Active matrix electroluminescent device with improved resolution

Abstract

The present invention relates to an electroluminescent display device comprising an array of electroluminescent pixels consisting of a plurality of pixels deposited on a substrate (210), each pixel being formed by at least three elementary light-emitting regions, each elementary light-emitting region belonging to a different elementary light-emitting region group, each elementary light-emitting region comprising an electroluminescent stack (205) of organic layers, referred to as an "OLED stack", and a transparent upper electrode (207) placed between the control electrode (202) and the transparent upper electrode (207), the electroluminescent display device being characterized in that: two adjacent control electrodes (202a, 202b; 202b, 202c, 202c; 202c, 202a) are separated by a space (211) forming a trench, which covers at least the vertical sides of adjacent electrodes and electrically insulates them from each other, and two adjacent control electrodes (202a, 202a; the electrodes (202a, 202b, 2024, 202c) are separated by a space (211) forming the trench, which space is filled by a filling element (203) such that adjacent electrodes are electrically insulated from each other and fill the natural space between the two electrodes. In each group of basic light emitting regions, the entire OLED stack and its respective upper electrodes (205a and 207a, 205b and 207b, 205c and 207c) are separated from adjacent components belonging to the other group by an encapsulation layer (290) that protects the upper surface and sides of the OLED stack from ambient air.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic devices and components, and more specifically to electroluminescent devices of the OLED (Organic Light Emitting Diode) type. The invention particularly relates to improving the efficiency and brightness of the color gamut of OLED type displays, as well as increasing their resolution. Through this invention, it is possible to manufacture microdisplays with extremely high spatial resolution, i.e., microdisplays with exceptionally high pixel and subpixel densities. Background Technology

[0002] Organic light-emitting diodes (OLEDs) are a mature product used in the manufacture of thin lighting systems and displays. OLED-based displays typically consist of 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 in Figure 1 The diagram is schematic and will be explained below. In a color display, each pixel is subdivided into subpixels of different colors (usually three or four, including the three primary colors of red, green, and blue, and possibly a white subpixel), which work together to emit a point of light (pixel) of the desired color. Figure 2 Three known examples are shown for arranging subpixels of different colors to form pixels capable of displaying the desired color.

[0003] The color of a pixel or subpixel can be generated in two different ways. In the first implementation, an OLED diode that emits white light is used, and the emitted white light is passed through a color filter. Figure 3 A cross-section of this display is shown. An OLED stack covering the entire matrix surface is deposited above the sub-pixel electrodes, and this OLED stack (in this example) emits white light. In this case, the RGB (red-green-blue) or RGBW (red-green-blue-white) primary colors of the sub-pixels are generated by color filters located above the OLED stack.

[0004] This implementation has two advantages. First, the same common OLED layer can be used for all sub-pixels; this layer is unstructured at the matrix level, and color is generated by the filter. Another advantage is that very small actively addressed sub-pixels can be achieved, which improves the spatial resolution of the display. However, this approach has two disadvantages: First, the filter absorbs a significant portion of the light intensity emitted by the pixel. Therefore, to achieve the target light intensity, the light emission of the OLED diode needs to be increased. It is well known that the large number of holes and electrons passing through the organic layer causes electrochemical side reactions in the organic compounds, ultimately leading to their degradation. Since the operating lifetime of OLED devices decreases with increasing current density or brightness, it is desirable not to increase the light intensity emitted by the OLED diodes above a certain value. Second, the display sharpness of this device is limited by crosstalk, which will be explained below.

[0005] Another way to achieve primary colors is to structure the OLED layer into sub-pixels with different emission colors. This is the second well-known implementation method, which avoids the first problem mentioned above, which involves light intensity loss, by not using color filters. Since the structuring process of OLED layers is quite complex and the achievable spatial resolution is rather limited, even in this case, it is preferable to maintain the maximum number of common layers (i.e., layers covering the entire surface of the matrix), typically charge carrier transport layers, and only structuring the emitting layers. However, as with the first implementation, it is observed that adjacent pixels or sub-pixels may interact through capacitive coupling or through parasitic currents (particularly through parasitic currents flowing within the plane of the common conductive layer of the OLED stack).

[0006] Figure 4 An example of such parasitic currents within the plane of the conductive layer is shown, which will be explained below. This undesirable interaction between adjacent pixels is referred to by those skilled in the art as “crosstalk,” which primarily causes undesirable color variations in color displays. The theoretical aspects of crosstalk in OLED devices have been studied for a long time (see, for example, D. Braun’s “Crosstalk in passive matrix polymer LED displays,” published in Synthetic Metals, Vol. 92, pp. 107–113, 1998).

[0007] This problem becomes more pronounced as subpixel sizes decrease. Besides digitally correcting for the consequences of crosstalk (which is equivalent to accepting the crosstalk phenomenon and reducing its impact on the image), there are different approaches to overcome crosstalk at its source, namely reducing the physical phenomenon at the pixel or subpixel level.

[0008] To reduce crosstalk, WO 2019 / 193290 (MicroOled) proposes a method to divide two adjacent pixels by using a filling element with an insulating surface that separates their base electrodes and their OLED layers.

[0009] It is well known that each pixel can also be separated to isolate it from other surrounding pixels to avoid short-circuit problems associated with moisture in the encapsulation layer. Document EP 2927985 (Universal Display Corp.) describes a structure in which each pixel is sealed and isolated from its neighboring pixels. Manufacturing such a structure requires numerous complex process steps. It is also known to divide pixel areas using additional separating elements, such as partitions, as described in US 9419245 (Japan Display Inc.). The processes described in both documents are complex and incur significant additional costs.

[0010] More generally, care must be taken to ensure that the manufacturing processes used to produce display devices do not become overly complex or include steps that may introduce new problems. For example, documents US2021 / 0265432 A1 and US2024 / 0057428 A1 each describe a method for constructing OLED-type pixels by photolithography and etching, in which the OLED stack is indeed protected by a mask deposited over the top electrode, which is used to define the pixels during etching. However, in these methods, the sidewalls of the OLED stack are still exposed to etching: this operation can damage the OLED stack and limit the display spatial resolution achievable using these methods.

[0011] US2022 / 0376204 A1 describes a method in which the separation between pixels is achieved through a structure with a T-shaped cross section, which is complex to manufacture.

[0012] The structure of existing technology devices is as follows Figure 5 As shown, this structure allows for high light intensity, which will be discussed in more detail below. It features three primary emitting regions (subpixels) of different colors and eliminates the need for color filters, ensuring excellent device efficiency and brightness. Since the subpixels are also separated at the level of their OLED layers, there is virtually no crosstalk, resulting in good image sharpness. This device offers numerous functional advantages. However, because the OLED layers of the subpixels are different, they must be deposited separately, and unfortunately, there is currently no known industrial process capable of miniaturizing this device to a primary emitting region (subpixel) size of less than approximately 20 μm.

[0013] In view of the above, one object of the present invention is to overcome at least partially the disadvantages of the prior art and to provide an architecture for an OLED display device of the color microdisplay type, which has excellent brightness, preferably by using a basic color emitting region, and is able to significantly reduce and preferably eliminate lateral parasitic currents even for very small pixels (typically less than 5 μm) or structures with very small inter-pixel spacing. Another object is to provide a reliable and simple manufacturing process for manufacturing such a device. Summary of the Invention

[0014] According to the present invention, the above-mentioned problems are solved by an electroluminescent display device comprising an electroluminescent pixel matrix deposited on a substrate in a matrix arrangement of rows and columns, wherein the electroluminescent pixel matrix is ​​composed of a plurality of pixels.

[0015] Each pixel consists of at least three basic luminescent regions, each of which belongs to a different group of basic luminescent regions. Each group of basic luminescent regions is distinguished from the basic luminescent regions belonging to other groups by its emitted color.

[0016] Each of the aforementioned basic light-emitting regions includes an electroluminescent stack composed of organic layers, referred to as an "OLED stack," which includes at least one light-emitting organic layer.

[0017] The OLED stack is disposed between the control electrode and the transparent top electrode, through which light emitted by the OLED stack passes.

