Active matrix light-emitting device with improved resolution

Abstract

The invention relates to a light-emitting display device (200) comprising a matrix of pixels, wherein each pixel is formed of three elementary emitting zones (201a, 201b, 201c) each comprising an OLED stack (205a, b, c) having a different colour, and wherein each zone is protected by a photoresist (280), two neighbouring control electrodes (202a, b; 202b, c; 202c, a) belonging to two neighbouring emitting zones (201a, b; 201b, c; 201c, a) each belonging to a different group of elementary emitting zones are separated by a trench (211) and have an insulating surface (223) covering the flanks of the neighbouring electrodes, and two neighbouring control electrodes (202a, a; 202b, b, 202c, c) belonging to two neighbouring emitting zones (201a, a; 201b, b; 201c, c) each belonging to the same group are separated by a trench (211) filled with a filling element (203), wherein, in each group of elementary emitting zones, the assembly of the OLED stack with its upper electrode is separated from the neighbouring assemblies by an encapsulating layer (290).

Description

[0001] ACTIVE MATRIX LIGHT-EMITTING DEVICE WITH IMPROVED RESOLUTION

[0002] Technical field of the invention

[0003] The invention relates to the field of optoelectronic devices and components, and more specifically to OLED (Organic Light Emitting Device) type electroluminescent devices. It relates more particularly to improving the efficiency and luminance of the display color range as well as the resolution of an OLED type display screen. 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.

[0004] State of the art

[0005] Organic light-emitting diode (OLED) devices are well-established products for manufacturing thin lighting systems and displays. OLED-based displays typically 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. 1] 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) that cooperate to emit a luminous point (pixel) of the desired color. [Fig. 2] shows three known examples of arranging subpixels of different colors to form a pixel capable of displaying the desired color.

[0006] 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 color filters located above the OLED stack. These color filters can be photosensitive resins.These resins can be deposited directly onto the encapsulation system, or, alternatively, they can be deposited onto a glass wafer, which is fixed by gluing onto the top electrode of the device.

[0007] This embodiment has two advantages. First, a common OLED layer, unstructured at the matrix level, can be used for all subpixels, with the color being generated by the filters. Another advantage is that it is possible to produce very small actively addressed subpixels, which improves the spatial resolution of the screen.

[0008] 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 that eventually degrade 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.

[0009] Another way to achieve 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. As the process of structuring 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.

[0010] 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).

[0011] This problem becomes more noticeable as the subpixel 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 various approaches to combating crosstalk at the source, i.e., to reduce the physical phenomenon at the pixel or subpixel level.

[0012] To reduce crosstalk, 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.

[0013] OLED stacks are known to be sensitive to atmospheric gaseous species, primarily oxygen and water vapor, which degrade the interface between the electrode and the organic films forming the OLED stack. A degraded subpixel eventually stops emitting light: it appears as a black dot. 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 color filters, the glass wafer on which the filters are deposited serves as surface protection for the OLED stack, while the glue can provide lateral coating.

[0014] It is known to separate each pixel to isolate it from the other pixels around it, to avoid short-circuit problems related to humidity in the encapsulation layers. EP 2 927 985 (Universal Display Corp.) describes a structure in which each pixel is hermetically sealed and isolated from its neighboring pixels. Manufacturing 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 US 9 419245 (Japan Display Inc.). The processes described in these two documents are complex and generate significant additional cost.

[0015] The structure of a prior art device, which allows to obtain a high light intensity, is shown schematically in [Fig. 5], which will be discussed below in greater detail. It has three elementary emitting areas (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 their OLED layers, there is practically no crosstalk, and the image sharpness 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 unfortunately, no industrial process is known with which this device could be miniaturized with a size of the elementary emitting area (sub-pixel) smaller than about 20 μm.

[0016] 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 very small pixels (typically less than 5 pm) or for structures with very small inter-pixel space. This architecture must be compatible with efficient encapsulation.

[0017] Another objective is to propose a manufacturing process for such a device, which is industrially reliable and simple.

[0018] Objects of the invention

[0019] According to the invention, the problem is solved by a new architecture of a top-emitting OLED electroluminescent device, and by a new method for manufacturing it. In this method, photolithography and etching methods are used to structure the stack of OLED layers. In this method, the removal (stripping) of photoresists is avoided so as not to weaken the OLED layers. Instead of removing the photoresists, they are integrated into the encapsulation system.

[0020] A first subject of the invention is 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, each elementary emission zone comprising an electroluminescent stack of organic layers, called "OLED stack", which comprises at least one light-emitting organic layer, said OLED stack being arranged between a control electrode and a transparent upper electrode, said transparent upper electrode being traversed by the light emitted by the OLED stack,said electroluminescent display device being characterized in that: two neighboring control electrodes belonging to two neighboring elementary emitting zones which each belong to a different group of elementary emitting zones are separated by a space forming a trench and having an insulating layer or surface which covers at least the vertical sides of said neighboring electrodes and electrically insulates them from each other, and two neighboring control electrodes belonging to two neighboring elementary emitting zones which each belong to the same group of elementary emitting zones are separated by a space forming a trench, said space being filled with a filling element which electrically insulates said neighboring control electrodes from each other and fills the natural space between said two electrodes, in each group of elementary emitting zones,the entire OLED stack with its corresponding upper electrode is separated from neighboring sets belonging to another group by a first encapsulation layer which protects said OLED stack on its upper face and its lateral sides against the ambient air, thus forming protected islands, each island comprising sets of OLED stacks of the same group, with their upper electrode, each elementary emitting zone being protected by a photoresist.,

[0021] This device according to the invention comprises several groups of elementary emitting zones, each group being distinguished from another group by its emission color. Each of these groups comprises a different OLED stack, selected so as to emit light of the desired color. Thus, the color of the light emitted by the elementary emitting zones is not generated by a color filter which reduces the intensity of the light emitted by the electroluminescent display device, but all of the light emitted by each elementary emitting zone directly has the desired color.

[0022] Apart from the advantages that the presence of photoresist layers presents for the manufacturing process of the devices according to the invention, the protection of the elementary zones by a photoresist improves the quality of their encapsulation compared to the ambient air which is likely to degrade the organic layers of the OLED device.

