Electroluminescent device having sub-interlayers for high luminous efficiency with device life

An electroluminescence device is constituted by sequentially stacking a glass substrate, a transparent electrode, a luminescent layer, an interlayer containing a semiconductor having a band gap of 2.4 eV or more, a current-limiting layer containing a conductive powder, and a backplate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electroluminescence (to be referred to 
as an EL hereinafter) device which can be used to display characters or 
graphic patterns and, more particularly, to a thin film-powder hybrid type 
EL device. 
2. Description of the Prior Art 
An EL display using an EL device can display characters or graphic patterns 
with high display quality and therefore is one of flat displays which have 
been rapidly, widely spread as a terminal of a portable type computer or a 
terminal of a work station in recent years. 
The EL devices are classified into an AC thin film type EL device having a 
structure in which a thin-film luminescent layer and insulating layers 
arranged at two sides of the luminescent layer are sandwiched by 
electrodes, and a DC powder type EL device having a structure in which a 
luminescent layer consisting of a zinc sulfide powder and a 
current-limiting layer consisting of a Cu-coated zinc sulfide powder are 
sandwiched by electrodes. These two types are already put into practical 
use. In recent years, however, in addition to the above two types of EL 
devices, a thin film-powder hybrid type EL device (to be referred to as a 
hybrid type EL device herinafter) having a combination of a thin-film 
luminescent layer and a current-limiting layer using a powder is proposed 
as a high-cost performance EL device which can realize high display 
quality with low cost (e.g., GB2176340 and GB2176341). 
FIG. 4 is a sectional view showing a basic arrangement of the hybrid type 
EL device. A basic structure, a manufacturing method, and an operation 
mechanism of the hybrid type EL device will be described below with 
reference to FIG. 4. 
A film of a transparent electrode material such as ITO is formed as a 
transparent electrode 2 on a glass substrate 1 by sputtering or a vacuum 
vapor deposition method and patterned into a predetermined shape by using, 
e.g., photolithography. A luminescent layer 3 is formed on the transparent 
electrode 2 by a vacuum vapor deposition method, a sputtering method, an 
MOCVD method or the like. A material which is often used as the material 
of the luminescent layer 3 is obtained by doping, as a luminescent center, 
a transition metal such as Mn and Cu, a rare-earth metal such as Tb, Sm, 
Dy, Eu and Ce or a fluoride or chloride thereof into a Group II-VI 
compound or Group IIa-VIb compound such as ZnS, ZnSe, CaS and SrS. 
Subsequently, a current-limiting layer 4 is formed on the luminescent 
layer 3. The current-limiting layer 4 serves as a resistor for preventing 
an excessive current from flowing through the luminescent layer 3. The 
current-limiting layer 4 normally consists of a film formed by using a 
conductive fine powder having a resistivity of 3.times.10.sup.3 
.OMEGA..multidot.cm to 1.times.10.sup.6 .OMEGA..multidot.cm and a binder 
resin by a spray method and having a film thickness of 1 to 30 .mu.m, and 
preferably, 5 to 30 .mu.m. Examples of the conductive fine powder are 
Cu-coated ZnS, MnO.sub.2, PbS, CuO, PbO, Tb.sub.4 O.sub.7, Eu.sub.2 
O.sub.3, PrO.sub.2, carbon and barium titanate. These compounds are used 
singly or in the form of mixtures. In order to increase contrast, a black 
or dark substance is preferably used (however, the substance need not be 
black or dark). A film consisting of Al or the like is formed as a 
backplate 5 to have a film thickness of about 1 .mu.m on the 
current-limiting layer 4 by using a vacuum vapor deposition method or the 
like. The backplate 5 is mechanically scribed by using a diamond needle, 
thereby completing a dot-matrix type or segment type hybrid EL device. 
Driving is normally performed by applying a DC pulse voltage from a driving 
power source 9 by using the transparent electrode 2 as an anode and the 
backplate 5 as a cathode. Alternatively, the device can be driven by an AC 
voltage. In a dot-matrix type device capable of displaying characters or 
graphic patterns, a time-division driving method of sequentially scanning 
lines along the row direction is used. Electrons are injected from an 
interface between the current-limiting layer and the luminescent layer 
into the luminescent layer. These electrons are accelerated by a high 
electric field in the luminescent layer and are bombarded against 
luminescent centers in a high-energy state. Then, the excited luminescent 
centers emit light when they are relaxed. 
A hybrid type EL device having a structure similar to the above basic 
hybrid type EL structure is known. For example, a hybrid type EL device in 
which a dark thin film layer is inserted between the luminescent layer 3 
and the current-limiting layer 4 shown in FIG. 4 is reported (e.g., U.S. 
Pat. No. 4,672,364 and GB2176341A). Since the dark thin film layer is 
inserted, light emitted from the luminescent layer toward a backplate is 
absorbed by this thin film layer. As a result, since the light is 
prevented from being irregularly reflected by the current-limiting layer, 
the contrast of display can be increased. Especially when a material which 
is not dark such as a Cu-coated zinc sulfide powder is used as the 
current-limiting layer, a significant effect can be obtained in an 
improvement in contrast by inserting a dark thin film layer. Examples of 
the material of the dark thin film layer are ZnTe (dark brown), CdTe 
(black), CdSe (black/brown), chalcogenide glass (black), Sb.sub.2 S.sub.3 
(black/brown), and other arbitrary dark materials such as oxides and 
sulfides of transition metals and rare-earth metals, e.g., PbS, PbO, CuO, 
MnO.sub.2, Tb.sub.4 O.sub.7, Eu.sub.2 O.sub.3, PrO.sub.2 and Ce.sub.2 
S.sub.3. The film thickness of the thin film layer is normally 2 .mu.m or 
less. 
In the hybrid EL device having the conventional basic structure as shown in 
FIG. 4, when Mn-doped zinc sulfide is used for the luminescent layer, a 
ratio (luminous efficiency) of luminescent energy of the device to energy 
applied to the device is 0.02% W/W to 0.05% W/W. 
In the conventional hybrid EL device in which the dark thin film layer is 
inserted between the luminescent layer and the current-limiting layer as 
described above, a luminous efficiency of the device is decreased to be 
smaller than that of the device having no dark thin film layer. 
When the above hybrid type EL devices are used as a dot-matrix type display 
for displaying characters or graphic patterns, even if a luminous 
efficiency of the device is 0.05% W/W which is the highest luminous 
efficiency obtained by the above conventional devices, this luminous 
efficiency is still unsatisfactory. 
If the above hybrid EL devices are used as a display having a small or 
middle capacity of about 640 .times.200 dots, a luminance of 50 cd/m.sup.2 
which is a practical luminance of a display can be obtained by the 
luminous efficiency described above. If, however, the above devices are 
used as a display having a middle or large capacity of about 640.times.400 
dots or 1,024.times.800 dots, which is currently mainly used, a voltage 
application time per device, i.e., a so-called duty ratio is decreased. As 
a result, a luminance is decreased to about 20 cd/m.sup.2 to 40 cd/m.sup.2 
which are practically unsatisfactory. 
