Method for manufacturing an optoelectronic device with color conversion by localized deposition of photoluminescent particles on predefined conversion zones with structured surface potential

Abstract

The invention relates to a method for manufacturing an optoelectronic device (1) with a diode matrix (20), comprising the following steps: producing an electret layer (30) having conversion zones (Zc) separated two by two by a spacing zone (Ze) with zero surface potential, where each conversion zone (Zc) is formed of a plurality of elementary zones called polarized (32) with non-zero surface potential spaced two by two by an elementary zone called non-polarized (33) with zero surface potential, so that the conversion zone (Zc) has a structured surface potential; producing color conversion pads (P), by bringing the electret layer (30) into contact with a colloidal solution (S) containing photoluminescent particles (p). Figure for the abstract: Fig. 4A

Description

Title of the invention: Method for manufacturing an optoelectronic device with color conversion by localized deposition of photoluminescent particles on predefined conversion zones with structured surface potential Technical field

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

[0002] There are optoelectronic devices comprising a matrix of identical light-emitting diodes covered at least in part by color conversion pads. Such optoelectronic devices can form display screens or image projection systems comprising a matrix of luminous pixels of different colors.

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

[0004] The light-emitting diodes are therefore preferably identical to each other, and emit light radiation of the same wavelength. They can be formed from a semiconductor material comprising elements from column III and column V of the periodic table, such as a III-V compound, in particular gallium nitride (GaN), indium gallium nitride (InGaN) or aluminum gallium nitride (AlGaN). They are arranged so as to form a matrix of light-emitting diodes having a front face through which the generated light radiation is transmitted.

[0005] The light conversion pads may be formed from a binder matrix comprising particles of a photoluminescent material such as yttrium garnet. and aluminum (YAG, for Yttrium Aluminum Garnet, in English) activated by the cerium ion YAG:Ce. The photoluminescent particles can also be quantum dots, i.e. in the form of semiconductor nanocrystals whose quantum confinement is substantially three-dimensional. They can also be nanoplatelets, i.e. nanoparticles having an essentially two-dimensional shape (two-dimensional quantum confinement).

[0006] The manufacturing method may comprise the deposition and then the structuring of a photoluminescent layer to form first light conversion pads, for example adapted to convert blue into red. These steps are carried out again to form second light conversion pads, for example adapted to convert blue into green. However, this method has the disadvantage of being poorly suited to diode matrices with a small pixel pitch, for example of the order of 5 μm, since problems of alignment or overlapping of the light conversion pads with each other may be present.

[0007] Document WO2014 / 136023A1 describes another manufacturing method, which uses an electret layer covering the diode matrix. The method firstly comprises a step of writing electrical charge patterns on the upper face of a dielectric layer to obtain the electret layer then locally charged. For this, a polarized AFM (Atomic Force Microscopy) tip is used to locally inject the electrical charges. Then, a step of localized deposition of colloidal nanocrystals on the electrical charge patterns is carried out. For this, the electret layer is brought into contact with a colloidal solution containing the nanocrystals, which are naturally deposited on the electrical charge patterns under the effect of a dielectrophoretic force.However, this method has the disadvantage of having to inject the electrical charges sequentially, by moving the AFM tip on the surface of the upper face to form the electrical charge patterns.

[0008] Document WO2021 / 023656A1 describes a similar method, 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 lower face of the pad is structured to form polarized teeth, which come into contact with the dielectric layer. This produces the electret layer, the upper face of which has the electrical charge patterns. The electret layer is then brought into contact with a colloidal solution, the nanocrystals present then being deposited on the electrical charge patterns by dielectrophoresis. However, this method has the particular disadvantage of having to precisely position the pad with respect to the matrix of diodes. However, the uncertainty in positioning the buffer with respect to the diode matrix can become problematic, particularly for diode matrices with a small pixel pitch, for example of the order of 5 pm. Indeed, this uncertainty or inaccuracy in positioning can lead to poor positioning of the light conversion pads with respect to the diodes, and therefore to a degradation in the performance of the optoelectronic device. Statement of the invention

[0009] The invention aims to remedy at least in part the drawbacks of the prior art, and more particularly to propose a method of manufacturing an optoelectronic device which has improved performance.

[0010] For this, the object of the invention is a method of manufacturing an optoelectronic device, comprising the following steps: • provide a matrix of diodes, having a front face intended to receive or transmit light radiation; • produce an electret layer, extending over the front face of the diode matrix, an upper face of which, opposite the front face, has conversion zones, each being located perpendicular to a diode and intended to be covered by a color conversion pad, separated two by two by a spacing zone with zero surface potential; • produce the color conversion pads, by bringing the electret layer into contact with a colloidal solution containing photoluminescent particles, which are deposited on the electret layer in the conversion zones, thus forming the color conversion pads; • following the step of producing the electret layer, each conversion zone is formed from a plurality of elementary zones called polarized with non-zero surface potential spaced two by two by an elementary zone called non-polarized with zero surface potential, so that the conversion zone has a structured surface potential.

[0011] Some preferred, but non-limiting, aspects of this method are as follows.

[0012] The polarized elementary zones can be arranged symmetrically with respect to a center of the conversion zone.

[0013] Each conversion zone may comprise between three and nine polarized elementary zones, and preferably between three and seven polarized elementary zones.

[0014] The polarized elementary zones can all be located at a distance from an edge of the conversion zone.

[0015] The electret layer may have a homogeneous relative permittivity.

