Facebook Patent | High reliability varifocal electrostatic lens

Patent: High reliability varifocal electrostatic lens

Drawings: Click to check drawins

Publication Number: 20210080688

Publication Date: 20210318

Applicant: Facebook

Abstract

A varifocal lens includes a substrate having an inclined region, a primary electrode disposed over the inclined region of the substrate, a dielectric layer disposed over the primary electrode, a deformable membrane disposed over and at least partially spaced away from the dielectric layer, a secondary electrode disposed over a surface of the deformable membrane facing toward or away from the dielectric layer and overlying at least a portion of the primary electrode, and a fluid between the membrane and the substrate, wherein a surface of the dielectric layer facing the secondary electrode comprises a textured surface.

Claims

1. A varifocal lens comprising: a substrate having an inclined region; a primary electrode disposed over the inclined region of the substrate; a dielectric layer disposed over the primary electrode; a deformable membrane disposed over and at least partially spaced away from the dielectric layer; a secondary electrode disposed over a surface of the deformable membrane facing toward or away from the dielectric layer and overlying at least a portion of the primary electrode; and a primary fluid between the deformable membrane and the substrate, wherein a surface of the dielectric layer facing the secondary electrode comprises a textured surface.

2. The varifocal lens of claim 1, wherein the inclined region is located peripheral to an optically active area of the lens.

3. The varifocal lens of claim 2, further comprising a secondary fluid located outside of the optically active area.

4. The varifocal lens of claim 3, wherein the secondary fluid is in fluid communication with the primary fluid.

5. The varifocal lens of claim 1, wherein a slope of the inclined region varies as a function of position.

6. The varifocal lens of claim 1, wherein the primary electrode is bonded to the inclined region of the substrate.

7. The varifocal lens of claim 1, wherein the deformable membrane is bonded to the substrate.

8. The varifocal lens of claim 1, wherein the secondary electrode is bonded to the surface of the deformable membrane.

9. The varifocal lens of claim 1, wherein a surface of the dielectric layer facing the secondary electrode comprises one or more fluid channels.

10. The varifocal lens of claim 1, wherein a thickness of the deformable membrane varies with position.

11. The varifocal lens of claim 1, further comprising an elastic spacer located between the primary electrode and the secondary electrode.

12. The varifocal lens of claim 1, further comprising a barrier coating disposed over at least one surface of the deformable membrane.

13. The varifocal lens of claim 1, further comprising a hydrophilic layer disposed over the secondary electrode facing the dielectric layer and a hydrophobic layer disposed over the dielectric layer facing the secondary electrode.

14. An actuator assembly comprising: a primary substrate having an inclined region; a primary electrode affixed to the inclined region of the primary substrate; a secondary electrode disposed over and spaced away from the primary electrode, the secondary electrode affixed to a secondary substrate; and an elastic spacer disposed between and contacting each of the primary electrode and the secondary electrode.

15. The actuator assembly of claim 14, wherein the secondary substrate comprises a deformable transparent membrane.

16. The actuator assembly of claim 14, further comprising a dielectric layer disposed over the primary electrode.

17. The actuator assembly of claim 14, further comprising a dielectric layer disposed over the primary electrode and spaced away from the elastic spacer.

18. The actuator assembly of claim 14, wherein the inclined region comprises a peripheral area of the primary substrate.

19. A method comprising: forming a primary electrode directly over an inclined region of a primary substrate; forming a secondary electrode directly over a secondary substrate, the secondary substrate located over and at least partially spaced away from the primary electrode; applying a first voltage gradient between the primary electrode and the secondary electrode to decrease a distance between the secondary substrate and the primary substrate within the inclined region; and applying a second voltage gradient less than the first voltage gradient to increase the distance between the secondary substrate and the primary substrate within the inclined region.

20. The method of claim 19, further comprising applying a mechanical force to the secondary substrate during the act of applying the second voltage.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C. .sctn. 119(e) of U.S. Provisional Application No. 62/901,748, filed Sep. 17, 2019, the contents of which are incorporated herein by reference in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The accompanying drawings illustrate a number of exemplary embodiments and are a part of the specification. Together with the following description, these drawings demonstrate and explain various principles of the present disclosure.

