METHOD FOR PRODUCING AN OPTOELECTRONIC DEVICE WITH COLOR CONVERSION BY LOCALIZED SEPARATION OF LIGHT-EMISSITING PARTICLES ON PREDEFINED CONVERSION ZONES WITH STRUCTURAL POTENTIAL

Description

DOMAINE TECHNIQUE

[0001] The field of the invention is that of manufacturing methods for optoelectronic devices comprising an array of diodes for emitting or detecting electroluminescent radiation, combined with color conversion pads. The invention finds application particularly in display screens and image projectors. ÉTAT DE LA TECHNIQUE ANTÉRIEURE

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

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

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

[0005] Light conversion pads can be formed from a binding matrix containing particles of a photoluminescent material such as yttrium aluminum garnet (YAG, for Yttrium Aluminium Garnet, (in English) activated by the cerium ion YAG:Ce. Photoluminescent particles can also be quantum dots (quantum dots, (in English), that is, in the form of semiconductor nanocrystals whose quantum confinement is essentially three-dimensional. It can also be nanoplatelets ( nanoplatelets, in English), that is to say nanoparticles having an essentially two-dimensional shape (two-dimensional quantum confinement).

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

[0007] Document WO2014 / 136023A1 describes another manufacturing process, which uses an electret layer covering the diode array. The process first involves inscribing patterns of electrical charges onto the top surface of a dielectric layer to obtain the electret layer, which is then locally charged. For this, an AFM tip (for Atomic Force Microscopy, (in English) a polarized layer is used to locally inject electrical charges. Then, a localized deposition step of colloidal nanocrystals is performed on the electrical charge patterns. For this, the electret layer is brought into contact with a colloidal solution containing the nanocrystals, which are naturally deposited onto the electrical charge patterns under the influence of a dielectrophoretic force. However, this process has the drawback of requiring the sequential injection of electrical charges, by moving the AFM tip across the surface of the top face to form the electrical charge patterns.

[0008] Document WO2021 / 023656A1 describes a similar process, where the electrical charge patterns are defined by a stamping technique, i.e., by bringing an electrically polarized pad into contact with a dielectric layer intended to form the electret layer. The underside of the pad is structured to form polarized teeth, which come into contact with the dielectric layer. This produces the electret layer, the upper surface of which displays the electrical charge patterns. The electret layer is then brought into contact with a colloidal solution, and the nanocrystals present are deposited onto the electrical charge patterns by dielectrophoresis. However, this process has the drawback, notably, of requiring precise positioning of the pad relative to the diode array.However, the uncertainty in the buffer's positioning relative to the diode array can become problematic, particularly for diode arrays with small pixel pitches, for example, on the order of 5 µm. Indeed, this uncertainty or positioning inaccuracy can lead to incorrect positioning of the light conversion pads relative to the diodes, and therefore to a degradation of the optoelectronic device's performance.

[0009] Document DE 10 2004 021231 A1 describes a method for depositing a material onto a solid body, where electrostatic forces are exerted between the material and the solid body during deposition. The material contains at least one photoluminescent light-converting agent. This process is particularly suitable for coating optoelectronic components with a light-converting layer. EXPOSÉ DE L'INVENTION

[0010] The invention aims to remedy at least in part the disadvantages of the prior art, and more particularly to propose a method for manufacturing an optoelectronic device which has improved performance.

[0011] To this end, the object of the invention is a method for manufacturing an optoelectronic device, comprising the following steps: • provide a diode matrix, having a front face intended to receive or transmit light radiation; • create an electret layer, extending over the front face of the diode matrix, the upper face of which, opposite the front face, has conversion zones, each located perpendicular to a diode and intended to be covered by a color conversion pad, separated in pairs by a spacing zone with zero surface potential; • create 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 electret layer formation step, each conversion zone is formed of a plurality of elementary zones called polarized with a non-zero surface potential, spaced two by two by an elementary zone called unpolarized with a zero surface potential, so that the conversion zone presents a structured surface potential. ;

[0012] Some preferred, but not exhaustive, aspects of this process are as follows.

[0013] The polarized elementary zones can be arranged symmetrically with respect to a center of the conversion zone.

[0014] Each conversion zone can have between three and nine polarized elementary zones, and preferably between three and seven polarized elementary zones.

[0015] The elementary polarized zones can all be located at a distance from a boundary of the conversion zone.

[0016] The electret layer can exhibit a homogeneous relative permittivity.

[0017] The electret layer can exhibit a relative permittivity with a first value in the conversion zones and a second value greater than the first value outside the conversion zones.

[0018] The electret layer can be formed from first portions located in the conversion zones and made of a material having the first relative permittivity value, and from second portions located outside the conversion zones and made of a material having the second relative permittivity value.

[0019] The electret layer can be formed of a continuous sublayer covering the diode matrix and made of a material having the first relative permittivity value, and portions covering the sublayer, located outside the conversion areas and made of a material having the second relative permittivity value.