[0016] The electret layer may have a relative permittivity having a first

[0017]

[0018]

[0019]

[0020]

[0021]

[0022] value in the conversion zones and a second value greater than the first value outside the conversion zones. The electret layer may be formed of first portions located in the conversion zones and made of a material having the first relative permittivity value, and second portions located outside the conversion zones and made of a material having the second relative permittivity value. The electret layer may be formed from a continuous sub-layer covering the diode matrix and made of a material having the first relative permittivity value, and from portions covering the sub-layer, located outside the conversion zones and made of a material having the second relative permittivity value. The invention also relates to an optoelectronic device, comprising: • a matrix of diodes having a front face intended to receive or transmit light radiation; • an electret layer, extending over the front face of the diode matrix, an upper face of which, opposite the front face, has conversion zones, each being located perpendicular to a diode and intended to be covered by a color conversion pad, separated two by two by a spacing zone with zero surface potential; • color conversion pads, located on the electret layer and positioned in the conversion zones; • where each conversion zone is formed from a plurality of elementary zones called polarized with non-zero surface potential spaced two by two by an elementary zone called non-polarized with zero surface potential, so that the conversion zone has a structured surface potential. Diodes can have identical light emission or absorption properties. Diodes can be made from an organic or inorganic semiconductor compound. There is also a question of a method of manufacturing an optoelectronic device, comprising the following steps: • provide a matrix of diodes, having a front face intended to receive or transmit light radiation; • produce an electret layer, extending over the front face of the diode matrix, an upper face of which, opposite the front face, has conversion zones, each being located perpendicular to a diode and intended to be covered by a color P conversion pad, separated two by two by a spacing zone with zero surface potential; • create the color conversion plots, by bringing the layer into contact electret with a colloidal solution containing photoluminescent particles, which are deposited on the electret layer in the conversion areas, thus forming the color conversion pads; • following the creation of the electret layer: the surface potential in each conversion zone is uniformly non-zero; the conversion zones have a first relative permittivity value and the spacing zones have a second relative permittivity value greater than the first value.

[0023] The electret layer may be formed of first portions located in the conversion zones and made of a material having the first relative permittivity value, and second portions located outside the conversion zones and made of a material having the second relative permittivity value.

[0024] The electret layer may be formed from a continuous sub-layer covering the diode matrix and made from a material having the first relative permittivity value, and from portions covering the sub-layer, located outside the conversion zones and made from a material having the second relative permittivity value.

[0025] There is also a question of an optoelectronic device, comprising: • a matrix of diodes having a front face intended to receive or transmit light radiation; • an electret layer, extending over the front face of the diode matrix, an upper face of which, opposite the front face, has conversion zones, each being located perpendicular to a diode and intended to be covered by a color conversion pad, separated two by two by a spacing zone with zero surface potential; • color conversion pads, located on the electret layer and positioned in the conversion zones; • where the surface potential in each conversion zone is uniformly non-zero; the conversion zones have a first relative permittivity value and the spacing zones have a second relative permittivity value greater than the first value. Brief description of the drawings

[0026] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which:

[0027] Figures 1A to 1C illustrate different steps of a method of manufacturing an optoelectronic device where the conversion zones have a potential of uniformly non-zero surface;

[0028] [Fig.2] illustrates a variation of the vertical component of the gradient of the electric field, in the configuration of [Fig.1B];

[0029] [Fig.3A] is a schematic and partial view, in cross-section, of an optoelectronic device where the conversion zones have a uniformly non-zero surface potential, according to another arrangement of the diode matrix;

[0030] [Fig.3B] illustrates a variation of the vertical component of the gradient of the electric field, in the configuration of [Fig.3A];

[0031] [Fig.4A] is a schematic and partial view, in cross-section, of an optoelectronic device according to an embodiment where the conversion zones have a structured surface potential;

[0032] [Fig.4B] is a top view of the conversion zone illustrating the arrangement of the polarized elementary zones;

[0033] [Fig.4C] illustrates a variation of the vertical component of the gradient of the electric field, in the configuration of [Fig.4A];

[0034] [Fig.5A] is a schematic and partial view, in cross-section, of an optoelectronic device according to another embodiment where the conversion zones have a structured surface potential;

[0035] [Fig.5B] illustrates a variation of the vertical component of the gradient of the electric field, in the configuration of [Fig.5A];

[0036] Figures 6A to 6F are top views of a conversion zone of an optoelectronic device according to different embodiments;

[0037] Figures 7A to 7C illustrate the variation of the vertical component of the gradient of the electric field, for different embodiments of the optoelectronic device;

[0038] [Fig.8A] illustrates a variation of the vertical component of the gradient of the electric field, for an optoelectronic device according to an embodiment where the electret layer has a homogeneous relative permittivity;

[0039] [Fig.8B] is a schematic and partial view, in cross-section, of an optoelectronic device according to an embodiment where the electret layer has an inhomogeneous relative permittivity;

[0040] [Fig.8C] illustrates a variation of the vertical component of the gradient of the electric field, for the configuration of [Fig.8B];

[0041] [Fig.9A] is a schematic and partial view, in cross-section, of an optoelectronic device according to an embodiment where the electret layer has an inhomogeneous relative permittivity and where the conversion zones have a uniformly non-zero surface potential;

[0042] [Fig.9B] illustrates a variation of the vertical component of the gradient of the electric field, for the configuration of [Fig.9A];

[0043] [Fig. 10A] is a schematic and partial view, in cross-section, of an optoelectronic device according to another embodiment where the electret layer has an inhomogeneous relative permittivity and where the conversion zones have a uniformly non-zero surface potential;

[0044] [Fig.lOB] illustrates a variation of the vertical component of the gradient of the electric field, for the configuration of [Fig.lOA];

[0045] Figures 1 1A to 11E illustrate different steps of a method of manufacturing an optoelectronic device similar to that of [Fig.9A].

[0046] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0047] In the figures and in the remainder of the description, the same references represent identical or similar elements. In addition, the different elements are not shown to scale so as to favor the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and can be combined with each other. Unless otherwise indicated, the terms "substantially", "approximately", "of the order of" mean to within 10%, and preferably to within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are included, unless otherwise indicated.

