JP3750199B2 - Method for manufacturing thin-film electroluminescence device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing a thin film electroluminescence element.
[0002]
[Prior art]
A thin film electroluminescence (hereinafter referred to as EL) display element as one of flat display elements is a clear, high-contrast, low-viewing-angle dependency, and therefore, as a display element for a computer terminal, a display element for mounting in a vehicle, etc. Research and development is ongoing.
[0003]
FIG. 6 is a cross-sectional view of a typical thin film EL device. On the glass substrate 1, the 1st electrode layer 2, the 1st insulating layer 3, the light emitting layer 4, the 2nd insulating layer 5, and the 2nd electrode layer 6 are laminated | stacked in order, and a thin film EL element is produced. The thin film EL element is covered with a sealing plate 7 and a side wall 8, and after silicone oil 9 is injected therein, it is hermetically sealed. A drive power supply V is connected to both electrode layers, and a bipolar pulse voltage is applied to cause EL emission.
[0004]
The first electrode layer 2 is a transparent conductive layer such as indium tin oxide (hereinafter referred to as ITO), and the first insulating layer 3 and the second insulating layer 5 are composed of silicon nitride (hereinafter referred to as Si ₃ N ₄ ). referred) film and silicon oxide (hereinafter referred to as SiO ₂₎ a laminated film the Si ₃ N ₄ film is adjacent to the luminescent layer 4, the second electrode layer 6 is often a metal film.
A monochrome thin film electroluminescent display using a phosphor of ZnS: Mn that emits yellow-orange light as the light emitting layer 4 has already been put into practical use, but colorization is indispensable with diversification of display contents.
[0005]
As the phosphor of the light emitting layer 4 used in the color thin film EL display, CaS: Eu, ZnS: Sm, SrS: Eu, etc. for red, ZnS: Tb, CaS: Ce, etc. for green, etc. SrS: Ce or the like is used, but there are problems as described below, and any practical color EL display has not been realized.
[0006]
[Problems to be solved by the invention]
All of these light emitting layer thin films have the problems of (1) low emission luminance and (2) short lifetime. In particular, the short life of (2) was a big problem for practical use.
This time, we have discovered that the reason why the lifetime is short is due to impurities such as carbon dioxide, oxygen or moisture contained in or on the surface of the light emitting layer.
[0007]
An object of the present invention, after a long emission also is to provide a method of manufacturing small thin-film EL element of decrease in brightness.
[0008]
[Means for Solving the Problems]
To achieve the above object , according to a reference example of the present invention, a light emission comprising a first electrode layer, a first insulating layer, and a material obtained by adding a rare earth element to at least an alkaline earth sulfide on a glass substrate. In the thin film electroluminescent element in which the layer, the second insulating layer, and the second electrode layer are sequentially stacked, carbon dioxide, oxygen, or moisture contained in or on the surface of the light emitting layer is removed.
[0009]
The residual amount of oxygen is preferably 1 × 10 ¹⁶ molecules / cm ² or less.
The residual amount of carbon dioxide is preferably 1 × 10 ¹⁷ molecules / cm ² or less.
The residual amount of moisture is preferably 3 × 10 ¹⁶ molecules / cm ² or less.
According to the present invention, a first electrode layer, a first insulating layer, a light emitting layer made of a material obtained by adding a rare earth element to at least an alkaline earth sulfide, a second insulating layer, a second insulating layer on a glass substrate. In the method for manufacturing a thin film electroluminescent element in which electrode layers are sequentially stacked, a removal step of removing impurity molecules in the light emitting layer is performed before forming the second insulating layer.
[0010]
Here, the removing step is assumed to be sputtering of the surface of the light emitting layer.
The gas used for the sputtering preferably contains hydrogen gas.
Further, according to the reference example of the present invention, the removal step may be vacuum heat treatment of the light emitting layer.
According to the reference example of the present invention, the heat treatment is preferably performed in a vacuum of 1 × 10 ⁻¹ Pa or less and the temperature of the light emitting layer is set to 250 to 600 ° C.
[0011]
Further, according to the reference example of the present invention, on the glass substrate, the first electrode layer, the first insulating layer, the light emitting layer made of a material obtained by adding a rare earth element to at least alkaline earth sulfide, the second insulating layer. In the method of manufacturing a thin film electroluminescent element in which a layer and a second electrode layer are sequentially stacked, it is preferable that the second insulating layer is formed by holding the light emitting layer after being formed in vacuum.