[0003] FIG. 1 is a cross-sectional schematic illustration of a varifocal electrostatic lens including a dielectric layer disposed between conductive electrodes and over a sloped support located peripheral to an optically active area of the lens according to some embodiments.

[0004] FIG. 2 is a cross-sectional schematic illustration of a varifocal electrostatic lens having a sloped support defined by a quadratic Bezier curve according to some embodiments.

[0005] FIG. 3 shows the stable variation in optical power with applied voltage for the sloped support lens design shown in FIG. 2 averaged over two optical zones according to some embodiments.

[0006] FIG. 4 shows the temporal response of the optical power for a varifocal electrostatic lens associated with the application and removal of an applied voltage according to certain embodiments.

[0007] FIG. 5 shows a sloped support design for an exemplary 3D varifocal lens according to some embodiments.

[0008] FIG. 6 shows the height of the sloped support for the exemplary 3D varifocal lens of FIG. 5 according to some embodiments.

[0009] FIG. 7 illustrates a segment of a sloped support according to certain embodiments.

[0010] FIG. 8 shows a side view of the sloped support of FIG. 7 with contour lines having a variable z-coordinate according to certain embodiments.

[0011] FIG. 9 is a schematic illustration showing the effects of applying a first voltage to the varifocal electrostatic lens of FIG. 1 according to some embodiments.

[0012] FIG. 10 is a schematic illustration showing the effects of stiction when applying a second voltage subsequent to and less than the first voltage according to some embodiments.

[0013] FIG. 11 is a schematic illustration showing the effects of both a mechanical force applied via a transducer and a second applied voltage on the varifocal electrostatic lens of FIG. 1 according to some embodiments.

[0014] FIG. 12 shows a cross-sectional schematic view of a varifocal electrostatic lens having a pinhole defect in the dielectric layer according to certain embodiments.

[0015] FIG. 13 shows a varifocal electrostatic lens having a self-healing electrode according to some embodiments.

[0016] FIG. 14 depicts a varifocal electrostatic lens having a deformable membrane with a radially-dependent thickness according to various embodiments.

[0017] FIG. 15 shows a varifocal electrostatic lens having a textured dielectric layer according to some embodiments.

[0018] FIG. 16 is a plot of normalized specific effective bonding energy versus an adhesion parameter for the dielectric layer-electrode interface of an example varifocal electrostatic lens according to some embodiments.

[0019] FIG. 17 is a plot showing the effect of a pulsed drive voltage on the operation of an example varifocal electrostatic lens according to various embodiments.

[0020] FIG. 18 is a plan view of an example varifocal electrostatic lens having a profiled electrode according to certain embodiments.

[0021] FIG. 19 shows exemplary cross-sectional views of various support profiles for the lens of FIG. 18 according to some embodiments.

[0022] FIG. 20 is a plan view showing a varifocal electrostatic lens having segmented electrodes according to some embodiments.

[0023] FIG. 21 is a plan view illustration showing a varifocal electrostatic lens having segmented electrodes according to further embodiments.

[0024] FIG. 22 is a schematic illustration of a constant voltage amplitude, variable frequency drive scheme for a varifocal electrostatic lens according to some embodiments.

[0025] FIG. 23 illustrates cross-sectional views of example segmented electrode geometries, including electrodes formed over a sloped support and having (A) a constant width, (B) a radially-dependent width, and (C) a width that varies with azimuthal angle according to certain embodiments.

[0026] FIG. 24 shows the incorporation of fluid channels into the dielectric layer of a varifocal electrostatic lens architecture according to some embodiments.

[0027] FIG. 25 is a cross-sectional schematic view of an elastic spacer disposed between and separating a pair of conductive electrodes of a varifocal electrostatic lens according to some embodiments.

[0028] FIG. 26 shows a dielectric layer overlying a primary electrode and an elastic spacer disposed between and separating the primary electrode from a secondary electrode according to various embodiments.

