Method for manufacturing an optoelectronic device

Abstract

The invention relates to a method for manufacturing an optoelectronic device comprising a diode array (10) and a photoluminescent pad arranged opposite at least one diode, the method comprising the steps of: making an electret layer (E1) on the diode array (10) by local polarization or depolarization, optically, to form a surface potential pattern (M1); making a photoluminescent pad (P1) by contacting the electret layer (E1) with a gel-like solution containing photoluminescent particles (p1) and then depositing the photoluminescent particles (p1) on an upper surface (F1) of the electret layer (E1) opposite the predetermined surface potential pattern (M1), thereby forming the photoluminescent pad (P1).

Description

TECHNICAL FIELD

[0001] The field of the invention is a method for manufacturing an optoelectronic device comprising an array of diodes for emitting or detecting electroluminescent radiation, the array of diodes being associated with a color conversion structure having photoluminescent pads. The invention applies in particular in display screens and image projectors. BACKGROUND

[0002] There exist optoelectronic devices comprising an array of diodes formed of identical light-emitting diodes, the array being at least partially covered by photoluminescent pads, thereby ensuring color conversion. Such optoelectronic devices can form a display screen or an image projection system comprising an array of light-emitting pixels formed of different colors.

[0003] In such optoelectronic devices, each light-emitting pixel comprises one or more light-emitting diodes associated with a photoluminescent pad. In order to obtain light-emitting pixels adapted to emit light radiation of different colors, for example blue, green or red, all the light-emitting diodes can be adapted to emit the same light, for example blue, and the green pixels and the red pixels comprise a photoluminescent pad adapted to at least partially absorb the incident blue light emitted by the light-emitting diodes and, in response, to emit green light or red light.

[0004] The light-emitting diodes are therefore preferably identical to one another and emit light radiation having substantially the same wavelength. The light-emitting diodes can be formed on the basis of a semiconductor material comprising elements of column III and column V of the periodic table, for example a III-V compound, in particular gallium nitride (GaN), indium gallium nitride (InGaN) or aluminum gallium nitride (AlGaN). The light-emitting diodes are arranged to form an array of light-emitting diodes having a front surface through which the generated light radiation is transmitted. These light-emitting diodes can be constituted by organic light-emitting diodes.

[0005] The photoluminescent pads can be formed of a binding matrix comprising particles of a photoluminescent material, for example yttrium aluminum garnet (YAG, for the English term Yttrium Aluminium Garnet) YAG:Ce activated by cerium ions. The photoluminescent particles can also be quantum dots, i.e. in the form of semiconductor nanocrystals in which the quantum confinement is substantially three-dimensional. In particular, these photoluminescent particles can be constituted by InP, perovskite or CdSe crystals.

[0006] The manufacturing method can comprise depositing then structuring a photoluminescent layer to form, for example, a first photoluminescent pad adapted to convert blue into green. These steps are performed again to form, for example, a second photoluminescent pad adapted to convert blue into red. However, this method has the drawback of being hardly suitable for diode arrays having a small pixel pitch, for example in the range of 5 pm, to the extent that there can be a problem of photoluminescent pads being aligned or covering each other.

[0007] Document WO2014 / 136023 describes another manufacturing method which uses an electret layer covering a diode array. This method first comprises a step of imparting a charge pattern on the upper face of a dielectric layer to obtain an electret layer. To do this, a polarized AFM tip is used to locally inject charges. Then, a step of locally depositing colloidal nanocrystals on the charge pattern is performed. To do this, the electret layer is brought into contact with a colloidal solution containing nanocrystals which are naturally deposited on the charge pattern under the effect of dielectrophoretic forces. However, this method has the drawback, among others, of having to inject charges sequentially to form a charge pattern in the surface by moving the AFM tip above the surface of the upper face.

[0008] Document WO2021 / 023656 describes a similar method in which the charge pattern is defined by a stamping technique, i.e. by bringing an electrically polarized buffer into contact with a dielectric layer intended to form an electret layer. The lower face of the buffer is structured to form polarized teeth which come into contact with the dielectric layer. Thus, an electret layer is obtained which has a charge pattern on the upper face. After that, the electret layer is brought into contact with a colloidal solution and then the nanocrystals present are deposited on the charge pattern by dielectrophoresis. However, this method has the drawback, among others, of having to position the buffer accurately with respect to the diode array. However, positioning uncertainty of the buffer with respect to the diode array can become problematic, in particular for diode arrays having a small pixel pitch, for example in the range of 5 pm. Indeed, such positioning uncertainty can lead to incorrect positioning of the photoluminescent pads with respect to the diodes and thus to a degradation of the performance of the optoelectronic device. SUMMARY

[0009] The aim of the application is to overcome at least some of the drawbacks of the prior art and more particularly to provide a method for manufacturing an optoelectronic device in which the formation of a charge pattern, which will be called a surface potential pattern herein, is performed in the electret layer by an optical process, either by locally polarizing the electret layer or by locally depolarizing the electret layer. This step allows all the surface potential patterns to be formed simultaneously in the electret layer without the need to use an AFM tip or a buffer as previously described and thus to form photoluminescent pads which have a suitable positioning with respect to the diode array.

[0010] To this end, the application aims at a method for manufacturing an optoelectronic device comprising: an array of diodes, the array of diodes being adapted to emit or receive optical radiation; and a color conversion structure, the color conversion structure at least partially covering the array of diodes and comprising a photoluminescent mat arranged opposite at least one diode.

[0011] The manufacturing method comprises the following steps:

[0012] o A / providing an array of diodes;

[0013] o B / making an electret layer, the electret layer covering the array of diodes, and the electret layer having a predetermined surface potential pattern on its upper face opposite the array of diodes, in which pattern the surface potential is not zero;

[0014] o C / making a photoluminescent mat by contacting the electret layer with a gelatinous solution comprising photoluminescent particles, then depositing the photoluminescent particles on the upper face of the electret layer opposite the predetermined surface potential pattern, thereby forming the photoluminescent mat.

