JPS5835360B2 - Thin film EL panel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film EL device that emits EL (Electro Luminescence) light upon application of an alternating current electric field, and in particular, by making full use of a novel technology in the laminated structure of the thin film EL device. The present invention relates to a manufacturing technology for thin film EL panels exhibiting good display characteristics.

Conventionally, for AC-operated thin film EL elements, a high electric field (about 10'V〆h) is regularly applied to the light-emitting layer, and in order to improve dielectric strength, luminous efficiency, stability of operation, etc.
A semiconductor light-emitting layer such as ZnS or Zn5e doped with ~2.0 wt% Mn (or Cu, AA, Br, etc.) is made of Y20.
A three-layer structure ZnS:Mn (or Zn5e:Mn) EL device sandwiched between dielectric thin films such as a and TiO2 has been developed, and improvement in the light emitting characteristics has 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.

Furthermore, regarding the light emission of this thin film EL element, it has a hysteresis characteristic in which the luminance differs for the same applied voltage in the process of increasing the applied voltage and in the process of descending from the high voltage side. In the process of increasing the applied electrostriction to a thin film EL element with hysteresis characteristics, when light, electric field, heat, etc. are applied, the thin film EL element
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.

FIG. 1 shows the basic structure of a ZnS:Mn thin film EL device as an example of a thin film EL device.

The structure of the thin film EL element will be explained in detail based on FIG.
A first dielectric layer 3 made of I203 Si3 N4, SiO□, 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 used for vapor deposition is a pellet in which Mn, which is an active substance, is set at a concentration depending on the purpose.

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 an AI layer is further layered thereon.
A back electrode 6 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 is driven.

When AC voltage is applied between the electrodes 2 and 6, the ZnS light emitting layer 4
The electrons that are excited and accelerated to the conduction band by the electric field generated in the ZnS light emitting layer 4 and have sufficient energy are induced between the dielectric layers 3 and 5 on both sides of the The Mn luminescence center is directly excited, and when the excited Mn luminescence center returns to the ground state, it emits yellow light.

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, the electrons emit light in a wide wavelength range with a peak of about 5850. Exhibits strong 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 laminated, and on the ZnS light emitting layer 4, S is N4
A 1 superimposed on the film 5a and the S t s N4 film 5a
203 film 5b is laminated in a two-layer structure, and furthermore, a back electrode 6 arranged in parallel in a direction orthogonal to the transparent electrode 2 is provided on the second dielectric layer, A thin film EL element is constructed.

In order to seal this thin film EL element, the peripheral edges of the glass substrate 1 and the rear glass plate 8 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.

Further, 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 electrically connected to a drive control circuit (not shown). It is connected.

When an AC 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 lower dynamic electrostriction 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 many advantages such as a wider operating temperature range and faster response speed.

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 are preferably made of a material with a high dielectric constant as much as possible, and a material with a high dielectric strength, in order to increase the effective electric field strength of the ZnS light emitting layer 4.

From this point of view, Si3N4 is of good quality.

Further, as the back electrode 6 used in the thin film EL panel, it is desirable to use a material that is easy to produce, has good adhesion to the dielectric layer 5, and has high conductivity, and aluminum thin film is generally used. There is.

However, an aluminum thin film has an extremely high light reflectance among metals, and therefore, under bright ambient light, the back electrode 6 using an aluminum thin film prevents external light that has entered the EL panel 5 through the glass substrate 1 from entering the EL panel 5 through its interface. This causes problems such as a decrease in 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. If the ambient light is extremely bright, the luminance 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 questions, 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 none.

In view of the above-mentioned problems, the present invention is novel and useful, achieving improved display quality by preventing light reflection without compromising the manufacturing and characteristic requirements required for the back electrode of a thin-film EL panel. The purpose is to provide a thin film EL panel.

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 showing one embodiment of the present invention.

On a glass substrate 1 made of heat-resistant glass such as Pyrex, transparent electrodes 2 each having a band-like bottom shape as shown in FIG. 2 are arranged in parallel.
A first dielectric layer 3 and a ZnS light emitting layer 4 are laminated thereon.

Further, on the ZnS light emitting layer 4, Si3N, film 5 as A1
A second dielectric layer with a two-layer structure consisting of a 203 film 5b is deposited.

On the Al2O3 film 5b constituting the second dielectric layer,
The 203-X film 11 is laminated to a thickness of about 50-100 mm.

The Al 2 O 3

Al2O3 is completely oxidized alumina oxide and is an insulator, but the A12A1203-X film 11 is incompletely oxidized and retains properties as metal aluminum, and exhibits good conductivity due to its metallic properties.

A molybdenum (Mo) film 12 is laminated on the A1203-X film 11 to a thickness of about 100-300X for the purpose of imparting a light absorption effect.

The Mo film 12 is an extremely thin metal film, and the light that has entered the EL panel is caused by this M film.

It is absorbed by the film 12, and the Mo film 12 itself forms a black background when observed with the naked eye.

In addition to the Mo film 12, a thin film made of a metal having a low light reflectance, such as a transition metal thin film such as a zirconium (Zr) film, a titanium (Tj) film, a yttrium (Y) film, a tantalum (Ta) film, or a nickel (Nj) film. Others can be substituted.

The details of the blackening mechanism are still unclear, but the oxygen-deficient A1゜Os-X film 11 and the Mo film 12
This is thought to be due to light interference occurring at the interface with the

On the Mo film 12, back electrodes 13 made of aluminum (A1) are arranged in parallel in a direction orthogonal to the transparent electrodes 2 with a film thickness of about 5,000 to 10,000 A.

The back electrode 13 is an A layered over the entire area on the Al2O3 film 5b.
By etching the 12O3X film 11, Mo film 12, and AI metal layer according to a predetermined pattern shape, they are arranged in parallel in strips.

At this time, the A1203-X film 11 and the Mo film 12 are also etched at the same time, but the Al2O3 film 5b remains without being etched.

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.
0, and is supplied with power via the lead terminal 10.

The other end of the lead terminal 10 is electrically and mechanically connected to the first circuit board 14, and the envelope containing the thin film EL element is connected to the first circuit board 14 by a certain distance through the lead terminal 10. It is supported elastically in a floating state.

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 envelope side, and forms a display background color for the thin film EL element.

Further, the background film 15 functions to absorb light transmitted through the gap between the back electrodes 13.

On the other side of the first circuit board 14, electronic components 16 such as ICs and LSIs are connected via component connectors 16' attached to the board 14 surface.
epackage) method, and constitutes a drive circuit for a thin film EL element.

Various electronic parts 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 connections between the circuit boards are made by inserting and fixing mounting screws 20 into screw holes provided at the corners of the boards, so that the circuit boards are 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 a scanning drive circuit, a data drive circuit, 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 arranged. can.

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

At this time, the external light that has entered the inside of the element through the glass substrate 1 passes between the dielectric layer 5b and the back electrode 1 before reaching between the back electrode 13.
Since the light is absorbed by the light-absorbing Mo film 12 interposed between the glass substrates 1 and 3, the light is not emitted to the outside from the glass substrate 1 as reflected light, and good display quality is maintained.

FIG. 4 shows the relationship between ambient light and contrast ratio of the thin film EL panel having the above structure.

The horizontal axis shows ambient light, and the vertical axis shows contrast ratio.

The contrast ratio C is a value determined by the following equation.

Further, numeral 11 in the figure indicates a case where the structure of the back electrode is different from that of the conventional A1, and corresponds to the structure of FIG. 2.

The light emitting layer 1iB has a thickness of 50 ft-L and a reflectance γ of 53.6%.

12 is a case where the blackened back electrode structure according to the present invention is adopted, and the structure is such that the A1203-X film has 70 A% M
This is data when the O film is 100' and the 1A1 back electrode is 10.0OOA.

The luminance B was 29 ft-L, and the reflectance γ was 18.7%.

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.

Further, 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 type.

Although the above embodiment describes a yellow thin film EL panel with a multi-IJ lux electrode structure, the present invention is not limited to this, and segment type electrode structures and others may also be used. Naturally, the present invention can also be applied to thin film EL panels, and can also be applied to multicolor thin film EL panels in which light emitting layers, electrode layers, etc. are formed in multiple stages.

[Brief explanation of drawings]

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. FIG. 3 is a cross-sectional configuration diagram of essential parts of a thin film EL panel showing one embodiment of the present invention. FIG. 4 is a graph showing the relationship between ambient light and the contrast ratio of a thin film EL panel. 2...Transparent electrode, 4...ZnS light emitting layer, 5a...S i3 N4 film, 5b...
・A1□03 membrane, 11...A1203-X membrane,
12... Molybdenum film, 13... Back electrode.

Claims (1)

[Claims] 1. In a thin film EL panel in which a transparent light emitting layer that generates EL light emission in response to applied voltage is interposed between a transparent electrode placed on the display side and an Al electrode placed on the back side. ,
A1203-X layer (0<
1. A thin film EL panel characterized in that a light-absorbing conductive film made of a laminate of a metal layer having a low light reflectance and a metal layer having a low light reflectance is inserted.