High-resolution active matrix electroluminescent device

Abstract

Electroluminescent display device (200) comprising a matrix of electroluminescent pixels formed of a plurality of pixels, each pixel being formed of at least three elementary emitting zones each of which is distinguished from the others by its emission color, and each elementary emission zone comprising an OLED stack (205) arranged between a lower control electrode (202) and a transparent upper electrode (206), said electroluminescent display device being characterized in that the upper electrode (206) comprises - a first part (206-1) which belongs to each elementary emitting zone individually and which is physically and electrically separated from the same first part (206-1) of all the other elementary emitting zones;and - a second part (206-2) located between the elementary emitting zones and which forms an electrical network connected across the entire pixel matrix to connection bars (217) and physically and electrically isolated from the first parts (206-1); and - a layer of a transparent and conductive material (250) which establishes an electrical connection between the second part (206-2) and the first parts (206-1) of each elementary emitting zone, thus enabling the electrical supply of the OLED devices of each elementary emitting zone. Figure for the abstract: [Fig. 31];

Description

Title of the invention: High-resolution active matrix electroluminescent device Technical field of the invention

[0001] The invention relates to the field of optoelectronic devices and components, and more specifically to active matrix OLED (Organic Light Emitting Diode) electroluminescent devices (AMOLED - Active Matrix OLED). It relates more particularly to improving the efficiency and luminance of the display color range as well as the resolution of an AMOLED type display screen (also known as "microdisplay"). It makes it possible to manufacture micro-screens with very high spatial resolution, i.e. with a particularly high pixel and sub-pixel density, and with excellent industrial reliability. State of the art

[0002] AMOLED microdisplays generally comprise a matrix structure of individual pixels, which is controlled by a grid of vertical and horizontal conductive tracks; this structure can allow individual addressing of the pixels. This is illustrated schematically in [Fig.l] which will be explained below. In color displays each pixel is subdivided into subpixels of different colors (typically three or four, including the primary colors red, green and blue, and possibly a white subpixel) which cooperate to emit a luminous point (pixel) of the desired color. [Fig.2] shows three known examples of arrangement of subpixels of different colors to form a pixel capable of displaying the desired color.

[0003] In an OLED-based display screen, the color of a pixel or sub-pixel can be generated in two different ways. In a first embodiment, an OLED diode is used that emits white light, and the emitted white light is passed through a color filter. [Fig. 3] shows a cross-section of such a screen, which represents the so-called "top emission" geometry, i.e., emission from above, the "top" being the face opposite the substrate, or in other words, the face directed towards the observer. Above the electrodes of the sub-pixels is deposited an OLED stack that covers the entire surface of the matrix and which (in this example) emits white light. The RGB (Red-Green-Blue) or RGBW (Red-Green-Blue-White) primary colors of the sub-pixels are in this case generated by colored filters located above the OLED stack. These colored filters can be photosensitive resins.These resins can be deposited directly onto the system. encapsulation, or, alternatively, they can be deposited on a glass wafer, which is fixed by gluing to the upper electrode of the device.

[0004] This embodiment has two advantages. First, it is possible to use the same common OLED layer, unstructured at the matrix level, for all the sub-pixels, the color being generated by the filters. Another advantage is that it is possible to produce very small active addressing sub-pixels, which makes it possible to improve the spatial resolution of the screen.

[0005] This embodiment, however, has two drawbacks: First, the color filter absorbs a significant fraction of the light intensity emitted by the pixel. For a targeted light intensity, it is therefore necessary to increase the light emission of the OLED diode. Knowing that the operational lifetime of OLED devices decreases with increasing current density or luminance, because the large number of holes and electrons passing through the organic layer causes electrochemical side reactions of the organic compounds which end up degrading these organic compounds, it would be desirable not to increase the light intensity emitted by the OLED diode beyond a certain value. Second, the display sharpness of such a device is limited by the crosstalk phenomenon, which will be explained below.

[0006] Another way of producing the primary colors is to structure the OLED layers into sub-pixels with different emission colors. This is a second well-known embodiment, which does not use colored filters and thus avoids the first problem of loss of light intensity. Since the process of structuring the OLED layers is quite complex and the achievable spatial resolution quite limited, it is preferred even in this case to keep a maximum of common layers (i.e. layers covering the entire surface of the matrix), generally the charge carrier transport layers, and to structure only the emitting layers. However, as in the first embodiment, it is observed that neighboring pixels or sub-pixels can interact, by capacitive coupling or by parasitic currents passing in particular through common conductive layers of the OLED stack, in the plane of the conductive layers.

[0007] An example for this parasitic current in the plane of the conductive layers is illustrated in [Fig. 4] which will be explained below. This unwanted interaction between neighboring pixels is known to those skilled in the art as "crosstalk"; it leads especially to the unwanted modification of colors in the case of color displays. The theoretical aspects of the crosstalk phenomenon in OLED devices have been studied for a long time (see for example the publication by D. Braun "Crosstalk in passive matrix polymer LED displays" published in 1998 in the journal Synthetic Metals 92, pp. 107-113).

[0008] This problem becomes more noticeable when the sub-pixel size decreases. Apart from digitally correcting the consequences of crosstalk (which amounts to accepting the crosstalk phenomenon and reducing its impact on the image), there are different approaches to combating crosstalk at the source, i.e. to reduce the physical phenomenon at the pixel or sub-pixel level.

[0009] To reduce crosstalk in the case of an AMOLED display based on white-emitting OLED diodes and colored filters, WO 2019 / 193290 (MicroOled) proposes a method for delimiting two neighboring pixels by a filling element with an insulating surface which separates their base electrodes as well as their OLED layers.

[0010] Other structures of the (sub-)pixel matrix in which the OLED layers are interrupted (isolated) at the edges of the (sub-)pixels by separators located between the (sub-)pixels are known from WO 2021 / 071630 and WO 2023 / 154188 (Applied Materials) for producing R, G, B sub-pixels.

[0011] A significant problem with the cited state-of-the-art architectures remains the connection of the upper electrode of the OLED device (which is most often the cathode) which is an electrode common to all the pixels, and which is (like the OLED layers) interrupted at the edges of the pixel by the separators.

[0012] In WO 2021 / 071630, this problem is circumvented by using an arrangement of pixels in the form of RGB stripes, as shown in the left image of [Fig. 2]. Such an arrangement makes it possible to isolate the pixels horizontally only, but to keep the continuity of the layers (including the cathode) vertically, which makes it possible to connect cathodes in the form of columns from the outside of the matrix. The major disadvantage of this solution is that it is limited to an arrangement of pixels of the RGB-stripe type, as shown in the example on the left of [Fig. 2]. Another disadvantage is linked to the fact that in the case where there is a point defect in the stack of OLED layers, this can propagate over the entire length of the column concerned.

[0013] Document WO2023 / 154188 describes an architecture and an associated method for depositing OLED layers and the cathode layer which allow the realization of a local contact at the level of the (sub-)pixel by the substrate. However, in industrial practice this method is not practicable for small (sub-)pixels of the order of a few pm.

[0014] WO 2019 / 193290 describes an AMOLED display structure with a common cathode layer that is deposited by a conformal deposition method, for example by the atomic layer deposition (ALD) technique by chemical vapor deposition (CVD) in order to obtain electrical continuity across the separators between the (sub-)pixels. The materials used in this case are typically transparent conductive oxides (TCO - Transparent Conductive Oxide), such as ZnO, aluminum-doped ZnO (AZO - Aluminum-doped Zinc Oxide), SnO2, indium tin oxide (ITO - Indium Tin Oxide). However, these materials have relatively low electrical conductivity and do not allow the entire surface of the screen to be powered without a significant voltage drop. For example, the square resistance of a TCO such as AZO deposited by ALD and with a thickness of 100 nm is around 1000 Ohm / square. The current to be supplied for an OLED micro-screen is around 10 mA (a rather low estimate). Therefore, the voltage drop is around several Volts, for a supply voltage that is typically around 5 V to 10 V.

[0015] Another problem related to AMOLED micro-displays is to guarantee their lifetime under varied conditions of use. It is known that OLED stacks are sensitive to gaseous species in the atmosphere, mainly oxygen and water vapor, which degrade the interface between the electrode and the organic films forming the OLED stack. A degraded sub-pixel eventually stops emitting light: it appears as a black point. OLED-based optoelectronic devices must therefore be encapsulated to protect OLED stacks from the ambient atmosphere. In the case where the screen colors are generated by colored filters, the glass slice on which the filters are deposited serves as a surface protection for the OLED stack, the glue being able to ensure lateral coating.

