TW202519084A - Light-emitting diode display screen with enhanced light extraction and display pixels for such a screen - Google Patents

Abstract

The present disclosure relates to a display pixel (3') comprising a light-emitting zone (8) comprising at least one light-emitting diode, a support (9) transparent to the radiation emitted by the light-emitting zone (8), the height of the support (9) being higher than 5 µm , and an intermediate layer (12) transparent to the radiation emitted by the light-emitting zone (8), and interposed between the light-emitting zone (8) and the support (9), the refractive index of the intermediate layer (12) being strictly less than 1.5, and being less than the refractive index of the support (9) with a refractive index deviation higher than or equal to 0.2.

Description

Light emitting diode display screen with enhanced light extraction and display pixel for such a screen

The present description generally relates to display screens that include display pixels that include light-emitting diodes based on semiconductor materials, and to methods for the manufacture of such display screens.

It is known to produce display screens comprising display pixels each comprising at least one light-emitting diode, for example based on semiconductor materials (such as gallium nitride GaN) having a majority of compounds of at least one Group III element and one Group V element, hereinafter referred to as Group III-V compounds.

The light extraction efficiency (LEE) of a display screen is usually 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 a display screen is as high as possible.

One exemplary method for manufacturing a display screen includes placing display pixels on a panel and depositing a planarization layer to obtain a substantially flat emitting surface.

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

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

One embodiment provides a display pixel intended to be placed and attached to a panel of a display screen, the display pixel comprising: - a light-emitting region comprising at least one light-emitting diode; - a support transparent to the radiation emitted by the light-emitting region and intended for use in processing the display pixel, the height of the support being higher than 5 μm; and - an intermediate layer transparent to the radiation emitted by the light-emitting region, the intermediate layer being made of a solid material and inserted between the light-emitting region and the support, the refractive index of the intermediate layer being strictly less than 1.5 and less than the refractive index of the support by a refractive index deviation higher than or equal to 0.2.

The intermediate layer allows light rays emitted by a luminescent region with high incidence to be reflected toward the luminescent region, and only allows light rays emitted by a luminescent region with low incidence to pass through. Light rays reflected by the intermediate layer toward the luminescent region are then sent back to the intermediate layer by scattering and reflection phenomena occurring in the luminescent region, and can pass through the intermediate layer when their incidence is low. Therefore, the intermediate layer advantageously makes it possible to increase the amount of light rays emitted by the display pixels with low incidence. This advantageously enables the light extraction efficiency of a display screen including such display pixels to be increased, because the reflection of light rays on the emitting surface of the display screen is reduced. Advantageously, the support is used to handle the display pixels, specifically when each individual display pixel is placed and attached to the panel. The dimensions of the support, in particular its height, advantageously ensure good mechanical strength of the display pixel during processing. Since the intermediate layer is made of a solid material, the intermediate layer allows a strong mechanical bond between the support and the light-emitting area to be obtained.

According to one embodiment, the support is a one-piece glass support. Advantageously, this is a material with good mechanical strength and good optical transparency.

According to one embodiment, the display pixel further comprises a bonding layer, which is inserted between the support and the intermediate layer. This advantageously makes the manufacture of the display pixel easier.

According to one embodiment, the light emitting region includes a light emitting diode having a linear, conical or truncated pyramidal semiconductor element.

According to one embodiment, the LED comprises a textured surface. Advantageously, this allows increasing the diffusion of the radiation emitted by the LED.

According to one embodiment, for at least one LED, the luminescent region further comprises an electrically insulating block, which covers the LED and is interposed between the intermediate layer and the LED. In particular, the block allows the LED to be protected, especially when the LED comprises a wired, conical or truncated pyramidal semiconductor element, a flat top surface is obtained, and optionally the emission wavelength of the display pixel is adjusted.

According to one embodiment, the block is photoluminescent.

According to one embodiment, the block is diffusive for the radiation emitted by the LED. This advantageously allows increasing the diffusion of the radiation emitted by the LED.

According to one embodiment, the block is transparent to the radiation emitted by the LED.

According to one embodiment, the luminescent region further comprises a reflective layer opposite to the intermediate layer, wherein the block is inserted between the reflective layer and the intermediate layer. This advantageously allows preventing light rays from escaping from the luminescent region on the side opposite to the support.

According to one embodiment, the luminous area further comprises a reflective wall surrounding the block. Advantageously, this allows preventing the light rays from escaping at the side edges of the luminous area.

According to one embodiment, the display pixel includes a conductive bonding pad on the face opposite the support member. Advantageously, this enables the bonding pad of the display pixel to be attached to the panel by handling the display pixel through the support member.