Consumption power of a display is in inverse proportion to a luminous 
efficiency. When the above hybrid EL devices are used as a display having 
a small or middle capacity of about 640.times.200 dots with an A5-size 
panel area, the consumption power of the hybrid EL devices is about 25 W 
during entire surface light emission while it is about 10 W in the same 
panel when, e.g., AC thin film EL devices are used. That is, the 
consumption power of the hybrid EL device is very high. 
Since the consumption power of the device is very high, power to be applied 
to the device is increased to shorten the life of the device. 
In the hybrid EL device as shown in FIG. 4, the current-limiting layer 4 
prevents the resistivity of the luminescent layer 3 from being decreased 
to flow an excessive current through the EL device, thereby preventing 
thermal destruction of the device. 
As the resistance of the current-limiting layer 4 is increased, stability 
of the device with respect to destruction is improved. If, however, the 
resistance is too high, a voltage drop in the current-limiting layer 4 is 
increased to increase a drive voltage of the EL device. Therefore, the 
value of the resistance is limited. When the film thickness of the 
current-limiting layer 4 is 5 .mu.m to 30 .mu.m, the current-limiting 
layer 4 preferably has a resistance of 10 to 2,000 .OMEGA. per unit area 
(1 cm.sup.2) in a direction of film thickness, i.e., has a resistivity of 
about 1.times.10.sup.4 .OMEGA..multidot.cm to 2.times.10.sup.6 
.OMEGA..multidot.cm. 
Since the material of the conductive fine powder described above must have 
the above resistivity after it is fixed by a binder, it desirably has a 
resistivity of about 1.times.10.sup.4 .OMEGA..multidot.cm to 
2.times.10.sup.6 .OMEGA..multidot.cm. 
In an initial stage of development of the above hybrid type EL device, a 
Cu-coated ZnS powder which is conventionally used in a powder type EL 
device is often used as the material of the conductive fine powder. 
Recently, however, an MnO.sub.2 powder is used which increases display 
contrast because it is black and does not change its resistance over time 
due to no movement of Cu. 
These powders are prepared by mechanically pulverizing or milling coarse 
powders or tabular materials having a comparatively large particle size 
produced by a precipitation or electrolytic process. 
In the above conventional hybrid type EL device, however, a luminance 
variation is produced during an operation or a life of the device is 
shortened. 
In addition, in the above conventional hybrid type EL device, a luminous 
efficiency is as low as at most about 0.1 lm/W. Therefore, this 
conventional hybrid type EL device cannot provide brightness suitable for 
a practical use. 
OBJECT AND SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an electroluminescence 
device which has a high luminous efficiency and a high luminance, largely 
reduces consumption power, and has a long life. 
In order to achieve the above object, there is provided an 
electroluminescence device in which a first electrode having transparency, 
a luminescent layer, a current-limiting layer and a second electrode are 
sequentially stacked on a substrate having transparency and an electrical 
insulating property, wherein an interlayer containing a first 
semiconductor having a band gap of 2.4 eV or more is formed in contact 
with the luminescent layer. 
According to another aspect of the present invention, there is provided an 
electroluminescence device in which a first electrode having transparency, 
a luminescent layer, a current-limiting layer consisting of a binder and a 
conductive powder mainly containing carbon black, and a second electrode 
are sequentially stacked on a substrate having transparency and an 
electrical insulating property. 
According to still another aspect of the present invention, there is 
provided an electroluminescence device in which a first electrode having 
transparency, a luminescent layer, a current-limiting layer consisting of 
a conductive powder and a binder, and a second electrode are sequentially 
stacked on a substrate having transparency and an electrical insulating 
property, wherein the conductive powder contained in the current-limiting 
layer is electrically in point contact with the surface of the luminescent 
layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described below with reference 
to FIGS. 1 to 5. 
As shown in FIG. 1, the first embodiment is constituted by sequentially 
stacking a transparent electrode 2, a luminescent layer 3, an interlayer 6 
containing a semiconductor having a band gap of 2.4 eV or more, a 
current-limiting layer 4 and a backplate 5 on a transparent glass 
substrate 1. 
The semiconductor having a band gap of 2.4 eV or more contained in the 
interlayer 6 inserted between the luminescent layer 3 and the 
current-limiting layer 4 includes a compound semiconductor. Examples of 
the compound semiconductor consisting of two elements are CuBr (2.9 eV) 
and .gamma.AgI (2.8 eV) of Group I-VII; CaS (5.4 eV), CaSe (5.0 eV), CaTe 
(4.3 eV), MgSe (5.6 eV), MgTe (4.7 eV), ZnO (3.2 eV), ZnS (3.7 eV), ZnSe 
(2.6 eV), SrO (5.8 eV), SrS (4.8 eV), SrSe (4.6 eV), SrTe (4.0 eV), CdS 
(2.4 eV), BaO (4.2 eV), BaS (4.0 eV), BaSe (3.7 eV) and BaTe (3.4 eV) of 
Group II-VI; HgI.sub.2 (2.5 eV) of Group II-VII; AlAs (2.4 eV), GaN (3.4 
eV) and AlP (3.0 eV) of Group III-V; Al.sub.2 O.sub.3 (&gt;5 eV), Al.sub.2 
S.sub.3 (4.1 eV), Al.sub.2 Se.sub.3 (3.1 eV), Al.sub.2 Te.sub.3 (2.5 eV, 
Ga.sub.2 O.sub.3 (4.4 eV), GaS (2.5 eV) and In.sub.2 O.sub.3 (3.5 eV) of 
Group III-VI; SiC (2.9 eV) of Group IV--IV; TiO.sub.2 (3.0 eV) and 
SnO.sub.2 (4.3 eV) of Group IV-VI; and As.sub.2 O.sub.3 (4.0 eV), As.sub.2 
S.sub.3 (2.5 eV), Sb.sub.2 O.sub.3 (4.2 eV) and Bi.sub.2 O.sub.3 (3.2 eV) 
of Group V-VI. Examples of the compound semiconductor consisting of three 
elements are PbCO.sub.3 (4.4 eV), H.sub.3 BO.sub.3 (5.1 eV) and ZnIn.sub.3 
Se (2.6 eV). Note that numerals in parentheses represent a (self) band gap 
of each substance in bulk. 
In addition to compound semiconductors, organic semiconductors and 
amorphous semiconductors having a band gap of 2.4 eV or more can be used. 
Also, oxides and nitrides such as BaTiO.sub.x, TaO.sub.x, SiN.sub.x, SiON 
and SiAlON which are originally insulators but have semiconducting 
properties because they are offset from stoichiometry can be used. In 
addition to the above substances, any substance having a band gap of 2.4 
eV and semiconducting properties can be used. 
These substances may contain various impurities such as Ag, Cu, Ni, W, P, 
Sb, Li, Cl and B as long as they have a band gap of 2.4 eV or more. 
The above substances can be used singly, in the form of mixed crystals such 
as ZnSSe and CaSTe, or in the form of mixtures such as a combination of 
ZnS and MgTe. 
The interlayer 6 may be a thin film or a film consisting of a fine powder. 
The arrangement of the interlayer 6 may be a single-layered film of the 
compound semiconductor described above or a multilayered film of these 
films. 
Alternatively, the arrangement of the interlayer 6 may be a multilayered 
structure or a mixed structure of the films with another substance, e.g., 
a nitride such as Si.sub.3 N.sub.4 and AlN, an oxynitride such as SiON and 
SiAlON, an oxide such as Ta.sub.2 O.sub.3 and TiO.sub.2, a carbide such as 
SiC and Wsi and a silicide. 