[0018] The electroluminescent display device is characterized in that:

[0019] Two adjacent control electrodes of two adjacent basic light-emitting regions belonging to different basic light-emitting region groups are separated by a space forming a trench. This space has an insulating surface that at least covers the vertical sidewalls of the adjacent electrodes and electrically insulates them from each other.

[0020] Two adjacent control electrodes of two adjacent basic light-emitting regions belonging to the same basic light-emitting region group are separated by a space forming a trench, which is filled by a filling element that electrically insulates the adjacent electrodes from each other and fills the natural space between the two electrodes.

[0021] In each group of basic light-emitting regions, the entire OLED stack and its corresponding top electrode are separated from adjacent components belonging to another group of basic light-emitting regions by an encapsulation layer. This encapsulation layer protects the top surface and sidewalls of the OLED stack from ambient air, thus forming protected islands. Each island comprises a group of OLED stacks and their top electrodes from the same group. Each island is understood as a region extending vertically from the top to the bottom of the pixel matrix.

[0022] According to one aspect of the invention, the trench extends to the substrate along a z-axis perpendicular to the substrate.

[0023] According to another aspect of the invention, the space forming a trench between two adjacent light-emitting areas belonging to the same group is filled by a filling element having an insulating surface. This filling element fills the natural space between two adjacent control electrodes, making the upper electrode substantially flat.

[0024] According to another aspect, the width of the trench space forming between two adjacent light-emitting regions belonging to different groups is between 0.3 μm and 1.0 μm. According to yet another aspect, the depth of the trench space is between 150 nm and 800 nm, preferably between 150 nm and 450 nm.

[0025] The above-described electroluminescent display device constitutes the first objective of this invention.

[0026] The thickness of the control electrode is between about 150 nm and about 800 nm, preferably between about 150 nm and about 450 nm. Advantageously, the thickness of the control electrode is greater than the thickness of the OLED stack.

[0027] According to the invention, the geometry of the trench is selected to, on the one hand, create good spatial and electrical separation between the control electrodes of adjacent primary light-emitting regions, particularly for critical etching steps, and on the other hand, to have the widest possible opening of the primary light-emitting regions (sub-pixels), even for very small sub-pixel pitches. Here, the opening of the primary light-emitting region should be understood as the ratio of its effective area (i.e., the horizontal surface of the control electrodes, which may be reduced due to the overflow of the insulating layer) to the product of the pitch of the primary light-emitting regions in the x-direction and the pitch of the primary light-emitting regions in the y-direction.

[0028] In an advantageous device according to the invention, the spacing between the basic light-emitting regions is less than about 20 μm, preferably less than about 15 μm, more preferably less than about 10 μm, and even more preferably between about 1 μm and about 5 μm.

[0029] The gap width between the control electrodes is advantageously less than about 1 μm, preferably between about 0.3 μm and about 1.0 μm.

[0030] In an advantageous embodiment of the invention, the sub-pixel spacing is typically between about 1 μm and about 5 μm, and the gap width between control electrodes is typically between about 0.3 μm and about 1.0 μm. For example, for a sub-pixel spacing of 3 μm in the x-direction, a spacing of 9 μm in the y-direction, and an electrode spacing of 1 μm, the surface area of ​​the control electrodes is 2 μm × 8 μm = 16 μm. 2Therefore, if the insulating layer does not overflow on the electrode, the opening is 16μm / (3μm×9μm)=0.59.

[0031] The method according to the invention utilizes known integrated circuit manufacturing techniques, particularly photolithography and etching. In order to implement these techniques, it is necessary to ensure that the etching process used only attacks the material that must be removed, while leaving the material that must be retained intact.

[0032] This geometry is advantageously achieved through one or more of the following features, which constitute a particular aspect of the invention:

[0033] - The thickness of the control electrode in the basic light-emitting region is between approximately 150 nm and approximately 800 nm.

[0034] - The thickness of the control electrode in the basic light-emitting region is greater than the thickness of the OLED stack in the basic light-emitting region.

[0035] - The insulating layer must be very thin and defect-free. Its thickness is preferably between about 10 nm and about 30 nm. It is preferably deposited using a conformal deposition technique, preferably ALD (atomic layer deposition), to simultaneously protect the sidewalls of the OLED stack.

[0036] - Fill elements exist only in the horizontal space between subpixels, but the trenches remain empty in the vertical space. To ensure the continuity of the top electrode, the fill elements must also exist between the first row of pixels and the top connecting strip, and between the bottom last row of pixels and the bottom connecting strip.

[0037] - The square space between four adjacent basic light-emitting areas preferably does not include filling elements to obtain a continuous trench from the top to the bottom of the pixel matrix, thereby separating groups of different basic light-emitting areas.

[0038] - The surface of the control electrode exhibits good resistance to etching of the OLED layer, which is typically accomplished using oxygen plasma. Advantageously, the electrode comprises a metal layer covered with a thin layer of transparent conductive oxide (TCO), which exhibits good resistance to this type of etching. This TCO layer is advantageously made of SnO2, which may be doped; this will be explained below.

[0039] - The encapsulation layer is selected from materials that are highly resistant to various wet and dry stages of photolithography (deposition and development of photoresist) and etching of OLED stacks (especially by oxygen plasma). Advantageously, the encapsulation layer can be made of Al2O3.

[0040] A second aspect of the present invention is a method for manufacturing an electroluminescent display device, the device comprising an electroluminescent pixel matrix deposited on a substrate in a matrix arrangement of rows and columns, the electroluminescent pixel matrix being composed of a plurality of pixels.

[0041] Each pixel consists of at least three basic luminescent regions, each of which belongs to a different group of basic luminescent regions. Each group of basic luminescent regions is distinguished from the basic luminescent regions belonging to other groups by its emitted color.

[0042] Each basic light-emitting region comprises an electroluminescent stack made of organic layers, referred to as an "OLED stack," which includes at least one light-emitting organic layer.

[0043] In the method:

[0044] The substrate is provided with control electrodes for each basic light-emitting region, an insulating layer between two adjacent electrodes, and filling elements are provided between two adjacent basic light-emitting regions belonging to the same group of basic light-emitting regions.

[0045] In the first set of steps, a first set of basic light-emitting regions is fabricated by first depositing a first OLED stack, a top electrode, and a first encapsulation layer formed using a conformal deposition technique. Then, photoresist (according to known photolithography methods established in microelectronics) is applied at the locations of the first set of basic light-emitting regions. This photoresist protects the horizontal surface and sidewalls of the encapsulation layer at the locations of the first set of basic light-emitting regions. Areas not protected by the photoresist are etched down to the top surface of the control electrode. Finally, the photoresist is removed.

[0046] In the second set of steps, a second set of basic light-emitting regions is fabricated by first depositing a second OLED stack, a top electrode, and a second encapsulation layer formed using a conformal deposition technique. Then, photoresist (according to known photolithography methods established in microelectronics) is applied at the locations of the second set of light-emitting regions. This photoresist protects the horizontal surface and sidewalls of the encapsulation layer at the locations of the second set of basic light-emitting regions. The areas not protected by the photoresist are etched down to the top surface of the control electrode for the third set of basic light-emitting regions and the surface of the first encapsulation layer for the first set of basic light-emitting regions. Finally, the photoresist is removed.

[0047] In the third set of steps, a third set of basic light-emitting regions is fabricated by first depositing a third OLED stack, an upper electrode, and a third encapsulation layer formed using conformal deposition technology. Then, photoresist (according to known photolithography methods established in microelectronics) is applied at the location of the third set of light-emitting regions. This photoresist protects the horizontal surface and sidewalls of the encapsulation layer at the location of the third set of basic light-emitting regions. The areas not protected by the photoresist are etched down to the surface of the first encapsulation layer of the first and second sets of basic light-emitting regions. Finally, the photoresist is removed. Attached Figure Description

[0048] Figures 1 to 6A vertical cross-section of an optoelectronic device of the OLED display type is schematically shown, along with conventionally known aspects of OLED devices and displays.

[0049] Figures 7 to 34 Various aspects and embodiments of the invention are illustrated; these figures are not intended to limit the scope of the invention.

[0050] More specifically, Figures 7 to 14 The structure of the OLED display device according to the present invention and some key steps in its manufacturing process are shown.

