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

Abstract

The present description relates to a display pixel (3') that is intended to be placed on and attached to a panel (2) of a display screen (10), the display pixel (3') comprising: a light-emitting region (8) comprising at least one light-emitting diode, LED; a support (9) that is transparent to the radiation emitted by the light-emitting region (8), the height of the support (9) being greater than 5 µm; and an interlayer (12) made of a solid material, the interlayer (12) being transparent to the radiation emitted by the light-emitting region (8) and being inserted between the light-emitting region (8) and the support (9), the refractive index of the interlayer (12) being strictly lower than 1.5 and being lower than the refractive index of the support (9) with a refractive index difference of 0.2 or greater. The invention also relates to the corresponding display screen (10), to a method for manufacturing the pixels (3'), and to a method for manufacturing the screen (10).

Description

DESCRIPTION TITLE: LED DISPLAY SCREEN WITH IMPROVED LIGHT EXTRACTION AND DISPLAY PIXELS FOR SUCH A SCREEN This patent application claims priority from French patent application FR23 / 06210, which will be considered as forming an integral part of this description. technical field

[0001] This description relates in general to display screens comprising display pixels made of light-emitting diodes based on semiconductor materials and their manufacturing processes. Previous technique

[0002] It is known to produce a display screen comprising display pixels, each display pixel comprising at least one light-emitting diode, for example a semiconductor material based on a compound comprising predominantly at least one element from group III and one element from group V (for example gallium nitride GaN), hereafter called a III-V compound.

[0003] The light extraction efficiency (LEE) of a display screen is generally defined as the ratio of the number of photons escaping from the display screen to the number of photons emitted by the light-emitting diodes (LEDs) of the display pixels. Ideally, the LEE of a display screen should be as high as possible.

[0004] An example of a manufacturing process for a display screen includes placing display pixels on a slab and depositing a planarization layer to obtain a substantially flat emission face.

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

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

[0007] One embodiment provides for a display pixel intended to be placed and fixed on a panel of a display screen, said display pixel comprising: - an electroluminescent area comprising at least one light-emitting diode; - a support transparent to the radiation emitted by the electroluminescent area and intended for use in manipulating the display pixel, the height of the support being greater than 5 pm; and - an interlayer transparent to the radiation emitted by the electroluminescent zone, made of a solid material, and interposed between the electroluminescent zone and the support, the refractive index of the interlayer being strictly less than 1.5 and being less than the refractive index of the support with a refractive index difference greater than or equal to 0.2.

[0008] The interlayer allows light rays emitted by the electroluminescent zone at a high angle of incidence to be reflected back towards the electroluminescent zone, while only light rays emitted by the electroluminescent zone at a low angle of incidence can pass through. Light rays reflected by the interlayer back towards the electroluminescent zone, through diffusion and reflection phenomena occurring within the electroluminescent zone, are then directed back towards the interlayer and can pass through it when their angle of incidence is low. The interlayer thus allows, in a way It is advantageous to increase the number of light rays emitted by the display pixel at a low angle of incidence. This advantageously increases the light extraction efficiency of a display screen containing such display pixels, since it reduces light reflections on the display's emitting surface. Advantageously, the substrate is used to handle the display pixel, particularly during the placement and individual fixing of each display pixel on the panel. The dimensions of the substrate, especially its height, advantageously ensure good mechanical stability of the display pixel during handling. Since the interlayer is made of a solid material, it advantageously provides a strong mechanical bond between the substrate and the electroluminescent area.

[0009] In one embodiment, the support is a single-piece glass support. Advantageously, this is a material with good mechanical strength and good optical transparency properties.

[0010] In one embodiment, the display pixel further comprises a bonding layer interposed between the substrate and the interlayer layer. This advantageously simplifies the manufacturing of the display pixel.

[0011] According to one embodiment, the electroluminescent zone comprises light-emitting diodes including wire-like, conical, or frustoconical semiconductor elements.

[0012] In one embodiment, the light-emitting diode comprises a textured surface. This advantageously increases the diffusion of the radiation emitted by the light-emitting diode.

[0013] In one embodiment, the light-emitting area further comprises, for at least one LED, an electrically insulating block covering the LED and interposed between the interlayer and the LED. This block serves, in particular, to protect the LEDs, especially when they include wire-like, conical, or frustoconical semiconductor elements, to provide a flat top surface, and optionally to adjust the emission wavelength of the display pixel.

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

[0015] In one embodiment, the block diffuses the radiation emitted by the light-emitting diode. This advantageously increases the diffusion of the radiation emitted by the light-emitting diode.

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

[0017] In one embodiment, the electroluminescent zone further comprises a reflective layer opposite the interlayer, the block being interposed between the reflective layer and the interlayer. This advantageously prevents light rays from escaping from the electroluminescent zone on the side opposite the support.

[0018] In one embodiment, the electroluminescent zone further comprises reflective walls surrounding the block. This advantageously prevents light rays from escaping over the lateral edges of the electroluminescent zone.

