JPH05315073A - El element - Google Patents

Abstract

PURPOSE:To provide even distribution of rightness by providing a voltage applying lead out part in many spots, many earth or individually separate electrodes, and a resistor and/or capacitor, when necessary, between an EL element and a driving circuit. CONSTITUTION:An Al lower part electrode 2 is provided in a Pyrex plate 1, and an Si3N4 lower part insulating layer 3 is formed by a reactive spattering method to pile a light emitting layer 4 by ZnS of adding TbO. Next, an Si3N4 upper pat insulating layer 5 and an ITO upper part electrode 6 are overlapped. The electrode 6, having sheet resistance, is patterned so as to provide a lead-out part 9 by each five spots from each side. By this constitution, since a voltage applying drawout electrode is set up in many spots, an influence of decreasing effective applied voltage to an EL element by resistance of a transparent conductive film is decreased, and uniformity of brightness can be obtained. A resistor or capacitor is provided between an individualized EL element and a driving circuit, to perform wiring, and when a resistance value is changed, film thickness distribution of the light emitting layer and insulating layer of the EL element and brightness distribution by nonuniformity of film material of the light emitting layer are adjusted to obtain uniform brightness.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an EL device.

[0002]

2. Description of the Related Art A current EL device has a structure as shown in FIG. 1, in which dielectric insulating films 3 and 5 are provided on both sides of the EL light emitting layer in order to apply a high electric field to the EL light emitting layer. It has a double insulating structure in which electrodes 2 and 6 are formed on the upper and lower sides so as to enclose the light emitting layer and the two insulating films. In order to use the EL element as a display or a light source, a transparent conductive film or a semitransparent metal thin film is generally used for at least one of the upper and lower electrodes. There are roughly three causes of variations in the brightness of EL elements. One is due to the film quality of the light emitting layer, such as the concentration distribution of impurities existing in the light emitting layer and serving as the light emission center and the non-uniformity of crystallinity of the light emitting layer.
This can be suppressed to some extent by optimizing the film forming method and the film forming conditions. The second is caused by the film thickness distribution of the light emitting layer and the insulating layer, and the brightness is high in a thin film area because the electric field strength is high when a voltage is applied. Also regarding this, by studying the film formation method and film formation conditions,
Although it can be suppressed to some extent, film formation on a large area or a long substrate is necessary when making a large area display or a linear light source of a long length surface light source. There is a limit to how small it can be made, and in some cases, a width of several + percent brightness distribution may occur. Therefore,
When making an EL light source or an EL display having a large area or a long length, it is necessary to reduce the width of the luminance distribution due to the film quality and the film thickness distribution of the light emitting layer in some way. The third is the luminance distribution caused by the wiring resistance of the electrode for driving the EL light emitting layer. For example, as a backlight of a liquid crystal display such as a word processor, there is one using a dispersion type EL panel. This has a structure in which a light emitting source obtained by hardening an EL light emitting material with a binder is surrounded by a transparent electrode such as a metal electrode ITO. As shown in FIG. 2, each layer has an area approximately equal to the display area. Therefore, the electrode take-out portions 8 and 9 are provided at one place on the metal electrode 2 and at one place on the transparent electrode 6, respectively. Since a transparent electrode material such as ITO has a higher resistivity than a metal, the potential drops as the distance from the electrode extraction portion increases. Therefore, when it is used as an electrode material of an EL panel, the electric field strength applied to the EL light emitting film is weakened at a position far from the electrode extraction portion, and the brightness is lowered. That is E
The luminance is high near the electrode extraction portion of the L panel, and has a luminance distribution in which the luminance decreases as the distance from the electrode extraction portion increases. As a countermeasure, there is a method of reducing the sheet resistance by thickening the transparent electrode, but the increase of the film thickness lowers the transmittance of the transparent conductive film, lowers the emission brightness, and leaves some variation in the brightness. . Further, an EL element using a transparent conductive film for both upper and lower electrodes is formed in the waveguide region, and the light from the EL light emitting layer is propagated through the waveguide and is guided to the end face of the waveguide. Although an EL element has been proposed, in this case, it is preferable that the transparent electrode be thin from the viewpoint of the efficiency of emitting light to the end face. It is difficult to suppress the luminance distribution by each.

