Display screen having light-emitting diodes with improved light extraction and display pixels for such screen

Abstract

This disclosure relates to a display pixel (3') comprising a light-emitting zone (8) including at least one light-emitting diode, a support (9) that is transparent to the radiation emitted by the light-emitting zone (8) and has a height greater than 5 μm, and an intermediate layer (12) that is transparent to the radiation emitted by the light-emitting zone (8) and interposed between the light-emitting zone (8) and the support (9), wherein the refractive index of the intermediate layer (12) is strictly less than 1.5, is smaller than the refractive index of the support (9), and has a refractive index deviation of 0.2 or more.

Description

Technical Field

[0001] This specification generally relates to a display screen including display pixels containing light-emitting diodes based on semiconductor materials, and a method for manufacturing the same.

Background Art

[0002] It is known to manufacture a display screen including display pixels, each display pixel including at least one light-emitting diode, for example, a semiconductor material based on a compound mainly composed of at least one group III element and at least one group V element, hereinafter referred to as a III-V compound (for example, gallium nitride GaN).

[0003] The light extraction efficiency (LEE) of a display screen is generally defined by the ratio between the number of photons escaping from the display screen and the number of photons emitted by the light-emitting diodes of the display pixels. It is desirable that the extraction efficiency of the display screen be as high as possible.

[0004] One exemplary method for manufacturing a display screen includes arranging display pixels on a panel and depositing a planarization layer to obtain a substantially flat light-emitting surface.

[0005] One drawback of existing display screens is that a portion of the photons emitted by each display pixel do not escape from the display screen.

Summary of the Invention

[0006] One embodiment overcomes some or all of the disadvantages of known display screens.

[0007] One embodiment provides a display pixel intended to be arranged and attached on a panel of a display screen, the display pixel including - a light-emitting zone including at least one light-emitting diode, and - a support that is transparent to the radiation emitted by the light-emitting zone and is intended to be used when handling the display pixel, the height of the support being higher than 5 μm. - An intermediate layer that is transparent to the radiation emitted by the light-emitting zone, made of a solid material, and interposed between the light-emitting zone and the support, wherein the refractive index of the intermediate layer is strictly less than 1.5, is smaller than the refractive index of the support, and has a refractive index deviation of 0.2 or more, and Includes.

[0008] The intermediate layer allows high-angle light rays emitted by the light-emitting zone to be reflected back towards the light-emitting zone, while allowing only low-angle light rays emitted by the light-emitting zone to pass through. Due to scattering and reflection phenomena occurring within the light-emitting zone, light rays reflected back towards the light-emitting zone by the intermediate layer are then returned to the intermediate layer and can pass through the intermediate layer when the angle of incidence of the light ray is low. Thus, the intermediate layer advantageously allows for an increase in the number of light rays emitted by the display pixels at low angles of incidence. This advantageously allows for an increase in the light extraction efficiency of the display screen containing such display pixels, as the reflection of light rays from the light-emitting surface of the display screen is reduced. Advantageously, the support is used to handle the display pixels, particularly when arranging and mounting individual display pixels onto the panel. The dimensions of the support, especially its height, advantageously ensure good mechanical strength of the display pixels during handling. Since the intermediate layer is made of a solid material, it allows for a strong mechanical bond between the support and the light-emitting zone.

[0009] According to one embodiment, the support is an integrated glass support. Advantageously, this is a material that has good mechanical strength and good light transmission properties.

[0010] According to one embodiment, the display pixel further includes a bonding layer interposed between the support and the intermediate layer. This advantageously allows for easier manufacturing of the display pixel.

[0011] According to one embodiment, the light-emitting zone includes a light-emitting diode having a wire-shaped, conical, or frustoconical semiconductor element.

[0012] According to one embodiment, the light-emitting diode includes a textured surface. Advantageously, this allows for increased diffusion of radiation emitted by the light-emitting diode.

[0013] According to one embodiment, the light-emitting zone further includes, for at least one light-emitting diode, an electrically insulating block that covers the light-emitting diode and is interposed between the intermediate layer and the light-emitting diode. In particular, the block protects the light-emitting diode and, especially when the light-emitting diode includes a wire, conical, or frustoconical semiconductor element, provides a flat upper surface and allows the emission wavelength of the display pixel to be optionally adjusted.

[0014] According to one embodiment, the block is photoluminescent.

[0015] According to one embodiment, the block is diffusive with respect to radiation emitted by the light-emitting diode. This advantageously allows for increased diffusion of radiation emitted by the light-emitting diode.

[0016] According to one embodiment, the block is transparent to radiation emitted by the light-emitting diode.

[0017] According to one embodiment, the light-emitting zone further includes a reflective layer on the opposite side of the intermediate layer, and a block is interposed between the reflective layer and the intermediate layer. This advantageously allows light rays to be prevented from escaping from the light-emitting zone on the side opposite to the support.

[0018] According to one embodiment, the light-emitting zone further includes a reflective wall surrounding the block. Advantageously, this allows light rays to escape at the side edges of the light-emitting zone.

[0019] According to one embodiment, the display pixel includes a conductive bonding pad on the side opposite to the support. Advantageously, this allows the bonding pad of the display pixel to be attached to the panel by handling the display pixel through the support.

[0020] One embodiment also - a panel, - display pixels as defined above, wherein a support for the display pixels is located on the side opposite to the panel, - a planarization layer covering the panel and the display pixels and provides a display screen including.