[0015] According to the application, the step B of making an electret layer comprises the following steps:

[0016] • B1 / making an electret layer, the upper face of the electret layer having an initial surface potential which is not zero or zero over its entire surface; then

[0017] • B2a / in the case where the initial surface potential is not zero: irradiating a region of the electret layer with so-called depolarization optical radiation which is at least partially absorbed by the electret layer, said irradiated region being different from a non-irradiated region intended to form the surface potential pattern, the absorption of the depolarization optical radiation in the irradiated region causing the local surface potential to be eliminated, then the non-irradiated region defining the surface potential pattern; or

[0018] • B2b / in the case where the initial surface potential is zero: irradiating a region of the electret layer with so-called polarization optical radiation which is at least partially absorbed by the electret layer, the absorption of the polarization optical radiation in the irradiated region causing a local surface potential which is not zero to be formed, then the irradiated region defining the surface potential pattern.

[0019] Some preferred but non-limiting aspects of the method are as follows.

[0020] The method can comprise, before step B2a or B2b, a step of arranging an opaque mask made of a material that is opaque to depolarized light radiation or polarized light radiation and that extends only over the area of the electret layer intended to form the surface potential pattern; then, during step B2a or B2b, the depolarized light radiation or the polarized light radiation can be emitted in the direction of the opaque mask and of the electret layer and is absorbed by the electret layer in the areas not covered by the opaque mask.

[0021] The diodes can be constituted by light-emitting diodes. The electret layer can be made of a material that is adapted to partially absorb the light radiation emitted by the light-emitting diodes so that the local surface potential is eliminated. During step B2a, some diodes can be selectively activated to illuminate the electret layer in the areas not intended to form the surface potential pattern so that the local surface potential is eliminated, then the non-illuminated areas define the surface potential pattern. Alternatively, during step B2b, the diodes can be selectively activated to illuminate the electret layer only in the areas intended to form the surface potential pattern.

[0022] In relation to step B2a, the electret layer can be made of a self-polarizing organic dielectric material so that step B1 can subsequently comprise depositing an electret layer covering the array of diodes, then the electret layer has an initial surface potential that is not zero over its entire surface.

[0023] In relation to step B2b, the electret layer is made of a photochromic dielectric material so that step B1 can subsequently comprise depositing an electret layer made of a photochromic dielectric material covering the array of diodes, then the electret layer has a surface potential that is zero over its entire surface.

[0024] In relation to step B2a, the electret layer can be made of a dielectric material so that step B1 comprises a step of depositing an electret layer made of a dielectric material covering the array of diodes, then the electret layer has an initial surface potential that is zero over its entire surface; then the electret layer is subjected to a predetermined electric field (so-called polarization field) so that a surface potential that is not zero is formed over the entire surface of the electret layer.

[0025] The array of diodes can comprise an upper electrode layer covering the diodes and adapted to polarize the diodes electrically. During the step of subjecting the electret layer to the polarization electric field, the electret layer can then be arranged between the upper electrode layer and an additional electrode, between which a predetermined potential difference is applied.

[0026] The electret layer made during step B can be a first electret layer. The photoluminescent mat made during step C can then be constituted by a first photoluminescent mat adapted to convert incident light radiation having a first wavelength into light radiation having a second wavelength different from the first wavelength.

[0027] Then after step C, the method can comprise the following steps:

[0028] o D / making a second electret layer, the second electret layer covering the array of diodes and the first electret layer, the upper surface of the second electret layer opposite the array of diodes having a second predetermined surface potential pattern in which the surface potential is not zero, the diodes positioned opposite the second surface potential pattern being different from the diodes positioned opposite the first surface potential pattern;

[0029] o E / making a second photoluminescent mat by contacting the second electret layer with a gel-like solution containing second photoluminescent particles different from the first photoluminescent particles of step C, then depositing the second photoluminescent particles on the upper surface of the second electret layer opposite the second predetermined surface potential pattern, thereby forming the second photoluminescent mat.

[0030] The diodes of the array can be constituted by light-emitting diodes adapted to emit light radiation of the same wavelength. The diodes can then form, together with the first and second photoluminescent mats, an array of red, green, blue light-emitting pixels.

[0031] The array of diodes can have a size greater than or equal to 100 mm in a plane parallel to the array of diodes.

[0032] The array of diodes can have a pitch less than or equal to 10 pm, or 5 pm, or 2 pm. BRIEF DESCRIPTION OF DRAWINGS

[0033] Other aspects, objectives, advantages and features of the application will become more apparent from the following detailed description of preferred embodiments thereof, given by way of non-restrictive example only and with reference to the drawings, in which:

[0034] Figures 1A-1H Different steps of a method for manufacturing an optoelectronic device are illustrated, in which at least one of the electret layers is made of a self-polarized dielectric material;

[0035] Figures 2A-2C Different steps of a variant of a method for manufacturing an optoelectronic device are illustrated, in which the local depolarization is performed by means of diodes of the array of diodes that are selectively activated;

[0036] Figures 3A-3C Different steps of a variant of a method for manufacturing an optoelectronic device are illustrated, in which the electret layer is made of a photochromic dielectric material that is locally polarized by an optical process;

[0037] Figures 4A-4FDifferent steps of one variant of a method for manufacturing an optoelectronic device are shown, wherein at least one of the electret layers is made of a dielectric material that is electrically polarized by an electrostatic process. DETAILED DESCRIPTION

[0038] In the rest of the drawings and the description, identical references denote identical or similar elements. Moreover, the elements are not shown to scale in order to improve the clarity of the drawings. Furthermore, different embodiments and variants are not mutually exclusive and can be combined together. Unless otherwise indicated, the terms "substantially", "approximately", "in the range of" mean within a 10% margin, preferably within a 5% margin. Moreover, unless otherwise stated, the terms "between... and..." and the like mean inclusive of the boundaries.

[0039] The present invention relates to a method for manufacturing an optoelectronic device comprising a diode array covered by a color conversion structure having photo luminescent pads. The formation of the photo luminescent pads is obtained by depositing photo luminescent particles on a surface potential pattern of the upper surface of an electret layer. As will be described in detail later, the surface potential pattern is defined by locally depolarizing or locally polarizing the electret layer by an optical process. Moreover, the diodes can be constituted by emission diodes, such as light emitting diodes, or photodiodes.

