METHOD FOR PRODUCING AN OPTOELECTRONIC COLOR CONVERSION DEVICE WITH A ONE-STEP OPTICALLY SHAPING OF SURFACE POTENTIAL PATTERNS IN AN ELECTRICAL LAYER

Description

TECHNICAL FIELD

[0001] The field of the invention is that of manufacturing methods for optoelectronic devices comprising an array of diodes for emitting or detecting electroluminescent radiation, combined with a color conversion structure of photoluminescent pads. The invention finds particular application in display screens and image projectors. PREVIOUS STATE OF THE ART

[0002] Optoelectronic devices exist that comprise an array of identical light-emitting diodes, at least partially covered by photoluminescent pads that enable color conversion. Such optoelectronic devices can form display screens or image projection systems with an array of luminous pixels of different colors.

[0003] In such an optoelectronic device, each luminous pixel comprises one or more light-emitting diodes (LEDs) associated with a photoluminescent pad. To obtain luminous pixels capable of emitting light of different colors, for example blue, green, or red, the LEDs can be adapted to emit a single light, for example blue, and the green and red pixels have photoluminescent pads adapted to absorb at least part of the incident blue light emitted by the LEDs, and to emit green or red light in response.

[0004] Light-emitting diodes (LEDs) are therefore preferably identical and emit light of approximately the same wavelength. They can be made from a semiconductor material comprising elements from groups III and V of the periodic table, such as a III-V compound, notably gallium nitride (GaN), indium gallium nitride (InGaN), or gallium aluminum nitride (AlGaN). They are arranged to form an array of LEDs with a front face through which the generated light is transmitted. They can also be organic LEDs.

[0005] Photoluminescent pads can be formed from a binding matrix containing particles of a photoluminescent material such as yttrium aluminum garnet (YAG, for Yttrium Aluminium Garnet(in English) activated by the cerium ion YAG:Ce. Photoluminescent particles can also be quantum dots ( quantum dots, (in English), that is, in the form of semiconductor nanocrystals whose quantum confinement is substantially three-dimensional. These can also include, in particular, InP, perovskite, or CdSe crystals.

[0006] The manufacturing process may involve the deposition and subsequent structuring of a photoluminescent layer to form initial photoluminescent pads, for example, those adapted to convert blue to green. These steps are repeated to form secondary photoluminescent pads, for example, those adapted to convert blue to red. However, this process has the disadvantage of being poorly suited to diode arrays with small pixel pitches, for example, on the order of 5 µm, since alignment or overlap problems between the photoluminescent pads can occur.

[0007] Document WO2014 / 136023 describes an alternative manufacturing process that uses an electret layer covering the diode array. The process begins with a step of inscribing electrical charge patterns onto the top surface of a dielectric layer to create the electret layer. This is achieved by using a polarized AFM tip to locally inject the electrical charges. Next, a localized deposition step is performed, involving colloidal nanocrystals deposited onto the electrical charge patterns. For this, the electret layer is brought into contact with a colloidal solution containing the nanocrystals, which are then naturally deposited onto the electrical charge patterns by a dielectrophoretic force. However, this process has the drawback of requiring sequential injection of the electrical charges, by moving the AFM tip across the top surface to form the electrical charge patterns.

[0008] Document WO2021 / 023656 describes a similar process, where the electrical charge patterns are defined by a stamping technique, i.e., by bringing an electrically polarized pad into contact with a dielectric layer intended to form the electret layer. The underside of the pad is structured to form polarized teeth, which come into contact with the dielectric layer. This produces the electret layer, the upper surface of which displays the electrical charge patterns. The electret layer is then brought into contact with a colloidal solution, and the nanocrystals present are deposited onto the electrical charge patterns by dielectrophoresis. However, this process has the drawback, notably, of requiring precise positioning of the pad relative to the diode array.However, the uncertainty in the positioning of the buffer relative to the diode array can become problematic, particularly for diode arrays with small pixel pitches, for example on the order of 5 µm. Indeed, this positioning uncertainty can lead to incorrect positioning of the photoluminescent pads relative to the diodes, and therefore to a degradation of the optoelectronic device's performance.

[0009] WO 2021 / 076724 discloses a method for manufacturing an optoelectronic device according to the prior art.

[0010] US 2022 / 282152 discloses a method for manufacturing an electroluminescent display device using an electret layer according to the prior art.

[0011] US 3276031 discloses the deformation of an electret layer using a depolarizing light.

[0012] WO 2015 / 186074 discloses the inscription of images in an electret layer. DESCRIPTION OF THE INVENTION

[0013] The invention aims to remedy, at least in part, the drawbacks of the prior art, and more particularly to propose a method for manufacturing an optoelectronic device in which the formation of electrical charge patterns, referred to herein as surface potential patterns, is carried out optically in an electret layer, either by localized polarization or depolarization of the electret layer. This step makes it possible to simultaneously create all the surface potential patterns in the electret layer, without requiring the use of an AFM tip or a buffer as described previously, and thus to produce photoluminescent pads that exhibit good positioning relative to the diode array.

[0014] For this purpose, the object of the invention is a method for manufacturing an optoelectronic device comprising: a matrix of diodes, adapted to emit or receive light radiation; and a color conversion structure, covering at least part of the matrix of diodes, and containing photoluminescent pads arranged each opposite at least one diode.

[0015] The manufacturing process involves the following steps: ∘ A / provide the diode matrix; ∘ B / create an electret layer, covering the diode matrix, and whose upper face, opposite the diode matrix, presents predefined surface potential patterns where the surface potential is non-zero; o C / create the photoluminescent pads, by bringing the electret layer into contact with a colloidal solution containing photoluminescent particles, which then deposit on the upper face of the electret layer opposite the predefined surface potential patterns, thus forming the photoluminescent pads.