[0016] It is known to separate each pixel to isolate it from the other pixels surrounding it, to avoid short-circuit problems related to humidity in the encapsulation layers. Document EP 2 927 985 (Universal Display Corp.) describes a structure in which each pixel is hermetically sealed and isolated from its neighboring pixels. The manufacture of such a structure requires numerous and complex process steps. It is also known to delimit the pixel areas by additional separating elements, such as walls, as described in document US 9 419 245 (Japan Display Inc.). The methods described in these two documents are complex and generate a significant additional cost.

[0017] The structure of a prior art device, which makes it possible to obtain high light intensity, is shown schematically in [Fig. 5], which will be discussed below in greater detail. It has three elementary emitting zones (sub-pixels) of different color and does not need colored filters, which ensures excellent efficiency and brightness of the device. Since the sub-pixels are also separated at the level of all their OLED layers, there is practically no crosstalk, and the sharpness of the image is good. This device has many functional advantages. However, since the OLED layers of said sub-pixels are different, they must be deposited separately, and no industrial process is known. with which this device could be miniaturized with a size of the elementary emitting zone (sub-pixel) less than approximately 20 pm.

[0018] In view of the above, an objective of the present invention is to remedy, at least partially, the drawbacks of the prior art mentioned above, and to propose an architecture for an OLED display device of the color micro-display type, which has excellent brightness, preferably by using elementary color emitting zones, and which makes it possible to significantly reduce, and preferably eliminate, lateral parasitic currents, even for pixels of very small size (typically less than 5 μm) or for structures with very small inter-pixel space. This architecture must be compatible with efficient encapsulation.

[0019] The problem of presenting an AMOLED type micro-display technology with a conformal cathode common to all the pixels, which is applicable to all common pixel arrangements, and which makes it possible to power the pixels over the entire surface of the screen without significant voltage drop, has not yet been solved. The present invention seeks to provide a solution. This solution should also ensure the encapsulation of the pixels to protect them against oxygen and humidity, and this individually in order to avoid the propagation of local defects. And finally, another objective of the present invention is to propose a method for manufacturing such a device, which is industrially reliable and simple. Objects of the invention

[0020] According to the invention, the problem is solved by an electroluminescent display device comprising a matrix of electroluminescent pixels formed of a plurality of pixels deposited on a substrate, in a matrix arrangement in rows and columns, each pixel being formed of at least three elementary emitting zones, each of said at least three elementary emitting zones belonging to a different group of elementary emitting zones which is distinguished from the elementary emitting zones belonging to other groups by its emission color,

[0021] each elementary emission zone comprising an electroluminescent stack of organic layers called “OLED stack”, which comprises at least one light-emitting organic layer,

[0022] said electroluminescent display device comprising electrical connection bars located outside said pixel matrix and dedicated to powering the upper electrode,

[0023] said OLED stack being arranged between a lower control electrode and a transparent upper electrode, said transparent upper electrode being traversed by the light emitted by the OLED stack.

[0024] According to a first aspect of the invention, the upper electrode (206) comprises

[0025] - a first part which belongs to each elementary emitting zone individually and which is physically and electrically separated from the same first part of all other elementary emitting zones; and

[0026] - a second part located between the elementary emitting zones and which forms a electrical network connected across the entire pixel matrix to said electrical connection bars and physically and electrically isolated from said first parts; and

[0027] a layer of a transparent and conductive material which establishes an electrical connection between the second part and the first parts of each elementary emitting zone, thus enabling the electrical supply of the OLED devices of each elementary emitting zone.

[0028] At least one part of said transparent and conductive material which establishes an electrical connection between the second part and the first parts of each elementary emitting zone is oriented along a substantially vertical plane.

[0029] Said layer of transparent conductive material also serves as encapsulation of the OLED stack and effectively protects it against the ambient atmosphere.

[0030] According to a second aspect, said electroluminescent display device is characterized in that:

[0031] two neighboring control electrodes belonging to two neighboring elementary emitting zones are separated by a space forming a trench and having an insulating surface which covers at least the vertical sides of said neighboring control electrodes and electrically insulates them from each other, and two neighboring control electrodes belonging to two neighboring elementary emitting zones are separated by a space forming a trench and having an insulating surface which covers at least the vertical sides of said neighboring control electrodes and electrically insulates them from each other, for each of the elementary emitting zones, the entire OLED stack with its corresponding upper electrode is separated from the neighboring elementary emitting zones by a conductive and transparent encapsulation layer which protects said OLED stack on its upper face and on all its lateral sides against the ambient air,thus forming a protected island.

[0032] Said first aspect and said second aspect of the invention may be combined, and each variant of the first aspect may be combined with each variant of the second aspect.

[0033] In a first variant of the electroluminescent display device according to the first or second aspect, said layer of a transparent and conductive material has been deposited by a conformal deposition method, and encapsulates the assembly shown by said OLED stack and the upper electrode individually, forming for each elementary emitting zone an encapsulated island.

[0034] In a second variant of the electroluminescent display device according to the first and / or second aspect, which is, for each of the two aspects, compatible with the first variant, the electroluminescent display device according to the invention is characterized in that said layer of transparent and conductive material is made of a material selected from the group formed by: SnO2, ZnO, ITO, AZO, all these materials possibly being doped.

[0035] In a third variant of the electroluminescent display device according to the first and / or the second aspect and / or the third aspect, which is, for each of the two aspects, compatible with the first variant and / or the second variant, the electroluminescent display device according to the invention is characterized in that it comprises an encapsulation system comprising, listed from bottom to top, said layer of a transparent and conductive material, at least one layer of a polymer material in contact with said layer of a transparent and conductive material, and at least one transparent inorganic layer, which may be a layer of an oxide.

[0036] Said layer of a polymer material (280) in contact with said layer of a transparent and conductive material can be structured according to the arrangement of the elementary emitting zones.

[0037] Such a device forms a first object of the present invention.

[0038] A second object of the present invention is represented by a method of manufacturing an electroluminescent display device comprising a matrix of electroluminescent pixels formed of a plurality of pixels deposited on a substrate, in a matrix arrangement in rows and columns,

[0039] each pixel being formed of at least three elementary emitting zones, each of which belongs to a different group of elementary emitting zones which is distinguished from the elementary emitting zones belonging to other groups by its emission color, and

[0040] each elementary emission zone comprising an electroluminescent stack of organic layers, called “OLED stack”, which comprises at least one light-emitting organic layer, and

[0041] said OLED stack being arranged between a lower control electrode and a transparent upper electrode, said transparent upper electrode being crossed by the light emitted by the OLED stack, and

[0042] said electroluminescent display device comprising electrical connection bars dedicated to powering the upper electrode, and

[0043] in which method:

[0044] (i) a substrate provided with a control electrode is supplied for each elementary emitting zone and an insulating layer between two neighboring control electrodes, said insulating layer covering the sides of said neighboring control electrodes as well as the substrate between said two neighboring control electrodes, and

[0045] (ii) in a first group of steps, a first OLED stack, an upper electrode and, using a conformal deposition technique, a first layer of a transparent conductive oxide are first deposited, then a photoresist is arranged at the location of the elementary emission zones of the first group which protects

[0046] - the upper horizontal surface, which is the surface above the electrode of order, and

[0047] - the flank of the control electrode and

[0048] - at least a portion of the lower horizontal surface located between two electrodes neighboring commands,

[0049] and then the areas not protected by the photoresist are etched up to the upper surface of the control electrode for the elementary emission areas not protected by the photoresist and up to the surface of the insulating layer located in the natural space between two neighboring control electrodes,

[0050] and finally, optionally, said photoresist is removed;

[0051] (iii) in a second group of steps, a second OLED stack, an upper electrode and, using a conformal deposition technique, a second layer of a transparent conductive oxide are deposited, then a photoresist is arranged at the location of the elementary emission zones of the second group, and then the zones not protected by the photoresist are etched up to the upper surface of the control electrode for the elementary emission zones not protected by the photoresist and up to the surface of the insulating layer located in the natural space between two neighboring control electrodes,

[0052] and finally, optionally, said photoresist is removed;

[0053] (iv) in a third group of steps, a third OLED stack, an upper electrode and, using a conformal deposition technique, a third layer of a transparent conductive oxide are deposited, then a photoresist is arranged at the location of the elementary emission zones of the second group, and then the zones not protected by the photoresist are etched up to the upper surface of the control electrode for the elementary emission zones not protected by the photoresist and up to the surface of the insulating layer located in the natural space between two neighboring control electrodes,

[0054] and finally, optionally, said photoresist is removed. In a first variant of this method, the photoresists are removed, and at the end of the third group, of steps a polymeric encapsulation layer followed by a transparent inorganic layer, preferably an oxide layer, and even more preferably an alumina or silica layer.

[0055] In a second variant of this process, the photoresists are not removed, and a transparent inorganic layer is deposited at the end of the third group of steps, preferably an oxide layer, and even more preferably an alumina or silica layer. Brief description of the figures

[0056] Figures 1 to 6 illustrate general, known aspects of certain types of OLED devices and displays.