[0040] Generally, an electret layer is a dielectric layer comprising fixed electric charges or almost permanent dipole polarization. Moreover, an electret layer has a surface potential on its upper surface that is not zero. This is reflected by the fact that an electret layer generates an external electric field in the absence of an applied field. By extension, we will also call "electret layer" a dielectric layer that initially has a surface potential that is zero on its entire surface and aims at forming an electret layer having a surface potential pattern.

[0041] In the context of the present application, we take advantage of the fact that an electret layer can be depolarized by absorbing so-called depolarizing light radiation, as explained in the article entitled "Characterisation of light-erasable giant surface potential built up in evaporated Alq3 thin films" by Sugi et al., Thin Solid Films 464-465 (2004), pages 412-415, and in the article entitled "Self-Assembled Electret for Vibration-Based Power Generator" by Tanaka et al., Sci Rep 10, 6648 (2020). This depolarization subsequently causes the surface potential of the electret layer to be eliminated. Indeed, the absorption of depolarizing light radiation causes the creation of electron-hole pairs, which, according to one approach, compensate for the charge polarization, which leads to the elimination of the surface potential. In addition, the electret layer can also be polarized by absorbing so-called polarizing light radiation.

[0042] Thus, as will be described in detail later, according to one embodiment, the electret layer is first made, the electret layer initially having a surface potential that is not zero over its entire surface. Then, a predetermined area of the electret layer is polarized by irradiating it with depolarizing light radiation that can be at least partially absorbed by the electret layer. The irradiated area then has a surface potential that is zero, while the non-irradiated area retains its surface potential that is not zero, and thus forms a surface potential pattern on which the photoluminescent particles will subsequently be deposited in a localized manner by dielectrophoresis during a next step. In addition, the photoluminescent mat is naturally positioned opposite (i.e. "perpendicular to") the surface potential pattern, without being located outside these predefined patterns. Thus, even if the diode array has a large size (in particular when the diode array is formed using 100 mm or 200 mm wafer technology) and / or the pixel pitch of the diode array is small (for example in the range of 5 pm or less, for example 2 pm), this method allows the surface potential pattern to be precisely defined on the upper surface of the electret layer.

[0043] Furthermore, according to another embodiment, the electret layer is first made, the electret layer initially having a surface potential of zero over its entire surface. Then, a predetermined area of the electret layer is polarized by irradiating it with polarized light radiation that can at least partially be absorbed by the electret layer. The irradiated area then has a surface potential that is not zero (while the non-irradiated area remains with a surface potential of zero), and thus a surface potential pattern is formed, onto which the photo-luminescent particles will subsequently be deposited in a localized manner by dielectrophoresis during a next step. As before, this method allows to precisely define a surface potential pattern on the upper surface of the electret layer.

[0044] Furthermore, the photo-luminescent mat is adapted to at least partially convert the incident light radiation having a first wavelength λ1 into luminescent light radiation having a longer wavelength λ2. For illustrative purposes, the photo-luminescent mat can be adapted to absorb blue light, i.e. having a wavelength between about 440 nm and 490 nm, and to emit in the green band, i.e. at a wavelength between about 495 nm and 560 nm, and possibly in the red band, i.e. at a wavelength between 600 nm and 650 nm, or in the infrared band. In this context, the wavelength is to be understood as the wavelength at which the emission spectrum has an intensity peak. For illustrative purposes only, a light emitting diode can have an emission spectrum with an intensity peak between 380 nm and 490 nm. In the case of an array of light emitting diodes, the incident light radiation is the radiation emitted by the diodes, while in the case of a photodiode, the incident light radiation consists of light radiation originating from the external environment and directed towards the photodiode. It is to be noted that in the case of a photodiode, the photo-luminescent mat allows to filter a part of the spectral range of the incident light radiation, for example to perform a spectral analysis.

[0045] The photo-luminescent mat is formed of particles made of at least one photo-luminescent material, preferably the particles having a maximum size between 0.2 nm and 1000 nm, for example between 0.2 nm and 100 nm, for example between 1 nm and 30 nm. The size and / or composition of the photo-luminescent particles are chosen according to the desired luminescent wavelength. The particles can have any shape, for example spherical, angular, flat, elongated, etc.

[0046] The photo-luminescent particles can consist of quantum dots, i.e. semiconductor nanocrystals whose quantum confinement is essentially three-dimensional, or aggregates 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. The quantum dots can also consist of nanoplatelets, i.e. nanoparticles having an essentially two-dimensional shape. Furthermore, the smallest dimension (thickness) is less than the other two length and width dimensions, preferably by a ratio of at least 1.5.

[0047] In particular, the photoluminescent particles can be formed of at least one semiconductor compound, which can for example be chosen among cadmium selenide (CdSe), indium phosphide (InP), indium gallium phosphide (InGaP), cadmium sulfide (CdS), zinc sulfide (ZnS), cadmium oxide (CdO) or zinc oxide (ZnO), cadmium zinc selenide (CdZnSe), zinc selenide (ZnSe) doped with for example copper or manganese, graphene, or other potentially suitable semiconductor materials. The nanoparticles can also have a core / shell type of structure, for example CdSe / ZnS, CdSe / CdS, CdSe / CdS / ZnS, PbSe / PbS, CdTe / CdSe, CdSe / ZnTe, InP / ZnS, or others.

[0048] Figures 1A-1H Different steps of a method for manufacturing an optoelectronic device 1 according to one embodiment are illustrated. In this example, at least one of the electret layers E1, E2 is made of a self-polarizing dielectric material, in this document, both electret layers are made of a self-polarizing dielectric material. In this example, the surface potential pattern is optically made by locally depolarizing an electret layer initially having a surface potential not equal to zero over its entire surface.