[0016] According to the invention, step B of the electret layer fabrication comprises the following steps: B1 / produce an electret layer whose upper face has, over its entire surface, a non-zero or zero initial surface potential; then B2a / in the case where the initial surface potential is non-zero: illuminate areas of the electret layer with light radiation called depolarization radiation capable of being absorbed at least in part by the electret layer, said illuminated areas being distinct from unilluminated areas intended to form the surface potential patterns, the absorption of the depolarization light radiation in the illuminated areas causing a cancellation of the local surface potential, the unilluminated areas then defining the surface potential patterns;B2b / or, in the case where the initial surface potential is zero: illuminate areas of the electret layer with light radiation of a polarization capable of being absorbed at least in part by the electret layer, the absorption of the polarized light radiation in the illuminated areas causing the formation of a non-zero local surface potential, the illuminated areas then defining the surface potential patterns. ;

[0017] Some preferred but not exhaustive aspects of this process are as follows.

[0018] The process may include, prior to step B2a or B2b, a step of disposing of an opaque mask, in a material opaque to light radiation of depolarization or polarization, extending only over the areas of the electret layer intended to form the surface potential patterns; then, during step B2a or B2b, the light radiation of depolarization or polarization may be emitted towards the opaque mask and the electret layer, and is absorbed by the electret layer in the areas not covered by the opaque mask.

[0019] The diodes can be light-emitting diodes (LEDs). The electret layer can be made of a material suitable for partially absorbing the light emitted by the LEDs, thus canceling the local surface potential. In step B2a, diodes can be selectively activated to illuminate the electret layer in areas not intended to form surface potential patterns, thereby canceling the local surface potential, with the unlit areas then defining the surface potential patterns. Alternatively, in step B2b, diodes can be selectively activated to illuminate the electret layer only in areas intended to form surface potential patterns.

[0020] In connection with step B2a, the electret layer can be made of a self-polarizing organic dielectric material, so that step B1 can then consist of depositing the electret layer covering the diode matrix, the electret layer then presenting, over its entire surface, a non-zero initial surface potential.

[0021] In connection with step B2b, the electret layer can be made of a photochromic dielectric material, so that step B1 can then consist of depositing an electret layer, in the photochromic dielectric material, covering the diode matrix, the electret layer then presenting, over its entire surface, a zero surface potential.

[0022] In connection with step B2a, the electret layer can be made of a dielectric material, so that step B1 can include the following steps: depositing an electret layer, in the dielectric material, covering the diode matrix, the electret layer then presenting, over its entire surface, an initial surface potential of zero; then subjecting the electret layer to an electric field called predefined biasing, causing the formation of a non-zero surface potential over the entire surface of the electret layer.

[0023] The diode array may include a top electrode layer covering the diodes and adapted to electrically bias them. During the step of subjecting the electret layer to the biasing electric field, the electret layer may then be positioned between the top electrode layer and an added electrode, between which a predefined potential difference is applied.

[0024] The electret layer produced in step B can be a first electret layer. The photoluminescent pads produced in step C can then be first photoluminescent pads adapted to convert incident light radiation of a first wavelength into light radiation of a second wavelength different from the first wavelength.

[0025] The process can then include the following steps, following step C: o D / create a second electret layer, covering the diode matrix and the first electret layer, and whose upper face, opposite the diode matrix, presents second predefined surface potential patterns where the surface potential is non-zero, said second surface potential patterns being located opposite diodes distinct from those opposite which the first surface potential patterns are located; o E / create the second photoluminescent pads, by bringing the second electret layer into contact with a colloidal solution containing second photoluminescent particles, different from the first photoluminescent particles of step C, which are then deposited on the upper face of the second electret layer opposite the second predefined surface potential patterns, thus forming the second photoluminescent pads.

[0026] The matrix diodes can be light-emitting diodes adapted to emit light at the same wavelength. They can then form, with the first and second photoluminescent pads, a matrix of red, green, and blue luminous pixels.

[0027] The diode matrix may have a dimension, in a plane parallel to the diode matrix (10), greater than or equal to 100mm.

[0028] The diode matrix can have a periodicity step of less than or equal to 10µm, or even 5µm, or even 2µm. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Other aspects, objectives, advantages, and features of the invention will become clearer upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which: THE Figures 1A to 1Hillustrate different stages of a manufacturing process for an optoelectronic device, where at least one of the electret layers is made of a self-polarizing dielectric material; figures 2A to 2C illustrate different stages of a variant of the manufacturing process for an optoelectronic device, where localized depolarization is achieved by means of diodes, of the diode matrix, selectively activated; the figures 3A to 3C illustrate different stages of a variant of the manufacturing process for an optoelectronic device, where the electret layer is made of a photochromic dielectric material that is locally optically polarized; the figures 4A to 4F illustrate different stages of a variant of the manufacturing process of an optoelectronic device, where at least one of the electret layers is made of a dielectric material that is electrically polarized by electrostatic means. DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0030] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale to ensure clarity. Moreover, the different embodiments and variants are not mutually exclusive and may be combined. Unless otherwise stated, the terms "approximately," "around," and "in the order of" mean within 10%, and preferably within 5%. Furthermore, the terms "between ... and ..." and equivalents mean inclusive of the bounds, unless otherwise specified.

[0031] The invention relates to a method for manufacturing an optoelectronic device comprising a diode array covered by a color conversion structure with photoluminescent dots. The photoluminescent dots are created by depositing photoluminescent particles onto surface potential patterns on the upper face of an electret layer. As detailed below, the surface potential patterns are defined by locally depolarizing or locally polarizing the electret layer optically. Furthermore, the diodes can be emitting diodes (e.g., light-emitting diodes) or photodiodes.

[0032] In general, an electret layer is a dielectric layer containing fixed electric charges or a quasi-permanent dipole polarization. Furthermore, the electret layer exhibits a non-zero surface potential on its upper surface. This means that the electret layer generates an external electric field in the absence of an applied field. By extension, the term 'electret layer' will also be used to refer to a dielectric layer that initially has a zero surface potential across its entire surface and is intended to form an electret layer exhibiting surface potential patterns.