[0029] FIG. 27 illustrates the formation of a defect extending through the dielectric layer of FIG. 26 and into the primary electrode according to some embodiments.

[0030] FIG. 28 shows the incorporation of a dielectric fluid over the dielectric layer of the structure of FIG. 26 according to some embodiments.

[0031] FIG. 29 depicts the flow of the dielectric fluid into the defect extending through the dielectric layer and into the primary electrode according to certain embodiments.

[0032] FIG. 30 shows a dielectric layer overlying a primary electrode and spaced away from an elastic spacer disposed between and separating the primary electrode from a secondary electrode according to various embodiments.

[0033] FIG. 31 is a plan view of an example varifocal electrostatic lens having a profiled electrode according to certain embodiments.

[0034] FIG. 32 is a contour map showing the displacement field for an example varifocal electrostatic lens according to some embodiments.

[0035] FIG. 33 is a contour map showing the surface optical power for an example varifocal electrostatic lens according to some embodiments.

[0036] FIG. 34 illustrates sectional profiles of an example varifocal lens showing variation in the electrode profile angle and membrane displacement as a function of position according to certain embodiments.

[0037] FIG. 35 is a plot of vertical displacement versus location for the varifocal electrostatic lens of FIG. 34 according to some embodiments.

[0038] FIG. 36 shows a contour plot of two forms of tolerancing errors in the height of a sloped support for an exemplary circular varifocal electrostatic lens according to some embodiments.

[0039] FIG. 37 shows the error in average optical power and cylindricity as a function of applied voltage resulting from the sloped support tolerances depicted in FIG. 36 according to some embodiments.

[0040] FIG. 38 shows the incorporation of a reinforcement layer over a top surface of a lens membrane according to various embodiments.

[0041] FIG. 39 is a plot of maximum radial strain on a top surface of a lens membrane with and without the reinforcement layer of FIG. 38 according to some embodiments.

[0042] FIG. 40 shows the relationship between optical power and voltage as a function of the thickness of a compliant electrode according to some embodiments.

[0043] FIG. 41 shows a plot of the maximum strain on an electrode as a function of electrode thickness according to some embodiments.

[0044] FIG. 42 shows a cross-sectional view of an example support profile containing a secondary fluid volume according to some embodiments.

[0045] FIG. 43 shows a cross-sectional schematic illustration of a varifocal electrostatic lens including a separate fluid volume located over a sloped support peripheral to an optically active area of the lens according to some embodiments.

[0046] FIG. 44 is a schematic illustration showing the effects of applying a first voltage to the varifocal electrostatic lens of FIG. 43 according to some embodiments.

[0047] FIG. 45 is an illustration of exemplary augmented-reality glasses that may be used in connection with embodiments of this disclosure.

[0048] FIG. 46 is an illustration of an exemplary virtual-reality headset that may be used in connection with embodiments of this disclosure.

[0049] FIG. 47 is an illustration of exemplary haptic devices that may be used in connection with embodiments of this disclosure.

[0050] FIG. 48 is an illustration of an exemplary virtual-reality environment according to embodiments of this disclosure.

[0051] FIG. 49 is an illustration of an exemplary augmented-reality environment according to embodiments of this disclosure.

[0052] Throughout the drawings, identical reference characters and descriptions indicate similar, but not necessarily identical, elements. While the exemplary embodiments described herein are susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, the exemplary embodiments described herein are not intended to be limited to the particular forms disclosed. Rather, the present disclosure covers all modifications, equivalents, and alternatives falling within the scope of the appended claims.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0053] The present disclosure is directed generally to liquid lenses and more particularly to adjustable liquid lenses having electrostatically-driven membranes. Adjustable lenses may be used to vary the focal length in exemplary optical systems. In accordance with various embodiments, an adjustable lens may be implemented using the principle of electrostatic zipping of a fluid filled pouch, where a laterally-moving zipping actuator may be used to generate displacement of a lens membrane and tunable operation of the lens.

