OPTOELECTRONIC DEVICE AND METHOD FOR ITS MANUFACTURING

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of technologies for microelectronics and optoelectronics. Its particularly advantageous application is the manufacture of optoelectronic devices, in particular pixels based on light-emitting diodes (LEDs). STATE OF THE ART

[0002] A self-emissive display is an example of an optoelectronic device comprising a plurality of pixels that emit their own light. Each pixel is typically formed by several LEDs or micro-LEDs.

[0003] US patent 2017 / 0309798 A1 describes a high-brightness, low-power LED display. More specifically, this document describes a microdisplay with integrated LEDs and its manufacturing process, which includes an organic bonding layer.

[0004] A pixel typically comprises at least three sub-pixels, each emitting a different color of light, usually green, red, and blue. RGB (Red Green Blue) sub-pixels can be created by adding different color conversion modules above similar LEDs. For example, to form a pixel, one could use three LEDs emitting only blue, and place a blue-to-red conversion module and a blue-to-green conversion module above two of the three blue LEDs. This avoids the need to create or locally replicate different types of LEDs. This solution typically minimizes the manufacturing costs of a self-emissive display.

[0005] One possibility is that these LEDs are so-called "smart LEDs," typically comprising an optically active structure connected to dedicated transistor-based driver electronics. Groups of smart LEDs connected to independent driver electronics typically form "smart pixels."

[0006] The optoelectronic device can thus include a color conversion layer arranged on an emitting layer and / or an electronics layer below the emitting layer with interconnections between the electronics layer and the emitting layer.

[0007] To protect and handle the components, and / or to improve light extraction efficiency, a thick glass layer is formed over the emitting layer, possibly including a color conversion layer. Assembly processes are already known for assembling this thick glass layer, in the form of a transparent glass substrate, with RGB sub-pixels, including, for example, color conversion modules.

[0008] A first example of a "SiOx / SiOx bonding" assembly process allows two surfaces, each coated with a layer of SiOx, to be bonded together. One drawback of this solution is that a step in this assembly process requires consolidation annealing, for example at 200°C for 2 hours, to form a bonding layer between the SiOx / SiOx layers. Advantageously, this bonding layer is transparent to light transmission; however, such an annealing step is detrimental to color conversion modules, which are components sensitive to such temperatures. These color conversion modules can be degraded by excessively high temperatures, thus reducing their conversion efficiency.

[0009] A consolidation annealing step such as the one described above in a SiOx / SiOx bonding process can also be detrimental to an optoelectronic device containing a temperature-sensitive electronic layer pre-arranged beneath an emitting layer (on the side opposite the light emission path). Indeed, if this electronic layer corresponds to a silicon-based substrate carrying transistors, for example, thin-film transistors (TFTs) of the IGZO (indium gallium zinc oxide) type, these transistors generally cannot withstand temperatures exceeding 150°C.

[0010] Another example of assembly involves a transparent, UV-activated organic adhesive bonding layer. A drawback of this solution is that the bonding layer has unsatisfactory mechanical properties, leading to problems with expansion and deformation. This compromises the reliability and strength of the optoelectronic device. Another disadvantage of this solution, which includes a UV activation step, is that it is not possible to use pre-opacified glass substrates. However, transparent glass substrates are difficult for microelectronics industry automation to handle, as these systems typically rely on optical detection for substrate manipulation and positioning. Therefore, this solution is not fully compatible with standard microelectronics manufacturing processes.Another drawback of this solution is that the transparent organic glue-based bonding layer does not prevent the color conversion modules from being exposed to oxygen. This reduces the lifespan of the color conversion modules.

[0011] There is therefore a need to improve the process of assembling a transparent layer onto a structure comprising a layer of components sensitive to temperature and / or environmental conditions, particularly an oxidizing atmosphere. One object of the present invention is to meet this need by at least partially overcoming the drawbacks of known solutions.

[0012] In particular, one object of the present invention is to provide an optoelectronic device comprising a layer of temperature-sensitive components and a transparent support layer, which is reliable and compatible with microelectronic manufacturing processes. Another object of the present invention is to provide a method for manufacturing such an optoelectronic device.

[0013] The other objects, features, and advantages of the present invention will become apparent from an examination of the following description and accompanying drawings. It is understood that other advantages may be incorporated. In particular, certain features and advantages of the device may apply mutatis mutandis to the process, and vice versa. SUMMARY OF THE INVENTION

[0014] To achieve the objectives mentioned above, the present invention relates, in a first aspect, to an optoelectronic device, according to claim 1 in the appendix, comprising stacked along a direction z: at least one emitting layer comprising optically active structures, configured to emit or receive radiation at a wavelength λ, a bonding layer, a transparent support layer, the optoelectronic device further comprising, in the stacking along the z direction, at least one so-called sensitive layer comprising at least one so-called sensitive structure having a temperature resistance below a temperature Tmax, the optoelectronic device being characterized in that the bonding layer is based on a low temperature inorganic bonding material, and in that the bonding layer includes cavities directly above the optically active structures, between the transparent support layer and the emitting layer comprising said optically active structures.

