LED chip, exposure head, image forming apparatus, and method for manufacturing an LED chip.

Abstract

To provide an LED chip in which the ratio of stray light to normal light from a light emitting element is reduced without impairing the light emitting characteristics of the light emitting element, and a method for manufacturing the same.SOLUTION: An embodiment of the present disclosure relates to an LED chip having a light-emitting region in which a plurality of light-emitting elements are arranged two-dimensionally on a main surface of a substrate, and a contact region arranged outside the light-emitting region, the plurality of light-emitting elements have a second electrode that is continuous across the plurality of light-emitting elements, the light-emitting region has long sides extending in a first direction and short sides extending in a second direction intersecting the first direction, and an end of the second electrode in the first direction has a portion that is non-parallel to a third direction perpendicular to the first direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to, for example, an LED chip, an exposure head, an image forming apparatus, and a method for manufacturing an LED chip.

Background Art

[0002] Conventionally, as a technology related to an exposure head used in an electrophotographic image forming apparatus, the technology described in Patent Document 1 is known.

[0003] The exposure head described in Patent Document 1 includes a substrate on which a plurality of light emitting elements are arranged along the axial direction of the photosensitive drum, and a lens that condenses the light emitted from the plurality of light emitting elements. In the exposure head, the light emitted from the plurality of light emitting elements is condensed through the lens to expose the photosensitive drum.

[0004] Therefore, the exposure head described in Patent Document 1 is arranged close to the photosensitive drum together with a developing device that develops a latent image formed on the photosensitive drum with toner. Therefore, the exposure head is arranged close to the developing device. Further, the exposure head includes an LED (Light Emitting Diode) as a light emitting element. The light emitting element may be an organic light emitting element.

[0005] Here, in the exposure head, ghost spots may occur on the photosensitive drum due to stray light, and when the ratio of stray light to the normal light for exposure increases, the print quality deteriorates.

[0006] In an organic light emitting element, among the electrodes arranged sandwiching the organic light emitting layer, the electrode on the light emitting side may be formed of a metal having a high reflectivity such as Al or Ag. When the light emitted from the organic light emitting element becomes unintentional stray light due to scattering in the light emitting element substrate, the housing of the exposure head where the organic light emitting element is installed, or on the surface of the photosensitive drum, the electrode formed of the highly reflective metal can reflect this stray light. Therefore, ghost spots are generated on the photosensitive drum by the stray light transmitted through the lens array.

[0007] The configuration described in Patent Document 1 comprises an organic light-emitting element arranged on a glass substrate and a second electrode arranged on the side opposite to the projection surface of the light emitted from the organic light-emitting element, i.e., the photosensitive drum. The second electrode is provided with means for preventing stray light reflection. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2006-236727 [Overview of the project] [Problems that the invention aims to solve]

[0009] The stray light countermeasure configuration described in Patent Document 1 requires roughness treatment of the second electrode of the organic light-emitting element and the application of an anti-reflective layer between the organic light-emitting layer and the second electrode. Therefore, there was a risk of impairing the light-emitting characteristics of the organic light-emitting element itself.

[0010] One aspect of this disclosure provides a method in which the ratio of stray light to normal light from a light-emitting element is reduced without impairing the light-emitting characteristics of the light-emitting element. O The present invention provides an LED chip and a method for manufacturing the same. [Means for solving the problem]

[0011] One aspect of the present disclosure includes a light-emitting region in which a plurality of light-emitting elements are arranged two-dimensionally on the main surface of a substrate, and a contact region arranged outside the light-emitting region, wherein the plurality of light-emitting elements each have a first electrode, an organic layer, and a second electrode on the light-emitting side, the second electrode being continuous across the plurality of light-emitting elements, and in a plan view with respect to the main surface, the light-emitting region has a long side extending in a first direction and a short side extending in a second direction intersecting the first direction. Of the plurality of light-emitting elements, the light-emitting element positioned at the furthest end in the first direction is such that at least three or more light-emitting elements are arranged in a direction that intersects the first direction and is not perpendicular to the first direction, and in the plan view, the region enclosed by the outer edge formed by connecting the outer edge of the light-emitting region and the outer edge of the contact region is defined as a closed region, and in the plan view, the closed region is contained within the second electrode, and in the plan view, the end of the second electrode in the first direction has a portion that is non-parallel to the outer edge of the closed region that is closest to the end of the second electrode in the first direction, and the non-parallel portion is located on the opposite side from the light-emitting region with respect to the line formed by connecting the points furthest from the light-emitting region in the trajectory of the arc when the center of a circle with a predetermined margin width radius moves along the outer edge of the closed region. Regarding LED chips.

[0012] Another aspect of the present disclosure is a method for manufacturing an organic EL element comprising at least one organic layer between a first electrode and a second electrode, comprising the steps of: facing a deposition mask having a plurality of openings and a substrate on which the first electrode and the organic layer are arranged; aligning the substrate and the deposition mask; and forming the second electrode by depositing a deposition material on the substrate through the openings of the deposition mask, wherein the openings of the deposition mask have a long side extending in a first direction, a short side extending in a second direction intersecting the first direction, and a portion at the end in the first direction that is non-parallel to a third direction intersecting the first direction. 、 In the alignment step, the substrate and the deposition mask are The opening is positioned to enclose a closed region formed by connecting the outer edge of the exposed portion of the wiring and the outer edge of the region where the first electrode and the organic layer are in contact. This relates to a method for manufacturing OLED chips. [Effects of the Invention]

[0013] According to one aspect of this disclosure, the ratio of stray light to normal light from an organic light-emitting element is reduced without impairing the light-emitting properties of the organic light-emitting element. O We can provide LED chips and methods for manufacturing the same. [Brief explanation of the drawing]

[0014] [Figure 1] (a) A schematic diagram of a part of an OLED chip viewed from above, (b) A cross-sectional view of the OLED chip in (a) along line A-A', (c) An enlarged view of the region R enclosed by the dashed line of the OLED chip in (a), (d) A diagram showing an example of the shape of the light-emitting region of the OLED chip in (a), (e) A cross-sectional view of the OLED chip in (a) along line BB'. [Figure 2] Enlarged view illustrating the shape of the second electrode. [Figure 3] (a), (b) Schematic diagram of a part of an OLED chip viewed from above. [Figure 4] (a), (b) Schematic diagram of a part of an OLED chip viewed from above. [Figure 5] (a) A schematic diagram of a plan view of a part of an OLED chip having a color filter, (b) A cross-sectional view of the OLED chip of (a) along line A-A'. [Figure 6] (a) Schematic diagram of a part of an OLED chip having a color filter when viewed in plan, (b) Cross-sectional view taken along line A-A' of the OLED chip in (a) [Figure 7] Cross-sectional view showing an example of an exposure head [Figure 8] Schematic diagram for explaining a head substrate and a lens array in an exposure head [Figure 9] Schematic diagram for explaining a manufacturing method of a part of an OLED chip [Figure 10] Perspective view of an image forming apparatus [Figure 11] Schematic cross-sectional view of the image forming apparatus in FIG. 10 [Figure 12] Schematic diagram of an example of a part of an OLED chip [Embodiments for Carrying Out the Invention]

[0015] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. Note that dimensions, materials, shapes, relative arrangements, etc. of the components described below are not intended to limit the scope of the present disclosure to them unless specifically described otherwise. In this manual, even if an LED chip is an OLED chip having an organic light-emitting layer, it may still be referred to as an LED chip.

[0016] [First Embodiment] An example of the LED chip in the present embodiment will be described using FIGS. 1 to 4. The light emitting element 69 included in the LED chip 53 has a first electrode 63, a second electrode 67, and an organic layer 66 disposed between the first electrode and the second electrode on a substrate 61. A protective layer, a color filter, etc. may be provided on the second electrode 67. When providing a color filter, a planarization layer may be provided between the protective layer. The planarization layer can be made of an acrylic resin or the like.

[0017] A specific example of the LED chip configuration will be explained using drawings. Figure 1(a) is a schematic plan view showing a partial example of an LED chip 53 using the light-emitting element of this embodiment, and Figure 1(b) is a schematic cross-sectional view along the line A-A' in Figure 1(a). A plan view is a plan view taken from a direction perpendicular to a certain plane (the normal direction of the plane).

[0018] As shown in Figure 1(a), the LED chip 53 of this embodiment has a light-emitting region 60 in which a plurality of light-emitting elements 69 are arranged two-dimensionally on the main surface of the substrate 61, and a contact region 64a arranged outside the light-emitting region 60.

[0019] As shown in Figure 1(b), the plurality of light-emitting elements 69 each have a first electrode 63 disposed on the main surface of the substrate 61, an organic layer 66 disposed thereon and including at least a light-emitting layer, and a second electrode 67 (upper electrode) disposed on the light-emitting side. The second electrode 67 is continuous across the plurality of light-emitting elements 69. In a plan view with respect to the main surface, the light-emitting region 60 has a long side extending in a first direction X and a short side extending in a second direction Y' intersecting the first direction; a rectangular example is shown here. In this plan view, the end of the second electrode 67 in the first direction X has a portion that is not parallel to a third direction Y perpendicular to the first direction X. Further details will be described later.

[0020] Furthermore, the LED chip 53 has an insulating layer 62 that covers the end of the first electrode 63 and has an opening 65 on the first electrode 63, functioning as a bank, and a protective layer 68 that is placed on the second electrode 67. In addition, the LED chip 53 has wiring 64 arranged in the contact area 64a for applying voltage to the second electrode 67. It also has a pad portion 70 for inputting control signals from the image forming apparatus body to each LED chip 53. The LED chip 53 has a moisture-resistant ring 116 surrounding the light-emitting area 60, the contact area 64a, and the pad portion 70. The moisture-resistant ring 116 can suppress the intrusion of moisture into the light-emitting element.

[0021] In this specification, the light-emitting region 60 of the LED chip refers to the entire light-emitting region of the multiple light-emitting elements arranged on the substrate of the LED chip in a plan view. Therefore, the shape of the light-emitting region 60 of the LED chip is the shape of the outer edge when all the light-emitting regions of the multiple light-emitting elements are considered as a single light-emitting region, and may include non-emitting regions such as bank regions.

[0022] Specifically, the outer edge shape of the light-emitting region 60 is, for example, the region connecting the ends of the openings 65 of the insulating layer 62 of the outermost multiple light-emitting elements. Therefore, as shown in Figure 1(b), in the cross-sectional view along line A-A' of the LED chip, the light-emitting region 60 is the region demarcated by the dotted line.

[0023] The outer edge shape of the light-emitting region will be explained in more detail using Figure 1(c). Figure 1(c) shows an enlarged view of the region R enclosed by the dashed line of the LED chip in (a). Here, among the four light-emitting elements located furthest out in the first direction X, the outermost corners of the insulating layer 62 aperture 65 of the light-emitting element located furthest out in the second direction Y are defined as corners C1 and C2. Similarly, among the four light-emitting elements located furthest out in the opposite direction of the first direction X, the insulating layer of the light-emitting element located furthest out in the second direction is defined as follows. 62 The outermost corners of the opening 65 are designated as corners C3 and C4.

