Patent Grant
8648527
1. Field of the Invention
The present invention relates to a display apparatus including an organic electroluminescence (EL) device, and more particularly, to a full-color display apparatus in which one pixel includes multiple subpixels having different emission colors.
2. Description of the Related Art
In recent years, organic light-emitting devices that emit light spontaneously with a low drive voltage of about several volts are drawing attention. The organic electroluminescence (EL) device utilizes its excellent features such as surface emitting characteristics, light weight, and visibility and is being put into practical use as a light-emitting apparatus of a thin display, a lighting equipment, a head-mounted display, or a light source for a printhead of an electrophotographic printer.
The organic EL device has structure in which an emission layer made of an organic material and multiple layers made of organic materials having separated functions are sandwiched between an anode and a cathode, and an electrode on at least one light exit side is transparent. Due to this stack structure, light traveling in a direction at a critical angle or larger in each interface determined by a refractive index of the emission layer, a medium on the light exit side, and a refractive index of air into which light is finally released is totally reflected to be confined as propagating light in the device. The propagating light is absorbed by organic compound layers and metal electrodes in the device and is not extracted out of the device, with the result that light extraction efficiency is lowered.
For improving the light extraction efficiency, there have been proposed a number of methods of changing a traveling direction of light to break the total reflection condition, such as a method of providing fine uneven structure or lens structure on the surface on the light exit side so as to extract the propagating light out of the device. In particular, as a method having high improvement effects, there has been proposed a method of providing a transparent layer, the refractive index of which is equal to or higher than that of an emission layer, adjacently to a light exit side of a transparent electrode, and further providing a region for causing disturbance in reflection/scattering angles of light on the light exit side of the transparent layer or in the transparent layer (Japanese Patent Application Laid-Open No. 2004-296429).
According to the above-mentioned method, based on the classical Snell's law, propagating light in the emission layer which occupies about 80% of the light emitted by the emission layer is pulled in a high-refractive-index transparent layer whose refractive index is higher than that of the emission layer to be converted into propagating light in the transparent layer. The propagating light thus obtained is extracted out of the device through the region for causing disturbance in reflection/scattering angles of light on the surface of the transparent layer or in the transparent layer.
However, when the method of causing light to propagate through the high-refractive-index transparent layer is applied to a display apparatus such as a display, a peculiar problem occurs. Light which is guided to the high-refractive-index transparent layer and is finally output to the air through the region for causing disturbance in reflection/scattering angles of light includes light traveling at an angle equal to or higher than a critical angle, which is originally supposed to be totally reflected. This light is recognized as light emitted from a position different from an actual light-emitting point due to parallax caused by the thickness of the high-refractive-index transparent layer, and hence, there arises a problem of blur in a displayed image. In order to solve this problem, there has been proposed a method of adjusting the thickness of a substrate (although not the high-refractive-index transparent layer), through which light propagates, to a predetermined proportion or less of a pixel size (Japanese Patent Application Laid-Open No. 2005-322490).
Further, when the light guided to the high-refractive-index transparent layer enters the region for causing disturbance in reflection/scattering angles, the light is not necessarily extracted to an air side through one incidence. Light whose traveling direction has been changed by the region for causing disturbance in reflection/scattering angles is also totally reflected again to propagate through the high-refractive-index transparent layer in the case where the light travels at an angle equal to or larger than a critical angle in an interface between the high-refractive-index transparent layer and the air. Consequently, the light propagates laterally through the high-refractive-index transparent layer and is eventually output to the air side at a position away from the light-emitting point at which the total reflection condition has been broken. Therefore, there still arises a problem of blur in a displayed image. In particular, as the refractive index of the transparent layer is higher, the amount of high-angle component light is larger, and hence, the number of times at which the light enters the region for causing disturbance in reflection/scattering angles decreases, and the waveguide length in the lateral direction up to the point where the light is extracted to the air side increases, which renders the problem more serious.