[0051] Figures 15 to 26 The various steps of the method for manufacturing an OLED display device according to the present invention are shown in more detail.

[0052] Figures 27 to 34 Other specific aspects of the invention are illustrated.

[0053] Figure 1 A circuit diagram of a known type of OLED matrix display is shown.

[0054] Figure 2 Three known examples are shown for arranging subpixels of different colors to form pixels capable of displaying the desired color.

[0055] Figure 3 The diagram schematically illustrates a vertical cross-section of a prior art OLED display with a white light-emitting OLED and a color filter. Multiple pixels are shown in the figure.

[0056] Figure 4 It schematically shows something similar to Figure 3 The figure shows a vertical cross-section of an OLED display, where each pixel is formed by three sub-pixels. The diagram also illustrates a single pixel with its three sub-pixels.

[0057] Figure 5 It schematically shows something similar to Figure 4 The vertical cross-section of the OLED display, in one embodiment, shows that each sub-pixel emits a different color and no color filter is used.

[0058] Figure 6 The document WO 2019 / 193290 was reproduced. Figure 5 .

[0059] Figure 7 A top view is shown of an intermediate product manufactured using the steps of the method according to the present invention.

[0060] Figure 8 Schematic illustration along Figure 7The AA line shown represents a vertical section of the structured stack in the zx plane, which is located at the corresponding Figure 7 On the substrate of the intermediate product.

[0061] Figure 9 Schematic illustration along Figure 7 The BB line shown represents a vertical section of the structured stack in the zy plane, which is located at the corresponding Figure 7 On the same intermediate product substrate.

[0062] Figure 10 Schematic illustration along Figure 7 The AA line shown represents a vertical cross-section of a structured stack in the zx plane, which lies on a substrate and corresponds to a ratio of Figure 8 The intermediate products are a later step.

[0063] Figure 11 Schematic illustration along Figure 7 The BB line shown represents a vertical cross-section of a structured stack in the zy plane, which lies on a substrate and corresponds to a ratio of Figure 9 The intermediate products are a later step.

[0064] Figure 12 A top view is shown of an intermediate product manufactured using the steps of the method according to the present invention, the manufacturing stages of which correspond to... Figure 10 and Figure 11 .

[0065] Figure 13 Schematic illustration along Figure 7 The AA line shown represents a vertical cross-section of the structured stack in the zx plane, which lies on a substrate and corresponds to a series of additional manufacturing steps. Figure 12 Intermediate products.

[0066] Figure 14 Schematic illustration along Figure 7 The BB line shown represents a vertical cross-section of a structured stack in the zy plane, which lies on a substrate and corresponds to... Figure 13 The same intermediate products.

[0067] Figure 15 The first series of steps of an embodiment of the method for manufacturing an OLED microdisplay type device having three sets of pixels according to the present invention are shown.

[0068] Figure 16 It shows the continuation Figure 15 The second series of process steps.

[0069] Figure 17 It shows the continuation Figure 16 The third series of process steps.

[0070] Figure 18 It shows the continuation Figure 17 The fourth series of process steps; which yields the first group of sub-pixels.

[0071] Figure 19 It shows the continuation Figure 18 The fifth series of process steps.

[0072] Figure 20 It shows the continuation Figure 19 The sixth series of process steps.

[0073] Figure 21 It shows the continuation Figure 20 The eighth series of process steps.

[0074] Figure 22 It shows the continuation Figure 21 The ninth series of process steps.

[0075] Figure 23 It shows the continuation Figure 22 The tenth series of process steps; which yields the second group of sub-pixels.

[0076] Figure 24 It shows the continuation Figure 23 The eleventh series of process steps.

[0077] Figure 25 It shows the continuation Figure 24 The process steps of the twelfth series.

[0078] Figure 26 It shows the continuation Figure 25 The thirteenth series of process steps; which yields the third group of sub-pixels. This intermediate product corresponds to... Figure 13 and Figure 14 .

[0079] Figure 27 Reference Figure 7 The diagram shows an opening in a shadow mask used for depositing OLED stacks according to the method of the present invention.

[0080] Figure 28 Reference Figure 7 The diagram shows the opening of a shadow mask used for depositing an upper electrode in the method according to the present invention.

[0081] Figure 29 Reference Figure 7 This shows a variation.

[0082] Figure 30 Schematic illustration along Figure 7The BB line shown represents a vertical cross-section of a structured stack in the zy plane, which lies on a substrate and corresponds to... Figure 7 A variation of an intermediate product; the cross-section is similar to Figure 9 The part.

[0083] Figure 31 Schematic illustration along Figure 7 The BB line shown represents a vertical cross-section of a structured stack in the zy plane, which lies on a substrate and corresponds to... Figure 30 The steps following the intermediate products; the cross-section is similar to Figure 11 The part.

[0084] Figure 32 Schematic illustration along Figure 7 The BB line shown represents a vertical cross-section of a structured stack in the zy plane, which lies on a substrate and corresponds to a ratio of Figure 14 The intermediate product is in a state of being one step behind.

[0085] Figure 33 A vertical cross-section of a device according to a variation of the invention is shown schematically.

[0086] Figure 34 A drawing of an image obtained by scanning electron microscopy on a cross-section of the device is shown, illustrating... Figure 33 The variant shown.

[0087] The following is a list of reference numerals used in the accompanying drawings and this specification:

[0088] 10 OLED displays (known type)

[0089] 12-pixel matrix

[0090] 14 OLED diodes

[0091] 1612 control circuit

[0092] 18, 20 Field Effect Transistors

[0093] 22 capacitors

[0094] 30 lines of control circuit

[0095] 32-channel video control circuit

[0096] 34-column power supply circuit

[0097] 36 control units

[0098] 38-row conductor tracks

[0099] 40 conductive tracks (video signal)

[0100] 42 conductive tracks

[0101] 50 pixels

[0102] 51, 52, 53, 54 sub-pixels (red 51, blue 52, green 53, white 54) 70 OLED display (known type)

[0103] 71 substrate

[0104] 72, 73, 74 sub-pixel driving electrodes

[0105] 75 gap filling element

[0106] 76 OLED layers

[0107] 77-layer encapsulation

[0108] 78 glass plate

[0109] 8076 electroluminescent layer

[0110] 81, 82, 83, 84 Charge Injection and Transport Layers

[0111] 85 electrode

[0112] 90 pixels

[0113] Sub-pixel filters 91, 92, and 93 (blue 91, red 92, green 93)

[0114] 95, 96, 97 Red, Green, and Blue Electroluminescent Layers

[0115] 98-pixel electrode

[0116] 99 common electrode

[0117] 100 OLED display devices

[0118] 101 subpixels

[0119] 102 base electrodes

[0120] 104 divider

[0121] 105 OLED stack

[0122] 106 upper injection layer

[0123] 107 Common Conformal Electrode

[0124] 108 planarization layer

[0125] 109 color filter

[0126] 110 substrate

[0127] 111 Natural Space (“Gap”)

[0128] The flange of 123 on 112102

[0129] 113 pixels

[0130] 123 Filler element with insulating surface

[0131] 200 The apparatus according to the invention

[0132] 201 subpixels

[0133] 202 sub-pixel driving electrodes

[0134] 203 Gap-filling element with insulating surface

[0135] 205 OLED stacked

[0136] 207 upper electrode

[0137] 210 substrate

[0138] The natural gap between electrodes 211 and 202

[0139] 212223 or 203 on the edge of 202

[0140] Busbar of upper electrode 207 of 217

[0141] 218217 teeth

[0142] 223 insulation layer

[0143] 225 Isolated Island

[0144] 270 non-functional subpixel rows

[0145] 280 photoresist

[0146] 290 package layer

[0147] 300 for 205 deposition of shadow mask

[0148] 310300 opening

[0149] 400 for 207 deposition of shadow mask

[0150] 410400 opening Detailed Implementation

[0151] In this specification, the term "basic light-emitting area" refers to the smallest light-emitting area that can be addressed individually. In the case of a color display in which pixels are formed by several basic light-emitting areas, those skilled in the art typically use the term "sub-pixel" to refer to such a basic light-emitting area.

