Multilayer reflective module, and associated system and associated manufacturing method

Abstract

The invention relates to a multilayer reflective module (1) for a motor vehicle part, the module comprising a first substrate (10), a multilayer stack (13) arranged on the first substrate (10) and configured to reflect a reflected light beam (2') having a determined wavelength, the multilayer stack (13) comprising at least one layer forming a metal mirror (14), a Fabry-Pérot layer (15) configured to form, by the Fabry-Pérot effect, the light beam (2') reflected by the metal mirror, the layer (15) having a nanometric thickness (d15), and a metal layer (16) overlying the Fabry-Pérot layer, the metal layer (16) being discontinuous on the nanometric scale so as to generate a localised surface plasmon resonance effect.

Description

Multilayer reflective module, associated system and manufacturing process

[0001] The present invention relates to the field of reflective multilayer modules. Its particularly advantageous application lies in the field of vehicle bodywork or signaling, especially for vehicle front parts or for the interior of such vehicles. STATE OF THE ART

[0002] It is common to display a design or visual element on a vehicle part, either for decoration or signaling purposes. This is achieved using paints or colored elements. Current commercial colors are limited by their instability in the atmosphere, color fading, and environmental toxicity. One can explore more stable, ecological, and / or economical solutions that utilize ambient light, at least during the day.

[0003] To achieve this, there are multilayer reflective modules configured to reflect a portion of the visible spectrum and thus emit a specific color. Modules exploiting the Fabry-Pérot cavity effect are particularly well-known. In a Fabry-Pérot cavity, a reflected color, called the "structural color," appears when light is confined within a nanometric cavity bounded by two roughly parallel surfaces. These modules comprise a substrate on which a stack is formed, including at least one reflective mirror layer and one Fabry-Pérot absorber layer, for example, a conductive polymer layer. The thickness of the absorber layer typically determines the wavelengths of the reflected light beam that will emerge from the polymer layer through interference. These specific wavelengths correspond to a color in the visible spectrum and reach the observer's eyes.He therefore has the impression that the layer of material has a particular color.

[0004] A multilayer electroactive reflective module for an automotive part is described in document WO2025021836A1. The module comprises a first substrate, a multilayer stack interposed between two electrodes, the multilayer stack itself including a metallic mirror, a Fabry-Pérot cavity based on a conductive polymer, a solid polymer electrolyte, and a counter electrode. However, this solution can prove relatively complex to implement. Furthermore, the perceived color intensity for a user remains limited in this solution.

[0005] One object of the present invention is therefore to provide a solution improving the reflection of a reflective module comprising a Fabry-Pérot cavity, and more particularly to improve the vibrancy of the color perceived by a user

[0006] The other objects, features, and advantages of the present invention will become apparent from an examination of the following description and accompanying drawings. It is understood that other advantages may be incorporated. SUMMARY

[0007] To achieve this objective, according to a first aspect, a multilayer reflective module is planned for an automotive part, the module comprising: a first substrate, a multilayer stack arranged on the first substrate and configured to receive an incident light beam presenting a light spectrum and reflect a reflected light beam having a determined wavelength, the multilayer stack comprising: at least one layer forming a metallic mirror, a polymer-based layer, called a "Fabry-Pérot" layer, surmounting the metallic mirror, and configured to form, by the Fabry-Pérot effect, the light beam reflected on the metallic mirror, said layer having a nanometric thickness.

[0008] Advantageously, the multilayer stacking further includes a metallic layer on top of the Fabry-Pérot layer, the metallic layer being discontinuous at the nanoscale so as to generate a localized surface plasmon resonance effect.

[0009] Thus, the free electrons in the discontinuous metallic layer can resonate with the incident light through a localized surface plasmon resonance (LSPR) effect. Coupling with the electrons in the metallic mirror, this induces hybridization, modifying the electric field applied to the Fabry-Pérot cavity and thereby altering the reflected wavelength. The absorbance of the Fabry-Pérot cavity is increased across a large portion of the visible spectrum. This increased absorbance across a part of the visible spectrum enhances the perceived color intensity.

[0010] Furthermore, this near-point-like variation in electron density within the discontinuous metallic layer possesses the symmetry of an oscillating dipole. The incident beam can resonate with the localized surface plasmon regardless of the angle of incidence. Therefore, the increase in color intensity is not dependent on the viewing angle, as can be the case in other solutions employing layers configured to act as broadband absorbers.

[0011] The dimensions of the discontinuous metallic layer can also be adjusted to modulate the wavelength of the beam reflected by the Fabry-Pérot cavity, and therefore the color perceived by the user. This makes it possible to modify the perceived color without having to adjust the thickness of the Fabry-Pérot layer.

[0012] The reflective module can therefore have a reduced environmental impact. The module can be made more compact and lighter.

[0013] A second aspect concerns an electroactive reflective system for an automotive part, the system comprising at least one reflective module according to the first aspect.

[0014] A third aspect concerns a manufacturing process for the reflective module according to the first aspect, the process comprising: a supply of the first substrate, a formation of the multilayer stack comprising: a deposition of at least one layer forming the metallic mirror on the first substrate, a deposition of the Fabry-Pérot layer on the layer forming the metallic mirror, a deposition of the discontinuous metallic layer on the Fabry-Pérot layer.