[0024] At this time, as shown in Figure 1(d), the shape formed by the lines connecting angles C1, C2, C3, and C4 is the outer edge shape of the light-emitting region 60. For example, in Figure 1, the light-emitting region 60 is a parallelogram having a long side extending in a first direction X and a short side extending in a second direction Y' that intersects the first direction X. Note that angles C1, C2, C3, and C4 may be rounded depending on the processing and alignment accuracy in the manufacturing process. Even in such cases, the outer edge shape can be identified by defining the point where the two lines enclosing these angles intersect as the tip of the angle.

[0025] Here, the element light-emitting regions of multiple light-emitting elements may have interruptions or misalignments along the long and short sides of the light-emitting region 60, but the outer edge of the LED chip's light-emitting region 60 is defined by the approximate line of the outer edge of these element light-emitting regions, as described above. For example, the first direction X and the second direction Y' are directions parallel to the approximate straight line of the outermost light-emitting region of the element light-emitting regions of the multiple light-emitting elements.

[0026] The element light-emitting region of each light-emitting element refers to the portion where the first electrode 63, the organic layer 66, and the second electrode 67 are stacked at the opening 65 of the insulating layer 62. The non-light-emitting region refers to the portion other than the light-emitting region.

[0027] In a plan view, the length of the longer side of the light-emitting region 60 in this embodiment is at least five times the length of the shorter side. The light-emitting region 60 occupies the largest area of ​​the LED chip 53. Therefore, the length of the longer side of the LED chip 53 is also at least five times the length of the shorter side of the LED chip 53.

[0028] (Arrangement and shape of the second electrode) The shape of the second electrode 67 of the LED chip 53 will be explained using Figure 1. In order to reduce stray light in the LED chip 53, it is preferable to make the area of ​​the second electrode 67, which generates unintended stray light due to reflection, as small as possible. On the other hand, the second electrode 67 has an area necessary for the light-emitting element 69 to perform its intended function. Therefore, it is preferable to make the area of ​​the second electrode 67 as small as possible without impairing the light-emitting characteristics of the light-emitting element 69.

[0029] In this embodiment, one example is described in which the contact region 64a is located at both ends in the longitudinal direction of the light-emitting region 60, which is formed by arranging the light-emitting elements 69 in a two-dimensional manner in the longitudinal and transverse directions. However, the contact region 64a may be located at any location on the substrate 61.

[0030] Furthermore, since the second electrode 67 extends to the contact region 64a and is deposited therein, if the contact region 64a is located far from the light-emitting region 60, the area of ​​the second electrode increases. Therefore, it is preferable that the contact region 64a be located close to the light-emitting region 60. Also, from the viewpoint of electrical resistance, it is preferable that the contact region 64a be located close to the light-emitting region 60.

[0031] In this embodiment, the second electrode has a portion that is not parallel to the third direction Y at the end in the first direction X, as a result of a portion being removed. By having this portion that is not parallel to the third direction Y (having a notch), the area of ​​the second electrode can be reduced compared to the case where there is no notch.

[0032] This will be explained in detail. When the contact region 64a is outside the light-emitting region 60, theoretically, the area of ​​the second electrode 67 can be minimized by depositing the second electrode 67 along the outermost periphery of the light-emitting region 60 and the contact region 64a. For example, in the structure shown in Figure 1(a), the area of ​​the second electrode 67 can be minimized by making the closed region 71, which includes multiple light-emitting elements 69 represented by the dashed lines connecting the four corners of the contact region 64a, the deposition region for the second electrode 67.

[0033] However, when forming the second electrode 67 by vacuum deposition through an opening in the deposition mask, for example, there is a gap between the substrate on which the second electrode is formed by deposition and the deposition mask, and the film formed by deposition has a blurred portion. The film thickness in the blurred portion tends to be thinner, resulting in higher electrical resistance, which is undesirable. Therefore, the shape of the second electrode 67 requires an isotropic margin width (M) corresponding to the predetermined alignment accuracy of the deposition apparatus used. Consequently, the region 72, represented by the dashed line encompassing region 71, must be the deposition region for the second electrode 67, and the area of ​​the second electrode 67 that contributes to unintended light reflection becomes larger than region 71.

[0034] Figure 1(e) shows a cross-sectional view of the LED chip in Figure 1(a) along line BB'. A transistor 115 and an insulator 101 for driving the light-emitting element are arranged on the substrate 100. An insulating layer 102, a plug 111 placed on the insulating layer 102, a conductive layer 107, an insulating layer 103, and a plug 112 placed on the insulating layer 103 are arranged on the transistor 115 and the insulator 101 in this order from the substrate 100 side.

[0035] Furthermore, on the insulating layer 103, a conductive layer 108, an insulating layer 104, a plug 113 placed on the insulating layer 104, a conductive layer 117 that functions as a conductive layer 109 and pad electrode, an insulating layer 105, and a plug 114 placed on the insulating layer 105 are arranged in this order from the substrate side. On the insulating layer 105, a conductive layer 110 that functions as the first electrode 63 of the light-emitting element is placed, and an insulating layer 106 is placed over the insulating layer 105, the conductive layer 110, and the conductive layer 117.

[0036] The insulating layer 101 may be a silicon oxide film such as LOCOS. The insulating layers 102, 103, 104, and 105 can be formed by films having at least one of silicon oxide, silicon oxynitride, silicon nitride, silicon nitride, and aluminum oxide, or by a lamination thereof. Here, an example is shown where insulating layers 102, 103, 104, and 105 are silicon oxide films.

[0037] The insulating layer 106 is preferably a film with low moisture permeability. The insulating layer 106 can be, for example, a silicon nitride film, an aluminum oxide film, or a laminate thereof.

[0038] The conductive layers 107, 108, and 109 may be layers of metal such as copper, aluminum, or cobalt, and may also be laminated with a layer such as titanium nitride, and may function as wiring, for example. The conductive layer 110 can be aluminum, an aluminum alloy, or a laminate of aluminum or an aluminum alloy with titanium nitride. The first electrode 63 will be described in more detail later.

[0039] The moisture-resistant ring 116 includes, for example, a plug 111, conductive layers 107, plug 112, conductive layers 108, plug 113, conductive layers 109, plug 114, and an insulating layer 106. By surrounding the light-emitting region with the moisture-resistant ring 116, which is composed of these layers with low moisture permeability, it is possible to suppress moisture from reaching the light-emitting element. However, the moisture-resistant ring is not limited to these configurations; the conductive layer portion may be replaced with an insulating layer with low moisture permeability, such as a nitride film, or part of it may be a film containing silicon oxide or the like. Even with such configurations, moisture permeation can be suppressed in other parts, so it functions substantially as a moisture-resistant ring. Therefore, the moisture-resistant ring 116 of this embodiment includes configurations in which part of the layer does not suppress moisture permeation, as long as it functions substantially as a moisture-resistant ring.

[0040] Figure 2 is a magnified view of the area around the contact region 64a. Circle 80 is a hypothetical circle for illustrative purposes, centered at a corner of the contact region 64a, with a radius of the margin width (M) corresponding to the alignment accuracy represented by the dashed line.

[0041] As shown in Figure 2, by removing a portion of the second electrode 67 outside the circle 80 (by providing a notch 81), the second electrode 67 takes on a shape in which the end in the first direction X is non-parallel to the third direction Y. This makes it possible to reduce the area of ​​the formed second electrode 67 compared to when the second electrode 67 is deposited in a region 72 having a long side with the tangent to the circle 80 and a short side extending in the third direction.

[0042] With this configuration, even when the alignment is at its maximum deviation, there is no area where the second electrode 67 cannot cover the contact area 64a, and the area of ​​the second electrode 67 that contributes to unintended light reflection can be reduced while maintaining sufficient electrical contact. In this embodiment, the contact area 64a is shown as rectangular, so the corner of the contact area 64a is used as the center of the circle 80, but the center of the circle 80 is not limited to this.

[0043] Even if the contact area 64a is not rectangular, the trajectory of the circle 80 can be drawn by connecting the points furthest from the light-emitting area 60 in an arc such that the center of the circle 80 moves along the outermost line of the contact area 64a. By removing at least a portion of the second electrode 67 (by providing a notch 81) in the outer region 73 of the shape derived in this way, the area of ​​the second electrode 67 can be reduced without impairing the light-emitting characteristics of the light-emitting element 69.

[0044] Alternatively, as shown in Figure 3(a), the shape may be obtained by cutting off the corner where a line passing through the outermost edges of the light-emitting region 60 and the contact region 64a and parallel to the longer side of the light-emitting region 60 intersects with a line passing through the outermost edges of the light-emitting region 60 and the contact region 64a and parallel to the shorter side of the light-emitting region 60. Alternatively, as shown in Figure 3(b), the shape may be obtained in which, in the configuration of Figure 3(a), the side of the second electrode 67 parallel to the third direction Y is shifted toward the light-emitting region 60 in the first direction X.

[0045] As shown in Figure 4(a), the end of the second electrode 67 in the first direction may have a curved shape. For example, the end of the second electrode 67 in the first direction may have a curve, specifically a shape in which a curve with a center of curvature on the light-emitting region 60 side is continuous. In this case as well, the area of ​​the second electrode 67 can be further reduced while the second electrode 67 covers the wiring 64. As shown in Figure 4(b), only the corners of the second electrode 67 may have a curved shape with curvature, and the central part in the third direction Y (direction perpendicular to the long side of the light-emitting region) may be straight.

[0046] Preferably, the length of the portion of the second electrode 67 that is not parallel to the third direction Y at the end of the second electrode 67 in the first direction is longer than 1 / 3 of the distance L (Figure 2) from the end of the second electrode 67 in the third direction to the part of the second electrode 67 that contacts the wiring 64. Furthermore, the length of the portion of the portion of the second electrode 67 that is not parallel to the third direction Y at the end of the second electrode 67 in the first direction may be longer than half the distance L from the end of the second electrode 67 in the third direction to the part of the second electrode 67 that contacts the wiring 64. Figure 2 shows an example where the length of the portion of the portion not parallel to the third direction Y in the third direction is approximately equal to the distance L from the end of the second electrode 67 in the third direction to the part of the second electrode 67 that contacts the wiring 64.

[0047] During film deposition by vacuum deposition, variations in the shape of the second electrode 67 can occur due to factors such as the distance between the deposition source and the substrate, the taper angle in the thickness direction of the deposition mask opening, and whether the LED chip is deposited near the center or on the outer edge of the substrate. However, in a plan view with respect to the main surface of the substrate 61, the edge of the second electrode 67 in the first direction X has a portion that is non-parallel to the third direction Y which is perpendicular to the first direction X, thereby reducing the area of ​​the second electrode 67 without impairing the light emission characteristics of the light-emitting element 69. Therefore, unintended light reflection by the second electrode 67 can be reduced without impairing the light emission characteristics of the light-emitting element 69.

[0048] Furthermore, by having a notch, not only can the area of ​​the second electrode be reduced, but the circumference of the second electrode can also be reduced. Organic EL elements, which are an example of light-emitting elements in this embodiment, are known to degrade due to water in the atmosphere. One of the points where water can enter the organic EL element is the periphery of the second electrode 67. Therefore, by reducing the circumference of the second electrode 67, the penetration of water into the light-emitting element can be suppressed.