In order to increase a luminous efficiency, the semiconductor is preferably 
at least one semiconductor selected from the group consisting of ZnS, 
ZnSe, CaS, CaSe, SrS, SrSe and CdS. 
Although the luminescent layer 3 is generally doped with an element serving 
as a luminescent center, the interlayer 6 in this embodiment may consist 
of a semiconductor doped with an element serving as the luminescent 
center. 
When the interlayer 6 consists of a semiconductor doped with an element 
serving as the luminescent center, the luminescent layer 3 and the 
interlayer 6 are essentially distinguished from each other as substances 
containing different types of semiconductors or substances containing 
semiconductors of the same type but having different band gaps. 
The thickness of the interlayer 6 to be inserted is preferably 10 nm to 300 
nm. If the thickness is smaller than 10 nm, it is difficult to form a 
continuous film, and a luminance variation is easily caused. If the 
thickness is larger than 300 nm, not only a luminous efficiency is 
decreased, but also a driving voltage is increased to increase the cost of 
a driver IC or to cause breakdown. The thickness is optimally 50 nm to 150 
nm though it depends on film formation conditions. 
Although an insertion position of the interlayer 6 is preferably between 
the luminescent layer 3 and the current-limiting layer 4, it may be 
between the luminescent layer 3 and the transparent electrode 2. 
Alternatively, the luminescent layer 3 may be divided to insert the 
interlayer 6 between the divided layers. 
Since the material such as ZnS, CaS or SrS for use in the luminescent layer 
3 normally has a band gap of 3 to 5 eV and is of n-type, an energy 
difference between a conduction band and a Fermi level is about 1.0 to 1.5 
eV. The number of electrons excited on the conduction band is almost zero 
at room temperature, and therefore the luminescent layer 3 is an 
insulator. When a high electric field of about 1 MV/cm or more is applied 
to the luminescent layer 3, however, electrons become thermions, and the 
conductivity of the luminescent layer 3 is largely increased. Luminescence 
of the EL device occurs in this state. 
The current-limiting layer 4 consists of a semiconductor having a 
resistivity of 3.times.10.sup.3 .OMEGA..multidot.cm to 1 .times.10.sup.6 
.OMEGA..multidot.cm close to that of a conductor at room temperature. 
Therefore, an energy difference between a conduction band and Fermi level 
is much smaller than that of the luminescent layer 3. The energy 
difference actually calculated from a temperature coefficient of a 
resistance is 0.2 eV or less. Therefore, electrons are present on the 
conduction band even at room temperature. 
The luminescent layer 3 and the current-limiting layers 4 having the above 
electrical properties are formed in contact with each other, and a voltage 
is applied from the driving power source 9 shown in FIG. 1 by using the 
current-limiting layer 4 as a cathode and the luminescent layer 3 as an 
anode, thereby obtaining luminescence of the EL device. For this purpose, 
an electric field having a certain value or more is applied. 
The value of the electric field is naturally larger than a value (A) of an 
electric field required to set the luminescent layer in a thermionic 
conduction state. In addition, the value must be larger than an electric 
field value (B) which allows electrons to go over an energy barrier (like 
a Schottky barrier) present between the current-limiting layer 4 and the 
luminescent layer 3. The latter value (B) is substantially the same as but 
slightly smaller than the former value (A). Therefore, the electric field 
value (A) required to set the luminescent layer 3 in a thermionic 
conduction state is normally an electric field value in the luminescent 
layer 3 during light emission. 
When the interlayer 6 is inserted between the current-limiting layer 4 and 
the luminescent layer 3, however, a heterojunction is formed between the 
interlayer 6 and the luminescent layer 3. If the interlayer 6 consists of 
an n-type semiconductor, an energy barrier such as a notch or a spike is 
formed on the surface of the heterojunction regardless of whether the 
luminescent layer 3 is of n- or p-type. Therefore, the intensity of the 
energy barrier obtained when electrons are injected from the 
current-limiting layer 4 into the luminescent layer 3 becomes much larger 
than that obtained when no interlayer 6 is formed. For this reason, the 
electric field value (B) required to allow electrons to go over the energy 
barrier present between the current-limiting layer 4 and the luminescent 
layer 3 becomes larger than the electric field value (A) required to set 
the luminescent layer 3 in a thermionic conduction state. As a result, the 
intensity of the electric field in the luminescent layer 3 during light 
emission becomes larger than that obtained when no interlayer 6 is formed. 
If the interlayer 6 consists of a p-type semiconductor and the luminescent 
layer 3 is of p-type, an energy barrier called a notch is formed on the 
surface of the heterojunction as described above. The intensity of the 
electric field in the luminescent layer 3 during light emission becomes 
larger than that obtained when no interlayer 6 is formed. If the 
interlayer 6 consists of a p-type semiconductor and the luminescent layer 
3 is of n-type, no energy barrier is formed on the surface of the 
heterojunction. However, an energy difference between a conduction band 
and a Fermi level of the p-type semiconductor having a band gap of 2.4 eV 
or more is 2 eV or less which is a value larger than an energy difference 
of 1.0 to 1.5 eV between a conduction band and a Fermi level of the n-type 
luminescent layer 3. Therefore, the interlayer 6 itself serves as an 
energy barrier (C) against electrons. Also in this case, therefore, the 
electric field value (D) required to allow electrons to go over the energy 
barrier (C) becomes larger than the electric field value (A) required to 
set the luminescent layer 3 in a thermionic conduction state. As a result, 
the intensity of the electric field in the luminescent layer 3 during 
light emission becomes larger than that obtained when no interlayer 6 is 
formed. 
In any case, by inserting a semiconductor having a band gap of 2.4 eV or 
more as the interlayer 6 between the current-limiting layer 4 and the 
luminescent layer 3, the intensity of the electric field in the 
luminescent layer 3 during light emission can be increased to increase a 
luminous efficiency. 
In a structure in which the luminescent layer 3 is divided into two or more 
layers and the interlayer 6 is formed between the divided layers, the 
intensity of an electric field in at least one luminescent layer is 
increased for the same reason as described above, and a luminous 
efficiency is increased as a whole. 
When the interlayer 6 is inserted between the luminescent layer 3 and the 
transparent electrode 2, since electrons flow in an opposite direction, 
the above description cannot be directly applied. For basically the same 
reason as described above, however, an energy barrier is formed regardless 
of whether the semiconductor is of n- or p-type, and the electric field 
intensity of the luminescent layer 3 is increased to increase the luminous 
efficiency. 
If a semiconductor having a band gap smaller than 2.4 eV is used as the 
interlayer 6, an energy difference between a conduction band and a Fermi 
level of the interlayer 6 becomes smaller than that of the luminescent 
layer 3. Therefore, even if a new energy barrier such as a notch or a 
spike is formed on the surface of the heterojunction, the intensity of the 
energy barrier is decreased as a whole, and the electric field intensity 
in the luminescent layer 3 is not increased. For this reason, the luminous 
efficiency cannot be increased. 
