JP2820198B2 - EL element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EL device.

[0002]

2. Description of the Related Art Conventionally, terbium and fluorine as luminescent center elements have been added to a base material made of zinc sulfide, and the composition ratio of terbium and fluorine has been set to 0.5 or more and 2.5 or less. An EL device having the structure described in
No. 83 is disclosed.

[0003]

According to the above-mentioned prior art, it has been found that the light emission threshold voltage greatly changes with the progress of the light emission operation time. This means that the light emission luminance changes with the progress of the light emission operation time. In view of the above points, the present invention has been made by the inventor's
An object of the present invention is to provide an EL element which can reduce a change in a light emission threshold voltage and a change in light emission luminance.

[0004]

According to the first aspect of the present invention,
A first electrode, a light emitting layer, a second insulating layer, and a second electrode on the insulating substrate;
In an EL element in which a pole is formed and at least a light extraction side is formed of an optically transparent material, the light emitting element includes a base material of a II-VI compound semiconductor, terbium, oxygen, and a halogen element. The technical means is employed in which the atomic ratio of the halogen element to the terbium (halogen element / terbium) is 0.05 or more and less than 0.5, which is constituted by addition. Is what you do.

[0005] Here, when the atomic ratio of halogen element / terbium is 0.5 or more, that is, when the amount of halogen element relatively increases, the amount of change in the light emission threshold voltage with respect to the integration of the light emission operation time of the light emitting layer sharply increases. Increase. Practically, the amount of change is preferably within a range of several percent of the initial value.
Considering this point, the upper limit of the atomic ratio of halogen element / terbium is less than 0.5.

On the other hand, when the atomic ratio of halogen element / terbium is less than 0.05, that is, when the halogen element content is relatively small, the emission luminance itself decreases. Therefore, the lower limit of the atomic ratio of halogen element / terbium is 0.05. According to a second aspect of the present invention, in the first aspect, the atomic ratio of oxygen to the terbium (oxygen / terbium) contained in the light emitting layer is 0.05 or more and less than 0.5. Means.

Here, the presence of oxygen is intended to improve the luminance of the light emitting layer. However, if the atomic ratio of oxygen / terbium is 0.5 or more, that is, if oxygen is relatively increased, the dielectric breakdown voltage of the light emitting layer is increased. Decrease rapidly. On the other hand, when the oxygen / terbium atomic ratio is less than 0.05, that is, when the amount of oxygen is relatively small, the emission luminance decreases. Therefore, the oxygen / terbium atomic ratio is 0.05 or more and less than 0.5.

A third aspect of the present invention employs the technical means according to the first or second aspect of the present invention, wherein the base material made of the II-VI compound semiconductor is zinc oxide. The invention according to claim 4 is the invention according to any one of claims 1 to 4, wherein the halogen element is at least one selected from the group consisting of fluorine, chlorine, and bromine. To adopt.

The invention according to claim 5 employs the technical means according to claim 4, wherein the halogen element is fluorine or chlorine.

[0010]

According to the first and third to fifth aspects of the present invention, the shift of the light emitting threshold voltage with respect to the time of the light emitting operation time is reduced, and the change amount of the light emitting luminance with respect to the applied voltage is greatly reduced. be able to. Further, since the amount of halogen is small, there is a secondary effect that a minute destruction generated in the light emitting layer can be reduced.

According to the second aspect of the present invention, by specifying the amount of oxygen, it is possible to reduce the minute destruction occurring in the light emitting layer while improving the light emission luminance of the light emitting layer.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to specific embodiments. In FIG. 1, a thin film EL element 100 includes a glass substrate 11 as an insulating substrate, a first transparent electrode 12 as a first electrode, a first insulating layer 13, a light emitting layer 14, a second insulating layer, and a second electrode. Of the second transparent electrode. These components are all made of a transparent material, and light is extracted in the direction of the arrow in the figure.

Next, a method of manufacturing the above-structured EL device will be described. That is, in the first step, the first transparent electrode 12 is formed on the glass substrate 11. The first transparent electrode 12 is made of Zn.
It is made of O—Ga ₂ O ₅ and is formed on the glass substrate 11 by a vacuum evaporation method. A pellet-shaped target material obtained by adding gallium oxide (Ga ₂ O ₅ ) to zinc oxide (ZnO) powder is used, and an ion plating device is used as a film forming device.

