Organic electroluminescent display with filter layer

An organic electroluminescent display includes a substrate (1), and, in order from the substrate, a hole injection electrode, at least one organic layer, an electron injecting electrode, and a sealing plate, and wherein the substrate further includes thereon an element-isolating structure (7,8) for isolating planar structures of the organic layer and the electron injection electrode from each other during film formation, the element isolating structure being a solid structure containing a base part formed on the substrate side and an overhang part larger in width than the base part, and provided on a portion where the organic layer is isolated from the electron injecting electrode as well as other portions, so that the element isolating structure can function as a spacer for the sealing plate, and at least one type of filter layer (14a-14c) is interleaved between the element-isolating structure serving as the spacer and the substrate.

FIELD OF THE INVENTION 
The present invention relates generally to an organic electroluminescent 
display (which will hereinafter be often called an organic EL display for 
short) using an organic compound, and more particularly to a spacer 
located between a substrate and a sealing plate thereof. 
DESCRIPTION OF THE BACKGROUND 
In recent years, organic EL devices have been under intensive 
investigation. One organic EL device basically comprises a hole injecting 
electrode, a thin film formed on the hole injecting electrode by 
evaporating a hole transporting material such as triphenyldiamine (TPD), a 
light emitting layer of a fluorescent material such as an aluminum 
quinolinol complex (Alq.sup.3) laminated on the hole transporting thin 
film, and a metal electrode (an electron injecting electrode) formed 
thereon from a metal having a low work function such as magnesium or Mg. 
This organic EL device attracts attentions because it can achieve a very 
high luminance ranging from several hundreds to tens of thousands 
cd/m.sup.2 with a voltage of approximately 10 volts. 
In a typical process of providing such an organic EL display in a film 
form, for instance, an ITO transparent electrode in a film form is first 
provided. Then, only light emitting portions are exposed from the ITO 
transparent electrode while the rest thereof is covered with an insulating 
layer. Finally, organic layers and electron injecting electrodes, each in 
a film form, are provided on the transparent electrode so that a given 
light emitting pattern can be obtained. In this case, while the electron 
injecting electrodes serve as common electrodes, a given voltage is 
applied between each ITO transparent electrode providing a light emitting 
portion and the associated electron injecting electrode, so that the 
desired light emitting portion can give out light. Consequently, it is 
preferable that the electron injecting electrodes providing common 
electrodes and organic layers connected thereto are isolated for each 
segment group, each data line (scanning line) or the like, so that they 
can be independently driven. To this end, various means for element 
isolation have so far been developed in the art. 
An element-isolating structure set forth in JP-A-9-330792 (as spacer, and 
overhang members) is known for the element-isolating means. This 
element-isolating structure is obtained by providing an insulating layer 
on a hole injecting electrode according to a film pattern, forming a 
spacer layer such as a polyimide layer thereon, coating a positive resist 
material on the spacer layer to form a photo-pattern for element 
isolation, and developing the photo-pattern for removal of unexposed 
portions and the spacer layer underneath them. Details of this 
element-isolating structure are disclosed in the specification, and so are 
no longer described. 
When the organic EL device is exposed to the outside air, on the other 
hand, the electrodes oxidize while the organic layers degrade due to 
moisture. For this reason, it is required to use a structure in which they 
are airtightly confined to shield them from the outside air, for instance, 
by providing a protective or sealing film after the provision of the 
electron injecting electrode or providing a sealing plate on the side of 
the electron injecting electrode that is not opposite to the substrate. 
Among these, the sealing plate is particularly effective for protecting 
the organic layers against mechanical external force, and so can be a 
structural member indispensable for displays. If the sealing plate is 
pressed on the peripheral portion of the substrate where a spacer higher 
than laminated organic EL device structures such as organic layers and 
electron injection electrode, and an adhesive agent serving as a sealing 
material have been provided, the sealing plate can then be located at a 
position spaced away from the substrate by the height of the spacer, i.e., 
at a position that does not interfere with the organic EL structures such 
as organic layers and electron injecting electrode. 
In most cases, however, a glass or synthetic resin plate actually used as 
the sealing plate is uneven in thickness or irregular in surface shape, or 
is otherwise distorted. Even though the sealing plate is located at an end 
position higher than the organic EL structures, the organic EL device 
structures often interfere with the sealing plate due to a distortion of 
the sealing plate, etc., resulting in damage to, and a breakdown of, the 
organic EL device structures. Such interference with the sealing plate may 
be avoided by imparting an adequate height to the spacer. If a spacer 
usually formed by means of photolithography is too thick, however, it will 
then have an adverse influence on the photolithographic step to be carried 
out after the provision of the spacer, resulting in a distortion of other 
pattern configuration located in the vicinity of the spacer. That is, when 
it is necessary to carry out the photolithographic step subsequently to 
the provision of the spacer, the thickness of the spacer provided prior to 
the photolithographic step is limited to approximately 10 .mu.m. Thus, the 
spacer-incorporating step should be carried out after the provision of the 
element-isolating structure. 
A printing process of forming a polyimide or other resin film of, e.g., 20 
to 50 .mu.m in thickness is suitable for the provision of a thick spacer. 
However, a problem inherent in the printing process is that exposed 
portions of the surface of the electrode on which organic films are to be 
provided are susceptible to contamination, often resulting in defects such 
as light emission variations. 
A material for forming a thick resist of about 20 to 50 .mu.m in one 
coating operation by means of photolithograpy, on the other hand, is known 
in the art. In order for the formation of a thick resist to have no 
influence on the element-isolating structure, however, the material to be 
selected for the element-isolating structure is under severe limitations. 
In either case, some considerable expense incurs due to the need of an 
additional step. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide an organic EL display 
which can surely be protected against interference with a sealing plate, 
with a simplified arrangement yet with no need of adding an extra 
production step. 
This object is achieved by the inventions defined below as (1) to (3). 
(1) An organic EL display comprising a substrate, and, in order from said 
substrate, a hole injecting electrode, at least one organic layer, an 
electron injecting electrode, and a sealing plate, wherein: 
said substrate further includes thereon a element-isolating structure for 
isolating planar structures of said organic layer and said electron 
injecting electrode from each other during film formation, 
said element-isolating structure being a solid structure comprising a base 
part formed on a substrate side and an overhang part larger in width than 
said base part, and being provided on a portion where said organic layer 
is isolated from said electron injecting electrode as well as other 
portion, so that said element-isolating structure can function as a spacer 
for said sealing plate. 
