Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – In combination with or also constituting light responsive...
Reexamination Certificate
2001-06-27
2003-03-04
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
In combination with or also constituting light responsive...
C257S059000, C257S072000, C257S448000, C438S149000, C438S022000
Reexamination Certificate
active
06528824
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting device which is constricted forming an EL (electro-luminescent) element on a substrate, the EL element being such that a light emissive material (herein below, termed “EL material”) which can emit the light of fluorescence or phosphorescence by applying an electric field is sandwiched between a non-transparent electrode (cathode) and a transparent electrode (anode). Concretely, the invention relates to enhancement in the efficiency of deriving light from an EL element.
By the way, in the invention, the “light-emitting device” shall signify an image display device or a luminescent device which employs the EL element. Besides, the “light-emitting device” shall cover all of a module in which a connector, for example, an anisotropic conductive film (FPC: Flexible Printed Circuit), a TAB (Tape Automated Bonding) tape or a TCP (Tape Carrier Package) is attached to the EL element, a module in which a printed wiring board is disposed at the end of a TAB tape or a TCP, and a module in which an IC (integrated circuit) is directly mounted on the light emitting element in accordance with a COG (Chip On Glass) scheme.
2. Description of the Related Art
In recent years, techniques for forming TFTs (thin film transistors) on substrates have made great progress, and display devices (light-emitting devices) of active matrix type applying the TFTs have been being developed. Especially, a TFT employing a poly-silicon film exhibits a field effect mobility (also, simply termed “mobility”) higher than that of a TFT employing a conventional amorphous silicon film and is capable of higher speed operation. Therefore, the control of pixels having been performed by driver circuits outside a substrate before can be performed by driver circuits formed on the same substrate as that of the pixels.
With such a light-emitting device of active matrix type, various advantages, for example, curtailment in a manufacturing cost, miniaturization in an electro-optic equipment, enhancement in an available percentage and increase in throughput, are attained by forming various circuits and elements on an identical substrate.
Further, researches have been vigorously made on light-emitting devices (EL displays) of active matrix type each having EL elements as spontaneous emission type elements.
Here in this specification, in the EL display being an example of the light-emitting device, the EL element has a structure in which an EL layer is sandwiched between a pair of electrodes (an anode and a cathode), and in which the EL layer has a multilayer structure ordinarily. Typically mentioned is the multilayer structure of “hole transporting layer/light emitting layer/electron transporting layer” proposed by Tang et al., Eastman Kodak Company. The multilayer structure exhibits a very high emission efficiency, and most of the EL display devices being currently under researches and developments adopt this structure.
Alternatively, the multilayer structure may be so formed that the anode is successively overlaid with a hole injecting layer/hole transporting layer/light emitting layer/electron transporting layer, or a hole injecting layer/hole transporting layer/light emitting layer/electron transporting layer/electron injecting layer. The light emitting layer may well be doped with a fluorescent coloring matter or the like.
In this specification, all layers interposed between the cathode and the anode shall be generally called the “EL layer”. Accordingly, the hole injecting layer, hole transporting layer, light emitting layer, electron transporting layer and electron injecting layer mentioned above are all included in the “EL layer”.
Herein, a predetermined voltage is applied to the EL layer of the above structure by the pair of electrodes, whereby light is emitted by the recombination of carriers taking place in the light emitting layer. By the way, in this specification, a light emitting element which is formed of the anode, EL layer and cathode shall be called the “EL element”.
The EL layer included in the EL element is more deteriorated by heat, light, moisture, oxygen, etc. In general, therefore, the fabrication of the active matrix type EL display proceeds in such a way that EL elements are formed after wiring lines and TFTs have been formed in a pixel portion.
Besides, after the formation of the EL elements, a substrate provided with the EL elements (an EL panel) and a cover member are stuck together so as to prevent the EL elements from being exposed to the open air, and the resulting structure is sealed (packaged) by a sealing member or the like.
After air-tightness has been enhanced by the treatment of the packaging or the like, a connector (such as FPC or TAB tape) by which terminals led out of the elements or circuits formed on the substrate are connected with external signal terminals is attached, whereby the active matrix type EL display is finished up.
Recently, EL display devices each having EL elements have been developed. The EL element is a spontaneous emission type element of current drive type which utilizes light generation based on the recombination of electrons and holes injected into an EL layer from electrodes at both the surfaces of the EL element by applying a voltage, and from which emitted light is derived as planar one. However, a light deriving efficiency in the case where the light is emitted in the EL layer is derived as the planar emitted light out of the EL element is very low and is usually 20% or below.
Besides, the light emitted in the EL layer is wave-guided within the transparent electrode, depending upon the angle of incidence of the light. The light thus wave-guided is termed as the “wave-guided light”. Part of the wave-guided light is absorbed to disappear, while the remainder is propagated within a solid thin film forming the transparent electrode, to escape to the end faces of the transparent electrode. In each pixel, therefore, the wave-guided light can be derived only partially as the planar emitted light, and light leakage to the adjacent pixel occurs in some cases.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a structure in which light emitted in an EL layer is prevented from escaping from the end faces of a transparent electrode, thereby to enhance the efficiency of deriving the light and to solve the problem that an image blurs due to light leakage to an adjacent pixel.
The construction of the invention is shown in FIG.
1
. By the way, a light-emitting device in the invention is such that a plurality of pixels are formed in the shape of a matrix within a pixel portion, and that each pixel includes a light emitting element
104
composed of a transparent electrode
101
, an EL layer
102
and a non-transparent electrode
103
and is connected through wiring with a thin film transistor (TFT) (not shown) for driving the light emitting element
104
. The “wiring” here signifies one which is made of a conductive material in order to establish electrical connection.
When carriers are respectively injected into the EL layer
102
from the transparent electrode
101
and the non-transparent electrode
103
formed on an insulating surface
100
, they are recombined in the EL layer
102
, thereby to emit light. Incidentally, the “transparent electrode 101” signifies an electrode which can transmit the light (visible light) emitted in the EL layer
102
and which is therefore disposed on a side where the light is emitted. In contrast, the “non-transparent electrode 103” signifies an electrode which cannot transmit the light and which is therefore disposed on a side where the light is not emitted.
Herein, a light shield portion
105
is interposed between the transparent electrodes
101
included in adjacent pixels, in order that the light emitted in the EL layer
102
in the pixel
1
may be prevented from leaking to the pixel
2
or pixel
3
which adjoins the pixel
1
. Incidentally, the light shield portion
105
which is formed on this occasion m
Maruyama Junya
Yamagata Hirokazu
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Huynh Andy
Nelms David
Semiconductor Energy Laboratory Co,. Ltd.
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