In the conventional hybrid type EL device as shown in FIG. 4, if Mn-doped 
zinc sulfide is used for as the luminescent layer, its luminous efficiency 
is 0.02% W/W to 0.05% W/W (e.g., GB176340A or Digest (1984, p. 30) of 
Society of Information Display (to be referred to as SID hereinafter)). 
As shown in Table 2 at the upper right corner of page 31 of the above SID 
Digest (1984), in a conventional hybrid type EL device in which a dark 
thin film layer is inserted between a luminescent layer and a 
current-limiting layer, a luminous efficiency is 0.01% W/W to 0.02W/W even 
if the device uses chalcogenide glass which provides the highest luminance 
in luminance characteristics of devices in each of which ZnTe, CdTe, CdSe, 
chalcogenide (black) or Sb.sub.2 S.sub.3 is inserted between a luminescent 
layer (ZnS:Mn) and a current-limiting layer (MnO.sub.2). This luminous 
efficiency is a half or less than that obtained when no dark thin film 
layer is formed. The fact that a luminous efficiency is decreased when a 
dark thin film layer is inserted is also described in GB2176341A. 
In this embodiment, the interlayer 6 consisting of a semiconductor having a 
band gap of 2.4 eV or more is inserted between the luminescent layer 3 and 
the current-limiting layer 4. A luminous efficiency is significantly 
increased by inserting the interlayer 6 for the following reason. That is, 
the height of an electron barrier formed when electrons are injected from 
the current-limiting layer 4 into the luminescent layer 3 is increased by 
the inserted interlayer 6, and the electric field intensity in the 
luminescent layer 3 is increased accordingly. As a result, an energy 
supplied from the electric field to the electrons is increased. 
The reason why a luminous efficiency is not increased by a thin film layer 
formed between a luminescent layer and a current-limiting layer in the 
conventional structure is not clear. However, all of conventionally used 
thin film layers consist of substances having dark colors, and such a 
black substance has a band gap smaller than 2.4 eV since a band gap of 2.4 
eV corresponds to an absorption end of 517 nm. Actually, band gaps of the 
conventionally used substances are 2.1 eV, 1.5 eV and 1.7 eV for ZnTe, 
CdTe and CdSe, respectively. 
To further illustrate this invention, and not by way of limitation, the 
following example is given, which has the same structure as described in 
said first embodiment. 
EXAMPLE 1 
An electroluminescence device having the structure shown in FIG. 1 was 
manufactured as follows. 
That is, an ITO film as a transparent electrode 2 was formed to have a 
thickness of about 500 nm on a transparent glass substrate 1 (corning 
7059) by a reactive sputtering method, and this transparent electrode 2 
was patterned into stripes at a pitch of five stripes per 1 mm of 
photolithography. This patterning is performed in, e.g., the X direction 
on an X-Y plane. Subsequently, film formation was performed at a substrate 
temperature of 200.degree. C. and a deposition rate of 80 nm/min. by using 
a two-source electron beam vapor deposition method in which ZnS and Mn 
were independently controlled, thereby forming a ZnS film containing 0.5 
wt % of Mn and having a thickness of 1 .mu.m as a luminescent layer 3. 
Thereafter, the resultant structure was annealed in vacuum at a 
temperature of 550.degree. C. for about two hours. 
Pellets of ZnSe (band gap=2.6 eV) having a purity of 99.999% were used as a 
deposition source to form a 90-nm thick ZnSe film as an interlayer 6 at a 
substrate temperature of 250.degree. C. by an electron beam vapor 
deposition method. 
Subsequently, a paint prepared by dispersing an MnO.sub.2 powder in a 
solution mixture of a resin and thinner was coated by a spraying method 
and dried to form a current-limiting layer 4 having a resistivity of 
1.times.10.sup.5 .OMEGA..multidot.cm and a film thickness of 12 .mu.m. 
Al was used to form a 1-.mu.m thick film as a backplate 5 by an electron 
beam vapor deposition method. The current-limiting layer 4 and the 
backplate 5 were patterned into stripes in, e.g., the Y direction on the 
X-Y plane by using a diamond needle. The entire device was covered with 
cover glass as a countermeasure against humidity, thereby completing the 
manufacture of an EL device having a dot-matrix structure. 
FIG. 2 shows current density vs. luminance/luminous efficiency 
characteristics of the EL device manufactured as described above. As shown 
in FIG. 2, the luminous efficiency of the EL device having the interlayer 
6 is increased to be twice or more that of an EL device not having an 
interlayer. 
When the conventional hybrid type EL device was driven under the conditions 
of 60 Hz, 30 .mu.s and 100 mA/cm.sup.2 (corresponding to driving 
conditions for 640.times.400 dots), the luminance of only about 20 to 30 
cd/cm.sup.2 could be obtained. In the EL device of Example 1 in which the 
interlayer 6 was inserted, however, a practically satisfactory luminance 
of 70 cd/cm.sup.2 or more could be obtained under the same driving 
conditions. A 640.times.400 dot-matrix display was manufactured by using 
the EL devices of this example. As a result, a luminous efficiency at a 
current value required to obtain a luminance of 50 cd/cm.sup.2 was 
increased from 0.05% W/W of a conventional device to 0.16% W/W, i.e., 
increased three times or more by insertion of the interlayer 6. For this 
reason, consumption power was largely reduced from 25 W of the 
conventional device to 8W, i.e., reduced to about 1/3. In addition, since 
the consumption power was reduced, a luminance life of the EL device was 
prolonged to be 10 times or more that of the conventional device. 
In the above embodiment and example, the interlayer 6 is inserted between 
the luminance layer 3 and the current-limiting layer 4. However, the 
luminous efficiency is effectively increased by inserting the interlayer 6 
between the luminescent layer 3 and the transparent electrode 2, between 
the divided luminescent layers, or between all these portions. 
In the above example, zinc sulfide containing Mn is used in the luminescent 
layer. In addition to Mn, however, rare-earth metals such as Tb, Sm and Tm 
or their fluorides or chlorides can be used in the luminescent layer to 
achieve the same effect. 
As shown in FIG. 3, the second embodiment of the present invention is 
constituted by sequentially stacking a transparent electrode 2, a 
luminescent layer 3, a first interlayer 6, a second interlayer 7, a 
current-limiting layer 4 and a backplate 5 on a transparent glass 
substrate 1. 
As in the first embodiment, the first interlayer 6 contains a semiconductor 
having a band gap of 2.4 eV or more, and preferably, CaS, SrS or BaS. The 
second interlayer 7 prevents oxidation of the first interlayer 6. 
The following example, which has the same structure as described in said 
second embodiment, is given. 
EXAMPLE 2 
An electroluminescence device having the structure shown in FIG. 3 was 
manufactured as follows. 
An ITO film having a thickness of about 400 nm was formed as a transparent 
electrode 2 on a glass substrate 1 by a reactive sputtering method, and 
this transparent electrode 2 was patterned into stripes at a pitch of 
three stripes per 1 mm in the X direction on an X-Y plane by 
photolithography. Subsequently, ZnS containing 0.6 wt % of Mn was used to 
form a film having a thickness of about 0.8 .mu.m as a luminescent layer 3 
at a substrate temperature of 200.degree. C. by a resistance heating vapor 
deposition method. 
