US-12622122-B2 - Process of making monolithic RGB micro LED display using down converting macromolecules

US12622122B2US 12622122 B2US12622122 B2US 12622122B2US-12622122-B2

Abstract

A method of forming a multicolour light emitting array, the method comprising: providing a first light emitting device configured to emit light with a first primary peak wavelength and a second light emitting device configured to emit light with the first primary peak wavelength; forming a colour conversion region at least partially associated with the first light emitting device and the second light emitting device, wherein the colour conversion region is configured to absorb light with the first primary peak wavelength and emit light with a second primary peak wavelength longer than the first primary peak wavelength; and photo-bleaching a portion of the colour conversion region associated with the first light emitting device such that the colour conversion region associated with the first light emitting device is at least partially transparent to light with the first primary peak wavelength, thereby to enable light with the first primary peak wavelength to be emitted by a first pixel associated with the first light emitting device and light with the second primary peak wavelength to be emitted by a second pixel associated with the second light emitting device.

Inventors

Samir Mezouari
Geoff Dumas

Assignees

PLESSEY SEMICONDUCTORS LTD

Dates

Publication Date: 20260505
Application Date: 20211108
Priority Date: 20201113

Claims (11)

1 . A method of forming a multicolor light emitting array, the method comprising: providing a first light emitting device configured to emit light with a first primary peak wavelength and a second light emitting device configured to emit light with the first primary peak wavelength and a third light emitting device configured to emit light with the first primary peak wavelength; forming a color conversion region on the first second and third light emitting devices, wherein the color conversion region is configured to absorb light with the first primary peak wavelength and emit light with a second primary peak wavelength longer than the first primary peak wavelength; masking a portion of the color conversion region on the third light emitting device, and photo-bleaching a portion of the color conversion region on the first light emitting device and the second light emitting device such that the color conversion region on the first light emitting device and the second light emitting device is at least partially transparent to light with the first primary peak wavelength; subsequently forming a further color conversion region on the color conversion region, wherein the further color conversion region is at least partially transparent to light with the second primary peak wavelength, and configured to absorb light with the first primary peak wavelength and emit light with a third primary peak wavelength longer than the first primary peak wavelength and shorter than the second primary peak wavelength; masking a portion of the further color conversion region on the portion of the color conversion region on the second light emitting device and the third light emitting device and photo-bleaching a portion of the further color conversion region on the portion of the color conversion region on the first light emitting device such that the further color conversion region on the portion of the color conversion region on the first light emitting device is transparent to light with the first primary peak wavelength, thereby to enable light with the first primary peak wavelength to be emitted by a first pixel associated with the first light emitting device, light with the third primary peak wavelength to be emitted by a second pixel associated with the second light emitting device and light with the second primary peak wavelength to be emitted by a third pixel associated with the third light emitting device.
2 . The method of forming a multicolor light emitting array according to claim 1 , wherein photo-bleaching comprises irradiating the color conversion region and/or the further color conversion region, with light having a wavelength of between 340 nm and 460 nm and an irradiance of at least 10 W/cm 2 , and the temperature of the color conversion region and/or the further color conversion region is between 50° C. and 110° C.
3 . The method of forming a multicolor light emitting array according to claim 1 , wherein the light emitting devices form part of a high resolution monolithic array.
4 . The method of forming a multicolor light emitting array according claim 3 , wherein the monolithic array comprises a plurality of epitaxial crystalline semiconductor layers.
5 . The method of forming a multicolor light emitting array according to claim 1 , wherein the color conversion region and/or the further color conversion region comprises organic semiconductors configured to absorb light with the first primary peak wavelength and re-emit light with a different primary peak wavelength.
6 . The method of forming a multicolor light emitting array according to claim 5 , wherein the organic semiconductors are conjugated organic semiconductors.
7 . The method of forming a multicolor light emitting array according to claim 1 , wherein the color conversion region is configured to emit light with a primary peak wavelength corresponding to red light.
8 . The method of forming a multicolor light emitting array according to claim 1 , wherein the further color conversion region is configured to emit light with a primary peak wavelength corresponding to green light.
