a mechanical load or a mechanical or electrical contact or an electrical or optical component.  
      This assembly is also called an actuator.  
      The mobile structure  10  is insulated from the fixed electrodes  12 ,  14  by one or more insulating layers  20 . These layers are located on the fixed structure as illustrated in  FIG. 1A , but they may also be located on the mobile structure, which for example comprises a dual layer comprising an insulating layer and an electrode layer. The assembly consisting of the fixed electrodes and possibly the insulating layer(s) is supported on a substrate  22 .  
      The pivot  18  maintains a point of the mobile electrode at a minimum height and possibly fixed height from the substrate  22 . This height is measured along the ZZ′ axis perpendicular to the plane of the insulating layer  20 . According to one example, the height of the pivot is for example between a few tens of nanometers, for example 50 nm, and 10 μm or 20 μm. Its height may be of the order of a few μm.  
      The length L of the membrane  10  may be of the order of a few hundred μm or may for example be between 50 μm and 1 mm. Its width measured along a direction perpendicular to the plane of  FIG. 1A  or  1 B is of the order of a few μm or a few tens of μm, for example between 5 μm and 50 μm. The thickness e of the membrane may between 500 nm and 5 μm, for example equal to about 1 μm. All these values are given for guidance and devices according to the invention can be made with numeric values outside the ranges mentioned above.  
      The mechanical stiffness of the membrane is such that it can be brought into the high position under the effect of mechanical forces when the voltage is released (see  FIG. 1A ).  
      A potential difference is applied between the mobile electrode  10  and each fixed electrode  12 ,  14 . This potential difference generates an electrostatic force in attraction or in repulsion between the two electrodes in each pair of electrodes (mobile electrode, fixed electrode). This force is easily controllable with the potential difference. Means of controlling this potential difference are provided but are not shown in the Figure. The membrane and the pad may be made of a conducting or semiconducting material or may comprise elements made from such materials, so that a voltage can be applied to the membrane through the pad  18 .  
      If the potential difference (ddp) between the fixed electrode  12  and the mobile electrode  10  is decreased, and if the ddp between the fixed electrode  14  and the mobile electrode  10  is increased, the mobile structure progressively tilts towards the fixed electrode  14  and the load  16  moves upwards along the ZZ′ axis ( FIG. 1A ).  
      If the ddp between the fixed electrode  12  and the mobile electrode  10  is increased, and if the ddp between the fixed electrode  14  and the mobile electrode  10  is decreased, the mobile structure gradually tilts towards the fixed electrode  12 , and the load  16  moves downwards along the ZZ′ axis ( FIG. 1B ).  
      Thus, the pivot forms a bearing point for the mobile structure when it is attracted by one of the fixed electrodes  12 ,  14 : in fact, the central or mobile part of the membrane moves upwards and downwards under the combined effect of electrostatic and mechanical forces, therefore of different natures. The amplitude of the movement of this part is greater than the height of the pivot  18 .  
      In one actuation device according to the invention, each of the fixed electrodes progressively forces part of the mobile electrode facing it into contact with the substrate as a function of the applied voltage.  
      The mobile electrode, part of which is pressed into contact with the substrate, then bears on the pivot, the other part of the mobile electrode for which the applied voltage is released being separated from the substrate under the effect of mechanical return forces.  
      This combined action of firstly electrostatic forces and secondly mechanical return forces result in a large amplitude greater than the height of the pivot.  
      In the above description, the pivot is a pad. However, other means could be used to make the pivot; for example mechanical arms on each side of the point at which the load is placed, which is advantageous to limit the lateral movement of this point (perpendicular to the plane in  FIGS. 1A and 1B ). A design with a single lateral arm is possible but is less stable than the above. Once again, the choice of materials from which the arm(s) is (are) made is used to apply a voltage to the membrane through the arm(s).  
      The pivot  18  may be made in the mobile part or in the fixed parts. It may be placed below or in the plane of the mobile part  10 .  
      The fluid between the mobile electrode and the fixed electrodes may be air or another fluid, more or less viscous. Its permeability is preferably as large as possible, with good resistance to the electrical field and to aging.  
       FIGS. 2A and 2B  show a top and side view respectively of an embodiment in which the pivot comprises arms  28  extending on each side of the mobile membrane  10 , approximately in a plane defined by this mobile part, for example when it is at rest.  
      In the example in  FIGS. 2A and 2B , the ends  27 ,  29  of these arms are kept fixed with respect to the substrate, using means not shown in these Figures, for example by embedment in this plane.  
      As a variant, the arms can extend on each side of the mobile membrane but below it, forming a step below which a point on the membrane can never lower in the direction of the substrate.  
      According to another variant, there is only a single arm on one side. The solution with two arms has the advantage of symmetry, particularly mechanical symmetry of the system.  
      This embodiment, with one or more arms can generate large forces and limit necking or bonding effects on mechanical parts close to the mobile structure; in the embodiment shown in  FIGS. 1A and 1B , the mobile structure can be degraded by friction on the pad  18 .  
      According to one particular embodiment shown in  FIG. 3 , one or several actuators(s)  33 ,  35 ,  37  may be suspended or connected to a membrane  30 , each by one pad  32 ,  34 ,  36  that maintains a constant distance between the actuator and this membrane. Furthermore, a pivot  41 ,  43 ,  45  holds at least one point of each actuator at a minimum distance from the substrate as explained above.  
      The membrane  30  may be more or less flexible or rigid, for example it may be semi-rigid. It may support optical components, which is one example application to the domain of adaptive optics.  
      In the above examples, the ends of the mobile membranes  10 ,  33 ,  35 ,  37  may be more or less free with respect to the substrate  22  or the insulating layer  20  that covers it; these lateral ends are not necessarily embedded in or on this layer or this substrate. Thus in the example shown in  FIG. 3 , the ends of each actuator connected to the membrane  30  by a pad  32 ,  34 ,  36  may very well be free.  
      The ends of the mobile electrode can also be kept in contact with the substrate by the simple effect of low voltages between the mobile electrode and the corresponding fixed electrode.  
      In the embodiment illustrated in  FIG. 4A , the ends  11 ,  13  of the mobile element  10  of the actuator are integrated in or on the insulating layer  20  or the substrate  22 . For example, these ends may be fixed on the surface of the insulating layer. According to one variant, only one of the two ends is thus embedded.  
      According to another embodiment ( FIG. 4B ), the ends of the mobile element  10  of the actuator comprises magnetic means or magnetic zones  21 ,  23 . The mobile part itself may be partially made of a magnetic material; for example it comprises an insulating layer (for example made of nitride), a first layer of magnetic material (for example FeNi), a second layer of insulating material (for example nitride). Magnets  19 ,  25 , fixed with respect to the substrate  22  are then used to hold the magnetic or magnetised ends of the mobile element fixed with respect to the substrate  22 .  
       FIG. 5  shows an example of integration of an actuator in a plane, in this case the upper plane of a substrate  23  or an insulating layer deposited on it.  
      All elements (electrodes  52 ,  54 , beam  60 , pivot  68 ) are formed in this layer or this plane by etching. In particular, a cavity is etched under the beam  60  which is thus released from the substrate and can move like the charge  66  along the arrow indicated in the Figure along a direction approximately perpendicular to the electrodes.  
      A sacrificial layer used during etching may be made of oxide or a polymer material depending on the selectivity of etching with respect to the structure.  
      This embodiment is very compact.  
      According to one variant, magnets  53 ,  55  are integrated into the electrodes  52 ,  54 , the lateral parts of the beam  60  incorporating magnetic elements  61   63 , for example cores made of a magnetic material such as FeNi. The magnets and the magnetic material may be deposited on the mobile structure and on the fixed structure, and protected by a layer that resists etching of the sacrificial layer under the beam  60 .  
      More complex shapes may be made.  
      For example, the thickness and the shape of the mobile part  60  can be varied. It can be thinner at its ends (as illustrated in  FIG. 5 ) to limit the voltage applied to it, and for which the mobile electrode is pressed into contact on the fixed electrode.  
      According to another variant, the mobile part  60  may be free at its ends and attached to the pad  68 .  
      In the embodiments presented, the insulator  20  may for example be made of nitride or oxide. In the case in  FIG. 5 , an insulator, once again for example nitride or oxide, may be formed on the electrode  52 ,  54 , and/or on the mobile electrode  60 .  
      In the various embodiments presented, the different elements of the structure (membrane, electrodes, mobile part, pad) may be made of silicon, or nitride if they are at least partly covered by a metal, or aluminium. Other materials would also be possible.  
      The actuators can be made in a configuration allowing greater movement. In the configuration illustrated in  FIG. 5 , the beam applies a natural mechanical resistance to elongation which limits its movement.  
      The configuration in  FIG. 6  is a top view of a substrate  23 —pivot  78 —beam  70 —fixed electrodes  62 ,  64  assembly. The fixed electrodes are actually located under an insulating layer that covers the substrate  22 . The shape of the beam forms an angle or an elbow  77  which gives better movement of the load  76 . This angle is a right angle in  FIG. 6 , but it could also be an angle of less than 90° or greater than 90°.  
      However, this configuration can rotate the point at which the load is fixed.  
      The configuration in  FIG. 7  compensates for this defect using four arms and four fixed electrodes  82 ,  84 ,  92 ,  94 . Facing electrodes  92 ,  94 , and  82 ,  84  may be connected together. References  79 ,  80  denote two pivots. Reference  86  denotes the load that is not rotated in this embodiment.  
      The ends of these embodiments in  FIGS. 6 and 7  do not necessarily have to be embedded. They can be pressed in contact with the substrate through voltages, as already mentioned above within the framework of another embodiment.  
      Once again, the pad  78  may be replaced by arms not shown in  FIG. 6 , but similar to those shown in  FIG. 2A , and arranged on each side of the membrane. As already described above, a single arm is also possible.  
      During manufacturing, the ends of the membrane will be held in place by the pad  78 , or by the lateral arms.  
      Regardless of the embodiment used, the two parameters for adjustment of the force are the voltages between electrodes.  
      The choice of the thickness of the mobile membrane provides an easy means of adjusting the stiffness of the actuator for resistance to shocks, vibrations, response times, etc. The actuator becomes more rigid as the mobile part becomes thicker. The voltage to be applied for the same displacement is then greater.  
      Regardless of which configuration is selected, displacements may also be increased linearly with the length of the mobile parts that form lever arms.  
      The configuration in  FIGS. 8A-8C  is more symmetric and also facilitates larger displacements.  
      Three fixed electrodes (one central electrode  132  and two lateral electrodes  134 ,  136 ) are made in a substrate  123 .  
      The mobile part or mobile membrane or mobile electrode comprises three parallel zones or strips  135 ,  137 ,  139 , the free ends of which are connected through a common part  140  that supports a load  146  and that is approximately perpendicular to it. The other end of each of these strips is kept fixed with respect to the substrate  123 , either by an electrostatic voltage or by a fixing or by embedment, or by magnetic means, these different variants having been described above particularly with reference to  FIGS. 4A and 4B .  
      For greater efficiency, the lateral electrodes  134 ,  136  are offset from the central electrode  132  towards the mobile end  140  of the actuator. It would also be possible but less efficient to make 3 electrodes without any offset between them.  
      The central part  137  may be supported on a pivot  98 . According to one variant, a pivot is provided under each lateral part, but there is no pivot under the central part.  
      By varying the voltages between the fixed electrodes  132 ,  134 ,  136  and the mobile electrode, it is possible to actuate the load in a low position ( FIG. 8B ) and in a high position ( FIG. 8C ) with respect to the substrate  123 .  
      Each of the fixed electrodes can be used to press the part of the mobile electrode facing it progressively into contact with the substrate, as a function of the applied voltage.  
      When the central part  137  of the mobile electrode is attracted towards and pressed into contact with the substrate due to the electrostatic effect, it then bears on the pivot  98 , the lateral parts  135 ,  139  for which the attraction voltages to the substrate are released, moving away from the substrate under the effect of mechanical return forces (case in  FIG. 8C ), which contributes to moving the load  146  away from the substrate.  
      When the lateral parts  135 ,  139  of the mobile electrode are attracted towards and pressed into contact with the substrate by an electrostatic effect, the central part  137  for which the attraction voltage towards the substrate is released, and which then still bears on the pivot  98 , moves away from the substrate under the effect of mechanical return forces (case in  FIG. 8B ) which contributes to moving the load  146  towards the substrate.  
      When the lateral parts are each supported on a pad and the central part does not have a pivot, the operation of the system as described above is still based on the same principles; namely attraction of lateral parts towards the substrate by electrostatic effect, the central part moving upwards under the effect of mechanical return forces when the attraction voltage to this central part is released; and when the central part is attracted towards the substrate by an electrostatic effect, the lateral parts move upwards under the effect of mechanical return forces when the attraction voltages of these lateral parts towards the substrate are released.  
      This combined action of firstly electrostatic forces and secondly mechanical return forces result in a large amplitude for the free end  140 .  
      The arms  135 ,  139  may be moved away from the central part  137 , either in the lateral or angular direction, to improve stability at the embedment end. Diagrammatically,  FIGS. 8D and 8E  respectively show the case of arms moved sideways and arms moved in the angular direction.  
      The arms  135 ,  137 ,  139  are shown as straight lines in  FIGS. 8A-8E , but they may be in any shape.  
      According to one variant, a device according to the invention may include only two arms, for example arms  135  and  137 , and for example a pivot under one of the two arms. The device is then less stable.  
      The invention may also be used to make electrical or optical micro-switches and variable capacitances.  
       FIG. 9A  shows a top view of a electrical switch  196  in the high position, and  FIGS. 9B and 9C  show a side view of the same switch in the low position.  
      In these Figures, the actuator is similar to the actuator in  FIG. 1A , the load then being an electrical contact  196 .  
      In  FIG. 9A , references  200  and  201  denote an electrical input track and output track respectively, reference  202  being a ground strip.  
      As can be seen in  FIGS. 9B and 9C  the system is used to control closing and opening of a switch  196 . When it is in the low position, this switch closes the circuit between tracks  200  and  201  for example. It may also come into contact with a track of a circuit made in the layer  224 , this circuit not being shown in the Figures.  
       FIG. 10A  shows a top view of a bistable switch in the high position, and  FIGS. 10B and 10C  show a side view of the same bistable switch in the low position.  
      References identical to those in FIGS.  9  A-C denote similar or corresponding elements.  
      Magnetic means are also provided: firstly, fixed means  242 ,  244  on the substrate or with respect to the substrate; secondly the mobile membrane  210  itself is provided with magnetic means; this membrane may be at least partly magnetic or it may comprise portions  232 ,  234  made of a magnetic material.  
      The magnetic means  244  are preferably separated from the contact  196  to limit disturbances.  
      Unlike the system shown in  FIGS. 9B and 9C , the system does not consume any electrical energy in the two positions shown in  FIGS. 10B and 10C ; these are magnetic means that hold the system in the high and low positions.  
      Another embodiment will be described with reference to  FIGS. 11A-11C .  
      In fact, this embodiment is practically the same as that shown in  FIGS. 8A-8C , to which magnetic means have been added on the fixed part and on or in the mobile part  310 . For example, magnetic pads or magnets  342 , 344  are placed on the layer  320  that is itself supported on a substrate  322 , the beam or the mobile electrode  310  itself comprising magnetic means. For example, it contains a magnetic material, for example iron nitride (FeNi) locally or over its entire length.  
      Preferably, the magnetic means or the magnetic material incorporated in the mobile electrode  302  is encapsulated so as to protect it during use.  
      According to one example, the mobile electrode is composed of three superposed layers: 
          a first layer made of Si 3 N 4 ,     a second layer made of FeNi,     a third layer made of Si 3 N 4 .        

      For example, a magnetic layer may be deposited in the same way as magnets  342 ,  344  are deposited, by electrodeposition or by cathodic sputtering.  
      The insulating layer (e.g. nitride) may also be discontinuous to reduce the effects of loads.  
      As can be seen in  FIGS. 11B and 11C  (seen in sectional views along the AA′ and BB′ axes in  FIG. 11A  respectively), the device also comprises two parts  350 ,  352  of an electrical contact, which is closed when the end of the mobile electrode carrying the load  316  is in the low position.  
       FIG. 11A  is a top view of the complete device. Compared with  FIG. 8A , the relative positions of firstly the central fixed electrode  332  and secondly the lateral fixed electrodes  334 ,  336  are inverted.  
      Furthermore, pads or pivots  398 ,  399  are provided under each side portion  335 , 339  of the mobile electrode, but not under its central portion  337 .  
      Only two magnetic pads  342 ,  344  are shown in  FIGS. 11B and 11C . In fact, as shown in  FIG. 11A , it is possible to place two or several magnets on the substrate, under the central part  337  of the mobile electrode, and to place two or several magnets on the substrate, under each of the lateral parts  334 ,  336  of this electrode.  
      Thus, a set of stable intermediate positions can be defined between the highest position of the load ( FIG. 11C ) and the lowest position, in other words the position in which the electrical contact  350 - 352  is closed. This embodiment in  FIG. 11B  can also form a variable capacitor, for which the means  350 ,  352  may form armatures, but in stable positions. Such a structure has the advantage that it is not sensitive to vibrations.  
      Without the magnetic means (and therefore with a structure similar to that shown in  FIGS. 8A-8C  together with means  350 ,  352 ), a variable capacitor with continuous operation is also formed; impedance measurement means are then used to measure the value of the capacitance obtained and to use voltages applied to electrodes to adjust the relative distance of elements of the capacitor as a function of this measurement. However, such measurement means induce noise that affects operation of the capacitor. The embodiment shown in FIGS.  11  A-C, with stable positions predefined by the magnetic means, eliminates this type of impedance measurement means and therefore noise generated by them.  
      In a system like that shown in  FIGS. 11A-11C  or  10 A- 10 C combining electrostatic means and magnetic means, the dimensions of the magnets and electrodes will be chosen so as to obtain an electrostatic attraction force at the time of actuation greater than the magnetic force concerned when a contact is made between the mobile part and the fixed part, itself greater than the mechanical return force.  
      An attempt is also made to size magnets and the electrode surface so as to obtain a sufficient difference between the electrostatic or zipping force and the magnetic force applied at the time of the contact. This difference is preferably at least 10%, so that there is no sensitivity to magnet manufacturing non-uniformities or necking (or bonding) effects between the mobile electrode and the substrate, or the effects of loads in dielectric materials.  
      The electrostatic or zipping forces and the magnetic forces involved at the time of the contact are greater or very much greater than return forces of the mechanical structure, preferably in a ratio equal to at least 10.  
      The same considerations are valid for the embodiment shown in  FIG. 5 , when it comprises magnetic means.  
      Different variants can be envisaged. In particular, the mobile part may be wound or turned so as to minimise its overall dimensions. Furthermore, the number of arms in this mobile part may be different depending on the application.  
      In general, a process for making a device according to the invention uses substrate and/or layer etching and layer deposition techniques known in microelectronics. Such techniques are described in documents 1-4 already mentioned.  
       FIGS. 12A-12B  show steps in the formation of a device according to the invention, like that shown in  FIG. 4B .  
      An insulating layer  520  and electrodes  501 ,  503  are formed on a substrate  500  ( FIG. 12A ), possibly together with magnets  520 ,  521  by electrodeposition (for example of CO and Pt).  
      A pad  518  may be formed by deposition of a layer and etching. As indicated in  FIGS. 12A and 12B  it may be arranged asymmetrically about the fixed electrodes  501 ,  503  so that the amplitude of a point on the central part of the membrane, possibly a load placed at this point, can be more than the height of the pad.  
      A first very thin sacrificial layer  530  (for example made of 1.1 μm thick polymer) is deposited followed by a second sacrificial layer  532 . The next step is etching, insolation, development of this layer and finally creep.  
      The next step is to form a mechanical layer  540  (for example made of nitride) and possibly a magnetic layer  542  (for example FeNi). The mobile part or electrode of the actuator can be etched in this mechanical layer  540 . The sacrificial layer is then etched, thus freeing the mechanical layer ( FIG. 12B ).  
      According to one variant illustrated in  FIGS. 12 C-12  D, the sacrificial layer  532  extends beyond the pads  520 ,  521 . The result is that after the sacrificial layer has been removed, the shape of the layer  540  is as illustrated in  FIG. 12D , with no contact with the substrate or the layer  530  between the pads  520 ,  521 . The membrane  540  is held in place only by firstly the magnetic means  520 ,  521 , and secondly  542 .  
      For example, the membrane may comprise a conducting layer on an insulating layer. As illustrated in  FIG. 12E , it may also comprise three layers consisting of an insulating layer  540 - 1  (for example made of nitride Si3N4), one or several electrode layers  540 - 2 , and an insulating layer  540 - 3  (for example also made of nitride Si3N4). Conductors  540 - 4 ,  540 - 5  connect the conducting zones to voltage supply means (not shown in the Figure). This variant can also be used to make an actuation device as illustrated and explained below with reference to  FIGS. 13A-14B .  
      Variants of this process can be used to adapt membrane shapes and arrangements of the electrodes and magnetic means, for example to make devices like those shown in  FIGS. 6, 7 ,  8 A- 8  E,  9 A- 11 C. A device without magnetic means can also be made, as already explained above.  
      In the embodiments presented above, the mobile electrode comprises a flexible part that may be raised uniformly to a given potential and that returns to its initial configuration by mechanical return forces. The potential differences between the mobile electrode and each of the fixed electrodes determine the movement of this flexible electrode, regardless of whether it is of the type illustrated in  FIG. 1A  (two fixed electrodes) or  8 A (three fixed electrodes) or has more than three fixed electrodes. The number of potential differences applied is equal to the number of fixed electrode−mobile electrode pairs.  
      The invention also relates to the case in which the mobile part is no longer uniformly conducting but comprises at least two conducting parts separated by an insulating portion.  
       FIG. 13A  corresponds to the case in  FIG. 1A , but the flexible part has an insulating zone  11  separating two conducting zones  13 ,  15 .  
      This device operates in the same way as the device in  FIG. 1A , a potential difference possibly being applied to each of the conducting parts  13 ,  15  of the flexible part.  
      As in the case in  FIG. 1A , the number of potential differences (in this case two) applied can be the same as the number of fixed electrode−mobile electrode pairs.  
      In this variant, each of the fixed electrodes is used to progressively press the mobile electrode facing it into contact with the substrate as a function of the applied voltage.  
      The mobile electrode, part of which is pressed into contact with the substrate, then bears on the pivot, the other mobile electrode being moved away from the substrate under the effect of the mechanical return forces.  
      This combined action of firstly electrostatic forces and secondly mechanical return forces can give a large amplitude, greater than the height of the pivot  FIG. 13B  corresponds to the case shown in  FIG. 8A , but the three parallel strips  135 ,  137 ,  139  are connected through a common part  141  that is insulating.  
      This device operates in the same way as that shown in  FIG. 8A , and a potential may be applied to each of the conducting parts  135 ,  137 ,  139  of the flexible part.  
      As is the case in  FIG. 8A , the number of potential differences (in this case three) applied can be the same as the number of fixed electrode−mobile electrode pairs.  
      In these two examples, neither the role of the pivot(s) or the load are different from what was described above with reference to  FIGS. 1A and 8A . Similarly, explanations given with reference to  FIGS. 8A-8C  relating to the set of electrostatic forces and mechanical return forces remain valid.  
      The invention also relates to the case in which the mobile part is no longer uniformly conducting but includes at least two conducting parts separated by an insulating portion, in which the fixed electrodes would be replaced by a single fixed electrode.  
       FIG. 14A  corresponds to the case in  FIG. 1A , but the flexible part comprises an insulating zone  11  separating two conduction zones  13 ,  15 . A single fixed electrode  17  is also made in or on the layer  20  or  22 .  
      This device operates in the same way as that in  FIG. 1A , a potential possibly being applied to each of the conducting parts  13 ,  15  of the flexible part independently.  
      As in the case in  FIG. 1A , the number of potential differences (in this case two) applied can be the same as the number of fixed electrode−mobile electrode pairs.  
       FIG. 14B  corresponds to the case in  FIG. 8A , but the three parallel strips  135 ,  137 ,  139  are connected through an insulating common part  141 . Furthermore, a single fixed electrode  133  is made in or on the layer  120  or  123 .  
      This device operates in the same way as that shown in  FIG. 8A , a potential can be applied to each of the conducting parts  135 ,  137 ,  139  of the flexible part.  
      As in the case in  FIG. 8A , the number of potential differences (in this case three) applied can be the same as the number of fixed electrode−mobile electrode pairs.  
      In these other two examples, neither the role of the pivot(s) nor that of the load are different from what was explained above with reference to  FIGS. 1A and 8A .  
      Similarly, the explanations given with reference to  FIGS. 1A-1B  and  8 A- 8 C concerning the set of electrostatic forces and mechanical return forces remain valid.  
      In the examples in  FIGS. 13 A-14B , the number of potential differences applied can be the same as the number of fixed electrode−mobile electrode pairs.  
      The principle described above with reference to  FIGS. 13A-14B  may be applied to all other embodiments already described above; unlike these embodiments, mobile electrodes and fixed electrodes can be configured keeping the same number of potential differences to be applied, equal to the number of fixed electrode−mobile electrode pairs.  
      In particular, a device like that illustrated in  FIGS. 13A and 14A  may be applied to a system like that illustrated in  FIG. 3 , the shape of the actuators  41 ,  43 ,  45  being illustrated in  FIG. 13A  or  14 A.  
      Similarly, the ends of actuators in  FIGS. 13A, 14A  may be fixed with respect to the substrate as explained with reference to  FIGS. 4A and 4B .  
      Concerning the embodiments in  FIGS. 13B and 14B , the ends of each strip (on the side opposite the insulating zone  141 ) are held fixed with respect to the substrate  123 , either by electrostatic voltage or by fixing or embedment or by magnetic means, these different variants already having been described above, particularly with reference to  FIGS. 4A and 4B .  
      The devices in  FIGS. 13A and 14A  are applicable to manufacturing of electrical switches like those shown in  FIGS. 9A-9C , or bistable switches like those shown in  FIGS. 10A-10C .  
      The variants of  FIG. 8D  or  8 E or  11 A (two side pivots, no central pivot) are equally applicable to the devices in  FIGS. 13B and 14B . These devices in  FIGS. 13B and 14B  are equally applicable to manufacturing of switches like those shown in  FIGS. 11B, 11C .  
      Loads such as loads  16 ,  146 ,  316  can also be applied to the devices shown in  FIGS. 13A-14B .  
      In all of the embodiments explained above with reference to  FIGS. 1A-14B , the number of potential differences applied can be the same as the number of fixed electrode−mobile electrode pairs.  
      The mobile electrode or mobile membrane can bear on the pivot when one of the fixed electrode attracts the mobile electrode or the part of the mobile electrode facing this fixed electrode, the other part of the mobile electrode being able to move away from the substrate under the effect of mechanical return forces.  
      Therefore an actuator according to the invention uses two types of forces with different natures; electrostatic forces during attraction of a portion of the mobile part towards the substrate and mechanical return forces when this electrostatic attraction is released.  
      Therefore, the flexibility of a mobile electrode or a mobile membrane of an actuator according to the invention is such that it can be progressively pressed into contact with the fixed part of the device as a function of the voltage, and a stiffness or combined shape and/or dimension and/or nature of material characteristics so that it will return to its initial position not in contact with the substrate, when the electrostatic voltage is released.  
      As already mentioned above, this combined effect of different natures of electrostatic and mechanical forces enables the movement amplitude of the mobile part to be greater than the height of the means forming the pivot.  
      Therefore a process for operation of an actuator according to the invention comprises the following steps: 
          preferably progressive application of a voltage between a part of the mobile electrode or the mobile membrane and a fixed electrode,     possibly release of a voltage applied beforehand between the other part of the mobile electrode or the mobile membrane and a fixed electrode.        

      The invention is applicable to the case of micro-mirrors or micro-lenses that can be electrically actuated in rotation.  
      A first example of a micro-mirror or micro-lens according to the invention is shown in  FIGS. 15A and 15B .  
      The micro-mirror or micro-lens comprises a mobile part  610  and a fixed part  614 . The mobile part  610  is globally in the shape of a plate (for a micro-mirror) or a frame (for a micro-lens). It is designed to be moved in rotation about an axis  612 . The axis passes through the mobile part  610  and is approximately parallel to a main plane of the mobile part  610 . Means  613  of connecting the mobile part  610  with the fixed part  614  materialise this axis  612 . These connecting means may be in the form of two torsion arms  613  derived from the mobile part  610  and have one end fixed to the fixed part  614  (for example by embedment).  
      The two torsion arms  613  are in line with each other.  
      The mobile part  610  is thus suspended above the fixed part  614 .  
      The mobile part  610  comprises main faces, one of which faces the fixed part  614  and the other of which is provided with a reflecting zone  617  (cross-hatched) that will reflect light in the case of a micro-mirror. The reflecting zone  617  is shown as only partially occupying the face of the mobile part  610  but it could occupy it fully.  
      In the case of a micro-lens, the zone  617  represents a refracting zone, this could be a lenticular refracting part, fixed for example by bonding to the frame  610 . The axis  612  can pass through the geometric centre of the mobile part  610 .  
      The micro-mirror or the micro-lens also comprises electrical means of controlling the rotational displacement of the mobile part  610 .  
      In the example in  FIG. 15A , these means comprise two zipping effect actuators  619 , and addressing means (not visible in  FIGS. 15A and 15B ) of these actuators.  
      A zipping effect actuator  619  means the following, as above: 
          either an actuator formed from two pairs of electrodes  620 ,  621 , with two fixed electrodes  620  ( FIG. 15B ) and one mobile electrode  621  with a free end  621 . 1 , the mobile electrode  621  being designed to come into contact with the fixed electrode  620  from its free end  621 . 1 , it being brought into contact on a variable surface area as a function of an applied voltage between the two electrodes;     or, for each actuator or for one of the actuators, as explained above with reference to  FIGS. 13A-14B , two electrodes in the mobile part of the said actuator or each actuator, separated by an insulating zone, and only one or two fixed electrodes (as for example shown on the diagrams in  FIGS. 13A and 14A ).        

      When the voltages between the mobile and fixed parts are released, the corresponding part of the actuator returns to the initial position at a distance from the substrate, under the effect of mechanical return forces.  
      These two types of actuators can be combined in a single device: 
          the two actuators  619 , each being of the type with two mobile electrodes insulated from each other, but one being positioned facing a fixed electrode and the other facing two fixed electrodes,     or one of the actuators  619  being of the type with two mobile electrodes insulated from each other, but being positioned facing a fixed electrode or two fixed electrodes, while the other actuator  619  is of the type with a single mobile electrode positioned facing the two fixed electrodes.        

      In all cases, the mobile electrode  621  or the actuator  619  is flexible or supple as in the examples already described above, and operates as already mentioned above.  
      Each fixed electrode  620  is fixed to the fixed part  614  ( FIG. 15B ). Each actuator  619  is fixed to one of the two drive arms  623  that projects from the mobile part  610  and that is directed along the rotation axis  612 . This drive arm  623  is sufficiently rigid, but it may be driven in rotation about the axis  612 .  
      The actuators  619  may be addressed or actuated either separately or simultaneously as will be seen later.  
      The size of the mobile part  610  may be between 100 μm or a few hundred micrometers and few millimetres or 5 mm, and a thickness of about a few tens of micrometers, or between 10 μm and 100 μm. Obviously the indicated dimensions are not limitative.  
      The mobile part is preferably sufficiently stiff such that the reflecting or refracting zone  617  that it carries remains as plane as possible, so as to maintain its optical quality regardless of the conditions and particularly during accelerations.  
      The mobile electrode  621 , or the mobile part of the actuator  619 , may be in the shape of an approximately straight body  621 . 2  starting from the drive arm  623 , with an approximately constant width terminating at its free end  621 . 1  by an end part  621 . 3  that may be the same width as the body  621 . 2 , or advantageously can be wider than the body (as illustrated in  FIG. 15A ). In this case, the end part  621 . 3  may be qualified as a starter.  
      In  FIG. 15A , the two actuators  619  are distributed on each side of the optical component  610 , and the two bodies  621 . 2  are approximately parallel to each other or extend along two directions approximately parallel to each other. However, other forms would be possible.  
      The fixed electrode  620  may be of an arbitrary shape to the extent that the mobile electrode  621  can be pressed into contact with it or onto the dielectric layer  624  that covers it. As mentioned above, there may be several fixed electrodes in some embodiments, particularly embodiments using the principles of the devices in  FIGS. 1A and 13A  already commented upon above.  
      Therefore the fixed electrode may consist of a single electrode for all mobile electrodes or there may be two or three or four conducting zones insulated from each other, thus forming two or three or four fixed electrodes for the mobile electrodes respectively.  
      A starter  621 . 3  wider than the body  621 . 2  reduces the voltage or the attraction threshold Vc and the separation threshold voltage Vd of the corresponding mobile electrode.  
      When an actuator  619  is at rest, no actuation voltage is applied to it, its two mobile parts being brought into one position not in contact with the substrate due to the mechanical return forces. The mobile and fixed electrodes  620 ,  621  are then separated by a space  625  that may be full of a gas (air or other) or that may contain a vacuum. This inter-electrode space  625  is illustrated in  FIG. 15B . It may be delimited by the frame  615 . 1 . It is preferable to place a layer of dielectric material  624  in this space  625  between the fixed electrodes  620  and the mobile electrodes  621  to prevent a short circuit when a mobile electrode  621  comes into contact with a fixed electrode  620 .  
      This dielectric layer  624  can be seen in  FIG. 15B , and it covers the fixed electrodes  620 . The thickness of the dielectric layer  624  may be between a minimum value and a maximum value, the minimum value possibly being determined by the breakdown of the insulator to which an electric field is applied generated by a given actuation voltage, applied between the two electrodes of an actuator, the maximum value being determined by the maximum distance between the two electrodes of an actuator when the mobile part  610  is in the rest position without the attraction force being too small for a given actuation voltage. For example, for an actuation voltage of 100V, the minimum thickness of the dielectric layer  624  (for example made of oxide or nitride of a semiconducting material, for example silicon) may be about 0.2 micrometers.  
      For guidance, the mobile electrode  621  may have: 
          a length between a few tens of micrometers and a few millimetres, for example between 10 μm or 20 μm and 1 mm or 5 mm or 10 mm,     a thickness of between a few tens of micrometers and a few micrometers, for example between 0.1 μm and 10 μm; the thickness makes the mobile electrode  621  sufficiently supple or flexible in a direction approximately perpendicular to the main plane of the base  614 ,     and a body width  621 . 2  very much greater than its thickness, for example between 50 μm and 100 μm thick. The inter-electrode space  625  may be between a few micrometers and a few tens of micrometers at rest.        

      It is advantageous if the fixed part  614  comprises a recess  626  facing the mobile part  610  ( FIG. 15B ). The mobile part  610  can penetrate into the recess  626  when it is moved into an inclined position with a large angle. An inclined position with such an angle of inclination would not be possible if the recess  626  was not present because the mobile part  610  would collide with the fixed part.  
      The fixed electrodes  620  are preferably located on the fixed part outside the recess  626  so as to keep the inter-electrode space  625  relatively small when the actuators are in the rest position.  
      The depth of the recess  626  is chosen to be sufficient such that the mobile part can be inclined at an angle θmax without colliding with the fixed part  614 . The angle θmax corresponds to the maximum angle occupied by the mobile part when the addressing means output a maximum actuation voltage.  
      The recess  626  may be a hole passing through the fixed part  614  or simply a blind hole in this fixed part  614 .  
      If it is a through hole, it can be made starting from the face of the fixed part  614  on which the fixed electrodes  620  will fit (this face is said to be the front face), or starting from the other face which is said to be the back face.  
      This recess  626  will be made by dry etching or preferably by wet etching in the material from which the fixed part  614  is made, usually a semiconducting material.  
      In this configuration, the drive arms  623  are prolonged by the torsion arms  613  as shown in  FIG. 15A .  
      The actuators  619  may be located on each side of the mobile part  610 , as illustrated in  FIG. 15A .  
      But this is not compulsory and it would also be possible to have only one actuator  619  on one side of the support of the optical component  610 .  
      With reference to  FIG. 15A , it would possible to have only one of the two actuators shown, for example the actuator seen in section in  FIG. 15B .  
      In practice, a torsion arm  613  will have a smaller cross-section than a drive arm  623 , this cross section assuring a certain flexibility in torsion. The cross section of the drive arm  623  is larger so that it remains rigid during the drive.  
      Thus, the dimension of the torsion arms  613  may be optimised so that they are sufficiently flexible in torsion and sufficiently stiff in vertical bending. They are advantageously relatively thick and their width will be less than their thickness.  
      If the torsion arm  613  is not sufficiently stiff in vertical bending, the actuator  619  may tend to pull the mobile part  610  downwards rather than drive it in rotation. The movement of the mobile part  610  may then not be a pure rotation, which can give a lateral translation movement to a reflected or transmitted light beam resulting from a light beam incident on the reflecting or refracting zone  17 . This additional translation effect may also be beneficial and in this case the fact that the torsion arm  613  is not sufficiently rigid in vertical bending would be advantageous.  
      At least one of the actuators  619  comprises means  630  forming a pivot for its mobile electrode or its mobile electrodes  621 .  
      These means  630  will form a pivot in a zone placed between a zone of the actuator connected to the drive arm  623  and a free end  621 . 1  of the actuator.  
      The means  630  forming the pivot may be formed by at least one pad fixed with respect to the fixed part  614 , as explained above with reference for example to  FIG. 1A, 1B  or  4 A,  4 B. Each pad then projects from the fixed part  614  towards the mobile part  621 .  
      Conversely, one of the pads  630  may be fixed to the mobile electrode  621  and project towards the fixed part  614 .  
      For the actuator provided with a pad, the pad forms a bearing zone for the mobile electrode  621 , when it is attracted by the fixed electrode  620 .  
      As a variant, the means  630  forming the pivot may be formed from at least one side arm with the mobile electrode  621  connecting the mobile electrode  621  to the fixed part  614 . The arm  630  may be as described above with reference to  FIG. 2A , or it may project from the mobile electrode and it may have an end fixed to the fixed part  614 , for example by embedment.  
      Two arms, arranged on each side of the mobile electrode, make the structure symmetric. A better lateral stability of the mobile electrodes is then achieved.  
      As already described above with reference to  FIGS. 1A-14B , the means  630  forming the pivot are used to maintain a zone or a portion of the mobile electrode  621  at a distance from the fixed part  614  when the free end of the mobile electrode  621  is attracted by the fixed electrode  620 .  
      The distance L between the zone in which a pivot of the mobile electrode and the portion of this mobile electrode or these actuator means connected to the drive arm  623 , enables a lever effect so that the mobile part  610  can be inclined. The edge of the mobile part  610  located on the same side of the axis  612  as the mobile electrode or the actuator  621  that is pressed into contact with the fixed electrode  620 , moves upwards and the opposite edge moves downwards.  
      With this configuration, the distance d between the axis of rotation  612  and the fixed part  614  at the contact surface may be of the order of a few micrometers, for example d is between 3 μm and 10 μm.  
      A device can be made with an actuator with means  630  forming the pivot, as illustrated in  FIG. 16A . The actuator then comprises two parts  619 - 1  and  619 - 2  separated by an insulating portion  631 , and can be located facing one or two fixed electrodes (based on the principle that was described above with reference to  FIGS. 13A and 14A ).  
      In fact, this insulating part may be inserted in means forming the support of an optical component  617 , as illustrated in  FIG. 16A . They could also be located as illustrated in  631 - 1 , offset from these means forming the support.  
      In  FIG. 16B , the mobile part does not contain an insulating part; it is then a single mobile electrode located facing two fixed electrodes as explained above, for example with reference to FIG.  1 A (the fixed electrodes cannot be seen in  FIG. 16B  but they are contained in the substrate or the fixed part  614 ).  
      In the cases illustrated in the two  FIGS. 16A and 16B , the mobile part (therefore including the two parts  619 - 1 ,  619 - 2  and the two arm portions  623  located on each side of the support means  610  of the optical component) is located on only one side of the axis  612 .  
      This configuration has the advantage that the mobile means  610  forming a support to the optical component  617  are positioned close to an edge  614 . 1  of the fixed part  614 . The structure obtained is more compact than in the embodiments described above with reference to  FIGS. 15A and 15B . Such a structure is particularly attractive during integration of a component  617  such as a micro-mirror or a micro-lens in an optical system.  
      The device in  FIGS. 16A and 16B  also comprises means  630  forming a pivot, that can have one of the shapes already described above with reference to any one of the embodiments.  
      Another advantage of the configurations in  FIGS. 16A and 16B  is that the mobile part  610  may rotate in both directions with respect to a rest position obtained when none of the actuators  619  is activated.  
       FIGS. 17A, 17B  illustrate other configurations of an optical device according to the invention.  
       FIG. 17A  shows two actuators, firstly  619 . 1 ,  619 . 3  and secondly  619 . 2 ,  619 . 4 , located on the same side of the axis  612 .  
      Each actuator comprises two folded parts such that the two corresponding free ends are connected to the same side of the mobile means  610 . Each actuator thus cooperates with a drive arm  623 . 1 ,  623 . 2  located on one side of the mobile part  610 .  
      Part of each actuator comprises means  630  forming a pivot.  
      The free ends  621 . 1  and  621 . 3  of the mobile electrodes of these two actuators may be mechanically common, as illustrated in  FIG. 17A . The starters  621 . 3  of these mobile electrodes may also be fixed together.  
      In each actuator, one of the actuator arms  619 . 1 ,  619 . 2  is provided with means forming the pivot  630  and the other arm  619 . 3 ,  619 . 4  does not have such means.  
      Therefore, each actuator operates on the principle that was already described above with reference to  FIGS. 1A-16B ; one of the parts may be attracted towards the substrate by an electrostatic effect, while the other part is subject to a mechanical return that moves it away from the substrate.  
      References  710  that can be seen in  FIG. 17A  (and in  16 A) illustrate contact pads fixed on the frame (or the uprights)  615 ; these pads are designed to supply power to the mobile electrodes of the actuators.  
      One and/or the other of the actuators may comprise one or two mobile electrodes (as explained above with reference to  FIGS. 1A, 13A ,  14 A), and a number of fixed electrodes such that the actuator can be controlled by two different voltages.  
      In  FIG. 17A , each actuator is actually composed of two parts each forming a mobile electrode, these two parts being separated from an electrically insulating zone  631 . 2 . In fact, considering the mechanical link between the free ends of the two actuators, a single insulating portion  631 . 2  is sufficient for the two actuators.  
      As already mentioned above, the two actuators have their other ends connected to the drive arms  623 . 1  and  623 . 2 . Each drive arm is provided with an electrically insulating zone  631 . 1  and  631 . 3  for this purpose.  
      In the configuration in  FIG. 17A , an axis perpendicular to the rotation axis  612  passing through the centre of the mobile part is an axis of symmetry for the two actuators.  
      The configuration in  FIG. 17B  also comprises two actuators distributed on each side of an axis  612 . 1  perpendicular to the axis  612 . The mobile parts  621  of the actuators that are located on the same side of the axis  612  are terminated with a common starter  621 . 3 . Means  630  forming pivot are associated with each actuator. Non-simultaneous actuation of the two actuators can drive the mobile part  610  in rotation, but simultaneous actuation of the two actuators will drive the mobile part  610  in upwards translation, and it will then move away from the fixed part  614 .  
      In the case shown in  FIGS. 17A and 17B , the actuators are curved in shape, so that a mechanical link can be made between them.  
      We will now describe an example of a method for manufacturing a device (for example a micro-mirror or a micro-lens) according to the invention. It is assumed that the addressing means apply appropriate voltages onto the mobile electrodes of the actuators to displace the mobile part in rotation, while the fixed electrodes are brought to a constant voltage (usually the ground). But other schemes for assignment of voltages could be envisaged.  
      Refer to  FIGS. 18A  to  18 L. It is assumed that the semiconducting substrates are conducting.  
      A first substrate  1000  formed from a base layer  1001  made of a semiconducting material, for example silicon, is used covered by a sandwich  1002  formed from two insulating layers  1002 . 1 ,  1002 . 2  (for example made of silicon oxide) located on each side of an intermediate layer  1002 . 3  made of semiconducting material (for example silicon), the sandwich  1002  itself being covered by a surface layer  1003  made of a semiconducting material (for example silicon).  
      This substrate is illustrated in  FIG. 18A . The insulating layer referenced  1002 . 1  is the lower layer of the sandwich and the layer  1002 . 2  is the upper layer of the sandwich.  
      Such a substrate  1000  may be a double SOI (Silicon on Insulator) substrate. The surface layer  1003  is thicker than the intermediate layer  1002 . 3 . The layers made of semiconducting material  1001 ,  1002 . 3 ,  1003  are conducting.  
      In this example it is assumed that the micro-mirror or the micro-lens is similar to that in  FIGS. 15A, 15B , the drive arms  623  and the torsion arm  613  are end to end.  
      We will begin by delimiting the pattern of a first region of the fixed part  614 , namely the frame  615 . 1  or the uprights of a first region of the mobile part  610 , from a first region of the torsion arm  613  and the drive arm  623 , by a photolithography step. The next step is to etch these different elements in the surface layer  1003  and in the upper insulating layer  1002 . 2  ( FIG. 18B ). This etching step may be a dry etching step. Therefore, the first regions are formed from a semiconducting material of the surface layer  1003  and the material in the upper insulating layer  1002 . 2 .  
      The mobile part  610  may remain entire or it may be etched, for example so as to obtain a frame with a central recess, depending for example on whether a micro-mirror or a micro-lens is being made. An enclosed etching is shown in dashed lines in  FIG. 18B .  
      The mobile electrodes of the actuators will be made later in the intermediate layer  1002 . 3 .  
      The torsion arms  613 , the frame  615  and the mobile part  610  will be used to route addressing signals to the mobile electrodes of the actuators. These addressing signals propagate in the frame and the torsion arms from contact pads supported by the frame and that will be made later.  
      For example, one of the torsion arms will be used for addressing actuators located on one side of the axis  612  and the other torsion arm will be used for addressing actuators on the other side of the axis  612 .  
      Insulating trenches  1004  at the frame  615 . 1  and an insulating trench  1006  at the first region of the mobile part  610  can be made in the surface layer  1003  and also in the upper insulating layer  1002 . 2  ( FIG. 18C ), so that the addressing signals intended for the mobile electrodes located on one side of the axis  612  do not propagate to the mobile electrodes located on the other side of the axis that will receive other addressing signals. These trenches may be trenches of air or they may be filled with a dielectric material later.  
      If two uprights are to be provided instead of a frame, these uprights are electrically insulated due to their configuration.  
      The insulation trenches  1004  intersect the frame  615 . 1  in two parts  1005 . 1 ,  1005 . 2 , one part  1005 . 1  carrying one of the contact pads transmitting addressing signals and the other part  1005 . 2  carrying the other contact pad transmitting the other addressing signal. The pads are not visible at this step ( FIG. 18C ).  
      Similarly, the surface layer  1003  corresponding to the first region of the mobile part  610  is separated into two parts  1007 . 1 ,  1007 . 2  by the insulating trench  1006 .  
      One of the torsion arms projects from one of the parts  1007 . 1  and the other projects from the other part  1007 . 2 . The insulating trench  1006  is directed mainly along the axis of rotation  612 . The insulation trench  1006  can be seen in  FIG. 18C .  
      In a second semiconducting substrate  1200  (for example made of silicon) that will be used as the second region of the fixed part  614 , namely the base  616 , a first setback part  1201  is made by etching and will contribute to forming the space  625  between the fixed and mobile electrodes of the actuators and possibly a second setback part  1202  that will form the recess  626  that will be located under the mobile part  610 . The first setback part  1201  is not as deep as the second setback part  1202 . The depth of the first setback part  1201  may be of the order of a few micrometers as was mentioned above, because at least one actuator comprises means forming a pivot.  
      The means  630  forming a pad type pivot  630 . 1  may be made by dry etching, for example during etching of the first setback part as illustrated in  FIG. 18D . As for the fixed electrodes, the pad is made from the semiconducting material of the second substrate  1200 .  
      The second setback part  1202  is located in a central zone of the first setback part  1201 . This etching may be a dry etching. The second substrate  1200  thus etched will materialise the fixed electrodes  620 . The fixed electrodes are thus included in the base. The next step is to cover the second substrate  1200  thus etched with a layer of insulating material  1203 , for example silicon nitride or an oxide ( FIG. 18D ). The layer of insulating material  1203  materialises the insulating layer  624  ( FIG. 15B ) inserted between the fixed electrodes  620  and the mobile electrodes  621 , and between the fixed electrodes  620  and the means forming the pivot  630 .  
      The next step is to fix the two substrates  1000 ,  1200  together by placing the first setback part  1201  facing the etched surface layer  1003  ( FIG. 18E ).  
      This fixing may be done by a molecular bonding process after preparing the surfaces to be assembled appropriately. Such a molecular bonding process is known as SDB for Silicon Direct Bonding. The second setback part  1202  faces the first region of the mobile part  610 .  
      For example, coarse mechanical grinding followed by wet etching can be used to remove the base layer  1001  and the lower insulating layer  1002 . 1  of the sandwich  1002  of the first substrate  1000  ( FIG. 18F ) from the silicon.  
      The intermediate layer  1002 . 3  and the upper insulating layer  1002 . 2  will then be etched to access the surface layer  1003  so as to delimit contact pads. The zones thus etched are referenced  1008  in  FIG. 18G . Interconnection holes  1009  are also etched in the surface layer  1003  and, once metallised, will be used to make contact areas between the mobile electrodes and the parts  1007 . 1 ,  1007 . 1  of the first region of the mobile part  610 . These interconnection holes  1009  are excavated in the torsion arms  613  in a zone in which they project from the mobile part  610 , but other locations would also be possible. There is the same number of interconnection holes  1009  as mobile electrodes. Contact points will be used to electrically connect the said parts  1007 . 1 ,  1007 . 2  to the mobile electrodes. This etching step is illustrated in  FIGS. 18G and 18H .  
      Metal is then deposited so as to make the contact pads  710  and contact points  711  in the etched zones  1008  and the interconnection holes  1009  ( FIG. 18I ). The deposited material may be tungsten or aluminium or any other conventionally used metal or alloy.  
       FIGS. 18J and 18K  are sectional and top views respectively showing the result of an etching step in the intermediate layer  1002 . 3  with the purpose of delimiting the contour of the mobile electrodes  621  with their starters  621 . 3  and their bodies  621 . 2 , and a second region of the mobile part  610 , of a second region of the torsion arms and drive arms (that are coincident). Therefore, the second region of the mobile part, the second region of the torsion arms and the second region of the drive arms are formed in the semiconducting material of the intermediate layer  1002 . 3 .  
      The first and second regions of the mobile part, the torsion arms and the drive arms are superposed and therefore form a stack of the surface layer  1003 , the upper insulating layer  1002 . 2  and the intermediate layer  1002 . 3 . An insulating trench  712  could be provided between the two mobile electrodes located on each side of the axis  612  and that are fixed to the same torsion arm  613  and an insulating trench  713  between the mobile part  610  and the mobile electrodes  621 .  
       FIG. 18L  is a section of the micro-mirror or the micro-lens in a plane AA in  FIG. 18J . The contact pads  710  and the contact points  711  that were not in  FIG. 18C  can be seen.  
      The reflecting zone  617  of a micro-mirror may be made by the semiconducting material of the intermediate layer  1002 . 3  located in the second region of the mobile part  610 , if it has sufficient reflectivity. It could also be made by metallisation, for example with gold or silver or aluminium or other, of the said second region of the mobile part.  
      Concerning the manufacture of a micro-lens, a lenticular refracting pellet  617  can be transferred onto the frame forming the mobile part  610 , for example by bonding. It is assumed that this pellet is as outlined in  FIG. 18K . The zone  617  could also represent the reflecting zone of a micro-mirror.  
      The terms “left”, “right”, “up”, “down”, “lower”, “upper”, “horizontal”, “vertical” and others are applicable to the embodiments shown or described with reference to the Figures. They are used only for description and are not necessarily applicable to the position occupied by the micro-mirror when it is in operation.  
      Although several embodiments of micro-mirrors have been described, this invention is not strictly limited to these embodiments. In particular, the number of actuators is not limited to two as illustrated. This number may be arbitrary, there is at least one actuator on one side of the axis and at least one actuator on the other side.  
       FIG. 19  shows an electrostatic actuator used for displacement in rotation and/or in translation of an object  800  and comprising three or more actuators.  
      The object  800  may have a closed contour with a curvature. It is shown as being circular in shape in  FIG. 19 , but other shapes are possible (for example elliptical).  
      The shape of actuators is then adapted to the shape of the object. For example, they may be in the shape of an arc of a circle, as illustrated in  FIG. 19 .  
      This object  800  may an optical component or a support for an optical component, in particular the component may be a mirror for beam aiming applications, or scanning or adaptive optics, or beam shaping, alignment of the mirrors of a laser cavity, or alignment of optical components in general.  
      For example, two mirrors may be made parallel with the required separating distance using this actuator.  
      Such a system may be useful for an optical interferometry system, or for a tuneable Fabry-Pérot filter, or for a laser cavity.  
      But such an actuator system may also be used for alignment of a lens with an optical system, or for centring or adjustment of the distance between these two elements.  
      Such a system may also be used to adjust the distance between a focusing lens and, for example, an optical storage medium to write or read and/or adjust the focusing point on this medium by rotation of the lens.  
      In this application, the actuator may also be used to adjust the position of a mirror with respect to the medium.  
      The actuator may be used to drive a deformable adaptive optic mirror.  
      It may also be used to make a variable inductance or a variable resistance.  
      It is shown diagrammatically in  FIG. 19  in which reference  800  denotes the moving part; it may be an optical component such as a mirror, for example a 20 μm thick mirror or a support for an optical component.  
      Arms  802 , preferably thin arms, for example 2 μm thick, support the mirror  800  above the cavity during manufacturing.  
      Actuation means  803  of the type shown in  FIGS. 1A, 13A ,  14 A, are arranged around the part  800  to be moved.  FIG. 19  shows 3 actuation devices. Each of them may for example be of the order of 2 μm thick. Reference  812  denotes means forming a pivot, for example a pad, as in the embodiments already presented above.  
      One or several loops  804  enable radial stretching between the actuation means  803  and the central part  800 . For example, a loop with a thickness of about 20 μm. These radial stretching means are optional, and can be used to increase the possibility of displacement of means  800  with respect to the actuation means  803 .  
      Therefore, each stretching loop  804  enables artificial elongation between the means  803  and the central part  800  during displacement. This facilitates large displacements.  
      Each loop is stiff in vertical bending, due to its high thickness (for example between 10 μm and 20 μm or 40 μm) and it is flexible in lateral bending due to its small width l (for example between 1 and 5 μm) and its large length L (greater than 50 or 100 μm, or between 50 and 200 μm).  FIG. 24  shows such a loop  804 .  
      A starter  805  may be used to limit the starting field or voltage for one or several actuation means  803 , as already explained above.  
      The device may also comprise pins  806  located between means  800  and the substrate (therefore not visible in the top view in  FIG. 19 ), in order to prevent bonding of these means  800  on this substrate.  
      Reference  807  denotes connection pads of actuators (for the mobile electrode or the mobile electrodes).  
      Reference  808  denotes connection pads of the fixed electrodes arranged in the openings  809  of the contact points.  
      References  810  denote sealing stops, for example oxide stops, and reference  811  denotes a sealing bead between two rows of stops. This bead  811  may for example be made of a photosensitive polymer.  
      Fixed electrodes  813  are arranged in the substrate of the device in order to interact with the mobile electrodes  803  as already explained above with reference to  FIGS. 1A-15 .  
      Electrical connections tracks  814  connect the fixed electrodes  813  to the pads  808 .  
      In the case of a mirror  800 , it is possible to have circular mirrors or other shape mirrors with dimensions of up to a few mm in width, for example with a diameter or width or maximum dimension equal to 10 mm.  
      The central part of the block  800  can be hollowed out, for example to position a lens in the recess obtained.  
      The thickness of this part  800  may be between a few μm and a few tens of μm, for example between 5 μm and 30 μm, and also for example of the order of 20 μm, for a diameter for example between 200 μm and 500 μm or 1 mm, which gives a small deformation of the mirror  800  itself during the displacement.  
      Arms  802  are used for manufacturing the mirror. These arms are sufficiently thin (for example 2 μm thick and 10 μm wide) so that they can be flexible and easily bent. Their length may easily be adapted to not hinder the movement of the mirror  800 .  
      Actuation means  803  may be positioned radially, which facilitates the movement of the mirror but limits the capacitance. Such a variant is illustrated in  FIG. 23 , on which references identical to those in  FIG. 19  denote similar or corresponding elements.  
      The arms of an actuator  803  are thick, for example between 1 μm and 10 μm thick (for example 3 μm) and their width is between 10 μm and 150 μm or 200 μm, for example. A width of the end part  805  greater than 500 μm enables a small starting voltage.  
      These arms  803  may be wound or folded to limit their size.  
      Actuators enable displacement of the means  800  outside the plane defined by their rest position due to an actuation movement as explained above, using both electrostatic attraction forces and mechanical return forces.  
      Steps in manufacturing of the mirror and the mobile electrodes in such a device will now be described with reference to  FIGS. 20A-20E .  
      In a first step ( FIG. 20A ), a semiconducting on insulator type component is selected, for example an SOI type, comprising a substrate  900  made of a first semiconducting material; it may for example be a silicon substrate that may be between 100 μm and 500 μm thick, for example 450 μm. An insulating layer  901 , typically made of SiO 2 , for example of the order of 10 μm thick, is supported on this substrate  900 , this layer  901  itself supporting a layer  902  made of a second semiconducting material, for example also made of silicon, between 1 or 5 micrometers and 10 or 50 micrometers thick, for example of the order of 20 μm.  
      The next step ( FIG. 20B ) is a thermal oxidation of this SOI substrate; the result obtained is thus two layers,  903 ,  904  made of silicon oxide on each side of the substrate.  
      A layer  905  of a photosensitive resin is deposited on the oxide layer  903  that is itself supported on the layer  902 .  
      The next step ( FIG. 20C ), is etching of the oxide  903  and partial etching of the silicon layer  902  by lithography using the resin  905 , then the formation of patterns  906 . These patterns will be used to delimit the central support  800 , the electrodes  803  and possibly the stretching means  804 .  
      The next step ( FIG. 20D ) is to etch the oxide  903  by lithography in zones that will form the actuators  803  and etching of the silicon layer  902 , for example to about 18 μm, until the end of etching is detected. Zone  800  is then protected by the oxide  903 .  
      The back face of the substrate ( FIG. 20E ) can then be etched, the oxide  904  on the back face and the silicon  900  being etched by lithography. Etching may be a KOH or TMAH etching or a deep dry etching.  
      The final step is etching of the oxide  901 . The trench  809  is also obtained by etching.  
      The mobile part of the device is then ready.  
      We will now describe manufacturing of the fixed electrodes and stops  806  with reference to  FIGS. 21A-21E .  
      The first step ( FIG. 21A ) is to form an insulating layer  920 ,  921 , for example by oxidation, on each side of a semiconducting substrate  922 , for example silicon, and then a metallic deposit, lithography and etching of the fixed electrodes  813 , for example made of aluminium.  
      An oxide layer  924  is deposited on the face of the substrate on which the electrodes  813  were made, for example using the PECVD technique ( FIG. 21B ), this layer is then planarised.  
      The next step ( FIG. 21C ), is to form the sealing stops  810 , pads  812  and anti-bonding pads  806  by deposition. This is followed by etching.  
      A sealing bead  811  may then be made by lithography of a photosensitive polymer layer deposited between the stops  810 .  
      The next step ( FIG. 21D ) is to assemble the two substrates (that in  FIG. 20E  and that in  FIG. 21C ), by sealing using the sealing bead  811 . For reasons of clarity,  FIG. 21D  does not show all elements of the mobile part; in particular, only one bead  804  and only one actuator  803  are shown.  
       FIGS. 22A-22C  illustrate a diagrammatic operation of the device that has just been described.  
      In  FIG. 22A , the fixed electrodes  813 - 2  and  813 - 4  are electrodes to which the highest voltages are assigned, while electrodes  813 - 1  and  813 - 3  are assigned lower voltages. The result is a movement of the flexible membranes and inclination of the mirror or the optical component or the support  800 , as indicated in  FIG. 22A .  
      The component or the support  800  may be returned to the high position as illustrated in FIG.  22 B, by assigning the highest voltages to the fixed electrodes  813 - 1  and  813 - 4 , while the electrodes  813 - 2  and  813 - 3  are assigned the lower voltages. The two flexible membranes  803  and the component  800  are then in the high position.  
      A low position may be reached ( FIG. 22C ) by assigning the highest voltages to the electrodes  813 - 2  and  813 - 3 , while the lowest voltages are assigned to the other electrodes.  
     BIBLIOGRAPHIC REFERENCES  
     
         
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