[0020] The invention also relates to an optoelectronic device, comprising: • a diode matrix having a front face intended to receive or transmit light radiation; • an electret layer, extending over the front face of the diode matrix, the 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 in pairs 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 of a plurality of elementary zones called polarized with non-zero surface potential spaced in pairs by an elementary zone called unpolarized with zero surface potential, so that the conversion zone has a structured surface potential.

[0021] Diodes can exhibit identical emission or absorption properties of light radiation.

[0022] Diodes can be made from an organic or inorganic semiconductor compound.

[0023] It also describes a manufacturing process for an optoelectronic device, comprising the following steps: • Provide a diode matrix, having a front face intended to receive or transmit light radiation; • Create an electret layer, extending over the front face of the diode matrix, the upper face of which, opposite the front face, has conversion zones, each located perpendicular to a diode and intended to be covered by a color conversion pad P, separated in pairs by a spacing zone with zero surface potential; • Create the color conversion pads by contacting the electret layer 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 creation of the electret layer: the surface potential in each conversion zone is uniformly non-zero;The conversion zones exhibit a first relative permittivity value, and the spacing zones exhibit a second relative permittivity value that is higher than the first value.

[0024] The electret layer can be formed from first portions located in the conversion zones and made of a material having the first relative permittivity value, and from second portions located outside the conversion zones and made of a material having the second relative permittivity value.

[0025] The electret layer can be formed of a continuous sublayer covering the diode matrix and made of a material having the first relative permittivity value, and portions covering the sublayer, located outside the conversion areas and made of a material having the second relative permittivity value.

[0026] There is also mention of an optoelectronic device, comprising: • a diode matrix having a front face intended to receive or transmit light radiation; • an electret layer, extending over the front face of the diode matrix, the 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 in pairs 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. BRÈVE DESCRIPTION DES DESSINS

[0027] Other aspects, objectives, advantages, and features of the invention will become clearer upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which: THE figures 1A à 1C illustrate different stages of a manufacturing process for an optoelectronic device where the conversion zones exhibit a uniformly non-zero surface potential; the figure 2 illustrates a variation in the vertical component of the electric field gradient, in the configuration of the fig.1B ; there figure 3A is a schematic and partial cross-sectional view of an optoelectronic device where the conversion zones exhibit a uniformly non-zero surface potential, according to a different arrangement of the diode matrix; the figure 3B illustrates a variation in the vertical component of the electric field gradient, in the configuration of the fig.3A ; there figure 4A is a schematic and partial cross-sectional view of an optoelectronic device according to an embodiment where the conversion zones exhibit a structured surface potential; the figure 4B is a top view of the conversion zone illustrating the arrangement of the polarized elementary zones; the figure 4C illustrates a variation in the vertical component of the electric field gradient, in the configuration of the fig.4A ; there figure 5A is a schematic and partial cross-sectional view of an optoelectronic device according to another embodiment where the conversion zones exhibit a structured surface potential; the figure 5B illustrates a variation in the vertical component of the electric field gradient, in the configuration of the fig.5A ; THE figures 6A à 6F are top views of a conversion zone of an optoelectronic device according to different embodiments; the figures 7A à 7C illustrate the variation of the vertical component of the electric field gradient for different embodiments of the optoelectronic device; the figure 8A illustrates a variation in the vertical component of the electric field gradient for an optoelectronic device in an embodiment where the electret layer has a homogeneous relative permittivity; figure 8B is a schematic and partial cross-sectional view of an optoelectronic device in an embodiment where the electret layer has an inhomogeneous relative permittivity; the figure 8C illustrates a variation in the vertical component of the electric field gradient, for the configuration of the fig.8B ; there figure 9A is a schematic and partial cross-sectional view of an optoelectronic device according to an embodiment, not forming part of the present invention as defined by the annexed claims but useful for understanding its context, where the electret layer has an inhomogeneous relative permittivity and where the conversion zones have a uniformly non-zero surface potential; the figure 9B illustrates a variation in the vertical component of the electric field gradient, for the configuration of the fig.9A ; there figure 10A is a schematic and partial cross-sectional view of an optoelectronic device according to another embodiment, which is also not part of the present invention as defined by the annexed claims but is useful for understanding its context, where the electret layer has an inhomogeneous relative permittivity and where the conversion zones have a uniformly non-zero surface potential; the figure 10B illustrates a variation in the vertical component of the electric field gradient, for the configuration of the fig.10A ; THE figures 11A à 11E illustrate different stages of a manufacturing process for an optoelectronic device similar to that of the fig.9A . EXPOSÉ DÉTAILLÉ DE MODES DE RÉALISATION PARTICULIERS

[0028] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale to ensure clarity. Moreover, the different embodiments and variants are not mutually exclusive and may be combined. Unless otherwise stated, the terms "approximately," "around," and "in the order of" mean within 10%, and preferably within 5%. Furthermore, the terms "between ... and ..." and equivalents mean inclusive of the bounds, unless otherwise specified.

