GB2176047A - Cathode ray tubes - Google Patents
Cathode ray tubes Download PDFInfo
- Publication number
- GB2176047A GB2176047A GB08510865A GB8510865A GB2176047A GB 2176047 A GB2176047 A GB 2176047A GB 08510865 A GB08510865 A GB 08510865A GB 8510865 A GB8510865 A GB 8510865A GB 2176047 A GB2176047 A GB 2176047A
- Authority
- GB
- United Kingdom
- Prior art keywords
- thin
- film
- screen
- cathode ray
- crystallites
- 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.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
- H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
- H01J29/18—Luminescent screens
- H01J29/20—Luminescent screens characterised by the luminescent material
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
- C09K11/7783—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals one of which being europium
- C09K11/7784—Chalcogenides
- C09K11/7787—Oxides
Abstract
A thin-film cathode ray tube screen incorporates, in the thin-film, crystallites of average size in the range 0.025 mu m to 0.55 mu m (preferably 0.05 mu m to 0.35 mu m) thereby to enhance the brightness characteristics of the screen. The thin-film is formed of Yttrium Oxide (Y2O3) doped with 5 to 10 weight percent of Europium Oxide (Eu2O). The method of manufacturing the screen, includes depositing a thin-film on a substrate, and then annealing in the temperature range 1000 DEG C to 1500 DEG C (preferably between 1050 DEG C and 1250 DEG C) in order to promote the growth of crystallites within the thin-film. Preferably, the method includes sputter deposition of the phosphor material in the form of a thin-film followed by thermal annealing in air. <IMAGE>
Description
SPECIFICATION
Cathode ray tubes
The present invention relates to a thin-film cathode ray tube screen, and to a method of manufacturing a thin-film cathode ray tube screen.
Thin film deposition is a potentially attractive method of CRT screen manufacture because of the control which can be exercised over the process.
The properties of thin film CRT screens are well known and usually one attempts to achieve the ideal case of the optically perfect, non-scattering film. However, the light-trapping characteristic of these films militates against the general adoption of this technology.
An object of the present invention is to provide a thin-film cathode ray tube screen with substantially improved brightness characteristics as compared with conventional thin-film cathode ray tube screens.
The present invention provides a thin-film cathode ray tube screen incorporating, in the thin-film, crystallites of average size in the range 0.025 am to 0.55 Fm (preferably 0.05pm to 0.35 Fm) thereby to enhance the brightness characteristics of the screen.
The present invention also provides a method of manufacturing a thin-film cathode ray tube screen, the method including depositing a thin-film on a substrate, and then annealing in the temperature range 1000"C to 1 500 C (preferably between 1050"C and 12500C) in order to promote the growth of crystallites within the thin-film.
Preferably, the method includes spatter deposition of the phosphor material in the form of a thinfilm followed by thermal annealing in air.
Preferably the thin-film is formed of Yttrium Ox
ide (Y2O3) doped with 5 to 10 weight percent of Eu
ropium Oxide (Eu2O).
The method is applicable to all suitable oxygendominated cathodoluminescent materials, e.g. Ytt
rium aluminium oxide: terbium.
In the present invention, the use of an annealing temperature of 1200 C may provide crystallites which are approximately 0.3 Fm in size, while resulting in the light output being increased by a factor of 2 to 3 as compared to conventional thin-film screens. The film remains in intimate contact with the substrate. Thus by annealing at temperatures
at which crystallites of approximately 0.3 to 0.5 iim are formed, a phosphor screen is obtained which
has an efficiency about 30% of a powder screen, a very high resolution capability and an ability to withstand high electron beam powers. Such a screen has applications, in for example, projection
cathode ray tubes.
The method of the present invention provides for the controlled growth of crystals in the film to a
size which promotes brightness characteristics of the thin-film sceen.
In order that the invention may more readily be
understood, a description is now given, by way of
example only, with reference to the accompanying
drawings, in which:
Figures 1 and 2 are graphs illustrating the significant effect of the methods embodying the present invention; and
Figure 3 is the photo-luminescence spectrum of a thin-film screen embodying the present invention, annealed to 1200"C.
Films of binary oxide Y2:Eu being 2-3pm thick were deposited on sapphire substrates by RF magnetron sputtering. Substrate temperature was controlled during deposition using an external heater.
After deposition films were annealed at various temperatures by heating in air, to a maximum of 1500"C.
Both luminescent and structurai changes in the thin film were examined as a function of annealing temperature. UV photoluminescence and cathodoluminescence were measured. Structure was studied. Optical reflectance and transmission were measured. Screen resolution limit was estimated using optical projection of a TV test chart.
Measurements of the total emission of some samples were made using an integrating sphere in order to compare the intrinsic efficiency with that of a powder screen.
The results show that the brightness increases progressively as the thin film is annealed to higher temperature (Figure 1) until at about 1200"C it levels off, to one third that o'f the best available powder phosphor screen (i.e. 6 lumens/watt). Figure 2 shows that the film becomes opaque at the higher annealing temperatures. The reason for the increased opacity is the progressive growth of crystallites with temperature, which crystallites are uniform in size. There is indication of orientation.
At 1200"C, the average size of these is 0.1 > m (cf 1 2 m for a typical powder). Good adhesion to the substrate is retained for all annealing temperatures. As deposited, films are predominantly amorphous, with "crystallisation" (shown by the appearance of sharp diffraction lines and the normal crystal luminescence spectrum). Screens annealed at 1000"C are capable of displaying 250 line pairs/mm, reducing to 150 line pairs/mm at 1200"C.