[0033] The invention exploits the fact that an electret layer can be depolarized by the absorption of depolarizing light, as explained in the article by Sugi et al. entitled "Characterization of light-erasable giant surface potential built up in evaporated Alq3 thin films," Thin Solid Films 464-465 (2004), 412-415, and the article by Tanaka et al. entitled "Self-Assembled Electret for Vibration-Based Power Generator," Sci Rep 10, 6648 (2020). Such depolarization results in the cancellation of the surface potential of the electret layer. Indeed, the absorption of depolarizing light leads to the creation of electron-hole pairs which, according to one approach, compensate for the polarization of charges, resulting in the cancellation of the surface potential. Furthermore, an electret layer can also be polarized by the absorption of light radiation known as polarization radiation.

[0034] Thus, as detailed below, in one embodiment, an electret layer is first created, initially exhibiting a non-zero surface potential across its entire surface. Predefined areas of the electret layer are then depolarized by illuminating them with depolarizing light radiation capable of being at least partially absorbed by the electret layer. The illuminated areas then exhibit a zero surface potential, while the unilluminated areas retain their non-zero surface potential, thus forming surface potential patterns where, in the subsequent step, the photoluminescent particles are deposited in a localized manner by dielectrophoresis. Therefore, the photoluminescent spots are naturally located opposite (i.e., "perpendicular to") the surface potential patterns, and not outside these predefined patterns.This process then makes it possible to define precisely the surface potential patterns on the top face of the electret layer, even when the diode matrix has a large dimension (especially when it is made in 100 mm or 200 mm wafer technology) and / or when the pixel pitch of the diode matrix is ​​small (for example on the order of 5 µm or less, for example 2µm).

[0035] Alternatively, according to another embodiment, an electret layer is first created, initially exhibiting a zero surface potential across its entire surface. Predefined areas of the electret layer are then polarized by illuminating them with light of a polarization suitable for at least partial absorption by the electret layer. The illuminated areas then exhibit a non-zero surface potential (while the unilluminated areas retain their zero surface potential), thus forming surface potential patterns where, in the subsequent step, photoluminescent particles are deposited in a localized manner by dielectrophoresis. This process, as before, allows for the precise definition of the surface potential patterns on the upper surface of the electret layer.

[0036] Furthermore, photoluminescent pads are designed to convert, at least partially, incident light of a first wavelength λ₁ into luminescent light of a longer wavelength λ₂. For example, they can be adapted to absorb blue light, i.e., light with a wavelength between approximately 440 nm and 490 nm, and emit green light, i.e., light with a wavelength between approximately 495 nm and 560 nm, or even red light, i.e., light with a wavelength between 600 nm and 650 nm, or even infrared light. Here, wavelength refers to the wavelength at which the emission spectrum exhibits a peak intensity. For illustrative purposes only, light-emitting diodes can exhibit an emission spectrum with a peak intensity between 380nm and 490nm.In the case of a light-emitting diode (LED) array, the incident light is the radiation emitted by the diodes, whereas in the case of photodiodes, it is the light coming from an external environment and directed towards the photodiodes. It should be noted that in the case of photodiodes, the photoluminescent pads allow for filtering a portion of the spectral range of the incident light, for example, to perform spectral analysis.

[0037] Photoluminescent pads are made of particles of at least one photoluminescent material, preferably nanoparticles with a maximum size between 0.2 nm and 1000 nm, for example, between 0.2 nm and 100 nm, and for example, between 1 nm and 30 nm. The size and / or composition of the photoluminescent particles are chosen according to the desired luminescence wavelength. The shape of the particles can be any shape, for example, spherical, angular, flattened, elongated, etc.

[0038] Photoluminescent particles can be quantum dots ( quantum dots, (in English), that is, semiconductor nanocrystals whose quantum confinement is essentially three-dimensional, or even clusters of quantum dots. The average size of the quantum dots can then be between 0.2 nm and 50 nm, for example between 1 nm and 30 nm. They can also be nanoplatelets ( nanoplatelets(in English), that is, nanoparticles having an essentially two-dimensional shape. Also, the smallest dimension (thickness) is smaller than the other two dimensions of length and width, preferably by a ratio of at least 1.5.

[0039] Photoluminescent particles can notably be formed of at least one semiconductor compound, which can be chosen, for example, from cadmium selenide (CdSe), indium phosphorus (InP), gallium indium phosphorus (InGaP), cadmium sulfide (CdS), zinc sulfide (ZnS), cadmium oxide (CdO) or zinc oxide (ZnO), zinc cadmium selenide (CdZnSe), zinc selenide (ZnSe) doped, for example, with copper or manganese, graphene, or from other suitable semiconductor materials. Nanoparticles can also exhibit a core / shell type structure, such as CdSe / ZnS, CdSe / CdS, CdSe / CdS / ZnS, PbSe / PbS, CdTe / CdSe, CdSe / ZnTe, InP / ZnS or others.

[0040] THE Figures 1A to 1H illustrate different stages of a manufacturing process for an optoelectronic device 1 according to one embodiment. In this example, at least one of the electret layers E1, E2, and here both electret layers, are made of a self-polarizing dielectric material. In this example, the surface potential patterns are created by localized optical depolarization of an electret layer that initially has a non-zero surface potential across its entire surface.

[0041] Furthermore, the optoelectronic device 1 comprises an RGB (red, green, blue) pixel array. Each RGB pixel is composed of several R, G, or B sub-pixels, each containing at least one light-emitting diode (one diode per sub-pixel). In this description, a sub-pixel associated with a given color is called a "pixel." Alternatively, the optoelectronic device 1 could comprise a photodiode array.