It is an object of the present invention to provide a display apparatus using an organic electroluminescence (EL) device which is capable of efficiently extracting, out of the device, propagating light which propagates through a transparent layer having a refractive index higher than that of an organic compound layer, to thereby reduce blur in a display image.
That is, according to an exemplary embodiment of the present invention, there is provided a display apparatus, including multiple pixels each including multiple subpixels having different emission colors,
each of the multiple subpixels including an organic electroluminescence device which includes:
in which the display apparatus further includes a transparent layer having a refractive index higher than a refractive index of the organic compound layer, the transparent layer being disposed on a light exit side of the organic electroluminescence device,
in which the display apparatus further includes a light extraction structure provided on the transparent layer and an outer side of each of the multiple subpixels, and
in which the display apparatus further includes a light absorbing member disposed in a region between pixels adjacent to each other, and the light absorbing member is not exposed in a region between subpixels adjacent to each other within each of the multiple pixels.
According to the present invention, the display apparatus in which blur in a display image is reduced while light extraction efficiency is enhanced can be provided.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
A display apparatus of the present invention includes multiple pixels each including multiple subpixels having different emission colors, and each subpixel includes an organic electroluminescence (EL) device. The organic EL device includes a first electrode, multiple organic compound layers including an emission layer having a light-emitting region provided on the first electrode, and a second electrode. The organic EL device emits light through use of energy generated by the recombination of holes and electrons which are injected into the organic compound layers by application of a voltage across the first and second electrodes. One of the first electrode and the second electrode is a reflective electrode, and the other thereof is a transparent electrode. Further, one of the first electrode and the second electrode is an anode and the other thereof is a cathode. In the display apparatus of the present invention, the reflective electrode is formed as the first electrode on a support substrate, and emitted light is extracted from the transparent electrode side. In the display apparatus of the present invention, in order to effectively extract light emitted in the organic EL device outside, a high-refractive-index transparent layer having a refractive index higher than those of the organic compound layers is provided adjacently to the transparent electrode. Further, a light extraction structure for extracting the light is disposed adjacently to the high-refractive-index transparent layer. This configuration enables light from the emission layer to reach the light extraction structure without being totally reflected, and to be effectively extracted outside.
According to the present invention, in order to solve a problem of blur on a display, a visible light absorbing member is arranged in a region between pixels adjacent to each other. Thus, blur in a display image caused by color mixing in an inter-pixel region can be suppressed.
Hereinafter, the present invention is described by way of embodiments.
In the display apparatus of the present invention, as illustrated in
In the display apparatus of the present invention, a light-emitting region of each of the subpixels 1, 2, and is determined by an aperture area of a patterned reflective electrode 9 formed on a support substrate 8 (described later) side. In this case, cross-sectional structure of a site indicated by line 2-2 of
Further, in the configuration of
The subpixels 1, 2, and 3 are formed of organic EL devices having respective emission colors. In
By adjusting the film thickness between a light-emitting position of the emission layer 17 and a reflective surface of the reflective electrode 9 of the organic compound layer 10, a light radiation distribution in the emission layer 17 can be controlled. In a display apparatus, by setting the film thickness of each organic compound layer so that the luminance becomes high particularly in the front direction, an emission color is also controlled by optical interference, and light is radiated in the front direction more efficiently. Specifically, by adjusting the optical distance from the light-emitting position of the emission layer 17 to an interface between the transparent electrode 14 and the reflective electrode 9 to be n/4 (n=1, 3, 5, . . . ) of an emission wavelength, front luminance in the light extraction direction from the emission layer 17 can be further enhanced.
In order to enhance the light extraction efficiency, it is preferred that the reflectivity of the reflective electrode 9 be higher. For example, as a material for the reflective electrode 9, a silver (Ag) electrode is more preferred than an aluminum (Al) electrode. As means for further enhancing the reflectivity, a procedure for stacking layers having different refractive indices as in a dielectric multi-layered film mirror may be used.
