JP2010015716A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device for obtaining excellent image quality by suppressing chromaticity deviation in the plane of the display device. <P>SOLUTION: In the display device in which a plurality of pixels each having at least a single color light-emitting element and a color filter 10 provided on the upper surface thereof are arranged, a transmission band of transmission spectrum in the color filter 10 is made to be narrower as a difference between the peak wavelength of emission spectrum and the peak wavelength of the transmission spectrum in the color filter 10 becomes larger in at least one set of identical color-emitting elements out of a plurality of light-emitting elements. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a display device in which a plurality of light emitting elements are arranged, and is particularly suitable for a display device using an organic compound as a light emitting element.

  In a display device in which a plurality of light emitting elements are arranged, it is a big problem that the chromaticity of the same color light emitting pixels in the surface is different. In particular, in the case of an organic EL display device using an organic EL element as a light emitting pixel, the thickness of the organic EL element is approximately the same as the wavelength of light, and therefore, chromaticity deviation is likely to occur due to the influence of interference. The main factor causing the chromaticity shift in the organic EL element is that the film thickness of the organic layer serving as the interference portion is not formed as designed.

  For such a problem, a technique for adjusting the film thickness of an organic layer to be formed by appropriately measuring the film thickness has been proposed (see Patent Document 1). In addition, a technique of a resonator structure in which a metal thin film is provided on an electrode on the light extraction side is disclosed (see Patent Document 2). In this case, since interference is positively used, color due to film thickness change is disclosed. The degree response increases.

JP 2005-322612 A JP 2003-109775 A

  In a display device, in order to suppress a chromaticity shift between a plurality of pixels in a plane, it is desirable to stabilize the process. However, in reality, there is a limit to the stabilization of the process, and the chromaticity shift between a plurality of pixels in the surface may become remarkable.

  Therefore, an object of the present invention is to provide a display device that can suppress a chromaticity shift in the surface of the display device and obtain a good image quality.

  In order to achieve the above-described object, the display device of the present invention has the following characteristics in a display device in which a plurality of pixels each having at least a single color light emitting element and a color filter provided on the upper surface thereof are arranged. ing.

  That is, in the display device of the present invention, the transmission spectrum in the color filter increases as the difference between the peak wavelength of the emission spectrum and the peak wavelength of the transmission spectrum in the color filter increases. Narrow the transmission band.

  In the display device of the present invention, in accordance with the difference between the peak wavelength of the emission spectrum and the peak wavelength of the transmission spectrum in the color filter, by appropriately setting the optical characteristics of the color filter, in-plane chromaticity shift is suppressed, Good image quality can be obtained.

  Hereinafter, embodiments of the display device of the present invention will be described.

  The display device according to the embodiment of the present invention has a configuration in which a plurality of pixels each having at least a single color light emitting element and a color filter provided on the upper surface thereof are arranged. The color filter has an appropriate configuration according to the difference between the peak wavelength of the emission spectrum and the peak wavelength of the transmission spectrum in the color filter between at least one set of the same color light emitting elements.

  That is, the larger the difference between the peak wavelength of the emission spectrum and the peak wavelength of the transmission spectrum in the color filter, the narrower the transmission band of the transmission spectrum in the color filter. Further, the larger the difference between the peak wavelength of the emission spectrum and the peak wavelength of the transmission spectrum in the color filter, the thicker the color filter. Further, the greater the difference between the peak wavelength of the emission spectrum and the peak wavelength of the transmission spectrum in the color filter, the higher the pigment concentration of the color filter.

  Here, the light emitting element can be an organic light emitting element. In this case, a metal thin film can be used for the electrode on the light extraction side. Further, an ink jet method can be used for forming the color filter.

  Next, embodiments of the display device of the present invention will be specifically described. In the following description, an organic EL display device will be described as an example of a display device to which the present invention can be applied.