[0054] Electrostatic zipping actuators may be implemented in various devices, including liquid lenses, to provide high forces and large displacements. As will be appreciated, however, such actuators may disadvantageously exhibit high pull-in voltages due in part to a minimum achievable electrode gap. In addition, in certain aspects, dynamic fluid flow particularly through small channels or gaps within the lens and/or static friction such as between one or more actuator electrodes and an intervening dielectric layer may inhibit the realization of continuously-tunable, rapidly adjustable operation. Moreover, defects in the dielectric layer, which are ubiquitous in the manufacture of such materials or which may be formed during operation, may adversely affect the electrical performance of the electrostatic actuator. Notwithstanding recent developments, the realization of high reliability varifocal electrostatic lenses capable of rapid and repeated actuation would be beneficial.

[0055] The following will provide, with reference to FIGS. 1-49, detailed descriptions of adjustable liquid lens architectures and systems using adjustable lenses. The discussion associated with FIGS. 1-15 includes a description of example varifocal electrostatic lens geometries and their design during various modes of operation. The discussion associated with FIG. 16 includes a description of the adhesion dynamics between components of an electrostatically operated lens. The discussion associated with FIG. 17 includes a description of an example driving scheme for a varifocal electrostatic lens according to certain embodiments. The discussion associated with FIGS. 18-23 includes a description of example electrode configurations in accordance with various embodiments. The discussion associated with FIG. 24 includes a description of the implementation of drainage channels to mediate the hydrodynamics of a lens fluid during various modes of operation of an electrostatic lens. The discussion associated with FIGS. 25-30 includes a description of varifocal electrostatic lens architectures including an elastic spacer located between paired electrodes. The discussion associated with FIGS. 31-35 includes a description of displacement profiles for a further example varifocal electrostatic lens. The discussion associated with FIGS. 36 and 37 includes a description of the sensitivity in optical performance of varifocal lenses to geometric tolerances in the electrode shape. The discussion associated with FIGS. 38 and 39 relates to the effect of adding a reinforcement layer to the top surface of a lens membrane. The discussion associated with FIGS. 40 and 41 relates to the effect of electrode thickness on the performance of a varifocal lens. The discussion associated with FIGS. 42-44 includes a description of the addition of a secondary fluid volume to the varifocal electrostatic lens design. The discussion associated with FIGS. 45-49 relates to exemplary virtual reality and augmented reality device architectures that may include one or more varifocal electrostatic lenses as disclosed herein.

[0056] An electrostatic lens may include a pair of conductive electrodes and one or more dielectric layers disposed between the electrodes where the electrode-dielectric layer-electrode stack may be located proximate to a transparent membrane of a liquid lens. Referring to FIG. 1, an example electrostatic lens 100 may include a transparent substrate 110, an inclined (i.e., sloped) support 120 located peripheral to an optical aperture 112 of lens 100, a primary electrode 130 disposed over the sloped support 120, and a dielectric layer 140 disposed over the primary electrode 130. A deformable transparent membrane 150 may extend over the optical aperture 112 of the lens and may include a secondary electrode (not shown) located on either the bottom (inner) or top (outer) surface of the transparent membrane 150 and proximate to the primary electrode 130.

[0057] In various aspects, a surface of the support 120 may be “inclined” with respect to a major surface of the membrane 150. The secondary electrode may be located within a peripheral region of the transparent membrane, outside of the optical aperture 112, for example. Transparent membrane 150 may be configured to contain a dielectric fluid (i.e., lens fluid) 125 between the membrane 150 and the substrate 110.

[0058] The geometry of a sloped support (e.g., sloped support 120) may be designed using a Bezier curve. A Bezier curve may be defined by a set of control points P.sub.0 through P.sub.n that determine its shape. In accordance with various embodiments, a quadratic or higher order Bezier curve (e.g., created using control points P.sub.0-P.sub.3) may be used to model and design the profile of a sloped support so as to generate a stable optical response in the electrostatic lens during reversible actuation. As used herein, a “stable” optical response may, in certain examples, refer to a monotonic and continuous increase in optical power with an increase in applied voltage.

