Method for producing a pixel of an OLED micro-screen

Abstract

A method for producing a pixel of an OLED microscreen includes the steps of: a) providing a substrate having a structured first electrode; b) forming a dielectric layer on the structured first electrode; c) forming openings in the dielectric layer such that the structured first electrode has free areas, d) forming a spacer layer that is transparent and conductive, and includes: a first part extending over the dielectric layer, and a second part extending over the free areas; e) removing the first part of the spacer layer; f) forming a stack of organic light-emitting layers that is configured to emit a white light; and g) forming a second electrode on the stack; step d) being carried out such that the second part of the spacer layer has first, second and third thicknesses that are designed to allow, respectively, the transmission of red, green and blue light.

Claims

1. A method for manufacturing a pixel of an organic light-emitting diode microscreen, comprising: a) providing a substrate comprising a structured first electrode; b) forming a dielectric layer on the structured first electrode; c) forming openings in the dielectric layer, such that the structured first electrode has free areas, the openings being intended to receive red, green and blue sub-pixels; d) forming a spacer layer that is transparent in a visible spectrum, is electrically conductive, and includes: a first part extending over an upper surface of the dielectric layer and outside of the openings, and a second part extending over the free areas of the structured first electrode, inside the openings, so that an upper surface of the second part of the spacer layer is at a lower level than the upper surface of the dielectric layer; e) removing the first part of the spacer layer; e1) forming a dielectric film directly on a top surface of the dielectric layer; f) forming a stack of organic light-emitting layers that is configured so as to emit a white light, the stack of organic light-emitting layers includes: a first part positioned outside of the openings and directly on an upper planar surface of the dielectric film with respect to a light emitting direction of the white light, the upper planar surface facing in the light emitting direction, and a second part extending over the second part of the spacer layer, buried inside the openings, so that an upper surface of the second part of the stack of organic light-emitting layers is at a lower level than the upper surface of the dielectric layer, the first part and the second part of the stack of organic light-emitting diodes being discontinuous; and g) forming a second electrode on the stack of organic light-emitting layers, the second electrode being arranged to form an optical resonator with the structured first electrode, wherein the step d) is carried out such that the second part of the spacer layer has different first, second and third thicknesses in the respective openings such that the optical resonator allows, respectively, transmission of red, green and blue light from the white light emitted by the stack of organic light-emitting layers.

2. The method as claimed in claim 1, wherein step e) is carried out such that the second part of the spacer layer and the dielectric layer have a step height greater than or equal to 100 nm at the end of step e).

3. The method as claimed in claim 1, wherein step e) is carried out through chemical-mechanical polishing.

4. The method as claimed in claim 1, wherein the spacer layer formed in step d) comprises at least one oxide that is electrically conductive and transparent in the visible spectrum.

5. The method as claimed in claim 4, wherein the oxide or oxides are selected from among indium tin oxide, tin oxide SnO2 and zinc oxide ZnO.

6. The method as claimed in claim 1, wherein step d) is carried out such that the first thickness is 100 nm, the second thickness is 50 nm, and the third thickness is 10 nm.

7. The method as claimed in claim 1, wherein the openings formed in step c) have a width of between 500 nm and 10 m.

8. The method as claimed in claim 1, wherein the dielectric layer formed in step b) is made of a material chosen from among SiO2 and SiN.

9. The method as claimed in claim 1, wherein the dielectric layer formed in step b) has a thickness of between 150 nm and 300 nm.

10. The method as claimed in claim 1, wherein the first and second electrodes are made of a metal material, preferably selected from among Al, Ag, Pt, Cr, Ni, W, and/or made of a transparent conductive oxide.

11. The method as claimed in claim 1, wherein: the substrate provided in step a) is transparent in the visible spectrum, the structured first electrode provided in step a) is semi-transparent in the visible spectrum, the second electrode formed in step g) is reflective in the visible spectrum.

12. The method as claimed in claim 1, wherein: the substrate provided in step a) is made of a semiconductor material, preferably silicon, or made of glass, the structured first electrode provided in step a) is reflective in the visible spectrum, the second electrode formed in step g) is semi-transparent in the visible spectrum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages will become apparent from the detailed disclosure of various embodiments of the invention, the disclosure being accompanied by examples and references to the appended drawings.

(2) FIGS. 1 to 8 are schematic sectional views along the normal to the substrate, illustrating steps of a method according to the invention.

(3) It should be noted that, for the sake of legibility and ease of understanding, the drawings described above are schematic and not to scale.

DETAILED DISCLOSURE OF THE EMBODIMENTS

(4) For the sake of simplicity, elements that are identical or that perform the same function in the various embodiments will bear the same references.

(5) As illustrated in FIGS. 1 to 8, one subject of the invention is a method for manufacturing a pixel of an organic light-emitting diode microscreen, comprising the successive steps of: a) providing a substrate 1 comprising a structured first electrode E1; b) forming a dielectric layer 2 on the structured first electrode E1; c) forming openings 20 in the dielectric layer 2, such that the structured first electrode E1 has free areas ZL, the openings 20 being intended to receive red, green and blue sub-pixels PR, PV, PB; d) forming a spacer layer 3 that is transparent in the visible spectrum and is electrically conductive, and comprises: a first part 30 extending over the dielectric layer 2, and a second part 31 extending over the free areas ZL of the structured first electrode E1, inside the openings 20; e) removing the first part 30 of the spacer layer 3; f) forming a stack 4 of organic light-emitting layers that is configured so as to emit a white light and comprises: a first part 40 extending over the dielectric layer 2, and a second part 41 extending over the second part 31 of the spacer layer 3, inside the openings 20; g) forming a second electrode E2 on the stack 4 of organic light-emitting layers so as to obtain an optical resonator with the first electrode E1; step d) being carried out such that the second part 31 of the spacer layer 3 has first, second and third thicknesses in the openings 20 that are designed such that the optical resonator allows, respectively, the transmission of red, green and blue light from the white light emitted by the stack 4 of organic light-emitting layers.

(6) Steps a) and b) are illustrated in FIG. 1. Step c) is illustrated in FIG. 2. Step d) is illustrated in FIGS. 3 to 5. Step e) is illustrated in FIG. 6. Step f) is illustrated in FIG. 7. Step g) is illustrated in FIG. 8.

(7) Substrate and Types of Architecture

(8) According to a first architecture, known as a bottom-emitting architecture: the substrate 1 provided in step a) is transparent in the visible spectrum, and may be made of glass, the structured first electrode E1 provided in step a) is semi-transparent in the visible spectrum, and may for example be made of a transparent conductive oxide, the second electrode E2 formed in step g) is reflective in the visible spectrum, and may for example be made of a metal material.

(9) According to a second architecture, known as a top-emitting architecture: the substrate 1 provided in step a) is made of a semiconductor material, preferably silicon, or made of glass, the structured first electrode E1 provided in step a) is reflective in the visible spectrum, and may for example be made of a metal material, the second electrode E2 formed in step g) is semi-transparent in the visible spectrum, and may for example be made of a transparent conductive oxide.
Structured First Electrode

(10) The structured first electrode E1 is advantageously made of a metal material, preferably selected from among Al, Ag, Pt, Cr, Ni, W, or made of a transparent conductive oxide.

(11) The first electrode E1 is preferably an anode. However, the first electrode E1 may be a cathode if the structure of the stack 4 of organic light-emitting layers is inverted.

(12) Step a) may comprise the steps of: a.sub.1) providing the substrate 1; a.sub.2) depositing the first electrode E1 on the substrate 1 through blanket deposition, using a deposition technique known to those skilled in the art; a.sub.3) structuring the first electrode E1 through lithography.

(13) The patterns of the structured first electrode E1 are preferably separated by a width of between 0.5 m and 1 m. This width makes it possible to obtain a pitch of a matrix-array of sub-pixels of a microscreen of preferably between 4 m and 5 m.

(14) When the architecture is a bottom-emitting architecture, the structured first electrode E1 has a thickness designed to be semi-transparent in the visible spectrum. The first electrode E1 may then for example be made of a transparent conductive oxide (for example ITO).

(15) When the architecture is a top-emitting architecture, the structured first electrode E1 has a thickness designed to be reflective in the visible spectrum. The first electrode E1 may then for example be made of a metal material.

