JP2002151274A - Luminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroluminescent element with improved emission efficiency. SOLUTION: With an electroluminescent element equipped with electrodes and a luminescent layer, at least one of the electrodes is a transparent electrode, which a mesa-shaped fine structural body having a plurality of mesa-shaped transparent bodies is arranged opposite to the side the transparent electrodes face the luminescent layer, with the shorter side of the mesa-shaped fine structural body toward it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a self-luminous type light emitting device such as an electroluminescence (EL) element.

[0002]

2. Description of the Related Art Electronic display devices are roughly classified into two types depending on how light is used. One is a light-receiving type display device which forms a display device by operating as a so-called shutter which transmits and blocks external light without the control element itself forming the device emitting light. The other is a self-luminous display device in which the device itself emits light and allows the user to recognize it as luminance.

As a light receiving type display device, a liquid crystal display device (L
CD) is well known and is now widespread. As self-luminous display devices, organic EL (electroluminescence), inorganic EL, plasma display panel (PDP), light emitting diode display device (LED), fluorescent light, etc. There are a display tube display (VFD), a field emission display (FED), and the like. Some of them have been put into practical use, and others are being actively developed. A light-receiving display device represented by an LCD generally requires a backlight because it requires a light source, and the backlight is always turned on regardless of the state of display information, and consumes almost the same power as in the entire display state. Will be.

On the other hand, a self-luminous display device consumes power only in a portion that needs to be lit according to display information, and thus has the advantage of lower power consumption than a light-receiving display device. In principle.

An LCD which is a representative of a light receiving type display device
Uses polarization control by birefringence of liquid crystal,
Although the so-called viewing angle dependency, in which the display state changes greatly depending on the viewing direction, is strong, the self-luminous display device hardly has this problem. Further, since the LCD utilizes a change in molecular orientation caused by the dielectric anisotropy of the liquid crystal, which is an organic elastic substance, the response time to an electric signal is 1 ms or more in principle.

On the other hand, in the above-mentioned technology which is being developed as a self-luminous display, a so-called carrier transition such as electrons / holes, electron emission, plasma discharge, and the like are used. The liquid crystal display is so fast that it is incomparable to liquid crystal, and there is no problem of moving image afterimage caused by the slow response of the LCD.

[0007]

Although a self-luminous display device has many advantages as described above, only a CRT is currently being fully put into practical use, and it is expected that the demand will further increase in the future. LCD is still used as a flat display device
Is the mainstream. One of the major reasons is the low luminous efficiency. LCDs must always be lit with a backlight, but the backlight is simply illumination, and is a technology that has been completed in all its characteristics such as luminous efficiency, brightness, and lifespan. There is practically no problem in continuing.

On the other hand, in the above-mentioned self-luminous display device, the basic characteristic that light is emitted stably and efficiently for a long time has not reached a practical level. In order to stably improve the luminous efficiency, light-emitting materials are being developed in all technologies. However, in a full-color display, it is necessary to solve this problem for all three primary colors of R, G and B. Is not easy.

Therefore, a technique for improving the luminous efficiency without depending on the luminescent material is required. In particular, in an EL device, there is a large problem that light emitted from a light-emitting substance is totally reflected at a substrate or an interface with the atmosphere which constitutes the device, and most of the light emitted is deactivated without reaching the outside of the device.

FIG. 10 is a configuration diagram of a conventional EL device 1. In FIG. 10, a transparent substrate 2 on which a transparent electrode 5 is formed is shown.
A light-emitting layer 3 and a counter electrode 4 are laminated on the electrode 5 to form an electrode 5,
The light emitting layer 3 emits light by applying an electric field between the electrodes 4, and the light 8 is extracted through the transparent electrode 5 and the transparent substrate 2. If the opposite electrode 4 does not need to emit light on both sides, a reflective metal electrode is usually used in many cases in order to improve the brightness of the light emission 8. Regardless of the organic EL or the inorganic EL, the light emitting layer 3 generally has low moisture resistance, and has a very short light emission life when exposed to the air. Therefore, it is necessary to isolate the light emitting layer 3 from the air with the sealing body 6 and the adhesive 7.

