FR3055944A1 - LUMINOUS CONVERSION FOR A HIGH RESOLUTION LIGHT SOURCE - Google Patents

Abstract

In particular, the invention relates to a light module comprising a semiconductor material serving as an electroluminescent source, a layer covering the semiconductor material that modifies the spectrum of the light emitted by the semiconductor material, the layer having a thickness less than 100 μm.

Description

FIELD OF THE INVENTION

The invention relates to the field of land vehicle light modules, that is to say modules which can be integrated into a vehicle light device and which make it possible, when the vehicle is in use, to project light illuminating the road or interior and / or allowing the vehicle to make itself more visible. Examples of such luminous devices are the position lights or the dipped beam and / or main beam headlights (commonly called “headlights”).

BACKGROUND

A land vehicle is fitted with light devices, in particular lighting and / or signaling devices, such as front headlights or rear lights, intended to illuminate the road in front of the vehicle, at night or in the event of reduced light. They can also be used to illuminate the passenger compartment of the vehicle. These light devices can include one or more light modules. Each lighting function can be provided by one or more modules.

In these light modules of land vehicles, electroluminescent light sources are increasingly used. These light sources can be constituted by light-emitting diodes or LEDs (acronym for “Light Emitting Diode”), by organic light-emitting diodes or OLEDs (acronyms for “organic lightemitting diodes”, or by polymeric light-emitting diodes or PLED ( English acronyms for "polymer light-emitting diodes").

Monolithic electroluminescent light sources have recently become known; for example a solid state monolithic light source (also known as a "monolithic array of LEDs", translation of the English expression "monolithic array of LEDs"). A monolithic light source comprises hundreds or thousands of LEDs which are located on the same substrate, the LEDs being separated from the others by lines (or “lanes” in English) or streets (or “streets” in English ). In this context, LEDs are also called pixels. These light sources are said to have a high density of LEDs because the number of pixels is large, by several hundred LEDs per cm ² . Each of the LEDs is electrically independent of the others and therefore lights up autonomously from the other LEDs in the array. Thus, each LED of the matrix is controlled individually by the electronic circuit which manages its electrical supply (circuit called "driver" in English).

In these light modules of land vehicles, a phosphor substance is present in the form of a layer deposited on the surface of the light source. The purpose of this layer is to convert the wavelength of the light emitted, for example blue light (with a wavelength between 400 and 480 nanometer (nm) emitted by the LEDs is transformed into white light. deposited layer can be a phosphor layer.

However, the materials used today for the conversion of the light emitted by the light source are not suitable for monolithic light sources. Indeed, the LED dimensions of these monolithic sources are very significantly reduced in order to accommodate a very large number of LEDs per unit area, and the reduction in the dimensions of the LEDs makes the conversion materials used inoperative. In addition, the large number of LEDs causes a phenomenon of crosstalk (called in English “cross talk”) which disturbs the emission of light: the light emitted by an electroluminescent element interferes with at least the light emitted by the electroluminescent elements of its neighborhood. In other words, the phosphors used today do not allow the light emitted to be properly converted while retaining the pixelation of the light beam created by a monolithic source.

SUMMARY OF THE INVENTION

For this, a light module is proposed comprising a semiconductor material serving as an electroluminescent source, a layer covering the semiconductor material which modifies the spectrum of the light emitted by the semiconductor material, the layer having a thickness of less than 100 μm.

According to different embodiments, the light module can comprise one or more of the following characteristics combined together:

the layer covering the semiconductor material comprises particles which modify the spectrum of the light emitted by the semiconductor material;

- The particles have a diameter which is less than a value between 1 and 5 μm;

the layer covering the semiconductor material has a thickness of between 5 and 20 μm;

- the particles are luminophoric particles;

- particles are quantum dots;

- the layer is a yeast and aluminum garnet crystal;

- the semiconductor material serving as an electroluminescent source is a monolithic matrix of electroluminescent elements;

- the light-emitting elements are light-emitting diodes;

- the density of electroluminescent elements is equal to or greater than 2500 electroluminescent elements per cm ² ;

- the spectrum of the light emitted by the semiconductor material is modified to produce white light.