[0049] (substrate) The substrate 61 can be made of any material capable of supporting the first electrode 63, the organic layer 66, and the second electrode 67. Although not shown in Figure 1(b), the substrate 61 may also contain active elements such as transistors. Furthermore, an interlayer insulating layer or wiring layer may be arranged between the substrate 61 and the first electrode 63, either as a single layer or in multiple layers.

[0050] For the substrate 61, for example, glass, plastic, silicon, etc., can be used. In this embodiment, an example using a silicon substrate is shown. While the thermal conductivity of a glass substrate is approximately 0.55 to 1.1 W / m·K, the silicon substrate has a much higher thermal conductivity of approximately 162 W / m·K.

[0051] Organic light-emitting elements are known to dissipate heat depending on the length of their light emission time and the magnitude of their light emission. Therefore, it is preferable to efficiently dissipate the heat generated when the light-emitting element 69 is driven.

[0052] By using a silicon substrate as the substrate 61, even when the light-emitting element 69 formed on the substrate 61 generates heat due to operation, the heat can be efficiently dissipated by utilizing the heat transfer of the substrate 61. Furthermore, when the substrate 61 is cooled from the back side by an air cooling mechanism or the like, the light-emitting element 69, which is the heat source, can be efficiently cooled.

[0053] Furthermore, from the viewpoint of thermal conductivity, a thinner substrate 61 is preferable. For example, the standard thickness of an 8-inch silicon wafer is 725 μm, but this can be thinned in a background process or similar. However, when mounting multiple LED chips 53 onto other equipment, a thinner substrate 61 may reduce the yield due to breakage such as cracking during handling. To avoid this, it is preferable for the substrate 61 to have a certain thickness.

[0054] For example, the thickness of the substrate 61 can be 200 μm to 700 μm. More preferably, the thickness of the silicon substrate is 378 μm to 408 μm. For example, a silicon substrate thinned by a back grinder in the range of 378 μm to 408 μm can be used. Note that the substrate 61 may have switching elements such as transistors, wiring layers, interlayer insulating layers (not shown), etc., and the thickness of the silicon substrate mentioned above is the thickness excluding these wiring layers, interlayer insulating layers, and other structures.

[0055] (1st electrode) The first electrode 63 may be transparent or opaque. If it is opaque, a metallic material with a reflectance of 70% or more at the emission wavelength is preferred for the first electrode 63. Suitable materials for the first electrode 63 include metals such as Al and Ag, alloys to which Si, Cu, Ni, Nd, etc. are added, and materials such as ITO, IZO, AZO, and IGZO. For example, a Ti / TiN / AlCu (sum of film thickness of 65 nm) layered structure can be used for the first electrode 63.

[0056] The emission wavelength referred to here is the spectral range emitted from the organic layer 66. The first electrode 63 may be a multilayer electrode with a barrier electrode made of metals such as Ti, W, Mo, or Au, or an alloy thereof, as long as its reflectivity is higher than the desired value, or it may be a multilayer electrode with a transparent oxide film electrode such as ITO or IZO.

[0057] On the other hand, if the first electrode 63 is a transparent electrode, a reflective layer may be provided below the first electrode 63. Examples of materials that can be used for the transparent electrode include ITO, IZO, AZO, and IGZO. For the purpose of optimizing the optical distance, as described later, an insulating film may be provided between the reflective layer and the transparent conductive film.

[0058] (2nd electrode) In this embodiment, the light-emitting element 69 emits light from the second electrode. Therefore, the second electrode 67 is arranged on the organic layer 66 and is semi-transparent. The second electrode 67 can be a semi-transparent conductive layer that transmits some of the light that reaches its surface and reflects other parts (i.e., semi-transparent reflectivity). As the material for the second electrode 67, one with a small work function is preferred. For example, alkali metals such as lithium, alkaline earth metals such as calcium, aluminum, titanium, manganese, silver, lead, chromium, or other metal elements or mixtures containing these can be used.

[0059] Alternatively, alloys combining these individual metals can be used as the material for the second electrode 67. For example, magnesium-silver, aluminum-lithium, aluminum-magnesium, silver-copper, zinc-silver, etc., may be used. These electrode materials may be used individually or in combination of two or more types. The second electrode may also be a single-layer or multi-layer structure.

[0060] In particular, silver is preferred, and a silver alloy is even more preferred in order to suppress silver aggregation. The ratio of the alloy is not a concern as long as silver aggregation is suppressed. For example, it may be 1:1. As the semipermeable material, an alloy mainly composed of magnesium or silver is particularly preferred. The second electrode 67 may also be a laminated structure of layers having the above material, as long as it has a desirable transmittance and reflectance. Furthermore, the second electrode 67 may be shared by multiple light-emitting elements 69.

[0061] By using a second electrode 67 made of a semi-permeable material, the element may have a top-emission configuration that satisfies the above interference conditions. The method for forming the electrodes is not particularly limited, but DC and AC sputtering methods are preferred because they provide good film coverage and make it easier to reduce resistance.

[0062] For example, the second electrode 67 can have a layered structure of magnesium and silver (sum of film thickness 15 nm).

[0063] The first electrode 63 and the second electrode 67 may be individually arranged for each of the multiple light-emitting elements 69, while the other is continuous across the multiple light-emitting elements 69. Alternatively, the first electrode 63 and the second electrode 67 may be individually arranged in each of the multiple light-emitting elements 69.

[0064] In this embodiment, an example is shown where the second electrode 67 is common to multiple light-emitting elements 69. This reduces the amount of wiring connecting the power supply wiring to the cathodes 67 of the multiple light-emitting elements 69.

[0065] Since the second electrode 67 supplies current to the organic layer 66 via the wiring 64, it is preferable that it has low resistance. If the resistance of the second electrode 67, which is a common electrode, is high, it may cause an increase in the driving voltage of the light-emitting element 69 and uneven brightness due to shading, potentially impairing the light emission characteristics. Therefore, the portion removed to reduce the area of ​​the second electrode 67 (notch 81) is preferably in an external region rather than an internal region extending from the contact region 64 towards the light-emitting region 60, which may increase the resistance.

[0066] (organic layer) The organic layer 66 is placed on the first electrode 63 and can be formed by known techniques such as vapor deposition or spin coating.

[0067] The organic layer 66 only needs to have at least an emissive layer, and may be composed of multiple layers. If the organic layer is an organic compound layer, the multiple layers may include one or a combination thereof of a hole injection layer, a hole transport layer, an electron blocking layer, an emissive layer, a hole blocking layer, an electron transport layer, and an electron injection layer.

[0068] The light-emitting layer emits light when holes injected from the anode and electrons injected from the cathode recombine in the organic layer. The light-emitting layer can consist of a single layer or multiple layers. Each light-emitting layer may contain a red light-emitting material, a green light-emitting material, blue It can have colored light-emitting materials, and by mixing the different light-emitting colors, it is possible to obtain white light.

[0069] Furthermore, each light-emitting layer may contain light-emitting materials of complementary colors, such as a blue light-emitting material and a yellow light-emitting material. In any case, it is preferable to emit light at a wavelength appropriate for the application, and by using an organic light-emitting element, the emission wavelength can be adjusted by the light-emitting material.

[0070] Furthermore, different colors of light may be emitted by changing the material and composition of the light-emitting layer for each light-emitting element 69. Alternatively, multiple light-emitting elements 69 may share a common light-emitting layer, or each light-emitting element 69 may have its own light-emitting layer. If each light-emitting element 69 has its own light-emitting layer, the light-emitting layer may be patterned for each light-emitting element 69.

[0071] The light-emitting element 69 according to this embodiment may have a first reflective surface, a second reflective surface, and a light-emitting layer disposed between the first reflective surface and the second reflective surface. The first reflective surface may be a first electrode 63, or a reflective layer disposed between the first electrode 63 and an insulating layer.

[0072] To optimize the optical distance between the first reflective surface and the emission position of the organic layer 66 including the light-emitting layer, if the optical path length Lr is from the top surface of the first reflective surface to the emission position of the organic layer 12, and the phase shift in the reflective layer is Φr, Lr=(2m-(Φr / π))×(λ / 4)···(1) m is a non-negative integer. The thickness of the first electrode 63 or the first reflective surface and the organic layer 66 may be optimized to approximately satisfy equation (1) above.

[0073] Furthermore, the optical distance Ls from the light emission position to the second reflective surface approximately satisfies equation (2) below, where Φs is the phase shift when light of wavelength λ is reflected at the reflective surface. In this embodiment, m'=0. Ls=(2m'-(Φs / π))×(λ / 4)=-(Φs / π)x(λ / 4)...(2)

[0074] Therefore, the total interference L approximately satisfies the following conditions. L=Lr+Ls=(2m-Φ / π)×(λ / 4)...(3)

[0075] Here, Φ is the sum of the phase shifts Φr + Φs when light of wavelength λ is reflected by the first electrode 63 or the reflective layer and the second electrode 67.

[0076] The above condition being "approximately satisfied" means that in equations (1) through (3), the acceptable range is approximately λ / 8 or approximately 20 nm.

[0077] Furthermore, since it can be difficult to pinpoint the light emission position of the light-emitting layer, in the above configuration, the light emission position was substituted at the interface on the first reflective surface side or the interface on the second reflective surface side of the functional layer. Considering the tolerance range mentioned above, even with this substitution, the effect of strengthening the light can be achieved.

[0078] Furthermore, it is well known that under interference conditions that intensify light, the distribution of radiant light from the light-emitting element is modulated from a Lambertsian distribution, with an increase in the forward-facing component and a decrease in the oblique-facing component. Therefore, using a light-emitting element with a top-emission configuration that satisfies the interference conditions is preferable for suppressing stray light and, consequently, improving print quality.

[0079] For example, a hole injection layer (film thickness 8 nm), a hole transport layer (37 nm), an emissive layer (20 nm), a hole blocking layer (34 nm), an electron transport layer (20 nm), and an electron injection layer (0.5 nm) may be stacked on the first electrode 63.

[0080] (Contact area and pad area) In the contact region 64a, the wiring 64 only needs to ensure electrical contact with the second electrode 67, and can be made using metallic materials such as aluminum (Al), titanium (Ti), or titanium nitride (TiN). Alternatively, a mixture of these materials or a laminated structure may be used.

[0081] When the organic layer 66 is formed by vapor deposition or the like, it is sufficient that current can be maintained between the second electrode 67 and the wiring 64, so the organic layer 66 may partially cover the wiring 64. The pad portion 70 also needs to be electrically connected to the head substrate 50 by wire bonding or the like, so it can be made from the same material as the wiring 64.

[0082] (protective layer) The protective layer 68 is an insulating layer and preferably contains an inorganic material that is translucent and has low permeability to oxygen and moisture from the outside. For example, the protective layer 68 can be made using inorganic materials such as silicon nitride (SiN), silicon oxynitride (SiON), silicon oxide (SiOx), aluminum oxide (Al2O3), and titanium oxide (TiO2).