[0015] According to the present invention, the bonding layer is based on an inorganic adhesive material described as "low-temperature," meaning that it can be used at a temperature that does not degrade the at least one temperature-sensitive structure. The mechanical properties of such an adhesive material, which is compatible with the presence of at least one temperature-sensitive structure, are more suitable for an optoelectronic device than an organic adhesive generally used in known solutions. Mechanical strength is improved. The device's resistance to aging is improved. The device's reliability is superior to that of known devices. However, such a low-temperature inorganic adhesive material is generally opaque.

[0016] According to the present invention, the bonding layer comprises cavities positioned above the optically active structures, between the transparent support layer and the emitting layer comprising the optically active structures. These cavities above the optically active structures allow optical transmission through the bonding layer. Thus, the bonding layer, made of a low-temperature inorganic adhesive material, does not impede the emission or reception of light to the optically active structures.

[0017] According to one example, the so-called sensitive layer is arranged between the emitting layer comprising the optically active structures and the bonding layer, at least one so-called sensitive structure being a color converter module.

[0018] In another example, the so-called sensitive layer is supported by a substrate arranged beneath the emitting layer, which includes the optically active structures, on the side opposite the bonding layer. At least one of the so-called sensitive structures is a transistor, preferably a thin-film transistor.

[0019] In one example, the device comprises a first sensitive layer arranged between the emitting layer and the bonding layer, and a second sensitive layer arranged between a substrate and the emitting layer, comprising the optically active structures, on the side opposite the bonding layer. The optically active structures are typically light-emitting diodes (LEDs). The first sensitive layer typically includes at least one first sensitive structure, such as a color converter module. The second sensitive layer typically includes at least one second sensitive structure, such as a transistor, preferably a thin-film transistor.

[0020] According to one example, the bonding layer forms adhesive bands that delimit the cavities.

[0021] Each cavity typically forms a sealed, airtight space enclosing the color converter module, preventing it from coming into contact with the device's surroundings. This limits the degradation of the color converter module and preserves its conversion efficiency.

[0022] In one embodiment, the cavities have a pressure lower than atmospheric pressure, preferably at least one decade lower than atmospheric pressure. Advantageously, the cavities are hermetically sealed, limiting any oxidation of the color conversion module.

[0023] Thus, unlike known solutions based on continuous transparent bonding layers (using organic adhesives or SiOx / SiOx bonding), the optoelectronic device according to the present invention comprises a structured inorganic bonding layer. Contrary to a common misconception, the structuring of the bonding layer does not compromise the bond between the transparent support layer and the emitting layer containing the optically active structures, or between the transparent support layer and the sensitive layer when the latter is present between the emitting layer containing the optically active structures and the transparent support. The use of a low-temperature inorganic bonding material makes it possible to compensate for or overcome the reduction in mechanical strength associated with the structuring of the bonding layer.The optoelectronic device comprising an inorganic bonding layer structured according to the invention thus exhibits mechanical strength typically equal to or greater than that of a known device comprising a continuous organic bonding layer. Such a device also offers increased compatibility with microelectronic technologies. In particular, an inorganic bonding layer is less critical than an organic adhesive-based layer in terms of equipment contamination during the device manufacturing process. The device according to the invention is therefore easier and / or less expensive to manufacture using standard microelectronic industry processes.

[0024] In one embodiment, the inorganic bonding material can be opaque. Advantageously, the bonding layer, outside the cavities, does not allow the emitted or received radiation to pass through. The emission or reception zone is thus indirectly partitioned by the passage through the cavities.

[0025] Another aspect of the present invention relates to a method for manufacturing such an optoelectronic device according to claim 13 in the appendix. The method according to the present invention comprises at least the following steps: to provide a stack comprising at least one emitting layer including optically active structures, configured to emit or receive radiation at a wavelength λ, and at least one so-called sensitive layer including so-called sensitive structures having a temperature resistance below a temperature Tmax, to form, on the stack, a first bonding layer based on a low-temperature inorganic adhesive material, said first part having first openings aligned with the optically active structures, to provide a transparent support layer, to form, on a first face of the transparent support layer, a second bonding layer based on the low-temperature inorganic adhesive material, said second part having second openings configured to correspond with the first openings,The second bonding layer is placed side-by-side with the first bonding layer. The stack, comprising the sensitive layer and the transparent support layer, is assembled by low-temperature bonding between the first and second bonding layers. The first and second openings then form cavities directly above the optically active structures.