[0048] The invention relates to a method for manufacturing an optoelectronic device comprising a matrix of diodes, at least some of the diodes of which are covered by color conversion pads, so as to form a matrix of luminous pixels of different colors. The diodes may be emissive diodes so that the optoelectronic device may be, for example, a display screen. They may thus be organic (OLED) or inorganic (LED) light-emitting diodes. Alternatively, the diodes may be detectors so that the optoelectronic device may be a matrix photodetector. These may be organic or inorganic photodetectors.

[0049] The production of the color conversion pads is obtained by the localized deposition of photoluminescent particles on an electret layer. Each conversion pad is located opposite a diode.

[0050] Generally speaking, an electret layer is a dielectric layer containing electrical charges or a quasi-permanent dipole polarization. Also, the electret layer has, on at least a portion of its upper face, a non-zero surface potential. This results in the fact that the electret layer emits an external electric field in the absence of an applied field.

[0051] In the context of the invention, a conversion zone is defined as being a predefined surface of the electret layer located perpendicular to a diode, and covered or intended to be covered by a conversion pad. The surface potential, in such a conversion zone, is not uniformly non-zero as in the prior art (i.e. non-zero over the entire surface of the conversion zone), but is structured there. In other words, each conversion zone is formed of several elementary zones called polarized where the surface potential is non-zero, spaced two by two by a non-polarized elementary zone where the surface potential is zero.

[0052] Thus, it appears that the localized deposition of the photoluminescent particles in the conversion zone is more homogeneous than in the prior art, thus improving the properties of the optoelectronic device. In addition, it appears that the localized deposition of the photoluminescent particles outside the conversion zones is reduced, which improves the contrast of the pixels of the optoelectronic device.

[0053] Generally speaking, the color conversion pads are formed from particles made of at least one photoluminescent material, and preferably from nanoparticles of which at least one maximum dimension is between 0.2nm and 1000nm, for example between 20nm and a few hundred nanometers. 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, for example spherical, angular, flattened, elongated, etc.

[0054] The photoluminescent particles may be quantum dots, i.e. semiconductor nanocrystals whose quantum confinement is substantially three-dimensional. The average size of the quantum dots may then be between 0.2 nm and 50 nm, for example between 1 nm and 30 nm. They may also be nanoplatelets, i.e. nanoparticles having an essentially two-dimensional shape, with a length that may be of the order of 20 nm to a few hundred nanometers. Also, the smallest dimension (thickness) is less than the other two dimensions of length and width, preferably by a ratio of at least 1.5.

[0055] The photoluminescent particles may in particular be formed from at least one semiconductor compound, which may be chosen, for example, from cadmium selenide (CdSe), indium phosphorus (InP), indium gallium 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 semiconductor materials that may be suitable. Nanoparticles can also have a core / shell structure, such as CdSe / ZnS, CdSe / CdS, CdSe / CdS / ZnS, PbSe / PbS, CdTe / CdSe, CdSe / ZnTe, InP / ZnS or other. The particles can also have a perovskite crystal structure with atoms such as those listed for nanoparticles, but also Cs, Mn, Br.

[0056] Furthermore, the light conversion pads are adapted to convert at least in part an incident light radiation of a first wavelength Xi into a luminescence light radiation of longer wavelength X2. For illustration purposes, they can be adapted to absorb blue light, i.e. light with a wavelength between approximately 440nm and 490nm, and to emit in the green, i.e. at a wavelength between approximately 495nm and 560nm, or even in the red, i.e. at a wavelength between 600nm and 650nm. Wavelength is here understood to mean the wavelength at which the emission spectrum has an intensity peak.

[0057] For purely illustrative purposes, the diodes may be emissive and have an emission spectrum in the visible or infrared (for example in the NIR or the SWIR), or even ultraviolet (200-400 nm). In the case of an array of emissive diodes, the incident light radiation is the radiation emitted by the diodes, whereas in the case of photodiodes, it is the light radiation coming from an external environment and directed towards the photodiodes. In the latter case, the diodes are then adapted to absorb incident light radiation of different wavelengths all contained in the same predefined absorption spectrum.

[0058] Figures 1A to 1C illustrate different steps of an example of a method for manufacturing an optoelectronic device 1, making it possible to highlight a problem linked to the localized deposition of the photoluminescent particles p in the conversion zone Zc and outside the conversion zone Zc. In this example, the diodes D are light-emitting diodes.

[0059] Here and for the remainder of the description, a direct three-dimensional orthogonal reference frame XYZ is defined, where the X and Y axes form a main plane in which the diode matrix 20 extends, and where the Z axis is oriented along the thickness of the diode matrix 20 in the direction of the front face. The terms 'lower' and 'upper' are defined with respect to an increasing positioning along the +Z direction.

[0060] With reference to [Fig. 1 A], the matrix 20 of light-emitting diodes D is provided. The diodes D rest here on a control substrate 10, and are electrically polarized here by one or more lower electrode layers 21 and by one or more upper electrode layers 25. Other configurations are possible, in particular in the case where the control substrate 10 is electrically conductive. The matrix of diodes 20 has a rear face, by which it is assembled and connected to the control substrate 10, and a front face, opposite the rear face, which is intended to receive or transmit light radiation. In this example where the diodes D are emissive, the front face transmits the light radiation emitted by the diodes. In this example, provision is made to produce color conversion pads above the diodes shown. But certain diodes may not be associated with color conversion pads.

[0061] In this example, the control substrate 10 comprises a control circuit of CMOS type (not shown), and has electrical connection pads 11 which are flush with the upper face and come into contact with lower electrode layers 21 of the diodes D. These lower electrode layers 21 are here layers distinct from each other, in the sense that each lower electrode layer 21 of a diode D is physically distinct from that of the adjacent diode. This configuration is described in detail in document WO2017 / 194845 A1. Other configurations are possible.