One embodiment also provides a display screen comprising: - a panel; - display pixels as defined above, supports for the display pixels being located on opposite sides of the panel; and - a planarization layer covering the panel and the display pixels.

The intermediate layer in each display pixel advantageously allows for increased light extraction efficiency of the display screen, since reflections of light rays off the emitting surface of the display screen are reduced.

One embodiment also provides a method for manufacturing a display pixel as defined above, the method comprising the steps of: - forming a plurality of copies of the light-emitting region of the display pixel on a semiconductor board; - forming the intermediate layer on the light-emitting regions; and - attaching a plate of material constituting the support to the intermediate layer; and - separating the display pixels.

One embodiment also provides a method for manufacturing a display screen, the method comprising the steps of: - forming display pixels as previously defined; - individually placing and attaching each display pixel on a panel; and - forming a planarization layer covering the display pixels and the panel between the display pixels.

The display pixel supports allow the display pixels to be individually handled during the steps of placing and attaching the display pixels to the panel.

According to one embodiment, handling each display pixel during the step of individually placing and attaching each display pixel to the panel includes using a fixture that handles the display pixel via the support of the display pixel.

The same features are marked by the same reference numerals in the various figures. Specifically, the common structural and/or functional features between the various embodiments may have the same reference numerals and may have the same structure, size, and material properties.

For clarity, only the operations and elements that are useful for understanding the embodiments described herein are shown and described in detail.

Unless otherwise indicated, when referring to two elements being connected together, this means a direct connection without any intermediate elements other than conductors, and when referring to two elements being coupled together, this means the two elements may be connected or the elements may be coupled via one or more other elements.

In the following disclosure, unless otherwise indicated, 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", "higher", "lower", etc., or directional qualifiers such as "horizontal", "vertical", etc., reference is made to the orientation shown in the figures.

Unless otherwise specified, the expressions “approximately,” “substantially,” and “approximately” mean within 10%, and preferably within 5%.

In the following description, the internal transmittance of a layer corresponds to the ratio between the intensity of the radiation leaving the layer and the intensity of the radiation entering the layer. The absorption of a 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 passing through the layer is less than 60%. In the following description, a layer is said to absorb radiation when the absorption of radiation in the layer is higher than 60%. When the radiation has a generally "bell-shaped" spectrum with a maximum, such as a Gaussian spectrum, the wavelength of the radiation or the center or dominant wavelength of the radiation is the wavelength at which the spectrum maximum is reached. In the following description, 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 indicated, the refractive index is considered to be substantially constant within the wavelength range of the useful radiation, for example equal to the average value of the refractive index within the wavelength range of the useful radiation. The refractive index is a dimensionless number that characterizes the optical properties of the medium, in particular absorption and scattering. The refractive index is equal to the real part of the complex optical index. The refractive index can be determined, for example, by elliptical polarization techniques.

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

FIG. 1 partially and highly schematically illustrates an example of a display screen 1 .

The display screen 1 comprises a panel 2 and display pixels 3, which are attached to the panel 2, a single display pixel 3 being shown in FIG. 1 . For some applications, it is desired that the emitting surface 6 of the display screen 1 is substantially planar. To this end, the display screen 1 comprises a planarization layer 4 covering the display pixels 3 and the panel 2 between the display pixels 3, and a layer stack 5 covering the planarization layer 4 and delimiting the emitting surface 6 of the display screen 1. The planarization layer 4 allows the display pixels 3 to be encapsulated and protected. The layer stack 5 allows some optical properties of the display screen 1 to be improved in a known manner. The stack 5 comprises, for example, an anti-reflection coating.

The display pixel 3 comprises a substrate 7 on which a light emitting region 8 is formed. The display pixel 3 is attached to the panel 2 on the side of the substrate 7. The display pixel 3 further comprises a support 9, such as a glass block, to enable processing of the display pixel 3. The light emitting region 8 is then inserted between the substrate 7 and the support 9.

FIG. 2 illustrates light ray paths obtained by simulation during operation of the display screen 1 shown in FIG. 1. In FIG. 2, the light emitting area 8 is simulated by a point light source. As can be seen from this figure, some of the rays emitted by the light source are reflected at the interface between the layer stack 5 and the air and remain trapped in the display 1, resulting in a reduction in the extraction efficiency of the emitted rays.

FIG. 3 is a partially schematic, highly schematic, cross-sectional view of an embodiment of screen 10.

The display screen 10 shown in FIG. 3 includes all the elements of the display screen 1 shown in FIG. 1 , with the difference that the display pixel 3 is replaced by a display pixel 3 ′, each display pixel 3 ′ includes all the elements of the display pixel 3 and further includes an intermediate layer 12 inserted between the light-emitting area 8 and the support 9.

