CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. National Phase Application under 35 U.S.C. § 371 of International Patent Application No. PCT/EP2019/067237, filed Jun. 27, 2019, which claims priority of French Patent Application No. 18 55855, filed Jun. 28, 2018. The entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention concerns an emitting device. The present invention also concerns a display screen comprising a set of such emitting devices and a method for fabricating such an emitting device.

BACKGROUND OF THE INVENTION

Display screens often comprise a set of “picture elements”, also called “pixels”, that are each able to emit light, so that the image on the screen may be controlled by turning on or off the individual pixels. In color screens, each pixel comprises several sub-pixels, each sub-pixel being configured to emit a specific color, so that the color emitted by the pixel may be tuned by controlling which sub-pixel(s) is or are turned on or by tuning the electrical current applied to each sub-pixel in order to change the relative emission intensity of each sub-pixel.

Semiconducting structures such as Light-Emitting Diodes (LED) are commonly used for varying purposes such as lighting due to their potential good light-emission efficiency. Because of this potential high efficiency, LEDs have been suggested for making high-efficiency display screens.

LED structures usually take the shape of a stack of planar semiconducting layers. Light is emitted when an electrical current flows through the stack. However, although some technologies and materials for making LED structures allow for a good emission efficiency over one part specific of the visible spectrum, for example in the blue range, the same technologies usually lead to much lower efficiencies when used for making an LED structure emitting over a different part of the spectrum. Fabricating pixels wherein each sub-pixel has a LED structure emitting in a different part of the visible spectrum than the other sub-pixels is thus difficult and may notably require using different types of materials for each sub-pixel.

According to one way of obtaining the sub-pixels, radiation converters are placed onto the surface of the LED structure in order to convert the light emitted by the portion of the structure underneath the converter into a light having a different wavelength from the light originally emitted by the layer. Thus, working sub-pixels may be obtained by placing over specific areas of the LED structure different radiation converters so that by selectively supplying the area underneath each different converter with electrical current, the light emitted by the semiconducting layer or layers is converted into a light having a specific color.

However, during the placement step, the position of the radiation converters is difficult to control. For example, if the radiation converters are particles contained in photosensitive resins and deposited using photolithography, part of the insolation light is scattered by the particles and may end up insolating some undesired part of the resin. Even using other techniques, when two radiation converters are to be placed next to each other, some intermixing may occur and result in the color of the sub-pixel being different from the expected color. Such effects are all the stronger as the spatial pitch between the pixels decreases.

SUMMARY OF THE INVENTION

In consequence, there is a need for an emitting device, notably a pixel, that has small-dimensioned sub-pixels, while permitting a good control of the wavelength of the light emitted by each sub-pixel.

For this, the present description concerns an emitting device comprising:a first light emitter, the first light emitter being adapted to emit a first radiation, anda second light emitter, the second light emitter being adapted to emit a second radiation, the second radiation being different from the first radiation,

the first light emitter comprising a first semiconducting structure and a first radiation converter, the second light emitter comprising a second semiconducting structure and a second radiation converter, each semiconducting structure comprising a semiconducting layer adapted to emit a third radiation different from the first radiation and the second radiation, each radiation converter comprising a set of particles, each particle being able to convert the third radiation into the first or second radiation emitted by the corresponding light emitter, the particles of the first radiation converter being attached by a bulk of photosensitive resin to a surface of the first light emitter, such as a surface of the first semiconducting structure, and the particles of the second radiation converter being attached by grafting to a surface of the second light emitter, such as a surface of the second semiconducting structure.

According to specific embodiments, the emitting device comprises one or several of the following features, taken separately or according to any possible combination:the second radiation converter comprises a stack of at least one layer of particles and at least one grafting layer of organic molecules, the layer of particles being attached to a surface of the second light emitter by the grafting layer.a mean wavelength of the second radiation is strictly inferior to a mean wavelength of the first radiation.the emitting device comprises at least one third emitter, the third light emitter being adapted to emit a fourth radiation, the fourth radiation being different from the first radiation and the second radiation, the third light emitter comprising at least one third semiconducting structure, the third semiconducting structure comprising a third semiconducting layer, the third semiconducting layer being adapted to emit the fourth radiation.the emitting device comprises at least one fourth light emitter, the fourth light emitter being adapted to emit a fifth radiation, the fifth radiation being different from the first radiation and the second radiation, the fourth light emitter comprising a fourth semiconducting structure and a fourth radiation converter, the fourth semiconducting structure comprising a semiconducting layer adapted to emit a third radiation different from the fifth radiation, the radiation converter of the fourth light emitter comprising a set of particles, each particle being able to convert the third radiation into the fifth radiation.the emitting device comprises at least one at least one wall able to prevent a radiation emitted by one light emitter from reaching another light emitter.

The present description also concerns a method for fabricating an emitting device comprisinga first light emitter, the first light emitter being adapted to emit a first radiation, anda second light emitter, the second light emitter being adapted to emit a second radiation, the second radiation being different from the first radiation,

the method comprising steps for:fabricating at least one first semiconducting structure and at least one second semiconducting structure, the first semiconducting structure comprising a first semiconducting layer, the second semiconducting structure comprising a second semiconducting layer, each first and second semiconducting layer being adapted to emit a third radiation different from the first radiation and the second radiation,positioning, onto a surface of the first light emitter, a bulk of photosensitive resin comprising particles able to convert the third radiation of the first semiconducting layer into the first radiation,depositing, onto to a surface of the second light emitter, a grafting layer, anddepositing, onto the grafting layer, a layer of particles able to convert the third radiation of the second semiconducting layer into the second radiation, each particle being attached to the surface of the second light emitter by the grafting layer.

The present description also concerns an emitting device comprising:a first light emitter, the first light emitter being adapted to emit a first radiation, the first light emitter comprising at least one first semiconducting structure, the first semiconducting structure comprising a first semiconducting layer, the first semiconducting layer being adapted to emit a second radiation, andat least one second light emitter, each second light emitter being adapted to emit a third radiation, the third radiation being different from the first radiation, the second light emitter comprising at least one second semiconducting structure, the second semiconducting structure comprising a second semiconducting layer adapted to emit a fourth radiation,

each light emitter further comprising a radiation converter, each radiation converter comprising a mixture of first particles and second particles, each first particle being able to convert the second radiation into the first radiation, each second particle being able to convert the fourth radiation into the third radiation.

According to specific embodiments, the emitting device comprises one or several of the following features, taken separately or according to any possible combination:each first particle is transparent to the second radiation and each second particle is transparent to the fourth radiation.at least one of the following properties is verified:the mixture of first particles and second particles is embedded in a photosensitive resin,the mixture of first particles and second particles is attached to a surface of the first and second light emitters by grafting, andone radiation among the second radiation and the fourth radiation is an ultraviolet radiation, the other radiation among the second radiation and the fourth radiation being a blue radiation.

The present description also concerns a method for fabricating an emitting device comprising a first light emitter and at least one second light emitter, the first light emitter being adapted to emit a first radiation, each second light emitter being adapted to emit a third radiation, the third radiation being different from the first radiation, the method comprising steps for:providing at least one first semiconducting structure and at least one second semiconducting structure, the first semiconducting structure comprising a first semiconducting layer, the first semiconducting layer being adapted to emit a second radiation, the second semiconducting structure comprising a second semiconducting layer adapted to emit a fourth radiation, anddepositing a mixture of first particles and second particles, each first particle being able to convert the second radiation into the first radiation, each second particle being able to convert the fourth radiation into the third radiation.

According to a specific embodiment, at least one of the following properties is verified:the step for depositing comprises depositing a bulk of resin comprising the mixture onto each of the first and second semiconducting structure, andthe step for depositing comprises depositing a grafting layer onto a surface of the first and second light emitters and depositing the mixture onto the grafting layer, each particle of the mixture being attached to the respective surface of each of first and second light emitters by the grafting layer.

A display screen comprising a set of emitting devices as previously defined is also proposed.