According to the present invention and the reference example of the present invention, carbon dioxide or oxygen in the light emitting layer or adsorbed moisture on the surface of the light emitting layer is removed, so that carbon dioxide, oxygen molecules or water molecules remaining during driving emit light. Even if they diffuse into the layer and these oxygen or oxygen molecules act on the emission center to reduce the luminance, it is estimated that the effect is small.
[0012]
By sputtering the surface of the light emitting layer using plasma, moisture on the surface of the light emitting layer can be removed. In particular, when hydrogen is contained in the sputtering gas, carbon dioxide and oxygen molecules inside the light emitting layer can be removed. Further, by heating the light emitting layer in a vacuum, it is possible to remove adsorbed gases such as moisture and oxygen adsorbed on the surface of the light emitting layer. The removal of moisture requires 250 ° C. or higher. However, if the temperature is too high, sulfur in the light emitting layer evaporates and the luminance of the light emission is lowered, so that the heating temperature is 250 to 600 ° C., preferably 350 to 500 ° C. ° C is suitable.
[0013]
Further, if the second insulating layer is formed after the light emitting layer is formed and then kept in vacuum after the light emitting layer is formed, moisture or the like is not adsorbed to the light emitting layer.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The thin film EL element according to the reference example of the present invention has the structure already described with reference to FIG. The first electrode layer 2 is a transparent electrode such as ITO, and the first insulating layer 3 and the second insulating layer 5 are a silicon nitride (Si ₃ N ₄ ) film and a silicon oxide (SiO ₂ ) film laminated, and silicon nitride. The film was adjacent to the light emitting layer 4, and the second electrode layer 6 was a laminate of metal layers such as aluminum and nickel.
[0015]
As the light emitting layer 4, either CaS: Eu or SrS: Eu is used for red, a stack of these and ZnS: Sm, a stack of CaS: Ce and this and ZnS: Tb for green, and SrS: for blue Ce or the like can be used.
In the following examples and reference examples , the sputtering method was used for forming the insulating layer and the vapor deposition method was used for forming the light emitting layer. However, similar effects can be obtained by using other film forming methods.
Example 1
FIG. 5 is a schematic cross-sectional view of a sputtering apparatus for an insulating layer of a thin film EL element used in an example of the present invention.
[0016]
In this sputtering apparatus, in addition to the RF power source 16a that sputters the target 13 connected to the cathode 12, the anode 14 on which the glass substrate 1 is placed has another RF power source 16b so that this side can be sputtered. (13.56 MHz) is connected. The glass substrate 1 can be etched using the RF power source 16b. At this time, the anode 14 is grounded.
[0017]
The thin film EL device of this example was manufactured by the following procedure.
(1) ITO was formed into a film as the transparent electrode layer 2 on the surface of the glass substrate 1 by sputtering, and patterned into a stripe shape by a wet process.
(2) SiO 2 and Si ₃ N ₄ were sequentially laminated as the first insulating layer 3 by reactive sputtering, and the film thickness was 200 nm.
[0018]
(3) As the light emitting layer 4, a strontium sulfide (SrS: Ce) film having Ce as an emission center was formed by electron beam evaporation. The substrate temperature during film formation was 500 ° C., and the thickness of the light emitting layer 4 was about 1 μm.
(4) The glass substrate 1 laminated up to the light emitting layer 4 is taken out into room temperature and humidity and then transferred to the sputtering apparatus in which the first insulating layer 3 is formed, and in this sputtering apparatus in which the insulating layer 3 is formed. Then, the surface of the light emitting layer was sputtered with a mixed gas of Ar and H ₂ at a gas pressure of 0.1 Pa and an input power of 500 W for 4 minutes to remove impurities.
[0019]
(5) After removing the impurities from the light emitting layer 4, an Si ₃ N ₄ film and an SiO ₂ film were sequentially laminated as the second insulating layer 5 under the same conditions as the first insulating layer 3 in the same sputtering apparatus. The light emitting layer 4 is sandwiched between Si ₃ N ₄ .
(6) A laminated film of Al and Ni was laminated as the second electrode layer 6 by electron beam evaporation, and the stripes in the direction perpendicular to the stripes of the transparent electrode layer 2 were patterned by a wet process.
