METHOD FOR PRODUCING A PIXEL OF AN OLED DISPLAY DEVICE

Description

technical field

[0001] The invention relates to the technical field of organic light-emitting diode (OLED) microdisplays.

[0002] The invention finds its application in particular in the manufacture of virtual or augmented reality glasses and headsets, camera viewfinders, head-up displays, pico-projectors, etc. Prior art

[0003] A pixel of an upward-emitting organic light-emitting diode microdisplay known from the prior art, in particular from document EP 1 672 962 A1, comprises successively: a substrate; a first electrode, reflective in the visible range, and formed on the substrate; a spacer layer, formed on the first electrode; a stack of organic electroluminescent layers, configured to emit white light, and formed on the spacer layer; a second electrode, semi-transparent in the visible range, and formed on the stack; the first and second electrodes forming an optical resonator.

[0004] The spacing layer has first, second, and third portions with thicknesses adapted so that the optical resonator allows the transmission of red, green, and blue light from the white light emitted by the stacking, respectively, in order to define red, green, and blue sub-pixels.

[0005] Such a state-of-the-art pixel makes it possible to eliminate the need for colored filters thanks to the Fabry-Pérot type optical resonator, which acts as an interference filter. The range of filtered wavelengths is determined by the thicknesses of the first, second, and third portions of the spacer layer, allowing adjustment of the thickness of the optical cavity (delimited by the first and second electrodes) so that the optical resonator permits the transmission of red, green, and blue light from the white light emitted by the stack of organic electroluminescent layers.

[0006] This type of filtering can be achieved similarly for a downward-emitting micro-screen. To simplify terminology, we will continue to refer to it as a resonator, even though the interference effects are much less pronounced with downward emission.

[0007] However, such a state-of-the-art pixel is not entirely satisfactory insofar as the electronic control of the red, green, and blue sub-pixels is likely to lead to crosstalk phenomena (“ crosstalk (in English) between adjacent subpixels due to the presence of lateral electrical conduction between adjacent subpixels through the spacing layer and / or conductive layers within the stack of organic light-emitting layers. US2011 / 127500 describes a multicolor OLED device exhibiting resonant structures for each color subpixel. Description of the invention

[0008] The invention aims to remedy, in whole or in part, the aforementioned drawbacks. To this end, the invention relates to a method for manufacturing a pixel of an organic light-emitting diode micro-display as described in claim 1.

[0009] Thus, such a process according to the invention makes it possible to obtain a Fabry-Pérot type optical resonator while significantly reducing crosstalk effects between adjacent sub-pixels. This is made possible by the fact that: (i) remove the first part of the spacer layer in step e), (ii) bury the second part of the stack of organic electroluminescent layers (i.e. the effective part located between the electrodes) inside the openings in step f).

[0010] Such a process according to the invention therefore makes it possible to avoid lateral electrical conduction that may be caused by the first part of the spacing layer and by the presence of conductive layers within the stack of organic electroluminescent layers.

[0011] Furthermore, such a method according to the invention makes it possible to ensure the presence of the spacer layer on the edges of the first structured electrode and thus avoid edge effects. This is made possible by burying the second part of the spacer layer inside the openings during step d). Definitions

[0012] By "microscreen," we mean a screen in which each pixel has an area less than or equal to 30 µm by 30 µm. By "substrate," we mean a self-supporting physical support, made of a base material preferably allowing the integration of an electronic device or component. For example, a substrate is typically a slice (" wafer(in English) cut from a single-crystal ingot of semiconductor material. A "structured electrode" is defined as an electrode with a discontinuous surface delimiting a set of patterns. A "dielectric layer" is defined as a layer made of a dielectric material, having an electrical conductivity at 300 K of less than 10⁻⁸ S·cm⁻¹. "Free areas" are defined as areas of the first electrode that are not covered by the dielectric layer. The "visible range" is defined as an electromagnetic spectrum between 380 nm and 780 nm. "Transparent" is defined as a spacer layer with an intensity transmission coefficient greater than or equal to 70%, preferably greater than or equal to 80%, more preferably greater than or equal to 85%, and even more preferably greater than or equal to 90%, averaged over the visible range.By "electrically conductive," we mean that the spacer layer has an electrical conductivity at 300 K greater than or equal to 10² S / cm. By "within the openings," we mean that the surface of the second part of the spacer layer is located at a lower level than the surface of the dielectric layer. Similarly, we mean that the surface of the second part of the stack of organic electroluminescent layers is located at a lower level than the surface of the dielectric layer. By "thickness," we mean the dimension along the normal to the surface of the pixel or subpixel.