[0083] In particular, inorganic materials such as SiN, SiON, and Al2O3 are preferred in terms of protective performance. Chemical vapor deposition (CVD), atomic layer deposition (ALD), and sputtering are preferred for forming the protective layer 14. For example, after forming the second electrode, the material may be transported to another chamber without breaking the vacuum and a silicon nitride film with a thickness of 2 μm may be formed by CVD to serve as the protective layer. Alternatively, a protective layer may be provided using atomic layer deposition (ALD) after film formation by CVD.

[0084] The protective layer 68 may be a single layer or a laminated structure combining the above materials and formation methods, provided it has sufficient moisture-blocking performance. For example, it may be a laminate of silicon nitride layers or a high-density layer formed by atomic deposition. Furthermore, the protective layer 68 may have an organic layer, provided it maintains moisture-blocking performance. Examples of organic layers include polyacrylate, polyimide, polyester, epoxy, etc. Moreover, the protective layer 68 may be arranged across multiple light-emitting elements 69.

[0085] For example, the protective layer 68 may be formed by transporting the device substrate to another chamber while maintaining a vacuum after the formation of the second electrode 67, and depositing a silicon nitride film with a thickness of 2 μm using the CVD method.

[0086] Alternatively, an anti-reflective layer may be provided on top of the protective layer 68. The anti-reflective layer is formed such that the optical thickness (product of refractive index and thickness) of the film, which has a different refractive index from the protective layer 68, is λ / 4 when the wavelength at which reflection is to be suppressed is λ. However, the wavelength of light emitted from the light-emitting element 69 is generally broader than that of a semiconductor laser, with a larger full width at half maximum.

[0087] Therefore, to obtain a sufficient anti-reflective effect over a broad emission wavelength, a multilayer structure is preferable to a single-layer structure. The anti-reflective layer material may be magnesium fluoride, silicon dioxide, or a polymer, similar to the planarization layer. Considering the cost of the manufacturing process related to film formation, this can be appropriately selected from the case using the color filter described later.

[0088] (Color filter) In this embodiment, an example is shown in which a color filter is not provided on the light-emitting side of the light-emitting element, but a color filter may be provided on the protective layer. For example, a color filter that takes into account the size of the light-emitting element 69 may be provided on a separate substrate and bonded to the substrate on which the light-emitting element is provided, or a color filter may be patterned on the protective layer as shown above using photolithography technology. The color filter may be made of polymer. The color filter transmits the desired light from the light-emitting element 69 and absorbs light of unwanted wavelengths.

[0089] In display device applications, color filters can be provided to enhance the color purity of red, green, and blue light-emitting elements. Alternatively, they can be provided to separate the light from a white light-emitting element into red, green, and blue.

[0090] When used in an exposure head of an image forming apparatus, the photosensitive drum can be made of a color filter that transmits light having a wavelength necessary for photosensitization. On the other hand, to address stray light, ingenuity is required in the arrangement of the color filter. For example, by not providing a color filter on the light-emitting region and instead providing a color filter that absorbs light from the light-emitting element in the non-light-emitting region, stray light can be absorbed without reducing the amount of light incident on the photosensitive drum.

[0091] Alternatively, a color filter that transmits light of the emission wavelength can be provided on the light-emitting region 60, and a color filter that absorbs light from the light-emitting element 69 can be provided in the non-light-emitting region. With this configuration, stray light can be absorbed without reducing the amount of light incident on the photosensitive drum. The color filter provided in the non-light-emitting region may be a black resist.

[0092] (flattening layer) A planarization layer may be provided between the color filter and the protective layer. The planarization layer may be composed of an organic compound, which may be low molecular weight or high molecular weight, but is preferably high molecular weight.

[0093] The planarization layer may be provided above or below the color filter, and its constituent materials may be the same or different. Specifically, polyvinylcarbazole resin, polycarbonate resin, polyester resin, ABS resin, acrylic resin, polyimide resin, phenolic resin, epoxy resin, silicone resin, urea resin, etc., can be used. By providing a planarization layer on top of the color filter, the penetration of moisture and oxygen from the outside into the color filter can be reduced and protected.

[0094] [Second Embodiment] In this embodiment, an example configuration is described in which the LED chip 53 of the first embodiment has a color filter. Since it is the same as the first embodiment except for the presence of a color filter, the explanation will be omitted. The color filter 91 can be fabricated, for example, by forming a planarization layer 90 on the protective layer 68 to flatten the irregularities of the protective layer 68 caused by the light-emitting element 69, and then using photolithography technology.

[0095] Figure 5 shows an example in which a first color filter 91 that absorbs light from the light-emitting element 69 is provided in the area excluding the light-emitting region 60 and the pad portion 70. Figure 5(a) is a plan view of the LED chip 53, and Figure 5(b) is a schematic cross-sectional view along the line A-A' in Figure 5(a). Since the pad portion 70 needs to be electrically connected, no color filter is placed on the pad portion 70.

[0096] Furthermore, the first color filter 91 is not placed on the light-emitting element 69, and a transparent planarization layer 90 is provided instead. Therefore, stray light from unintended directions can be absorbed without reducing the amount of light emitted from the LED chip 53. The first color filter 91 may also be a black resist that absorbs light other than the emission wavelength from the light-emitting element 69.

[0097] Figure 6 shows an example in which a color filter is provided in the area excluding the pad portion 70. Figure 6(a) is a plan view of an example of a part of the LED chip 53, and Figure 6(b) is a schematic diagram of a cross-section along line A-A' of the configuration in Figure 6(a). A second color filter 92 that transmits light of the emission wavelength is provided on the light-emitting element 69, and a first color filter 91 that absorbs light from the light-emitting element 69 is provided on the light-emitting region 60 and in the area excluding the pad portion 70. This allows stray light from unintended directions to be absorbed without reducing the normal amount of light emitted from the LED chip. The first color filter 91 may also be a black resist that absorbs light of wavelengths other than those corresponding to the light from the light-emitting element 69.

[0098] [Third Embodiment] Next, the exposure head 4 will be described using Figure 7. Figure 7 is a schematic cross-sectional view of the exposure head 4 of this embodiment. The exposure head 4 of this embodiment has an LED chip 53 according to the first or second embodiment.

[0099] The exposure head 4 has an elongated shape (longitudinal shape) that extends in the axial direction of the photosensitive drum 2. The exposure head 4 comprises a head substrate 50, a light-emitting element 69 mounted on the head substrate 50, a lens array 52, and a holding member that holds the head substrate 50 and the lens array 52. ​​The holding member comprises a housing 54, which will be described later, and a housing support member 55 that supports the housing 54. Here, the exposure head 4 is equipped with an LED (Light Emitting Diode) as a light-emitting element that emits light, and for example, an organic light-emitting element can be used.

[0100] (Enclosure) As shown in Figure 7, the housing 54 holds the lens array 52 and the substrate 50. In this embodiment, the housing 54 is a metal component formed by bending a plate material that has been plated, such as a galvanized steel sheet or a cold-rolled steel sheet. Here, as an example of an exposure method used in an electrophotographic image forming apparatus, there is a laser beam scanning exposure method in which the irradiation beam of a semiconductor laser is scanned by a rotating polygon mirror or the like and the photosensitive drum is exposed through an f-θ lens or the like. The exposure head 4 described in this embodiment is arranged adjacent to the photosensitive drum 2 and is used in an LED exposure method in which the photosensitive drum 2 is exposed using light-emitting elements 69 arranged along the axial direction of the photosensitive drum 2.

[0101] The housing 54 can be made of metal, for example. For example, the housing 54 may be made by pressing a sheet metal, such as a thin iron plate, into a U-shape. The shape of the housing 54 will be described below.

[0102] The flat portion 54U faces the photosensitive drum 2 in the optical axis direction of the lenses of the lens array 52. ​​Note that this flat portion 54U is not limited to a flat surface, but may be a slightly curved surface. The housing 54 has an extension portion 54R that extends from one side of the flat portion 54U in the short direction toward the photosensitive drum 2. The housing 54 also has an extension portion 54L that extends from the other side of the flat portion 54U in the short direction toward the photosensitive drum 2.

[0103] The extensions 54R and 54L form substrate support portions in the housing 54 for supporting the head substrate 50 inserted through the second opening 54b. The flat portion and the substrate support portions (extensions 54R, 54L) are integrated and form the housing 54 that holds the lens array 52 and the head substrate 50, and are formed in a substantially U-shape. Because the housing 54 is formed in a substantially U-shape, the second opening 54b is formed on the side opposite to the flat portion 54U. The second opening 54b is formed between the substrate support portions (extensions 54L, 54R) that extend from the flat portion 54U toward the side away from the photosensitive drum.

[0104] The head board 50 is inserted through the second opening 54b, that is, from the bottom of the U-shaped housing 54, and is bonded with adhesive to the inside of each board support portion (the inside of the extension portion 54L and the inside of the extension portion 54R). Note that the position of the head board 50 in the focal direction is determined by a jig (not shown), so the exposure head 4 does not have a means for positioning the head board 50 in the focal direction.

[0105] Furthermore, the lens array 52 is also inserted into the first opening 54a formed in the flat portion 54U and then bonded to the flat portion 54U with adhesive. The lens array 52 is fixed to the flat portion 54U (housing 54) after its position and tilt in the focal direction have been adjusted using a jig so that the distance in the focal direction between the lens array 52 and all the LED chips 53 mounted on the head substrate 50 is a predetermined value. The lens array 52 is also fixed to the flat portion 54U with adhesive at multiple locations in the longitudinal direction. In other words, the exposure head 4 of this embodiment has multiple bonding locations in the longitudinal direction of the flat portion 54U for bonding and fixing the lens array 52 inserted into the first opening 54a to the flat portion 54U.

[0106] After the head board 50 and lens array 52 are positioned and fixed relative to the housing 54, the gap between the board 50 inserted into the second opening 54b and the housing 54 (extensions 54L, 54R) is sealed longitudinally with a sealant 59. This reduces contamination of the light-emitting element 69 by toner and dust from the outside. Here, the sealant 59 only seals the gap (boundary) between the board 50 and the housing 54, and most of the FFC connector 57 and the head board 50 are exposed.

[0107] Similarly, a sealant 59 is applied to the gap between the lens array 52 inserted into the first aperture 54a and the housing 54 (flat portion 54U), and the gap is sealed longitudinally by the sealant 59. More specifically, as shown in Figure 4, the sealant 59 seals the gap between the side wall of the lens array 52 along the longitudinal direction of the housing 54 and the edge of the first aperture 54a. This reduces the possibility that dust such as toner will flow in through the gap between the side wall of the lens array 52 and the first aperture 54a, and that the light emitted from the light-emitting element 69 will be blocked by the dust.

[0108] Furthermore, the gaps sealed by the sealant 59 are not only the gap between one side wall of the lens array 52 and the edge of the first opening 54a, but also the gap between the other side wall of the lens array 52 and the edge of the first opening 54a. The other side wall of the lens array 52 refers to the side wall opposite to the side wall of the lens array 52. ​​Here too, the gap (boundary) between the housing 54 and the lens array 52 is sealed by the sealant 59. This reduces contamination of the light-emitting element 69 by toner and dust from the outside.

