1. Field of the Invention
The present invention relates to an electroluminescence display apparatus comprising an electroluminescence (hereinafter also referred to as EL) element and a thin film transistor (hereinafter referred to as TFT) element.
2. Description of the Related Art
In recent years, the EL display apparatus employing EL elements has attracted attention as being the display apparatus to replace CRTs and LCDs.
Furthermore, research and development have been conducted on display apparatuses having TFTs as the switching elements to drive the EL elements.
FIG. 1 is a top plan view showing a display pixel and periphery in an organic EL display apparatus of the related art, FIG. 2A shows a cross-sectional view along line Axe2x80x94A of FIG. 1, and FIG. 2B shows a cross-sectional view along line Bxe2x80x94B of FIG. 1.
As shown in FIG. 1, a display pixel is formed in a region surrounded by gate signal lines 51 and drain signal lines 52. A first TFT 30 is provided in proximity to an intersection of both signal lines, and a source 13sof the TFT 30 serves as a capacitance electrode 55, which forms a capacitor with a holding capacitance electrode line 54 to be described later, and is connected to a gate 41 of a second TFT 40. A source 43s of the second TFT 40 is connected to an anode 61 of an organic EL element 60, and a drain 43d at the other end is connected to a power source line 53, which is a current source that is supplied to the organic EL element 60.
Furthermore, in the proximity of the TFTs, the holding capacitance electrode line 54 is positioned in parallel with the gate signal lines 51. The holding capacitance electrode line 54 is formed from a material such as chromium, and the capacitance electrode 55 is connected to the source 13s of the TFT 30. The electric charge is stored between the holding capacitance electrode line 54 and the capacitance electrode 55, via a gate insulating film 12, thus forming a capacitor. This holding capacitor is provided to hold a voltage that is applied to the gate electrode 41 of the second TFT 40.
As shown in FIGS. 2A and 2B, the organic EL display apparatus is formed by laminating in sequence the TFT and the organic EL element onto a substrate 10, such as a substrate formed from glass or synthetic resin, a conductive substrate, or a semiconductor substrate. However, when a conductive substrate or a semiconductor substrate is used for the substrate 10, an insulating film is formed, such as from SiO2 or SiN, on which the TFT and organic EL display element are formed.
The first TFT 30, which is a switching TFT, will be described first.
As shown in FIG. 2A, gate signal lines 51 also serving as gate electrodes 11 and formed from a refractory metal, such as chromium or molybdenum, and the holding capacitance electrode 54 are formed on the insulating substrate 10, such as of quartz glass or no-alkali glass. Next, the gate insulating film 12 and an active layer 13, which is formed from a poly-silicon (p-Si) film, are formed in sequence.
On the entire surface of the gate insulating film 12, the active layer 13 and stopper insulating films 14, is formed an interlayer insulating film 15 in which a SiO2 film, a SiN film, and a SiO2 film are laminated in sequence. A drain electrode 16, which is filled with a metal, such as A1, is provided at a contact hole formed at a position corresponding to a drain 13d of the interlayer insulating film 15. Furthermore, a planarization insulating film 17, which is formed from an organic resin, is formed on the entire surface of the substrate so as to planarize the surface.
The second TFT 40, which is a TFT for driving the organic EL element, will be described next.
As shown in FIG. 2B, the gate electrodes 41, which is formed from a refractory metal, such as Cr or Mo, the gate insulating film 12, and the active layer 43 which is formed from a p-Si film, are formed in sequence on the insulating substrate 10 which is made of quartz glass or no-alkali glass. In the active layer 43 are provided channels 43c, and on both sides of the channels 43c, the source 43s and the drain 43d. On the entire surface of the gate insulating film 12 and the active layer 43 is formed the interlayer insulating film 15 in which a SiO2 film, a SiN film, and a SiO2 film are laminated in sequence. A power source line 53 connected to a power source (not shown) and filled with a metal, such as A1, is provided at a contact hole formed to correspond to the drain 43d. Furthermore, the planarization insulating film 17, which is formed from an organic resin or the like, is formed on the entire surface so as to planarize the surface. A contact hole is formed at a position corresponding to the source 43s of the planarization insulating film 17 and the interlayer insulating film 15, and a transparent electrode, namely, the anode 61 of the organic EL element, which is formed from ITO (indium tin oxide) and contacting the source 43s via this contact hole, is provided on the planarization insulating film 17.