[0015] A fourth aspect concerns a part of a motor vehicle comprising a reflective module according to the first aspect or a reflective system according to the second aspect. BRIEF DESCRIPTION OF THE FIGURES

[0016] The aims, objects, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which:

[0017] Larepresents a cross-sectional view of the principle of the reflective module and the associated system, according to an example of implementation.

[0018] Larepresents an automotive part including a reflective system, according to an example of implementation

[0019] Figures 3A and 3B represent a schematic cross-sectional view of a reflective system, according to two embodiment examples.

[0020]

[0021] Lare represents an explanatory diagram of the Fabry-Pérot effect for a Fabry-Pérot layer.

[0022] The diagram represents a view of the multilayer stacking according to an example implementation.

[0023] Laillustrates three particular examples of discontinuous metallic layers, for three dimensions t m distinct.

[0024] Laillustre as an example of the characteristic dimensions of a metallic island in the discontinuous metallic layer.

[0025] Laillustre illustrates, as an example, a relationship between the parameters r eq and t m of a metal island according to an example of implementation.

[0026] Figures 9 and 10 illustrate a cross-sectional view of two reflective modules according to two embodiment examples.

[0027] Figures 11A to 11G illustrate steps in the manufacturing process of a reflective module, according to several examples of implementation.

[0028]

[0029] The drawings are provided by way of example and are not intended to limit the invention. They are schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, the relative dimensions of the substrates and layers, the waveguide, and the thickness of a layer or substrate relative to its other dimensions are not representative of reality. DETAILED DESCRIPTION

[0030] Before beginning a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are stated below.

[0031] As an example, the discontinuous metallic layer comprises isolated or partially fused metallic islands. Depending on the size of the metallic islands and their spatial distribution, the wavelength of the beam reflected by the Fabry-Pérot cavity, and therefore the color perceived by the user, can be modulated.

[0032] According to one example, each metallic island has, along a transverse direction included in a plane substantially parallel to the main extension plane of the multilayer stack, a dimension r eq substantially less than or equal to 50 nm.

[0033] According to a particularly advantageous embodiment of the invention, the discontinuous metallic layer (16) differs fundamentally from periodic structures, such as ordered nanoparticle arrays. The layer (16) thus exhibits a stochastic (i.e., random) structural arrangement on the surface of the Fabry-Pérot layer (15).

[0034] This arrangement is a direct and advantageous consequence of a simple and industrially proven manufacturing process, such as physical vapor deposition (PVD), for example by thermal evaporation or sputtering. During this type of process, the growth of the metallic islands (160) on the dielectric layer (15) occurs through nucleation and coalescence, naturally generating a random spatial distribution.

[0035] This results in intrinsic shape variability, as these islets (160) may have irregular contours and are generally not perfectly circular or hemispherical. Consequently, the characteristic dimensions of these islets, such as an equivalent transverse dimension denoted t m, are not uniform over the whole of the layer, they follow a statistical distribution, advantageously a Gaussian distribution, resulting in average parameter values ​​taken over all the metallic islands (160).

[0036] The inherent and deliberate irregularity of the deposition process ensures that these parameters exhibit significant deviations around the average value, for example, by at least ±10% (plus or minus ten percent), thus guaranteeing the absence of any long-range spatial periodicity. This approach allows for the simple and economical production of islands with average dimensions t m can be extremely thin, for example on the order of 20 nm (nanometers).

[0037] This controlled irregularity, both geometric (shape and position) and dimensional (size), of the isolated or partially fused islands (160) is a fundamental aspect of this embodiment. It has the beneficial effect of broadening the spectral response of the localized surface plasmon resonance. This broadening makes the color effect not only more intense but also particularly robust to variations in viewing angle and inevitable manufacturing tolerances, thus guaranteeing consistent and superior visual quality across the entire finished part. As an example, each metallic island exhibits, along a direction substantially perpendicular to the main extension plane of the multilayer stack, a dimension t m substantially less than or equal to 50 nm, preferably substantially less than or equal to 20 nm.

[0038] These dimensions of metallic islands are particularly suitable for increasing the vibrancy of the color perceived in the visible range.

[0039] In one example, the discontinuous metallic layer is based on, and preferably consists of, at least one of aluminum, gold, and silver. In another example, the discontinuous metallic layer is based on, and preferably consists of, aluminum. This discontinuous metallic layer thus induces a low-sensitivity reflective coating (LSPR) effect while being more resistant to oxidation, compared to a discontinuous metallic layer based on silver, for example. The cost of the reflective module is also reduced.

[0040] According to one example, the Fabry-Pérot layer has a thickness between 75 nm and 250 nm, preferably between 150 nm and 250 nm.

[0041] According to one example, the Fabry-Pérot layer comprises at least one polymer chosen from the group consisting of polyethers, polycarbonates, polyesters, polynitriles, polyalcohols, polyamines, polysiloxanes, fluoropolymers, biopolymers and their derivatives.

