JPH04192290A - Membrane electroluminescence (el) device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field]

The present invention is a thin film E used as a display device of electronic equipment.
Regarding the L device.

[Conventional technology]

Generally, this type of thin film EL device is known to have a structure as shown in FIG. 8, for example. This thin film EL device has strip-shaped transparent electrodes 20 made of ITO (tin-doped indium oxide) formed in parallel patterns at intervals on a glass substrate 19, and an oxide Al2
O3,5ho2 or TlO2 or nitride 513N
A first insulating film 21 made of 4 is formed. On top of this, a light-emitting layer 22 having a composition in which a small amount of Ml is added as a luminescent center to a base material such as ZnS or Zn5e, and a second insulating film 23 made of the above-mentioned oxide or nitride are formed in order, Furthermore, strip-shaped back electrodes 24 made of Al are patterned in parallel at intervals in a direction perpendicular to the transparent electrode 20. The thin film EL device manufactured in this way has a transparent electrode 20 and a back electrode 24.
By selectively applying a voltage to the picture electrode 20.24
By emitting light in any combination of the light emitting layers 22 at the intersections in the form of dots, it is possible to perform a desired tomatolinox display.

[Invention or problem to be solved]

However, in the conventional thin film EL device described above, the light emitting layer 2
2. Most of the isotropic light generated is the glass substrate 19.
Transparent electrode 20. There is a problem in that the light is trapped inside the thin film EL device due to total reflection at optical interfaces such as the light emitting layer 22, resulting in poor light extraction efficiency. This thing,
This will be explained in detail below. First, the light emitting layer 22, the insulating film 2
1.23, when the refractive index of the transparent electrode 20 and the glass substrate 19 are expressed as ne, nl, nd, and ng, respectively, ne>n
Since i, nd, ng > 1, all light that forms an angle of 0 or more with the normal to the light extraction surface is totally reflected and is confined inside the thin film EL device. . Here, the total reflection critical angle θ is given by the following equation based on Snell's law. θ-5in-'(1/ne) In other words, out of the light emitted within the light-emitting layer 22 at a solid angle of 4π, only the amount of light corresponding to the solid angle f114π(1-cosθ) is extracted. Therefore, the emission intensity of light that can be taken out to the outside, that is, the external emission intensity B○, and the luminescent layer 2
The relationship between the luminescence intensity of the light generated by B1 and the internal luminescence intensity B1 is given by the following equation. Here, when the light-emitting layer 22 is made of ZnS:Mn (Zn5 doped with Mn), the refractive index of the light-emitting layer 22 is IIe~2.3, so the external emission intensity is B. ~00997Bi. Therefore, the light emitting layer 22
The problem is that only about 10% of the light generated can be extracted to the outside, resulting in poor light extraction efficiency. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a thin film EL device that can improve light extraction efficiency.

[Means to solve the problem]

In order to achieve the above object, the thin film EL device of the present invention has a light emitting layer that is interposed between opposing electrodes and emits electroluminescence when a voltage is applied to the electrodes. It is characterized by having a microlens for condensing light on the extraction side. Further, it is desirable that the size of the microlens is equivalent to the size of a pixel including a light emitting portion, which is a portion of the light emitting layer that emits light. Further, the size of the microlens is smaller than the size of a pixel including a light-emitting part that is a light-emitting part of the light-emitting layer, and the size of the pixel is an integral multiple of the size of the microlens. \desirable.

[Effect]

According to the above configuration, the light generated by the light emitting layer and incident on the microlens is incident on the hemispherical surface of the microlens, which serves as an interface with the outside. Therefore, the angle between the normal at the point where the light reaches the hemispherical surface and the direction in which the light travels is the angle between the normal at the point at which the light reaches the interface with the outside and the direction in which the light travels. Since the angle formed with the direction in which the microlens is applied is smaller than that in the case without the microlens, the light is extracted to the outside without being totally reflected at the interface. Therefore, the external emission intensity B○1 in this field & is equal to the emission intensity Bα of the light that has reached the microlens. Here, the refractive index of the microlens is nQ and L,
The refractive index of the light emitting layer is nz, and the intensity of light emitted from the light emitting layer is B1. Then, the above external emission intensity BO
+ can be found using the following formula. Here, the total reflection critical angle θ1-sin-'(n(!/'n
z). Since n(!>1, the total reflection critical angle θ1 is the total reflection critical angle 0 when there is no microlens.
= Thicker than s in(1/nz). For this reason,
Light extraction efficiency when the above microlens is present (1
-cO801) is larger than the light extraction efficiency (1-cos θ) without the microlens. This will be explained with reference to FIGS. 1 and 7. In the conventional example, as shown in FIG. 7, light La makes an angle θa with the vertical axis, and light Lb makes an angle θb with the vertical axis. When reaching the interface with the outside, the light La+ forming an angle θa smaller than the critical angle θ of total reflection without the microlens can be extracted to the outside, but the light La+ forming an angle θa smaller than the critical angle θ of total reflection without the microlens can be extracted to the outside. Since the light Lb forming the angle θb is totally reflected at the interface and confined within the thin film EL device, the light extraction efficiency is poor. On the other hand, according to the present invention, as shown in FIG. 1, since the microlens is provided on the side from which light is taken out, the hemispherical inner surface of the microlens becomes the interface with the outside. Therefore, the light emitting layer 5
Since the angle between the normal line at the point where the light from the light reaches the interface with the outside and the direction in which the light has traveled is smaller than in the conventional example, the light Lb that forms an angle θb with the vertical axis can also be taken out to the outside. This improves the light extraction efficiency. Furthermore, due to the light condensing effect of the microlens 1, the luminance of the light emitted when viewed from the outside is significantly improved. Further, if the size of the microlens is equivalent to the size of a pixel including a light emitting part which is a light emitting part of the light emitting layer, one microlens corresponds to one pixel. Therefore, when viewed externally, the light emitting section appears enlarged. Therefore, the size of the light emitting part is l
It can be made smaller and reduces power consumption. In addition, the size of the microlens is less than the thickness of a pixel including a light emitting part, which is the light emitting part of the light emitting layer, and the size of the pixel is an integral multiple of the size of the microlens. In addition, the height of the microlens can be reduced, and the external dimensions can be reduced.