[0029] The invention relates to a method for manufacturing an optoelectronic device comprising a diode array, at least some of whose diodes are covered by color conversion pads, so as to form an array of luminous pixels of different colors. The diodes may be emitting 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 detecting diodes, so that the optoelectronic device may be an array photodetector. These may be organic or inorganic photodetectors.

[0030] The color conversion pads are created by the localized deposition of photoluminescent particles onto an electret layer. Each conversion pad is located opposite a diode.

[0031] In general, an electret layer is a dielectric layer containing electric charges or a quasi-permanent dipole polarization. Furthermore, the electret layer exhibits a non-zero surface potential on at least part of its upper surface. This means that the electret layer emits an external electric field in the absence of an applied field.

[0032] In the context of this invention, a conversion zone is defined as a predefined area 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 within it. In other words, each conversion zone is formed of several elementary, so-called polarized areas where the surface potential is non-zero, separated in pairs by an elementary, unpolarized area where the surface potential is zero.

[0033] Thus, it appears that the localized deposition of photoluminescent particles in the conversion zone is more homogeneous than in the prior art, thereby improving the properties of the optoelectronic device. Furthermore, it appears that the localized deposition of photoluminescent particles outside the conversion zones is reduced, which improves the contrast of the pixels in the optoelectronic device.

[0034] Generally, color conversion pads are made of particles of at least one photoluminescent material, preferably nanoparticles with at least one maximum dimension between 0.2 nm and 1000 nm, for example, between 20 nm 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 shape, for example, spherical, angular, flattened, elongated, etc.

[0035] Photoluminescent particles can be quantum dots, that is, semiconductor nanocrystals whose quantum confinement is essentially three-dimensional. The average size of quantum dots can then range from 0.2 nm to 50 nm, for example, from 1 nm to 30 nm. They can also be nanoplatelets ( nanoplatelets, (in English), that is, nanoparticles having an essentially two-dimensional shape, with a length that can range from 20 nm to a few hundred nanometers. Also, the smallest dimension (thickness) is smaller than the other two dimensions of length and width, preferably by a ratio of at least 1.5.

[0036] Photoluminescent particles can notably be formed of at least one semiconductor compound, which can be chosen, for example, from cadmium selenide (CdSe), indium phosphorus (InP), gallium indium phosphorus (InGaP), cadmium sulfide (CdS), zinc sulfide (ZnS), cadmium oxide (CdO) or zinc oxide (ZnO), zinc cadmium selenide (CdZnSe), zinc selenide (ZnSe) doped, for example, with copper or manganese, graphene, or from other suitable semiconductor materials. Nanoparticles can also exhibit a core / shell structure, such as CdSe / ZnS, CdSe / CdS, CdSe / CdS / ZnS, PbSe / PbS, CdTe / CdSe, CdSe / ZnTe, InP / ZnS, or others. Particles can also have a perovskite crystal structure containing atoms such as those listed for nanoparticles, but also Cs, Mn, and Br.

[0037] Furthermore, light conversion pads are designed to convert, at least partially, incident light of a first wavelength λ₁ into luminescent light of a longer wavelength λ₂. For example, they can be adapted to absorb blue light, i.e., light with a wavelength between approximately 440 nm and 490 nm, and emit green light, i.e., light with a wavelength between approximately 495 nm and 560 nm, or even red light, i.e., light with a wavelength between 600 nm and 650 nm. Here, wavelength refers to the wavelength at which the emission spectrum exhibits a peak intensity.

[0038] For illustrative purposes only, diodes can be emissive and exhibit an emission spectrum in the visible or infrared (for example, in the NIR or SWIR), or even ultraviolet (200-400 nm). In the case of an emissive diode array, 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 within the same predefined absorption spectrum.

[0039] THE figures 1A à 1C illustrate different stages of an example of an optoelectronic device manufacturing process 1, highlighting a problem related to the localized deposition of photoluminescent particles p in and outside the conversion zone Zc. In this example, the diodes D are light-emitting diodes.

[0040] Here and for the remainder of the description, we define a three-dimensional orthogonal XYZ coordinate system, where the X and Y axes form a principal plane in which the diode matrix 20 extends, and where the Z axis is oriented along the thickness of the diode matrix 20 towards the front face. The terms 'lower' and 'upper' are defined with respect to an increasing position along the +Z direction.

[0041] With reference to the fig.1A The matrix 20 of light-emitting diodes D is provided. The diodes D rest on a control substrate 10 and are electrically biased by one or more lower electrode layers 21 and one or more upper electrode layers 25. Other configurations are possible, particularly when the control substrate 10 is electrically conductive. The diode matrix 20 has a rear face, through 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. In this example, where the diodes D are emissive, the front face transmits the light emitted by the diodes. In this example, color conversion pads are planned above the diodes shown. However, some diodes may not be associated with color conversion pads.

[0042] In this example, the control substrate 10 includes a CMOS-type control circuit (not shown) and has electrical connection pads 11 that are flush with the top face and make contact with the lower electrode layers 21 of the diodes D. These lower electrode layers 21 are distinct from one another, in the sense that each lower electrode layer 21 of a diode D is physically separate from that of the adjacent diode. This configuration is described in detail in document WO2017 / 194845 A1. Other configurations are possible.