[0062] The diodes D are here inorganic light-emitting diodes. They can be produced in a conventional manner, for example by epitaxy of semiconductor layers from a growth substrate, then by transfer to the control substrate 10. Each diode D can be formed from a stack of: a lower semiconductor portion 22 (located on the side of the control substrate) doped with a first type of conductivity, for example p-type, in electrical contact with a lower electrode layer 21; an active zone 23 where the light radiation of the light-emitting diode is emitted; and an upper semiconductor portion 24 doped with a second type of conductivity, for example n-type, in electrical contact with an upper electrode layer 25. The diodes D can be produced from the same semiconductor compound, for example based on an IILV compound such as GaN, InGaN, AlGaN.An electrically insulating filler material 26 fills the space between the diodes D.

[0063] Preferably, the diodes D are structurally identical, so that the light radiation emitted is identical from one diode to another in terms of wavelength. In this example, the diodes D are adapted to emit light radiation in the blue, that is to say whose emission spectrum has an intensity peak at a wavelength between approximately 440nm and 490nm.

[0064] The front face of the diode matrix 20 is covered by an electret layer 30. The electret layer 30 is made of at least one dielectric material, for example inorganic, such as a silicon oxide, nitride or oxynitride, for example SiO2, Si3 N4, A12O3 (in particular in the case of OLED), among others. It may have a thickness of the order of a few hundred nanometers, for example approximately 400nm. Note that organic dielectric materials may also be suitable, such as for example PMMA, PVDF, PET, CGC etc.

[0065] A conversion zone Zc is defined as being a surface of the electret layer 30 located opposite (perpendicular) a diode D, and more precisely its active layer 23. In this example, the surface potential 31 is uniformly non-zero there (i.e. non-zero over the entire surface of the zone Zc). The conversion zones Zc are separated laterally two by two by a spacing zone Ze where the surface potential there is zero (more precisely, the surface potential of each zone spacing Ze is uniformly non-zero, i.e. non-zero over the entire surface of the zone Ze).

[0066] The formation of the Zc conversion zones, i.e. the formation of the non-zero surface potential 31 in the Zc conversion zones, can be carried out in different ways. An AFM tip can be used as in document WO2014 / 136023A1 or a stamping technique as in document WO2021 / 023656A1. An electret layer 30 whose surface potential is initially non-zero over the entire front face can also be locally depolarized optically, by means of activation of the diodes, as described in patent application FR2308637 filed on 08 / 10 / 2023. An electrostatic polarization of the electret layer whose surface potential is initially zero over the entire front face can also be locally carried out, by means of activation of the upper electrodes, as described in patent application FR2309260 filed on 09 / 04 / 2023.

[0067] Thus, the conversion zones Zc with uniformly non-zero surface potential 31 are present only opposite the diodes D. In other words, the electret layer 30 has a zero surface potential everywhere, except in the conversion zones Zc opposite the diodes.

[0068] With reference to [Fig.lB], the color conversion pads are then produced by localized deposition of photoluminescent particles p on the electret layer 30 on the conversion zones Zc. For this, the procedure is similar to that described in documents WO2014 / 136023A1 and WO2021 / 023656A1. Thus, a colloidal solution S containing the photoluminescent particles p is placed in contact with the upper face of the electret layer 30. The photoluminescent particles p are suitable for converting blue light into, for example, red light. The entire stack can thus be immersed in the colloidal solution S, or a drop of such a solution can be deposited on the electret layer 30. Due to the non-zero surface potential 31 located in the conversion zones Zc, a non-uniform electric field is generated which causes a localized deposition of the photoluminescent particles p by dielectrophoresis.Also, the photoluminescent particles p are deposited essentially on the conversion zones Zc (and therefore opposite the diodes). The contact time of the colloidal solution S on the electret layer 30 depends in particular on the quantity of photoluminescent particles p to be deposited and therefore on the desired thickness of the conversion pads P, as well as on the value of the surface potential. For example, the thickness of the conversion pads P can be of the order of a few hundred nanometers, for example equal to approximately 400 nm. The colloidal solution S is then removed and the electret layer 30 can be dried.

[0069] With reference to [Fig.lC], an optoelectronic device 1 is obtained where the conversion pads P are present essentially in the conversion zones Zc, and therefore in with regard to the diodes D. A thin-layer encapsulation (e.g. in Al2O3) of the conversion pads P can then be carried out (not shown).

[0070] The preceding steps can then be repeated to produce other color conversion pads located opposite other diodes, forming for example green pixels. Indeed, the color conversion pads are adapted here to convert blue light (wavelength between approximately 440nm and 490nm) into red light (wavelength between approximately 600nm and 650nm). On the other hand, the color conversion pads are adapted here to convert blue light into green light (wavelength between approximately 495nm and 560nm).

[0071] However, it appears that the photoluminescent particles p may not be deposited homogeneously in the conversion zones Zc, which leads to the formation of conversion pads P, each of which has a non-uniform thickness, such that the conversion properties of the pads P are not spatially uniform. In addition, it appears that the photoluminescent particles p may be deposited outside the conversion zones Zc, thus degrading the contrast associated with each emissive pixel.

[0072] [Fig.2] illustrates the spatial variation of the intensity (in log) of the vertical component VzE2 of the gradient of the squared norm of the electric field E, to which the dielectrophoretic force F is proportional, calculated at a distance of 100nm above the electret layer 30, in a structural configuration similar to that of [Fig.1B].

[0073] Generally speaking, a photoluminescent particle of dimension r and dielectric constant ep located in a solution of dielectric constant em (dielectric permittivity) undergoes, due to the spatial inhomogeneity of the electric field E, a dielectrophoretic force F defined by the relation:

[0074] j^2x^xr3x^x^xV^ || E || 2d

[0075] In this configuration, the diodes D have a lateral dimension of 2 pm and are arranged periodically at a pitch of 4 pm. Also, the conversion zones Zc have a lateral dimension of 2 pm and are spaced 2 pm apart from each other. The surface potential 31 is uniformly non-zero in the conversion zones Zc, and is uniformly zero in the spacing zones Ze. The fill factor FFd of the diodes is here equal to 50% (=2 pm / 4 pm).

