Facebook Patent | Anti-Reflective Coatings For Transparent Electroactive Transducers
Patent: Anti-Reflective Coatings For Transparent Electroactive Transducers
Publication Number: 20200309995
Publication Date: 20201001
Applicants: Facebook
Abstract
An anti-reflective coating may include an optically transparent electrically conductive layer disposed over a substrate, and a dielectric layer disposed over the electrically conductive layer. The substrate may include an electroactive material. An optical element may include such an anti-reflective coating, where a primary anti-reflective coating may be disposed over a first surface of the electroactive layer and a secondary anti-reflective coating may be disposed over a second surface of the electroactive layer opposite the first surface.
BACKGROUND
[0001] Polymeric and other dielectric materials may be incorporated into a variety of optic and electro-optic device architectures, including active and passive optics and electroactive devices. Electroactive materials, including electroactive polymer (EAP) materials, for instance, may change their shape under the influence of an electric field. EAP materials have been investigated for use in various technologies, including actuation, sensing and/or energy harvesting. Lightweight and conformable, electroactive polymers may be incorporated into wearable devices such as haptic devices and are attractive candidates for emerging technologies including virtual reality/augmented reality devices where a comfortable, adjustable form factor is desired.
[0002] Virtual reality and augmented reality eyewear devices or headsets may enable users to experience events, such as interactions with people in a computer-generated simulation of a three-dimensional world or viewing data superimposed on a real-world view. Virtual reality/augmented reality eyewear devices and headsets may also be used for purposes other than recreation. For example, governments may use such devices for military training, medical professionals may use such devices to simulate surgery, and engineers may use such devices as design visualization aids.
[0003] These and other applications may leverage one or more characteristics of thin film electroactive materials, including the Poisson’s ratio to generate a lateral deformation (e.g., lateral expansion or contraction) as a response to compression between conductive electrodes. Example virtual reality/augmented reality assemblies containing electroactive layers may include deformable optics, such as mirrors, lenses, or adaptive optics. Deformation of the electroactive polymer may be used to actuate optical elements in an optical assembly, such as a lens system.
[0004] Although thin layers of many electroactive polymers and piezoceramics can be intrinsically transparent, in connection with their incorporation into an optical assembly or optical device, a variation in refractive index between such materials and adjacent layers, such as air, may cause light scattering and a corresponding degradation of optical quality or performance. Thus, notwithstanding recent developments, it would be advantageous to provide polymeric or other dielectric materials having improved actuation characteristics, including a controllable and robust deformation response in an optically transparent package.
SUMMARY
[0005] As will be described in greater detail below, the instant disclosure relates to actuatable and transparent optical elements and methods for forming such optical elements. The optical elements may include an anti-reflective coating that improves the optical clarity of the optical element while exhibiting mechanical stability, e.g., strain and/or fatigue tolerance, over multiple actuation cycles.
[0006] An optical element may include a layer of electroactive material sandwiched between conductive electrodes. The electroactive layer may include a polymer or ceramic material, for example, whereas the electrodes may each include one or more layers of any suitable conductive material(s), such as transparent conductive oxides (e.g., TCOs such as ITO), graphene, etc. In accordance with various embodiments, the optical transmissivity of an optical element may be improved by incorporating an anti-reflective coating (ARC) into the optical element geometry. For instance, layers of an anti-reflective coating may be disposed over either or both electrodes and may include one or more material layers used to decrease the gradient in refractive index between the electrode and an adjacent medium.
[0007] The electrodes, which may constitute a portion of the ARC coating, may be used to affect large scale deformation, i.e., via full-area coverage, or the electrodes may be patterned to provide spatially localized stress/strain profiles. In particular embodiments, a deformable optical element and an electroactive layer may be co-integrated whereby the deformable optic may itself be actuatable. In addition, various methods of forming optical elements are disclosed, including solution-based and solid-state deposition techniques.
[0008] In accordance with certain embodiments, an optical element including an electroactive layer disposed between transparent electrodes and also including an anti-reflective coating (ARC) may be incorporated into a variety of device architectures where capacitive actuation and the attendant strain realized in the electroactive layer (i.e., lateral expansion and compression in the direction of the applied electric field) may induce deformation in one or more adjacent active layers within the device and accordingly change the optical performance of the active layer(s). Lateral deformation may be essentially 1-dimensional, in the case of an anchored thin film, or 2-dimensional. In some embodiments, the engineered deformation of two or more electroactive layers that are alternatively placed in expansion and compression by oppositely applied voltages may be used to induce bending or curvature changes in a device stack, which may be used to provide optical tuning such as focus or aberration control.
[0009] According to various embodiments, an optical element may include an anti-reflective coating disposed over a substrate. The anti-reflective coating may include an optically transparent and electrically conductive layer, i.e., an electrode, and a dielectric layer disposed over the electrically conductive layer. As will be appreciated, the substrate may include an electroactive material.
[0010] The anti-reflective coating may be optically transparent and accordingly exhibit less than 10% haze and a transmissivity within the visible spectrum of at least 50%. For instance, the anti-reflective coating may be configured to maintain at least 50% transmissivity over 10.sup.6 actuation cycles and an induced engineering strain of up to approximately 1%. In some embodiments, the anti-reflective coating may exhibit a reflectivity within the visible spectrum of less than approximately 3%.
[0011] In some embodiments, the electrically conductive layer, i.e., an electrode, may be disposed over a portion of the substrate and may include a material such as a transparent conducting oxide (e.g., ITO), graphene, nanowires, or carbon nanotubes. A refractive index of the electrically conductive layer may be constant or may vary along at least one dimension thereof, e.g., the refractive index of the electrically conductive layer may vary as a function of its thickness. In some embodiments, an electrically conductive mesh may be disposed adjacent to the electrically conductive layer. The electrically conductive mesh may be less transparent than the electrically conductive layer but have an electrical conductivity greater than the electrically conductive layer.