[0023] In particular embodiments, which can be combined with each other: said device comprises an additional encapsulation layer which covers the upper face of said device as well as the lateral flanks of the photoresists, knowing that said additional encapsulation layer is located above said first encapsulation layer, and above the photoresist layers; said emission colors are red, blue and green; the width of said trench space is between 0.3 pm and 1.0 pm, and / or the depth of said trench space is between about 150 nm and about 850 nm, and preferably between 150 nm and 450 nm; the thickness of said control electrodes is between about 150 nm and about 800 nm, and preferably between 150 nm and 450 nm; the thickness of said control electrodes is greater than the thickness of the OLED stacks;said filling element fills the natural space between two neighboring control electrodes so that said upper electrode is substantially planar; the pitch of the elementary emitting zones is less than about 20 pm, preferably less than about 15 pm, more preferably less than about 10 pm, and even more preferably between about 1 pm and about 5 pm, and / or the width of the space between control electrodes is less than about 1 pm, and preferably between about 0.3 pm and about 1.0 pm; on the filling element with an insulating surface, the angle alpha relative to the horizontal upper surface of the electrode does not exceed at any point a value which is about 40°, preferably about 30°, more preferably about 25°, and even more preferably about 20°, knowing that it can be a positive or negative angle;at least one of the photoresists is a colored filter capable of attenuating or eliminating the second-order light waves emitted by the elementary emitting zone above which it has been deposited; said control electrode has an overhang, and preferably comprises two layers, namely a lower layer and an upper layer, the materials of which are chosen so that the material of said lower layer is etched more easily than said upper layer under the chosen etching conditions; said photoresist is a negative photoresist.;

[0024] A second subject of the invention is a method for 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, 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, called "OLED stack", which comprises at least one light-emitting organic layer, in which method: a substrate is provided with a control electrode for each elementary emitting zone and an insulating layer between two neighboring electrodes,and provided with filling elements between two neighboring elementary emitting zones belonging to the same group of elementary emitting zones, in a first group of steps, a first OLED stack, an upper electrode and, using a conformal deposition technique, a first encapsulation layer are first deposited, then a first photoresist is arranged at the location of the elementary emission zones of the first group, which protects the horizontal surface and the flank of said encapsulation layer at the location of said elementary emission zones of the first group, and the zones not protected by the photoresist are etched up to the upper surface of the control electrode, in a second group of steps, a second OLED stack, a second upper electrode and, using a conformal deposition technique, a second encapsulation layer are first deposited on said substrate,then a second photoresist is arranged at the location of the emission zones of the second group which protects the horizontal surface and the flank of said encapsulation layer at the location of said elementary emission zones of the second group, and the zones not protected by said first and second photoresists are etched up to the upper surface of the control electrode for the elementary emission zones of the third group, and up to the surface of the first encapsulation layer for the elementary emission zones of the first group.

[0025] In a third group of steps, a third OLED stack, a third upper electrode and, using a conformal deposition technique, a third encapsulation layer are first deposited on said substrate, then a third photoresist is arranged at the location of the emission zones of the third group, which protects the horizontal surface and the flank of said encapsulation layer at the location of said elementary emission zones of the third group, and the zones not protected by said first, second and third photoresists are etched.

[0026] After the last step, an additional encapsulation layer can be deposited over the entire substrate. Advantageously, all encapsulation layers are deposited by a conformal technique, preferably ALD.

[0027] In another variant of the method, said control electrode is produced in such a way that it has an overhang, and preferably by successively depositing two layers, namely a lower layer and an upper layer, the materials of which are chosen so that the material of said lower layer is etched more easily than said upper layer under the chosen etching conditions.

[0028] In this particular case, it is advantageous if said photoresist is a negative photoresist.

[0029] Brief description of the figures

[0030] Figures 1 to 6 schematically represent an optoelectronic device of the OLED display type, and illustrate general, known aspects of OLED devices and displays. Figures 7 to 31 illustrate aspects and embodiments of the invention, and are not intended to limit the scope of the invention.

[0031] More particularly, Figures 15 to 17 illustrate the structure of an OLED display device according to the invention, and Figures 8 to 27 illustrate in greater detail steps of a method for manufacturing an OLED display device according to the invention. Figures 27 to 35 refer to variants of the invention.

[0032] [Fig. 1] shows the electrical diagram of a known type OLED matrix display.

[0033] [Fig. 2] shows three known examples of arranging subpixels of different colors to form a pixel capable of displaying the desired color.

[0034] [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.

[0035] [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 subpixels. The figure shows a single pixel with its three subpixels.

[0036] [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.

[0037] [Fig. 6] reproduces Figure 5 of document WO 2019 / 193290.

[0038] [Fig. 7] shows a top-view of an intermediate product according to the invention, manufactured using steps of the process according to the invention.

[0039] [Fig. 8] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zx plane along line AA indicated in [Fig. 7], on a substrate which represents the intermediate product of [Fig. 7],

[0040] [Fig. 9] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zy plane along line BB indicated in [Fig. 7], on a substrate which represents the same intermediate product of [Fig. 7],

[0041] [Fig. 10] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zx plane along line AA indicated in [Fig. 7], on a substrate which represents a stage subsequent to that of the intermediate product of [Fig. 8],

[0042] [Fig. 11] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zy plane along line BB indicated in [Fig. 7], on a substrate which represents a step later than that of the intermediate product of [Fig. 9],

[0043] [Fig. 12] shows a top-view of an intermediate product according to the invention, manufactured using steps of the process according to the invention, at a manufacturing stage which corresponds to that of [Fig. 10] and [Fig. 11],

[0044] [Fig. 13] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zx plane along line AA indicated in [Fig. 7], on a substrate which represents the intermediate product of [Fig. 12] after a sequence of additional manufacturing steps.

[0045] [Fig. 14] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zy plane along line BB indicated in [Fig. 7], on a substrate which represents the same intermediate product of [Fig. 13],

[0046] [Fig. 15] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zx plane along line AA indicated in [Fig. 7], on a substrate which represents the intermediate product of [Fig.

[0047] 12] after a sequence of additional manufacturing steps. This stack represents an intermediate product in the manufacture of an optoelectronic device of the OLED display type according to the invention.