[0076] We also consider a relative permittivity ere of the electret layer 30 which is homogeneous (spatially uniform) throughout the layer and equal to 4, and a relative permittivity er>m of the colloidal solution which is also homogeneous and equal to 2.

[0077] It appears that the dielectrophoretic force Fz is not constant in the Zc conversion zones. Indeed, it has a maximum, located at the edge of the Zc conversion zone, with a value here of 21.7, and a minimum located at the center of the Zc conversion zone. Zc conversion, with a value here of 19.5.

[0078] Furthermore, the intensity of the force Fz decreases outside the conversion zone Zc, down to a minimum of 19.5 also located at the center of the spacing zone Ze. It also appears that these minima of the dielectrophoretic force Fz are located at the same distance from the edge of the conversion zone Zc, so that the rate of decrease is symmetrical on either side of this edge. Consequently, the variation of the force Fz is identical in the conversion zones Zc and in the spacing zones Ze, so that, from the point of view of the dielectrophoretic force, it is not possible to distinguish the conversion zones Zc from the spacing zones Ze.

[0079] Also, the photoluminescent particles p are deposited more on the edge of the conversion zone Zc, then on either side of it in a substantially symmetrical manner.

[0080] This leads to the formation of conversion pads P which not only do not have a uniform thickness in the conversion zones Zc, but, in addition, are not correctly positioned. The conversion properties are then degraded, and the contrast of the luminous pixels is not optimal.

[0081] [Fig.3A] is a schematic and partial view, in cross-section, of a matrix of diodes 20 covered by an electret layer 30, and by a colloidal solution S (the photoluminescent particles p are not shown), in another structural configuration. As for [Fig.1B], the electret layer 30 comprises conversion zones Zc located perpendicular to the diodes D, where the surface potential 31 is uniformly non-zero (i.e. non-zero over the entire surface of the zone Zc), separated two by two by spacing zones Ze with uniformly zero surface potential (i.e. non-zero over the entire surface of the zone Ze).

[0082] The conversion zones Zc have a lateral dimension of 2 pm, and are arranged periodically at a pitch of 18 pm. Also, the spacing zones Ze have a lateral dimension of 16 pm. The filling factor FFd is therefore 11% (=2 pm / 18 pm). In this example, the electret layer 30 has a homogeneous relative permittivity equal to 4, and the colloidal solution S has a homogeneous relative permittivity equal to 2.

[0083] [Fig.3B] illustrates the spatial variation of the intensity (in log) of the vertical component VzE2 of the gradient of the squared norm of the electric field E, to which the dielectrophoretic force F is proportional, calculated at a distance of 100nm above the electret layer 30, in the structural configuration of [Fig.3B].

[0084] As for [Fig.2], it appears that the dielectrophoretic force Fz is not constant in the Zc conversion zones. Indeed, it has a maximum, located at the edge of the Zc conversion zone, with a value here, in log(VzE2), of 21.8, and a minimum, located at the center of the Zc conversion zone, with a value here of 18.9.

[0085] Furthermore, the intensity of the force Fz decreases outside the conversion zone Zc, down to a minimum of 15.4 at the center of the spacing zone Ze. This minimum is therefore much lower than that present in the conversion zone Zc.

[0086] Since the center of the spacing zone Ze is further from the edge, the force Fz has, in the spacing zone, a slightly higher decay rate from the maximum of 21.8 than that defined in the conversion zone Zc.

[0087] Also, although the photoluminescent particles p will mainly be deposited in the Zc conversion zone, deposition will still take place in the Ze spacing zone, from the edge of the Zc conversion zone. In addition, the localized deposition in the Zc conversion zone is not uniform: it will be greater at the edge than at the center of the Zc conversion zone, leading to a non-uniform conversion rate.

[0088] The inventors have demonstrated that structuring the surface potential in the Zc conversion zones makes it possible to limit the drawbacks of the configurations which have just been presented. The surface potential is said to be structured insofar as each Zc conversion zone has several elementary zones 32 with non-zero surface potential (more precisely uniformly non-zero, i.e. non-zero over the entire surface of the zone 32) spaced two by two by an elementary zone 33 with zero surface potential (more precisely uniformly zero, i.e. zero over the entire surface of the zone 33). This distinguishes it from the Zc conversion zones of [Fig. 1A] to IC where the surface potential is uniformly non-zero, i.e. non-zero over the entire surface of the Zc zone.

[0089] Indeed, a structured surface potential will make it possible to improve the homogeneity of the localized deposition of the photoluminescent particles p in the conversion zone Zc, and therefore the thickness of the conversion pad P, while limiting the deposition outside the conversion zones Zc (therefore differentiating, in terms of dielectrophoretic force, the conversion zones Zc from the spacing zones Ze).

[0090] Thus, a so-called polarized elementary zone 32 is a part of the surface of the conversion zone Zc where the surface potential is non-zero over the entire surface of the zone 32 (therefore uniformly non-zero). In addition, a so-called non-polarized elementary zone 33 is a part of the surface of the conversion zone Zc where the surface potential is zero over the entire surface of the zone 33 (therefore uniformly non-zero). Also, each conversion zone Zc is formed of several polarized elementary zones 32 separated two by two by a non-polarized elementary zone 33.

[0091] In each conversion zone Zc, the polarized elementary zones 32 are preferably arranged symmetrically with respect to an axis contained in the XY plane and passing through the center of the conversion zone Zc. By way of example, the zones polarized elements 32 can be arranged symmetrically with respect to the X axis and / or the Y axis.

[0092] Along the same axis of the XY plane, for example along the X axis, each conversion zone Zc may comprise at least two polarized elementary zones 32, for example between two and twenty polarized elementary zones 32. Preferably, it comprises between three and nine polarized elementary zones 32, or even preferably between three and seven polarized elementary zones 32. Thus, the homogeneity of the localized deposition of the photoluminescent particles p in the conversion zone Zc is improved. The polarized elementary zones 32 may have a dimension for example of the order of 1 / 5th, 1 / 10th, or even 1 / 20th of the dimension of the conversion zone Zc along the same axis considered (for example along the X axis). Thus, by way of example, for a conversion zone Zc of 2pm width, the polarized elementary zones 32 may have a width of approximately 100 to 500nm. The unpolarized elementary zones 33 can have a width of the same order.