[0003]

[Purpose] An object of the present invention is to provide a display using an EL device, a surface light source such as a backlight for liquid crystal, a facsimile,
It is to suppress the width of the luminance distribution, which is a problem when an EL element is used as a linear light source for illuminating a document surface such as copier, as small as possible. Another object of the present invention is to prevent a decrease in brightness caused by the resistance of the transparent conductive film.

[0004]

According to a first aspect of the present invention, in an EL element using a transparent conductive film as at least one of upper and lower electrodes for driving the EL element, a large number of lead-out portions for voltage application are provided. The present invention relates to an EL device for Second of the present invention
Are characterized in that, in an EL element using a transparent conductive film for at least one of upper and lower electrodes for driving the EL element, at least one electrode selected from the group consisting of an upper electrode and a lower electrode is individually separated. And an EL element. That is, the second aspect of the present invention is that the first aspect of the present invention has a large number of electrode extraction portions, whereas the number of electrodes themselves is a large number. The third aspect of the present invention is
In an EL element using a transparent conductive film for at least one of upper and lower electrodes for driving the EL element, at least one electrode selected from the group consisting of an upper electrode and a lower electrode is individually separated, and The present invention relates to an EL element having a resistor and / or a capacitor provided between drive circuits.

In order to suppress the luminance distribution caused by the resistance of the transparent conductive film, as shown in FIG. 2, conventionally, there are a large number of electrode lead-out portions, one for each of the upper and lower electrodes 6, 2. You can do it. For example, as shown in FIG. 4, if a large number of electrode lead-out portions 9 are provided from the peripheral portion of the upper transparent electrode 6 and driven, the central portion has a slightly lower luminance than the peripheral portion, but in the case of the configuration of FIG. The width of the relatively large luminance distribution seen can be reduced. Edge emitting type E shown in FIG.
In the case of the L element, if the electrode lead-out portions 8 and 9 are provided at a constant interval in parallel with the waveguide end face as shown in FIG. The variation in brightness in the direction parallel to the end face of the waveguide can be eliminated. However, although the luminance distribution in the direction parallel to the light extraction direction still remains, this luminance distribution is independent of the luminance distribution at the end face of the waveguide, so that light emission from the end face of the waveguide is It can be used as a linear light source.