[0048] [Fig. 16] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zy plane along line BB indicated in [Fig. 7], on a substrate which represents the same intermediate product of [Fig. 13],

[0049] [Fig. 17] schematically shows a perpendicular cross-section of a structured stack of layers on a substrate after a sequence of additional manufacturing steps starting from the intermediate product of [Fig. 15],

[0050] [Fig. 18] illustrates a first sequence of steps of an embodiment of the method according to the invention for manufacturing an OLED microdisplay type device according to the invention, having three groups of pixels. [Fig. 19] illustrates a second sequence of method steps which follows those of [Fig. 18],

[0051] [Fig. 20] illustrates a third sequence of process steps which follows those of [Fig. 19],

[0052] [Fig. 21] illustrates a fourth sequence of process steps which follows those of [Fig. 20],

[0053] [Fig. 22] illustrates a fifth sequence of process steps which follows those of [Fig. 21],

[0054] [Fig. 23] illustrates a sixth sequence of process steps which follows those of [Fig. 22],

[0055] [Fig. 24] illustrates a seventh sequence of process steps which follows those of [Fig. 23],

[0056] [Fig. 25] illustrates an eighth sequence of process steps which follows those of [Fig. 24],

[0057] [Fig. 26] illustrates a ninth sequence of process steps which follows those of [Fig. 24], and which corresponds to the intermediate product of [Fig. 15],

[0058] [Fig. 27] illustrates a tenth sequence of process steps which follows those of [Fig. 26], according to a variant of the process according to the invention, and which corresponds to the intermediate product of [Fig. 16],

[0059] [Fig. 28] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zy plane along the line BB indicated in Fig. 7, on a substrate which represents a variant of the intermediate product of Fig. 7; this section is analogous to that of Fig. 9.

[0060] [Fig. 29] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zy plane along the line BB indicated in Fig. 7, on a substrate which represents a stage subsequent to that of the intermediate product of Fig. 28; this section is analogous to that of Fig. 11.

[0061] [Fig. 30] schematically shows a perpendicular cross-section of a device according to the invention, according to one of its variants. [Fig. 31] shows a drawing from an image obtained by scanning electron microscopy on a cross-section of a device which illustrates the variant shown in Fig. 30.

[0062] [Fig. 32] is based on [Fig. 20] of which it illustrates a possible drawback.

[0063] [Fig. 33] refers to a variant of the invention which provides a solution to the drawback illustrated in [Fig. 32],

[0064] [Fig. 34] schematically illustrates a preparatory process step for the intermediate device of [Fig. 33],

[0065] [Fig. 35] schematically illustrates an embodiment of the intermediate device shown in [Fig. 33] which should be avoided.

[0066] The following reference numerals are used in these figures and in the description that follows:

[0067] 10 OLED display of known type

[0068] 12 Pixel Matrix Unit

[0069] 14 OLED Diode

[0070] 16 Control circuit for 14

[0071] 18.20 Transistors of 16

[0072] 22 Capacitor of 16

[0073] 30 Control circuit for lines

[0074] 32 Video Addressing Circuit

[0075] 34 Power supply circuit

[0076] 36 Control unit

[0077] 38 Conductive track of a scanning line

[0078] 40 Conductive track of a column

[0079] 42 Conductive track for powering the pixel columns

[0080] 50.51-54 Pixel (50), sub-pixel (51-54)

[0081] 70 OLED display device of known type

[0082] 71 Substrate of 70

[0083] 72-74 Subpixel control electrodes

[0084] 75 Gap-fill element

[0085] 76 Stack of organic layers forming an OLED

[0086] 77 Encapsulation Layer

[0087] 78 Protective cover (glass slice) 80 Electroluminescent layer of 76

[0088] 81.82 Load transport layers of 76

[0089] 83,84 First (83) and second (84) charge injection and transport layer

[0090] 85 Common electrode of 76

[0091] 90 Pixel

[0092] 91-93 Colored filters

[0093] 95-97 Color-emitting electroluminescent layers for subpixels

[0094] 98a, b, c Addressing electrodes for 95,96,97

[0095] 99 Common electrode

[0096] 100 OLED Display

[0097] 101a,b,c Subpixels

[0098] 102a,b,c Subpixel control electrodes 101

[0099] 104 Separator

[0100] 105 OLED Stack

[0101] 106 Upper injection layer

[0102] 107 Conformal electrode (common to sub-pixels 101)

[0103] 108 Smoothing layer

[0104] 109 Color Filter

[0105] 110 Substrate of 100

[0106] 111 Natural space (gap) between neighboring electrodes 102

[0107] 112 Ledge of 123 on 102

[0108] 113 Pixels of 100

[0109] 123 Filling element with insulating surface

[0110] 200 OLED display according to the invention

[0111] 201 a, b, c Subpixels

[0112] 202a, b, c Control electrode of 201 a, b, c

[0113] 203 Filling element with insulating surface

[0114] 205a, b, c Stack of organic layers forming an OLED

[0115] 207a, b, c Upper electrode

[0116] 210 Substrate of 200

[0117] 211 Natural space (gap) between neighboring subpixels

[0118] 212 Ledge of 223 on 202

[0119] 213 Ledge of 203 on 202

[0120] 217 Connection bar

[0121] 223 Insulation layer

[0122] 225 a,b,c Elementary emitting zone island (column) 280a, b, c Photoresist

[0123] 290a, b, c Subpixel encapsulation layer 291 Additional encapsulation layer

[0124] Detailed description of the invention

[0125] In the present description, the expression "elementary emission zone" designates the smallest emission zone which is individually addressable. In the case of color displays in which several elementary emission zones form a pixel, the person skilled in the art usually uses the term "sub-pixel" to designate such an elementary emission zone.

[0126] The term "photoresist", commonly used by those skilled in the French-speaking profession, refers to a photosensitive resin.

[0127] The term "insulator" refers to electrical insulation.

[0128] The expression "an area not protected by a photoresist is etched" (and its equivalent expressions) means that the etching may also target an area on which a photoresist is located, said photoresist being buried under one or more layers, knowing that during said etching, said layers may be removed, totally or partially from this etching. In particular, this "etching of an area not protected by a photoresist" may lead to the stripping of a photoresist which was previously buried under a layer which can be etched under these etching conditions, but this etching must then be carried out under conditions such that it stops on the photoresist.

[0129] The expression indicating that a (first) layer is located “above” another (second) layer should not be understood as implying that the second layer must necessarily be deposited directly above the first layer: there may be one or more other (intermediate) layers between said first and said second layer. Furthermore, the terms “below” and “above” refer to the substrate of the electroluminescent display device, which is here, by definition, “at the bottom”.