[0021] The intermediate layer of each display pixel advantageously enables an increase in the light extraction efficiency of the display screen since light reflection at the light emitting surface of the display screen is reduced.

[0022] One embodiment also provides a method for manufacturing display pixels as defined above, comprising - forming a plurality of copies of the light emitting zones of the display pixels on a semiconductor plate, - forming an intermediate layer on the light emitting zones, - attaching a plate of the material constituting the support to the intermediate layer, - separating the display pixels and provides a method including.

[0023] One embodiment also provides a method for manufacturing a display screen, comprising - forming display pixels as defined above, - individually arranging and attaching each display pixel on a panel, - forming a planarization layer covering the panel between the display pixels and provides a method including.

[0024] The support of the display pixels enables the display pixels to be handled individually in the step of arranging and attaching the display pixels on the panel.

[0025] According to one embodiment, handling each display pixel in the step of individually arranging and attaching each display pixel on the panel includes using a gripper for handling the display pixel via the support of the display pixel.

[0026] The features and advantages described above, as well as other features and advantages, are described in detail below in the description of specific embodiments given as examples rather than limitations with reference to the attached drawings. [Brief explanation of the drawing]

[0027] [Figure 1] An example of the display screen is shown partially and very schematically. [Figure 2] Figure 1 shows the optical path of the display screen. [Figure 3] A partial and schematic representation of one embodiment of the display screen is shown. [Figure 4] Figure 3 shows the optical path of the display screen. [Figure 5] The left side shows a schematic diagram of the light beam path of the display pixels in the display screen shown in Figure 1, and the right side shows a schematic diagram of the light beam path of the display pixels in the display screen shown in Figure 3. [Figure 6] Figure 3 shows a partial and schematic representation of one embodiment of the display pixels of the display screen shown. [Figure 7] Another embodiment of the display pixels of the display screen shown in Figure 3 is partially and schematically shown. [Figure 8] A more detailed embodiment of the display pixels shown in Figure 6 is partially and schematically illustrated. [Figure 9] This shows one embodiment of a three-dimensional light-emitting diode. [Figure 10] Another embodiment of a three-dimensional light-emitting diode is shown. [Modes for carrying out the invention]

[0028] Similar features are designated by the same reference numerals in various figures. In particular, structural and / or functional features common to various embodiments may have the same reference numerals and may have the same structural, dimensional, and material properties.

[0029] For clarity, only the operations and elements useful for understanding the embodiments described herein are illustrated and described in detail.

[0030] Unless otherwise specified, when referring to two elements connected to each other, this means a direct connection with no intermediate elements other than conductors; when referring to two elements joined to each other, this means that these two elements can be connected, or that these two elements can be joined through one or more other elements.

[0031] In the following disclosures, unless otherwise specified, when referring to absolute position modifiers such as “front,” “back,” “up,” “down,” “left,” and “right,” or relative position modifiers such as “upward,” “downward,” “higher,” and “lower,” or orientation modifiers such as “horizontal” and “vertical,” it refers to the orientation shown or the usual position of use.

[0032] Unless otherwise specified, the expressions “approximately,” “about,” “substantially,” and “of the order of” mean within 10%, preferably within 5%.

[0033] In the following explanation, the internal transmittance of a layer corresponds to the ratio of the intensity of radiation entering the layer to the intensity of radiation leaving the layer. The absorptance of a layer is equal to the difference between 1 and the internal transmittance. In the following explanation, a layer is said to be transparent to radiation if the absorptance of radiation passing through the layer is less than 60%. In the following explanation, a layer is said to be absorpting to radiation if the absorptance of radiation within the layer is greater than 60%. If the radiation has a roughly "bell-shaped" spectrum, such as a Gaussian spectrum with a maximum value, the wavelength of the radiation, or the central or dominant wavelength of the radiation, is the wavelength at which the spectrum reaches its maximum value. In the following explanation, the refractive index of a material corresponds to the refractive index of the material for the wavelength range of radiation emitted by the optoelectronic device. Unless otherwise specified, the refractive index is considered to be substantially constant over the useful wavelength range of radiation, for example, equal to the average refractive index over the useful wavelength range of radiation. The refractive index is a dimensionless number that characterizes the optical properties of a medium, particularly absorption and scattering. The refractive index is equal to the real part of the complex refractive index. The refractive index can be determined, for example, by ellipsometry.

[0034] Furthermore, the terms "insulator" and "conductor" are interpreted to mean "electrically insulating" and "conductive," respectively.

[0035] Figure 1 shows a partial and highly schematic example of display screen 1.

[0036] The display screen 1 includes a panel 2 and display pixels 3 mounted on the panel 2, with a single display pixel 3 shown in Figure 1. In some applications, it is desirable that the light-emitting surface 6 of the display screen 1 be substantially planar. For this purpose, the display screen 1 includes a planarization layer 4 covering the display pixels 3 and the panel 2 between the display pixels 3, and a stack of layers 5 covering the planarization layer 4 and defining the light-emitting surface 6 of the display screen 1. The planarization layer 4 allows the display pixels 3 to be encapsulated and protected. The stack of layers 5 allows some optical properties of the display screen 1 to be improved in known ways. The stack 5 includes, for example, an anti-reflective coating.