[0043] The D diodes here are inorganic light-emitting diodes. They can be fabricated conventionally, for example by epitaxy of semiconductor layers from a growth substrate, then transferred to the control substrate 10. Each D diode can be formed from a stack of: a lower semiconductor portion 22 (located on the control substrate side) doped with a first type of conductivity, for example p-type, in electrical contact with a lower electrode layer 21; an active region 23 where 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 D diodes can be fabricated from the same semiconductor compound, for example based on a III-V compound such as GaN, InGaN, or AlGaN.An electrically insulating filling material 26 fills the space between the diodes D.

[0044] Preferably, the D diodes are structurally identical, so that the emitted light is identical from one diode to another in terms of wavelength. In this example, the D diodes are suitable for emitting light in the blue range, that is, light whose emission spectrum has a peak intensity at a wavelength between approximately 440 nm and 490 nm.

[0045] The front face of the diode array 20 is covered by an electret layer 30. The electret layer 30 is made of at least one dielectric material, for example an inorganic material such as a silicon oxide, nitride, or oxynitride, for example SiO₂, Si₃N₄, Al₂O₃ (particularly in the case of OLEDs), among others. It can be a few hundred nanometers thick, for example approximately 400 nm. Note that organic dielectric materials can also be suitable, such as PMMA, PVDF, PET, COC, etc.

[0046] A conversion zone Zc is defined as an area of ​​the electret layer 30 located opposite (perpendicular to) a diode D, and more precisely its active layer 23. In this example, the surface potential 31 y is uniformly non-zero (i.e., non-zero over the entire surface of the zone Zc). The conversion zones Zc are separated laterally in pairs by a spacing zone Ze where the surface potential y is zero (more precisely, the surface potential of each spacing zone Ze is uniformly zero, that is, zero over the entire surface of the zone Ze).

[0047] 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 achieved in various ways. An AFM tip, as described in document WO2014 / 136023A1, or a stamping technique, as described in document WO2021 / 023656A1, can be used. An electret layer 30, whose surface potential is initially non-zero across its entire front face, can also be locally depolarized optically by means of diode activation, as described in patent application FR2308637 filed on August 10, 2023. Alternatively, an electrostatic polarization of the electret layer, whose surface potential is initially zero across its entire front face, can be locally achieved by means of upper electrode activation, as described in patent application FR2309260 filed on September 4, 2023.

[0048] Thus, the Zc conversion zones with a 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 Zc conversion zones opposite the diodes.

[0049] With reference to the fig.1B The color conversion pads are then created by localized deposition of photoluminescent particles p onto the electret layer 30 in the conversion zones Zc. This is done in a manner similar to that described in documents WO2014 / 136023A1 and WO2021 / 023656A1. A colloidal solution S containing the photoluminescent particles p is placed in contact with the upper surface of the electret layer 30. The photoluminescent particles p are adapted to convert blue light into, for example, red light. The entire stack can be immersed in the colloidal solution S, or a drop of such a solution can be deposited onto 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 localized deposition of the photoluminescent particles p by dielectrophoresis.The photoluminescent particles p are deposited primarily 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 thus on the desired thickness of the conversion pads P, as well as the surface potential. For example, the thickness of the conversion pads P can be on the order of a few hundred nanometers, for example, approximately 400 nm. The colloidal solution S is then removed, and the electret layer 30 can be dried.

[0050] With reference to the fig.1C , we obtain an optoelectronic device 1 where the conversion pads P are present essentially in the conversion zones Zc, and therefore opposite the diodes D. A thin film encapsulation (e.g. in Al 2 O 3 ) of the conversion pads P can then be carried out (not shown).

[0051] The previous steps can then be repeated to create other color conversion pads located opposite other diodes, forming, for example, green pixels. Indeed, the color conversion pads described earlier are designed to convert blue light (wavelength between approximately 440nm and 490nm) into red light (wavelength between approximately 600nm and 650nm). However, the color conversion pads here are designed to convert blue light into green light (wavelength between approximately 495nm and 560nm).

[0052] However, it appears that the photoluminescent particles p may not be deposited homogeneously within the Zc conversion zones, leading to the formation of P conversion patches with non-uniform thicknesses, resulting in spatially non-uniform conversion properties. Furthermore, it appears that the photoluminescent particles p may be deposited outside the Zc conversion zones, thereby degrading the contrast associated with each emitting pixel.

[0053] There figure 2 illustrates the spatial variation of the intensity (in log) of the vertical component ∇ z E 2< of the gradient of the squared magnitude of the electric field E, to which the dielectrophoretic force F is proportional, calculated at a distance of 100 nm above the electret layer 30, in a structural configuration similar to that of the fig.1B .

