CA1243762A - Thin film electroluminescent display device - Google Patents
Thin film electroluminescent display deviceInfo
- Publication number
- CA1243762A CA1243762A CA000464835A CA464835A CA1243762A CA 1243762 A CA1243762 A CA 1243762A CA 000464835 A CA000464835 A CA 000464835A CA 464835 A CA464835 A CA 464835A CA 1243762 A CA1243762 A CA 1243762A
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- CA
- Canada
- Prior art keywords
- display device
- electroluminescent display
- dark field
- layer
- field layer
- 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
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Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B33/00—Electroluminescent light sources
- H05B33/12—Light sources with substantially two-dimensional radiating surfaces
- H05B33/22—Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of auxiliary dielectric or reflective layers
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- Electroluminescent Light Sources (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A thin film electroluminescent display device comprising a transparent electrode layer, a segmented electrode layer, an electroluminescent phosphor layer between the electrode layers, and an improved dark field material disposed as a layer between the phosphor and segmented electrode layers. The improved dark field layer is of a composition of a dielectric material, such as the preferred magnesium oxide, and a noble metal, which in the preferred version is gold. These materials comprising the dark field composition may be co-evaporated by an electron beam evaporation or other suitable deposition technique. The composition of dark field material provides for contrast enhancement, is non-toxic, and is readily analyzable.
A thin film electroluminescent display device comprising a transparent electrode layer, a segmented electrode layer, an electroluminescent phosphor layer between the electrode layers, and an improved dark field material disposed as a layer between the phosphor and segmented electrode layers. The improved dark field layer is of a composition of a dielectric material, such as the preferred magnesium oxide, and a noble metal, which in the preferred version is gold. These materials comprising the dark field composition may be co-evaporated by an electron beam evaporation or other suitable deposition technique. The composition of dark field material provides for contrast enhancement, is non-toxic, and is readily analyzable.
Description
i2 D-22,048 A THIN ~IL~ PJL~CTROLUMINESC~NT DISPLAY DEVIC~
BACKGROU~D OF TH~ INVENTION
The present invention relates in general to a ~hin film elec-troluminescen~ display device and is concerned, more par~icularly, with an improved dark field material for s~lch a thin film elec~roluminescent display device.
~ lec~roluminescen~ devices ~enerally comprise a phosphor layer disposed between two elec~rode layers with olle of the electrodes being transparen~ so as to permit viewability of the phosphor layer. It is known to provid~ a dark field layer behind the phosphor layer in order to improve the con~rast ratio of the device when u~ing a seymented back electrode layer; that is to say, to provide visibility of the phosphor layer overlying the back electrod~ segments even under ambient condi~ions of high brightness. See. U.S. Patent 3~560,7~4 for an example of a dark field layer, the material of which may comprise ~rsenic sulphide, arseniG
selenide, arsenic sulfoselenide or mixtures thereof.
However, these arsenic co~pounds ei~her do not provide a satisfactory dark color or ~hey change color during use.
Perhaps ~he most common dark field material presently being used is cadmium telluride (CdTe). Althou~h the CdTe layer provides for enhancement in contrast between ~he displayed information and the background, one of the problems associated with the CdTe composition is that it i5 toxic and the material does not meet sa~ety specifica~ions for commercial produc~s as reguired by OSHA (Occupational Safe~y and Heal~h Act~.
,.
~L2~376~
D-22,048 Accordi~g to one prior solution ~o ~his toxicity proble~5 an electroluminescent device has a dark field layer comprising a cermet of chromium oxide - chromiu~
(Cr203/Cr). Although overcoming the toxici~y problem, ,.-7~;~
D-22,048 this cermet comprises a combination Df ~ metal (Cr~ and an o~de ~Cr203) of the same base metal9 thereby renderins the dar~ field composition d1fficult, if not impossible, for an61ysis of the constituent proportions. Such analysi~ is important to enable 5 precise control of the constituent proportion for providin~ optimum results.
Accordin~ly, it is an object of the present invention to provide an improved electroluminescent display device and in particular an improved dark field material for such a device.
Another object of the present invention is to provide an improved dark field in accordanre with the precedin~ object and which is characterized by an improved contrast ratio of the device.
Still another object of the present invention is to provide a dark field material in accordance with the precedin~ objects and which is non-to~ic and meets the safety specifications for commercial products required by OSHA.
