Display device

Abstract

In a display device, the ends of the hole transport layer, the light emission layer, and the electron transport layer disposed in a pixel are separately disposed from the ends of the corresponding layers of adjacent pixels. The electron transport layer has a first region and a second region with a film thickness greater than the first region. The second region overlaps with a common electrode, while the first region does not overlap with the common electrode.

Description

[0001] Cross-references to related applications

[0002] This application claims priority based on Japanese Patent Application No. 2021-187175, filed on November 17, 2021, the entire contents of which are incorporated herein by reference. Technical Field

[0003] Embodiments of the present invention relate to display devices. Background Technology

[0004] In recent years, display devices using organic electroluminescence (EL) luminescent materials have been developed. These devices have an organic EL layer containing the luminescent material. Within the organic layer of the organic EL element, the luminescent material is excited through electron-hole recombination, and it emits light when it returns to its ground state. Summary of the Invention

[0005] The purpose of this embodiment is to provide a display device that can suppress the reduction of light extraction efficiency, suppress leakage current generation, and prevent accidental light emission from the light-emitting layer.

[0006] One embodiment of the display device includes a pixel, the pixel comprising a pixel electrode, a hole transport layer, a light-emitting layer, an electron transport layer, and a common electrode.

[0007] The ends of the hole transport layer, the light emission layer, and the electron transport layer in the pixel are disposed separately from the ends of the hole transport layer, the light emission layer, and the electron transport layer in the adjacent pixel.

[0008] The electron transport layer includes a first region having a first film thickness and a second region having a second film thickness greater than the first film thickness.

[0009] The second region overlaps with the common electrode, while the first region does not overlap with the common electrode. Attached Figure Description

[0010] Figure 1 This is an overall perspective view of the display device according to Embodiment 1.

[0011] Figure 2 This is a partial top view showing an example of the general structure of a display device.

[0012] Figure 3 yes Figure 2 The cross-sectional view of the display device shown along line A1-A2.

[0013] Figure 4 This is a cross-sectional view of a comparative example display device.

[0014] Figure 5 It is Figure 4 A partially enlarged cross-sectional view.

[0015] Figure 6 This is a cross-sectional view showing an example of the general configuration of the display device according to this embodiment.

[0016] Figure 7 It is Figure 6 A partial enlarged cross-sectional view.

[0017] Figure 8 It is a top view of a display device having a rectangular hole transport layer, a light-emitting layer, a second region of an electron transport layer, and a common electrode.

[0018] Figure 9 It is a top view of a display device having a circular hole transport layer, a light-emitting layer, a second region of an electron transport layer, and a common electrode. Detailed Implementation

[0019] Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, the disclosure is merely an example, and appropriate modifications that can be readily conceived by those skilled in the art while maintaining the spirit of the invention are of course included within the scope of the present invention. Additionally, regarding the accompanying drawings, for the purpose of clearer explanation, there are instances where the width, thickness, shape, etc., of various parts are schematically represented compared to the actual embodiment; however, this is merely an example and does not constitute a limitation on the interpretation of the present invention. Furthermore, in this specification and the various figures, elements identical to those described in previously existing figures are sometimes labeled with the same reference numerals, and detailed descriptions are appropriately omitted.

[0020] Hereinafter, a display device according to one embodiment will be described in detail with reference to the accompanying drawings.

[0021] In this embodiment, the first direction X, the second direction Y, and the third direction Z are orthogonal to each other, but they may also intersect at an angle other than 90 degrees. The direction of the third direction Z toward the tip of the arrow is defined as up or above, and the direction of the third direction Z opposite to the direction of the tip of the arrow is defined as down or below. In addition, the first direction X, the second direction Y, and the third direction Z are sometimes referred to as the X direction, the Y direction, and the Z direction, respectively.

[0022] Furthermore, in the cases of "a second component above the first component" and "a second component below the first component," the second component may be connected to the first component or disposed separately from it. In the latter case, a third component may be sandwiched between the first component and the second component. On the other hand, in the cases of "a second component on the first component" and "a second component below the first component," the second component is connected to the first component.

[0023] Furthermore, there is an observation position for viewing the display device at the tip of the arrow pointing from the third direction to Z. Observing from this observation position toward the XY plane defined by the first direction X and the second direction Y is called a top view. Observing a cross-section of the display device on the XZ plane defined by the first direction X and the third direction Z, or on the YZ plane defined by the second direction Y and the third direction Z, is called a cross-sectional view.