[0019] According to one embodiment, the display pixel includes electrically conductive mounting pads on one face opposite the support. This advantageously allows the display pixel mounting studs to be fixed to a panel by manipulating the display pixel via the support.

[0020] One embodiment also includes a display screen comprising: - a slab; - display pixels as defined above, with the display pixel supports located on the side opposite the panel; and - a planarization layer covering the slab and display pixels.

[0021] The interlayer of each display pixel advantageously increases the light extraction efficiency of the display screen by reducing the reflections of light rays on the emitting face of the display screen.

[0022] One embodiment also provides a method for manufacturing the display pixels as defined above, comprising the following steps: - formation on a semiconductor plate of several copies of the electroluminescent area of ​​the display pixel; - formation of the intercalated layer on the electroluminescent areas; and - fixing, onto the intermediate layer, a plate of the material composing the support; and - separation of display pixels.

[0023] One embodiment also provides a method for manufacturing a display screen, comprising the following steps: - formation of display pixels as defined previously; - the individual placement and fixing of each pixel display on a screen; and - formation of a planarization layer covering the display pixels and the panel between the display pixels.

[0024] The display pixel support allows individual manipulation of the display pixel during the placement and fixing stage of the display pixel on the panel.

[0025] According to one embodiment, the handling of each display pixel during the step of placing and individually fixing each display pixel on the slab includes the use of a gripper manipulating the display pixel by the display pixel support. Brief description of the drawings

[0026] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the attached figures, among which:

[0027] Figure 1 represents, in a partial and very schematic way, an example of a display screen;

[0028] Figure 2 illustrates the paths of light rays for the display screen of Figure 1;

[0029] Figure 3 represents, in a partial and very schematic way, one embodiment of a display screen;

[0030] Figure 4 illustrates the paths of light rays for the display screen in Figure 3;

[0031] Figure 5 schematically illustrates the paths of light rays for one display pixel of the display screen in Figure 1 on the left and for one display pixel of the display screen in Figure 3 on the right;

[0032] Figure 6 represents, in a partial and schematic way, one embodiment of a display pixel of the display screen of Figure 3;

[0033] Figure 7 represents, in a partial and schematic way, another embodiment of a display pixel of the display screen of Figure 3;

[0034] Figure 8 represents, in a partial and schematic way, a more detailed embodiment of the display pixel shown in Figure 6;

[0035] Figure 9 represents one embodiment of a three-dimensional light-emitting diode; and

[0036] Figure 10 represents another embodiment of a three-dimensional light-emitting diode. Description of the implementation methods

[0037] The same elements have been designated by the same reference numerals in the different figures. In particular, structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0038] For the sake of clarity, only the steps and elements useful for understanding the implementation methods described have been represented and are detailed.

[0039] Unless otherwise specified, when referring to two connected elements, this means directly connected without any intermediate elements other than conductors, and when referring to two coupled elements, this means that these two elements can be connected or linked through one or more other elements.

[0040] In the description that follows, when referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "inferior", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., unless otherwise specified, reference is made to the orientation of the figures or to a ... in a normal position of use.

[0041] Unless otherwise specified, the expressions "approximately", "roughly", "about", and "on the order of" mean within 10%, preferably within 5%.

[0042] In the following description, the internal transmittance of a layer corresponds to the ratio of the intensity of the radiation exiting the layer to the intensity of the radiation entering the layer. The absorption of the layer is equal to the difference between 1 and the internal transmittance. In the following description, a layer is said to be transparent to radiation when the absorption of radiation through the layer is less than 60%. In the following description, a layer is said to be absorbent to radiation when the absorption of radiation in the layer is greater than 60%. When radiation has a spectrum with a general "bell" shape, for example, a Gaussian shape, with a maximum, the wavelength of the radiation, or central or principal wavelength of the radiation, is the wavelength at which the maximum of the spectrum is reached.In the following description, the refractive index of a material refers to the material's refractive index over the wavelength range of the radiation emitted by the optoelectronic device. Unless otherwise specified, the refractive index is considered to be substantially constant over this range. of wavelengths of useful radiation, for example, equal to the average of the refractive index over the wavelength range of useful 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.

[0043] Furthermore, here the terms "insulator" and "conductor" are considered to mean "electrically insulating" and "electrically conductive" respectively.

[0044] Figure 1 is a partial and highly schematic cross-sectional view of an example of a display screen 1.

[0045] The display screen 1 comprises a panel 2 and display pixels 3 attached to the panel 2, with a single display pixel 3 shown in Figure 1. For certain applications, it is desirable for the emitting face 6 of the display screen 1 to be substantially flat. To this end, 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 5 of layers covering the planarization layer 4 and delimiting the emitting face 6 of the display screen 1. The planarization layer 4 serves, in particular, to encapsulate and protect the display pixels 3. The stack 5 of layers is known to improve certain optical properties of the display screen 1. The stack 5 includes, for example, anti-reflective coatings.