[0057] Figures 7 to 31 illustrate aspects and embodiments of the invention; they are not intended to limit the scope of the invention.

[0058] More particularly, figures 7 to 19 illustrate the structure of an OLED display device according to the invention, and certain key steps in its manufacture.

[0059] Figures 20 to 31 illustrate in greater detail steps of a method of manufacturing an OLED display device according to the invention.

[0060] [Fig. 1] shows the electrical diagram of a known type OLED matrix screen.

[0061] [Fig.2] shows five known examples of arranging sub-pixels of different colors to form a pixel capable of displaying the desired color.

[0062] [Fig.3] schematically shows a perpendicular cross-section of a state-of-the-art OLED display with a white-emitting OLED and color filters. This figure shows several pixels.

[0063] [Fig.4] schematically shows a perpendicular cross-section of an OLED display similar to that of [Fig.3], in which each pixel is formed of three sub-pixels. The figure shows a single pixel with its three sub-pixels.

[0064] [Fig.5] schematically shows a perpendicular cross-section of an OLED display similar to that of [Fig.4], in an embodiment with sub-pixels each emitting in a different color, and which does not use color filters.

[0065] [Fig.6] reproduces [Fig.5] of document WO 2019 / 193290.

[0066] [Fig.7] shows a top-view of an intermediate product according to the invention, manufactured using steps of the process according to the invention.

[0067] [Fig.8] schematically shows a perpendicular cross-section of a structured stack of layers deposited on a substrate which represents the intermediate product of [Fig.7]. [Fig.8] represents this section in a zx or zy plane, respectively, according to three different cutting lines indicated in [Fig.7], namely: aa (top figure), bb (middle figure), cc (bottom figure).

[0068] [Fig.9] shows a top-view of an intermediate product according to the invention, manufactured using steps of the method according to the invention. This intermediate product corresponds to the same manufacturing stage as the intermediate product of [Fig.8], but carries a stencil having a rectangular opening through which the OLED stack is deposited, in a sequence of subsequent steps, by successive evaporation of organic layers.

[0069] [Fig. 10] shows a top-view of an intermediate product which corresponds to a manufacturing stage which follows that of [Fig.9]. The intermediate product here carries a stencil having a rectangular opening through which the upper electrode is deposited, in a sequence of subsequent steps.

[0070] [Fig. 11] schematically shows a perpendicular cross-section of a structured stack of layers deposited on a substrate which represents the intermediate product after deposition of the upper electrode using the stencil shown in [Fig. 10],

[0071] [Fig. 12] shows a top-view of the intermediate product which corresponds to the same stage of manufacture as that of [Fig. 11].

[0072] [Fig. 13] schematically shows a perpendicular cross-section of the intermediate product of [Fig. 11] after deposition of a transparent conductive oxide (TCO) layer according to a section aa indicated in [Fig.7].

[0073] [Fig. 14] schematically shows a perpendicular cross-section of the intermediate product of [Fig. 12] along a section dd indicated in [Fig. 12].

[0074] [Fig. 15] schematically shows a perpendicular cross-section of the intermediate product of [Fig. 12] along a dd section indicated in [Fig. 12]; this figure shows the side of the OLED stack.

[0075] [Fig. 16] schematically shows a perpendicular cross-section of a device after sequences of steps allowing the deposition and structuring of 3 OLED devices with red, green, and blue emission, according to a section aa indicated in [Fig.7],

[0076] [Fig. 17] schematically shows a perpendicular cross-section of a device after sequences of steps allowing the deposition and structuring of 3 OLED devices with red, green, and blue emission, (TCO) according to a bb section indicated in [Fig.7].

[0077] [Fig. 18] schematically shows a perpendicular cross-section of the intermediate product of [Fig. 16] and [Fig. 17] after the deposition of a polymer layer followed by the deposition of an oxide layer, according to a section bb indicated in [Fig.7].

[0078] [Fig. 19] schematically shows a perpendicular cross-section of the same intermediate product as that shown in [Fig. 18], along a section bb indicated in [Fig.7]. This figure represents an alternative embodiment to that shown in [Fig. 18].

[0079] [Fig.20] schematically shows a perpendicular cross-section of an intermediate product obtained from the substrate of [Fig.8], by a first sequence of process steps, represented in a zx or zy plane, respectively, according to three different section lines indicated in [Fig.7], namely: aa (top figure), bb (bottom figure).

[0080] [Fig.21] illustrates a second sequence of process steps which follows those of [Fig.20].

[0081] [Fig.22] illustrates a third sequence of process steps which follows those of [Fig.21],

[0082] [Fig.23] illustrates a fourth sequence of process steps which follows those of [Fig.22]. This sequence of steps is optional.

[0083] [Fig.24] illustrates a fifth sequence of process steps which follows those of [Fig.23],

[0084] [Fig.25] illustrates a sixth sequence of process steps which follows those of the [Fig.24].

[0085] [Fig.26] illustrates a seventh sequence of process steps which follows those of [Fig.25],

[0086] [Fig.27] illustrates an eighth sequence of process steps which follows those of [Fig.26]. This sequence of steps is optional.

[0087] [Fig.28] illustrates a ninth sequence of process steps which follows those of [Fig.27],

[0088] [Fig.29] illustrates a tenth sequence of process steps which follows those of the [Fig.28].

[0089] [Fig.30] illustrates an eleventh sequence of process steps which follows those of [Fig.29].

[0090] [Fig.31] illustrates a twelfth sequence of process steps which follows those of [Fig.30]. This sequence of steps is optional.

[0091] The numerical references used in the figures and in this description are listed below.

[0092] 10 OLED display (of known type)

[0093] 12 Pixel Matrix

[0094] 14 OLED Diode

[0095] 16 Control circuit of 14

[0096] 18.20 Transistor

[0097] 22 Capacitor

[0098] 30 Control circuit (addressing circuit) for lines

[0099] 32 Video control circuit (addressing circuit)

[0100] 34 Power supply circuit for columns

[0101] 36 Control unit

[0102] 38 Conductive track addressing the lines

[0103] 40 Conductive track for video signal

[0104] 42 Conductive track addressing the columns

[0105] 50 Pixel

[0106] 51,52,53,54 Subpixel (red 51, blue 52, green 53, white 54)

[0107] 70 OLED display (of known type)

[0108] 71 Substrate

[0109] 72,73,74 Sub-pixel control electrode

[0110] 75 Gap-fill element

[0111] 76 Layers (stack) OLED

[0112] 77 Encapsulation layer

[0113] 7 8 Glass slice

[0114] 80 Electroluminescent layer of 76

[0115] 81,82,83,84 Charge injection and transport layer

[0116] 85 Electrode

[0117] 90 Pixel

[0118] 91,92,93 Subpixel filter (blue 91, red 92, green 93)

[0119] 95,96,97 Electroluminescent layers Red, Green, Blue

[0120] 98 Electrode for pixel

[0121] 99 Common electrode

[0122] 100 OLED display device

[0123] 101 Sub-pixel (elementary emitting area)

[0124] 102 Base electrode (control electrode of 101)

[0125] 104 Separator

[0126] 105 OLED Stack

[0127] 106 Upper injection layer

[0128] 107 Common conformal electrode

[0129] 108 Planarization layer (smoothing layer)

[0130] 109 Color Filter

[0131] 110 Substrate

[0132] 111 Natural space (“gap”)

[0133] 112 Edge of 123 on 102

[0134] 113 Pixel

[0135] 123 Filling element with insulating surface

[0136] 200 Device according to the invention

[0137] 201 Sub-pixels (elementary emitting area)

[0138] 202 Sub-pixel control electrode

[0139] 205 OLED stack (OLED device)

[0140] 206 Upper electrode

[0141] 210 Substrate

[0142] 211 Natural space (“gap”) between electrodes 202

[0143] 212 Edge of 223 on 202

[0144] 217 Busbar for the upper electrode 206

[0145] 223 Insulation layer

[0146] 225 islet

[0147] 250 Transparent Conducting Oxide (TCO) Layer

[0148] 280 Polymer layer (photoresist)

[0149] 281 Inorganic layer

[0150] 282 Encapsulation system

[0151] 300 Stencil for depositing 205

[0152] 310 Opening of 300

[0153] 400 Stencil for depositing 206

[0154] 410 Opening of 400

[0155] For layers 202, 205, 206 and 250, the letter a, b, or c indicates membership in a group of elementary emitting zones, while the numbers 1, 2 and 3 designate the position of this layer on the elementary emitting zone: for example, the reference 250-1 designates the upper horizontal part of layer 250, the reference 250-2 its lower horizontal part (located in the natural space between neighboring electrodes 202), and the reference 250-3 its side (i.e. its substantially vertical part). Detailed description 1. Terminology