(2) The organic EL display according to (1), wherein said element-isolating 
structures serving as said spacer has a height of 1 to 20 .mu.m. 
(3) The organic EL display according to (1) or (2), wherein at least one 
type of filter layer is interleaved between said element-isolating 
structure serving as said spacer and said substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Some preferred embodiments of the invention will now be explained at great 
length. 
One organic EL display of the present invention comprises a substrate, and, 
in order from the substrate, a hole injecting electrode, at least one 
organic layer, an electron injecting electrode, and a sealing plate. The 
substrate further includes thereon an element-isolating structure for 
isolating planar structures of the organic layer and electron injecting 
electrode from each other during film formation. The element-isolating 
structure is a solid structure comprising a base part formed on a 
substrate side and an overhang region larger in width than the base part, 
and is provided on a portion where the organic layer is isolated from the 
electron injecting electrode as well as on other portion, so that the 
element-isolating structure can function as a spacer for the sealing 
plate. 
The element-isolating structure is located at a site other than the portion 
where the elements are isolated from each other in such a manner that it 
can also function as a spacer, whereby the spacer can be provided at the 
step of providing the element-isolating structure. In addition, by 
locating the element-isolating structure at a suitable site, it is also 
possible to locate the spacer within the organic EL display, thereby 
avoiding interference between the sealing plate and the organic EL device 
structures, which may otherwise be caused by a distortion, etc. of the 
sealing plate. 
The element-isolating structure is a solid structure which, as disclosed in 
JP-A-9-330792, comprises a base part (spacer) and an overhang part 
provided above the base part and larger in width than the base part. 
Usually, the element-isolating structure is provided at a portion where 
elements are isolated from each other. Particles sputtered or deposited by 
evaporation to regions other than the element-isolating structure and the 
region shaded thereby are built up to form elements in the respective 
regions. 
No particular limitation is imposed on the material used to form the 
element-isolating structure. However, it is preferable to use a material 
that does not interfere with structural layers used with the organic EL 
display and makes no electrical connections between them, because the 
element-isolating structure is provided on the hole injecting electrode 
and insulating layer, on which the organic layer, electron injecting 
electrode, etc. are provided. Although the base, and overhang parts may be 
formed of the same or different materials, it is preferable to use a 
different material for each part because an overhang configuration is 
easily obtained. The material used for the formation of the base part 
includes an organic resin film such as a polyimide or acrylic resin film, 
an inorganic insulating film such as an SiO.sub.2, SiN.sub.x, a-Si or SOG 
(spin on glass) film, and a metal thin film that can be easily thickened 
and has limited stress, for instance, an Al film, with the polyimide 
resin, SiO.sub.2, SOG, and Al films being preferred. The material usable 
for the formation of the overhang part is preferably a photosensitive 
material such as a photoresist or photosensitive polyimide. Use may also 
be made of a hard insulating or semiconducting film such as an SiO.sub.2, 
SiN.sub.x, Al.sub.2 O.sub.3, CrO.sub.x, a-Si or SiC film, or an 
electrically conductive thin film such as a Cr, Ta, Mo, Ni, W, Ti, TiN, 
ZnO or ITO thin film. Use may further be made of a laminate comprising a 
photosensitive film laminated on an insulating or semiconductive film, or 
an electrically conductive thin film. Among these, the photoresist, 
SiO.sub.2, Cr, and Ti are preferred. 
The size of the base part is not particularly critical, and the base part 
can well serve its own function if its width is 1 .mu.m or more. However, 
it is preferable that the base part has a width of at least 5 .mu.m and a 
height (thickness) of at least 0.2 .mu.m, and especially about 0.5 .mu.m 
to about 10 .mu.m. The size of the overhang part is again not particularly 
critical. However, the overhang part has preferably a structure in which 
the overhang length is usually equal to or greater than the half of the 
thickness of the base part. The overhang part has preferably a height 
(thickness) of the order of 0.1 to 10 .mu.m, and especially 0.2 to 5 
.mu.m. The total thickness of the base, and overhang parts is of the order 
of 1 to 20 .mu.m, and especially 0.7 to 10 .mu.m. 
To provide the element-isolating structure, a base part layer made up of 
the aforesaid material for the base part is first provided on the 
substrate with the hole injecting electrode, insulating film, etc. 
provided thereon. To this end it is preferred that the resin or SOG film 
is provided by a spin or roll coating technique; the insulating or 
semi-conducting film is provided by a sputtering or CVD technique; and the 
metal film is provided by evaporation, etc. Then, a photosensitive 
overhang part layer is provided on the base part layer as mentioned just 
above. Simultaneously with or after patterning of the overhang part layer 
by exposure, and development, the base part layer is etched, and then 
over-etched in such a manner that the base part layer is smaller in size 
than the overhang part layer, thereby obtaining an overhang body. 
Preferably, the element-isolating structure of the invention serving as a 
spacer is higher (larger) than that for ordinary element isolation. If the 
element-isolating structure is higher than such an ordinary 
element-isolating structure, it is then possible to avert trouble with 
element isolation. In this regard, it is to be noted that the ordinary 
element-isolating structure may often deform or break down due to 
interference between it and the sealing plate. 
No particular limitation is imposed on how to make the element-isolating 
structure serving as a space higher than the ordinary element-isolating 
structure. For instance, when a color display is usually assembled, some 
filter layers such as color, and fluorescent filter layers are provided on 
a hole injecting electrode or an insulating film. If these filter layers 
are provided over a site where the element-isolating structure serving as 
a spacer is provided, the height of the element-isolating structure then 
increases by the thicknesses of the filter layers. Usually, these filter 
layers, when they have different colors, are not provided on the same 
region. However, if a plurality of such color filters are laminated 
together on the same region, it is then possible to achieve a much higher 
element-isolating structure. Each filter layer has preferably a thickness 
of the order of 2 to 20 .mu.m, and especially 5 to 20 .mu.m. 
The shape and size of the element-isolating structure serving as a spacer, 
and where it is located may be appropriately determined depending on the 
size, structure, etc. of the display to be assembled. 