[0012] The dielectric layer may include any suitable dielectric material(s), including silicon dioxide, zinc oxide, aluminum oxide, and/or magnesium fluoride, although additional dielectric materials are contemplated. In some embodiments, the dielectric layer may be configured as a multi-layer stack. By way of example, a multi-layer stack may include a layer of zinc oxide disposed directly over the electrically conductive layer and a layer of silicon dioxide disposed over the layer of zinc oxide. Additional layers may be used, such as in an architecture that includes alternating layers of a first dielectric material and a second dielectric material. Independent of the number of dielectric layers, according to some embodiments, a refractive index of the dielectric layer may be less than a refractive index of the electrically conductive layer, which, in turn, may be less than a refractive index of the substrate.
[0013] Also disclosed is an optical element that may include a transparent electroactive layer, a primary anti-reflective coating disposed over a first surface of the electroactive layer, and a secondary anti-reflective coating disposed over a second surface of the electroactive layer opposite the first surface. The primary anti-reflective coating may include a primary conductive layer disposed directly over the first surface of the electroactive layer and a primary dielectric layer disposed over the primary conductive layer, while the secondary anti-reflective coating may include a secondary conductive layer disposed directly over the second surface of the electroactive layer and a secondary dielectric layer disposed over the secondary conductive layer.
[0014] In some embodiments, the electroactive layer may include a piezoelectric polymer, an electrostrictive polymer, a piezoelectric ceramic, or an electrostrictive ceramic. The electroactive layer may include a polymer layer, such as a dielectric elastomer. Example polymer materials include a PVDF homopolymer, a P(VDF-TrFE) co-polymer, a P(VDF-TrFE-CFE) ter-polymer, or a P(VDF-TrFE-CTFE) ter-polymer. In further embodiments, the electroactive layer may include a ceramic layer, such as a piezoelectric ceramic, an electrostrictive ceramic, a polycrystalline ceramic, or a single crystal ceramic. Example electroactive ceramics may include one or more ferroelectric ceramics, such as perovskite ceramics.
[0015] In example optical elements, each of the primary anti-reflective coating and the secondary anti-reflective coating may be configured to maintain at least 50% transmissivity therethrough over 10.sup.6 actuation cycles and an accompanying engineering strain of up to approximately 1%. An optical element may further include a liquid lens or other optical element disposed over one of the primary dielectric layer and the secondary dielectric layer and may, in certain embodiments, be incorporated into a head-mounted display.
[0016] According to further embodiments, a method may include forming an electrically conductive layer over an electroactive substrate and forming a dielectric layer over the electrically conductive layer to form an optical element, where the optical element exhibits less than 10% haze and a transmissivity within the visible spectrum of at least 50%. In various methods, the electrically conductive layer and the dielectric layer may be formed sequentially or simultaneously, such as by co-extrusion.
[0017] In certain embodiments, an electroactive layer may be pre-stressed and thus exhibit a non-zero stress state when zero voltage is applied between the primary electrode and the secondary electrode.
[0018] Many electroactive materials, including various electroactive ceramics, have a relatively large refractive index (e.g., n>2). As will be appreciated, in optical devices including electroactive materials, a refractive index mismatch, i.e., a discontinuous change in the refractive index between such materials and air (n=1), for example, may create undesirable reflective losses.
[0019] In accordance with some embodiments, an anti-reflective coating may operate to gradually decrease the refractive index between that of the electroactive layer and an adjacent, typically lower index material. In various embodiments, an anti-reflective coating may include multiple layers of varying refractive index and/or one or more layers having a refractive index gradient. In some embodiments, an optically transparent electrically conductive layer, i.e., an electrode, may be incorporated into the anti-reflective coating.
[0020] In optical elements having a multi-layer architecture, an optical element may include a tertiary electrode overlapping at least a portion of the secondary electrode, and a second electroactive layer disposed between and abutting the secondary electrode and the tertiary electrode. In an example device, one of the first electroactive layer and the second electroactive layer may be in a state of lateral compression while the other of the first electroactive layer and the second electroactive layer may be in a state of lateral expansion.
[0021] Features from any of these or other embodiments may be used in combination with one another in accordance with the general principles described herein. These and other embodiments, features, and advantages will be more fully understood upon reading the following detailed description in conjunction with the accompanying drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] 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 instant disclosure.
[0023] FIG. 1 is an illustration of an anti-reflective coating including a dielectric layer disposed over an electrically conductive layer according to some embodiments.
[0024] FIG. 2 shows an anti-reflective coating having a pair of dielectric layers disposed over an electrically conductive layer according to some embodiments.
[0025] FIG. 3 shows an anti-reflective coating having a dielectric layer disposed over a pair of electrically conductive layers according to some embodiments.
[0026] FIG. 4 depicts an anti-reflective coating configured as a multi-layer stack according to certain embodiments.
[0027] FIG. 5 depicts an anti-reflective coating configured as a multi-layer stack according to further embodiments.
[0028] FIG. 6 is an illustration of an anti-reflective coating including a graded index dielectric layer disposed over an electrically conductive layer according to some embodiments.
[0029] FIG. 7 is an illustration of an anti-reflective coating including a dielectric layer having a textured surface disposed over an electrically conductive layer according to certain embodiments.
[0030] FIG. 8 shows an optical element having an anti-reflective coating disposed over opposing surfaces according to some embodiments.