In the example of
Further, a translucent electrode may be used in place of the transparent electrode 12 of the second electrode. In this case, the reflectivity of the second electrode increases, with the result that the characteristics as an optical resonator are exhibited. However, a high-angle radiation optical component from the emission layer 17 is generated to some degree. Therefore, it may also be effective to use the translucent electrode even though an increase in the light extraction efficiency through use of the translucent electrode is smaller than that obtained by using the transparent electrode 12. This means that the effect does not particularly depend on whether or not the second electrode is transparent.
The high-refractive-index transparent layer 13 may be used as a barrier layer against the intrusion of gas such as water vapor or oxygen. In order for the high-refractive-index transparent layer 13 to function as a barrier layer, the film thickness thereof may be about several μm, although it depends on a material to be used and is within a range of 0.5 μm or more and 6.0 μm or less. The preferred film thickness also depends on the size of the light extraction structure 6, and hence, the film thickness does not need to be defined in the present invention. It is not preferred that the film thickness of the high-refractive-index transparent layer 13 be larger than 6.0 μm, because light easily propagates for a long distance in the high-refractive-index transparent layer 13, and the light is easily extracted from the light extraction structure 6 on an adjacent pixel 4. The film thickness of the high-refractive-index transparent layer 13 is more preferably 0.5 μm or more and 10.0 μm or less from a viewpoint of the enhancement of the light extraction efficiency.
Although the refractive indices of the organic compound layers 10 and 11, and an organic compound layer including a red emission layer vary depending on the material, the refractive indices thereof are generally about 1.6 to 2.0 in a blue light-emitting region, about 1.5 to 1.9 in a green light-emitting region, and about 1.5 to 1.8 in a red light-emitting region. Thus, the high-refractive-index transparent layer 13 only needs to have a refractive index at least higher than those of the organic compound layers 10 and 11, and the organic compound layer including the red emission layer used in the organic EL devices in the respective blue, green, and red light-emitting regions.
Further, as a material for the high-refractive-index transparent layer 13, titanium oxide, zirconium oxide, and zinc oxide can be used. However, it is difficult to process those materials. In the present invention, it is preferred that the high-refractive-index transparent layer 13 be formed of a silicon nitride (SiNx) film or the like. No particular limitation is imposed on the element composition and element compositional ratio of the silicon nitride (SiNx) film, and other elements may be mixed with nitrogen and silicon as main components. As a film formation process for obtaining the silicon nitride film, chemical vapor deposition (CVD) is used. Although the optical constant of the silicon nitride film also varies depending on the film formation conditions such as a substrate temperature and a film formation speed, the silicon nitride film only needs to be a transparent layer having a refractive index higher than those of the organic compound layers 10 and 11, and the organic compound layer including the red emission layer in the present invention. The light transmittance of the high-refractive-index transparent layer 13 is preferably 85% or more, more preferably 90% or more in a visible light region.
It is preferred that the light extraction structure 6 according to the present invention be formed by directly processing the high-refractive-index transparent layer 13, and the difference in refractive index between the high-refractive-index transparent layer 13 and the light extraction structure 6 be eliminated.
The light extraction structure 6 has a shape protruding at least in a light extraction direction, and a cross-sectional shape thereof may be a cone, a polygon, or a combination thereof. When such a structure is present, in the case where light of a high-angle radiation component, which cannot be extracted from a pixel, enters, the light at an arbitrary angle can be variously intensified by varying a light angle through use of internal reflection. Simultaneously, the light extraction efficiency is also enhanced.
In particular, the light extraction structure 6 having a cross-section in the shape of an isosceles triangle with an apex angle of 120° to 135° can effectively enhance the light extraction efficiency of front luminance. In the present invention, the light extraction structure 6 in which two base angles are about 25° can further enhance the front luminance, and hence, it is preferred to apply the present invention to a display. Accordingly, the light extraction efficiency of the organic EL device, which is generally considered to be about 20%, is enhanced remarkably. The light extraction structure 6 may be designed in such a manner that multiple conical structures surround the outer circumference of each light-emitting region (subpixel). Further, it is desired that the ring-shaped light extraction structure 6 (in which conical structures are linked in a loop shape) be arranged so as to surround the outer circumference of each subpixel in the case where the subpixels 1, 2, and 3 have a circular shape.