[0024] [Implementation Method]

[0025] Figure 1 This is an overall perspective view of the display device according to Embodiment 1. The display device DSP has a display area DA and a peripheral area FA disposed around the display area DA on a substrate SUB1. The display device DSP has a plurality of pixels PX disposed within the display area DA. In the display device DSP, light LT from the back is transmitted to the front and vice versa.

[0026] A substrate SUB2, serving as a sealing material, is provided on the upper surface of the display area DA. The substrate SUB2 is fixed to the substrate SUB1 by a sealing material (non-display) surrounding the display area DA. The display area DA formed on the substrate SUB1 is sealed by the substrate SUB2 and the sealing material to prevent exposure to the atmosphere.

[0027] Region EA at the end of substrate SUB1 is located outside substrate SUB2. A wiring board PCS is provided in region EA. A drive element DRV for outputting image signals and drive signals is provided on the wiring board PCS. Signals from the drive element DRV are input to pixels PX in display area DA via the wiring board PCS. Pixels PX emit light based on the image signals and various control signals.

[0028] Figure 2This is a partial top view showing an example of the general configuration of a display device. Multiple pixels PX include a pixel PXR that emits red light, a pixel PXG that emits green light, and a pixel PXB that emits blue light. Pixels PXR, PXG, and PXB are also referred to as the first pixel, the second pixel, and the third pixel, respectively. Pixels PXR and PXB are arranged adjacent to each other along a first direction X and a second direction Y. Pixel PXG and PXB are arranged adjacent to each other along the first direction X and the second direction Y. Pixel PXB is arranged adjacent to pixel PXR along the first direction and adjacent to pixel PXG along the second direction Y.

[0029] Figure 3 yes Figure 2 The cross-sectional view of the display device shown along line A1-A2.

[0030] Regarding the substrate BA1, examples include substrates made of glass or resin materials. As the resin material, examples include acrylic acid, polyimide, polyethylene terephthalate, and polyethylene naphthalate, which can be formed by laminating a single layer or multiple layers of one of these materials.

[0031] An insulating layer UC1 is provided on the substrate BA1. The insulating layer UC1 is formed, for example, by forming a silicon oxide film and a silicon nitride film as a single layer or in a stacked manner.

[0032] A light-shielding layer BM can also be disposed on the insulating layer UC1, overlapping with the transistor Tr. The light-shielding layer BM suppresses changes in transistor characteristics caused by light intrusion from the back side of the channel of the transistor Tr. When the light-shielding layer BM is formed of a conductive layer, a back-gate effect can also be imparted to the transistor Tr by applying a specified potential.

[0033] An insulating layer UC2 is provided, covering an insulating layer UC1 and a light-shielding layer BM. The insulating layer UC2 can be made of the same material as the insulating layer UC1. Alternatively, the insulating layer UC2 can be made of a different material than the insulating layer UC1. For example, the insulating layer UC1 can be made of silicon oxide, and the insulating layer UC2 can be made of silicon nitride. Alternatively, both insulating layers UC1 and UC2 can be combined into an insulating layer UC.

[0034] A transistor Tr is disposed on the insulating layer UC. The transistor Tr has a semiconductor layer SC, an insulating layer GI, a gate electrode GE (scan line), an insulating layer ILI, a source electrode SE (signal line), and a drain electrode DE.

[0035] As the semiconductor layer SC, amorphous silicon, polycrystalline silicon, or oxide semiconductors are used.

[0036] As an insulating layer, GI is formed, for example, by setting silicon oxide or silicon nitride as a single layer or in a stacked manner.

[0037] For example, a molybdenum-tungsten alloy (MoW) can be used as the gate electrode GE. The gate electrode GE can also be integrally formed with the scan line GL.

[0038] An insulating layer ILI is provided over the semiconductor layer SC and the gate electrode GE. The insulating layer ILI is formed, for example, by forming a single layer or a stacked layer of silicon oxide or silicon nitride.

[0039] A source electrode SE and a drain electrode DE are provided on the insulating layer ILI. The source electrode SE and the drain electrode DE are connected to the source region and drain region of the semiconductor layer SC through contact holes provided in the insulating layers ILI and GI, respectively. The source electrode SE can also be integrally formed with the signal line.