[0031] FIG. 9 is a schematic illustration of an example head-mounted display according to various embodiments.
[0032] FIG. 10 is an illustration of an exemplary artificial-reality headband that may be used in connection with embodiments of this disclosure.
[0033] FIG. 11 is an illustration of exemplary augmented-reality glasses that may be used in connection with embodiments of this disclosure.
[0034] FIG. 12 is an illustration of an exemplary virtual-reality headset that may be used in connection with embodiments of this disclosure.
[0035] 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 instant disclosure covers all modifications, equivalents, and alternatives falling within the scope of the appended claims.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0036] The present disclosure is generally directed to optical elements, and more particularly to optical elements that include an electroactive layer with an anti-reflective coating (ARC) formed over at least one surface thereof. The electroactive layer may be capacitively actuated to deform an optical element and hence modify its optical performance. By way of example, the optical element may be located within the transparent aperture of an optical device such as a liquid lens, although the present disclosure is not particularly limited and may be applied in a broader context. By way of example, the optical element may be incorporated into an active grating, tunable lens, accommodative optical elements, or adaptive optics and the like. According to various embodiments, the optical element may be optically transparent.
[0037] As used herein, a material or element that is “transparent” or “optically transparent” may, for example, have a transmissivity within the visible light spectrum of at least approximately 50%, e.g., approximately 50, 60, 70, 80, 90, 95, 97, 98, 99, or 99.5%, including ranges between any of the foregoing values, and less than approximately 80% haze, e.g., approximately 1, 2, 5, 10, 20, 30, 40, 50, 60 or 70% haze, including ranges between any of the foregoing values. In accordance with some embodiments, a “fully transparent” material or element may have a transmissivity (i.e., optical transmittance) within the visible light spectrum of at least approximately 80%, e.g., approximately 80, 90, 95, 97, 98, 99, or 99.5%, including ranges between any of the foregoing values, and less than approximately 10% haze, e.g., approximately 0, 1, 2, 4, 6, or 8% haze, including ranges between any of the foregoing values.
[0038] In accordance with various embodiments, an optical element may include a primary electrode, a secondary electrode overlapping at least a portion of the primary electrode, and an electroactive layer disposed between and abutting the primary electrode and the secondary electrode, where the optical element is at least partially optically transparent. One or more additional dielectric layers forming an anti-reflective coating may be disposed over either or both surfaces of the electroactive layer. The electroactive layer may include one or more electroactive materials.
Electroactive Materials
[0039] An optical element may include one or more electroactive materials, such as electroactive polymers or ceramics and may also include additional components. As used herein, “electroactive materials” may, in some examples, refer to materials that exhibit a change in size or shape when stimulated by an electric field. In some embodiments, an electroactive material may include a deformable polymer or ceramic that may be symmetric with regard to electrical charge (e.g., polydimethylsiloxane (PDMS), acrylates, etc.) or asymmetric (e.g., poled polyvinylidene fluoride (PVDF) or its copolymers such as poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE)). Further PVDF-based polymers may include poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P(VDF-TrFE-CFE)) or poly(vinylidenefluoride-trifluoroethylene-chlorotrifluoroethylene (P(VDF-TrFE-CTFE)).
[0040] For piezoelectric polymers like PVDF homopolymer, the piezoelectric response may be tuned by altering the crystalline content and the crystalline orientation within the polymer matrix, e.g., by uniaxial or biaxial stretching, optionally followed by poling. The origin of piezoelectricity in PVDF homopolymer is believed to be the .beta.-phase crystallite polymorph, which is the most electrically active and polar of the PVDF phases. Alignment of the .beta.-phase structure may be used to achieve the desired piezoelectric effect. Poling may be performed to align the .beta.-phase and enhance the piezoelectric response. Other piezoelectric polymers, such as PVDF-TrFE and PVDF-TrFE-CFE may be suitably oriented upon formation and the piezoelectric response of such polymers may be improved by poling with or without stretching.
[0041] Additional examples of materials forming electroactive polymers may include, without limitation, styrenes, polyesters, polycarbonates, epoxies, halogenated polymers, such as PVDF, copolymers of PVDF, such as PVDF-TrFE, silicone polymers, and/or any other suitable polymer or polymer precursor materials including ethyl acetate, butyl acrylate, octyl acrylate, ethylethoxy ethyl acrylate, 2-chloroethyl vinyl ether, chloromethyl acrylate, methacrylic acid, dimethacrylate oligomers, isocyanates, allyl glycidyl ether, N-methylol acrylamide, or mixtures thereof. Example acrylates may be free-radical initiated. Such materials may have any suitable dielectric constant or relative permittivity, such as, for example, a dielectric constant ranging from approximately 2 to approximately 30.
[0042] In the presence of an electrostatic field (E-field), an electroactive material may deform (e.g., compress, elongate, bend, etc.) according to the magnitude and direction of the applied field. Generation of such a field may be accomplished, for example, by placing the electroactive material between two electrodes, i.e., a primary electrode and a secondary electrode, each of which is at a different potential. As the potential difference (i.e., voltage difference) between the electrodes is increased (e.g., from zero potential) the amount of deformation may also increase, principally along electric field lines. This deformation may achieve saturation when a certain electrostatic field strength has been reached. With no electrostatic field, the electroactive material may be in its relaxed state undergoing no induced deformation, or stated equivalently, no induced strain, either internal or external.