[0042] According to one example, the Fabry-Pérot layer is based on, and preferably consists of, polymethyl methacrylate and has a thickness between 200 and 250 nm, preferably substantially equal to 200 nm.

[0043] As an example, the reflective module is a passive module. It is not necessary to apply a potential difference to the stack to modulate its thickness and therefore the perceived color. Depending on the dimensions of the discontinuous metallic layer and the spatial distribution of the metallic islands, the perceived color can be modified according to the desired application. The cost of the module is thus reduced. Furthermore, the perceived color can be modified according to the refractive index of the stacking materials, and in particular of the Fabry-Pérot cavity, and the thickness of the Fabry-Pérot layer.

[0044] In one example, the module is free of electrodes electrically linking the multilayer stack and configured to apply a potential difference to the stack.

[0045] Alternatively, the reflective module could be an electroactive module, configured to impose a potential difference on the Fabry-Pérot layer. To achieve this, the module could include electrodes electrically connecting the multilayer stack and configured to apply a potential difference to the stack.

[0046] In one example, the discontinuous metallic layer and the metallic mirror are separated, in a direction substantially perpendicular to the principal extension plane of the stack, by a distance less than the wavelength of the incident beam. This avoids diffraction effects.

[0047] In one example, the multilayer stack is topped with a second substrate. This substrate protects the reflective module, which is particularly advantageous for automotive applications.

[0048] Preferably, the first substrate, and if necessary the second substrate, are flexible substrates. This allows the reflective module to better adapt to a non-planar, for example curved, surface.

[0049] Preferably, the first and, where applicable, the second substrate are based on polyethylene terephthalate or its derivatives.

[0050] As an example, the Fabry-Pérot layer has a transmittance greater than or equal to 80%. This transmittance further improves the transmission of the beam reflected out of the module.

[0051] According to one example, the system comprises a plurality of said reflective modules juxtaposed along at least one direction parallel to a principal extension direction of said reflective modules.

[0052] As an example, for each discontinuous metallic layer of a reflective module, each metallic island exhibits, along a transverse direction included in a plane substantially parallel to the main extension plane of the multilayer stack, a dimension r eq substantially less than or equal to 50 nm, and / or along a direction substantially perpendicular to the principal extension plane of the multilayer stack, a dimension t m substantially less than or equal to 50 nm, preferably substantially less than or equal to 20 nm, at least one dimension among r eq and t m being distinct between modules of the plurality of modules.

[0053] According to one example, the system further includes a lateral light source and a waveguide above at least one reflective module, the waveguide being configured to transmit a light beam from the light source to at least one reflective module.

[0054] According to one example, the deposition of the discontinuous metallic layer is done by evaporation.

[0055] In one example, the discontinuous metallic layer deposition is configured such that each metallic island exhibits, along a transverse direction included in a plane substantially parallel to the main extension plane of the multilayer stack, a dimension r eq substantially less than or equal to 50 nm.

[0056] In one example, the deposit of the discontinuous metallic layer is configured so that each metallic island has, in a direction substantially perpendicular to the main extension plane of the multilayer stack, a dimension t m substantially less than or equal to 50 nm, preferably substantially less than or equal to 20 nm.

[0057] According to one example, the deposition of the discontinuous metallic layer includes a selection of deposition parameters such as to select at least one of the dimensions r eq and t m .

[0058] A substrate or layer "based" on species A is understood to be a substrate or layer comprising only that species A or that species A and possibly other species.

[0059] Several embodiments of the invention implementing successive manufacturing process steps are described below. Unless explicitly stated, the adjective "successive" does not necessarily imply, although this is generally preferred, that the steps follow each other immediately; intermediate steps may separate them.

[0060] Furthermore, the term "step" refers to the completion of a part of the process, and can designate a set of sub-steps.

[0061] Furthermore, the term "step" does not necessarily imply that the actions carried out during a step are simultaneous or immediately successive. Some actions in a first step may be followed by actions related to a different step, and other actions from the first step may be repeated later. Thus, the term "step" does not necessarily refer to unitary actions that are inseparable in time and in the sequence of phases of the process.

[0062] It is specified that, within the framework of the present invention, the thickness of a layer or substrate is measured along a direction perpendicular to the surface along which this layer or substrate has its maximum extent. The thickness is thus taken along a direction perpendicular to the principal faces of the substrate on which the different layers rest.

[0063] It is specified that, within the scope of the present invention, the terms "on," "overcomes," "covers," "underlying," "opposite," and their equivalents do not necessarily mean "in contact with." Thus, for example, the deposition, transfer, bonding, assembly, or application of a first layer onto a second layer does not necessarily mean that the two layers are directly in contact with each other, but rather means that the first layer at least partially covers the second layer, either by being directly in contact with it or by being separated from it by at least one other layer or element. "In contact" is understood to mean that a thin interface may exist, for example, due to manufacturing variability.

[0064] In the detailed description that follows, terms such as "longitudinal," "transverse," "upper," and "lower" may be used. These terms should be interpreted relatively in relation to the position of the elements of the reflective module or system once assembled, with the direction normal to the principal extension plane of the stacking layers being considered the vertical direction. A lateral or transverse dimension is understood as a dimension in a plane parallel to or coinciding with the principal extension plane of the stacking layers.