[0026] Thus, the process makes it possible to manufacture the optoelectronic device described above.

[0027] Preferably, the process further includes opacifying a second face of the transparent support layer before aligning the first and second bonding layers, and removing the second opacified face after assembling the stack comprising the sensing layer with the transparent support layer. Opacification prior to assembly advantageously allows the use of equipment and automated systems in the microelectronics industry that employ optical substrate detection. The opacified support layer also exhibits increased resistance to plasma or cleaning processes and wet etching processes. The manufacturing cost is thus reduced. BRIEF DESCRIPTION OF THE FIGURES

[0028] The aims, objects, features, and advantages of the invention will become clearer from the detailed description of embodiments thereof, which are illustrated by the following accompanying drawings, in which: figures 1A to 8 schematically illustrate the manufacturing steps of an optoelectronic device according to an embodiment of the present invention. Figures labeled A and B, respectively, preceded by the same number, schematically illustrate two variants of the manufacturing process according to the present invention, for the same step.

[0029] The drawings are provided as examples and are not intended to limit the invention. They are schematic representations of the principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, the dimensions of the various constituent elements of the emitting layers are not necessarily representative of reality. DETAILED DESCRIPTION

[0030] Before undertaking a detailed review of embodiments of the invention, it is noted that the invention may include the following optional features, at least as long as they remain within the scope of these claims in the appendix, which may be used in combination or alternatively: In one example, the z-coordinate layer stacking follows this order: the emitting layer containing the optically active structures, the sensitive layer containing at least one sensitive structure, the bonding layer, and the transparent support layer. In another example, the z-coordinate layer stacking follows this order: the sensitive layer containing at least one sensitive structure, the emitting layer containing the optically active structures, the bonding layer, and the transparent support layer. In yet another example, the z-coordinate layer stacking follows this order: a first sensitive layer containing at least one sensitive structure, the emitting layer containing the optically active structures, a second sensitive layer containing at least one other sensitive structure, the bonding layer, and the transparent support layer.

[0031] As an example, optically active structures are light-emitting diodes (LEDs). The emitting layer, comprising these optically active structures, is typically formed from a doped or undoped semiconductor material. It can be made of sapphire or even a material based on III-V compounds, such as GaN, GaAs, or InP. Alternatively, it can be a silicon substrate, or a silicon-on-insulator (SOI) substrate, according to established Anglo-Saxon terminology.

[0032] According to one example, at least one sensitive structure of the sensitive layer is a color converter module.

[0033] According to one example, at least one color converter module includes quantum dots.

[0034] According to one example, at least one sensitive structure of the sensitive layer is a transistor, preferably a thin-film transistor.

[0035] As an example, the inorganic low-temperature bonding material is opaque.

[0036] In one example, the inorganic low-temperature bonding material is metal-based, amorphous metal-based, amorphous silicon-based, or amorphous germanium-based. In another example, the inorganic low-temperature bonding material is titanium-based. In yet another example, the bonding layer comprises a titanium-based sublayer and an amorphous silicon-based layer.

[0037] In one example, the maximum temperature (Tmax) is less than 180°C, preferably less than 150°C. In another example, the bonding layer has a thickness between 3 nm and 100 nm, preferably between 5 nm and 10 nm.

[0038] As an example, the cavities are subjected to a pressure lower than atmospheric pressure, preferably at least a decade lower. This implies, in particular, that the cavities are airtight. Thus, when the sensitive layer is positioned between the emitting layer (which contains the optically active structures) and the bonding layer, the sensitive layer structures are not exposed to a humid or oxidizing atmosphere. Consequently, the sensitive layer structures degrade less rapidly over time, slowing the aging of the device.

[0039] In one example, the transparent support layer is glass-based.

[0040] As an example, cavities are transparent to radiation emitted or received by optically active structures.

[0041] According to one example, the bonding layer is formed by an assembly of first and second parts of the inorganic bonding material, deposited respectively on the emitting layer comprising the optically active structures (or the sensitive layer when present between the emitting layer comprising the optically active structures and the bonding layer) and on one face of the transparent support layer.

[0042] In one example, at least one emitting layer comprising the optically active structures is based on GaN or GaAs.

[0043] As an example, low-temperature bonding is performed at a temperature Tc lower than the temperature Tmax, preferably such that Tc ≤ Tmax - 20°C, and preferably such that Tc ≤ Tmax - 50°C. Tc and Tmax are expressed in degrees Celsius (°C). The bonding process is configured to bond the transparent support layer to the sensitive layer while preserving the sensitive structures.

[0044] As an example, the Tmax temperature corresponds to a temperature beyond which sensitive structures begin to degrade thermally.