A further object of the present invention is to provide an improved dark field layer in a thin film electroluminescent display device in which for at least some applications, only a single transparent dielectric layer of the device is employed in comparison with the typical first and second transparent dielectric layers used in the past in electroluminescent thin film display de~ices.
Still a furtber object of the present invention is to provide an improved dark field material for a thin film electroluminescent display device in which the dark field layer is formed of constituents which are readily analyzable, and thus precisely controllable, to provide enhanced fle~ibility in controllin~
parameters of the dark field layer such as contrast ratio.
~3~7~2 According to one aspect of the present invention there is provided an electroluminescent display device comprising a transparent electrode layer, a segmented electrode layer, an electroluminescent phosphor layer disposed between said electrode layers, and a dark field layer of a composition of a dielectric material with a noble metal, said dark field layer being interposed between said electroluminescent phosphor layer and said segmented electrode layer, wherein there is only a single transparent dielectric layer adjacent the electrolumines-cent phosphor layer.
BRIEF DESCRIPTION OF THE DRAWINGS
Numerous other objects, features and advantages of theinvention should now become apparent upon a reading of -the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic cross-sectional view showing the multiple layers of a thin film elec-troluminescent display device including the dark field layer oE -this invention; and FIG. 2 is a schematic cross-sectional view showing an alternative construction of the thin film electroluminescent display device showing a single transparent dielectric layer rather than the two dielec-tric layers depicted in FIG. 1.
~3~7~
D-22,048 DESCRIP~ION OF PREFERRED E~80DI~ENT
In accordance with the present invention, the dark field msterial for a thin film ele~trolum;nescent display devic~ is formed by a composition of 8 dielectric material with a noble metal. The dark field layer serves the basic purpose oi` enhancin~ the contrcst between the displayed information which is usually in segment form and the back~round. In order to eliminste the prior art problem associated with CdTe d~rk field layers, which are toxic, and yet provide suitable analyzability o~ the dark field composition, it has been found in accordance with the present invention that a composition of 7 for example, magnesium oxide and gold which are co-evaporated, preferably by an electron beam technique, provide a dark field material that is non-toxic, is readily analyzabl~e ~nd meets the safety specifications for commerclal products. A layer of such material has not previously be~n employed at all in the construction oP electroluminescent display devices, although, a ~O/Au film has been previously evaluated as a solar absorbin~
material for solar pane-ls. In this re~ard, see U.S. Patent 4,312,915; also see the article by Fan and Zavracky, Applied Physics Letters, Volume 29, No. 8, 15 October, 1976, pa~e 478-480. Also see the article by Berthier and Lafait in Thin Solid Films 89 (1982~
213~220 entitled "~ptical Properties of Au-M~O Cermet Thin Films:
Percolation Threshold and Grain Size Effect". The latter article is concerned primarily with the method of deposition and associated optical properties.
In addition to the advantage of non-to~icity of the composition of this inventlon, the lsyer has also been found to unexpectedly provide contrast enhancement.
Uith reference to the drawin~, it is noted that in FIG. 1 tbere is shown a ~ersion of an electroluminescent display device lncorporatin~ the dark field of this invention. In FIG. 2, one of the two transparent dielectric layers shown in FIG. 1 has been removed because, in accordance with the present invention~ the 3t;~
D--22 ,048 improved dar~ field layer also functions n~ a substltute for one of the dielectric layerg. In other words the dielectric/noble metal composition serves both as the dark field and as the second dielectric.
In FIGS. 1 and Z, li~e reference charscters are used to identify li~e layers of each embodiment disclosed. Thus, there is showm a glass substrate 10 on which are formed a number of multiple thin-film layers, which may be enclosed by a glass seal 11. These layers include a transpare~t electrode 12, a first transparent dielectric layer 14, ar electroluminescent phosphor lay~r 16, a second transparent dielectric layer 18, a dark field layer 20, and a back se~mented electrode 22. In FIGS. 1 and 2 the transparent dielectric layers may be of yttria, and the electroluminescent phosphor layer may be of, for e~ample, zinc sulphide. In the embodiment of FIG. 1, the second transparent dielectric layer 18 is shown, but it is noted that in the embodiment of FIG. 2, this layer i5 not present., The dark field layer 20 in FIG. 2 ;nstead serves both as the dark field and as the second dielectric layer.