  An organic light emitting element corresponding to a pixel of an organic EL element has a laminated structure in which an organic light emitting layer is sandwiched between a pair of electrodes including an anode and a cathode. In many cases, an organic layer such as an electron injection layer, an electron transport layer, a hole injection layer, and a hole transport layer is included between the electrodes in addition to the organic light emitting layer. When a driving voltage is applied between both electrodes, holes are injected from the anode and electrons are injected from the cathode. The injected holes and electrons recombine in the organic light emitting layer to emit light. In an organic EL display device in which a plurality of such organic light emitting elements are arranged, a color filter is arranged above the organic light emitting elements.

When the organic layer thickness deviates from the design value, the emission spectrum of the organic light emitting element changes due to interference. At this time, as the difference between the peak wavelength of the emission spectrum and the peak wavelength of the transmission spectrum in the color filter is larger, the chromaticity shift can be reduced by narrowing the half-value width of the transmission spectrum in the color filter. In order to narrow the transmission band of the transmission spectrum in the color filter, it is effective to increase the film thickness of the color filter and increase the pigment concentration of the color filter. The change in the light intensity due to the light absorption of the substance can be expressed as the following formula (1). The following formula (1) represents the attenuation in the substance having the initial light intensity I ₀ .

  Here, d is the distance from the surface, and the extinction coefficient k depends on the wavelength λ. From the above formula (1), it can be seen that the thicker the film thickness of the substance and the higher the consumption coefficient k, the more light is absorbed. In order to narrow the transmission band of the transmission spectrum in the color filter, it is only necessary to increase the absorption other than the desired transmitted light, so that the film thickness is increased and the pigment concentration is increased to increase the consumption coefficient k. It can be seen that is effective.

<Embodiment 1>
The display device according to Embodiment 1 of the present invention will be described below.

  FIG. 1 is a schematic cross-sectional view of an organic EL element that is a light emitting pixel.

  The organic EL display device of Embodiment 1 is a display device in which R (red), G (green), and B (blue) pixels are two-dimensionally arranged in a certain order. A light emitting pixel composed of R, G, and B organic light emitting elements has a laminated structure as shown in FIG. In addition, the organic light emitting element which comprises the organic electroluminescence display of Embodiment 1 is a top emission system which takes out light from the sealing substrate side.

  The organic EL display device of Embodiment 1 has a laminated structure as shown in FIG. That is, on the glass substrate 1, it consists of a metal reflective layer 2, a transparent conductive layer 3, a hole transport layer 4, a light emitting layer 5, an electron transport layer 6, an electron injection layer 7, a transparent electrode 8, silicon nitride (SiN), and the like. A passivation film 9, a resin layer (not shown), and a color filter 10 are provided. Here, the transparent conductive layer 3 is considered as an anode, and the transparent electrode 8 is considered as a cathode. The metal reflection layer 2 may also serve as an anode. The light emitting layer 5 is made of an organic light emitting material exhibiting an emission color corresponding to each light emitting pixel. The color filter 10 corresponds to the light emitting pixel. For example, a color filter in a blue light emitting pixel made of a blue organic EL element is a color filter that mainly transmits a wavelength in a blue band.

  Conventionally known organic EL materials can be used as the material used for each organic layer. Examples of the material of the metal reflection layer 2 include aluminum, silver, and alloys thereof, but a material having reflection characteristics can be used. The material of the transparent conductive layer 3 is preferably indium oxide such as ITO or IZO, but other materials may be used as long as the material has transparency and conductivity. Here, the metal reflective layer 2 may also serve as an electrode by being electrically connected to the transparent conductive layer 3. Regarding the film forming method, conventionally known methods can be used for both the organic material and the electrode material, and the method is not particularly limited.

  As a method for forming the organic layer, a vapor deposition method is generally used. However, when the organic layer is formed using the vapor deposition method, variations in the film thickness occur in the plane. In order to solve such a problem, there is a countermeasure method such as rotating the substrate, but it is still difficult to completely solve the problem. In the case where the organic layer is thicker toward the center, the present invention will be described using the B light emitting pixel as an example.