[0042] Here and for the remainder of the description, we define a three-dimensional orthogonal XYZ coordinate system, where the X and Y axes form a principal plane in which a support substrate 11 extends, and where the Z axis is oriented along the thickness of the diode array 10 towards the front face. The terms 'lower' and 'upper' are defined with respect to an increasing position along the +Z direction.

[0043] With reference to the fig.1AAn array of light-emitting diodes (LEDs) 10 is provided. In this example, the diodes are divided into three types, labeled D1, D2, and D3, depending on whether they are intended to form pixels P1, P2, and P3 of different colors. The diodes are mounted on a substrate 11 and are electrically biased by a lower electrode layer 12 and an upper electrode layer 13. Other configurations are possible, particularly when the substrate 11 is electrically conductive.

[0044] Diodes D1, D2, and D3 are fabricated here using conventional methods, for example, by semiconductor layer epitaxy. Each diode D1, D2, and D3 consists of a stack of a lower semiconductor portion doped with a first type of conductivity, for example, p-type, an active region where the light-emitting diode is emitted, and an upper semiconductor portion doped with a second type of conductivity, for example, n-type. Diodes D1, D2, and D3 can be fabricated from the same semiconductor compound, for example, a III-V compound such as GaN, InGaN, or AlGaN, among others.

[0045] Preferably, diodes D1, D2, and D3 are structurally identical, so that the emitted light is substantially the same from one diode to another in terms of wavelength. In this example, diodes D1, D2, and D3 are suitable for emitting blue light, that is, light whose emission spectrum has a peak intensity at a wavelength between approximately 440 nm and 490 nm.

[0046] A front face of the diode array 10 is substantially flat, possibly with surface microstructures to improve light extraction. Here, it is formed by the upper face of the top electrode layer 13, which is adapted to electrically bias the diodes. It can also be formed by a thin passivation layer (not shown) that covers the diodes and the top electrode layer.

[0047] With reference to fig. 1B and 1CNext, a first electret layer E1 is created, which at least partially covers the diode matrix 10. Its upper face F1 exhibits initial surface potential patterns M1 where the surface potential is non-zero. These patterns M1 are surrounded, at least partially, by regions of the upper face F1 where the surface potential is zero. As previously mentioned, an electret layer has a non-zero surface potential on its upper face due to the presence of electric charges or dipole polarization (vertical orientation of the dipoles). Here, the surface potential of the upper face F1 is non-zero only within predefined patterns M1, called surface potential patterns, while it is practically zero outside these patterns M1. It can be approximately 10V. The electrical potential patterns M1 are therefore the surfaces of the upper face where the electrical potential is non-zero.They extend in relation to at least one diode, and are intended to form the surfaces where photoluminescent particles will be deposited during the production of the photoluminescent pads.

[0048] With reference to the fig.1BAn electret layer E1 is deposited, at least partially covering the diode array 10. In this example, the electret layer E1 is made of a self-polarizing dielectric material, meaning that it was not necessary to polarize the dielectric layer in a dedicated step. It therefore forms an electret layer whose upper face F1 has a non-zero initial surface potential across its entire surface. By "over its entire surface," we mean at least across the entire surface of the upper face of the electret layer that is facing the diode array. In this example, the electret layer E1 covers all diodes D1, D2, and D3, but it could cover only some of the diodes, for example, only those intended to form the red and green pixels. Its upper face has several zones F1.1, F1.2, and F1.3, located respectively opposite diodes D1, D2, and D3.

[0049] Furthermore, the material of the electret layer E1 is chosen to be at least partially absorbent at the wavelength of depolarizing light (e.g., in the ultraviolet), and at least partially transparent at the wavelength of the light emitted by the diodes (e.g., in the blue). "At least partially absorbent" means that the absorption rate is at least 20% (or even less, for example, at least 10%), or at least 50%, at the wavelength of the depolarizing light. And "at least partially transparent" means that the transmission rate is at least 50% at the wavelength of the light emitted by the diodes. The electret layer can be a few tens to hundreds of nanometers thick, and preferably no more than 2 µm.

[0050] As an example, the self-polarizing dielectric material can be an organic material chosen from BCPO (bis-4-(N-carbazolyl)phenyl)phenylphosphine oxide), DPEPO (bis[2-(diphenylphosphino)phenyl]ether oxide), mCBP-CN (3,3'-di(carbazol-9-yl)-5-cyano-1,1'-biphenyl) and PO9 (3,6-bis(diphenylphosphoryl)-9-phenylcarbazole).

[0051] Il peut également être un matériau organique choisi parmi : le TPBi (2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)), le o-ethyl-TPB, le m-ethyl-TPBi, le p-ethyl-TPBi, le Alq3 (tris(8-hydroxyquinolinato)aluminum), le Al(7-Prq)3 (tris(7-propyl-8-hydroxyquinolinolato) aluminum(III)), le Al(q-Cl)3 (tris(5-chloro-8-hydroxyquinolinato)aluminum), le OXD-7 (2,2'-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole]), le BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), le Gaq3 (tris(8-hydroxyquinoline) gallium), le Balq (bis(2-methyl-8-quinolinate)4-phenylphenolate), le Ir(ppy)3 (tris(2-phenylpyridine)iridium(III)), le Ir(ppy)2acac (bis(2-phenylpyridine)iridium(III) acetylacetonate), le Ir(ppy)2tmd (bis(2-phenylpyridine)iridium(III)(2,2,6,6-tetramethylheptane-3,5-diketonate)), le Bpy-OXD (1,3-Bis[2-(2,2'-bipyridine-6-yl)-1,3,4-oxadiazo-5-yl]benzene), le 2CzPN (4,5-di (9H-carbazol-9-yl) phthalonitrile), le 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene, le 4CzPN (3,4,5,6-tetrakis (carbazol-9-yl)-1,2-dicyanobenzene), le DCJTB (4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran), le DACT-II (9-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-N,N,N',N'-tetraphenyl-9H-carbazole-3,6-diamine), le mCP (1,3-Bis(N-carbazolyl)benzene), le α-NPD (N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine), le Znq2 (bis(8-hydroxyquinoline)zinc), et le B3PyMPM (bis-4,6-(3,5- di-3-pyridylphenyl)-2-methylpyrimidine).,

[0052] En référence à la fig.1CThe electret layer E1 is locally depolarized optically to define the first surface potential patterns M1. To achieve this, an opaque layer is deposited on the electret layer E1, which is then structured by photolithography and etching to obtain an opaque mask 2. This mask extends only over diodes D1, i.e., over the F1.1 regions. It does not extend over diodes D2 and D3. The opaque mask 2 can be made of a photosensitive resin opaque to the depolarization light, in this case, ultraviolet. Alternatively, the opaque mask 2 can be the photolithography mask at the stepper motor.