[0093] The polarized elementary zones 32 may be arranged in each conversion zone Zc from the edge thereof, i.e. by being adjacent to it. Alternatively, they may not be adjacent to the edge, but may be spaced apart from it. This configuration is advantageous, since it makes it possible to prevent the dielectrophoretic force from having an intensity peak located at the edge, which limits the deposition of the photoluminescent particles p in the spacing zone near the edge. This improves the contrast of the luminous pixels.

[0094] [Fig.4A] is a schematic and partial cross-sectional view of a diode matrix covered by an electret layer, which is in contact with a colloidal solution. [Fig.4B] is a top view of the arrangement of the polarized elementary zones 32 located in a conversion zone Zc. [Fig.4C] illustrates the spatial variation of the intensity (in log) of the vertical component VZE2 of the gradient of the squared norm of the electric field E, to which the dielectrophoretic force F is proportional, calculated at a distance of 100nm above the electret layer 30, in the structural configuration of [Fig.4A].

[0095] In this configuration, the diodes D have a lateral dimension of 2 pm and are arranged periodically at a pitch of 4 pm. Also, the conversion zones Zc have a lateral dimension of 2 pm and are spaced 2 pm apart from each other. The electret layer 30 has a homogeneous relative permittivity equal to 4, and the colloidal solution S has a homogeneous relative permittivity equal to 2.

[0096] Each conversion zone Zc comprises a polarized elementary zone 32 of 500nm on each side, located in the center of the conversion zone Zc, spaced by a distance of 500nm along the X and Y axes from a peripheral polarized elementary zone 32 of 250nm in width. This is attached to the border Zcb of the conversion zone Zc. Thus, along the X or Y axis, the conversion zone Zc comprises three polarized elementary zones 32 separated two by two by a non-polarized elementary zone 33.

[0097] The dielectrophoretic force thus exhibits a spatial variation in the conversion zone Zc which is reduced compared to the variation illustrated in [Fig.2]. Thus, the localized deposition of the photoluminescent particles py is made more uniform. The positioning of the conversion pad P is also improved, insofar as the conversion zone Zc is now distinguishable from the spacing zone Ze, in terms of dielectrophoretic force. Also, the conversion pad P will be positioned correctly opposite the diode D, and no longer straddling the border as in the case of [Fig.2].

[0098] [Fig.5A] is a schematic and partial cross-sectional view of a diode matrix covered by an electret layer, which is in contact with a colloidal solution. [Fig.4C] illustrates the spatial variation of the intensity (in log) of the vertical component VZE2 of the gradient of the squared norm of the electric field E, to which the dielectrophoretic force F is proportional, calculated at a distance of 100nm above the electret layer 30, in the structural configuration of [Fig.5A].

[0099] In this configuration, the diodes D have a lateral dimension of 3 pm and are arranged periodically at a pitch of 19 pm. Also, the conversion zones Zc have a lateral dimension of 3 pm and are spaced 16 pm apart from each other. The electret layer 30 has a homogeneous relative permittivity equal to 4, and the colloidal solution S has a homogeneous relative permittivity equal to 2.

[0100] Each conversion zone Zc comprises a polarized elementary zone 32 of 500nm on each side, located in the center of the conversion zone Zc, spaced along the X and Y axes by a peripheral polarized elementary zone 32 of 250nm width. This is attached to the border Zcb of the conversion zone Zc. Thus, along the X or Y axis, the conversion zone Zc comprises three polarized elementary zones 32 separated two by two by a non-polarized elementary zone 33.

[0101] The dielectrophoretic force thus exhibits a spatial variation in the conversion zone Zc which is reduced compared to the variation illustrated in [Fig.3B]. Thus, the localized deposition of the photoluminescent particles py is made more uniform. The positioning of the conversion pad P is also improved, insofar as the conversion zone Zc is now distinguishable from the spacing zone Ze, in terms of dielectrophoretic force. Also, the conversion pad P will be correctly positioned opposite the diode D.

[0102] Figures 6A to 6F are top views of different examples of arrangement of the polarized elementary zones 32 in a conversion zone Zc. These examples are given for illustrative purposes, it being understood that other arrangements are obviously possible. Here, the conversion zone Zc has a square shape in the XY plane, but other shapes are possible (rectangular, polygonal, circular, etc.)

[0103] [Fig.6A] illustrates an arrangement identical to that of [Fig.4B]. The conversion zone Zc comprises three polarized elementary zones 32 along the X axis as well as along the Y axis. The central polarized elementary zone 32 has a width Iref, and the peripheral polarized elementary zone 32 has a width lref / 2. This extends from the border Zcb of the conversion zone Zc, i.e. by being attached to the border. In addition, it extends here continuously along the border Zcb. Furthermore, the polarized elementary zones 32 are spaced apart by a non-polarized elementary zone 33 of width Iref.

[0104] [Fig.6B] illustrates an arrangement which differs from that of [Fig.6A] essentially in that the peripheral polarized elementary zone 32 here has a width Iref equal to that of the central polarized elementary zone 32. In addition, the peripheral polarized elementary zone 32 is not attached to the border Zcb, but is spaced from it by a non-polarized elementary zone 33 with a width here of lref / 2.

[0105] [Fig.6C] illustrates an arrangement which differs from that of [Fig.6A] essentially in that lateral polarized elementary zones 32 distinct from each other are distributed along the border, and thus surround the central polarized elementary zone 32. Here they have a width lref / 2 and are attached to the border Zcb.

[0106] [Fig.6D] illustrates an arrangement which differs from that of [Fig.6A] essentially in that the lateral polarized elementary zones 32 have a width Iref. They are spaced from each other, along the X axis and the Y axis, by a non-polarized elementary zone 33 of width Iref. They are also spaced from the border, here by a width lref / 2.

[0107] [Fig.6E] illustrates an arrangement which differs from that of [Fig.6C] essentially in that the lateral polarized elementary zones 32 are not all identical to each other. Those located at the top of the conversion zone Zc have an L shape where the two branches here have the same length Iref and a width lref / 2. Those located along one side of the conversion zone Zc have a length Iref and a width lref / 2.

[0108] [Fig.6F] illustrates an arrangement which differs from that of [Fig.6E] essentially in that the lateral polarized elementary zones 32 are distant from the border, here by a width lref / 2 along the X axis and the Y axis. In addition, intermediate polarized elementary zones 32 are located between the central polarized elementary zone 32 and the lateral polarized elementary zones 32 along the X and Y axes. Here they have the shape of a square with side lref / 2.

[0109] Figures 7A to 7C illustrate a spatial variation of the intensity (in log) of the vertical component VZE2 of the gradient of the squared norm of the electric field E, calculated at a distance of 100nm above the electret layer 30, for different arrangements of the polarized elementary zones 32 in the conversion zones Zc. Here, the conversion zones Zc have a dimension of 2pm and are spaced from each other by a spacing zone of 2pm. The electret layer 30 has a homogeneous relative permittivity equal to 4, and the colloidal solution has a homogeneous relative permittivity equal to 2.

[0110] In [Fig.7A], each Zc conversion zone has three 32 polarized elementary zones with a width of 125nm, including a central 32 zone and two lateral 32 zones distant from the Zcb border. The filling factor, along the X axis, is here 19% (3x0.125 / 2). It is noted that the Zc conversion zone is clearly distinguishable from the Ze spacing zones, from a dielectrophoretic force point of view, which improves the positioning of the P conversion pad as well as the thickness homogeneity. In addition, the fact that the lateral 32 polarized elementary zones are distant from the border makes it possible to reduce the intensity of the dielectrophoretic force, which thus limits the deposition of the p photoluminescent particles in the Ze spacing zones, close to the Zc conversion zone, thus improving the contrast of the luminous pixels.

[0111] In [Fig.7B], the conversion zone Zc comprises five polarized elementary zones 32 with a width of 125nm. The lateral polarized elementary zones 32 are distant from the border. It is noted that this configuration makes it possible to further improve the positioning of the conversion pad P opposite the diode, to improve the thickness uniformity of the conversion pad P, and to limit the deposition of the photoluminescent particles p in the spacing zones Ze, near the conversion zone Zc.

[0112] In [Fig.7C], the conversion zone Zc comprises seven polarized elementary zones 32 with a width of 125nm. The lateral polarized elementary zones 32 are attached to the edge. If we further improve the positioning of the conversion pad P opposite the diode and the thickness uniformity of the conversion pad P, we note that the presence of the lateral polarized elementary zones 32 attached to the edge can lead to a deposition of the photoluminescent particles p in the spacing zones Ze near the edge of the conversion zone Zc.

[0113] According to one embodiment, the electret layer can be formed from several portions of materials having a different relative permittivity.

[0114] In this respect, figures 8A to 8C illustrate a comparison between a configuration where the electret layer is homogeneous, i.e. having the same relative permittivity value throughout the electret layer, and a configuration where the electret layer is not not homogeneous in terms of relative permittivity.

[0115] We first consider a configuration where the electret layer has a constant (uniform) relative permittivity throughout the layer. Here,

[0116] [Fig.8A] illustrates a spatial variation of the intensity (in log) of the vertical component VZE2 of the gradient of the squared norm of the electric field E, calculated at a distance of 100nm above the electret layer 30, for a configuration where the electret layer is homogeneous (constant relative permittivity everywhere in the layer).

[0117] In this configuration, the diodes have a lateral dimension of 2 pm and are arranged periodically at a pitch of 4 pm. Also, the Zc conversion zones have a lateral dimension of 2 pm and are spaced 2 pm apart from each other. The electret layer has a uniform relative permittivity equal to 4, and the colloidal solution has a uniform relative permittivity equal to 2. The Zc conversion zone is structured so as to form four elementary zones polarized 32 along the X axis.

[0118] [Fig.8B] is a schematic and partial view, in cross-section, of a matrix of diodes 20 covered by an electret layer 30 and a colloidal solution S.

[0119] The configuration is similar to that described with reference to [Fig.8A], and differs only in that the electret layer 30 is not homogeneous, but is formed from a succession of distinct portions 34, 35 having different relative permittivities. Thus, the portions 34 facing the diodes here have a relative permittivity of 4 and are made of a so-called low-k material, for example a silicon oxide or nitride. The portions 35 located between the diodes have a high relative permittivity, here equal to 20, and are made of a so-called high-k material, for example a titanium or tantalum oxide.

[0120] [Fig.8C] illustrates a spatial variation of the intensity (in log) of the vertical component VZE2 of the gradient of the squared norm of the electric field E, calculated at a distance of 100nm above the electret layer 30, for the configuration of [Fig.8B]. We note that the variation is similar, however it has a more significant minimum in the spacing zones Ze, here 18.5 instead of 19 in the case of [Fig.8A]. Also, the risks of deposition of photoluminescent particles p in the spacing zones Ze are reduced, and the deposition takes place more in the conversion zones Zc.

[0121] According to another embodiment, the Zc conversion zones may not be structured and may therefore have a uniformly non-zero surface potential. In this case, a permittivity relative to the Zc conversion zones and to the Ze spacing zones is defined.

[0122] As illustrated in [Fig.9A], in the case where the electret layer 30 is inhomogeneous and is formed from a succession of portions 34, 35 of materials having a different relative permittivity, the relative permittivity of the conversion zones Zc is equal to that portions 34, and the relative permittivity of the spacing zones Ze is equal to that of portions 35. As indicated previously, portions 34 are made of a low-k material, for example a silicon oxide or nitride, and portions 35 are made of a high-k material, for example a titanium or tantalum oxide.