The sealing plate used herein may be either transparent or opaque, if the 
emitted light is taken out of the substrate side. However, if the emitted 
light is taken out of the sealing plate side, too, the sealing plate may 
be made up of a transparent or semitransparent material. The transparent 
or semitransparent material used to this end includes glass, quartz, and 
resins such as polyimide, polyethylene terephthalate, polycarbonate, and 
polypropylene, with the glass being most preferred. Use may also be made 
of metals such as Al, SUS, Ti, and Ni. For the organic EL display 
according to the invention, it is possible to select from glass materials 
a specific glass material that is susceptible to distortion and so 
relatively inexpensive, because a distortion of the sealing plate is 
absorbed by the element-isolating structure serving as a spacer. 
Some exemplary embodiments of the organic EL display according to the 
invention are explained with reference to FIGS. 1 to 4. 
FIG. 1 is a plan schematic illustrative of one exemplary embodiment of the 
organic EL display according to the invention, FIG. 2 is a sectional 
schematic as taken along the A--A' line in FIG. 1, and FIG. 3 is a 
sectional schematic illustrative of another embodiment of the invention. 
FIG. 4 is a plan view illustrative of one pattern of the hole injecting 
electrode and insulating film before the element-isolating structure is 
provided. 
In an organic EL display shown in FIG. 1, 2, or 4 by way of example, a hole 
injecting electrode (an ITO transparent electrode) 2 is provided over a 
predetermined region shown by a broken line on a substrate 1. Then, an 
insulating film 12 is provided on an area of the hole injecting electrode 
2 except a light emitting portion 3 and a terminal portion 4 shown by 
solid lines. Finally, an organic layer, and an electron injecting 
electrode are provided on the insulating film 12 to emit light according 
to a predetermined pattern. 
After the hole injecting electrode 2 and insulating film 12 are provided as 
shown in FIG. 4, an ordinary element-isolating structure 8 and an 
element-isolating structure 9 serving as a spacer are simultaneously 
provided to construct the organic EL display according to the invention, 
as shown in FIGS. 1, and 2. As illustrated, the ordinary element-isolating 
structure 8 is so provided that segment groups divided for each display 
function are isolated from one another. Each area isolated by the 
element-isolating device 8 is provided with an organic layer 10 shown by a 
one-dotted line and an electron injecting electrode shown by a two-dotted 
line, each in a film form, so that common electrodes 5, 6, and 7 are 
provided for each area. 
The element-isolating structure 9 serving as a spacer, which is provided 
simultaneously with the ordinary element-isolating structure 8, is located 
at a position that is undetrimental to light emission and on an area other 
than the portion where the ordinary element-isolating structure 8 is 
provided. As illustrated, the size and shape of the element-isolating 
structure 9 may be appropriately determined in such a manner that they are 
undetrimental to light emission. In some cases, the area of the electron 
injecting electrode film 11 formed becomes small as the area of the 
element-isolating structure 9 becomes large, or the area of the electron 
injecting electrode film 11 is divided by the area of the 
element-isolating structure 9, resulting in an increase in the resistance 
value of the electron injecting electrode 11 connected to the respective 
common electrodes 5, 6, and 7. It is thus preferable that the size and 
shape of the element-isolating structure 9 are designed in such a manner 
that the resistance value increase is avoidable. In the embodiment 
illustrated, two element-isolating structures 9 are provided, one in each 
of regions defined by 7 segments arranged in an 8-shaped configuration. 
Each element-isolating structure 9 is preferably provided with a notch 14 
that is open at an angle of up to 90.degree.. Through this notch 14 a 
portion of the electron injecting electrode 11 provided on the 
element-isolating structure 9 makes a connection with a portion of the 
electron injecting electrode 11 provided on a region where the 
element-isolating structure 9 is not provided, thereby reducing resistance 
increases. 
Another embodiment of the organic EL display according to the invention is 
explained with reference to FIG. 3. The embodiment comprises first to 
third color filter layers 14a, 14b, and 14c as color displays, and the 
first to third color filter layers 14a, 14b, and 14c, for instance, 
correspond to red, green, and blue filters, respectively. First to third 
filter layers 14a, 14b, and 14c are also laminated on the portion where 
the element-isolating structure 9 serving as a spacer is provided, thereby 
making the spacer higher than the ordinary element-isolating structure. 
According to this embodiment, filter layers 14a, 14b, and 14c can be 
provided on the region on which the element-isolating structure 9 is 
provided, simultaneously with filter layers 14a, 14b, and 14c which must 
usually be provided on the light emitting portion 3 or the like. This is 
achieved with no addition of any extra step. To ensure the flatness of the 
portion on which the hole injecting electrode 2 is provided, it is 
preferable to provide an overcoat layer 13 on the portion on which the 
hole injecting electrode 2, and insulating layer 12 are provided. 
To take the emitted light out of the substrate side, it is usually 
preferable that the hole injecting electrode is a transparent electrode. 
The transparent electrode may be made up of ITO (tin-doped indium oxide), 
IZO (zinc-doped indium oxide), ZnO, SnO.sub.2, In.sub.2 O.sub.3, etc., 
with ITO (tin-doped indium oxide) being preferred. The transparent 
electrode has preferably at least a certain thickness enough for electron 
injection, e.g., of 10 to 200 nm, and especially 50 to 120 nm. 
The transparent electrode is preferably formed by a sputtering technique, 
although it may be formed by an evaporation or other technique. When 
sputtering is applied to the formation of the ITO transparent electrode, 
it is preferable to use a target obtained by doping In.sub.2 O.sub.3 with 
SnO.sub.2. When a film form of metal or barrier electrode is formed, it is 
preferable to form a sintered body of the aforesaid starting metal or its 
alloy by means of DC or RF sputtering. A film form of ITO transparent 
electrode obtained by sputtering is much more reduced than that obtained 
by evaporation in terms of the change-with-time of light emission 
luminance. The input power is preferably in the range of 0.1 to 4 
W/cm.sup.2. Input power for a DC sputtering system in particular is 
preferably in the range of 0.1 to 10 W/cm.sup.2, and especially 0.5 to 7 
W/cm.sup.2. The film formation rate is preferably in the range of 5 to 100 
nm/min., and especially 10 to 50 nm/min. 
No particular limitation is imposed on the sputtering gas used; that is, 
use may be made of inert gases such as Ar, He, Ne, Kr, and Xe, or their 
mixture. The sputtering pressure of such sputtering gas may usually be in 
the range of about 0.1 Pa to 20 Pa. 
