JP2009187748A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device having high display quality without degrading a manufacturing yield. <P>SOLUTION: The display device comprises: a support substrate 101; a first electrode 60 arranged on the support substrate; a second electrode 64 arranged oppositely to the first electrode, and having optical transparency and light reflectivity; an organic active layer 62 arranged between the first electrode and the second electrode, and including a luminescent layer 62A; a reflective layer 115 arranged between the support substrate and the first electrode; an interference elimination layer 116 arranged between the first electrode and the reflective layer, having film thickness larger than a main wavelength of light emitted from the luminescent layer, and eliminating optical interference that may occur between the reflective layer and the second electrode; and an optical adjustment layer 80 arranged on the second electrode, and maximizing emission intensity at the main wavelength of the light emitted from the luminescent layer and emitted through the second electrode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a display device, and more particularly to a display device having a structure including a self-luminous display element.

  In recent years, organic electroluminescence (EL) display devices have attracted attention as flat display devices. Since this organic EL display device includes an organic EL element that is a self-luminous element, the viewing angle is wide, the backlight can be thinned, the power consumption can be reduced, and the response speed can be reduced. It has the feature of being fast.

  Because of these features, organic EL display devices are attracting attention as potential candidates for next-generation flat display devices that replace liquid crystal display devices. As an organic EL display device, a bottom emission method in which EL light generated in the organic EL element is extracted from the array substrate side and an EL light generated in the organic EL element is extracted from the sealing substrate side to the outside. There is a top emission method.

  The organic EL element is provided on an array substrate together with a pixel circuit and the like, and is configured by holding an organic active layer containing an organic compound having a light emitting function between an anode and a cathode. Each pixel is separated by a partition wall.

  In the bottom emission method, the ratio (aperture ratio) of the light emitting area of the organic EL element per pixel is limited by the pixel circuit and wiring. Top emission methods that can ease the restrictions on the aperture ratio are becoming mainstream.

  On the other hand, in an organic EL element having a resonator structure, only light having a resonance wavelength out of light generated in the light emitting layer is amplified and extracted, and thus light having a spectrum with a high peak intensity and a narrow width can be extracted. It is known that it is possible to expand the color reproduction range of a display device composed of this organic EL element (microcavity effect).

  However, when the peak width of the spectrum of the extracted light is narrowed as in the organic EL element having the resonator structure as described above, the wavelength of the light is greatly shifted when the light emitting surface is viewed from an oblique direction. The viewing angle dependency of the emission characteristics is increased, for example, the emission intensity is decreased.

With respect to such a problem, according to Patent Document 1 and the like, attention is paid to the fact that the viewing angle dependency is a particularly serious problem with white (white) that is very easily perceived. Is disclosed, and a technique for reducing the viewing angle dependency of white is disclosed.
JP 2002-367770 A

  As described above, when the microcavity effect is used, since the resonance condition inside the organic EL element changes depending on the viewing angle, the display characteristics may also change. In addition, there is a problem that a manufacturing margin (in particular, film thickness control of the organic active layer) satisfying the resonance condition is narrow, and the microcavity effect cannot be obtained due to a slight film thickness change.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a display device having a good display quality without causing a decrease in manufacturing yield.

A display device according to an aspect of the present invention includes:
A support substrate;
A first electrode disposed on the support substrate;
A second electrode disposed opposite the first electrode and having light transmission and light reflection properties;
An organic active layer disposed between the first electrode and the second electrode and including a light emitting layer;
A reflective layer disposed between the support substrate and the first electrode;
Disposed between the first electrode and the reflective layer, and having a film thickness that is thicker than the emission main wavelength of the light emitting layer, eliminates light interference that may occur between the reflective layer and the second electrode. An interference cancellation layer;
An optical adjustment layer that is disposed on the second electrode and maximizes the emission intensity at the emission main wavelength of the light emitting layer emitted through the second electrode;
It is characterized by having.

  According to the present invention, it is possible to provide a display device with good display quality without causing a decrease in manufacturing yield.

  A display device according to an embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a self-luminous display device such as an organic EL (electroluminescence) display device will be described as an example of the display device.

  As shown in FIG. 1, the organic EL display device 1 includes an array substrate 100 having an active area 102 for displaying an image. The active area 102 is composed of a plurality of pixels PX arranged in a matrix. Further, FIG. 1 shows a color display type organic EL display device 1 as an example, and the active area 102 includes a plurality of types of color pixels, for example, a red pixel PXR, a green pixel PXG, and a blue color corresponding to three primary colors. A pixel PXB is used.