[0046] The display pixel 3 comprises a substrate 7 on which an electroluminescent area 8 is formed. The display pixel 3 is fixed to the panel 2 on the side of the substrate 7. The display pixel 3 further comprises a support 9, for example a glass block, so as to allow handling of the display pixel 3. The electroluminescent area 8 is then interposed between the substrate 7 and the support 9.

[0047] Figure 2 illustrates the simulated paths of light rays during the operation of the display screen 1 shown in Figure 1. In Figure 2, the electroluminescent area 8 is simulated by a point light source. As shown in this figure, some rays emitted by the light source are reflected at the interface between the layer stack 5 and the air and remain trapped within the screen 1, resulting in a decrease in the efficiency of emitted ray extraction.

[0048] Figure 3 is a partial and very schematic cross-sectional view of one embodiment of a display screen 10.

[0049] The display screen 10 shown in Figure 3 includes all the elements of the display screen 1 shown in Figure 1, with the difference that the display pixels 3 are replaced by display pixels 3', each display pixel 3' comprising all the elements of the display pixels 3 and further comprising an intercalated layer 12 interposed between the electroluminescent area 8 and the support 9.

[0050] The interlayer 12 is transparent to the radiation emitted by the electroluminescent zone 8. The refractive index of the interlayer 12 is as close as possible to 1, preferably strictly less than the refractive index of the substrate 9 and strictly less than the refractive index of the material or materials composing the electroluminescent zone 8 in contact with the interlayer 12. In one embodiment, the refractive index of the interlayer 12 is strictly less than 1.5, preferably in the range of 1 to 1.3. In one embodiment, the interlayer 12 is in a material selected from the group comprising magnesium fluoride (MgF2) and organic polymers, in particular acrylates. The fact that the interlayer 12 is a layer of a solid material advantageously facilitates the bond between the support 9 and the electroluminescent zone 8, and in particular provides a strong mechanical bond between the support 9 and the electroluminescent zone 8. In one embodiment, the thickness of the interlayer 12 is less than or equal to 2 pm, preferably less than or equal to 1 pm, and more preferably less than or equal to 500 nm. In another embodiment, the thickness of the interlayer 12 is greater than or equal to 10 nm. In one embodiment, the interlayer 12 comprises a lower face 13 and an upper face 14 that are opposite and flat. In another embodiment, the faces 13 and 14 are parallel to the emitting face 6.In one embodiment, the interlayer 12 is a layer deposited using a conformal deposition method. In another embodiment, the interlayer 12 is made of a material that allows for deposition using a spinner.

[0051] The support 9 is transparent to the radiation emitted by the electroluminescent area 8. In one embodiment, the support 9 is made of a material selected from the group comprising glass and sapphire. In one embodiment, the height of the support 9 is greater than 5 µm, preferably between 20 µm and 500 µm. The thickness of the support 9 is sufficient to ensure the mechanical stability of the assembly comprising the support 9, the interlayer 12, the electroluminescent area 8, and the substrate 7 during a handling step of the display pixel 3', in particular during the placement and individual fixing of each display pixel 3' on the panel 2. By way of comparison, the thickness of the electroluminescent zone 8 may be greater than 500 nm, preferably between 1 pm and 50 pm, the thickness of the interlayer layer 12 may be less than or equal to 2 pm, preferably less than or equal to 1 pm, and more preferably less than or equal to 500 nm, as previously stated, and the thickness of the substrate 7, when present, may be less than 100 pm. The aspect ratio of the support 9, i.e., the ratio between the height and the maximum width of the support 9, may be between 0.01 and 10, preferably between 0.05 and 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 difference in refractive index between the refractive index of the support 9 and the refractive index of the interlayer 12 is greater than 0.2. In one embodiment, the support 9 comprises an upper face 15, on the side opposite the electroluminescent area 8.Preferably, the upper face 15 is flat.

[0052] According to one embodiment, the maximum height of the 3' display pixel is between 20 pm and 500 pm. The aspect ratio of the 3' display pixel, that is, the ratio between the maximum height and width of the 3' display pixel, can be between 0.01 and 10, preferably between 0.05 and 2.

[0053] An embodiment of a method for manufacturing a 3' display pixel includes forming a plate comprising several copies of the 3' display pixel followed by separating the 3' display pixels. In particular, an embodiment of a method for manufacturing a 3' display pixel includes the following steps: - formation on a semiconductor plate of several copies of the electroluminescent zone 8; - formation of the intercalated layer 12 on the electroluminescent areas 8; and - fixing, on the intermediate layer 12, of a plate of the material composing the support 9; - separation of display pixels 3'.

[0054] The separation of the 3' display pixels can be achieved by cutting the plate, in particular by mechanical sawing or laser cutting.

[0055] One embodiment of a method for manufacturing the display screen 10 includes the individual placement and fixing of each display pixel 3' on the panel 2, followed by the formation of the planarization layer 4 covering the display pixels 3' and the panel 2 between the display pixels 3', and, where present, the stacking 5 of layers. In particular, according to one embodiment, the manipulation of each display pixel 3' during the step of individual placement and fixing of each display pixel 3' on the panel 2 includes the use of a gripper that manipulates the display pixel 3' by means of the support 9. According to one embodiment, the gripper exerts suction on the upper surface 15 of the support 9. Advantageously, for this purpose, the upper surface 15 of the support 9 is flat.

