JPH11102785A - EL element - Google Patents

Abstract

(57) Abstract: An object of the present invention is to reduce the rate of increase in light emission luminance with respect to an applied voltage in a region where light emission luminance is low. SOLUTION: A 1 sandwiched between a first electrode 2 and a second electrode 7.
The thickness of the light-emitting layer 4 was changed in one light-emitting region so that the light-emitting layer 4 had a thin film region 41 and a thick film region 42. In the thin film region 41, the light emission starting voltage is lower than that in the thick film region 42, and as the applied voltage is increased, the thin film region 41 emits light first, and then the thin film film 41 becomes thinner. The region 41 and the thick region 42 emit light. Therefore, when viewed as one whole light emitting region, the rise (increase rate) of the light emission luminance with respect to the applied voltage can be reduced. As a result, it is possible to easily perform gradation in a region where light emission luminance is low.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an EL (electroluminescence) element.

[0002]

2. Description of the Related Art
The element is configured by stacking a first electrode, a first insulating layer, a light emitting layer, a second insulating layer, and a second electrode on a glass substrate. The EL element has a characteristic that the emission luminance does not increase linearly with the applied voltage. In particular, in a region where the light emission luminance is low, the light emission luminance increases exponentially with respect to the applied voltage, and the light emission luminance largely changes with a small voltage change. For this reason, for example, in order to perform gradation display with a drive voltage, precise voltage control is required.

The present invention has been made in view of the above problems, and has as its object to reduce the rate of increase in light emission luminance with respect to an applied voltage in a region where light emission luminance is low.

[0004]

In order to achieve the above object, according to the first aspect of the present invention, a first electrode (2) and a second electrode (2) are provided.
The light-emitting layer (4) is characterized in that the light-emitting layer (4) has a region (41) having a small thickness and a region (42) having a large thickness in one light-emitting region sandwiched between the electrodes (7). . The light emission start voltage is lower in the thin film thickness region (41) than in the thick film thickness region (42). For this reason, as the applied voltage is increased, first, the thin film thickness region (41) emits light, and thereafter, the thin film thickness region (41) and the thick film thickness region (4).
2) emits light. Accordingly, when viewed as one whole light emitting region, the rise (increase rate) of the light emission luminance with respect to the applied voltage can be made smaller than that of a conventional light emitting region having a uniform film thickness.

[0005] This makes it possible to easily perform gradation, for example, in the case where gradation is performed in a region where light emission luminance is low. Further, for example, in the case of performing nighttime dimming as in an automobile meter, nighttime dimming can be easily performed by using light emission in the thin film region (41). In this case, as in the second aspect of the present invention, the thin film region (41)
If the external shape of the region (42) having a large film thickness is similar to that of the region (42),
At the time of low-luminance light emission due to light emission in the thin film region (41);
It is possible to eliminate a sense of incongruity in display at the time of high-luminance light emission by light emission in the thin film region (41) and the thick film region (42).

In particular, when dot matrix display is performed by arranging a plurality of first electrodes (2) and a plurality of second electrodes (7) at right angles, each pixel has a square shape. Since the outer shape of the thin region (41) is similar to that of the thick region (42), the difference in display between low-luminance light emission and high-luminance light emission can be made inconspicuous. In the first and second aspects of the present invention, the light emitting layer (4) only needs to have a thin film region (41) and a thick film region (42) in one light emitting region. Alternatively, the film thickness may be changed in three or more steps.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on specific embodiments. (First Embodiment) FIG. 1 is a schematic view showing a longitudinal section of an EL element according to a first embodiment of the present invention, and FIG. 2 is a plan view thereof. A section taken along the line AA ′ in FIG. 2 corresponds to FIG.

In the EL device, the following thin films are sequentially formed on a glass substrate 1 which is an insulating substrate. First,
On the glass substrate 1, a first electrode 2 made of ITO and having a thickness of 200 nm is formed. This first electrode 2 is shown in FIG.
As shown in the figure, a large number of stripes extending in the x-axis direction are provided along the y-axis direction.