[0040] An insulating layer PAS is provided, covering the source electrode SE, the drain electrode DE, and the insulating layer ILI. An insulating layer PLL is provided, covering the insulating layer PAS.

[0041] The insulating layer PAS is formed using an inorganic insulating material. Examples of inorganic insulating materials include those consisting of a single layer or stacked layers of silicon oxide or silicon nitride. The insulating layer PLL is formed using an organic insulating material. Examples of organic insulating materials include photosensitive acrylic and polyimide. By providing the insulating layer PLL, the steps formed by the transistor Tr can be flattened.

[0042] A pixel electrode PE is provided on the insulating layer PLL. The pixel electrode PE is connected to the drain electrode DE through contact holes provided in the insulating layer PAS and PLL.

[0043] Pixel electrodes (PEs) are formed, for example, through a three-layer stacked structure of indium zinc oxide (IZO), silver (Ag), and IZO.

[0044] In this embodiment, the structure from the substrate BA1 to the insulating layer PLL is referred to as the backplane BPS.

[0045] A boss (BK) is provided between adjacent pixel electrodes PE. The boss BK is made of the same organic material as the insulating layer PLL. The boss BK opens in such a way that a portion of the pixel electrode PE is exposed. Furthermore, the end of the opening OP is preferably a gently tapered shape in cross-section. If the end of the opening OP is a steeply shaped form, it will cause poor coverage of the subsequently formed organic EL layer ELY.

[0046] An organic EL layer ELY is disposed between adjacent protrusions BK, overlapping with the pixel electrode PE. The organic EL layer ELY includes a hole transport layer HTL, an emissive layer ELL, and an electron transport layer ETL. The detailed structure of the hole transport layer HTL, the emissive layer ELL, and the electron transport layer ETL will be described later.

[0047] A common electrode CE is provided on the organic EL layer ELY. The common electrode CE is formed by making a magnesium-silver alloy (MgAg) film that allows light emitted from the organic EL layer ELY to be transmitted. In this embodiment, the pixel electrode PE is the anode, and the common electrode CE is the cathode. The light emitted from the organic EL layer ELY is extracted upwards via the common electrode CE. That is, the display device DSP has a top-emitting structure. Details regarding the common electrode CE will be described later.

[0048] An insulating layer SEY is provided covering the common electrode CE. The insulating layer SEY functions to prevent moisture from penetrating the organic EL layer ELY from the outside. Preferably, the insulating layer SEY has high gas barrier properties. Examples of insulating layers SEY include those formed by sandwiching an organic insulating layer between two nitrogen-containing inorganic insulating layers. Materials for the organic insulating layer include acrylic resin, epoxy resin, and polyimide resin. Materials for the nitrogen-containing inorganic insulating layer include silicon nitride and aluminum nitride.

[0049] A substrate BA2 is provided on the insulating layer SEY. The substrate BA2 is formed of the same material as the substrate BA1. A transparent inorganic or organic insulating layer may also be provided between the substrate BA2 and the insulating layer SEY. The organic insulating layer may also have the function of bonding the insulating layer SEY to the substrate BA2.

[0050] Figure 4 This is a cross-sectional view of the comparative example display device. Figure 4 In the illustrated display device DSPr, a hole transport layer (HTL), an electron transport layer (ETL), and a common electrode (CE) are disposed across pixels PXR, PXG, and PXB. In pixels PXR, PXG, and PXB, as light-emitting layers (ELL), light-emitting layers ELR, ELG, and ELB are respectively provided. The ends of light-emitting layers ELR and ELG, ELG and ELB, and ELB and ELR are connected to the ends of the light-emitting layers of adjacent pixels.

[0051] Figure 5 It is Figure 4 A partially enlarged cross-sectional view. Figure 5As an example, an enlarged cross-sectional view of pixel PXB is shown. For ease of observation, cross-sectional lines have been omitted for some of the constituent elements. An electric field EF is generated between the pixel electrode PE (anode) and the common electrode CE (cathode) according to the applied voltage. Since the common electrode CE is located to the adjacent pixel PX, pixel PXB does not have element isolation or a current-crowding structure. In this case, the electric field EF extends not only between the pixel electrode PE of pixel PXB and the area of ​​the opposing common electrode CE, but also to the adjacent pixels PX.