[0043] In some instances, the physical origin of the compressive nature of electroactive materials in the presence of an electrostatic field (E-field), being the force created between opposite electric charges, is that of the Maxwell stress, which is expressed mathematically with the Maxwell stress tensor. The level of strain or deformation induced by a given E-field is dependent on the square of the E-field strength, as well as the dielectric constant and elastic compliance of the electroactive material. Compliance in this case is the change of strain with respect to stress or, equivalently, in more practical terms, the change in displacement with respect to force. In some embodiments, an electroactive layer may be pre-strained (or pre-stressed) to modify the stiffness of the optical element and hence its actuation characteristics.
[0044] In some embodiments, an electroactive polymer may include an elastomer. As used herein, an “elastomer” may, in some examples, refer to a material having viscoelasticity (i.e., both viscosity and elasticity), relatively weak intermolecular forces, and generally low elastic modulus (a measure of the stiffness of a solid material) and a high strain-to-failure compared with other materials. In some embodiments, an electroactive polymer may include an elastomer material that has an effective Poisson’s ratio of less than approximately 0.35 (e.g., less than approximately 0.3, less than approximately 0.25, less than approximately 0.2, less than approximately 0.15, less than approximately 0.1, or less than approximately 0.05). In at least one example, the elastomer material may have an effective density that is less than approximately 90% (e.g., less than approximately 80%, less than approximately 70%, less than approximately 60%, less than approximately 50%, less than approximately 40%) of the elastomer when densified (e.g., when the elastomer is compressed, for example, by electrodes to make the elastomer more dense).
[0045] In some embodiments, the term “effective density,” as used herein, may refer to a parameter that may be obtained using a test method where a uniformly thick layer of an electroactive ceramic or polymer, e.g., elastomer, may be placed between two flat and rigid circular plates. In some embodiments, the diameter of the electroactive material being compressed may be at least 100 times the thickness of the electroactive material. The diameter of the electroactive layer may be measured, then the plates may be pressed together to exert a pressure of at least approximately 1x10.sup.6 Pa on the electroactive layer, and the diameter of the layer is remeasured. The effective density may be determined from an expression (DR =Duncompressed I Dcompressed), where DR may represent the effective density ratio, Duncompressed may represent the density of the uncompressed electroactive layer, and Dcom.sub.pressed may represent the density of the compressed electroactive layer.
[0046] In some embodiments, the optical elements described herein may include an elastomeric electroactive polymer having an effective Poisson’s ratio of less than approximately 0.35 and an effective uncompressed density that is less than approximately 90% of the elastomer when densified. In some embodiments, the term “effective Poisson’s ratio” may refer to the negative of the ratio of transverse strain (e.g., strain in a first direction) to axial strain (e.g., strain in a second direction) in a material.
Electrodes
[0047] In some embodiments, optical elements may include paired electrodes, which allow the creation of the electrostatic field that forces constriction of the electroactive layer. In some embodiments, an “electrode,” as used herein, may refer to an electrically conductive material, which may be in the form of a thin film or a layer. Electrodes may include relatively thin, electrically conductive metals or metal alloys and may be of a non-compliant or compliant nature.
[0048] In some embodiments, the electrodes may include a metal such as aluminum, gold, silver, tin, copper, indium, gallium, zinc, alloys thereof, and the like. An electrode may include one or more electrically conductive materials, such as a metal, a semiconductor (such as a doped semiconductor), carbon nanotubes, graphene, carbon black, transparent conductive oxides (TCOs, e.g., indium tin oxide (ITO), zinc oxide (ZnO), etc.), or other electrically conducting material. Further example transparent conductive oxides include, without limitation, aluminum-doped zinc oxide, fluorine-doped tin oxide, indium-doped cadmium oxide, indium zinc oxide, indium gallium tin oxide, indium gallium zinc tin oxide, and indium zinc tin oxide.
[0049] In some embodiments, the electrode or electrode layer may be self-healing, such that damage from local shorting of a circuit can be isolated. Suitable self-healing electrodes may include thin films of materials which deform or oxidize irreversibly upon Joule heating, such as, for example, graphene.
[0050] In some embodiments, a primary electrode may overlap (e.g., overlap in a parallel direction) at least a portion of a secondary electrode. The primary and secondary electrodes may be generally parallel and spaced apart and separated by a layer of electroactive material. A tertiary electrode may overlap at least a portion of either the primary or secondary electrode.
[0051] An optical element may include a first electroactive layer (e.g., elastomer material) which may be disposed between a first pair of electrodes (e.g., the primary electrode and the secondary electrode). A second optical element, if used, may include a second electroactive layer and may be disposed between a second pair of electrodes. In some embodiments, there may be an electrode that is common to both the first pair of electrodes and the second pair of electrodes.
[0052] In some embodiments, one or more electrodes may be optionally electrically interconnected, e.g., through a contact layer, to a common electrode. In some embodiments, an optical element may have a first common electrode, connected to a first plurality of electrodes, and a second common electrode, connected to a second plurality of electrodes. In some embodiments, electrodes (e.g., one of a first plurality of electrodes and one of a second plurality of electrodes) may be electrically isolated from each other using an insulator, such as a dielectric layer. An insulator may include a material without appreciable electrical conductivity, and may include a dielectric material, such as, for example, an acrylate or silicone polymer.
[0053] In some embodiments, a common electrode may be electrically coupled (e.g., electrically contacted at an interface having a low contact resistance) to one or more other electrode(s), e.g., a secondary electrode and a tertiary electrode located on either side of a primary electrode.
[0054] In some embodiments, electrodes may be flexible and/or resilient and may stretch, for example elastically, when an optical element undergoes deformation. In this regard, electrodes may include one or more transparent conducting oxides (TCOs) such as indium oxide, tin oxide, indium tin oxide (ITO) and the like, graphene, carbon nanotubes, etc. In other embodiments, relatively rigid electrodes (e.g., electrodes including a metal such as aluminum) may be used.