[0065] By "juxtaposed" elements we mean here that these elements are arranged side by side according to their main extension plane or arranged one above the other according to the direction of stacking, this direction being perpendicular to the main extension plane.

[0066] A parameter that is "approximately equal to / greater than / less than" a given value means that the parameter is equal to / greater than / less than the given value, within ±10% of that value. A parameter that is "approximately between" two given values ​​means that the parameter is at least equal to the smaller of the two given values, within ±10% of that value, and at most equal to the larger of the two given values, within ±10% of that value.

[0067] By "nanometric", and more specifically "nanometric thickness" or "nanometric size", we mean a dimension, for example a thickness, greater than or equal to 1 nm and strictly less than 1 µm.

[0068] Within the framework of the invention, the visible spectrum corresponds to the range of wavelengths between 350 and 900 nm, and preferably between 400 and 800 nm.

[0069] Generally, a material or layer is considered flexible if it can bend without being damaged or breaking, and more specifically if the mechanical and electrical properties of the film remain unchanged even under a significant stress of 2.5% with a concave and convex radius of curvature of 0.5 mm. The deformation (flexibility) of the reflective module can be evaluated using the following equation: deformation = (ts - tp - tf) / (2.rc), where: ts is the thickness of the substrate layer(s); tp is the total thickness of the stacked layers; tf is the total thickness of the electrode layers, with tf = 0 when the reflective module does not include an electrode; rc is the radius of curvature.

[0070] The expression "A and / or B" means (A), (B), or (A and B). The expression "A, B and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0071] The multilayer reflective module 1 and the reflective system 3 comprising it are now described according to several embodiment examples.

[0072] As illustrated, for example, by 1a and 1a, the reflective module 1 comprises a first substrate 10, also referred to as substrate 10, on which a multilayer stack 13 is deposited. The substrate 10 has a lower surface 10a and an upper surface 10b. The stack 13 can be arranged on the upper surface 10b. The multilayer stack 13 is configured to receive an incident light beam 2, 2'' and reflect a reflected light beam 2'. The incident beam 2 can, in particular, be a beam of ambient light. The incident light beam 2 has a wavelength spectrum, for example, that of visible light. The reflective system 3 comprises a light source 31 configured to emit a light beam 2''. For the multilayer stack 13, it is understood that the light beams 2 and 2'' can be considered as incident beams.The reflective module 1 can achieve an ambient light reflectivity greater than or equal to 80%, for example greater than or equal to 90%.

[0073] According to one example, the light source 31 is a semiconductor light source. In a non-limiting embodiment, the semiconductor light source is an LED. By LED, we mean any type of light-emitting diode, whether in non-limiting examples LEDs (Light Emitting Diode), OLEDs (Organic LED), AMOLEDs (Active-Matrix-Organic LED), or FOLEDs (Flexible OLED).

[0074] The light source 31 is preferably configured to emit the beam 2'' with a wavelength in the visible range. Note that the term "a wavelength," for example for the beam 2'' and / or the reflected beam 2', is not limited to a single, monochromatic wavelength but can refer to a range of wavelengths. The beam emitted by the light source 31 can be directed to the stack by a waveguide 12, which will be described in more detail later.

[0075] The reflective module 1 may further comprise a second substrate 11 placed above the multilayer stack 13, for example, above the waveguide 12. The second substrate 11 has a lower surface 11a and an upper surface 11b. The waveguide 12 may be arranged on the lower surface 11a. The multilayer stack 13, for example with the waveguide, may therefore be sandwiched between the first 10 and second 11 substrates. The second substrate 11 may form an entrance interface for the incident light beam 2 and an exit interface for the reflected beam 2'. The second substrate 11 is therefore preferably configured to allow at least these beams 2, 2' to pass through. The substrate 11 preferably has a transmittance greater than or equal to 75%, and preferably approximately equal to 80%.

[0076] The reflective module 1, and the system 3 comprising it, can be incorporated into parts such as vehicle parts, for example, car parts. The illustration shows, as an example, a rear car body part incorporating a reflective system 3. The reflective module or the reflective system 3 can be incorporated into other parts, for example, inside the passenger compartment or on other body parts.

[0077] As illustrated for example in, the light source 31 can be located away from the multilayer stack 13. The light source 31 can be placed in a location in the vehicle different from that of the multilayer stack 13. This can be a lateral light source, for example, relative to the multilayer stack 13.

[0078] In order to transmit the 2" beam emitted by the light source 31 to the multilayer stack 13, the module 1 may include a waveguide 12. The waveguide 12 may be configured to transmit the 2" light beam from the light source 31 to one or more reflective modules 1. For this purpose, the waveguide 32 may include internal total reflection elements configured to conduct the 2" light beam from the light source 31.