More specifically, the inside of the ion plating apparatus is evacuated while maintaining the temperature of the glass substrate 11 constant. Thereafter, an argon gas is introduced into the apparatus to keep the pressure constant, and the beam power and the high-frequency power are adjusted so that the film forming rate is in the range of 6 to 18 nm / min. In the second step, 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 1 is kept constant, a mixed gas of argon and oxygen is introduced into the sputtering apparatus, and a film is formed with a high-frequency power of 1 kw.

In a third step, zinc sulfide is used as a base material on the first insulating layer 13 and terbium (T
b), zinc (terbium sulfide) (ZnS-) obtained by adding fluorine (F) as a halogen element and oxygen (O).
Tb, O, F) The light emitting layer 14 is formed by an RF magnetron sputtering method. The target used for sputtering is a mixture of terbium oxide and terbium fluoride, which is obtained by baking and hardening zinc sulfide (ZnS-Tb, O, F) to which an emission center material is added by baking. Was. At this time, the ratio of terbium to fluorine in the light emitting layer 14 can be changed by adjusting the mixing ratio of terbium oxide and terbium fluoride.

The conditions for forming the light emitting layer 14 will be specifically described.
A glass substrate 11 for forming a light emitting layer is set on a substrate holder and transported to a film forming chamber provided with the above target. Next, after evacuation of the film formation chamber to 10 ^-5 Pa or higher, a mixed gas of argon, helium, and hydrogen sulfide is introduced into the film formation chamber, and the pressure in the film formation chamber is adjusted to 0.4 Pa. .

When the pressure in the film forming chamber is stabilized, the sputtering pressure is readjusted to 4 Pa. The high frequency power required for sputtering is set to 150 watts, and after performing presputtering for about 20 minutes, the light emitting layer is actually formed. At this time, the light emitting layer deposition rate was 25 nm / min. In the fourth step, a second insulating layer 15 made of tantalum pentoxide is formed on the light emitting layer 14.
The first insulating layer 13 is formed in the same manner as described above.

In a fifth step, a second transparent electrode 16 made of zinc oxide (ZnO) is formed on the second insulating layer 15 by a method similar to that of the first transparent electrode 12 described above. By the way, the thickness of each layer in the present embodiment is different from the first transparent electrode 12.
And 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,
4 is 300 nm. The thickness of each of these layers indicates a numerical value in the central portion.

In the EL device prepared by the above method, the ratio of fluorine to terbium in the light emitting layer (F / T
b) Various characteristics depending on the ratio of oxygen to terbium (O / Tb) will be described below. First, characteristics according to the ratio of fluorine to terbium (F / Tb) in the light emitting layer will be described. That is, the ratio (F / Tb) is set to 0.05, 0.3,
Five samples each having 1.0 and 1.6 were prepared, and a durability test was performed for 1000 hours while continuously emitting light. Then, the amount of change in the threshold voltage after the durability with respect to the initial threshold voltage (165 V) was determined. In each sample, the ratio of oxygen to terbium (O / Tb) contained in the light emitting layer was set to 0.3.

FIG. 4 shows the results. In FIG. 4, the circles indicate the average value, and the upper and lower lines indicate the maximum value and the minimum value, respectively. As is clear from FIG. 4, the threshold voltage is significantly changed when F / Tb is 0.5 or more. Next, based on the results shown in FIG. 4, four samples each having an F / Tb of 0.3 and an F / Tb of 1.0 were prepared, and the lapse of the light emission operation time of the light emission threshold voltage in the samples. Was determined. Note that the ratio of oxygen to terbium (O / Tb) in the light emitting layer of each sample was set to 0.3.

In FIG. 2, a circle indicates an average value, and an upper line and an underline indicate a maximum value and a minimum value, respectively. FIG.
As is clear from the graph, when the F / Tb is 1.0, the light emission threshold voltage changes remarkably with the passage of time compared to the initial stage of the light emission operation, and a maximum of 15 hours after the light emission time of 1,000 hours elapses. It can be seen that the percentage moves toward the lower voltage side. On the other hand, when F / Tb is 0.3, it can be seen that the amount of change in the light emission threshold voltage is shifted by at most 3% at the beginning of the light emission operation.