[0156] In the present description, the expression "elementary emitting zone" designates the smallest emission zone which is individually addressable. In the case of color screens in which several elementary emitting zones form a pixel, the person skilled in the art usually uses the term "sub-pixel" to designate such an elementary emission emitting zone. 2. General aspects of OLED displays

[0157] [Fig.l] schematically shows the circuit of an OLED display 10 of known type which comprises a pixel matrix unit 12 capable of producing an image, and a control unit 36. The OLED diodes 14 and their control circuits 16 are arranged so as to form pixels in the pixel matrix unit 12, said pixel matrix comprising rows (horizontal) and columns (vertical). Each control circuit 16 of a pixel 12 comprises a plurality of transistors 18, 20 typically produced in CMOS (Complementary Metal Oxide Semiconductor) technology in the case of micro-screens, or thin film transistors (TFT - Thin Film Transistor), and a capacitor 22. The control unit 36 ​​controls a control circuit for the rows 30 and a video addressing circuit 32, as well as a power supply circuit 34 for addressing the pixel columns; it ensures the addressing of the pixel circuits and controls the light emission of the OLED diodes 14. The row control circuit is connected to the conductive tracks 38 addressing the scanning lines of the pixel matrix. It selects the scanning lines (i.e., the conductive tracks 38 addressing the lines) according to a signal from the control unit 36, and applies a voltage to turn on the transistors 18 located on the selected scanning line.

[0158] The video addressing circuit 32 is connected to conductive tracks 40 addressing the columns of the video signal. The video addressing circuit 32 receives a video signal from the control unit 36 ​​and sends a voltage to the conductive tracks 40 of the columns of the video signal according to the conductive tracks of the lines selected by the corresponding control circuit 30. This voltage signal is written to the capacitor 22 through the transistor 18 of the OLED diode 14 of the selected pixel line. The control transistor 20 sends a current corresponding to the recorded voltage to the OLED diode 14, and as a result the OLED diode 14 of the selected line 38 emits light.

[0159] The power supply circuit 34 is connected to the power supply conductive tracks 42 of the pixel columns; it supplies the OLED diodes 14 via the conductive tracks 42 and the transistors 20 of the selected pixel row.

[0160] This principle of addressing an OLED diode forming a pixel in a pixel matrix, known from WO 2019 / 193 290 A1 (MicroOled), can be applied, in a manner also known as such, to the addressing of an OLED diode forming a sub-pixel in a pixel matrix of a color display device, in which each pixel comprises a plurality of sub-pixels (most often three or four) of different colors; this will be explained here in relation to [Fig. 2] which shows five examples for the geometric arrangement of these sub-pixels 51, 52, 53, 54 to form a pixel 50 capable of displaying the desired color. These geometric arrangements are known to those skilled in the art under the names “RGB Stripe”, “RGB Quad”, “RGBW Quad”, “Delta” and “Honeycomb”. In these figures the sub-pixels are of red 51, blue 52 and green 53 colors, and may comprise, as in the case of the RGBW Quad, in addition a white sub-pixel 54 to increase the brightness of the pixel 50.

[0161] The addressing principle just described in relation to [Fig.l] and [Fig.2] is one of the addressing principles that can be implemented in relation to the present invention. The color can be obtained by controlling the color emitted by the OLED layers forming the sub-pixels or by color filters that modify the white color of the light emitted by the sub-pixels, as will be explained below in relation to [Fig.3], [Fig.4] and [Fig.5] which schematically show OLED micro-displays according to the state of the art; they illustrate the problem that the present invention seeks to solve.

[0162] In [Fig.3] is shown an overall schematic view of the structure of the device 70: we can distinguish the substrate 71 (typically of CMOS type, the addressing circuits and components are not shown), the control electrodes 72, 73, 74 of the elementary emitting zones (sub-pixels) separated by a gap-fill element 75, the stack of organic OLED layers 76 capable of emitting white light, the encapsulation layer 77, the colored filters of blue 91, red 92 and green 93 forming a pixel 90, the glass slice 78 as a protective cover. The size of the sub-pixels is typically of the order of 3.5 pm to 5 pm. It is noted that in this device according to the state of the art the OLED layer 76 extends over all the pixels of the device.

[0163] [Fig.4] shows an enlarged view of a device similar to that shown in [Fig.3]; this view is limited to a single pixel 90. The sub-pixels are defined, on the one hand, by the electrodes 72,73,74 which allow their individual addressing, and by the corresponding color filters 91,92,93 which modify the light emitted by the white emission OLED stack 76 which extends over the entire surface of the device. The space between two neighboring sub-pixel control electrodes 72, 73 may be filled by a filling element 75. Said OLED stack 76 here comprises the light-emitting layer 80 itself, which is sandwiched between two charge transport layers 81, 82. More precisely, in a typical device, layer 81 comprises a hole injection and transport layer, and layer 82 an electron injection and transport layer.But it is also possible to use a so-called "inverse" stack, in this case the layer 82 comprises a hole injection and transport layer, and the layer 81 an electron injection and transport layer. The layers 81 and 82 can respectively comprise a single layer which fulfills both the functions of injection and transport of the respective charges, or several layers, for example a layer for injection and another for transport of the respective charges; this is represented in [Fig.4] by the four layers 81, 82, 83, 84. A common electrode 85 evacuates the charges.

[0164] This device according to the state of the art has parasitic currents; this is illustrated in [Fig.4]. Indeed, if when a sub-pixel (for example 73) is switched on, the main current passes directly through (marked by a thick arrow) the OLED layer in the shortest direction (i.e. vertical relative to the substrate 71), part of the current propagates along other conduction paths, insofar as these conduction paths have a sufficiently low resistivity. Thus, a parasitic current is observed which propagates in the charge transport layer 81, namely in the plane of the substrate, and which then passes through the OLED layer in the neighboring sub-pixel 72 or 73. This parasitic current is marked by two dotted arrows. It leads to a parasitic light emission in the neighboring sub-pixels, which modifies the image resolution of the display and reduces the fidelity of its color.The present invention seeks to provide a means for reducing this parasitic current.

[0165] [Fig. 5] shows another device of known type in which the color of a pixel 90 is not generated, as in the devices of [Fig. 4] and [Fig. 5], by a white emission OLED element matched with color filters for each of the three sub-pixels, but by three sub-pixels provided with electroluminescent layers 95, 96, 97 which emit directly in red, blue and green. In this embodiment, each elementary emitting zone (sub-pixel) 95, 96, 97 has its own addressing electrode 98a, 98b, 98c, but the first charge injection and transport layer 83 (for example holes), and / or the second charge injection and transport layer (for example electrons) 84 and the common electrode 99 are common to simplify device manufacturing. The problem of parasitic currents is the same as that described in relation to [Fig.4]; the contribution of the hole injection and transport layer 83 is preponderant in these parasitic currents.

[0166] In terms of luminous efficiency, the device of [Fig. 5] is significantly better than that of [Fig. 3]. On the other hand, its industrial manufacture can be quite difficult, since the organic materials that constitute an OLED device are generally deposited by a vacuum thermal evaporation process. To generate sub-pixels of different color, as in the device of [Fig. 5], a stencil (called a "shadow mask" in English) is used which is placed close to the substrate on which the OLED device is to be produced and which has openings that correspond to the position of a first type of sub-pixel during the deposition of a first type of stack of layers, for example for a red OLED. Then the operation is repeated for a second type of stack, for example for a green OLED, using a second stencil having openings that correspond to the position of the second type of sub-pixel.Then we can perform a third operation of this type in order to create a third type of sub-pixel, for example with a blue OLED.

[0167] This method does not allow the production of sub-pixels smaller than about 20 pm with a sufficiently reliable process, knowing that for micro-screens a sub-pixel size of the order of 2 pm to 5 pm would be required. In the semiconductor field, structures of this size are produced by photolithography and etching methods, but since the organic materials used in OLED devices are extremely sensitive to water and oxygen, among other things, photolithography processes cannot be used as such to structure these materials. It is observed that when trying to transpose the photolithography and etching methods known from the semiconductor field to the manufacture of OLED micro-displays, the OLED stack is attacked laterally, i.e. in its edge which is not protected, during the etching operations.This attack leads to a localized degradation of the OLED stack, which risks propagating laterally. In a favorable case, this will simply reduce the emissive surface of the sub-pixel (which is already not desirable, especially since this propagation is an evolutionary process, and any reduction in the emissive surface will lead to an increase in the current density of the device which will reduce its operational lifetime); in an unfavorable case, this ends up completely destroying the sub-pixel. According to an essential characteristic of the present invention, the edges and edges of the elementary emitting zones (sub-pixels) are protected on all sides.

