Electroluminescent device with improved resolution and reliability

Description

Technical field of the invention

[0001] The invention relates to the field of optoelectronic devices and components, and more specifically to OLED (Organic Light Emitting Device) type electroluminescent devices. It particularly concerns improving the reliability of the display color gamut and resolution of an OLED display screen. It applies to both single OLED devices and tandem OLED devices. State of the art

[0002] Organic electroluminescent devices (OLEDs) are of considerable interest in flat panel lighting systems and thin-screen displays. The operational lifespan of OLEDs decreases with increasing current density or luminance because the large number of holes and electrons passing through the organic layer causes electrochemical side reactions in the organic compounds. One particular approach to addressing this issue is the use of two or more stacked OLEDs (so-called "tandem" devices), which aims to achieve longer operating times under high luminance. In a tandem OLED structure, several light-emitting units are stacked in series across interconnecting layers such as a transparent conductive layer (TCL) or a charge generation layer (CGL).Furthermore, electron injection layers (EILs) also play a significant role in reducing the electron injection barrier of the TCL or CGL in the first light-emitting unit. With the same current density, compared to a single light-emitting device, tandem OLEDs with two superimposed light-emitting units can exhibit double the luminance. Consequently, the efficiency and operational lifespan of tandem OLEDs can be improved compared to those of conventional single-unit OLEDs.

[0003] OLED displays typically comprise a matrix structure of individual pixels, controlled by a grid of vertical and horizontal conductive tracks; this structure allows for individual pixel addressing. This is schematically illustrated in the figure 1which will be explained below. In color screens, each pixel is subdivided into sub-pixels of different colors (typically three or four, including red, green, and blue) which cooperate to emit a point of light (pixel) of the desired color. figure 3(a)This shows a section of such a screen. Above the subpixel electrodes is a stacked OLED that covers the entire surface of the matrix and (in this example) emits white light. The RGB (Red-Green-Blue) or RGBW (Red-Green-Blue-White) primaries of the subpixels are generated in this case by color filters located above the OLED stack. Another way to achieve primary colors is to structure the OLED layers into subpixels with different emission colors. Since the process of structuring OLED layers is quite complex and the achievable resolution rather limited, it is preferable in this case to keep as many layers as possible in common (i.e., layers covering the entire surface of the matrix), generally the charge carrier transport layers, and to structure only the emitting layers.However, in both previous cases, we observe that neighboring pixels or sub-pixels can interact, either through capacitive coupling or through parasitic currents passing in particular through common conductive layers of the OLED stack.

[0004] An example of this parasitic current is illustrated on the figure 3(b) which will be explained below. This undesirable interaction between neighboring pixels is known to those skilled in the art as "crosstalk"; it primarily leads to undesirable color shifts 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, D. Braun's publication "Crosstalk in passive matrix polymer LED displays" published in 1998 in the journal Synthetic Metals 92, pp. 107-113).

[0005] Crosstalk, a well-known phenomenon in single-diode OLED devices, is exacerbated in tandem-diode OLED devices. The interconnecting layers of the tandem stacked structures exhibit relatively high electrical conductivity, and parasitic currents are observed in the plane of the layers. This problem becomes more noticeable as the sub-pixel size decreases. Aside from digitally correcting the effects of crosstalk (which essentially means accepting the crosstalk phenomenon and reducing its impact on the image), various approaches exist to combat crosstalk at its source, that is, to mitigate the physical phenomenon at the pixel or sub-pixel level.

[0006] For a simple OLED device, it is known to separate each pixel to isolate them from one another to avoid short-circuit problems related to moisture in the encapsulation layers. EP 2,927,985 describes a structure in which each pixel is hermetically sealed and isolated from its neighboring pixels. Fabrication of such a structure requires numerous and complex process steps. It is also known to delimit pixel areas with additional separator elements, such as walls, as described in US 9,419,245. These processes are complex and result in a significant additional cost. CN 197346778 A, US 2014 / 103385 A1, CN 106783924 A, EP 3301548 A1, US 2016 / 181331 A1, and FR 2992098 A1 describe OLED devices with different separators between two neighboring pixels.

[0007] In view of the foregoing, an objective of the present invention is to remedy, at least partially, the disadvantages of the prior art mentioned above, and to propose an architecture for an OLED display device which makes it possible to significantly reduce lateral parasitic currents, even for very small pixels (typically less than 5 µm), for structures with very small inter-pixel spacing, or for tandem diode displays.

[0008] Another objective of the invention is to propose a method which makes it possible to limit parasitic currents between pixels for a miniature electroluminescent device. Object of the invention

[0009] The invention relates to an electroluminescent display device comprising a plurality of pixels deposited on a substrate, each pixel being formed of one or more elementary emitting areas, wherein each elementary emitting area comprises a base electrode deposited on said substrate and an electroluminescent layer deposited on said base electrode, and said device comprising a common electrode deposited above said electroluminescent layer. The invention is characterized by claim 1.

[0010] According to an example not in accordance with the claimed invention, two adjacent base electrodes belonging to two adjacent elementary emitting zones are separated by an insulating surface filling element which fills the area between said adjacent base electrodes and which electrically isolates them from each other.

[0011] At least the surface of said insulating surface filling element which is in contact with said base electrodes is made of an insulating material; the entire insulating surface filling element may be made of an insulating material.

[0012] According to another example not in accordance with the claimed invention, said filling element overflows with its insulating material onto a part of the surface of said base electrodes.

