Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2001-02-02
2003-08-26
Braun, Fred L (Department: 2852)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C428S917000, C445S025000
Reexamination Certificate
active
06611098
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hermetic encapsulation package and a method of fabrication thereof. More particularly, it relates to a hermetic encapsulation package and a method of fabrication thereof, which are especially suitable for hermetically sealing organic EL (electroluminescent) elements used for plain light sources or display devices in which an electric field is applied to a light emitting layer of organic compounds to emit light therefrom.
2. Description of the Related Art
Electroluminescent elements (hereinafter referred to as EL elements) include inorganic EL elements and organic EL elements. Both EL elements are self luminescent and thus provide high visibility. In addition, since they are perfect solid-state elements, they provide improved resistance to a shock and can be handled easily. For these reasons, the EL element is being developed as pixels for use in graphic displays or television image display devices, or plain light sources. In particular, unlike the inorganic EL element, the organic EL element is not constrained to the requirements of alternating-current drive and high voltages. In addition, the variety of organic compounds employed by the organic EL element conceivably makes it relatively easy to provide multiple colors. Thus, application of the organic EL element for full-color displays or the like is expected and a structure of the organic EL element is being developed to provide high luminance at low voltages. The inorganic EL element is excited with an electric field to emit light. On the other hand, the organic EL element emits light by so-called carrier injection, in which positive holes are injected from the anode and electrons from the cathode for the operation of the organic EL element. The positive and negative carriers injected from both electrodes move to the opposite electrodes and are re-combined to form excitons therein. Relaxation of the excitons produces the emission of light which is in turn the light emission from the organic EL element.
The organic EL element was previously studied intensively using anthracene single crystal of high purity, however, such an organic EL element provided low luminance and low luminous efficiency with less stability irrespective of the necessity for the application of high voltages. However, in 1987, Tang et al from Eastman Kodak Company announced that they employed a two-layer stacked structure of organic thin film to provide a stable high-luminosity light emission at low voltages. Since then, the research and development of the organic EL element has been suddenly energized. In this structure, an organic layer sandwiched by a pair of electrodes was fabricated of two stacked layers of a light-emitting layer and a hole transport layer. The organic layer provides an outstanding property of 1,000 cd/m
2
upon application of 10V (Tang et. al., Appl. Phys. Lett., 51 (12), 913 (1987)). These days, in some cases, provided are not only the light-emitting layer and the hole transport layer but also an electron transport layer between the cathode and the light-emitting layer. Alternatively, a hole injection layer may be interposed between the hole transport layer and the anode. In addition, various studies on the materials used for each layer have yielded many results concerning an increase in luminous efficiency and longevity, leading to an increasing expectation of applying the organic EL element for flat panel display devices with the organic EL elements being arranged in a matrix of X-Y plane. Thus, this has led to the development of a monochromatic passive matrix panel with 256×64 dots, a ¼ VGA 5-inch diagonal color panel, and a VGA 10-inch diagonal color panel. (For example, reference can be made to Display and Imaging, Vol. 5, pp273-277 (1997) by Hitoshi Nakata et al; Fundamental and Practical Techniques of Organic EL Element by Hitoshi Nakata, the Japan Society of Applied Physics, Organic Molecular Bioelectronics Division, Sixth Lecture Notes, pp147-154 (1997); Flat Panel Display 1998, p234, Nikkei Business Publications, Inc., etc.)
The organic EL element has a structure in which an organic thin film of thickness equals to or less than 1 &mgr;m sandwiched by two electrodes. Exposure of the element after fabricated to the surrounding atmosphere would cause the organic layer and the material of the electrodes to react somehow with gas (such as moisture and oxygen) in the atmosphere. This may cause non-light-emitting regions to appear on the element, referred to as dark spots, which degrade the light emission properties. Therefore, it is practically necessary to provide the element with an encapsulating mechanism to seal out the atmosphere immediately after the fabrication of the element. The sealing methods include a direct technique of providing a protective layer on the outer surface of the element or molding the element with resin or the like. An alternative method is an indirect technique of providing the element with a hollow structure using a cap or the like to seal out the atmosphere. In some cases, the element is directly protected and further provided with another sealing means.
Specific examples of the direct technique have been reported. In a method (Japanese Patent Laid-Open Publication No. Hei 3-37991), the element is molded with oxygen absorbent resin. In a method (Japanese Patent Laid-Open Publication No. Hei 7-169567), a gas barrier layer and a gas absorbent layer are employed at the same time. In a method (Japanese Patent Laid-Open Publication No. Hei 8-236271), the sealed space is filled with an elastic resin. In a method (Japanese Patent Laid-Open Publication No. Hei 8-124677), a stress relaxation layer is interposed between the rear surface and an adhesion layer of the organic EL element upon face-to-face bonding of a sealing material such as a glass plate to the rear surface of the organic EL element with the adhesive. In a method (Japanese Patent Publication No.2813495), an insulating polymer layer is provided on the outer surface of the element and further an insulating glass or the like is provided thereupon. In a method (Japanese Patent Publication No.2813499), an insulating inorganic compound material is provided on the outer surface of the element, a hygroscopic layer is deposited thereupon, and further an insulating glass layer or an insulating polymer film is provided thereupon. In a method (Japanese Patent Laid-Open Publication No. Hei 4-363890), the element is held in a fluorine-based inert liquid. In a method (Japanese Patent Laid-Open Publication No. Hei 5-182759), a non-permeable substrate is fixed to the element via a photo curing resin having moisture resistance. Finally, in a method (Japanese Patent Laid-Open Publication No. Hei 9-274990), a protective layer is provided on the outer surface of the element, the element is then molded with a sealing layer having a certain physical property, and a cap is further provided to seal out the atmosphere.
On the other hand, specific examples for the indirect technique previously reported include a method (Japanese Patent Laid-Open Publication No. Hei 9-148066) for fixing a desiccant within a hermetically sealed space in a spaced apart relationship from the element. Further included in the examples is a method (Japanese Patent Laid-Open Publication No. Hei 3-261091) for holding the element in a hermetically sealed space filled with a desiccant of phosphorus pentoxide (P
2
O
5
).
In the direct technique, either the protective layer is directly provided on the element or the element itself is molded directly with resin or the like. This causes great concerns to rise that the organic EL element formed of an organic film having a thickness of less than 1 &mgr;m may be susceptible to damage. The damage may be caused not only by force or heat applied directly to the element during the process but also by stress or the like generated on the interface between the element and a protective agent. It is therefore preferable to employ a method in which the element is
Mori Kenji
Sakaguchi Yoshikazu
Braun Fred L
Hayes & Soloway P.C.
NEC Corporation
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