[0152] Figure 1 The circuitry of a known type of OLED display 10 is schematically shown, comprising a pixel matrix unit 12 capable of generating images and a control unit 36. OLED diodes 14 and their control circuitry 16 are arranged to form pixels in the pixel matrix unit 12, which includes rows (horizontal) and columns (vertical). Each control circuitry 16 of the pixel 12 includes multiple transistors 18, 20 and capacitors 22. In the case of microdisplays, the transistors 18, 20 are typically manufactured using CMOS (Complementary Metal-Oxide-Semiconductor) technology or thin-film transistor (TFT) technology. The control unit 36 ​​controls a row control circuitry 30 and a video addressing circuitry 32, as well as a power supply circuitry 34 for addressing pixel columns; thereby ensuring the addressing of the pixel circuitry and controlling the emission of light from the OLED diodes 14. The row control circuitry is connected to conductive tracks 38 that address the scan rows of the pixel matrix. The row control circuitry selects scan lines 38 based on signals from the control unit 36 ​​and applies voltage to turn on the transistors 18 located on the selected scan lines 38.

[0153] Video addressing circuit 32 is connected to the conductive track 40 of the addressing video signal column. Video addressing circuit 32 receives video signals from control unit 36 ​​and sends a voltage to the video conductive track 40 of the column according to the conductive track of the row selected by the corresponding control circuit 30. This voltage signal is written to capacitor 32 through transistor 18 of the OLED diode 14 of the selected pixel row. Control transistor 20 sends a current corresponding to the recording voltage to the OLED diode 14, causing the OLED diode 14 of the selected line 38 to emit light.

[0154] The power supply circuit 34 is connected to the power conductive rail 42 of the pixel column; thereby powering the OLED diode 14 through the conductive rail 32 and the transistor 20 of the selected pixel row.

[0155] The addressing principle of OLED diodes forming pixels in a pixel matrix, known from WO 2019 / 193290 A1 (Micro OLED), can be applied in the same known manner to the addressing of OLED diodes forming sub-pixels in a pixel matrix of a color display device, where each pixel comprises multiple (most commonly three or four) sub-pixels of different colors; this will be combined here. Figure 2This illustration shows three examples of how subpixels 51, 52, 53, and 54 form a geometric arrangement capable of displaying the desired color in pixel 50. In these figures, the subpixels are red 51, blue 52, and green 53, and as shown in the right-hand diagram, a white subpixel 54 may also be included to increase the brightness of pixel 50. The arrangement in the left-hand diagram is called an "RGB Stripe," which is the most common. The arrangement in the middle diagram is called an "RGB Quad," and the arrangement in the right-hand diagram is called an "RGBW Quad."

[0156] The above text combined Figure 1 and Figure 2 The addressing principle described is one of the addressing principles that can be implemented in this invention. Color display can be achieved by controlling the color emitted by the OLED layer forming the sub-pixels or by using a color filter that changes the color of the white light emitted by the sub-pixels, which will be discussed below. Figure 3 , Figure 4 and Figure 5 These figures, for illustration purposes, schematically depict prior art OLED microdisplays, thereby illustrating the problem that the present invention seeks to address.

[0157] exist Figure 3 The diagram shows an overall schematic of the device 70, from which the following can be identified: a substrate 71 (typically CMOS type, addressing circuitry and components not shown), sub-pixel control electrodes 72, 73, and 74 separated by gap-filling elements 75, a stack of organic OLED layers 76 capable of emitting white light, an encapsulation layer 77, blue 91, red 92, and green 93 color filters forming pixels 90, and a glass sheet 78 serving as a protective cover. Sub-pixel sizes are typically in the range of 3.5 μm to 5 μm. Notably, in this prior art device, the OLED layer 76 extends to cover all pixels of the device.

[0158] Figure 4 It shows something similar to Figure 3An enlarged view of the device shown; this view is limited to a single pixel 90. Subpixels are defined on one hand by electrodes 72, 73, 74 that allow them to be individually addressed, and on the other hand by corresponding color filters 91, 92, 93 that alter the light emitted by the white light-emitting OLED stack 76, which extends to cover the entire surface of the device. The space between two adjacent subpixel control electrodes 72, 73 can be filled by filler elements 75. The OLED stack 76 here includes an electroluminescent layer 80 itself, sandwiched between two charge transport layers 81, 82. More specifically, in a typical device, layer 81 includes a hole injection and transport layer, and layer 82 includes an electron injection and transport layer. However, a so-called "reverse" stack can also be used, in which layer 82 includes a hole injection and transport layer, and layer 81 includes an electron injection and transport layer. Layers 81 and 82 may each comprise a single layer, which simultaneously performs the functions of injecting and transporting their respective charges, or layers 81 and 82 may comprise multiple layers, for example, one layer for injection and another layer for transporting their respective charges. A common electrode 85 is used for discharging charges.

[0159] Such devices, according to existing technology, suffer from parasitic currents; this is in Figure 4 As shown in the diagram. In practice, when a sub-pixel (e.g., 73) is turned on, the main current (marked by the thick arrow) passes directly through the OLED layer along the shortest direction (i.e., the direction perpendicular to the substrate 71); however, provided the conductive paths have sufficiently low resistivity, some of the current will propagate along these other conductive paths. Therefore, parasitic currents can be observed propagating in the charge transport layer 81, i.e., within the substrate plane, and then through the OLED layer in adjacent sub-pixels 72 or 73. These parasitic currents are marked by two dashed arrows. This results in stray light emission in adjacent sub-pixels, thereby altering the image resolution of the display and reducing its color fidelity. The present invention aims to provide a method for reducing such parasitic currents.

[0160] Figure 5 Another known type of device is shown, in which the color of pixel 90 is not as... Figure 4 Instead of generating light by matching white-light-emitting OLED elements with color filters for each sub-pixel, as in the previous device, this is achieved through three sub-pixels equipped with electroluminescent layers 95, 96, and 97 that directly emit red, blue, and green light. In this implementation, each sub-pixel 95, 96, and 97 has its own addressing electrodes 98a, b, and c, but the first charge injection and transport layer 83 (e.g., holes) and / or the second charge injection and transport layer 84 (e.g., electrons) and the common electrode 99 are shared to simplify device fabrication. The issue of parasitic currents and related... Figure 4 The problem is the same; hole injection and the contribution of transport layer 83 to these parasitic currents are dominant.

[0161] In terms of luminous efficiency, Figure 5 The device in the middle is significantly better than Figure 3 The device itself. On the other hand, its industrial manufacturing can be quite difficult because the organic materials that make up an OLED device are typically deposited via a thermal vacuum evaporation process. To produce sub-pixels of different colors, such as... Figure 5 The device requires the use of a shadow mask placed near the substrate where the OLED device is to be fabricated, with openings corresponding to the locations of the first type of sub-pixels during the deposition of a first type of layer (e.g., a red OLED). This operation is then repeated for a second type of layer (e.g., a green OLED) using a second shadow mask with openings corresponding to the locations of the second type of sub-pixels. A third such operation can then be performed to create a third type of sub-pixel, such as a blue OLED.

[0162] This method cannot reliably produce subpixels smaller than approximately 20 μm, as the required subpixel size for microdisplays is on the order of 2 μm to 5 μm. In the semiconductor field, structures of this size are produced using photolithography and etching methods, but these materials cannot be directly fabricated using photolithography due to their extreme sensitivity to water and oxygen. It has been observed that when attempting to apply known semiconductor photolithography and etching methods to the fabrication of OLED microdisplays, the OLED stack is laterally eroded at its unprotected edges during the etching operation. This attack leads to localized degradation of the OLED stack and can potentially spread laterally. In favorable conditions, this only reduces the emission area of ​​the subpixel (which is already undesirable, especially since this diffusion is an evolving process, and any reduction in emission area will lead to an increase in device current density, thus reducing its lifetime); in unfavorable conditions, this can ultimately completely destroy the subpixel. However, according to a fundamental feature of the invention, the edges and sidewalls of the primary light-emitting region (subpixel) are protected in all directions.

[0163] The starting point of this invention is document WO 2019 / 193290. Figure 5 The image is used here as... Figure 6 The figure is reproduced and the reference numerals have been adjusted. The figure shows a pixel 113 of an OLED display device 100 deposited on a substrate 110 (typically CMOS type), having three sub-pixels 101a, 101b, and 101c, each sub-pixel being controlled by a separate control electrode 102a, 102b, and 102c.

[0164] The white OLED stack 105 shared by all pixels of the display is separated between two adjacent sub-pixels (101a, 101b; 101b, 101c; 101c, 101a) by a separator 104, which occupies the natural space 111 (also referred to as a “gap”) between the electrodes 102a, 102b; 102b, 102c; 102c, 102a of the two adjacent sub-pixels 101a, 101b; 101b, 101c; 101c, 101a. This separator 104, displayed as a trench, includes a fill element 123 with an insulating surface. The fill element 123 has a flange 112 extending onto a small portion of the control electrode 102, forming the boundary of the latter. The conformal electrode 107 is common to all sub-pixels, optionally, as is the upper injection layer 106.

[0165] This prior art structure satisfactorily solves the crosstalk problem, but because it uses the same white light-emitting OLED stack's basic light-emitting regions (sub-pixels) 101a, 101b, 101c to form pixel 113, and its light passes through color filters 109 (arranged in the form of a plate on smoothing layer 108) to produce the basic colors R, G, and B at the output of device 100, it does not solve the problem of providing a highly efficient and extremely bright device. It is desirable to be able to manufacture a device with a similar structure, but without using color filters, instead using OLED stacks emitting different colors for each group of sub-pixels, such as the three basic colors of red, blue, and green. It is desirable to be able to manufacture this device in the form of a microdisplay, with the size of its basic light-emitting region being less than 20 μm, preferably less than 5 μm, and more preferably between about 1 μm and about 5 μm. To achieve this goal, it is necessary to invent a new microdisplay manufacturing process; and the inventors of this application have successfully implemented such a process.

[0166] The device according to the invention will now be described, and will be described by way of its structure, its manufacturing process, and the different stages of its manufacturing. As shown in this application, the device comprises three sets of basic light-emitting regions (sub-pixels).

[0167] Figure 7 A top view of an intermediate product according to the invention is shown, which is manufactured using the process steps according to the invention. The structure of the substrate and its different deposited structured layers is schematically shown in two figures, corresponding to... Figure 7 The same intermediate product is shown, and the vertical cross-section of the structured stack is schematically illustrated, i.e. Figure 8 Corresponding to along Figure 7 The cross section of line AA in the zx plane shown, and Figure 9 Corresponding to along Figure 7 The cross section of the BB line in the zy plane is shown.

[0168] The intermediate product includes a substrate 210 (which typically includes active matrix addressing circuitry produced using TFT or CMOS technologies well known to those skilled in the art), and sub-pixel electrodes 202a, 202b, 202c separated by natural spaces 211 (“gaps”) having trench shapes. The trenches extend into the substrate 210 in the depth direction (i.e., along the z-axis perpendicular to the substrate). An insulating layer 223 is deposited in the trench using a conformal deposition method, i.e., a method covering the entire surface, whether horizontal, vertical, or suspended. For this purpose, atomic layer deposition (ALD) or plasma-enhanced chemical vapor deposition (PECVD) techniques can be used. The material of the insulating layer is advantageously selected from the group consisting of Si3N4, SiO2, and Al2O3. Of these three materials, Al2O3 is preferred.

[0169] The insulating layer 223 covers at least the vertical surface of the electrode 202, and typically also covers the surface of the entire natural space 211 between the electrodes 202. In an advantageous embodiment, the insulating layer 223 also slightly covers the pixel edges (i.e., the upper horizontal surface) of the electrode 202, thereby forming a flange 212 on the control electrode 202.

[0170] like Figure 7 and Figure 9 As shown, the natural space (trench) 211 between electrodes 202 is filled by a filler element 203 with an insulating surface, but only the horizontal space between two sub-pixels (i.e., along the x-axis) is filled. The vertical space between two sub-pixels (i.e., along the y-axis) does not contain any filler element and forms a trench from the top to the bottom of the matrix formed by all (sub)pixels. The surface of the filler element 203 is typically made of photoresist or a dielectric material such as SiO2, Si3N4, or other dielectric materials; optionally, the entire filler element 203 is made of such a dielectric material. Similar to the insulating layer 223, for the same reason, the filler element 203 may have a flange 212 on the control electrode 202.

[0171] A variation of this implementation will combine Figures 30 to 32 The following description is provided. In this variant, a filling element 203 is first deposited in the natural space 211, followed by the deposition of an insulating layer 223.

[0172] like Figure 7 As shown, the substrate also includes connecting strips 217 located at the top and bottom of the matrix. These connecting strips 217 are in the form of horizontal metal lines (busbars) for connecting the upper electrode of the OLED display device, which will be discussed in detail below. Figure 12 Please provide an explanation.

[0173] This substrate structure allows for the subsequent creation of islands 225 of fully isolated and encapsulated basic OLED light-emitting regions; such islands 225 in... Figure 10The middle part is represented by a box with a dashed outline. Figure 7 In the middle, these islands have a vertical columnar shape that runs through the active area from top to bottom, which also comes from Figure 10 and Figure 11 The comparison is evident; these two figures will be explained below. The function of the filler element 203 here is to ensure the continuity of the upper electrode 207 along the vertical column (y).

[0174] Now refer to Figure 10 and Figure 11 Both figures show the same device at the same intermediate stage of manufacturing. Figure 8 and Figure 9 similar, Figure 10 Corresponding to along Figure 7 The cross section of line AA in the zx plane shown. Figure 11 Corresponding to along Figure 7 The cross-section of the BB line in the zy plane is shown. On the other hand, Figure 10 and Figure 11 Corresponding to the ratio Figure 7 This indicates a more advanced manufacturing stage, namely, following... Figure 8 and Figure 9 The subsequent manufacturing stage.

[0175] like Figure 10 As shown, an organic layer stack 205a is first deposited to form an OLED stack (i.e., an OLED diode capable of emitting light), typically deposited using a thermal evaporation method; this technique for depositing OLED stacks currently constitutes the standard in the OLED device industry. This is a directional deposition, meaning the layers are primarily formed on the horizontal surface and not on the vertical surface, such as... Figure 10 As shown. The OLED stack 205a is formed by an upper electrode 207a, which must be transparent. From Figure 10 and Figure 11 The comparison shows that the upper electrode 207a is common to each group of sub-pixels in a column.

[0176] The organic layer forming the OLED stack 205a is particularly sensitive to water and oxygen, and must be protected from the effects of these molecules. For this purpose, an encapsulation layer 290a is deposited, covering the entire morphology of the device, including both horizontal and vertical surfaces. The encapsulation layer 290a typically consists of a thin layer of transparent insulating material, advantageously between about 10 nm and about 30 nm in thickness, preferably selected from the group consisting of Si3N4, SiO2, and Al2O3. These materials have the advantage of high resistance to etching steps used to remove the OLED stack; this etching can be performed using oxygen plasma. The encapsulation layer 290a is advantageously deposited using conformal deposition methods such as PECVD or ALD.

[0177] This results in a sealed, isolated space around all the subpixels in column 225a (also referred to here as an “island”); these subpixels belong to the same subpixel group (e.g., the red subpixel group or the blue subpixel group).

[0178] In order to connect the upper electrode 207a to the connector strip 217, the deposition of the organic material of the OLED stack 205 should not protrude too much on the connector strip 217, and the deposition of the electrode layer 207 must at least partially cover the busbar. Figure 12 A top view of the substrate after layer 207 deposition is shown.

[0179] Compared with existing technologies, this intermediate device has several advantages and improvements.

[0180] First, this intermediate device allows for excellent electrical isolation between OLED layers of adjacent sub-pixels, thereby significantly reducing crosstalk, with the same effect as described in WO 2019 / 193290.

[0181] Secondly, the organic layer structure of the OLED stack in the form of sealed, isolated islands improves the reliability of the device. In particular, point defects (such as water entering through pinholes in the encapsulation layer) will not propagate beyond the size of the sub-pixel in the horizontal direction because they will be blocked by the natural space 211 between adjacent sub-pixels arranged in the form of trenches.