[0049] Moreover, the optoelectronic device 1 comprises an array of light-emitting pixels of RGB (red, green, blue) type. Here, each RGB pixel is formed of several sub-pixels of light of R, G or B type, each sub-pixel comprising at least one light-emitting diode (one diode per sub-pixel). In the description, a sub-pixel associated with a given color is a so-called "pixel". Alternatively, the optoelectronic device 1 can comprise an array of photodiodes.

[0050] In this document, and for the following description, an orthogonal three-dimensional direct reference frame XYZ is defined, in which the X and Y axes form a main plane in which the support substrate 11 extends, and in which the Z axis is oriented along the direction of the front surface according to the thickness of the diode array 10. The terms "lower" and "upper" are defined with respect to an increasing positioning according to the +Z direction.

[0051] Reference is made to Figure 1A The light-emitting diode array 10 is provided. In this example, the diodes are distributed in three types denoted D1, D2, D3, according to whether they are intended to form pixels P1, P2, P3 of different colors. Here, the diodes are disposed on the support substrate 11 and are here polarized by the lower electrode layer 12 and the upper electrode layer 13. Other arrangements are possible, in particular in case the support substrate 11 is electrically conductive.

[0052] The diodes D1, D2, D3 are formed here in a conventional manner, for example by epitaxy of a semiconductor layer. Each diode D1, D2, D3 is formed from a stack of a lower semiconductor portion doped with a first conductivity type, for example p-type, and an upper semiconductor portion doped with a second conductivity type, for example n-type, of an active region in which the light radiation of the light emitting diode is emitted. The diodes D1, D2, D3 can be made from the same semiconductor compound, for example a compound based on group III-V, for example GaN, InGaN, AlGaN, etc.

[0053] Preferably, the diodes D1, D2, D3 are structurally identical, so that the emitted light radiation is substantially the same from one diode to another in terms of wavelength. In this example, the diodes D1, D2, D3 are adapted to emit light radiation in the blue band, i.e. their emission spectrum has an intensity peak at a wavelength of between approximately 440 nm and 490 nm.

[0054] The front surface of the diode array 10 is a substantially flat surface, the possible presence of a surface microstructure then allowing the light extraction to be improved. Here, the front surface of the diode array 10 is formed by the upper surface of the upper electrode layer 13 adapted to polarize the diodes. The front surface of the diode array 10 can also be formed by a passivation thin layer (not shown) covering the diodes and the upper electrode layer.

[0055] Next, with reference to Figure 1B and Figure 1C , a first electret layer E1 is formed, which at least partially covers the diode array 10, and the upper surface F1 of which has a first surface potential pattern M1 of non-zero surface potential. These patterns M1 are at least partially surrounded by regions of the upper surface F1 of zero surface potential. As indicated previously, the electret layer has a non-zero surface potential at its upper surface due to the presence of charges or dipole polarizations (vertical orientation of the dipoles). In this case, the surface potential of the upper surface F1 is only non-zero in predetermined patterns M1, so-called surface potential patterns, while it is substantially zero outside these patterns M1. The surface potential can have a value of approximately 10 V. The potential patterns M1 are thus surfaces in which the potential is non-zero in the upper surface. The potential patterns M1 extend opposite at least one diode and are intended to form the surface on which the photoluminescent particles will be deposited during the making of the photoluminescent mat.

[0056] With reference to Figure 1BThe electret layer E1 at least partially covers the diode array 10. In this example, the electret layer E1 is made of a self-polarizing dielectric material, i.e. the dielectric layer does not need to be polarized in a dedicated step. Thus, an electret layer is formed whose upper surface F1 has a non-zero initial surface potential over its entire surface. By "over its entire surface" is understood at least over the entire surface of the upper surface of the electret layer opposite the diode array. In this example, the electret layer E1 covers all diodes D1, D2 and D3, but can cover only a part of the diodes, for example only the diodes intended to form red and green pixels. The upper surface of the electret layer E1 has several areas F1.1, F1.2 and F1.3 respectively positioned opposite the diodes D1, D2 and D3.

[0057] Furthermore, the material of the electret layer E1 is chosen to be at least partially absorbing at the wavelength of the depolarizing light radiation, for example in the ultraviolet band, and at least partially transparent at the wavelength of the light radiation emitted by the diodes, for example in the blue band. By "at least partially absorbing" is understood that the absorption is at least 20% (or less, for example at least 10%) to at least 50% at the wavelength of the depolarizing light radiation. And by "at least partially transparent" is understood that the transmission is at least 50% at the wavelength of the light radiation emitted by the diodes. The electret layer can have a thickness of several tens to several hundreds of nanometers, preferably at most equal to 2 pm.

[0058] For example, the self-polarizing dielectric material can be an organic material chosen from the following: 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).

[0059] The self-polarizing dielectric material can also be an organic material selected from the group consisting of TPBi (2,2',2"-(1,3,5-benzene- triyl)-tris(1 -phenyl-1 -H-benzimidazole)), o-Ethyl-TPB, m-Ethyl-TPBi, p-Ethyl-TPBi, Alq3 (tris(8-hydroxyquinoline)aluminum), Al(7-Prq)3 (tris(7-propyl-8- hydroxyquinoline)aluminum(III)), Al(q-Cl)3 (tris(5-chloro-8-hydroxyquinoline)aluminum), OXD-7 (2,2'-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole]), BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), Gaq3 (tris(8-hydroxyquinoline)gallium), Balq (bis(2-methyl-8-quinolinate)4-phenylphenol), Ir(ppy)3 (tris(2-phenylpyridine)iridium(III)), Ir(ppy)2acac (bis(2-phenylpyridine)iridium(III)acetylacetonate), Ir(ppy)2tmd (bis(2-phenylpyridine)iridium(III) (2,2,6,6-tetramethylheptane-3,5-dione)), Bpy-OXD (1,3-bis[2-(2,2'-bipyridin-6-yl)-1,3,4-oxadiazol-5-yl]benzene), 2CzPN (4,5-bis(9H-carbazol-9-yl)benzophenone), 1,2,3,5-tetra(carbazol-9-yl)-4,6-dicyanobenzene, 4CzPN (3,4,5,6-tetra(carbazol-9-yl)-1,2-dicyanobenzene), DCJTB (4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-9- yl)-4H-pyrane), DACT-II (9-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]-N,N,N',N'- tetraphenyl-9H-carbazole-3,6-diamine), mCP (1,3-bis(N-carbazolyl)benzene), a-NPD (N,N'-bis(1 -naphthyl)-N,N'-diphenyl-1,1 '-biphenyl-4,4'-diamine), Znq2 (bis(8- hydroxyquinoline)zinc), and B3PyMPM (bis-4,6-(3,5-di-3-pyridylphenyl)-2- methylpyrimidine).