[0013] According to yet another feature of the invention, a separator is located above said filling element and separates the electroluminescent layers of two adjacent elementary emitting zones; this eliminates leakage currents which propagate horizontally to the substrate in the electroluminescent layers.

[0014] Part of said common electrode is deposited by a conformal deposition technique, preferably by ALD (Atomic Layer Deposition).

[0015] According to another example not in accordance with the claimed invention, an electroluminescent display device comprises a plurality of pixels deposited on a substrate, each pixel being formed of one or more elementary emitting areas, each elementary emitting area comprising a base electrode deposited on said substrate and an OLED stack comprising an electroluminescent layer deposited on said base electrode. Said electroluminescent display device comprises a common electrode deposited above said OLED stack. It is characterized in that: Two adjacent base electrodes belonging to two adjacent elementary emitting areas are separated by an insulating surface filling element which fills the area between said adjacent base electrodes and electrically insulates them from each other, at least the surface of said insulating surface filling element which is in contact with said base electrodes is made of an insulating material; A separator is located above said filling element and separates the electroluminescent layers of the OLED stack of two adjacent elementary emitting areas.

[0016] The common electrode is advantageously deposited using a conformal deposition technique, preferably ALD (Atomic Layer Deposition) or CVD (Chemical Vapor Deposition), to ensure continuity across the separators. The OLED stack layers are advantageously deposited using a directional (i.e., non-conformal) deposition technique, such as thermal evaporation, to allow for their separation by the separator.

[0017] Advantageously, the filling element, with its insulating material, extends over a portion of the surface of the base electrodes. In one embodiment, between two adjacent separators, and delimited by them, lies an upper electrode, deposited between the OLED stack and the common electrode. This upper electrode offers no functional advantage; on the contrary, in the case of an upward-emitting device, it absorbs light. It can be useful for protecting the OLED stack during the deposition of the common electrode.

[0018] In an advantageous embodiment this upper electrode is absent, and it is the common electrode which fulfills the function of electrode for each elementary emitting zone, that is to say the function of cathode for a top-emitting device, or of anode for a reverse device.

[0019] In one embodiment, a charge carrier injection layer extends between two adjacent separators and is delimited by them. This layer is deposited between the OLED stack and the common electrode. This charge carrier injection layer is capable of injecting charge carriers into the OLED stack (electrons in the case of a standard OLED device, or holes in the case of an inverse OLED device; the terms "standard" and "inverse" are defined below) and protects the OLED stack during the deposition of the common electrode. This charge carrier injection layer may, in particular, be made of molybdenum oxide or tungsten oxide, with a preferred thickness between 0.5 nm and 5 nm.

[0020] We recall here that a person skilled in the art calls a "standard" OLED device an OLED device in which the injection of holes is done on the face near the substrate and the injection of electrons on the face opposite the substrate, whereas in a so-called "inverse" device, electrons are injected on the face near the substrate, and holes on the face opposite the substrate.

[0021] In another embodiment, the insulating surface filling element and the separator constitute a barrier element extending vertically from the substrate. The separator may fill an upper portion of the area between the adjacent base electrodes.

[0022] In yet another embodiment, the entire insulating surface filling element is made of an insulating material. This separator may include a common electrode.

[0023] These embodiments can be combined with each other.

[0024] In all these embodiments, the display device may include an encapsulation system deposited above the common electrode. This encapsulation system may include a polymer layer and an inorganic layer, preferably an oxide. It may also include an inorganic layer, preferably an oxide, deposited between the common electrode and the polymer layer. Finally, it may include a smoothing layer deposited either above the common electrode or above the encapsulation system.

[0025] The OLED display device according to the invention may include a system of colored filters, deposited on the common electrode, or preferably on the encapsulation system, or even more preferably on said smoothing layer.

[0026] The display device according to the invention may comprise two superimposed OLED stacks, which are then typically separated by a charge generation layer.

[0027] Another example not in accordance with the claimed invention describes an electroluminescent display device comprising a plurality of pixels deposited on a substrate, each pixel being formed of one or more elementary emitting areas, each elementary emitting area comprising a base electrode deposited on said substrate and an OLED stack comprising an electroluminescent layer deposited on said base electrode. Said electroluminescent display device includes a common electrode deposited above said OLED stack. It is characterized in that: Two adjacent base electrodes belonging to two adjacent elementary emitting areas are separated by an insulating surface filling element which fills the area between said adjacent base electrodes and electrically insulates them from each other. At least the surface of said insulating surface filling element which is in contact with said base electrodes is made of an insulating material; A separator is located above said filling element, separates the electroluminescent layers of the OLED stack of two adjacent elementary emitting areas, and fills an upper part of the area between said adjacent base electrodes.

[0028] The insulating surface filling element typically includes an insulating layer in contact with the adjacent base electrodes, capable of electrically insulating them from one another; it may include other functional layers, such as the common electrode. The separator extending in the natural space (which is typically trench-shaped) between two adjacent elementary emitting zones typically includes the smoothing layer (planarization layer) deposited over the common electrode; if this smoothing layer is absent, it may include a void (i.e., air).

[0029] These embodiments can be combined with each other.

[0030] The common electrode is advantageously deposited by a conformal deposition technique, preferably ALD or CVD. Advantageously, the filler element, with its insulating material, extends over a portion of the surface of the base electrodes. The OLED stack layers are deposited by a directional deposition technique, for example, thermal evaporation.