[0054] In general, a photoluminescent particle of dimension r and dielectric constant εp located in a solution of dielectric constant εm (dielectric permittivity) undergoes, due to the spatial inhomogeneity of the electric field E a dielectrophoretic force F defined by the relation: F → = 2 × π × r 3 × ε m × ε p − ε m ε p + 2 × ε m × ∇ E → 2

[0055] In this configuration, the diodes D have a lateral dimension of 2 µm and are arranged periodically at 4 µm intervals. Similarly, the conversion zones Zc have a lateral dimension of 2 µm and are spaced 2 µm apart. The surface potential 31 is uniformly non-zero in the conversion zones Zc and uniformly zero in the spacing zones Ze. The diode fill factor FF d is therefore 50% (=2 µm / 4 µm).

[0056] We also consider a relative permittivity ε r,e of the electret 30 layer which is homogeneous (spatially uniform) throughout the layer and equal to 4, and a relative permittivity ε r,m of the colloidal solution which is also homogeneous and equal to 2.

[0057] It appears that the dielectrophoretic force Fz is not constant in the conversion zones Zc. Indeed, it exhibits a maximum, located at the edge of the conversion zone Zc, with a value here of 21.7, and a minimum located at the center of the conversion zone Zc, with a value here of 19.5.

[0058] 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 boundary of the conversion zone Zc, so the rate of decrease is symmetrical on both sides of this boundary. Consequently, the variation of the force Fz is identical in the conversion zones Zc and in the spacing zones Ze, so that, from the perspective of the dielectrophoretic force, it is not possible to distinguish the conversion zones Zc from the spacing zones Ze.

[0059] 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 way.

[0060] This leads to the formation of conversion plots P that not only lack uniform thickness in the conversion zones Zc, but are also incorrectly positioned. The conversion properties are then degraded, and the contrast of the bright pixels is not optimal.

[0061] There figure 3A is a schematic and partial cross-sectional view of a diode matrix 20 covered by an electret layer 30 and a colloidal solution S (the photoluminescent particles p are not shown), in a different structural configuration. As for the fig.1B , the electret layer 30 has 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 Zc zone), separated in pairs by spacing zones Ze with uniformly zero surface potential (i.e. zero over the entire surface of the Ze zone).

[0062] The conversion zones Zc have a lateral dimension of 2 µm and are arranged periodically at 18 µm intervals. Similarly, the spacing zones Ze have a lateral dimension of 16 µm. The filling factor FF d is therefore 11% (=2 µm / 18 µm). In this example, the electret layer 30 has a homogeneous relative permittivity of 4, and the colloidal solution S has a homogeneous relative permittivity of 2.

[0063] There figure 3B illustrates the spatial variation of the intensity (in log) of the vertical component ∇ z E 2< of the gradient of the squared magnitude of the electric field E, to which is proportional the dielectrophoretic force F, calculated at a distance of 100 nm above the electret layer 30, in the structural configuration of the fig.3B .

[0064] As for the fig.2 It appears that the dielectrophoretic force F z is not constant in the conversion zones Zc. Indeed, it has a maximum, located at the edge of the conversion zone Zc, with a value here, in log(V z E 2< ), of 21.8, and a minimum, located at the center of the conversion zone Zc, with a value here of 18.9.

[0065] Furthermore, the intensity of the force F z 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 significantly lower than that present in the conversion zone Zc.

[0066] Since the center of the spacing zone Ze is further from the edge, the force F z exhibits, in the spacing zone, a rate of decrease from the maximum of 21.8 slightly higher than that defined in the conversion zone Zc.

[0067] Therefore, although the photoluminescent particles will primarily be deposited in the conversion zone Zc, some deposition will still occur in the spacing zone Ze, starting from the edge of the conversion zone Zc. Furthermore, the localized deposition in the conversion zone Zc is not uniform: it will be greater at the edge than in the center of the conversion zone Zc, leading to a non-uniform conversion rate.

[0068] The inventors have demonstrated that structuring the surface potential in the Zc conversion zones mitigates the drawbacks of the configurations just described. The surface potential is said to be structured in that each Zc conversion zone has several elementary zones 32 with a non-zero surface potential (more precisely, uniformly non-zero, i.e., non-zero over the entire surface of zone 32) separated in pairs by an elementary zone 33 with a zero surface potential (more precisely, uniformly zero, i.e., zero over the entire surface of zone 33). This distinguishes it from the Zc conversion zones of fig.1A à 1C where the surface potential is uniformly non-zero, i.e. non-zero over the entire surface of the Zc zone.

[0069] Indeed, a structured surface potential will improve the homogeneity of the localized deposition of 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 (thus differentiating, in terms of dielectrophoretic force, the conversion zones Zc from the spacing zones Ze).

[0070] Thus, a so-called polarized elementary zone 32 is a portion of the surface of the conversion zone Zc where the surface potential is non-zero across the entire surface of zone 32 (i.e., uniformly non-zero). Furthermore, a so-called unpolarized elementary zone 33 is a portion of the surface of the conversion zone Zc where the surface potential is zero across the entire surface of zone 33 (i.e., uniformly zero). Each conversion zone Zc is therefore composed of several polarized elementary zones 32 separated in pairs by an unpolarized elementary zone 33.