[0182] Third, the isolated island 225 allows for the structuring of OLED layers using photolithography, which enables the production of, for example, OLEDs based on... Figure 13 and Figure 14 The device, according to the invention, features three distinct groups of OLED stacks (red 205a, green 205b, and blue 205c) and improved spatial resolution, achieving a basic emitting area size of less than 5 μm with optimal efficiency and without the risk of damaging the edges of the OLED stacks during the etching step. This technology also enables the production of devices according to the invention with a matrix of three groups of RGB subpixels, eliminating the need for color filters while still maintaining such high resolution.

[0183] like Figure 13 As shown, a natural space 211 between two adjacent basic light-emitting regions belonging to different basic light-emitting region groups, and between two adjacent electrodes 202a, 202b; 202b, 202c belonging to different basic light-emitting region groups, extends to the substrate 210 in the depth direction (z-axis). The bottom and sidewalls of the natural space are covered by an insulating layer 223. Therefore, the natural space 211 forms a trench between the two adjacent electrodes 202a, 202b; 202b, 202c.

[0184] The insulating layer 223 is different from the encapsulation layer 290 that protects the sidewalls of the OLED stack 207; this difference is not necessarily related to the chemical properties of the two insulating layers 223, 290 (it is known that the two layers 223, 290 may have the same chemical properties or may have different chemical properties), but rather to their deposition timing in the step sequence of the method according to the invention.

[0185] Now, will be combined Figures 15 to 25 This describes how three sets of basic light-emitting regions (sub-pixels) are deposited. These figures illustrate one region from each of these three sets of basic light-emitting regions. To produce an apparatus having three sets of basic light-emitting regions (sub-pixels) that each emits a different color of light (these sets are exemplified herein and denoted by the letters R, G, and B (red, green, and blue), respectively, representing a preferred embodiment), three sets of manufacturing steps are required. Each set of steps includes a photoresist layer deposition and structuring step, followed by an etching step of at least one of the entire encapsulation layer, cathode, and OLED stack, and finally, photoresist removal (“stripping”).

[0186] Within the scope of this specification, techniques commonly used in the field of microelectronics can be used with respect to photoresist. These techniques typically involve depositing a photoresist layer, exposing it to form a structure on a surface, and then developing it. These techniques are known to those skilled in the art and are not described herein; these steps related to the local deposition of photoresist are summarized herein by the term "laying out" the photoresist.

[0187] This allows for the creation of an OLED microdisplay-type device, such as... Figure 12 , Figure 13 and Figure 14 As shown, the device has three sub-pixels that are electrically and hermetically isolated, each sub-pixel having an OLED stack that emits different colors, namely R(205(a)), G(205(b)) and B(205(c)).

[0188] In the first set of steps, such as Figures 15 to 18 The diagram illustrates the deposition of the first set of basic luminescent regions (subpixels) that emit light of the first color (e.g., red).

[0189] First, the substrate 210 is configured with control electrodes 202a, 202b, 202c for each basic light-emitting region (the control electrode 202 is typically an anode), an insulating layer 223 between two adjacent electrodes 202a, 202b, 202c, and filling elements 203 in the natural space 211 between two adjacent control electrodes 202 belonging to the same group of basic light-emitting regions. The insulating layer advantageously has flanges 224 on the surface of the electrodes 202.

[0190] The substrate 210 is typically a silicon wafer on which circuitry structured according to CMOS technology is configured to address primary light-emitting regions; this technology is known in itself and will not be described here. The substrate 210 typically includes an insulating layer (not shown), which may in particular be an oxide, nitride, or oxynitride; Si3N4 is commonly used. Electrical contacts between pixels are achieved by etching vertical channels arranged in this insulating layer; this is also known and is not shown in the figure. Pixel control electrodes 202, typically selected to have high reflectivity, are deposited on this insulating layer.

[0191] In a highly advantageous embodiment, the thickness of the control electrode 202 is between approximately 150 nm and approximately 800 nm. Values ​​that are too high would compromise the resolution of the microdisplay because it would require increasing the space between the two primary light-emitting regions. It is also highly advantageous that the thickness of the control electrode 202 is greater than the thickness of the OLED stack 205 deposited on this electrode.

[0192] The lower electrode 202 may include one or more layers. For example, the lower electrode 202 may be made of silver, aluminum, copper, chromium, or other metals with high reflectivity. If aluminum is used, it is highly advantageous to protect it with a thin layer of transparent conductive oxide (TCO) that has high resistance to wet etching and oxygen plasma. This TCO is referred to herein as a "hard TCO".

[0193] Preferably, it is selected from the group consisting of SnO2 and doped SnO2, wherein the doping is preferably arsenic and / or fluorine and / or nitrogen and / or niobium and / or phosphorus and / or antimony and / or aluminum and / or titanium.

[0194] In the first subgroup step, the result is as follows: Figure 15 As shown, the following materials are sequentially deposited on the substrate 210: (a) a first OLED stack 205a, which is deposited using a directional deposition technique, i.e., a deposition technique that essentially deposits only on a horizontal surface, such as evaporation; (b) an upper electrode 207a; and (c) a first encapsulation layer 290a. The upper electrode 207a has the opposite polarity to the control electrode 202; it is typically a cathode. The upper electrode is typically deposited using a directional deposition technique; it can also be deposited using a conformal technique.

[0195] According to a key feature of the invention, the encapsulation layer 290a is deposited using a conformal deposition technique (such as ALD); this ensures that the encapsulation layer 290a also covers and protects the edges (also referred to as sidewalls) of the OLED stack. This protection is necessary in subsequent etching steps. The first encapsulation layer 290 must be transparent; it is advantageously made of aluminum oxide. In a variation, several transparent encapsulation layers (such a stack is included herein in the term "first encapsulation layer") are deposited at this stage, using the same or different materials; at least the first of these layers must be deposited using a conformal deposition technique, while the others preferably are.

[0196] It is noteworthy that at the end of the first subgroup step, the OLED stack deposited on the electrodes 202b of the second group of basic light-emitting regions and the electrodes 202c of the third group of basic light-emitting regions is a first-type OLED stack 205a. As will be explained below, in subsequent group steps, it will subsequently be replaced by a second-type OLED stack 205b, and finally, for the location of the third basic light-emitting region, it will be replaced by a third-type OLED stack 205c.

[0197] In the second subgroup step, the result is as follows: Figure 16 As shown, photoresist 280a is disposed on the first group of basic light-emitting regions in these groups. The photoresist 280a must protect the horizontal surface of the basic light-emitting region and also its sidewalls (i.e., it can be a vertical side).

[0198] In the third subgroup step, the result is as follows: Figure 17 As shown, the stack formed by the encapsulation layer 290a, the upper electrode 207a, and the OLED stack 205a (listed from top to bottom) is etched in the area not protected by the photoresist 280a. The etching process must be selected so that etching stops at the upper horizontal surfaces of electrodes 202b and 202c. For etching of the encapsulation layer and electrodes, wet etching is typically used, such as the wet etching commonly used in microelectronics, which involves etching with a 2.38% (w / w) aqueous solution of tetramethylammonium hydroxide (CAS No.: 75-59-2); such products are commercially available, for example, from ThermoFischer Scientific. TM (Electronic grade, catalog number 44940). Alternatively, dry etching methods, such as RIE (Reactive Ion Etching) or IBE (Ion Beam Etching), can also be used. Etching of OLED stacks is typically performed using oxygen plasma.

[0199] like Figure 17 As shown, at the end of this subgroup step, due to etching, not only are the control electrodes 202b and 202c stripped, but the trench 211 used for depositing the organic layer 207 and the encapsulation layer 290 is also emptied in the trench portion not covered by the photoresist 280a.

[0200] In the fourth sub-step, photoresist 280a is removed, and the result is as follows: Figure 18 As shown. This can be accomplished using appropriate techniques known to those skilled in the art.

[0201] If oxygen plasma is used to etch the layer deposited directly on the upper electrode for this purpose, it is best to avoid using aluminum as the top surface of the upper electrode, as the oxygen plasma will form an insulating aluminum oxide layer. Aluminum can be used if its upper surface is protected by a transparent conductive layer that will not be eroded by the oxygen plasma; for this purpose, a tin dioxide (SnO2) layer is preferred.