[0037] The display pixel 3 includes a substrate 7 on which a light-emitting zone 8 is formed. The display pixel 3 is attached to the panel 2 on the substrate 7 side. The display pixel 3 further includes a support 9, such as a glass block, to enable handling of the display pixel 3. In this case, the light-emitting zone 8 is interposed between the substrate 7 and the support 9.

[0038] Figure 2 shows the ray paths obtained by simulation during the operation of the display screen 1 shown in Figure 1. In Figure 2, the light emission zone 8 is simulated by a point light source. As can be seen from this figure, some of the light rays emitted by the light source are reflected at the interface between the layer stack 5 and the air and remain trapped inside the display 1, resulting in a decrease in the extraction efficiency of the emitted light rays.

[0039] Figure 3 is a partial and highly schematic cross-sectional view of one embodiment of the display screen 10.

[0040] The display screen 10 shown in Figure 3 includes all the elements of the display screen 1 shown in Figure 1, but differs in that the display pixels 3 are replaced by display pixels 3', each display pixel 3' includes all the elements of the display pixel 3, and further includes an intermediate layer 12 interposed between the light-emitting zone 8 and the support 9.

[0041] The intermediate layer 12 is a layer that is transparent to the radiation emitted by the light-emitting zone 8. The refractive index of the intermediate layer 12 is as close to 1 as possible, preferably strictly less than the refractive index of the substrate 9, and strictly less than the refractive index of one or more materials constituting the light-emitting zone 8 that are in contact with the intermediate layer 12. According to one embodiment, the refractive index of the intermediate layer 12 is strictly less than 1.5, preferably in the range of 1 to 1.3. According to one embodiment, the intermediate layer 12 is made of a material selected from the group including magnesium fluoride (MgF2) and organic polymers, particularly acrylates. The fact that the intermediate layer 12 is a layer made of a solid material is advantageous in that it facilitates bonding between the support 9 and the light-emitting zone 8, in particular allowing for a strong mechanical bond between the support 9 and the light-emitting zone 8. According to one embodiment, the thickness of the intermediate layer 12 is 2 μm or less, preferably 1 μm or less, more preferably 500 nm or less. According to one embodiment, the thickness of the intermediate layer 12 is 10 nm or more. According to one embodiment, the intermediate layer 12 includes opposing flat bottom surface 13 and top surface 14. According to one embodiment, surfaces 13 and 14 are parallel to the light-emitting surface 6. According to one embodiment, the intermediate layer 12 is a conformally deposited layer. According to one embodiment, the intermediate layer 12 is made of a material suitable for spin-on deposition.

[0042] The support 9 is transparent to radiation emitted by the light-emitting zone 8. According to one embodiment, the support 9 is made of a material selected from the group including glass and sapphire. According to one embodiment, the height of the support 9 is greater than 5 μm, preferably 20 μm to 500 μm. The thickness of the support 9 is large enough so that the support 9 can provide mechanical support to the assembly including the support 9, the intermediate layer 12, the light-emitting zone 8, and the substrate 7 during the handling steps of the display pixels 3', particularly during the placement and individual mounting of each display pixel 3' on the panel 2. For comparison, the thickness of the light-emitting zone 8 may be greater than 500 nm, preferably 1 μm to 50 μm, the thickness of the intermediate layer 12 may be 2 μm or less, preferably 1 μm or less, more preferably 500 nm or less, as described above, and the thickness of the substrate 7, if present, may be less than 100 μm. The aspect ratio of the substrate 9, i.e., the ratio of the height to the maximum width of the substrate 9, can be 0.01 to 10, preferably 0.05 to 2. The refractive index of the support 9 is strictly greater than 1.3, preferably in the range of 1.4 to 1.6. Preferably, the refractive index deviation between the refractive index of the support 9 and the refractive index of the intermediate layer 12 is greater than 0.2. According to one embodiment, the support 9 includes an upper surface 15 on the side opposite to the light-emitting zone 8. Preferably, the upper surface 15 is flat.

[0043] According to one embodiment, the maximum height of the display pixel 3' is 20 μm to 500 μm. The aspect ratio of the display pixel 3', that is, the ratio of the height to the maximum width of the display pixel 3', can be 0.01 to 10, preferably 0.05 to 2.

[0044] One embodiment of a method for manufacturing a display pixel 3' includes forming a plate containing a plurality of copies of the display pixel 3', and then separating the display pixels 3'. In particular, one embodiment of a method for manufacturing a display pixel 3' is, - The step of forming multiple copies of the light-emitting zone 8 on a semiconductor plate, - The step of forming an intermediate layer 12 on the light-emitting zone 8, - The step of attaching a plate of material constituting the support 9 to the intermediate layer 12, - A step of separating display pixel 3' and Includes.

[0045] The step of separating the display pixels 3' can be carried out by cutting the plate, particularly by mechanical sawing or laser cutting.

[0046] One embodiment of a method for manufacturing a display screen 10 includes arranging and individually mounting each display pixel 3' on a panel 2, and subsequently forming a planar layer 4 covering the display pixels 3' and the panel 2 between the display pixels 3', and forming a stack of layers 5 if present. In particular, according to one embodiment, the handling of each display pixel 3' during the step of arranging and individually mounting each display pixel 3' on the panel 2 includes the use of a gripper that handles the display pixels 3' with a support 9. According to one embodiment, the gripper exerts an attractive force on the upper surface 15 of the support 9. Advantageously for this purpose, the upper surface 15 of the support 9 is flat.