FIG. 11 shows the conventional EL device 1 shown in FIG.
FIG. 3 is an explanatory view of a light-emitting ray path of FIG. 11, the same reference numerals as those in FIG. 10 denote the same components as those in FIG. Light emitted from a conventional EL device propagates through each film as shown in FIG. Generally, the refractive index of the material of the light emitting layer 3 is about 1.6, the typical refractive index of ITO as the transparent electrode 5 is about 1.8, and the glass of the substrate 2 is about 1.5. From this relationship, the light ray 8 emitted from the light emitting layer 3 does not cause total reflection at the interface with the transparent electrode 5 and, on the contrary, sets the penetration angle to an acute angle.
However, a part of the interface between the transparent electrode 5 and the glass of the transparent substrate 2 is confined in the transparent electrode 5 by total reflection, and is deactivated while propagating in the transparent electrode 5. Further, some of the light beams
Deactivated at the interface between the glass and the atmosphere by total reflection.
In the conventional EL device 1 shown in FIG. 10, the internal deactivation due to these total reflections is close to 80% of the total luminous flux, and most of the luminescence is not used effectively.

Conventionally, as a method of solving this problem of total reflection, [OPTICS LETTERS / Vol. 2
2, No. 6 / March 15, 1997, p396
-398]. It has been proposed by Gu et al. To use a mesa (trapezoidal) shaped substrate. They mounted on a glass substrate a height of 2.2 mm, a base length of 3 mm, and a slope angle of 34 mm.
A mesa structure having a square bottom surface with a degree of 0 ° is formed on the top surface.
An organic EL device having a diameter of 5 mm is manufactured and its effect is examined.

FIG. 9 is an explanatory diagram of the propagation path of the emitted light beam when the mesa structure is used. In FIG. 9, reference numeral 9 denotes a mesa structure. Further, in FIG. 9, 3 is a light emitting layer, 5
Denotes a transparent electrode, and 8 denotes a light beam. A part of the light rays 8 generated from the light emitting layer 3 is inactivated by total reflection at the interface between the transparent electrode 5 and the mesa structure 9, but most of the light rays totally reflected at the interface between the mesa structure 9 and the atmosphere are formed. After propagating in the mesa structure 9, the light is emitted into the atmosphere at an angle changed by total reflection on the slope. By taking into account the attenuation coefficient of the material forming the mesa structure 9, the height, width, and angle of the slope are made appropriately, thereby significantly reducing the internally deactivated light rays and reducing the luminous efficiency as compared with the conventional structure. Can be improved. G. FIG. Gu and the like also form the mesa structure 9 with a material having a higher refractive index than the transparent electrode 5 such as TiO2, thereby preventing total reflection at the interface between the transparent electrode 5 and the mesa structure 9, and forming a mesa structure with glass. It is stated that the luminous efficiency can be further improved than when the body 9 is made.

However, G. From the size of the element reported by Gu et al., It is clear that one mesa structure is provided for one pixel constituting the display device. In such a large mesa structure, the light beam is attenuated before propagating inside the mesa structure and reaching the slope, so that a sufficient effect cannot be obtained. Further, if a light emitting element is manufactured after a mesa structure is formed on a substrate, it becomes difficult to form a drive circuit and an electrode on the substrate. In particular, an active matrix drive display device requiring a complicated and fine drive circuit cannot be manufactured.

Further, G. In order to form an electrode and a light emitting layer only on the upper surface of the mesa structure such as Gu or the like, a method such as mask evaporation must be used, and it is difficult to produce a large and high-definition display device. Conversely, even if an electrode and a light emitting layer are formed on the entire surface in the same manner as in the related art ignoring the substrate shape, it is difficult to produce a uniform display device due to the influence of unevenness due to protrusions of the mesa structure.

In any case, G. Although the report of Gu et al. Is effective as a basic experiment, it has many problems in actual industrialization. Also, Japanese Patent Application Laid-Open No. Hei 10-189243 reports a tapered element which is not a mesa structure, but which effectively extracts a light beam which has been deactivated by total internal reflection. However, Japanese Patent Application Laid-Open No. 10-18924 discloses
The structure of No. 3 is based on a rather complicated principle that a light ray needs to jump over a valley of a tapered portion as shown in FIG. 6 of Japanese Patent Application No. 10-189243. It is difficult to obtain the effect. Further, since both the electrode and the light emitting layer are formed in the tapered portion, a defect occurs if the entire tapered portion cannot be covered. G. FIG.
The method of forming an electrode and a light emitting layer by providing an uneven shape on a substrate together with the method of Gu or the like has to be said to have a serious problem in actual effect and reliability.

As described above, the tapered structure has no dependency on the light emitting material and is effective in principle to improve the luminous efficiency of the self-luminous display device. There was no.

[0018]

In order to solve the above-mentioned problems, in the present application, a plurality of transparent mesa-shaped fine structures are arranged on a short side of a pixel constituting a display device on a side opposite to a light emitting layer of a transparent electrode. Are arranged closer to the transparent electrode. G. FIG.
By arranging a plurality of fine structures in one pixel instead of one structure such as Gu, etc., one mesa structure can be made smaller and the problem of attenuation due to internal propagation can be solved.

Further, a structure in which the transparent electrode is formed on the opposite side of the light emitting layer from the substrate is used as a final path through which the transparent electrode passes light rays. A number of transparent mesa-shaped microstructures are formed in a sealed body that shields the element from the atmosphere, and these are sealed in such a way that they come into contact with the transparent electrodes, so that the electrodes can be processed without any special processing on the substrate. The light emitting portion such as the light emitting layer is formed flat as before, and the luminous efficiency can be greatly improved only by processing the sealing body.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of the first embodiment of the present invention. In FIG. 1, an electroluminescent device 10 is manufactured by forming an electrode 4, a light emitting layer 3, and a transparent electrode 5 on a substrate 2 in this order. The electrode 4 may be transparent or non-transparent, but the transparent electrode 5 is transparent and has a structure through which light is emitted to the outside. Finally, the sealing body 6 is provided for reliability. The sealing body 6 is naturally transparent for extracting light emission. For example, glass, plastic, transparent resin, or the like can be used.

FIG. 2 is an enlarged view of the light emitting layer 3, the transparent electrode 5, and the sealing body 6 according to the first embodiment.
On the surface of the sealing body 6, a number of transparent mesa-shaped fine structures 11, which are one of the features of the present invention, are formed. This can be performed relatively easily by etching or laser processing. The electroluminescent device 1 is sealed by the sealing body 6 so that the transparent electrode 5 and the mesa-shaped fine structure 11 are in contact with each other.
0 can improve the luminous efficiency according to the principle of FIG. The mesa structure of the present invention (that is, the mesa-shaped fine structure 11) is described in G.A. Unlike Gu or the like, each mesa structure is finely composed in large numbers, so that the influence of attenuation can be ignored.

FIG. 3 shows a block diagram of a second embodiment of the present invention. The second embodiment is characterized in that the reflectors 12 are provided on the slopes (tapered portions) of the mesa-shaped microstructure 11, respectively, as compared with the first embodiment of FIG. Here, the same reference numerals in FIG. 3 as those in FIG.
Indicates the same as Thus, the mesa-shaped fine structure 11
The efficiency is further improved by providing the reflector 12 on the inclined surface of. That is, as shown in detail in FIG. 4, all the light beams can be emitted from the mesa-shaped fine structure 11 to the atmosphere by the reflector 12.

FIG. 5 shows a configuration diagram of a third embodiment of the present invention. The third embodiment is different from the first embodiment of FIG. 1 in that the transparent electrode 5 and the mesa-shaped fine structure 11 are different from each other.
The feature is that the space between them is optically brought into close contact with a substance such as the matching oil 13. Here, in FIG. 5, the same reference numerals as those in FIG. 1 indicate the same components as those in FIG. As in the third embodiment, the luminous efficiency of the device can be more effectively improved by optically bringing the transparent electrode 5 and the mesa-shaped fine structure 11 into close contact with each other with a substance such as the matching oil 13.

FIG. 6 shows a configuration diagram of the fourth embodiment of the present invention. The fourth embodiment is different from the first embodiment of FIG. 1 in that electrodes facing each other are formed so that an electric field is applied only to a portion where the mesa-shaped microstructure 11 is arranged. There are features. Here, in FIG. 6, the same reference numerals as those in FIG. 1 indicate the same components as those in FIG. As in the fourth embodiment, the opposing electrode 5 is formed so that an electric field is applied only to the portion where the mesa-shaped fine structure 11 is arranged. The luminous efficiency is further improved without being consumed.