[0079] Depending on the angle of reflection of the 2" beam in the waveguide 12, the 2" beam from the source 31 can be transmitted to a reflecting module 1 or continue its propagation in the waveguide 12. For example, the waveguide 12 can include optical patterns 1210 configured to modify the optical path of a portion of the 2" beam from the source 31 to send it to the corresponding reflecting module 1, as illustrated for example in Figures 3A and 3B. A person skilled in the art is able to produce a waveguide in accordance with the arrangement of one or more reflective modules 1. These optical patterns can, for example, be arranged at regular intervals along the waveguide 12, in accordance with a juxtaposition of reflective modules 1 and / or opposite a reflective module 1 in a light output array 121. A waveguide 12 can be common to several reflective modules 1.Other structures can be provided as an alternative or complement to optical patterns by a person skilled in the art, for example suspended particles.

[0080] As an example, the light guide 11 is a surface light guide. A surface light guide is defined as an optical guiding element in which one dimension is much smaller than the other two dimensions in space, for example, smaller by one or more orders of magnitude. Here, the thickness of the waveguide 12 is much smaller than its length and width. In a non-limiting embodiment, the waveguide 12 has a thickness between 125 and 2000 micrometers. The waveguide 12 is thus very thin.

[0081] As an example, waveguide 12 is a flexible waveguide. Because it is flexible, it can adapt to flat or curved surfaces.

[0082] The waveguide 12 is preferably at least partially transparent. The term transparent indicates that the material from which it is made allows visible light to pass through, and in particular the light emitted by the light source 31.

[0083] As an example, the waveguide 12 is based on, and preferably made of, polycarbonate (PC), for example with a refractive index of 1.58, polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU), or polyethylene terephthalate (PET). Such materials allow for the production of a transparent waveguide 12.

[0084] As illustrated for example in, system 3 can comprise a plurality of reflective modules 1 juxtaposed along at least one direction called "of juxtaposition", parallel to or coincident with a principal extension direction of these modules 1. Preferably, the reflective modules 1 are juxtaposed along at least two directions called "of juxtaposition" of a plane parallel to or coincident with a principal extension plane of these modules 1.

[0085] The Fabry-Pérot effect is illustrated by way of example. The Fabry-Pérot layer 15, nanometric in thickness and typically on the order of one or several hundred nm, forms a Fabry-Pérot cavity in which the incident beam 2 is confined. This cavity produces, from the light it receives, interferences of a determined wavelength. These interferences result in multiple reflections of rays of a given wavelength propagating inside the cavity. In fact, it is through an interference phenomenon, and not absorption as when pigments or dyes are used, that the module produces a colored rendering for an observer. According to the invention, the thickness of the Fabry-Pérot layer 15 partially determines the wavelength(s) of a beam 2', which will be reflected onto a reflective metallic mirror 14.A change in the thickness d15 of the conductive polymer layer 15 will therefore change the wavelengths that will be at the phase output of the cavity by constructive interference, for example λ1, λ2, and λ3.

[0086] To improve the reflective properties of the reflective module 1, the multilayer stack further includes a discontinuous metallic layer 16, as illustrated, for example, in Figure 1. The metallic layer 16 can be placed on the Fabry-Pérot layer 15, for example, directly in contact with it. This discontinuous metallic layer 16 exhibits discontinuities at the nanoscale. More specifically, the discontinuous metallic layer 16 comprises metallic islands 160, which can also be referred to as metallic droplets. These metallic islands 160 can be produced by a physical deposition technique, for example, by evaporation. The metallic islands 160 together form discontinuities at the nanoscale, whether isolated or partially fused together. It is therefore understood that the discontinuous metallic layer 16 has vacant areas delimited by the islands 160.

[0087] The free electrons of the discontinuous metallic layer 16 can resonate with the incident light via LSPR. Coupling with electrons from the metallic mirror 14, this induces hybridization, modifying the electric field applied at the Fabry-Pérot cavity and thus altering the reflected wavelength. This increases the absorbance of the multilayer stack 13 over a portion of the spectrum of the incident beam 2' and enhances the perceived color intensity. The wavelength spectrum of the reflected beam 2' is therefore reduced by the discontinuous metallic layer.

[0088] Depending on the dimensions of the metallic islands 160, the properties of LSPR and therefore of hybridization are modified. The wavelength of the reflected beam 2' will thus be modified.

[0089] More specifically, and as illustrated for example by Figures 6 to 8, each metallic island 160 has, along a transverse direction included in a plane substantially parallel to the main extension plane of the multilayer stack, a dimension r eq Each metallic island 160 can have, along a direction substantially perpendicular to the main extension plane of the multilayer stack, a dimension t m .

[0090] The 160 metallic islands may not be perfectly circular and may be hemispherical. m can therefore represent the equivalent thickness by mass, related to the amount of aluminum evaporated and the deposition surface area. r eq This can correspond to the equivalent radius, defined as the radius of a circular particle that would cover the same area as the measured one. Both parameters above can be controlled by the mass of evaporated metal.

[0091] r eq and t mare on the nanometer scale, and preferably less than or equal to 100 nm. r eq may be significantly less than or equal to 50 nm. m may be substantially less than or equal to 50 nm, preferably substantially less than or equal to 20 nm. m is preferably between 1 nm and 15 nm, for example between 4 nm and 15 nm. Some variability in shape can be observed between the metallic islands 160. This is particularly the case when the islands are formed by evaporation. The parameters r eq and t m islands can be median parameters or values ​​of Gaussian mean parameters taken over the set of metallic islands 160.