[0047] Figure 4 shows the simulated optical path of the display screen 10 shown in Figure 3. In Figure 4, the light-emitting zone 8 is simulated by a point light source. The light extraction efficiency of the display screen 10 is increased compared to the light extraction efficiency of the display screen 1. Simulations can be estimated to show that the light extraction efficiency of the display screen 10, which has an intermediate layer 12 with a refractive index of 1.2, can be increased by 30% to 40% compared to the light extraction efficiency of the display screen 1.

[0048] Figure 5 schematically shows, on the left, the ray paths R1 and R2 of display pixel 3 of display screen 1 shown in Figure 1, and on the right, the ray paths R1' and R2' of display pixel 3' of display screen 10 shown in Figure 3. For illustrative purposes, the refractive indices of the planarization layer 4, support 9, light-emitting zone 8, and layer stack 5 are substantially equal in Figure 5.

[0049] Without the intermediate layer 12, the light ray R2 emitted by the light-emitting zone 8 is reflected by the light-emitting surface 6, which corresponds to the interface between the stack of layers 5 and the air, because of its high angle of incidence to the light-emitting surface 6. The light-emitting surface 6 allows only the light ray R1 emitted by the light-emitting zone 8, which has a low angle of incidence to the light-emitting surface 6, to pass through.

[0050] The intermediate layer 12 reflects light rays R2' emitted by the light-emitting zone 8 toward the light-emitting zone 8 when the angle of incidence to the light-emitting surface 6 is high, and allows light rays R1' emitted by the light-emitting zone 8 to pass through when the angle of incidence to the light-emitting surface 6 is low and most of them barely escape the display screen 10. The light rays R2' reflected toward the light-emitting zone 8 by the intermediate layer 12 are then returned to the intermediate layer 12 due to scattering and reflection phenomena occurring within the light-emitting zone 8, and can pass through the intermediate layer 12 when their angle of incidence to the light-emitting surface 6 is low. This increases the total number of light rays that ultimately reach the light-emitting surface 6 at low angles of incidence, and thus the light extraction efficiency of the display screen 10 is increased. In other words, the intermediate layer 12 thus allows the reflection of light rays emitted by the light-emitting zone 8 at the interface between the layer stack 5 and the air to be reduced or eliminated, and thus creates a kind of recycling of light rays R2' in the light-emitting zone 8.

[0051] According to one embodiment, the light-emitting zone 8 of each display pixel 3' includes at least one light-emitting diode, preferably a set of light-emitting diodes. Each light-emitting diode may be a three-dimensional light-emitting diode or a planar light-emitting diode. According to one embodiment, the light-emitting diode LED includes a semiconductor layer of a group III-V compound, such as GaN, AlN, InN, InGaN, AlGaN or AlInGaN, or a semiconductor layer of a group II-VI compound.

[0052] A three-dimensional light-emitting diode (LED) includes a three-dimensional semiconductor element, such as a wire, cone, frustocone, or pyramidal element, particularly a microwire or nanowire, on which the active zone of the LED extends. The terms "microwire" or "nanowire" refer to an elongated three-dimensional structure along a preferred direction, having at least two dimensions called a minor axis dimension, which are 5 nm to 2.5 μm, preferably 50 nm to 2.5 μm, and a third dimension called a major axis dimension, which is at least 1, preferably at least 2, times the minor axis dimension. In some embodiments, the minor axis dimension may be about 3 μm or less, preferably 100 nm to 3 μm, more preferably 1 μm to 1.5 μm. In some embodiments, the height of each microwire or nanowire may be 500 nm or more, preferably 1 μm to 50 μm.

[0053] Figure 6 is a schematic partial cross-sectional view of one embodiment of the display pixels 3' of the display screen 10 shown in Figure 3, where the light-emitting zone 8 includes nanowire or microwire light-emitting diode LEDs.

[0054] Light-emitting zone 8 is located from bottom to top in Figure 6. - A reflective layer 16 for radiation emitted by the light-emitting diode LED, - A set of light-emitting diode LEDs (two sets of eight light-emitting diode LEDs are schematically shown as an example), where each light-emitting diode LED has a common shape of a nanowire or microwire, -Here, an insulating block 18 is placed on the reflective layer 16, wherein each block 18 faces one of the light-emitting diode LEDs or an assembly of light-emitting diode LEDs, completely surrounds (one or more) light-emitting diode LEDs, and each block 18 is a block that is transparent to radiation emitted by the light-emitting diode LEDs, and / or a block that scatters radiation emitted by the light-emitting diode LEDs, and / or a photoluminescent block, -Walls 22 between blocks 18, where each wall 22 is opaque to radiation emitted by light-emitting diodes (LEDs), and Includes.

[0055] Display pixel 3' is, from bottom to top in Figure 6, - A substrate 7 including a lower surface 23 and an upper surface 24 facing the lower surface 23, wherein the upper surface 24 is preferably flat, at least in the case of a light-emitting diode LED, - An emitting zone 8, wherein the reflective layer 16 of the emitting zone 8 is placed on the upper surface 24, - The luminescent zone 8, in particular the intermediate layer 12 covering block 18 and wall 22, -Optionally, one or more color filters 26 covering at least some of the blocks 18, where a single filter 26 covering block 18 is shown as an example, and the intermediate layer 12 is interposed between block 18 and one or more color filters 26, -Bonding layer 28, -Support 9 and Includes.

