JPS61245489A - Electric field luminous 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 an AC-driven electroluminescent element (hereinafter abbreviated as BL element) used as a flat display device in a terminal device of a converter.

(Prior art and its problems) As the third factor, a schematic diagram of the cross-sectional structure of a general EL element is shown.

A transparent electrode 32 made of ITO or the like is disposed on a glass substrate 31. First insulating layer 339 light emitting layer 34. second insulating layer 35 and)k
It has a structure in which back electrodes 36 such as 1 are sequentially laminated. The light-emitting layer 34 is a phosphor thin film made of a compound such as ZaS or Zn8e or a mixed crystal thereof, and doped with dope, TbFs*8fnFs, etc. as a luminescent center substance. When a high electric field of 106 volts/cIL or more is applied to the light-emitting layer 34, an electron avalanche occurs, and as a result, a large number of thermoelectrons collide and excite the light-emitting center, causing one light emission. At this time, the insulating layers 33 and 35 limit the current flowing through the light emitting layer 34, prevent the KL element from dielectric breakdown, and operate the element stably.

Figure 3 shows a so-called AC driven thin film E with a double insulation structure.
Although it is an L element, practical luminance characteristics and reliability were obtained for the first time by adopting such a structure. However, in a conventional AC-driven thin film IL device with a double insulation structure, the emission starting voltage is 1000 for a period of several tens of hours to 300 hours after voltage application.
Since there is a so-called aging characteristic in which the voltage increases from volt to several tens of volts, an aging process of at least several tens of hours is essential until the luminescence starting voltage becomes approximately constant and the luminescence characteristics are stabilized. Although this aging process is driven by high frequency and high voltage, the aging time can be somewhat shortened, but in this case, dielectric breakdown of the EL element tends to become severe. Further, although the aging process time can be somewhat shortened by setting the operating ambient temperature to 100 to 200°C, in this case too, dielectric breakdown of the EL element becomes severe.

Therefore, in the prior art, a long aging process of several tens of hours or more is required at room temperature, which greatly impairs productivity.

(Problems to be Solved by the Invention) An object of the present invention is to provide a high-luminance, stable, and reliable FiL element that does not require an aging process to stabilize light emission characteristics.

(Means for Solving the Problems) According to the present invention, in an electroluminescent device in which a light-emitting layer and at least one insulating layer are sandwiched between a pair of electrodes, at least one of which is a transparent electrode. , the above-mentioned electroluminescent device is obtained, wherein the light emitting layer has a laminated structure of a heat-treated light-emitting layer and a non-heat-treated light-emitting layer.

(Function) Since the emission threshold voltage of a thin film BL element increases over a long period of several tens of hours or more after voltage application, a long aging of several tens of hours or more is required to stabilize the emission characteristics. This phenomenon of an increase in the emission threshold voltage due to aging is almost independent of the insulating film constituting the thin-film IL element, and is a common property of double-insulated thin-film FiL elements fabricated using conventional techniques, and is a phenomenon that stabilizes the emission characteristics. Therefore, long-term aging was considered essential.

This increase in the luminescence threshold voltage due to aging is caused by the film formation process using vacuum evaporation methods, heat treatment steps introduced to improve the crystallinity of the luminescent layer and uniformly distribute the luminescent center substance, etc. Defects induced at the interface or in the film,
Alternatively, it is thought that this phenomenon may be caused by defects induced by hot electrons flowing through the light emitting layer, but the details are unknown.

On the other hand, 2 was fabricated by removing the heat treatment step after forming the light emitting layer.
The heavily insulated thin film IL device had somewhat lower luminance and emission threshold voltage 10 to 15 inches higher than the heat-treated device. However, the present inventor has found through various experiments that even if the heat treatment step is removed, a FILL element produced by, for example, a binary evaporation method so that the luminescent center substance is uniform during the formation of the luminescent layer, has the same level of performance as a heat-treated element. It has become clear that not only can luminance and luminescence threshold voltage be obtained, but also that the luminescence threshold voltage decreases with aging. Therefore, the luminescent layer is divided into a heat-treated layer and a main-treated layer. When an EL element was produced by laminating the layers, an L element with very small variation due to aging could be obtained, resulting in the present invention. First, FIG. 2 shows the characteristics before and after aging of the F3L element whose light-emitting layer has been heat-treated and the untreated BL element alone. In a heat-treated element, only the emission threshold voltage increases due to aging, but the emission brightness does not change.

On the other hand, in the element that was not heat-treated, the emission threshold voltage decreased and the emission brightness slightly increased due to aging.