[0013] The method according to the invention may include one or more of the following characteristics.

[0014] According to one feature of the invention, step e) is carried out so 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).

[0015] By "step height", we mean the dimension - along the normal to the surface of the pixel - separating the surface of the dielectric layer from the surface of the second part of the spacing layer.

[0016] Thus, one advantage of such a step height is the ability to significantly reduce crosstalk between red, green, and blue sub-pixels. Indeed, lateral electrical conduction, which can be caused by the presence of conductive layers within the stack of organic electroluminescent layers, is greatly limited by this step height.

[0017] According to one feature of the invention, step e) is carried out by mechano-chemical polishing.

[0018] Thus, one advantage provided is the speed of the operation of removing the first part of the spacing layer.

[0019] According to one feature of the invention, the spacer layer formed during step d) comprises at least one oxide, electrically conductive and transparent in the visible range.

[0020] According to one feature of the invention, the oxide or oxides are selected from indium tin oxide, tin oxide SnO2, zinc oxide ZnO.

[0021] According to one feature of the invention, step d) is carried out so that the first thickness is 100 nm, the second thickness is 50 nm, and the third thickness is 10 nm.

[0022] According to one feature of the invention, the openings formed during step c) have a width between 500 nm and 10 µm.

[0023] According to one feature of the invention, the dielectric layer formed during step b) is made of a material chosen from SiO2 and SiN.

[0024] According to one feature of the invention, the dielectric layer formed during step b) has a thickness between 150 nm and 300 nm.

[0025] Thus, one advantage is to combine both: a thickness large enough to obtain a satisfactory step height (typically greater than or equal to 100 nm) between the second part of the spacer layer and the dielectric layer after the material consumption due to the mechano-chemical polishing carried out during step b); a thickness small enough not to unduly increase the formation time of the dielectric layer.

[0026] According to one feature of the invention, the first and second electrodes are made of a metallic material, preferably selected from Al, Ag, Pt, Cr, Ni, W, and / or made of a transparent conductive oxide.

[0027] Such metallic materials possess both a high intensity reflection coefficient in the visible range and high electrical conductivity. An oxide, electrically conductive and transparent in the visible range, is preferred when the electrode needs to be transparent or semi-transparent.

[0028] According to one feature of the invention, the substrate provided in step a) is transparent in the visible range, the first structured electrode provided in step a) is semi-transparent in the visible range, the second electrode formed in step g) is reflective in the visible range.

[0029] By "transparent" we mean that the substrate has an intensity transmission coefficient greater than or equal to 70%, preferably greater than or equal to 80%, more preferably greater than or equal to 85%, even more preferably greater than or equal to 90%, averaged over the visible domain.

[0030] By "semi-transparent", we mean that the first structured electrode has an intensity transmission coefficient between 30% and 70% averaged over the visible range.

[0031] By "reflective", we mean that the second electrode has an intensity reflection coefficient greater than or equal to 70%, preferably greater than or equal to 80%, more preferably greater than or equal to 85%, even more preferably greater than or equal to 90%, averaged over the visible range.

[0032] Thus, one advantage obtained is a so-called downward emission structure, that is, through the substrate.

[0033] According to one feature of the invention, the substrate provided in step a) is made of a semiconductor material, preferably silicon, or made of glass, the first structured electrode provided in step a) is reflective in the visible range, the second electrode formed in step g) is semi-transparent in the visible range.

[0034] By "semiconductor" we mean that the material has an electrical conductivity at 300 K between 10⁻⁸ S.cm⁻¹ and 10² S.cm⁻¹.

[0035] By "reflective", we mean that the first structured electrode has an intensity reflection coefficient greater than or equal to 70%, preferably greater than or equal to 80%, more preferably greater than or equal to 85%, even more preferably greater than or equal to 90%, averaged over the visible range.

[0036] By "semi-transparent", we mean that the second electrode has an intensity transmission coefficient between 30% and 70% averaged over the visible range.

[0037] Thus, one advantage is obtaining a so-called upward-emitting structure, that is, through the second electrode. The substrate can then include a control circuit for the red, green, and blue sub-pixels without compromising the luminous efficiency of the micro-screen. A TFT (Thin-Film Transistor) type circuit will be chosen. Thin Film Transistors (in English) when the substrate is made of glass, and a CMOS type circuit (" Complementary Metal Oxide Semiconductor » in English) when the substrate is made of a semiconductor material, especially Si. Brief description of the drawings

[0038] Other features and advantages will become apparent in the detailed description of different embodiments of the invention, the description being accompanied by examples and references to the accompanying drawings.