[0052] If the electric field EF expands, the characteristics between the voltage V applied to the pixel PX and the flowing current I (called the VI characteristic) will lead to problems such as an increase in the threshold Vth and a decrease in the slope efficiency of the light output relative to the current I. As a result, the light extraction efficiency in the pixel PX decreases.

[0053] Furthermore, when the light-emitting layer ELB emits light, holes flow in the hole transport layer HTL, which can sometimes generate leakage current LK. If the holes reach the light-emitting layer ELR of the adjacent pixel PXR or the light-emitting layer ELG of the pixel PXG, there is a risk that the light-emitting layers ELR and ELG will emit light unexpectedly.

[0054] In this embodiment, a current crowding structure is achieved by isolating the hole transport layer (HTL), electron transport layer (ETL), and common electrode (CE) according to the pixel PX and by changing the film thickness of the electron transport layer (ETL). This improves the light extraction efficiency in the pixel PX. Furthermore, by isolating components according to the pixel PX, leakage current generation can be suppressed, preventing accidental emission of the light-emitting layer.

[0055] Figure 6 This is a cross-sectional view showing an example of the general configuration of the display device according to this embodiment. Figure 7 It is Figure 6 A partially enlarged cross-sectional view. Within pixels PX (PXR, PXG, and PXB), the hole transport layer HTL, the light-emitting layer ELL (ELR, ELG, and ELB), the electron transport layer ETL, and the common electrode CE are isolated according to pixel PX. That is, the hole transport layer HTL, light-emitting layer ELL, electron transport layer ETL, and common electrode CE in one pixel PX are not connected to the hole transport layer HTL, light-emitting layer ELL, electron transport layer ETL, and common electrode CE of adjacent pixels PX.

[0056] Each pixel PX has an electron transport layer (ETL) with a thinner first region ETL1 and a thicker second region ETL2. The second region ETL2 is disposed inside the opening OP. The end of the second region ETL2 is separated from the bottom end of the opening OP. The thicknesses of the first region ETL1 and the second region ETL2 are set as t1 and t2, respectively. The thickness t1 is preferably about 10% of the thickness t2. For example, when the thickness t2 is 50 nm, the thickness t1 is preferably 5 nm.

[0057] The second region ETL2 overlaps with the common electrode CE, while the first region ETL1 does not overlap with the common electrode CE.

[0058] The first region ETL1 and the second region ETL2 are formed as follows: First, a film of material that will become the electron transport layer ETL is formed to a thickness t2. Next, a film of material that will become the common electrode CE is formed. Then, using a mask, the portion that will become the second region ETL2 and the portion that will become the common electrode CE are covered, and the portion that will become the first region ETL1 is etched to a thickness t1. This etching can be either dry etching or wet etching.

[0059] Etching the portion that becomes the second region ETL2 could potentially damage the underlying light-emitting layer ELL.

[0060] Conversely, if the electron transport layer (ETL) is set with a film thickness t2 without etching, there is a risk that the current crowding effect cannot be fully obtained.

[0061] exist Figure 6 and Figure 7 In the example shown, if a predetermined voltage is applied to the pixel electrode PE and the common electrode CE, an electric field EF is generated only in the second region ETL2, which overlaps with the common electrode CE. In the first region ETL1, which does not overlap with the common electrode CE, the electric field EF does not extend. Because the film thickness t1 of the first region ETL1 is relatively thin, no electrons move from the second region ETL2 to the first region ETL1, and no leakage current is generated. This embodiment can achieve a current crowding structure because it can generate an electric field EF only in the second region ETL2.

[0062] The planar shapes of the hole transport layer (HTL), the light-emitting layer (ELL), the second region (ETL2) of the electron transport layer (ETL), and the common electrode (CE) can be, for example, rectangular or circular shapes. Figure 8 It is a top view of a display device having a rectangular hole transport layer, a light-emitting layer, a second region of an electron transport layer, and a common electrode. Figure 9 It is a top view of a display device having a circular hole transport layer, a light-emitting layer, a second region of an electron transport layer, and a common electrode.