[0059] By way of example, and with reference to FIG. 2, a sloped support 220 may be modeled as a quadratic Bezier curve, which enables a stable optical response during the zipping and unzipping of overlying membrane 250. A plot of optical power versus voltage for the sloped support design of FIG. 2 is shown in FIG. 3. Furthermore, with reference to FIG. 4, such a lens may also be stable when the applied voltage is removed. In the plot of FIG. 4, a voltage is applied over the normalized time range of 0 to 1, held constant over the normalized time range of >1 to 2, then gradually removed over the normalized time range of >2 to 3, and maintained at zero for normalized time >3.

[0060] A sloped support design for an exemplary 3D varifocal lens shape is shown in FIGS. 5 and 6. Referring to FIG. 5 and sloped support 500, circumferential contours 501-507 illustrate the edge of the zipped region of an overlying membrane for successive applied voltages. The profile shape is shown also in the top-down plan view of FIG. 6. According to certain embodiments, each contour line (also referred to herein as a design line) (e.g., contour lines 501-507) may correspond to the edge of the pulled down region of the membrane for a given applied voltage.

[0061] In the example of a non-circular lens, and with reference to FIGS. 7 and 8, sloped support 700 may include individual design lines 701, 702, etc. that may have a non-circular shape in the plane of the lens and, as shown in FIG. 8, a variable height in the direction (e.g., z-direction) normal to the lens. As will be appreciated, a sloped support may be designed so that a continuum of design lines may be accessed by applying a steadily varying DC voltage, or so that a discrete set of design lines may be accessed using a segmented electrode.

[0062] The sloped support may be elastic or inelastic and configured to accommodate bending of the membrane during actuation. In embodiments where bending of the membrane is non-negligible, an offset may be incorporated into the sloped support prior to the membrane engaging a first design line, e.g., during a zipping operation.

[0063] In certain embodiments, the one or more design lines (e.g., contour lines 501-507) may each correspond to a target lens shape. A target lens shape may be spherical or non-spherical, for example. In certain embodiments, the spacing between adjacent design lines may be configured so that a local gradient within the sloped support results in an equilibrium position for the overlying membrane when a particular voltage is applied. For a sloped support with negligible curvature, a constant “peel angle” may be realized between the sloped support and the membrane. A correction to the peel angle may be used when the sloped support surface has significant local curvature. During design, such a correction may be derived experimentally or empirically using calculations that represent the electrostatic forces on the lens. Additional corrections may be implemented based on the local shape and corresponding stress state of the membrane.

[0064] According to some embodiments, the sloped support design lines may have a height such that for each target lens shape, the volume of fluid enclosed by the lens is constant if the fluid is incompressible and there is no fluid exchange with a secondary fluid or with a secondary fluid volume. For a compressible fluid, on the other hand, the fluid volume (and pressure) may change to maintain the target lens shape.

[0065] According to some embodiments, by applying a voltage to one or more of the electrodes (i.e., the primary electrode and the secondary electrode), the resulting voltage gradient may create an electrostatic force that attracts transparent membrane 150 (including the attached secondary electrode) to the primary electrode 130. The electrostatic attraction and the effect of the attendant displacement on the lens shape is illustrated schematically in the electrostatic lens 900 of FIG. 9, where under the application of a first voltage (V1), transparent membrane 150 may be drawn to support 120 forming an attached region 180 with transition points 160, 170 that are each associated with a particular design line, inducing curvature in the transparent membrane 150. The electrostatically-induced displacement of the transparent membrane 150 and the attendant redistribution of fluid 125 between the substrate 110 and the transparent membrane 150 may induce a desired degree of curvature 135 in the membrane and a corresponding change in the focal power of the lens 900.