No particular limitation is imposed on a method of producing the light extraction structure 6. For example, a resist pattern is formed on a film of SiNx or the like by photolithography, and after that, the resist pattern is subjected to dry etching to form intended structure. Alternatively, an intended mold pattern is transferred onto SiNx by nanoimprinting, and after that, SiNx is processed by dry etching.
As in
On the other hand, emission colors from the subpixels, which are separately controlled for gradation, are to be mixed from the light extraction structure 6 provided on the inter-pixel region 21. For example, color mixing of a red subpixel 3 and a blue subpixel 1 which are included in the different pixels 4 and are adjacent to each other with the inter-pixel region 21 interposed therebetween ends up becoming additive color mixing which is not intended, because the gradation control of each subpixel is not matched with an emission color intended to be extracted. Thus, light of the unintended additive color mixing is extracted.
Here, a deviation ellipse of MacAdam is considered as an example. A green color is not sensitive to chromaticity deviation, compared with red and blue colors, and a blue color is very sensitive to chromaticity deviation. Thus, blur in a display image is described by way of an example of the blue subpixel 1 having a blue emission color in the configuration of
In an aperture layout of pixels in a general display apparatus, the arrangement of pixels at an equal pitch is mainstream and an aperture ratio is generally at most about 50%, and hence, the area occupied by the inter-pixel region 21 is large. Thus, for example, unintended color mixing from a blue region, occurring in the inter-pixel region 21, forms a region having different chromaticity, which causes blur in a display image. In order to prevent blur, the present invention has a feature in that the visible light absorbing member 5 is arranged as illustrated in
In contrast, it is preferred that the subpixels be in contact with each other through the intermediation of the light extraction structures 6 on a pixel basis as illustrated in
The aperture shape of the subpixels 1, 2, and 3 is not limited to a circular shape and may be a rectangular shape as illustrated in
Regarding the width of the inter-pixel region 21, that is, the distance between the pixels 4 adjacent to each other, the propagation distance of light needs to be considered. The propagation distance of light is defined as the distance between a light-emitting point and a point where the intensity of light at the light-emitting point becomes a half. The propagation distance of light is related to the film thickness and absorptance of the high-refractive-index transparent layer 13, an emission color, and the like. In the present invention, for the above-mentioned reason, the effect of solving a problem of blur by the visible light absorbing member 5 does not depend on an emission color. However, the width of the inter-pixel region 21 in which the visible light absorbing member 5 is arranged is at least a width which can separate the light extraction structures 6 from each other. It is preferred that the width of the inter-pixel region 21 in which the visible light absorbing member 5 be arranged is larger than that of the light extraction structure 6. Further, in
As the visible light absorbing member 5, it is preferred to use a photosensitive black resist. Further, by irradiating the visible light absorbing member 5 with desired light, heating the visible light absorbing member 5, or changing an atmosphere, the wavelength region for absorbing light may be changed to cause the visible light absorbing member 5 to absorb light of a desired color. For example, by irradiating the visible light absorbing member 5 with light to effect photopolymerization, a transparent portion may be changed to a brown color or a black color. Further, materials used for a color filter or the like may be used alone or in combination to be provided in the inter-pixel region 21 as the visible light absorbing member 5. Preferred examples of a method of providing the visible light absorbing member 5 include patterning using photolithography, and coating of an ink jet type or a nozzle jet type and patterning. Note that, in order not to inhibit light extraction, it is preferred that the visible light absorbing member 5 be provided so as not to overlap the light extraction structure 6.
