Organic thin film electroluminescence display unit

A two-dimensional organic thin film electroluminescence (EL) display unit has a plurality of one-dimensional organic EL arrays extending in a first direction and adhered together in a second direction perpendicular to the first direction. The EL array has a transparent substrate having a main surface directed to the second direction, and a multilayer EL structure formed on the main surface and including a plurality of first layer transparent electrodes extending perpendicular to the array, an organic EL thin film and a second layer metallic electrode extending along the array. The EL array emits luminescence in the third direction perpendicular to the first and second directions. The first layer electrodes and the second layer electrode drive the EL array in a matrix drive. The organic EL display unit exhibits excellent image quality, contrast and brightness.

BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
The present invention relates to an organic thin film electroluminescence 
(EL) display unit and, more particularly, to a two-dimensional organic 
thin film EL display unit capable of being driven by a pair of electrodes. 
(b) Description of the Related Art 
Some organic thin films are known to have an EL effect when the organic 
thin films are interposed between two electrodes, i.e., between an anode 
and a cathode. In these organic thin films, holes and electrons injected 
from the electrodes are recombined to provide an energy for generating 
luminescence based on the EL phenomenon. This EL phenomenon is generally 
called "organic thin film EL" and being developed by active researches for 
a display unit because of its higher energy efficiency and a lower voltage 
driving capability, as compared to other display devices. The organic EL 
display unit can be driven by a direct current as low as at several volts 
to several tens of volts. 
The organic thin film EL phenomenon can be observed even in a single 
organic EL thin film. To obtain a high energy luminance at a lower applied 
voltage, it is desirable to improve the injection efficiency of the 
carriers injected into the organic EL film from each electrode. For this 
purpose, a multilayer structure including a carrier injection layer or 
carrier transport layer interposed between the electrode and organic EL 
thin film is proposed in some literatures, in order to reduce the energy 
barrier between the electrode and the organic EL thin film to thereby 
enhance mobility of the carriers between the electrode and the organic EL 
thin film. 
Examples of the literatures include: Patent Publication No. JP-A-1982-51781 
which proposes a multilayer structure of anode/organic hole transport 
layer/organic EL thin film/cathode; Appl. Phys. Lett. 55, 1489 (1989) 
presented by Adachi et al. and entitled Organic electroluminescent device 
having a hole conductor as an emitting layer which proposes another 
multilayer structure of anode/organic EL thin film/organic electron 
transport layer/cathode; and Patent Publication No. JP-A-1994-314594 which 
proposes another multilayer structure of anode/a plurality of organic hole 
injection and transport layers/organic EL thin film/a plurality of organic 
electron injection and transport layers/cathode. The order of the films in 
these multilayer structures may be reversed from the recited orders. 
FIG. 1 shows one of the conventional multilayer structures as mentioned 
above, which includes anode 41/organic hole transport layer 42/organic EL 
thin film 43/cathode 44 consecutively formed on a supporting substrate 40. 
Materials for at least one of the electrodes should be transparent for 
emission of the generated luminescence, and indium-tin-oxide (ITO) is 
generally used as the material for the anode 41 for this purpose. 
Materials for the cathode 44 is selected from metals such as Mg, Al and 
In, which have a low work function for reducing barrier for the injected 
electrons, and which may or may not be doped with Ag or Li, as described 
in Patent Publication No. JP-A-1993-121172, for example. 
Materials for the organic hole transport layer 42 can be selected from 
aromatic tertiary amine, porphyrin derivatives etc. and material for the 
organic EL thin film 43 can be selected from 8-hydroxy quinoline metallic 
complex, butadiene derivatives, coumalin derivatives, benzoxazole 
derivatives, oxadiazole derivatives, oxazole derivatives, thiadiazole 
derivatives, styreneamine derivatives, bisstyrylbenzen derivatives, 
bis-styrylanthracene derivatives, perylene derivatives, aminopyrene 
derivatives, etc. Material for the organic electron transport layer, if 
provided, can be selected from naphtalimide derivatives, perylene 
tetracarbon acid diimide derivatives, quinacridone derivatives etc. The 
electrodes 41 and 44 and organic thin films 42 and 43 are consecutively 
formed on the supporting substrate 40, such as glass or resin film, by a 
dry deposition method, such as vacuum evaporation or sputtering, or a wet 
deposition method, such as spin-coating or dipping in a solution wherein 
the above mentioned materials are dispersed or dissolved in a resin or 
solvent. When a transparent electrode is formed as a first layer electrode 
41, the supporting substrate 40 should be also transparent for emission of 
the luminescence. 
A two-dimensional luminescent display unit using the organic thin film EL 
is proposed wherein a plurality of unit pixels or EL cells each formed by 
the organic thin film EL multilayer structure as described above are 
arranged on a supporting substrate in a two-dimensional array (see, for 
example, Patent Publication No. JP-A-1995-78690). FIG. 2 shows the 
proposed two-dimensional display unit, wherein a plurality of first layer 
stripe electrodes 41a extending parallel to one another, an organic 
multilayer structure 43b including at least one organic EL thin film and a 
plurality of second layer stripe electrodes 44a extending perpendicular to 
the first layer stripe electrodes 41a and parallel to one another are 
consecutively formed on a supporting substrate 40. The crossing portions 
of the first layer electrodes 41a and the second layer electrodes 44a 
constitute EL cells arranged in a two-dimensional array and driven by the 
pair of electrode groups 41a and 44a in a matrix drive. 
The two-dimensional EL display unit as described above, however, suffers 
from degradation in the image quality when the EL cells have scattering or 
variation of luminescence or defects in some cells because the 
luminescence are generally observed from the front to thereby emphasize 
the defects. In addition, since one of the first and second layer 
electrode groups 41a and 44a is transparent and the other is metallic, the 
EL device has a poor contrast due to the reflection of external light by 
the metallic electrodes in the cells which are not luminous at that 
instant, the metallic electrodes being disposed behind the screen. 
Further, patterning by use of a known photolithographic technique is 
difficult to apply to the organic EL materials because the EL materials 
have generally insufficient resistance to acidic or alkali solution or 
organic solvent, which are essential to the process in fabrication of the 
EL display unit. Especially, for a color display unit, a variety of 
organic EL materials are used for imaging different colors, some of which 
may have insufficient resistance. Patent Publication No. JP-A-1995-142169 
proposes the solution for this problem, wherein a multilayer structure 
including organic EL thin films for generating three primary colors is 
interposed between the anode and cathode to generate white luminescence, 
which is then filtered by a color filter such as used in a liquid crystal 
display device. The solution, however, has disadvantages in that the drive 
voltage requested for driving the organic EL thin film generally rises due 
to the large thickness of the multilayer structure, that a shutter 
mechanism is required for the filter, and that EL energy is absorbed by 
the inserted color filter. 
Patent Publication No. JP-A-1981-62284 describes another two-dimensional 
organic EL display unit wherein a plurality of one-dimensional EL arrays 
each disposed on a stripe supporting substrate are arranged by adhesion to 
obtain a two-dimensional display unit. In the proposed display unit, 
however, the display unit has similar defects of degradation in the image 
quality because of the scattering in the luminescence. Further, both the 
latter display units have similar defects of a low brightness in the 
screen because of the small cell area, especially in the case of a fine 
cell. 
SUMMARY OF THE INVENTION 
In view of the above, it is an object of the present invention to provide 
an improved organic thin film EL display unit capable of reducing 
scattering of the EL cells, improving the contrast, and alleviating the 
reduction of the luminescence accompanied by miniaturization of the cells, 
and especially suited for a color display unit. 
In accordance with the present invention, there is provided a 
two-dimensional organic thin film electroluminescent (EL) display unit 
comprising a supporting substrate and a plurality of one-dimensional 
organic EL arrays overlying the supporting substrate and arranged in a 
first direction, 
the organic EL arrays including a transparent substrate having a main 
surface directed to the first direction and a multilayer structure 
overlying the main surface, the multilayer structure including a plurality 
of first layer stripe electrodes extending parallel to one another, at 
least one organic EL film overlying the first layer electrodes, and a 
second layer stripe electrode overlying the organic EL film and extending 
perpendicular to the first layer stripe electrodes, each of the organic EL 
arrays including a plurality of EL cells arranged in a second direction 
perpendicular to the first direction, 
each of the first layer stripe electrodes and second layer stripe electrode 
driving the EL cells to emit luminescence in a third direction 
perpendicular to the first and second directions. 
In accordance with the two-dimensional organic EL display unit, since the 
multilayer structure in each cell is deposited perpendicular to the 
direction of emission of the luminescence, defects or scattering of the 
luminescence less degrade the image quality or contrast. Further, the cell 
area for luminescence can be increased in the direction parallel to the 
mission of the luminescence without increasing the cell size in the screen 
of the display unit, thereby enhancing the rightness per unit area in the 
screen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 3 shows an organic thin film EL display unit according to an 
embodiment of the present invention. The EL display unit is fabricated by 
arranging and adhering 101 in number of one-dimensional EL arrays 30 
together in the direction perpendicular to the direction of the EL arrays 
30 and perpendicular to the main surface of the transparent substrate of 
the EL array 30. Each of the EL array 30 includes 64 EL cells for emitting 
EL from a first side surface of the EL array 30 in the upward direction as 
viewed in the drawing. A lead electrode 25 is provided for driving a 
corresponding EL array 30 at the interface between the EL array 30 and the 
adjacent EL array 30, the lead electrode 25 being disposed in an electric 
contact with metallic electrodes 14 in the EL cells. Thus, 100 lead 
electrodes 25 constituting an electrode group (second electrode group) 44a 
are disposed between the 101 EL arrays 30. 
64 stripe transparent electrodes 12 are adhered to a supporting substrate 
31 having 64 stripe patterns printed thereon so that corresponding rows in 
the EL arrays 30 are connected together at the second side surface of the 
EL array 30 opposed to the first side surface, to thereby form an 
electrode group (first electrode group) 41a. A scanning circuit (not 
shown) is connected to the first electrode group 41a for providing 
positive shift pulses to the 64 transparent electrodes 12, whereas an 
image data output circuit is connected to the second electrode group 44a 
for providing negative image data pulses to the second electrode group 44a 
in synchronism with the scanning positive pulses, thereby obtaining a 
two-dimensional monochrome display unit having a 100 (horizontal).times.64 
(vertical) EL cells. 
FIG. 4 shows the details of the one-dimensional organic thin film EL array 
30 shown in FIG. 3. The one-dimensional EL array 30 has a 100 mm 
long.times.10 mm wide.times.1 mm thick transparent substrate 20, separated 
by light reflecting separators 15 in the direction of the array. The 
separators 15 are disposed within the transparent substrate 20 at a 
constant pitch of 1.5 mm. The bottom surface of the transparent substrate 
20 called the second side surface 23 herein is coated with a black 
insulating paint to form a black layer 22. On the main surface of the 
transparent substrate 20 on which the multilayer EL cells are formed and 
the black layer 22, there are provided 64 stripe transparent electrodes 12 
made of sputtered indium oxide and extending from the main surface to the 
black layer 22 in parallel with one another. 
The transparent electrodes 12 are 1 mm wide and arranged alternately with 
the light reflecting separator 15 at a constant pitch. A 50 nm-thick 
organic hole transport layer made of 1,1-bis-(4-diparatrilaminophenyl) 
cyclohexane and a 70 nm-thick organic EL thin film made of 
tris(8-quinolinol) aluminum are deposited by a vacuum sputtering technique 
to form an organic multilayer structure 13, followed by vacuum evaporation 
of a 7 mm-wide metallic electrode 14 made of Al--Li alloy along the 
elongate side of the transparent substrate 20, thereby finishing a 
one-dimensional EL array for generating yellow-green luminescence. 
When power is supplied between the anode formed by the stripe transparent 
electrode 12 and the cathode formed by the metallic electrode 14 in the 
one-dimensional array 30, the organic EL thin film in the organic 
multilayer structure 13 constituting the one-dimensional cell array 
generates yellow-green luminescence at the 64 crossing portions formed by 
and interposed between the stripe transparent electrodes 12 and the 
metallic electrode 14. Each of the cell forms 1 mm.times.7 mm rectangle. 
The luminescence emitted from each cell is reflected by the metallic 
electrode 14 to be incident on the transparent substrate 20 and does not 
diffuse to the adjacent cells because the light reflecting separator 15 
disposed within the transparent substrate 20 separates the luminescence 
between the cells. 
FIG. 5 shows a cross-section at the central portion of the organic thin 
film EL display unit of FIG. 3. In the display unit, since it is formed by 
a plurality of one-dimensional luminescent arrays 30 adhered in the 
direction perpendicular to the array, the luminescence incident on the 
transparent substrate 20 from each cell is reflected also by the metallic 
electrodes 14 of the adjacent array to be emitted as the luminescence from 
the specific cell through the first side surface of the transparent 
substrate 20, which forms an optical open end of each cell. In this 
embodiment, although the equivalent luminescent area of each cell in the 
screen is 1 mm wide, which is equal to the thickness of the transparent 
substrate 20, and 1 mm long, which is equal to the width of the 
transparent electrode 12, the cell area which functions as a luminescent 
area for this specific cell equals 1 mm.times.7 mm which is seven times as 
large as a conventional cell area in the screen. The brightness of the 
luminescence per cell at the first side surface equaled 3 times as large 
as the brightness of a conventional 1 mm wide and 1 mm long cell. The 
reason for the 3 times and not 7 times is due to the absorption of the 
luminescence within the transparent substrate 20. 
Other one-dimensional cell for EL of other colors are obtained by doping a 
small amount of fluorescent material into other organic multilayer 
structures such as described above. One-dimensional arrays for blue-green 
luminescence and red-orange luminescence were exemplarily obtained by 
doping the organic EL multilayer with coumalin and DCM 
(4-(Dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran), 
respectively, and combined with the yellow-green luminescence 
one-dimensional array as described above by consecutively adhering the 
three color arrays in succession to form a two-dimensional color display 
unit. 
FIG. 6 shows a method employed by us for forming the transparent substrate 
20 of the organic thin film EL display unit of FIG. 3. The transparent 
substrate 20 was obtained by arranging a plurality of 1 mm-wide aluminum 
foil ribbon in parallel to one another within a mold or die 50 at a 
constant pitch of 1.5 mm, pouring polycarbonate resin into the mold 50, 
solidifying the same to form a plurality of 1 mm-thick stripe 
polycarbonate, and forming a 10 mm-wide stripe substrate 20 by cutting. 
FIG. 7 shows a configuration of the screen of an organic thin film EL 
display unit according to another embodiment of the present invention. The 
EL display unit of FIG. 7 has a curved or slightly stepped screen. The 
curved screen can be obtained by adhering a plurality of one-dimensional 
EL arrays 30, with the first side surface of the one-dimensional arrays 30 
being increasingly slipped off in the direction normal to the screen, 
especially greater at the horizontal edge portions of the screen. The 
configuration of the screen in the organic EL display unit is similar to 
that of a CRT display unit. 
FIG. 8 shows another curved configuration in the screen of an organic thin 
film EL display unit. The curved surface can be obtained by a different 
widths of the one-dimensional EL arrays 30, which provide a curved or 
slightly stepped surface at the screen of the display unit, similarly to 
the slip-off of the one-dimensional arrays in the displayunit of FIG. 7. 
The display units as shown in FIGS. 7 and 8 may have a smoothed surface at 
the screen by coating a specific resin at the stepped portions of the 
screen for smoothing. 
FIG. 9 shows another configuration of the curved surface of the screen in a 
display unit. The curved surface can be obtained by a curved first side 
surface in each of the one-dimensional EL array 30 which provides 
different widths of the array as viewed along the direction of the array, 
specifically by a large width center, a small width ends and smoothly 
tapered bridge portions of the array 30. 
Although the present invention is described with reference to preferred 
embodiments thereof, the present invention is not limited thereto and it 
will be apparent from those skilled in the art that various modifications 
or alterations can be easily made therefrom without departing from the 
scope of the present invention as set forth in the appended claims.