[0056] Figure 4 illustrates the light ray paths, obtained by simulation, for the display screen 10 of Figure 3. In Figure 4, the electroluminescent area 8 is simulated here 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. It can be estimated by simulation that the light extraction efficiency of the screen 10, with an interlayer 12 of refractive index of 1.2, can be increased by 30% to 40% compared to the light extraction efficiency of display screen 1.

[0057] Figure 5 schematically illustrates on the left the paths of light rays RI and R2 for a display pixel 3 of the display screen 1 of Figure 1 and on the right the paths of light rays RI' and R2' for a display pixel 3' of the display screen 10 of Figure 3. For illustration purposes, the refractive indices of the planarization layer 4, the support 9, the electroluminescent area 8, and the stack 5 of layers are substantially equal in Figure 5.

[0058] Without an interlayer layer 12, the R2 light rays emitted by the electroluminescent zone 8, whose angle of incidence is high relative to the emission face 6, are reflected onto the emission face 6, which corresponds to the interface between the stack of layers 5 and the air. The emission face 6 only allows the passage of the RI light rays emitted by the electroluminescent zone 8, whose angle of incidence is low relative to the emission face 6.

[0059] The interlayer 12 reflects, towards the electroluminescent zone 8, the light rays R2' emitted by the electroluminescent zone 8 whose angle of incidence is high relative to the emission face 6, and allows only the light rays RI' emitted by the electroluminescent zone 8 whose angle of incidence is low relative to the emission face 6 to pass through. These latter rays will, for the most part, manage to escape from the display screen 10. The light rays R2' reflected by the interlayer 12 towards the electroluminescent zone 8, through diffusion and reflection phenomena occurring within the electroluminescent zone 8, are then directed back towards the interlayer layer 12 and can pass through the interlayer layer 12 when their angle of incidence is low relative to the emission face 6. The The total number of light rays ultimately reaching the emission face 6 at a low angle of incidence is thus increased, thereby increasing the light extraction efficiency of the display screen 10. In other words, the interlayer layer 12 reduces, or even eliminates, reflections of rays emitted by the electroluminescent area 8 at the interface between the stack of layers 5 and the air, thus creating a kind of recycling of the light rays R2' at the electroluminescent area 8.

[0060] In one embodiment, the light-emitting area 8 of each display pixel 3' comprises at least one light-emitting diode, preferably assemblies of light-emitting diodes. Each light-emitting diode may be a three-dimensional or a planar light-emitting diode. In one embodiment, the LEDs comprise semiconductor layers of III-V compounds, for example GaN, AIN, InN, InGaN, AlGaN, or AlInGaN, or of II-VI compounds.

[0061] A three-dimensional light-emitting diode (LED) comprises a three-dimensional semiconductor element, for example, a wire, conical, frustoconical, or pyramidal element, in particular a microwire or nanowire, over which the active area of ​​the LED extends. The term "microwire" or "nanofil" designates a three-dimensional structure elongated in a preferred direction, at least two dimensions of which, called minor dimensions, are between 5 nm and 2.5 pm, preferably between 50 nm and 2.5 pm, the third dimension, called major dimension, being at least equal to 1 times, preferably at least 2 times, the largest of the minor dimensions. In some embodiments, the minor dimensions may be less than or equal to about 3 pm. preferably between 100 nm and 3 pm, more preferably between 1 pm and 1.5 pm. In some embodiments, the height of each microwire or nanowire may be greater than or equal to 500 nm, preferably between 1 pm and 50 pm.

[0062] Figure 6 is a partial, schematic cross-sectional view of an embodiment of a display pixel 3' of the display screen 10 shown in Figure 3 in which the electroluminescent area 8 comprises nanowire or microwire LED light-emitting diodes.

[0063] The electroluminescent zone 8 comprises, from bottom to top in figure 6: - a ref lechissance 16 layer for the radiation emitted by the light-emitting diodes LEDs; - sets of LEDs (two sets of eight LEDs are shown schematically as an example), each LED having the general shape of a nanowire or microwire; - insulating blocks 18 here resting on the reflective layer 16, each block 18 being located opposite one of the LEDs or a set of LEDs and completely surrounding the LED(s), each block 18 being a block transparent to the radiation emitted by the LEDs, and / or a block diffusing the radiation emitted by the LEDs, and / or a photoluminescent block; and - walls 22 between blocks 18, each wall 22 being opaque to the radiation emitted by the LED light-emitting diodes.

[0064] The 3' display pixel comprises, from bottom to top in figure 6: - the substrate 7 comprising a lower face 23 and an upper face 24 opposite the lower face 23, the upper face 24 being preferably flat at least at the level of the light-emitting diodes LEDs; - the electroluminescent zone 8, the ref lechisance layer 16 of the electroluminescent zone 8 resting on the upper face 24; - the intermediate layer 12 covering the electroluminescent zone 8, in particular the blocks 18 and the walls 22; - possibly, a color filter 26 or more of a color filter, covering at least some of the blocks 18, a single filter 26 covering a block 18 being shown as an example, the intercalated layer 12 being interposed between the blocks 18 and the filter 26 or filters; - a bonding layer 28; and - support 9.