[0045] For example, low-temperature bonding is performed at room temperature or approximately 20°C. Advantageously, this type of bonding does not require post-processing, unlike polymer bonding, which requires UV activation that can damage sensitive structures. Similarly, hydrophilic oxide / oxide bonding requires consolidation annealing, which can also damage sensitive structures.

[0046] In one example, the process further includes opacifying a second side of the transparent support layer before aligning the first and second bonding layers, and removing the opacified second side after assembling the stack comprising the sensitive layer with the transparent support layer. This opacification facilitates handling of the transparent support layer, particularly by optically sensing equipment and automated systems used in the microelectronics industry. Advantageously, low-temperature bonding does not require the support layer to be transparent during assembly, unlike UV-activated organic bonding.

[0047] In one example, opacification is performed without temperature limitations, typically at a temperature To above Tmax. Opacification is typically carried out separately, before assembly. Therefore, opacification can be performed without temperature restrictions, including at temperatures above 200°C. Opacification consists of depositing at least one opaque layer, generally a metal, such as Ti or TiN, possibly encapsulated by a dielectric. Opacification by depositing such an opaque layer is more robust to subsequent wet cleaning or removal processes using high-frequency (HF) and can be advantageously implemented as part of the device manufacturing process.

[0048] As an example, low-temperature bonding is performed under a pressure Pc lower than atmospheric pressure Patm, preferably such that Pc ≤ 10⁻³ < Patm, and preferably such that Pc ≤ 10⁻⁸ < Patm. The pressure Pc is, for example, on the order of 5 × 10⁻⁶ < Patm. Low-temperature bonding is typically performed under vacuum or ultra-high vacuum. This allows for the preservation of suspended bonds after the removal of the native oxide for amorphous silicon-based bonding layers. The quality of the bond is improved. Consequently, the cavities thus created are airtight and under vacuum. This protects sensitive structures, which are hermetically sealed, from a humid or oxidizing atmosphere.

[0049] In one example, the inorganic low-temperature bonding material is chosen to be metal-based, amorphous metal-based, or amorphous silicon-based. In another example, the inorganic low-temperature bonding material is chosen to be amorphous germanium-based.

[0050] In one example, the first and second openings are formed symmetrically in the first and second parts of the bonding layer. This allows for a better distribution of mechanical stresses between the bonding layer, the support layer, and the sensitive layer. The distribution of mechanical stresses is more homogeneous. The mechanical stresses within the device are potentially limited. The symmetrical formation of the first and second openings does not necessarily imply that the first and second parts of the bonding layer are of equal thickness.

[0051] According to one example, the first part of the bonding layer is first formed continuously on the sensitive layer of the stack, then the first openings are formed in the first part of the bonding layer.

[0052] According to one example, the second part of the bonding layer is first formed continuously on the first face of the transparent support layer, and then the second openings are formed in the second part of the bonding layer.

[0053] Unless otherwise required, technical features described in detail for a given embodiment may be combined with technical features described in the context of other embodiments described by way of example and without limitation, so as to form another embodiment that is not necessarily illustrated or described. Such an embodiment is obviously not excluded from the invention.

[0054] An "optoelectronic device" is defined as a device capable of emitting, transmitting, or receiving light. Depending on the specific application, such an optoelectronic device may include light-emitting diodes (LEDs), particularly LEDs that form the sub-pixels of a pixel in an emissive screen.

[0055] The invention can be implemented more broadly for various optoelectronic devices. For example, the invention can be implemented in laser or photovoltaic devices.

[0056] The LEDs or optoelectronic devices typically have dimensions, in projection in a basic xy plane, of less than 100 µm X 100 µm, preferably less than 10 µm X 10 µm.

[0057] Unless explicitly stated otherwise, it is specified that, within the framework of the present invention, the relative arrangement of a second layer interposed between a first and a third layer does not necessarily mean that the layers are directly in contact with each other, but rather means that the second layer is either directly in contact with the first and third layers, or separated from them by at least one other layer or element. Thus, the terms and phrases "to rest upon," "to overcome," "to cover," or "to re-cover" do not necessarily mean "in contact with."

[0058] The steps of the process as claimed are understood in a broad sense and may possibly be carried out in several sub-steps.

[0059] In this patent application, the terms "light-emitting diode," "LED," or simply "diode" are used synonymously. An "LED" may also be understood to mean a "micro-LED" or a "smart LED."

[0060] A substrate, layer, or device "based" on a material M is defined as a substrate, layer, or device comprising only that material M, or that material M and possibly other materials, such as alloying elements, impurities, or dopants. Thus, a GaN-based diode typically comprises GaN and AlGaN or InGaN alloys.

[0061] A coordinate system, preferably orthonormal, comprising the x, y, z axes is shown in some of the attached figures. This coordinate system can be applied by extension to the other figures.