[0109] As described above, the head substrate 50 and the lens array 52 are held by the housing 54, so that the light-emitting element 69 and the incident surface of the lens face each other. As a result, the light emitted from the light-emitting element 69 enters the incident surface of the lens and is emitted from the exit surface of the lens toward the photosensitive drum 2, exposing the photosensitive drum 2.

[0110] Ideally, all light emitted from the light-emitting element 69 should enter the lens at the incident surface. However, due to the light emission distribution, some light from the light-emitting element 69 may be emitted at an oblique angle. For example, oblique light that does not enter the lens array directly from the light-emitting element 69 and is reflected after entering the inner wall of the exposure head housing is light that has traveled an unintended path and can become stray light. In addition, light that enters the photosensitive drum 2 normally from the light-emitting element 69 through the lens array 52 may be reflected at the surface of the photosensitive drum 2 or scattered by toner or dust that may be present in the light ray path. Fresnel reflection also occurs at the end face of the lens array. If this light passes through the lens array again and is further reflected by the second electrode 67 of the light-emitting element 69, this light can become stray light.

[0111] When the light-emitting element 69 is an organic light-emitting element, the main contributor to reflection in a top-emission configuration is the second electrode, which has high reflectivity and is located closest to the lens array on the same side as the organic layer 66. In order to suppress the aforementioned stray light, it is preferable to make the area of ​​this second electrode as small as possible without impairing the light-emitting characteristics of the organic light-emitting element.

[0112] Therefore, in the exposure head 4 of this embodiment, by using the LED chip 53 described in the first or second embodiment, the area of ​​the second electrode 67 can be reduced compared to the case where the second electrode does not have a notch, and stray light can be suppressed. Furthermore, by suppressing stray light, when the exposure head 4 is used in an image forming apparatus, ghost spots caused by stray light can be reduced and print quality can be improved.

[0113] (Housing support member) The housing support member 55 supports the housing 54, which holds the head substrate 50 and the lens array 52, along its longitudinal direction, and is integrally provided with the housing 54. The housing support member 55 is a longitudinally shaped member that extends in the axial direction of the photosensitive drum 2. As shown in Figure 4, the housing support member 55 is formed in a U-shape. The housing support member 55 has a left side wall 55L, which is a first side wall, a right side wall 55R, which is a second side wall opposite the left side wall 55L, and a bottom surface 55D that faces the flat surface 54U of the housing 54 between the left side wall 55L and the right side wall 55R. The bottom surface 55D of the housing support member 55 is provided with a plurality of openings 55a in the longitudinal direction, which is the axial direction of the photosensitive drum 2.

[0114] The opening 55a of the housing support member 55 is located opposite to the mounting surface (front surface of the head board 50) on which the light-emitting elements 69 of the head board 50 are mounted (the back surface of the head board 50). The opening 55a is located between the left wall 55L and the right wall 55R in the short direction perpendicular to the longitudinal direction.

[0115] (Substrate and lens array) Here, the head substrate 50 and lens array 52 of the exposure head 4 will be described using Figure 8. First, the head substrate 50 will be described. Figure 8(a) is a schematic perspective view of the head substrate 50. Figure 8(b) shows the arrangement of multiple light-emitting elements 69 provided on the head substrate 50, and Figure 8(c) shows an enlarged view of Figure 8(b).

[0116] An LED chip 53 is mounted on the head board 50. As shown in Figure 8(a), the LED chip 53 is provided on one side of the head board 50, and a long flexible flat cable (FFC) connector 57 is provided on the other side. Here, one side of the head board 50 is the side on which the LED chip 53 is provided (top side, front side). The other side of the board is the side opposite to the side on which the LED chip 53 is provided (bottom side, back side).

[0117] The FFC connector 57 is mounted on the other side (bottom surface, back surface) of the head board 50 such that its longitudinal direction aligns with the longitudinal direction of the head board 50. The long FFC connector 57 is provided to receive control signals (drive signals) from the control circuit section of the main body of the image forming apparatus, and these control signals are transferred to each LED chip 53. The LED chips 53 are driven (light up, turn off) by the control signals input to the head board 50.

[0118] The LED chip 53 mounted on the head board 50 will now be described. As shown in Figures 8(b) and 8(c), multiple light-emitting elements 69 are arranged on one side of the head board 50. For example, LED chips 53-1 to 53-29 (29 in total) are arranged. Each LED chip 53-1 to 53-29 has multiple light-emitting elements 69 arranged along its longitudinal direction, for example, 516 light-emitting elements 69 are arranged.

[0119] In the longitudinal direction of the LED chip 53, the distance k2 between the centers of adjacent light-emitting elements 69 corresponds to the resolution of the image forming apparatus 100. For example, when the resolution of the image forming apparatus 100 in this embodiment is 1200 dpi, the light-emitting elements 69 in the longitudinal direction of LED chips 53-1 to 53-29 are arranged such that the distance k2 between the centers of adjacent light-emitting elements 69 is 21.16 μm. Therefore, the exposure range of the exposure head 4 in this embodiment is approximately 314 mm.

[0120] The photosensitive layer of the photosensitive drum 2 is formed with a width of 314 mm or more. Since the length of the long side of A4 size recording paper and the length of the short side of A3 size recording paper are 297 mm, the exposure head 4 in this embodiment has an exposure range that can form images on A4 size and A3 size recording paper. Although Figure 8 shows an example in which multiple light-emitting elements 69 are arranged in the longitudinal direction, the light-emitting elements 69 may also be arranged in the short direction in addition to the longitudinal direction.

[0121] LED chips 53-1 to 53-29 are arranged in multiple rows along the axis of the photosensitive drum 2. Specifically, LED chips 53-1 to 53-29 are arranged alternately in two rows along the axis of the photosensitive drum 2. 8 As shown in (b), the odd-numbered LED chips 53-1, 53-3, ... 53-29 are mounted in a row along the length of the substrate 50, counting from the left. The even-numbered LED chips 53-2, 53-4, ... 53-28 are also mounted in a row along the length of the substrate 50, counting from the left. The LED chips 53 are arranged in this manner.

[0122] As a result, as shown in Figure 8(c), the distance k1 between the centers of light-emitting elements 69 located at one end of one LED chip 53 and the other end of the other LED chip 53 in the longitudinal direction of the LED chip 53 can be made equal to the distance k2 between the centers of adjacent light-emitting elements 69 on a single LED chip 53.

[0123] In this embodiment, the light-emitting element 69 is an organic light-emitting element and is a current-driven light-emitting element. The organic light-emitting elements are arranged in a line along the main scanning direction (the axial direction of the photosensitive drum 2) on a TFT (Thin Film Transister) substrate, for example, and are electrically connected in parallel by power supply wiring also provided along the main scanning direction.

[0124] Next, the lens array 52, which is a lens assembly, will be described. Figure 8(d) is a schematic diagram of the lens array 52 as seen from the photosensitive drum 2 side. Figure 8(e) is a schematic perspective view of the lens array 52. ​​As shown in Figure 8(d), the lens array 52 focuses the light emitted from the light-emitting element 69 onto the photosensitive drum 2. The lens array 52 is a lens assembly having multiple lenses.

[0125] These multiple lenses are arranged in two rows along the alignment direction of the multiple light-emitting elements 69. Each lens is arranged alternately such that one lens from the other row is positioned so as to be in contact with both adjacent lenses in the alignment direction of the lenses in one row. Each lens is a cylindrical glass rod lens, having a light incident surface 52b into which light emitted from the light-emitting elements 69 enters, and a light exit surface 52a into which light incident from the light incident surface exits (see Figure 7). Note that the material of the lens is not limited to glass; it may also be made of plastic. The shape of the lens is not limited to a cylinder; for example, it may be a polygonal prism such as a hexagonal prism.

[0126] The dotted line Z shown in Figure 8(e) indicates the optical axis of the lens. Here, the optical axis of the lens refers to the line connecting the center of the light-emitting surface of the lens and the focal point of the lens. The lens array 52 is a lens assembly having multiple lenses, and the aforementioned "optical axis" refers to the optical axis of any of these multiple lenses. Strictly speaking, the multiple lenses in the lens array 52 may be slightly tilted relative to each other. This is due to tolerances during assembly.

[0127] However, deviations of a tolerance magnitude mentioned here will not be considered when defining the direction of the optical axis. Therefore, we will assume that the optical axes of each of the multiple lenses are all in the same direction. The lens array 52 has the role of focusing the light emitted from the light-emitting element 69 onto the surface of the photosensitive drum 2.

[0128] The lens array 52 is mounted to the housing 54 during the assembly of the exposure head 4 such that the distance between the light-emitting surface of the light-emitting element 69 and the light-incident surface of the lens is approximately equal to the distance between the light-emitting surface of the lens and the surface of the photosensitive drum 2.

[0129] Furthermore, as shown in Figure 8(b), in the exposure head 4, multiple LED chips 53 are arranged on the exposure head substrate 50. Therefore, by reducing the area of ​​the second electrode 67 in the LED chip 53, the area of ​​the entire exposure head 4 that contributes to unintended light reflection by the second electrode 67 is reduced in proportion to the number of LED chips 53. Accordingly, it is preferable that more than half of the arranged LED chips 53 are the LED chips 53 described in Embodiment 1 or 2, and it is even more preferable that all LED chips are the LED chips 53 described in the first or second embodiment.

[0130] In this embodiment, an example is shown in which the LED chips 53 are arranged alternately in two rows, a so-called staggered arrangement. As can be seen in Figure 8(c), a region is created where the ends of two LED chips 53 overlap in the longitudinal direction. This region corresponds to the location where the ends of the second electrode 67 of the LED chip are present, and therefore, when viewed as a whole, the exposure head 4 becomes a part where the localized reflection area is large. Therefore, by reducing the area of ​​the second electrode 67 at its end, the reflection area in this overlapping region can be reduced, thereby effectively reducing stray light caused by unintended light reflection.

[0131] When an LED chip is used in an exposure head 4, exposure occurs linearly, so the ratio of the length direction (first direction X) to the width direction (second direction Y) of the light-emitting area 60 is larger than when the LED chip is used in a display device or the like. In addition, the ratio of the length direction (first direction X) to the width direction (third direction Y) of the LED chip substrate is also larger.

[0132] Specifically, for example, the length of the longer side of the LED chip (or light-emitting area 60) is 5 times or more the length of the shorter side of the LED chip (or light-emitting area 60), and may also be 10 times or more. For example, the length of the longer side of the LED chip (or light-emitting area 60) can be 20 times or more the length of the shorter side of the LED chip (or light-emitting area 60).

[0133] The length of the long side of the LED chip is determined by the axial length of the photosensitive drum 2, the number of LED chips arranged in that axial direction, and the arrangement of the LED chips 53. The length of the short side of the LED chip 53 is determined by whether the light-emitting elements 69 are arranged in the light-emitting area 60 in a direction perpendicular to the axis of the photosensitive drum 2, and by the arrangement of the pads 70 and contact areas 64a.

[0134] Furthermore, organic light-emitting elements are known to dissipate heat depending on the length of their light emission time and the magnitude of their light emission. This heat can cause thermal expansion of the circuit board on which the organic light-emitting elements are formed, as well as the head board 50 on which multiple elements are mounted. This can cause a shift in the relative positional relationship between the lens array and the light-emitting elements 69, potentially increasing the proportion of stray light relative to the normal light.