  At least the active area 102 of the array substrate 100 is sealed with a sealing substrate 200. The sealing substrate 200 is an insulating substrate such as a light transmissive glass substrate or a plastic sheet. The inner surface of the sealing substrate 200 facing the array substrate 100 is formed flat, for example.

  The array substrate 100 and the sealing substrate 200 are bonded together by a sealing member 300 arranged in a frame shape so as to surround the active area 102. The seal member 300 may be, for example, a photosensitive resin (for example, an ultraviolet curable resin) or a frit.

  Each pixel PX (R, G, B) includes a pixel circuit 10 and a display element 40 that is driven and controlled by the pixel circuit 10. Note that the pixel circuit 10 illustrated in FIG. 1 is an example, and it is needless to say that a pixel circuit having another configuration may be applied.

  In the example shown in FIG. 1, the pixel circuit 10 includes a drive transistor DRT, a first switch SW1, a second switch SW2, a third switch SW3, a storage capacitor element CS, and the like. The drive transistor DRT has a function of controlling the amount of current supplied to the display element 40. The first switch SW1 and the second switch SW2 function as a sample / hold switch. The third switch SW3 has a function of controlling the supply of drive current from the drive transistor DRT to the display element 40, that is, the on / off of the display element 40. The storage capacitor element CS has a function of holding the potential between the gate and source of the drive transistor DRT.

  The drive transistor DRT is connected between the high potential power supply line P1 and the third switch SW3. The display element 40 is connected between the third switch SW3 and the low potential power line P2. The gate electrodes of the first switch SW1 and the second switch SW2 are connected to the first gate line GL1. The gate electrode of the third switch SW3 is connected to the second gate line GL2. The source electrode of the first switch SW1 is connected to the video signal line SL.

  The drive transistor DRT, the first switch SW1, the second switch SW2, and the third switch SW3 are configured by, for example, a thin film transistor (TFT), and the semiconductor layer is formed by polysilicon here.

  In the case of such a circuit configuration, the first switch SW1 and the second switch SW2 are turned on based on the ON signal supplied from the first gate line GL1, and the high potential is set according to the amount of current flowing through the video signal line SL. A current flows from the power supply line P1 to the drive transistor DRT, and the storage capacitor element CS is charged according to the current flowing through the drive transistor DRT. As a result, the drive transistor DRT can supply the same amount of current as that supplied from the video signal line SL to the display element 40 from the high potential power supply line P1.

  Then, the third switch SW3 is turned on based on the ON signal supplied from the second gate line GL2, and the driving transistor DRT is connected to the first potential from the high potential power supply line P1 according to the capacitance held in the storage capacitor element CS. A predetermined amount of current corresponding to a predetermined luminance is supplied to the display element 40 via the three switch SW3. Thereby, the display element 40 emits light with a predetermined luminance.

  The display element 40 includes an organic EL element 40 (R, G, B) that is a self-luminous display element. That is, the red pixel PXR includes an organic EL element 40R that mainly emits light corresponding to the red wavelength. The green pixel PXG includes an organic EL element 40G that mainly emits light corresponding to the green wavelength. The blue pixel PXB includes an organic EL element 40B that mainly emits light corresponding to the blue wavelength.

  The various organic EL elements 40 (R, G, B) have basically the same configuration, and are disposed on the wiring substrate 120 as shown in FIG. In addition, the wiring board 120 is insulated on an insulating support substrate 101 such as a glass substrate or a plastic sheet, such as an undercoat layer 111, a gate insulating film 112, an interlayer insulating film 113, and an organic insulating film (planarization layer) 114. In addition to the layers, it is configured to include various switches SW, drive transistors DRT, storage capacitor elements Cs, various wirings (gate lines, video signal lines, power supply lines, etc.) and the like.

  That is, in the example shown in FIG. 2, on the undercoat layer 111, the semiconductor layer 21 of a transistor element (corresponding to the third switch SW3 in the circuit configuration shown in FIG. 1) 20 such as a switch or a drive transistor. Is arranged. The semiconductor layer 21 is covered with the gate insulating film 112.