【Example】

Hereinafter, the present invention will be explained in detail with reference to illustrated embodiments. FIG. 1 shows a detailed view of the main parts of a first embodiment of the thin film EL device of the present invention. As shown in FIG. 1, in the above embodiment, a light emitting layer 5 is provided between the transparent electrode 3 and the back electrode 7. A first insulating film 4 is provided between the transparent electrode 3 and the light emitting layer 5. Further, a second insulating film 6 is provided between the back electrode 7 and the light emitting layer 5. A glass substrate 2 is provided on the light extraction side surface of the transparent electrode 3. Further, a microlens 1 is provided on the surface of the glass substrate 2 on the side from which light is extracted. Further, in the above embodiment, as shown in FIG. 2, the size of the light emitting section 8 of the pixel defined by the transparent electrode 3 and the back electrode 7 is d, and the size of the pixel is C. . Further, the size of the cap between the light emitting parts 8 is defined as e. Further, the size f of the microlens 1 is made equal to the size C of the pixel. Therefore, since only one microlens 1 corresponds to one pixel, the light emitting section 8 appears enlarged from the outside. Therefore, it is possible to reduce the size d of the light emitting section 8,
It is possible to reduce power consumption. In the above embodiment, a voltage is applied to the transparent electrode 3 and the back electrode 7 to cause the light emitting layer 5 to emit light. In the embodiment described above, the microlens 1 is provided on the side from which light is extracted from the light emitting layer 5, so that the interface with the outside on the side from which light is extracted has a unispherical shape. I wanted to,
The angle between the normal at the point where the light reaches the hemispherical interface and the direction in which the light has traveled becomes smaller,
As shown in FIG. 1, light La is incident on the microlens 1. Lb is the light La that is taken out to the outside without being totally reflected at the interface, and is taken out to the outside. Due to the condensing effect of the microlens 1, the traveling direction of Lb becomes perpendicular to the surface of the glass substrate 2 from which light is extracted. As described above, according to the above embodiment, compared to the conventional example shown in FIG. 7 which does not include the microlens 1, the light extraction efficiency can be improved, and the luminance when viewed from the outside can be significantly improved. An example of a method for manufacturing the microlens of the first embodiment is shown in FIG. Figure 3 shows the Ha process of the microlens (A)→(
It is sectional drawing shown in order of B)-(C). (A) First, polymethyl methacrylate, which is an acrylic resin, is applied onto a sufficiently cleaned glass substrate 2 so as to have a uniform thickness, thereby forming a film 31 made of the polymethyl methacrylate. (B) Next, a photoresist (not shown) is applied onto the film 3, and then exposed and developed. Furthermore, the sputter etching method (this method involves etching the upper film 31 made of polymethyl methacrylate using the upper photoresist as a mask, and then peeling off the photoresist to form an etched pattern on the film 31). (C) Next, the etching pattern 32 is heated and shaped at a temperature of 100°C to 200°C to form a hemispherical microlens 1. Acrylate is transparent. It is easy to process and has a refractive index of 149, which is almost the same as the refractive index of glass (approximately 1.5). Next, a second embodiment is shown in FIG. 4. This embodiment is similar to the first embodiment described above except for the microlens part. Therefore, the same number is assigned to B'yf as in the first embodiment, and the explanation will focus on the microlens part.In this embodiment, as shown in FIG. The size C is six times the size of the microlens 41. That is, c=6Xy, and each pixel corresponds to 6' x 36 microlenses 41. Therefore, in this implementation, In this example, the light extraction efficiency can be improved by the microlens 41, and the height of the microlens 41 can be kept sufficiently low, so that the external dimensions can be reduced. The microlens 41 of this example can be manufactured by a process similar to the manufacturing process of the microlens 1 of the first example described above.Next, a third example is shown in FIG. It differs from the first embodiment described above only in that a microlens 51 is provided on the 8th side via a protection@55.
The points that are different from the embodiment will be explained with emphasis on. In the above embodiment, as shown in FIG. 5, the light emitting part 8 side of the pixel is coated with a thickness of several thousand to several micrometers by plasma CVD.
A protective film 55 made of a SiN film (Mo'') is formed on the protective film 55. Then, a microlens 51 is formed on the protective film 55 by a method similar to the microlens manufacturing method of the first embodiment described above. In addition, the above-mentioned pixel and the above-mentioned microlens 51 are made to have the same size.In this embodiment, a protective film with a thickness of several thousand to several μm is used instead of the glass substrate side having a thickness of about 1 mm. The microlens 51 is provided on the 55 side.Therefore, compared to the case where the microlens is formed on the glass substrate side, the microlens 51 can be disposed closer to the light emitting section 8, and the light emitting point can reach the microlens. Therefore, the light extraction efficiency can be particularly improved, and the luminance seen from the outside can be particularly improved. In this example, the size of the pixel and the size of the microlens are The size of the pixel may be the same, or the size of the pixel may be an integral multiple of the microlens.Next, a fourth embodiment is shown in FIG. 6(B).In this embodiment, the microlens portion This embodiment is different from the first embodiment described above. Therefore, the same parts as in the first embodiment are given the same numbers, and the parts related to the microlens will be explained with emphasis. As shown in figure (A),
An EL element 66 including a glass substrate 2 and a light emitting section 8;
Microlens array 61 created in a separate process
and are formed in close contact with each other as shown in FIG. 6(B). Here, if a substance such as air is present in the area between the microlens array 61 and the EL element 66, refraction or total reflection of light will occur in the area, reducing the light extraction efficiency. The microlens array 61 and the EL element 66 were brought into close contact with each other completely so that there was no gap between the microlens array 61 and the EL element 66. In the above embodiment as well, as in the first embodiment, the provision of the microlens array 61 improves the light extraction efficiency and improves the luminance when viewed from the outside.