[0060] Reference Figure 1C, the electret layer E1 is locally depolarized optically to define a first surface potential pattern M1. To this end, the opaque layer is deposited here on the electret layer E1, after which structuring takes place by means of photolithography and etching to obtain an opaque mask 2, which here extends only opposite the diode D1, i.e. only over the area F1.1. The opaque mask 2 thus does not extend opposite the diodes D2 and D3. The opaque mask 2 can be made of a photosensitive resin that is opaque to depolarizing light radiation (here, ultraviolet light). Alternatively, the opaque mask 2 can be a photolithography mask at the level of the stepper.

[0061] Afterwards, the electret layer E1 is subjected to depolarizing light radiation of wavelength λ.dp, which is then absorbed only by the electret layer E1 in the areas F1.2 and F1.3 (not covered by the opaque mask 2) and not by the electret layer E1 in the area F1.1. Furthermore, the absorption of the depolarizing light radiation leads to a local depolarization in the areas F1.2 and F1.3 of the upper surface F1 of the electret layer E1. The area F1.1 of the upper surface F1 of the electret layer E1 is thus used for the surface potential pattern M1. The depolarizing light radiation can be situated in the ultraviolet wave band, i.e. have a dominant wavelength of between 100 nm and 380 nm, for example. After this step, the resin 2 is removed here.

[0062] Afterwards, reference is made to Figure 1D, a first photoluminescent mat P1 is formed by locally depositing first photoluminescent particles pi on the electret layer E1 opposite the first surface potential pattern M1. To this end, a process similar to the one described in documents WO2014 / 136023 and WO2021 / 023656 is followed. Thus, a colloidal solution containing the first photoluminescent particles pi is brought into contact with the upper face F1 of the electret layer E1. Thus, the whole stack can be immersed in the colloidal solution or a drop of such a solution is deposited on the electret layer E1. As the non-zero surface potential prevails in the surface potential pattern M1, a non-uniform electric field is generated which, by dielectrophoresis, causes the local deposition of the photoluminescent particles pi. Moreover, the photoluminescent particles pi are deposited substantially opposite the first pattern M1 and substantially do not lie outside the pattern M1 (i.e. not opposite the regions F1.2 and F1.3). The duration of the contact of the colloidal solution on the electret layer E1 depends in particular on the amount of photoluminescent particles pi to be deposited, the concentration of the particles, the size of the particles, the surface potential, etc. For example, the thickness of the photoluminescent mat P1 can be in the range of a few hundred nanometers, for example equal to approximately 400 nm. After that, the colloidal solution is removed and the electret layer E1 can be dried. It should be noted that the surface potential of the pattern M1 has become substantially zero. In practice, the photoluminescent particles pi are grafted to the surface of the electret layer E1 at the level of the pattern M1 until a substantially complete decay of the potential of the pattern M1 is achieved.

[0063] After that, with reference to Figure 1E and Figure 1F , a second electret layer E2 is formed, the second electret layer E2 at least partially covering the diode array 10 and the upper face F2 of the second electret layer E2 also having a second surface potential pattern M2 in which the surface potential is non-zero. The second surface potential pattern M2 is not located opposite the first photoluminescent mat P1 here, so that a second photoluminescent mat P2 is opposite diodes different from the diodes D1 to form a light-emitting pixel of another color.

[0064] To this end, with reference to Figure 1E , the second electret layer E2 is also deposited to cover the first electret layer E1 and the first photoluminescent mat P1, the second electret layer E2 here also being made of a self-polarizing dielectric material. Thus, the upper face F2 of the second electret layer E2 has a non-zero surface potential over its entire surface. This second electret layer E2 can be made of the same material as the material of the first electret layer E1. The second electret layer E2 is also chosen to at least partially absorb the wavelength of the depolarized light radiation (here in the ultraviolet band) and to be at least partially transparent to the wavelength of the light radiation emitted by the diodes (here in the blue band). The electret layer E2 can have a thickness in the range of a few tens of nanometers to a few hundred nanometers, preferably at most equal to 2 pm.

[0065] With reference toFigure 1F The second electret layer E2 is optically partially depolarized to define a second surface potential pattern M2, which is defined in the upper surface F2 of the second electret layer E2. To this end, an opaque layer is deposited on the second electret layer E2, after which structuring takes place by means of photolithography and etching to obtain an optical mask 2, which here extends only opposite the diode D3. The optical mask 2 thus does not extend opposite the diodes D1 and D2. Alternatively, as indicated earlier, the mask 2 can be a photolithographic mask at the level of the stepper photolithography machine.

[0066] The second electret layer E2 is then subjected to depolarizing light radiation, which is then absorbed by the second electret layer E2 only in the areas F2.1 and F2.2 (not covered by the opaque mask 2) and not in the area F2.3. Moreover, the absorption of the depolarizing light radiation results in a partial depolarization in the areas F2.1 and F2.2 of the upper surface F2 of the electret layer E2. The area F2.3 of the upper surface F2 of the electret layer E2 thus forms the second surface potential pattern M2.

[0067] Preferably, if the potential of the pattern M1 is not completely zero, a part of the depolarizing light radiation is transmitted by the second electret layer E2, then by the photoluminescent pad P1, and is then absorbed by the first electret layer E1, which causes the first surface potential pattern M1 to be partially depolarized. The risk of deposition of second photoluminescent particles p2 opposite the first photoluminescent pad P1 is then further limited.