(16) Dielectric Layer

(17) The dielectric layer 2 formed in step b) is advantageously made of a material chosen from among SiO.sub.2 and SiN.

(18) Step b) may be carried out using a deposition technique known to those skilled in the art.

(19) The dielectric layer 2 formed in step b) advantageously has a thickness of between 150 nm and 300 nm.

(20) Step c) may be carried out using an etching technique known to those skilled in the art so as to obtain etching sidewalls that are steep enough that the second part 31 of the spacer layer 3 and the dielectric layer 2 have a step height greater than or equal to 100 nm at the end of step e), in order to guarantee the discontinuity of the deposition of the stack 4 of organic light-emitting layers. The openings 20 formed in step c) advantageously have a width of between 500 nm and 10 m. The openings 20 in the dielectric layer 2 may have a rectangular cross section. The term cross section is understood to mean a section taken along the normal to the surface of the pixel, that is to say in the thickness of the dielectric layer 2. As a variant, the openings 20 in the dielectric layer 2 may have a differently-shaped cross section, which would be beneficial to the extraction of light, for example a parabolic cross section.

(21) Formation of the Spacer Layer

(22) The spacer layer 3 formed in step d) advantageously comprises at least one oxide that is electrically conductive and is transparent in the visible spectrum (hereinafter referred to as TCO for transparent conductive oxide). The oxide or oxides are advantageously selected from among indium tin oxide, tin oxide SnO.sub.2 and zinc oxide ZnO. The zinc oxide ZnO is preferably aluminum-doped. The tin oxide SnO.sub.2 is preferably aluminum-doped. It is also possible to contemplate other derivatives of indium tin oxide, of tin oxide SnO.sub.2 and of zinc oxide ZnO.

(23) Step d) is carried out such that the second part 31 of the spacer layer 3 has the first, second and third thicknesses in the openings 20 intended to receive, respectively, the red, green and blue sub-pixels PR, PV, PB. To this end, step d) may comprise the successive steps of: d.sub.1) depositing a first TCO 3a on the dielectric layer 2 and in the openings 20 in the dielectric layer 2; d.sub.2) masking the openings 20 intended to receive the blue sub-pixels PB; d.sub.3) depositing a second TCO 3b on the first TCO; d.sub.4) masking the openings 20 intended to receive the green sub-pixels PV; d.sub.5) depositing a third TCO 3c on the second TCO.

(24) Step d.sub.1) is illustrated in FIG. 3. Steps d.sub.2) and d.sub.3) are illustrated in FIG. 4. Steps d.sub.4) and d.sub.5) are illustrated in FIG. 5.

(25) Steps d.sub.1), d.sub.3) and d.sub.5) are carried out using deposition techniques known to those skilled in the art. Steps d.sub.2) and d.sub.4) may be carried out using a photosensitive resin 5. The first thickness of the second part 31 of the spacer layer 3 corresponds to the thickness of the first TCO 3a deposited in step d.sub.1). The second thickness of the second part 31 of the spacer layer 3 corresponds to the sum of the thicknesses of the first and second TCO 3a, 3b deposited, respectively, in steps d.sub.1) and d.sub.3). The third thickness of the second part 31 of the spacer layer 3 corresponds to the sum of the thicknesses of the first, second and third TCO 3a, 3b, 3c deposited, respectively, in steps d.sub.1), d.sub.3) and d.sub.5). It should be noted that the first, second and third TCO 3a, 3b, 3c may be made of identical or different materials.

(26) Step d) is advantageously carried out such that the first thickness is 100 nm, the second thickness is 50 nm, and the third thickness is 10 nm. The values of these thicknesses are understood within the usual tolerances linked to the experimental deposition conditions, and not as being perfectly equal values within the mathematical sense of the term.

(27) Removal of the Spacer Layer

(28) Step e) is advantageously carried out such that the second part 31 of the spacer layer 3 and the dielectric layer 2 have a step height greater than or equal to 100 nm at the end of step e).

(29) Step e) is advantageously carried out through chemical-mechanical polishing. Step e) is carried out so as to free up the surface of the dielectric layer 2. Moreover, such a step e) makes it possible to level out the surface of the dielectric layer 2.