The composition of the dark field layer 20, which in its broadest sense comprises a dielectric material, preferably a ceramic, and a noble metal, preferably ~old, may be deposited by co-evaporation using standard deposition techniques. In accordance with one technigue, co-evaporation is used with e-beam equipment.
The evaporation may take place in one chamber of a two-chamber system. The two chamber system has two e-beam guns, each with its own power supply. In the preferred version, ma~nesium oxide may be in pellet form and loaded into one crucible, and gold is disposed in the secoDd crucible. The deposition may be measured by means oP
conventional crystal monitors. One crystal monitor is placed over each crucible bein~ disposed as close as possible to the position where the substrate is. The co-evaporation technigue usin~ separate crucibles is carried out iD a vacuum of preferably better tha~ 1 x torr. The volume percentage of ~old is varied with the gold concentration preferably in the range of 6%-10~ by volume.
~2~6~
~-2~,04fl The percentage of gold in the composition is instrumental in controlling ~he resistivi~y of the cerme~.
In one test that was carried out~ the dark field layer had a thickness of 0,5 micron. The preerred film thickness is in the range of 5000-9000 Angstroms. The la~eral resistance between back electrode seg~en~s i8 on the order of 10 megohms while the perpendicular resis~ance across the f;lm thickness is on the order of lK ohm or less. A contrast ratio of 2:1 is mea~ured at an ambient light lsvel of 2500 foot-candles with the back electrode segments at 160 ~ol~s and 60 foo~-candles, Wi~h those parameters, display devices have baen operdted successfully up to 500 hours of operating time, With regard to measurements of contrast be~ween the displayed informa~ion and the background, such measursments have been taken by shining a Sylvania Sun-Gun lamp at ~he lighted and unlighted display segments. The Sun-Gun lamp was set at an ou~put of 3500 foot-candles. In two differen~ respective devices ~hat were ts~te~, the contrast ratio measured wa~ 4.2 and 5.3, respectively.
In accordance with another technigue for forming the dark field layer~ sputkering may be used in a reac~ive a~mosphere of say argon and oxygen in a ratio of 70%-30%, respectively.
One of the primdry advantages of the composition MgO/Au is that the material itself as well as the process forming it, is non-toxic, ~lso, ~he admixed .
~2~
D-22,09n - 6a -~etal (Au) and the metal of the ~etal oxide (~y) are ~WQ
different ma~erials and thus the ratio be~een these constituents is readily analyzable and, ~hus, provides f~r an added degree of control over such parameters o~
the dark field layer as electrical conductivi~y and optical absorption.
3~
D~22,Ob8 Reference has been made to the preferred layer construction of magnesium oxide and ~old. Howsver, it is understood that in accordance with other embodiments of the inYention the composition may comprise other noble metals in plac of the gold such as platinum or silver. The dielectric portion of the composition may be a ceramic. This can be a metal o~ide or a metal nitride (such as aluminum nitride) or can even be a semiconductor such as silicon dio~ide or ger~anium dio%ide. Ths noble metal portion of the composition is in the form of a relatively stable metal thus not tendin~ to react with the metnllic in the ceramic portion of the composition. The noble metal, such a gold does not readily oxidize if it is mixed with the magnesium ox;de.
Havin~ now described fl limited number of embodiments of the p~e~e~t lnvention, it should now be apparent to those skilled in the art that numerous other embodiments are contemplated as falling within the scope of this inYention as defined by the appended claims, for e~mple, the dark field layer may be deposited by techniques other than co-e~aporation or electron beam evaporation, such as by sputtering.
,, , 3~2 " SUPPLEMENTARY DISCLOSURE
In the Principal Disclosure there is shown an electro-luminescent display device comprising a transparent electrode layer, an electroluminescent phosphor layer, and a dark field layer. This embodiment has since been modified to provide an improved dark field layer in a thin film electroluminescent display device in which, for at least some applications, only a single transparent dielectric layer of the device is utilized and to provide an improved dark field material in which the dark field layer is formed of constituents which are readily analyzable, and thus precisely controllable, to provide enhanced flexibility in controlling parameters of the dark field layer such as spectral transmission.
According to another aspect there is provided an electro-luminescent display device comprising a glass substrate, a -trans-parent electrode layer, a dielectric layer, an electroluminescent phosphor layer over said dielectric layer, a dark field layer disposed above said phosphor layer and a segmented electrode layer, said dark field layer of a non-toxic composition of a dielectric materlal with a noble metal having a spec-tral transmission of less than about 20% in the range of about 400 nanometers to about 800 nanometers (nm).