[0062] In this patent application, the terms thickness for a layer and height for a structure or device will be preferred. Thickness is measured along a direction normal to the principal plane of extension of the layer, and height is measured perpendicular to the xy base plane. Thus, a layer typically has a thickness along the z-axis when it extends primarily along an xy plane, and a protruding element, for example, a color conversion module, has a height along the z-axis. The relative terms "on," "under," and "below" preferentially refer to positions taken along the z-direction. In this application, "vertical" and "vertically" mean "directed along the z-direction," and "laterally" mean "directed along a direction of the xy plane."

[0063] For the purposes of this invention, an object or material is considered "transparent" if it allows at least 90% of the light intensity of a beam of light passing through it to pass through. Conversely, a material or surface is considered "opaque" if it absorbs or blocks at least 85% of the intensity of an incident beam of light.

[0064] The "temperature resistance" of a structure is defined as the maximum temperature at which the integrity of the structure is not thermally degraded.

[0065] The term "low-temperature inorganic bonding material" refers to an inorganic material that can be used in a low-temperature bonding process, i.e., processed at a temperature below 200°C, preferably below 180°C, and preferably below 150°C. Low-temperature inorganic bonding materials are typically processed at room temperature, without the need for consolidation annealing.

[0066] Dimensional values ​​are understood to be within manufacturing and measurement tolerances.

[0067] The terms "approximately," "about," and "on the order of" mean, when referring to a value, "within 10%" of that value, or, when referring to an angular orientation, "within 10°" of that orientation. Thus, a direction approximately normal to a plane means a direction at an angle of 90±10° to the plane.

[0068] THE figures 1A to 8 illustrate the steps in the realization of an optoelectronic device comprising optically active structures surmounted by a sensitive layer 3 and a transparent support layer.

[0069] In this embodiment, the optically active structures are GaN-based LEDs configured to emit light at a first wavelength λ1 in the blue or UV region. These LEDs are typically mounted on a GaN-based substrate and encapsulated to form the emitting layer 2. The LEDs can exhibit a planar (2D) architecture within the emitting layer 2. In this case, each LED can comprise a plurality of layers stacked along the z-axis. Such a layer stacking typically includes an active layer sandwiched between an electron-injection layer and a hole-injection layer. The active layer emits light at wavelength λ1 by radiative recombination of electrons and holes. Alternatively, the LEDs can exhibit a three-dimensional (3D) architecture within the emitting layer 2.In this case, each LED can comprise an array of semiconductor nanopyramids and / or nanowires, preferably mainly oriented along the z-axis, embedded in a matrix based on a dielectric material. The semiconductor nanowires typically each comprise an active region interposed between an electron injection region and a hole injection region. The active region emits light of wavelength λ1 by radiative recombination of electrons and holes. The sensitive layer 3 is a layer comprising temperature-sensitive structures. In this embodiment, the sensitive layer 3 comprises color conversion modules 31, 32, 33. A color conversion module can be, for example, in the form of a diffusing photoluminescent block comprising phosphors, or a photoluminescent block comprising particles of at least one photoluminescent material, dispersed, for example, in a transparent matrix (i.e.photosensitive resin). Luminophores are configured, when excited by light emitted by LEDs, to emit light at a different wavelength than the LEDs. Photoluminescent particles can take the form of quantum dots, that is, semiconductor nanocrystals with essentially three-dimensional quantum confinement.Quantum dots can be formed from at least one semiconductor compound, which can be chosen from cadmium selenide (CdSe), indium phosphorus (InP), gallium indium phosphorus (InGaP), cadmium sulfide (CdS), zinc sulfide (ZnS), cadmium oxide (CdO) or zinc oxide (ZnO), zinc cadmium selenide (CdZnSe), zinc selenide (ZnSe) doped for example with copper or manganese, graphene or from i.e. other suitable semiconductor materials. Quantum dots can also have a core / shell structure, such as CdSe / ZnS, CdSe / CdS, CdSe / CdS / ZnS, PbSe / PbS, CdTe / CdSe, CdSe / ZnTe, InP / ZnS, or others. The size and / or composition of the photoluminescent particles are chosen according to the desired luminescence wavelength.