[0063] exist Figure 8 and Figure 9 In the diagram, the common electrode CE and the second region have the same planar shape. The first region ETL1, the light-emitting layer ELL, and the hole transport layer HTL have the same planar shape. For ease of understanding, the figures are shown below. Figure 8 and Figure 9 The diagram shows the planar shape of the common electrode CE and the planar shape of the light-emitting layer ELL; other constituent elements with the same planar shape are omitted from the illustration. Figure 8 In the diagram, the common electrode CE and the light-emitting layer ELL have a rectangular shape when viewed from above. Figure 9 In the diagram, the common electrode CE and the light-emitting layer ELL have a circular shape when viewed from above. Furthermore, in... Figure 8 and Figure 9 Within each of them, the opening OP located on the boss BK has the same shape as the common electrode CE and the light-emitting layer ELL.

[0064] The lengths of the common electrode CE in pixels PXR, PXG, and PXB along the first direction X are set as dr, dg, and db, respectively. Figure 8 In this context, the length is roughly equivalent to the long or short side of the common electrode CE. Figure 9 In this case, the length is comparable to the diameter of the common electrode CE.

[0065] Figure 9 The length (diameter) of the circular common electrode CE and the second region ETL2 shown is preferably 3 μm or more and 10 μm or less, and more preferably 1 μm or more and 3 μm or less. In a pixel PX with such a length range, current crowding effect can be obtained, and electric field propagation can be suppressed.

[0066] If the length is greater than 10 μm, although the device isolation effect can be achieved, the electric field crowding effect cannot be obtained, and the electric field may spread. The length should preferably be greater than 3 μm and less than 10 μm.

[0067] The wiring WL connected to the common electrode CE has wirings WLX, WLR, WLG, and WLB. Wiring WLX extends along a first direction X. Wiring WLR extends from wiring WLX along a second direction Y and is connected to the common electrode CE of pixel PXR. Wiring WLB extends from wiring WLX along the second direction Y and is connected to the common electrode CE of pixel PXB.

[0068] The wiring WLG includes wirings WLG1, WLG2, and WLG3, and is connected to the common electrode CE of the pixel PXG. Wiring WLG1 extends along the second direction Y, and wiring WLG2 extends along the first direction X. Wiring WLG3 extends along the second direction Y and is connected to the common electrode CE. At the connection between wiring WLG3 and the common electrode CE, it is preferable to increase the width of wiring WLG3. By increasing the width of wiring WLG3, the bonding area between the common electrode CE and wiring WLG3 can be increased. In a structure with a dense electric field, light emission is enhanced in this part. However, by increasing the bonding area between the common electrode CE and wiring WLG3, the dense electric field can be suppressed. By suppressing the dense electric field, leakage current to the wirings around the pixel is reduced, and light emission can be suppressed.

[0069] The structure of the pixel PX used in the display device DSP has been described above, but this embodiment is not limited to a display device. The structure of the pixel electrode PE, hole transport layer HTL, light-emitting layer ELL, electron transport layer ETL, and common electrode CE in this embodiment can also be used as a light source for an organic laser irradiation device, for example.

[0070] The display device of this embodiment can suppress the reduction of light extraction efficiency, suppress leakage current generation, and prevent accidental emission of the light-emitting layer by implementing a component isolation structure and a current congestion structure. Therefore, it is possible to improve the brightness and reliability of the light emitted by the display device.

[0071] Some embodiments of the present invention have been described, but these embodiments are provided by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents.

Claims

1. A display device, characterized in that, The display device includes pixels, and each pixel includes a pixel electrode, a hole transport layer, a light-emitting layer, an electron transport layer, and a common electrode. The ends of the hole transport layer, the light-emitting layer, and the electron transport layer of the pixel are disposed separately from the ends of the hole transport layer, the light-emitting layer, and the electron transport layer of the adjacent pixel. The electron transport layer includes a first region and a second region, the first region having a first film thickness, and the second region having a second film thickness that is thicker than the first film thickness. The second region overlaps with the common electrode, while the first region does not overlap with the common electrode.

2. The display device according to claim 1, characterized in that, The second region and the common electrode have a rectangular shape when viewed from above.

3. The display device according to claim 1, characterized in that, The second region and the common electrode have a circular shape when viewed from above.

4. The display device according to claim 3, characterized in that, The diameter of the circular shape is greater than 3 μm and less than 10 μm.

5. The display device according to claim 3, characterized in that, The diameter of the circular shape is greater than 1 μm and less than 3 μm.

6. The display device according to claim 1, characterized in that, The first film thickness is 10% of the second film thickness.

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