The intermediate layer 12 is a layer transparent to the radiation emitted by the luminescent region 8. The refractive index of the intermediate layer 12 is as close to 1 as possible, preferably strictly smaller than the refractive index of the substrate 9, and strictly smaller than the refractive index of the one or more materials constituting the luminescent region 8 in contact with the intermediate layer 12. According to one embodiment, the refractive index of the intermediate layer 12 is strictly smaller 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 consisting of magnesium fluoride (MgF ₂ ) and an organic polymer, in particular acrylate. The fact that the intermediate layer 12 is a layer made of solid material advantageously allows the bonding between the support 9 and the luminescent region 8 to be promoted, and in particular a strong mechanical bonding between the support 9 and the luminescent region 8 to be obtained. According to one embodiment, the thickness of the intermediate layer 12 is less than or equal to 2 μm, preferably less than or equal to 1 μm, and more preferably less than or equal to 500 nm. According to one embodiment, the thickness of the intermediate layer 12 is greater than or equal to 10 nm. According to one embodiment, the intermediate layer 12 comprises a relatively and flat lower surface 13 and an upper surface 14. According to one embodiment, the faces 13 and 14 are parallel to the 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.

The support 9 is transparent to the radiation emitted by the luminescent area 8. According to one embodiment, the support 9 is made of a material selected from the group comprising glass and sapphire. According to 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 large enough so that the support 9 can provide mechanical support for the assembly comprising the support 9, the intermediate layer 12, the luminescent area 8 and the substrate 7 during the display pixel 3' processing steps, specifically during the placement and individual attachment of each display pixel 3' on the panel 2. In comparison, the thickness of the luminescent region 8 may be greater than 500 nm, preferably between 1 μm and 50 μm, the thickness of the intermediate layer 12 may be less than or equal to 2 μm, preferably less than or equal to 1 μm and more preferably less than or equal to 500 nm, as previously indicated, and when present, the thickness of the substrate 7 may be less than 100 μm. The aspect ratio of the substrate 9, i.e. the ratio between the height and the maximum width of the substrate 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 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 comprises an upper surface 15 on the side opposite to the light emitting area 8. Preferably, the upper surface 15 is flat.

According to one embodiment, the maximum height of the display pixel 3' is between 20 μm and 500 μm. The aspect ratio of the display pixel 3', ie the ratio between the height and the maximum width of the display pixel 3', may be between 0.01 and 10, preferably between 0.05 and 2.

One embodiment of a method for manufacturing a display pixel 3' includes forming a plate including a plurality of copies of the display pixel 3' and then separating the display pixel 3'. Specifically, one embodiment of a method for manufacturing a display pixel 3' includes the following steps: - forming a plurality of copies of the light-emitting region 8 on a semiconductor plate; - forming an intermediate layer 12 on the light-emitting region 8; and - attaching a plate of material constituting the support 9 to the intermediate layer 12; - separating the display pixel 3'.

Separating the display pixels 3' may be performed by cutting the board, in particular by mechanical sawing or laser cutting.

One embodiment of a method for manufacturing a display screen 10 comprises the placement and individual attachment of each display pixel 3' to a panel 2, followed by the formation of a planarization layer 4 covering the display pixel 3' and the panel 2 between the display pixels 3', and, if present, a layer stack 5. Specifically, according to one embodiment, the handling of each display pixel 3' during the step of placing and individually attaching each display pixel 3' to the panel 2 comprises the use of a fixture for handling the display pixel 3' by means of a support 9. According to one embodiment, the fixture applies suction to an upper surface 15 of the support 9. For this purpose, advantageously, the upper surface 15 of the support 9 is flat.

FIG. 4 illustrates a simulated light path of the display screen 10 shown in FIG. 3. In FIG. 4, the light emitting area 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. It can be estimated by simulation that in the case of the intermediate layer 12 having a refractive index of 1.2, the light extraction efficiency of the display screen 10 can be increased by 30% to 40% compared to the light extraction efficiency of the display screen 1.

FIG5 schematically illustrates on the left the light ray paths R1 and R2 of the display pixel 3 of the display screen 1 shown in FIG1, and schematically illustrates on the right the light ray paths R1' and R2' of the display pixel 3' of the display screen 10 shown in FIG3. For illustrative purposes, the refractive indices of the planarization layer 4, the support 9, the luminescent region 8 and the layer stack 5 are substantially equal in FIG5.

In the absence of the intermediate layer 12, the light ray R2 emitted by the luminescent region 8 at a high incidence relative to the emitting surface 6 is reflected on the emitting surface 6, which corresponds to the interface between the layer stack 5 and the air. The emitting surface 6 only allows the light ray R1 emitted by the luminescent region 8 at a lower incidence than the emitting surface 6 to pass through.