[0070] Another example of a photoluminescent material is trivalent cerium ion-activated yttrium aluminum garnet (YAG), also known as YAG:Ce or YAG:Ce 3+. Typically, a photoluminescent block comprises an array of inorganic or organic material in which nanometer-sized single-crystal particles of a semiconductor material, also called semiconductor nanocrystals or nanoluminophore particles, are optionally dispersed. Color conversion modules 31, 32, and 33 are mounted above the LEDs in emitting layer 2. Here, color conversion modules 31 and 32 are configured to convert the first wavelength A1 from the LEDs into another wavelength. Typically, color conversion module 31 is configured to convert the first wavelength λ1 into a second wavelength λ2 in the red region.The color conversion module 32 is configured to convert the first wavelength λ1 into a third wavelength λ3 in the green range. Schematically, to form a pixel, at least three sub-pixels—green, red, and blue—are required. Thus, to obtain the blue sub-pixel (in the 430nm to 490nm range), it suffices to transmit the first wavelength λ1 from a first LED located below position 33. To obtain the red sub-pixel (in the 580nm to 700nm range), the color conversion module 31 is placed above a second LED. To obtain the green sub-pixel (in the 500nm to 560nm range), the color conversion module 32 is placed above a third LED. These color conversion modules 31 and 32 are integrated within a transparent layer, for example, made of silicon oxide. This layer 3, placed above the emitting layer 2, is a temperature-sensitive layer.It is also referred to as the "conversion layer" 3 hereafter. The color conversion modules 31, 32 degrade, for example, above approximately 150°C. To preserve the functionality / integrity and performance of these color conversion modules 31, 32, the subsequent manufacturing steps involving the sensitive layer 3 must not exceed 150°C. In one scenario, the first wavelength λ1 emitted by the LEDs is in the UV range, and three color conversion modules 31, 32, 33 are used to convert the first wavelength λ1 into wavelengths in the red, green, and blue ranges, respectively.

[0071] According to a preferred approach, groups of LEDs in the emitting layer 2 are connected to independent control electronics to form "smart pixels." The optoelectronic device can thus include an electronics layer beneath the emitting layer 2. This electronics layer can correspond to a silicon-based substrate 1 bearing transistors, for example, complementary metal-oxide-semiconductor (CMOS) transistors or thin-film transistors (TFTs), such as LTPS (low-temperature polycrystalline silicon) or IGZO (indium gallium zinc oxide) transistors, the latter generally not withstanding temperatures exceeding 150°C. This electronics layer can then be referred to as the sensitive layer 3', comprising at least one sensitive structure, the sensitive structure corresponding, for example, to a thin-film transistor.

[0072] Interconnections between the electronic layer 3' and the emitting layer 2 are typically present. Such an assembly allows for the creation of so-called "smart LEDs." A smart LED typically comprises an optically active structure connected to dedicated driver electronics, based on transistors.

[0073] There Figure 1A This illustrates the first part of the optoelectronic device, which, stacked along the z-axis, comprises a substrate 1, for example silicon-based, an emitting layer 2, for example GaN-based, and a temperature-sensitive conversion layer 3. figure 1B illustrates in an alternative a first part of the optoelectronic device comprising, in stacking along z, a substrate 1 carrying an electronic layer 3' comprising temperature-sensitive or non-temperature-sensitive transistors 34, an emitting layer 2, and a temperature-sensitive conversion layer 3.

[0074] The following steps in manufacturing the optoelectronic device aim to form, by assembly, a transparent support layer on the conversion layer 3.

[0075] As illustrated in the figure 2A first bonding layer 4a is continuously formed on the conversion layer 3. This first bonding layer 4a is based on an inorganic low-temperature bonding material, for example, a metal and / or amorphous silicon or amorphous germanium. The formation of this first bonding layer 4a is carried out at low temperature in order to preserve the structures 31, 32, 33 of the conversion layer 3. An example of low-temperature deposition of amorphous silicon, at temperatures of 75°C and 100°C, is disclosed in the document "Low-temperature deposition of amorphous silicon solar cells," C. Koch et al., Solar Energy Materials and Solar Cells, Volume 68, Issue 2, May 2001, Pages 227-236. This inorganic low-temperature bonding material is typically opaque.During the development of the present invention, it was identified that absorption due to the opacity of the inorganic bonding material is not significant, for example, when dealing with a 10nm thick silicon interface. However, it was found that reflection from the bonding layer drastically reduces the emission from the underlying structures. The solution developed consists of creating openings in the bonding layer, above the emission zones of layers 2 and 3, to specifically avoid unwanted reflections.

[0076] As illustrated in the figure 3 , the first 40a apertures are formed in known ways, typically by lithography and etching, in the first 4a part of the bond layer, above the emission areas S1, S2 of the emission layer 2 and conversion layer 3. Layer 3 is exposed through the first 40a apertures.

[0077] There figure 4Aillustrates a transparent support layer 5 in the form of a glass substrate, having a first face 501 and a second face 502. This transparent support layer 5 is provided independently of the stacking of electronic, emission 2, conversion 3 layers.

[0078] According to a preferred option illustrated in the figure 4BThe transparent support layer 5 is first opacified on one side, for example, by depositing a metallic opaque layer 503 on that side. At this stage, opacification can be carried out without temperature limitations, independently of the rest of the stack of electronic layers, emission layer 2, conversion layer 3. This allows for the implementation of robust opacification processes, with opacification resistant to chemical cleaning treatments or resin removal processes used in photolithography. The opacified transparent support layer 5 can be easily manipulated by automated systems in microelectronics equipment that use optical sensing.