  FIG. 2 is an explanatory diagram showing respective emission spectra of the light emitting element at the end and the light emitting element at the center in the B light emitting pixel. FIG. 3 is an explanatory diagram showing the film thickness and spectral transmittance of the B color filter.

  As shown in FIG. 2, the peak wavelength of the emission spectrum is on the longer wavelength side due to interference because the light emitting element at the center is thicker in the organic layer. Further, as shown in FIG. 3, the transmission band of the transmission spectrum becomes narrower as the color filter film thickness increases. Table 1 below shows the chromaticity after the emission spectrum is transmitted through the color filter in the CIE color system. When the film thickness of the color filter is the same for the light emitting elements at the end portion and the central portion, as is apparent from Table 1 below, there is a difference in chromaticity of 0.008 for CIEx and 0.028 for CIEy.

  Here, as shown in FIG. 2, the peak wavelength of the emission spectrum is 465 nm for the light emitting element at the end and 475 nm for the light emitting element at the center. Since the peak wavelength of the transmission spectrum of the color filter is 450 nm, it is considered that the color filter film thickness of the light emitting element in the central portion having a large difference from the peak wavelength of the transmission spectrum is increased according to the present invention. From Table 1 below, when the film thickness of the color filter in the light emitting element at the center is doubled, the chromaticity is (0.126, 0.084), and the chromaticity difference from the light emitting element at the end is small. I understand that.

  The method for reducing the chromaticity deviation of B has been described above. However, the present invention is not limited to B, and can be similarly applied to R and G. As a method for manufacturing the color filter, a conventionally known method such as a photolithography method or an ink jet method can be used. However, in order to change the film thickness of the color filter in an arbitrary light emitting pixel, an ink jet method capable of controlling the film thickness by the amount of dropped droplets is simple in terms of process.

  Since the present invention is a technique for arranging a color filter according to the characteristics of the light emitting element, it is important to know the characteristics of the light emitting element before attaching the color filter. The chromaticity variation caused by the organic layer thickness can be predicted in advance. Predict the chromaticity of each light-emitting pixel from the in-plane organic layer film thickness distribution by using an optical film thickness measuring instrument such as spectroscopic ellipsometry during or after the organic film formation. It is possible. In addition, since the in-plane distribution of the organic layer by the film forming apparatus is often constant at all times, it is possible to grasp the distribution of the in-plane light emitting element characteristics once the display device is created in advance. .

<Embodiment 2>
Next, a display device according to Embodiment 2 of the present invention will be described.

  In Embodiment 2, an organic EL display device using a microresonator structure will be described. The organic EL display device using a microresonator structure is an organic EL display device that uses a metal thin film of about 5 to 30 nm as a cathode electrode instead of the transparent electrode 8 that is a cathode electrode. The organic EL display device using this microresonator structure has a structure that utilizes the resonance of light between the metal thin film and the metal reflective layer 2. However, when the resonator structure is used, since the resonance effect is strong, as shown in Table 2 below, the change in chromaticity with respect to the film thickness shift of the organic layer becomes large.

  For the reasons described above, in the case of an organic EL display device using a microresonator structure, the chromaticity shift between a plurality of pixels in the surface becomes remarkable, and therefore the present invention is particularly effective. In the case of a microresonator structure, the effect of the present invention will be described using R as an example.

  FIG. 4 is an explanatory diagram showing respective emission spectra of the light emitting element at the end and the light emitting element at the center in the R light emitting pixel. FIG. 5 is an explanatory diagram showing the film thickness and spectral transmittance of the R color filter. Here, it is assumed that the element at the center is thicker than the element at the end.