[0065] Figure 7 is a partial, schematic cross-sectional view of another embodiment of a display pixel 3' of the display screen 10 shown in Figure 3, in which the light-emitting area 8 comprises at least one planar LED. A planar LED, also called a two-dimensional LED, is fabricated by forming a stack of substantially planar semiconductor layers on a substrate, followed by delimiting the LED, for example by etching trenches in the stack of semiconductor layers.

[0066] The display pixel 3' shown in Figure 7 comprises all the elements of the display pixel 3' shown in Figure 6, with the difference that the light-emitting diode (LED) comprises a stack of substantially planar layers. According to one embodiment, the diode electroluminescent LED includes a top face 29 which is diffusing for the radiation emitted by the light-emitting diode LED.

[0067] In Figures 6 and 7, substrate 7 may correspond to a single-piece structure. It may not be present. Substrate 7 may correspond to an integrated circuit configured to drive the LED(s) in the light-emitting region 8 and comprising electronic components, including insulated-gate field-effect transistors, also known as MOS transistors, or thin-film transistors, also known as TFTs (Thin-Film Transistors). These are then referred to as smart 3' display pixels.When substrate 7 is absent (not shown), the LED(s) can be placed on an integrated circuit, in particular a control circuit, comprising electronic components, and the connection can be made via conductive pads (not shown) made in the lower part of the display pixel 3', the lower part then being that opposite the support 9 with respect to the electroluminescent area 8. The conductive pads are then electrically connected with an electrode layer described later.

[0068] In figures 6 and 7, the reflective layer 16 is shown continuously on the upper face 24 of the substrate 7. In practice, the reflective layer 16 can be interrupted to allow the connection of the LEDs to the substrate 7.

[0069] In the embodiments described above, the reflective layer 16 may be a conductive layer, in particular a metallic layer, for example made of iron, copper, aluminum, tungsten, silver, titanium, hafnium, zirconium, or a combination of at least two of these. compounds. Preferably, the reflective layer 16 is made of a material compatible with the manufacturing processes used in microelectronics. Preferably, the reflective layer 16 is made of aluminum or silver. In one embodiment, the thickness of the reflective layer 16 is between 100 nm and 300 nm. Alternatively, the reflective layer 16 may be a Bragg mirror comprising a stack of layers with different refractive indices. In this case, the reflective layer 16 is composed of dielectric materials, such as silicon dioxide (SiCt), silicon nitride (SiN), titanium dioxide (TiO2), or any other oxide or nitride transparent to the wavelength of the radiation emitted by the electroluminescent region 8. When the reflective layer 16 is a Bragg mirror, it may have a thickness of up to 10 pm.

[0070] The bonding layer 28 enables the attachment of the support 9 to the interlayer 12. In one embodiment, the bonding layer 28 is made of a polymer configured to harden when exposed to radiation, for example, ultraviolet radiation. The bonding layer 28 may be an optical adhesive, for example, an optical adhesive marketed by Norland under the name NOA. In one embodiment, the thickness of the bonding layer 28 is greater than 1 µm, preferably between 5 µm and 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. In one embodiment, the refractive index of the interlayer 12 is strictly less than the refractive index of the bonding layer 28, in particular by a difference greater than 0.2. The refractive index of the bonding layer 28 can be substantially equal to the refractive index of the support 9.

[0071] The aspect ratio of each block 18, that is, the ratio between the height and the maximum width of the block 18, may be between 0.01 and 10, preferably between 0.05 and 2. The height of each block 18, measured perpendicular to the upper face 24, may be between 500 nm and 15 pm. The refractive index of each block 18 is between 1.4 and 2. In one embodiment, the refractive index of the interlayer 12 is strictly less than the refractive index of each block 18, in particular with a difference greater than 0.2. According to one embodiment, the upper face of block 18 is flat and parallel to the upper face 24 of the substrate 7. According to another embodiment, the side wall(s) of block 18 are perpendicular to the upper face 24. As an alternative, the side wall(s) of block 18 may be inclined with respect to the upper face 24.

[0072] According to one embodiment, when block 18 is a photoluminescent block, it includes phosphors adapted, when excited by the light emitted by the associated LED, to emit light at a wavelength different from the wavelength of the light emitted by the associated LED.

[0073] According to one embodiment, each photoluminescent block 18 comprises particles of at least one photoluminescent material, for example in a transparent matrix. An example of a photoluminescent material is trivalent cerium ion-activated yttrium aluminum garnet (YAG), also called YAG:Ce or YAG:Ce 3+ The average particle size of conventional photoluminescent materials is generally greater than 5 pm.

