Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-09-21
2003-11-04
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C427S066000, C313S504000, C313S506000, C313S505000
Reexamination Certificate
active
06641933
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting organic compound (including a complex that contains a metal in its molecular formula) capable of providing Electro Luminescence (EL), and an EL display device utilizing the same. Typically, the present invention relates to a high-molecular type EL display device which utilizes a light-emitting organic compound made of a high-molecular compound.
The present invention also relates to an electronic apparatus including the above-mentioned EL display device as its display portion. It should be noted that the above-mentioned EL display device will be also referred to as the OLED (Organic Light-emitting Diode).
2. Description of the Related Art
Development of a display device including an EL layer as a self-light emitting element that utilizes EL phenomenon (i.e., the EL display device) has been proceeded in these years. Since the EL display device is of the self-light emitting type, no back light is required to be contained therein, unlike a liquid crystal display device or the like. Moreover, the EL display device exhibits a wide viewing angle. From the above features, the EL display device is advantageous to be used as a display portion for a portable device which is likely to be used outdoors.
A light-emitting layer as a principal portion of the EL element is made of an insulating material. When a voltage is applied across a cathode and an anode with the light-emitting layer interposed therebetween, carriers (electrons and holes) are injected into the light-emitting layer and recombined to emit light. Thus, a current flowing through the light-emitting layer is caused by the recombination of carriers. An EL material that can be used for the EL display device is described in, for example. Japanese Patent Application Laid-Open No. Hei 2-311591.
In a light-emitting element such as a light-emitting diode in which a semiconductor junction is formed, Na (sodium) that may exhibit an adverse effect as a movable ion causes a resistance value of the light-emitting layer to decrease, and therefore, can cause a current flow other than that caused by the carrier recombination. When such an unnecessary current flows, an amount of heat generation is increased and the light-emitting layer is more likely to deteriorate. The same disadvantage may occur in the EL device. However, any sufficient countermeasure against the disadvantage caused by the movable ion has not been provided for the EL material.
SUMMARY OF THE INVENTION
The present invention is intended to provide an EL display device with high reliability. The present invention is also intended to provide an electronic apparatus with a highly reliable display portion by utilizing such an EL display device as its display portion.
In accordance with the present invention, in order to prevent a current from flowing due to reasons other than the carrier recombination, a volume resistivity of a thin film made of a light-emitting organic compound in an EL device is set to be in the range of 3×10
10
&OHgr;cm or larger. A volume resistivity of a thin film made of a light-emitting organic compound in an EL device is set to be in the range from 1×10
11
to 1×10
12
&OHgr;cm (preferably, in the range from 1×10
12
to 1×10
13
&OHgr;cm). In order to obtain the volume resistivity value in the above range, the concentration of ionic impurities contained in the thin film made of the light-emitting organic compound is set to be equal to 0.1 ppm or lower (preferably, equal to 0.01 ppm or lower). The ionic impurity refers to an element belonging to Group I or II in the periodic table, and typically to sodium (Na) or potassium (K).
Accordingly, in order to obtain the above-mentioned structure, it is necessary to use such a light-emitting organic compound that contains ionic impurities at the concentration of 0.1 ppm or lower (preferably, at the concentration of 0.01 ppm or lower).
In the case of sodium, the above-mentioned concentration range can be calculated to be 7×10
17
atoms/cm
3
or lower (preferably, 7×10
16
atoms/cm
3
or lower). However, it is appropriate to consider that the total concentration of all of the ionic impurities should meet the above-mentioned concentration range.
When a light-emitting organic compound made of a low-molecular compound (hereinafter, referred to as the low-molecular type EL compound) is used for obtaining the above-mentioned light-emitting organic compound, the low-molecular type EL compound can be purified by a zone purification method, a sublimation purification method, a recrystallization method, a distillation method, a filtration method, a column chromatography method, or a reprecipitation method.
On the other hand, when a light-emitting organic compound made of a high-molecular compound (hereinafter, referred to as the high-molecular type EL compound) is used, values of molecular weight are likely to vary over a certain range since degree of polymerization cannot be completely controlled. Thus, a melting temperature of the resultant material cannot be decided unambiguously at a certain value, and therefore, it becomes difficult to perform purification. In this case, it is appropriate to perform a dialysis method or a high-performance liquid chromatography method. In particular, it is appropriate to perform an electrodialysis method for efficiently eliminating ionic impurities in the dialysis method.
In either of the above-mentioned purification methods, a purification process is required to be repeated several times in order to reduce the concentration of the ionic impurities to a level of 0.1 ppm or lower. More specifically, it is desirable to repeat a purification process at least three times or more, and more preferably, five times or more. Instead of repeating the same purification process, it is of course possible to perform two or more different processes.
In the case where the filtration method is employed, it is preferable to use a filter provided with openings having a diameter of 0.1 &mgr;m (this diameter is particularly referred to as the diameter of particle-eliminating opening). Preferably, a filter with openings having a diameter of 0.05 &mgr;m is used. A filter provided with openings having a diameter of 0.1 &mgr;m only allows particles having a diameter of 0.1 &mgr;m or smaller to pass therethrough. Similarly, a filter provided with openings having a diameter of 0.05 &mgr;m only allows particles having a diameter of 0.05 &mgr;m or smaller to pass therethrough.
As set forth above, in accordance with the present invention, a light-emitting organic compound containing ionic impurities at the concentration of 0.1 ppm or lower (preferably, at the concentration of 0.01 ppm or lower) is formed., and by using it, an EL device including a thin film made of a light-emitting organic compound having a volume resistivity in the range of 3×10
10
&OHgr;cm or larger. A volume resistivity of a thin film made of a light-emitting organic compound in an EL device is set to be in the range of 1×10
11
to 1×10
12
cm (preferably, in the range from 1×10
12
to 1×10
13
&OHgr;cm) is formed so as to fabricate an EL display device by utilizing such an EL device.
For the light-emitting organic compound to be used in the present invention. as the low-molecular type EL compound, a compound having a molecular weight in the range of 1×10
2
to 8×10
2
g/mol (typically, in the range of 3×10
2
to 5×10
2
g/mol) can be used, while a compound having a molecular weight in the range of 8×10
2
to 2×10
6
g/mol (typically, in the range of 1×10
4
to 1×10
5
g/mol) can be used as the high-molecular type EL compound.
The typical low-molecular type EL compounds that can be used in the present invention include Alq
3
(tris-8-quinolinolato aluminum complex). Its molecular formula can be expressed as per enclosure.
[Formula 1]
The other possible compounds include distyl allylene amine derivative that can be o
Konuma Toshimitsu
Mizukami Mayumi
Yamazaki Shunpei
Garrett Dawn L.
Kelly Cynthia H.
Robinson Eric J.
Robinson Intellectual Property Law Office P.C.
Semiconductor Energy Laboratory Co,. Ltd.
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