In the above-mentioned example, the EL light emitting layer and the upper and lower electrodes are all constructed by using a single thin film, but in reality, at least one layer of the EL light emitting layer and the upper and lower electrodes is composed of several sheets. The electrodes may be formed separately and the electrodes may be taken out from each. A region that does not emit light is generated due to the separation formation, but the width of the region that does not emit light is reduced to several μ by photolithography technology.
If it is set to m to several + μm, it can be used as a uniform light source because the region that does not emit light can be ignored. Particularly in the edge emitting EL device, since the distance between the end face of the waveguide and the EL light emitting layer is relatively large, linear light emission with no boundary is generated at the end face of the waveguide even if the width of the non-light emitting region is several + μm to several hundred μm. can get. Further, when obtaining a large-area surface light source, as shown in FIG. 7, a single thin film is used for the EL light emitting layer 4, and the upper and lower electrodes 6, 6 are used.
2 may be formed in stripes in which the width of the non-light emitting region is several μm to several + μm and are orthogonal to each other. At this time, in order to reduce the influence of the resistance of the transparent conductive film described above, it is desirable to take out the electrodes from both sides of the stripe. In the case of dividing the region emitting light in the edge emitting EL device, at least one of the transparent conductive films may be individually separated and wired as shown in FIG. As described above, the EL light emitting layer 4, the upper and lower electrodes 6,
If at least one of the two is individually separated, the surface emitting light source can be used as an EL display and the edge emitting EL
Although the element can be used as a printer light source, it serves as a means for correcting the luminance distribution due to the film quality of the light emitting layer and the film thickness distribution of the light emitting layer and the insulating layer described above. That is, by separately separating the light emitting portions of the EL, it becomes possible to make the brightness uniform by individually adjusting the voltage applied to the EL element when the brightness varies among the elements. In order to adjust the applied voltage, an alternating current resistance between the EL light emitting element and the driving circuit, such as IT
If wiring is performed through the O film, the applied voltage for driving each EL element may be changed depending on the resistance value. FIG. 9 shows an equivalent circuit of the EL element including the resistor. Since the EL element can be regarded as a capacitor, its capacitance value is C ₁ , C _2, ... In addition, the impedance value of the resistor is Z ₁ , Z ₂ ...
And If the value of the AC applied voltage is V, the value of the voltage applied to each EL element is (C ₁ · V) / (C ₁ + Z ₁ ), (C ₂ ·
V) / (C ₂ + Z ₂ ), ... When the EL elements are formed on the same substrate, the values of C ₁ , C _2, ... Are determined by the film thicknesses of the upper and lower insulating layers and the light emitting layer that make up the EL element. _The luminance can be adjusted by changing the applied voltage applied to the EL element by changing the values of ₁ , Z ₂ ...

[0007]

EXAMPLES The following are specific examples of the present invention. Example 1 First, an EL panel having the structure shown in FIG. 4 was prepared. The board is 50m
An m-square Pyrex plate was used. As the lower electrode 2, A
1 was formed into a film by a vacuum vapor deposition method and patterned. A Si ₃ N ₄ film was formed thereon as a lower insulating layer 3 by a reactive sputtering method. The target is Si,
N ₂ was used as the sputtering gas, and the film thickness was 3000 Å. The film thickness distribution was within ± 3% within a 45 mm square.
Next, a TbOF-doped ZnS film was formed as the light emitting layer 4. The target is ZnS powder and 5 wt% TbOF.
Ar60 was used as the sputtering gas by using a mixture of powders.
%, He 40% mixed gas was used. The film thickness is 6000
The thickness was set to Å and a film was formed in a 40 mm square area, and the film thickness distribution was still within 3%. A Si ₃ N ₄ film was formed thereon as the upper insulating layer 5 under the same conditions as the lower insulating layer 3. Finally, an ITO film was formed as the upper electrode 6 by the RF sputtering method. Ar was used as the sputtering gas. The film thickness was 1000Å, and the sheet resistance was 40Ω / □. The upper ITO electrode was patterned so that it had five lead-out portions 9 from each side as shown in FIG.
In this way, the EL whose luminance distribution due to the film thickness distribution is reduced as much as possible
A device was prepared, and the luminance distribution was measured by changing the method of taking out the electrodes. First, one place on the lower Al electrode 2 and the upper ITO electrode 6
In addition, the brightness was measured at one location, that is, the wiring method of FIG. The drive uses a 5 KHz sine wave and the applied voltage is 23
It was set to 0V. The brightness at the location near the electrode outlet is 1730
a cd / m ^2, the luminance decreases as the distance from the electrode lead-out portion, in the farthest position 1410cd / m ²
The brightness is reduced by about 18%. On the other hand, when a voltage is applied to all of the upper electrode lead-out portions 9 provided at 20 places, the luminance of the peripheral portion is 1930 cd /
m ^2, even in the darkest central, at 1780cd / m ^2, 8%
It fell within the decline. As for the brightness distribution of the EL panel, it is desirable that the minimum value falls within 10% of the maximum value, and it is well within the range, and the effect of multiple wirings was confirmed.