[0068] Thereafter, with reference to Figure 1G A second photoluminescent pad P2 is then formed by locally depositing second photoluminescent particles p2 on the electret layer E2 opposite the second surface potential pattern M2. To this end, a colloidal solution containing the second photoluminescent particles p2 is brought into contact with the upper surface F2 of the second electret layer E2, following a procedure similar to that used for the first photoluminescent pad P1. As a result of the non-zero surface potential prevailing in the second pattern M2, a non-uniform electric field is generated, which causes the photoluminescent particles p2 to be locally deposited by dielectrophoresis. Moreover, the photoluminescent particles p2 are deposited substantially opposite the second pattern M2 and substantially not outside the pattern M2 (i.e. not opposite the areas F2.1 and F2.2), obtaining the second photoluminescent pad P2. It should be noted that the surface potential of the pattern M2 becomes substantially zero as a result of the grafting of the photoluminescent particles p2. Thereafter, the colloidal solution is removed and the electret layer can be dried.

[0069] Thereafter, with reference to Figure 1H, obtaining an optoelectronic device 1 comprising the array of diodes 10 and a color conversion structure formed by the photo luminescent pads P1 and P2. In this example, the diode D2 forms a blue pixel, the diode D1 associated with the photo luminescent pad P1 forms for example a red pixel, and the diode D3 associated with the photo luminescent pad P2 forms a green pixel. To form the photo luminescent pads, the method implements a step of optically locally depolarizing the electret layers E1 and E2 having an initial surface potential not equal to zero over the entire surface of the upper surface. Thus, we avoid having to resort to a step of locally injecting charges in an electret layer initially devoid of charges, as in the prior art example mentioned earlier. Moreover, the method is faster and forms the photo luminescent pads with spatial precision, even in the case where the array of diodes is made from large size substrates (for example 100 mm or 200 mm) and / or the pixel pitch of the array of diodes is very small (for example 5 pm or less).

[0070] Figures 2A-2C The different steps of the method for manufacturing an optoelectronic device according to a variant are illustrated. In this example, the surface potential pattern is made optically by locally depolarizing an electret layer initially having a surface potential not equal to zero over its entire surface.

[0071] The method differs from the method of Figures 1A-1H essentially in that the depolarizing optical radiation corresponds to the optical radiation emitted by the diodes. In this case, the array of diodes is adapted to selectively activate the diodes D1, D2 and D3 and for this includes the lower electrode 12 and the upper electrode 13 arranged to be able to carry out this selective activation.

[0072] Moreover, the material of the electret layer E1 is adapted to only partially absorb the optical radiation emitted by the diodes D1, D2, D3 and to transmit the non-absorbed part. Thus, the absorbed part enables the local depolarization of the electret layer in the area of the upper surface opposite the activated diode. The areas of the upper surface positioned opposite the non-activated diodes then retain their surface potential not equal to zero, which in turn defines the surface potential pattern.

[0073] With reference to Figure 2A , the array of diodes 10 is provided covered by an electret layer E1. The upper surface F1 of the electret layer E1 has a surface potential not equal to zero over its entire surface. The electret layer E1 is then made of a dielectric material adapted to only partially absorb the optical radiation emitted by the diodes, here the optical radiation situated in the blue (or near blue) band.

[0074] With reference to Figure 2B, selectively activating the diodes, i.e. only activating some of the diodes. In this case, only diodes D2 and D3 are activated, while diode D1 is not activated. The emitted optical radiation is then partially absorbed by the electret layer E1 in the regions F1.2 and F1.3 in the upper surface F1 which are located opposite diodes D2 and D3, which is reflected by a local depolarization of the electret layer E1 opposite these diodes. However, in view of the fact that diode D1 is not activated, the electret layer E1 remains locally polarized in the region F1.1, thus defining a first surface potential pattern M1.

[0075] Thereafter, with reference to Figure 2C , in the same way as previously (see Figure 1D ), a first photoluminescent pad P1 is formed by contacting the electret layer E1 with a gel-like solution containing photoluminescent particles p1. The first photoluminescent pad P1 is then naturally deposited on the electret layer E1 in the surface potential pattern M1, so that the photoluminescent pad P1 is located opposite diode D1, and not opposite diodes D2 and D3.

[0076] The manufacturing method can be performed in the same way as previously (not shown). Thus, a second electret layer E2 is deposited, which here covers the array of diodes 10 as well as the first pad P1 and the electret layer E1. The upper surface of the electret layer E2 has a surface potential which is not zero over its entire surface. Thereafter, this second electret layer E2 is optically locally depolarized in the same way as previously. Figure 2B Thus, only diodes D1 and D2 are activated, so that the regions F2.1 and F2.2 of the upper surface F2 of the electret layer E2 are depolarized. However, diode D3 is not activated, so that the region F2.3 has a surface potential which is not zero, and thus a second surface potential pattern M2 is formed. It should be noted that, alternatively, the optical local depolarization of the second electret layer E2 can be performed as in the method of Figures 1A-1H , i.e. using a dedicated depolarization optical radiation which is different from the optical radiation emitted by the diodes.

[0077] Thus, in this variant, the manufacturing method makes use of the selective activation of the array of diodes 10 to locally depolarize the electret layers E1, E2, and thus to define the surface potential patterns. In particular, this allows to simplify the production process, in particular the depolarization step.

[0078] Figures 3A-3C Different steps of a method for manufacturing an optoelectronic device according to another variant are illustrated.

[0079] This method is similar to Figures 1A-1HThe method differs substantially in that the electret layer E1 is made of a photochromic dielectric material, which is optically locally polarized to form the surface potential pattern, instead of being formed by depolarizing an electret layer having an initial non-zero surface potential. In other words, the surface potential pattern is optically made by locally polarizing an electret layer which initially has a surface potential of zero over its entire surface.