[0020]
In order to investigate the degassing component from the light emitting layer, temperature-programmed desorption gas analysis (hereinafter referred to as TDS) of the light emitting layer was performed. FIG. 2 is a graph of temperature-programmed desorption gas analysis of O ₂ molecules (mass number 32) of the light emitting layer from which impurities have not been removed. The vertical axis is an arbitrary unit proportional to the number of detected molecules, and the scale is common to the following TDS graphs (FIGS. 3 and 4). From FIG. 2, it can be seen that the O ₂ molecules started to desorb at around 400 ° C., and most of them were desorbed at around 650 ° C. The total amount of desorbed O ₂ molecules was about 3 × 10 ¹⁶ molecules / cm ² . FIG. 3 is a graph of thermal desorption gas analysis of CO ₂ molecules (mass number 44) of the light emitting layer from which impurities have not been removed. The vertical axis is an arbitrary unit proportional to the number of detected molecules. From FIG. 3, it can be seen that CO ₂ molecules also started desorption from around 400 ° C. and desorbed to around 800 ° C. The total amount of desorbed CO ₂ molecules was about 3 × 10 ¹⁷ molecules / cm ² .
[0021]
After completion of the impurity removal step according to the present invention, when the TDS is taken into the TDS apparatus while the light emitting layer on the substrate is kept in vacuum, the total desorption amount of O ₂ molecules is about 1 × 10 ¹⁶ molecules / cm ² or less, The total desorption amount of CO ₂ molecules was about 1 × 10 ¹⁷ molecules / cm ² or less. It can be seen that both O ₂ molecules and CO ₂ molecules are reduced to about 1/3 by the impurity removal process. When hydrogen gas is not included in the sputtering gas, the decrease in O ₂ and CO ₂ is small, and it can be seen that hydrogen gas is important.
Example 2
The manufacturing method of the thin film EL element of this example was the same as that of Example 1 except that the impurity removal step (4) was changed. As sputtering conditions, the gas was Ar only, the substrate temperature was room temperature, and the sputtering time was 2 min.
[0022]
TDS was performed on water in the same manner as in Example 1. FIG. 4 is a graph of temperature-programmed desorption gas analysis of water molecules (mass number 18) in the light emitting layer from which impurities have not been removed. The vertical axis is an arbitrary unit proportional to the number of detected molecules. From FIG. 4, it can be seen that desorption of water molecules started from around 150 ° C., and most of the water molecules were completely desorbed at around 550 ° C. The total amount of desorbed water molecules was about 1 × 10 ¹⁷ molecules / cm ² .
[0023]
As in Example 1, after the impurity removal step according to the present invention is completed, when the TDS is performed while the light emitting layer is held in a vacuum, the total amount of desorbed water molecules is about 3 × 10 ¹⁶ molecules / cm 3. ^{It was 2} or less, and was about 1/3 or less when the impurity removal step was not performed.
The light emitting layer side of the thin film EL element of Examples 1 and 2 obtained as described above is covered with a box made of a glass sealing plate 7 and a side wall 8 and sealed by injecting silicone oil 9 to form a thin film EL. An apparatus (FIG. 6) was produced. A drive power supply V was connected between both electrode layers of this thin-film EL device, and a pulse voltage of both polarities was applied to evaluate a change in light emission luminance with time. FIG. 1 is a graph of the change over time of the light emission luminance of a thin film EL device manufactured by the manufacturing method of the present invention . FIG. 1 also shows a change with time (curve c) of a thin film EL device using an EL element of a light emitting layer that is not subjected to impurity removal. Curve a corresponds to the element manufactured in Example 1, and curve b corresponds to the thin film EL device using the element manufactured in Example 2. The light emission luminance of the thin film EL element after driving for 50,000 hours in terms of 60 Hz is about 60% of the initial luminance in the EL element of Example 1 (curve a), and about 45% of the initial luminance in the EL element of Example 2. % (Curve b). On the other hand, in the EL element (curve c) of the light emitting layer where impurities are not removed, it is reduced to 50% in 10,000 hours, and the effect of removing impurities on the light emission is clear.
[0024]
From the above analysis, carbon dioxide, oxygen, or moisture present inside or on the surface of the light emitting layer has a significant effect on the lifetime of the thin-film EL element in the deterioration of light emission luminance over time. It was found that a thin film EL element having a layer has a long lifetime.
Reference example 1
The manufacturing method of the thin film EL element of this reference example was the same as that of Example 1 except that the impurity removal step (4) was different.
