JPS5827506B2 - Blackened electrode structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a blackened electrode structure which is an effective technique for EL display panels etc. using thin film EL elements that emit EL (Electro Luminescence) light upon application of an alternating electric field. It is.

Conventionally, for AC-operated thin-film EL elements, a high electric field (about 10 6 /cIfL) is regularly applied to the light-emitting layer to improve dielectric strength, luminous efficiency, stability of operation, etc.
0.1 to 2.0 wt% Mn (or Cu, Al,
A three-layer structure ZnS:Mn (Z is Zn5e: Mn) in which a semiconductor light-emitting layer of ZnS, Zn5e, etc. doped with Br, etc. is sandwiched with a dielectric thin film of Y2O3, TiO2, etc.
) EL devices have been developed, and improvements in light emitting properties have been confirmed.

This thin film EL element emits light with high brightness when an alternating current electric field of several KHz is applied, and is characterized by long life.

It was also discovered that the light emission of this thin film EL element has a hysteresis characteristic in which the luminance of the light emitted by the same applied voltage differs in the process of increasing the applied voltage and in the process of decreasing the voltage from the high voltage side. In the process of increasing the applied voltage to a thin film EL element with hysteresis characteristics, when light, electric field, heat, etc. are applied, the thin film EL element has hysteresis characteristics.
The element is excited to a state of luminescence brightness corresponding to its intensity,
It is known that there is a memory phenomenon in which the luminance remains in a high state even if light, electric field, heat, etc. are removed and the state is returned to its original state.

A thin film EL device application technology that effectively utilizes this memory phenomenon to utilize a thin film EL device as a memory device is currently being researched and developed in the industry.

As an example of a thin film EL device, the basic structure of a ZnS:Mn thin film EL device is shown in FIG.

The structure of the thin film EL element will be explained in detail based on FIG.
A first dielectric layer 3 made of l2O3, Si3N4.5i02, etc. is formed in an overlapping manner by sputtering, electron beam evaporation, or the like.

A ZnS light emitting layer 4 is formed on the first dielectric layer 3 by electron beam evaporation of a ZnS:Mn sintered pellet.

At this time, the ZnS:Mn sintered pellet for vapor deposition contains pellets I/Mn, which is an active substance, and whose concentration is set according to the purpose.
is used.

A second dielectric layer 5 made of the same material as the first dielectric layer 3 is laminated on the ZnS light emitting layer 4, and A
A back electrode 6 made of a material such as No. 1 is formed by vapor deposition.

The transparent electrode 2 and the back electrode 6 are connected to an AC power source 7, and the thin film EL element is driven.

When an AC voltage is applied between the electrodes 2 and 6, the ZnS light emitting layer 4
The above AC voltage is induced between the dielectric layers 3 and 5 on both sides of the ZnS light emitting layer 4. Therefore, the electric field generated in the ZnS light emitting layer 4 excites electrons into the conduction band and accelerates them to obtain sufficient energy. , directly excites the Mn luminescent center, and emits yellow light when the excited Mn luminescent center returns to the ground state.

That is, when the electrons accelerated by a high electric field excite the electrons of the Mn atoms that have entered the Zn site, which is the luminescence center in the ZnS luminescent layer 4, and fall to the ground state, a strong emission occurs in a wide wavelength range with a peak of approximately 5850A. Exhibits luminescence.

The thin film EL element having the structure described above can be used as a flat thin display device that takes advantage of the space factor to display characters, symbols, still images, moving images, etc. in computer output display terminal equipment and various other display devices that contain characters and figures. It can be used as a means of displaying images, etc.

FIG. 2 shows an example of a conventional thin film EL panel.

This thin film EL panel adopts a matrix electrode structure in which the transparent electrode 2 and the back electrode 6 shown in FIG. The crossing position corresponds to one picture element on the panel when viewed from a plan view.

To explain based on FIG. 2, transparent electrodes 2, a first dielectric layer 3, and a ZnS light emitting layer 4 are arranged in parallel on a glass substrate 1.
are sequentially stacked, and the ZnS light emitting layer 4-H includes a Si3N4 film 5a and an Al2O3 layer superimposed on the Si3N4 film 5a.
A second dielectric layer is laminated in a two-layer structure from the film 5b, and a back electrode 6 arranged in parallel in a direction orthogonal to the transparent electrode 2 is provided on the second dielectric layer. An EL element is configured.

In order to seal this thin film EL element, the glass substrate 1 and the peripheral edge of the back glass plate 80 are adhesively fixed to form an envelope.

A thin film EL element is built into the envelope, and an insulating liquid 9 such as silicone oil is sealed therein.