[0168] The invention will be explained here by way of example with a substrate structure similar to that of [Fig.5] of WO 2019 / 193290 which is reproduced here as [Fig.6], with adjusted reference numerals, but it is also applicable to other structures which serve to separate OLED devices between pixels, such as for example the structures described in WO 2021 / 071630 or WO 2023 / 154188, discussed above.

[0169] [Fig.6] shows a pixel 113 of an OLED display device 100 deposited on a substrate 110 (typically of CMOS type) with three elementary emitting zones (sub-pixels) 101a, 101b, 101c each of which is controlled by an individual control electrode 102a, 102b, 102c. The white OLED stack 105, which is common to all the pixels of the screen in question, is separated between two neighboring sub-pixels (101a, 101b; 101b, 101c; 101c, 101a) by a separator 104 which occupies the natural space 111 (also called the “gap”) between the electrodes 102a, 102b; 102b, 102c; 102c, 102a of two neighboring sub-pixels 101a, 101b; 101b, 101c; 101c, 101a. This separator 104, which is in the form of a trench, comprises a filling element 123 with an insulating surface. The filling element 123 has a rim 112 which extends over a small part of the control electrode 102, forming the border of the latter. The conformal electrode 107 is common to all the subpixels, as well as the upper injection layer 106, the latter being optional.

[0170] This prior art structure very satisfactorily solves the crosstalk problem, but since it uses elementary emitting areas (sub-pixels) 101a, 101b, 101c with the same white emitting OLED stack to form a pixel 113, whose light passes through color filters 109 (arranged in the form of a plate which is placed on a smoothing layer 108) in order to generate elementary colors R, G and B at the output of the device 100, it does not solve the problem of providing a very efficient and very bright device. It would be desirable to be able to manufacture a device of similar structure, but without color filters and with OLED stacks emitting a different color for each group of sub-pixels, for example the three elementary colors red, blue and green.It would be desirable to be able to manufacture this device in the form of a micro-display with a size of the elementary emitting zones less than 20 pm, preferably less than 5 pm, and even more preferably between approximately 1 pm and approximately 5 pm. To achieve this objective, it was necessary to invent a new method for manufacturing a micro-display; the inventors of the present application have succeeded in doing so. 3. Description of a device according to the invention

[0171] In this section 3, as well as in the following section 4, the device according to the invention will now be explained, which will be described by its structure, by its manufacturing method, and at different stages of its manufacturing. This device, as shown here, comprises three groups of elementary emitting zones (sub-pixels) of different types. The expression “type” of elementary emitting zone or OLED stack refers here to its emission color, and the expressions “elementary emitting zone of a first type”, “elementary emitting zone of a second type” and “elementary emitting zone of a third type” will be used in what follows. In the figures showing a top view, these different types of elementary emitting zones are identified by the letters R, G and B which designate the emission color.

[0172] [Fig.7] shows a top-view of an intermediate product according to the invention, manufactured using steps of the method according to the invention. In this example, the arrangement of the sub-pixels is of the “RGB-quad” type, as shown in [Fig.2], the middle example. This example does not limit the scope of the present invention, which applies to any type of arrangement of sub-pixels.

[0173] The structure of the substrate with its different deposited structured layers is shown schematically in [Fig.8] which represents the same intermediate product of [Fig.7]. [Fig.8] schematically shows three perpendicular cross-sections of a structured stack of layers: the figure at the top represents a section in a zx plane along the line aa indicated in [Fig.7], the figure in the middle represents a section in a zy plane along the line bb indicated in [Fig.7], and the figure at the bottom represents a section in a zy plane along the line cc indicated in [Fig.7],

[0174] As explained in relation to [Fig.7] and [Fig.8], this intermediate product comprises in particular a substrate 210, which typically comprises active matrix type addressing circuits. In a known manner, these addressing circuits, which are not shown in these figures, can be produced in TFT (Thin Film Transistor) or CMOS (Complementary Metal Oxide Semiconductor) technology. The substrate also supports electrodes 202a, 202b, 202c of the sub-pixels; these electrodes are separated by a natural space 211 which has the shape of a trench.

[0175] The intermediate product also comprises an insulating layer 223. This is a thin layer deposited by a conformal deposition method such as, for example, the plasma-enhanced chemical vapor deposition (PECVD) technique or by ALD. This thin insulating layer is typically made of Si3N4, SiO2, or Al2O3. It covers at least the vertical surfaces of the electrodes 202 and typically the entire space 211. It may also slightly cover the edge of the pixel (i.e., the upper horizontal surface of the electrode 202; this edge bears the numerical reference 212 in [Fig. 8].

[0176] As can be seen in [Fig.8], this space 211 which has the shape of a trench separates the two neighboring electrodes 202a, 202b; 202b, 202c; 202c, 202c of two neighboring elementary emission zones up to the substrate, an insulation layer 223 being arranged at the bottom of said trench 211 and on the vertical walls of the electrodes 202. The deposition of said insulation layer 223 must be done in such a way that even after its deposition, a trench remains between two neighboring electrodes of two neighboring elementary emission zones.

[0177] In addition, compared to [Fig.6], the device according to the invention comprises large connection pads for the upper electrode of the OLED device at the top and bottom of the matrix, in the form of horizontal metal lines (“bus bars”, numerical reference 217).

[0178] This substrate structure then makes it possible to create islands of isolated and encapsulated OLED sub-pixels. First, the stack of organic layers that form the OLED stack 205 is deposited. By a sequence of successive layer deposition steps, according to a directional deposition method known and used in the OLED device industry, the organic layers that form the OLED stack are deposited through the opening 310 of a stencil 300 that delimits the deposition zone; this is illustrated in [Fig. 9]. This is a directional deposition, that is to say the layers will form mainly on the horizontal surfaces, but not on the surfaces vertical, as can be seen in [Fig.l 1] which represents a perpendicular cross-section. The thermal evaporation technique can be used as a directional deposition technique.

[0179] As described above in relation to [Fig.4], said OLED stack comprises a light-emitting layer itself, as well as one or more charge carrier injection and transport layers.

[0180] In a sequence of manufacturing steps, a top electrode 206 is then added, which is typically a thin layer of silver that is deposited by the same method as the OLED layers. This silver layer must be semi-transparent because the light emitted by the OLED device leaves the device through this layer. For this deposition, a stencil 400 having an opening 410 wider than that 310 of the stencil 300 used for the layers 205 is used in order to establish an electrical contact between the top electrode 206 and the busbars 217; this is illustrated in [Fig. 10].Since this is also a directional deposition, the layers will form mainly on horizontal surfaces, but not on vertical surfaces, which means that the layer 206 is discontinuous between the part which is at the top of the OLED device (reference number 206-1) and the part 206-2 which is at the bottom of the space 211; consequently, the OLED device is not powered.

[0181] It is to allow the deposition of frames 206-2 of the upper electrode 206 at the bottom of the free space 211 between two neighboring electrodes 202 that the deposition of the insulation layer 223 must be done in such a way that even after the deposition of said insulation layer 223, a trench remains between two neighboring electrodes of two neighboring elementary emission zones. These frames form a connected network, as will be explained below in relation to [Fig. 12].

[0182] [Fig. 11] shows a perpendicular cross-section of the intermediate product resulting from this deposition of the upper electrode 206 through the opening 410 of the stencil 400, while [Fig. 12] shows a top view of this same intermediate product.

[0183] As can be seen in [Fig. 12], the portion 206a-2 of the layer 206a forms a network connected through the substrate. To power the OLED devices 205a on the pixel, it is therefore necessary to create an electrical connection between the network formed by the layers 206-2 and the top of the OLED 205. This is accomplished by depositing a layer of a transparent conductive oxide (TCO) 250 by a conformal deposition method, typically ALD; this layer is illustrated in [Fig. 13]. Thanks to the conformal deposition, the layer 250a covers the horizontal surface 250a-1 of each elementary emitting zone, the surface 250a-2 at the bottom of the natural space 211 between neighboring electrodes 202 as well as the flank 250a-3 of this natural space 211, thus ensuring electrical continuity over the entire surface of the intermediate product. In this case, even a low conductivity of the 250a layer is sufficient to power the pixel, as will be explained below in connection with [Fig.14] and [Fig.15].

[0184] [Fig. 14] shows the section marked dd in [Fig. 12], i.e. directly at the edge of the pixel. The part 250-3 of the layer 250 which covers the vertical flank of the pixel 202 (and which is outside the section shown here) must carry the current from the part 206-2 of the upper electrode layer (which is therefore connected via said continuous network formed by this layer to the busbar 217) to the part 206-1 in order to power the OLED device 205. For this, it has the surface S shown in [Fig. 15] which corresponds to that of the flank 250-3 of the layer 250. In this figure, which shows the flank of a green elementary emitting zone 202b of [Fig. 12], the typical dimensions in the case of an AMOLED micro-screen according to the invention have been indicated.In an advantageous embodiment, the largest dimension of length or width of an elementary emitting zone 201 is between about 3 pm and about 5 pm, and the thickness of the OLED stack is between about 0.3 pm and about 0.5 pm.