[0135] When the primary light source for exposure decreases, the proportion of stray light relative to the primary light increases, which could lead to a decrease in print quality.

[0136] Therefore, by using a silicon substrate as the substrate 61, in a configuration in which multiple LED chips 53 are mounted on the head substrate 50, heat is efficiently transferred to the head substrate 50 via the substrate 61 even when the light-emitting element 69 formed on the substrate 61 generates heat due to operation. Conversely, when the head substrate 50 is cooled from the back side by an air cooling mechanism or the like, it is advantageous in that the light-emitting element 69, which is the heat source, can be cooled efficiently.

[0137] Furthermore, the organic layer 66 can be configured to have a light-emitting layer that emits red light, taking into consideration the wavelength dependence of the photosensitive drum 2's photosensitivity.

[0138] The LED chip 53 may have a color filter as shown in the second embodiment. By having a color filter, the amount of normal light incident on the photosensitive drum 2 is not reduced, and stray light from unintended directions can be absorbed, thereby improving print quality.

[0139] [Fourth Embodiment] Next, a part of the manufacturing process for the LED chip 53 will be explained with reference to Figure 9, but this disclosure is not limited thereto.

[0140] In a deposition chamber, for example, the second electrode 67 of the LED chip 53 of the first or second embodiment can be formed on the substrate 61 by the following configuration. A partial method for manufacturing the LED chip 53 includes the steps of facing a deposition mask having a plurality of openings and a substrate on which the first electrode and organic layer are arranged, and aligning the substrate and the deposition mask. Furthermore, a partial method for manufacturing the LED chip 53 includes the step of forming the second electrode by depositing a deposition material on the substrate through the openings of the deposition mask.

[0141] Here, the opening of the deposition mask has a long side extending in a first direction X, a short side extending in a second direction Y' intersecting the first direction X, and a portion at the end of the first direction X that is non-parallel to a third direction Y intersecting the first direction X.

[0142] First, as shown in Figure 9(a), a substrate 61 held by a substrate holding arm 120 and a deposition mask 111 having multiple openings, which is placed on a mask stage 200, are placed opposite each other. Here, a first electrode 63, an insulating layer 62, and an organic layer 66 are formed on the substrate 61. Wiring 64, pads 70, circuits for driving light-emitting elements 69, etc., may also be formed on the substrate 61.

[0143] Next, as shown in Figure 9(b), for example, either the substrate 61 or the deposition mask 111, or both, are moved to align the substrate 61 and the deposition mask 111. After this, as shown in Figure 9(c), the substrate 61 Next, the second electrode 67 is formed on the substrate 61 by depositing the deposition material 300 through multiple openings in the deposition mask 111.

[0144] In the deposition mask 111, each of the multiple openings has a long side extending in a first direction X, a short side extending in a second direction Y' intersecting the first direction X, and a portion at the end of the first direction X that is non-parallel to a third direction Y intersecting the first direction X. Therefore, the second electrode 67 deposited through these openings also has a long side extending in a first direction X, a short side extending in a second direction Y' intersecting the first direction X, and a portion at the end of the first direction X that is non-parallel to a third direction Y intersecting the first direction X.

[0145] Therefore, the area of ​​the second electrode 67 can be reduced compared to the case where the second electrode 67 does not have a portion that is non-parallel to the third direction Y at the end of the first direction X. This makes it possible to suppress unintended light from being reflected by the second electrode, which would affect the light emission characteristics of the LED chip 53 or result in stray light in the exposure head 4 having the LED chip 53. Therefore, when the exposure head 4 of this embodiment is used in an image forming apparatus, ghost spots caused by stray light can be reduced and print quality can be improved.

[0146] The manufacturing apparatus for the LED chip 53 described herein is an example, and the disclosure is not limited thereto. The light-emitting element 69 has multiple functional layers, and the deposition apparatus used to manufacture it consists of a number of deposition chambers corresponding to these functional layers. In addition to the deposition chambers, the apparatus may also include multiple process chambers such as a preparation chamber, a pre-processing chamber, a transport chamber, a relay chamber, and a substrate stock chamber.

[0147] [Fifth Embodiment] (Image forming apparatus) First, the schematic configuration of the image forming apparatus 100 will be described using Figures 10 and 11. Figure 10 is a perspective view of the image forming apparatus 100. Figure 11 is a schematic cross-sectional view of the image forming apparatus in Figure 10. The image forming apparatus 100 shown in Figures 10 and 11 is a copier equipped with a reader, but the embodiment may also be other image forming apparatuses, such as a printer without a reader. Furthermore, the embodiment is not limited to a color image forming apparatus equipped with multiple photosensitive drums 2 as shown in Figure 11, but may also be a color image forming apparatus equipped with one photosensitive drum 2 or an image forming apparatus that forms monochrome images.

[0148] The image forming apparatus 100 shown in Figure 11 includes four image forming units 1Y, 1M, 1C, and 1K (hereinafter collectively referred to simply as "image forming unit 1") that form toner images of yellow, magenta, cyan, and black, respectively.

[0149] Furthermore, the image forming units 1Y, 1M, 1C, and 1K each include a photosensitive drum 2Y, 2M, 2C, and 2K (hereinafter collectively referred to simply as "photosensitive drum 2"), which is an example of a photoreceptor. The photosensitive drum 2 may also be a photosensitive belt.

[0150] Furthermore, the image forming units 1Y, 1M, 1C, and 1K are equipped with charging rollers 3Y, 3M, 3C, and 3K (hereinafter collectively referred to simply as "charging rollers 3") which serve as charging means for charging the photosensitive drums 2Y, 2M, 2C, and 2K, respectively.

[0151] Furthermore, the image forming units 1Y, 1M, 1C, and 1K are equipped with LED (Light Emitting Diode, hereinafter referred to as LED) exposure heads 4Y, 4M, 4C, and 4K (hereinafter collectively referred to simply as "exposure head 4") as exposure means for exposing the photosensitive drums 2Y, 2M, 2C, and 2K.

[0152] Furthermore, the image forming units 1Y, 1M, 1C, and 1K are equipped with developing units 24Y, 24M, 24C, and 24K (hereinafter collectively referred to simply as "developing unit 24"), which are developing means for developing the electrostatic latent image on the photosensitive drum 2 with toner and developing toner images of each color on the photosensitive drum 2. The symbols Y, M, C, and K indicate the color of the toner.

[0153] The image forming apparatus 100 shown in Figure 11 employs a so-called "bottom exposure method," in which the photosensitive drum 2 is exposed from below. The following explanation will proceed on the premise of an image forming apparatus employing a bottom exposure method. Although not shown in the figures, an image forming apparatus employing a "top exposure method," in which the photosensitive drum is exposed from above, may also be used as an embodiment.

[0154] The image forming apparatus 100 includes an intermediate transfer belt 9 to which the toner image formed on the photosensitive drum 2 is transferred, and primary transfer rollers 6 (Y, M, C, K) that sequentially transfer the toner image formed on the photosensitive drum 2 to the intermediate transfer belt 9. The intermediate transfer belt 9 is located above the image forming unit 1. In addition to the intermediate transfer method using the intermediate transfer belt 9, a direct transfer method in which the toner image is transferred directly from the photosensitive drum 2 to the paper may also be used.

[0155] Furthermore, the image forming apparatus 100 includes a secondary transfer roller 16 as a transfer means for transferring the toner image on the intermediate transfer belt 9 to the recording paper P transported from the feeding unit 11, and a fuser 19 as a fixing means for fixing the secondary transferred image to the recording paper P.

[0156] Furthermore, the toner bottles 22Y, 22M, 22C, and 22K (hereinafter collectively referred to simply as "toner bottles 22") that contain refill toner for each color are units that can be attached to and replaced by the image forming apparatus 100. The toner bottles 22 are positioned above the intermediate transfer belt 9. The toner bottles 22 supply the appropriate amount of toner to each developing unit of the four image forming sections from the corresponding toner bottles using a toner supply mechanism (not shown) that is not shown.

[0157] The image forming apparatus 100 also includes a feeding unit 11 for feeding recording paper P. The feeding unit 11 has sheet cassettes 12a and 12b, feeding rollers 13a and 13b, and a registration roller 15. The sheet cassettes 12a and 12b are located at the bottom of the image forming unit 1. The recording paper P contained in the sheet cassettes 12a and 12b is fed one sheet at a time by the feeding rollers 13a and 13b and transported to the secondary transfer unit T2 at a predetermined timing by the registration roller 15.

[0158] (Image formation process) Next, the image forming process of the image forming apparatus 100 described above will be briefly explained. The charging roller 3Y charges the surface of the photosensitive drum 2Y. The exposure head 4Y exposes the surface of the photosensitive drum 2Y that has been charged by the charging roller 3Y. As a result, an electrostatic latent image is formed on the photosensitive drum 2Y. Next, the developing unit 24Y develops the electrostatic latent image formed on the photosensitive drum 2Y with yellow toner.

[0159] The yellow toner image developed on the surface of the photosensitive drum 2Y is transferred onto the intermediate transfer belt 9 by the primary transfer roller 6Y. Magenta, cyan, and black toner images are formed using a similar image formation process and transferred onto the intermediate transfer belt 9 in a superimposed manner.

[0160] The toner images of each color transferred onto the intermediate transfer belt 9 are transported by the intermediate transfer belt 9 to the secondary transfer section T2. ​​The toner images transported to the secondary transfer section T2 are transferred collectively to the recording paper P transported from the feeding section 11 by the secondary transfer roller 16. The recording paper P on which the toner images have been transferred is transported to the fuser 19. The fuser 19 fixes the toner images to the recording paper P using heat and pressure. The recording paper P that has been fixed by the fuser 19 is discharged by the discharge roller 20 to the discharge tray 21 located above the toner bottle 22. The print quality of the print on the recording paper P can be evaluated by visual sensory evaluation.

[0161] [Sixth Embodiment] In this embodiment, an example of a light-emitting element 69 used in any of the first to fifth embodiments of the LED chip will be described.

[0162] [Configuration of organic light-emitting element] An example of a light-emitting element 69, an organic light-emitting element, is provided on a substrate by forming an insulating layer, a first electrode, an organic compound layer, and a second electrode. A protective layer, a color filter, a microlens, etc., may be provided on the cathode. If a color filter is provided, a planarization layer may be provided between it and the protective layer. The planarization layer can be made of acrylic resin or the like. The same applies when a planarization layer is provided between the color filter and the microlens.

[0163] [substrate] Examples of substrates include quartz, glass, silicon wafers, resins, and metals. The substrate may also be equipped with switching elements such as transistors and wiring, and an insulating layer may be provided on top of them. The insulating layer can be made of any material that allows for the formation of contact holes between it and the first electrode, while ensuring insulation from wiring that is not connected. For example, resins such as polyimide, silicon oxide, and silicon nitride can be used. Using a silicon substrate allows for efficient heat dissipation from the light-emitting element.

[0164] [electrode] A pair of electrodes can be used. The pair of electrodes may be an anode and a cathode. When an electric field is applied in the direction in which the organic light-emitting element emits light, the electrode with the higher potential is the anode, and the other is the cathode. Alternatively, the electrode that supplies holes to the light-emitting layer can be the anode, and the electrode that supplies electrons can be the cathode.