[0130] [Fig. 1] 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).

[0131] Each control circuit 16 of a pixel 12 comprises a plurality of transistors 18, 20 typically made in CMOS (Complementary Metal Oxide Semiconductor) technology in the case of micro-screens, or thin-film transistors (known as TFT (Thin Film Transistor)), and a capacitor 22. The control unit 36 ​​controls a control circuit for the lines 30 and a video addressing circuit 32, as well as a power supply circuit 34 for addressing the pixel columns. The control unit 36 ​​ensures the addressing of the pixel circuits and controls the light emission of the OLED diodes 14. The control circuit of the lines 30 is connected to the conductive tracks 38 addressing the scanning lines of the pixel matrix. It selects the scan lines 38 according to a signal from the control unit 36, and applies a voltage to turn on the transistors 18 located on the selected scan line 38.

[0132] 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 video conductive tracks 40 of the columns according to the conductive tracks of the rows 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 row. The control transistor 20 sends a current corresponding to the recorded voltage to the OLED diode 14, and thereby the OLED diode 14 of the selected row 38 emits light.

[0133] The power supply circuit 34 is connected to the power supply conductor tracks 42 of the pixel columns; it supplies the OLED diodes 14 via the power supply conductor tracks 42 and the transistors 20 of the selected pixel row.

[0134] 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 show three examples for the geometric arrangement of these sub-pixels 51,52,53,54 to form a pixel 50 capable of displaying the desired color. In these figures the sub-pixels are red 51, blue 52 and green 53, and may include, as in the figure on the right, in addition a white sub-pixel 54 to increase the brightness of the pixel 50. The arrangement in the figure on the left is known by the acronym "RGB Stripe", it is the most widespread.The arrangement in the middle figure is known as "RGB quad", and the one on the right is known as "RGBW quad". The addressing principle just described in relation to [Fig. 1] 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 microdisplays according to the state of the art; they illustrate the problem that the present invention seeks to solve.

[0135] 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 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 blue 91, red 92 and green 93 colored filters 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.

[0136] [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 layer 82 comprises a hole injection and transport layer, and layer 81 an electron injection and transport layer. Layers 81 and 82 may 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. A common electrode 85 evacuates the charges. This device according to the state of the art has parasitic currents; this is illustrated in [Fig. 4]. Indeed, if when lighting a sub-pixel (for example 73) the main current passes (marked by a thick arrow) directly through 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 crosses the OLED layer in the neighboring sub-pixel 72 or 73. This parasitic current is marked in [Fig. 4] 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.

[0137] [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 sub-pixel 95,96,97 has its own addressing electrode 98a,b,c, 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 the device manufacturing. The problem of parasitic currents is the same as that described in relation to [Fig.4]; the contribution of the first charge injection and transport layer (for example holes) 81 is predominant in these parasitic currents.

[0138] In terms of luminous efficiency, the device in [Fig. 5] is significantly better than that in [Fig. 3]. However, its industrial manufacture can be quite difficult, since the organic materials that make up an OLED device are generally deposited by a vacuum thermal evaporation process. To generate sub-pixels of different colors, as in the device in [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 made and which has openings that correspond to the position of a first type of sub-pixel during the deposition of a first type of layer stack, 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, using a third stencil.

[0139] 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 organic materials.

[0140] It is observed that when trying to transpose the photolithography and etching methods known from the semiconductor field to the manufacture of OLED microdisplays, the OLED stack is attacked laterally, i.e. in its unprotected edge, 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 to compensate for the loss of luminance, which will reduce the operational lifetime of the device). In an unfavorable case, this ends up completely destroying the sub-pixel, which then appears as a black point.

[0141] 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.

[0142] The starting point of the invention is the device of Figure 5 of WO 2019 / 193290, which is reproduced here in [Fig. 6], with adjusted reference numerals. This figure shows a pixel 113 of an OLED display device 100 deposited on a substrate 110 (typically of CMOS type) with three sub-pixels 101 a, 101 b, 101 c each of which is controlled by an individual control electrode 102a, 102b, 102c.

[0143] 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 sub-pixels 101a, 101b;

[0144] 101 b, 101 c; 101 c, 101 a neighbors. 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 sub-pixels, as is the upper injection layer 106, the latter being optional.

[0145] 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 colored 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 colored 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 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.

[0146] We will now explain the device according to the invention, which will be described by its structure, by its manufacturing method, and at different stages of its manufacturing. This device, as represented here, comprises three groups of elementary emitting zones (sub-pixels).

[0147] [Fig. 7] shows a top-view of an intermediate product according to the invention, manufactured using steps of the method according to the invention. The structure of the substrate with its different deposited structured layers is shown schematically in two figures which represent the same intermediate product of [Fig. 7], and which schematically show a perpendicular cross-section of a structured stack of layers, namely [Fig. 8] which represents a section in a zx plane along the line AA indicated in [Fig. 7], and [Fig. 9] which represents a section in a zy plane along the line BB indicated in [Fig. 7],

[0148] This intermediate product comprises a substrate 210 (which typically comprises active matrix type addressing circuits, produced using TFT or CMOS technology, well known to those skilled in the art), and electrodes 202a, 202b, 202c of sub-pixels separated by a natural space 211 ("gap") which has the shape of a trench. In this trench, an insulating layer 223 is deposited by a conformal deposition method, that is to say a method which covers the entire surface, whether horizontal, vertical or overhanging. For this purpose, the atomic deposition technique (ALD) or the plasma-enhanced chemical vapor deposition technique (PECVD) can be used. The material of this insulating layer is advantageously selected from the group formed by SisN4, SiC>2 and AI2O3. Among these three materials, AI2O3 is preferred.

[0149] Said insulating layer 223 covers at least the vertical surfaces of the electrodes 202 and typically the surfaces of the entire natural space 211 between the electrodes 202. In an advantageous embodiment it also slightly covers the edge of the pixel (i.e. the upper horizontal surface) of the electrodes 202, thus forming a rim 212 on the control electrode 202.

[0150] As can be seen in [Fig. 7] and in [Fig. 9], the natural space (trench) 211 between the electrodes 202 is filled by a filling element 203 with an insulating surface, but only the horizontal space (i.e. along an x ​​axis) between two sub-pixels.