[0066] A liquid lens may include an optical liquid material, i.e., dielectric fluid, adapted to change its shape. According to certain embodiments, dielectric fluid 125 disposed between the substrate 110 and the membrane 150 may include siloxanes, phenylated compounds (e.g., polyphenylthioethers, polyphenylethers such as 3-, 4-, 5- and 6-ring polyphenyl ethers, phenylmethyl silicone fluids, and polyol esters), naphthalated compounds (e.g., naphthalenesulfonic acid and sodium alkyl naphthalene sulfonate), compounds containing halogens, phosphorus, or sulfur (e.g., sulfonate salts, arsenic trisulphide, diphenyl sulphide, carbon disulphide, and the like), polyimidothioethers (e.g., polyimidothioether, polyphenylthioethers, polyphenyl ethers, phenylated siloxane oils, naphthalated hydrocarbons, phenylated siloxane polymers, phenylated silicone fluids, and the like), nanoparticle suspensions (e.g., suspensions of anatase, rutile, ZnO, or SiO.sub.2), and nanocomposite, high refractive index polymers (e.g., TiO.sub.2 particles bound to a polyimidothioether), for example. The dielectric fluids disclosed herein may be characterized by a dielectric constant of at least approximately 5, e.g., at least 5, at least 10, at least 20, or at least 50, including ranges between any of the foregoing values.

[0067] Substrate 110 may include a transparent material, such as a polycarbonate, polyacrylate, or epoxy composition within an optically active area thereof. In certain embodiments, substrate 110 may include a peripheral non-transparent region. A non-transparent region of the substrate, e.g., a portion of the substrate located outside of optical aperture 112 under support 120, may include any suitable polymer, metal, or other mechanically stable material such as carbon fibers. According to various embodiments, the substrate 110 may include regions that are planar, concave, or convex.

[0068] The electrodes (i.e., the primary electrode and the secondary electrode) may include one or more electrically conductive materials, such as a metal, carbon nanotubes, graphene, oxidized graphene, fluorinated graphene, hydrogenated graphene, other graphene derivatives, carbon black, and transparent conductive oxides (TCOs, e.g., indium oxide, indium tin oxide (ITO), indium zinc oxide, zinc oxide (ZnO), tin oxide, indium gallium zinc oxide, etc.). Example metals suitable for forming the electrodes may include aluminum, silver, copper, gold, or platinum, as well as alloys thereof. The conductive material(s) may be in the form of nanoparticles, nanoflakes, nanowires, and other structured shapes. In some embodiments, the electrodes may have an electrical conductivity of approximately 50 S/cm to approximately 60.times.10.sup.4 S/cm. The electrodes (i.e., the primary electrode and the secondary electrode) may be formed using any suitable deposition process, such as a sol gel process, screen printing, inkjet printing, vacuum sputtering, and the like.

[0069] According to some embodiments, the electrodes (e.g., the primary electrode and the secondary electrode) may have an average thickness of approximately 10 nm to approximately 10 .mu.m, e.g., 10, 20, 50, 100, 200, 500, 1000, 2000, 5000, or 10000 nm, including ranges between any of the foregoing values.

[0070] In certain embodiments, a method of controlling the surface roughness of an electrode may include forming the electrode on a highly smooth surface, separating the electrode from the highly smooth surface to reveal an electrode smooth surface, inverting the electrode, and bonding the electrode to a transparent membrane with the electrode smooth surface exposed.

[0071] The electrodes (i.e., the primary electrode and/or the secondary electrode) in some embodiments may be configured to stretch elastically. The electrode(s) may be formed with a corrugated or ribbed structure that allows deformation without mechanical or electrical failure, e.g., during zipping or unzipping of the membrane. In some embodiments, an electrode may include a polymer composite including a low surface tension polymer matrix having conductive particles dispersed throughout the matrix. The polymer matrix may include silicones, acrylates, silicone-acrylates, and other elastomers. Example low surface tension polymers may include poly(tetrafluoroethylene), polyvinylidene fluoride, or poly(dimethyl siloxane). Example conductive particles may include metal nanoparticles, metal nanowires, graphene nanoparticles, graphene flakes, transparent conducting oxide nanoparticles, and the like. The electrodes may include a graphene composite. Further example electrodes may include poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).

[0072] In some embodiments, as disclosed further herein, an electrode may be formed over the transparent membrane prior to, or after stretching the membrane. In certain embodiments, a curing step may be used to form the electrodes. The act of curing, which may include heating or exposure to actinic radiation (e.g., UV light, visible light, e-beam radiation, or x-rays) may be performed before or after stretching the membrane.

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