[0092] As these parameters, and in particular the thickness t mAs the adjacent islands increase, they coalesce to form a continuous film. A continuous film eliminates the geometric confinement for the LSPR phenomenon, and therefore the associated increase in perceived color vividness is lost.

[0093] As illustrated, the perceived color is modified according to the dimensions of the islands 160, and according to the examples illustrated for t m equal to 5 nm (perceived yellow color), t m equal to 8 nm (perceived red color), t m equal to 10 nm (perceived blue color), in the case of a discontinuous metallic layer 16 of aluminum. This illustrates, as an example, a relationship between r eq and t m to obtain different perceived colors, for a discontinuous metallic layer made of aluminum. The parameters of r eq and t m The parameters to be used may depend on the metal of the discontinuous metallic layer 16. To obtain a given color, the parameters of r eq and t mThe parameters to be used can be obtained through simulation. It is possible to adapt the nature of the Fabry-Pérot layer, its thickness and the parameters of the discontinuous metallic layer, such as the type of metal and its geometry, for example via the amount of metal evaporated, to obtain the desired perceived color.

[0094] The dimensions of metallic islands can, for example, be determined from images acquired by scanning electron microscopy. These dimensions can, for example, be estimated or calculated. m can be determined from the evaporation mass and the depositional surface area. For r eq Using a scanning electron microscope, it is possible to count the number of metallic islands 160 for a given surface, and then calculate the equivalent radius r eq .

[0095] As illustrated in Figure 1, the discontinuous metallic layer 16 can be separated from the metallic mirror 14 by a distance d less than the wavelength of the incident beam 2. This distance d can, for example, be less than or equal to 400 nm. The distance d can be approximately equal to the thickness d15 of the Fabry-Pérot layer. The total thickness d separating the discontinuous metallic layer 16 and the metallic mirror 14 can be given by d = λ / [2ncos(θ)], where: λ is the wavelength of the light beam, n is the refractive index of the Fabry-Pérot cavity material, and θ is the angle of incidence of the light beam. In the case of normal incidence, θ can be equal to 0°.

[0096] The reflective module 1 and the multilayer stack 13 are now described in more detail with reference to Figures 9 and 10. Examples of the dimensions of the reflective module 1 are given. Each module 1 can extend along a plane parallel to the main extension plane of the layers of the stack 13. Each reflective module 1 can, in this plane, have lateral dimensions, in directions perpendicular to each other, ranging from a few millimeters for small areas to a few meters for large areas. The thickness of the multilayer stack 13 can be substantially greater than or equal to 200 nm, and substantially less than or equal to 500 nm. It is therefore clear that the reflective module 1 is compact and thus more easily integrated into existing parts, for example, automotive parts, particularly compared to existing solutions using liquid electrolytes.

[0097] The first 10 and / or the second 11 substrates can extend along at least one direction of the main extension plane of the layers of the stack 13, over a distance d1 less than or equal to 5 mm, preferably 3 mm, relative to the layers of the stack 18. As an example, the first substrate can have a thickness substantially equal to 1.1 mm.

[0098] The first substrate 10 and / or the second substrate 11 are preferably flexible substrates. This facilitates the incorporation of the reflective modules into existing parts and increases the mechanical strength of the reflective module 1.

[0099] For example, substrate 10 and / or the second substrate 11 are manually deformable without tools. For example, the first substrate 10 and / or the second substrate 11 are polymer-based or made of polymer. More specifically, the first substrate 10 and / or the second substrate 11 are polymer-based or made of polyethylene terephthalate (PET), PMMA, or their derivatives. Note that other polymers may be considered.

[0100] In the case of a plurality of juxtaposed reflective modules 1, the first 10 and / or the second 11 substrates may be common to a plurality of modules 1. Alternatively, it may be provided that each module includes its own substrate(s), distinct between different modules 1.

[0101] The metallic mirror 14 can be formed of at least one metallic layer 140, for example based on or made of aluminum. Good reflection of the incident beam 2 is thus obtained. The metallic mirror 14 may also include layers that improve chemical compatibility with the Fabry-Pérot layer 15. For this purpose, the metallic mirror 14 may include a layer based on or made of gold 142. The gold layer 142 can thus be in contact with the Fabry-Pérot layer 15 without risking degradation of this layer or of the metallic mirror 14. It should be noted that several metallic mirrors 14 can be used in the stack 13, or even in the reflective module 1. For example, one or more substrates 10 and one or more mirrors 14 can be superimposed. In order to adhere the gold layer 142 to the aluminum layer 140, the mirror 14 may include an adhesion layer based on or made of chromium 141 between these layers 140 and 142.The metallic mirror 14 is preferably of nanometer thickness. For example, the aluminum layer 140 may have a thickness approximately between 40 nm and 80 nm, for example between 50 nm and 70 nm, and preferably approximately 50 nm. The chromium layer may have a thickness approximately 5 nm. The gold layer may have a thickness approximately 7 nm.