[0151] The vertical space (i.e. along a y axis) between two sub-pixels does not contain a filling element and forms a trench which goes from the top to the bottom of the matrix formed by all the (sub-)pixels. The surface of said filling element 203 typically consists of a photoresist or a dielectric material such as SiC>2, SisN4 or other; alternatively, said entire filling element 203 consists of such a dielectric material. Like the insulating layer 223, the filling element 203 may have a rim 213 on the control electrode 202, for the same reasons.

[0152] As can be seen in [Fig. 7], the substrate also comprises connection bars 217 at the top and bottom of the matrix, in the form of horizontal metal lines (bus bars), for the connection of the upper electrode of the OLED display device, as will be explained below in relation to [Fig. 12],

[0153] This substrate structure subsequently allows the creation of islands 225 of elementary OLED emitting zones which are completely isolated and encapsulated; such an island 225 is represented in [Fig. 10] by the box with dotted outlines. In [Fig. 7] these islands have a vertical column shape which crosses the active zone from top to bottom, as also emerges from the comparison between [Fig. 10] and [Fig. 11]; these two figures will be explained below. The function of the filling element 203 is here to ensure the continuity of the upper electrode 207 along the vertical column (y).

[0154] Reference is now made to [Fig. 10] and [Fig. 11], both of which show the same device at the same intermediate stage of manufacture. Like [Fig. 8] and [Fig. 9], [Fig. 10] represents a section in a zx plane along line AA indicated in [Fig. 7], and [Fig. 11] represents a section in a zy plane along line BB indicated in [Fig. 7]. On the other hand, [Fig. 10] and [Fig. 11] represent a more advanced stage of manufacture than that shown in [Fig. 7], namely a stage of manufacture which follows that of [Fig. 8] and [Fig. 9].

[0155] As shown in [Fig. 10], a first stack of organic layers 205a is first deposited, which forms the OLED stack (i.e., an OLED diode capable of emitting light), typically by the thermal evaporation method; this technique for depositing the layers of an OLED stack is currently the standard in the OLED device industry. It is a directional deposition, i.e., the layers will form mainly on horizontal surfaces, but not on vertical surfaces, as shown in Figure 10. The OLED stack 205a is completed by a top electrode 207a, which must be transparent. As can be seen from the comparison between [Fig. 10] and [Fig. 11], the top electrode 207a is common for each group of subpixels in a column.

[0156] As mentioned above, the organic layers that form an OLED stack are very sensitive, in particular to water and oxygen, and they must be protected against these molecules. To this end, an encapsulation layer 290a of the sub-pixel 201a is deposited on the OLED stack 205a, which covers the entire topography of the device, in particular both the horizontal and vertical surfaces. It typically consists of a thin layer of a transparent insulating material. Its thickness is advantageously between approximately 10 nm and approximately 30 nm. Its material is preferably selected from the group formed by SisN^ SiC>2 and AI2O3. These materials have the advantage of being highly resistant to the etching step intended to remove the OLED stack; this etching can be carried out by an oxygen plasma. This encapsulation layer 290a of the sub-pixel 201a is advantageously deposited by a conformal deposition method such as PECVD or ALD.

[0157] This results in a hermetically isolated space around the OLED device from all the sub-pixels in each column 225a, 225b, 225c (also called an “island” here); these sub-pixels belong to the same group of sub-pixels (for example to the group of red sub-pixels or to the group of blue sub-pixels).

[0158] In order to connect the upper electrode 207a to the connection bar 217 (also called "busbar"), the deposition of the organic materials of the OLED stack 205 should not protrude too much on the connection bars 217, and the deposition of the electrode layer 207 must at least partially cover the connection bars 217. [Fig. 12] shows a top view of the substrate after the deposition of the layer 207.

[0159] This intermediate device has several advantages and improvements over the state of the art.

[0160] First, it allows excellent electrical isolation of OLED layers between neighboring sub-pixels, and therefore leads to a reduction in crosstalk which is of the same quality as that described in WO 2019 / 193290.

[0161] Second, the structure of the organic layers of the OLED stack in the form of hermetically isolated islands improves the reliability of the device. In particular, a point defect (e.g., water entering through a pinhole in the encapsulation layer) cannot propagate further than the dimension of a subpixel in the horizontal direction because it will be stopped by the natural gap 211 between neighboring subpixels that has been arranged in the form of a trench.

[0162] The isolated islands 225 allow structuring of the OLED layer with photolithography methods, which makes it possible to produce for example the device according to [Fig. 13] and [Fig. 14]. Said device is an innovative device compared to the state of the art, with three groups of sub-pixels 201 a, 201 b, 201 c, each of which comprises a different OLED stack (red 205 a, green 205 b and blue 205 c); this device can be manufactured with an improved spatial resolution which can reach an elementary emitting zone size of a size less than 5 pm. This device has a matrix with three groups of sub-pixels 201 a, 201 b, 201 c of RGB type, without color filter, with an excellent resolution.In industrial practice, this process has proven to be quite complex, as it includes various stages of etching and removal of photosensitive resins; this process is likely to weaken layers of the OLED stack and the encapsulation system. Thus, one would like to minimize the sequences of resin stripping steps (comprising a sequence of several individual steps). Furthermore, the etchings that must stop on the encapsulation layer of neighboring sub-pixels are quite difficult to control, and one would like to minimize them. The solution that the inventors found to this problem leads to a new architecture that is not only easier to implement industrially, but also enhances the efficiency of the encapsulation system. This solution will be explained below in relation to Figures 15 to 27.

[0163] According to the invention, in the device according to [Fig. 13] and [Fig. 14] each sub-pixel 201 a, 201 b, 201 c is protected by a photoresist 280 a, 280 b, 280 c, as illustrated in the zx plane in [Fig. 15], [Fig. 16] shows the corresponding figure in the zy plane. According to the invention, this photoresist 280 a, 280 b, 280 c is intended to remain in place in the finished device, and for this reason it must have good optical transparency in the spectral range of the sub-pixel that it covers. The method according to the invention, which will be explained below in great detail, presents an industrial solution to the question of how it is possible to deposit said photoresist 280a, 280b, 280c on each sub-pixel 201a, 201b, 201c.

[0164] The deposition and structuring of this photoresist can be done using methods known to those skilled in the art familiar with microelectronic circuit manufacturing techniques. It is possible to adapt the type of resin used to the emission color of the sub-pixel, in order to minimize optical absorption by the photoresist layer. For example, SU-8 type or TELR type photoresist resins, which are known products, can be used.