[0055] In some embodiments, the electrodes (e.g., the primary electrode and the secondary electrode) may have a thickness of approximately 0.35 nm to approximately 1000 nm, e.g., approximately 0.35, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, 500, or 1000 nm, including ranges between any of the foregoing values, with an example thickness of approximately 10 nm to approximately 50 nm. In some embodiments, a common electrode may have a sloped shape, or may be a more complex shape (e.g., patterned or freeform). In some embodiments, a common electrode may be shaped to allow compression and expansion of an optical element or device during operation.
[0056] The electrodes in certain embodiments may have an optical transmissivity of at least approximately 50%, e.g., approximately 50%, approximately 60%, approximately 70%, approximately 80%, approximately 90%, approximately 95%, approximately 97%, approximately 98%, approximately 99%, or approximately 99.5%, including ranges between any of the foregoing values.
[0057] In some embodiments, the electrodes described herein (e.g., the primary electrode, the secondary electrode, or any other electrode including any common electrode) may be fabricated using any suitable process. For example, the electrodes may be fabricated using physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), evaporation, spray-coating, spin-coating, dip-coating, screen printing, Gravure printing, ink jet printing, aerosol jet printing, doctor blading, and the like. In further aspects, the electrodes may be manufactured using a thermal evaporator, a sputtering system, stamping, and the like.
[0058] In some embodiments, a layer of electroactive material may be deposited directly on to an electrode. In some embodiments, an electrode may be deposited directly on to the electroactive material. In some embodiments, electrodes may be prefabricated and attached to an electroactive material. In some embodiments, an electrode may be deposited on a substrate, for example a glass substrate or flexible polymer film. In some embodiments, the electroactive material layer may directly abut an electrode. In some embodiments, there may be a dielectric layer, such as an insulating layer, between a layer of electroactive material and an electrode. Any suitable combination of processes and/or structures may be used.
Dielectric Materials
[0059] According to some embodiments, an anti-reflective coating may include a conductive electrode, as described above, and one or more dielectric layers disposed over the electrode.
[0060] According to certain embodiments, a dielectric layer may include a material such as silicon dioxide, zinc oxide, aluminum oxide, and/or magnesium fluoride, although additional dielectric materials may be used. For instance, the dielectric layer may include one or more compounds selected from AlO.sub.3, Bi.sub.2O.sub.3, CeO.sub.2, Cr.sub.2O.sub.3, HfO.sub.2, In.sub.2O.sub.3, MgO, MoO.sub.3, La.sub.2O.sub.3, Nd.sub.2O.sub.3, PbO, SiO.sub.2, Sm.sub.2O.sub.3, SnO.sub.2, Ta.sub.2O.sub.5, TiO.sub.2, Ti.sub.4O.sub.2, Ti.sub.3O.sub.5, Ti.sub.2O.sub.3, TiO, WO.sub.3, Y.sub.2O.sub.3, ZrO.sub.2, ZnO, BaF.sub.2, CaF.sub.2, CeF.sub.3, AlF.sub.3, BaF.sub.2, CaF.sub.2, CaF.sub.3, LaF.sub.3, LiF, MgF.sub.2, NaF, PbF.sub.2, SmF.sub.3, SrF.sub.2, and YF.sub.3.
[0061] In some embodiments, the anti-reflective coating may include combinations of one or more of the aforementioned oxides and/or one or more of the aforementioned fluorides. Example anti-reflective coatings may include: (a) one of the above-identified oxides, (b) one of the above-identified fluorides, (c) two of the above-identified oxides, (d) one of the above-identified oxides combined with one of the above-identified fluorides, (e) two of the above-identified oxides combined with one of the above-identified fluorides, (f) two of the above-identified oxides combined with two of the above-identified fluorides, or (g) three of the above-identified oxides.
[0062] In some embodiments, the dielectric layer may include a first oxide layer, a second oxide layer, and an optional third oxide layer, where each of the oxide layers may include an oxide compound independently selected from AlO.sub.3, Bi.sub.2O.sub.3, CeO.sub.2, Cr.sub.2O.sub.3, HfO.sub.2, In.sub.2O.sub.3, MgO, MoO.sub.3, La.sub.2O.sub.3, Nd.sub.2O.sub.3, PbO, SiO.sub.2, Sm.sub.2O.sub.3, SnO.sub.2, Ta.sub.2O.sub.5, TiO.sub.2, Ti.sub.4O.sub.2, Ti.sub.3O.sub.5, Ti.sub.2O.sub.3, TiO, WO.sub.3, Y.sub.2O.sub.3, ZrO.sub.2, and ZnO.
[0063] In further embodiments, the dielectric layer may include a first layer including an oxide compound selected from AlO.sub.3, Bi.sub.2O.sub.3, CeO.sub.2, Cr.sub.2O.sub.3, HfO.sub.2, In.sub.2O.sub.3, MgO, MoO.sub.3, La.sub.2O.sub.3, Nd.sub.2O.sub.3, PbO, SiO.sub.2, Sm.sub.2O.sub.3, SnO.sub.2, Ta.sub.2O.sub.5, TiO.sub.2, Ti.sub.4O.sub.2, Ti.sub.3O.sub.5, Ti.sub.2O.sub.3, TiO, WO.sub.3, Y.sub.2O.sub.3, ZrO.sub.2, and ZnO, and a second layer including a fluoride compound selected from BaF.sub.2, CaF.sub.2, CeF.sub.3, AlF.sub.3, BaF.sub.2, CaF.sub.2, CaF.sub.3, LaF.sub.3, LiF, MgF.sub.2, NaF, PbF.sub.2, SmF.sub.3, SrF.sub.2, and YF.sub.3. In some embodiments, the first layer may be disposed directly over the electroactive layer and the second layer may be disposed directly over the first layer. In other embodiments, the second layer may be disposed directly over the electroactive layer and the first layer may be disposed directly over the second layer.
[0064] In still further embodiments, the dielectric layer may include first and second oxide layers each independently selected from AlO.sub.3, Bi.sub.2O.sub.3, CeO.sub.2, Cr.sub.2O.sub.3, HfO.sub.2, In.sub.2O.sub.3, MgO, MoO.sub.3, La.sub.2O.sub.3, Nd.sub.2O.sub.3, PbO, SiO.sub.2, Sm.sub.2O.sub.3, SnO.sub.2, Ta.sub.2O.sub.5, TiO.sub.2, Ti.sub.4O.sub.2, Ti.sub.3O.sub.5, Ti.sub.2O.sub.3, TiO, WO.sub.3, Y.sub.2O.sub.3, ZrO.sub.2, and ZnO, and a third layer including a fluoride compound selected from BaF.sub.2, CaF.sub.2, CeF.sub.3, AlF.sub.3, BaF.sub.2, CaF.sub.2, CaF.sub.3, LaF.sub.3, LiF, MgF.sub.2, NaF, PbF.sub.2, SmF.sub.3, SrF.sub.2, and YF.sub.3. For such a structure, the third (fluoride) layer may be disposed between the first and second (oxide) layers. Alternatively, the third (fluoride) layer may be disposed between one of the oxide layers and the electroactive layer.
[0065] In certain embodiments, two or more dielectric layers may be formed sequentially. Alternatively, the dielectric materials may be co-deposited. For instance, the above-described combinations of oxides and fluorides may be deposited simultaneously rather than as discrete, sequential layers. Moreover, according to some embodiments, the composition of a dielectric layer may be varied spatially, e.g., throughout its thickness, by changing the relative ratio(s) of two or more co-deposited compounds. For each of the embodiments described, the oxide(s) and/or fluoride(s) in a given layer of the anti-reflective coating may be the same as or different than the oxide(s) and/or fluoride(s) in other layers.
[0066] A dielectric layer may have any suitable thickness, including, for example, a thickness of approximately 10 nm to approximately 1000 nm, e.g., approximately 10, 20, 50, 100, 200, 500, or 1000 nm, including ranges between any of the foregoing values, with an example thickness range of approximately 50 nm to approximately 100 nm.
[0067] In various embodiments, the dielectric layer(s) may be fabricated using any suitable process. For example, the dielectric layer(s) may be fabricated using physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), evaporation, spray-coating, spin-coating, dip-coating, screen printing, Gravure printing, ink jet printing, aerosol jet printing, doctor blading, and the like. In further aspects, the electrodes may be manufactured using a thermal evaporator, a sputtering system, stamping, and the like.
Optical Elements
[0068] In some applications, an optical element used in connection with the principles disclosed herein may include a primary electrode, a secondary electrode, and an electroactive layer disposed between the primary electrode and the secondary electrode. An anti-reflective coating (ARC), which may include the primary electrode or the secondary electrode as well as one or more additional dielectric layers, may be formed over respective surfaces of the electroactive layer.
[0069] In some embodiments, there may be one or more additional electrodes, and a common electrode may be electrically coupled to one or more of the additional electrodes. For example, optical elements may be disposed in a stacked configuration, with a first common electrode coupled to a first plurality of electrodes, and a second common electrode electrically connected to a second plurality of electrodes. The first and second pluralities may alternate in a stacked configuration, so that each optical element is located between one of the first plurality of electrodes and one of the second plurality of electrodes.
[0070] In some embodiments, an optical element may have a thickness of approximately 10 nm to approximately 300 .mu.m (e.g., approximately 10 nm, approximately 20 nm, approximately 30 nm, approximately 40 nm, approximately 50 nm, approximately 60 nm, approximately 70 nm, approximately 80 nm, approximately 90 nm, approximately 100 nm, approximately 200 nm, approximately 300 nm, approximately 400 nm, approximately 500 nm, approximately 600 nm, approximately 700 nm, approximately 800 nm, approximately 900 nm, approximately 1 .mu.m, approximately 2 .mu.m, approximately 3 .mu.m, approximately 4 .mu.m, approximately 5 .mu.m, approximately 6 .mu.m, approximately 7 .mu.m, approximately 8 .mu.m, approximately 9.mu.m, approximately 10 .mu.m, approximately 20 .mu.m, approximately 50 .mu.m, approximately 100 .mu.m, approximately 200 .mu.m, or approximately 300 .mu.m), with an example thickness of approximately 200 nm to approximately 500 nm.
[0071] The application of a voltage between the electrodes can cause compression or expansion of the intervening electroactive layer(s) in the direction of the applied electric field and an associated expansion or contraction of the electroactive layer(s) in one or more transverse dimensions. In some embodiments, an applied voltage (e.g., to the primary electrode and/or the secondary electrode) may create at least approximately 0.1% strain (e.g., an amount of deformation in the direction of the applied force resulting from the applied voltage divided by the initial dimension of the material) in the electroactive element(s) in at least one direction (e.g., an x, y, or z direction with respect to a defined coordinate system).
[0072] In some embodiments, the electroactive response may include a mechanical response to the electrical input that varies over the spatial extent of the device, with the electrical input being applied between the primary electrode and the secondary electrode. The mechanical response may be termed an actuation, and example devices or optical elements may be, or include, actuators.