  As shown in FIG. 4, the light emitting element at the center has a thick organic layer, so that the peak wavelength of the emission spectrum is on the long wavelength side due to interference. Further, as shown in FIG. 5, the transmission band of the transmission spectrum becomes narrower as the color filter film thickness increases. Table 3 below shows the chromaticity after the emission spectrum is transmitted through the color filter in the CIE color system. When the film thickness of the color filter is the same for the light emitting elements at the end and the center, as shown in Table 3 below, there is a difference in chromaticity of 0.009 for CIEx and 0.009 for CIEy. However, if the thickness of the color filter at the end is doubled according to the present invention, the chromaticity is the same at the end and the center.

  By using the present invention, an in-plane chromaticity difference can be reduced, so that a high-quality image without chromaticity unevenness can be obtained. In particular, the present invention is effective in the case of an element structure that is easily affected by a film thickness deviation, such as a microresonator structure, and a cost reduction effect due to an improvement in yield can be expected. In both Embodiments 1 and 2, the in-plane chromaticity difference is reduced by changing the film thickness of the color filter. However, as described above, the same effect can be obtained by changing the pigment concentration of the color filter. It is obvious that an effect can be obtained.

  An object of the present invention is to reduce the in-plane variation by changing the optical characteristics of the color filter in the plane of the display device, and thus does not depend on the laminated structure of the organic EL elements. That is, the present invention is also effective for a bottom emission method in which light is extracted from the TFT substrate side. Regarding the light emitting layer, even when the R, G, B light emitting pixels are formed using the white light emitting layer, the usefulness of the present invention does not change.

  Hereinafter, the display device of the present invention will be described with reference to specific examples.

  As Example 1, two organic EL substrates including TFTs and a color filter substrate were bonded to produce an organic EL display device having three colors RGB shown in FIGS. 1 and 2.

  First, an organic EL substrate including a TFT will be described. A TFT drive circuit (omitted) made of low-temperature polysilicon was formed on a glass substrate 1 as a support, and a planarizing film (omitted) made of acrylic resin was formed thereon to form a substrate. On this, an aluminum alloy (AlNiPd) was formed and patterned as a metal reflective layer 2 by a sputtering method of about 100 nm, and IZO was formed and patterned as a transparent conductive layer 3 by a sputtering method by 20 nm. Further, an element isolation film (omitted) was formed from an acrylic resin to prepare a substrate with an anode. This was ultrasonically washed with isopropyl alcohol (IPA), then boiled and dried. Further, after UV / ozone cleaning, an organic compound was deposited by vacuum deposition.

  First, RGB hole transport layers 4 were formed using a shadow mask. That is, α-NPD was deposited to 60 nm as the R hole transport layer 4R. Further, an α-NPD film having a thickness of 40 nm was formed as the G hole transport layer 4G. Further, an α-NPD film having a thickness of 20 nm was formed as the B hole transport layer 4B.

  Next, as the light emitting layer 5, each of the RGB light emitting layers 5 was formed using a shadow mask. In the R light emitting layer 5R, the host Alq3 and the light emitting compound DCM [4- (dicyanomethylene) -2-methyl-6 (p-dimethylaminostyryl) -4H-pyran] were co-evaporated (weight ratio 99: 1). To form a film. The film thickness of the R light emitting layer 5R is 60 nm. In the G light emitting layer 5G, Alq3 as a host and the light emitting compound coumarin 6 were co-evaporated (weight ratio 99: 1) to form a film. The film thickness of the G light emitting layer 5G is 40 nm. In the B light-emitting layer 5B, the host Balq and the light-emitting compound Perylene were co-deposited (weight ratio 90:10) to form a film. The film thickness of the B light emitting layer 5B is 30 nm.

Next, as a common electron transport layer 6, bathophenanthroline (Bphen) is formed to a thickness of 10 nm by vacuum deposition, and as a common electron injection layer 7, Bphen and Cs ₂ CO ₃ are co-evaporated (weight ratio). 90:10) to form a film having a thickness of 40 nm.

The degree of vacuum at the time of organic layer deposition was 3 × 10 ⁻⁴ Pa.

  And it moved to the sputtering device without breaking the vacuum, and a 40-nm ITO transparent electrode was formed as the transparent electrode 8. Further, as the passivation film 9, silicon nitride oxide was formed to a thickness of 700 nm.