[0165] According to the invention, this photoresist layer 280a, 280b, 280c acts as encapsulation of the sub-pixel that it covers, that is to say it protects it against molecules that risk degrading the layers forming the OLED stack 205a, 205b, 205c, these molecules are in particular oxygen and water, which are contained in the ambient air.

[0166] In order to reinforce this encapsulation, it is advantageous to add above the photoresist 280a, 208b, 280c an encapsulation layer 291 called additional encapsulation layer, preferably continuous (i.e. common to the sub-pixels forming the pixel), which is advantageously an additional thin inorganic, dielectric and transparent layer, as illustrated in [Fig. 17]. This additional encapsulation layer 291 can be made of AI2O3, for example. It is advantageous for it to be deposited by a conformal method, because in this case it also covers the side of the photoresist, as illustrated in [Fig. 17].

[0167] We now describe a manufacturing method according to the invention of a device according to the invention, starting from an intermediate product according to [Fig. 18], comprising on a substrate 201 successively the electrodes 202a, 202b, 202c, the OLED stacks 205a of the first group of elementary emitting zones, the upper electrodes 207, and the encapsulation layer 290 of the sub-pixel.

[0168] A first group of steps, shown schematically in figures [Fig. 18] to [Fig. 20], allows the production of a first photoresist on the intermediate product illustrated in [Fig. 18] (which is identical to that shown in [Fig. 10] and [Fig. 11]).

[0169] In a first subgroup of steps, the result of which is shown schematically in [Fig. 19], a first photoresist 280a is arranged on a first group of elementary emitting zones 201a (sub-pixels) emitting light of a first color, for example red. This photoresist 280a must protect the horizontal surface of the elementary emitting zone 201a, but also its side (i.e. its lateral surface, which can be vertical). It is structured according to known methods.

[0170] In a second subgroup of steps, the result of which is illustrated in [Fig. 20], the stack formed by (listed from top to bottom) the encapsulation layer 290a of the sub-pixel, the upper electrode 207a, and the OLED stack 205a 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 the etching of the encapsulation layer 290 and the upper electrode 207, 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.

[0171] A second group of steps, shown schematically in figures [Fig. 21] to [Fig. 23], allows a second photoresist to be produced on the intermediate product illustrated in [Fig. 20].

[0172] In a first subgroup of steps, the result of which is shown schematically in [Fig. 21], 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 207b, preferably with the same material as that used for the upper electrode of the first group of elementary emitting zones, and (c) a second sub-pixel encapsulation layer 290b, preferably with the same material as that used for the first encapsulation layer 290a of the first group of elementary emitting zones.

[0173] It is noted that at the end of this first subgroup of steps, the OLED stack deposited on the electrode 202c of the third group of elementary emitting zones is an OLED stack of the second OLED stack 205b type. As will be explained below, during the subsequent groups of steps, it will subsequently be replaced by an OLED stack of the third OLED stack 205c type. It is also noted that the elementary emitting zones of the first group 201a comprise a stack called here “transient stack” constituted by an OLED stack 205b of the second OLED stack type, an upper electrode 207b and an encapsulation layer 290b; this transient stack will be removed subsequently.

[0174] The encapsulation layer 290 covers in particular the sides of the OLED stack. It is designated here, depending on its position relative to the final device, by the numerical references 290a, 290b, 290c while it may be the same material. It may be continuous and then extends over the three elementary emission zones 201a, 201b, 201c.

[0175] In a second subgroup of steps, the result of which is shown schematically in [Fig. 22], a second photoresist is arranged on the second group of elementary emitting zones 202b (sub-pixels), as described in relation to the first group of steps.

[0176] In a third subgroup of steps, the result of which is illustrated in [Fig. 23], the stack formed by (listed from top to bottom) the encapsulation layer 290b, the upper electrode 207b, and the OLED stack 205b is etched on the areas not protected by the photoresist, i.e. at the location of the subpixels 201a and 201c (visible in FIG. 17), as described in relation to the first group of steps. At the end of these subgroups of steps, the first photoresist 280a and the upper horizontal surface of the electrode 202c of the third group of elementary emission areas 201c are stripped.

[0177] A third group of steps, shown schematically in figures [Fig. 24] to [Fig. 27], makes it possible to arrange a third photoresist on the intermediate product illustrated in [Fig. 23]. In a first subgroup of steps, the result of which is shown schematically in [Fig. 24], the following are successively deposited on this substrate 210: (a) a third OLED stack 205c, deposited using a directional deposition technique;

[0178] (b) an upper electrode 207c, preferably with the same material as that used for the upper electrode of the first group of elementary emitting zones, and (c) a third encapsulation layer 290c, preferably with the same material as that used for the first and / or second encapsulation layer of the first or second group of elementary emitting zones. As explained in relation to the first group of steps, the encapsulation layer covers in particular the sides of the OLED stack. It is designated here, depending on its position relative to the final device, by the reference numerals 290a, 290b, 290c while it may be the same material. It may be continuous and then extends over the three elementary emitting zones.

[0179] In a second subgroup of steps, the result of which is shown schematically in [Fig. 25], a third photoresist 280c is arranged on the third group of elementary emitting zones 201c (sub-pixels), as described in relation to the first group of steps.

[0180] 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 encapsulation layer, the upper electrode, and the OLED stack is etched on the areas not protected by a photoresist, as described in relation to the first group of steps. At the end of these subgroups of steps, the first, second, and third photoresists are stripped. This produces the OLED microdisplay device 200 according to the invention, which has the same topography as that of FIG. 15, but is obtained by a different method that better preserves the integrity of the OLED stacks; this device 200 has a more efficient encapsulation system than that of FIG. 15.

[0181] In a fourth subgroup of steps, which is optional and the result of which is illustrated in [Fig. 27], an additional encapsulation layer 291 is deposited on the entire upper surface of the device. This deposition covers the photoresist 280a, 280b, 280c. It is advantageously carried out with a conformal deposition technique, capable of depositing said encapsulation layer also on the side of the photoresist 280a, 280b, 280c.

[0182] The material of this additional encapsulation layer 291 may be the same as that of the individual encapsulation layers 290a, 290b, 290c of each sub-pixel, or it may be a different material. Said additional encapsulation layer 291 may be made in several successive layers (not shown in the figures), using the same material or different materials.