[0031] In one embodiment, a top electrode extends between two adjacent separators and is delimited by them. This electrode is deposited between the OLED stack and the common electrode. It can serve to protect the OLED stack during the deposition of the common electrode. Alternatively, it may be absent, in which case the common electrode acts as the electrode for each elementary emitting region, i.e., the cathode for a standard dielectric device or the anode for an inverse device. In a variant of this embodiment, a charge carrier injection layer extends between the OLED stack and the common electrode and is delimited by them.This charge carrier injection layer is capable of injecting charge carriers into the OLED stack (electrons in the case of a top-emitting OLED device, or holes in the case of an inverted OLED device), and it protects the OLED stack during common electrode deposition. This charge carrier injection layer can be made of molybdenum oxide or tungsten oxide, with a preferred thickness between 0.5 nm and 5 nm.

[0032] In all these embodiments, the display device may include an encapsulation system deposited above the common electrode. This encapsulation system may include a polymer layer and an inorganic layer, preferably an oxide. It may also include an inorganic layer, preferably an oxide, deposited between the common electrode and the polymer layer. Finally, it may include a smoothing layer deposited either above the common electrode or above the encapsulation system.

[0033] The OLED display device according to the invention may include a system of colored filters, deposited on the common electrode, or preferably on the encapsulation system, or even more preferably on said smoothing layer.

[0034] The display device according to the invention may comprise two superimposed OLED stacks, which are then typically separated by a charge generation layer. Description of the figures

[0035] THE figures 1 to 3 illustrate general, known aspects of OLED devices and displays. figures 4 to 8 They illustrate aspects and embodiments of the invention; they are not intended to limit the scope of the invention. figure 1 This shows the electrical schematic of a known type of OLED matrix display. figure 2 It shows three known examples of how different colored subpixels can be arranged to form a pixel capable of displaying the desired color. figure 3 schematically shows a perpendicular cross-section of a pixel in a state-of-the-art OLED display with a white-emitting OLED and color filters. figure 3(a) shows several pixels; the figure 3(b) shows a single pixel with three sub-pixels. The figure 3(c) shows a way of representing a colored pixel without color filters. figure 4is a cross-sectional view illustrating a device following an example not in accordance with the claimed invention. figure 5 is a cross-sectional view illustrating a structured device according to an embodiment of the invention. figure 6 schematically shows a perpendicular cross-section of a tandem-type device according to another example not in accordance with the claimed invention: the figure 6(b) schematically shows a detail of the figure 6(a) , namely the stacking of organic layers forming the OLED layer. The figure 6(c) shows a variant, the figure 6(d) schematically illustrates the stacking of OLED layers above the separator in this variant. figures 7 and 8 mount variants of the devices shown, respectively, on the Figures 4 and 5 .

[0036] The following numerical references are used in this description: 10 OLED display (of a known type) 12 Pixel matrix 14 OLED diode 16 12-channel control circuit 18 Field-effect transistor 20 Field-effect transistor 22 Capacitor 30 Control circuit for lines 32 Video control circuit 36 Control unit 34 Power supply circuit for columns 38 Conductive track for lines 40 Lead track (video signal) 42 Conductive track for columns 50 Pixel 51 Red subpixel 52 Blue subpixel 53 Green sub-pixel 54 White subpixel 70 OLED display (of a known type) 71 Substrate 75 Gap-fill element 72,73, 74 Subpixel control electrode 76 OLED layers 77 Encapsulation layer 80 Electroluminescent layer of 76 81,82 Injection and load transport layer 83 Injection and load transport layer 84 Injection and load transport layer 85 Electrode 90 Pixel 91 Blue filter for sub-pixel 92 Red filter for sub-pixel 93 Green filter for sub-pixel 98 Electrode for pixel 95,96, 97 Red, Green, Blue Electroluminescent Layers 99 Common electrode 100 Device according to the invention 102 Base electrode for each sub-pixel 103 Insulating surface filler 104 Separator 105 OLED Stack 107 Common conforming electrode 106 Top injection layer (optional) 109 Colored filter 110 Substrate 108 Planarization (smoothing) layer 111 Natural space ("gap") 112 Rim of 103 by 102 120 Pixel 121 Subpixels 130 Tandem device according to the invention 131 First OLED stack 133 Second OLED stack 132 Load generation layer 1311, 1331 Electron injection and transport layer of 131 or 133 1312, 1332 Electroluminescent (or emitting) layer of 131 or 133 1313, 1333 131 or 133 hole injection and transport layer 140 Stacking on separator 104 141, 143 First and second stacking on separator 104 200 Device according to the invention 201 Subpixels 202 Subpixel control electrode 203 Insulating surface filler 204 Separator 205 OLED Stack 206 Top injection layer (optional) 207 Common conforming electrode 209 Colored filter 208 Smoothing layer 211 Natural gap between electrodes 202 210 Substrate 212 Edge of 203 out of 202 213 Pixel 221 Polymer layer 220 Encapsulation system 223 Insulation layer 222 Oxide layer Detailed description

[0037] There figure 1 schematically illustrates the circuit of an OLED display 10 of a known type that includes a pixel matrix unit 12 capable of producing an image, and a control unit 36. OLED diodes 14 and their control circuits 16 are arranged to form pixels in the pixel matrix unit 12,said pixel matrix comprising rows (horizontal) and columns (vertical). Each control circuit 16 one pixel 12 comprises a plurality of thin-film transistors 18,20 (typically in CMOS (Complementary Metal Oxide Semiconductor) or TFT (Thin Film Transistor) technology) and a capacitor 22. The control unit 36 orders a control circuit for the lines 30 and a video addressing circuit 32, as well as an electrical power supply circuit 34 for addressing pixel columns; it handles pixel circuit addressing 36 and controls the light emission of OLED diodes 14. The line control circuit is connected to the conductive tracks. 38 addressing the scan 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 TFTs 18 located on the sweep line 38 selected. 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 onto the video conductive tracks 40 columns according to the conductive tracks of the lines selected by the control circuit 30 corresponding. This voltage signal is recorded in the capacitor 32 through the TFT 18 of the OLED diode 14 of the selected pixel line. The TFT 20 The control unit sends a current corresponding to the voltage recorded at the OLED diode. 14, and therefore the OLED diode 14 of the selected line 38 emits light.