The intermediate layer 12 allows the light ray R2' emitted from the luminescent region 8 with a higher incidence than the luminescent surface 6 to be reflected toward the luminescent region 8, and allows the light ray R1' emitted from the luminescent region 8 with a lower incidence than the luminescent surface 6 and mostly managed to escape from the display screen 10 to pass through. The light ray R2' reflected from the intermediate layer 12 toward the luminescent region 8 is then sent back to the intermediate layer 12 by the scattering and reflection phenomena occurring in the luminescent region 8, and can pass through the intermediate layer 12 when its incidence is lower than the luminescent surface 6. Therefore, the total number of light rays that finally reach the luminescent surface 6 with low incidence is increased, so that the light extraction efficiency of the display screen 10 is increased. In other words, the intermediate layer 12 therefore allows the reflection of the radiation emitted by the luminescent region 8 at the interface between the layer stack 5 and the air to be reduced or even eliminated, thereby producing a kind of recycling of the light radiation R2' at the luminescent region 8.

According to one embodiment, the light emitting region 8 of each display pixel 3' comprises at least one light emitting diode, preferably a collection 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 comprises a semiconductor layer of a III-V compound, such as GaN, AlN, InN, InGaN, AlGaN or AlInGaN, or a II-VI compound.

The three-dimensional light-emitting diode comprises a three-dimensional semiconductor element, such as a wire, a pyramid, a truncated pyramid or a prism pyramid element, in particular a microwire or a nanowire, on which the active region of the light-emitting diode extends. The term "microwire" or "nanowire" refers to a three-dimensional structure elongated along a preferred direction, wherein at least two dimensions, referred to as minor dimensions, are between 5 nm and 2.5 μm, preferably between 50 nm and 2.5 μm, and a third dimension, referred to as a major dimension, is at least 1 times, preferably at least 2 times, the largest of the minor dimensions. In some embodiments, the minor dimension may be less than or equal to about 3 μm, preferably between 100 nm and 3 μm, and more preferably between 1 μm and 1.5 μm. In some embodiments, the height of each microwire or nanowire may be greater than or equal to 500 nm, preferably between 1 μm and 50 μm.

FIG. 6 is a schematic partial cross-sectional view of an embodiment of a display pixel 3' of the display screen 10 shown in FIG. 3, wherein the light emitting region 8 comprises a nanowire or microwire light emitting diode LED.

From bottom to top in FIG. 6 , the luminescent region 8 comprises: - a reflective layer 16 for the 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), each light-emitting diode LED having the general shape of a nanowire or microwire here; - Insulating blocks 18, here placed on the reflective layer 16, each block 18 facing one of the LEDs or the assembly of LEDs and completely surrounding the LEDs, each block 18 being a block transparent to the radiation emitted by the LEDs, and/or a block scattering the radiation emitted by the LEDs, and/or a photoluminescent block; and - walls 22 between the blocks 18, each wall 22 being opaque to the radiation emitted by the LEDs.

In FIG. 6 , from bottom to top, the pixel 3 ′ is shown to include: - a substrate 7 including a lower surface 23 and an upper surface 24 opposite to the lower surface 23, the upper surface 24 being preferably flat at least at the light-emitting diode LED; - a light-emitting region 8, the reflective layer 16 of the light-emitting region 8 being placed on the upper surface 24; - an intermediate layer 12 covering the light-emitting region 8, specifically the block 18 and the wall 22; - optionally, a color filter 26 or more than one color filter covering at least some of the blocks 18, a single filter 26 covering the block 18 is shown by way of example, the intermediate layer 12 being inserted between the block 18 and the filter 26 or filters; - a bonding layer 28; and - a support 9.

FIG7 is a schematic partial cross-sectional view of another embodiment of a display pixel 3' of the display screen 10 shown in FIG3, wherein the light emitting region 8 comprises at least one planar light emitting diode LED. Planar light emitting diodes, also called 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 into the stack of semiconductor layers.

The display pixel 3' shown in Fig. 7 comprises all the elements of the display pixel 3' shown in Fig. 6, with the difference that the light emitting diode LED comprises a stack of substantially planar layers. According to one embodiment, the light emitting diode LED comprises an upper surface 29 which is diffuse for the radiation emitted by the light emitting diode LED.

In Figures 6 and 7, the substrate 7 may correspond to a single-piece structure. The substrate may not exist. The substrate 7 may correspond to an integrated circuit that is configured to drive one or more light-emitting diodes LED in the light-emitting area 8 and includes electronic components, specifically insulated gate field effect transistors, also known as MOS transistors, or thin film transistors, also known as TFT transistors. These are called smart display pixels 3'. When the substrate 7 does not exist (not shown), the light-emitting diode (s) may be transferred onto an integrated circuit including electronic components, specifically a control circuit, and may be connected via a conductive pad (not shown) made on the lower part of the display pixel 3', which is the part opposite to the light-emitting area 8 and the support 9. The conductive pads are then electrically connected to the electrode layer described later.