[0056] Figure 7 is a schematic partial cross-sectional view of another embodiment of the display pixel 3' of the display screen 10 shown in Figure 3, wherein the light-emitting zone 8 includes at least one planar light-emitting diode LED. Planar light-emitting diodes, also known as two-dimensional light-emitting diodes, are manufactured by forming a stack of substantially planar semiconductor layers on a substrate and then defining the light-emitting diodes, for example, by etching trenches within the stack of semiconductor layers.

[0057] The display pixel 3' shown in Figure 7 includes all the elements of the display pixel 3' shown in Figure 6, but differs in that the light-emitting diode LED includes a stack of substantially flat layers. According to one embodiment, the light-emitting diode LED includes a top surface 29 that is diffusive to radiation emitted by the light-emitting diode LED.

[0058] In Figures 6 and 7, the substrate 7 may correspond to a single, integrated structure. The substrate may not be present. The substrate 7 is configured to drive one or more light-emitting diodes (LEDs) in the light-emitting zone 8 and may correspond to an integrated circuit including electronic components, particularly insulated-gate field-effect transistors, also known as MOS transistors, or thin-film transistors, also known as TFT transistors. These are called intelligent display pixels 3'. If the substrate 7 is absent (not shown), the (one or more) light-emitting diodes can be moved onto an integrated circuit including electronic components, particularly a control circuit, and the connection can be made via a conductive pad (not shown) made on the underside of the display pixel 3', in which case the underside is on the opposite side of the support 9 from the light-emitting zone 8. In this case, the conductive pad is electrically connected to an electrode layer, which will be described later.

[0059] In Figures 6 and 7, the reflective layer 16 is shown continuously on the upper surface 24 of the substrate 7. In practice, the reflective layer 16 can be interrupted to allow the light-emitting diode LED to be connected to the substrate 7.

[0060] In the embodiments described above, the reflective layer 16 can be a conductive layer, in particular a metallic layer made of, for example, iron, copper, aluminum, tungsten, silver, titanium, hafnium, zirconium, or a combination of at least two of these compounds. Preferably, the reflective layer 16 is formed from a material that is compatible with manufacturing methods used in microelectronics. Preferably, the reflective layer 16 is made of aluminum or silver. According to one embodiment, the thickness of the reflective layer 16 is 100 nm to 300 nm. Alternatively, the reflective layer 16 can be a Bragg mirror comprising a stack of layers having different refractive indices. In this case, the reflective layer 16 is composed of a dielectric material such as silicon oxide (SiO2), silicon nitride (SiN), titanium oxide (TiO2), or any other oxide or nitride that is transparent to the wavelength of radiation emitted by the emission zone 8. When the reflective layer 16 is a Bragg mirror, it can be up to 10 μm thick.

[0061] The bonding layer 28 allows the substrate 9 to be attached to the intermediate layer 12. According to one embodiment, the bonding layer 28 is made of a polymer configured to harden when exposed to radiation, such as ultraviolet light. The bonding layer 28 may correspond to an optical adhesive, for example, an optical adhesive commercially available from Norland under the name NOA. According to one embodiment, the thickness of the bonding layer 28 is greater than 1 μm, preferably 5 μm to 30 μm. The refractive index of the bonding layer 28 is strictly greater than 1.3, preferably in the range of 1.4 to 1.6. According to one embodiment, the refractive index of the intermediate layer 12 is strictly less than the refractive index of the bonding layer 28, and in particular has a deviation greater than 0.2. The refractive index of the bonding layer 28 may be substantially equal to the refractive index of the support 9.

[0062] The aspect ratio of each block 18, i.e., the ratio of the height to the maximum width of the block 18, can be 0.01 to 10, preferably 0.05 to 2. The height of each block 18, measured perpendicular to the top surface 24, can be 500 nm to 15 μm. The refractive index of each block 18 is 1.4 to 2. According to one embodiment, the refractive index of the intermediate layer 12 is strictly lower than the refractive index of each block 18, and in particular has a deviation greater than 0.2. According to one embodiment, the top surface of the block 18 is flat and parallel to the top surface 24 of the substrate 7. According to one embodiment, one or more side walls of the block 18 are perpendicular to the top surface 24. Alternatively, one or more side walls of the block 18 may be inclined with respect to the top surface 24.

[0063] According to one embodiment, if block 18 is a photoluminescent block, the photoluminescent block includes a phosphor adapted to emit light of a different wavelength than the light emitted by the associated light-emitting diode LED when excited by the light emitted by the associated light-emitting diode LED.

[0064] According to one embodiment, each photoluminescent block 18 contains, for example, particles of at least one photoluminescent material in a transparent matrix. An example of a photoluminescent material is YAG:Ce or YAG:Ce 3+ It is yttrium aluminum garnet (YAG), also known as trivalent cerium ion-activated yttrium aluminum garnet (YAG). The average particle size of conventional photoluminescent materials is generally greater than 5 μm.

[0065] According to one embodiment, each photoluminescent block 18 includes a matrix of an inorganic or organic material in which nanometer-sized single crystal particles of a semiconductor material, also called semiconductor nanocrystals or nanofluorescent particles, are optionally dispersed. The internal quantum yield QY of the photoluminescent material int QY is equal to the ratio of the number of photons emitted to the number of photons absorbed by the photoluminescent material. int It is higher than 5%, preferably higher than 10%, and more preferably higher than 20%.