[0038] The power supply circuit 34 is connected to the power supply conductive tracks 42 columns of pixels; it powers the OLED diodes 14 via the conductive tracks 32 and TFTs 20 of the selected pixel line.

[0039] This principle of addressing an OLED diode forming a pixel in a pixel matrix, known as such, can be applied, also known as such, to addressing an OLED diode forming a subpixel in a pixel matrix of a color display device, in which each pixel comprises a plurality of subpixels (most often three or four) of different colors; this will be explained here in relation to the figure 2 . THE figures 2(a), (b) and (c) They show three examples of the geometric arrangement of these sub-pixels. 51,52,53,54 to form a pixel 50capable of displaying the desired color. In these figures, the sub-pixels are red. 51, blue 52 and green 53, and can understand, as on the figure 2(c) in addition to a white sub-pixel 54 to increase pixel brightness 50. The arrangement of the figure 2(a) is known by the acronym "RGB Stripe", it is the most widespread. The arrangement of the figure 2(b) is known by the acronym "RGB quad", and that of the figure 2(c) under the acronym "RGBW quad".

[0040] The addressing principle that has just been described in relation to the figures 1 and 2is one of the addressing principles that can be implemented in relation to the present invention. 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 the figure 3 .

[0041] There figure 3 schematically illustrates OLED microdisplays according to the prior art; it demonstrates the problem that the present invention seeks to solve. On the figure 3(a) is shown an overall schematic view of the device's structure 70 : we distinguish the substrate 71 (CMOS or TFT type, addressing circuits and components are not shown), control electrodes 72,73,74 sub-pixels separated by a gap-fill element 75, the OLED layer 76capable of emitting white light, the encapsulation layer 77, the blue colored filters 91, red 92 and green 93 forming a pixel 90, the glass slice 78 as a protective cover. The sub-pixel size is typically on the order of 3.5 µm to 5 µm. It should be noted that in this device, according to the prior art, the OLED layer 76 extends over the entire surface of the device.

[0042] There figure 3(b) shows an enlarged view of a device similar to the one depicted on the figure 3(a) 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 for their individual addressing, and by the corresponding colored filters 91,92,93 which modify the light emitted by the OLED layer 76white emission that extends over the entire surface of the device. The space between two adjacent sub-pixel control electrodes 72,73 can be filled by a filler element 75. The said OLED layer 76 includes the electroluminescent layer 80 properly speaking, which is sandwiched between two load-carrying layers 81, 82. More specifically, in a typical device, the layer 81 includes a layer for injection and transport of holes, and the layer 82 an electron injection and transport layer. But it is also possible to use a so-called "inverse" stacking, in which case the layer 82 includes a layer for injection and transport of holes, and the layer 81 an electron injection and transport layer. The layers 81 And 82These can respectively comprise a single layer that performs both the injection and transport functions of the respective charges, or several layers, for example, one layer for injection and another for transport of the respective charges. A common electrode 85 removes the loads.

[0043] This device, according to the prior art, exhibits parasitic currents; this is illustrated on the figure 3(b) Indeed, if during the lighting of a sub-pixel (for example 73 The main current flows (marked by a thick arrow) directly through the OLED layer in the shortest direction (i.e., vertically relative to the substrate). 71 Part of the current propagates along other conduction paths, provided these paths have sufficiently low resistivity. Thus, a parasitic current is observed propagating 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 indicated by two dashed arrows. It leads to stray light emission in neighboring sub-pixels, which alters the display's image resolution and reduces its color fidelity. The present invention aims to provide a means of reducing this parasitic current.

[0044] There figure 3(c) shows another device of a known type in which the color of a pixel 90 is not generated, as in the devices of figures 3(a) and 3(b) , by a white emission OLED element matched with color filters for each of the three sub-pixels, but by three sub-pixels equipped 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 layer of injection and transport of charges 83 (e.g., holes), and / or the second layer for injecting and transporting charges (e.g., electrons) 84 and the common electrode 99 are common to simplify device manufacturing. The problem of stray currents is the same as that described in relation to the figure 3(b) ; the contribution of the injection and hole transport layer 83 is predominant in these parasitic currents.

[0045] There figure 4 illustrates a cross-sectional view of a device 100 according to an example not in accordance with the claimed invention.

[0046] It includes a substrate 110 on which three sub-pixels are deposited 121a, 121b, 121c defining a pixel 120. In this example, each sub-pixel represents an elementary emitting area.

[0047] The substrate 110is specially adapted to the device 100, This could include a substrate made of silicon, glass, or plastic for a flexible device. The substrate 110 It can notably be a known type of CMOS silicon substrate that includes the pixel addressing circuits. 120 and sub-pixels 121 ; these aspects of pixel and sub-pixel addressing are not part of the present invention.