[0071] 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. For example, the polarized elementary zones 32 can be arranged symmetrically with respect to the X axis and / or the Y axis.

[0072] Along the same axis of the XY plane, for example along the X-axis, each conversion zone Zc can 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 more preferably between three and seven polarized elementary zones 32. This improves the homogeneity of the localized deposition of photoluminescent particles p in the conversion zone Zc. The polarized elementary zones 32 can have a dimension, for example, on the order of 1 / 5 ep, 1 / 10 ep, or even 1 / 20 ep of the dimension of the conversion zone Zc along the same axis (for example, along the X-axis). Thus, as an example, for a conversion zone Zc 2 µm wide, the polarized elementary zones 32 can have a width of approximately 100 to 500 nm. The unpolarized elementary zones 33 can exhibit a width of the same order.

[0073] The polarized elementary zones 32 can be arranged in each conversion zone Zc starting from its edge, i.e., adjacent to it. Alternatively, they can be spaced apart from the edge. This configuration is advantageous because it prevents the dielectrophoretic force from having an intensity peak at the edge, thus limiting the deposition of photoluminescent particles p in the spacing zone near the edge. This improves the contrast of the luminous pixels.

[0074] There figure 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. figure 4B is a top view of the arrangement of the 32 polarized elementary zones located in a Zc conversion zone. figure 4C illustrates the spatial variation of the intensity (in log) of the vertical component ∇ z E 2< of the gradient of the squared magnitude of the electric field E, to which is proportional the dielectrophoretic force F, calculated at a distance of 100 nm above the electret layer 30, in the structural configuration of the fig.4A .

[0075] In this configuration, the diodes D have a lateral dimension of 2 µm and are arranged periodically at 4 µm intervals. Similarly, the conversion zones Zc have a lateral dimension of 2 µm and are spaced 2 µm apart. The electret layer 30 has a homogeneous relative permittivity of 4, and the colloidal solution S has a homogeneous relative permittivity of 2.

[0076] Each conversion zone Zc comprises a polarized elementary zone 32, 500 nm on each side, located at the center of the conversion zone Zc, separated by a distance of 500 nm along the X and Y axes from a peripheral polarized elementary zone 32, 250 nm wide. This peripheral zone is adjacent to the edge Zc b of the conversion zone Zc. Thus, along the X or Y axis, the conversion zone Zc comprises three polarized elementary zones 32 separated in pairs by an unpolarized elementary zone 33.

[0077] The dielectrophoretic force thus exhibits a spatial variation in the conversion zone Zc that is reduced compared to the variation illustrated on the 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, since the conversion zone Zc is now distinguishable from the spacing zone Ze in terms of dielectrophoretic strength. Therefore, the conversion pad P will be correctly positioned relative to the diode D, and no longer straddling the edge as in the case of the fig.2 .

[0078] There figure 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. figure 5B illustrates the spatial variation of the intensity (in log) of the vertical component ∇ z E 2< of the gradient of the squared magnitude of the electric field E, to which is proportional the dielectrophoretic force F, calculated at a distance of 100 nm above the electret layer 30, in the structural configuration of the fig.5A .

[0079] In this configuration, the diodes D have a lateral dimension of 3 µm and are arranged periodically at 19 µm intervals. Similarly, the conversion zones Zc have a lateral dimension of 3 µm and are spaced 16 µm apart. The electret layer 30 has a homogeneous relative permittivity of 4, and the colloidal solution S has a homogeneous relative permittivity of 2.

[0080] Each conversion zone Zc comprises a polarized elementary zone 32, 500 nm on each side, located at the center of the conversion zone Zc, separated along the X and Y axes by a peripheral polarized elementary zone 32, 250 nm wide. This peripheral zone is adjacent to the edge Zc b of the conversion zone Zc. Thus, along the X or Y axis, the conversion zone Zc comprises three polarized elementary zones 32 separated in pairs by an unpolarized elementary zone 33.

[0081] The dielectrophoretic force thus exhibits a spatial variation in the conversion zone Zc that is reduced compared to the variation illustrated on the 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, since the conversion zone Zc is now distinguishable from the spacing zone Ze in terms of dielectrophoretic strength. Therefore, the conversion pad P will be correctly positioned relative to the diode D.

[0082] THE figures 6A à 6F These are top views of different arrangements of the polarized elementary zones 32 within 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.).

[0083] There fig.6A illustrates an arrangement identical to that of the fig.4B The conversion zone Zc comprises three polarized elementary zones 32 along both the X and Y axes. The central polarized elementary zone 32 has a width Iref, and the peripheral polarized elementary zone 32 has a width Iref / 2. This latter zone extends from the boundary Zc b of the conversion zone Zc, i.e., it is adjacent to the boundary. Furthermore, it extends continuously along the boundary Zc b. In addition, the polarized elementary zones 32 are separated by an unpolarized elementary zone 33 of width Iref.

[0084] There fig.6B illustrates an arrangement that differs from that of the fig.6A essentially, the peripheral polarized elementary zone 32 has a width Iref equal to that of the central polarized elementary zone 32. Furthermore, the peripheral polarized elementary zone 32 is not adjacent to the boundary Zc b, but is separated from it by an unpolarized elementary zone 33 with a width here of Iref / 2.