(30) Step e) may be accompanied by removal of part of the underlying dielectric layer 2 when the first part 30 of the spacer layer 3 has an excessively thin thickness.

(31) The photosensitive resins 5 used in steps d.sub.2) and d.sub.4) remaining in the openings 20 are then removed after step e) using stripping techniques that are known to those skilled in the art.

(32) As illustrated in FIG. 6B, a dielectric film 2 is then advantageously formed on the free surface of the dielectric layer 2 and on the second part 31 of the spacer layer 3. By way of non-limiting example, the dielectric film 2 may be made of a material chosen from among Al2O3, HfO2, Ta2O5. The dielectric film 2 advantageously has a thickness of between 1 nm and 10 nm, preferably of between 1 nm and 5 nm. The dielectric film 2 may be formed through atomic layer deposition (ALD). The dielectric film 2 is then etched in the openings 20, at the bottom of the trench, so as to free up the second part 31 of the spacer layer 3. The dielectric film 2 is etched at the bottom of the openings 20 so as not to unduly reduce the dimensions of the red, green and blue sub-pixels PR, PV, PB, while at the same time guaranteeing an electrical insulation function. The etching of the dielectric film 2 in the bottom of the openings 20 may be carried out through lithography. The dielectric film 2 that is obtained is arranged so as to avoid a short circuit between the first and second electrodes E1, E2. Where appropriate, step f) is carried out such that the first part 40 of the stack 4 of organic light-emitting layers extends over the dielectric film 2.

(33) Stack of Organic Light-Emitting Layers

(34) The stack 4 of organic light-emitting layers that is formed in step f) has a constant thickness for each red, green and blue sub-pixel PR, PV, PB.

(35) By way of non-limiting example, the stack 4 may comprise three emissive layers in a tandem architecture. More precisely, when the structured first electrode E1 is an anode and the second electrode E2 is a cathode, the stack 4 may comprise: a first hole transport layer that is formed on the structured first electrode E1; a first emissive layer, emitting a blue light, that is formed on the first hole transport layer; a first electron transport layer that is formed on the first emissive layer; a charge generation layer (also known as an interconnect layer) that is formed on the first electron transport layer; a second hole transport layer that is formed on the charge generation layer; a second emissive layer, emitting a green light, that is formed on the second hole transport layer; a third emissive layer, emitting a red light, that is formed on the second emissive layer; a second electron transport layer that is formed on the third emissive layer and is intended to be coated with the second electrode E2.

(36) As variants, the stack 4 may comprise: three emissive layers emitting, respectively, blue, green and red light without being arranged in a tandem architecture (conventional structure); two emissive layers emitting, respectively, yellow and blue light that are arranged in a conventional structure; two emissive layers emitting, respectively, yellow and blue light that are arranged in a tandem structure.

(37) Step f) is carried out using deposition techniques known to those skilled in the art.

(38) Second Electrode

(39) The second electrode E2 is advantageously made of a metal material, preferably selected from among Al, Ag, Pt, Cr, Ni, W, or made of a transparent conductive oxide.

(40) The second electrode E2 is preferably a cathode. However, the second electrode E2 may be an anode if the structure of the stack 4 of organic light-emitting layers is inverted.

(41) Step g) is carried out using a deposition technique known to those skilled in the art. Step g) is preferably carried out through a sufficiently conformal deposition so as to guarantee the change in the step between the first and second parts 40, 41 of the stack 4 of organic light-emitting layers.

(42) The second electrode E2 is advantageously coated with an encapsulation layer (not illustrated) designed to protect the second electrode E2 and the stack 4 of organic light-emitting layers from air and humidity.

(43) When the architecture is a bottom-emitting architecture, the second electrode E2 has a thickness designed to be reflective in the visible spectrum. The second electrode E2 may then for example be made of a metal material.

(44) When the architecture is a top-emitting architecture, the second electrode E2 has a thickness designed to be semi-transparent in the visible spectrum. The second electrode E2 may then for example be made of a transparent conductive oxide (for example ITO).

(45) The invention is not limited to the disclosed embodiments. Those skilled in the art are able to consider the technically effective combinations of the embodiments and to replace them with equivalents.