Example 2 An edge emitting EL device shown in FIG. 3 was prepared and the luminance distribution was measured. The substrate 1 was made of Pyrex glass having a size of 50 mm × 75 mm, and a Cr / CrO ₂ film was formed as 1000 Å by a sputtering method as a light shielding layer. The first waveguide cladding layer 12 and the waveguide core layer 13 were formed thereon by plasma CVD. SiH ₄ , CO ₂ , and N ₂ are used as the source gas, the film thicknesses of the clad layer and the core layer are 5 μm and 20 μm, respectively, and the refractive indices are 1.46 and 1.57, respectively. Further, an ITO transparent electrode (lower electrode) 2, on the waveguide core layer 13,
Si ₃ N ₄ lower insulating layer 3, ZnS: TbOF light emitting layer 4, S
The i ₃ N ₄ upper insulating layer 5 and the ITO transparent electrode (upper electrode) 6 were formed in this order by the same method and conditions as in Example 1 to obtain an EL light emitting device. The upper and lower ITO transparent electrodes were patterned as shown in FIG. The size of the EL emitting layer is 10
mm x 70 mm, the electrode extraction part is 10 mm both up and down
There are 7 places on the pitch. Finally, the second waveguide cladding layer 12 was formed to a thickness of 5 μm under the same conditions as the cladding layer on the light shielding layer. The luminance was measured by measuring the luminance of the upper surface through the second cladding layer and the upper ITO transparent electrode and the luminance of the end face from the end face of the waveguide to evaluate the luminance distribution. The results are shown in FIG. In the figure, α _{1 to} α ₇ are extraction electrodes of the upper ITO electrode, β ₁ to
β ₇ is an extraction electrode of the lower ITO electrode. The brightness is defined by the end face brightness at the waveguide end face (AA) and the straight line (BB ') parallel to the waveguide end face, and the straight line (C- parallel to the light extraction direction).
The upper surface luminance at C ') was measured and shown in the graph. There are two wiring methods, one in which the upper and lower extraction electrodes are used, one in which (i) α ₁ and β ₁ are used [(b) in FIG. 10], and (ii) α ₁ . A total of three types were carried out, using only β ₇ [(c) of FIG. 10], and (iii) using all of the upper and lower extraction electrodes [(d) of FIG. 10]. The maximum value of the brightness at A-A 'and BB' (L
Table 1 shows a summary of the values of ΔL calculated by (Lmax−Lmin) / Lmax × 100 as a guideline of the luminance distribution.

[Table 1] When the upper and lower extraction electrodes are taken from one side as in the case of (i), the potential drop due to the ITO electrode occurs at the upper and lower electrodes, and the brightness at a place far from the extraction electrode is considerably reduced. .. Even if the extraction electrodes are provided on both sides as in (ii), a decrease in brightness is unavoidable at the central portion. In either case, it is expected that the brightness will be further reduced by making the length longer. In contrast, (ii
When a large number of extraction electrodes are provided as in i), it can be used as a uniform linear light source with almost no brightness distribution.
In any of the cases (i), (ii), and (iii), a luminance distribution of several% can be seen on CC ′ parallel to the light extraction direction. , It does not affect the luminance distribution on the end face. As described above, in the case of the edge emitting EL element using the transparent conductive film for both the upper and lower electrodes, it is understood that the effect of reducing the luminance distribution by providing a large number of extraction electrodes is particularly large.

