GB2329280A

GB2329280A - An organic electroluminescent device

Info

Publication number: GB2329280A
Application number: GB9819650A
Authority: GB
Inventors: Yoshihisa Tsuruoka; Toshio Miyauchi
Original assignee: Futaba Corp
Current assignee: Futaba Corp
Priority date: 1997-09-09
Filing date: 1998-09-09
Publication date: 1999-03-17
Anticipated expiration: 2018-09-09
Also published as: KR19990029645A; GB9819650D0; GB2329280B; KR100304488B1; JPH1187052A

Abstract

An organic electroluminescent device, comprising substrate 1, anodes 2, insulation 3, wiring conductor 4, take out electrodes 5, hole transport layer 6, organic luminescent layer 7 and cathodes 8, is capable of leading out the cathodes whilst keeping their pitch fine. The substrate is provided with parallel take out electrodes 5 which are made of a material different from that of the cathodes. The cathodes are each provided with a connection end of a width smaller than that of the take out electrodes, thus ensuring that even if the cathode pattern is deviated in a width direction a satisfactory connection is made. The lead out electrodes may be made of the same material as the parallel anodes. The cathodes are made perpendicular to the anodes to form a matrix display. There may only be one anode and one cathode.

Description

This invention relates to an organic electroluminescence device including an organic luminous layer, and more particularly to an organic electroluminescence device including cathodes formed by vapor deposition of metal.

An organic electroluminescence device (hereinafter also referred to as "organic EL device") includes an electron injection electrode, a positive hole injection electrode, and a thin film containing a fluorescent organic compound and arranged between the electron injection electrode and the hole injection electrode. The film is injected with electrons and positive holes to recombine them with each other, to thereby produce excitons, resulting in carrying out display using light (fluorescence or phosphorescence) emitted during deactivation of excitons.

Conventionally, such an organic EL device is generally constructed in such a manner as shown in Fig. 3 by way of example.

The organic EL device includes a glass substrate 100, on which an anode 101 made of indium tin oxide (ITO), a hole transport layer 102 made of a triphenylamine derivative (diamine), an organic layer 103 made of tris (8-quinolylite) aluminum (III) (Alq3), and a cathode 104 made of alloy of Mg and Ag are laminatedly formed in order. The organic layers each are formed into a thicknessof about 50 nm. A film for each of the layers are formed by vacuum deposition. In the organic EL device, application of a DC voltage of 10V betweRa the cathode 104 and the anode 101 permits the device to emit light of a green luminous color at luminance of 1000 calm2.

In theorganic EL device thus constructed, the cathode is made of metal decreased in work function such as elemental metal selected from the group consisting of, for example, Li, Na, Mg, Ca and the like or alloy selected from the group consisting of, for example, Al:Li, Mg:In, Mg:Ag and the like. Also, in the organic EL device, it is required to lead out the cathode 104 onto the substrate 100 in order to connect the anode 101 and cathode 104 to an external drive circuit.

Unfortunately, the metal material decreased in work function which is used for the cathode is increased in activity, to thereby be readily oxidized, so that a terminal portion of the cathode connected to the external drive circuit may be peeled, deteriorated and increased in resistance due to oxidation thereof.

Also, a thickness of the metal film required to permit the metal film to effectively act as the cathode is merely as small as 200 nm or less. However, such a thickness of the metal film fails to permit it to exhibit sufficient strength when it is used for the terminal, resulting in electrical disconnection or a failure in contact often occurring due to flaw.

Thus, the conventional organic EL device fails to permit metal for the cathode to be directly used as a connection terminal for the external circuit.