[0053] Next, the electret layer E1 is subjected to depolarizing light of wavelength λdp, which is absorbed by the electret layer E1 only in areas F1.2 and F1.3 (not covered by the opaque mask 2), and not in area F1.1. Thus, the absorption of the depolarizing light causes localized depolarization in areas F1.2 and F1.3 of the upper surface F1 of the electret layer E1. Areas F1.1 of the upper surface F1 of the electret layer E1 therefore form the surface potential patterns M1. For example, the depolarizing light can be in the ultraviolet, i.e., with a principal wavelength between 100 and 380 nm. Following this step, resin 2 is removed.

[0054] With reference to the fig.1DThe first photoluminescent pads P1 are then produced by localized deposition of the first photoluminescent particles p1 onto the electret layer E1 opposite the first surface potential patterns M1. This is done in a manner similar to that described in documents WO2014 / 136023 and WO2021 / 023656. A colloidal solution containing the first photoluminescent particles p1 is placed in contact with the upper face F1 of the electret layer E1. The entire stack can be immersed in the colloidal solution, or a drop of such a solution can be deposited onto the electret layer E1. Due to the non-zero surface potential located within the surface potential patterns M1, a non-uniform electric field is generated, which causes localized deposition of the photoluminescent particles p1 by dielectrophoresis. Therefore, the photoluminescent particles p1 are deposited primarily opposite the first patterns M1, and practically not outside of them (i.e.(not in relation to zones F1.2 and F1.3). The contact time of the colloidal solution on the electret layer E1 depends in particular on the quantity of photoluminescent particles p1 to be deposited, the particle concentration, their size, the surface potential, etc. For example, the thickness of the photoluminescent particles P1 can be on the order of a few hundred nanometers, for example, approximately 400 nm. The colloidal solution is then removed, and the electret layer E1 can be dried. Note that the surface potential of the M1 motifs has become practically zero. Indeed, the photoluminescent particles p1 attach to the surface of the electret layer E1 at the level of the M1 motifs until the potential of the M1 motifs is almost completely attenuated.

[0055] With reference to fig. 1E and 1FNext, a second electret layer E2 is created, which at least partially covers the diode matrix 10, and whose upper face F2 also features second surface potential patterns M2 where the surface potential is non-zero. The second surface potential patterns M2 are not located opposite the first photoluminescent pads P1, so that the second photoluminescent pads P2 are opposite diodes other than diodes D1, thus forming luminous pixels of a different color.

[0056] For this reason, with reference to the fig.1EThe second electret layer E2, here also made of a self-polarizing dielectric material, is deposited so as to cover the first electret layer E1 as well as the first photoluminescent pads P1. Its upper surface F2 therefore exhibits a non-zero surface potential across its entire surface. This second electret layer E2 can be made of the same material as the first electret layer E1. It is also chosen to be at least partially absorbent at the wavelength of depolarizing light (here in the ultraviolet), and at least partially transparent at the wavelength of the light emitted by the diodes (here in the blue). The electret layer E2 can have a thickness on the order of tens to hundreds of nanometers, and preferably no more than 2 µm.

[0057] With reference to the fig.1FThe second electret layer E2 is locally depolarized optically to define the second surface potential patterns M2 defined on its upper face F2. To achieve this, an opaque layer is deposited on the second electret layer E2, which is then structured by photolithography and etching to obtain an optical mask 2. This mask extends only in relation to diodes D3 and therefore does not extend in relation to diodes D1 and D2. Alternatively, as previously mentioned, mask 2 can be the photolithography mask at the stepper motor.

[0058] Next, the second electret layer E2 is subjected to depolarizing light, which is then absorbed by the second electret layer E2 only in regions F2.1 and F2.2 (not covered by the opaque mask 2), and not in regions F2.3. Thus, the absorption of the depolarizing light causes localized depolarization in regions F2.1 and F2.2 of the upper face F2 of the electret layer E2. The regions F2.3 of the upper face F2 of the electret layer E2 therefore form the second surface potential patterns M2.

[0059] Preferably, if the potential of the M1 motifs is not completely zero, some of the depolarizing light radiation is transmitted through the second electret layer E2, then through the photoluminescent pads P1, and subsequently absorbed by the first electret layer E1, thus locally depolarizing the first surface potential motifs M1. This further reduces the risk of second photoluminescent particles p2 subsequently being deposited opposite the first photoluminescent pads P1.

[0060] With reference to the fig.1GThe second photoluminescent patches, P2, are then produced by localized deposition of second photoluminescent particles, p2, onto the electret layer E2 opposite the second surface potential patterns, M2. This is done as with the first photoluminescent patches, P1, by placing a colloidal solution containing the second photoluminescent particles, p2, in contact with the upper face, F2, of the second electret layer, E2. Due to the non-zero surface potential located in the second patterns, M2, a non-uniform electric field is generated, causing localized deposition of the photoluminescent particles, p2, by dielectrophoresis. Thus, the photoluminescent particles, p2, are deposited primarily opposite the second patterns, M2, and substantially not outside of them (i.e., not opposite areas F2.1 and F2.2), resulting in the second photoluminescent patches, P2.Note that the surface potential of the M2 motifs becomes essentially zero as the p2 photoluminescent particles are grafted. The colloidal solution is then removed and the electret layer can be dried.

