JP3487618B2 - Electroluminescence element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescence element (hereinafter, referred to as an EL element) used for, for example, a surface light source for a backlight of instruments and the like. In particular, the present invention relates to a stable thin-film EL device with little deterioration due to emission life characteristics and the like. 2. Description of the Related Art An EL element utilizes a phenomenon of emitting light when an electric field is applied to a phosphor such as zinc sulfide (ZnS).
2. Description of the Related Art Heretofore, attention has been paid to constituting a self-luminous flat display. FIG. 3 is a schematic diagram showing a typical cross-sectional structure of a conventional EL element 30. As shown in FIG. The EL element 30 is provided on an optically transparent glass substrate 31 as an insulating substrate.
First electrode 32 made of TO (Indium Tin Oxide) film, first insulating layer 33 made of tantalum pentoxide (Ta ₂ O ₅ ), etc., and light emitting layer 3
4. A second insulating layer 35 and a second electrode 36 made of an ITO film are sequentially laminated. The ITO film is a transparent conductive film obtained by doping tin (Sn) into indium oxide (In ₂ O ₃ ) and has a low resistivity, and thus has been widely used for a transparent electrode. The light emitting layer 34 is made of, for example, zinc sulfide as a base material, and manganese (Mn) or terbium as a light emitting center.
(Tb), samarium (Sm) or the like is used. In the EL device 30 having the above structure,
Manganese is used as a constituent material of the light emitting layer 34 for obtaining yellow light emission.
(Mn), terbium (Tb) as a constituent material of the light emitting layer 4 for obtaining green light emission, and zinc sulfide to which samarium (Sm) is added as a constituent material of the light emitting layer 34 for obtaining red light emission are being studied. Further, in order to improve the light emission luminance of the EL element having the zinc sulfide light emitting layer to which these rare earth elements and the like are added, studies have been made on heat treatment at a high temperature. Further, as a conventional method, for example, in Japanese Patent Application Laid-Open No. 62-76283, the atomic composition ratio of a rare earth element and a halogen element is approximately 0.5 or more,
It has been proposed to improve the light emission brightness by making it 2.5 or less. [0004] However, even in an EL device having high luminance obtained by the conventional method, the light emission threshold voltage moves to the low voltage side or the high voltage side as the light emission operation time elapses. Phenomenon occurs. Then, when the light emission threshold voltage moves to the low voltage side, the gradient of the graph showing the relationship between the applied voltage and the light emission luminance becomes gentle,
Conversely, when the light emission threshold voltage moves to the high voltage side, the slope becomes steep. Therefore, the light emission luminance with respect to a normal operating voltage exceeding the light emission threshold voltage changes with the light emission operation time, and the reliability of the EL element becomes poor.
Furthermore, in the conventional high-luminance EL element, a dark spot is generated on the light-emitting surface with the elapse of the light-emitting operation time, and the light-emitting area is reduced. Therefore, the present invention has been made to solve the above-described problems, and has as its object to provide an EL element having high reliability. A first structure of the present invention for solving the above-mentioned problem is that a light-emitting layer including a light-emitting center is arranged between a first electrode and a second electrode. Wherein the light emitting layer is formed of samarium (Sm) and chlorine ( Cm).