In addition, the lead terminal portions 10 of the transparent electrode 2 and the back electrode 6 are extended to the outside of the envelope via the joint between the glass substrate 1 and the back glass plate 8, and are connected to a driving control garden path (not shown) and an electrical connection. connected.

When an alternating current voltage is applied through the transparent electrode 2 and the back electrode 6, a light emitting display is performed on a pixel-by-pixel basis from the front surface of the glass substrate 1.

Thin-film EL panels have a lower operating voltage than conventional cathode ray tubes (CRTs), are superior in weight and strength compared to plasma display panels (FDPs), which are similar flat display devices, and are superior to liquid crystal (LCD) panels. ) has a wider operating temperature range and faster response speed, etc.
It has advantages.

Furthermore, since it is a pure solid matrix type panel, it has a long operating life, and its address accuracy makes it very effective as an input/output display means for computers and the like.

The dielectric layers 3 and 5 used in the thin film EL panel need to increase the effective electric field strength of the ZnS light emitting layer 4, and are preferably made of materials with as high a dielectric constant as possible and a high dielectric strength voltage.

From this point of view, Si3N is of good quality.

In addition, as the back electrode 6 used in thin film EL panels,
It is desirable to use a material that is easy to manufacture, has good adhesion to the dielectric layer 5, and has high conductivity, and generally an aluminum thin film is used.

However, the aluminum thin film has an extremely high light reflectance among metals (reflectance of 90% or more), and therefore, the back electrode 6 using the aluminum thin film cannot pass through the glass substrate 1 into the EL panel under bright ambient light. This has the problem of causing intruding external light to be reflected at the interface, resulting in deterioration of display quality.

That is, each thin film layer constituting the thin film EL panel has extremely high transparency, and external light incident from the glass substrate 1 passes through each thin film layer and reaches the back electrode 6.
Since the EL light emitted from the ZnS light-emitting layer 4 and the reflected light reflected from the back electrode 6 cause mutual interference, the contrast ratio between the light-emitting and non-light-emitting pixels decreases. However, if the ambient light is extremely bright, the brightness of the EL emission and the reflected light will be about the same, and the display performance will deteriorate significantly.

Therefore, it has long been desired to develop an effective technology to solve the above problems, but considering reliability, practicality, etc.
At present, no definitive solution has been found.

In order to prevent reflected light, it is possible to use a non-reflective electrode material for the back electrode 6, but it is possible to use an inexpensive material that is a single metal and has both non-reflectivity and high conductivity comparable to aluminum. There are currently no such cases.

In view of the above-mentioned problems, the present invention prevents light reflection without compromising the manufacturing requirements and display characteristics required for the back electrode constituting a thin film EL panel, etc.
The purpose of the present invention is to provide a new and useful blackened electrode structure that can improve display quality.

Hereinafter, the present invention will be described in detail according to embodiments with reference to the drawings.

FIG. 3 is a cross-sectional view of the main part of a matrix electrode structure thin film EL panel for explaining one embodiment of the present invention.

FIG. 4 is a cross-sectional view of the main part of the blackened electrode structure shown in FIG. 3.

Transparent electrodes 2 formed into strips as in FIG. 2 are arranged in parallel on a glass substrate 1 made of heat-resistant glass such as Pyrex.
A first dielectric layer 3 and a ZnS light emitting layer 4 are laminated thereon.

Further, on the ZnS light emitting layer 4, there are Si 3 N4 films 5a, A
A second dielectric layer with a two-layer structure consisting of an 12O3 film 5b is deposited.

On the Al2O3 film 5b constituting the second dielectric layer,
A thin film 11a with a thickness of 60A consisting of a mixture of Al2O3 and a thin film 11b with a thickness of 30A made of a mixture of AI and Al2O3 are sequentially and alternately
A total of four layers are laminated to form a thin film laminated portion 11 having light absorbing properties.

Each of the thin films 11a and 11b of the thin film stacking section 11 is laminated in multiple stages on the Al2O3 film 5b by a split vapor deposition method, but in order to impart a light absorption function, the film thickness of each of the thin films 11a and 11b is set to 30 mm.
It is desirable to laminate the layers in multiple stages so that the number of laminated interfaces is as large as possible without losing the transparent state by making the layers thinner than about 0A, preferably about 100 people.

In addition, the structure of the thin film laminated portion 11 may be a structure in which thin films made of KAI are laminated in two to five layers with a film thickness of about 60 mm other than the above, and the light absorption function can also be imparted.

Further, an Al metal layer is deposited on the thin film laminated portion 11 at a temperature of 150° C. or higher while controlling the film thickness to 1,000 to 10,000 holes to form a metal layer for the back electrode 13 .

The back electrodes 13 are arranged in parallel in strips by etching the thin film laminated portion 11 and the Al metal layer, which are deposited over the entire surface of the Al2O3 film 5b, according to a predetermined pattern shape.