In the drawings:
FIG. 3 is a graph illustrating the transmission curves of three cermet samples having varying concentrations of gold as the noble metal.
Referring to the figures, initially, one of the experi-ments that was carried out with the MgO-Au cermet involved using 25~ by volume of gold in the dark field layer. The films were formed to be totally opaque but were highly conductive, therefore all subsequent films were made with less gold, ranging between 6%-14% (by volume) of. gold. Figure 3 illustrates the transmiss-ion curves of three cermets with varying amounts of gold as the noble metal. In this particular embodiment, gold is used as the noble metal but it is possible to substitute platinum or silver as the noble metal and to develop transmission curves in wave-lengths having a range of about 400 nanometers (nm) to about 800 nm (the visible range). Curve A illustrates a cermet sample with 93.5% MgO and 6.5% Au for the range from 400 nm-800 nm and a thickness of about 4500 Angstroms. Curve C illustrates a -SD 2~ 7~
cermet sample with 86% MgO and 14% Au for the same wavelength range and a film thickness of about A800 Angstroms. The sample of curve A exhibited good dielectric properties, but the film was too transparent; the sample of Curve C was sufficiently opaque, but did not satisfy the electrical requirements of lateral resist-ance of greater than or equal to 10 megaohms (M n ).
The sample of curve B, on the other hand, which had 92% MgO and 8% Au and a film thickness of about 9000 Angstroms, satisfied the optical as well as the electrical requirements by having a spectral transmission below 20%, a lateral resistance in the order of 10 megaohms and a perpendicular resistance below lK ohm. Spectral transmission values of above 20% (as in Curve A) would most likely prove to be transparent while values too far below 20% could be sufficiently opaque but may prove to be too conductive. The present film was used in a display device with a second dielectric layer as well without an additional dielectric layer where the dark field acts itself as a second dielectric.
The preferred film thickness of the sample of Curve C
was between about 5000 and about 9000 Angstroms for the cerme-t utilizing gold as the noble metal and a spectral transmission percent of about 20% for a wavelength that approached 800 nm (see Figure 3). It is evident from this embodiment that for other noble metal cermets, the volume percent of metal and the film thickness can be varied to arrive at the preferred optical (% spectral transmission) and electrical (perpendicular and lat-eral resistances) properties.
. .
BACKGROU~D OF TH~ INVENTION
The present invention relates in general to a ~hin film elec-troluminescen~ display device and is concerned, more par~icularly, with an improved dark field material for s~lch a thin film elec~roluminescent display device.
~ lec~roluminescen~ devices ~enerally comprise a phosphor layer disposed between two elec~rode layers with olle of the electrodes being transparen~ so as to permit viewability of the phosphor layer. It is known to provid~ a dark field layer behind the phosphor layer in order to improve the con~rast ratio of the device when u~ing a seymented back electrode layer; that is to say, to provide visibility of the phosphor layer overlying the back electrod~ segments even under ambient condi~ions of high brightness. See. U.S. Patent 3~560,7~4 for an example of a dark field layer, the material of which may comprise ~rsenic sulphide, arseniG
selenide, arsenic sulfoselenide or mixtures thereof.
However, these arsenic co~pounds ei~her do not provide a satisfactory dark color or ~hey change color during use.
Perhaps ~he most common dark field material presently being used is cadmium telluride (CdTe). Althou~h the CdTe layer provides for enhancement in contrast between ~he displayed information and the background, one of the problems associated with the CdTe composition is that it i5 toxic and the material does not meet sa~ety specifica~ions for commercial produc~s as reguired by OSHA (Occupational Safe~y and Heal~h Act~.
,.
~L2~376~
D-22,048 Accordi~g to one prior solution ~o ~his toxicity proble~5 an electroluminescent device has a dark field layer comprising a cermet of chromium oxide - chromiu~
(Cr203/Cr). Although overcoming the toxici~y problem, ,.-7~;~
D-22,048 this cermet comprises a combination Df ~ metal (Cr~ and an o~de ~Cr203) of the same base metal9 thereby renderins the dar~ field composition d1fficult, if not impossible, for an61ysis of the constituent proportions. Such analysi~ is important to enable 5 precise control of the constituent proportion for providin~ optimum results.