[0061] With reference to the fig.1HThis yields an optoelectronic device 1, comprising a diode array 10 and a color conversion structure formed of photoluminescent pads P1 and P2. In this example, diodes D2 form blue pixels, diodes D1 associated with photoluminescent pads P1 form, for example, red pixels, and diodes D3 associated with photoluminescent pads P2 form green pixels. To form the photoluminescent pads, the process employs a localized optical depolarization step of electret layers E1 and E2, which initially have a non-zero surface potential across their entire upper surface. This avoids the need for a localized injection step of electrical charges into an electret layer that is initially charge-free, as in the previously mentioned prior art examples.Also, the process is fast and the production of photoluminescent pads is spatially precise, even in the context of a diode matrix made from a large substrate (for example 100 or 200 mm) and / or whose pixel pitch is very small (for example 5 µm or less).

[0062] THE figures 2A to 2C illustrate different stages of a manufacturing process for an optoelectronic device according to one embodiment variant. In this example, the surface potential patterns are created by localized optical depolarization of an electret layer which initially has a non-zero surface potential across its entire surface.

[0063] This process differs from that of figures 1A-1Hessentially, the depolarization light radiation corresponds to the light radiation emitted by the diodes. In this case, the diode matrix is ​​adapted to selectively activate diodes D1, D2 and D3, and therefore includes lower electrodes 12 and upper electrodes 13 arranged to allow this selective activation.

[0064] Furthermore, the electret layer material E1 is adapted to absorb only part of the light emitted by diodes D1, D2, and D3, and to transmit the unabsorbed portion. Thus, the absorbed portion allows for local depolarization of the electret layer in the areas of the upper surface opposite the activated diodes. The areas of the upper surface opposite the unactivated diodes then retain their non-zero surface potential, thereby defining the surface potential patterns.

[0065] With reference to the fig.2AA diode matrix 10 is provided, covered by an electret layer E1. The upper face F1 of this layer has a non-zero surface potential over its entire surface. The electret layer E1 is then made of a dielectric material adapted to absorb only part of the light emitted by the diodes, here in the blue (or near-blue) range.

[0066] With reference to the fig.2BThe diodes are activated selectively, meaning that only some of them are activated. Here, only diodes D2 and D3 are activated, not diode D1. The emitted light is then partially absorbed locally by the electret layer E1 in regions F1.2 and F1.3 of the upper surface F1 located opposite diodes D2 and D3, resulting in a local depolarization of the electret layer E1 opposite these diodes. Conversely, since diodes D1 are not activated, the electret layer E1 remains locally polarized in regions F1.1, which then define the first surface potential patterns M1.

[0067] With reference to the fig.2C , we then produce the first photoluminescent pads P1, in the same way as before (cf. fig.1D), by bringing the electret layer E1 into contact with a colloidal solution containing the photoluminescent particles p1. These then naturally deposit themselves on the electret layer E1 in the surface potential patterns M1, so that the photoluminescent spots P1 are positioned opposite the diodes D1 and not opposite the diodes D2 and D3.

[0068] The manufacturing process can be continued in the same way as before (not shown). A second electret layer E2 is deposited, covering the diode matrix 10 as well as the first pads P1 and the electret layer E1. The top surface of the electret layer E2 has a non-zero surface potential across its entire surface. This second electret layer E2 is then locally depolarized optically, in the same manner as the fig.2BThus, only diodes D1 and D2 are activated, so as to depolarize regions F2.1 and F2.2 of the upper face F2 of the electret layer E2. Conversely, diodes D3 are not activated, so that regions F2.3 have a non-zero surface potential, thus forming the second surface potential patterns M2. Note that, alternatively, the localized optical depolarization of the second electret layer E2 can be carried out as in the process of figures 1A-1H that is, by using a dedicated depolarization light radiation, distinct from that emitted by the diodes.

[0069] Thus, in this embodiment, the manufacturing process utilizes the selective activation of the diodes in matrix 10 to locally depolarize the electret layer(s) E1, E2, thereby defining the surface potential patterns. This simplifies the manufacturing process, particularly the depolarization steps.

[0070] THE figures 3A to 3C illustrate different stages of a manufacturing process for an optoelectronic device according to another embodiment variant.

[0071] This process differs from that of figures 1A-1H Essentially, the electret layer E1 is made from a photochromic dielectric material that is locally optically polarized to form the surface potential patterns, rather than by depolarizing an electret layer with an initially non-zero surface potential. In other words, the surface potential patterns are created by localized optical polarization of an electret layer that initially has a zero surface potential across its entire surface.

[0072] The photochromic material of the E1 electret layer is then adapted to absorb at least part of a predefined polarization of light, for example between 100nm and 380nm, leading to an electrical polarization of the layer. Finally, it is also at least partially transparent to the light emitted by the diodes, for example in the blue range. The photochromic material can be a compound of a matrix material such as poly(methyl methacrylate) (PMMA) or polystyrene (PS), containing 1 to 20 wt% of a photochromic material which can be chosen from among spiropyrans (SP) or 1',3'-dihydrol, 3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2 112 0-(2H)-indole] or N,N'-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13H27) or 1,2-bis-[2-methyl-5-(p-cyanophenyl)-3-thienyl]perfluorocyclopentene (DTE-CN). This last material is notably presented in the article by Castagna et al.entitled Photochromic Electret: A New Tool for Light Energy Harvesting, The Journal of Physical Chemistry Letters, 3(1), 51-57, 2012.

[0073] With reference to the fig.3A A diode matrix 10 is provided, covered by an electret layer E1. The upper face F1 of this layer has a surface potential that is substantially zero over its entire surface. The electret layer E1 is then made of a photochromic material.