[0085] There fig.6C illustrates an arrangement that differs from that of the fig.6A essentially in that distinct lateral polarized elementary zones 32 are distributed along the border, and thus surround the central polarized elementary zone 32. Here they have a width Iref / 2 and are adjacent to the border Zc b.

[0086] There fig.6D illustrates an arrangement that differs from that of the fig.6A essentially in that the lateral polarized elementary zones 32 have a width Iref. They are spaced from each other, along the X and Y axes, by an unpolarized elementary zone 33 of width Iref. They are also spaced from the boundary, here by a width Iref / 2.

[0087] There fig.6E illustrates an arrangement that differs from that of the fig.6C essentially, the lateral polarized elementary zones 32 are not all identical. Those located at the top of the conversion zone Zc have an L-shape where the two branches have the same length Iref and a width Iref / 2. Those located along one side of the conversion zone Zc have a length Iref and a width Iref / 2.

[0088] There fig.6F illustrates an arrangement that differs from that of the fig.6E essentially in that the lateral polarized elementary zones 32 are distant from the boundary, here with a width Iref / 2 along the X and Y axes. 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 a square shape with side Iref / 2.

[0089] THE figures 7A à 7C illustrate a spatial variation in the intensity (in log) of the vertical component ∇ z E 2< of the gradient of the squared magnitude of the electric field E, calculated at a distance of 100 nm 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 2 µm and are spaced from each other by a 2 µm spacing zone. The electret layer 30 has a homogeneous relative permittivity of 4, and the colloidal solution has a homogeneous relative permittivity of 2.

[0090] On the fig.7A Each conversion zone Zc has three polarized 32 elementary zones, each 125 nm wide: a central 32 zone and two lateral 32 zones located away from the Zc b boundary. The fill factor along the X-axis is 19% (3 x 0.125 / 2). The conversion zone Zc is clearly distinguishable from the Ze spacing zones in terms of dielectrophoretic force, which improves the positioning of the conversion pad P and the thickness homogeneity. Furthermore, the distance of the lateral polarized 32 elementary zones from the boundary reduces the intensity of the dielectrophoretic force, thus limiting the deposition of photoluminescent particles p in the Ze spacing zones near the conversion zone Zc, thereby improving the contrast of the luminous pixels.

[0091] On the fig.7B The conversion zone Zc comprises five polarized elementary zones 32, each 125 nm wide. The lateral polarized elementary zones 32 are located away from the edge. This configuration further improves the positioning of the conversion pad P relative to the diode, enhances the thickness uniformity of the conversion pad P, and limits the deposition of photoluminescent particles p in the spacing zones Ze, near the conversion zone Zc.

[0092] On the fig.7C The conversion zone Zc comprises seven polarized elementary zones 32, each 125 nm wide. The lateral polarized elementary zones 32 are adjacent to the edge. Further improvement of the positioning of the conversion pad P relative to the diode and the uniformity of its thickness reveals that the presence of these lateral polarized elementary zones 32 adjacent to the edge can lead to the deposition of photoluminescent particles p in the spacing zones Ze near the edge of the conversion zone Zc.

[0093] According to one embodiment, the electret layer can be formed from several portions of materials having a different relative permittivity.

[0094] In this respect, the figures 8A à 8C illustrate a comparison between a configuration where the electret layer is homogeneous, i.e. exhibiting the same relative permittivity value throughout the electret layer, and a configuration where the electret layer is not homogeneous in terms of relative permittivity.

[0095] We first consider a configuration where the electret layer has a constant (uniform) relative permittivity throughout the layer.

[0096] There figure 8A illustrates a spatial variation of the intensity (in log) of the vertical component ∇ z E 2< 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).

[0097] In this configuration, the diodes have a lateral dimension of 2 µm and are arranged periodically at 4 µm intervals. Similarly, the Zc conversion zones have a lateral dimension of 2 µm and are spaced 2 µm apart. The electret layer has a uniform relative permittivity of 4, and the colloidal solution has a uniform relative permittivity of 2. The Zc conversion zone is structured to form four elementary zones polarized along the X-axis.

[0098] There figure 8B is a schematic and partial cross-sectional view of a diode matrix 20 covered by an electret layer 30 and a colloidal solution S.

[0099] The configuration is similar to that described in reference to the fig.8A It differs only in that the electret layer 30 is not homogeneous, but is formed of a succession of distinct portions 34, 35 with different relative permittivities. Thus, the portions 34 facing the diodes have a relative permittivity of 4 and are made of a so-called low-k material, for example, silicon oxide or silicon 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, titanium or tantalum oxide.

[0100] There figure 8C illustrates a spatial variation of the intensity (in log) of the vertical component ∇ z E 2< of the gradient of the squared magnitude of the electric field E, calculated at a distance of 100 nm above the electret layer 30, for the configuration of the fig.8B We note that the variation is similar, however it shows a larger minimum in the Ze spacing zones, here 18.5 instead of 19 in the case of the fig.8A . Also, the risks of deposition of photoluminescent particles p in the Ze spacing zones are reduced, and deposition takes place more in the Zc conversion zones.