[0048] The elementary emitting areas (sub-pixels) are formed by several layers, which will be listed here starting with the layer deposited directly on the substrate, which is an electrode. 102, for each sub-pixel; these electrodes 102 sub-pixels are designated here by the symbols 102a, 102b, 102c. Above the electrode are deposited the OLED electroluminescent layers forming a stack 105, an upper injection layer 106,which is optional, then a compliant electrode 107 common. Depending on the type of device, a planarization layer can be added. 108 and colored filters 109. More specifically, the planarization layer is particularly advantageous when color filters are used to avoid optical losses. Even without optical filters, the planarization layer can form the basis for an additional encapsulation system, which might include, for example, an inorganic layer and / or a glass cover. The need for color filters depends on the emission color of the OLED layers forming the sub-pixels, as explained above.

[0049] Two neighboring elementary emitting zone electrodes (sub-pixels) (for example, the electrodes 102a And 102b ), whether or not they belong to the same pixel, are separated by a space 111referred to here as a natural space (in English, "gap"). According to an essential feature of the invention, this natural space 111 is filled by a filling element with an insulating surface 103 called a "gap fill". This filling element has an insulating surface. 103 may slightly overlap the sub-pixel electrode 102 to form a rim 112. In a particular embodiment, not only the surface of the filling element 103 but its entire volume is made of insulating material. It can be made, for example, from a composition based on a photosensitive resin (also called photoresist) or silica.

[0050] A separator with an insulating surface 104 is positioned above the filler element 103 with an insulating surface. Its walls can be vertical. It separates the stack of OLED layers. 105 and the top injection layer 106 of two sub-pixels102 neighbors. In a particular embodiment, not only its surface but its entire volume is made of insulating material. It can be manufactured from a photosensitive resin; negative-type photosensitive resins can be used, allowing for the production of fairly steep or even overhanging side walls. Inorganic dielectric materials can also be used.

[0051] OLED stacking 105 is typically deposited by thermal evaporation. This technique forms a deposit in a very directional manner, and thus the OLED stack 105 It essentially deposits only on horizontal surfaces and does not deposit on the vertical walls of the separators. The layers of the OLED stack 105 are therefore interrupted by the separator, in other words: they are not continuous across the separator, they are pixelated.

[0052] The upper injection layer 106The pixelated upper electrode can be replaced by a pixelated upper electrode (i.e., each elementary emission zone has its own upper injection layer or upper electrode layer). This upper electrode layer can be made from a thin metal such as aluminum (Al), silver (Ag), or another; this layer can also be deposited by thermal evaporation, in which case it will be deposited only on horizontal surfaces. Note that in the figures, this upper electrode layer, when it replaces the aforementioned upper injection layer, corresponds to the layer identified by the numerical marker. 106.

[0053] To connect the upper injection layer 106 or the top electrode, or the last layer of the OLED stack 105In the case where no top injection layer and no pixelated electrode are deposited, an additional common electrode is required for all the pixels. 107 so that it is not cut off by the separators 104. This common electrode 107 must be deposited using a technique that ensures conformal deposition. This can be achieved by atomic layer deposition (ALD) or chemical vapor deposition (CVD) of a transparent conductive oxide (TCO). Suitable TCOs include zinc oxide (ZnO), possibly doped with aluminum (AZO), snO₂, and indium tin oxide (ITO); these TCOs are well-known to those skilled in the art. At the periphery (not shown in the figure), this common electrode 107is connected to a suitable electrical potential to turn on the OLED 105 when the pixel electrode 102 The corresponding address is provided. If a superior electrode has been deposited 106 Through the evaporation of a metal, this electrode will be (more or less) pixelated by the separators. 104, and in this case the common conforming electrode 107 will create the electrical link between the small blocks of the upper injection layer 106.

[0054] In this embodiment of the device 101, lateral stray currents in OLED 105 are completely blocked. Another advantage of this architecture is that the common electrode conforms 107, notably filed by ALD, is a thin, dense, and waterproof film that acts as an encapsulation and protects the OLED stack 105moisture and oxygen. If a defect occurs, for example through a pinhole in the encapsulation, and in particular a defect that causes a black spot, this defect cannot spread over a larger area, since the separator 104 and the common electrode 107 They isolate each pixel (more or less) completely against diffusion, for example, from water. Thus, if the defect only affects a sub-pixel, it may not even be visible to the device's user.

[0055] The method of implementation of the figure 4 retains its advantage in the case where the separator wall 104 is not completely vertical and does not completely isolate the neighboring elementary emitting areas: this still significantly increases the lateral resistance between two OLED stacks 105 neighbors and reduces the crosstalk phenomenon.

[0056] We describe here in more detail the different layers that form a device according to this first embodiment; this description represents only one example and does not limit the scope of the invention.

[0057] The substrate 110 active matrix can be a CMOS (silicon) substrate, comprising CMOS technology transistors, or a glass or plastic type substrate comprising TFT type transistors (typically a-Si, poly-Si, metal or organic oxide).

[0058] The pixel electrode 102is a layer of aluminum (Al) or other metal, typically 20 nm to 1000 nm thick, preferably 100 nm to 300 nm thick, optionally coated with a thin layer of TiN or MoO3 or a transparent conductive oxide (TCO) or similar material. The pixel electrode can be made of TCO, particularly in the embodiment of a display that emits downwards through a transparent substrate, or in the embodiment of a transparent display that emits both upwards and downwards.