The step of forming the visible light absorbing member 5 may be performed before or after the step of providing the light extraction structure 6. In the former case, for example, a patterned black resist region may be provided on the bank 7 between the subpixels formed on the support substrate 8 of
By providing the visible light absorbing member 5 in the inter-pixel region 21 as described above, blur between pixels can be eliminated effectively.
Further, on the other hand, by using the visible light absorbing member 5 made of a black resist, the effect of reducing reflection of outside light can also be expected.
Note that, there is no particular limitation on a circuit and wiring for driving the display apparatus of the present invention, and the arrangement and characteristics of TFTs to be used, and the circuit, wiring, and TFTs may be designed as desired so as to obtain required performance.
Further, in the display apparatus of the present invention, the light extraction structure 6 is used for extracting light to be confined in the device outside, and the light extraction structure 6 may be further sealed with sealing glass such as a glass cap or a sheet glass. The sealing glass may be provided with a color filter for improving chromaticity and a circularly polarizing plate for reducing the reflection of outside light.
Hereinafter, the present invention is described by way of specific examples. In the examples, although a ring-shaped light extraction structure having cross-sectional structure in the shape of an isosceles triangle is used as an example, the present invention is not limited to this example.
As Example 1, a display apparatus, in which an organic EL device had cross-sectional structure of
In this example, first, a TFT drive circuit (not shown) made of low-temperature polysilicon was formed on a glass substrate, and a flattening film (not shown) made of an acrylic resin was formed on the TFT drive circuit to obtain a support substrate 8. Next, as a reflective electrode 9, an Ag alloy film was formed on the support substrate 8 by sputtering so as to have a film thickness of about 150 nm. The reflective electrode 9 made of an Ag alloy was a highly reflective film having a spectral reflectivity of 80% or more in a visible light wavelength region (λ=380 nm to 780 nm). Further, a film of indium tin oxide (ITO) was formed as a transparent electrode 14 by sputtering. After that, a polyimide-based resin was spin-coated as the bank 7, and apertures were respectively provided in intended subpixels by photolithography. The diameter of the aperture of each of the subpixels was 27 μm, and all of the subpixels were arranged at equal intervals of 60 μm.
After that, respective organic compound layers 10 and 11, and an organic compound layer including a red emission layer were successively formed and stacked by vacuum deposition. In the display apparatus of this example, for each of the subpixels 1, 2, and 3, the film thickness of a hole transport layer 16 was changed so that the optical film thickness from an emission layer of each color to the reflective electrode 9 corresponded to ¾ of each emission color wavelength. Regarding a blue color, a fluorescent material was used as a light-emitting dopant in the emission layer, and regarding green and red colors, a phosphorescent material, which was expected to exhibit higher internal quantum efficiency, was used as the light-emitting dopant in the emission layer. The refractive index of a layer having the highest refractive index in the organic compound layers of each subpixel was 1.86 in the blue subpixel, 1.80 in the green subpixel, and 1.78 in the red subpixel.
Next, a film of indium zinc oxide (IZO) was formed as a transparent electrode 12 by sputtering. Then, a silicon nitride (SiN) film was formed so as to have a thickness of 4 μm by CVD. The refractive index of the SiN film was 1.89 in a wavelength of 450 nm (blue color region), 1.88 in a wavelength of 520 nm (green color region), and 1.86 in a wavelength of 620 nm (red color region). Thus, the refractive index in any subpixel was higher than that of the organic compound layer.
Hexamethyldisilazane was spin-coated on the SiN film to modify the surface, and thereafter, a photoresist (AZ1500) was spin-coated to obtain a film having a film thickness of about 2.5 μm. Then, the photoresist was developed with a developer (AZ312MIF) to obtain a resist pattern. Post-baking was conducted on the developed photoresist at 120° C. for 3 minutes to reflow a resist shape. The SiN film was etched together with the resist pattern by dry etching using carbon tetrafluoride and oxygen, to thereby process the SiN film into the ring-shaped light extraction structure so as to surround each subpixel. At this time, the film thickness of the high-refractive-index transparent layer 13 having a refractive index higher than those of the organic compound layers 10 and 11, and the organic compound layer including the red emission layer was 1 μm. Further, the height of the ring-shaped light extraction structure 6 was 2.9 μm, the width thereof was 10 μm, the cross-sectional shape thereof was a triangle having an apex angle of 120° and an inside base angle of 30° and an outside base angle of 30°.