[0039] Figures 1 to 8 are schematic cross-sectional views along the normal to the substrate, illustrating steps of a process according to the invention.

[0040] It should be noted that the drawings described above are schematic and not to scale for the sake of readability and to simplify their understanding. Detailed description of the implementation methods

[0041] Identical elements or elements performing the same function will bear the same references for the different embodiments, for the sake of simplification.

[0042] As illustrated in figures 1 to 8 An object of the invention is a method for manufacturing a pixel of an organic light-emitting diode micro-display, comprising the following successive steps: a) provide a substrate 1 comprising a first structured electrode E1; b) form a dielectric layer 2 on the first structured electrode E1; c) form openings 20 in the dielectric layer 2 such that the first structured electrode E1 has free areas ZL, the openings 20 being intended to accommodate red, green and blue sub-pixels PR, PV, PB; d) form a spacing layer 3, transparent in the visible range and electrically conductive, comprising: a first part 30 extending over the dielectric layer 2, and a second part 31 extending over the free areas ZL of the first structured electrode E1, inside the openings 20; e) remove the first part 30 of the spacing layer 3;f) form a stack 4 of organic electroluminescent layers, configured to emit white light, and comprising: a first part 40 extending over the dielectric layer 2, and a second part 41 extending over the second part 31 of the spacing layer 3, inside the openings 20; g) form a second electrode E2 on the stack 4 of organic electroluminescent layers so as to obtain an optical resonator with the first electrode E1; step d) being executed so that the second part 31 of the spacing layer 3 has first, second and third thicknesses in the openings 20 adapted so that the optical resonator permits respectively the transmission of red, green and blue lights from the white light emitted by the stack 4 of organic electroluminescent layers.

[0043] Steps a) and b) are illustrated in the figure 1 Step c) is illustrated in the figure 2 Step d) is illustrated in figures 3 to 5 Step e) is illustrated in the figure 6 Step f) is illustrated in the figure 7 Step g) is illustrated in the figure 8 . Substrate and types of architectures

[0044] According to a first architecture known as downward emission: the substrate 1 provided in step a) is transparent in the visible range, and can be made of glass, the first structured electrode E1 provided in step a) is semi-transparent in the visible range, and can be made for example in a transparent conductive oxide, the second electrode E2 formed in step g) is reflective in the visible range, and can be made for example in a metallic material.

[0045] According to a second architecture, known as upward emission: the substrate 1 provided in step a) is made of a semiconductor material, preferably silicon, or made of glass, the first structured electrode E1 provided in step a) is reflective in the visible range, and can for example be made of a metallic material, the second electrode E2 formed in step g) is semi-transparent in the visible range, and can for example be made of a transparent conductive oxide. First structured electrode

[0046] The first structured electrode E1 is advantageously made of a metallic material, preferably selected from Al, Ag, Pt, Cr, Ni, W, or made of a transparent conductive oxide.

[0047] The first electrode E1 is preferentially an anode. However, the first electrode E1 can be a cathode if the structure of the stack of 4 organic electroluminescent layers is reversed.

[0048] Step a) may include the following steps: a 1) provide substrate 1; a 2) deposit the first electrode E1 on substrate 1 by a full plate type deposition, according to a deposition technique known to the person skilled in the art; a 3) structure the first electrode E1 by a lithography.

[0049] The patterns of the first structured electrode E1 are preferentially separated by a width between 0.5 µm and 1 µm. This width allows for a sub-pixel matrix pitch of a micro-screen preferably between 4 µm and 5 µm.

[0050] When the architecture is downward emitting, the first structured electrode E1 has a thickness adapted to be semi-transparent in the visible range. The first electrode E1 can then be made, for example, from a transparent conductive oxide (e.g., ITO).

[0051] When the architecture is upward emitting, the first structured electrode E1 has a thickness adapted to be reflective in the visible range. The first electrode E1 can then be made, for example, of a metallic material. Dielectric layer

[0052] The dielectric layer 2 formed during step b) is advantageously made of a material chosen from SiO 2 and SiN.

[0053] Step b) can be carried out by a deposition technique known to a person skilled in the art.

[0054] The dielectric layer 2 formed during step b) advantageously has a thickness between 150 nm and 300 nm.