  On the gate insulating film 112, the gate electrode 20G of the transistor element 20 and the like are disposed. The gate electrode 20G is covered with an interlayer insulating film 113. On the interlayer insulating film 113, the source electrode 20S and the drain electrode 20D of the transistor element 20 are disposed.

  The source electrode 20S and the drain electrode 20D are in contact with the semiconductor layer 21 through contact holes that penetrate the gate insulating film 112 and the interlayer insulating film 113 to the semiconductor layer 21, respectively. The source electrode 20S and the drain electrode 20D are covered with the first organic insulating film 114.

  A reflective layer 115 is disposed on the first organic insulating layer 114. The reflective layer 115 is formed using a light reflective conductive material such as aluminum (Al). The reflective layer 115 may be arranged in an island shape in each pixel, or may be arranged over the entire active area 102. Such a reflective layer 115 is covered with a second organic insulating layer 116.

  The first organic insulating layer 114 and the second insulating layer 116 are made of a photosensitive resin material such as an acrylic resin. In particular, the first organic insulating layer 114 is formed through a photolithography process so as to form a concavo-convex structure on the surface (surface on which the reflective layer 115 is laminated). The second organic insulating layer 116 is formed by a technique such as coating with a resin material so as to alleviate the influence of the unevenness of the lower layer and flatten the surface.

  In this embodiment, the organic EL element 40 is disposed on the second organic insulating layer 116. The organic EL element 40 has a configuration in which an organic active layer 62 is held between a first electrode 60 and a second electrode 64, and a detailed structure will be described below.

  That is, the first electrode 60 is disposed on the second organic insulating layer 116 in an independent island shape for each pixel PX, and functions as an anode. The first electrode 60 is in contact with the drain electrode 20D through a contact hole that penetrates the first organic insulating layer 114 and the second organic insulating layer 116 to the drain electrode 20D.

  The first electrode 60 is formed using a light-transmitting conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).

  The organic active layer 62 is disposed on the first electrode 60 and includes at least a light emitting layer. The organic active layer 62 can include functional layers other than the light emitting layer, and includes, for example, functional layers such as a hole injection layer, a hole transport layer, a blocking layer, an electron transport layer, an electron injection layer, and a buffer layer. it can. Such an organic active layer 62 may be composed of a single layer in which a plurality of functional layers are combined, or may have a multilayer structure in which the functional layers are laminated. In the organic active layer 62, the light emitting layer may be an organic material, and layers other than the light emitting layer may be an inorganic material or an organic material. In the organic active layer 62, the functional layer other than the light emitting layer may be a common layer. The light emitting layer is formed of an organic compound having a light emitting function that emits red, green, or blue light.

  The organic active layer 62 may include a thin film formed of a polymer material. Such a thin film can be formed by a selective coating method such as an inkjet method. The organic active layer 62 may include a thin film formed of a low molecular material. Such a thin film can be formed by a technique such as mask vapor deposition.

  The second electrode 64 is common to the plurality of pixels PX, is disposed on the organic active layer 62 of each pixel PX, and functions as a cathode. Such a second electrode 64 has light transmissivity and light reflectivity, and is configured as a semi-transmissive layer made of a mixture of silver (Ag) and magnesium (Mg).

  Further, the array substrate 100 includes a partition wall 70 that separates adjacent pixels PX (R, G, B) in the active area 102. For example, the partition walls 70 are arranged so as to cover the periphery of each first electrode 60 and are formed in a lattice shape or a stripe shape in the active area 102. Such a partition 70 is formed by patterning a resin material, for example. The partition wall 70 is covered with the second electrode 64.

  Next, the main configuration of the organic EL display device in this embodiment will be described in more detail.

  That is, as shown in FIG. 3, the first organic insulating layer 114 is disposed on the support substrate 101. Note that a layer between the support substrate 101 and the first organic insulating layer 114 is omitted. The first organic insulating layer 114 corresponds to a concavo-convex layer having a concavo-convex structure on its surface, and the concavo-convex shape has a pitch of adjacent convex portions (or adjacent concave portions) of 30 μm or less and a concave / convex depth ( That is, the height from the top of the convex portion to the bottom of the concave portion is 0.5 μm or more. In the example shown here, the first organic insulating layer 114 was formed of an acrylic resin, the pitch was 9 μm, and the depth of the unevenness was 1.5 μm.