On the glass substrate 1 on which the first electrode 2 is formed, a first insulating layer 3 is formed uniformly. This first insulating layer 3 is made of optically transparent SiO _x N _y (silicon oxynitride).
A first insulating lower layer 31 having a thickness of 50 to 100 nm,
Thickness 200 mainly composed of Ta ₂ O ₅ (tantalum oxide)
The first insulating upper layer 32 having a thickness of about 300 nm is formed in two layers.

The light emitting layer 4 is formed on the first insulating upper layer 32. The light emitting layer 4 includes, as shown in FIGS.
There are a thin film region 41 and a thick film region 42. In the thick film region 42, a stripe extending in the y-axis direction
A large number are provided at predetermined intervals along the axial direction. The width of the thick region 42 is half the width of the second electrode 7.

The light emitting layer 4 is made of ZnS (zinc sulfide) to which Mn (manganese) is added.
The thickness is 800 nm in the thick part. On the light emitting layer 4,
The second insulating layer 6 is formed uniformly. Second insulating layer 6
Are a 100 nm thick second insulating lower layer 61 made of optically transparent Si ₃ N ₄ (silicon nitride), a 200 nm thick second insulating middle layer 62 mainly composed of Ta ₂ O ₅ ,
It is formed of three layers of the second insulating layer 63 with a thickness of 100nm consisting _x N _y.

Then, on the second insulating upper layer 63, a layer 45 of optically transparent ZnO (zinc oxide) as a main component is formed.
A second electrode 7 having a thickness of 0 nm is formed. The second electrode 7 is
As shown in FIG. 2, a large number of stripes extending in the y-axis direction are provided along the x-axis direction. E mentioned above
The L element can be manufactured as follows.

First, ITO is uniformly deposited on a glass substrate 1 by D.
After C sputtering, the first electrode 2 is formed by etching in a stripe shape. Next, a first insulating lower layer 31 made of SiO _x N _y and a first insulating upper layer 32 mainly composed of Ta ₂ O ₅ are formed by sputtering. Specifically, the temperature of the glass substrate 1 is maintained at 300 ° C., a mixed gas of argon (Ar), nitrogen (N ₂ ) and a small amount of oxygen (O ₂ ) is introduced into the sputtering apparatus, and the gas pressure is reduced to 0. The pressure was maintained at 0.5 Pa, a SiO _x N _y film was formed using silicon as a target at a high frequency power of 3 KW, and then a film containing Ta ₂ O ₅ as a main component was sputtered with Ar and O ₂ at a gas pressure of 0. held in 6P _a, 6 wt% of Al ₂ O to Ta ₂ O _5
Using a mixed sintering target containing ₃ under a condition of high frequency power of 4 KW, a film is formed.

Next, on the first insulating upper layer 32, ZnS: M containing ZnS as a base material and Mn added as a light emission center.
The light emitting layer 4 made of n is uniformly formed. Specifically, the temperature of the glass substrate 1 was kept constant, and the inside of the evaporation apparatus was 5 × 1
0 ^-4 Pa was maintained below, deposition rate 0.1 to 0.3 nm /
Electron beam evaporation is performed under the condition of sec. Next, this layer is dry-etched to obtain thin and thick regions. Specifically, the temperature of the glass substrate 1 is maintained at 70 ° C., a mixed gas of Ar and CH ₄ (methane) is introduced into the RIE apparatus, the pressure is maintained at 7 Pa, and dry etching is performed with high-frequency power of 1 kW. Do. After performing this etching, heat treatment of the light emitting layer 4 is performed at 400 to 600 ° C. in a vacuum.