[0102] As an example, the Young's modulus of the Fabry-Pérot 15 coating is approximately between 0.2 and 4 MPa. The elongation at break can be approximately greater than or equal to 100%, for example, approximately between 150% and 160%. The reflective modulus 1 thus exhibits a long service life despite the stresses that may be exerted on the modulus. Preferably, the Fabry-Pérot 15 coating has a transmittance greater than or equal to 80%.

[0103] The Fabry-Pérot 15 layer can be based on at least one polymer selected from polyethers, polycarbonates (e.g. polybutylene glutarate abbreviated PBG), polyesters (e.g. polymethyl methacrylate abbreviated PMMA), polynitriles (e.g. polyacrylonitrile abbreviated PAN), polyalcohols (e.g. polyvinyl alcohol abbreviated PVA), polyamines (e.g. polyethyleneimine abbreviated PEI), polysiloxanes (e.g. polydimethylsiloxane abbreviated PDMS), fluoropolymers (e.g. polyvinylidene fluoride abbreviated PVDF, and poly(vinylidene fluoride-co-hexafluoropropylene), abbreviated P(VDF-co-HFP)), biopolymers (e.g. lignin, chitosan and cellulose) and their derivatives. the Fabry-Pérot 15 layer may for example include a copolymer in which at least one of the monomer motifs corresponds to the polymers mentioned above.

[0104] The Fabry-Pérot 15 layer preferably has a thickness d15 between 100 and 250 nm, preferably between 180 nm and 220 nm, and more preferably substantially equal to 200 nm.

[0105] As illustrated, for example, the reflective module 1, and preferably each reflective module 1, can include a mask 17 configured to partially block the transmission of the incident beams 2 and reflected beams 2'. This mask 17 can, according to an example not shown, be placed on the upper surface 11b of the second substrate 11. In a direction normal to the multilayer stack 13, the mask 17 can cross the waveguide 12, for example, by being positioned beneath the second substrate 11. The mask 17 can define areas blocking light transmission and areas allowing the incident beams 2 and reflected beams 2' to pass through. For a reflective module 1, the mask 17 thus creates a pattern. Note that this mask 17 can be shared by several juxtaposed reflective modules 1.

[0106] As illustrated in Figures 9 and 10, the second substrate 11 can overcome the discontinuous metallic layer 16, either directly or via the waveguide 12.

[0107] Reflective module 1 can be manufactured according to the example described below. Note that the process can include any step necessary to obtain the characteristics of reflective module 1 described above. The deposition parameters and techniques can be configured to obtain the thicknesses described previously.

[0108] The process may include a formation of the multilayer stack 13 as introduced above.

[0109] For this purpose, and as illustrated by Figures 11A and 11B for example, the process can include depositing the metallic mirror 14 onto the first substrate 10. As previously mentioned, the mirror 14 can comprise several successive layers of metal. These layers 140, 141, 142 can be formed by any physical deposition technique, for example by sputtering, electron beam evaporation, flash evaporation, or induction evaporation.

[0110] On the formed metallic mirror 14, the process may include the deposition of the Fabry-Pérot layer 15, as illustrated, for example, in Figure 1. Numerous deposition techniques can be used, depending in particular on the nature of the polymer. Deposition can be by droplet application, by slide application, or by centrifugation (generally referred to as spin-coating). For example, the deposition of the Fabry-Pérot layer 15 may involve the application of a precursor solution to form a preliminary layer. This deposited layer can then form the Fabry-Pérot layer 15 through heat treatment and / or UV radiation and / or drying.

[0111] On the surface 15a of the Fabry-Pérot layer 15, the discontinuous metallic layer can be deposited as illustrated in Figures 11C and 11D. The discontinuous metallic layer 16 can be formed by any physical deposition technique, for example, sputtering, electron beam evaporation, flash evaporation, or induction evaporation. Preferably, the electron beam evaporation technique is used. This is a physical vapor deposition technique that uses an intense electron beam to vaporize a source material under high vacuum. This technique is compatible with a wide variety of source materials and offers a broad range of well-controlled deposition parameters. It is thus easy to select the parameters. m and r eqdesired. The geometry of the metallic islands can be controlled by adjusting the amount of metal evaporated, particularly aluminum. Electron beam evaporation is indeed a cumulative technique. Controlling the sample exposure time during evaporation allows, in particular, obtaining the desired parameters t m and r eq desired.

[0112] The module 1 being manufactured can be placed in the chamber of a deposition reactor for this step. For example, during the deposition of the discontinuous metallic layer 16, the temperature of the deposition chamber is less than or equal to 100°C. This temperature is below the melting point of many polymers. This therefore prevents their degradation during the deposition of this layer. This is particularly advantageous when the reflective module 1 comprises one or more flexible substrates 1 to 11.

[0113] The second substrate 11 can be deposited on the discontinuous metal layer 16, as illustrated for example in [figure]. The process may include a step of depositing the waveguide 12, preferably on the discontinuous metal layer 16. The deposition of the waveguide 12 may precede the deposition of the second substrate 11, as illustrated for example in [figure]. The mask 17 can be formed on the second substrate 11, as illustrated for example in [figure].