Example 3 An example in which a resistor is placed between the EL light emitting element and the driving circuit and wiring is shown below. Although a commercially available chip component may be used as the resistor, it is desirable to form it on the same substrate as the EL element by a thin film process because it takes time and effort for wiring when the number of elements increases. Examples of the material for the resistor include carbon, semiconductors such as Si, and high resistance metals such as tungsten and tantalum. ITO, In ₂ O ₃ , SnO ₂ , ZnO used as a transparent electrode of an EL element.
It is convenient for the process to use etc. It is necessary to change the resistance value of the resistor according to the brightness distribution of each EL element, but if the state of the thickness distribution of the EL light emitting layer and the insulating layer, which is a major cause of the brightness distribution, is investigated, the required resistance value is , Can be calculated. A large resistance value, that is, a resistor with a small cross-sectional area, is placed in a portion where the film thickness is expected to be high, and a small resistance value is placed in a portion where the film thickness is expected to be low and the luminance is expected to be low The electrodes and the resistor may be patterned so as to do so. For example, when ITO is used as a resistor, the lead-out portion 9 of the upper ITO electrode of the EL element is used as a resistor as shown in FIG.
The resistance value may be adjusted by the width (cross-sectional area) or length. Further, the EL element mainly has a double insulation structure and is often driven by an alternating current of several KHz, so that a capacitor can be used as a resistor. In this case as well, the capacitor is preferably formed on the same substrate as the EL element, and the portion of the double-insulated EL element without the EL light emitting layer can be used as the capacitor. Specifically, as shown in FIG. 12, if the upper and lower ITO electrodes of the EL element are extended to a portion where there is no EL light emitting layer, the extended portion and the upper and lower electrodes,
The portion where the upper and lower insulating layers overlap can be used as a capacitor. When the ITO electrode described above is used as a mere resistor, C ₁ and C _{2 in} FIG.
...... changes, but Z ₁ , Z ₂ ...... does not change, so correct brightness adjustment is possible only at a specific frequency. However, if a capacitor is used, Z ₁ , Z ₂ ...... can be changed to C ₁ , C ₂ Since it has the same frequency characteristics as ..., it has the advantage of being able to handle all frequencies within several + Hz to several KHz. The resistance value of the capacitor with respect to alternating current can be changed by the electrode area of the capacitor and the film thickness of the insulating film. In this case, the film thickness of the insulating film is
Since it is the same as the insulating film of the EL element, the brightness can be adjusted by adjusting the size of the electrode area. However, the electrode area must be determined in consideration of the film thickness distribution of the insulating layer of the capacitor. However, if the film thickness distribution deviates from that previously examined, or if the luminance distribution remains due to other causes such as uneven distribution of emission centers in the film and uneven crystallinity, the ITO resistor or , Part of the upper ITO electrode of the capacitor is trimmed by instantaneous laser irradiation,
The brightness can be adjusted by changing the resistance value. Of course, at the beginning, the areas of the resistors and capacitors may be the same, and adjustment may be performed by laser trimming while checking the luminance distribution.

According to the first and second aspects of the present invention, when a transparent conductive film is used as an electrode for driving an EL light emitting element, a large number of lead-out electrodes for voltage application are provided, or a large number of electrodes themselves are provided. Therefore, the effect of the effective applied voltage drop applied to the EL light emitting element due to the resistance of the transparent conductive film can be reduced, and the brightness can be made uniform. In particular, the effect is large in the edge emitting EL element using the transparent conductive film for both the upper and lower electrodes. A third aspect of the present invention is an EL element having a structure in which at least one of the EL light emitting layer, the upper electrode and the lower electrode is individually formed, and a resistor or a capacitor is provided between the individual EL element and the driving circuit. Since the wiring is provided and adjusted, the resistance value can be changed to adjust the brightness distribution due to the film thickness distribution of the light emitting layer and the insulating layer of the EL element and the non-uniformity of the film quality of the light emitting layer, etc. Can be realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a conventional EL device.

FIG. 2 is a plan view of a conventional EL panel in which there is one extraction portion from each of the upper and lower electrodes.

FIG. 3 is a cross-sectional view of a typical edge emitting EL device.

FIG. 4 is a plan view for explaining a portion taken out from the upper and lower electrodes according to the first embodiment of the present invention.

FIG. 5 is a plan view of a case where lead-out portions from upper and lower electrodes are formed in a mode different from FIG. 4 (Example 2 of the present invention).

FIG. 6 is a plan view of a case where there is only one extraction portion from each of the upper and lower electrodes in the edge emitting EL element (conventional type).