The slope of the rising part of the light emission does not change regardless of whether heat treatment is performed or not. When an EL device was constructed by laminating a heat-treated light-emitting layer and an untreated light-emitting layer to an appropriate thickness, a device with almost no fluctuation in light-emission threshold voltage due to aging was realized. The details will be shown in Examples.

(Example) Hereinafter, a detailed explanation will be given based on FIG. 1 showing a cross-sectional view of the structure of a WL element according to an example of the present invention.

A transparent electrode 2 such as ITO is placed on the glass substrate 1 at a thickness of 2000λ.
degree and then kl*OB, TiO2 and 8
The insulating layer 3 is formed to a thickness of approximately 3000 to 4000^ using a magnetron sputtering device using a target obtained by mixing i3N4 powders at a ratio of 1:2:1 and sintering them. The light emitting layer 4 has a substrate temperature of 200°C and a vacuum level of 10"" Tor.
High-purity Zn8 and metal Mn are resistance-heated from separate crucibles at a temperature below r, the Mn concentration is controlled to be 0.7 to 1.0 molt, and a thickness of about 3000 λ is formed. After that, 550℃～
Heat treatment was performed for 2 hours at 600°C and a vacuum level of around 1O-6 Torr, and then the second light-emitting layer 5 was heated for 2 hours under the same conditions as above.
000λ is formed. Thereafter, Y and Os are formed to a thickness of 500 to 1000 λ in the same vacuum chamber to form the adhesive layer 6. Thereafter, a second insulating layer 7 made of Ta-8i-0 is formed using a magnetron sputtering device using a compound of Ta, Si, and O as a target. The film thickness is about 3000^. Finally h
1. 500 to 1000 back electrodes 8 are formed.

Adhesive 1f! j 6 serves to strengthen the adhesive force between the second insulating layer 7 and the back electrode 8, and is not necessarily necessary.

The double-insulated thin film FiL device fabricated in this way operated very stably for more than 2000 hours without any change in the wall pressure of the light emitting layer 11iiL due to aging.

In addition, the luminance of light emission was improved by more than 10 degrees compared to the initial luminance.

Conventional thin-film FiL elements are heat-treated after the formation of a luminescent layer, but compared to the gL element of the present invention, the initial characteristics show that the luminance is about 2.0 layers higher, but due to aging, the luminescence threshold voltage increases by several tens of hours or more. The aging process was essential because the voltage increased by 20 to 40 V over the period of time and stabilized. Furthermore, when the insulating layer is heat-treated, its insulating voltage tends to decrease somewhat. By making the light-emitting layer into a heat-treated layer and an untreated layer as in the present invention, changes in characteristics due to aging can be prevented. is the insulating layer 3 and the second insulating layer 7, 8isN* p k
l＊os e YtOs e T'i0t t Tat
O+ * Smass epb'rtos, BcTi
(%, 8i01, etc.), no drift in the emission threshold voltage was observed.Also, if the luminescent center substance added to the luminescent layer is TbF3 instead of i, an edge color can be obtained, and if it is 8mF7, a red color can be obtained. .

The light-emitting layer or the second light-emitting layer matrix is made of Zn8xS in addition to Zn8.
Similar effects could be obtained using e1-X and Zn8e.

(Effects of the invention) As described above, by forming one light-emitting layer into two layers: a heat-treated layer and a non-heat-treated layer, there is no change in the light-emission threshold voltage due to aging, and the device has high reliability and high brightness characteristics. A thin film EL device is obtained.

This thin film BL element does not require an aging process, which conventionally required several tens of hours to 300 hours, and thus contributes to improved productivity and lower cost of the element.

Although the above-mentioned embodiments have been described with reference to a double-insulated thin film EL device, the present invention can also be applied to an EL device having a structure in which the insulating layer between the light-emitting layer and the transparent electrode or back electrode is removed.

[Brief explanation of the drawing]

FIG. 2 is a schematic diagram illustrating changes in light emission characteristics due to aging of a BL element. 1.31... Glass substrate 2.32... Transparent electrode 3.33... Insulating layer 7.35... Second insulating layer 8.36... Back electrode 6... Adhesive layer 4. 34...Light emitting layer 5...Second light emitting layer O 1 Figure 7I-2 Applied voltage (v)

Claims (1)

[Claims] In an electroluminescent device in which a luminescent layer and at least one insulating layer are sandwiched between a pair of electrodes, at least one of which is a transparent electrode, the luminescent layer is heat-treated and the luminescent layer is not heat-treated. The electroluminescent device is characterized in that it has a laminated structure with.