[0114] The manufacturing process for the reflective system 3 may include, for each module 1, the manufacturing steps previously stated. The manufacturing process for the reflective substrate 3 may further include the electrical connection of the light source 31 to the waveguide 12.

[0115] In a non-limiting embodiment, the vehicle is a motor vehicle. A motor vehicle is defined as any type of motorized vehicle. This embodiment is taken as a non-limiting example in the following description. In the description, the vehicle is thus also referred to as a motor vehicle. In a non-limiting variant of this embodiment, the vehicle is a combustion engine vehicle, an electric vehicle, or a hybrid vehicle.

[0116] The invention is not limited to the embodiments described above and extends to all embodiments covered by the invention. The present invention is not limited to the examples described above. Many other embodiments are possible, for example, by combining features described above, without departing from the scope of the invention. In particular, other deposition techniques can be considered by those skilled in the art, depending on the nature of the deposited layer. Furthermore, the features described with respect to one aspect of the invention can be combined with another aspect of the invention.

Claims

Multilayer reflective module (1), the module comprising: a first substrate (10), a multilayer stack (13) disposed on the first substrate (10) and configured to receive an incident light beam (2) having a light spectrum and to reflect a reflected light beam (2') having a determined wavelength, the multilayer stack (13) comprising: at least one layer forming a metallic mirror (14), a polymer-based layer, called a "Fabry-Pérot" layer (15) overlying the metallic mirror (14), and configured to form, by the Fabry-Pérot effect, the light beam (2') reflected on the metallic mirror, said layer (15) having a nanometric thickness (d 15 ),Characterized in that the multilayer stack (13) further comprises a metallic layer (16) overlying the Fabry-Pérot layer, the metallic layer (16) being discontinuous at the nanoscale so as to generate a localized surface plasmon resonance effect. Reflective module (1) according to the preceding claim, in which the discontinuous metallic layer (16) comprises metallic islands (160) isolated or partially fused together, which exhibit a variability of shape and whose dimension parameters follow a Gaussian mean. reflective module (1) according to the preceding claim, characterized in that the statistical distribution of the characteristic dimensions of the metallic islands (160) has a deviation around the mean value of at least ±10%. Reflective module (1) according to any one of claims 2 to 3, wherein the average value of said characteristic dimensions of the metallic islands (160) is on the order of 20 nm. Reflective module (1) according to any one of claims 2 to 4, wherein each metallic island (160) has, along a transverse direction included in a plane substantially parallel to the main extension plane of the multilayer stack (13), a dimension r eq substantially less than or equal to 50 nm. Reflective module (1) according to any one of claims 2 to 5, wherein each metallic island (160) has, in a direction substantially perpendicular to the principal extension plane of the multilayer stack (13), a dimension t m substantially less than or equal to 50 nm, preferably substantially less than or equal to 20 nm. Reflective module (1) according to any one of the preceding claims, wherein the discontinuous metallic layer (16) is based on at least one of aluminium, gold and silver. Reflective module (1) according to any one of the preceding claims, wherein the discontinuous metallic layer is aluminum-based. Module (1) according to any one of the preceding claims, wherein the Fabry-Pérot layer (15) comprises at least one polymer selected from the group consisting of polyethers, polycarbonates, polyesters, polynitriles, polyalcohols, polyamines, polysiloxanes, fluoropolymers, biopolymers and their derivatives. Module (1) according to any one of the preceding claims, wherein the Fabry-Pérot layer (15) comprises, and preferably is made of, polymethyl methacrylate and has a thickness (d 15 ) between 200 and 250 nm, preferably approximately equal to 200 nm. Module (1) according to any one of the preceding claims, the reflective module (1) being a passive module. Module (1) according to any one of the preceding claims, wherein the discontinuous metallic layer (16) and the metallic mirror (14) are spaced, in a direction substantially perpendicular to the principal extension plane of the stack (13), by a distance d less than the wavelength of the incident beam (2). Reflective system (3) for an automotive part (4), the system comprising at least one reflective module (1) according to any one of the preceding claims. System (3) according to the preceding claim, comprising a plurality of said reflective modules (1) juxtaposed along at least one direction parallel to a principal extension direction of said reflective modules (1). System (3) according to any one of the two preceding claims, further comprising a lateral light source (31) and a waveguide (12) surmounting at least one reflective module (1), the waveguide (12) being configured to transmit a light beam (2'') from the light source (31) to at least one reflective module (1). Method of manufacturing the reflective module according to any one of claims 1 to 10, the method comprising: supplying the first substrate (10), forming the multilayer stack (13) comprising: deposition of at least one layer forming the metallic mirror (14) on the first substrate (10), deposition of the Fabry-Pérot layer (15) on the layer forming the metallic mirror (14), deposition of the discontinuous metallic layer (16) on the Fabry-Pérot layer (15). Method according to the preceding claim, wherein the deposition of the discontinuous metallic layer (16) is done by evaporation. Motor vehicle part (4) comprising a reflective module (1) according to any one of claims 1 to 10 or a reflective system (3) according to any one of claims 11 to 13.

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