[0101] According to another embodiment, which is not part of the present invention as defined by the attached claims but is useful for understanding its context, the conversion zones Zc may be unstructured and may therefore exhibit a uniformly non-zero surface potential. In this case, a permittivity is defined relative to the conversion zones Zc and the spacing zones Ze.

[0102] As illustrated by the fig.9A , in the case where the electret layer 30 is inhomogeneous and is formed of 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 of the portions 34, and the relative permittivity of the spacing zones Ze is equal to that of the portions 35. As previously stated, the portions 34 are made of a low-k material, for example a silicon oxide or nitride, and the portions 35 are made of a high-k material, for example a titanium or tantalum oxide.

[0103] As illustrated by the fig.9B The variation of the dielectropheretic force, here the log of ∇ z E 2< , is not identical in the conversion zones Zc and in the spacing zones Ze. Indeed, the minimum in the conversion zones Zc is higher than in the spacing zones Ze. Therefore, photoluminescent particles p will preferentially deposit in the conversion zones Zc rather than in the spacing zones Ze.

[0104] As illustrated by the fig.10A The electret layer 30 is inhomogeneous and consists of a sublayer made of the same material with a constant relative permittivity, here a low-k material, and portions 40 of a so-called very high-k material, whose relative permittivity is at least 100. This sublayer covers only the Ze spacing zones and not the Zc conversion zones. These portions are made, for example, of a perovskite and / or ferroelectric material, such as BaSrTiO3, BaTiO3, SrTiO3, PbZrTiO3, or KNN, among others. The relative permittivity can be as high as 250. Therefore, the relative permittivity of the Zc conversion zones is equal to that of the electret layer sublayer (e.g., 4), and the relative permittivity of the Ze spacing zones is equal to that of the 40 portions (e.g., 250).

[0105] As illustrated by the fig.10B The variation of the dielectrophoretic force, here the log of ∇ z E 2< , is also not identical in the conversion zones Zc and in the spacing zones Ze. Indeed, the minimum in the conversion zones Zc is higher than in the spacing zones Ze, and the latter exhibit a minimum value over a larger area. Therefore, the photoluminescent particles p will preferentially deposit in the conversion zones Zc rather than in the spacing zones Ze.

[0106] THE figures 11A à 11E illustrate an example of a process for creating 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.

[0107] An electret layer 41 made of the low-k material can thus be deposited, covering the entire diode matrix 20 ( fig.11A ). Then, through-holes are made opening onto the diode matrix 20, to form portions 34 located opposite the diodes ( fig.11B ). The openings are through-holes here, but they might not be. A layer 42 made of 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 mechano-chemical planarization is performed with a stop on sections 34 ( fig.11D ). 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.11E ).

[0108] Specific embodiments have just been described. Various variations and modifications will be apparent to those skilled in the art. The scope of the present invention is defined by the following claims.

Claims

1. A method for manufacturing an optoelectronic device (1), including the following steps: ∘ providing a diode array (20), having a front face intended to receive or transmit light radiation; ∘ producing an electret layer (30), extending on the front face of the diode array (20), an upper face of which, opposite the front face, has conversion zones (Zc), each being situated 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 placing the electret layer (30) in 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 of a plurality of so-called polarized elementary zones (32) with non-zero surface potential, spaced apart two-by-two by a so-called non-polarized elementary zone (33) with zero surface potential, such that the conversion zone (Zc) has a structured surface potential.

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

3. The manufacturing method according to claim 1 or 2, wherein each conversion zone (Zc) includes between three and nine polarized elementary zones (32), and preferably between three and seven polarized elementary zones (32).

4. The manufacturing method according to any one of claims 1 to 3, wherein the polarized elementary zones (32) are all situated at a distance from a border (Zcb) of the conversion zone (Zc).

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

6. The 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 of the conversion zones (Zc).

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

8. The manufacturing method according to claim 6, wherein the electret layer (30) is formed of a continuous sublayer covering the diode array and made of a material having the first relative permittivity value, and portions (40) covering the sublayer, situated outside of the conversion zones (Zc) and made of a material having the second relative permittivity value.

9. An optoelectronic device (1), including: ∘ a diode array (20) having a front face intended to receive or transmit light; ∘an electret layer (30), extending on the front face of the diode array (20), an upper face of which, opposite the front face, has conversion zones (Zc), each being situated 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), situated on the electret layer (30) and positioned in the conversion zones (Zc); characterized in that each conversion zone (Zc) is formed of a plurality of so-called polarized elementary zones (32) with non-zero surface potential spaced apart two-by-two by a so-called non-polarized elementary zone (33) with zero surface potential, such that the conversion zone (Zc) has a structured surface potential.

10. The optoelectronic device (1) according to the preceding claim, wherein the diodes (D) have light emission or absorption properties identical to one another.

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