[0185] If layer 250 has for example a square resistance of 10,000 Ohm / square (which is the worst case), said electrical connection between parts 206-2 and 206-1 has a resistance of the order of 1,000 Ohm. Since pixel 202 has four sides, the resulting resistance is 250 Ohm. A typical pixel current is of the order of 10 nA, the voltage drop between parts 206-2 and 206-1 will therefore be 2,500 nV or 2.5 pV, which is completely negligible. The voltage drop across the active surface of the screen therefore depends only on the conductivity of the network formed by layer 206-2 which is generally sufficient, as it is a metal layer (typically silver or aluminum).

[0186] The layer 206a serves at the same time as an encapsulation layer, i.e. as protection of the OLED stack 205a against oxygen, water, and other substances likely to degrade the OLED layers. This encapsulation function makes it possible to structure the OLED layers by photolithography and etching methods, which are methods known in the semiconductor world, but which have not yet been used in the manufacture of OLED micro-displays. In order not to make this section 3 “Description of a device according to the invention” too cumbersome, the description of the sequences of steps allowing this structuring of the OLED layers is described in a separate section below.

[0187] Thus it is possible to deposit and structure OLED stacks 205a, 205b, 205c of different emission colors. [Fig. 16] and [Fig. 17] show as an example the result of such an operation to obtain pixels emitting in red, green and blue. The device shown schematically in [Fig. 16] and [Fig. 17] can operate as an electroluminescent display device. However, it is preferable to complete this device by depositing additional encapsulation layers. One of the advantages of the present invention lies in the simplification of the encapsulation system compared to those known from the state of the art.

[0188] A state-of-the-art encapsulation system may comprise, as described for example in documents WO 2011 / 128802 or US 9,082,999, a tri-layer alumina / polymer / alumina complex. The present invention makes it possible, in an advantageous embodiment, to simplify this encapsulation system by using the TCO layer 250 as the first layer of an encapsulation system 282, for example of a tri-layer complex. Such a tri-layer complex in encapsulation system format 282 may comprise, listed from top to bottom: at least one transparent inorganic layer 281, a transparent polymer layer 280, a transparent and conductive oxide layer 250. Such an encapsulation system may be deposited by a sequence of successive layer deposition steps. Said transparent inorganic layer 281 may be an oxide layer, preferably made of alumina or silica.

[0189] Two variants of this embodiment are shown in [Fig. 18] and [Fig. 19], respectively, where the references 280 and 281 designate, respectively, the polymer layer and the transparent inorganic layer, preferably an oxide layer, the latter being able to be in particular silica or alumina. In the case of [Fig. 19], the polymer layer 280 is structured according to the arrangement of the elementary emitting zones. This configuration is interesting in particular in the case where there was previously a structuring of the OLED layers by photolithography methods as described later. In this case, the polymer layers 280a, 280b, 280c can be the photosensitive resins used during the photolithography process.

[0190] This substrate structure according to the invention makes it possible to create islands 225 of elementary OLED emitting zones which are hermetically isolated and encapsulated around the OLED stack 205 which represents the most fragile zone of the microdisplay device 200; such an island 225, each of which represents a single elementary emitting zone, is represented in [Fig. 19] by the box with dotted outlines.

[0191] Thus, the invention not only solves the problem of presenting a high luminance AMOLED type technology which can allow the manufacture of very small elementary emitting zones and which is immune to crosstalk, but also that of presenting such a technology which results, using a reliable industrial process, in a product well protected against oxygen and humidity in the air, and more generally in a durable product.

[0192] 4. Method for structuring OLED layers by depositing elementary emitting zones with different emission colors

[0193] We will now describe, in relation to [Fig.20] to [Fig.31], how the three groups of elementary emitting zones (sub-pixels) are deposited and structured. These figures show for each of these three groups of elementary emitting zones one of these zones. To produce a device with three groups of elementary emitting zones (sub-pixels) each emitting light of a different color (these groups being designated here, by way of example, which represents an advantageous embodiment, by the letters R, G and B (Red, Green, Blue)), three groups of manufacturing steps are required. Each group of steps comprises steps of depositing and structuring a photoresist layer, followed by at least one step of etching the entire encapsulation layer, the cathode and the OLED stack, and finally, optionally, the removal ("stripping") of the photoresist.

[0194] Within the scope of the present description, with regard to the photoresist, techniques which are customary in the field of microelectronics can be used. They typically comprise the deposition of a layer of photoresist, its exposure to structure it on the surface, and then its development. These techniques are known to those skilled in the art and will not be described here, even if they are not commonly used in the field of AMOLED devices.

[0195] The starting point is the intermediate product shown in [Fig.8]. To obtain this intermediate product, a substrate 210 is first provided with a control electrode 202a, 202b, 202c for each elementary emitting zone (this control electrode 202 typically being the anode) and an insulating layer 223 between two neighboring electrodes 202a, 202b, 202c. This insulating layer 223 advantageously has a rim 212 on the surface of the electrode 202.

[0196] The substrate 210 is typically a silicon wafer with circuits structured according to CMOS technology which are configured to address the elementary emitting zones; this technology is known as such and will not be explained here. This substrate 210 typically comprises an insulating layer (not shown in the figures) which may in particular be an oxide, a nitride or an oxynitride; Si3N4 is typically used. The electrical contacts between the pixels are made via vertical channels arranged through this insulating layer by etching; this is also known and is not shown in the figures. On this insulating layer is deposited the electrode 202 for controlling the elementary emitting zones, which is typically chosen so as to be highly reflective.

[0197] In a very advantageous embodiment, the control electrode 202 has a thickness of between approximately 150 nm and approximately 800 nm. Too large a value impairs the resolution of the micro-display because it requires increasing the space between two elementary emitting zones. It is also very advantageous that the thickness of the control electrode 202 is greater than the thickness of the OLED stack 205 which will be deposited on this electrode.

[0198] Said lower electrode 202 may comprise one or more layers. It may for example be made of silver, aluminum, copper, chromium or another metal with high reflectivity. If aluminum is used, it is very advantageous to protect it with a thin layer of a transparent conductive oxide (abbreviated TCO, Transparent Conductive Oxide) having a high resistance to wet etching and oxygen plasma. This TCO is advantageously selected from the group formed by SnO2, ZnO, ITO (Indium Tin Oxide), AZO (Aluminium doped Zinc Oxide), doped SnO2, this doping preferably being arsenic and / or fluorine and / or nitrogen and / or niobium and / or phosphorus and / or antimony and / or aluminum and / or titanium.

[0199] In a first group of steps, shown schematically in [Fig.20] to [Fig.23], a first group of elementary emitting zones (sub-pixels) is deposited, emitting light of a first color, for example red.

[0200] In a first subgroup of steps, the result of which is illustrated in [Fig.20], the following are successively deposited on this substrate 210: (a) a first OLED stack 205a, deposited with a directional deposition technique, i.e. a deposition technique, such as evaporation, which deposits substantially only on a horizontal surface; (b) an upper electrode 206a, and (c) a first TCO layer 250a. Said upper electrode 206a has a polarity opposite to that of the control electrode 202; it is typically a cathode. Said upper electrode is typically deposited with a directional deposition technique; it may be deposited by a conformal technique.

[0201] According to an essential characteristic of the invention, said TCO layer 250a is deposited using a conformal deposition technique, such as ALD; this ensures that it also covers and protects the edge of the OLED stack. This protection is essential during the subsequent etching steps. Since the TCO layer 250a is an electrical conductor, there is therefore electrical continuity between the upper horizontal part 250a-1 of the TCO layer, its lower horizontal part 250a-3 located in the space between the electrodes 202, and its flank 250a-3 (i.e., its lateral part, which is substantially vertical). Said first TCO layer 250 must be transparent; it can, for example, be made of ZnO, AZO, SnO2, ITO.In a variant, several transparent encapsulation layers are deposited at this stage (such a stack is included here in the expression "first encapsulation layer"), using the same material or not; at least the first of these layers must have been deposited by a conformal deposition technique, while the other layers are preferably.

[0202] It is noted that at the end of the first subgroup of steps, the OLED stack deposited on the electrode 202b of the second group of elementary emitting zones and on the electrode 202c of the third group of elementary emitting zones is an OLED stack of the first OLED stack type 205-1. As will be explained below, during the subsequent groups of steps, it will subsequently be replaced by an OLED stack of the second OLED stack type 205-2, and finally, for the locations of third elementary emitting zones, by an OLED stack of the third OLED stack type 205-3.