[0073] The optical element may be deformable from an initial state to a deformed state when a first voltage is applied between the primary electrode and the secondary electrode and may further be deformable to a second deformed state when a second voltage is applied between the primary electrode and the secondary electrode.
[0074] An electrical signal may include a potential difference, which may include a direct or alternating voltage. In some embodiments, the frequency may be higher than the highest mechanical response frequency of the device, so that deformation may occur in response to the applied RMS electric field but with no appreciable oscillatory mechanical response to the applied frequency. The applied electrical signal may generate non-uniform constriction of the electroactive layer between the primary and secondary electrodes. A non-uniform electroactive response may include a curvature of a surface of the optical element, which may in some embodiments be a compound curvature.
[0075] In some embodiments, an optical element may have a maximum thickness in an undeformed state and a compressed thickness in a deformed state. In some embodiments, an optical element may have a density in an undeformed state that is approximately 90% or less of a density of the optical element in the deformed state. In some embodiments, an optical element may exhibit a strain of at least approximately 0.1% when a voltage is applied between the primary electrode and the secondary electrode.
[0076] In some embodiments, an optical device may include one or more optical elements, and an optical element may include one or more electroactive layers. In various embodiments, an optical element may include a primary electrode, a secondary electrode overlapping at least a portion of the primary electrode, and an electroactive layer disposed between the primary electrode and the secondary electrode.
[0077] In some embodiments, the application of an electric field over an entirety of an electroactive layer may generate substantially uniform deformation between the primary and secondary electrodes. In some embodiments, the primary electrode and/or the secondary electrode may be patterned, allowing a localized electric field to be applied to a portion of the optical element, for example, to provide a localized deformation.
[0078] An optical device may include a plurality of stacked elements. For example, each element may include an electroactive layer disposed between a pair of electrodes. In some embodiments, an electrode may be shared between elements; for example, a device may have alternating electrodes and an electroactive layer located between neighboring pairs of electrodes. Various stacked configurations can be constructed in different geometries that alter the shape, alignment, and spacing between elements. Such complex arrangements can enable compression, extension, twisting, and/or bending when operating such an actuator.
[0079] In some embodiments, an optical device may include additional elements interleaved between electrodes, such as in a stacked configuration. For example, electrodes may form an interdigitated stack of electrodes, with alternate electrodes connected to a first common electrode and the remaining alternate electrodes connected to a second common electrode. An additional optical element may be disposed on the other side of a primary electrode. The additional optical element may overlap a first optical element. An additional electrode may be disposed abutting a surface of any additional optical element.
[0080] In some embodiments, an optical device may include more (e.g., two, three, or more) such additional electroactive layers and corresponding electrodes. For example, an optical device may include a stack of two or more optical elements and corresponding electrodes. For example, an optical device may include between 2 optical elements to approximately 5, approximately 10, approximately 20, approximately 30, approximately 40, approximately 50, approximately 100, approximately 200, approximately 300, approximately 400, approximately 500, approximately 600, approximately 700, approximately 800, approximately 900, approximately 1000, approximately 2000, or greater than approximately 2000 optical elements.
Fabrication of Optical Elements
[0081] Various fabrication methods are discussed herein. As will be appreciated by one skilled in the art, the disclosed fabrication methods may be used to form one or more layers or features within an optical element, including organic (i.e., polymeric) and inorganic (i.e., ceramic) electroactive materials, transparent conductive electrodes disposed adjacent to such electroactive materials, and one or more dielectric layers. In certain embodiments, the structure and properties of an optical element may be varied, e.g., across a spatial extent, by varying one or more process parameters, such as wavelength, intensity, substrate temperature, other process temperature, gas pressure, radiation dosage, chemical concentration gradients, chemical composition variations, or other process parameter(s).
[0082] According to some embodiments, deposition methods, including spin-coating, screen printing, inkjet printing, evaporation, chemical vapor deposition, vapor coating, physical vapor deposition, thermal spraying, extrusion, hydrothermal synthesis, Czochralski growth, isostatic pressing, lamination, etc., may be used to form an electroactive layer, electrode and/or dielectric layer. In certain embodiments, an electrode may be deposited directly onto an electroactive layer and a dielectric layer may be deposited directly onto the electrode. In alternate embodiments, an electroactive layer may be deposited onto a provisional substrate and transferred to an electrode or an electroded substrate.
[0083] In some embodiments, an electroactive layer, an electrode or a dielectric layer may be fabricated on a surface (e.g., substrate) enclosed by a deposition chamber, which may be evacuated (e.g., using one or more mechanical vacuum pumps to a predetermined level such as 10.sup.-6 Torr or below). A deposition chamber may include a rigid material (e.g., steel, aluminum, brass, glass, acrylic, and the like). A surface used for deposition may include a rotating drum. In some embodiments, the rotation may generate centrifugal energy and cause the deposited material to spread more uniformly over any underlying sequentially deposited materials (e.g., electrodes, polymer elements, ceramic elements, and the like) that are mechanically coupled (e.g., bonded) to the surface. In some embodiments, the surface may be fixed and deposition and curing systems may move relative to the surface, or both the surface, the deposition, and/or curing systems may be moving simultaneously.
[0084] In some embodiments, a deposition chamber may have an exhaust port configured to open to release at least a portion of reaction by-products, as well as monomers, oligomers, monomer initiators, conductive materials, etc. associated with the formation of one or more material layers. In some embodiments, a deposition chamber may be purged (e.g., with a gas or the application of a vacuum, or both) to remove such materials. Thereafter, one or more of the previous steps may be repeated (e.g., for a second optical element, and the like). In this way, individual layers of an optical element may be maintained at high purity levels.