Accordin~ly, it is an object of the present invention to provide an improved electroluminescent display device and in particular an improved dark field material for such a device.
Another object of the present invention is to provide an improved dark field in accordanre with the precedin~ object and which is characterized by an improved contrast ratio of the device.
Still another object of the present invention is to provide a dark field material in accordance with the precedin~ objects and which is non-to~ic and meets the safety specifications for commercial products required by OSHA.
A further object of the present invention is to provide an improved dark field layer in a thin film electroluminescent display device in which for at least some applications, only a single transparent dielectric layer of the device is employed in comparison with the typical first and second transparent dielectric layers used in the past in electroluminescent thin film display de~ices.
Still a furtber object of the present invention is to provide an improved dark field material for a thin film electroluminescent display device in which the dark field layer is formed of constituents which are readily analyzable, and thus precisely controllable, to provide enhanced fle~ibility in controllin~
parameters of the dark field layer such as contrast ratio.
~3~7~2 According to one aspect of the present invention there is provided an electroluminescent display device comprising a transparent electrode layer, a segmented electrode layer, an electroluminescent phosphor layer disposed between said electrode layers, and a dark field layer of a composition of a dielectric material with a noble metal, said dark field layer being interposed between said electroluminescent phosphor layer and said segmented electrode layer, wherein there is only a single transparent dielectric layer adjacent the electrolumines-cent phosphor layer.
BRIEF DESCRIPTION OF THE DRAWINGS
Numerous other objects, features and advantages of theinvention should now become apparent upon a reading of -the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic cross-sectional view showing the multiple layers of a thin film elec-troluminescent display device including the dark field layer oE -this invention; and FIG. 2 is a schematic cross-sectional view showing an alternative construction of the thin film electroluminescent display device showing a single transparent dielectric layer rather than the two dielec-tric layers depicted in FIG. 1.
~3~7~
D-22,048 DESCRIP~ION OF PREFERRED E~80DI~ENT
In accordance with the present invention, the dark field msterial for a thin film ele~trolum;nescent display devic~ is formed by a composition of 8 dielectric material with a noble metal. The dark field layer serves the basic purpose oi` enhancin~ the contrcst between the displayed information which is usually in segment form and the back~round. In order to eliminste the prior art problem associated with CdTe d~rk field layers, which are toxic, and yet provide suitable analyzability o~ the dark field composition, it has been found in accordance with the present invention that a composition of 7 for example, magnesium oxide and gold which are co-evaporated, preferably by an electron beam technique, provide a dark field material that is non-toxic, is readily analyzabl~e ~nd meets the safety specifications for commerclal products. A layer of such material has not previously be~n employed at all in the construction oP electroluminescent display devices, although, a ~O/Au film has been previously evaluated as a solar absorbin~
material for solar pane-ls. In this re~ard, see U.S. Patent 4,312,915; also see the article by Fan and Zavracky, Applied Physics Letters, Volume 29, No. 8, 15 October, 1976, pa~e 478-480. Also see the article by Berthier and Lafait in Thin Solid Films 89 (1982~
213~220 entitled "~ptical Properties of Au-M~O Cermet Thin Films:
Percolation Threshold and Grain Size Effect". The latter article is concerned primarily with the method of deposition and associated optical properties.
In addition to the advantage of non-to~icity of the composition of this inventlon, the lsyer has also been found to unexpectedly provide contrast enhancement.
Uith reference to the drawin~, it is noted that in FIG. 1 tbere is shown a ~ersion of an electroluminescent display device lncorporatin~ the dark field of this invention. In FIG. 2, one of the two transparent dielectric layers shown in FIG. 1 has been removed because, in accordance with the present invention~ the 3t;~
D--22 ,048 improved dar~ field layer also functions n~ a substltute for one of the dielectric layerg. In other words the dielectric/noble metal composition serves both as the dark field and as the second dielectric.
In FIGS. 1 and Z, li~e reference charscters are used to identify li~e layers of each embodiment disclosed. Thus, there is showm a glass substrate 10 on which are formed a number of multiple thin-film layers, which may be enclosed by a glass seal 11. These layers include a transpare~t electrode 12, a first transparent dielectric layer 14, ar electroluminescent phosphor lay~r 16, a second transparent dielectric layer 18, a dark field layer 20, and a back se~mented electrode 22. In FIGS. 1 and 2 the transparent dielectric layers may be of yttria, and the electroluminescent phosphor layer may be of, for e~ample, zinc sulphide. In the embodiment of FIG. 1, the second transparent dielectric layer 18 is shown, but it is noted that in the embodiment of FIG. 2, this layer i5 not present., The dark field layer 20 in FIG. 2 ;nstead serves both as the dark field and as the second dielectric layer.