[0183] The present invention may be implemented with several variants, all of which are part of the invention. According to a first variant, the photoresists 280a, 280b, 280c may be color filters, to improve the spectral purity of the light emitted by the elementary emitting zones 201a, 201b, 201c. In particular, such a color filter may be selected so as to absorb only the second-order light emitted by the OLED stack of an elementary emitting zone.

[0184] A second variant is shown schematically in [Fig. 28], [Fig. 29] and [Fig. 30]. It is compatible with all the other variants of the invention. This variant concerns the positioning of the insulating layer 223 relative to the filling element 203: the filling element 203 is first deposited in the natural space 211 between two neighboring electrodes 202 belonging to the same group of elementary emitting zones, and then the insulating layer 223. This variant has the advantage of avoiding the attack of the filling element 203 during the etching of the OLED stacks, which is particularly advantageous.

[0185] [Fig. 28] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zy plane along the line BB indicated in [Fig. 7], on a substrate which represents a variant of the intermediate product of [Fig. 7]; this section is analogous to that of [Fig. 9], In this variant the section AA corresponds to [Fig. 8],

[0186] [Fig. 29] schematically shows a perpendicular cross-section of a structured stack of layers, represented in a zy plane along the line BB indicated in [Fig. 7], on a substrate which represents a stage subsequent to that of the intermediate product of [Fig. 18]. In this variant, the section AA corresponds to [Fig. 10].

[0187] A third variant is illustrated in [Fig. 30] and [Fig. 31]: it is compatible with all the other variants of the invention. This variant concerns the filling element with insulating surface 203 (also called “gap fill”) which fills the natural space 211 between two neighboring electrodes of the same group 202a, 202a; 202b, 202b; 202c, 202c. As stated above, the filling element 203 advantageously has a rim 213 on the control electrode 202, and the thickness of the control electrodes 202 is advantageously greater than that of the OLED stacks 205.

[0188] These thicknesses, as well as that of said filling element 203, are advantageously chosen so as to prevent the angle alpha on the filling element with insulating surface 203 from exceeding at any point a value X which is approximately 40°, preferably approximately 30°, more preferably approximately 25°, and even more preferably approximately 20°, knowing that it can be a positive or negative angle. This definition of the angle alpha is clarified in [Fig. 30] in which, for two different geometries, the largest angle alpha has been indicated.

[0189] Thus, the filler element 203 acts as a smoothing element for the deposition of the common electrode layer 207. This common electrode 207 is deposited by a directional deposition technique, and this creates a risk of electrical discontinuity in the case where at any point on the surface of the control electrode, the angle alpha exceeds a value of approximately 40° (positive or negative) relative to the horizontal upper surface of the control electrode. This is explained by the fact that a directional deposition technique does not deposit the same thickness of material on a horizontal surface as on a sloping surface (and does not deposit anything at all on a vertical surface).

[0190] [Fig. 31] shows a schematic drawing from a scanning electron microscopy image of a corresponding cross-section.

[0191] A fourth variant, which is compatible with all other variants, is shown in [Fig. 33] to [Fig. 35]. It aims to remedy a potential problem linked to the fact that the flanks of the control electrodes 202 are exactly vertical. The deposition of the organic layers forming an OLED stack 205 is done by evaporation. This is a directional process, but in industrial practice it happens that a thin layer of organic material is also deposited on the vertical flanks of electrodes 202; this is illustrated, in a very exaggerated manner, in [Fig. 32] which is based on [Fig. 20], where this deposition of the OLED stack 205a on the flank bears the numerical reference 205aF. This parasitic deposition of an organic layer on the sides of the electrode 202 can create a conduction path for moisture when the side of the LED stack is opened after etching which removes the photoresist 280a.

[0192] To avoid this parasitic deposition on the flank, the shape of the electrode can be designed with flanks slightly inclined inwards, thus forming an overhang. This is shown schematically in [Fig. 33]. As shown schematically in [Fig. 34], such an overhang can be achieved, for example, by depositing the electrode 202a in two layers, namely a lower layer 202a1 and an upper layer 202a2, the materials of which are chosen so that the material of said lower layer 202a1 is etched more easily than said upper layer 202a2, under the chosen etching conditions. For example, the lower layer 202a1 can be made of aluminum, and said upper layer 202a2 can be made of TiN or a transparent conductive oxide (TCO = Transparent Conducting Oxide) such as ITO (Indium-Tin-Oxide) or SnO2.An engraving can be done in one or more (typically two) steps, with identical or different conditions for each step.

[0193] In this fourth variant, the photoresist 280a is preferably made of a negative photoresist type material (i.e. a photosensitive resin for which the part exposed to light becomes insoluble in the developer and where the unexposed photosensitive resin part remains soluble), because a positive photoresist (i.e. a photosensitive resin for which the part exposed to light becomes soluble in a developer, while the unexposed part remains insoluble) risks remaining in place below the overhang where the light cannot access certain areas in the shadow of the overhang; this is illustrated schematically in [Fig. 35] where these residues of positive photoresist in the area of ​​the overhang carry the numerical reference 280aS.In this case, pixels 202b and 202c will no longer have an overhang because of the 280bS, 2080cS residues which fill the overhang, and when depositing the following OLED stacks (205b and 205c), pixels 202b, 202c will be exposed to the parasitic OLED deposition problem explained above.

Claims

CLAIMS 1. 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 (201 a, 201 b, 201 c), 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 (201 a, 201 b, 201 c) comprising an electroluminescent stack of organic layers (205a, 205b, 205c), called "OLED stack", which comprises at least one light-emitting organic layer, said OLED stack (205a, 205b, 205c) being arranged between a control electrode (202a, 202b, 202c) and a transparent upper electrode (207a, 207b, 207c), said transparent upper electrode (207a, 207b, 207c) being traversed by the emitted light by the OLED stack (205a, 205b, 205c), said electroluminescent display device (200) being characterized in that: two control electrodes (202a, 202b; 202b, 202c;202c, 202a) neighboring elements belonging to two neighboring elementary emitting zones (201 a, 201 b; 201 b, 201c; 201c, 201 a) which each belong to a different group of elementary emitting zones are separated by a space (211) forming a trench and having an insulating layer or surface (223) which covers at least the vertical sides of said neighboring electrodes and electrically insulates them from each other, and two neighboring control electrodes (202a, 202a; 202b, 202b, 202c, 202c) belonging to two neighboring elementary emitting zones (201 a, 201 a; 201 b, 201 b;201c, 201c) neighboring each of which belongs to the same group of elementary emitting zones are separated by a space (211) forming a trench, said space being filled with a filling element (203) which insulates said neighboring control electrodes electrically from each other and fills the natural space between said two electrodes, in each group of elementary emitting zones (201 a, 201 b, 201c), the entire OLED stack with its corresponding upper electrode (205a with 207a, 205b with 207b, 205c with 207c) is separated from neighboring sets belonging to another group by a sub-pixel encapsulation layer (290a, 290b, 290c) which protects said OLED stack on its upper face and its lateral flanks against the ambient air,; thus forming protected islands (225), each island comprising sets of OLED stacks from the same group, with their upper electrode, each elementary emitting zone (201 a, 201 b, 201 c) being protected by a photoresist (280 a, 280 b, 280 c).