In FIGS. 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 may be interrupted to allow a light emitting diode LED to be connected to the substrate 7.

In the above-mentioned embodiments, the reflective layer 16 can be a conductive layer, specifically a metal layer, for example made of iron, copper, aluminum, tungsten, silver, titanium, uranium, zirconium or a combination of at least two of these compounds. Preferably, the reflective layer 16 is formed of a material compatible with the 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 between 100 nm and 300 nm. Alternatively, the reflective layer 16 can be a Bragg mirror comprising a stack of layers with different refractive indices. In this case, the reflective layer 16 consists of a dielectric material such as silicon oxide ( _SiO2 ), silicon nitride (SiN), titanium oxide ( _TiO2 ), or any other oxide or nitride transparent to the wavelength of radiation emitted by the light emitting region 8. In the case where the reflective layer 16 is a Bragg mirror, it may be at most 10 μm thick.

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, which is arranged to harden when exposed to radiation, such as ultraviolet radiation. The bonding layer 28 may correspond to an optical adhesive, such as the optical adhesive sold by the company Norland under the name NOA. According to 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. According to one embodiment, the refractive index of the intermediate layer 12 is strictly less than the refractive index of the bonding layer 28, specifically with a deviation higher than 0.2. The refractive index of the bonding layer 28 may be substantially equal to the refractive index of the support member 9.

The aspect ratio of each block 18, i.e. the ratio between the height and the maximum width of the block 18, can be between 0.01 and 10, preferably between 0.05 and 2. The height of each block 18 measured perpendicularly to the upper surface 24 can be between 500 nm and 15 μm. The refractive index of each block 18 is between 1.4 and 2. According to one embodiment, the refractive index of the intermediate layer 12 is strictly lower than the refractive index of each block 18, in particular with a deviation greater than 0.2. According to one embodiment, the upper surface of the block 18 is flat and parallel to the upper surface 24 of the substrate 7. According to one embodiment, the side wall(s) of the block 18 are perpendicular to the upper surface 24. Alternatively, the side wall(s) of block 18 may be inclined relative to upper surface 24.

According to one embodiment, when block 18 is a photoluminescent block, it includes a phosphor that, when excited by light emitted by an associated light emitting diode LED, is adapted to emit light of a wavelength different from the wavelength of light emitted by the associated light emitting diode LED.

According to one embodiment, each photoluminescent block 18 includes at least one particle of a photoluminescent material, for example, in a transparent matrix. An example of a photoluminescent material is yttrium-aluminum garnet (YAG) activated by trivalent ribonium ions, also known as YAG:Ce or YAG:Ce ³⁺ . It is known that the average particle size of the photoluminescent material is generally greater than 5 μm.

According to one embodiment, each photoluminescent block 18 comprises a matrix of inorganic or organic material, in which nano-sized single crystal particles of semiconductor material are optionally dispersed, hereinafter also referred to as semiconductor nanocrystals or nanophosphor particles. The internal quantum yield QY _int of the photoluminescent material is equal to the ratio of the number of photons emitted by the photoluminescent substance to the number of photons absorbed. The internal quantum yield QY _int of the semiconductor nanocrystal is higher than 5%, preferably higher than 10%, and more preferably higher than 20%.

According to one embodiment, when block 18 includes phosphors, different phosphors may be provided depending on the set of light emitting diodes LEDs.

According to 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, even more preferably from 1 nm to 100 nm, and in particular from 2 nm to 30 nm. For sizes below 50 nm, the light conversion properties of semiconductor nanocrystals mainly depend on quantum confinement phenomena. Semiconductor nanocrystals correspond to quantum boxes (in the case of three-dimensional confinement) or quantum wells (in the case of two-dimensional confinement).

According to one embodiment, the semiconductor material of the semiconductor nanocrystal is selected from the group consisting of cadmium selenide (CdSe), indium phosphide (InP), cadmium sulfide (CdS), zinc sulfide (ZnS), zinc selenide (ZnSe), cadmium telluride (CdTe), zinc telluride (ZnTe), cadmium oxide (CdO), cadmium zinc oxide (ZnCdO), cadmium zinc sulfide (CdZnS), cadmium zinc selenide (CdZnSe), silver indium sulfide ( _AgInS2 ), PbScX3 _type calcium titanate, wherein X is a halogen atom, specifically iodine (I), bromine (Br) or chlorine (Cl), and a mixture of at least two of these compounds. According to one embodiment, the semiconductor material of the semiconductor nanocrystal is selected from the materials cited in the publication by Le Blevenec et al. entitled Physica Status Solidi (RRL) - Rapid Research Letters, Vol. 8, No. 4, pp. 349-352, April 2014.