[0123] As illustrated in [Fig.9B], the variation of the dielectropheretic force, here the log of VZE2, is not identical in the Zc conversion zones and in the Ze spacing zones. Indeed, the minimum in the Zc conversion zones is higher than in the Ze spacing zones. Also, the photoluminescent particles p will be deposited preferentially in the Zc conversion zones rather than in the Ze spacing zones.

[0124] As illustrated in [Fig.10A], the electret layer 30 is inhomogeneous and is formed of a sub-layer formed of the same material with constant relative permittivity, here a low-k material, and of portions 40 made of a so-called very high-k material, the relative permittivity of which is equal to at least 100, covering only the Ze spacing zones and not the Zc conversion zones. These portions are made for example of a perovskite and / or ferroelectric material, of BaSrTiO3, BaTiO3, SrTiO3, PbZrTiO3, KNN, among others. The relative permittivity can be equal to 250. Also, the relative permittivity of the Zc conversion zones is equal to that of the sub-layer of the electret layer (e.g.: 4), and the relative permittivity of the Ze spacing zones is equal to that of the portions 40 (e.g.: 250).

[0125] As illustrated in [Fig.10B], the variation of the dielectrophoretic force, here the log of VZE2, is also not identical in the Zc conversion zones and in the Ze spacing zones. Indeed, the minimum in the Zc conversion zones is higher than in the Ze spacing zones, and these have a minimum value over a larger area. Also, the photoluminescent particles p will be deposited preferentially in the Zc conversion zones rather than in the Ze spacing zones.

[0126] Figures 1 1A to 11E illustrate an example of a method for producing an electret layer formed from a succession of several portions having different relative permittivities, here portions having the same low relative permittivity, and portions having the same high relative permittivity.

[0127] It is thus possible to deposit an electret layer 30 formed from the low-k material, which covers the entire diode matrix 20 ([Fig. 11 A]). Then, through openings are made opening onto the diode matrix 20, to form portions 34 located opposite the diodes ([Fig. 11B]). The openings are through here, but they could not be. A layer 42 formed from a high-k material, or here a metallic material such as Ti or Ta, is then deposited so as to cover the diode matrix 20 and the portions 34 ([Fig. 11C]). Then, a mechanical-chemical planarization is carried out with a stop on portions 34 ([Fig.llD]). Finally, an oxidation annealing of the metal is carried out to obtain the high-k material of portions 35, here a Ti or Ta oxide ([Fig.llE]).

[0128] Particular embodiments have just been described. Different variants and modifications will appear to those skilled in the art.

Claims

Claims

1. Method for manufacturing an optoelectronic device (1), comprising the following steps: • providing a diode matrix (20), having a front face intended to receive or transmit light radiation; • producing an electret layer (30), extending over the front face of the diode matrix (20), an upper face of which, opposite the front face, has conversion zones (Zc), each being located perpendicular to a diode (D) and intended to be covered by a color conversion pad (P), separated two by two by a spacing zone (Ze) with zero surface potential; • producing the color conversion pads (P), by bringing the electret layer (30) into contact with a colloidal solution (S) containing photoluminescent particles (p), which are deposited on the electret layer (30) in the conversion zones (Zc), thus forming the color conversion pads (P);• characterized in that, following the step of producing the electret layer (30), each conversion zone (Zc) is formed from a plurality of elementary zones called polarized (32) with non-zero surface potential spaced two by two by an elementary zone called non-polarized (33) with zero surface potential, so that the conversion zone (Zc) has a structured surface potential.;

2. Manufacturing method according to claim 1, wherein the polarized elementary zones (32) are arranged symmetrically with respect to a center of the conversion zone (Zc).

3. Manufacturing method according to claim 1 or 2, in which each conversion zone (Zc) comprises between three and nine polarized elementary zones (32), and preferably between three and seven polarized elementary zones (32).

4. Manufacturing method according to any one of claims 1 to 3, in which the polarized elementary zones (32) are all located at a distance from an edge (Zcb) of the conversion zone (Zc).

5. A manufacturing method according to any one of claims 1 to 4, wherein the electret layer (30) has a homogeneous relative permittivity.

6. A manufacturing method according to any one of claims 1 to 4, wherein the electret layer (30) has a relative permittivity having a first value in the conversion zones (Zc) and a second value greater than the first value outside the conversion zones (Zc).

7. Manufacturing method according to claim 6, in which the electret layer (30) is formed of first portions located in the conversion zones (Zc) and made of a material having the first relative permittivity value, and second portions located outside the conversion zones (Zc) and made of a material having the second relative permittivity value.

8. Manufacturing method according to claim 6, in which the electret layer (30) is formed of a continuous sub-layer covering the diode matrix and made of a material having the first relative permittivity value, and of portions (40) covering the sub-layer, located outside the conversion zones (Zc) and made of a material having the second relative permittivity value.

9. Optoelectronic device (1), comprising: • a diode matrix (20) having a front face intended to receive or transmit light radiation; • an electret layer (30), extending over the front face of the diode matrix (20), an upper face of which, opposite the front face, has conversion zones (Zc), each being located perpendicular to a diode (D) and intended to be covered by a color conversion pad (P), separated two by two by a spacing zone (Ze) with zero surface potential; • color conversion pads (P), located on the electret layer (30) and positioned in the conversion zones (Zc);• characterized in that each conversion zone (Zc) is formed from a plurality of elementary zones called polarized (32) with non-zero surface potential spaced two by two by an elementary zone called non-polarized (33) with zero surface potential, so that the conversion zone (Zc) has; a structured surface potential.

10. Optoelectronic device (1) according to the preceding claim, in which the diodes (D) have identical light radiation emission or absorption properties.

11. Optoelectronic device (1) according to claim 9 or 10, wherein the diodes are made from an organic or inorganic semiconductor compound.

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