[0059] The display subpixel typically has a size between 1 µm and 100 µm, preferably between 2 µm and 50 µm, and even more preferably between 2 µm and 10 µm. The distance between subpixels is on the order of 0.1 µm to 10 µm, and preferably between 0.2 µm and 1.0 µm.

[0060] The filler element 103(The "gap-fill") can be a photosensitive resin, an epoxy resin, or an inorganic dielectric such as SiO₂, Si₃N₄, or Al₂O₃. The width of the gap (rim) 112 ) on the electrode is between 0 and 0.5 µm, preferably between 0.05 µm and 0.25 µm.

[0061] The separator 104 It can be composed of a photosensitive resin, an epoxy, an inorganic dielectric such as SiO2, Si3N4, Al2O3 etc. Its width is approximately equal to the distance between the pixels.

[0062] OLED stacking 105 It can be a white OLED, single-cell, tandem-cell, or multi-cell, typically with a thickness between 50 nm and 500 nm, and preferably between 80 nm and 250 nm. OLED stacking 105 It can emit from the top or the bottom, or emit on both sides. The layer deposition of the OLED stack 105 is achieved by a directive method such as thermal evaporation.

[0063] The upper injection layer 106 (or, where applicable, the upper electrode) is deposited in the space between two separators 104 neighbors. If a top electrode is deposited, it can be made of a reflective metal such as aluminum (Al) or silver (Ag), typically 25 nm to 100 nm thick for bottom emission, and 1 nm to 15 nm thick for top or both-sided emission. Deposition can be carried out using a directional method such as thermal evaporation.

[0064] The common electrode 107, deposited above the upper injection layer 106 or the upper electrode (if one is present) or above the OLED stack 105Otherwise, it is typically a transparent conductive oxide such as ZnO, AZO, ITO, SnO2, or others. It is deposited using a highly conformal deposition method such as ALD, PECVD, or others. Its thickness is typically between 20 nm and 300 nm.

[0065] The planarization layer (smoothing layer) 108 is typically an organic material (such as a photosensitive resin or an epoxy resin) deposited from a solution (by spin coating or spray-coating or similar).

[0066] The color filter 109 is a state-of-the-art color filter, made from colored resins for example. It can be made from colored photosensitive resin, or from patterned interference filters, or similar materials.

[0067] An embodiment of a device according to the invention is illustrated on la figure 5 .

[0068] The architecture incorporates most of the components presented in relation to the first embodiment; the figure shows three elementary emitting zones. 201a, 201b, 201c which form a pixel 213. The device 200, presented in a cross-sectional view, includes a substrate 210 and electrodes 202 of sub-pixels separated by a natural space 211 which has the shape of a trench. An insulating layer 223 is situated in this natural space 211, and more specifically on its walls, with a rim 212 (overlap) on the electrode pixels 202. It acts as a filler element with an insulating surface. 203.

[0069] Electroluminescent coatings 205 OLEDs forming a stack are deposited on the sub-pixel electrode 202 and on said insulation layer 223, then a top injection layer 206or a top electrode (the first is preferred, but both are optional), a conforming electrode 207, a planarization layer (also called a smoothing layer) 208 which is optional and acts as a separator 204, and colored filters 209. In the absence of a smoothing layer 208 the natural space can remain empty above the common electrode 207, this void acting as a separator 204, or it can be filled by elements of the encapsulation system.

[0070] This embodiment allows the use of the natural space between the sub-pixel electrodes. 202, which have vertical walls, like the walls of sub-pixel electrodes. 202 They are conductive, they must be covered with a layer of insulation. 223 ; The latter can slightly overlap the edge of the electrode pixel 202,This reduces the risk of short circuits but increases the complexity of the manufacturing process. This insulating layer 223 It can be a thin dielectric layer, for example, a layer of alumina, silica, or similar, deposited by a conformal deposition process such as ALD, PECVD, or similar. An organic layer can be used, for example, a thin layer of photosensitive resin; this can typically be produced by photolithography, allowing a slight overlap as shown in the diagram. figure 4 to avoid short circuits on the edge.

[0071] We describe here in more detail the different layers that form a device according to this second embodiment; this description represents only one example and does not limit the scope of the invention.

[0072] The substrate 200, the pixel electrode 202, OLED stacking 205, the common electrode 220optional, the conforming electrode 207, the planarization layer 208 optional, the color filter 209 they repeat the compositions of the first embodiment.

[0073] A pixel electrode is deposited 202 A thin layer (not shown in the figure) of a conductive material capable of injecting charge carriers (electrons or holes, depending on the OLED device geometry) into an organic OLED layer. This thin layer protects the pixel surface during the etching of the insulating layer. 223. Its thickness is between 1 nm and 50 nm, and preferably between 5 nm and 15 nm. This thin layer may be made of TiN, or preferably of a transparent conductive oxide (in particular: tin oxide (SnO₂), tin-doped indium oxide (ITO), zinc oxide (ZnO), aluminum-doped zinc oxide (AZO)). If said etching of the insulating layer 223involving an oxygen plasma, it is preferable that the said thin layer be in oxide.

[0074] To create the insulating layer 223,A thin layer of TiO₂ (typically between 5 nm and 20 nm thick) can be deposited by ALD over the entire substrate surface. Next, a layer of a known type of photosensitive polymer (e.g., TEKR-003PM) is deposited by spin-coating; the thickness can be between 0.5 µm and 1 µm for the reference shown. The active pixel area is then defined by photolithography, with a small overlap (typically between 0.1 µm and 0.2 µm) at the pixel boundaries. The TiO₂ is then removed by wet etching using HF; this does not attack the TiN layer, which thus protects the pixel electrode. This choice of material (TiO₂ on TiN) is essential for the successful implementation of this embodiment of the invention. The photosensitive polymer layer is then removed to open the pixel spacing. The remaining part of the TiO2 layer thus forms the insulating layer. 223.

[0075] In another embodiment, it is advantageous to use the insulating layer 223 Another insulating material such as aluminum oxide, silicon oxide, or silicon nitride, deposited conformally by ALD or CVD. Instead of wet etching of this layer, dry etching techniques, particularly reactive dry etching (RIE), can be used.

[0076] Next, the organic layers are deposited to form the OLED diode, as well as the cathode. This results in the structure shown, in which the pixels are separated by a trench, and the walls of this trench are insulated by the insulating layer. 223.

[0077] The said trench may eventually extend into the substrate 210, especially if its production involves an engraving step.

[0078] Other than TiO2, the insulation layer 223It may be a thin dielectric film made of another material, for example Al₂O₃, SiO₂, Si₃N₄, or similar, deposited by ALD, PECVD, or similar processes. The layer thickness is typically on the order of 5 nm to 25 nm, shaped by photolithography.

[0079] The upper electrode, which is optional, can be made of a very thin layer of silver or aluminum, between 4 nm and 10 nm thick. If it is absent, it is the common electrode. 207 which then fulfills the function of an electrode for each elementary emitting zone. In this case, between two neighboring separators, and delimited by them, an injection layer advantageously extends. 206 charge carriers are injected into a material capable of injecting charge carriers into the OLED stack; molybdenum oxide or tungsten oxide can be used. The layer typically has a thickness between 0.5 nm and 5 nm.

[0080] The present invention applies equally to cases where the elementary emitting areas are pixels or sub-pixels, and to cases where they emit white or colored light; the presence of colored filters 109 is necessary to enable the display of color sub-pixels if the OLED layers of said sub-pixels all emit white light.

[0081] It should be noted that, for the sake of simplification, neither the figure 4 neither the figure 5 do not show the device's encapsulation system. The encapsulation system may include, as known from US document 8,693,396 or US document 9,082,999, a trilayer alumina / polymer / alumina complex. The smoothing layer 108 can be deposited above the last layer of the three-layer system. The present invention allows, in one embodiment, for simplifying this encapsulation system by using the common conformal electrode 107as the first layer of the three-layer complex. This variant is shown on the figure 7 (variant of the device of the figure 4 ) and on the figure 8 (variant of the figure 5 ), where the landmarks 220,221 And 222 These refer, respectively, to the encapsulation system, the polymer layer, and the oxide layer, the latter of which can be, in particular, silica or alumina. The smoothing layer 108 is then located above the last encapsulation layer, in this case the oxide layer 222. Note that the common conformal electrode 107 It acts as a barrier to the surrounding atmosphere and protects the underlying layers. It can represent the encapsulation system on its own (given that the smoothing layer and possibly the colored filter act as mechanical protection), although this is not the preferred embodiment.

[0082] We describe here in relation to the figure 6Another example not conforming to the claimed invention, with a tandem-type OLED device structure. figure 6(a) shows such a device 130 which is characterized by the superposition of two OLED stacks 131, 133 which are separated by a charge generation layer 132. For the structure of the insulating surface filling element 103 and the insulating surface separator 104 The device follows the first embodiment described above. This figure does not show the smoothing layer and the color filters, which are optional, depending on the color emitted by the elementary emitting areas forming the pixels, nor the encapsulation layer.

[0083] There figure 6(b) shows in greater detail the stacking of layers forming OLED stacks. The first 131 and the second 133OLED stacks each include their own electron injection and transport layer. 1311,1331, which injects electrons into the electroluminescent layer 1312, 1332, and its hole injection and transport layer 1313, 1333, which injects holes into said electroluminescent layer 1312,1332. The electron injection and transport layer 1311 of the first OLED stack 131 and the injection and transport layer of holes 1333 of the second OLED stack 133 are separated by a charge generation layer 132. In one variant (not shown in the figures) the order of the layers can be reversed, and thus the electron injection and transport layer can be below the respective electroluminescent layer and the hole injection and transport layers above the respective electroluminescent layer.

[0084] In an advantageous variant illustrated on the figure 6(c)the electroluminescent layer 1312,1332 (shown on the figure 6(b) (Only) is structured, meaning it is deposited only on the elementary emitting zones, excluding the areas occupied by the insulating surface filler elements and the separator. Such a structured deposit can be achieved using a stencil; this is a known technique. In this variant, only the injection and hole transport layer 1313,1333 and / or the electron injection and transport layer 1311,1331 are deposited across the entire surface of the display, including the area occupied by the insulating surface filler elements and the separator. In this area, a stack is formed 141,143 which is schematically represented on the figure 6(d)This is not an "OLED stack" because it does not include the electroluminescent layer and therefore does not emit light. However, without the insulating surface separator element, a parasitic current would pass through these injection and transport layers, contributing to the cross-talk phenomenon that the present invention aims to eliminate. It would, in principle, be possible to also deposit the injection and transport layer with holes. 1313,1333 and the electron injection and transport layer 1311,1331 using the stencil technique, but this increases the process time, risks reducing industrial output, and would thus generate an unacceptable additional cost. Examples

[0085] The examples below do not conform to the claimed invention.

[0086] These examples relate to two embodiments and the materials used to produce the corresponding structures of the different embodiments.