Next, a photosensitive black resist was spin-coated onto the SiN film which was directly processed as the visible light absorbing member 5 so as to have a film thickness of 1 μm. Then, as illustrated in
The width of the inter-subpixel region 20 (visible light absorbing member 5) was 13 μm. Thus, there were no sites having a width smaller than that of a bottom portion of the ring-shaped light extraction structure 6 in the inter-pixel region 21 (visible light absorbing member 5).
In order to check the degree of blur in the display apparatus thus produced, a human image was displayed against the background of the blue sky, and an emission color of a contour portion in a white site such as the skin was checked. In the contour portion of the human in the display image obtained in this example, no change in emission color derived from blur was found.
Further, in this example, the light extraction efficiency was enhanced about twice and the front luminance was enhanced about three times, compared with the case where no ring-shaped extraction structure 6 was provided. An increase in the emission intensity was found mainly in a front direction in which light was emitted.
A display apparatus having the same configuration as that of Example 1 was produced by a production process similar to that of Example 1 with the exception that the visible light absorbing member 5 was not formed in the inter-subpixel region 20. When the degree of blur in the obtained display apparatus was checked in the same way as in Example 1, a change in emission color derived from blur was found in a contour portion of a human in a display image, and a bluish-violet blur was visually recognized in the contour portion. On the other hand, the light extraction efficiency was enhanced about 2.3 times and the front luminance was enhanced about 3.1 times, compared with the case where no ring-shaped extraction structure 6 was provided. Similarly to Example 1, an increase in luminance was found at all the viewing angles.
A display apparatus as illustrated in
When the degree of blur in the obtained display apparatus was checked in the same way as in Example 1, no change in emission color derived from blur was found in a contour portion of a human in a display image.
The light extraction efficiency in this example was enhanced about 2.3 times and the front luminance was enhanced about 3.1 times, compared with the case where no ring-shaped extraction structure 6 was provided. An increase in luminance was found toward the front direction.
A display apparatus having the same configuration as that of Example 1 was produced by a production method similar to that of Example 1 with the exception that the pitch of the subpixels was set to be smaller on a pixel basis so as to bring the ring-shaped light extraction structures 6 of the respective subpixels included in the pixel 4 into contact with each other, and the visible light absorbing member 5 was provided only in the inter-pixel region 21. The width of the inter-pixel region 21 (visible light absorbing member 5) was 26.0 μm at the minimum in directions of an axis 1, an axis 2, and an axis 3, and there were no sites having a width smaller than that of a base portion of the ring-shaped light extraction structure in the inter-pixel region 21.
When the degree of blur in the obtained display apparatus was checked in the same way as in Example 1, no change in emission color derived from blur was found in a contour portion of a human in a display image.
The light extraction efficiency in this example was enhanced about 2 times and the front luminance was enhanced about 3 times, compared with the case where no ring-shaped extraction structure 6 was provided. An increase in luminance was found toward the front direction.
A display apparatus having the same configuration as that of Example 1 was produced by a production method similar to that of Example 1 with the exception that the light extraction structures 6 of the respective subpixels having a rectangular shape included in the pixel 4 were brought into contact with each other as illustrated in
When the degree of blur in the obtained display apparatus was checked in the same way as in Example 1, no change in emission color derived from blur was found in a contour portion of a human in a display image.
The light extraction efficiency in this example was enhanced about 2 times and the front luminance was enhanced about 3 times, compared with the case where no ring-shaped extraction structure 6 was provided. An increase in luminance was found toward the front direction.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2011-212118, filed Sep. 28, 2011, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
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