The organic layer formed after the provision of the respective 
element-isolating structures 8 and 9 comprises at least one hole 
transporting layer and at least one light emitting layer, and includes an 
electron injecting electrode thereon. The organic layer may be provided 
with a protective electrode in the form of the uppermost layer. It is here 
to be noted that the hole transporting layer may be dispensed with. The 
electron injecting electrode is then formed of a metal, compound or alloy 
material having a low work function by means of evaporation or sputtering, 
and preferably sputtering. 
For the material forming the electron injecting electrode, it is preferable 
to use a substance having a low work function so as to achieve efficient 
electron injection, for instance, alkaline metals, alkaline earth metals, 
or alloys containing 0.1 to 20 at% of these metals. However, it is to be 
understood that the invention imposes no particular limitation on the 
material for the electron injecting electrode. 
In the electron injecting electrode film formed by the sputtering 
technique, the atoms or atom groups upon sputtering have a kinetic energy 
relatively higher than would be obtained with the evaporation technique, 
so that the adhesion of the electron injecting electrode film to the 
organic layer at their interface is improved due to a surface migration 
effect. In addition, an oxide layer is removed in vacuum from the surface 
of the electrode by pre-sputtering or moisture or oxygen is removed from 
the organic layer interface, on which they are adsorbed, by reverse 
sputtering to form a clean electrode-organic layer interface or a clean 
electrode, so that consistent organic EL displays of high quality can be 
produced. For the target, the alloy having the aforesaid composition 
range, and pure metal may be used alone or in combination with an 
additional target comprising the subordinate component or components or 
with the addition of the subordinate component or components thereto. It 
is also acceptable to use a mixture of materials having largely varying 
vapor pressures as the target, because there is only slight a deviation of 
the composition of the resultant film from the target composition. There 
is thus no limitation on the material used with the sputtering technique, 
whereas there are some limitations such as vapor pressure on the 
evaporation technique. The sputtering technique is additionally 
advantageous over the evaporation technique in terms of consistent film 
thickness and quality as well as productivity, because it is unnecessary 
to feed the raw material over an extended period of time. 
The electron injecting electrode formed by the sputtering technique is a 
film so very dense that the penetration of moisture into the film is much 
more reduced as compared with a coarse film prepared by evaporation, and 
so the chemical stability of the film is much more increased. This ensures 
the production of organic EL displays having an ever longer service life. 
Preferably, the sputtering gas pressure during sputtering is in the range 
of 0.1 to 5 Pa. By regulating the sputtering gas pressure within this 
range, it is possible to easily obtain an AlLi alloy having an Li 
concentration in the aforesaid range. By altering the sputtering gas 
pressure in the aforesaid range during film formation, it is also possible 
to easily obtain an electron injecting electrode having such an Li 
concentration gradient as defined above. 
For the sputtering gas, use is made of inert gases employed with ordinary 
sputtering systems. For reactive sputtering, reactive gases such as 
N.sub.2, H.sub.2, O.sub.2, C.sub.2 H.sub.4, and NH.sub.3 may be used in 
addition to these gases. 
In the practice of the invention, it is possible to use an RF sputtering 
process using an RF power source or the like as the sputtering technique. 
In view of the ease with which the film forming rate is controlled, and 
less damage to an organic EL device structure, however, it is preferable 
to use a DC sputtering process. Power for operating a DC sputtering system 
is in the range of preferably 0.1 to 10 W/cm.sup.2, and especially 0.5 to 
7 W/cm.sup.2. The film formation rate is preferably in the range of 5 to 
100 nm/min., and especially 10 to 50 nm/min. 
The thin film form of electron injecting electrode may have at least a 
certain thickness enough for the injection of electrons, e.g., of at least 
1 nm, and preferably at least 3 nm. Thus, a film thickness of the order of 
3 to 500 nm is usually preferable although there is no upper limit 
thereon. 
The organic EL display of the invention has preferably a protective 
electrode on the electron injecting electrode, i.e., on the side of the 
electron injecting electrode that is not opposite to the organic layer. By 
the provision of the protective electrode, the electron injecting 
electrode is protected against the air, moisture, etc., so that the 
degradation of the constituting thin film can be prevented, resulting in 
the stabilization of electron injection efficiency and an ever greater 
increase in the service life of the device. The protective electrode has a 
very low resistance, and so may also function as an interconnecting 
electrode when the electron injecting electrode has a high resistance. The 
protective electrode may be formed of at least one of Al; Al and a 
transition metal. In particular, favorable results are obtained when Al or 
Al and a transition metal are used as the interconnecting electrode to be 
described later. TiN, on the other hand, provides a film having a striking 
sealing effect because of its good corrosion resistance. For TiN, an about 
10% deviation from its stoichiometric composition is acceptable. In 
addition, Al alloys, and transition metal alloys may contain transition 
metals, especially, scandium or Sc, niobium or Nb, zirconium or Zr, 
hafnium or Hf, neodymium or Nd, tantalum or Ta, copper or Cu, silicon or 
Si, chromium or Cr, molybdenum or Mo, manganese or Mn, nickel or Ni, 
palladium or Pd, platinum or Pt and tungsten or W in the total amount of 
up to 10 at%, especially up to 5 at%, and more especially up to 2 at%. 
When the protective electrode functions as the interconnecting material, 
the thin film resistance becomes lower with a decrease in the content of 
the transition metal. 
The protective electrode may have at least a certain thickness enough to 
make sure of electron injection efficiency and prevent penetration of 
moisture, oxygen or organic solvents, for instance, of at least 50 nm, 
preferably at least 100 nm, and especially 100 to 1,000 nm. With too thin 
a protective electrode layer, sufficient connection with terminal 
electrodes is not obtainable because the ability of the protective 
electrode to cover steps becomes low. When the protective electrode layer 
is too thick, on the other hand, the growth rate of dark spots becomes 
high because of an increase in the stress of the protective electrode 
layer. It is here to be noted that when the protective electrode functions 
as an interconnecting electrode, its thickness may be usually of the order 
of 100 to 500 nm so as to make up for the high film resistance of the 
electron injecting electrode due to its thinness, and that when the 
protective electrode functions as other interconnecting electrode, its 
thickness may be of the order of 100 to 300 nm. 
Preferably but not exclusively, the total thickness of the electron 
injecting electrode plus the protective electrode is usually of the order 
of 100 to 1,000 nm. 
In addition to the aforesaid protective electrode, an additional protective 
film may be formed after the formation of the electrode. The protective 
film may be formed of either an inorganic material such as SiO.sub.X or an 
organic material such as Teflon, and a chlorine-containing carbon fluoride 
polymer. The protective film may be either transparent or opaque, and has 
a thickness of the order of 50 to 1,200 nm. The protective film may be 
formed either by the aforesaid reactive sputtering process or conventional 
processes such as general sputtering, evaporation or like other processes. 
In the practice of the invention, it is preferred to form a sealing layer 
on the device in order to prevent oxidation of the organic layers and 
electrodes. The sealing layer for preventing penetration of moisture may 
be formed by bonding sealing plates such as glass plates with adhesive 
resin layers of low hygroscopicity such as commercially available sheets 
of photo-curable adhesives, epoxy adhesives, silicone adhesives, and 
crosslinking ethylene-vinyl acetate copolymer adhesives. Instead of the 
glass plates, metal or plastic plates may also be used. 
Next, the organic layers provided in the EL device of the invention are 
explained. 
The light emitting layer has functions of injecting holes and electrons, 
transporting them, and recombining holes and electrons to create excitons. 
For the light emitting layer, it is preferable to use a relatively 
electronically neutral compound. 
The hole injecting and transporting layer has functions of facilitating 
injection of holes from the anode, providing stable transportation of 
holes and blocking electrons, and the electron injecting and transporting 
layer has functions of facilitating injection of electrons from the 
cathode, providing stable transportation of electrons and blocking holes. 
These layers are effective for increasing the number of holes and 
electrons injected into the light emitting layer and confining holes and 
electrons therein for optimizing the recombination region to improve light 
emission efficiency. 
The thickness of the light emitting layer, the hole injecting and 
transporting layer, and the electron injecting and transporting layer is 
not critical and varies with a particular formation technique although it 
is usually of the order of preferably 5 to 500 nm, and especially 10 to 
300 nm. 
The thickness of the hole injecting and transporting layers, and the 
electron injecting and transporting layer is approximately equal to, or 
about 1/10 times to about 10 times as large as, the thickness of the light 
emitting layer although it depends on the design of the 
recombination/light emitting region. When the electron or hole injecting 
and transporting layer is separated into an injecting layer and a 
transporting layer, it is preferable that the injecting layer is at least 
1 nm thick and the transporting layer is at least 20 nm thick. The upper 
limit on thickness is usually about 500 nm for the injecting layer and 
about 500 nm for the transporting layer. The same film thickness applies 
when two injecting and transporting layers are provided. 
In the organic EL display according to the invention, the light emitting 
layer contains a fluorescent material that is a compound capable of 
emitting light. The fluorescent material used herein, for instance, may be 
at least one compound selected from compounds such as those disclosed in 
JP-A 63-264692, for instance, quinacridone, rubrene, and styryl dyes. Use 
may also be made of quinoline derivatives such as metal complex dyes 
containing 8-quinolinol or its derivative as ligands, for instance, 
tris(8-quinolinolato) aluminum, tetraphenylbutadiene, anthracene, 
perylene, coronene, and 12-phthaloperinone derivatives. Use may further be 
made of phenylanthracene derivatives disclosed in Japanese Patent 
Application No. 6-110569, and tetraarylethene derivatives disclosed in 
Japanese Patent Application No. 6-114456. 
Preferably, the fluorescent compound is used in combination with a host 
substance capable of emitting light by itself; that is, it is preferable 
that the fluorescent compound is used as a dopant. In such a case, the 
content of the fluorescent compound in the light emitting layer is in the 
range of preferably 0.01 to 10% by weight, and especially 0.1 to 5% by 
weight. By using the fluorescent compound in combination with the host 
substance, it is possible to vary the wavelength performance of light 
emission, thereby making light emission possible on a longer wavelength 
side and, hence, improving the light emission efficiency and stability of 
the device. 
Quinolinolato complexes, and aluminum complexes containing 8-quinolinol or 
its derivatives as ligands are preferred for the host substance. Such 
aluminum complexes are typically disclosed in JP-A's 63-264692, 3-255190, 
5-70733, 5-258859, 6-215874, etc. 
Exemplary aluminum complexes include tris(8-quinolinolato)aluminum, 
bis(8-quinolinolato)magnesium, bis(benzo{f}-8-quinolinolato)zinc, 
bis(2-methyl-8-quinolinolato)aluminum oxide, tris(8-quinolinolato)indium, 
tris(5-methyl-8-quinolinolato)aluminum, 8-quinolinolatolithium, 
tris(5-chloro-8-quinolinolato)gallium, 
bis(5-chloro-8-quinolinolato)calcium, 
5,7-dichloro-8-quinolinolatoaluminum, tris(5,7-dibromo-8-hydroxyquinolinol 
ato)aluminum, and poly[zinc(II)-bis(8-hydroxy-5-quinolinyl)methane]. 
Use may also be made of aluminum complexes containing other ligands in 
addition to 8-quinolinol or its derivatives, for instance, 
bis(2-methyl-8-quinolinolato) (phenolato) aluminum (III), 
bis(2-methyl-8-quinolinolato) (o-cresolato) aluminum (III), 
bis(2-methyl-8-quinolinolato) (m-cresolato) aluminum (III), 
bis(2-methyl-8-quinolinolato) (p-cresolato) aluminum (III), 
bis(2-methyl-8-quinolinolato) (o-phenyl-phenolato)aluminum (III), 
bis(2-methyl-8-quinolinolato) (m-phenylphenolato)aluminum (III), 
bis(2-methyl-8-quinolinolato) (p-phenylphenolato)aluminum (III), bis 
(2-methyl-8-quinolinolato) (2,3-dimethylphenolato)aluminum (III), 
bis(2-methyl-8-quinolinolato) (2,6-dimethylphenolato)aluminum (III), 
bis(2-methyl-8-quinolinolato) (3,4-dimethylphenolato)aluminum (III), 
bis(2-methyl-8-quinolinolato) (3,5-dimethyl-phenolato) aluminum (III), 
bis(2-methyl-8-quinolinolato) (3,5-di-tert-butylphenolato)aluminum (III), 
bis(2-methyl-8-quinolinolato) (2,6-diphenylphenolato)aluminum (III), 
bis(2-methyl-8-quinolinolato) (2,4,6-triphenylphenolato)aluminum (III), 
bis(2-methyl-8-quinolinolato) (2,3,6-trimethyl-phenolato)aluminum (III), 
bis(2-methyl-8-quinolinolato) (2,3,5,6-tetramethylphenolato)aluminum 
(III), bis(2-methyl-8-quinolinolato) (1-naphtholato)aluminum (III), 
bis(2-methyl-8-quinolinolato) (2-naphtholato)aluminum (III), 
bis(2,4-dimethyl-8-quinolinolato) (o-phenylphenolato)aluminum (III), 
bis(2,4-dimethyl-8-quinolinolato) (p-phenylphenolato)aluminum (III), 
bis(2,4-dimethyl-8-quinolinolato) (m-phenylphenolato) aluminum (III), 
bis(2,4-dimethyl-8-quinolinolato) (3,5-dimethylphenolato)aluminum (III), 
bis(2,4-dimethyl-8-quinolinolato) (3,5-di-tert-butylphenolato)aluminum 
(III), bis(2-methyl-4-ethyl-8-quinolinolato) (p-cresolato)aluminum (III), 
bis(2-methyl-4-methoxy-8-quinolinolato) (p-phenylphenolato)aluminum (III), 
bis(2-methyl-5-cyano-8-quinolinolato) (o-cresolato)aluminum (III), and 
bis(2-methyl-6-trifluoromethyl-8-quinolinolato) (2-naphtholato)aluminum 
(III). 
Besides, use may be made of bis(2-methyl-8-quinolinolato)aluminum 
(III)-.mu.-oxo-bis(2-methyl-8-quinolinolato) aluminum (III), 
bis(2,4-dimethyl-8-quinolinolato)aluminum 
(III)-.mu.-oxo-bis(2,4-dimethyl-8-quinolinolato)aluminum (III), 
bis(4-ethyl-2-methyl-8-quinolinolato)aluminum 
(III)-.mu.-oxo-bis(4-ethyl-2-methyl-8-quinolinolato)aluminum (III), 
bis(2-methyl-4-methoxyquinolinolato)aluminum 
(III)-.mu.-oxo-bis(2-methyl-4-methoxyquinolinolato)aluminum (III), 
bis(5-cyano-2-methyl-8-quinolinolato)aluminum 
(III)-.mu.-oxo-bis(5-cyano-2-methyl-8-quinolinolato)aluminum (III), 
bis(2-methyl-5-trifluoromethyl-8-quinolinolato)aluminum 
(III)-.mu.-oxo-bis(2-methyl-5-trifluoromethyl-8-quinolinolato)aluminum 
(III), etc. 
Other preferable host substances include phenyl-anthracene derivatives 
disclosed in JP-A-8-12600, tetraarylethene derivatives disclosed in 
JP-A-8-12969, etc. 
In the practice of the invention, the light emitting layer may also serve 
as an electron injecting and transporting layer. In this case, it is 
preferable to use tris(8-quinolinolato)aluminum or the like, which may be 
provided by evaporation. 
If necessary or preferably, the light emitting layer is formed of a mixed 
layer of at least one compound capable of injecting and transporting holes 
with at least one compound capable of injecting and transporting 
electrons. Preferably in this case, a dopant is incorporated in the mixed 
layer. The content of the dopant compound in the mixed layer is in the 
range of preferably 0.01 to 20% by weight, and especially 0.1 to 15% by 
weight. 
In the mixed layer with a hopping conduction path available for carriers, 
each carrier migrates in the polarly prevailing substance, so making the 
injection of carriers having an opposite polarity unlikely to occur. This 
leads to an increase in the service life of the device due to less damage 
to the organic compound. By incorporating the aforesaid dopant in such a 
mixed layer, it is possible to vary the wavelength performance of light 
emission that the mixed layer itself possesses, thereby shifting the 
wavelength of light emission to a longer wavelength side and improving the 
intensity of light emission, and the stability of the device as well. 
The compound capable of injecting and transporting holes and the compound 
capable of injecting and transporting electrons, both used to form the 
mixed layer, may be selected from compounds for the injection and 
transportation of holes and compounds for the injection and transportation 
of electrons, as will be described later. Especially for the compounds for 
the injection and transportation of holes, it is preferable to use amine 
derivatives having strong fluorescence, for instance, hole transporting 
materials such as triphenyldiamine derivatives, styrylamine derivatives, 
and amine derivatives having an aromatic fused ring. 
For the compounds capable of injecting and transporting electrons, it is 
preferable to use metal complexes containing quinoline derivatives, 
especially 8-quinolinol or its derivatives as ligands, in particular, 
tris(8-quinolinolato) aluminum (Alq.sup.3). It is also preferable to use 
the aforesaid phenylanthracene derivatives, and tetraarylethene 
derivatives. 
For the compounds for the injection and transportation of holes, it is 
preferable to use amine derivatives having strong fluorescence, for 
instance, hole transporting materials such as triphenyldiamine 
derivatives, styrylamine derivatives, and amine derivatives having an 
aromatic fused ring, as already mentioned. 
In this case, the ratio of mixing the compound capable of injecting and 
transporting holes with the compound capable of injecting and transporting 
electrons is determined while the carrier mobility and carrier density are 
taken into consideration. In general, however, it is preferred that the 
weight ratio between the compound capable of injecting and transporting 
holes and the compound capable of injecting and transporting electrons is 
of the order of 1/99 to 99/1, particularly 10/90 to 90/10, and more 
particularly 20/80 to 80/20. 
The thickness of the mixed layer must correspond to the thickness of a 
single molecular layer, and so is preferably less than the thickness of 
the organic compound layer. More specifically, the mixed layer has a 
thickness of preferably 1 to 85 nm, especially 5 to 60 nm, and more 
especially 5 to 50 nm. 
Preferably, the mixed layer is formed by co-evaporation where the selected 
compounds are evaporated from different evaporation sources. When the 
compounds to be mixed have identical or slightly different vapor pressures 
(evaporation temperatures), however, they may have previously been mixed 
together in the same evaporation boat for the subsequent evaporation. 
Preferably, the compounds are uniformly mixed together in the mixed layer. 
However, the compounds in an archipelagic form may be present in the mixed 
layer. The light emitting layer may generally be formed at a given 
thickness by the evaporation of the organic fluorescent substance or 
coating a dispersion of the organic fluorescent substance in a resin 
binder. 
For the hole injecting and transporting layer, use may be made of various 
organic compounds as disclosed in JP-A's 63-295695, 2-191694, 3-792, 
5-234681, 5-239455, 5-299174, 7-126225, 7-126226 and 8-100172 and EP 
0650955A1. Examples are tetraarylbenzidine compounds (triaryldiamine or 
triphenyl-diamine (TPD)), aromatic tertiary amines, hydrazone derivatives, 
carbazole derivatives, triazole derivatives, imidazole derivatives, 
oxadiazole derivatives having an amino group, and polythiophenes. Where 
these compounds are used in combination of two or more, they may be 
stacked as separate layers, or otherwise mixed. 
When the hole injecting and transporting layer is provided as a separate 
hole injecting layer and a separate hole transporting layer, two or more 
compounds are selected in a preferable combination from the compounds 
already mentioned for the hole injecting and transporting layer. In this 
regard, it is preferred to laminate layers in such an order that a 
compound layer having a lower ionization potential is disposed contiguous 
to the anode (ITO, etc.). It is also preferred to use a compound having 
good thin film forming ability at the anode surface. This order of 
lamination holds for the provision of two or more hole injecting and 
transporting layers, and is effective as well for lowering driving voltage 
and preventing the occurrence of current leakage and the appearance and 
growth of dark spots. Since evaporation is utilized in the manufacture of 
devices, films as thin as about 1 to 10 nm can be formed in a uniform and 
pinhole-free state, which restrains any change in color tone of light 
emission and a drop of efficiency by reabsorption even if a compound 
having a low ionization potential and absorption in the visible range is 
used in the hole injecting layer. Like the light emitting layer and so on, 
the hole injecting and transporting layer or layers may be formed by 
evaporating the aforesaid compounds. 
For the electron injecting and transporting layer which is provided if 
necessary, there may be used quinoline derivatives such as organic metal 
complexes containing 8-quinolinol or its derivatives as ligands, for 
instance, tris(8-quinolinolato)aluminum (Alq.sup.3), oxadiazole 
derivatives, perylene derivatives, pyridine derivatives, pyrimidine 
derivatives, quinoxaline derivative, diphenylquinone derivatives, and 
nitro-substituted fluorene derivatives. The electron injecting and 
transporting layer may also serve as a light emitting layer. In this case, 
it is preferable to use tris(8-quinolinolato)aluminum, etc. Like the light 
emitting layer, the electron injecting and transporting layer may then be 
formed by evaporation or the like. 
Where the electron injecting and transporting layer is a double-layered 
structure comprising an electron injecting layer and an electron 
transporting layer, two or more compounds are selected in a preferably 
combination from the compounds commonly used for electron injecting and 
transporting layers. In this regard, it is preferred to laminate layers in 
such an order that a compound layer having a greater electron affinity is 
disposed contiguous to the cathode. This order of lamination also applies 
where a plurality of electron injecting and transporting layers are 
provided. 
For the substrate material, transparent or translucent materials such as 
glass, quartz and resins are used. The substrate may be provided with a 
color filter film, fluorescent material-containing color conversion film 
or dielectric reflecting film for controlling the color of light emission. 
For the color filter film, a color filter employed with liquid crystal 
display devices may be used. However, it is preferable to control the 
properties of the color filter in conformity to the light emitted from the 
organic EL device, thereby optimizing the efficiency of taking out light 
emission and color purity. 
By using a color filter capable of cutting off extraneous light of such 
wavelength as absorbed by the EL device material or the fluorescent 
conversion layer, it is possible to improve the light resistance of the 
device and the contrast of what is displayed on the device. 
Instead of the color filter, an optical thin film such as a dielectric 
multilayer film may be used. 
The fluorescent color conversion film absorbs light emitted from an EL 
device and gives out light from the phosphors contained therein for the 
color conversion of light emission, and is composed of three components, a 
binder, a fluorescent material and a light absorbing material. 
In the practice of the invention, it is basically preferable to use a 
fluorescent material having high fluorescent quantum efficiency, and 
especially a fluorescent material having strong absorption in an EL light 
emission wavelength region. Laser dyes are suitable for the practice of 
the invention. To this end, for instance, it is preferable to use 
rohodamine compounds, perylene compounds, cyanine compounds, 
phthalocyanine compounds (including subphthalocyanine compounds, etc.), 
naphthaloimide compounds, fused cyclic hydrocarbon compounds, fused 
heterocyclic compounds, styryl compounds, and coumarin compounds. 
For the binder, it is basically preferable to make an appropriate selection 
from materials that do not extinguish fluorescence. It is particularly 
preferable to use a material that can be finely patterned by 
photolithography, printing or the like. It is also preferable to use a 
material that is not damaged during ITO film formation. 
The light absorbing material is used when light is not fully absorbed by 
the fluorescent material, and so may be dispensed with, if not required. 
For the light absorbing material, it is preferable to make a selection 
from materials that do not extinguish fluorescence. 
To form the hole injecting and transporting layer, the light emitting layer 
and the electron injecting and transporting layer, it is preferable to use 
a vacuum evaporation technique which enables a homogeneous thin film to be 
obtained. According to the vacuum evaporation process, it is possible to 
obtain homogeneous thin films in an amorphous state or with a crystal 
grain diameter of at most 0.1 .mu.m. The use of a thin film having a 
crystal grain diameter exceeding 0.1 .mu.m results in non-uniform light 
emission. To avoid this, it is required to increase the driving voltage of 
the device; however, there is a striking drop of charge injection 
efficiency. 
No particular limitation is imposed on vacuum evaporation conditions. 
However, an evaporation rate of the order of 0.01 to 1 nm/sec. is 
preferably applied at a degree of vacuum of up to 10.sup.-4 Pa. It is also 
preferable to form the layers continuously in vacuum. If the layers are 
continuously formed in vacuum, high properties are then obtained because 
the adsorption of impurities on the interface between the adjacent layers 
can be avoided. Furthermore, the driving voltage of the device can be 
lowered while the growth and occurrence of dark spots are inhibited. 
When the vacuum evaporation process is used to form the layers, each 
containing a plurality of compounds, it is preferable to carry out 
co-evaporation while boats charged with the compounds are individually 
placed under temperature control. 
The organic EL display of the invention is generally used as an EL device 
of the DC drive type while it may be of the AC or pulse drive type. The 
applied voltage is generally of the order of 2 to 20 volts. 