[0079] As illustrated in the figure 5Optionally, a transparent silicon oxide layer 6 can be deposited on the face of the transparent support layer 5 opposite the opaque face 503. Chemically mechanical polishing (CMP) can then be performed to obtain a surface finish suitable for the deposition of a second bonding layer 4b. The second bonding layer 4b is typically based on the same inorganic, low-temperature bonding material as the first bonding layer 4a. For example, it is based on amorphous silicon. The first and second bonding layers 4a and 4b typically have roughness values ​​Ra < 1 nm, preferably Ra < 0.5 nm.

[0080] As illustrated in the figure 6After continuous deposition of the second part 4b of the bonding layer, second apertures 40b are formed in known ways, typically by lithography and etching, within this second part 4b of the bonding layer. Layer 6 is exposed through these second apertures 40b. The second apertures 40b are configured to correspond at least partially, and preferably completely, to the first apertures 40a. Thus, the second apertures 40b have the same shapes and dimensions as the first apertures 40a, with symmetry about the xy plane. This optimizes the subsequent formation of the cavities 40 detailed later on the figure 8 .

[0081] As illustrated in the figure 7, after formation of the first and second parts 4a, 4b of the bonding layer on the stack of electronic layers, emission 2, conversion 3 on the one hand and on the transparent support layer 5 on the other hand, these are placed opposite each other and aligned with each other in order to be assembled.

[0082] There figure 8This illustrates the assembly. The metal-to-metal, amorphous silicon-to-amorphous silicon, or amorphous germanium-to-amorphous germanium assembly between parts 4a and 4b is typically performed at room temperature, for example, using a surface activation bonding process. According to this process, the surfaces of parts 4a and 4b can be activated by bombardment with argon atoms under vacuum before bonding. Such a process is described, for example, in the document "Surface activated bonding of silicon wafers at room temperature, H. Takagi et al., Appl. Phys. Lett. 68, 2222-2224 (1996)." This bonding process can be implemented in EVG®< ComBond®< equipment. Covalent bonds are typically formed between parts 4a and 4b to obtain the bonding layer 4 and the cavities 40.The cavities 40 are positioned directly above the optically active structures corresponding to the emission zones S1 and S2 of the emission layer 2 and the conversion layer 3, between the transparent support layer and the sensitive layer. These cavities 40, located above the optically active structures, allow optical transmission through the bonding layer; that is, they are transparent to the wavelengths emitted by the emission zones S1 and S2. After assembly, the opaque layer on the support layer 5, or the opacified face of the support layer 5, is removed, typically by mechanical trimming and / or chemical polishing, to obtain a transparent support layer 5 for the device. The opaque layer can also be removed by plasma etching or wet etching.

[0083] Thus, after assembly, the optoelectronic device typically comprises, in a z-shaped stacking arrangement: an electronic layer included in a substrate 1 comprising transistors, an emissive layer 2 comprising GaN-based LEDs, a conversion layer 3 comprising color conversion modules 31, 32, 33, a bonding layer 4 comprising cavities 40 above the emission areas S1, S2 of the emission layer 2 and conversion layer 3, a transparent support layer 5.

[0084] Advantageously, during the device's manufacture, the temperature-sensitive color conversion modules 31, 32, and 33 were not exposed to temperatures exceeding 150°C. The color conversion modules 31, 32, and 33 were thus preserved. Advantageously, the cavities 40 are airtight and under vacuum. This prevents the conversion layer 3 from being exposed to a humid or oxidizing atmosphere. The lifespan of the conversion layer 3 is therefore increased.

[0085] Advantageously, the pixels, each comprising, for example, RGB sub-pixels, are separated by cutting to be moved and then fixed to another substrate. The cutting can be done, for example, by mechanical sawing or laser cutting, specifically through the stacking at the assembly of parts 4a, 4b of the bonding layer 4. The cutting will be easier in the present invention than with a bonding layer based on organic glue.

[0086] The invention is not limited to the embodiments described above. The optically active layer 2 may include light-receiving components, such as detectors. The sensitive layer 3 may include any temperature-sensitive structure, in particular structures that thermally degrade above 200°C, or even above 150°C.

[0087] The scope of the present invention is defined by the following claims.

Claims

1. An optoelectronic device comprising as a stack along a z-direction: • at least one emitting layer (2) comprising optically active structures, configured to emit or receive radiation at a wavelength λ, • a bonding layer (4), • a transparent support layer (5), the optoelectronic device further comprising, in the stack along the z-direction, a so-called sensitive layer (3, 3') comprising at least one so-called sensitive structure (31, 32, 33, 34) having a resistance to a temperature lower than a temperature Tmax, the device being characterised in that the bonding layer (4) is based on a low-temperature inorganic adhesive material and in that the bonding layer (4) comprises cavities (40) in vertical alignment with the optically active structures, between the transparent support layer (5) and the emitting layer comprising said optically active structures.