[0074] According to one embodiment, each photoluminescent block 18 comprises a matrix of a material An inorganic or organic material in which single-crystal particles of nanometer size of a semiconductor material are possibly dispersed, also called semiconductor nanocrystals or nanoluminophore particles hereafter. The internal quantum efficiency QYint of a photoluminescent material is equal to the ratio of the number of photons emitted to the number of photons absorbed by the photoluminescent substance. The internal quantum efficiency QY int of semiconductor nanocrystals is greater than 5%, preferably greater than 10%, more preferably greater than 20%.

[0075] According to one embodiment, when the blocks 18 include phosphors, different phosphors can be provided depending on the light-emitting diode assemblies.

[0076] In one embodiment, the average size of the nanocrystals is in the range of 0.5 nm to 1000 nm, preferably from 0.5 nm to 500 nm, and even more preferably from 1 nm to 100 nm, particularly from 2 nm to 30 nm. For dimensions smaller than 50 nm, the photoconversion properties of semiconductor nanocrystals depend primarily on quantum confinement phenomena. The semiconductor nanocrystals then correspond to quantum dots (in the case of three-dimensional confinement) or quantum wells (in the case of two-dimensional confinement).

[0077] According to one embodiment, the semiconductor material of the semiconductor nanocrystals is chosen 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), and 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, in particular iodine (I), bromine (Br) or chlorine (Cl), and a mixture of at least two of these compounds. In one embodiment, the semiconductor material of the semiconductor nanocrystals is chosen from the materials cited in the publication by Le Blevenec et al. in Physica Status Solid! (RRL) - Rapid Research Letters Volume 8, No. 4, pages 349-352, April 2014.

[0078] In one embodiment, the dimensions of the semiconductor nanocrystals are chosen according to the desired wavelength of the radiation emitted by the semiconductor nanocrystals. For example, CdSe nanocrystals with an average size of approximately 3.6 nm are suitable for converting blue light into red light, and CdSe nanocrystals with an average size of approximately 1.3 nm are suitable for converting blue light into green light. In another embodiment, the composition of the semiconductor nanocrystals is chosen according to the desired wavelength of the radiation emitted by the semiconductor nanocrystals.

[0079] The matrix is ​​made of a material at least partially transparent to the radiation emitted by photoluminescent particles and / or LEDs, preferably more than 80%. The matrix is, for example, made of silica. The matrix is, for example, made of any polymer at least partially transparent, including silicone, epoxy, poly(methyl methacrylate) (PMMA) acrylic resin, or polyacetic acid (PLA). The matrix may, in particular, be made of a polymer at least partially transparent used with 3D printers. The matrix may be a glass deposited by spin-on glass (SOG), photosensitive or non-photosensitive. According to one embodiment, the matrix contains from 2% to 90%, preferably from 10% to 60%, by weight of nanocrystals, for example about 30% by weight of nanocrystals.

[0080] The height of the 18 photoluminescent blocks depends on the concentration of nanocrystals and the type of nanocrystals used. The height of the 18 photoluminescent blocks is preferably greater than the height of the light-emitting diodes when they are wire-shaped and less than or equal to the height of the walls 22. In top view, each 18 photoluminescent block can correspond to a square, a rectangle, an "L"-shaped polygon, etc., the area of ​​which can be equal to the area of ​​a square with a side measuring from 1 pm to 100 pm, preferably from 3 pm to 15 pm.

[0081] In one embodiment, when block 18 is a diffusing block, it comprises particles adapted to scatter the radiation emitted by the associated LED, distributed within a transparent matrix. Examples of such particles include titanium dioxide (TiO2), zirconium oxide (ZrCp), zinc sulfide (ZnS), or lead sulfide (PbS). The average size of the diffusing particles is typically in the range of 100 nm to 300 nm. The matrix is ​​at least partially transparent to the radiation emitted by the LEDs, preferably more than 80%. The matrix may be made of one of the materials described previously for photoluminescent blocks 18. The diffusing block 18 may or may not include quantum dots.

[0082] According to one embodiment, when block 18 is a photoluminescent block, it is also a diffusing block for the radiation emitted by photoconversion. Block 18 Photoluminescent block 18 can be diffusive due to the presence of phosphors. Alternatively, the photoluminescent block 18 may also include diffusing particles. The diffusive nature of block 18 can be characterized by the bidirectional scattering distribution function (BSDF), which includes the bidirectional reflectance distribution function (BRDF) and the bidirectional transmittance distribution function (BTDF). The bidirectional scattering distribution function can be determined using a dedicated measuring instrument.

[0083] According to one embodiment, when block 18 is a transparent block, it is composed of a material which may be one of the materials described previously for the matrix of photoluminescent blocks 18.

[0084] In one embodiment, the opaque walls 22 are reflective of the radiation emitted by the light-emitting diodes (LEDs). The walls 22 are at least partially made of a reflective material. The reflective material may be a metallic material, in particular iron, copper, aluminum, tungsten, silver, titanium, hafnium, zirconium, or a combination of at least two of these compounds. Preferably, the walls 22 are made of a material compatible with manufacturing processes used in microelectronics. Preferably, the walls 22 are made of aluminum or silver.