A 50-nm thick CaS film (band gap=5.4 eV) was formed as a first interlayer 6 
by an electron beam vapor deposition method, and a 100-nm thick ZnS film 
was formed as a second interlayer 7 by a resistance heating vapor 
deposition method. The substrate temperature during film formation was 
200.degree. C. for both the films. Subsequently, the resultant structure 
was annealed in vacuum at 550.degree. C. for two hours. 
A paint prepared by dispersing a powder mixture of carbon and barium 
titanate in a solution mixture of a resin and thinner was coated by a 
spraying method and dried, thereby forming a current-limiting layer 4 
having a resistivity of 8.times.10.sup.4 .OMEGA..multidot.cm and a film 
thickness of 15 .mu.m. 
An Al film having a thickness of about 1 .mu.m was formed as a backplate 5 
by a vacuum vapor deposition method. Lastly, the current-limiting layer 4 
and the backplate 5 were patterned into stripes in the Y direction by 
using a diamond needle. 
In the dot-matrix EL device manufactured as described above, a luminous 
efficiency was increased as in the first embodiment. For this reason, as 
compared with conventional devices, a luminance was largely increased, 
consumption power was reduced, and a life of the device was prolonged. 
In addition, the luminance of this device having a plurality of interlayers 
was more stable over time than that of a device having a single CaS 
interlayer. That is, the life of this device was longer than that of the 
conventional device. The reason for this result is assumed to be as 
follows. 
That is, although CaS is a substance having excellent electrical 
characteristics because it increases a luminous efficiency, it is very 
easily oxidized. Therefore, if the first interlayer 6 containing CaS is in 
contact with the upper current-limiting layer 4 consisting of an oxide, 
the interlayer 6 is gradually oxidized during light emission over a long 
time period, and the electrical characteristics required for CaS are lost. 
ZnS is a stable substance since it is not easily oxidized as compared with 
CaS. Therefore, when a multilayered structure of the interlayer 6 
containing CaS and the interlayer 7 containing ZnS was formed such that 
the interlayer layer 6 was arranged at the luminescent layer 3 side and 
the interlayer 7 containing ZnS was arranged at the current-limiting layer 
4 side, the interlayer 6 containing CaS increased the luminous efficiency 
of the device, and the interlayer 7 containing ZnS prevented oxidation of 
CaS. As a result, a high luminous efficiency and a long life for EL device 
were obtained. 
Such a multilayered structure is effective when a substance which is easily 
oxidized such as SrS or BaS is used in place of CaS. Any substance can be 
used in the second interlayer 7 for preventing oxidation as long as the 
substance essentially does not contain oxygen or contains only a little 
amount of oxygen and has a resistivity of 10.sup.3 .OMEGA..multidot.cm or 
less at a threshold voltage of the luminescent layer. Examples of the 
substance are, in addition to ZnS, Group II-VI substances such as ZnSe and 
CdS, silicon nitrides not containing oxygen, nitrides such as aluminum 
nitride, and oxynitrides thereof containing only a small amount of oxygen. 
These substances have a good function. In addition, silicides, carbides 
and borides of transition metals can be used. 
For the same reason as in the first embodiment, the film thickness is 
preferably 10 nm to 300 nm. 
According to the EL devices of the above first and second embodiments, the 
following advantages are obtained. That is, a luminous efficiency is 
increased to be much higher than those of conventional devices. Therefore, 
as compared with the conventional devices, a luminance can be increased, 
consumption power can be reduced, and a life of the device can be 
prolonged. In addition, a display using the EL devices of the present 
invention is significantly improved, and a range of applications of the 
display can be widened. 
The third embodiment of the present invention has a stacking structure 
similar to that of the device shown in FIG. 4 and is constituted by 
sequentially stacking a transparent electrode 2, a luminescent layer 3, a 
current-limiting layer 4 obtained by fixing a conductive powder by a 
binder resin, and a backplate 5 on a transparent insulating substrate 1. A 
conductive powder mainly consisting of carbon black was used as the 
conductive powder of the current-limiting layer 4. 
The carbon black includes various substances such as channel black, furnace 
black and acetylene black named in accordance with manufacturing methods 
and having different physical properties. Any of these substances can be 
used as long as a particle diameter is preferably 3 .mu.m or less. 
Examples of the conductive fine powder mainly consisting of the carbon 
black are a conductive fine powder consisting of only the carbon black and 
a powder prepared by mixing a conductive fine powder except for the carbon 
black in the carbon black. In particular, a mixture of the carbon black 
and a barium titanate-based semiconductor is preferable since a 
temperature coefficient of an electric resistance of the mixture easily 
becomes zero or more. 
This barium titanate-based semiconductor is formed by adding a small amount 
of yttrium or cerium in a ferroelectric such as barium titanate, strontium 
titanate, or lead titanate to obtain conductivity. The particle diameter 
of this semiconductor is also preferably 3 .mu.m or less. 
When the two type of substances are sandwiched between brass electrodes and 
a load of 6 kg is applied, resistivities of the substances in the form of 
a fine powder are 10.sup.-2 to 10.sup.1 .OMEGA..multidot.cm and 10.sup.6 
to 10.sup.8 .OMEGA..multidot.cm for the carbon black and the barium 
titanate-based semiconductor, respectively. Since a preferably resistivity 
of the conductive fine powder of the current-limiting layer 4 to 10.sup.4 
to 10.sup.6 .OMEGA..multidot.cm, a resistivity falling within this range 
can be obtained by mixing the two substances. 
A mixture of these powers is used in the form of a powder or 
solvent-dispersible sol and fixed by using a binder resin. Before the 
powder mixture is dispersed in a binder resin solution, a coupling agent 
may be used to improve dispersion properties of the mixture. In this case, 
an aluminum-based coupling agent can provide a most preferable effect. 
Examples of the binder resin are a vinyl-based resin, a polyester-based 
resin, a polyamide-based resin, a cellulose-based resin, a 
polyurethane-based resin, a urea-based resin, an epoxy-based resin, a 
melamine-based resin and a silicone-based resin. In particular, a polymer 
material having a polar group such as a hydroxy group, a carboxyl group, a 
sulfonyl group or a nitro group or a reactive group such as an epoxy 
group, an isocyanuric group or a silanol group can be preferably used. 
A volume mixing ratio of the binder resin, the carbon black fine powder and 
the barium titanate-based semiconductor fine powder preferably satisfies 
all of the following relations (1) to (3): 
EQU C/A.gtoreq.1.5 (1) 
EQU B.gtoreq.50% (2) 
EQU C.gtoreq.5% (3) 
(where A is the ratio of the solid volume of the barium titanate to the 
volume of the current-limiting layer, B is the ratio of the solid volume 
of the binder resin to the volume of the current-limiting layer, and C is 
the ratio of the solid volume of the carbon black to the volume of the 
current-limiting layer). 
The "solid volume" means not an apparent volume but a true volume in the 
case of a powder material and means a volume of a solidified material not 
containing a solvent or the like in the case of a resin material. 
If the relations (1) and (2) are not satisfied, the resistance of the 
current-limiting layer 4 tends to be increased. If the relation (2) is not 
satisfied, film formation properties are easily degraded, e.g., the 
current-limiting layer 4 cracks. 
In the internal structure of the current-limiting layer 4, local uniformity 
of an electrical resistance is most important. In the present invention, 
clusters of the carbon black are easily produced. Therefore, it is 
preferred to use a dispersion method not producing clusters or to remove 
clusters. After the carbon black is dispersed in the binder resin 
solution, large particles of the carbon black can be removed by filtering 
using a filter having a hole diameter of 5 .mu.m or less. 
The above third embodiment has been made in consideration of the fact that 
a luminance variation or a short life of the conventional hybrid type EL 
device is caused by a vicious cycle in which "the electric resistance of 
the current-limiting layer is reduced by a temperature rise caused by 
luminescence to flow a larger current, thereby further increasing the 
temperature". According to this embodiment, a mixture of the carbon black 
and the barium titanate-based semiconductor or the carbon black, in which 
a change in electrical resistance with respect to the temperature rise is 
positive or very small, is used as the current-limiting layer. Therefore, 
breakdown caused by heat generation in conventional devices using 
MnO.sub.2 can be prevented. 
The following examples, whose current-limiting layers contain carbon black 
as described in said third embodiment, are given. 
Electroluminescence devices having the structure shown in FIG. 4 were 
manufactured as follows. 
EXAMPLE 3 
An ITO film having a thickness of about 500 nm was formed as a transparent 
electrode 2 on a glass substrate 1 by a reactive sputtering method, and 
this transparent electrode 2 was patterned into a predetermined shape by 
photolithography. Subsequently, a ZnS film doped with 0.3 wt % of Mn was 
formed as a luminescent layer 3 to have a thickness of about 1 .mu.m by an 
electron beam vapor deposition method. 
Carbon black (SEAST 9H (tradename): TOKAI CARBON CO., LTD.) was dispersed 
in a solvent mixture solution of an aluminum-based coupling agent (AL-M 
(tradename): Ajinomoto Co., Inc.), and a solution mixture of a binder 
resin (MR-110 (tradename): Japan Zeon Co., Ltd.) and a thinner was added 
to the resultant mixture so that a volume ratio of the carbon black to the 
binder resin after solidification was 2:8. The resultant solution mixture 
was filtered by a 10-.mu.m thick teflon membrane filter and then by a 
5-.mu.m thick Teflon membrane filter. A paint prepared as described above 
was coated by a spraying method and dried to form a current-limiting layer 
4 having a resistivity of 4.times.10.sup.4 .OMEGA..multidot.cm and a film 
thickness of 15 .mu.m. The formed current-limiting layer 4 was a black 
layer with no void, solidified by the resin and having a substantially 
uniform thickness. 
An Al film having a thickness of about 1 .mu.m was formed as a backplate 5 
by a vacuum vapor deposition method, and the current-limiting layer 4 and 
the Al film 5 were simultaneously scribed by using a diamond needle to 
form a predetermined backplate pattern. 
When the EL devices manufactured as described above were connected to a 
driver to emit light, light was emitted uniformly from the entire surface, 
and no luminance variation was observed. 
EXAMPLE 4 
A mixture of 6:1 (volume ratio) of carbon black (SEAST 9H (tradename): 
TOKAI CARBON CO., LTD.) and a barium titanate-based semiconductor (PTC-SN 
(tradename): KYORITSU CERAMIC MATERIALS CO., LTD.) was dispersed in a 
solvent mixture solution of an aluminum-based coupling agent (AL-M 
(tradename): Ajinomoto Co., Inc.), and a solution mixture of a binder 
resin (MR-110 (tradename): Japan Zeon Co., Ltd.) and a thinner was added 
to the resultant mixture so that a volume ratio of the total volume of 
powders to the binder resin was 1.75:8.25. Following the same procedures 
as in Example 3, the prepared solution mixture was filtered by a 10-.mu.m 
thick Teflon membrane filter and then by a 5-.mu.m thick Teflon membrane 
filter, thereby preparing a paint. 
The prepared paint was coated by a spraying method and dried on a glass 
substrate 1 (a luminescent layer 3) having the luminescent layer 3 and a 
transparent electrode 2 manufactured following the same procedures as in 
Example 3, thereby forming a current-limiting layer 4 having a resistivity 
of 1.times.10.sup.6 .OMEGA..multidot.cm and a film thickness of 15 .mu.m. 
A backplate 5 was formed following the same procedures as in Example 3 and 
scribed by using a diamond needle to form a predetermined backplate 
pattern. 
When the EL devices manufactured as described above were connected to a 
driver to emit light, light was emitted uniformly from the entire surface, 
and no luminance variation was observed. 
EXAMPLE 5 
A mixture of 11:5 (volume ratio) of carbon black (SEAST 9H (tradename): 
TOKAI CARBON CO., LTD.) and a barium titanate-based semiconductor (PTC-SN 
(tradename): KYORITSU CERAMIC MATERIALS CO., LTD.) was dispersed in a 
solvent mixture solution of an aluminum-based coupling agent (AL-M 
(tradename): Ajinomoto Co., Ltd.), and a solution mixture of a binder 
resin (MR-110 (tradename): Japan Zeon Co., Ltd.) and a thinner was added 
to the resultant mixture so that a volume ratio of the total volume of 
powders and the binder resin was 4:6. 
Following the same procedures as in Example 3, the solution mixture 
prepared as described above was filtered by a 10-.mu.m thick Teflon 
membrane filter and then by a 5-.mu.m thick Teflon membrane filter, 
thereby preparing a paint. 
The prepared paint was coated by a spraying method and dried on a glass 
substrate 1 (a luminescent layer 3) having the luminescent layer 3 and a 
transparent electrode 2 manufactured following the same procedures as in 
Example 3, thereby forming a current-limiting layer 4 having a resistivity 
of 3.times.10.sup.5 .OMEGA..multidot.cm and a film thickness of 15 .mu.m. 
A backplate 5 was formed following the same procedures as in Example 3 and 
scribed by using a diamond needle to form a predetermined backplate 
pattern. 
When the EL devices manufactured as described above were connected to a 
driver to emit light, light was emitted uniformly from the entire surface, 
and no luminance variation was observed. 
A change in resistivity according to a temperature change of the 
current-limiting layer 4 manufactured in Example 5 was measured. The 
measurement result is shown in FIG. 5. As is apparent from FIG. 5, the 
resistivity of the current-limiting layer of Example 5 did not depend on a 
temperature by exhibited a substantially constant value. 
COMATIVE EXAMPLE 1 
An MnO.sub.2 powder prepared by an electrolytic process was milled by a 
ball mill to obtain an average particle size of 0.3 .mu.m, and a solution 
mixture of a binder resin (MR-110 (tradename): Japan Zeon Co., Ltd.) and a 
thinner was added to the resultant powder so that a volume ratio of the 
volume of the MnO.sub.2 powder to the volume of the binder resin was 3:7. 
Following the same procedures as in Example 3, the solution mixture 
prepared as described above was filtered by a 10-.mu.m thick Teflon 
membrane filter and then by a 5-82 m thick Teflon membrane filter, thereby 
preparing a paint. 
The prepared paint was coated by a spraying method and dried on a glass 
substrate 1 (a luminescent layer 3) having the luminescent layer 3 and a 
transparent electrode 2 manufactured following the same procedures as in 
Example 3, thereby forming a current-limiting layer 4 having a resistivity 
of 5.times.10.sup.4 .OMEGA..multidot.cm and a film thickness of 20 .mu.m. 
A backplate 5 was formed following the same procedures as in Example 3 and 
scribed by using a diamond needle to form a predetermined backplate 
pattern. 
When the EL devices manufactured as described above were connected to a 
driver to emit light, the temperature of a panel was increased as the 
luminance was increased, and breakdown was caused sequentially from 
devices at a brightest portion of the panel. 
A change in resistivity according to a temperature change of the 
current-limiting layer of Comparative Example 1 was measured following the 
same procedures as in Example 5. The measurement result is shown in FIG. 
5. 
As is apparent from FIG. 5, as compared with the resistivity of the 
current-limiting layer of Comparative Example 1, the resistivity of the 
current-limiting layer of Example 5 was substantially constant regardless 
of the temperature. 
According to the EL device of the above third embodiment, the following 
advantages are obtained. That is, a luminance variation in the EL device 
using the current-limiting layer can be improved and breakdown can be 
prevented, thereby improving the reliability of the EL device. 
In addition, in the EL device of this embodiment, the resistivity of the 
current-limiting layer is constant regardless of the temperature. 
Therefore, time variations of both required power and a luminance are 
small. 
The fourth embodiment has a stacking structure similar to that of the 
device shown in FIG. 4, in which a conductive powder contained in a 
current-limiting layer 4 is electrically in point contact with the surface 
of a luminescent layer 3. 
In order to form the conductive powder to be electrically in point contact 
with the luminescent layer 3, the conductive powder preferably has a nib 
which can be in point contact with the luminescent layer 3. 
For this purpose, the conductive powder desirably consists of particles 
having nibs or an aggregate of the particles. A practical shape of the 
particle having a nib is assumed to be a shape except for a sphere, a 
spheroid and a shape surrounded by another irregular continuous curved 
surface. Macroscopically, the shape of the particle includes a point which 
cannot be differentiable at least at one portion of the curved surface. 
Physically, the shape can be expressed as an object having a portion with 
a radius of curvature of 5 nm or less. A contact portion is assumed to be 
a point when the contact portion surface having a radius of curvature of 5 
nm or less is brought into physical contact with a plane. 
In order to set the minimum value of the radius of curvature of the contact 
portion of the conductive powder with respect to the luminescent layer 3 
to be 5 nm or less, the particle size of the conductive powder is 
preferably 10 nm or less, or the conductive powder preferably has a 
corresponding portion at least in a part thereof. 
Examples of the shape are a tetrahedron, a hexahedron, an octahedron, a 
dodecahedron, an icositetrahedron, a column, a spindle and a needle. 
Examples of particles having the above shapes are as follows. 
That is, examples of a hexahedral particle are a manganese(II) carbonate 
particle produced by a reaction between manganese sulfate and ammonium 
bicarbonate in an aqueous solution, a cubic hematite particle produced by 
hydrolysis of an iron(III) hydroxo complex in an alcohol solution, and an 
ITO (indium oxide: tin) ultrafine particle produced by a vapor phase 
method. 
An example of a columnar particle is a carbon fiber. 
An example of a spindle-like particle is a spindle-like hematite particle 
produced by a reaction between iron(III) chloride and sodium dihydrogen 
phosphate in an aqueous solution. 
When one type of particles having the above shapes or aggregates thereof 
are to be dispersed in the current-limiting layer 4 so as to be in contact 
with the surface of the luminescent layer 3, a part of the contact portion 
may not be in point contact (e.g., a contact of a portion having a radius 
of curvature of 5 nm or less) with the surface. For example, a particle 
may be in contact by its flat surface if particles or aggregates thereof 
are hexahedral or by its cylindrical surface if particles or aggregates 
thereof are columnar. That is, the contact portion is not necessarily in 
point contact with the surface. However, since the particles having the 
above shapes or aggregates thereof are in contact by their corners or 
sides with a certain possibility, the particles having these shapes can be 
used. 
An aggregate of needle-like crystals can be in point contact regardless of 
the direction of particles. In particular, the shape of a radial aggregate 
in which needle-like crystals radially extend from one point is most 
preferred. Even if crystals do not extend from one point, a similar shape 
can provide substantially the same effect. It is important that the nibs 
of needle-like crystals are directed in substantially all directions. 
An aspect ratio (length of major axis:length of minor axis) of such a 
needle-like crystal is preferably 5:1, and more preferably, 10:1. If minor 
axes are perpendicular to major axes, a ratio of the lengths of two minor 
axes perpendicular to each other is not particularly limited, but the 
lengths are preferably substantially the same. Although the size of the 
needle-like crystal represented by the length of the minor axis preferably 
falls within the range of 1 nm to 10 nm, a smaller size is more preferable 
as long as the size falls within this range. If the size is larger than 10 
nm, a contact density with respect to the luminescent layer is decreased 
to reduce a luminous efficiency. If the size is smaller than 1 nm, the 
crystal no longer exhibits its properties as a substance, and its specific 
characteristics cannot be obtained. The length of the major axis of this 
needle-like crystal preferably falls within the range of 50 nm to 200 nm. 
The structure of the nib portion of the needle-like crystal in the major 
axis direction is preferably a peak-head structure, i.e., a peaked 
structure. A structure in which the size is gradually decreased from a 
central portion toward the nib portion in the major axis direction (i.e., 
the number of constitutive atoms is decreased) to finally peak the nib 
portion (e.g., a radius of curvature is 5 nm or less), i.e., a so-called 
elongated spindle is most preferred. 
Although the needle-like crystals having the structure and size as 
described above can be singly used, the crystals are preferably radially 
aggregated in order to increase the probability of point contact. When the 
needle-like crystals are radially aggregated, point contact can be 
obtained regardless of the direction of contact. 
Since it is very difficult to radially aggregate needle-like crystals after 
the crystals are produced, the needle-like crystals and radial aggregates 
are conveniently, simultaneously produced. In this case, radially extended 
needle-like crystals are chemically bonded to each other at contact 
points. 
Examples of the radial aggregates of needle-like crystals are 
.alpha.-MnO.sub.2 and .gamma.-MnO.sub.2 produced by a reaction in an 
aqueous solution of potassium permanganate and manganese sulfate, 
.delta.-MnO.sub.2 produced by a reaction in an aqueous solution of 
potassium permanganate and hydrochloric acid, and tetrapod-like ZnO 
produced by a vapor phase reaction. 
These needle-like crystal radial aggregates sometimes form secondary 
particles to grow into larger particles in accordance with the reaction 
conditions. In this case, a luminous efficiency is reduced to cause 
undesired results. 
These conductive powders are used singly or in the form of mixtures and 
fixed by using a binder. Before the conductive powders are dispersed in a 
binder solution, they may be treated with a coupling agent to improve 
their dispersion properties. In this case, an aluminum-based coupling 
agent or a titanate-based coupling agent can provide a most preferable 
effect. 
Examples of the binder are a vinyl-based resin, a polyester-based resin, a 
polyamide-based resin, a cellulose-based resin, a polyurethane-based 
resin, a urea-based resin, an epoxy-based resin, a melamine-based resin, 
and a silicone-based resin. In particular, a polymer material having a 
polar group such as a hydroxyl group, a carboxyl group or a nitro group or 
a reactive group such as an epoxy group, an isocyanuric group or a silanol 
group can be preferably used. 
A volume mixing ratio of the conductive powder and a resin used as the 
binder preferably falls within the range of 2:3 to 6:4 (powder:binder). 
In this case, the volume means not an apparent volume but a true volume in 
the case of a powder material and means a volume of a solidified material 
not containing a solvent or the like in the case of a resin material. 
If an amount of the binder resin is larger than that of the above range, 
the resistance of the current-limiting layer 4 is easily increased. If an 
amount of the conductive powder is larger than that of the above range, 
the current-limiting layer 4 easily cracks to degrade film formation 
properties. 
The above fourth embodiment has been made in consideration of the fact that 
a luminous efficiency of a conventional hybrid type EL device is low 
because a contact state of the conductive powder in the current-limiting 
layer with respect to the luminescent layer is close to a surface contact. 
According to this embodiment, the conductive powder in the 
current-limiting layer 4 is electrically in point contact with the surface 
of the thin film of the luminescent layer 3. Therefore, the electric field 
intensity is locally increased at the contact portion to accelerate 
electrons, thereby realizing a high luminous efficiency. 
The following examples, whose conductive powders in current-limiting layers 
are electrically in point contact with the surfaces of luminescent layers 
as in said fourth embodiment, are given. 
An electroluminescence device having the structure shown in FIG. 4 was 
manufactured as follows. 
EXAMPLE 6 
Manganese sulfate was added to an aqueous solution of potassium 
permanganate to cause a reaction, and the resultant precipitate was washed 
with water and dried to obtain .gamma.-MnO.sub.2 needle-like crystal 
aggregates. This .gamma.-MnO.sub.2 was a particle consisting of 5 
nm.times.5 nm.times.150 nm needle like crystals and having an average 
particle size of about 500 nm. A radius of curvature of the nib of each 
needle-like crystal was about 4 nm. 
An ITO film having a thickness of about 500 nm was formed as a transparent 
electrode 2 on a glass substrate 1 by a reactive sputtering method, and 
this transparent electrode 2 was patterned into a predetermined shape by 
lithography. Subsequently, a ZnS film containing 0.3 wt % of Mn and having 
a thickness of about 1 .mu.m was formed by an electron beam vapor 
deposition method. In addition, a ZnSe thin film was formed to have a 
thickness of about 60 nm by an electron beam vapor deposition method. 
A solution mixture of a binder resin (MR-110 (tradename): Japan Zeon Co., 
Ltd.) and a thinner was added to the .gamma.-MnO.sub.2 powder prepared as 
described above so that a volume ratio of the powder to the binder resin 
after the material was solidified was 3:7, and the resultant material was 
dispersed for an hour by using a sand mill. 
A paint prepared as described above was coated by a spraying method and 
dried to form a current-limiting layer 4 having a resistivity of 
8.times.10.sup.4 .OMEGA..multidot.cm and a film thickness of 15 .mu.m. The 
formed current-limiting layer 4 was a black layer with no voids solidified 
by the binder resin and having a substantially uniform thickness. 
An Al film having a thickness of about 1 .mu.m was formed as a backplate 5 
by a vacuum vapor deposition method, and the current-limiting layer 4 and 
the backplate 5 were simultaneously scribed by using a diamond needle, 
thereby forming a predetermined backplate pattern. 
When the EL devices manufactured as described above were connected to a 
driver to emit light, light was uniformly emitted from the entire surface, 
no luminance variation was observed, and a luminous efficiency was 0.8 
lm/W. 
EXAMPLE 7 
Hydrochloric acid was added to an aqueous solution of potassium 
permanganate heated up to 90.degree. C. to cause a reaction, and the 
precipitate was washed with water and dried to obtain .delta.-MnO.sub.2 
needle-like crystal radial aggregates. In this .delta.-MnO.sub.2, 5 
nm.times.5 nm.times.150 nm needle-like crystals were radially grown, and 
an average particle size of the aggregate was 0.2 to 0.4 .mu.m. A radius 
of curvature of the nib of each needle-like crystal was 3 nm. 
An ITO film having a thickness of about 500 nm was formed as a transparent 
electrode 2 on a glass substrate 1 by a reactive sputtering method, and 
this transparent electrode 2 was patterned into a predetermined shape by 
photolithography. Subsequently, a ZnS film containing 0.3 wt % of Mn and 
having a thickness of about 1 .mu.m was formed as a luminescent layer 3 by 
an electron beam vapor deposition method. In addition, a ZnSe thin film 
was formed to have a thickness of about 60 nm by an electron beam vapor 
deposition method. 
A solution mixture of a binder resin (MR-110 (tradename): Japan Zeon Co., 
Ltd.) and a thinner was added to the .delta.-MnO.sub.2 powder prepared as 
described above so that a volume ratio of the powder and the binder resin 
after the material was solidified was 3:7, and the resultant material was 
dispersed for three hours by a sand mill. 
The paint prepared as described above was coated by a spraying method and 
dried to form a current-limiting layer 4 having a resistivity of 
2.times.10.sup.5 .OMEGA..multidot.cm and a film thickness of 10 .mu.m. The 
formed current-limiting layer 4 was a black layer with no voids solidified 
by the binder resin and having a substantially uniform thickness. 
An Al film having a thickness of 1 .mu.m was formed as a backplate 5 by a 
vacuum vapor deposition method. Thereafter, the current-limiting layer 4 
and the backplate 5 were simultaneously scribed by using a diamond needle, 
thereby forming a predetermined backplate pattern. 
When the EL devices manufactured as described above were connected to a 
driver to emit light, light was uniformly emitted from the entire surface, 
no luminance variation was observed, and a luminous efficiency was 1.1 
lm/W. 
COMATIVE EXAMPLE 2 
A .gamma.-MnO.sub.2 powder prepared by an electrolytic process was milled 
by using a ball mill into a substantially spherical powder having an 
average particle size of 0.3 .mu.m, and a solution mixture of a binder 
resin (MR-110 (tradename): Japan Zeon Co., Ltd.) and a thinner was added 
to the MnO.sub.2 powder so that a volume ratio of the powder and the 
binder resin was 3/7, thereby preparing a paint following the same 
procedures as in Example 6. 
The prepared paint was coated by a spraying method and dried on a glass 
substrate (a luminescent layer 3) having the luminescent layer 3 and a 
transparent electrode 2 manufactured following the same procedures as in 
Example 6, thereby forming a current-limiting layer 4 having a resistivity 
of 8.times.10.sup.4 .OMEGA..multidot.cm and a film thickness of 20 .mu.m. 
A backplate 5 was formed following the same procedures as in Example 6 and 
scribed by using a diamond needle, thereby forming a predetermined 
backplate pattern. 
When the EL devices manufactured as described above were connected to a 
driver to emit light, light was uniformly emitted from the entire surface 
and no luminance variation was observed, but a luminous efficiency was 0.1 
lm/W. 
According to the EL device of the above fourth embodiment, the following 
advantages can be obtained. That is, a luminous efficiency of the hybride 
EL device can be increased to realize low-consumption power activation. In 
addition, since a necessary luminance can be obtained with low power, life 
characteristics of the EL device can be improved.