[0165] For the anode, materials with the largest possible work function are preferable. For example, elemental metals such as gold, platinum, silver, copper, nickel, palladium, cobalt, selenium, vanadium, and tungsten, or mixtures containing these, or alloys combining them, as well as metal oxides such as tin oxide, zinc oxide, indium oxide, tin-indium oxide (ITO), and zinc-indium oxide can be used. Conductive polymers such as polyaniline, polypyrrole, and polythiophene can also be used.

[0166] These electrode materials may be used individually or in combination of two or more types. Furthermore, the anode may consist of a single layer or multiple layers.

[0167] When used as a reflective electrode, materials such as chromium, aluminum, silver, titanium, tungsten, molybdenum, or alloys or laminates thereof can be used. It is also possible to use the above materials as a reflective film without serving as an electrode. Furthermore, when used as a transparent electrode, oxide transparent conductive layers such as indium tin oxide (ITO) or indium zinc oxide can be used, but are not limited to these. Photolithography can be used to form the electrodes.

[0168] On the other hand, materials with a small work function are preferred for the cathode. Examples include alkali metals such as lithium, alkaline earth metals such as calcium, and elemental metals or mixtures containing aluminum, titanium, manganese, silver, lead, and chromium. Alternatively, alloys combining these elemental metals can also be used. For example, magnesium-silver, aluminum-lithium, aluminum-magnesium, silver-copper, and zinc-silver can be used. Metal oxides such as indium tin oxide (ITO) can also be used. These electrode materials may be used individually or in combination of two or more. The cathode may also be a single-layer or multi-layer structure. Among these, silver is preferred, and a silver alloy is even more preferred to reduce silver aggregation. The alloy ratio is not important as long as silver aggregation is reduced. For example, the ratio of silver to other metals may be 1:1, 3:1, etc.

[0169] The cathode may be a top-emission element using an oxide conductive layer such as ITO or silver with a thickness sufficient to be semi-permeable, or it may be a bottom-emission element using a reflective electrode such as aluminum (Al), and is not particularly limited. The method for forming the cathode is not particularly limited, but using DC and AC sputtering methods is more preferable because it provides good film coverage and makes it easier to reduce resistance. In both the top-emission and bottom-emission elements, the area of ​​the second electrode, which has high reflectivity and serves as a common electrode, can be reduced by making it the shape of the first or second embodiment.

[0170] [Pixel separation layer] The pixel separation layer is formed from a silicon nitride (SiN), silicon oxynitride (SiON), or silicon oxide (SiO) film, which is formed using chemical vapor deposition (CVD). To increase the in-plane resistance of the organic compound layer, it is preferable that the thickness of the organic compound layer, particularly the hole transport layer, be thinly deposited on the sidewalls of the pixel separation layer. Specifically, by increasing the taper angle of the sidewalls of the pixel separation layer and the thickness of the pixel separation layer, the vignetting during deposition can be increased, thereby thinning the film thickness on the sidewalls.

[0171] On the other hand, it is preferable to adjust the taper angle of the sidewalls of the pixel isolation layer and the thickness of the pixel isolation layer to such an extent that no voids are formed in the protective layer formed on top of it. Since no voids are formed in the protective layer, the occurrence of defects in the protective layer can be reduced. Since the occurrence of defects in the protective layer is reduced, reliability degradation such as the occurrence of dark spots and poor conductivity of the second electrode can be reduced.

[0172] According to this embodiment, charge leakage to adjacent pixels can be effectively suppressed even if the taper angle of the sidewall of the pixel isolation layer is not steep. This study found that sufficient reduction is possible when the taper angle is in the range of 60 degrees to 90 degrees. The thickness of the pixel isolation layer is preferably between 10 nm and 150 nm. Similar effects can also be obtained even if the device consists only of pixel electrodes without a pixel isolation layer. However, in this case, it is preferable to make the thickness of the pixel electrode less than half the thickness of the organic layer, or to make the pixel electrode ends have a forward taper of less than 60°, as this reduces short circuits in the organic light-emitting element.

[0173] [Organic compound layer] The organic compound layer may be formed as a single layer or as multiple layers. If there are multiple layers, they may be called a hole injection layer, a hole transport layer, an electron blocking layer, an emissive layer, a hole blocking layer, an electron transport layer, or an electron injection layer, depending on their function. The organic compound layer is mainly composed of organic compounds, but may also contain inorganic atoms and inorganic compounds. For example, it may contain copper, lithium, magnesium, aluminum, iridium, platinum, molybdenum, zinc, etc. The organic compound layer may be placed between the first electrode and the second electrode, or it may be placed in contact with the first electrode and the second electrode.

[0174] When there are multiple light-emitting layers, a charge-generating porosity may be provided between the first and second light-emitting layers. The charge-generating porosity may contain an organic compound with a minimum unoccupied molecular orbital energy (LUMO) of -5.0 eV or less. The same applies when the charge-generating porosity is provided between the second and third light-emitting layers.

[0175] [Protective layer] A protective layer may be provided on the second electrode. For example, by bonding a glass with a desiccant to the second electrode, the intrusion of water and other substances into the organic compound layer can be reduced, thereby reducing the occurrence of display defects. In another embodiment, a passivation film such as silicon nitride may be provided on the cathode to reduce the intrusion of water and other substances into the organic compound layer. For example, after forming the cathode, the material may be transported to another chamber without breaking the vacuum, and a silicon nitride film with a thickness of 2 μm may be formed by the CVD method to serve as a protective layer. A protective layer may also be provided using atomic deposition (ALD) after the film formation by the CVD method. The material of the film formed by the ALD method is not limited, but may be silicon nitride, silicon oxide, aluminum oxide, etc. Silicon nitride may be further formed on the film formed by the ALD method by the CVD method. The film formed by the ALD method may have a thinner film thickness than the film formed by the CVD method. Specifically, it may be 50% or less, or even 10% or less.

[0176] [Color Filter] A color filter may be provided on top of the protective layer. For example, a color filter that takes into account the size of the organic light-emitting element may be provided on a separate substrate and bonded to the substrate on which the organic light-emitting element is provided, or a color filter may be patterned on the protective layer as described above using photolithography technology. The color filter may be made of polymer.

[0177] [Planarization layer] A planarizing layer may be provided between the color filter and the protective layer. The planarizing layer is provided to reduce the unevenness of the layer below. It may also be called a material resin layer without limiting its purpose. The planarizing layer may be composed of an organic compound, which may be low molecular weight or high molecular weight, but high molecular weight is preferred.

[0178] The planarization layer may be provided above or below the color filter, and its constituent materials may be the same or different. Specifically, examples include polyvinylcarbazole resin, polycarbonate resin, polyester resin, ABS resin, acrylic resin, polyimide resin, phenolic resin, epoxy resin, silicone resin, urea resin, etc.

[0179] [Microlens] An LED chip may have optical components such as microlenses on its light-emitting side. Microlenses may be made of acrylic resin, epoxy resin, or the like. Microlenses may be used to increase the amount of light extracted from an organic light-emitting device or to control the direction of the extracted light. Microlenses may have a hemispherical shape. If they have a hemispherical shape, among the tangents tangent to the hemisphere, there is a tangent parallel to the insulating layer, and the point of contact between that tangent and the hemisphere is the vertex of the microlens. The vertex of the microlens can be similarly determined in any cross-sectional view. That is, among the tangents tangent to the semicircle of the microlens in the cross-sectional view, there is a tangent parallel to the insulating layer, and the point of contact between that tangent and the semicircle is the vertex of the microlens.

[0180] Furthermore, the midpoint of a microlens can also be defined. In the cross-section of a microlens, a line segment can be imagined from the point where one arc ends to the point where another arc ends, and the midpoint of this line segment can be called the midpoint of the microlens. The cross-section used to determine the vertices and midpoints may be a cross-section perpendicular to the insulating layer.

[0181] A microlens has a first surface with a convex portion and a second surface opposite to the first surface. It is preferable that the second surface is positioned closer to the functional layer than the first surface. To adopt such a configuration, it is necessary to form the microlens on the light-emitting device. If the functional layer is an organic layer, it is preferable to avoid processes that involve high temperatures during the manufacturing process. Furthermore, when adopting a configuration in which the second surface is positioned closer to the functional layer than the first surface, it is preferable that the glass transition temperatures of all organic compounds constituting the organic layer are 100°C or higher, and more preferably 130°C or higher.

[0182] [Opposite substrate] A counter substrate may be provided on the planarization layer. The counter substrate is called a counter substrate because it is provided in a position corresponding to the aforementioned substrate. The constituent material of the counter substrate may be the same as that of the aforementioned substrate. The counter substrate may be the second substrate if the aforementioned substrate is considered the first substrate. The counter substrate may not be provided if it is not needed.

[0183] [Organic layer] An organic compound layer (hole injection layer, hole transport layer, electron blocking layer, light-emitting layer, hole blocking layer, electron transport layer, electron injection layer, etc.) constituting an organic light-emitting element according to one embodiment of this disclosure is formed by the method shown below.

[0184] The organic compound layer constituting the organic light-emitting element according to one embodiment of the present invention can be formed using a dry process such as vacuum deposition, ionization deposition, sputtering, or plasma deposition. Alternatively, instead of a dry process, a wet process can be used in which the layer is formed by dissolving the compound in a suitable solvent and applying a known coating method (e.g., spin coating, dipping, casting, LB method, inkjet method, etc.).

[0185] When layers are formed using methods such as vacuum deposition or solution coating, crystallization is less likely to occur, resulting in excellent stability over time. Furthermore, when forming films using coating methods, it is possible to combine the film with an appropriate binder resin.

[0186] Examples of the binder resins mentioned above include, but are not limited to, polyvinylcarbazole resin, polycarbonate resin, polyester resin, ABS resin, acrylic resin, polyimide resin, phenolic resin, epoxy resin, silicone resin, and urea resin.

[0187] Furthermore, these binder resins may be used individually as homopolymers or copolymers, or as a mixture of two or more types. Additionally, known additives such as plasticizers, antioxidants, and UV absorbers may be used in combination as needed.

[0188] [Pixel circuit] The LED chip may have a pixel circuit connected to a light-emitting element. The pixel circuit may be an active-matrix type that independently controls the light emission of a first light-emitting element and a second light-emitting element. The active-matrix circuit may be voltage-programmed or current-programmed. The driving circuit has a pixel circuit for each pixel. The pixel circuit may include a light-emitting element, a transistor that controls the light emission brightness of the light-emitting element, a transistor that controls the light emission timing, a capacitor that holds the gate voltage of the transistor that controls the light emission brightness, and a transistor for connecting to GND without going through the light-emitting element.

[0189] An LED chip has a light-emitting region and a peripheral region arranged around the light-emitting region. The light-emitting region has a pixel circuit, and the peripheral region has a display control circuit. The mobility of the transistors constituting the pixel circuit may be smaller than the mobility of the transistors constituting the display control circuit.