[0203] In a second subgroup of steps, the result of which is illustrated in [Fig.21], a polymer layer 280a is arranged on the first of these groups of elementary emitting zones, which is typically a photoresist. This photoresist 280a must protect the horizontal surface of the elementary emitting zone, but also its side (i.e. its lateral surface, which may be vertical); this is shown in [Fig.21] in section bb.

[0204] In a third subgroup of steps, the result of which is illustrated in [Fig.22], the stack formed by (listed from top to bottom) the TCO layer 250, the upper electrode 206-1, and the OLED stack 205-1 is etched on the areas not protected by the photoresist 280a. The etching process must be chosen so that the etching stops at the upper horizontal surface of the electrodes 202b and 202c. For etching the encapsulation layer and the electrode, a wet etching is typically used, for example a wet etching usually used in microelectronics, namely stripping with an aqueous solution of tetramethylammonium hydroxide (CAS No.: 75-59-2) at 2.38% by mass; such a product is commercially available, for example from ThermoFischer Scientific™ (electronic grade, catalog no. 44940).Alternatively, a dry etching method can also be used, for example by RIE (Reactive-Ion Etching) or IBE (Ion Beam Etching). The etching of the OLED stack is typically carried out by an oxygen plasma.

[0205] In a fourth subgroup of steps, the result of which is illustrated in [Fig.23], the photoresist 280a is removed. This can be done by a suitable technique, known to those skilled in the art.

[0206] If an oxygen plasma is used to etch a layer deposited directly on the electrode or for the removal of the photoresist 202, it is preferable to avoid the upper surface of the upper electrode being made of metal (aluminum, Ag, etc.) because the oxygen plasma will create an insulating alumina layer. A metal can be used provided that its upper surface is protected by a transparent conductive layer which is not attacked by the oxygen plasma; for this reason, it is advantageous to use a layer of tin dioxide (SnO2) or ITO; other suitable TCO materials can be used.

[0207] The step of removing the photoresist is optional. The photoresist can be kept in place, and it can then serve as an encapsulation layer for the elementary emission zone.

[0208] In a second group of steps, shown schematically in [Fig.24] to [Fig.27], a second group of elementary emitting zones (sub-pixels) is deposited, emitting light of a second color, which is different from said first color, for example green. This figure refers to an embodiment in which the photoresist 280a was removed in the previous step. If the photoresist remained in place at the end of the first group of steps, the deposition of the elementary emitting zones of the second group is done on its upper surface.

[0209] In a first subgroup of steps, the result of which is illustrated in [Fig.24], the following are successively deposited on this substrate 210: (a) a second OLED stack 205b, deposited with a directional deposition technique; (b) an upper electrode 206b, preferably with the same material as that used for the upper electrode 206a of the first group of elementary emitting zones, and (c) a second TCO layer 250b, preferably with the same material as that used for the first TCO layer 250a of the first group of elementary emitting zones. It is noted that at the end of the first subgroup of steps, the OLED stack deposited on the electrode 202c of the third group of elementary emitting zones is an OLED stack 206b of the second OLED stack type. As will be explained below, in later stage groups it will subsequently be replaced by a third-type OLED stack 205c OLED stack.

[0210] It is also noted that the elementary emitting zones of the first group comprise a stack called here “transient stack” consisting of an OLED stack 205b of the second OLED stack type, an upper electrode 206b and a TCO layer 250b; this transient stack will be removed subsequently. The TCO layer 250b covers in particular the sides of the OLED stack 205b. The different portions of the TCO layer 250b are designated here, according to their position relative to the final device, by the numerical references 250b-1, 250b-2, 250b-3, while it is the same material, deposited by a conformal technique. This layer can be continuous and then extends over the three elementary emitting zones.

[0211] In a second subgroup of steps, the result of which is illustrated in [Fig.25], a photoresist 280b is arranged on a second of these groups of elementary emitting zones, as described in relation to the first group of steps.

[0212] In a third subgroup of steps, the result of which is illustrated in [Fig.26], the stack formed by (listed from top to bottom) the second TCO layer 250b, the upper electrode 206-b, and the OLED stack 205b is etched on the areas not protected by the photoresist 280b. The etching method and the materials of the different TCO layers must be chosen so that the etching stops at the upper horizontal surface of the electrode 202c and at the insulating layer 223 and the TCO layer 250a. Said insulating layer 223 may be made of Al2O3, which has the advantage of resisting oxygen plasma etching which is advantageously used to remove the OLED stack.

[0213] In a fourth subgroup of steps, the result of which is illustrated in [Fig.27], the photoresist 280b is removed, as described in relation to the first group of steps, and with the same remarks concerning the choice of techniques and protection of the upper aluminum electrode against a possible oxygen plasma. This step of removing the photoresist is optional. The photoresist can be kept in place, it can thus serve as an encapsulation layer for the elementary emission zone.

[0214] In a third group of steps, shown schematically in [Fig.28] to [Fig.31], a third group of elementary emitting zones (sub-pixels) is deposited, emitting light of a third color, which is different from said first color and said second color, for example blue. If photoresists have remained in place at the end of the first and / or second group of steps, the deposition of the elementary emitting zones of the third group is done on the upper surface of these photoresists.

[0215] In a first subgroup of steps, the result of which is illustrated in [Fig.28], the following are successively deposited on this substrate 210: (a) a third OLED stack 205c, deposited with a directional deposition technique; (b) an upper electrode 206c, preferably with the same material as that used for the upper electrode 206a and / or 206b of the first and second group of elementary emitting zones, and (c) a third TCO layer 250c, preferably with the same material as that used for the first and / or second encapsulation layer 250a, 250b of the first and second group of elementary emitting zones.

[0216] We note the presence of a transient stacking on the elementary emitting zones of the first and second groups.

[0217] In a second subgroup of steps, the result of which is illustrated in [Fig.29], a photoresist 280c is arranged on the third of these groups of elementary emitting zones, as described in relation to the first group of steps.

[0218] It should be noted that this second subgroup of steps is optional: layers 205c, 206c and 250c can be left in place throughout, if a certain loss of brightness resulting from the absorption by layers 205c, 206c and 250c of part of the light emitted by layers 205a and 205b. In return, this simplifies the manufacturing process. If this approach is chosen, layer 205c must be the one with the shortest emission wavelength, otherwise emission in a lower layer could create photoluminescence in layer c.

[0219] In a third subgroup of steps, the result of which is illustrated in [Fig. 30], the stack formed by (listed from top to bottom) the third TCO layer 250c, the upper electrode 206c, and the OLED stack 205c is etched on the areas not protected by the photoresist 280c. The etching process must be chosen so that the etching stops at the TCO layer 250a and 250b; to etch the OLED layer, an oxygen plasma is advantageously used. This third subgroup of steps is optional, for the same reasons that the second subgroup of steps just presented is optional.

[0220] In a fourth subgroup of steps, the result of which is illustrated in [Fig.31], the photoresist 280c is removed, as described in relation to the first group of steps, and with the same remarks concerning the choice of techniques and protection of the upper aluminum electrode against a possible oxygen plasma. This step of removing the photoresist is optional. The photoresist can be kept in place, it can thus serve as an encapsulation layer for the elementary emission zone.

[0221] A device of the OLED micro-display type is thus obtained, shown in [Fig. 31], with the three sub-pixels electrically and hermetically insulated, said sub-pixels having OLED stacks emitting in a different color, namely R (205-1), G (205-2) and B (205-3). The hermetic insulation, shown in [Fig. 31] under the firm of islands 225a, 225b, 225c, protects the OLED stack against the ambient atmosphere.

[0222] In subsequent steps, not shown here, the microdisplay device may be coated with one or more additional encapsulation layers. 5. Advantages of the invention

[0223] The invention has many advantages. It makes it possible to produce OLED microdisplays with three elementary sub-pixels, having a very fine resolution with sizes of elementary emission zones (sub-pixels) below 20 pm, preferably below 10 pm, and even more preferably below 5 pm thanks to the high resolution of the photolithography methods used. These micro-displays have excellent efficiency and brightness thanks to the use of different OLED stacks per group of sub-pixels, which are optimized with respect to an emission of the primary color of the respective sub-pixel, thanks to the density high surface area of ​​elementary emitting zones, and thanks to the absence of color filters. They have excellent reliability, thanks to the total protection, including lateral, of the OLED stacks during the etching steps and throughout the lifetime of the device. Each elementary emission zone being separated and isolated from neighboring elementary emission zones, the device avoids diatony.

[0224] The invention, which has been explained here in detail for a configuration of elementary emitting zones of the RGB Quad type, makes it possible to produce OLED micro-displays with all other possible sub-pixel arrangements, for example with the RGB Stripe, RGBW Quad, Delta, Honeycomb arrangements, etc.

[0225] The manufacturing method uses known techniques and methods for manufacturing semiconductor and microelectronic devices, as well as common methods for manufacturing OLEDs. A particular advantage of the method according to the invention lies in the fact that it does not require the OLED stacks to be deposited through stencils having small openings, i.e. the size of the elementary emitting zone. This is illustrated here by [Fig. 9] which shows the opening 310 of a stencil 300 placed on the surface of the substrate shown in [Fig. 8]. In the method according to the invention, the deposition of the OLED stack is common to all the elementary emitting zones.It is by etching a surface partially masked by photoresist pads, the latter using techniques allowing a lateral resolution significantly better than the stencil, that elementary emitting zones of very small dimensions are obtained; these dimensions can be approximately 5 pm or preferably less than 5 pm, or even less than 4 pm, or even less than 3 pm. In an advantageous embodiment these dimensions are between approximately 2 pm and approximately 5 pm.

[0226] The upper electrode 206 (generally the cathode) is also deposited in a common manner to all the elementary emitting zones, through the opening 410 of a stencil 400 which is shown schematically in [Fig. 10]. As can be seen by comparing [Fig. 10] with [Fig. 7], the opening covers the connection bar 217 to which the upper electrode 207 is therefore electrically connected.

Claims

1. Claims An electroluminescent display device (200) comprising a matrix of electroluminescent pixels formed of a plurality of pixels deposited on a substrate (210), in a matrix arrangement in rows and columns, each pixel being formed of at least three elementary emitting zones, each of said at least three elementary emitting zones belonging to a different group of elementary emitting zones which is distinguished from the elementary emitting zones belonging to other groups by its emission color, and each elementary emission zone comprising an electroluminescent stack of organic layers (205), called an "OLED stack", which comprises at least one light-emitting organic layer, and said OLED stack (205) being arranged between a lower control electrode (202) and a transparent upper electrode (206), said transparent upper electrode (206) being traversed by the light emitted by the OLED stack (205), said electroluminescent display device (200) comprising electrical connection bars (217) located outside the pixel matrix and dedicated to powering the upper electrode (206), said electroluminescent display device being characterized in that the upper electrode (206) comprises - a first part (206-1) which belongs to each elementary emitting zone individually and which is physically and electrically separated from the same first part (206-1) of all the other elementary emitting zones; and - a second part (206-2) located between the elementary emitting zones and which forms an electrical network connected across the entire pixel matrix to connection bars (217) and physically and electrically isolated from the first parts (206-1); and - a layer of a transparent and conductive material (250) which establishes an electrical connection between the second part (206-2) and the first parts (206-1) of each elementary emitting zone thus enabling the power supply of the OLED devices in each elementary emitting zone.

2. Electroluminescent display device comprising a matrix of electroluminescent pixels formed of a plurality of pixels deposited on a substrate (210), in a matrix arrangement in rows and columns, each pixel being formed of at least three elementary emitting zones, each of said at least three elementary emitting zones belonging to a different group of elementary emitting zones which is distinguished from the elementary emitting zones belonging to other groups by its emission color, each elementary emission zone comprising an electroluminescent stack of organic layers (205), called "OLED stack", which comprises at least one light-emitting organic layer, said OLED stack (205) being arranged between a lower control electrode (202) and a transparent upper electrode (206), said transparent upper electrode (206) being traversed by the light emitted by the OLED stack (205),said electroluminescent display device being characterized in that: two neighboring control electrodes (202a, 202b; 202b, 202c; 202c, 202a) belonging to two neighboring elementary emitting zones are separated by a space (211) forming a trench and having an insulating surface (223) which covers at least the vertical sides of said neighboring control electrodes and electrically insulates them from each other, and two neighboring control electrodes belonging to two neighboring elementary emitting zones are separated by a space forming a trench and having an insulating surface which covers at least the vertical sides of said neighboring control electrodes and electrically insulates them from each other, for each of the elementary emitting zones, the entire OLED stack with its corresponding upper electrode (205a with 207a, 205b with 207b,205c with 207c) is separated from the neighboring elementary emitting zones by a conductive and transparent layer (250) which protects said OLED stack on its face, upper and on all its lateral sides against the ambient air, thus forming a protected island (225).

3. Electroluminescent display device (200) according to claim 1 or 2, characterized in that said transparent conductive layer (250) has been deposited by a conformal deposition method, and encapsulates the assembly represented by said OLED stack (205) and the upper electrode (206) individually, forming for each elementary emitting zone an encapsulated island.

4. Electroluminescent display device (200) according to any one of claims 1 to 3, characterized in that said layer of transparent and conductive material (250) is made of a material selected from the group formed by: SnO2, ZnO, ITO, AZO, all these materials possibly being doped.

5. Electroluminescent display device (200) according to any one of claims 1 to 4, characterized in that it comprises an encapsulation system (282) comprising, listed from bottom to top, said layer (250) of a transparent and conductive material, at least one layer of a polymeric material (280) in contact with said layer of a transparent and conductive material (250), and at least one transparent inorganic layer (281).

6. Electroluminescent display device (200) according to claim 5, characterized in that said layer of a polymer material (280) in contact with said layer of a transparent and conductive material (250) is structured according to the arrangement of the elementary emitting zones (202).

7. Electroluminescent display device (200) according to any one of claims 1 to 6, characterized in that a part of said transparent and conductive material (250) which establishes an electrical connection between the second part (206-2) and the first parts (206-1) of each elementary emitting zone is oriented in a substantially vertical plane.

8. A method of manufacturing an electroluminescent display device (200) comprising a matrix of electroluminescent pixels formed from a plurality of pixels deposited on a substrate (210), in a matrix arrangement in rows and columns, each pixel being formed from at least three elementary emitting zones, each of which belongs to a different group of elementary emitting zones which is distinguished from the zones elementary emitters belonging to other groups by their emission color, and each elementary emission zone comprising an electroluminescent stack of organic layers (205), called “OLED stack”, which comprises at least one light-emitting organic layer, and said OLED stack (205) being arranged between a lower control electrode (202) and a transparent upper electrode (206), said transparent upper electrode (206) being crossed by the light emitted by the OLED stack (205), and said electroluminescent display device (200) comprising electrical connection bars (217) dedicated to powering the upper electrode (206), and in which method: (i) a substrate (210) is provided with a control electrode (202a, 202b, 202c) for each elementary emitting zone and an insulating layer between two neighboring control electrodes, said insulating layer covering the sides of said neighboring control electrodes as well as the substrate between said two neighboring control electrodes, and (ii) in a first group of steps, a first OLED stack (205a), an upper electrode (206a) and, using a conformal deposition technique, a first layer of a transparent conductive oxide (250a) are first deposited, then a photoresist (280a) is arranged at the location of the elementary emission zones of the first group, which protects - the upper horizontal surface (250a-1), which is the surface above the control electrode, and - the flank (250a-2) of the control electrode and - at least a portion of the lower horizontal surface (250a-3) located between two neighboring control electrodes, and then the areas not protected by the photoresist are etched up to the upper surface of the control electrode for the elementary emission areas not protected by the photoresist and up to the surface of the insulating layer located in the natural space between two neighboring control electrodes, and finally, optionally, said photoresist is removed; (iii) in a second group of steps, a second OLED stack (205b), an upper electrode (206b) and, using a conformal deposition technique, a second layer of a transparent conductive oxide (250b) are deposited, then a photoresist (280b) is arranged at the location of the elementary emission zones of the second group, and then the zones not protected by the photoresist are etched up to the upper surface of the control electrode for the elementary emission zones not protected by the photoresist and up to the surface of the insulating layer located in the natural space between two neighboring control electrodes, and finally, optionally, said photoresist is removed;(iv) in a third group of steps, a third OLED stack (205c), an upper electrode (206bc) and, using a conformal deposition technique, a third layer of a transparent conductive oxide (250c) are deposited, then a photoresist (280b) is arranged at the location of the elementary emission zones of the second group, and then the zones not protected by the photoresist are etched up to the upper surface of the control electrode for the elementary emission zones not protected by the photoresist and up to the surface of the insulating layer located in the natural space between two neighboring control electrodes, and finally, optionally, said photoresist is removed.;

9. Method according to claim 8, in which the photoresists are removed, and in which, at the end of the third group of steps, a polymeric encapsulation layer (280) is deposited followed by a transparent inorganic layer (281), preferably an oxide layer, and even more preferably an alumina or silica layer.

10. Method according to claim 8, in which the photoresists are not removed, and in which a transparent inorganic layer (281) is deposited at the end of the third group of steps, preferably an oxide layer, and even more preferably an alumina or silica layer.

11. A device according to any one of claims 1 to 7 or a method according to any one of claims 8 to 10, wherein said matrix arrangement is of the RGB-Stripe, RGB-Quad, RGBW-Quad, Delta or Honeycomb type.

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