[0066] According to one embodiment, if block 18 includes a phosphor, different phosphors can be provided according to a set of light-emitting diode LEDs.

[0067] According to one embodiment, the average size of the nanocrystals is in the range of 0.5 nm to 1000 nm, preferably 0.5 nm to 500 nm, more preferably 1 nm to 100 nm, and particularly 2 nm to 30 nm. For dimensions less than 50 nm, the photoconversion properties of semiconductor nanocrystals depend mainly on quantum confinement phenomena. In that case, the semiconductor nanocrystals correspond to quantum boxes (in the case of three-dimensional confinement) or quantum wells (in the case of two-dimensional confinement).

[0068] According to one embodiment, the semiconductor material for the semiconductor nanocrystal is selected from the group comprising cadmium selenide (CdSe), indium phosphide (InP), cadmium sulfide (CdS), zinc sulfide (ZnS), zinc selenide (ZnSe), cadmium telluride (CdTe), zinc telluride (ZnTe), cadmium oxide (CdO), zinc cadmium oxide (ZnCdO), zinc cadmium sulfide (CdZnS), zinc cadmium selenide (CdZnSe), silver indium sulfide (AgInS2), PbScX3 type perovskites where X is a halogen atom, particularly iodine (I), bromine (Br), or chlorine (Cl), and mixtures of at least two of these compounds. According to one embodiment, the semiconductor material for the semiconductor nanocrystal is selected from the materials cited in the publication Physica Status Solidi (RRL)-Rapid Research Letters, Vol. 8, No. 4, pp. 349-352, April 2014, by Le Blevenec et al.

[0069] According to one embodiment, the dimensions of the semiconductor nanocrystal are selected according to the desired wavelength of radiation emitted by the semiconductor nanocrystal. For example, CdSe nanocrystals with an average size of 3.6 nm are suitable for converting blue light to red light, and CdSe nanocrystals with an average size of 1.3 nm are suitable for converting blue light to green light. According to another embodiment, the composition of the semiconductor nanocrystal is selected according to the desired wavelength of radiation emitted by the semiconductor nanocrystal.

[0070] The matrix is ​​made of a material that is at least partially transparent (preferably more than 80%) to radiation emitted by photoluminescent particles and / or light-emitting diodes (LEDs). The matrix may be made of silica, for example. The matrix may be made of any at least partially transparent polymer, particularly silicone, epoxy, poly(methyl methacrylate) (PMMA) type acrylic resin, or polyacetic acid (PLA). In particular, the matrix can be made of a at least partially transparent polymer used with a three-dimensional printer. The matrix can be photosensitive or non-photosensitive spin-on glass (SOG). According to one embodiment, the matrix contains 2% to 90%, preferably 10% to 60%, of nanocrystals by weight, for example, about 30% of nanocrystals by weight.

[0071] The height of the photoluminescent block 18 depends on the concentration of the nanocrystals and the type of nanocrystals used. If the photoluminescent block 18 is wire-shaped, the height of the photoluminescent block 18 is preferably greater than the height of the light-emitting diode and less than or equal to the height of the wall 22. When viewed from above, each photoluminescent block 18 may correspond to a square, rectangle, L-shaped polygon, etc., and its area may be equal to the area of ​​a square with sides of 1 μm to 100 μm, preferably 3 μm to 15 μm.

[0072] According to one embodiment, if block 18 is a scattering block, the scattering block includes particles dispersed in a transparent matrix that are suitable for scattering radiation emitted by an associated light-emitting diode LED. The particles are, for example, titanium oxide (TiO2), zirconium oxide (ZrO2), zinc sulfide (ZnS), or lead sulfide (PbS). The average size of the scattering particles is generally in the range of 100 nm to 300 nm. The matrix is ​​at least partially transparent (preferably more than 80%) to radiation emitted by the light-emitting diode LED. The matrix can be made of any of the materials described above for the photoluminescent block 18. The scattering block 18 may or may not include quantum dots.

[0073] According to one embodiment, if block 18 is a photoluminescent block, the photoluminescent block is also a scattering block for radiation emitted by photoconversion. The photoluminescent block 18 can be diffusive by the presence of a phosphor. Alternatively, the photoluminescent block 18 may further contain scattering particles. The scattering properties of block 18 can be characterized by a bidirectional scattering distribution function (BSDF), which in particular includes a bidirectional reflectance distribution function (BRDF) and a bidirectional transmittance distribution function (BTDF). The bidirectional transmittance distribution function can be determined using a dedicated measuring instrument.

[0074] According to one embodiment, if the block 18 is a transparent block, the transparent block is made of a material that can be one of the materials described above for the matrix of the photoluminescent block 18.

[0075] According to one embodiment, the opaque wall 22 reflects radiation emitted by the light-emitting diode LED. The wall 22 is made of a reflective material, at least partially. The reflective material can be a metallic material such as iron, copper, aluminum, tungsten, silver, titanium, hafnium, zirconium, or a combination of at least two of these compounds. Preferably, the wall 22 is made of a material that is compatible with manufacturing methods used in microelectronics. Preferably, the wall 22 is made of aluminum or silver.

[0076] The height of the wall 22, measured perpendicular to the upper surface 24, is in the range of 300 nm to 200 μm, preferably 3 μm to 15 μm. The thickness of the wall 22, measured parallel to the upper surface 24, is in the range of 100 nm to 50 μm, preferably 0.5 μm to 10 μm.

[0077] According to one embodiment, the wall 22 can be made of a reflective material, or each wall 22 includes a reflective wall by being covered with a coating that reflects the wavelength of radiation emitted by the photoluminescent block 18 and / or light-emitting diode LED, for example, a polymer having TiO2 particles.

[0078] According to one embodiment, each wall 22 includes an opaque wall. For example, each wall 22 may include a wall coated with a layer of black resin. This resin is preferably adapted to absorb electromagnetic radiation across a spectral range including the emission spectrum of the emission zone 8 and the emission spectrum of any phosphor present. According to another embodiment, each wall 22 is made of a resin that is partially transparent to visible light. According to one embodiment, the wall 22 is not made entirely of black resin.

[0079] Preferably, the wall 22 surrounds the block 18. The wall 22 reduces crosstalk between adjacent blocks 18. Preferably, the intermediate layer 12 is in contact with the wall 22. In the embodiments shown in Figures 6 and 7, the intermediate layer 12 is shown to completely cover the wall 22. Alternatively, the wall 22 may pass through all or part of the intermediate layer 12.

[0080] The display pixels 3' may optionally include one, two, or three color filters 26 covering at least some of the blocks 18, for example, a single yellow filter, two filters (where the first filter is a yellow filter and the second is a red filter), or three filters (where the first filter is a red filter, the second is a green filter, and the third is a blue filter). The filters 26 may correspond to a stack of colored layers or layers with different refractive indices that form a Bragg filter. According to one embodiment, each filter 26 may include one or more layers adapted to absorb and / or reflect radiation emitted by the emission zone 8.

[0081] If the upper surface 29 of the light-emitting diode LED is a scattering surface, the upper surface 29 can be textured to allow scattering of the radiation emitted by the light-emitting diode LED. Textured surface 29 can be achieved by chemical etching or physical etching. If the diffusion obtained by the upper surface 29 is sufficient, the block 18 covering the upper surface 29 can be a block that is transparent to the radiation emitted by the light-emitting diode LED.

[0082] Figure 8 is a schematic partial cross-sectional view of a more detailed embodiment of the display pixel 3' shown in Figure 6.

[0083] In this embodiment, the light-emitting zone 8 is from bottom to top. - A seed layer 30 made of wire growth promoting material and arranged on the upper surface 24 of the substrate 7, - An insulating layer 32 that covers the seed layer 30 and includes an opening 34 that exposes a portion of the seed layer 30, - A light-emitting diode LED (six light-emitting diodes are shown), where each light-emitting diode LED is in contact with the seed layer 30 through one of the apertures 34, - An insulating layer 36 extending over the lower side surface of the light-emitting diode LED and over the insulating layer 32 between the light-emitting diode LEDs, - An electrode is formed to cover each light-emitting diode LED, and an electrode layer 38 extends further on the insulating layer 36 between the light-emitting diode LEDs, -Here, a reflective layer 16 corresponding to a conductive layer extending on the electrode layer 38 between light-emitting diodes (LEDs), wherein the reflective layer 16 is interposed between the electrode layer 38 and the insulating layer 36 between the light-emitting diodes (LEDs), - A dielectric protective layer 40 extending over layers 38 and 16, - Block 18 covering the light-emitting diode LED assembly, - An insulating layer 42 covering the top surface of each block 18, or only a portion of the block 18 (the insulating layer 42 may not be present), - An insulating layer 42, a protective layer 44 covering the sides of the block 18 and the electrode layer 38 between the blocks 18, -A wall 22 between blocks 18, each wall 22 including a core 46 surrounded by a reflective coating 48, - A protective layer 49 that covers the entire structure and is coated with an intermediate layer 12 not shown in Figure 8. Includes.

[0084] Figure 9 is a schematic partial cross-sectional view of one embodiment of a light-emitting diode LED of a display pixel 3'. According to one embodiment, each light-emitting diode LED includes a wire 50 that contacts a seed layer 30 through one of the apertures 34, and a shell 52 which includes a stack of semiconductor layers covering the sidewalls and top of the wire 50. Such a configuration is called a radial type. The assembly formed by each wire 50 and the associated shell 52 constitutes a light-emitting diode LED.

[0085] The shell 52 may include a stack of several layers, particularly an active layer 54 and a junction layer 56. The active layer 54 is the layer from which most, preferably all, of the radiation supplied by the light-emitting diode LED is emitted. For example, the active layer 54 may include a confinement means such as a single quantum well or multiple quantum wells. The junction layer 56 may include a stack of semiconductor layers that are the same III-V material as the wire 50, but with the opposite conductivity type to that of the wire 50.

[0086] Figure 10 is a schematic partial cross-sectional view of another embodiment of the light-emitting diode LED for display pixel 3'. The light-emitting diode LED shown in Figure 10 includes all the elements of the light-emitting diode LED shown in Figure 9, except that the shell 52 is located only on top of the wire 50. This configuration is called the axial type.

[0087] The formation of the light-emitting diode LEDs shown in Figures 9 and 10, i.e., the growth of the wire 50 within the aperture 64 and the formation of the shell 52 coating the wire 50, can be carried out, for example, by metal-organic chemical vapor deposition (MOCVD) or any other suitable method.