At this time, the thin film laminated portion 11 is also etched at the same time, but the Al2O3 film 5b remains without being etched.

Due to the interposition of the thin film laminated part 11 made of a multilayer film, the light that enters the EL panel is absorbed by this thin film laminated part 11,
Therefore, the amount of light reflected from the back electrode 13 is significantly reduced.

Therefore, when observed with the naked eye from the glass substrate 1 side, the back electrode 13 becomes a black background.

The details of the mechanism by which the reflectance of the back electrode 130 decreases are still unclear, but in a thin film with a multilayer structure of 10 to 250 layers, a continuous and uniform film is not produced in the divided deposition process. It is thought that the film becomes a discontinuous film with island-like interfaces, and a light absorption effect occurs.

Along with the light absorption effect, the back electrode 13 becomes a blackened electrode.

FIGS. 5 and 6 show the structure of the thin film laminated portion 11 and the relationship between the structure and the light reflectance from the back electrode 13 as measured data.

The horizontal axis represents the light wavelength in units of holes, and the vertical axis represents the reflectance in %.

In Fig. 5, curve 1 shows the EL emission spectrum of the ZnS light emitting layer 4. Curve r1 shows the case where two layers of AI thin film are laminated with a film thickness of 60A, and curve r2 shows the case where two layers of AI thin film are laminated with a film thickness of 40 to 5OU. This is the measurement data when

In Fig. 6, the curve r3 shows the AI thin film with a film thickness of 60 years.
In the case of layer stacking, the curve r4 is measurement data when two layers of AI thin films with a film thickness of 10 to 60 Å and one layer of thin films made of AI+Al2O3 with a film thickness of 10 to 60 Å are alternately stacked for a total of three layers.

Note that r5 indicates the reflectance of the back electrode 130.

Considering the reflectance corresponding to EL emission, the curve r
1 is 44.4%, curve r2 is 32.9%, curve r3 is 1
9.8%, and curve r4 shows a value of 21.4%.

Incidentally, in order to further achieve the object of the present invention, in addition to the above embodiments, Al2O3 film 5b constituting the second dielectric layer may be
A structure in which 2O3-x films are stacked in multiple stages may be used.

Al2O3-x is an alumina oxide obtained by removing oxygen atoms from Al2O3 and exhibiting characteristics similar to aluminum.

The Al2O3-x film is formed by laminating a multilayer film on the Al2O3 film 5b by several times of divided vapor deposition.

As an example, a case where this multilayer film has a three-layer structure will be described.

Al2O3 film 5b at a temperature of 150°C with a thickness of 10~
A first stage layer of about 50 mL is vacuum deposited, and after oxygen leakage, its surface is oxidized.

Next, a second layer is vacuum-deposited on the first layer in the same manner, but the film thickness is made thicker than that of the first layer.

Furthermore, a third stage layer is similarly vacuum-deposited on the second stage layer through an oxygen leak process.

By setting the multilayer film structure to 2 to 5 layers with each layer having a thickness of about 10 to 250', the fouling rate can be reduced to 14 to 28%.

In order to further reduce the reflectance, the number of laminated layers of the multilayer film is increased.

The same AI metal layer as above was formed on the A 1203-X film consisting of the above multilayer film at a temperature of 150°C or higher to a film thickness of 1000°C to 100°C.
The back electrode 13 is formed by vapor deposition under controlled conditions for a period of 0,000 hours.

The back electrode 13 is an A layered over the entire area on the Al2O3 film 5b.
By etching the 1203-E film and the AI metal layer according to a predetermined pattern shape, they are arranged in parallel in strips.

At this time, the Al2O3-X film is also etched at the same time, but the Al2O3 film 5b remains without being etched.

Due to the presence of the multilayered Al2O3 film, the light that has entered the EL panel is absorbed by this 1□03 film, and therefore the amount of light reflected from the back electrode 13 is greatly reduced.

Therefore, when observed with the naked eye from the glass substrate 1 side, the back electrode 13 becomes a black background.

As for the reflectance reduction mechanism of the back electrode 13, the A1□03-X film is not formed as a continuous uniform film in the same divisional deposition process as described above, but becomes a discontinuous film with island-like interfaces, and furthermore, the interface is caused by oxygen leakage. It is thought that because of the oxidation, this interface is composed of a cermet-like film and a light absorption effect occurs.

This laminated structure is not a mixture of A1 and A1203-X, but each layer is made of a single material, and due to the vapor deposition of the AI metal layer, the adhesion with the Al2O3 film 5b and the reliability as an electrode are inferior to the conventional back electrode. Never.

The thin film EL element having the above structure is sealed together with an insulating liquid 9 such as silicone oil in an envelope made of a dish-shaped rear glass plate 8 placed on a glass substrate 1.

In addition, the transparent electrode 2 and the back electrode 13 have their ends made of a phosphor bronze plate, a lead terminal 1 made of a copper-beam alloy plate, etc.
00 at one end, and power is supplied via the lead terminal 10.

The other end of the lead terminal 10 is electrically and mechanically connected to a first circuit board 14 outside the envelope. It is elastically supported in a floating state at a fixed distance from 14.

A background film 15 made of black vinyl or the like is coated on the main surface of the first circuit board 14 on the side where the envelope is installed, and forms a display background color for the thin film EL element.

Further, the background film 15 absorbs the light transmitted through the gap between the back electrodes 130.

On the other side of the first circuit board 14, an electronic component 16 such as an IC or LSI is connected via a component connector 1σ attached to the surface of the board 14.
The drive circuit for the thin film EL element is configured by mounting the thin film EL element using the package method.

Various electronic components 16 are similarly mounted on a second circuit board 17 arranged parallel to and opposite to the first circuit board 14.
A drive circuit, a control circuit, and other circuits are configured.

Electrical connection between the first circuit board 14 and the second circuit board 17 is achieved by mechanically fitting connector terminals 18 and 19 provided on mutually opposing main surfaces of the periphery of the boards.

Naturally, the circuit board can also be a multilayer board with two or more layers.

Mechanical connection between each circuit board is made by inserting and fixing mounting screws 20 into screw holes provided at the corners of the board.
Each circuit board is integrally connected.

As described above, a thin film EL panel mounted on the circuit board and integrated with the circuit board is constructed.

When using this thin film EL panel for information processing,
The drive circuit requires one drive circuit for scanning, one drive circuit for data, and a gate circuit, but if each drive circuit is classified separately and mounted on each circuit board, the circuit configuration can be simplified and aligned. can.

When a voltage is applied to the transparent electrode 2 and the back electrode 13 from the lead terminal 10 via a drive circuit, a drive circuit, etc., a pixel-by-pixel display based on the EL emission of the ZnS light emitting layer 4 from the glass substrate 1 is executed.

At this time, external light that has entered the inside of the element from the glass substrate 1 passes through the dielectric layer 5b and the back electrode 13 before reaching the back electrode 13.
Since the light is absorbed by the light-absorbing thin film laminated portion 11 interposed therebetween, the light is not emitted to the outside from the glass substrate 1 as reflected light, and good display quality is maintained.

As explained in detail above, according to the present invention, each laminated portion from the dielectric layer to the back electrode has good adhesion and is easy to manufacture, without impairing various requirements for the back electrode. Reflection of external light can be effectively prevented.

Therefore, the contrast ratio becomes high, and it becomes possible to maintain a high-quality display state without being affected by ambient light.

Furthermore, the structure of the present invention also serves as a means for providing a background color to the display, and also has the effect of improving the appearance of the display format.

The above example is a yellow thin film E with a matrix type electrode structure.
Although the L panel has been described, the present invention is not limited thereto, and can of course be applied to segment type electrode structures, etc., and also to thin film EL panels such as green and red. The present invention can also be applied to multicolor thin film EL panels formed in multiple stages and other display devices (for example, liquid crystal display devices, EC display devices, light emitting diode display devices, fluorescent tubes, etc.).

Furthermore, the effects of the present invention can be obtained in the same manner even if other films exhibiting light absorption properties are laminated in multiple layers in addition to the thin films of the above embodiments.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional configuration diagram showing the basic structure of a conventional thin film EL element. FIG. 2 is a cross-sectional configuration diagram of essential parts showing an example of a conventional thin film EL panel. FIGS. 3 and 4 are cross-sectional configuration diagrams of essential parts of a thin film EL panel for explaining one embodiment of the present invention. 5 and 6 are graphs showing the light reflection characteristics of the blackened electrode structure according to the present invention. 2...Transparent electrode, 4...ZnS light emitting layer, 5a...Si3N4 film, 5b...A
l2O3 film, 11... Thin film stacked part, 13...
...Back electrode.

Claims (1)

[Scope of Claims] 1. In a display device comprising a back electrode made of AI disposed on a transparent laminated part that performs optical display by applying a voltage, the transparent laminated part and the front and back electrodes A blackened electrode structure characterized in that a thin film laminated portion mainly containing Al as a constituent element is interposed between the blackened electrode structure and the thin film laminated portion has a function of absorbing light irradiated onto the back electrode surface. 2. The blackened electrode structure according to claim 1, wherein the thin film laminated portion is a laminated thin film having a thickness of 300 Å or less. 3 The thin film laminated portion includes a thin film made of Al and an AlKA
The blackened electrode structure according to claim 1, comprising a laminate with a thin film mixed with 1203.