EXAMPLE 
The present invention are explained more specifically with reference to 
some examples and comparative examples. 
Example 1 
A glass substrate was subjected thereon to the pigment dispersion type 
color filter coating step used most commonly for colorizing liquid crystal 
displays. Coating was carried out in such a manner that a filter film 
thickness of 1.5 to 2.0 .mu.m was obtained for each color, followed by 
patterning. The coating step for each color filter, e.g., a red filter, 
was carried out in the following manner. A red color filter solution was 
spin coated on the substrate at 1,000 rpm for 5 seconds, and prebaked at 
100.degree. C. for 3 minutes. The prebaked coating was irradiated with 
ultraviolet radiation of 20 mW from an exposure machine for 30 seconds, 
and then developed using an aqueous solution containing 
tetramethylammonium hydroxide (TMAH) at a concentration of about 0.1%. The 
development time was about 1 minute. Following this, curing was done at 
220.degree. C. for 1 hour so as to prevent dissolution of the film in 
another color filter solution to be subsequently coated, thereby 
completing a red color filter pattern. Other color filters (green, and 
blue) were provided at much the same step as mentioned above, although 
details of the filter forming conditions are more or less different from 
those of the red filter forming conditions due to the use of different 
materials (pigments). In this example, only the color filters are used due 
to relative ease of fabrication. However, it is possible to achieve light 
emission with high luminance by outputting green, and red by color 
conversion using fluorescent conversion filters. It is also possible to 
make a reasonable tradeoff between prevention of luminance drops and 
improvements in color purity by lamination of color filters and 
fluorescent conversion filters. 
In addition, an overcoat material was coated on an array of the color 
filters for the purpose of improving the flatness of the surface of the 
array on which an ITO film was provided, and then again cured at 
220.degree. C. for 1 hour. These films were laminated on a region serving 
as a spacer to obtain a height of 7 to 8 .mu.m at this filter film-forming 
step. 
An ITO transparent electrode (hole injecting electrode) in a film form of 
100 nm in thickness was provided on the substrate, with the color filters 
and overcoat layer provided thereon, by means of sputtering. The thus 
obtained ITO thin film was patterned and etched by photolithography to 
obtain a hole injecting electrode pattern as shown in FIG. 4. Then, 
SiO.sub.2 in an insulating film form of 300 nm in thickness was coated and 
patterned to obtain a hole injecting electrode and insulating film pattern 
as shown in FIG. 4. 
Next, polyimide was coated at a thickness of 2 .mu.m on the substrate with 
the ITO transparent electrode and insulating film provided thereon, to 
thereby form base parts of element-isolating structures 8 and 9. 
Subsequently, an overhang part-forming positive resist layer of 3 .mu.m in 
thickness was coated, exposed to light, and developed to obtain the 
element-isolating structures 8 and 9. At this time, the total thickness of 
the spacer defined by the filters and the element-isolating structures 
amounted to 12 to 13 .mu.m, thereby obtaining a spacer high enough to 
prevent interference between the sealing plate and the light emission 
portion. 
The substrate was cleaned on its surface with UV/O.sub.3, and fixed to a 
substrate holder in a vacuum evaporation system, which was evacuated to a 
vacuum of 1.times.10.sup.-4 Pa or lower. Then, 
4,4',4"-tris(-N-(3-methylphenyl)-N-phenylamino) triphenylamine (m-MTDATA) 
was evaporated at a deposition rate of 0.2 nm/sec. to a thickness of 40 nm 
to form a hole injecting layer. While the vacuum was maintained, 
N,N'-diphenyl-N,N'-m-tolyl-4,4'-diamino-1,1'-biphenyl (TPD) was evaporated 
at a deposition rate of 0.2 nm/sec. to a thickness of 35 nm to form a hole 
transporting layer. With the vacuum still kept, 
tris(8-quinolinolato)aluminum (Alq.sup.3) was evaporated at a deposition 
rate of 0.2 nm/sec. to a thickness of 50 nm to form a light emitting and 
electron injecting/transporting layer. With the vacuum still kept, this EL 
device structure substrate was then transferred from the vacuum 
evaporation system to a sputtering system wherein sputtering was carried 
out at a sputtering pressure of 1.0 Pa to form an AlLi electron injecting 
electrode film (with an Li concentration of 7.2 at%) of 50 nm in 
thickness. In this case, Ar was used as the sputtering gas at an input 
power of 100 W, a target size of 4 inches in diameter and a distance of 90 
mm between the substrate and the target. With the vacuum still maintained, 
this EL device substrate was transferred to another sputtering system 
wherein using an Al target, DC sputtering was carried out at a sputtering 
pressure of 0.3 Pa to form an Al protective electrode of 200 nm in 
thickness. At this time, Ar was used as the sputtering gas at an input 
power of 500 W, a target size of 4 inches in diameter and a distance of 90 
mm between the substrate and the target. 
Finally, a glass sealing plate was put over the substrate to obtain an 
organic EL display. One hundred such organic EL display samples, obtained 
as mentioned above, were estimated in the following manner. 
In a dry argon atmosphere, DC voltage was applied across the display 
samples to continuously drive them at a constant current density of 10 
mA/cm.sup.2. By visual surface observations, inspection was made of 
whether or not flaws, and non-light emitting spots were found, and whether 
or not damage to the organic layers, etc. was found due to interference 
with the glass sealing plate. As a result, 100 samples were all found to 
be free of any defects. 
Comparative Example 1 
One hundred organic EL display samples were prepared as in Example 1 with 
the exception that no element-isolating structure 9 serving as a spacer 
was provided, and estimated as in Example 1. As a result, fifty out of 100 
samples were found to be defective. 
According to the present invention, it is possible to provide an organic EL 
display which can surely prevent interference with a sealing plate, with a 
simple arrangement yet with no need of adding any extra step. 
While the invention has been described with reference to preferred 
embodiments, it will be obvious to those skilled in the art that various 
changes may be made and equivalents may be substituted for elements 
thereof without departing from the scope of the invention. In addition, 
many modifications may be made to adapt a particular situation or material 
to the teachings of the invention departing from the essential scope 
thereof. Therefore, it is intended that the invention not be limited to 
the particular embodiments disclosed as the best mode contemplated for 
carrying out the invention, but that the invention will include all 
embodiments falling within the scope of the appended claims.