[0055] Step c) can be performed by an etching technique known to those skilled in the art so as to obtain sufficiently steep etching flanks so 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 after step e), in order to ensure discontinuity in the deposition of the stack 4 of organic electroluminescent layers. The openings 20 formed during step c) advantageously have a width between 500 nm and 10 µm. The openings 20 of the dielectric layer 2 may have a rectangular cross-section. By "cross-section" is meant a section made along the normal to the pixel surface, i.e., through the thickness of the dielectric layer 2.As an alternative, the openings 20 of the dielectric layer 2 may have a cross-section of a different shape, which would be favorable to light extraction, for example a parabolic cross-section. Formation of the spacing layer

[0056] The spacer layer 3 formed in step d) advantageously comprises at least one oxide, electrically conductive and transparent in the visible range (hereinafter referred to as TCO for " Transparent Conductive Oxide " . The oxide(s) are advantageously selected from indium tin oxide, tin oxide (SnO₂), and zinc oxide (ZnO). Zinc oxide (ZnO) is preferentially doped with aluminum. Tin oxide (SnO₂) is also preferentially doped with aluminum. Other derivatives of indium tin oxide, tin oxide (SnO₂), and zinc oxide (ZnO) may also be considered.

[0057] Step d) is executed so that the second part 31 of the spacing layer 3 presents the first, second, and third thicknesses in the openings 20 intended to accommodate the red, green, and blue sub-pixels PR, PV, PB, respectively. To this end, step d) may include the following successive steps: d 1 ) deposit a first TCO 3a on the dielectric layer 2 and in the openings 20 of the dielectric layer 2; d 2 ) mask the openings 20 intended to accommodate the blue sub-pixels PB; d 3 ) deposit a second TCO 3b on the first TCO; d 4 ) mask the openings 20 intended to accommodate the green sub-pixels PV; d 5 ) deposit a third TCO 3c on the second TCO.

[0058] Step d1) is illustrated in the figure 3 Steps d2) and d3) are illustrated in the figure 4 Steps d4) and d5) are illustrated in the figure 5 .

[0059] Steps d1), d3), and d5) are carried out using deposition techniques known to those skilled in the art. Steps d2) and d4) can 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 d1). 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 d1) and d3). 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 d1), d3), and d5). It should be noted that the first, second and third TCOs 3a, 3b, 3c can be made of the same or different materials.

[0060] Step d) is advantageously carried out so 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 to be within the usual tolerances related to the experimental deposition conditions, and not as perfectly equal values ​​in the mathematical sense of the term. Removal of the spacing layer

[0061] Step e) is advantageously carried out so 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).

[0062] Step e) is advantageously carried out by chemical-mechanical polishing. Step e) is carried out in such a way as to free the surface of the dielectric layer 2. Moreover, such a step e) allows for the flattening of the surface of the dielectric layer 2.

[0063] Step e) may be accompanied by the removal of part of the underlying dielectric layer 2 when the first part 30 of the spacer layer 3 is too thin.

[0064] The photosensitive resins 5 used in steps d 2) and d 4) remaining in the openings 20 are then removed after step e) by " stripping » known to a person skilled in the art.

[0065] As illustrated in the figure 6bis, 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 examples, the dielectric film 2' can be made of a material chosen from Al 2 O 3 , HfO 2 , Ta 2 O 5 . The dielectric film 2' advantageously has a thickness between 1 nm and 10 nm, preferably between 1 nm and 5 nm. The dielectric film 2' can be formed by a deposition of atomic layers (ALD « Atomic Layer Deposition(in English). The dielectric film 2' is then etched into the openings 20 at the bottom of the trench, so as to release the second part 31 of the spacing layer 3. The dielectric film 2' is etched into the bottom of the openings 20 in such a way as not to unduly reduce the dimensions of the red, green, and blue sub-pixels PR, PV, PB, while still providing electrical insulation. The etching of the dielectric film 2' into the bottom of the openings 20 can be carried out by lithography. The resulting dielectric film 2' is arranged to avoid a short circuit between the first and second electrodes E1, E2. If necessary, step f) is carried out so that the first part 40 of the stack 4 of organic electroluminescent layers extends over the dielectric film 2'. Stack of organic electroluminescent layers

[0066] The stack of 4 organic electroluminescent layers formed during step f) has a constant thickness for each red, green and blue sub-pixel PR, PV, PB.