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

The substrate is made of a material that is at least partially transparent, preferably more than 80%, to the radiation emitted by the photoluminescent particles and/or the light-emitting diode LED. The substrate is made of silicon dioxide, for example. The substrate can be made of any at least partially transparent polymer, in particular of silicone, epoxy, acrylic resin of the poly(methyl methacrylate) (PMMA) type, or polyvinyl acetate (PLA). In particular, the substrate can be made of an at least partially transparent polymer used with a three-dimensional printer. The substrate can be photosensitive or non-photosensitive spin-on glass (SOG). According to one embodiment, the substrate contains from 2% to 90% by weight, preferably from 10% to 60% by weight of nanocrystals, for example about 30% by weight of nanocrystals.

The height of the photoluminescent block 18 depends on the concentration of the nanocrystals and the type of nanocrystals used. When the light-emitting diodes are linear, the height of the photoluminescent block 18 is preferably higher than the height of the light-emitting diodes 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, a rectangle, an "L"-shaped polygon, etc., and its area may be equal to the area of a square having sides measured from 1 μm to 100 μm, preferably from 3 μm to 15 μm.

According to one embodiment, when block 18 is a scattering block, it comprises particles suitable for scattering radiation emitted by an associated light-emitting diode LED, the particles being dispersed in a transparent matrix. The particles are, for example, titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), zinc sulfide (ZnS) or lead sulfide (PbS) particles. The average size of the scattering 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 light-emitting diode LED, preferably more than 80%. The matrix can be made of any of the materials described above for photoluminescent block 18. Scattering block 18 may or may not include quantum dots.

According to one embodiment, when the block 18 is a photoluminescent block, it is also a scattering block for emitting radiation by light conversion. The photoluminescent block 18 may be diffuse due to the presence of a phosphor. Alternatively, the photoluminescent block 18 may further include scattering particles. The scattering properties of the block 18 may be characterized by a bidirectional scattering distribution function (BSDF), which specifically includes a bidirectional reflectance distribution function (BRDF) and a bidirectional transmittance distribution function (BTDF). The bidirectional transmittance distribution function may be determined using a dedicated measurement instrument.

According to one embodiment, when the block 18 is a transparent block, it is made of a material that can be one of the materials used for the substrate of the photoluminescent block 18 described above.

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

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

According to one embodiment, the walls 22 may be made of a reflective material, or each wall 22 comprises a reflective wall by being covered with a coating that is reflective for the wavelength of radiation emitted by the photoluminescent block 18 and/or the light emitting diode LED, such as a polymer with TiO ₂ particles.

According to one embodiment, each wall 22 comprises an opaque wall. For example, each wall 22 may comprise a wall coated with a layer of black resin. This resin is preferably suitable for absorbing electromagnetic radiation in a spectral range that includes the emission spectrum of the luminescent region 8 and the emission spectrum of the phosphor when 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 completely made of black resin.

Preferably, the wall 22 surrounds the block 18. The wall 22 reduces crosstalk between adjacent blocks 18. Preferably, the intermediate layer 12 contacts the wall 22. In the embodiment shown in Figures 6 and 7, the intermediate layer 12 is shown as completely covering the wall 22. Alternatively, the wall 22 may pass through all or part of the intermediate layer 12.

The display pixel 3' may optionally include one, two or three filters 26 covering at least some of the blocks 18, for example a single yellow filter; two filters, the first filter being a yellow filter and the second filter being a red filter; or three filters, the first filter being a red filter, the second filter being a green filter and the third filter being a blue filter. The filters 26 may correspond to a stack of colored layers or layers of different refractive indices forming a Bragg filter. According to one embodiment, each filter 26 may include one or more layers suitable for absorbing and/or reflecting radiation emitted by the luminescent region 8.

When the upper surface 29 of the LED is a scattering surface, the upper surface can be textured to enable the radiation emitted by the LED to be scattered. The textured upper surface 29 can be achieved by chemical or physical etching. When the diffusion obtained by the upper surface 29 is sufficient, the block 18 covering the upper surface 29 can be a transparent block for the radiation emitted by the LED.