[0190] The slope of the current-voltage characteristics of the transistors constituting the pixel circuit can be smaller than the slope of the current-voltage characteristics of the transistors constituting the display control circuit. The slope of the current-voltage characteristics can be measured using the so-called Vg-Ig characteristic.

[0191] The transistors that make up the pixel circuit are transistors connected to light-emitting elements, such as the first light-emitting element.

[0192] Next, an example of a part of the LED chip according to this embodiment will be described with reference to the drawings.

[0193] Figure 12 is a schematic cross-sectional view showing an example of an LED chip having an organic light-emitting element and a transistor connected to this organic light-emitting element. The transistor is an example of an active element. The transistor may also be a thin-film transistor (TFT).

[0194] Figure 12 shows an example of a pixel, which is a component of the LED chip according to this embodiment. The pixel has sub-pixels 10. The sub-pixels are divided into 10R, 10G, and 10B based on their light emission. The light emission color may be distinguished by the wavelength emitted from the light-emitting layer, or the light emitted from the sub-pixel may be selectively transmitted or color-converted by a color filter or the like. In this embodiment, the sub-pixels are distinguished by three wavelengths using a color filter and light emission, but if only one or two wavelengths are required, the corresponding light-emitting layer or color filter may be one or two types, respectively. Each sub-pixel has a reflective electrode 2 which is the first electrode, an insulating layer 3 covering the end of the reflective electrode 2, an organic compound layer 4 covering the first electrode and the insulating layer, a transparent electrode 5, a protective layer 6, and a color filter 7 on an interlayer insulating layer 1.

[0195] The interlayer insulating layer 1 may have transistors and capacitive elements placed in the layer below or inside it. The transistor and the first electrode may be electrically connected via a contact hole or the like (not shown).

[0196] The insulating layer 3 is also called the bank or pixel isolation layer. It covers the edge of the first electrode and surrounds the first electrode. The portion without the insulating layer is in contact with the organic compound layer 4 and becomes the light-emitting region.

[0197] The organic compound layer 4 includes a hole injection layer 41, a hole transport layer 42, a first light-emitting layer 43, a second light-emitting layer 44, and an electron transport layer 45.

[0198] The second electrode 5, whether transparent, reflective, or semi-transparent, is made of a material with high light reflectivity and is commonly arranged across multiple light-emitting elements.

[0199] The protective layer 6 reduces the penetration of moisture into the organic compound layer. Although the protective layer is shown as a single layer, it may consist of multiple layers. Each layer may contain an inorganic compound layer and an organic compound layer.

[0200] The color filters 7 are classified into 7R, 7G, and 7B according to their color. The color filters may be formed on a planarization film (not shown). The color filters may also have a resin protective layer (not shown). Alternatively, the color filters may be formed on a protective layer 6, or they may be bonded together after being placed on an opposing substrate such as a glass substrate.

[0201] This disclosure includes, for example, the following configurations:

[0202] (Composition 1) An LED chip having a light-emitting region in which a plurality of light-emitting elements are arranged two-dimensionally on the main surface of a substrate, and a contact region arranged outside the light-emitting region, wherein the plurality of light-emitting elements each have a first electrode, an organic layer, and a second electrode on the light-emitting side, the second electrode being continuous across the plurality of light-emitting elements, and in a plan view with respect to the main surface, the light-emitting region has a long side extending in a first direction and a short side extending in a second direction intersecting the first direction, and in the plan view, the end of the second electrode in the first direction has a portion that is non-parallel to a third direction perpendicular to the first direction.

[0203] (Configuration 2) The LED chip according to configuration 1, wherein, in the plan view, the length of the longer side of the light-emitting region is five times or more the length of the shorter side.

[0204] (Composition 3) In the plan view, the end of the second electrode is a curved LED chip according to configuration 1 or 2.

[0205] (Composition 4) An LED chip according to any one of configurations 1 to 3, wherein, in the plan view, the length of the portion non-parallel to the third direction in the third direction is longer than 1 / 3 of the distance from the end of the second electrode in the third direction to the portion where the second electrode contacts the wiring.

[0206] (Composition 5) A color filter is placed on the aforementioned contact area. In the aforementioned plan view, the color filter encompasses the contact area, An LED chip according to any one of configurations 1 to 4, having an opening at a position overlapping with the aforementioned light-emitting region.

[0207] (Composition 6) In the aforementioned plan view, a first color filter overlapping the contact area, In the aforementioned plan view, it has a second color filter that overlaps with the light-emitting region, The second color filter is an LED chip according to any one of configurations 1 to 5, wherein the color of light transmitted is different from that of the first color filter.

[0208] (Composition 7) The LED chip according to configuration 6, wherein the first color filter has a lower transmittance to light from the plurality of light-emitting elements than the second color filter.

[0209] (Composition 8) The substrate is a silicon substrate, and the LED chip is as described in any of configurations 1 to 7.

[0210] (Composition 9) The substrate is an LED chip according to any one of configurations 1 to 8, having a thickness of 200 μm to 700 μm.

[0211] (Composition 10) The substrate is an LED chip according to any one of configurations 1 to 9, having a thickness of 200 μm to 408 μm.

[0212] (Composition 11) The substrate is an LED chip according to any one of configurations 1 to 10, having a thickness of 378 μm to 408 μm.

[0213] (Composition 12) An exposure head having a plurality of LED chips arranged in the longitudinal direction on a head substrate, each having sides parallel to the longitudinal direction and sides parallel to the short direction, wherein at least one of the LED chips is an LED chip according to any of configurations 1 to 11.

[0214] (Composition 13) The exposure head according to configuration 11, wherein two LED chips that are adjacent in the longitudinal direction are offset in the short direction among the plurality of LED chips.

[0215] (Composition 14) An exposure head comprising a housing that holds a head substrate on which a plurality of LED chips having sides parallel to the longitudinal direction and sides parallel to the short direction are arranged in the longitudinal direction, and a lens array positioned opposite the head substrate, wherein at least one of the LED chips is an LED chip according to any of configurations 1 to 13.

[0216] (Composition 15) The exposure head according to configuration 14, wherein the LED chip is arranged such that the second electrode faces the lens array.

[0217] (Composition 16) An image forming apparatus comprising: a photosensitive drum; an exposure head disposed opposite the photosensitive drum and exposing the photosensitive drum to form a latent image on the photosensitive drum; and a developing means for developing the latent image formed on the photosensitive drum with toner, wherein the exposure head is the exposure head described in any of configurations 11 to 15.

[0218] (Method 1) A method for manufacturing an organic EL element comprising at least one organic layer between a first electrode and a second electrode, comprising the steps of: facing a deposition mask having a plurality of openings and a substrate on which the first electrode and the organic layer are arranged; aligning the substrate and the deposition mask; and forming the second electrode by depositing a deposition material on the substrate through the openings of the deposition mask, wherein the openings of the deposition mask have a long side extending in a first direction, a short side extending in a second direction intersecting the first direction, and a portion at the end in the first direction that is non-parallel to a third direction perpendicular to the first direction. [Explanation of symbols]

[0219] 52a Light exit surface 53 LED chips 61 circuit boards 63 1st electrode 64 Wiring 64a Contact area 66 Organic layer 67 2nd electrode 69 Light-emitting element

Claims

1. A light-emitting region in which multiple light-emitting elements are arranged in a two-dimensional manner on the main surface of the substrate, It has a contact region located outside the light-emitting region, The plurality of light-emitting elements each have a first electrode, an organic layer, and a second electrode on the light-emitting side. The second electrode is continuous across the plurality of light-emitting elements, In a plan view of the main surface, the light-emitting region has a long side extending in a first direction and a short side extending in a second direction intersecting the first direction. Of the plurality of light-emitting elements, the light-emitting element located at the very end in the first direction is such that at least three or more light-emitting elements are arranged in a direction that intersects the first direction and is not perpendicular to the first direction. In the plan view, the region enclosed by the outer edges formed by connecting the outer edge of the light-emitting region and the outer edge of the contact region is defined as a closed region. In the aforementioned plan view, the closed region is contained within the second electrode. In the plan view, the end of the second electrode in the first direction has a portion that is non-parallel to the outer edge of the closed region that is closest to the end of the second electrode in the first direction. The OLED chip is characterized in that the non-parallel portion is located on the opposite side of the light-emitting region from the line formed by connecting the points furthest from the light-emitting region in the trajectory of the arc when the center of a circle with a predetermined margin width radius moves along the outer edge of the closed region.

2. The OLED chip according to claim 1, wherein, in the plan view, the length of the longer side of the light-emitting region is five times or more the length of the shorter side.

3. The OLED chip according to claim 1, wherein the non-parallel portion of the second electrode has a curve in the plan view.

4. The OLED chip according to claim 1, wherein, in the plan view, the length of the non-parallel portion in a third direction perpendicular to the first direction is longer than 1 / 3 of the distance from the end of the second electrode in the third direction to the portion of the second electrode that contacts the wiring.

5. A color filter is placed on the aforementioned contact area. In the aforementioned plan view, the color filter encompasses the contact area, The OLED chip according to claim 1, having an opening in a position that overlaps with the light-emitting region.

6. In the aforementioned plan view, a first color filter overlapping the contact area, In the aforementioned plan view, it has a second color filter that overlaps with the light-emitting region, The OLED chip according to claim 1, wherein the second color filter transmits a different color of light than the first color filter.

7. The OLED chip according to claim 6, wherein the first color filter has a lower transmittance to light from the plurality of light-emitting elements than the second color filter.

8. The OLED chip according to claim 1, wherein the substrate is a silicon substrate.

9. The OLED chip according to claim 1, wherein the substrate has a thickness of 200 μm to 700 μm.

10. The OLED chip according to claim 1, wherein the substrate has a thickness of 200 μm to 408 μm.

11. The OLED chip according to claim 1, wherein the substrate has a thickness of 378 μm to 408 μm.

12. Multiple OLED chips, each having sides parallel to the longitudinal direction and sides parallel to the short direction, are arranged on the head substrate in the longitudinal direction. An exposure head in which at least one of the OLED chips is the OLED chip described in claim 1.

13. The exposure head according to claim 12, wherein, of the plurality of OLED chips, two OLED chips adjacent in the longitudinal direction are offset in the short direction.

14. A head substrate on which multiple OLED chips, each having sides parallel to the longitudinal direction and sides parallel to the short direction, are arranged in the longitudinal direction, A lens array positioned opposite the head substrate, The housing holds it, An exposure head in which at least one of the OLED chips is the OLED chip described in claim 1.

15. The exposure head according to claim 14, wherein the OLED chip is arranged such that the second electrode faces the lens array.

16. Photosensitive drum and An exposure head is positioned opposite the photosensitive drum and exposes the photosensitive drum to form a latent image on the photosensitive drum, A developing means for developing the latent image formed on the photosensitive drum using toner, It has, An image forming apparatus wherein the exposure head is the exposure head described in any one of claims 12 to 15.

17. A method for manufacturing an OLED chip according to any one of claims 1 to 11, A step of placing a deposition mask having multiple openings and a substrate on which the first electrode, wiring, and organic layer are arranged facing each other, A step of aligning the substrate and the deposition mask, A method for manufacturing an OLED chip, comprising the step of forming the second electrode by depositing a deposition material onto the substrate through the opening of the deposition mask.

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