Next, in the sample used in the measurement of FIG. 4, when the voltage exceeding the light emission threshold voltage by 40 V is applied, the light emission luminance with respect to the elapse of the light emission operation time (the light emission luminance described here is the light emission luminance). (Indicating the emission luminance when a voltage exceeding the threshold voltage by 40 V) is obtained. The result is shown in FIG. In FIG. 3, the circles indicate the average value, and the upper and lower lines indicate the maximum value and the minimum value, respectively. FIG.
As is clear from the graph, when the F / Tb is 1.0, the change from the initial luminance (here, the luminance at the time when one hour has elapsed from the start of the light emission) with respect to the elapse of the light emission operation time is about 22%. On the other hand, in the case of F / Tb of 0.3, there was almost no change from the initial light emission luminance with the elapse of the light emission operation time, and the maximum was about 5%.

Next, the ratio (O / Tb) of oxygen and terbium contained in the light emitting layer is set to 0.05, 0.3, 0.5, 1.0, with F / Tb being 0.3. Four samples each adjusted to 1.6 were produced. With respect to these samples, a voltage was applied at a frequency of 60 Hz, and the voltage at which the breakdown occurred was measured for the breakdown voltage. The result is shown in FIG.

In FIG. 5, a circle indicates an average value, and an upper line and an underline indicate a maximum value and a minimum value, respectively. FIG.
As is clear from FIG. 4, it is understood that the dielectric breakdown voltage sharply decreases when O / Tb exceeds 0.5, in other words, the withstand voltage decreases. Next, the emission luminance of these samples was measured. FIG. 6 shows the results. Note that the emission luminance is E
It represents the light emission luminance when a constant voltage is applied after the L element starts to emit green light. As is clear from FIG. 6, when the O / Tb was in the range of 0.05 to 2.0, the emission luminance exceeded the emission luminance of the sample to which oxygen was not added.

5 and 6, by setting the ratio of O / Tb to 0.05 or more and less than 0.05, it is possible to provide an E light having a necessary and sufficient emission luminance and a high withstand voltage.
It can be seen that an L element is obtained. Note that F / Tb and O
By setting / Tb within the scope of the present invention, the CIE
On the chromaticity coordinates, it has been confirmed that the image has shifted to 0.03 in the x-axis direction, 0.04 in the y-axis direction, and to the green side.
In addition, it has been confirmed that microdestruction occurring on the light emitting surface of the EL element is not significantly reduced or generated at all.

In the present invention, T in the light emitting layer
The concentrations of b, O, and F (halogen elements) are well known EPM
A (Electron Probe Analysis)
-Electron beam microanalysis). In the present invention, as the base material made of the II-VI group compound semiconductor, zinc selenide or the like may be used in addition to zinc sulfide.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an EL device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram for describing the present invention.

FIG. 3 is a characteristic diagram for describing the present invention.

FIG. 4 is a characteristic diagram for describing the present invention.

FIG. 5 is a characteristic diagram for describing the present invention.

FIG. 6 is a characteristic diagram for describing the present invention.

[Explanation of symbols]

 Reference Signs List 10 EL element 11 Glass substrate 12 First transparent electrode 13 First insulating layer 14 Light emitting layer 15 Second insulating layer 16 Second transparent electrode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-6774 (JP, A) JP-A-61-273894 (JP, A) JP-A-2-33887 (JP, A) JP-A-2- 94290 (JP, A) JP-A-2-242585 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B 33/14 C09K 11/00

Claims (5)

(57) [Claims] A first electrode, a light emitting layer, and a second electrode on an insulating substrate;
An EL element in which an electrode is formed and at least a light extraction side is formed of an optically transparent material, wherein the light emitting element includes a base material made of a II-VI group compound semiconductor, terbium, oxygen, and a halogen element. EL characterized in that an atomic ratio of the halogen element to the terbium (halogen element / terbium) is 0.05 or more and less than 0.5 contained in the light emitting layer. element. 2. The method according to claim 1, wherein a ratio of oxygen to terbium (oxygen / terbium) contained in the light emitting layer is 0.05.
2. The EL device according to claim 1, wherein the value is not less than 0.5. 3. The EL device according to claim 1, wherein the base material composed of the II-VI group compound semiconductor is zinc oxide. 4. The EL according to claim 1, wherein the halogen element is at least one selected from the group consisting of fluorine, chlorine, and bromine.
element. 5. The EL device according to claim 4, wherein the halogen element is fluorine or chlorine.