[0087] We have created OLED micro-displays with a 1280 x 1024 pixel matrix, with 4 sub-pixels per pixel, in a "quad RGBW" type arrangement according to the figure 2(c) The pixel size was 9.4 µm x 9.4 µm, and the sub-pixel size was 4.7 µm x 4.7 µm. White pixels were used, colored by color filters. The overall dimensions of the micro-display screen were 12.03 mm x 9.63 mm.

[0088] We deposited it on a substrate 110 200 mm diameter silicon active matrix (CMOS technology) circuits for the pixel matrix comprising 2560 x 2048 sub-pixels. The electrode layer 102The pixels were made of aluminum, with dimensions of 3.7 µm x 3.7 µm. A silicon oxide layer was deposited and structured by photolithography to generate the gap-fill. (Alternatively, a photoresist varnish or a crosslinkable polymer can be deposited and then structured.) An organic separator is then deposited on top of the gap-fill (by depositing and structuring a negative photoresist or another type of crosslinkable varnish). Alternatively, the separator can be fabricated by depositing and structuring an inorganic material (such as Al₂O₃ or SiO₂) using anisotropic etching.

[0089] On this assembly, a stack of OLED layers (white light) is deposited by thermal evaporation through masks (to limit the deposit to the surface of individual pixels), with the following characteristics: Instead of a standard, semi-transparent metal cathode, an electron injection layer is deposited. 106A layer of molybdenum oxide, between 0.5 and 5 nm thick, is deposited by thermal evaporation. Above the MoO3 layer, a TCO layer (such as AZO, ZnO, or SnO2) is deposited by ALD; this deposit covers the cathode electrical connections mentioned above. The thickness is between 25 nm and 300 nm.

[0090] A thin-film encapsulation can be added on top of the TCO layer, but the TCO layer can also serve as the encapsulation layer on its own. Colored filters and, optionally, a glass cover or other means of protecting the microdisplay are deposited on top of this assembly (preferably on a smoothing layer placed over the encapsulation system). The silicon wafer is then cut to release the microdisplays, which can then be integrated into more complex electronic devices.

Claims

1. An electroluminescent display device (200) comprising a plurality of pixels (213) deposited on a substrate (210), each pixel being formed of one or more elementary emitting zones (201a, b, c), each elementary emitting zone comprising a base electrode (202a, b, c) deposited on said substrate (210) and an OLED stack (205) comprising an electroluminescent layer deposited on said base electrode (202a, b, c), and said device (200) comprising a common electrode (207) deposited above said OLED stack by a conformal deposition technique such as ALD (Atomic Layer Deposition) or CVD (Chemical Vapor Deposition), said device being characterized in that: - Two adjacent base electrodes (202a, 202b) belonging to two adjacent elementary emitting zones (201a, 201b) are separated by a natural gap (211) which has the shaped of a trench and acts as a separator between two adjacent base electrodes (202a, 202b), - An insulating layer (223) is disposed in said natural gap (211) and on the walls of the base electrodes (202a, 202b), - The layers of the OLED stack (205) are deposited on said base electrode (202a, b, c) and on said insulating layer (223) between said base electrodes (202a, b, c), and are interrupted by the separator (204); - A conformal common electrode (107, 207) is deposited above the OLED stack and the natural gap (211).

2. Device according to claim 1, characterized in that said substrate (210) is an active matrix substrate, such as a silicon CMOS type substrate or a glass or plastic type substrate comprising TFT type transistors.

3. A device according to any one of claims 1 to 2, characterized in that said insulating layer (223) extends over a portion of the surface of said base electrodes (202a, 202b).

4. A device according to any one of claims 1 to 3, characterized in that a transparent conductive layer capable of injecting charge carriers into the OLED stack, deposited between said OLED stack (205) and said common electrode (207), extends between two adjacent separators (204) and is delimited by them, the thickness of said transparent conductive layer preferably being between 0.5 nm and 5 nm.

5. A device according to claim 4, characterized in that said transparent conductive layer was deposited by a directional deposition technique, such as thermal evaporation.

6. Device according to claim 4 or 5, characterized in that said transparent conductive layer is a molybdenum oxide or a tungsten oxide7. A device according to any one of claims 1 to 6, characterized in that between two adjacent separators (204), and delimited by them, extends an upper electrode with a thickness between 4 nm and 10 nm, deposited by a directional deposition technique, such as thermal evaporation, said upper electrode layer preferably being made from a thin metal such as aluminum (Al) or silver (Ag).

8. A device according to any one of claims 1 to 7, characterized in that it comprises an encapsulation system (220) deposited above the common electrode (207).

9. A device according to claim 8, characterized in that said encapsulation system (220) comprises a polymer layer (221) and an inorganic layer, preferably an oxide (222).

10. A device according to claim 9, characterized in that it comprises an inorganic layer, preferably an oxide, deposited between the common electrode (207) and the polymer layer (221).

11. A device according to any one of claims 1 to 10, characterized in that it comprises a smoothing layer (108, 208) deposited either above said common electrode (107, 207) or above said encapsulation system (220).

12. A device according to any one of claims 1 to 11, characterized in that it comprises a colored filter system (209) deposited on the common electrode (207), or preferably on the encapsulation system (220), or more preferably on said smoothing layer (208).

13. A device according to any one of claims 1 to 12, characterized in that it comprises two superimposed OLED stacks.

14. A device according to claim 13, characterized in that the two OLED stacks are separated by a charge generation layer.