The organic EL element 60, provided at each pixel so as to enable light emission at each pixel, has a structure in which are formed in sequence the anode 61 made of a transparent electrode, such as ITO, a hole transport layer 62 having a first hole transport layer formed such as from MTDATA (4,4xe2x80x2,4xe2x80x3-tris(3-methylphenylphenylamino)triphenylamine) and a second hole transport layer formed such as from TPD (N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-di(3-methylphenyl)-1,1xe2x80x2-biphenyl-4,4xe2x80x2-diamine), an emissive layer 63 formed such as from Bebq2 (bis(10-hydroxybenzo[h]quinolinato) beryllium) including a Quinacridon derivative, an electron transport layer 64 formed such as from Bebq2, and a cathode 66 formed from an alloy, such as magnesium-indium. The hole transport layer 62, the emissive layer 63, and the electron layer 64 form an emissive element layer 65.
In this organic EL element, holes injected from the anode and electrons injected from the cathode recombine, and organic molecules forming the emissive layer are excited and yield exitons. Light is released from the emissive layer in the process where the exitons undergo radiation deactivation, and this light is released to the outside from the transparent anode via the transparent insulating substrate.
However, the emission efficiency of the emissive layer for emitting light of various colors differs with each color.
However, in the EL display apparatus of the related art shown in FIG. 3, emissive regions 1B, 1R, and 1G for the display pixel of the respective color are arranged in a matrix configuration at every intersection of a plurality of the gate signal lines 51 and a plurality of the drain signal lines 53 and all have identical emissive areas in size. Thus, in order to obtain the same luminance at the display pixels having a low emission efficiency, a current larger than that supplied to the other display pixels having a high emission efficiency must be supplied. This causes the life of those display pixels having a low emission efficiency, in particular, to shorten, and also possibly causes the life of the EL display apparatus to shorten.
Furthermore, when the emissive areas of the display pixels of various colors, each having a different emission efficiency, are set to be identical, color balance (white balance) is difficult to achieve, and higher currents must be supplied to certain emissive layers to achieve such a balance. Thus, a drawback is that deterioration occurs at the EL elements in the display pixels supplied with the higher currents.
It is therefore an object of the present invention, which takes into consideration the above-mentioned disadvantage of the related art, to provide a display apparatus having emissive elements, such as EL elements, in which the control of white balance is simple and the service life is long.
In order to achieve the above-mentioned object, the present invention is characterized by a color display device, in which a display pixel having an emissive element is provided for every color, wherein the emissive area of the display pixel of any one color, among the display pixels of various colors, is different in size from the emissive area of the display pixel of another color.
In another aspect of the present invention in the above-mentioned color display device, the emissive area of the display pixel is set in accordance with the emission efficiency of the emissive element provided at the display pixel.
In another aspect of the present invention, the emissive area of a display pixel of the various colors is respectively set larger for lower emission efficiency of the emissive element provided at the display pixel.
In another aspect of the present invention in the above-mentioned color display device, the emissive area of a display pixel of one color is set larger than the emissive area of a display pixel of another color having emissive element with emission efficiency higher than the emissive element provided at the display pixel of the one color.
In another aspect of the present invention, the emissive area of the display pixel having the emissive element of a color with the highest emission efficiency, among emissive elements respectively emitting different colors of light for color display, is set smaller than the emissive area of the display pixel having the emissive element of another color.
In another aspect of the present invention in the above-mentioned color display device, the emissive area of a display pixel of one color is set smaller than the emissive area of a display pixel of another color having emissive element with emission efficiency lower than the emissive element provided at the display pixel of the one color.
In another aspect of the present invention in the above-mentioned color display device, the emissive area of the display pixel having the emissive element of a color with the lowest emission efficiency, among emissive elements respectively emitting different colors of light for color display, is set larger than the emissive area of the display pixel having the emissive element of another color.
In another aspect of the present invention in the above-mentioned color display device, the emissive element is an electroluminescence element having an emissive layer between a first electrode and a second electrode.
In the present invention in the color display apparatus in which each display pixel comprises an emissive element, the emissive area of the display pixel corresponds to the emissive area of the emissive element. By setting the emissive area of the display pixel, namely, the emissive area of the emissive element, in accordance with the emission efficiency of the emissive element as in the foregoing, and by supplying, for example, the same power to the emissive elements of colors having different emission efficiencies, it becomes possible to have the same emission luminance at the various display pixels. In other words, in order to obtain a target display luminance for the respective colors, it is not necessary to supply only the emissive element of a particular color, having low emission efficiency, with a power higher than the other elements. Therefore, even for an emissive element for which deterioration accelerates as the amount of the supplied power increases, it is possible to prevent the deterioration from accelerating when a load is selectively placed on the emissive element having low emission efficiency and extend the life of the display device.
In another aspect of the present invention as in one of the above-mentioned color display devices, the emissive element is an organic electroluminescence element comprising the emissive layer using an organic compound between first electrode and second electrode.