[0202] In the second set of steps, such as Figures 19 to 22 The diagram illustrates a second set of primary luminescent regions (subpixels) that emit a second color of light (different from the first color, such as green).

[0203] In the first subgroup step, the result is as follows: Figure 19 As shown, the following materials are sequentially deposited on the substrate 210: (a) a second OLED stack 205b, which is deposited using a directional deposition technique; (b) an upper electrode 207b, which preferably uses the same material as the upper electrode 290a of the first group of basic light-emitting regions; and (c) a second encapsulation layer 290b', which preferably uses the same material as the first encapsulation layer 290a of the first group of basic light-emitting regions. It is noteworthy that at the end of the first subgroup step, the OLED stack deposited on the electrode 202c of the third group of basic light-emitting regions is a second-type OLED stack. As will be explained below, it will subsequently be replaced by a third-type OLED stack 205c in subsequent group steps. It should also be noted that the first group of basic light-emitting regions includes a stack referred to herein as a "transition stack," which consists of the second-type OLED stack 207b, the upper electrode 207b, and the encapsulation layer 290b; this transition stack will subsequently be removed. The encapsulation layer 290b specifically covers the sidewalls of the OLED stack 205b. Depending on their position relative to the final device, they are indicated herein by reference numerals 290a, 290b, and 290c, although they are made of the same material. The encapsulation layer may be continuous and then extend over the three basic light-emitting areas.

[0204] In the second subgroup step, the result is as follows: Figure 20 As shown, as described with respect to the first set of steps, photoresist 280b is arranged on the second set of basic light-emitting regions of these sets.

[0205] In the third subgroup step, the result is as follows: Figure 21As shown, the stack formed by the second encapsulation layer 290b, the upper electrode 207b, and the OLED stack 205b (listed from top to bottom) is etched in the area not protected by the photoresist 280b. The etching process and the materials of the different layers must be selected so that the etching stops at the upper horizontal surface of the electrode 202c, the insulating layer 223, and the encapsulation layer 290a. The insulating layer 223 can be made of Al2O3, which has the advantage of resisting oxygen plasma etching used to remove the OLED stack. The encapsulation layer 290 can use the same material.

[0206] like Figure 21 As shown, at the end of this subgroup step, due to etching, not only is the control electrode 202c stripped, but the organic layer 207 and encapsulation layer 290 deposited in the portion of trench 211 not covered by photoresist 280b are also cleared.

[0207] In the fourth subgroup step, the result is as follows: Figure 22 As shown, the removal of photoresist 280b is described in the first set of steps, and the same description is given regarding the choice of technology and the protection of the upper aluminum electrode against possible oxygen plasma.

[0208] In the third set of steps, such as Figures 23 to 26 The diagram schematically illustrates a third set of primary light-emitting regions (sub-pixels) that emit a third color of light (different from the first and second colors, such as blue).

[0209] In the first subgroup step, the result is as follows: Figure 23 As shown, the following materials are sequentially deposited on the substrate 210: (a) a third OLED stack 205c, which is deposited using a directional deposition technique; (b) an upper electrode 207c, which preferably uses the same material as the upper electrodes 207a and / or 207b of the first and second groups of basic light-emitting regions; and (c) a third encapsulation layer 290c, which preferably uses the same material as the first and / or second encapsulation layers 290a, 290b of the first and second groups of basic light-emitting regions.

[0210] It is worth noting that there are transitional layers on the first and second groups of basic luminescent regions.

[0211] In the second subgroup step, the result is as follows: Figure 24 As shown, as described with respect to the first set of steps, photoresist 280c is arranged on the third set of basic light-emitting regions of these sets.

[0212] In the third subgroup step, the result is as follows: Figure 25As shown, the etching process involves etching the stack formed by the third encapsulation layer 290c, the upper electrode 207c, and the OLED stack 205c (listed from top to bottom). The etching process must be selected such that etching stops at the encapsulation layers 290a and 290b; oxygen plasma is preferably used for etching the OLED layer.

[0213] like Figure 25 As shown, at the end of this subgroup step, due to etching, the organic layer 207 and encapsulation layer 290 deposited in the portion of trench 211 not covered by photoresist 280c are cleared.

[0214] In the fourth subgroup step, the result is as follows: Figure 26 As shown, the removal of photoresist 280c is described in the first set of steps, and the same description is given regarding the choice of technology and the protection of the upper aluminum electrode against possible oxygen plasma.

[0215] According to the apparatus of the present invention, an additional encapsulation layer may be provided after depositing one or more smoothing layers.

[0216] This invention offers numerous advantages. It allows the production of OLED microdisplays with three basic subpixels (typically RGB). Thanks to the high-resolution photolithography method used, these OLED microdisplays exhibit extremely fine resolution, with the size of their basic emitting regions (subpixels) below 20 μm, preferably below 10 μm, and more preferably below 5 μm. The use of different OLED stacks for each subpixel group (optimized for the primary color emission of their respective subpixels), the high surface density of the basic emitting regions, and the absence of color filters result in excellent efficiency and brightness. Comprehensive protection (including side protection) of the OLED stacks during the etching stage and throughout the device's lifespan ensures excellent reliability. Separation and isolation between each basic emitting region and adjacent basic emitting regions prevent crosstalk.

[0217] These microdisplays use Figure 2 The sub-pixel arrangement is schematically shown in the left-hand diagram. This arrangement is compatible with the positioning of the connecting strip 217 of the upper electrode.

[0218] The manufacturing method utilizes known technologies and processes for semiconductor and microelectronic device fabrication, as well as conventional processes for OLED manufacturing. A particular advantage of the method according to the invention is that it eliminates the need to deposit the OLED stack through a shadow mask with small openings (i.e., the size of the primary light-emitting region). This is achieved by... Figure 27 The diagram shows a placement... Figure 7The shadow mask 300 on the substrate surface is shown with an opening 310. In the method according to the invention, the deposition of the OLED stack is common to all basic light-emitting regions. By etching the surface partially masked by photoresist dots, which uses a technique that allows for significantly better lateral resolution than the shadow mask, very small-sized basic light-emitting regions are obtained; these dimensions can be about 5 μm or preferably less than 5 μm, even less than 4 μm, even less than 3 μm. In an advantageous embodiment, these dimensions are between about 2 μm and about 5 μm.

[0219] The upper electrode 207 (usually the cathode) also passes through, as Figure 28 The opening 410 of the shadow mask 400, schematically shown, deposits all the basic luminescent areas in a common manner. (See comparison...) Figure 28 and Figure 7 As can be seen, the opening covers the connecting strip 217, to which the upper electrode 207 is therefore electrically connected.

[0220] This invention can be implemented in many variations. The first variation is as follows: Figure 29 As shown, it is compatible with all other variations of the invention. Typically, in cases such as Figure 7 Around the active region of the substrate 210 shown, at least one row of non-functional sub-pixels 270 (“dummy regions”) is placed. In other words, on such a substrate 210, the first and last rows of the primary light-emitting regions (sub-pixels) may be non-functional. This is very useful (even necessary) to absorb the low mask accuracy during OLED stacking deposition: the dummy regions are used to limit the deposition of the OLED layer on that region and ensure good contact between the upper electrode 207 and the connecting strip 217.

[0221] exist Figure 29 In the variant shown, the rows of non-functional sub-pixels 217 can be replaced by comb-shaped connecting strips 217, where the comb teeth 218 represent dummy areas. The latter restricts the deposition of the OLED layer in this area while ensuring good electrical contact between the upper electrode 207 and the connecting strips 217, at least ensuring good electrical contact on the outside of the connecting strips 217.

[0222] The second variant is as follows Figure 30 , Figure 31 and Figure 32 As shown, it is compatible with all other variations of the invention. This variation involves the positioning of the insulating layer 223 relative to the fill element 203: the fill element 203 is first deposited in the natural space 211 between two adjacent electrodes 202, and then the insulating layer 223 is deposited. This variation has the advantage of avoiding erosion of the fill element 203 during the etching of the OLED stack.

