JPH02234393A - Multi-color display type thin film electroluminescence element - Google Patents

Abstract

PURPOSE:To improve luminous characteristics by arranging ZnS:Mn luminous layers on both sides of a ZnS:Tb, F luminous layer. CONSTITUTION:ZnS:Mn luminous layers 4a and 4b are arranged on both sides of a ZnS:Tb, F luminous layer. When the ZnS:Mn luminous layers are formed in two layers 4a and 4b and arranged on both sides of the ZnS:Tb, F luminous layer 5, strong luminescence is extracted near the interfaces with insulating layers 3 and 6 on both the anode side and cathode side of the ZnS:Mn luminous layers 4a and 4b. ZnS:Mn luminous layers 4a and 4b are arranged on both sides of the ZnS:Tb, F luminous layer 5, which is located at the position kept inside from the interfaces with the insulating layers 3 and 6, thus strong luminescence is extracted. Higher intensity can be obtained with the lower voltage accordingly.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to electroluminescent (hereinafter referred to as EL) elements used in display devices, etc. Display type thin film E
Regarding L elements.

[Conventional technology]

Conventionally, as a multi-color display type thin film EL element capable of emitting light of two primary colors red and green and intermediate colors thereof, a green light-emitting EL element having a ZnS:Tb,F light-emitting layer and a red light-emitting EL element having a ZnS:Sm,F light-emitting layer have been used. A three-terminal structure made by stacking light-emitting EL elements (JAPAN DISPLAY '83 DI
GEST), which has a light-emitting layer in which both the light-emitting parts of ZnS:Tb,F and Zns:sm,F are arranged planarly by patterning by photolithography (
Proceedings of '87s TD Ink
, Symp. ), a structure in which a red light-emitting EL device made of CaS:Eu and a blue-green light emitting EL device made of SrS:Ce are stacked with their transparent electrodes facing each other has been proposed (same document).

However, in the device with the first 3#i structure, the number of thin film layers in the entire device increases;
Characteristics tended to be unstable, and device formation was troublesome. Furthermore, devices in which the second light-emitting layer is patterned by lithography require extremely advanced microfabrication technology to form the light-emitting layer, which poses the problem that it is extremely difficult to fabricate large-area, high-definition displays. there were. Moreover, ZnS, which is the red emitter used in both of the above devices,
:Sm, F has a low luminance of about 1,000 cd/m at the maximum, so it is insufficient in luminance and is not practical as a display device such as an EL panel.

In addition, the third element also currently has insufficient brightness and has not yet reached the practical stage, and CaS and SrS, which are the base materials of the light emitters in both light emitting layers, deteriorate significantly due to moisture absorption, so the durability of the element is limited. The disadvantage was that it was easy to become sexually impaired.

Therefore, the present inventors first developed ZnS:Mn and 2ns:Tb,F between the transparent display side electrode and the back side electrode.
Two light emitting layers with different colors are placed together with an insulating layer,
A multicolor display type thin film that can emit light of two primary colors red and green and all intermediate colors ranging from red to green with high brightness by alternately arranging red light transmitting filters and green light transmitting filters in a planar manner on the display side. We have developed an EL element and have already filed a patent application (Japanese Patent Application No. 63-66299).

The above-mentioned single-filter type multicolor display type thin film EL device uses ZnS:Mn and ZnS used to form its light emitting layer.
: Both Tb and F are luminescent materials that can exhibit high brightness, and because they can obtain higher brightness than conventional materials and display multicolors using filters, they are suitable for device fabrication. Single-color display type EL that does not require particularly advanced microfabrication technology
It has the advantage that it can be manufactured using almost the same method as the device. [Problems to be Solved by the Invention] However, in order to obtain a display panel with higher definition and a larger area, it is desirable not to be satisfied with the current situation, but to obtain a higher pancreatic intensity at the lowest possible voltage.

Therefore, it is an object of the present invention to provide a multicolor display type thin film EL element that improves the light emitting characteristics of the filter-type multicolor display type thin film EL element and can obtain higher luminance without increasing the driving voltage. Purpose. [Means for Solving the Problems] The present invention provides Zns:M on both sides of a ZnS:Tb,F light emitting layer.
The above object is achieved by arranging the n-light emitting layer.

As mentioned above, ZnS is placed on both sides of the ZnS:Tb,F emitting layer.
The reason why the arrangement of the :Mn light-emitting layer improves the light-emitting characteristics and provides higher brightness is as follows.

ZnS:Mn and ZnS:Tb,F have different light emission mechanisms, and therefore the distribution of light emission intensity in the thickness direction of the light emitting layer is different (Marrelo. et a1, J.
Appl. Phys. 52 (5) 1981). ZnS
: In the case of Mn, light emission mainly occurs due to the collisional excitation of Mn ions by hot electrons, so when driven by alternating current, the light emission intensity decreases due to the luminescent layer with a high internal electric field on the cathode side.
It is high at the insulating layer interface and low at the anode side interface. On the other hand, in ZnS:Tb,F, the matrix (ZnS)
Since resonance transfer of energy from the Tb ions to the Tb ions is involved in light emission, the light emission is weak at the light emitting layer/insulating layer interface on both the anode side and the cathode side, and light emission occurs in a region that penetrates about 100 to 200 nm from the interface. becomes stronger.

Therefore, if these light-emitting layers are simply stacked, Zn
The light emission of S:Mn is strong on the cathode side, but weaker on the anode side, resulting in a decrease in luminous efficiency when driven with alternating current. Also, ZnS
: Since the light emission of Tb and F becomes weak at the position where the light is in contact with the insulating layer on both the anode side and the cathode side, a loss in light emission efficiency occurs in this part.

Therefore, the ZnS:Mn light-emitting layer was made into two layers, and this was
If placed on both sides of the S:Tb,F light emitting layer, ZnS:Mn
Strong light emission is extracted from the light emitting layer near the interface with the insulating layer on both the anode side and the cathode side. In addition, the ZnS:TbSF light emitting layer has ZnS:Mn light emitting layers arranged on both sides thereof,
Strong light emission can be extracted from the interface with the insulating layer because it is located deep inside. In this way, ZnS:Mn
Since the light emitting layer and the ZnS:Tb,F light emitting layer extract light in the most efficient state, high brightness can be obtained even at the same wAw-. Therefore, high brightness can be obtained without increasing the drive voltage. Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view showing an example of a multicolor display type thin film EL element of the present invention.

In the figure, (1) is a glass substrate;
On the top, a back electrode (2) made of a thin film of aluminum or a transparent conductive material such as indium-tin composite oxide (hereinafter referred to as ITO) or tin oxide containing fluorine is formed in a parallel stripe pattern. Then, on this back side electrode (2), an insulating layer (3) on the back side is sequentially formed.
, ZnS:Mn light-emitting layer (4a), Zns:Tb,F light-emitting layer (5), ZnS:Mn light-emitting layer (4b), display-side insulating layer (6), and further display-side insulating layer ( 6)
Above, a display side electrode (7) made of a thin film of the same transparent conductive material as described above is formed in a parallel stripe pattern in a direction perpendicular to the rear side electrode (2). and,
A red light transmitting filter (8) is placed on another glass substrate (9).
r) and green light transmitting filters (8g) are alternately formed with the same dimensions and spacing as each stripe of the display side electrode (7), and these red light transmitting filters (8r) and green light transmitting filters (8g) ) to the display side electrode (7
), an EL element is fabricated. That is, in this EL element, the light emitting layers (4a), (5), (4b) are connected between the back side electrode (2) and the display side electrode (7) via the insulating layers (3), (6). is placed, and
On the display side, red light transmitting filters (8') and green light transmitting filters (8g) are alternately formed in a planar shape. Note that although Figure 1 only shows the main parts of the EL element and does not show the ends, this EL element also has no insulation at the ends, as in the case of a thin film EL element with a normal double insulation structure. The extended portion of the layer (6) is a ZnS:Mn light emitting layer (4b),
ZnS:Tb,F light emitting layer (5), ZnS:Mn light emitting layer (
4a) and the side surfaces of the insulating layer (3), and the light emitting layer (4a)
), (5), and (4b) are completely covered with the insulating layers (3) and (6). The reason why multicolor display is possible with this EL element is as follows. In the EL element having the above configuration, when an AC voltage higher than the emission starting voltage of the light emitting layers (4a), (4b), and (5) is applied between both electrodes (2) and (7), both electrodes (2) and (7) , (7), the light-emitting layers (4a), (4b), and (5) emit light. This light emission is caused by the ZnS:Mn light emitting layer (4a), (
4b) has yellow-orange luminescence, and the ZnS:Tb,F luminescent layer (5
) emits green light, and their light-emitting layers (4a) and (5
) and (4b) are overlapped vertically, so the mixed color light reaches the display side surface, but in each region of the red light transmitting filter (8r), light with a shorter wavelength than red is cut off. The light is emitted as red light, and in each region of the green light transmitting filter (8g), light with longer wavelengths than green is cut off and emitted as green light. Therefore, the pattern of both electrodes (2) and (7) is finely set so that a large number of stripes are arranged on one pixel, and the display side electrode (7) is a stripe covered with a red light transmitting filter (8r). group (hereinafter referred to as the red electrode section) and a stripe group (hereinafter referred to as the red electrode section) covered with a green light transmitting filter (8g).
If the configuration is such that a voltage can be applied between the two primary colors (hereinafter referred to as the green electrode part) and the back side electrode (2) separately, the same pixel can be It can be displayed arbitrarily with neutral color light emission. That is, by using only the red electrode part, a red primary color luminescent display can be performed, by using only the green electrode part, a green primary color luminescent display can be performed, and by using both electrode parts, an intermediate color luminescent display can be performed by mixing both luminescent colors.