In this sort of organic EL element, in particular, when used in a color display device, where the emission efficiency differs according to the type of organic compound used as the emissive material in the emissive layer, and a different emissive material is to be used for every color, the above-mentioned problem of deterioration of the organic EL element having a low emission efficiency is liable to occur. However, this type of problem can be prevented according to the present invention.
In another aspect of the present invention, in a color display device in which a display pixel having an emissive element is provided for every color, the emissive area of the display pixel is set for every color in accordance with the emission efficiency of the emissive element provided at the display pixel, the chromaticity of each color emitted by respective emissive element, and the chromaticity of target display white of the display device.
In another aspect of the present invention, the emissive area of the display pixel of any one color, among the display pixel of various colors, is different in size from the emissive area of the display pixel of another color.
In another aspect of the present invention in a color display device having display pixel for red, for green, and for blue, respectively having emissive element, the emissive area of said display pixel for red, for green, and for blue is set on the basis of the emission efficiency of the emissive element of each display pixel, and a luminance ratio of red to green to blue in accordance with each chromaticity of red, green, and blue emitted by respective emissive element of the display pixel, and with the chromaticity of target display white of the display device.
In another aspect of the present invention in the above-mentioned color display device, the emissive area of the display pixel of any one color among the display pixel for red, for green, and for blue is different in size from the emissive area of the display pixel of another color.
In the color display device having emissive elements, the target white that is set can be represented, for example, by the addition of the lights of R, G, and B. In this sort of device, by setting the emissive area of each display pixel in accordance with the emission efficiency of the emissive element of each color R, G, and B as described above, with the chromaticity of the R, G, and B emitted by the respective emissive element, and with the chromaticity of target display white, for example, the display of a target white is simplified with the supply of the same amount of power to each emissive element of R, G, and B. In other words, the white balance is controlled by the emissive area of each emissive element so that the white balance, while these emissive elements are driven, becomes extremely easy to control. Furthermore, since the emission efficiency of the element is taken into consideration in the emissive area of each emissive element, it is possible to prevent the emissive element having low emission efficiency from deteriorating faster than the element having high emission efficiency.
In another aspect of the present invention in the above-mentioned color display device, the emissive area of the display pixel is set by smaller one of direct contact areas between an emissive element layer including the emissive layer of the organic electroluminescence element and the first electrode, and between the emissive element layer and the second electrode.
In another aspect of the present invention in the above-mentioned color display device, the emissive element is an organic electroluminescence element composed by forming in sequence a first electrode, an emissive element layer including at least an emissive layer using an organic compound, and a second electrode, the element is separated by an insulating film between layers of the first electrode and the emissive element layer in the proximity of an edge of the first electrode, and the emissive area of each display pixel in the organic electroluminescence element of the display pixel is set in accordance with the area of the insulating film covering the edge of the first electrode.
In another aspect of the present invention in the above-mentioned color display device, the insulating film, at the edge of the first electrode, is decreased thickness toward the center of the first electrode.
When the organic EL element is used as the emissive element in this manner, the organic compound is used for the emissive layer so that there is a wide selection range of materials and variation of emission colors (chromaticity and color purity), which are extremely advantageous in the color display apparatus and so forth.
On the other hand, along with the difference in emission efficiency due to the organic compound that is used in the emissive layer, the chromaticity (for example, the chromaticity of red, green, and blue) of the emitted light differs. Therefore, when the emissive area of the organic EL element is adjusted in accordance with the emission efficiency of the element as described above, a large load can be prevented from being imposed on the organic EL element having low emission efficiency. Furthermore, the emissive area of the organic EL element can be easily set by changing the electrode area or direct contact area between the emissive element layer and the first or second electrode.
Furthermore, covering the proximity of the edge of the first electrode with the insulating film as described above enables the emissive area of the organic EL element to be set to a desired area also by adjusting the contact area of the first electrode and the emissive element layer, which includes the emissive layer. In this case, when the thickness of the insulating film in the proximity of the edge of the first electrode is made thinner toward the center of the electrode, it is possible to prevent, at the emissive element layer that is formed on the first electrode and the insulating film, a disconnection from occurring at the proximity of the boundary between the first electrode and the insulating film. Furthermore, using the planarization film for the insulating film makes it possible to reliably prevent a disconnection at the second electrode that is formed on the insulating film and the emissive element layer.
In another aspect of the present invention in the above-mentioned color display device, the display pixel with the smallest emissive area is the display pixel comprising the emissive element for emitting green light, among colors red, green, and blue.
In another aspect of the present invention in the above-mentioned color display device, the display pixel with the largest emission area is the display pixel comprising the emissive element for emitting either red or blue light, among colors red, green, and blue, or the display pixel comprising the emissive element for emitting red light and the display pixel comprising the emissive element for emitting blue light.