Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2002-01-31
2004-04-20
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C313S506000
Reexamination Certificate
active
06724150
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device using an organic light emitting element and a manufacturing method thereof, and more particularly to a display device using an organic light emitting element capable of keeping a stable light emitting property for a long period.
Note that the organic light emitting element in this specification indicates an element in which an organic compound layer is sandwiched between two electrodes to produce light emission. As the organic light emitting element, there is a light emitting element using an organic light emitting diode (OLED). The organic light emitting diode is a phosphor in which an organic compound layer is sandwiched between two electrodes, and a hole is injected from one electrode and an electron is injected from the other electrode so that the hole and the electron are combined in the organic compound layer to thereby produce light emission.
2. Description of the Related Art
Recently, a display device using an organic light emitting element is actively researched. In the case of the display device using the organic light emitting element, greater reduction in its weight and thickness is possible as compared with a conventional CRT and an application to various uses is being progressed. Since it is now possible to connect a mobile telephone, a personal digital assistant (PDA), or the like with the Internet, the amount of information to be displayed has dramatically increased, and the need for color display and high resolution of a display device is increased.
On the other hand, it is important for a display device incorporated in such a personal digital assistant to be reduced in its weight. For example, in the case of the mobile telephone, a product which weighs less than 70 g is currently on the market. For weight reduction, a review of most of parts to be used such as individual electronic parts, a case, and a battery is being conducted. However, in order to realize further weight reduction, it is also necessary to promote weight reduction of a display device.
A display device in which a pixel portion is composed of an organic light emitting element is of a self light emission type and does not require a light source such as a back light used in a liquid crystal display device. Thus, it is being greatly promised as means for realizing reduced weight and thickness.
With the organic light emitting element, blue color light emission is possible and a self light emission display device capable of full color display can be realized. However, in the organic light emitting element, various deterioration phenomena are recognized. which hinder the practical use. Thus, it is considered necessary to solve such a problem as soon as possible.
For example, a dark spot is a point defect of non-light emission, which is observed in a pixel portion, and is recognized as a problem for markedly degrading display quality. It is said that the dark spot is a progress type defect which increases even without operating the element, if moisture is present. It is considered that the dark spot is caused by an oxidation reaction of a cathode made of alkali metal.
Therefore, the display device using the organic light emitting element is constructed such that an element substrate on which a light emitting element is provided and a sealing substrate which is provided so as to oppose the element substrate are bonded together through a seal member having adhesion so that the light emitting element is not exposed to outside air including moisture. The sealing substrate is made of stainless steel or metal such as aluminum, which is easy to process. A dry agent is disposed in a concaved portion of the surface of the sealing substrate.
The seal member is mixed with a filler to control a gap between the element substrate and the sealing substrate. Thus, the seal member has both a function for bonding together the sealing substrate and the element substrate and a function for controlling the gap between the sealing substrate and the element substrate. Therefore. when the gap between the element substrate and the sealing substrate is set to be a general value of 10 &mgr;m to 50 &mgr;m, it is necessary to change the thickness of the seal member in accordance with the size of the gap.
Note that the shortest distance between the light emitting element and a surface of the sealing substrate opposing the light emitting element is called a gap between the sealing substrate and the element substrate, or simply a gap.
Now, the seal member for controlling the gap between the element substrate and the sealing substrate is made of an organic resin material and has higher moisture permeability than an inorganic material such as a glass material. For example, at a temperature of 60° C. and a humidity of 90%, moisture permeability becomes 15 g/m
2
·24 hr. to 30 g/m
2
·24 hr. Even when the sealing substrate and the element substrate are sealed with the seal member, the organic light emitting element is deteriorated by a water vapor which is transmitted through the seal member and penetrated in a sealed region. The amount of water vapor to be transmitted through the seal member is determined by the product of an area of the seal member to be exposed to outside air and moisture permeability. Thus, it is desirable that the area of the seal member to be exposed to outside air is small. That is, it is desirable that the thickness of the seal member is minimized.
As the thickness of the seal member is increased, the amount of moisture to be transmitted through the seal member is increased. Even if the dry agent is provided, the light emitting element is deteriorated by the moisture which is not absorbed by the dry agent. That is, an object of the present invention is to reduce the amount of moisture to be transmitted through the seal member.
Also, a method of thinning a glass substrate may be conceived to achieve weight reduction of the personal digital assistant. However, the glass substrate is more likely to break as it becomes thinner and its shock resistance is reduced. In particular, when the sealing substrate made of metal and the element substrate made of glass are bonded together, because of a difference in thermal expansion coefficient, a distortion is caused due to a sudden change in a temperature and a crack is caused in the substrate made of glass. However, this becomes a critical defect in the case where such a substrate is used for the personal digital assistant.
Therefore, an object of the present invention, is to prevent the breaking of the substrate to improve the durability thereof in the case of a construction in which the glass substrate is reduced in thickness to realize a thin display device.
Thus, although the display device composed of the organic light emitting element is very effective for weight reduction of a display device, there remain problems to be solved in order to ensure the reliability of the organic light emitting element.
SUMMARY OF THE INVENTION
The present invention relates to a technique for solving such problems and an object of the present invention is to provide a display device using an organic light emitting element having high reliability and a manufacturing method thereof.
As the substrate made of glass has become thinner, when the element substrate made of glass and the sealing substrate made of metal are bonded together, because of a difference in a thermal expansion coefficient, the possibility that the element substrate made of glass is broken due to a sudden change in a temperature becomes high. In order to prevent this, according to the present invention, a substrate made of glass is used for the element substrate and the sealing substrate to obtain an identical thermal expansion coefficient. Thus, resistance thereof against a sudden change in a temperature is increased, and thus the object of the present invention is attained.
Further, according to the present invention, the surface of the sealing substrate made of glass is processed to have a concaved portion and a dry
Maruyama Junya
Yamazaki Shunpei
A Minh D
Fish & Richardson P.C.
Semiconductor Energy Laboratory Co,. Ltd.
Wong Don
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