[0085] The height of the walls 22, measured in a direction perpendicular to the upper face 24, is in the range of 300 nm to 200 pm, preferably from 3 pm to 15 pm. The thickness of the walls 22, measured in a direction parallel to the face upper 24, is in the range of 100 nm to 50 pm, preferably from 0.5 pm to 10 pm.

[0086] According to one embodiment, the walls 22 can be formed of a reflective material or each wall 22 comprises reflective walls by being covered with a coating reflective at the wavelength of the radiation emitted by the photoluminescent blocks 18 and / or the light-emitting diodes LEDs, for example polymer with TiO2 particles.

[0087] In one embodiment, each wall 22 comprises opaque surfaces. For example, each wall 22 may comprise surfaces coated with a layer of black-colored resin. This resin is preferably adapted to absorb electromagnetic radiation over the spectral range including the emission spectrum of the electroluminescent zone 8 and that of phosphors when present. In another embodiment, each wall 22 is made of a resin that is partially transparent to visible light. In yet another embodiment, the walls 22 are not made entirely of black-colored resin.

[0088] Preferably, the walls 22 surround the blocks 18. The walls 22 then reduce crosstalk between adjacent blocks 18. Preferably, the interlayer 12 is in contact with the walls 22. In the embodiments illustrated in Figures 6 and 7, the interlayer 12 is shown completely covering the walls 22. Alternatively, the walls 22 may pass through the interlayer 12, either partially or completely.

[0089] The display pixel 3' may include one, two, or three color filters 26, for example, a single yellow filter, two filters (the first being a yellow filter and the second a red filter), or three filters (the first being a red filter and the second a filter green and the third being a blue filter, covering at least some of the blocks 18. The filter 26 may correspond to a colored layer or to a stack of layers with different refractive indices forming a Bragg filter. According to one embodiment, each filter 26 may comprise one or more layers adapted to absorb and / or reflect the radiation emitted by the electroluminescent area 8.

[0090] When the upper surface 29 of the LED is a diffusing surface, it may have a texture that allows the diffusion of the radiation emitted by the LED. The texturing of the upper surface 29 may be achieved by chemical etching or physical etching. When the diffusion obtained by the upper surface 29 is sufficient, the block 18 covering the upper surface 29 may be transparent to the radiation emitted by the LED.

[0091] Figure 8 is a partial, schematic cross-sectional view of a more detailed embodiment of part of the display pixel 3' shown in Figure 6.

[0092] In this embodiment, the electroluminescent area 8 comprises, from bottom to top: - a germination layer 30 made of a material promoting the growth of threads and placed on the upper face 24 of the substrate 7; - an insulating layer 32 covering the germination layer 30 and comprising openings 34 exposing portions of the germination layer 30; - LED light-emitting diodes (six LEDs are shown), each LED being in contact with the germination layer 30 through one of the openings 34; - an insulating layer 36 extending over the lateral sides of a lower portion of a light-emitting diode LED and extending over the insulating layer 32 between the LED light-emitting diodes; - an electrically conductive layer 38 forming an electrode covering each LED and extending further over the insulating layer 36 between the LEDs; - a reference layer 16 corresponding here to a conductive layer extending over the electrode layer 38 between the LED light-emitting diodes, the reference layer 16 being able, as an alternative, to be interposed between the electrode layer 38 and the insulating layer 36 between the LED light-emitting diodes; - a dielectric protection layer 40 extending over layers 38 and 16; - blocks 18 covering the LED light-emitting diode assemblies; - an insulating layer 42 covering the upper face of each block 18, or only of some of the blocks 18, the insulating layer 42 possibly not being present; - a protective layer 44 covering the insulating layers 42, the lateral faces of the blocks 18 and the electrode layer 38 between the blocks 18; - the walls 22 between the blocks 18, each wall 22 comprising a core 46 surrounded by a reflective coating 48; and - a protective layer 49 covering the entire structure, and covered by the intermediate layer 12, not shown in figure 8.

[0093] Figure 9 is a partial, schematic cross-sectional view of an embodiment of the LEDs of the display pixel 3'. According to one embodiment, each LED comprises a wire 50 in contact with the seed layer 30 through one of the openings 34 and a shell 52 comprising a stack of semiconductor layers. covering the side walls and the top of the wire 50. Such a configuration is called radial. The assembly formed by each wire 50 and the associated shell 52 constitutes the light-emitting diode LED.

[0094] The shell 52 may comprise a stack of several layers, including an active layer 54 and a bonding layer 56. The active layer 54 is the layer from which the majority, and preferably all, of the radiation emitted by the light-emitting diode (LED) is emitted. For example, the active layer 54 may include containment means, such as a single quantum well or multiple quantum wells. The bonding layer 56 may comprise a stack of semiconductor layers of the same III-V material as the wire 50 but with the opposite conductivity to that of the wire 50.

[0095] Figure 10 is a partial, schematic cross-sectional view of another embodiment of the LEDs of the display pixel 3'. The LED shown in Figure 10 comprises all the elements of the LED shown in Figure 9, except that the shell 52 is present only at the top of the wire 50. Such a configuration is called axial.

[0096] The formation of the LEDs as shown in Figures 9 and 10, i.e. the growth of the wires 50 in the openings 64, and the formation of the shells 52 covering the wires 50 can be carried out for example by metal-organic chemical vapor deposition (MOCVD) or any other suitable process.

[0097] The germination layer 30 is made of a material that promotes thread growth. For example, the material composing the germination layer 30 could be a A nitride, carbide, or boride of a transition metal from group IV, V, or VI of the periodic table of elements, or a combination of these compounds. In another embodiment, the germination layer 30 may be omitted. In another embodiment, the germination layer 30 may be replaced by germination pads, for example, formed at the bottom of the openings 34.

[0098] Each insulating layer 32, 36, 40, 42, 44, 50 and the cores 46 can be made of a dielectric material, for example silicon dioxide (SiCt) or silicon nitride (Si x N y where x is approximately equal to 3 and y is approximately equal to 4 (for example, Si3N4), in silicon oxynitride (notably with the general formula SiO₂ x N y, for example Si2ON2), aluminum oxide (Al2O3), hafnium oxide (HfCt), titanium dioxide (TiCt) or diamond. Each insulating layer 32, 36, 40, 42, 44, 50 can have a single-layer structure or correspond to a stack of two or more layers.

[0099] The electrode layer 38 is at least partially transparent to allow the passage of electromagnetic radiation emitted by the light-emitting diodes. The material forming the electrode layer 38 can be a transparent and conductive material such as indium tin oxide (ITO), aluminum- or gallium-doped zinc oxide, or graphene. The thickness of the electrode layer 38 can range from 0.01 µm to 10 µm.

[0100] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will become apparent to them. Finally, the practical implementation of the described embodiments and variations is to be determined. the scope of the person's profession based on the functional indications given above.

Claims

CLAIMS 1. Display pixel (3') intended to be placed and fixed on a panel (2) of a display screen (10), said display pixel (3') comprising: - an electroluminescent zone (8) comprising at least one light-emitting diode (LED); - a support (9) transparent to the radiation emitted by the electroluminescent zone (8) and intended to be used to manipulate the display pixel (3'), the height of the support (9) being greater than 5 pm; and - an interlayer (12) transparent to the radiation emitted by the electroluminescent zone (8), made of a solid material, and interposed between the electroluminescent zone (8) and the support (9), the refractive index of the interlayer (12) being strictly less than 1.5 and being less than the refractive index of the support (9) with a refractive index difference greater than or equal to 0.

2.

2. Display pixel according to claim 1, wherein the support (9) is a single-piece glass support.

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

4. Display pixel according to any one of claims 1 to 3, wherein the electroluminescent zone (8) comprises light-emitting diodes (LEDs) comprising wire, conical, or truncated semiconductor elements.

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

6. Display pixel according to any one of claims 1 to 5, in which the electroluminescent zone (8) further comprises, for at least one light-emitting diode (LED), an electrically insulating block (18) covering the light-emitting diode (LED) and interposed between the interlayer (12) and the light-emitting diode (LED).

7. Display pixel according to claim 6, wherein the block (18) is photoluminescent.

8. Display pixel according to claim 6, in which the block (18) is diffusing for the radiation emitted by the light-emitting diode (LED).

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

10. Display pixel according to any one of claims 6 to 9, wherein the electroluminescent zone (8) further comprises a reflective layer (16) opposite the interlayer (12), the block (18) being interposed between the reflective layer (16) and the interlayer (12).

11. A display pixel according to any one of claims 6 to 10, wherein the electroluminescent area (8) further comprises reflective walls (22) surrounding the block (18).

12. Display pixel according to any one of claims 1 to 11, comprising fixing pads electrically conductive on a face opposite the support 13. Display screen (10) comprising: - a slab (2); - display pixels (3') according to any one of claims 1 to 12, the supports (9) of the display pixels (3') being located on the side opposite the panel (2); and - a planarization layer (4) covering the panel (2) and the display pixels (3').

14. Method for manufacturing the display pixels (3') according to any one of claims 1 to 12, comprising the following steps: - formation on a semiconductor plate of several copies of the electroluminescent zone (8) of the display pixel (3'); - formation of the interlayer (12) on the electroluminescent zones (8); and - fixing, on the intermediate layer (12), a plate of the material making up the support (9); and separation of the display pixels (3').

15. Method of manufacturing a display screen (10), comprising the following steps: - formation of display pixels (3') according to any one of claims 1 to 12; - the placement and individual fixing of each display pixel (3') on a panel (2); and - formation of a planarization layer (4) covering the display pixels (3') and the panel (2) between the display pixels (3').

16. The method of claim 15, wherein manipulating each display pixel (3') during the step of placing and individually fixing each display pixel (3') on the panel (2) comprises the use of a gripper manipulating said display pixel (3') by the support (9) of said display pixel (3').

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