A large number of mesa-shaped microstructures 11 according to the first to fourth embodiments can be formed as shown in FIG. FIG. 7 is an explanatory diagram of a step of forming the mesa-shaped fine structure 11. A resist patterned by exposure and development with a resist 14 and a photomask 15 having a predetermined shape is formed on the sealing body 6. The sealing body 6 is etched (for glass, using hydrofluoric acid or the like) to form a mesa-shaped fine structure 11.
Is prepared. Since etching using a resist usually results in a tapered cross section, the etching conditions (etchant,
The mesa shape (width Du, Db, height h, angle Θ) can be easily controlled by controlling time, temperature, etchant flow, and the like. The reflector 12 may be formed by vapor deposition, plating, or the like before removing resist such as silicon or metal. When the resist is removed, the mesa-shaped fine structure 11 is completed. In addition, laser processing can be used instead of etching. In FIG. 7, the mesa-shaped fine structure 11 is shown discretely for easy understanding, but it is better to form the mesa-shaped fine structure 11 densely as shown in FIGS.

Further, the mesa-shaped fine structure 11 may have a circular bottom as shown in FIG. 8 or may have a polygonal bottom. Here, JP-A-11-329
In Japanese Patent No. 726, a reflection film is provided on a side surface of a phosphor in an organic EL device in which light emitted from a light emitting element is absorbed by a phosphor to emit light. However, merely collecting the scattered light from the phosphor forward by the reflection film does not suppress the total reflection, which is a major problem for the luminous efficiency. Therefore, the effect of improving the luminous efficiency does not reach the present application.
In addition, G. As in the case of Gu or the like, it has one pixel and one structure, and the attenuation of light propagating in the phosphor becomes larger than the effect of the reflection film.

[0027]

EXAMPLES The present invention will be described in more detail with reference to Examples.

[0028]

Example 1 As an example of the present invention, an electroluminescent device 10 shown in FIG. 1 was manufactured as follows. Mg / Al as the reflective electrode 4 (that is, the electrode 4), a luminescent organic material Alq3 and the hole transport layer α-NPD as the luminescent layer 3, and ITO as the transparent electrode 5 were laminated on the substrate 2. The lamination order was such that the hole transport layer α-NPD and ITO were in contact. All of these fabrications were performed with the atmosphere shut off. The thickness of the light emitting layer is A
1q3 (2000 °) and α-NPD (1000 °). On the other hand, a transparent body having a large number of fine tapered mesa-shaped fine structures 11 as shown in FIG. Glass, transparent plastic, and transparent resin were patterned according to the method shown in FIG. 7 to form a tapered shape. The tapered shape was a square with a base of 20 μm on a side or a circle with a diameter of 20 μm and a height of 17 μm. The above-mentioned sealing body 6 has a transparent electrode 5 on the short side of the tapered shape.
And fixed to the substrate 2 with a sealing agent 7 so as to be in contact with the substrate, thereby producing an electroluminescent device. When a 7 V DC electric field was applied with the reflective electrode 4 having a negative polarity and the transparent electrode 5 having a positive polarity, light emission with a luminance of 500 cd / m ² at a current density of 0.2 mA / mm ² could be confirmed.

[0029]

Comparative Example 1-1 As a comparative example, a normal electroluminescent device in which the sealing body 6 of Example 1 was not provided with a tapered shape was similarly manufactured. 7 with the reflective electrode as negative polarity and the transparent electrode as positive polarity
When a DC electric field of V was applied, the current density was 0.2 mA /
In mm ² , only a light emission of 120 cd / m ² was confirmed.

[0030]

Comparative Example 1-2 As a comparative example, the conventional electroluminescent device of FIG. 10 was manufactured in the same manner. The reflective electrode 4 has a negative polarity, and the transparent electrode 5
When a direct current electric field of 7 V was applied with a positive polarity, light emission of only 120 cd / m ² at a current density of 0.2 mA / mm ² could be confirmed. According to the invention of the present application, it is possible to manufacture a display device with a luminance of four times or more with the same power. At this time, the light-emitting material, the electrode material, etc. were not changed at all, only the efficiency of taking out the light-emitting ability originally possessed by the light-emitting material to the outside required as a display device was improved,
The reliability such as the service life does not decrease at all.

[0031]

Embodiment 2 As a second embodiment of the present invention, an electroluminescent device 10 shown in FIG. 1 was manufactured as follows. Mg / Al as the reflective electrode 4 (that is, the electrode 4), a luminescent organic material Alq3 and the hole transport layer α-NPD as the luminescent layer 3, and ITO as the transparent electrode 5 were laminated on the substrate 2. The lamination order was such that the hole transport layer α-NPD and ITO were in contact. All of these fabrications were performed with the atmosphere shut off. The thickness of the light emitting layer was Alq3 (2000 °) and α-NPD (1000 °). On the other hand, as the sealing body 6, a transparent body having a large number of finely tapered mesa-shaped microstructures 11 having a reflector 12 formed on the slope as shown in FIG. 3 was prepared. Glass, transparent plastic, and transparent resin were patterned according to the method shown in FIG. 7 to form a reflector to form a tapered shape. The tapered shape was a square with a base of 20 μm on a side or a circle with a diameter of 20 μm and a height of 17 μm.
The above-mentioned sealing body 6 was covered so that the short side of the tapered shape was in contact with the transparent electrode 5 and was fixed to the substrate 2 with the sealing agent 7 to produce an electroluminescent device. When a 7 V DC electric field was applied with the reflective electrode 4 having a negative polarity and the transparent electrode 5 having a positive polarity,
It was possible to confirm the emission luminance 600 cd / m ² at a current density of 0.2 mA / mm ^2.

[0032]

Comparative Example 2-1 As a comparative example, a normal electroluminescent device in which the sealing body 6 of Example 1 was not provided with a tapered shape was similarly manufactured. When a 7 V DC electric field was applied with the reflective electrode 4 having a negative polarity and the transparent electrode 5 having a positive polarity, the current density was 0.2 mA.
At a luminance of / mm ² , only a light emission of 120 cd / m ² could be confirmed.

[0033]

Comparative Example 2-2 As a comparative example, the conventional electroluminescent device of FIG. 10 was manufactured in the same manner. When a DC electric field of 7 V was applied with the reflective electrode 4 having a negative polarity and the transparent electrode 5 having a positive polarity, light emission of only 120 cd / m ² at a current density of 0.2 mA / mm ² could be confirmed. According to the invention of the present application, it is possible to manufacture a display device with five times or more luminance with the same power. At this time, the light emitting material, electrode material, etc. were not changed at all, only the efficiency of taking out the light emitting ability originally possessed by the light emitting material to the outside required as a display device was improved, and the reliability such as the lifetime was improved. There is no drop at all. As mentioned above, although the Example of this invention was described, this invention is not limited to this.

[0034]

According to the present invention, the luminous efficiency of the self-luminous display device can be greatly improved.
In addition, the manufacturing process is not complicated, the manufacturing efficiency is high, and an active matrix drive display device can be produced without any trouble when complicated driving and electrodes are formed on the substrate. Furthermore, there is no need to change the light-emitting material, electrode material, etc., only to improve the efficiency of taking out the light-emitting ability originally possessed by the light-emitting material to the outside required as a display device,
It has an excellent effect that the reliability such as the life is not reduced at all.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main part of a first embodiment of the present invention.

FIG. 2 is an enlarged view of a light emitting layer, a transparent electrode, and a sealing body according to the first embodiment.

FIG. 3 is a main part configuration diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of the path of the emitted light beam according to the second embodiment.

FIG. 5 is a main part configuration diagram of a third embodiment of the present invention.

FIG. 6 is a main part configuration diagram of a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram of a manufacturing process of a self-luminous display device of the present invention.

FIG. 8 is an explanatory view of a tapered shape of the present invention.

FIG. 9 is an explanatory diagram of the path of the emitted light beam in the mesa structure.

FIG. 10 is a diagram showing a configuration of a conventional electroluminescent device.

FIG. 11 is an explanatory view of a path of light emitted from a conventional electroluminescent device.

[Explanation of symbols]

1, 10: electroluminescent device, 3: light emitting layer, 4: electrode, 5:
Transparent electrode, 6: sealing body, 7: sealant, 8: emission light beam,
9: mesa structure, 11: mesa-shaped fine structure, 12: reflector, 13: refractive index matching substance, 14: resist, 1
5: Photomask

Claims (4)

[Claims] 1. An electroluminescent device comprising an electrode and a light emitting layer, wherein at least one of the electrodes is a transparent electrode, and a mesa-shaped fine structure having a plurality of mesa shapes made of a transparent body is formed on the transparent electrode. On the opposite side facing the light-emitting layer, the short side of the mesa-shaped microstructure was arranged closer.
An electroluminescent device, comprising: 2. The electroluminescent device according to claim 1, wherein a sealing body for stably operating the light emitting layer in the air and the mesa-shaped fine structure are integrated. 3. The electroluminescent device according to claim 1, wherein a reflector is provided at a tapered portion of the mesa-shaped fine structure. 4. An electrode is formed only in a portion where the plurality of mesa-shaped microstructures are arranged.
4. The electroluminescent device according to any one of claims 1 to 3.