[0080] The photochromic material of the electret layer E1 is instead adapted to at least partially absorb a predetermined polarizing light radiation, for example between 100 nm and 380 nm, so that the layer is electrically polarized. Finally, the photochromic material of the electret layer E1 is also at least partially transparent to the light radiation emitted by the diodes, for example in the blue band. The photochromic material can consist of a matrix material, for example poly(methyl methacrylate) (PMMA) or polystyrene (PS), containing from 1% to 20% by weight of photochromic material, which can be selected from spiropyrans (SP) or 1',3'-dihydro, 3',3'trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'- (2H)-indole] or N,N'-tricosylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13H27) or 1,2-bis-[2-methyl-5-(p-cyanophenyl)-3-thienyl]perfluorocyclopentene (DTE-CN). The last material is described in particular in the article entitled "Photochromic Electret: A New Tool for Light Energy Harvesting" by Castagna et al., published in The Journal of Physical Chemistry Letters, 3(1), 2012 (pages 51-57).

[0081] With reference to Figure 3A , an array of diodes 10 is provided, covered by an electret layer E1. The upper surface F1 of the electret layer E1 has a surface potential substantially equal to zero over its entire surface. The electret layer E1 is instead made of a photochromic material.

[0082] Thereafter, with reference to Figure 3Bby subjecting the electret layer E1 to a polarized light radiation having a predetermined wavelength λ.p, which is only absorbed by the electret layer E1 in the area F1.1 and not by the electret layer E1 in the areas F1.2 and F1.3. As a result, the surface potential is not defined in the areas F1.2 and F1.3 and remains zero, whereas in the area F1.1 defining the surface potential pattern M1, the surface potential is not zero.

[0083] It should be noted that the partial polarization of the electret layer E1 can of course be performed by selective activation of the diode array 10.

[0084] Thereafter, with reference to Figure 3C , in the same way as before (see Figure 2C ), a first photoluminescent pad P1 is formed by contacting the electret layer E1 with a gel-like solution containing photo-luminescent particles p1. The first photoluminescent pad P1 is then naturally deposited on the electret layer E1 in the surface potential pattern M1, so that the photoluminescent pad P1 is positioned opposite the diode D1 and not opposite the diodes D2 and D3.

[0085] The manufacturing method can be performed in the same way as before (not shown), except that the use of a second electret layer E2 is not required. Thus, the electret layer E1 with the surface potential pattern M2 (for example positioned opposite the diode D3) is subjected to a second irradiation, and finally a photoluminescent pad P2 is made positioned opposite the surface potential pattern M2. Once all the photoluminescent pads have been deposited by dielectrophoresis, it is advantageous to perform an irradiation of the entire electret layer E1 with visible light in order to improve the transparency of this layer in the visible range of the light spectrum, if necessary.

[0086] Figures 4A-4F Different steps of a method for manufacturing an optoelectronic device according to another variant are shown.

[0087] The method differs from the method described in Figure 1A and in the subsequent figures essentially in that at least one of the electret layers, here the two electret layers E1, E2, is made of a dielectric material that is electrostatically polarized. To this end, we make use of the upper electrode layer 13. In other words, the surface potential pattern is made optically by locally depolarizing an electret layer that initially has a non-zero surface potential over its entire surface.

[0088] With reference to Figure 4A, a diode array 10 covered by an electret layer E1 is provided. The upper surface F1 of the electret layer E1 has an initial surface potential substantially equal to zero over its entire surface. The electret layer E1 is then made of inorganic dielectric material, even of organic dielectric material (PMMA, etc.), such as silicon oxide (Si x O y ), silicon nitride (Si x N y ), aluminum oxide (Al x O y ), titanium oxide (Ti x O y ), tantalum oxide (Ta x O y ), hafnium oxide (Hf x O y ).

[0089] With reference Figure 4B , a surface potential not equal to zero is defined over the entire surface of the upper surface of the electret layer E1. To this end, we make use of an upper electrode layer 13 extending under the entire surface of the electret layer E1. An additional electrode 14 is also needed to be arranged on the entire electret layer E1, and an electric potential difference is applied between the two electrodes 13, 14. A surface potential not equal to zero is thus established over the entire surface of the upper surface of the electret layer E1. Other techniques for charging the electret layer can be considered (plasma, ion implantation, corona discharge, etc.).

[0090] Subsequently, with reference Figure 4C , the surface potential pattern M1 is optically defined by locally depolarizing the electret layer E1 according to one of the previously described ways. Then, in the same way as in the previous way (see Figure 1C ), the photoluminescent mat P1 is formed by bringing the electret layer E1 into contact with a gelatinous solution containing the photoluminescent particles pi. The photoluminescent mat P1 is then naturally deposited on the electret layer E1 in the surface potential pattern M1, so that the photoluminescent mat P1 is positioned opposite the diode D1 and not opposite the diodes D2 and D3. The surface potential of the pattern M1 then becomes substantially equal to zero.

[0091] Subsequently, a second electret layer E2 having a surface potential pattern M2 is formed. In this case, the electret layer E2 is made, similarly to the electret layer E1, by electrostatically polarizing a layer having an initial electric potential equal to zero. Alternatively, the second electret layer can be formed similarly to the examples previously described with reference Figures 1A-1H 、 Figures 2A-2C and Figures 3A-3C .

[0092] With reference Figure 4D, first an electrode layer 15 is formed, which covers the entire diode array 10, here more specifically the photoluminescent pad P1 and the electret layer E1. Then, the electret layer E2 is deposited. The electret layer E2 extends completely over the electrode layer 15, here also ensuring the encapsulation of the photoluminescent particles of the pad P1. The upper surface of the electret layer E2 has an initial surface potential of substantially zero over its entire surface. The electret layer E2 can be made of the same dielectric material as the dielectric material of the electret layer E1.

[0093] With reference to Figure 4E , a surface potential of non-zero is defined over the entire surface of the upper surface of the electret layer E2. To this end, a potential difference is applied between the electrode layer 15 and an additional electrode 14 arranged over the entire electret layer E2. A surface potential of non-zero is then established over the entire surface of the upper surface of the electret layer E2. It is noted that the electrode layer 15 can not be used: then a potential difference can be applied between the electrode 14 and the electrode 13.