Note that the intermediate color light emission is visually recognized as a color intermediate between the two light emissions because of the matrix display, in which fine dots of red light emitting parts and green light emitting parts are arranged alternately on the pixel. By changing the intensity of both lights by changing the voltage, pulse width, number of pulses, frequency, etc. applied to the Color tone changes are also possible. Z constituting the light emitting layers (4a) and (4b) of the EL element
ns: Mn's original emission color is yellow-orange, but it has a wavelength of 5.
It has a wide emission spectrum ranging from 00 to 700 nm,
It contains a considerable red component in the wavelength range of 600 to 700 nm.

The red light emission of the above EL element is caused by this ZnS:Mn light emitting layer (
In order to obtain the yellow-orange luminescence of 4a) and (4b) by passing through the red light transmitting filter (8r) and cutting light on the shorter wavelength side than red, the red luminescence is obtained by transmitting the red light transmitting filter (8r). It is attenuated to some extent by the transmission of However, the above ZnS:Mn is 6,000
It has a high luminance of cd/rrf and a high luminous efficiency of 31 m/w, so compared to the luminescence of ZnS:Sm,F, which is common as a conventional red luminescent material, it has much higher luminance and a more red primary color. Nearby, color C R T (C
It can almost be defeated by the red color of the athode Ray Tube. In this EL element, as mentioned above, Zns:T
b, ZnS:Mn light emitting layer (4a) on both sides of the F light emitting layer (5)
), (4b) improves the light emission characteristics of the EL element as a whole, resulting in higher luminance than the EL element described in Japanese Patent Application No. 63-66299, which was previously developed by the present inventors. We are trying to obtain the following. That is, ZnS:M
ZnS:Mn constituting the n-emitting layers (4a) and (4b)
Since the luminescence intensity at the luminescent layer/insulating layer interface is high, ZnS
:Tb,F placed on both sides of the light emitting layer (5), ZnS:M
The n-emitting layer (4a) is in contact with the insulating layer (3), and the ZnS
The :Mn light emitting layer (4b) is brought into contact with the insulating layer (6) so that high luminance light emission by ZnS:Mn can be obtained. And Zn'S:Tb,F light emitting layer (5)
has ZnS:Mn light-emitting layers (4a) and (4b) on both sides.
By arranging it away from the insulating layers (3) and (6), the light emission by ZnS:Tb,F can be obtained with high brightness. These ZnS:Mn light emitting layers (4a),
The ZnS:Tb,F light-emitting layer (5) and the ZnS:Mn light-emitting layer (4b) can be formed using a vacuum evaporation method such as electron beam evaporation or resistance heating evaporation, a sputtering method such as high-frequency sputtering, or an ion plating method. This can be done using various existing vacuum thin film formation methods.
In particular, a ZnS:Mn luminescent layer (4
a), ZnS:Tb,F light emitting layer (5) and ZnS:M
n Luminescence 7! When (4b) is laminated continuously,
Crystal growth occurs continuously at these interfaces, which allows efficient light emission with low driving voltage. In the present invention, these ZnS:Mn light emitting layers (4a),
ZnS:Tb,F light emitting layer (5), ZnS:Mn light emitting layer (
The thickness of 4b) is usually the same as that of the ZnS:Mn emitting layer (4a),
In (4b), Zn
In the S:Tb,F light emitting layer (5), it is about 250 to 600 rv.

Regarding constituent members other than the light emitting layer, the red light transmission filter (8r) is preferably one that cuts light with a wavelength of 570 nm or less, but -a has a wavelength of 5B0.
Cuts light with a wavelength of 600 nm or more and cuts light with a wavelength of 600 nm or more.
Any material that transmits 0% or more may be used.

In addition, as a green light transmission filter (8g), if the lower limit of the wavelength of the light to be cut is too low, the brightness will be insufficient.
On the other hand, if it is too high, the color tone will become yellow-green, so this lower limit is 56.
It is preferable to have a wavelength in the range of 0 to 580nll1, but generally any material that can transmit 80% or more of light in a wavelength range of 550n1 or less and 450nm or more is sufficient.

To form these filters (8r) and (8g),
A paint containing a pigment and a binder having the required selective light absorption ability is prepared, and after drying, it is applied onto the display side electrode (7) in a pattern shape corresponding to the pattern by a printing application method such as screen printing. The coating may be applied and dried to a thickness of about 0.5 to 20 μm. Alternatively, the filters (8r) and (8g) may be formed on another glass substrate in a pattern shape corresponding to the pattern of the display side electrode (7), and then superimposed on the display side electrode (7). .

As the constituent material of the insulating layers (3) and (6), any existing insulating material can be used, such as TatO, AI. O
s, YzOi, S I OtXS i sNa, Tt
O. ,Nb! oSSB a T i O s, S r
T i O s, P b T i O c, etc. are used. A different material may be used for each insulating layer. Furthermore, each layer may be a laminate of two or more layers made of different constituent materials. The thickness of these insulating layers (3) and (6) is 200 mm.
The thickness of both electrodes (2) and (7) is about 100 to 300 nm, respectively. The means for forming the insulations N (3) and (6) and the electrodes (2) and (7) include vacuum evaporation methods such as electron beam evaporation and resistance heating evaporation, sputtering methods such as high frequency sputtering, or Various existing methods for forming thin films in vacuum, such as ion plating, can be used as appropriate depending on the type of material used. In the EL element of the present invention, in addition to patterning both the back side and display side electrodes (2) and (7) as in the example, only one of the two electrodes may be patterned, and the pattern may be Various settings can be made, not just parallel stripes. That is, one electrode is divided into a large number of electrode parts, the other electrode is used as a common electrode for these electrode parts, and one of the two types of filters is placed on each display side surface part corresponding to each electrode part. By having the same filters and making the filters of the adjacent surface portions different from each other, it is possible to display a multicolor display by changing the emitted light color in the same manner as described above.

Furthermore, in the present invention, in addition to changing the luminescent color of the entire element, if the electrode pattern is made finer using photolithography or the like, dynamic driving, that is, a dot matrix driving method using line sequential scanning, can be used for each pixel. It is possible to change the emission color between the two primary colors of red and green and their intermediate colors.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples. Example 1 A multicolor display type thin film EL device having the structure shown in FIG. 1 was manufactured in the following manner.

Vertical 3411 Horizontal 341IIl11 Thickness 1.11llm+
200 nm thick IT on one side of the glass substrate (1)
The back side electric scratcher (2) made of an O film was formed by electron beam evaporation to form a parallel stripe pattern with each stripe width of 300 μm.

Next, a back side insulating layer (3) made of a TazOsF1 film with a thickness of 400 nm is formed on this back side electrode (2) by high frequency sputtering method, and a ZnS layer with a thickness of 180 nm is formed on it by electron beam evaporation method. Mn light emitting layer (4a)
A ZnS:Tb,F light-emitting layer (5) with a thickness of 3QOnm and a ZnS:Mn light-emitting layer (4b) with a thickness of 120nm were successively laminated. Note that the lower ZnS:Mn light-emitting layer (
The reason why layer 4a) was made thicker than the upper ZnS:Mn light-emitting layer (4b) is that there is a layer with poor crystallinity called a dead layer of about 100 nm in the early stage of thin film deposition, and the light-emitting efficiency is low in this area. The reason for this is to grow a layer with good crystallinity by making it a little thicker. Next, the above ZnS
:T a with a thickness of 400 r+m on the Mn light emitting layer (4b) by high frequency sputtering method. 0. An insulating layer (6) on the display side made of a thin film was formed. Next, a display-side electrode (7) made of an ITO film with a thickness of 200 na+ was formed thereon by high-frequency sputtering in a similar parallel stripe pattern in a direction perpendicular to the stripe pattern of the back-side electrode (2). . A red light transmitting filter (8r) and a green light transmitting filter (8g) with a thickness of about 1 μm are alternately arranged on one surface of a glass substrate (9) different from the above display side electrode (7). It was formed into stripes with the same dimensions and spacing as each stripe. This glass substrate (9) is connected to its filters (8r) and (8g) as display side electrodes (7).
A multicolor display type EL device was fabricated by stacking the two so that they were facing each other. 1 between both electrodes (2) and (7) of this EL element.
Applying an AC voltage of 200μ with kHz pulse drive, Zn
S:Mn light emitting layer (4a), (4b) and ZnS:Tb,F
Luminescence N (5) is caused to emit light, and ZnS:Mn and ZnS:
Mixed color light emission of Tb and F was generated, and alternate red and green light emission was obtained on a plane by the transmitted light of the respective filters (8r) and (8g).

Comparative Example 1 As shown in FIG. 2, ZnS:Mn luminescent layer 0(1) and Zn
s: 3000 lI each of Tb and F light emitting layer (II)
A multicolor display type thin film EL device was fabricated using the same structure as in Example 1, except that the thin film EL device was laminated to a thickness of 1 by electron beam evaporation. FIG. 3 shows the EL elements of Example 1 and Comparative Example 1.
As shown in Figure 3, which shows the brightness-voltage characteristics when no filter is used in kl{z pulse drive, the brightness of Example 1 is higher than that of Comparative Example 1, and the maximum brightness of Example 1 is approximately 1 , 500cd/
nf, which was approximately 1.5 times higher than the maximum brightness of Comparative Example 1.

FIG. 4 shows the brightness voltage characteristics of the transmitted light of the red light transmitting filter (8r) of the EL elements of Example 1 and Comparative Example 1. Further, FIG. 5 shows the luminance-voltage characteristics of the transmitted light of the green light transmitting filters (8 g) of Example 1 and Comparative Example 1.

As shown in FIG. 4, the transmitted light of the red light transmission filter (8r) of Example 1 has higher brightness than that of Comparative Example 1, and its maximum brightness was 500 cd/po in Example 1. In Comparative Example 1, the value was only 320 cd/nf, and in Example 1, the value was about 1.5 times higher than in Comparative Example 1. Moreover, as shown in FIG. 5, the green light transmission filter of Example 1 (
The transmitted light of 8g) has higher brightness than that of Comparative Example 1,
The maximum brightness was 620 cd/rrr in Example 1, but only 400 cd/rrf in Comparative Example 1, and Example 1 showed a value about 1.5 times higher than Comparative Example 1. [Effects of the Invention] As explained above, the present invention provides a multicolor display type thin film EL element with high brightness by arranging ZnS:Mn light emitting layers on both sides of a ZnS:Tb,F light emitting layer. was completed. Therefore, according to the present invention, a high-definition, large-area display panel can be manufactured.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a multi-color display type thin film electroluminescent device of the present invention, and FIG. 2 is a sectional view showing an example of a multi-color display type “ill@electroluminescent device” other than the present invention. Figure 3 is a diagram showing the luminance-voltage characteristics of the electroluminescent elements of Example 1 and Comparative Example 1 under 1kHz pulse drive without a filter. FIG. 5 is a diagram showing the luminance-voltage characteristics of transmitted light of a red light transmitting filter when a luminescent element is driven with a 1 kHz pulse. FIG. It is a diagram showing the brightness-voltage characteristic of transmitted light of the filter. (2)... Back side electrode, (3)... Insulating layer, (4
a), (4b)-ZnS: Mn light emitting layer, (5)
=-ZnS: Tb,F light emitting layer, (6)
...Insulating layer, (7)...Display side electrode, (8r).
...Red light transmitting filter (8g)...Green light transmitting filter Figure 8 Voltage (V) 2...Back side electrode 3...Insulating layer 4a14b -ZnS:Mn light emitting layer 5=-ZnS:Tb ．． F light emitting layer 6...Insulating layer 7...Display side electrode 8r...Red light transmitting filter 8g...Green light transmitting filter 10-ZnS:Mn light emitting layer 1 1-ZnS:Tb1F light emitting layer figure pressure ( V) (V)

Claims (1)

[Claims] (1) A light-emitting layer is placed between a transparent display-side electrode and a back-side electrode with an insulating layer interposed therebetween, and red light-transmitting filters and green light-transmitting filters are alternately arranged in a planar manner on the display side. In a multicolor display type thin film electroluminescent device that performs multicolor display, the light emitting layer is composed of a ZnS:Mn light emitting layer and a
1. A multicolor display type thin film electroluminescent device comprising a nS:Tb,F light emitting layer, and characterized in that the ZnS:Mn light emitting layer is arranged on both sides of the ZnS:Tb,F light emitting layer.