[0223] Figure 30 Schematic illustration along Figure 7The BB line shown represents a vertical section of the structured stack in the zy plane, which is located corresponding to... Figure 7 On the substrate of the intermediate product variant; the cross section is similar to Figure 9 In this variation, section AA corresponds to Figure 8 .

[0224] Figure 31 Schematic illustration along Figure 7 The BB line shown represents a vertical section of the structured stack in the zy plane, which is located corresponding to... Figure 30 On the substrate after the intermediate product stage. In this variation, the AA section corresponds to Figure 10 .

[0225] Figure 32 Schematic illustration along Figure 7 The BB line shown represents a vertical section of the structured stack in the zy plane, which is located at a point greater than... Figure 14 The intermediate product is placed on the substrate one step later. In this variation, the AA section corresponds to... Figure 13 .

[0226] The third variant is as follows Figure 33 and Figure 34 As shown: It is compatible with all other variations of the invention. This variation involves a filler element 203 (also referred to as "gap filler") having an insulating surface, which fills the natural space 211 between two adjacent electrodes 202a, 202b; 202b, 202c; 202c, 202a. As described above, the filler element 203 advantageously has a flange on the control electrode 202, and the thickness of the control electrode 202 is advantageously greater than the thickness of the OLED stack 205. These thicknesses, and the thickness of the filler element 203, are advantageously chosen such that the angle α on the filler element having the insulating surface 203 relative to the horizontal upper surface of the electrode 202 does not exceed a value X at any point, which is about 40°, preferably about 30°, more preferably about 25°, and even more preferably about 20°, wherein the angle α can be a positive or negative angle. The definition of the angle α is as follows: Figure 33 The text clarifies that the maximum angle α is marked for two different geometries.

[0227] Therefore, the filler element 203 serves as a smoothing element for the deposition of the common electrode layer 207. This common electrode 207 is deposited using a directional deposition technique, which carries the risk of electrical discontinuities if, at any point on the control electrode surface, the angle α relative to the horizontal upper surface of the control electrode exceeds approximately 30° (positive or negative). This is because the material thickness deposited on a horizontal surface differs from that on an inclined surface (and no material is deposited at all on a vertical surface) using the directional deposition technique.

[0228] Figure 33 This situation is illustrated schematically, and Figure 34 A schematic diagram of a scanning electron microscope image based on a corresponding cross section is shown.

Claims

1. An electroluminescent display device comprising a matrix of electroluminescent pixels deposited in a matrix arrangement of rows and columns on a substrate (210), said matrix of electroluminescent pixels being composed of a plurality of pixels, each pixel being composed of at least three elementary light-emitting zones, each of said at least three elementary light-emitting zones belonging to a different elementary light-emitting zone group, each of said elementary light-emitting zone groups being distinguished from the elementary light-emitting zones belonging to the other groups by its emission color, each of said elementary light-emitting zones comprising an electroluminescent stack (205) composed of organic layers, called "OLED stack", comprising at least one light-emitting organic layer, said OLED stack (205) being arranged between a control electrode (202) and a transparent upper electrode (207) through which the light emitted by said OLED stack (205) passes, said electroluminescent display device being characterized in that: two adjacent control electrodes (202a, 202b; 202b, 202c; 202c, 202a) belonging to two adjacent elementary light-emitting zones of different elementary light-emitting zone groups are separated by a trench-forming space (211) having an insulating surface (223) covering at least the vertical side walls of the adjacent electrodes and electrically insulating them from each other, and two adjacent control electrodes (202a, 202a; 202b, 202b; 202c, 202c) belonging to two adjacent elementary light-emitting zones of the same elementary light-emitting zone group are separated by a trench-forming space (211) filled by a filling element (203) electrically insulating the adjacent electrodes from each other and filling the natural space between the two electrodes, in each elementary light-emitting zone group, the entire OLED stack and its corresponding upper electrode (205a and 207a, 205b and 207b, 205c and 207c) are separated from the adjacent stack belonging to another group by an encapsulation layer (290) protecting the upper surface of the OLED stack and its sides from the ambient air, thus forming a protected island (225) comprising the group of OLED stacks and their upper electrodes of the same group.

2. The apparatus of claim 1, wherein, said trench (211) extends to the substrate (210) along a z-axis perpendicular to said substrate.

3. The apparatus of claim 1 or 2, wherein, said emission colors are red, blue and green.

4. The apparatus of any one of claims 1 to 3, wherein, said trench-forming space has a width between 0.3 pm and 1.0 pm.

5. The apparatus of any one of claims 1 to 4, wherein, said trench-forming space has a depth between about 150 nm and about 800 nm, preferably between 150 nm and 450 nm.

6. The apparatus of any one of claims 1 to 5, wherein, said control electrode (202) has a thickness between about 150 nm and about 800 nm, preferably between 150 nm and 450 nm.

7. The apparatus of any one of claims 1 to 6, wherein, said control electrode (202) has a thickness greater than the thickness of said OLED stack (205).

8. The apparatus of any one of claims 1 to 7, wherein, said filling element (203) fills the natural space between two adjacent control electrodes (202) so that said upper electrode (207) is substantially flat.

9. The apparatus of any one of claims 1 to 8, wherein, The pitch of the elementary light emitting areas is less than about 20 μm, preferably less than about 15 μm, more preferably less than about 10 μm, still more preferably between about 1 μm and about 5 μm, and the space width between the control electrodes is less than about 1 μm, preferably between about 0.3 μm and about 1.0 μm.

10. The apparatus of any one of claims 1 to 9, wherein, On the filling element (203) having an insulating surface, the angle a with respect to the horizontal upper surface of the electrode (202) does not exceed a value of about 40°, preferably about 30°, more preferably about 25°, still more preferably about 20°, at any point, wherein the angle can be a positive angle or a negative angle.

11. A method of manufacturing an electroluminescent display device comprising a matrix of electroluminescent pixels deposited in a matrix arrangement of rows and columns on a substrate (210), the matrix of electroluminescent pixels being composed of a plurality of pixels, each pixel being composed of at least three elementary light emitting areas, each of the at least three elementary light emitting areas belonging to a different elementary light emitting area group, each of the elementary light emitting area groups being distinguished from the elementary light emitting areas belonging to the other groups by its emission color, each of the elementary light emitting areas comprising an electroluminescent stack (205) composed of organic layers, referred to as "OLED stack", comprising at least one light emitting organic layer, in the method: the substrate (210) is provided with a control electrode (202a, 202b, 202c) for each elementary light emitting area, and an insulating layer (223) between two adjacent electrodes (202a, 202b, 202c) and providing a filling element between two adjacent elementary light emitting areas belonging to the same elementary light emitting area group, in a first group of steps, a first OLED stack (205a), an upper electrode (207a) and a first encapsulation layer (290a) formed using a conformal deposition technique are first deposited, then a photoresist is arranged at the location of the elementary light emitting areas of the first group, the photoresist protecting the horizontal surface and the sidewalls of the encapsulation layer (290a) at the location of the elementary light emitting areas of the first group and etching the areas not protected by the photoresist down to the upper surface of the control electrodes (202b and 202c), and finally the photoresist is removed, in a second group of steps, a second OLED stack (205b), an upper electrode (207b) and a second encapsulation layer (290b) formed using a conformal deposition technique are first deposited, then a photoresist is arranged at the location of the elementary light emitting areas of the second group, the photoresist protecting the horizontal surface and the sidewalls of the encapsulation layer (290b) at the location of the elementary light emitting areas of the second group and etching the areas not protected by the photoresist down to the upper surface of the control electrode (202c) for the elementary light emitting areas of the third group and to the surface of the first encapsulation layer for the elementary light emitting areas of the first group, and finally the photoresist is removed, In a third set of steps, a third OLED stack (205c), an upper electrode (207c) and a third encapsulation layer (290c) formed using a conformal deposition technique are first deposited, then a photoresist is arranged at the location of the light emitting region of the third set, the photoresist protects the horizontal surface and sidewalls of the encapsulation layer (290c) at the location of the essential light emitting region of the third set and etches the area not protected by the photoresist until the surface of the first encapsulation layer for the essential light emitting regions of the first and second sets, and finally the photoresist is removed.

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