  On the other hand, on the support substrate 101, the first electrode 60 constituting the organic EL element 40 is disposed, and the second electrode 64 is disposed opposite to the first electrode 60. An organic active layer 62 is disposed between the first electrode 60 and the second electrode 64. In the example shown here, the organic active layer 62 includes, in addition to the light emitting layer 62A, a hole transport layer 62H disposed between the light emitting layer 62A and the first electrode 60, and the light emitting layer 62A and the second electrode 64. And an electron transport layer 62E disposed therebetween.

  A reflective layer 115 is disposed between the support substrate 101 and the first electrode 60. That is, the reflective layer 115 is disposed on the first organic insulating layer 114 and has a concavo-convex structure on the surface following the concavo-convex structure of the first organic insulating layer 114. That is, the uneven shape on the surface of the reflective layer 115 is substantially the same as that of the first organic insulating layer 114. Here, the reflective layer 115 is formed by sputtering aluminum.

  A second organic insulating layer 116 is disposed between the first electrode 60 and the reflective layer 115. That is, the second organic insulating layer 116 is disposed so as to cover the reflective layer 115, and the surface thereof is flattened. Such a second organic insulating layer 116 has a thickness that is thicker than the emission main wavelength of the light emitting layer, and functions as an interference eliminating layer that eliminates light interference that may occur between the reflective layer 115 and the second electrode 64. To do. That is, the film thickness of the second organic insulating layer 116 is not uniform, and the film thickness on the concave portion of the base is formed to be larger than the film thickness on the convex portion. is doing. Here, the second organic insulating layer 116 is formed of an acrylic resin.

  As a result, it is possible to suppress the multiple reflection / multiple interference effect inside the device, and to reduce the film thickness change and viewing angle dependency of the organic active layer 62.

  On the other hand, when the interference cancellation layer is applied, the effect of improving the emission color of the organic EL element using the multiple reflection / multiple interference effect inside the element is also suppressed, so that the color purity of the emission color is lowered. End up.

  Therefore, in this embodiment, the optical adjustment layer 80 that maximizes the emission intensity at the emission main wavelength of the light emitting layer 62A emitted from the light emitting layer 62A through the second electrode 64 is provided. The optical adjustment layer 80 is disposed on the second electrode 64. Such an optical adjustment layer 80 may be formed of an inorganic material such as ITO, SiON, or SiNx, or may be formed of an organic material as long as it is a light-transmitting material.

  In the example shown here, the optical adjustment layer 80 is formed of the same material as the hole transport layer 62H. At this time, the refractive index of the optical adjustment layer 80 was 1.85 at the emission main wavelength of the light emitting layer 62A. The film thickness of the optical adjustment layer 80 was 380 nm.

  According to such a configuration, it is possible to improve color purity in a display device using an interference cancellation layer that cancels the interference effect. That is, it is possible to provide a display device with good color reproducibility regardless of the change in film thickness or viewing angle of the organic active layer.

  As for the refractive index and film thickness of the optical adjustment layer 80 mentioned above, it is more desirable to set so that the following relational expression may be satisfied.

That is, the emission main wavelength of the light emitting layer 62A is λ, and the optical length from the light emitting layer 62A to the second electrode 64 in the organic active layer 62 (that is, in the example shown here, the film thickness of the light emitting layer 62A and the electron transport layer). The total thickness of 62E) is L, the refractive index of the light adjustment layer 80 is n, the thickness of the light adjustment layer 80 is d, the refractive index of the second electrode 64 is n ', and the thickness of the second electrode 64 is Is d ′ and m is an integer (m = 0, 1, 2,...),
n · d + n ′ · d ′ + L = λ / 4 × (2m + 1)
N and d are set so as to satisfy the relationship expressed by the following formula.

  According to the optical adjustment layer 80 satisfying such a relational expression, the emission spectrum of the light emitted from the light emitting layer 62A can be made narrower, and the color purity of the emitted color in the color pixel can be improved. It becomes.

  In particular, the integer m has a tendency that the smaller the value, the lower the transmittance, but the spectrum width tends to narrow. In the above relational expression, it is desirable to select a condition where the integer m is 2 or more.

  The emission main wavelength λ of the light emitting layer 62A has an emission intensity of 80% or more with respect to the emission intensity at the emission wavelength λ (peak), which is the maximum emission intensity, of the emission spectrum of the material forming the light emitting layer 62A. It is assumed that the wavelength range is obtained.