  The substrate formed up to the passivation film 9 was taken out from the sputtering apparatus, and an acrylic resin (not shown) having a thickness of 500 μm was formed on the passivation film 9 to obtain an organic EL substrate.

  Next, the color filter substrate will be described.

  On a glass serving as a color filter substrate, a black matrix (not shown) for light shielding between R, G, and B light-emitting pixels was formed in a lattice shape using a general photolithography method. This black matrix is not always necessary.

  Thereafter, each of the R, G, and B coloring materials is discharged into a partition wall (not shown) made of an existing material using an ink jet method. At this time, the thickness of the color filter was varied in the plane so as to reduce the variation in the plane of the organic EL display device. Specifically, the film thickness of the color filter disposed in the central pixel is made twice that of the edge pixel. Since the film thickness of the color filter is determined by the amount of dropped liquid, the amount of dropped liquid was controlled by the pixel according to the design film thickness of the color filter.

  The organic EL substrate produced as described above and the color filter substrate were bonded together to produce an organic EL display device composed of RGB three colors.

  Example 2 was prepared in the same manner as Example 1 except that silver was used as the cathode instead of the transparent electrode 8 with respect to the organic EL substrate. The film thickness of silver was 10 nm, and it was created with a sputtering apparatus. In addition, a black matrix (not shown) for light shielding between R, G, B and each light emitting pixel was formed on a glass serving as a color filter substrate in a lattice shape using a general photolithography method. This black matrix is not always necessary.

  Thereafter, each of the R, G, and B coloring materials is discharged into a partition wall (not shown) made of an existing material using an ink jet method.

  At this time, the pigment concentration of the color filter was varied in the plane so as to reduce the variation in the plane of the organic EL display device. Specifically, the pigment concentration of the color filter disposed in the pixel at the end is set to double that of the pixel at the center.

  The organic EL substrate produced as described above and the color filter substrate were bonded together to produce an organic EL display device composed of RGB three colors.

1 is a schematic cross-sectional view of an organic EL element that is a light-emitting pixel used in the present invention. Explanatory drawing which shows each light emission spectrum in the light emitting element of an edge part in the light emitting pixel of B, and the light emitting element of a center part. Explanatory drawing which shows the film thickness and spectral transmittance in the color filter of B. FIG. 7 is an explanatory diagram showing emission spectra of an end light emitting element and a central light emitting element in an R light emitting pixel. Explanatory drawing which shows the film thickness and spectral transmittance in a color filter of R.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Metal reflective layer 3 Transparent conductive layer 4 Hole transport layer 5 Light emitting layer 6 Electron transport layer 7 Electron injection layer 8 Transparent electrode 9 Passivation film 10 Color filter

Claims (6)

In a display device in which a plurality of pixels having at least a single color light emitting element and a color filter provided on the upper surface are arranged,
The transmission band of the transmission spectrum in the color filter is narrowed as the difference between the peak wavelength of the emission spectrum and the peak wavelength of the transmission spectrum in the color filter between at least one pair of the same color light emitting elements of the plurality of light emitting elements is increased. A display device.   The film thickness of the color filter is increased as the difference between the peak wavelength of the emission spectrum in the light-emitting element and the peak wavelength of the transmission spectrum in the color filter is increased between at least one set of the same-color light-emitting elements of the plurality of light-emitting elements. The display device according to claim 1.   The pigment concentration of the color filter is increased as the difference between the peak wavelength of the emission spectrum of the light emitting element and the peak wavelength of the transmission spectrum of the color filter is increased between at least one set of the same color light emitting elements of the plurality of light emitting elements. The display device according to claim 1.   The display device according to claim 1, wherein the light emitting element is an organic light emitting element.   The display device according to claim 4, wherein a metal thin film is used for the electrode on the light extraction side.   The display device according to claim 4, wherein an ink jet method is used for forming the color filter.

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