The composition of the dark field layer 20, which in its broadest sense comprises a dielectric material, preferably a ceramic, and a noble metal, preferably ~old, may be deposited by co-evaporation using standard deposition techniques. In accordance with one technigue, co-evaporation is used with e-beam equipment.
The evaporation may take place in one chamber of a two-chamber system. The two chamber system has two e-beam guns, each with its own power supply. In the preferred version, ma~nesium oxide may be in pellet form and loaded into one crucible, and gold is disposed in the secoDd crucible. The deposition may be measured by means oP
conventional crystal monitors. One crystal monitor is placed over each crucible bein~ disposed as close as possible to the position where the substrate is. The co-evaporation technigue usin~ separate crucibles is carried out iD a vacuum of preferably better tha~ 1 x torr. The volume percentage of ~old is varied with the gold concentration preferably in the range of 6%-10~ by volume.
~2~6~
~-2~,04fl The percentage of gold in the composition is instrumental in controlling ~he resistivi~y of the cerme~.
In one test that was carried out~ the dark field layer had a thickness of 0,5 micron. The preerred film thickness is in the range of 5000-9000 Angstroms. The la~eral resistance between back electrode seg~en~s i8 on the order of 10 megohms while the perpendicular resis~ance across the f;lm thickness is on the order of lK ohm or less. A contrast ratio of 2:1 is mea~ured at an ambient light lsvel of 2500 foot-candles with the back electrode segments at 160 ~ol~s and 60 foo~-candles, Wi~h those parameters, display devices have baen operdted successfully up to 500 hours of operating time, With regard to measurements of contrast be~ween the displayed informa~ion and the background, such measursments have been taken by shining a Sylvania Sun-Gun lamp at ~he lighted and unlighted display segments. The Sun-Gun lamp was set at an ou~put of 3500 foot-candles. In two differen~ respective devices ~hat were ts~te~, the contrast ratio measured wa~ 4.2 and 5.3, respectively.
In accordance with another technigue for forming the dark field layer~ sputkering may be used in a reac~ive a~mosphere of say argon and oxygen in a ratio of 70%-30%, respectively.
One of the primdry advantages of the composition MgO/Au is that the material itself as well as the process forming it, is non-toxic, ~lso, ~he admixed .
~2~
D-22,09n - 6a -~etal (Au) and the metal of the ~etal oxide (~y) are ~WQ
different ma~erials and thus the ratio be~een these constituents is readily analyzable and, ~hus, provides f~r an added degree of control over such parameters o~
the dark field layer as electrical conductivi~y and optical absorption.
3~
D~22,Ob8 Reference has been made to the preferred layer construction of magnesium oxide and ~old. Howsver, it is understood that in accordance with other embodiments of the inYention the composition may comprise other noble metals in plac of the gold such as platinum or silver. The dielectric portion of the composition may be a ceramic. This can be a metal o~ide or a metal nitride (such as aluminum nitride) or can even be a semiconductor such as silicon dio~ide or ger~anium dio%ide. Ths noble metal portion of the composition is in the form of a relatively stable metal thus not tendin~ to react with the metnllic in the ceramic portion of the composition. The noble metal, such a gold does not readily oxidize if it is mixed with the magnesium ox;de.
Havin~ now described fl limited number of embodiments of the p~e~e~t lnvention, it should now be apparent to those skilled in the art that numerous other embodiments are contemplated as falling within the scope of this inYention as defined by the appended claims, for e~mple, the dark field layer may be deposited by techniques other than co-e~aporation or electron beam evaporation, such as by sputtering.
,, , 3~2 " SUPPLEMENTARY DISCLOSURE
In the Principal Disclosure there is shown an electro-luminescent display device comprising a transparent electrode layer, an electroluminescent phosphor layer, and a dark field layer. This embodiment has since been modified to provide an improved dark field layer in a thin film electroluminescent display device in which, for at least some applications, only a single transparent dielectric layer of the device is utilized and to provide an improved dark field material in which the dark field layer is formed of constituents which are readily analyzable, and thus precisely controllable, to provide enhanced flexibility in controlling parameters of the dark field layer such as spectral transmission.