2. The device according to the preceding claim, wherein the temperature Tmax is less than 180°C, preferably less than 150°C.

3. The device according to any one of the preceding claims, wherein the low temperature inorganic adhesive material is opaque.

4. The device according to any one of the preceding claims, wherein the low temperature inorganic adhesive material is based on metal or amorphous silicon or amorphous germanium.

5. The device according to any one of the preceding claims, wherein the cavities (40) have a pressure lower than atmospheric pressure, preferably at least one decade lower than atmospheric pressure.

6. The device according to any one of the preceding claims, wherein the cavities (40) are transparent to the radiation emitted or received by the optically active structures.

7. The device according to any one of the preceding claims, wherein the transparent support layer (5) is glass-based.

8. The device according to any one of the preceding claims, wherein the bonding layer (4) is formed by assembling first and second parts (4a, 4b) of the inorganic adhesive material, respectively deposited onto the sensitive layer (3) and onto a face of the transparent support layer (5).

9. The device according to any one of the preceding claims, wherein said emitting layer (2) comprising the optically active structures is based on GaN or GaAs.

10. The device according to any one of the preceding claims, wherein the optically active structures are light-emitting diodes and wherein the so-called sensitive layer (3) is arranged between the emitting layer (2) and the bonding layer (4), said at least one sensitive structure (31, 32, 33) is a colour converter module.

11. The device according to any one of claims 1 to 9, wherein the optically active structures are light-emitting diodes and wherein the so-called sensitive layer (3') is carried by a substrate (1) arranged under the emitting layer (2) comprising the optically active structures, on the side opposite to the bonding layer (4), said at least one sensitive structure being a transistor (34), preferably a thin-film transistor.

12. The device according to any one of claims 1 to 9, wherein the optically active structures are light-emitting diodes, the device comprising a first so-called sensitive layer (3) arranged between the emitting layer (2) and the bonding layer (4), and a second so-called sensitive layer (3') arranged between a substrate (1) and the emitting layer (2) comprising the optically active structures, on the side opposite the bonding layer (4), the first sensitive layer (3) comprising at least one first sensitive structure such as a colour converter module, the second sensitive layer (3') comprising at least one second sensitive structure such as a transistor, preferably a thin-film transistor.

13. A method for manufacturing an optoelectronic device according to any one of claims 1 to 12, said method comprising at least the following steps of: • providing a stack comprising at least one emitting layer (2) comprising optically active structures, configured to emit or receive radiation at a wavelength λ, and at least one so-called sensitive layer (3, 3') comprising so-called sensitive structures (31, 32, 33, 34) having a resistance to a temperature lower than a temperature Tmax, • forming, on the stack, a first part (4a) of bonding layer based on a low-temperature inorganic adhesive material, said first part (4a) including first openings (40a) in vertical alignment with the optically active structures, • providing a transparent support layer (5), • forming, on a first face (501) of the transparent support layer (5), a second part (4b) of bonding layer based on the low-temperature inorganic adhesive material, said second part (4b) including second openings (40b) configured to be matched with said first openings (40a), • facing the second part (4b) of bonding layer with the first part (4a) of bonding layer, • assembling the stack comprising the sensitive layer (3, 3') with the transparent support layer (5) by low-temperature adhering between the first and second parts (4a, 4b) of bonding layer, the first and second openings (40a, 40b) thereby forming cavities (40) in vertical alignment with the optically active structures.

14. The method according to the preceding claim, wherein the first part (4a) of bonding layer is first continuously formed on the sensitive layer (3) of the stack, and then the first openings (40a) are formed in the first part (4a) of bonding layer.

15. The method according to one of claims 13 or 14, wherein the second part (4b) of bonding layer is first continuously formed on the first face (501) of the transparent support layer (5), and then the second openings (40b) are formed in the second part (4b) of bonding layer.

16. The method according to any one of claims 13 to 15, further comprising opacifying a second face (502) of the transparent support layer (5) before facing the first and second parts (4a, 4b) of the bonding layer with each other, and removing the second opacified face (503) after assembling the stack comprising the sensitive layer (3, 3') with the transparent support layer (5).

17. The method according to any one of claims 13 to 16, wherein assembling by low-temperature adhering is carried out under a pressure Pc lower than the atmospheric pressure Patm, preferably such as Pc ≤ 10-3.Patm, and preferably such as Pc ≤ 10-8.Patm.

18. The method according to any one of claims 13 to 17, wherein the low-temperature inorganic adhesive material is chosen based on metal or amorphous silicon or amorphous germanium.