A light device, in particular for lighting and / or signaling, preferably for a land vehicle, is also proposed, comprising the above light module.

BRIEF DESCRIPTION OF THE FIGURES

Different embodiments of the invention will now be described, by way of non-limiting examples, with reference to the appended drawings in which:

FIG. 1 schematically shows an example of a monolithic electroluminescent source with high pixel density;

Figures 2 to 4 schematically shows examples of light modules; and

FIG. 5 shows an example of a layer capable of covering a light source;

Figures 6 and 7 schematically show other example light modules.

DETAILED DESCRIPTION

The light module comprises a semiconductor material serving as an electroluminescent source. The light module therefore comprises an electroluminescent light source. The light-emitting source comprises light-emitting elements, which can have millimeter or even submillimeter dimensions. The source further comprises a substrate on which the electroluminescent elements are epitaxied. The electroluminescent elements use electroluminescence to emit light. Electroluminescence is an optical and electrical phenomenon during which a material emits light in response to an electric current passing through it, or to a strong electric field. This is to be distinguished from the emission of light due to the temperature (incandescence) or the action of chemicals (chemiluminescence).

The electroluminescent source can be a monolithic electroluminescent source which is a light emitting light source generally comprising a high number of electroluminescent elements. An example of a monolithic electroluminescent source is a monolithic array of LEDs (translation of the English expression "monolithic array of LEDs"). The electroluminescent elements are located on the same substrate, and preferably on the same face of the substrate which may for example be sapphire. The electroluminescent elements are deposited on or extending from at least one face of the substrate. The electroluminescent elements of the monolithic matrix are separated from each other by lines (called "lanes" in English or streets (called "streets" in English). These lines or streets are spaces, in principle empty of matter, separating the electroluminescent elements. The monolithic electroluminescent source forms a grid of electroluminescent elements or a matrix of electroluminescent elements. Each of the electroluminescent elements of the monolithic electroluminescent source is electrically independent of the others and emits or not light independently of the other elements of The matrix. Each element of the matrix is controlled individually by an electronic circuit called "driver" in English. The driver manages the power supply of the monolithic matrix, which amounts to saying that it manages the power supply of each electroluminescent element. Alternatively, electroluminescent elements can be grouped electrically, for example by supplying them electrically using a parallel or series connection, in order to reduce the number of elements to be managed. For example, the groups can comprise between two and four electroluminescent elements, this number making it possible to maintain a sufficiently pixelated light beam. The driver is therefore an electronic device which is capable of controlling the elements of a monolithic matrix of electroluminescent elements. Several drivers can be used to drive the electroluminescent elements of the matrix.

A light emitting element may be, but is not limited to, a light emitting diode (LED), an organic light emitting diode (OLED), a polymer light emitting diode (PLED). The electroluminescent source is therefore a semiconductor light and it comprises a substrate from which the electroluminescent elements are placed. An electroluminescent element is more generally called a pixel. Consequently, the light source comprises a plurality of pixels deposited on or extending from the first face of the substrate. Pixels (i.e., electroluminescent elements) emit light when the semiconductor material is supplied with electricity. We can therefore speak of a lit pixel when an electroluminescent element emits light.

The monolithic electroluminescent source is a light source with a high density of light elements, that is to say that it comprises a very large number of electroluminescent elements. By very high number, it is meant that the substrate of the light source comprises at least 500 electroluminescent elements on the same substrate. For example, if the pixels are less than 100 µm (micrometers) in size and the pitch is 200 µm, then the pixel density is 2,500 electroluminescent elements per square centimeter (cm ² ).

The pixel density of a high density monolithic electroluminescent source is preferably greater than 2500 pixels per cm ² , that is to say that the pitch is equal to or less than 200 μm.

FIG. 1 shows a top view of an example of a monolithic electroluminescent source 100 with high density of electroluminescent elements. FIG. 2 shows part of the side view of the example in FIG. 1. The electroluminescent elements 102 have been deposited on a substrate 110, for example sapphire. The electroluminescent elements 102 are in these examples LEDs. The LEDs have been placed so that they form a grid of LEDs also called an LED array. The LEDs are separated by straight lines or streets arranged vertically 104a and horizontally 104b. The regular pattern thus formed is perfectly integrated into the current manufacturing processes of electroluminescent light sources.

Still in the examples of FIGS. 1 and 2, the LEDs have a (substantially) square shape and have a dimension of 40 μm. It is understood that any shape can be envisaged, for example the pixels have a rectangular shape. This dimension relates to one of the sides of the square 106. The lines / streets 104a, 104b have any width of 10 μm. The pitch 108 between the LEDs is therefore 50 μm. The pitch is the distance between the center of a first pixel and the center of a second pixel near the first; this distance is also called "pixel pitch" in English. The pitch therefore depends on the size of the pixels and the width of the lines / streets. The electroluminescent elements 102 also have a height 109 which depends on the technology used for their manufacture. The height of an electroluminescent element is measured from the surface of the substrate on which the electroluminescent element is deposited or extends. For example, the LEDs can have a height of 100 µm. In practice, all LEDs have dimensions which are equal or substantially equal; the same for all lines / streets.

It is understood that LEDs can have other shapes, depending on the technology used for their manufacture. In this case the definition of the term dimension may vary. For example, if the LEDs have a rectangular shape, we can conventionally decide that the dimension of an LED is the distance from the shortest side of the rectangle.

The electroluminescent elements are each semiconductor, that is to say that they each comprise at least one semiconductor material. The light-emitting elements can be predominantly made of semiconductor material. This semiconductor material can be the same as or different from the semiconductor material of the substrate. The electroluminescent elements can more generally be all made of the same material or materials. The electroluminescent elements can be of the same nature, for example substantially identical or similar. All the electroluminescent elements can be positioned to form a regular pattern, for example a grid.

The light module can include one or more monolithic electroluminescent sources. Several light modules comprising such a monolithic electroluminescent source can be integrated into the light device according to the invention. The term “light module” therefore designates at least one monolithic electroluminescent source.

The light module further comprises a layer covering the semiconductor material. This layer modifies the spectrum of the light emitted by the semiconductor material. The spectrum is defined by a continuum of wavelengths, and the layer therefore modifies the wavelengths of the electromagnetic radiation forming the spectrum of the emitted light. Covering means that the layer is arranged relative to the semiconductor material so that the light it emits passes through the layer. The latter can be in contact with at least the surface of the semiconductor material through which the light produced by the semiconductor material escapes. Alternatively, a third material can serve as an interface between the layer and the surface of the semiconductor material through which the light produced by the semiconductor material escapes; this third material can be silicone which is a polymer. FIG. 2 shows a first example in which each electroluminescent element is individually covered by the layer 120. More precisely, the layer is in contact with the surface of the electroluminescent element through which the photons emitted by the semiconductor material escape . The path of the emitted photons is represented by the dotted arrows.

FIG. 3 shows a second example in which the covering of the electroluminescent elements by the layer 120 is no longer individual. More precisely, a single layer is in contact with the surfaces of the electroluminescent elements through which the photons emitted by the semiconductor material escape. The path of the photons is represented by the dotted arrows. In this example, the layer does not come into contact with the surfaces of the electroluminescent elements which lie against the lines / streets. Depending on the technology used, the lines / streets 104a can be partially or completely filled by the layer.

FIG. 4 shows a third example in which the covering of the electroluminescent elements by the layer 120 is not individual. It differs from that of FIG. 3 by the fact that the layer was slightly inserted during its deposition in the lines / streets 104a so that the surface of the layer 120 has slight indentations at the level of the lines or streets.

The layer is on the path of the photons emitted by the electroluminescent elements: the photons pass through the layer so that the spectrum of the emitted light is modified and that it produces white light. The spectrum of the light emitted by the semiconductor material is defined by a wavelength continuum which is modified by the layer which also produces a wavelength continuum. The light produced by the layer is white light, that is to say that the wavelengths of the spectrum are substantially between 380 and 700 nm. White light is obtained by additive synthesis, which implies that the layer does not modify certain wavelengths in the spectrum of the light emitted by the semiconductor material. Or in other words, the layer does not absorb all the light emitted by the light source. For example, blue light is not converted by the layer so that the yellow light produced by the layer, when added with blue light, produces substantially white light.