[0074] With reference to the fig.3BThe surface potential patterns M1 are then formed by localized optical polarization of the electret layer E1. Here, through an opaque mask 2 (a mask deposited on the electret layer, the photolithography mask, etc.) facing diodes D2 and D3, specifically in regions F1.2 and F1.3 of the upper face F1, light of a predefined polarization wavelength λp is applied. This light is absorbed by the electret layer E1 only in region F1.1, and not in regions F1.2 and F1.3. Thus, the surface potential is undefined in regions F1.2 and F1.3 and remains zero, while it is non-zero in region F1.1, which defines the surface potential patterns M1.

[0075] Note that the localized polarization of the electret layer E1 can obviously be achieved by the selective activation of the diodes of matrix 10.

[0076] With reference to the fig.3C, we then produce the first photoluminescent pads P1, in the same way as before (cf. fig.2C ), by bringing the electret layer E1 into contact with a colloidal solution containing the photoluminescent particles p1. These then naturally deposit themselves on the electret layer E1 in the surface potential patterns M1, so that the photoluminescent spots P1 are positioned opposite the diodes D1 and not opposite the diodes D2 and D3.

[0077] The manufacturing process can be continued in the same way as before (not shown), except that it is not necessary to use a second electret layer E2. Thus, a second exposure is made to the electret layer E1, which has surface potential patterns M2 (located, for example, opposite diodes D3), and finally, the photoluminescent pads P2 are made opposite the surface potential patterns M2. Once all the photoluminescent pads have been deposited by dielectrophoresis, exposure to visible light of the entire electret layer E1 is advantageously carried out to improve, if necessary, the transparency of this layer in the visible range of the spectrum.

[0078] THE figures 4A to 4F illustrate different stages of a manufacturing process for an optoelectronic device according to another embodiment variant.

[0079] This process differs from the process described in the... Figures 1Aand following essentially in that at least one of the electret layers, and here the two electret layers E1, E2, is made of a dielectric material that is electrically polarized electrostatically. For this purpose, the upper electrode layer 13 is used. In other words, the surface potential patterns are created by localized depolarization, optically, of an electret layer initially exhibiting a non-zero surface potential across its entire surface.

[0080] With reference to the fig.4A, a diode matrix 10 is provided, covered by an electret layer E1. The upper face F1 of this layer has, over its entire surface, an initial surface potential that is substantially zero. The electret layer E1 is then made of an inorganic dielectric material such as, for example, a silicon oxide (Si x O y ), a silicon nitride (Si x N y ), an aluminum oxide (Al x O y ), a titanium oxide (Ti x O y ), a tantalum oxide (Ta x O y ), a halfnium oxide (Hf x O y ), or even an organic dielectric material (PMMA...).

[0081] With reference to the fig.4BA non-zero surface potential is defined across the entire surface of the upper face of the electret layer E1. This is achieved by utilizing the upper electrode layer 13, which extends beneath the entire surface of the electret layer E1. An additional electrode 14, positioned above the entire electret layer E1, is also brought close to the surface, and a potential difference is applied between these two electrodes 13 and 14. A non-zero surface potential is thus created across the entire surface of the upper face of the electret layer E1. Other electret layer loading techniques are also possible (plasma, ion implantation, corona discharge, etc.).

[0082] With reference to the fig.4C, we then define the surface potential patterns M1, by localized depolarization of the electret layer E1 by optical means, according to one of the methods described previously. Then we produce the first photoluminescent pads P1, in the same way as before (cf. fig.1D ), by bringing the electret layer E1 into contact with a colloidal solution containing the photoluminescent particles p1. These then naturally deposit onto the electret layer E1 in the surface potential patterns M1, so that the photoluminescent spots P1 are positioned opposite the diodes D1 and not opposite the diodes D2 and D3. The surface potential of the patterns M1 then becomes essentially zero.

[0083] A second electret layer E2 is then created, exhibiting surface potential patterns M2. Here, the electret layer E2 is created like the electret layer E1 by electrostatically biasing a layer with an initial electric potential of zero. Alternatively, the second electret layer can be created as in the examples described previously with reference to fig.1A-1H , to fig.2A-2C and to fig.3A-3C .

[0084] With reference to the fig.4DFirst, an electrode layer 15 is created, covering the entire diode matrix 10, and more specifically the photoluminescent pads P1 and the electret layer E1. Then, an electret layer E2 is deposited. It extends completely over the electrode layer 15 and also encapsulates the photoluminescent particles of pad P1. The upper surface of the electret layer E2 has a near-zero initial surface potential across its entire surface. The electret layer E2 can be made of the same dielectric material as the electret layer E1.

[0085] With reference to the fig.4EA non-zero surface potential is defined across the entire surface of the upper face of the electret layer E2. This is achieved by applying a potential difference between electrode 15 and an additional electrode 14 positioned above the entire electret layer E2. A non-zero surface potential is thus created across the entire surface of the upper face of the electret layer E2. Note that electrode 15 could be omitted: in this case, a potential difference would be applied between electrode 14 and electrode 13.

[0086] With reference to the fig.4F , we then define the surface potential patterns M2, by localized depolarization of the electret layer E2 by optical means. Then we produce the photoluminescent pads P2, in the same way as before (cf. fig.1G), by bringing the electret layer E2 into contact with a colloidal solution containing the photoluminescent particles p2. These then naturally deposit onto the electret layer E2 in the surface potential patterns M2, so that the photoluminescent spots P2 are positioned opposite the diodes D2 and not opposite the diodes D1 and D2. The surface potential of the patterns M2 then becomes essentially zero.

[0087] Specific embodiments have just been described. Various variations and modifications will be apparent to those skilled in the art. The scope of the invention is defined by the claims.