[0088] The seed layer 30 is made of a material that promotes wire growth. For example, the material comprising the seed layer 30 may be a nitride, carbide, or boride of a transition metal from column IV, V, or VI of the periodic table of elements, or a combination of these compounds. According to another embodiment, the seed layer 30 may be omitted. According to another embodiment, the seed layer 30 may be replaced, for example, by a seed pad formed at the bottom of the opening 34.

[0089] Each insulating layer 32, 36, 40, 42, 44, 50 and core 46 are made of a dielectric material, such as silicon oxide (SiO2), silicon nitride (Si x N y )(wherein x is approximately 3 and y is approximately 4, for example, Si3N4), silicon oxynitride (especially the general formula SiO x N yThese can be made from materials such as Si2ON2, aluminum oxide (Al2O3), hafnium oxide (HfO2), titanium dioxide (TiO2), or diamond. Each insulating layer 32, 36, 40, 42, 44, and 50 can be a single layer or a stack of two or more layers.

[0090] The electrode layer 38 is at least partially transparent, allowing electromagnetic radiation emitted by the light-emitting diode to pass through. The material constituting the electrode layer 38 can be a transparent conductive material such as indium tin oxide (ITO), aluminum or gallium-doped zinc oxide, or graphene. The thickness of the electrode layer 38 can be 0.01 μm to 10 μm.

[0091] Various embodiments and variations are described. Those skilled in the art will understand that specific features of these embodiments can be combined, and other variations will be readily conceivable to them. Finally, actual implementation of the embodiments and variations described herein is within the capabilities of those skilled in the art based on the functional descriptions provided above.

[0092] This patent application claims priority to French Patent Application No. 23 / 06210, which is deemed to be an integral part of this specification.

Claims

1. A display pixel (3') intended to be positioned and mounted on the panel (2) of the display screen (10), A light-emitting zone (8) including at least one light-emitting diode (LED), A support (9) that is transparent to the radiation emitted by the light-emitting zone (8) and intended for use when handling the display pixel (3'), wherein the height of the support (9) is greater than 5 μm, An intermediate layer (12) is transparent to the radiation emitted by the light-emitting zone (8), made of a solid material, and interposed between the light-emitting zone (8) and the support (9), wherein the refractive index of the intermediate layer (12) is strictly less than 1.5, smaller than the refractive index of the support (9), and the refractive index deviation is 0.2 or more. Display pixels (3'), including the display pixels.

2. The display pixel according to claim 1, wherein the support (9) is an integrated glass support.

3. The display pixel according to claim 1 or 2, further comprising a bonding layer (28) interposed between the support (9) and the intermediate layer (12).

4. The display pixel according to any one of claims 1 to 3, wherein the light-emitting zone (8) includes a light-emitting diode (LED) having a wire-shaped, conical, or frustoconical semiconductor element.

5. The display pixel according to any one of claims 1 to 3, wherein the light-emitting diode (LED) includes a textured surface (29).

6. The display pixel according to any one of claims 1 to 5, wherein the light-emitting zone (8) further includes, for at least one light-emitting diode (LED), an electrical insulating block (18) that covers the light-emitting diode (LED) and is interposed between the intermediate layer (12) and the light-emitting diode (LED).

7. The display pixel according to claim 6, wherein the electrical insulating block (18) is photoluminescent.

8. The display pixel according to claim 6, wherein the electrical insulating block (18) is diffusive with respect to the radiation emitted by the light-emitting diode (LED).

9. The display pixel according to claim 6, wherein the electrical insulating block (18) is transparent to the radiation emitted by the light-emitting diode (LED).

10. The display pixel according to any one of claims 6 to 9, wherein the light-emitting zone (8) further includes a reflective layer (16) opposite to the intermediate layer (12), and the electrical insulating block (18) is interposed between the reflective layer (16) and the intermediate layer (12).

11. The display pixel according to any one of claims 6 to 10, wherein the light-emitting zone (8) further includes a reflective wall (22) surrounding the electrical insulating block (18).

12. The display pixel according to any one of claims 1 to 11, further comprising a conductive bonding pad on the surface opposite to the support (9).

13. Panel (2) and A display pixel (3') according to any one of claims 1 to 12, wherein the support (9) for the display pixel (3') is located on the opposite side from the panel (2'), The panel (2) and the flattening layer (4) covering the display pixels (3') A display screen (10) including the above.

14. A method for manufacturing a display pixel (3') according to any one of claims 1 to 12, The steps include forming multiple copies of the light-emitting zone (8) of the display pixel (3') on a semiconductor plate, The steps include forming an intermediate layer (12) on the light-emitting zone (8), The steps include attaching a plate of material constituting the support (9) to the intermediate layer (12), The steps of separating the display pixels (3') and Methods that include...

15. A method for manufacturing a display screen (10), The steps of forming a display pixel (3') according to any one of claims 1 to 12, The steps include: individually arranging and mounting each display pixel (3') on the panel (2); The steps include forming a planarization layer (4) that covers the display pixels (3') and the panel (2) between the display pixels (3'), and Methods that include...

16. The method according to claim 15, wherein handling each display pixel (3') in the step of individually arranging and mounting each display pixel (3') on the panel (2) includes using a gripper that handles the display pixel (3') via the support (9) of the display pixel (3').

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