According to another aspect there is provided an electro-luminescent display device comprising a glass substrate, a -trans-parent electrode layer, a dielectric layer, an electroluminescent phosphor layer over said dielectric layer, a dark field layer disposed above said phosphor layer and a segmented electrode layer, said dark field layer of a non-toxic composition of a dielectric materlal with a noble metal having a spec-tral transmission of less than about 20% in the range of about 400 nanometers to about 800 nanometers (nm).
In the drawings:
FIG. 3 is a graph illustrating the transmission curves of three cermet samples having varying concentrations of gold as the noble metal.
Referring to the figures, initially, one of the experi-ments that was carried out with the MgO-Au cermet involved using 25~ by volume of gold in the dark field layer. The films were formed to be totally opaque but were highly conductive, therefore all subsequent films were made with less gold, ranging between 6%-14% (by volume) of. gold. Figure 3 illustrates the transmiss-ion curves of three cermets with varying amounts of gold as the noble metal. In this particular embodiment, gold is used as the noble metal but it is possible to substitute platinum or silver as the noble metal and to develop transmission curves in wave-lengths having a range of about 400 nanometers (nm) to about 800 nm (the visible range). Curve A illustrates a cermet sample with 93.5% MgO and 6.5% Au for the range from 400 nm-800 nm and a thickness of about 4500 Angstroms. Curve C illustrates a -SD 2~ 7~
cermet sample with 86% MgO and 14% Au for the same wavelength range and a film thickness of about A800 Angstroms. The sample of curve A exhibited good dielectric properties, but the film was too transparent; the sample of Curve C was sufficiently opaque, but did not satisfy the electrical requirements of lateral resist-ance of greater than or equal to 10 megaohms (M n ).
The sample of curve B, on the other hand, which had 92% MgO and 8% Au and a film thickness of about 9000 Angstroms, satisfied the optical as well as the electrical requirements by having a spectral transmission below 20%, a lateral resistance in the order of 10 megaohms and a perpendicular resistance below lK ohm. Spectral transmission values of above 20% (as in Curve A) would most likely prove to be transparent while values too far below 20% could be sufficiently opaque but may prove to be too conductive. The present film was used in a display device with a second dielectric layer as well without an additional dielectric layer where the dark field acts itself as a second dielectric.
The preferred film thickness of the sample of Curve C
was between about 5000 and about 9000 Angstroms for the cerme-t utilizing gold as the noble metal and a spectral transmission percent of about 20% for a wavelength that approached 800 nm (see Figure 3). It is evident from this embodiment that for other noble metal cermets, the volume percent of metal and the film thickness can be varied to arrive at the preferred optical (% spectral transmission) and electrical (perpendicular and lat-eral resistances) properties.
. .
Claims (25)
1. An electroluminescent display device comprising a transparent electrode layer, a segmented electrode layer, an electroluminescent phosphor layer disposed between said electrode layers, and a dark field layer of a composition of a dielectric material with a noble metal, said dark field layer being interposed between said electroluminescent phosphor layer and said segmented electrode layer, wherein there is only a single transparent dielectric layer adjacent the electrolumin-escent phosphor layer.
2. An electroluminescent display device as set forth in claim 1 wherein the dark field layer has a film thickness in the range of 5000-9000 Angstroms.
3. An electroluminescent display device as set forth in claim 1 wherein the device has a contrast ratio of at least 2:1.
4. An electroluminescent display device as set forth in claim 1 wherein the composition of the dark field layer is deposited by co-evaporation from separate sources.
5. An electroluminescent display device as set forth in claim 1 wherein the noble metal comprises gold.
6. An electroluminescent display device as set forth in claim 1 wherein said dielectric material of the dark field layer comprises a metal oxide.
7. An electroluminescent display device as set forth in claim 6 wherein said metal oxide comprises magnesium oxide.
8. An electroluminescent display device as set forth in claim 1 wherein said dielectric material of the dark field layer comprises silicon dioxide.
9. An electroluminescent display device as set forth in claim 1 wherein said dielectric material of the dark field layer comprises germanium dioxide.
10. An electroluminescent display device as set forth in claim 1 wherein said dielectric material of the dark field layer comprises aluminum nitride.
