Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-07-24
2003-11-25
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C313S504000
Reexamination Certificate
active
06653796
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting device having a laminate of an organic EL layer and a photoconductive layer, and relates to an exposure device and a display device using the light-emitting device.
2. Description of the Related Art
Heretofore, Braun tubes (cathode-ray tubes) have been used in a large-size information display device exclusively. When information era comes and particularly, portability is regarded as important, flat-plate-like display devices which are thin in thickness and light in weight and which is low in operating voltage are in demand. A liquid-crystal display device is one of such flat-plate-like display devices. However, because of a back-lighting system required, the liquid-crystal display device is increased correspondingly in consumed electric power and has a limitation in reduction of thickness.
An organic EL (electroluminescent) device is a flat display device which can operate with a low voltage and which can be made thin because of no back-lighting system required. For example, a display device having a simple matrix structure shown in
FIG. 8
has been put to practical use as a display device including an organic EL device
1
. In the simple matrix structure, a number, X, of pixels connected to row electrodes
3
and arranged laterally in one row are selected so as to operate simultaneously. An on-off state of each pixel is set in accordance with a display information signal by switching devices connected to a number, Y, of column electrodes
5
respectively. When adjacent ones of the row electrodes
3
are selected sequentially so as to go through the whole display screen once, one scene is displayed.
For example, in an NTSC system, however, the scene is rewritten and displayed at the rate of 30 scenes per second or more (N scene/sec) in order to obtain a flickerless screen with an animation image displayed by the aforementioned scanning method. Hence, the period of time that the selected pixels are in an operating state is only 1/(N·Y) sec. For example, in the case of N=30 and Y=300, the period of time is {fraction (1/9000)} sec. In this case, voltage application for a plurality of cycles cannot be performed in one selection period if the frequency of a driving electric source is not higher than tens of kHz. A pulse voltage driving method in which a pulse voltage is given in synchronism with the selection period is, however, used generally as a practical method for driving respective pixels on one and the same condition. Hence, this is equivalent to the fact that the display device is driven by the frequency N, so that no higher luminance but luminance corresponding to the frequency can be expected.
In order to satisfy the necessary luminance (=average luminance×the number of scanning lines), a large peak current flows in the row electrodes
3
, the column electrodes
5
and the organic EL devices
1
. As a result, a voltage drop caused by the large peak current makes the image uneven. Moreover, because the luminance required of each organic EL device
1
increases, a burden for retrieving materials is needed and the life and stability is reduced. These disadvantages become more remarkable as the definition and screen of the display device become higher and larger respectively.
To eliminate the aforementioned disadvantages, therefore, a display panel having TFT such as a-Si or p-Si provided for each pixel has been described in JP-A-8-234683. In the display panel shown in
FIG. 9
, when a scanning signal is supplied to a selected row electrode
3
, a first TFT
7
is turned on so that a capacitor
9
is charged with the image signal voltage applied to the column electrode
5
. This signal voltage becomes a gate-source voltage of a second TFT
11
. Hence, a constant current corresponding to the gate-source voltage flows in the organic EL device
1
connected to the drain of the second TFT
11
, and goes from a first common electrode
13
toward a second common electrode
15
. As a result, the organic EL device
1
emits light with luminance approximately proportional to the current value.
Even in the case where the first TFT
7
is now turned off in order to select another row, the luminance of light emission is kept constant until all scans are terminated and the selection scanning of the row can be performed again because the image signal voltage is stored in the capacitors
9
(memory characteristic attained by the first TFT and the capacitors). Such memory characteristic attained by the TFT can be provided to thereby solve the problem of low luminance or the like in simple matrix driving.
As another display device provided to eliminate the aforementioned disadvantages, a display device attaining the memory characteristic without use of any TFT has been described in JP-A-9-185332. The display device shown in
FIG. 10
generally comprises an EL display device
1
for display light emission, and an address light device
17
for scanning and signal writing, disposed on the back of the EL display device
1
. The EL display device
1
includes, when viewed from the back, an electrode
19
, a photoconductive layer
21
, a light-emitting layer
23
, and an electrode
25
in sequence. The address light device
17
for scanning and signal writing is formed as a simple matrix structure.
When a voltage is applied between row electrodes
3
selected by linearly sequential scanning and column electrodes
5
in the address light device
17
, the light-emitting layer
27
is irradiated with ultraviolet light as signal light toward the photoconductive layer
21
. A portion of the photoconductive layer
21
, on which the signal light is incident, forms an electric conductor by absorbing the light. Hence, the portion of the photoconductor layer
21
is electrically connected to the rear driving electrode
19
. Hence, the electric potential applied between the front driving electrode
25
and the rear driving electrode
19
is applied to a predetermined dot portion of the light-emitting layer
23
.
As a result, forward light is emitted and, at the same time, backward light, that is, feedback light is emitted because of light emission of the EL display device
1
. The feedback light enters the photoconductive layer
21
, so that the photoconductive layer
21
is excited again to thereby generate new electron-hole pairs. Hence, the photoconductive layer
21
is kept in an electric conduction state, so that the driving voltage is continuously applied to a corresponding portion of the EL display device
1
. Because the display light-emitting layer is always driven during this state, the display light-emitting layer is kept in a light emission state even in the case where the column and row electrodes
5
and
3
in the address light device
17
are not in a selected state. Hence, light emission is continued by linearly sequential scanning until the second scanning cycle.
Hence, memory characteristic can be achieved by feedback light in each pixel in a simple structure without use of active driving represented by TFT, so that high-quality display can be performed under a high-duty-cycle driving condition.
As a further display device provided to eliminate the aforementioned disadvantages, a display device attaining memory characteristic by optical switches of bipolar transistors has been disclosed in JP-A-10-171375. The display device shown in
FIG. 11
comprises a glass substrate
31
, an npn-structure bipolar transistor portion
33
formed on the glass substrate
31
, and an organic EL device
1
formed on the bipolar transistor portion
33
. A rear electrode
35
is formed on the back surface of the bipolar transistor portion
33
. A rear electrode
35
and a front electrode
37
forming an XY matrix are formed on the front surface of the organic EL device
1
. Hence, when a predetermined voltage is applied between the front and rear electrodes, the organic EL device
1
emits light to thereby generate display light and, at the same time, the bipolar transistor portio
A Minh Din
Fuji Photo Film Co. , Ltd.
Wong Don
LandOfFree
Light-emitting device and exposure device and flat display... 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 exposure device and flat display..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light-emitting device and exposure device and flat display... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3117067