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

In this embodiment, the light-emitting region 8 includes from bottom to top: - a seed layer 30 made of a wire growth promoting material and disposed on the upper surface 24 of the substrate 7; - an insulating layer 32 covering the seed layer 30 and including an opening 34 exposing a portion of the seed layer 30; - LEDs (six LEDs are shown), each LED being in contact with the seed layer 30 via one of the openings 34; - an insulating layer 36 extending on the side of the lower portion of the LED LED and on the insulating layer 32 between the LED LEDs; - Conductive layer 38, forming an electrode covering each LED and further extending over insulating layer 36 between the LEDs; - Reflective layer 16, here corresponding to a conductive layer extending over electrode layer 38 between the LEDs, reflective layer 16 being inserted between electrode layer 38 and insulating layer 36 between the LEDs instead; - Dielectric protective layer 40, extending over layers 38 and 16; - Block 18, covering the LED assembly; - - an insulating layer 42, covering the top of each block 18, or only covering some of the blocks 18, the insulating layer 42 may not exist; - a protective layer 44, covering the insulating layer 42, the sides of the blocks 18 and the electrode layer 38 between the blocks 18; - 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 coated with an intermediate layer 12, not shown in FIG. 8.

FIG. 9 is a schematic partial cross-sectional view showing an embodiment of a light-emitting diode LED of a pixel 3'. According to one embodiment, each light-emitting diode LED comprises a wire 50 contacting the seed layer 30 through one of the openings 34, and a housing 52 comprising a semiconductor layer stack covering the sidewalls and top of the wire 50. This configuration is called a radial configuration. The assembly formed by each wire 50 and the associated housing 52 constitutes a light-emitting diode LED.

Housing 52 may include a stack of layers, specifically an active layer 54 and a bonding layer 56. Active layer 54 is the layer from which most, preferably all, of the radiation supplied by the light emitting diode LED is emitted. According to one example, active layer 54 may include a confinement member, such as a single quantum well or multiple quantum wells. Bonding layer 56 may include a stack of semiconductor layers of the same III-V material as line 50 but having an opposite conductivity type to line 50.

Fig. 10 is a schematic partial cross-sectional view of another embodiment of a light emitting diode LED for displaying pixel 3'. The light emitting diode LED shown in Fig. 10 includes all the elements of the light emitting diode LED shown in Fig. 9, with the difference that the housing 52 is only present at the top of the line 50. This configuration is called an axial configuration.

Forming the light emitting diode LED shown in FIGS. 9 and 10 , that is, growing the wire 50 in the opening 64 and forming the outer shell 52 of the wire 50 can be performed, for example, by Metal-Organic Chemical Vapor Deposition (MOCVD) or any other suitable method.

The seed layer 30 is made of a material that promotes wire growth. For example, the material constituting the seed layer 30 may be a nitride, carbide or boride of a transition metal from row IV, V or VI of the periodic table, or a combination of these compounds. According to another embodiment, the seed layer 30 may not exist. According to another embodiment, the seed layer 30 may be replaced by a seed pad formed at the bottom of the opening 34, for example.

Each insulating layer 32, 36, 40, 42, 44, 50 and the core 46 may be made of a dielectric material such as silicon oxide ( _SiO2 ), silicon nitride (Si _x N _y ), where x is about 3 and y is about 4, such as Si ₃ N ₄ , silicon oxynitride (specifically having the general formula SiO _x N _y , such as Si ₂ ON ₂ ), aluminum oxide (Al ₂ O ₃ ), hexagonal oxide (HfO ₂ ), titanium dioxide (TiO ₂ ), or diamond. Each insulating layer 32, 36, 40, 42, 44, 50 may be a single layer structure or a stack of two or more layers.

The electrode layer 38 is at least partially transparent, thereby allowing electromagnetic radiation emitted by the LED to pass through. The material constituting the electrode layer 38 may 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 may be between 0.01 μm and 10 μm.

Various embodiments and variants have been described. Those skilled in the art will appreciate that certain features of these embodiments may be combined, and those skilled in the art will readily conceive of other variants. Finally, based on the functional description provided above, the actual implementation of the embodiments and variants described herein is within the capabilities of those skilled in the art.

1: Display screen 2: Panel 3: Display pixel 3': Display pixel 4: Planarization layer 5: Layer stack 6: Emitting surface 7: Substrate 8: Light-emitting area 9: Support 10: Display screen 12: Intermediate layer 13: Bottom 14: Top 15: Top 16: Reflection layer 18: Insulation block 22: Wall 23: Bottom 24: Top/upper surface 26: Color filter 28: Bonding layer 29: Upper surface 30: Seed layer 32: Insulation layer 34: Opening 36: Insulation layer 38: Conductive layer 40: Insulation layer 42: Insulation layer 44: Protective layer 46: Core 48: Reflective coating 49: Protective layer 50: Wire 52: Shell 54: Active layer 56: Bonding layer R1, R2: Light ray path R1', R2': Light ray path LED: Light emitting diode

The foregoing features and advantages, as well as other features and advantages, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation, with reference to the accompanying drawings, in which:

FIG. 1 partially and highly schematically illustrates an example of a display screen;