This compares with values of 100 line pairs/mm for the best fine grain powder CRT screens. Films annealed at 1500 C show a much reduced brightness and an altered luminescence spectrum, similar to that reported for YAG:Eu.
The intrinsic efficiency of the thin film screens is between 0.3 and 0.5 of the brightest powder screens of Y2O3:Eu (average particle size 7 Fm).
All these results relate to samples deposited at á substrate temperature of 1500C. For samples deposited at higher temperatures, both the "crystallisation" point and the growth of large crystallites can be significantly altered.
The brightness increases observed with annealing are due to two effects:
1. improved conversion efficiency, through the healing of defects, etc., shown by the changes in the luminescence spectra and X-ray diffraction data.
2. the breakdown in the light trapping mechanism through the growth of crystallites sufficiently large to scatter the emitted light.
From optical and other measurements, it appears that the former is dominant below 100000 and the latter above this temperature. The conditions for maximum brightness probably represent the limit for thermally annealing this film/substrate combination. The limited "external" efficiency compared with the brightest powder screens is the result partly of the low intrinsic efficiency and partly the escape limitation imposed by the difference in refractive indices of film and substrate while they remain in good contact. An explanation for the lower intrinsic efficiency of the thin-film screens is not apparent; they are of like chemical composition and the annealing conditions are similar to those for powders. It is spectulated that it may be associated with the smaller volume of the individual crystallites in the thin films.Even at 1200 C, the thin film crystallite size is significantly smaller than a typrcal fine grain powder, explaining the superior resolution performance. The implication from examination of the adhesion is that the heat dissipation properties of the screen remain superior to those of powder screens for all temperatures.
The CRT screens made by thin film deposition and controlled growth of the phosphor crystals contain crystals which are well ordered, in good thermal contact with the substrate and about one tenth the size of so called "fine grain" powder crystals. Optical measurements show a resolution capability at least 2 1/2 times that of powder screens. Maximum luminous efficiencies equivalent to 6 lumens/watt have been observed for Y203:Eu.
Other results have produced increases in the mean size of granules/crystallites in the film from less than 0.1 pm to approximately 0.3 m moving from 700"C to 120000 annealing temperature.
Annealing above 150000 may lead to aluminium contamination from the sapphire substrate into the film, causing degradation in luminescent properties.
Claims (9)
1. A thin-film cathode ray tube screen incorporating, in the thin-film, crystallites of average size in the range 0.025 Fm to 0.55 pm thereby to enhance the brightness characteristics of the screen.
2. A screen according to Claim 1, incorporating crystallites of average size in the range 0.05 Fm to 0.35 am.
3. A screen according to Claim 1 or 2, wherein the thin-film is formed of Yttrium Oxide (Y,O,) doped with 5 to 10 weight percent of Europium
Oxide (Eu2O).
4. A thin-film cathode ray tube screen substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
5. A method of manufacturing a thin-film cathode ray tube screen, the method including depositing a thin-film on a substrate, and then annealing in the temperature range 100000 to 1500"C in order to promote the growth of crystallites within the thin-film.
6. A method according to Claim 5, comprising annealing in the temperature range 1050"C to 1250"C.
7. A method according to Claims 5 or 6, includ- ing sputter deposition of the phosphor material in the form of a thin-film followed by thermal annealing in air.
8. A method of manufacturing a thin-film cathode ray tube screen, the method being substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
9. A thin-film cathode ray tube sCreen manufactured by the method -of any one of Claims 5 to 8.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08510865A GB2176047A (en) | 1985-04-29 | 1985-04-29 | Cathode ray tubes |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08510865A GB2176047A (en) | 1985-04-29 | 1985-04-29 | Cathode ray tubes |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8510865D0 GB8510865D0 (en) | 1985-06-05 |
| GB2176047A true GB2176047A (en) | 1986-12-10 |
Family
ID=10578382
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08510865A Withdrawn GB2176047A (en) | 1985-04-29 | 1985-04-29 | Cathode ray tubes |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2176047A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0432744A2 (en) * | 1989-12-12 | 1991-06-19 | Kabushiki Kaisha Toshiba | Color cathode ray tube |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB874288A (en) * | 1959-02-26 | 1961-08-02 | Hughes Aircraft Co | Electronic storage device |
| GB901367A (en) * | 1957-04-19 | 1962-07-18 | Davohn Corp | Method of making luminescent screens and systems for producing coloured images therewith |
| GB1030139A (en) * | 1962-12-07 | 1966-05-18 | Rca Corp | Method of making luminescent screens |
-
1985
- 1985-04-29 GB GB08510865A patent/GB2176047A/en not_active Withdrawn
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB901367A (en) * | 1957-04-19 | 1962-07-18 | Davohn Corp | Method of making luminescent screens and systems for producing coloured images therewith |
| GB874288A (en) * | 1959-02-26 | 1961-08-02 | Hughes Aircraft Co | Electronic storage device |
| GB1030139A (en) * | 1962-12-07 | 1966-05-18 | Rca Corp | Method of making luminescent screens |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0432744A2 (en) * | 1989-12-12 | 1991-06-19 | Kabushiki Kaisha Toshiba | Color cathode ray tube |
| EP0432744A3 (en) * | 1989-12-12 | 1992-01-02 | Kabushiki Kaisha Toshiba | Color cathode ray tube |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8510865D0 (en) | 1985-06-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |