Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
  • G02B3/12—Fluid-filled or evacuated lenses
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
  • G02B3/12—Fluid-filled or evacuated lenses
  • G02B3/14—Fluid-filled or evacuated lenses of variable focal length
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/004—Optical devices or arrangements for the control of light using movable or deformable optical elements based on a displacement or a deformation of a fluid
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
  • G02B26/0825—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a flexible sheet or membrane, e.g. for varying the focus
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/0025—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration
  • G02B27/0068—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration having means for controlling the degree of correction, e.g. using phase modulators, movable elements
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/20—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators
  • H10N30/204—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators using bending displacement, e.g. unimorph, bimorph or multimorph cantilever or membrane benders
  • H10N30/2047—Membrane type
  • H10N30/2048—Membrane type having non-planar shape

Definitions

• the present invention relates to a deformable membrane optical device trapping fluid and provided with means for actuating the piezoelectric type membrane to adjust the radius of curvature of the membrane in its central portion.
• a deformable membrane optical device may be a liquid lens with variable focal length, a liquid lens with optical aberration correction, for adaptive optics, or a mirror with variable focus.
• Liquid lenses can be used for example in mobile phones with camera or camera function. Many developments are in progress including the autofocus function and the zoom function. When introducing these functions, it is sought to obtain the shortest possible response time but also to reduce the power consumption during the actuation and to increase the variations of the focal length with a given energy consumption. , while avoiding making complex the manufacture of such devices. More generally, we try to integrate as much as possible the constituents of these miniature cameras to reduce costs, space and energy consumption. These miniature cameras, operating in the visible, are known under the name Anglo-Saxon CCM for "compact camera module". The most successful liquid lens technology for this application is for the moment that based on the principle of electro-wetting.
• a deformable membrane mirror application the latter is reflective. It may be necessary to want to adjust the focal length of the mirror and therefore its radius of curvature.
• Such a mirror can be used in ophthalmology or adaptive optics.
• these optical devices, whether lens or mirror type can be used to stabilize images.
• the patent application FR 2 919 073 describes an optical device comprising a flexible membrane having a peripheral anchoring zone on a support, the membrane and the support trapping a given volume of fluid and piezoelectric actuating means for moving the fluid to level of the central area of the membrane, in order to deform the central area of the membrane.
• the volume is substantially constant in a given temperature range.
• the actuating means are formed of a plurality of radial micro-beams, which are fixed at one end to the support and whose other end acts on the membrane in an area between the central zone and the anchoring zone. .
• a disadvantage of this configuration is that it is cumbersome since the actuating means bear on the support.
• Another disadvantage is that for a given size, and a given power consumption, during actuation, the optical performance of the device is not optimal. Similarly, for a given size, and given optical performance, energy consumption is important during one actuation.
• a lens having a variable focal length comprises a cavity communicating with an expansion chamber, the cavity being delimited by a mobile wall anchored on a support.
• actuating means in ionic conductive polymer or, alternatively, piezoelectric material are reported on the membrane without being directly integral and transmit an actuating force substantially along the optical axis of the device.
• the actuating means take the form of a continuous crown with a plurality of radial fingers, attached near the membrane.
• the patent application WO2008 / 100154 shows an optical device comprising a cavity containing a gel or elastomer type material closed by transparent covers. Piezoelectric actuating means cooperate with one of the covers which is made of glass. The rigidity of this lid is a brake on the effectiveness of one actuation and the material contained in the cavity, since it is gel or elastomer type, does not provide the expected counter-reaction under the effect of the actuation for the actuation. deform the central area of the lids. It is the center of the membrane that deforms the gel or elastomer under the effect of one actuation and this membrane requires a high rigidity to obtain a given deformation. Such an optical device is inefficient.
• the present invention is precisely intended to provide a deformable membrane optical device such as a lens or a mirror that does not have the drawbacks mentioned above, namely the space requirement, the large energy consumption, the lack of efficiency of one actuation.
• Another object of the invention is to provide a deformable membrane optical device whose deformation of the membrane can be adjusted in a desired manner and very finely, whether the deformation is symmetrical or not, with respect to an optical axis of the optical device.
• Another object of the invention is to provide a deformable membrane optical device in which the optical aberrations are reduced.
• Another object of the invention is to provide a deformable membrane optical device in which the residual stresses appearing during manufacture are easier to manage during use.
• Yet another object of the invention is to provide a deformable membrane optical device, active compensation as a function of temperature, so as to maintain a constant focal length even if the ambient temperature varies.
• the present invention provides an optical deformable membrane device comprising an anchoring zone on a support contributing to imprisoning a quantity of liquid or gaseous fluid, a central zone capable of reversibly deforming from a rest position, actuating means for moving the fluid, biasing the membrane in an intermediate zone between the anchoring zone and the central zone.
• the actuating means comprise a continuous ring of piezoelectric material accommodating a plurality of piezoelectric actuators each formed of a pair of electrodes sandwiching the continuous ring, this continuous ring being mounted around the central zone without encroaching on it, the means for actuation being anchored to the diaphragm at least in the intermediate zone, the actuating means and the diaphragm to which they are anchored forming at least one piezoelectric bimorph, the actuating means contracting or extending radially during a actuation so as to cause a displacement of said fluid from the intermediate zone to the central zone of the membrane or vice versa, aimed at deforming the central zone relative to its rest position. This gives a lot of flexibility to obtain a desired distortion of the central area.
• the actuation means comprising several piezoelectric actuators, they have several pairs of electrodes sandwiching the continuous ring, at least one electrode of a pair may be common to two or more piezoelectric actuators.
• the actuating means can also be anchored on the anchoring zone of the membrane and possibly on the support directly. According to the anchoring or not of the actuating means to support the deformed membrane is different. Depending on the desired shape, it may be advantageous to anchor or not the actuating means to the support.
• the actuating means may be overlying the membrane and / or underlying the membrane and / or integrated in the membrane.
• the actuating means may be overlying the membrane and / or underlying the membrane and / or integrated in the membrane.
• the membrane may comprise a stack of layers, at least at the intermediate zone, among which a stiffer reinforcing layer and a less rigid layer, the more rigid layer forming part of the piezoelectric bimorph.
• the membrane has a continuous layer which extends at the level of the central zone, the intermediate zone and the anchoring zone.
• auxiliary actuating means anchored to the diaphragm comprising a discontinuous ring of piezoelectric material, housing one or more piezoelectric actuators, the discontinuous ring being concentrically mounted with the continuous ring, the auxiliary actuating means and the membrane to which they are anchored forming at least one piezoelectric bimorph. It is thus easy to obtain a desired deformation of the membrane in the central zone. It is also possible to provide means for compensating a variation in the focal length of the optical device as a function of the temperature. This allows the optical device to operate without any particular adjustment in a temperature range between about -20 ° C and + 60 ° C.
• the compensation means may be merged with the piezoelectric actuator (s) of a continuous ring.
• the compensation means may comprise one or more thermal bimorph elements arranged in a continuous ring, either anchored to the membrane at the anchoring zone by overflowing on the intermediate zone, or fixed to the support opposite the diaphragm relative to fluid audit.
• the piezoelectric actuators are operable separately from each other or all together simultaneously or they can be actuated simultaneously in groups. This gives great flexibility to obtain a desired deformation of the membrane in the central zone.
• the optical device may further comprise a protective cover fixed on the support.
• the hood may be provided with an opening at the center area or be waterproof and trap another fluid.
• the membrane may be made based on organic materials chosen from polydimethylsiloxane, polymethyl methacrylate, polyethylene terephthalate, polycarbonate, parylene, epoxy resins, photosensitive polymers and silicones, based on mineral materials chosen from silicon. , silicon oxide, silicon nitride, silicon carbide, polycrystalline silicon, titanium nitride, diamond carbon, tin and indium oxide, aluminum, copper, nickel , based on piezoelectric material.
• Each of the fluids is a liquid selected from propylene carbonate, water, a liquid index, an optical oil or an ionic liquid, or a gas selected from air, nitrogen, helium.
• the piezoelectric material may be based on PZT, aluminum nitride, polyvinylidene fluoride or its trifluoroethylene copolymers, zinc oxide, barium titanate, lead niobate, sillenites such as titanate of bismuth.
• the optical device can be a lens or a mirror.
• the present invention also relates to a shooting device which comprises at least one optical device thus characterized.
• FIGS. 1A to 1C show in section a plan view an optical device useful for understanding the invention, the membrane of the optical device of FIG. 1A being more flexible than that of the optical device of FIG. 1C, FIG. also in top view another optical device useful for understanding the invention with a single piezoelectric actuator;
• FIGS. 2A, 2B make it possible to understand the operation of a piezoelectric element provided with a pair of electrodes
• FIGS. 3A to 3G are top views of different variants of the optical device according to the invention.
• FIGS. 4A to 4C show in section the anchoring of the membrane, for different types of membrane
• Figures 5A to 5M show in section different arrangements between the membrane and the actuating means
• FIGS. 6A to 6E show different configurations of the support on which the membrane of an optical device according to the invention is anchored
• FIGS. 8A to 8G show different stages of manufacture of an optical device according to the invention.
• Figures 9A, 9B show an optical device according to the invention mounted in a shooting device
• FIGS. 10A, 10B, 10C make it possible to compare the efficiency between an optical device according to the invention and an optical device such as that described in the patent application FR 2 919 073.
• FIG. 1A, 1B a first embodiment of an optical device useful for understanding the invention.
• Figure 1C shows the same embodiment of the optical device but with a more rigid membrane.
• This optical device is built around an axis called optical axis XX '. It comprises a membrane 2 whose periphery is anchored in a sealed manner on a support 1 which in this example is bowl-shaped.
• the membrane 2 thus comprises an anchor zone referenced 2.3 which is superimposed on the support 1.
• the membrane 2 also comprises a central zone 2.1 which corresponds to an optical field of the optical device. It is materialized by dots.
• the bowl is intended to receive a liquid or gaseous fluid called first fluid 4. More generally, the membrane 2 and the support 1 contribute to forming a cavity 3 in which the fluid 4 is trapped.
• One of the faces of the membrane 2 is in contact with the fluid 4 contained in the cavity 3.
• the other face of the membrane 2 is in contact with a second fluid 4 'which may be ambient air.
• the second fluid 4 ' may be air or another gas or even a liquid.
• membrane 2 is meant any flexible film acting as a barrier between the first fluid 4 and the second fluid 4 'located on the other side of the barrier relative to the first fluid 4.
• the cavity 3 has a bottom 3.1 which is transparent to an optical beam (not shown) for propagating through the lens.
• the membrane 2 is transparent to the optical beam at least in the central zone 2.1. If the optical device is a mirror, the membrane 2 is reflective at least in its central zone 2.1.
• the optical beam can be a visible beam, but it can extend beyond the visible in the infrared for example.
• the membrane 2 is flexible and able to be deformed in a reversible manner, from a rest position shown in FIG. 1A, under the action of a displacement of the fluid 4 contained in the cavity 3 so as to vary the thickness of the fluid 4 located at the central zone 2.1 of the membrane 2 and thus bend the central zone 2.1 of the membrane 2.
• the fluid 4 contained in the cavity 3 is sufficiently incompressible to move towards the central zone 2.1 when the a force is applied to the membrane 2, this force being applied to the membrane 2 in an intermediate zone 2.2 situated between the central zone 2.1 and the anchoring zone 2.3. It has a substantially constant volume in a given temperature range.
• the fluid 4 contained in the cavity serves as "transmission" between the actuating means 5 and the central zone 2.1 of the membrane 2.
• This fluid 4 may be a liquid or a gas.
• the counter-reaction of the fluid is used for the actuation to obtain the deformation of the membrane in the central zone 2.1.
• FIGS. 1A, 1B the contour of the membrane 2 and the support 1 have been represented in squares whereas the central zone 2.1 has been represented circular.
• the membrane 2 and the support 1 could be circular, rectangular, ovoid or other and the central zone 2.1 could be square, rectangular ovoid or other.
• Piezoelectric actuators are provided to move the fluid 4 of the cavity 3. They solicit the membrane 2 in the intermediate zone 2.2.
• These actuating means 5 are configured in at least one circular crown C of piezoelectric material mounted concentrically around the central zone 2.1. This continuous ring C of piezoelectric material accommodates a piezoelectric actuator (not clearly visible in FIGS. 1A to 1C).
• Each continuous crown C extends in a main plane which is the plane of the membrane 2 when it is flat as in Figure 1A in the rest position.
• the central zone 2.1 of the membrane 2 could be curved at rest and the intermediate zone 2.2, it would be substantially flat.
• a piezoelectric actuator comprises a block 21 of piezoelectric material totally or partially sandwiched between two electrodes 20a, 20b intended, when powered, to apply an internal electric field to the piezoelectric material.
• the arrow represents the internal polarization of the piezoelectric material possibly produced during the manufacturing process.
• a power source bears the reference 23. This electric field is used to control a mechanical deformation of the block 21 of piezoelectric material.
• the block 21 of piezoelectric material may be monolayer or multilayer and extend beyond an electrode.
• the electrodes 20a, 20b located on either side of the block 21 of piezoelectric material are visible in Figures 2A, 2B. The inverse piezoelectric effect has thus been described.
• the electrodes are shown on the continuous ring C in piezoelectric material only in certain figures, in particular FIG. 5C, the reason being that their thickness can be negligible compared with that of the piezoelectric material and also of the membrane 2.
• the electrodes 20a, 20b are located on the two opposite major faces of the continuous ring C piezoelectric material, these main faces being substantially normal to the optical axis of the optical device.
• FIG. 2A shows the shape of the block 21 of piezoelectric material before and after the application of a bias voltage on the electrodes 20a, 20b. After the application of the bias voltage, the block 21 has elongated in the plane of the electrodes and contracted transversely to this plane or vice versa according to the sign of the polarization.
• the piezoelectric actuation means 5 are anchored directly to the membrane 2 in the intermediate zone 2.2, but they can also be anchored to the membrane 2 in the anchoring zone 2.3. This is of course not an obligation. On the other hand, they are not anchored to the membrane 2 in the central zone 2.1.
• the piezoelectric actuating means 5 and the membrane 2 when they are integral form at least one piezoelectric bimorph B, this piezoelectric bimorph being either heterogeneous or homogeneous. More specifically, each piezoelectric actuator and the membrane with which it is integral, form a piezoelectric bimorph. It is recalled that a piezoelectric bimorph comprises a layer of piezoelectric material, equipped with electrodes, contiguous to a layer which is made of piezoelectric material, when the bimorph is homogeneous or of non-piezoelectric material when the bimorph is heterogeneous. In our case, this layer of piezoelectric material or not is a layer of the membrane 2.
• the continuous ring C of piezoelectric material which receives, contracts or extends radially according to the polarization which is applied to the electrodes 20a , 20b, this deformation having the effect of moving the fluid and thus changing the curvature of the membrane 2 in the central zone 2.1. That is to say that the difference between the outer radius and the inner radius of the continuous ring C varies at the electrodes 20a, 20b when subjected to a bias voltage. It will be seen later that the direct effect can also be exploited in the optical device object 1 of the invention.
• FIG. 1A shows in fine continuous line the profile of the membrane 2 when it has been deformed by the actuating means 5.
• the deformation causes a greater thickness of fluid 4 to be at the level of the central zone 2.1 and a smaller fluid thickness 4 is at the intermediate zone 2.2.
• FIG. 1C there is shown in fine continuous line the profile of a membrane 2 having a lesser flexibility than that illustrated in FIG. 1A. It has been deformed by the same actuating means 5 subjected to the same actuating voltage. Its deformed has a much smaller maximum amplitude than in the previous case either in the central zone 2.1 or in the intermediate zone 2.2.
• the actuating means 5 comprise only one piezoelectric actuator. This means that only one pair of piezoelectric electrodes 20a, 20b supported by the continuous ring C has been provided. The electrodes of the pair are located on either side of the continuous ring of piezoelectric material C , one 20a being overlying the continuous crown C and the other underlying and not visible.
• the two electrodes 20a, 20b of the pair take the form of a circular continuous ring substantially modeled on that of piezoelectric material.
• FIG. 1B only the overlying electrode 20a is seen, the continuous ring of piezoelectric material and the overlying electrode are masked.
• at least one of the electrodes it would have been possible for at least one of the electrodes to be in the form of a crown portion, in other words to be in the form of a split ring as in FIG. 1D. This is the electrode 20a.
• one of the electrodes of the single piezoelectric actuator does not necessarily cover the entire face of the piezoelectric material on which it is located. Such a configuration facilitates asymmetrical actuation.
• the configuration of Figure 1B of course brings greater efficiency.
• the optical device according to the invention is comparable to that shown in FIG. 1, with the exception that the actuating means comprise at least one continuous ring of piezoelectric material comprising several piezoelectric actuators, each actuator comprising a pair of electrodes sandwiching the continuous crown.
• FIGS. 3A and 3B there is only one continuous ring C of piezoelectric material.
• FIG. 3A there are four piezoelectric actuators 5.1.
• the four electrodes 20a are substantially identical. and are arranged substantially regularly on the continuous ring C of piezoelectric material.
• FIG. 3B eight electrodes 20b are shown in the underlying ring sectors.
• radial zones z1 between two sectors of continuous ring reveal the piezoelectric material of the piezoelectric bimorph.
• These two figures can show the two opposite faces of the actuating means of a same optical device object of the invention. There are then eight piezoelectric actuators.
• FIG. 3C shows piezoelectric actuation means comprising two continuous rings C, C made of piezoelectric material, at least one of which accommodates a plurality of piezoelectric actuators 5.1.
• the two continuous crowns C, C are concentric, the continuous ring C being internal and the continuous ring C being external. It is assumed that the continuous ring C encroaches on the anchoring zone 2.3 of the membrane 2 but not the continuous ring C.
• the membrane 2 is circular.
• the overlying electrodes 20a of the actuators 5.1 piezoelectric capacitors located on the internal continuous ring C are elongated radial areas. We do not see the underlying electrodes.
• the ring sector electrodes have inner and outer radii which are substantially the same as those of the continuous ring C of piezoelectric material which supports them. It is possible that the ring sector electrodes 20a or 20b have at least one inner or outer radius which is different from the inner or outer radius of the continuous ring C of piezoelectric material. We refer to the 3D figure
• At least one longitudinal zone z2 reveals the piezoelectric material of the continuous ring C.
• the two electrodes 20a, 20b of a pair in a piezoelectric actuator do not need to be identical.
• several piezoelectric actuators can share the same electrode as has already been illustrated in FIGS. 3A and 3B.
• This common electrode can be used for all piezoelectric actuators or some of them for example.
• two adjacent piezoelectric actuators share the same electrode. This is what we wanted to illustrate to Figures 3A and 3B. Two piezoelectric actuators share the same electrode 20a, but they have their own electrode 20b.
• Each pair of electrodes 20a, 20b can be powered independently of the others, which means that all pairs of electrodes can be subjected to different voltages.
• the deformation of the membrane 2 in the central zone 2.1 can be antisymmetrical, non-axisymmetric and very many possibilities of deformation exist.
• the crown C of piezoelectric material is continuous makes its surface anchored on the membrane is large, which ensures an increased efficiency of the actuation, without penalizing itself from the point of view of stiffness in flexion as illustrated in FIG. 10C.
• discontinuous electrodes 20a, 20b on at least one of the faces of the continuous ring C of piezoelectric material, in a lens used in a camera or camera-type apparatus, makes it possible to simply address the "correction of moved by proposing a deformation of the diopter of the lens as well axisymmetric, anti-axisymmetric or other.
• the direct piezoelectric effect it is possible to use the direct piezoelectric effect to monitor the deformation of the membrane 2 when there are several piezoelectric actuators 5.1. It is possible to acquire the voltage that appears across one of the non-actuated piezoelectric actuators while other piezoelectric actuators of the same continuous ring are actuated. It is also possible to provide one or more piezoelectric actuators adapted to passively operate by direct piezoelectric effect, arranged in a ring specially dedicated to this monitoring as shown in Figure 3E.
• the inner ring Cint piezoelectric material accommodates at least one passive piezoelectric actuator 70 detecting the local deformation of the membrane 2 by direct effect.
• the inner ring Cint can be continuous or fragmented, each of the pieces hosting one or more piezoelectric actuators intended to operate by direct effect.
• the inner ring Cint is anchored to the membrane 2 in the intermediate zone 2.2, it does not encroach on the central zone 2.1 or on the anchoring zone 2.3.
• actuators dedicated to monitoring could be anchored to the anchoring area of the membrane.
• the internal ring Cint is divided into two pieces, each accommodating a passive piezoelectric actuator 70. It is of course possible for the same piezoelectric actuator to be intended to intermittently deform the membrane and be intended for monitor the deformation of the membrane intermittently. It can be passive at times and active to others.
• the actuating means 5 are formed of a plurality of elementary piezoelectric actuators 5.1 arranged on the continuous ring C of piezoelectric material.
• the continuous crown C is located around the inner ring Cint.
• the piezoelectric actuators 5.1 are actuated by the opposite effect.
• the optical device may comprise auxiliary actuating means 5 'with at least one discontinuous auxiliary ring Caux made of piezoelectric material accommodating a plurality of auxiliary piezoelectric actuators 5.2 operating by a reverse effect.
• the auxiliary ring Caux is mounted concentrically with the continuous crown C. It can be located outside as in Figure 3F or inside. In order not to unnecessarily multiply the figures, the variant with the inner auxiliary ring has not been shown. But we can refer to Figure 3E to realize the pace that would have such a configuration if the actuators 70 functioned by the opposite effect.
• This auxiliary crown Caux is anchored to the membrane 2 in the intermediate zone 2.2, it can encroach on the anchoring zone 2.3 but not on the central zone 2.1.
• the auxiliary actuating means 5 ' also form with the membrane 2 at least one piezoelectric bimorph.
• the actuating means 5 comprise a continuous ring C accommodating several piezoelectric actuators and that this continuous ring C is provided on one of its peripheries with bars oriented radially, these bars accommodating elementary piezoelectric actuators 5.10.
• the bars can thus be oriented towards the inside of the crown C or towards the outside.
• This membrane 2 comprises at least three zones as has already been described, called anchor zone 2.3, intermediate zone 2.2 and central zone 2.1. moving from its edge to its center.
• the intermediate zone 2.2 is that which is directly solicited by the actuating means 5 and possibly by the auxiliary actuating means.
• the central zone 2.1 dedicated to the optical field is deformed by the movements of the fluid 4. This deformation being reversible, the material of this central zone 2.1 will work in the field of elastic deformation. Its transparency or, on the contrary, its reflective properties are chosen according to whether the optical device is a lens or a mirror.
• the membrane 2 is monolayer and homogeneous from the central zone 2.1 to the anchoring zone 2.3 (FIG. 4A). It may alternatively be multilayer as in FIG. 4B, the two layers being referenced 2a, 2b. It has two superposed layers 2a, 2b in the central zone 2.1, in the intermediate zone 2.2 and in a part of the anchoring zone 2.3. In this anchoring zone 2.3, the overlying layer 2a of the stack extends directly on the support 1 beyond the underlying layer 2b.
• the anchoring zone 2.3 of the membrane 2 must have its own adhesion properties on the support 1.
• the overlying layer 2a of FIG. 4B can be chosen to have better adhesion properties on the support 1 than the underlying layer 2b.
• the intermediate zone 2.2 of the membrane 2 may have properties making it possible to accentuate the deformation induced by the actuating means 5, which means that it will preferably be chosen with a rigidity greater than that of the central zone 2.1. There is an interaction between the membrane 2 and the actuating means 5 in the intermediate zone 2.2 since it is in this zone that the piezoelectric bimorph is located.
• the direction of the deflection of the membrane 2 in the central zone 2.1 depends on the difference in mechanical properties between the piezoelectric material and the material or materials of the membrane 2 on which the continuous ring of piezoelectric material is anchored.
• the direction of polarization and the position of the continuous ring in piezoelectric material are also important.
• the membrane 2 may therefore be heterogeneous with at least one so-called main layer 2b which occupies the central zone 2.1 and which extends continuously over the entire surface of the membrane 2 and at least one reinforcing layer 2c which does not extend only on a part of the membrane 2 of which at least the intermediate zone 2.2.
• FIG. 4C which illustrates this case, the main layer 2b extends over the entire surface of the membrane 2 and the reinforcing layer 2c extends, in this example, on the anchoring zone 2.3 and on the intermediate zone 2.2.
• the reinforcing layer 2c directly encroaches on the support 1 in the same manner as in FIG. 4B.
• the actuating means 5 have not been represented.
• FIGS. 5A to 5C the membrane 2 is shown monolayer, but this is not limiting. It is this layer of the membrane 2 which contributes to forming the piezoelectric bimorph B.
• the actuating means 5 are overlying the membrane 2, they extend over the intermediate zone 2.2 and the zone anchor 2.3 and extend directly on the support 1. They are without contact with the fluid 4 trapped between the membrane 2 and the support 1.
• FIGS. 5D, 5E show two cases where the actuating means 5 are not anchored to the support 1. They do not encroach on the anchoring zone 2.3 of the membrane 2.
• the membrane 2 is monolayer, but it could be multilayer.
• the actuating means 5 are above the membrane 2. They are not in contact with the fluid 4 trapped between the membrane 2 and the support 1.
• the actuating means 5 are underlying the membrane 2, they are in contact with the fluid 4 trapped between the membrane 2 and the support 1.
• FIGS. 5F 51 will now show examples in which the membrane comprises a main layer 2b which extends continuously from the central zone 2.1 to the anchoring zone 2.3 and, at the intermediate zone 2.2, a reinforcing layer 2c which may be overlying the main layer 2b as in Figures 5F, 51 or underlying as in Figures 5G, 5H.
• the actuating means 5 are inserted between the main layer 2b and the reinforcing layer 2c.
• the actuating means 5 and the reinforcing layer 2c are not in contact with the fluid 4 trapped between the membrane 2 and the support 1.
• the reinforcing layer 2c is more rigid than the main layer 2b, it is it which will contribute to forming the piezoelectric bimorph B.
• the main layer 2b becomes passive with regard to the mechanical phenomena involved.
• the main layer 2b is configured to be as flexible as possible so as to avoid overconsumption of energy during the actuation to obtain a deformed given.
• FIGS. 1A and 1C show different deformations for the same energy consumption and different flexibility of membrane 2.
• the reinforcing layer 2c is inserted between the actuating means 5 and the main layer 2b.
• the actuating means 5 and the reinforcing layer 2c are in contact with the fluid 4 trapped between the membrane 2 and the support 1.
• the actuating means 5 are inserted between the reinforcing layer 2c and the main layer 2b of the membrane 2.
• the actuating means 5 and the reinforcing layer 2c are in contact with the fluid 4 trapped between the membrane 2 and the support 1.
• the reinforcing layer 2c is inserted between the actuating means 5 and the main layer 2b.
• the actuating means 5 and the reinforcing layer 2c are not in contact with the fluid 4 trapped between the membrane 2 and the support 1.
• the actuating means 5 are indirectly anchored to the support 1.
• the actuating means 5 are overlying the main layer 2b of the membrane 2, they are anchored on the support 1, they extend over the anchoring zone 2.3 of the membrane 2.
• reinforcement layer 2c it is overlying the actuating means 5, it extends only on the intermediate zone 2.2 and does not impinge on the anchoring zone 2.3.
• the reinforcing layer 2c it is however possible for the reinforcing layer 2c to extend into the central zone 2.1 as in FIG. 5K if its optical reflection or transmission properties are compatible with the application of the optical device, that is to say with the lens or the mirror. It is of course in this case that the deformation of the membrane at the level of the reinforcing layer 2c is compatible with what is sought as deformed for the membrane.
• FIG. 5M there is a reinforcing layer 2c and the main layer 2b present at the central zone 2.1 is not continuous until the anchoring zone 2.3 as before. It extends at intermediate zone 2.2 but stops before anchor zone 2.3. The reinforcing layer 2c then takes over.
• this layer 2b which extends at the level of the central zone 2.1 is thicker at the level of the central zone 2.1 than at the intermediate zone 2.2.
• the assembly between the reinforcing layer 2c and the main layer 2b occupying the central zone 2.1 must be sufficiently sealed so that the fluid 4 that the support 1 and the membrane 2 contribute to imprisoning can not escape the cavity, even when the actuating means 5 are actuated.
• the actuating means are comparable to those illustrated in Figure 3C, one of the crowns referenced C is overlying the membrane 2 and the other referenced C is underlying.
• FIG. 5L is yet another example of an optical device according to the invention in which the actuating means 5 are not in contact with the fluid 4 trapped between the support 1 and the membrane 2, they are overlying the membrane 2 which is monolayer.
• the membrane 2, provided actuating means 5, is capped with a protective cover 201 which is sealed to the support 1 as shown in Figure 5L.
• This cover 201 delimits a cavity 6.
• the fixing can be done for example by molecular bonding, by organic bonding, by anodic bonding, by eutectic bonding an alloy layer for example Au / Si or Au / Sn for example being interposed between the cover 201 and the support 1 to be sealed. These bonding techniques are commonly used in the field of microelectronics and microsystems.
• the cover 201 defines a cavity 6 in which is trapped a second fluid 4 ', the upper face of the membrane 2, that is to say that which is not in contact with the first fluid 4, is in contact with the second fluid 4 '.
• the cover 201 at least in its central part, and the second fluid 4 'must be transparent for the incident optical radiation that will be reflected on the membrane 2, or pass through the nature of the optical device.
• the cover 201 may be made of glass or organic material such as polyethylene terephthalate PET, polyethylene naphthalate, polymethyl methacrylate PMMA, PC polycarbonate if it must transmit wavelengths in the visible.
• the cover 201 provides protection for the membrane 2 because such deformable membrane 2 optical devices are fragile objects whose handling is difficult.
• Support 1 can be monolithic as it has been represented since the beginning of this description. As a variant illustrated in FIG. 6A, it may be formed by a frame 1.5 integral with a plate 1.1 to form the bowl 3.
• the plate 1.1 materializes the bottom of the bowl 3, it is transparent to an optical radiation that will cross it or may be reflective in the case of a mirror.
• the membrane 2 There is no change in the membrane 2, the actuating means, the fluid 4 relative to what has been described above.
• the transparent plate 1.1 may be of substantially constant thickness, with substantially parallel plane faces, as in FIG. 6A. At least one face could be structured as in Figures 6B, 6C, 6D, where the outer face is convex or concave. The choice is made according to the optical performance sought for the optical device. It lets an optical radiation pass through the lens.
• the frame 1.5 may be of semiconductor material such as silicon, which makes it suitable for integrating circuits associated with the processing of the control of the actuating means 5. The circuits are not shown so as not to overload the figures.
• the transparent plate 1.1 may be glass or plastic.
• the transparent plate 1.1 has a convex structure and in FIG. 6D it has a concave structure.
• the structuring of the transparent plate 1.1 can be obtained by machining or by molding for example.
• the support 1 is materialized by the frame 1.5 and the transparent plate 1.1 is replaced by a second membrane 200.
• the second membrane 200 comprises a layer that has substantially the same surface as the first membrane 2.
• the two membranes 2 , 200 are anchored to the frame 1.5, each on one of its main faces. They contribute to producing a housing for the liquid 4. This makes it possible to increase the optical performance of the membrane 2.
• the actuating means 5 are provided on only one of the membranes 2.
• the other membrane 20 is not actuated, but it deforms anyway when the actuating means 5 are actuated.
• second actuating means are provided for actuating the other membrane 200.
• the optical device can be realized by known techniques in microelectronics. Thin layer deposition techniques of the chemical vapor deposition type, such as physical vapor deposition, epitaxy, thermal oxidation, evaporation and film rolling can be used. The organic materials or sol gel type can be deposited by spraying. Molding, embossing, hot-embossing, and nano-printing techniques can be employed to structure the underside of the substrate as shown in FIGS. 6B-6D. Bonding techniques can also be used for bonding the membrane 2 to the support 1 or a bottom 3 to the frame 1.5 or the cover 201 to the support 1, these techniques can for example be chosen from direct bonding, eutectic bonding, anodic bonding, organic bonding. Thinning steps for example by lapping, chemical thinning or combination of both types can be provided after the bonding of the bottom to the frame. The optical device can be manufactured in batches and all the covers 201 of the different devices can be made collectively.
• the membrane 2 can be made from organic materials such as polydimethylsiloxane, polymethyl methacrylate, polyethylene terephthalate, polycarbonate, parylene, epoxy resins, photosensitive polymers, silicones such as those known under the name SiNR de in Shin-Etsu or under the name WL5150 from Dow Corning or mineral materials, such as silicon, silicon oxide, silicon nitride, silicon carbide, polycrystalline silicon, titanium nitride, carbon diamond, tin and indium oxide, aluminum, copper, nickel.
• silicones such as those known under the name SiNR de in Shin-Etsu or under the name WL5150 from Dow Corning or mineral materials, such as silicon, silicon oxide, silicon nitride, silicon carbide, polycrystalline silicon, titanium nitride, carbon diamond, tin and indium oxide, aluminum, copper, nickel.
• the reinforcing layer could be made of a piezoelectric material chosen from those mentioned for the continuous ring.
• the piezoelectric bimorph would then be homogeneous.
• the membrane has a thickness ranging from micron to millimeter. The thickness chosen depends on the material used and the deposit method used.
• the reinforcing layer will have a thickness of between ten nanometers and a few micrometers.
• Each of the fluids 4, 4 ' can be a liquid such as propylene carbonate, water, a liquid index, an optical oil or an ionic liquid, or any liquid to obtain a refractive index jump. relative to the fluid 4 present on the other side of the membrane 2.
• a liquid such as propylene carbonate, water, a liquid index, an optical oil or an ionic liquid, or any liquid to obtain a refractive index jump. relative to the fluid 4 present on the other side of the membrane 2.
• gas mention may be made of air, nitrogen, helium for example.
• the piezoelectric material of the actuating means 5 may be chosen from PZT or Titano Lead Zirconate of formula Pb (Zr x , TiO x ) O 3, aluminum nitride AlN, polyvinylidene fluoride (PVDF) and its copolymers. of trifluoroethylene (TrFE), zinc oxide ZnO, barium titanate BaTiO 3 , lead niobate P bO 3 , bismuth titanate Bi 4 TiO 2 O 2 or other sillenites which are oxides with a metal ratio / oxygen equal to 2/3. It is sought that the piezoelectric material has the highest possible mechanical coupling coefficient.
• the thickness of the ring of piezoelectric material ranges from a few hundred nanometers to a few micrometers.
• the thickness is to be adapted to the range of bias voltages to be applied, to the associated breakdown field of the piezoelectric material and to the desired optical performance.
• the electrodes of the actuating means may be made of platinum, or a platinum titanium bilayer if it is to be deposited on an oxide, the titanium acting as an adhesive between the platinum and the oxide.
• Another suitable material is ruthenium. This list is not exhaustive. The characteristic thicknesses for the electrodes range from a few tens of nanometers to about one micron.
• a layer of piezoelectric material such as PZT requires annealing at high temperature of the order of 800 ° C. Often the membrane material does not support these temperatures. It is therefore first necessary to make the actuating means piezoelectric material and then assemble them to the membrane. During the manufacture of the optical device according to the invention, these constraints must be taken into account during the preparation of the stack.
• the inventors have realized that since the various materials constituting the optical device object of the invention did not have the same coefficient of thermal expansion, the focal length of the optical device could be caused to change unwantedly.
• thermal compensation means 95 are formed of one or more thermal continuous bimorph elements 95.1 arranged in a continuous ring anchored to the membrane 2 at the anchoring zone 2.3, overflowing on the intermediate zone 2.2, as in FIG. bottom level 3.1 of the bowl 3 as in Figure 7B.
• These thermal bimorph elements 95.1 are dedicated to this compensation. Under the effect of an increase in the temperature at the origin in particular of an increase in the volume of the fluid 4 trapped between the membrane 2 and the support 1, and therefore of an unwanted deformation of the membrane 2, the elements thermal bimorphs 95.1 deform to increase the volume of the bowl 3 by increasing its thickness.
• a thermal bimorph element 95.1 formed of two superimposed layers made of materials having different thermal expansion coefficients does not pose a problem to a person skilled in the art.
• the support 1 is similar to that of Figure 6B.
• the thermal bimorph elements 95.1 are located, fluid side 4, on the frame 1.5 and overflow on the transparent plate 1.1.
• the transparent plate 1.1 is concave in its central part and has striations at its periphery.
• An expansion joint 96 is inserted between the plate 1.1 and the frame 1.5 to give flexibility along the optical axis and allow the volume of the bowl 3 to increase. The increase in the volume of the bowl 3 will come from the deformation.
• the membrane 2 at the edge of the anchoring zone 2.3 and / or the support 1.
• the objective is that a dilation of the fluid 4 trapped between the membrane 2 and the support 1 has no influence on the boom of the membrane 2 in the central zone 2.1 and thus on the focal length of the optical device.
• the means Compensation 95 of a variation of the focal distance under the effect of a temperature variation contribute to that the membrane is subjected to a substantially constant residual stress, whatever the climatic conditions. This prevents buckling or wrinkling of the membrane 2 in the event of excessive compressive stress or, on the contrary, excessive tension having the effect of degrading the performance of the optical device.
• the optical device is all the more powerful for a given energy consumption that its central zone 2.1 is flexible.
• An organic silicone material is particularly suitable. It is then preferable to stiffen the membrane 2 at the intermediate zone 2.2 by providing the reinforcing layer 2c, for example of a mineral material such as silicon oxide and / or silicon nitride on the organic layer which is extends from the central zone 2.1 to the anchor zone 2.3.
• the reinforcing layer 2c for example of a mineral material such as silicon oxide and / or silicon nitride on the organic layer which is extends from the central zone 2.1 to the anchor zone 2.3.
• a membrane 2 whose central zone 2.1 is made of silicon oxide or silicon nitride would also be suitable.
• the actuating means 5 once fixed on the membrane 2 do not disturb the expected behavior of the membrane 2.
• the deformed membrane 2 at rest must be compatible with the use that one wants to do the optical device.
• the membrane 2 can, at rest, to form a substantially plane, concave or convex diopter.
• the membrane 2 is subjected to a residual compressive stress sufficiently low that does not cause crimping or buckling.
• the membrane 2 must be subjected to a voltage stress sufficiently low so that it responds effectively to one actuation of the actuating means 5, which would not be the case if it was put in excessive tension. A compromise is therefore to be found between stress in tension and in compression.
• the reinforcing layer 2c must be sufficiently rigid to pass on the fluid 4, trapped between the membrane 2 and the support 1, the pressure applied by the actuating means 5 and thus generate the movements of the desired fluid 4.
• Some materials that can be used for the backing layer are listed below. It can be metallic materials such as titanium, titanium nitride, aluminum whose thickness is of the order of ten nanometers to a few micrometers and whose Young's modulus is between a few tens from GPa to a few hundred GPa. It can be materials such as silicon oxide, silicon nitride whose thickness is of the order of ten nanometers to a few micrometers and whose Young's modulus is between a few tens of GPa a few hundred GPa. Finally, it can be organic materials such as polymers photosensitive and in particular benzocyclobutenes (BCB) whose thickness will be of the order of a few tens of micrometers and whose Young's modulus is a few GPa
• the substrate 100 may be, for example, glass (FIG. 8A). It forms the support 1.
• a sacrificial material 101 is deposited in the bowl 3 (FIG. 8B).
• the sacrificial material 101 may be organic, a photosensitive resin for example, or a mineral material such as silicon oxide.
• the membrane 2 is formed on the sacrificial material 101, so that it projects over the edge of the bowl 3 and anchors therein (FIG. 8C).
• a selected material may be deposited in the materials listed above for membrane 2. Deposition may be by spin coating or chemical vapor deposition.
• the actuating means 5 are then formed at the intermediate zone 2.2 having contact with the support 1 or not. Firstly, one or more electrodes underlying the piezoelectric material are produced, and then the corona is deposited. Continuous circular piezoelectric material and then the electrode or electrodes, knowing that in the end, it takes several pairs of electrodes. We did not refer to the crown or the electrodes so as not to overload the figures.
• the techniques employed are the conventional ones used in microsystems such as thin film deposition, lithography and etching ( Figure 8D).
• the membrane 2 is then released by eliminating the sacrificial material. For this, it is possible to drill at least one hole 107, out of the optical field (central zone 2.1), in the substrate 100 until reaching the sacrificial material 101.
• the hole 107 is through and opens into the bowl 3 (FIG. 8E) .
• the removal can be chemical or thermal or oxygen plasma.
• the bowl 3 is then filled with the fluid 4 (FIG. 8F).
• the filling can be done by putting the bowl 3 in depression to promote the penetration of the fluid 4 and avoid the formation of bubbles if it is a liquid.
• the hole 107 is re-opened so that the fluid 4 can not escape (FIG. 8F).
• An organic material can be used. The order of the steps is not limiting.
• the actuating means 5 could also be formed after the release of the membrane 2 for example, before filling or after. It is also possible to form them on the sacrificial layer 101 before forming the membrane 2, if they must be definitively on the side of the fluid 4 trapped between the support 1 and the membrane 2. In such a configuration, the membrane 2 is overlying the actuating means 5.
• the membrane 2 at rest is curved, concave or convex
• an appropriate curvature is given to the free face of the sacrificial layer 101, since it serves as a mold for the membrane 2.
• Another solution to obtain a curved membrane 2 would be to flambé after releasing it. Buckling can be thermal.
• the determining parameters are then the difference in coefficients of thermal expansion between the membrane 2 and the substrate and the deposition temperature of the membrane 2.
• the optical device of the invention is made by assembling a support 1 and a cover 201 as described in Figure 5L. It is not mandatory that the cover 201 be full, in Figure 8G, it recessed in its central part, the opening bears the reference 202. A J joint glue is used to assemble the support 1 and the cover 201.
• Such an optical device with variable focal length can be used in a shooting device including that of a mobile phone camera.
• a recording device includes, in cascade, a lens 80 including at least one optical device with a variable focal length L according to the invention of the liquid lens type, an image sensor 81, for example of the CCD or CMOS type, carried by a
• the objective lens 80 comprises at least one lens 83 with a fixed focal length and a liquid lens L according to the invention. Thereafter this fixed focal length lens 83 will be called conventional optical block.
• the liquid lens L is contiguous with the conventional optical block 83 on the image sensor 81 side.
• the conventional optical unit 83 can be located between the lens liquid L and the image sensor 81.
• the conventional optical unit 83 is static.
• the liquid lens L can be likened to a MOEMS (optoelectromechanical microsystem).
• MOEMS opticalelectromechanical microsystem
• the liquid L lens with variable focal length is placed at a distance, which depends on the characteristics of the objective 80, the image sensor 81, but if this distance is small, the liquid lens L and the image sensor 81 will be able to make only one component by integrating them either in AIC technology (abbreviation Anglo-Saxon Above Integrated Circuit for above the unequal circuit), or in WLCSP (English abbreviation of Wafer Level Chip Scale Package) or on slice at the chip scale).
• the focal length of the liquid lens L is adapted by optimizing the pressure of the liquid at rest, but also the curvature of the diaphragm 2 at rest and the refractive index of the liquid.
• the camera also includes the zoom function as in FIG. 15B
• use will be made of an optical unit 83 with at least two lenses of fixed focal length 83.1 and 83.2 and two liquid lenses L and L ', one of which is between the two lenses 83.1, 83.2 of the optical unit 83 and the other contiguous to the optical unit 83 on the side of the image sensor 81 as in FIG. 9B.
• the optical devices according to the invention referenced L and L ' are represented very schematically, we do not see their actuating means 5.
• an optical device according to the invention having a given size, one can maximize the surface of the actuating means 5 by using a single continuous ring of piezoelectric material which accommodates one or more piezoelectric actuators.
• the energy provided by the actuating means can be maximized, which makes it possible either to improve the displacements of the fluid and thus to improve the performance of the optical device with a constant supply voltage, or to minimize the supply voltage at equivalent optical performance.
• FIG. 10A shows a two-dimensional axisymmetric model of the diaphragm equipped with continuous crown actuating means.
• the membrane formed of a homogeneous parylene layer has a radius of 2 millimeters and a thickness of 1 micrometer.
• the continuous crown has a width of 500 micrometers and a thickness of one micrometer. It is performed in PZT. The continuous crown is anchored to the support in the anchoring zone.
• FIG. 10B is a cyclic three-dimensional model of the membrane equipped with a beam 50 at the micrometric scale.
• the membrane formed of a homogeneous parylene layer has a radius of 2 millimeters and a thickness of 1 micrometer.
• the beam has a length of 500 micrometers, a width of 100 micrometers and a thickness of 1 micrometer. It is performed in PZT. The beam is anchored to the support in the anchoring zone.
• the graph of FIG. 10C shows the evolution of the deflection of the membrane in the central zone as a function of the bias voltage applied to the actuating means.
• the curve referenced A corresponds to the continuous ring and the curve referenced B corresponds to the beam.
• the two curves A, B are secant, the point of intersection is denoted I.
• the first regime RI which corresponds to polarization voltages lower than approximately 0.32 V
• the beam gives the best arrows.
• the continuous ring is the victim of a rigidity effect which is at the origin of a loss energy efficiency.
• the difference between the arrows is even of the order of 25% for the lowest bias voltage (0.1 V).

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