FIG. 2 illustrates an example of an optical path for the display screen shown in FIG. 1;

FIG. 3 partially and schematically illustrates an embodiment of a display screen;

FIG. 4 illustrates an example of an optical path for the display screen shown in FIG. 3;

FIG. 5 schematically illustrates on the left a beam path for a display pixel of the display screen shown in FIG. 1 and on the right a beam path for a display pixel of the display screen shown in FIG. 3 ;

FIG. 6 partially and schematically illustrates one embodiment of display pixels of the display screen shown in FIG. 3;

FIG. 7 partially and schematically illustrates another embodiment of the display pixels of the display screen shown in FIG. 3;

FIG. 8 partially and schematically illustrates a more detailed embodiment of the display pixel shown in FIG. 6;

FIG. 9 illustrates an embodiment of a three-dimensional light-emitting diode; and

FIG. 10 illustrates another embodiment of a three-dimensional light-emitting diode.

Domestic storage information (please note in the order of storage institution, date, and number) None Foreign storage information (please note in the order of storage country, institution, date, and number) None

2: Panel

3': Display pixels

4: Planarization layer

5: Layer stacking

6: Emitting surface

7:Substrate

8: Luminous area

9: Support parts

10: Display screen

12:Middle layer

13: Below

14: Above

15: Above

Claims (16)

A display pixel (3') intended to be placed and attached to a panel (2) of a display screen (10), the display pixel (3') comprising: - a light-emitting area (8) comprising at least one light-emitting diode (LED); - a support (9) transparent to the radiation emitted by the light-emitting area (8) and intended to be used in processing the display pixel (3'), the height of the support (9) being higher than 5 μm; and - An intermediate layer (12) is transparent to the radiation emitted by the luminescent region (8), the intermediate layer is made of a solid material and is inserted between the luminescent region (8) and the support member (9), the refractive index of the intermediate layer (12) is strictly less than 1.5, and is less than the refractive index of the support member (9) by a refractive index deviation greater than or equal to 0.2. A display pixel as described in claim 1, wherein the support member (9) is a one-piece glass support member. The display pixel as described in claim 1 or 2 further includes a bonding layer (28) inserted between the supporting member (9) and the intermediate layer (12). A display pixel as described in any one of claims 1 to 3, wherein the light-emitting area (8) includes a light-emitting diode (LED) having a linear, conical or truncated pyramidal semiconductor element. A display pixel as described in any one of claims 1 to 3, wherein the light emitting diode (LED) comprises a textured surface (29). A display pixel as described in any one of claims 1 to 5, wherein for at least one light-emitting diode (LED), the light-emitting region (8) further comprises an electrical insulating block (18), which covers the light-emitting diode (LED) and is inserted between the intermediate layer (12) and the light-emitting diode (LED). A display pixel as described in claim 6, wherein the block (18) is photoluminescent. A display pixel as described in claim 6, wherein the block (18) is diffuse with respect to radiation emitted by the light emitting diode (LED). A display pixel as described in claim 6, wherein the block (18) is transparent to radiation emitted by the light emitting diode (LED). A display pixel as described in any one of claims 6 to 9, wherein the light-emitting area (8) further includes a reflective layer (16), the reflective layer is opposite to the intermediate layer (12), and the block (18) is inserted between the reflective layer (16) and the intermediate layer (12). A display pixel as described in any one of claims 6 to 10, wherein the light-emitting area (8) further includes reflective walls (22) surrounding the block (18). A display pixel as described in any one of claims 1 to 11, comprising a conductive bonding pad on a side opposite to the support member (9). A display screen (10) comprising: - a panel (2); - display pixels (3') as in any one of claims 1 to 12, the support members (9) for the display pixels (3') being located on opposite sides of the panel (2'); and - a planarization layer (4) covering the panel (2) and the display pixels (3'). A method for manufacturing a display pixel (3') as claimed in any one of claims 1 to 12, the method comprising the following steps: - forming a plurality of copies of the light-emitting region (8) of the display pixel (3') on a semiconductor board; - forming the intermediate layer (12) on the light-emitting regions (8); and - attaching a plate of material constituting the support member (9) to the intermediate layer (12); and - separating the display pixels (3'). A method for manufacturing a display screen (10), the method comprising the following steps: - forming display pixels (3') as in any one of claims 1 to 12; - placing each display pixel (3') individually and attaching it to a panel (2); and - forming a planarization layer (4) covering the display pixels (3') and the panel (2) between the display pixels (3'). A method as described in claim 15, wherein processing each display pixel (3') during the step of individually placing and attaching each display pixel (3') to the panel (2) includes using a fixture that handles the display pixel (3') via the support member (9) of the display pixel (3').