【Effect of the invention】

As is clear from the above description, the thin film EL device of the present invention is equipped with a microlens for condensing light on the side from which light generated by the light emitting layer is taken out. The incident light is incident on the hemispherical surface of the microlens, which forms the interface with the outside. Therefore, the angle formed between the normal line at the point where the light reaches the hemispherical surface and the direction in which the light has traveled is smaller than in the case without the microlens. According to the invention, the light from the light-emitting layer is not totally reflected at the interface with the outside, and the efficiency of extracting the light to the outside and the luminance when viewed from the outside can be improved. The luminance of the light emission can be significantly improved due to the light effect.In addition, if the size of the microlens is equivalent to the size of the pixel including the light emitting part, which is the light emitting part of the light emitting layer, one pixel Since the microlens corresponds to the microlens, the light-emitting section from the outside appears to be enlarged.Therefore, the size of the light-emitting section can be reduced and power consumption can be reduced. The size of the lens is smaller than the size of a pixel including a light-emitting part, which is the light-emitting part of the light-emitting layer, and when the size of the pixel is an integral multiple of the size of the microlens, It is possible to lower the height of the lens and reduce its external dimensions.

[Brief explanation of the drawing]

FIG. 1 is a detailed view of the main parts of the first embodiment of the thin film EL device of the present invention, FIG. 2 is a sectional view showing the dimensions of each part of the first embodiment, and FIG. 3 is a detailed view of the first embodiment of the thin film EL device of the invention. 4 is a sectional view showing the dimensions of each part of the second embodiment, FIG. 5 is a sectional view showing the third embodiment, and FIG. FIG. 7 is a detailed view of a main part of a conventional thin film EL device, and FIG. 8 is a diagram explaining the structure of a conventional thin film EL device. 1.41.51... Microlens, 2.19... Glass substrate, 3,20... Transparent electrode,
4.6.21.23... Insulating film, 5,22... Light emitting layer, 7.24... Back electrode, 61... Microlens array.

Claims (3)

[Claims] (1) A thin film EL device having a light-emitting layer that is interposed between opposing electrodes and emits electroluminescence when a voltage is applied to the electrodes, with a microlens for condensing light on the side from which the light generated by the light-emitting layer is taken out. A thin film EL device characterized by the following. (2) The thin film EL device according to claim 1, wherein the size of the microlens is equivalent to the size of a pixel including a light emitting portion, which is a portion of the light emitting layer that emits light. (3) The size of the microlens is smaller than the size of a pixel that includes a light emitting part, which is the light emitting part of the light emitting layer, and the size of the pixel is an integral multiple of the size of the microlens. The thin film EL according to claim 1, characterized in that
Device.