[0025]
(4) The glass substrate 1 laminated up to the light emitting layer 4 is taken out into room temperature and humidity, and then transferred into the sputtering apparatus in which the first insulating layer 3 is formed, and in a vacuum of 1.5 × 10 ⁻³ Pa. Then, the substrate temperature was heated to 400 ° C., and the adsorption gas of the light emitting layer was degassed for 1 hour.
(4) After degassing the glass substrate laminated up to the light emitting layer 4 with the same temperature profile as in (4) in the TDS apparatus, when TDS is performed, the total amount of water molecules is about 3 × 10 ¹⁶ molecules / It was cm ² or less, and the removal of moisture was confirmed in the same manner as in Example 2.
[0026]
The substrate temperature needs to be 250 ° C. or higher at which water desorption begins and 600 ° C. or lower at which sulfur desorption begins from the light-emitting layer, as can be seen from TDS.
Further, the change with time of the light emission luminance of the thin-film EL device using this element was substantially the same as in Example 2.
Reference example 2
In this reference example, the substrate is held in vacuum from the time when the light emitting layer 4 is formed to the time when the second insulating layer 5 is formed, thereby preventing gas adsorption to the light emitting layer 4.
[0027]
The thin film EL device was manufactured by the following procedure.
(1) to (2) Same as Example 1.
(3) An SrS: Ce film was formed as the light emitting layer 4 by electron beam evaporation. The substrate temperature was 500 ° C., and the thickness of the light emitting layer 4 was about 1 μm.
(4) After the substrate is moved to another film formation chamber while maintaining the vacuum in the same vacuum apparatus, the second insulating layer is made of Si ₃ N ₄ and SiO _{2 under the} same conditions as the first insulating layer. A second insulating layer was sequentially laminated.
[0028]
(5) A thin film EL element was produced in the same manner as in Example 1.
Further, the change with time of the light emission luminance of the thin film EL device using this element was the same as that in Example 2.
This is because the light emitting layer is covered with a moisture resistant structure in the following step or less without being exposed to water vapor, that is, without adsorbing water molecules.
[0029]
【The invention's effect】
According to the present invention, a first electrode layer, a first insulating layer, a light emitting layer made of a material obtained by adding a rare earth element to at least an alkaline earth sulfide, a second insulating layer, a second insulating layer on a glass substrate. In the method for manufacturing a thin film EL element in which electrode layers are sequentially stacked, a removal step of removing impurity molecules in the light emitting layer is performed before the formation of the second insulating layer, and the removal step is performed on the surface of the light emitting layer. Since the thin film EL element of the present invention is driven by sputtering, the influence of oxygen on the light emission center due to impurities is reduced during driving, the luminance is reduced, and the lifetime is long. An EL device can be obtained.
[0030]
Also, special modifications are not required for film forming apparatus, a manufacturing method is not complicated. Therefore, there is almost no cost increase.
[Brief description of the drawings]
FIG. 1 is a graph of the time-dependent change in emission luminance of a thin film EL device manufactured by the manufacturing method of the present invention. FIG. 2 is a temperature programmed desorption gas analysis of oxygen (mass number 32) in a light emitting layer from which impurities are not removed. [Fig. 3] Graph of temperature-programmed desorption gas analysis of carbon dioxide (mass number 44) in the light emitting layer without removing impurities [Fig. 4] Water molecule (mass number of 18 in the light emitting layer without removing impurities) ) Temperature desorption gas analysis graph of FIG. 5] FIG. 5 is a schematic cross-sectional view of a sputtering apparatus for an insulating layer of a thin-film EL element used in an embodiment of the present invention. Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Glass substrate 2 2nd electrode layer 3 1st insulating layer 4 Light emitting layer 5 1st insulating layer 6 2nd electrode layer 7 Sealing plate 8 Side wall 9 Silicone oil V Drive power supply 10 Vacuum vessel 11 Gas inlet 12 Cathode 13 Target 14 Anode 15 Shutter 16a RF power supply 16b RF power supply 17a Matching box

Claims (2)

On a glass substrate, a first electrode layer, a first insulating layer, light emitting layer made of a material doped with a rare earth element to at least an alkaline earth sulfide, a second insulating layer are sequentially stacked second electrode layers the method of manufacturing a thin-film electroluminescent device, before formation of the second insulating layer was subjected to removal step of removing impurities molecules of the luminescent layer, the removing step is a sputter der Rukoto the surface of the light-emitting layer A method for producing a thin-film electroluminescent device. Method of manufacturing a thin film electroluminescent device according to claim 1 to the gas used in the sputtering characterized that you have contain hydrogen gas.

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