Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2002-05-03
2004-10-26
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S505000, C313S506000, C315S169300, C345S076000, C345S055000
Reexamination Certificate
active
06809473
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an organic electro-luminescence display element including a pair of electrodes and a film (organic electro-luminescence film), located between the electrodes, made of an organic compound and having an organic luminescent layer.
Further, the invention relates to a finder screen display device for displaying information in a finder screen (view-finder screen) of an optical device such as a shooting device (e.g., a camera), a telescope or a microscope which is provided with a finder. For example, the invention relates to the finder screen display device which can display information (e.g., shooting conditions such as a shift of a shooting scope on the finder screen, shooting mode and brightness of a shooting target) superimposed on the image viewed through the finder when using the shooting device such as a camera.
The invention also relates to a finder provided with the foregoing finder screen display device, and an optical device provided with this finder.
2. Description of the Background Art
In recent years, various kinds of information devices have been developed, and thereby there has been the growing need for flat display elements having thin forms and requiring lower power consumption than CRTs. Such flat display elements may be a liquid crystal display element, a plasma display (PDP).and others. In particular, attention has been directed to an electro-luminescence element which is of a self-luminescent type and can make clear display with a large angle of view.
The electro-luminescence elements can be roughly divided into an inorganic electro-luminescence element and an organic electro-luminescence element based on materials forming the elements. The inorganic electro-luminescence elements are already put into commercial products.
However, light emission of the inorganic electro-luminescence element is of a so-called collision excitation type, in which electrons accelerated by an applied high electric field collide with luminescent center for emitting light. Therefore, a high voltage of 100 V or more must be applied for driving the element. This increases a cost of peripheral devices. Since a good luminophor for blue is not available, display in full color cannot be performed by the inorganic electro-luminescence element.
In contrast to the above, the organic electro-luminescence element (organic EL element) is of a so-called injection type, in which the charges (holes and electrons) injected from positive and negative electrodes are recoupled to form excitons in the luminophor, and the excitons excite molecules of luminescent material to emit the light. Therefore, the organic EL element can be driven with a low voltage. Further, it is easy to change the molecular structure of the luminescent material because it is the organic material. Thereby, the color of emitted light can be arbitrarily determined. Accordingly, the organic electro-luminescence element is a significantly promising display element.
The prototype of the organic electro-luminescence element has a two-layer structure provided with a hole transport layer and an electron transport layer. This element was proposed by Tang and Vanslyke [C. W. Tang and S. A VanSlyke; Appl. Phys. Lett., 51 (1987) 913]. This element is formed of a positive electrode, a hole transport layer, an electron transport luminescent layer and a negative electrode which are layered on a glass substrate.
In this element, the hole transport layer functions to inject holes from the positive electrode into the electron transport luminescent layer. The hole transport layer also prevents electrons, which are injected from the negative electrode, from escaping into the positive electrode without being recoupled with the holes, and thereby functions to confine electrons in the electron transport luminescent layer. Owing to the electron confining effect by the hole transport layer, therefore, recoupling between the electrons and holes occurs more efficiently than the element of a single luminescent layer structure, and therefore allows significant reduction in drive voltage.
Further, Saito et al. have disclosed the fact that, in the element of the two-layer structure, not only the electron transport layer but also the hole transport layer can become a luminescent layer [C. Adachi, T. Tsutsui and S. Saito; Appl. Phys. Lett., 55 (1989) 1489].
Saito et al. have proposed, as an improvement of the element of the two-layer structure, an element of a three-layer structure in which a luminescent layer is interposed between the hole and electron transport layers [C. Adachi, T. Tsutsui and S. Saito; Jpn. J. Appl. Phys. 27 (1988) L269]. This element is formed of a positive electrode, a hole transport layer, a luminescent layer, an electron transport layer and a negative electrode layered on a glass substrate. The hole transport layer functions to confine the electrons in the luminescent layer, and the electron transport layer functions to confine the holes in the luminescent layer so that the luminescence efficiency is further improved.
The negative electrode of the organic electro-luminescence element is generally formed of a film of about 100 nm in thickness, which is made of metal having a small work function and is prepared by vapor deposition on an organic layer, and is opaque. In the organic electro-luminescence element, if transparent electrodes are used not only in the positive electrode but also in the negative electrode, the element forms a self-luminescent element having transparency so that it can be applied to a wider range.
In connection with this, a transparent organic electro-luminescence element is disclosed in Japanese Laid-Open Patent Publication No. 8-185984 (185984/1996). The element taught in this publication includes an organic luminescent film formed of an electron transport layer, a luminescent layer and a hole transport layer, and also includes a transparent conductive layer as well as a transparent thin layer, which has a thickness of several nanometers, and is made of a metal or alloy thereof having a low work function. The thin layer is interposed between the organic luminescent film and the transparent conductive layer. Further, the transparent conductive layer (negative electrode) made of Indium Tin Oxide (ITO) is formed on the thin film, and a transparent conductive layer (positive electrode) made of ITO is disposed on the hole transport layer side thereof.
If the transparent conductive layer is used as the negative electrode, an energy gap between the negative electrode and the electron transport layer may increase excessively so that the efficiency of injection of electrons into the organic luminescent film lowers, resulting in a low luminous efficiency. For overcoming the above problem, the thin layer which has a thickness of several nanometers and is made of metal or alloy thereof having a low work function is interposed between the organic luminescent film and the transparent conductive layer.
However, manufacturing of the element of the structure disclosed in Japanese Laid-Open Patent Publication No. 8-185984 suffers from the following problem because the element employs a thin layer of metal of a low work function. It is difficult to form the thin film of the metal having a low work function. Even if such a thin film is formed, oxidization or the like is likely to occur on the thin film, and therefore it is very unstable. Accordingly, it is very difficult to form a transparent conductive layer on such a thin film of the metal having a low work function.
Meanwhile, in a camera, as an example of an optical device provided with a finder, independently provided with a shooting optical system and a finder optical system, a phenomenon which is so-called “parallax” occurs as shown in FIGS.
30
(A),
30
(B) and
30
(C). In this phenomenon, an actual shooting scope
53
of a shooting optical system
45
shifts from a finder screen
52
viewed through a finder optical system
51
. According to general setting, the
Furukawa Keiichi
Hisamitsu Akihito
Kitahora Takeshi
Terasaka Yoshihisa
Ueda Hideaki
Minolta Co. , Ltd.
Morrison & Foerster / LLP
Patel Ashok
Santiago Mariceli
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