Another organic EL device is disclosed in Japanese Patent Application Laid-Open Publication No. 274694/1991, which is constructed as shown in Fig. 4. The organic EL device includes a structure of leading out a cathode 104 onto a substrate 100 having an anode 101 arranged thereon. In Fig. 4, reference numerals like those in Fig. 3 designate corresponding parts. The organic EL device includes a takeout electrode 105 arranged on the substrate 100 for leading out the cathode 104 onto the substrate 100. Also, the organic EL device includes an insulating layer 106 arranged for partially covering the anode 101 and takeout electrode 105. The insulating layer 106 is formed with an opening through which luminescence is taken out and a through-hole 108 via which the takeout electrode 105 and cathode 104 are connected to each other.

The cathode 104 is arranged so as to extend to the through-hole 108, to thereby be connected to the takeout electrode 105.

Unfortunately, the structure shown in Fig. 4 wherein the cathode 104 and takeout electrode 105 are connected to each other via the through-hole 108 fails to be satisfactorily applied to an organic EL device including a number of cathodes arranged at fine pitches such as, for example, an organic EL device of the matrix type wherein stripe-like anodes and cathodes are arranged so as to intersect each other. More particularly, in such an organic EL device, it is required that a number of through-holes are formed at fine pitches in a manner to correspond to the cathodes, which are connected to the takeout electrodes via the through-holes. However, in the organic EL device of the graphic type, it is required to render pitches of the cathodes considerably fine, resulting in formation of the through-holes in an insulating layer at such fine pitches being substantially impossible.

The present invention has been made in view of the foregoing disadvantage of the prior art.

Accordingly, it is an object of the present invention to provide an organic EL device which is capable of outwardly leading out cathodes while keeping pitches of the cathodes fine as in an organic EL device of the graphic type.

In accordance with the present invention, an organic electroluminescence device is provided. The electroluminescence device includes a substrate, at least one anode arranged on an inner surface of the substrate, a hole transport layer formed on the anode, a luminous layer formed on the hole transport layer, at least one cathode formed on the luminous layer, at least one takeout electrode formed of a material different from that of the cathode and arranged on the inner surface of the substrate, and at least one connection end each formed into a width smaller than that of the takeout electrode, arranged on an end of the cathode and connected onto an end of the takeout electrode.

Also, in accordance with the present invention, an organic electroluminescence device is provided. The organic electroluminescence device includes a substrate, a plurality of stripe-like anodes arranged on an inner surface of the substrate in a manner to be spaced from each other at predetermined intervals in a predetermined direction, a hole transport layer formed on the anodes, a luminous layer formed on the hole transport layer, a plurality of stripe-like cathodes formed on the luminous layer in a manner to be spaced from each other at predetermined intervals in a direction perpendicular to the anodes, a plurality of takeout electrodes formed of a material different from that of the cathodes and arranged on the inner surface of the substrate in a manner to be substantially parallel to the cathodes, and a connection end formed into a width smaller than that of each of the takeout electrode, arranged on an end of each of the cathodes and connected onto an end of each of the takeout electrodes.

In a preferred embodiment of the present invention, the takeout electrodes are made of a material of 4.5 eV in work function.

In a preferred embodiment of the present invention, the material iscselected from the group consisting of ITO, ZnO:Al, SnO2:Sb, In203 and Au.

These and other objects and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings; wherein: Fig. 1 is a sectional view showing an embodiment of an organic EL device according to the present invention; Fig. 2 is a plan view showing a connection between a connection end of each of cathodes and each of takeout electrode; Fig. 3 is a sectional view showing a conventional organic EL device; and Fig. 4 is a sectional view showing a conventional organic EL device.

Now, an organic EL device according to the present invention will be described hereinafter with reference to Figs. 1 and 2, which illustrate an embodiment of an organic EL device according to the present invention.

An organic EL device of the illustrated embodiment, as shown in Fig. 1, includes a glass substrate 1, which is formed on an inner surface thereof with at least one anode 2. In the illustrated embodiment, a plurality of stripe-like anodes 2 are arranged in parallel to each other at predetermined pitches. Each of the anodes 2 may be made of indium tin oxide (ITO), however, it is not limited to the material. It may be made of any other material so long as it has work function of 4.5 eV or more. For example, ZnO:Al, SnO2:Sb, In2 03, Au or the like may be suitably used for this purpose. The organic EL device of the illustrated embodiment also includes an insulating layer 3 of a frame-like shape arranged so as to surround the anodes 2. Such construction permits an inside of the insulating layer 3 in which the anodes 2 are arranged to serve as a display region. Then, the anodes 2 each are led out to an outside of the insulating layer 3 and then connected to each of wiring conductors 4.

The wiring conductors 4 each are connected to a negative terminal of an external drive circuit (not shown).

The substrate 1 is formed thereon with at least one takeout electrode 5 in a manner to be contiguous to an outer edge of the insulating layer 3. In the illustrated embodiment, a plurality of stripe-like takeout electrodes are arranged. The takeout electrodes 5 are arranged in parallel to each other at predetermined pitches.

The number of takeout electrodes 5 and pitches thereof are determined in conformity to cathodes 8 described hereinafter. Also, the takeout electrodes 5 are arranged in a manner to be perpendicular to the anodes 2. The takeout electrodes 8 are made of a material different from that of the cathodes 8. In the illustrated embodiment, they are made of a material identical with that of the anodes 2 or ITO. Thus, in the illustrated embodiment, the anodes 2 and takeout electrodes 5 may be patterned in the same step.

The takeout electrodes 5 each are connected to a negative terminal of an external drive circuit.

The anodes 2 each are provided thereon with a hole transport layer 6. The hole transport layer 6 may be formed of a triphenylamine derivative (diamine). The hole transport layer 6 is so formed that an edge thereof is deposited on the insulating layer 3.

The hole transport layer 6 is provided thereon with an organic luminous layer 7. The organic luminous layer 7 may be made of a material of a luminous color desired depending on applications of the device. In the illustrated embodiment, it may be made of tris (8quinolylite) aluminum (III) (Alq3).

The organic luminous layer 7 is provided thereon with at least one cathode 8. In the illustrated embodiment, a plurality of such stripe-like cathodes 8 are arranged. The cathodes 8 each may be formed of, for example, alloy of Mg and Ag. In the illustrated embodiment, the cathodes 8 are arranged so as to be spaced from each other at predetermined intervals in a direction perpendicular to the anodes 2.

Such arrangement of the anodes and cathodes wherein a plurality of stripe-like anodes 2 and a plurality of stripe-like cathodes 8 are arranged so as to intersect each other provides a matrix display region. Thus, feeding of a display signal to the cathodes 8 and anodes 2 desired permits regions on the organic luminous layer 7 corresponding to desired intersections between the cathodes and the anodes on the matrix to selectively emit light, resulting in providing graphical display desired.

The cathodes 8 each are so arranged that one of both ends thereof reaches an upper surface of the takeout electrode 5 while riding across the insulating layer 3. Also, as shown in Fig. 2 the cathodes 8 each are formed at the other end thereof with a connection terminal 9 of a width smaller than that of the cathode 8 in a manner to extend therefrom, so that the connection terminal 9 is connected onto an end of each of the takeout electrodes 5.

Now, setting of dimensions of the takeout electrode 5 and connection terminal 9 will be described hereinafter.

First of all, an interval A between the takeout electrodes 5 is reduced to a limit determined by electrical insulating characteristics thereof and a patterning process thereof. More specifically, it may be preferably set to be between 10 tt m and 50 gL m. A width B of the connection terminal 9 formed by mask vapor deposition is set to be a minimum value calculated on the basis of a reduction in voltage thereof and electrical characteristics thereof such as heat generation or the like. More specifically, it may be preferably set to be 50 to 100 fuzz m.

Supposing that pitches of the cathodes 8 and takeout electrodes 5 are set at 0.6 mm, a width of the takeout electrodes 5, an interval between the takeout electrodes 5 adjacent to each other and a width of the connection terminal 9 of each of the cathodes 8 are set to be 0.55 mm, 0.05 mm (50 zm) and 0.1 mm (100 IL jim), respectively.

When the cathodes 8 and connection terminals 9 are formed and connected to the takeout electrodes 5 at a final stage of the process, a pattern of the cathodes 8 and connection terminals 9 is caused to be deviated in a width direction thereof or a direction perpendicular to a longitudinal direction of the stripe-like pattern. However, the illustrated embodiment is so constructed that the connection terminals 9 reduced in width each are connected to the corresponding takeout electrode 5 increased in width at identical pitches. Such construction prevents a deterioration or variation in electrical characteristics of the connection between the takeout electrode 5 and the cathode 8, even when a position at which the cathodes and connection terminals 9 are formed is deviated. The example of dimensions described above permits an allowable tolerance of positioning to be +0.225 mm (= (0.55-0.1)/23 . As a result, actually a variation in connection resistance at the connection between the takeout electrode 5 and the cathode 8 was not observed. On the contrary, supposing that pitches of the cathodes and takeout electrodes, a width of the takeout electrodes and a width of the cathodes are 0.6 mm, 0.3 mm and 0.3 mm in the prior art, respectively; the allowable tolerance of positioning is caused to be l0.2 mm, resulting in a connection resistance at the connection between the takeout electrode and the cathode being always varied.

In the illustrated embodiment, the organic layers of the organic EL device each are formed into a thickness of about 50 nm. The layers each are made in the form of a film by vacuum vapor deposition Also, in the illustrated embodiment, as shown in Fig. 1, a structure on the upper side of the substrate 1 except the ends of the takeout electrodes 5 and those of the wiring conductors 4 of the anodes 2 is covered with a protective layer 10.

As can be seen from the foregoing, the present invention is so constructed that the substrate is provided on the inner surface thereof with the takeout electrodes, which are made of a material different from that of the cathodes and the cathodes each are provided on the end thereof with the connection of a width smaller than that of the takeout electrode, which is then connected onto the end of the takeout electrode. Such construction ensures satisfactory connection between the cathodes and the takeout electrodes even when the cathode pattern is deviated in the width direction, resulting in being effective to outwardly lead out the cathodes from the organic EL device. In particular, the present invention may be effectively applied to an organic EL device of the graphic type including a plurality of cathodes arranged in a stripelike pattern wherein cathodes are arranged at fine pitches, thus, it effectively prevents positional deviation caused in relation to leading-out of the cathodes from the device.

Claims

Claims:

1. An organic electroluminescence device, comprising: a substrate; at least one anode arranged on an inner surface of said substrate; a hole transport layer formed on said anode; a luminous layer formed on said hole transport layer; at least one cathode formed on said luminous layer; at least one takeout electrode formed of a material different from that of said cathode and arranged on the inner surface of said substrate; and at least one connection end each formed into a width smaller than that of said takeout electrode, arranged on an end of said cathode and connected onto an end of said takeout electrode.

2. An organic electroluminescence device, comprising: a substrate; a plurality of stripe-like anodes arranged on an inner surface of said substrate in a manner to be spaced from each other at predetermined intervals in a predetermined direction; a hole transport layer formed on said anodes; a luminous layer formed on said hole transport layer; a plurality of stripe-like cathodes formed on said luminous layer in a manner to be spaced from each other at predetermined intervals in a direction perpendicular to said anodes; a plurality of takeout electrodes formed of a material different from that of said cathodes and arranged on the inner surface of said substrate in a manner to be substantially parallel to said cathodes; and a connection end formed into a width smaller than that of each of said takeout electrode, arranged on an end of each of said cathodes and connected onto an end of each of said takeout electrodes.

3. An organic electroluminescence device as defined in claim 1 or 2, wherein said takeout electrodes are made of a material of 4.5 eV in work function.

4. An organic electroluminescence device as defined in claim 3, wherein said material is selected from the group consisting of ITO, ZnO:Al, SnO2:Sb, In2O3 and Au.