Next, on the light emitting layer 4, Si_ThreeN_FourConsists of
Second insulating lower layer 61, Ta_TwoO_FiveSecond insulation mainly composed of
Middle layer 62, SiO_xN_yA second insulating upper layer 63 made of
Each is formed in the same manner as the formation of the first insulating layer 3. However
And Si_ThreeN_FourThe film is SiO_xN _ySputter gas unlike film
O_TwoThe film is formed without introducing the compound. Next, the second insulating upper layer
A layer containing ZnO as a main component is uniformly formed on 63. Steam
As a dressing material, ZnO powder formed into pellets
And an ion plating device as the film forming device.
Used. Specifically, the temperature of the glass substrate 1 is kept constant.
The inside of the ion plating device was evacuated to vacuum
After that, Ar gas is introduced to keep the pressure constant,
The beam power and the power in the range of 6 to 18 nm / min
And high-frequency power are adjusted to form a film. Next, etch this film
To obtain a second electrode 7.

In the above EL device, the first electrode 2
In each of the light emitting regions (regions hatched in FIG. 2) sandwiched between the first and second electrodes 7, a thin region 41 and a thick region 42 are arranged in parallel. FIG.
5 shows the light emission luminance-voltage characteristics of the thin region 41, the thick region 42, and the entire light emitting region (pixel) sandwiched between the first electrode 2 and the second electrode 7.

A thin film region 41 and a thick film region 42
As shown in FIG. 3, there is a difference between the respective light emission start voltages due to the difference in the film thickness. That is, the light emission start voltage (voltage at point a in FIG. 3) of the thin film region 41 is low, and the light emission start voltage (voltage of point b in FIG. 3) of the thick film region 42 is high. . When this EL element is viewed in terms of panel luminance (light emission luminance of one pixel), a voltage near the light emission start voltage of the thin film region 41 (voltage at point c in FIG. 3)
In this case, since the light emitting area is smaller than the size of one pixel, the light emission luminance is low and the rise becomes gentle. When the voltage was further increased and reached the vicinity of the light emission start voltage of the thick region 42 (the voltage at point d in FIG. 3), the light emitting area was the sum of the thin region 41 and the thick region 42. Since the area, that is, one pixel emits light, the rise of the light emission luminance becomes a steep rise similar to the case where the thickness of the light emitting layer is uniform.

FIG. 4 shows a light emission luminance ratio (a light emission luminance at a light emission start voltage + 60 V) to a maximum value of light emission luminance in one pixel with respect to a difference in film thickness between the thick region 42 and the thin film region 41. 2) and the relationship between the rising angles. Here, the rising angle is a value defined by log (light emission luminance at light emission start voltage + 20 V) / 20. The light emission luminance is equal to the maximum voltage (light emission start voltage + 60).
V) is the emission luminance when voltage is applied. The areas of the thick region 42 and the thin region 41 are the same.

As shown in FIG. 4, a thick region 4
2 and the region 41 having a small thickness, the emission luminance ratio when the maximum voltage is applied decreases as indicated by the dashed line in the figure, and the rising angle increases as indicated by the solid line in the figure. Is also smaller. If the light emission luminance ratio is 0.3 or more, a practically necessary luminance can be obtained.
It is preferably not more than 00 nm. When the rising angle is 0.3 or less, light control can be easily performed, and the difference in film thickness is preferably 50 nm or more.

FIG. 5 shows the relationship between the ratio of the area of the thick region 42 to the area of one light-emitting region (pixel) and the ratio of the light-emitting luminance to the maximum value of the light-emitting luminance of one pixel, Show the relationship. The rising angle in this case is also a value determined by the above definition. The thickness difference between the thick region 42 and the thin region 41 is 200 nm.