The layer covering the semiconductor material has a thickness 122 which is less than 100 µm. The thickness of the layer is substantially the same for the electroluminescent elements; variations in thickness may locally occur, for structural reasons as for example explained in FIG. 4 or also for reasons of the manufacturing process. In all cases, the thickness is not more than 100 µm. A thickness of less than 100 μm gives the layer a form factor which is favorable for extracting light and transforming the light spectrum of a light source with a high density of electroluminescent elements, and in particular when the density of electroluminescent elements by surface unit is equal to or greater than 2500 pixels per cm ² . The form factor that can be considered is the ratio between the thickness 122 of the layer and the pitch 108 of the latter. This ratio is preferably less than or equal to 1, that is to say the thickness of the layer is less than or equal to the pitch of the pixel.

The layer covering the semiconductor material may comprise particles which modify the spectrum of the light emitted by the semiconductor material. In this case, the layer comprises said particles and a binder which makes it possible to agglomerate the electroluminescent elements on the semiconductor material. Preferably, the selected binder must have physicochemical characteristics enabling it to resist the energy transmitted in the form of heat emitted by the electroluminescent elements, the irradiation produced by the photons of the light emitted over a range of lengths d wave which covers all or part of the ultraviolet and / or visible light and / or infrared. In addition, the physico-chemical characteristics of the binder must favor the passage of light, that is to say favor the passage of light flux. The composition of the binder can be, but is not limited to, a silicone resin, a fluorinated resin, epoxy, etc.

The binder does not affect, as far as possible, the passage of light and it is the particles which modify the wavelengths of the spectrum of the emitted light. The particle sizes have a diameter which is less than 30 µm. In this way, it is possible to ensure that the layer with a thickness of 100 μm puisseο can comprise at least three sublayers of particles, said at least three sublayers being arranged one on the other. The term sublayer defines particles arranged one against the other on a plane of space (for example the plane determined by the emissive surfaces of the electroluminescent elements), or else adjacent to one another with a distance separating them less than to their diameter. Such a configuration makes it possible to maximize the amount of light whose spectrum is modified. The particles preferably have a general spherical shape, it being understood that any other shape can be envisaged. In the latter case, the maximum edge-to-edge distance is 100 µm.

The particles preferably have a diameter which is less than a value between 1 and 5 micrometers (pm), limits included. This particle size is particularly suitable for high density light sources of electroluminescent elements which have dimensions less than or equal to 200 μm. Indeed, a sufficient density of particles is thus obtained in the layer covering the semiconductor material to modify the spectrum of the light emitted, while reducing the total thickness of the layer. Thus, the thickness of the layer can be between 5 and 20 μm, providing a form factor which is favorable for transforming the spectrum of the light emitted.

It is understood that the diameter of the particles can be less than 1 μm, and that the thickness of the layer can be less and between lOOnm and lOpm.

FIG. 5 illustrates an example of a layer covering the semiconductor material (not shown) which comprises three sublayers of particles arranged one on the other.

The layer can comprise any material making it possible to transform the spectrum of light. For example, the layer can be a single crystal of ytrium garnet and aluminum (“Single crystal YAG” in English) which is a luminophore particularly suitable for transforming the light spectrum of LEDs into InGaN which emit blue light .

The layer can comprise particles selected from luminophoric particles which can be, for example, nanoparticles from Yttrium Aluminum garnets, quantum dots. Interestingly, the quantum dots make it possible to optimize parameters such as the absorption and / or emission spectrum of light. Their size is preferably between 1 and 10 nm, limits included, for emitting white light.

FIG. 6 schematically shows an example of a light module of a motor vehicle. The light module 10 comprises a high density monolithic electroluminescent source 12 on which a layer deposited on the semiconductor material like that discussed for example with reference to FIGS. 1 to 5, a PCB 14 which supports the source 12 and a device 19 which controls the electroluminescent elements of the monolithic light source 12. Any support other than a PCB can be envisaged. The light module can also comprise at least one heat sink 18 which can be arranged directly or indirectly on the source 12. In this example, the heat sink 18 is arranged indirectly on the source since the PCB 14 and a thermal interface 16 are located between the heat sink 18 and the source 12. The heat sink allows the transfer of heat from the light emitting source that the latter transmits to the PCB when using a light module. The heat sink allows heat dissipation via cooperation with the support 14 of the monolithic electroluminescent source, that is to say that the heat sink receives the heat produced by the electroluminescent source. The heat sink 18 is thus in heat communication with the PCB 14 which is itself in heat communication with the source 12. The transmission can be ensured by the fact that the heat sink is in one example arranged directly against the PCB 14. This means that the heat sink is in physical contact (ie material) with the interposer. The heat sink 18 can however be alternately arranged on the interposer via an intermediate element which improves the heat transfer. This intermediate element is also called the thermal interface 16. The intermediate element 16 may for example include thermal paste or a phase change material. The intermediate element may include copper, for example the thermal interface 16 is a copper plate.

The module according to the invention can comprise a high density monolithic electroluminescent source of electroluminescent elements called “3D” electroluminescent source, that is to say that the electroluminescent elements are not only deposited on the substrate of the source: they extend from the source substrate. Items can be grouped into one or more sets. Each assembly consists of several elements extending from a respective portion of the first face of the substrate. The electroluminescent elements can therefore be distributed in different light emission zones. In one example, these different zones can be selectively activatable. The elements may have a general shape of a stick and thus be called “sticks”. The electroluminescent elements can be supplied with electricity via the substrate on one side (eg the substrate forming for example the cathode) and via a layer of electrically conductive material which electrically binds the electroluminescent elements together on the other side (eg the layer of electrically conductive material forming for example the anode). The contact between the semiconductor material of each electroluminescent element and the semiconductor material of the substrate can therefore be adapted to an electrical conduction. The layer of electrically conductive material can cover the electroluminescent elements. The layer of electrically conductive material can also cover each surface portion of the substrate from which the light emitting elements extend, or an entire surface or face of the substrate from which the sets of light emitting elements extend. The layer of electrically conductive material can be electrically isolated from the semiconductor material of the substrate by any means. This allows the electroluminescent elements to be supplied with electricity by the substrate. Thus, the electroluminescent elements can be supplied with electricity simply, that is to say by supplying the conductive material of the substrate with one polarity and the layer of electrically conductive material with the other polarity.

The “3D” light-emitting source can be manufactured by a method comprising at least one step of supplying the substrate, then a step of integrally forming the rods with the substrate, by growth from the substrate. The layer of electrically conductive material can be produced by a step of depositing a metal finish, for example copper, to ensure the control of the rods. This step can also include the creation of aluminum or copper pads on one face of the substrate, suitable for wire wiring between the source and the control component. Wiring by wire or "bridging" (also called "wirebonding" or "wire bonding" in English or ribbon bonding ...) is one of the techniques used to make the electrical connections between the electroluminescent source and the device. source feed. The wiring is simply carried out by a wire (or bridge) welded between the two connection pads provided for this purpose on each of the elements. Welding can be carried out by ultrasound. The wire material can be aluminum, gold or copper. The wire diameter can be of the order of 20 µm. A wire of rectangular section can also be used.

FIG. 7 shows an example of such a monolithic electroluminescent light source called "3D". The light source S, here represented in section, comprises a substrate 210 from which rods 211, 212 extend in a preferred direction. This substrate 210 is, in particular in this example, silicon, which represents a much lower cost. to that of conventional LEDs, in which the substrates are made of sapphire. The rods 211, 212 can be obtained by crystal growth on this substrate 210.

The rods 211, 212 are arranged so as to form rods of an electroluminescent semiconductor material. The rods 211, 212, for example can be formed essentially of gallium nitride.

For example, these rods 211, 212 include a core of semiconductor material capable of being doped with electrons, around which is formed a first layer of semiconductor material capable of exhibiting electron deficits, in this case we speak sometimes of layer doped in “holes” or in positive charges. At the interface of this core and this first layer, an intermediate layer is formed in which the electrons and the electron deficits are recombined. Thus, each rod 211, 212, is an electroluminescent semiconductor element.

A nucleation layer 219 is formed on the substrate 210 and around the rods 211, 212.

The rods 211, 212 are here spaced about 30 μm apart and each have a height, taken from the nucleation layer 219 to their apex, of 2.5 μm. Their diameter is 1.5 µm.

The light source S therefore essentially comprises a substrate 210 forming a plate bristling with a multitude of small rods 211, 212, electroluminescent and submillimetric, namely whose largest dimension is less than a millimeter.

The light source S is divided into several light zones 201, 202 separated by walls 221, corresponding to a distribution of all the rods 211, 212.

Between each rod 211, 212 of the same zone 201, 202 is deposited an electrically conductive layer, electrically joining these rods, thus forming a separate anode 225, 226, for each of the light zones 201, 202.

The four anodes 225, 226, thus formed are in contact with the nucleation layer 219, which itself is in contact with the cathode formed by the substrate 210.

Thus, by connecting the anodes 225, 226 and the cathode 210 to a power source, it is possible to supply electricity independently to each of the different light zones 201, 202.

According to one embodiment, each anode is connected to one or more positive terminals of a connection means 220, intended to be connected to the positive terminal of an electrical power source (not shown) of a vehicle. Likewise, the cathode 210 is connected to the negative terminal of the connection means 220. The activation means therefore allows the electrical supply of each of these light zones 201, 202.

It is therefore possible to control this light source S, by selective activation of its light zones 201, 202, via the activation means 220.

Piloting can be carried out by a specific means distinct from the light device, or else, as in this example produced by a piloting device 229 integrated into the light device.

In this example, the control is carried out directly by a control device 229. The latter is connected on the one hand to the connection means 220 and on the other hand to the connector C. the connection means 220 is itself connected to each anode 225 , 226, via electrical conductors.

The control device 229 and the light source S are mounted on the same printed circuit board, not shown. The electrical conductors are formed by electronic tracks on this printed circuit board. Similarly, other electronic tracks connect the connection means 220 to the control device 229.

The light efficiency of the light zones 201, 202 can be improved by depositing a reflective layer 217, 218 on the nucleation layer 219. This reflective layer 217, 218 is for example deposited on the nucleation layer 219 before growth of the sticks, then holes are provided in this reflective layer 217, 218, as well as in the nucleation layer, before growth of the rods 211, 212, 213, 214, on the substrate 10.

To have a better light output, the sticks of the light zones can have the characteristics below:

- a diameter between 1.4 pm and 1.6 pm, for example 1 pm,

- a height of between 2 pm and 10 pm, for example 8 pm,

- a distance between each stick of between 3 and 10 μm.

The light source S comprises a layer 223 which is a light spectrum converter arranged above the rods 211, 212. The material of the layer can for example be YAG doped with cerium or europium. The thickness of the layer is less than 100 µm; for example, the layer is 5 µm thick and includes phosphor particles 1 µm in diameter.

Claims (12)

1. Light module comprising: - a semiconductor material serving as an electroluminescent source; a layer covering the semiconductor material which modifies the spectrum of the light emitted by the semiconductor material, the layer having a thickness of less than 100 μm. 2. The light module as claimed in claim 1, in which the layer covering the semiconductor material comprises particles which modify the spectrum of the light emitted by the semiconductor material. 3. Light module according to claim 2, wherein the particles have a diameter which is less than a value between 1 and 5 pm. 4. Light module according to claim 3, wherein the layer covering the semiconductor material has a thickness between 5 and 20 pm. 5. Light module according to one of claims 2 to 4, wherein the particles are phosphor particles. 6. Light module according to one of claims 2 to 4, wherein the particles are quantum dots. 7. Light module according to claim 1, in which the layer is an ytrium aluminum garnet crystal. 8. Light module according to one of claims 1 to 7, wherein the semiconductor material serving as an electroluminescent source is a monolithic matrix of electroluminescent elements. 9. Light module according to claim 8, wherein the light emitting elements are light emitting diodes. 10. Light module according to one of claims 8 to 9, in which the density 5 of electroluminescent elements is equal to or greater than 2500 electroluminescent elements per cm ² . 11. Light module according to one of claims 1 to 10, in which the spectrum of the light emitted by the semiconductor material is modified to produce 10 white light. 12. A light device, in particular for lighting and / or signaling, preferably of a land vehicle, comprising a light module according to one of claims 1-11. 1/3 100 122 106