Claims

1. A method for manufacturing an optoelectronic device (1) including: • an array of diodes (10), configurated to emit or receive a light radiation; and • a colour conversion structure, covering at least partially the array of diodes (10), and containing photoluminescent pads (P1) arranged opposite at least one diode; o the method including the following steps: ∘ A / providing the array of diodes (10); ∘ B / making an electret layer (E1), covering the array of diodes (10), and an upper face of which (F1), opposite to the array of diodes (10), has predefined surface potential patterns (M1) where the surface potential is non-zero; ∘ C / making the photoluminescent pads (P1), by contact of the electret layer (E1) with a colloidal solution containing photoluminescent particles (p1), which are then deposited over the upper face (F1) of the electret layer (E1) opposite the predefined surface potential patterns (M1), thereby forming the photoluminescent pads (P1); ∘ and wherein step B of making the electret layer (E1) includes the following steps: • B1 / making an electret layer (E1) whose upper face (F1) has, over its entire face, a non-zero or zero initial surface potential; then • B2a / in the case where the initial surface potential is non-zero: illuminate areas of the electret layer (E1) with a depolarisation light radiation which can be absorbed at least partially by the electret layer (E1), said illuminated areas being distinct from non-illuminated areas intended to form the surface potential patterns (M1), the absorption of the depolarisation light radiation in the illuminated areas causing a cancellation of the local surface potential, the non-illuminated areas then defining the surface potential patterns (M1); • B2b / or, in the case where the initial surface potential is zero: illuminate areas of the electret layer (E1) by a polarisation light radiation which can be absorbed at least partially by the electret layer (E1), the absorption of the polarisation light radiation in the illuminated areas causing a formation of a non-zero local surface potential, the illuminated areas then defining the surface potential patterns (M1).

2. The manufacturing method according to claim 1, including, prior to step B2a or B2b, a step of arranging an opaque mask (2), made of a material opaque to the depolarisation or polarisation light radiation, extending only over the areas of the electret layer (E1) intended to form the surface potential patterns (M1); then, during step B2a or B2b, the depolarisation or polarisation light radiation is emitted in the direction of the opaque mask (2) and the electet layer (E1), and is absorbed by the electret layer (E1) in the areas not covered by the opaque mask (2).

3. The manufacturing method according to claim 1, wherein: o the diodes are light-emitting diodes; o the electret layer (E1) is made of a material configured to partially absorb the light radiation emitted by the light-emitting diodes, which causes a cancellation of the local surface potential; o during step B2a, some diodes are selectively activated so as to illuminate the electret layer in the areas intended not to form the surface potential patterns (M1), which causes a cancellation of the local surface potential, the non-illuminated areas then defining the surface potential patterns (M1); o or, during step B2b, diodes are selectively activated so as to illuminate the electret layer only in the areas intended to form the surface potential patterns (M1).

4. The manufacturing method according to anyone of claims 1 to 3 in connection with step B2a, wherein the electret layer (E1) is made of a self-polarised organic dielectric material, so that step B1 consists in depositing the electret layer (E1) covering the array of diodes (10), the electret layer (E1) then having, over its entire surface, a non-zero initial surface potential.

5. The manufacturing method according to anyone of claims 1 to 3 in connection with step B2b, wherein the electret layer (E1) is made of a photochromic dielectric material, so that step B1 consists in depositing an electret layer (E1), made of the photochromic dielectric material, covering the array of diodes (10), the electret layer (E1) then having, over its entire surface, a zero surface potential.

6. The manufacturing method according to anyone of claims 1 to 3 in connection with step B2a, wherein the electret layer (E1) is made of a dielectric material, so that step B1 includes the following steps: o depositing an electret later (E1), made of the dielectric material, covering the array of diodes (10), the electret layer (E1) then having, over its entire surface, a zero initial surface potential; then o subjecting the electret layer (E1) to a predefined polarisation electric field, causing a formation of a non-zero surface potential over the entire surface of the electret layer (E1).

7. The manufacturing method according to the preceding claim, wherein: o the array of diodes (10) includes an upper electrode layer (13) covering the diodes and configured to electrically polarise the diodes, o during the step of subjecting the electret layer (E1) to the polarisation electric field, the electret layer (E1) is then arranged between the upper electrode layer (13) and an added-on electrode (14), between which a predefined potential difference is applied.

8. The manufacturing method according to anyone of claims 1 to 7, wherein: o the electret layer (E1) made during step B is a first electret layer; and the photoluminescent pads (P1) made during step C are first photoluminescent pads configured to convert an incident light radiation with a first wavelength into a light radiation with a second wavelength different from the first wavelength; o the method including the following steps, following step C: o D / making a second electret layer (E2), covering the array of diodes (10) and the first electret layer (E1), and an upper face (F1) of which, opposite to the array of diodes (10), has second predefined surface potential patterns (M2) where the surface potential is non-zero, said second surface potential patterns (M2) being located opposite diodes distinct from those opposite which the first surface potential patterns (M1) are located; o E / making the second photoluminescent pads (P2), by contact of the second electret layer (E2) with a colloidal solution containing second photoluminescent particles (p2), different from the first photoluminescent particles (p1) of step C, which are then deposited over the upper face (F2) of the second electret layer (E2) opposite the second predefined surface potential patterns (M2), thereby forming the second photoluminescent pads (P2).

9. The manufacturing method according to the preceding claim, wherein the diodes of the array (10) are light-emitting diodes configured to emit a light radiation at the same wavelength; and form with the first and second photoluminescent pads (P1, P2) an array of red, green, blue luminous pixels.

10. The manufacturing method according to anyone of claims 1 to 9, wherein the array of diodes (10) has a dimension, in a plane parallel to the array of diodes (10), larger than or equal to 100 mm.

11. The manufacturing method according to anyone of claims 1 to 10, wherein the array of diodes (10) has a pitch with a periodicity smaller than or equal to 10 µm, or 5 µm, or 2 µm.