[0067] As a non-limiting example, the 4-layer stack can have three emissive layers in a tandem architecture. More precisely, when the first structured electrode E1 is an anode and the second electrode E2 is a cathode, the 4-layer stack can have: a first hole transport layer formed on the first structured electrode E1; a first emissive layer emitting blue light, formed on the first hole transport layer; a first electron transport layer, formed on the first emissive layer; a charge generation layer (also called the interconnect layer), formed on the first electron transport layer; a second hole transport layer, formed on the charge generation layer; a second emissive layer emitting green light, formed on the second hole transport layer; a third emissive layer emitting red light, formed on the second emissive layer; a second electron transport layer, formed on the third emissive layer, and intended to be coated with the second electrode E2.

[0068] As variations, the 4-layer stacking can include: three emitting layers emitting blue, green and red lights respectively without being arranged in tandem architecture (conventional structure); two emitting layers emitting yellow and blue lights respectively arranged in conventional structure; two emitting layers emitting yellow and blue lights respectively arranged in tandem structure.

[0069] Step f) is executed by deposition techniques known to a person skilled in the art. Second electrode

[0070] The second electrode E2 is advantageously made of a metallic material, preferably selected from Al, Ag, Pt, Cr, Ni, W, or made of a transparent conductive oxide.

[0071] The second electrode E2 is preferentially a cathode. However, the second electrode E2 can be an anode if the structure of the stack of 4 organic electroluminescent layers is reversed.

[0072] Step g) is carried out by a deposition technique known to those skilled in the art. Step g) is preferably carried out by a sufficiently conforming deposition to ensure the transition of the step between the first and second parts 40, 41 of the stack 4 of organic electroluminescent layers.

[0073] The second electrode E2 is advantageously coated with an encapsulation layer (not shown) suitable for protecting the second electrode E2 and the stack of 4 organic electroluminescent layers from air and moisture.

[0074] When the architecture is designed for downward emission, the second electrode E2 has a thickness adapted to be reflective in the visible spectrum. The second electrode E2 can then be made, for example, from a metallic material.

[0075] When the architecture is upward emitting, the second electrode E2 has a thickness adapted to be semi-transparent in the visible range. The second electrode E2 can then be made, for example, from a transparent conductive oxide (e.g., ITO).

[0076] The invention is not limited to the embodiments described. A person skilled in the art is able to consider their technically operative combinations within the scope of the invention as defined by the attached claims.

Claims

1. 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), the dielectric layer (2) having a bottom surface, a top surface and flanks connecting the bottom surface to the top surface; 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 top surface of 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), such that the top surface of the second part (31) of the spacer layer (3) is located at a level lower than that of the top surface of the dielectric layer (2); 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 top surface of the dielectric layer (2), and - a second part (41) extending over the second part (31) of the spacer layer (3), inside the openings (20), such that the top surface of the second part (41) of the stack (4) is located at a level lower than that of the top surface of the dielectric layer (2), the stack of organic light-emitting layers having a discontinuity between the first part of the stack and the second part of the stack; 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.

2. Method according to Claim 1, wherein step e) is 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).

3. Method according to Claim 1 or 2, wherein step e) is carried out through chemical-mechanical polishing.

4. Method according to one of Claims 1 to 3, wherein the spacer layer (3) formed in step d) comprises at least one oxide that is electrically conductive and transparent in the visible spectrum.

5. Method according to Claim 4, wherein the oxide or oxides are selected from among indium tin oxide, tin oxide SnO2 and zinc oxide ZnO.

6. Method according to one of Claims 1 to 5, 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. Method according to one of Claims 1 to 6, wherein the openings (20) formed in step c) have a width of between 500 nm and 10 µm.

8. Method according to one of Claims 1 to 7, wherein the dielectric layer (2) formed in step b) is made of a material chosen from among SiO2 and SiN.

9. Method according to one of Claims 1 to 8, wherein the dielectric layer (2) formed in step b) has a thickness of between 150 nm and 300 nm.

10. Method according to one of Claims 1 to 9, wherein the first and second electrodes (E1, E2) 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. Method according to one of Claims 1 to 10, wherein: - the substrate (1) provided in step a) is transparent in the visible spectrum, - the structured first electrode (E1) provided in step a) is semi-transparent in the visible spectrum, - the second electrode (E2) formed in step g) is reflective in the visible spectrum.

12. Method according to one of Claims 1 to 10, wherein: - 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, - the second electrode (E2) formed in step g) is semi-transparent in the visible spectrum.