11. An electroluminescent display device as set forth in claim 1 wherein said dielectric material of the dark field layer is comprised of a metal oxide, a metal nitride or a semiconductor.
CLAIMS SUPPORTED BY SUPPLEMENTARY DISCLOSURE
CLAIMS SUPPORTED BY SUPPLEMENTARY DISCLOSURE
12. An electroluminescent display device comprising a glass substrate, a transparent electrode layer, a dielectric layer, an electroluminescent phosphor layer over said dielec-tric layer, a dark field layer disposed above said phosphor layer and a segmented electrode layer, said dark field layer of a nontoxic composition of a dielectric material with a noble metal having a spectral transmission of less than about 20% in the range of about 400 nanometers to about 800 nano-meters (nm).
13. The electroluminescent display device according to claim 12 that includes only a single transparent dielectric layer adjacent the electroluminescent phosphor layer.
14. The electroluminescent display device according to claim 12 wherein the dark field layer has a film thickness in the range of about 5000 to about 9000 Angstroms.
15. The electroluminescent display device according to claim 12 wherein the device has a contrast ratio of at least 2:1.
16. The electroluminescent display device according to claim 12 wherein the composition of the dark field layer is deposited by co-evaporation from separate sources.
17. The electroluminescent display device according to claim 12 wherein said noble metal comprises gold.
18. The electroluminescent display device according to claim 12 wherein said dielectric material of the dark field layer comprises a metal oxide.
19. The electroluminescent display device according to claim 18 wherein said metal oxide comprises magnesium oxide.
20. The electroluminescent display device according to claim 12 wherein said dielectric material of the dark field layer comprises silicon dioxide.
21. The electroluminescent display device according to claim 12 wherein said dielectric material of the dark field layer comprises germanium dioxide.
22. The electroluminescent display device accord-ing to claim 12 wherein said dielectric material of the dark field layer comprises aluminum nitride.
23. The electroluminescent display device accord-ing to claim 12 wherein said dielectric material of the dark field layer is comprised of a metal oxide, a metal nitride or a semiconductor.
24. The electroluminescent display device accord-ing to claim 12 wherein said noble metal comprises platinum.
25. The electroluminescent display device according to claim 12 wherein said noble metal comprises silver.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US54022383A | 1983-10-11 | 1983-10-11 | |
| US540,223 | 1983-10-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1243762A true CA1243762A (en) | 1988-10-25 |
Family
ID=24154526
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000464835A Expired CA1243762A (en) | 1983-10-11 | 1984-10-05 | Thin film electroluminescent display device |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0140246B1 (en) |
| CA (1) | CA1243762A (en) |
| DE (1) | DE3466342D1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4849674A (en) * | 1987-03-12 | 1989-07-18 | The Cherry Corporation | Electroluminescent display with interlayer for improved forming |
| DE3712855A1 (en) * | 1986-09-29 | 1988-04-07 | Ricoh Kk | THICK LAYER ELECTROLUMINESCENT DEVICE |
| US6610352B2 (en) | 2000-12-22 | 2003-08-26 | Ifire Technology, Inc. | Multiple source deposition process |
| US8133554B2 (en) | 2004-05-06 | 2012-03-13 | Micron Technology, Inc. | Methods for depositing material onto microfeature workpieces in reaction chambers and systems for depositing materials onto microfeature workpieces |
| JP5355076B2 (en) * | 2005-04-15 | 2013-11-27 | アイファイアー・アイピー・コーポレーション | Magnesium oxide-containing barrier layer for dielectric thick film electroluminescent displays |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3560784A (en) * | 1968-07-26 | 1971-02-02 | Sigmatron Inc | Dark field, high contrast light emitting display |
| US4312915A (en) * | 1978-01-30 | 1982-01-26 | Massachusetts Institute Of Technology | Cermet film selective black absorber |
| 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 |
| JPS5871589A (en) * | 1981-10-22 | 1983-04-28 | シャープ株式会社 | Thin film el element |
-
1984
- 1984-10-05 CA CA000464835A patent/CA1243762A/en not_active Expired
- 1984-10-11 EP EP19840112241 patent/EP0140246B1/en not_active Expired
- 1984-10-11 DE DE8484112241T patent/DE3466342D1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0140246A1 (en) | 1985-05-08 |
| EP0140246B1 (en) | 1987-09-16 |
| DE3466342D1 (en) | 1987-10-22 |
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