JPH02148688A - Thin film EL element - 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 [Field of Industrial Application] The present invention relates to a thin film EL device that emits light by applying a fart voltage to its electrodes.

[Conventional technology]

FIG. 2 is a partially cutaway perspective view of a conventional thin film EL element.
In the figure, 1 is a glass substrate, 2, 2. . . . indicates a plurality of band-shaped transparent electrodes formed on the glass substrate 1 at predetermined intervals. A plurality of transparent electrodes 2, 2. ...Glass substrate including the surface
A first insulator layer 30, a light emitter layer 4, and a second insulator layer 5 are laminated in this order on the upper surface. and second insulator layer 5
A plurality of front electrodes 6, 6. ... is the transparent electrode 2,
2. Transparent electrodes 2, 2 . . . . and the back electrodes 6, 6° . . . form a matrix.

The manufacturing process of a thin film EL element having such a configuration is as follows. A transparent electrode 2 is formed on a glass substrate 1 by electron beam evaporation, and etched with a hydrochloric acid solution to form a plurality of band-shaped transparent electrodes 2, 2 . ...obtain...

Next, transparent electrodes 2, 2 . After forming the first insulating layer 3 on a glass substrate l containing . Further, a second insulating layer 5 is formed on the light emitting layer 4 by a sputtering method, and band-shaped transparent electrodes 2, 2 . . . . A plurality of back electrodes 6, 6 . ... is deposited.

In the thin film EL device obtained in this way, the one currently in practical use is ZnS:Mn for the light emitter N4 shown in FIG.
It uses only yellow-orange light emission.

In order to display more information, multicolor display is required, and research and development of multicolor thin film EL elements is strongly desired.

Promising polychromatic materials for the light emitter layer 4 include SrS:Ce for blue light emission and ZnS:T for green light emission.
b, F, CaS:Eu or ZnS:Sm for red emission;
However, other than green thin-film EL devices using ZnS:Tb,F, sufficient brightness has not been obtained, and there is a strong desire for research and development to increase brightness as well as multicolor.

By the way, as mentioned above, there are two types of red thin-film EL elements: one using CaS:Eu and the other using ZnS:Sm,F as the material of the light emitting body N4, and although the brightness is comparable, the color In terms of brightness, CaS:Eu is better. Therefore, by improving the crystallinity of the CaS:Eu thin film, we are developing a method to increase the brightness of thin film EL devices using CaS:Eu as the light emitter. Currently 5kHz
A maximum brightness of 900 cd/m" can be obtained using z-sine wave driving.

In addition to the method of improving the crystallization of the luminescent layer, there is a method of adding a sensitizer to increase the brightness. It is known that in cathode luminescence, when Ce is added as a sensitizer to a CaS:Eu emitter layer, the luminous efficiency improves from 10% to 16%.

[Problem to be solved by the invention]

Practical level brightness of thin film EL element is 50-601
A luminance of 50 to 60 cd/m'' is required at a practical frequency of 1z, and a luminance of 10,000 cd/m'' is required when driven at 5 kHz. However, as mentioned above, the brightness currently available in thin film EL devices using CaS:Eu as the light emitter is a maximum of 900 cd/m when driven at 5kllz.
”, and even higher brightness is desired for practical use.

There are two ways to increase brightness, for example, by improving the manufacturing method of the luminescent layer and by using a material with a sensitizer added to the luminescent layer, but at present, it is not possible to achieve high brightness by improving the manufacturing method alone. Therefore, it is necessary to develop a material for the luminescent layer by adding an aggravating agent.

The present invention has been made in view of the above circumstances, and includes C as a sensitizer in the light emitting layer CaS:Eu of a red thin film EL element.
The purpose is to increase the brightness of the device by adding an appropriate amount of e.

[Means to solve the problem]

The thin film EL device of the present invention has a CaS:Eu emitter layer with C
The thin film EL device doped with Ce is characterized in that the concentration of Ce is 10-s to 1.0-1 mol%.

[Effect]

In the present invention, 10-
By adding 10 −1 mol % of Sm, the luminous efficiency is improved because Ce acts as a sensitizer, and a thin film EL device with high brightness can be obtained.

〔principle〕

It is generally known that when a light emitter in a light emitter layer is excited, energy transfer occurs between luminescent center atoms.

The efficiency of the transmission is determined by the amount of overlap between the emission spectrum of the energy supplier and the absorption spectrum of the energy consumer and the distance between the energy supplier and the energy consumer.

In other words, the greater the overlap between the emission spectrum and the absorption spectrum, or the shorter the distance between the energy supplier and the energy demander, the higher the energy transfer efficiency and the higher the brightness.

Therefore, when Ce is added to the CaS:Eu luminescent layer, the emission spectrum of Ce as an energy supplier and the absorption spectrum of Eu as an energy demander overlap greatly, and the luminous efficiency of Ce is lower than that of Eu. Since it is larger than the luminous efficiency, for example, in cathodoluminescence, the former is 22% and the latter is 10%, and Ce, which is an energy supplier, becomes a sensitizer for Eu, which is an energy demander. Therefore, adding Ce to the CaS:Eu light emitter layer is effective in increasing the brightness of a thin film EL element.

〔Example〕

Hereinafter, the present invention will be explained based on drawings showing embodiments thereof. FIG. 1 is a partially cutaway perspective view of a thin film EL device according to the present invention, in which 1 is a glass substrate (Corning 7059).
2.2. . . . indicates a plurality of transparent electrodes made of rTO formed on the glass substrate 1 in a strip shape at predetermined intervals. On the top surface of the glass substrate 1, including the surface of a plurality of transparent electrodes 2゜2,..., a first insulator N3 of SiO□/Ta, 05 composite film, and a light emitter layer 4 of CaS: Eu + Ce.
and a second insulating layer 5 of a TaJs/Sing composite film are laminated in this order. On the upper surface of the second insulating layer 5, a plurality of strip-shaped back electrodes 6, 6°, . ... are laminated at predetermined intervals in a direction perpendicular to the longitudinal direction, and are made of ITO transparent electrodes 2.2.
. . . and Al back electrodes 6, 6 . ... forms a matrix.

Next, a method for manufacturing a thin film EL element having such a structure will be described. ITO is deposited on glass substrate 1 by electron beam.
The transparent electrode 2 is formed by vapor deposition by 2000 people. The obtained substrate 1 is heated at 120° C. for 1 minute to remove surface moisture, and then a resist having a thickness of 1 μm or less is applied onto the transparent electrode 2 and heat-treated.

Next, the resist is exposed and developed using a band-shaped mask to form a band-shaped resist pattern, and the transparent electrode 2 is etched with a 40% hydrochloric acid solution.

Furthermore, the remaining resist is removed using acetone to form band-shaped transparent electrodes 2, 2. ...obtain... And transparent electrode 2,
2. SiO was deposited on the glass substrate 1 containing ... under the following conditions.
A first insulator N3 of the □/Tag's composite film is formed. First, the incident power is 2 kW, and the Ar gas pressure is 1 mTorr.
SiO□ with a thickness of 0.1 μm is laminated by RF sputtering using SiO□ as a target under the following conditions. Next, the incident power is 1kW, and the gas pressure ratio of Ar and Ox is Ar10.
□-1, using Ta metal as a target under the conditions of gas pressure of 1 mTorr, stacking 0.4 μm thick Taxes by reactive RF sputtering method. Said first insulation N3
On top, Eu is 0.4mol1%, Ce is 10-”4
CaS consisting of Xl0-1 mol%: Eu, C
Using the e-sintered body as a target, a CaS:Eu,Ce thin film, which is the light emitting layer 4, is formed with a thickness of 1.5 μm by electron beam evaporation.

The conditions for the vapor deposition are an acceleration voltage of 5 to 1 and a current of 10 to 1.
0-150mA, substrate temperature 680℃, evaporation rate 25
It's c to Hitohachi. On the light emitter layer 4, Taxes/Si
A second insulator layer 5 made of an NG composite film is formed under the same conditions as the first insulator layer 3. That is, the incident power is 1 kW.

Gas pressure specific force of Ar and 02<Ar10□=1. Ta metal was targeted at a gas pressure of 1 mTorr, and a 0.4 μm thick Ta metal was deposited using the reactive RF spa lettering method.
After forming zOs, the incident power is 2 - 1^r and the gas pressure is 1 mTorr, and 5i (h is the target and R
A Sing with a thickness of 0.1 μm is formed by F sputtering. Then, on the second insulating layer 5, a strip-shaped back electrode 6.6. made of A1 and having a thickness of 2000 layers is formed by using a strip-shaped strip and a resistance wire heating method. ... is deposited. At this time, the strip-shaped back electrodes 6, 6 . ... are band-shaped transparent electrodes 2, 2 .・
. . . Patterns are formed at predetermined intervals in a direction perpendicular to the longitudinal direction. That is, the transparent electrodes 2, 2 . . . . and the back electrode 6°6, . . . form a matrix.

In this example, the concentration of Ce added to the CaS:Eu light emitter layer 4 is 10-3 to 4 x 10-'mol%.
Although it is closed, it is not limited to this, 10-' to 10-1m
It may be within the range of ol%. The reason why it is set to be 10-1 mol% or more is because if it is 10-1 mol% or less, energy transfer to Eu will not be sufficient and the luminous efficiency of Eu will not improve. 1m
If it is more than ol%, the structure of CaS host crystal is disturbed and Eu
and decreases the excitation efficiency and luminescence efficiency of Ce.
This is because the chromaticity is poor (because the luminescence from the rays) also appears.

FIG. 3 is a graph showing the measurement results of the emission spectrum when the thin film EL element of the present invention is driven by a sine wave with a frequency of 5 kHz, with the electroluminescence intensity on the vertical axis and the wavelength (nm) on the horizontal axis. . In Fig. 3, the luminous layer 4
Eu is 0, 4mo 1%, Ce is Q, 4mo 1%
The case of using CaS:Eu and Ce is shown,
Also, as a comparative example, CaS:C with 0.1 mo1% of Ce
The cases in which CaS:Eu and CaS:Eu containing 0.4 mol% of Eu are used are shown.

The spectrum represented by the solid line in Figure 3 is the actual measured value, and the spectrum represented by the broken line is the
This is the value of the original emission spectrum excluding the spectrum caused by interference of light reflected by the light.

As is clear from FIG. 3, in the device of the present invention, no light emission other than that caused by εut + ions was observed, and therefore, when Ce was added, there was no light emission from Ce itself.

FIG. 4 shows E! u is 0.4mo1%
.

C whose Ce is 10-' to 4 Xl0-' a+o1%
aS: A thin film εL element using Eu and Ce at a frequency of 5 k
Driven by Hz sine wave, luminous efficiency and threshold voltage +3
Measurement results of saturated luminance at 0V and luminescent layer 4 of the present invention
3 is a graph showing the results of measuring the photoluminescence peak intensity of In Figure 4, the horizontal axis is the concentration of Ce (o+o1%), and the right vertical axis is the saturated luminance (cd/m''
) and photoluminescence peak intensity (arbitrary scale)
The left vertical axis shows the luminous efficiency (l m/W).

In FIG. 4, the luminous efficiency is shown by a dashed line, the photoluminescence peak intensity is shown by a broken line, and the saturated brightness is shown by a solid line.
The measured values of luminous efficiency, photoluminescence peak intensity, and saturated luminance when 4mol1% of CaS:Eu is used for the light emitter layer 4 are plotted on the vertical axis.

Shown in order of b and c. As is clear from Figure 4, C
When e is added, the saturated brightness is up to 1.7 times higher and the luminous efficiency is 1.9 times higher than when no Ce is added, and the photoluminescence peak intensity also increases over a wide range of Ce concentrations (mo1%). improved over time.

〔Effect of the invention〕

As detailed above, in the thin film EL device according to the present invention, CaS:f! Ce is added to the luminescent layer of u from 10-5 to 10-
Since it is added at a concentration of 1 mol %, the present invention has excellent effects such as improved luminous efficiency and higher brightness.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of a thin film EL device according to the present invention;
FIG. 2 is a partially cutaway perspective view of a conventional thin film EL device, FIG. 3 is a graph showing the measurement results of the emission spectra of the thin film EL devices of the present invention and comparative examples, and FIG. 4 is a graph of the thin film EL device of the present invention. It is a graph showing the measurement results of luminous efficiency and saturated luminance, and the measurement results of photoluminescence peak intensity of only the light emitter layer. 1... Glass substrate 2... Transparent electrode 3... First insulator layer 4... Luminous layer 5... Second insulator layer 6.
...At the time of back electrode Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Noboru Kono

Claims (1)

[Claims] 1. In a thin film EL device formed by adding Ce to a CaS:Eu light emitting layer, the concentration of Ce is 10^-^5 to 10^-^1 mol%.
A thin film EL device characterized by: