CA1223054A - Electroluminescent display device - Google Patents

Electroluminescent display device

Info

Publication number
CA1223054A
CA1223054A CA000410828A CA410828A CA1223054A CA 1223054 A CA1223054 A CA 1223054A CA 000410828 A CA000410828 A CA 000410828A CA 410828 A CA410828 A CA 410828A CA 1223054 A CA1223054 A CA 1223054A
Authority
CA
Canada
Prior art keywords
layer
light
conductor
interfering
electroluminescent display
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000410828A
Other languages
French (fr)
Inventor
Leei Chang
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sun Chemical Corp
Original Assignee
Sun Chemical Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sun Chemical Corp filed Critical Sun Chemical Corp
Application granted granted Critical
Publication of CA1223054A publication Critical patent/CA1223054A/en
Expired legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00Electroluminescent light sources
    • H05B33/12Light sources with substantially two-dimensional radiating surfaces
    • H05B33/22Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of auxiliary dielectric or reflective layers

Landscapes

  • Electroluminescent Light Sources (AREA)
  • Devices For Indicating Variable Information By Combining Individual Elements (AREA)

Abstract

ELECTROLUMINESCENT DISPLAY DEVICES

ABSTRACT OF THE DISCLOSURE
A thin-film electroluminescent display device com-prises a glass substrate, a transparent conductor, a phosphor layer between two insulating layers, an opaque back conductor, and a black layer of a material that interferes with the incoming light, thus eliminating the problem of reflection when the display is viewed under conditions of high ambient illumination, e.g. direct sunlight.

Description

12230~;4 ala Sinkholes.) ELECTROLUMINESCENT D SPLAY DEVIL S

_C'KG~OUI~I) OF TIE INVENTION
conventional thin-film electroluminescent displays are multi layer devices consisting of a glass substrate, a transparent conductor, a phosphor layer between two ins-feting layers, and an opaque back conductor generally alum-numb Light is produced in the phosphor layer by the applique-lion of an AC voltage to the two conductive layers, and emission occurs as a result of the excitation of activator ions by injected electrons.
A major concern in using any type of display, for example in an aircraft instrument panel, is the ability of the viewer to read the display under conditions of high ambient illumination, e.g. direct sunlight. Under such conditions, the opaque back conductor which has high metallic reflectance reflects more light than the electroluminescent element emits, and so the display is rendered ineffective.
There have been many attempts to provide a phosphor-emitting display device that operates with a high contrast ratio under high ambient illumination conditions with a mint mum sacrifice of emission brightness.
'AL

~223054 Solutions to the problem include the incorporation of a dark material into the glass or of a dark dye into the phosphor dielectric layer; these methods proved unsatisfactory because they result in the reduction of the intensity of the emitted light as well as of the reflected light. An overlay of a perforated opaque layer on the viewing side of the glass substrate of the device has been proposed, but this is unsatisfactory because it restricts the viewing angle.

The incorporation of a light-absorbing layer on the viewing side of the back conductor was suggested in US. Patent No. 3,560,784. The absorbing materials have an index of refraction substantially equal to that of the phosphor layer and provide a contiguous and continuous transition at the interface of thy phosphor layer and the l.. ight-absorbing layer, thus minimizing the reflection of light on this interface. The light absorbing layer is substantially transparent at the interface and a gradually increasing concentration of light-absorbing material is introduced within the dark layer toward the back layer. This method has the disadvantages of requiring elaborate material and process control as well as complex apparatus to create this tapered concentration of absorptive materials within a thin film layer.

SUMMARY OF THE INVENTION
It has now been found that the problem of reflection when the display is viewed under conditions of high ambient illumination can be eliminated by employing as the black layer a material that is capable of combining the interference effect with the ability to absorb the light transversing through, that is, induced absorption.

According to the present invention there is provided in a thin-film electroluminescent display device comprising a glass viewing surface, a transparent conductor, a light-emitting phosphor layer between two insulators, and an opaque back 1;~230S~
conductor, the improvement which comprises including in said device a layer of light absorptive material having optical properties such that incident light is refracted into said layer and absorbed therein upon multiple internal reflection being the surfaces thereof so as to minimize the reflection of incident light and thereby improve contrast on the viewing surface.

BRIEF DESCRIPTION OF THE DRAWINGS
-Fig. l is a simplified diagrammatic view showing the passage of incident light between an insulating layer and the back conductor in an electroluminescent display device.
- 2 '.

~2;~05~

Fig. 2 is an enlarged cross-sectional view of a conventional electroluminescent display device.
Fig. 3 is an enlarged cross-sectional view of the preferred embodiment of this invention.
Fig. 4 is an enlarged cross-sectional view of an-other embodiment of this invention.
Fig. 5 is an enlarged cross-sectional view of still another embodiment of this invention.
'it. is an enlarged cross-sectional view of an-lo other embodiment of this invention.

D~TAI IT DfiJSC~IPTION OF THY INVENTION
Fig. shows a conventional display that consists of a Klaus substrate 1, a transparent conductor 2, a trays-parent insulator 3, a phosphor layer 4, an insulating layer 5, and an aluminum conductor 6. The aluminum layer has a high metallic reflection which, when used under high ambient lighting conditions such as direct sunlight, reflects more light toward the observer than the electroluminescent eye-mint emits and thus renders the display ineffective.
Fig. 3 illustrates the preferred embodiment of the present invention. The first layer 12 deposited directly on the glass substrate 11 is a transparent, electrically conduct live coating. This first layer is generally a composition of tin oxide and indium oxide. Glass substrates with this coat-in are available commercially, for example Nesatron glass.
The second layer 13 and the fourth layer 14 are insulators required to prevent electrical breakdown. Such materials as yttrium oxide (YO-YO), alumni oxide (Allah tantalum oxide (Tao), or the like are suitable for these layers.
The third layer 15 is the phosphor which is the source of light. Suitable materials include, but are not limited to, ZnS:Mn(orange), CaS:Ce(green), SrS:Ce(blue), ZnS:Te,Mn(red), and the like.

The fifth layer 16 is the black layer to improve contrast. It is a hard film of a semi-conducting highly dispersive material. It has a suitable optical dispersion in the visible spectrum to create the desired induced Abe sorption between the dielectric layer 14 and the back metal electrode layer 17 of the thin-film electroluminescent disk play. Examples of suitable materials include, but are not limited to!, lanthanum hexaboride (Lab), chromium oxide (Cry), titanium oxide (Shea, vanadium oxide (VOW), and lo boron carbide (BC4). These materials are by nature refract tory ceramics and as such have an intrinsic stability against short circuit and blow-out.
The final layer 17 is the back conductor, Usually aluminum.
As illustrated in Fig. 1, the incoming light 18 is made to reflect between the two boundaries of the black layer 16 so that each time it traverses through the black layer a portion is absorbed; in other words, the light is trapped by the black layer. In addition, very little light is reflected from the black layer, so it is an effective antireYlection material.
The black layer luff of this invention it preferably incorporated in front of he back electrode 17, as in Fig.
3. It is, however, within the scope of this invention to place it in other locations in an electroluminescent display device, for example as a replacement for insulation layer 14 (Fig. 4), between insulation layer 13 and the phosphor 15 (Fig. 5), or as an electrode to replace the back electrode 17 (Fig. 6).
- 30 Although the thicknesses of the layers are not critical, in general the coating 12 on the glass is about 200 to AYE, and preferably about AYE; the phosphor layer 15 is about 1,000 to AYE, and preferably about AYE, between two films of electric insulation 13 and 14, each about 500 to AYE, and preferably about AYE each; the ~223054 aluminum electrode 17 is about 200 to Lowe, and prefer-ably about Lowe; and thickness of tube black layer of this invention 16 depends upon the material selected. When a layer of Lab is used, it may be about 200 to AYE, and preferably about AYE; a layer of Two is generally about 400 O O
to Lowe thick, and preferably about AYE; a layer of V203 is generally about 300 to Lowe thick, and preferably about AYE; a layer of Cry is generally about 200 to Lowe thick, and preferably about AYE; and a layer of BC4 is lo generally about 50 to AYE, and preferably about loo. The small amount of' residual reflection may appear green, magenta or told, depending upon the optical thickness of the black layer or the position of the quarter wave peaks in the visit bye spectrum. Thus the color can be varied by changing the thickness of the layer.
Experiments were carried out to illustrate the effectiveness of various materials as the black layer in electroluminescent (EL) display devices. When used with an aluminum electrode, the material was deposited between it and the insulating layer 14. The displays were tested with a Sylvania SG-77 Sun Gun, and the results are tabulated below:
Material Two Lab V203 Cry BC4 O O O O O
Vacua Hartz AYE AYE AYE AYE Lola monitor Thickness Vital Appearance metallic metallic metallic metallic metallic in Reflection yellow blue purple silver Visual Appearance absorbing absorbing absorbing absorbing brownish in Transmission grew grew grew brown grew Electric 100 to 100 to 3,000 >20 >100 >100 Resistivity<3,000 ohms Amy. megaohm/sq. megaohm/sq.
ohms El Test without * >100 ft.- - - -Al eastward (a) Bert El Test with $ >100 ft.-Al Electrode (a) lam Bert (a) _ (a) (a) = works satisfactorily ~Z~30~;4 From the above it can be seen that, if the nests-tivity is sufficiently low as in the case of Two and Lab, the material can be used directly s the back surface elect trove.
S In each case the black layer improved the contrast to the point where the gun could be placed six inches in front of the display (a third of the distance used to Sims-late sunlight and, therefore, nine times the brightness) without obliterating the glow of the display.
I The use of this light-interfering black layer no-dupes to a minimum (about one per cent) the reflectance from both interfaces, the one between the black layer and the adjacent layer toward the viewer and the one between the black layer and the back metal conductor. In edition, there is no sacrifice of emission brightness, brightness levels of more than one thousand foot-lamberts being obtained, in contrast with about one hundred foot-lamberts for typical television Cuts. Moreover, lifetimes in excess of guy hours were achieved.
The products of this invention can be made by any known and convenient means. Preferably, however, such thin-film electroluminescent display devices are produced by vacuum deposition, such as electron beam evaporation tech-piques, resulting in the production of large area substrates with high resolutions. Generally the entire structure is sealed to prevent contamination from the external environ-mint.
The display devices of this invention are suitable for use as electroluminescent panels, e.g., numerical disk plays or other types of information display panels such as are used in aircraft instrument panels, computer terminals, word processors, and the like, in the form of vertical scale displays, round dial displays, illuminated retitles, matrix displays, and so forth.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a thin-film electroluminescent display device comprising a glass viewing surface, a transparent conductor, a light-emitting phosphor layer between two in-sulators, and an opaque back conductor, the improvement comprises a layer of light absorptive material having opti-cal properties such that incident light is refracted into said layer and absorbed therein upon multiple internal re-flection between the surfaces thereof so as to minimize the reflection of incident light and thereby improve contrast on the viewing surface.
2. The device of claim 1, wherein the light-interfering layer is a hard film of a semi-conducting highly dispersive material.
3. The device of claim 1, wherein the light-interfering material is selected from the group consisting of lanthanum hexaboride, chromium oxide, titanium oxide, vanadium oxide and boron carbide.
4. The device of claim 1, wherein the light-interfering layer is located between the back conductor and an insulating layer.
5. The device of claim 1, wherein the light-interfering layer is located between the phosphor and the insulator adjacent to the transparent conductor.
6. The device of claim 1, wherein the light-interfering layer is located between the phosphor and the opaque conductor, replacing the insulating layer.
7. The device of claim 1, wherein the light-interfering layer replaces the opaque back conductor.
8. In a thin-film electroluminescent display device comprising a glass viewing surface, a transparent conductor, a light-emitting phosphor layer between two in-sulators, and an opaque back conductor, the improvement comprising a layer of material that interferes with incoming light to minimize reflection and improve contrast on the viewing surface, said light-interfering material being selected from the group consisting of lanthanum hexaboride, chromium oxide, titanium oxide, vanadium oxide and boron carbide, said layer having optical properties such that in-cident light is refracted into said layer and absorbed therein upon multiple internal rflection between surfaces thereof.
CA000410828A 1981-09-21 1982-09-03 Electroluminescent display device Expired CA1223054A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US30396581A 1981-09-21 1981-09-21
US303,965 1981-09-21

Publications (1)

Publication Number Publication Date
CA1223054A true CA1223054A (en) 1987-06-16

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
CA000410828A Expired CA1223054A (en) 1981-09-21 1982-09-03 Electroluminescent display device

Country Status (5)

Country Link
JP (1) JPS5858583A (en)
CA (1) CA1223054A (en)
DE (1) DE3231727A1 (en)
FR (1) FR2513415B1 (en)
GB (1) GB2106317B (en)

Families Citing this family (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS60180093A (en) * 1984-02-24 1985-09-13 ホ−ヤ株式会社 Thin film el element
JPS625598A (en) * 1985-07-01 1987-01-12 シャープ株式会社 Thin film el element
US4849674A (en) * 1987-03-12 1989-07-18 The Cherry Corporation Electroluminescent display with interlayer for improved forming
JPS6293897A (en) * 1985-10-19 1987-04-30 日本精機株式会社 Thin film electroluminescence device
CA1302547C (en) * 1988-12-02 1992-06-02 Jerzy A. Dobrowolski Optical interference electroluminescent device having low reflectance
KR910017908A (en) * 1990-03-14 1991-11-05 이헌조 EL display element
JPH0712359A (en) * 1993-06-25 1995-01-17 Tomeji Kawasaki Exhaust apparatus for cooking for multiple dwelling house
JPH07211458A (en) * 1994-01-17 1995-08-11 Fuji Electric Co Ltd Thin film electroluminescent element
US5504389A (en) * 1994-03-08 1996-04-02 Planar Systems, Inc. Black electrode TFEL display
GB9901334D0 (en) 1998-12-08 1999-03-10 Cambridge Display Tech Ltd Display devices
CA2352390A1 (en) * 2001-07-04 2003-01-04 Luxell Technologies Inc. Contrast enhancement apparatus
AU2003236752A1 (en) 2002-06-11 2003-12-22 Hofstra, Peter, G. Oled display with contrast enhancing interference members
US7495388B2 (en) 2004-01-08 2009-02-24 Samsung Electronics Co., Ltd. Display device, and method of manufacturing the display device
US8212474B2 (en) 2004-01-08 2012-07-03 Samsung Electronics Co., Ltd. Display device, and method of manufacturing the display device
JP4757186B2 (en) * 2006-12-28 2011-08-24 キヤノン株式会社 Organic light emitting device array and organic light emitting device array package

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4099091A (en) * 1976-07-28 1978-07-04 Matsushita Electric Industrial Co., Ltd. Electroluminescent panel including an electrically conductive layer between two electroluminescent layers
CA1144265A (en) * 1978-12-29 1983-04-05 John M. Lo High contrast display device having a dark layer
FI60332C (en) * 1980-04-24 1981-12-10 Lohja Ab Oy ELEKTROLUMINENSSTRUKTUR

Also Published As

Publication number Publication date
FR2513415A1 (en) 1983-03-25
GB2106317A (en) 1983-04-07
FR2513415B1 (en) 1987-08-28
DE3231727A1 (en) 1983-04-07
GB2106317B (en) 1985-06-19
JPS5858583A (en) 1983-04-07

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