2. Device (200) according to claim 1, characterized in that it comprises an additional encapsulation layer (291) which covers the upper face of said device as well as the lateral flanks of the photoresists (280a, 280b, 280c).

3. Device according to claim 1 or 2, wherein said insulating layer (223) has been deposited above said filling element (203).

4. Device according to any one of claims 1 to 3, characterized in that said emission colors are red, blue and green.

5. Device according to any one of claims 1 to 4, characterized in that the width of said trench-forming space is between 0.3 μm and 1.0 μm.

6. Device according to any one of claims 1 to 5, characterized in that the depth of said trench-forming space is between approximately 150 nm and approximately 850 nm, and preferably between 150 nm and 450 nm.

7. Device according to any one of claims 1 to 6, characterized in that the thickness of said control electrodes (202a, 202b, 202c) is between approximately 150 nm and approximately 800 nm, and preferably between 150 nm and 450 nm.

8. Device according to any one of claims 1 to 7, characterized in that the thickness of said control electrodes (202a, 202b, 202c) is greater than the thickness of the OLED stacks (205a, 205b, 205c).

9. Device according to any one of claims 1 to 8, characterized in that said filling element (203) fills the natural space between two neighboring control electrodes (202) so that said upper electrode (207) is substantially flat.

10. Device according to any one of claims 1 to 9, characterized in that the pitch of the elementary emitting zones is less than approximately 20 pm, preferably less than approximately 15 pm, more preferably less than approximately 10 pm, and even more preferably between approximately 1 pm and approximately 5 pm, and in that the width of the space between control electrodes is less than approximately 1 pm, and preferably between approximately 0.3 pm and approximately 1.0 pm.

11. Device according to any one of claims 1 to 10, characterized in that on the filling element with insulating surface (203), the angle alpha relative to the horizontal upper surface of the electrode (202) does not exceed at any point a value which is approximately 40°, preferably approximately 30°, more preferably approximately 25°, and even more preferably approximately 20°, knowing that it can be a positive or negative angle.

12. Device according to any one of claims 1 to 11, characterized in that at least one of the photoresists (280a, 280b, 280c) is a colored filter capable of attenuating or eliminating the second-order light waves emitted by the elementary emitting zone (201a, 201b, 201c) above which it has been deposited.

13. Device according to any one of claims 1 to 12, characterized in that said control electrode (202a, 202b, 202c) has an overhang, and preferably comprises two layers, namely a lower layer (202a1, 202b1, 202c1) and an upper layer (202a2, 202b2, 202c2), the materials of which are chosen so that the material of said lower layer (202a1, 202b1, 202c1) is etched more easily than said upper layer (202a2, 202b2, 202c2) under the chosen etching conditions.

14. Device according to claim 13, characterized in that said photoresist (280a, 280b, 280c) is a negative photoresist.

15. A method of manufacturing an 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 (205a, 205b, 205c), called "OLED stack", which comprises at least one light-emitting organic layer, in which method: a substrate (210) is provided with a control electrode (202a, 202b, 202c) for each elementary emitting zone and an insulating layer or surface (223) between two electrodes (202a, 202b,202c) neighbors, and provided with elements of, filling (203) between two neighboring elementary emitting zones belonging to the same group of elementary emitting zones, in a first group of steps, a first OLED stack (205a), an upper electrode (207a) and, using a conformal deposition technique, a first sub-pixel encapsulation layer (290a) are first deposited, then a first photoresist (280a) is arranged at the location of the elementary emission zones of the first group, which protects the horizontal surface and the flank of said first sub-pixel encapsulation layer (290a) at the location of said elementary emission zones of the first group, and the zones not protected by the photoresist are etched up to the upper surface of the control electrode (202b and 202c), in a second group of steps, a second OLED stack (205b), an upper electrode (207b) are deposited on said substrate and, using a conformal deposition technique,a second sub-pixel encapsulation layer (290b), then a second photoresist (280b) is arranged at the location of the emission zones of the second group, which protects the horizontal surface and the flank of said second sub-pixel encapsulation layer (290b) at the location of said elementary emission zones of the second group, and the zones not protected by said second photoresist (290b) are etched up to the upper surface of the control electrode (202c) for the elementary emission zones of the third group, in a third group of steps, a third OLED stack (205c), an upper electrode (207c) and, using a conformal deposition technique, a third sub-pixel encapsulation layer (290c) are deposited on said substrate,then a third photoresist (280c) is arranged at the location of the emission zones of the third group, which protects the horizontal surface and the flank of said third sub-pixel encapsulation layer (290c) at the location of said elementary emission zones of the third group, and the zones not protected by said third (280c) photoresist are etched., 16. Method according to claim 15, in which, after the last step, an additional encapsulation layer (291) is deposited over the entire substrate.

17. The method of claim 15 or 16, wherein all sub-pixel encapsulation layers (290a, 290b, 290c) are deposited by a conformal technique which is preferably the ALD technique.

18. Method according to any one of claims 15 to 17, in which said control electrode (202a, 202b, 202c) is produced so that it has an overhang, and preferably by successively depositing two layers, namely a lower layer (202a1, 202b1, 202c1) and an upper layer (202a2, 202b2, 202c2) whose materials are chosen so that the material of said lower layer (202a1, 202b1, 202c1) is etched more easily than said upper layer (202a2, 202b2, 202c2) under the chosen etching conditions.

19. The method of claim 17, wherein said photoresist (280a, 280b, 280c) is a negative photoresist.

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