FIG. 7 is a plan view showing a specific example of the present invention in a mode different from that of FIGS. 4 and 5, in which upper and lower electrodes are individually formed into stripes.

FIG. 8 is a plan view showing an example of division of upper and lower electrodes of the edge-emitting EL device according to the present invention.

FIG. 9 shows an equivalent circuit of the EL device of the present invention.

FIG. 10 is a plan view of an edge emitting EL device according to Example 2 of the present invention and shows a luminance distribution on each surface corresponding thereto. (A) is a plan view of the EL element, and (B) and (B ') show α ₁ and β ₁
A-A 'surface when voltage is applied from the electrode extraction part of B, B
The respective luminance distributions on the −B ′ surface and the CC ′ surface are shown. (C),
(C ') shows the respective luminance distributions of the AA' plane, the BB 'plane, and the CC' plane when voltage is applied from the electrode extraction portions of α ₁ and β ₇ . (D), (d ') _{is, α 1 ~α 7, A-} A when a voltage is applied to the electrode lead-out portion of the β ₁ ~β _7' surface, B-
The respective luminance distributions on the B ′ surface and the CC ′ surface are shown.

FIG. 11 is a plan view (a) and (b) to (d) of an EL element when the lead-out portion of the electrode is used as a resistor (the present invention).
The luminance distribution of the light receiving surface in the case of is shown. (B) shows the case where no resistor is used, (C) shows the same length and cross-sectional area of the resistor, and (D) adjusts the length of each resistor to make the brightness distribution almost constant. It shows the case.

FIG. 12 is a plan view of an EL element in the case where an electrode lead-out portion is used as a capacitor (the present invention).

[Explanation of symbols]

 1 Substrate 2 Lower Electrode 3 Lower Insulating Layer 4 Light Emitting Layer 5 Upper Insulating Layer 6 Upper Electrode 8 Lower Electrode Extraction Section 9 Upper Electrode Extraction Section 12 Waveguide First and Second Clad Layer 13 Waveguide Core Layer

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[Procedure amendment]

[Submission date] June 10, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 10

[Correction method] Change

[Correction content]

FIG. 10 is a plan view of an edge emitting EL device according to Example 2 of the present invention and shows a luminance distribution on each surface corresponding thereto. (A) is a plan view of the EL element, and (B) is a plane AA ′, a plane BB ′ when a voltage is applied from the electrode extraction portions of α ₁ and β ₁ .
(E) shows each luminance distribution of the CC ′ plane. (C) is
A when voltage is applied from the electrode extraction part of α ₁ and β ₇
The A ′ surface, the BB ′ surface, and (F) show the respective luminance distributions of the CC ′ surface. (D) is an A-A 'surface, a BB' surface when a voltage is applied from the electrode extraction portions of α _{1 to} α ₇ and β _{1 to} β ₇ .
(G) shows each luminance distribution on the CC ′ plane.

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 10

[Correction method] Change

[Correction content]

[Figure 10]

Claims (5)

[Claims] 1. An EL element using a transparent conductive film for at least one of upper and lower electrodes for driving the EL element,
An EL element having a large number of extraction portions for voltage application. 2. An EL element using a transparent conductive film for at least one of upper and lower electrodes for driving the EL element,
An EL device, wherein at least one electrode selected from the group consisting of an upper electrode and a lower electrode is individually separated. 3. An EL element using a transparent conductive film for at least one of upper and lower electrodes for driving the EL element,
An EL element, wherein at least one electrode selected from the group consisting of an upper electrode and a lower electrode is individually separated, and a resistor and / or a capacitor is provided between the EL element and a drive circuit. 4. The EL element according to claim 3, wherein the resistor is a portion of the transparent electrode having a reduced cross-sectional area or an extended length. 5. The EL element according to claim 3, wherein the capacitor is provided with a portion having no light emitting layer in a part of the basic structure of the EL element, and the portion is used as the capacitor.