l) a group II-VI compound semiconductor was added, contained in said light emitting layer, chlorine for samarium (Sm)
That is, the atomic composition ratio of (Cl) is 0.05 or more and less than 0.5 . That is, the present invention relates to a samarium (S
m) and the chlorine (Cl) II-VI group compound semiconductor light-emitting layer with the addition of salt to the addition amount of the samarium (Sm)
The atomic composition ratio of the added amount of elemental (Cl) is about 0.05 or more,
By setting it to less than 5, the occurrence of dark spots on the light emitting surface can be suppressed, the shift of the light emitting threshold voltage with the elapse of the light emitting operation time is reduced, and the amount of change in the light emitting luminance characteristics with respect to the applied voltage is also greatly reduced. And technical means based on the experimental results discovered by the inventors. If less than about 0.05, added chlorine (Cl)
Was observed, but the brightness did not reach a practical level. As a result, the change of the light emission luminance with respect to the normal operating voltage exceeding the light emission threshold voltage is reduced, and the reliability of the light emission operation time over time is significantly improved. Hereinafter, the present invention will be described with reference to specific examples. FIG. 1 is a schematic view showing a cross section of a thin film EL device 10 according to the present invention. In the thin-film EL device 10 of FIG. 1, light is extracted in the direction of the arrow. Thin film EL device 10
Is formed by sequentially laminating the following thin films on a glass substrate 11 which is an insulating substrate. A first transparent electrode (first electrode) 12 made of optically transparent zinc oxide (ZnO) is formed on a glass substrate 11, and an optically transparent tantalum pentoxide (Ta ₂ O ₅ ) is formed on the upper surface thereof. ) Consisting of the first insulating layer 1
3, and a light emitting layer 14 made of zinc sulfide (ZnS) doped with samarium (Sm) as a light emitting center, a second insulating layer 15 made of optically transparent tantalum pentoxide (Ta ₂ O ₅ ), optically transparent A second transparent electrode (second electrode) 16 made of zinc oxide (ZnO) is formed. Next, a method of manufacturing the above-described thin film EL device 10 will be described below. First, a first transparent electrode 12 is formed on a glass substrate 11. Gallium oxide (Ga ₂ O ₃ ) is added to zinc oxide (ZnO) powder, mixed and formed into pellets, and an ion plating apparatus is used as a film forming apparatus. Specifically, the above glass substrate 1
While the temperature of Step 1 is kept constant, the inside of the ion plating apparatus is evacuated to a vacuum. Thereafter, argon (Ar) gas is introduced to keep the pressure constant, and the beam power and the high-frequency power are adjusted so that the film forming speed is in the range of 6 to 18 nm / min. Next, a first insulating layer 13 made of tantalum pentoxide (Ta ₂ O ₅ ) is formed on the first transparent electrode 12 by a sputtering method. Specifically, the temperature of the glass substrate 11 is kept constant, a mixed gas of argon (Ar) and oxygen (O ₂ ) is introduced into the sputtering apparatus, and the film is formed with a high frequency power of 1 kW. On the first insulating layer 13, zinc sulfide
(ZnS) as the base material and samarium (Sm) as the emission center
-Added zinc sulfide: Samarium (ZnS: Sm) light emitting layer 14
From MOCVD (Metal Organic Chemical Vapor Depositio
n: metal organic chemical vapor deposition) method. Specifically, the glass substrate 11 was maintained at 450 ° C., and the reaction chamber was placed under a reduced pressure atmosphere. Then, diethyl zinc (Zn (C ₂ H ₅ ) ₂ ) was diluted with hydrogen using a hydrogen carrier gas. Hydrogen sulfide (H
Flow ₂ S). In addition, samarium tridipivaloyl methanide (Sm (C ₁₁ H ₂₀ O ₂ ) ₃ ) is introduced into the reaction chamber for adding a luminescent center. At this time, the temperature of the samarium tridipivaloyl methanate (Sm (C ₁₁ H ₂₀ O ₂ ) ₃ ) source is heated to 150 ° C. or higher, and hydrogen (H ₂ ) is used as a carrier gas. In addition, hydrogen chloride is added to add chlorine (Cl) as a halogen element.
(HCl) gas is diluted with hydrogen (H ₂ ), and this mixed gas is introduced into the reaction chamber. And keep the total pressure of the reaction chamber constant,
The light emitting layer 14 is formed. At this time, the atomic composition ratio of the amount of chlorine (Cl) added to the amount of samarium (Sm) is at least 0.
The flow rate of the hydrogen chloride (HCl) gas is adjusted so that the value is at least 05 and less than 0.5, preferably around 0.5. The concentrations of samarium (Sm) and chlorine (Cl) in the zinc sulfide (ZnS) film are EP
MA (Electron Probe Micro Anarysis)
Confirm with. Next, a second insulating layer 15 made of tantalum pentoxide (Ta ₂ O ₅ ) is formed on the light emitting layer 14 in the same manner as the first insulating layer 13 described above. And zinc oxide (ZnO)
The second transparent electrode 16 made of a film is connected to the first transparent electrode 1 described above.
The second insulating layer 15 is formed on the second insulating layer 15 in the same manner as in the second embodiment.
In this embodiment, the thickness of each layer is the same as that of the first transparent electrode 1.
2. The second transparent electrode 16 has a thickness of 300 nm, the first insulating layer 13 and the second insulating layer 15 have a thickness of 400 nm, and the light emitting layer 14 has a thickness of 600 nm. The thickness of each layer is described with reference to the central portion. FIG. 2 shows the degree of change of the light emission threshold voltage with the elapse of the light emission operation time when an AC voltage of 1 kHz is used in the actually manufactured sample. FIG. 2 also shows the degree of change in light emission luminance with the elapse of the light emission operation time when a voltage exceeding the light emission threshold voltage by 60 V is applied. In this figure, the sample in which the amount of chlorine (Cl) added exceeds the atomic composition ratio of 0.5 with respect to the amount of samarium (Sm), the amount of hydrogen chloride (HCl) gas introduced into the reaction chamber in the present embodiment described above This is a conventional sample that has been increased. As shown in the lower data on the left side of FIG. 2, an EL device having an atomic composition ratio of chlorine (Cl) to samarium (Sm) of more than 0.5 (in the figure, Cl / Sm = 0.8, Cl / Sm = 2 , Cl / Sm = 3 of 3
For species), light emission threshold voltage with the lapse of time as compared with the light emitting operation is started early is changing significantly, after 10 ³ hours at emission time, has moved to the 35V low voltage side at maximum. On the other hand, in the EL device of the present invention in which the atomic composition ratio of the amount of chlorine (Cl) added to the amount of samarium (Sm) is less than 0.5 (in the figure, Cl / Sm <0.5), the light emission threshold voltage Changes by a maximum of 1 V at the beginning of the light emission operation. The initial values of the light emission threshold voltages were all around 150 V. As shown in the upper right data of FIG. 2, the EL device of the present invention in which the atomic composition ratio of the amount of chlorine (Cl) to the amount of samarium (Sm) is less than 0.5 (Cl / Sm <0.5
For (3), there is almost no change from the initial light emission luminance with the elapse of the light emission operation time, and
When the voltage exceeding V was applied, the amount of change in the emission luminance with respect to the initial luminance was at most about 6%. The initial value of the emission luminance is the largest for a sample with an atomic composition ratio of 0.8, about 200 cd / m
^{In the case of 2} , those having an atomic composition ratio of less than 0.5 had a luminance of about 70% thereof, which was within a range in which there was no practical problem. The initial value was about 50% for samples with an atomic composition ratio of 2 or more. Further, regarding the dark spot generated on the light emitting surface with the passage of time, the EL element of the present invention in which the atomic composition ratio of the added amount of chlorine (Cl) to the added amount of samarium (Sm) is less than 0.5 at%, the samarium (Sm ), The atomic composition ratio of the amount of chlorine (Cl) added to the amount of chlorine added was 0.5 or more, which was sufficiently suppressed, and the number of dark spots that could be visually confirmed was almost zero. did it. In this embodiment, samarium (Sm) is used as a rare earth element and chlorine (Cl) is used as a halogen element.
It goes without saying that the present invention is not limited to this element, and that other rare earth elements and halogen elements have similar effects under similar conditions. As described above, by using the present invention, an EL device having higher reliability than the conventional method can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a longitudinal section of an EL device according to a specific example of the present invention. FIG. 2 shows the change in the light emitting threshold voltage of the EL element of the device according to the embodiment of the present invention with the elapse of the light emitting operation time, and the change of the light emission luminance with the application of a voltage exceeding the light emitting threshold voltage by 60 V with the elapse of the light emitting operation time FIG. FIG. 3 is a schematic view showing a longitudinal section of a conventional EL element. DESCRIPTION OF SYMBOLS 10, 30 EL element (electroluminescence element) 11, 31 Glass substrate (insulating substrate) 12, 32 First transparent electrode (first electrode) 13, 33 First insulating layer 14, 34 Light emitting layer 15 , 35 second insulating layer 16, 36 second transparent electrode (second electrode)

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yu Hattori 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Japan Electric Equipment Co., Ltd. In-company (56) References JP-A-64-63296 (JP, A) JP-A-2-242585 (JP, A) JP-A-2-94290 (JP, A) JP-A-62-76283 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H05B 33/00-33/28

Claims (1)

(57) [Claim 1] An electroluminescent element having a structure in which a light emitting layer including a light emitting center is disposed between a first electrode and a second electrode, wherein the light emitting layer is formed of samarium ( Sm) and a group II-VI compound semiconductor to which chlorine (Cl) is added, and is based on samarium (Sm) contained in the light emitting layer.
An electroluminescent device, wherein the atomic composition ratio of chlorine (Cl) is 0.05 or more and less than 0.5.