9 . The method of forming a multicolor light emitting array according to claim 1 , wherein the color conversion region and/or the further color conversion region is a layer with a thickness less than or equal to 500 nm.
10 . The method of forming a multicolor light emitting array according to claim 1 , wherein forming the color conversion region and/or the further color conversion region comprises depositing organic semiconductors in a solvent, wherein the concentration of organic semiconductors in the solve is 2.5% by weight.
11 . The method of forming a multicolor light emitting array according to claim 1 , wherein forming the color conversion region and/or the further color conversion region comprises one of a spin coating and a slit coating.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a 35 U.S.C. § 371 U.S. National Stage application of International Application No. PCT/GB2021/052887, filed on Nov. 8, 2021, which claims the benefit of priority of Great Britain Application No. 2017935.4, filed on Nov. 13, 2020, which are incorporated herein by reference in their entirety. FIELD OF THE INVENTION The invention relates to an array of light emitting diodes (LEDs) and a method for forming an array of LEDs. In particular, but not exclusively, the invention relates to a multicolour monolithic array of light emitting diodes using down-converting organic semiconductors and a method for forming a multicolour monolithic array of light emitting diodes using down-converting organic semiconductors. BACKGROUND OF THE INVENTION It is known that light emitting diode (LED) devices provide efficient sources of light for a wide range of applications. Increases in LED light generation efficiency and extraction, along with the production of smaller LEDs (with smaller light emitting surface areas) and the integration of different wavelength LED emitters into arrays, has resulted in the provision of high quality colour arrays with multiple applications, in particular in display technologies. In order to provide high resolution LED arrays, such as micro LED arrays, the light emitting surface area defining the pixel surface is reduced compared with the light emitting surface of conventional LEDs, as is the pixel pitch. However, as the pixel pitch in such arrays is reduced to very small pitches (e.g., less than 5 μm) in order to provide higher resolution arrays, a number of difficulties arise. For example, quantum dots (QDs) are typically used as colour conversion regions to achieve a full colour red green blue (RGB) display, where blue LEDs are typically used as the source of input light. Such QDs are typically used to convert blue input light to red light and green light using appropriate QDs. However, such QD layers are generally required to be of the order of 20 μm to 30 μm thick in order to achieve full colour saturation. Therefore, at these thicknesses, the minimum pixel that can be produced is restricted to a width of above 20 μm. Further difficulties are known to arise in processing QDs for light wavelength colour conversion in micro LED arrays, such as degradation in efficiency and lifetime of the wavelength converting QDs when forming layers of material comprising QDs using photolithography and inkjet printing, for example. Accordingly, there are significant challenges in the pursuit of high resolution micro LED arrays, for which it would be beneficial to have a pixel pitch that is less than 10 μm. SUMMARY OF THE INVENTION In order to mitigate for at least some of the above described problems, there is provided a light emitting diode array comprising a plurality of light emitting pixels and a method of forming a light emitting diode array comprising a plurality of light emitting pixels in accordance with the appended claims. There is provided a method of forming a multicolour light emitting array, the method comprising: providing a first light emitting device configured to emit light with a first primary peak wavelength and a second light emitting device configured to emit light with the first primary peak wavelength; forming a colour conversion region at least partially associated with the first light emitting device and the second light emitting device, wherein the colour conversion region is configured to absorb light with the first primary peak wavelength and emit light with a second primary peak wavelength longer than the first primary peak wavelength; and photo-bleaching a portion of the colour conversion region associated with the first light emitting device such that the colour conversion region associated with the first light emitting device is at least partially transparent to light with the first primary peak wavelength, thereby to enable light with the first primary peak wavelength to be emitted by a first pixel associated with the first light emitting device and light with the second primary peak wavelength to be emitted by a second pixel associated with the second light emitting device. There is also provided a multicolour light emitting array comprising: a first pixel associated with a first light emitting device and a second pixel associated with a second light emitting device, wherein the first light emitting device is configured to emit light with a first primary peak wavelength and the second light emitting device is configured to emit light with the first primary peak wavelength; a colour conversion region at least partially associated with the first light emitting device and the second light emitting device, wherein the colour conversion region is configured to absorb light with the first primary peak wavelength and emit light with a second primary peak wavelength longer than the first primary peak wavelength, wherein a porti