[0094] Thereafter, with reference to Figure 4F , a surface potential pattern M2 is defined by locally depolarizing the electret layer E2 by an optical process. Then, in the same way as before (see Figure 1G ), a photoluminescent pad P2 is formed by bringing the electret layer E2 into contact with a gel-like solution containing photoluminescent particles p2. The photoluminescent pad P2 is then deposited naturally on the electret layer E2 in the surface potential pattern M2, such that the photoluminescent pad P2 is positioned opposite the diode D3, instead of opposite the diodes D1 and D2. The surface potential of the pattern M2 then becomes substantially zero.

[0095] The specific embodiments have been described above. Various variants and modifications can be thought of by the person skilled in the art.

Claims

1. A method for manufacturing an optoelectronic device, the optoelectronic device comprising: a diode array configured to emit or receive optical radiation; and a color conversion structure at least partially covering the diode array and comprising a photoluminescent mat arranged opposite at least one diode, the method for manufacturing an optoelectronic device comprising: providing the diode array; making an electret layer covering the diode array, and having a first predetermined surface potential pattern opposite the diode array, in which surface potential is not zero; and making the photoluminescent mat by contacting the electret layer with a gel-like solution comprising first photoluminescent particles, then depositing the first photoluminescent particles on an upper surface of the electret layer opposite the first predetermined surface potential pattern, thereby forming the photoluminescent mat, wherein the step of making the electret layer comprises: (B1) making an electret layer having an initial surface potential, which is not zero or zero, on its entire surface; (B2a) in the case where the initial surface potential is not zero: irradiating regions of the electret layer with depolarized optical radiation capable of being at least partially absorbed by the electret layer, the irradiated regions being different from non-irradiated regions intended to form the surface potential pattern, the absorption of the depolarized optical radiation in the irradiated regions causing the local surface potential to be eliminated, the non-irradiated regions then defining the surface potential pattern; and (B2b) in the case where the initial surface potential is zero: irradiating regions of the electret layer with polarized optical radiation capable of being at least partially absorbed by the electret layer, the absorption of the polarized optical radiation in the irradiated regions causing a local surface potential to be formed which is not zero, the irradiated regions then defining the surface potential pattern.

2. The method for manufacturing an optoelectronic device according to claim 1, further comprising: before the step B2a or the step B2b, arranging an opaque mask made of a material that is opaque to the depolarized optical radiation or polarized optical radiation and extending only over the regions of the electret layer intended to form the surface potential pattern; and during the step B2a or the step B2b, the depolarized optical radiation or polarized optical radiation is emitted in the direction of the opaque mask and the electret layer and is absorbed by the electret layer in the regions not covered by the opaque mask.

3. The method for manufacturing an optoelectronic device according to claim 1, wherein: the diodes are light-emitting diodes; the material making the electret layer is configured to partially absorb the optical radiation emitted by the light-emitting diodes, causing the local surface potential to be eliminated; and during the step B2a, some diodes are selectively activated to irradiate the electret layer in regions not intended to form the surface potential pattern, causing the local surface potential to be eliminated, the non-irradiated regions then defining the surface potential pattern; or during the step B2b, diodes are selectively activated to irradiate the electret layer only in regions intended to form the surface potential pattern. ​ 4. The method for manufacturing an optoelectronic device according to claim 1, wherein, The electret layer associated with said step B2a is made of a self-polarized organic dielectric material, so that said step B1 comprises depositing said electret layer made of said organic dielectric material, covering said array of diodes, so that said electret layer has a non-zero initial surface potential over the whole surface of the electret layer.

5. The method of manufacturing optoelectronic devices of claim 1, wherein, The electret layer associated with said step B2b is made of a photochromic dielectric material, so that said step B1 comprises depositing an electret layer made of said photochromic dielectric material, covering said array of diodes, so that said electret layer has a zero surface potential over the whole surface of the electret layer.

6. The method of manufacturing optoelectronic devices of claim 1, wherein, The electret layer associated with said step B2a is made of a dielectric material, so that said step B1 comprises: depositing an electret layer made of said dielectric material, covering said array of diodes, so that said electret layer has a zero initial surface potential over the whole surface of the electret layer; and subjecting said electret layer to a predetermined polarization electric field, so that a non-zero surface potential is formed over the whole surface of the electret layer.

7. The method for manufacturing an optoelectronic device according to claim 6, wherein: said array of diodes comprises an upper electrode layer covering said diodes and configured to polarize said diodes electrically, and during the step of subjecting said electret layer to said polarization electric field, said electret layer is arranged between said upper electrode layer and an additional electrode, a predetermined potential difference being applied between said upper electrode layer and said additional electrode.

8. The method for manufacturing an optoelectronic device according to claim 1, wherein: said electret layer is a first electret layer, and said photoluminescent mat is a first photoluminescent mat configured to convert incident light radiation having a first wavelength into light radiation having a second wavelength different from said first wavelength; after the step of making said photoluminescent mat, the method for manufacturing an optoelectronic device further comprises: making a second electret layer covering said array of diodes and said first electret layer, an upper surface of said second electret layer opposite said array of diodes having a second predetermined surface potential pattern in which the surface potential is non-zero, diodes located opposite said second predetermined surface potential pattern being different from diodes located opposite said first predetermined surface potential pattern; and making a second photoluminescent mat by contacting said second electret layer with a gel-like solution containing second photoluminescent particles different from said first photoluminescent particles, then depositing said second photoluminescent particles on an upper surface of said second electret layer opposite said second predetermined surface potential pattern, thereby forming said second photoluminescent mat.

9. The method for manufacturing an optoelectronic device according to claim 8, wherein, The diodes of said array of diodes are light-emitting diodes configured to emit light radiation of the same wavelength; and together with said first and second photoluminescent mats form an array of red, green, blue light-emitting pixels.

10. The method for manufacturing an optoelectronic device according to claim 1, wherein, Said array of diodes has a dimension greater than or equal to 100 mm in a plane parallel to said array of diodes.

11. The method of manufacturing an optoelectronic device according to claim 1, wherein, The diode array has a pitch of less than or equal to 10 μm. The diode array has a pitch of less than or equal to 10 μm.

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