Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2003-10-10
2004-10-12
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S022000, C438S082000, C438S099000, C257S040000, C257S059000, C257S103000
Reexamination Certificate
active
06803246
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light emitting device using a phosphor or a light emitting element and a method of manufacturing the same. More particularly, the present invention relates to a light emitting device manufactured using an organic compound for a phosphor or a light emitting element and a method of manufacturing the same. Note that light emission in this specification includes fluorescence and phosphorescence and that the present invention includes light emission by any one of them or both.
2. Description of the Related Art
In a typical display device using liquid crystal, a back light is used and it is constructed such that an image is displayed by the back light. Although a liquid crystal display device is used as an image display means in various electronic devices, it has a structural defect such as a narrow view angle. On the other hand, since a display device using a phosphor for a pixel portion has a wide view angle and superior visibility, it is noted as a next generation display device.
A light emitting element using an organic compound for a phosphor (hereinafter referred to as an organic light emitting element) has a structure such as an appropriate combination of a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and the like, which are made of the organic compound, is provided between an anode and a cathode. Here, although the hole injection layer and the hole transport layer are separately indicated, these are identical in a sense that hole transportability (hole mobility) is a particularly important characteristic. For convenience, the hole injection layer is a layer in the side which is in contact with the anode. A layer in the side which is in contact with the light emitting layer is separately called the hole transport layer. A layer which is in contact with the cathode is called the electron injection layer and a layer in the side which is in contact with the light emitting layer is called the electron transport layer. There is a case where the light emitting layer also serves as the electron transport layer and thus it is called a light emitting electron transport layer. A light emitting element composed of a combination of these layers indicates a rectifying characteristic and thus it is considered that such light emitting element is one of diodes. In this specification, these are generically called an organic compound layer.
Both a small molecular system organic compound and a polymer system organic compound are known as organic compounds for forming the organic light emitting element. With respect to an example of the small molecular system organic compound, 4,4′-bis[N-(naphthyl)-N-phenyl-amino]-biphenyl (hereinafter referred to as “&agr;-NPD”) and 4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (hereinafter referred to as “MTDATA”) as copper phthalocyanine (CuPc) aromatic amine system materials are known for the hole injection layer and tris-8-quinolinolato aluminum complex (Alq
3
) and the like are known for the light emitting layer. With respect to the polymer system organic compound, polyaniline, polyethylenedioxythiophene (PEDOT) as a polythiophene derivative, and the like are known.
In view of the variety of material, it is said that the small molecular system organic compound produced by an evaporation method has remarkable variety as compared with the polymer system organic compound. However, in any case, an organic compound purely made of only a base constitutional unit is rare. Thus, as a result of different kinds, there is the case where an impurity is mixed during a manufacturing process or various additives such as pigments are added. Also, these materials include a material deteriorated by moisture and a material which is easy to oxidize. Since mixing of moisture, oxygen, and the like from an atmosphere is easily allowed, it requires careful handling.
The light emitting mechanism is considered as a phenomenon such that an electron injected from a cathode and a hole injected from an anode are recombined in a light emitting layer made from a phosphor to form a molecular exciton and the molecular exciton emits light when it is returned to a ground state. As an excitation state, there are light emitting (fluorescence) from a singlet excitation state and light emission (phosphorescence) from a triplet excitation state. Since the intensity reaches several thousands to several tens of thousands of cd/m
2
, it is considered that this light emission mechanism can be applied, in principle, to a display device and the like.
On the other hand, there are various deterioration phenomena with respect to the organic light emitting element and thus these are regarded as problems. In particular, when the organic light emitting element is driven for a long time, there is a deterioration phenomenon such that a light emitting intensity decreases with the passage of time. Although this deterioration phenomenon is dependent on a drive condition such as a voltage applied to the organic light emitting device, the time when the light emitting intensity reaches a half of an initial value (a half life) is about 500 to 5000 hours. Thus, this becomes a large hindrance to practical use.
As one of reasons for deterioration of the organic light emitting element, it is known that the deterioration is progressed by only exposing it to air. One of reasons of such deterioration is considered that an alkali metal material composing a cathode reacts with moisture or oxygen. Thus, the organic light emitting element is sealed in a closed space and further the closed space is filled with a drying agent to take a measure for minimizing the deterioration.
However, even if such a sealing structure is used, the deterioration of the organic light emitting element cannot be completely prevented under the current state. In view of such a condition, it can be expected that the deterioration of the organic light emitting element is progressed even with a trace of moisture or oxygen present. Also, it can be considered that some factor other than such a factor is present.
With respect to an oxygen molecular, a highest occupied level of a molecular orbit (HOMO) is degenerated, and thus it is a specific molecular having a triplet state in a ground level. Generally, an excitation process from a triplet to a singlet is a forbidden transition (spin forbidden transition) and thus is hard to produce. Therefore, the oxygen molecular having the singlet state is not generated. However, if a molecular having the triplet excitation state (
3
M*) which is a higher energy state than the singlet state is present around the oxygen molecular, the following energy transfer is produced and thus a reaction whereby the oxygen molecular having the singlet state is generated can be induced.
3
M*+
3
O
2
→M+
1
O
2
Formula 1
It is said that 75% of excitation states of molecular in the light emitting layer of the organic light emitting element are the triplet state. Therefore, when the oxygen molecular is mixed into the organic light emitting element, generation of the oxygen molecular having a singlet state is allowed by the energy transfer as indicated in the reaction formula (1). Since the oxygen molecular having the single excitation state has an ionic (charges are unbalanced) characteristic, a possibility that the molecular reacts to the unbalance of charges generated in the organic compound is considered.
For example, with respect to bathocuproine (hereinafter referred to as “BCP”), since a methyl group has an electron donating characteristic, carbon directly bonded to a conjugated ring is positively charged. As indicated by the following structural formula (I), when a positively charged carbon molecular is present, there is a possibility that singlet oxygen having an ionic characteristic reacts to it and carboxylic acid and hydrogen can be produced as indicated by the following structural formula (I
Arai Yasuyuki
Mizukami Mayumi
Yamazaki Shunpei
Semiconductor Energy Laboratory Co,. Ltd.
Tran Long
LandOfFree
Light emitting device and method of manufacturing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light emitting device and method of manufacturing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light emitting device and method of manufacturing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3309910