As shown in FIG. 5, as the area ratio increases, the emission luminance ratio when the maximum voltage (emission start voltage + 60 V) is applied increases, as indicated by the dashed line in the figure. Further, the rising angle has a characteristic that it becomes minimum near the area ratio of 35%. Also in this case, if the emission luminance ratio is 0.3 or more, practically necessary luminance can be obtained, and therefore, the area ratio is preferably 20% or more. The rising angle varies depending on the film thickness difference. When the film thickness difference is set to 200 nm, if the area ratio is set to 80% or less, the rising angle is set to 0.3 or less to easily perform light control. be able to. (Second Embodiment) In the first embodiment, a thin film region 41 and a thick film region 42 are arranged in parallel in one pixel. However, as shown in FIG. The outer shape of the thin region 41 and the thick region 42 may have similar shapes (squares). In this case, in the display per pixel, at the time of low-luminance light emission in which the thin film region 41 emits light,
In both high-luminance light emission in which both the thin-film region 41 and the thick-film region 42 emit light, a square pixel display is obtained, so that the display can be made inconsistent. In particular, it is possible to make the difference in display between low-luminance light emission and high-luminance light emission when displaying characters inconspicuous.

In the first and second embodiments, the first electrode 3 is a horizontal scanning electrode and the second electrode 7 is a vertical signal electrode. However, the first electrode 3 is a vertical signal electrode.
The second electrode 7 may be a horizontal scanning electrode. In addition, as the light emitting layer 4, ZnS: T is used in addition to the ZnS: Mn light emitting layer.
A light-emitting layer such as bOF or SrS: Ce may be used. In this case, the same effect as described above can be obtained.

The first electrode 2 and the second electrode 7 include
In addition to using both as transparent electrodes, it is also possible to configure so that either one is not a transparent electrode. In this case, Ta (tantalum) metal, Ag (silver), M
It can be formed of a metal such as o (molybdenum) or W (tungsten), and an auxiliary metal electrode for lowering resistance may be added as necessary. (Third Embodiment) The present invention can be applied not only to the thin film EL device as in the first and second embodiments, but also to an organic EL device as shown in FIG. This organic EL element has a configuration in which a light emitting layer 4 is sandwiched between a first electrode 2 and a second electrode 7.
There are two structures (the hole injection layer and the electron injection layer are not shown in FIG. 7). In any of these structures, if the light-emitting layer 4 has the thin-film region 41 and the thick-film region 42 in one light-emitting region, the same effect as in the above-described embodiment can be obtained. Can be. (1) First electrode (cathode) / light-emitting layer / hole injection layer / second electrode (anode) (2) First electrode (anode) / light-emitting layer / electron injection layer / second electrode (cathode) (3) First electrode (anode) / hole injection layer / light emitting layer / electron injection layer / second electrode (cathode) (4) First electrode (anode or cathode) / light emitting layer / second electrode (anode or cathode) In any of the above-described embodiments, when the thickness of the light emitting layer 4 is changed in one light emitting region, the change in the film thickness is not limited to two steps, and may be three or more steps as necessary.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a longitudinal section of an EL element according to a first embodiment of the present invention.

FIG. 2 is a plan view of the EL element shown in FIG.

FIG. 3 is a diagram showing light emission luminance-voltage characteristics of a thin film region 41, a thick film region 42, and one light emitting region as a whole.

FIG. 4 is a diagram showing a relationship between a light emission luminance ratio with respect to a maximum value of light emission luminance and a rising angle with respect to a difference in film thickness between a thick film region 42 and a thin film region 41.

FIG. 5 is a diagram illustrating a relationship between a light emission luminance ratio with respect to a maximum value of light emission luminance and a rising angle with respect to a ratio of an area of a thick film region to an area of one light emission region.

FIG. 6 is a plan view of an EL device according to a second embodiment of the present invention.

FIG. 7 is a schematic view showing a vertical cross section of an organic EL device according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... 1st electrode, 3 ... 1st insulating layer, 4 ...
Light-emitting layer, 6: second insulating layer, 7: second electrode.

Claims (2)

[Claims] 1. An EL device comprising a light emitting layer (4) between a first electrode (2) and a second electrode (7), wherein the first electrode (2), the second electrode (7) and An EL element, wherein the light emitting layer (4) has a thin film thickness region (41) and a thick film thickness region (42) within one light emitting region sandwiched between. 2. The EL device according to claim 1, wherein the thin region (41) and the thick region (42) have similar shapes.