[0085] In some embodiments, the deposition of the materials (e.g., monomers, oligomers, monomer initiators, conductive materials, dielectric layers, etc.) of the optical element may be performed using a deposition process, such as chemical vapor deposition (CVD). CVD may refer to a vacuum deposition method used to produce high-quality, high-performance, solid materials. In CVD, a substrate may be exposed to one or more precursors, which may react and/or decompose on the substrate surface to produce the desired deposit (e.g., one or more electrodes, electroactive polymer layers, etc.). Frequently, volatile by-products are also produced, which may be removed by gas flow through the chamber.
[0086] In some embodiments, methods for fabricating an optical element (e.g., an actuator) may include masks (e.g., shadow masks) to control the patterns of one or more deposited materials.
[0087] Methods of forming an optical element include forming a dielectric layer, electrodes and an electroactive layer sequentially (e.g., via vapor deposition, coating, printing, etc.) or simultaneously (e.g., via co-flowing, coextrusion, slot die coating, etc.). By way of example, an electroactive layer may be deposited using initiated chemical vapor deposition (iCVD), where suitable monomers of the desired polymers may be used to form the desired coating. According to a further example, a co-extrusion process having a high drawing ratio may enable the formation of plural thin layers (e.g., electroactive layers, electrode layers and/or dielectric layers), which may be used to form a multi-morph architecture from a larger billet of electroactive, conductive, and optionally passive support materials. Alternatively, the electroactive layers may be extruded individually.
[0088] A method of fabricating an optical element may include depositing a curable material onto a primary electrode, curing the deposited curable material to form an electroactive layer (e.g., including a cured elastomer material) and depositing an electrically conductive material onto a surface of the electroactive layer opposite the primary electrode to form a secondary electrode. A dielectric layer may, in turn, be deposited over one or both of the primary electrode and the secondary electrode. In some embodiments, a method may further include depositing an additional curable material onto a surface of the secondary electrode opposite the electroactive layer, curing the deposited additional curable material to form a second electroactive layer including a second cured elastomer material, and depositing an additional electrically conductive material onto a surface of the second electroactive layer opposite the secondary electrode to form a tertiary electrode. In such case, a dielectric layer may be deposited over the tertiary electrode.
[0089] In some embodiments, a method of fabricating an optical element may include vaporizing a curable material, or a precursor thereof, where depositing the curable material may include depositing the vaporized curable material onto a primary electrode. In some embodiments, a method of fabricating an optical element may include printing the polymer or precursor thereof (such as a curable material) onto an electrode. In some embodiments, a method may also include combining a polymer precursor material with at least one other component to form a deposition mixture. In some embodiments, a method may include combining a curable material with particles of a material having a high dielectric constant to form a deposition mixture.
[0090] According to some embodiments, a method may include positioning a curable material between a first electrically conductive material or layer and a second electrically conductive material or layer. The positioned curable material may be cured to form a cured elastomer material. In some embodiments, the cured elastomer material may have a Poisson’s ratio of approximately 0.35 or less. In some embodiments, at least one of the first electrically conductive material or the second electrically conductive material may include a curable electrically conductive material, and the method may further include curing the at least one of the first electrically conductive material or the second electrically conductive material to form an electrode. In this example, curing the at least one of the first electrically conductive material or the second electrically conductive material may include curing the at least one of the first electrically conductive material or the second electrically conductive material during curing of the positioned curable material.
[0091] In some embodiments, a curable material and at least one of a first electrically conductive material or a second electrically conductive material may be flowable during positioning of the curable material between the primary and secondary electrodes. A method of fabricating an optical element may further include flowing a curable material and at least one of the first electrically conductive material or the second electrically conductive material simultaneously onto a substrate.
[0092] In some embodiments, an optical element (e.g., actuator) may be fabricated by providing an electrically conductive layer (e.g., a primary electrode) having a first surface, depositing (e.g., vapor depositing) an electroactive layer or precursor layer onto the primary electrode, and depositing another electrically conductive layer (e.g., a secondary electrode) onto the electroactive (or precursor) layer. In some embodiments, the method may further include repeating one or more of the above to fabricate additional layers (e.g., a second optical element, other electrodes, alternating stacks of electroactive layers and electrodes, and the like. An optical device may have a stacked configuration. In some embodiments, the method may include depositing a dielectric layer over the primary electrode or over the secondary electrode on respective surfaces opposite the electroactive layer.
[0093] In some embodiments, an optical element may be fabricated by first depositing a primary electrode, and then depositing a curable material (e.g., a monomer) on the primary electrode (e.g., deposited using a vapor deposition process). In some embodiments, an inlet to a deposition chamber may open and may input an appropriate monomer initiator for starting a chemical reaction. In some embodiments, “monomer,” as used herein, may refer to a monomer that forms a given polymer (i.e., as part of an electroactive element). In other examples, polymerization (i.e., curing) of a polymer precursor such as a monomer may include exposure to electromagnetic radiation (e.g., visible, UV, x-ray or gamma radiation), exposure to other radiation (e.g., electron beams, ultrasound), heat, exposure to a chemical species (such as a catalyst, initiator, and the like), or some combination thereof.
[0094] Deposited curable material may be cured with a source of radiation (e.g., electromagnetic radiation, such as UV radiation and/or visible light) to form an electroactive polymer layer that includes a cured elastomer material, for example by photopolymerization. In some embodiments, a radiation source may include an energized array of filaments that may generate electromagnetic radiation, a semiconductor device such as a light-emitting diode (LED) or semiconductor laser, other laser, fluorescence or an optical harmonic generation source, and the like. A monomer and an initiator (if used) may react upon exposure to radiation to form an electroactive element.
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