  Next, the emission spectrum when the optical adjustment layer 80 was applied was measured by taking a blue pixel (emission main wavelength is 470 nm to 480 nm) as an example. Here, the refractive index of the optical adjustment layer 80 is 1.85 and the film thickness is 380 nm so as to satisfy the above relational expression. At this time, m = third order was selected.

  This configuration is the best case (Best) with an optical adjustment layer, and for comparison, a case without an optical adjustment layer and a non-best case with optical adjustment (Worst) are shown simultaneously. As a non-best case, the right side in the above relational expression is λ / 2. The measurement results are shown in FIG.

  In the case without the optical adjustment layer, the half width of the obtained emission spectrum was 58 nm. On the other hand, in the best case, the half-value width of the emission spectrum is 44 nm, and it can be seen that the color purity of the emission spectrum is improved by the optical adjustment layer. Similarly, in the case with the optical adjustment layer, in the non-best case, the half-value width of the emission spectrum was 67 nm, confirming that the color purity of the emission spectrum was lower than in the case without the optical adjustment layer.

  Next, FIG. 5 shows emission spectra of a general top surface light emitting element having no interference eliminating layer and a top surface light emitting element having an interference eliminating layer and having an optical adjustment layer under the best conditions.

  A general top light emitting device has improved color purity due to the cavity effect, and the half width of the emission spectrum at this time was 49 nm. On the other hand, in the top light-emitting element having the interference canceling layer and the optical adjustment layer under the best conditions, the half-value width of the emission spectrum is 44 nm even though the cavity effect is improved, and a steep emission spectrum is obtained. It was confirmed that it was obtained.

  As described above, according to the present embodiment, it is possible to provide a display device with high color purity in the display device using the interference cancellation layer that cancels the interference effect.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the spirit of the invention in the stage of implementation. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

FIG. 1 is a diagram schematically showing a configuration of an organic EL display device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing a structure when the organic EL display device shown in FIG. 1 is cut. FIG. 3 is a diagram schematically showing an element structure of one pixel. FIG. 4 is a diagram illustrating a verification result of the effect obtained by applying the optical adjustment layer. FIG. 5 is a diagram illustrating a verification result of the effect obtained by applying the interference cancellation layer and the optical adjustment layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Organic EL display device PX (R, G, B) ... Pixel 40 ... Organic EL element (display element)
DESCRIPTION OF SYMBOLS 60 ... 1st electrode 62 ... Organic active layer 64 ... 2nd electrode 80 ... Optical adjustment layer 100 ... Array substrate 101 ... Supporting substrate 114 ... 1st organic insulating layer 115 ... Reflective layer 116 ... 2nd organic insulating layer

Claims (6)

A support substrate;
A first electrode disposed on the support substrate;
A second electrode disposed opposite the first electrode and having light transmission and light reflection properties;
An organic active layer disposed between the first electrode and the second electrode and including a light emitting layer;
A reflective layer disposed between the support substrate and the first electrode;
Disposed between the first electrode and the reflective layer, and having a film thickness that is thicker than the emission main wavelength of the light emitting layer, eliminates light interference that may occur between the reflective layer and the second electrode. An interference cancellation layer;
An optical adjustment layer that is disposed on the second electrode and maximizes the emission intensity at the emission main wavelength of the light emitting layer emitted through the second electrode;
A display device comprising: The emission main wavelength of the light emitting layer is λ,
In the organic active layer, the optical length from the light emitting layer to the second electrode is L,
The refractive index of the optical adjustment layer is n, the thickness of the optical adjustment layer is d,
The refractive index of the second electrode is n ′, the thickness of the second electrode is d ′,
When m is an integer (m = 0, 1, 2,...),
n · d + n ′ · d ′ + L = λ / 4 × (2m + 1)
The display device according to claim 1, wherein the relationship of the formula shown below is satisfied.   The display device according to claim 2, wherein the integer m is 2 or more. The organic active layer has a hole transport layer between the light emitting layer and the first electrode,
The display device according to claim 1, wherein the optical adjustment layer is formed of the same material as the hole transport layer.   The display device according to claim 1, wherein the optical adjustment layer is made of a light-transmitting inorganic material. Furthermore, it has a concavo-convex layer disposed between the insulating substrate and the reflective layer and having a concavo-convex structure on the surface thereof,
The display device according to claim 1, wherein the interference elimination layer is formed such that a film thickness on the concave portion of the concavo-convex layer is larger than a film thickness on the convex portion.

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