Aluminum nitride passivated phosphors for electroluminescent displays
A novel structure is provided to improve the luminance and operating stability of phosphors used in ac thick film dielectric electroluminescent displays. The novel structure comprises aluminum nitride barrier layers in contact with the phosphor films to prevent phosphor degradation due to reaction with oxygen. The barrier layers can be deposited using vacuum deposition processes that are compatible with the processes used to deposit and anneal the phosphor films. The invention is particularly applicable to phosphors used in electroluminescent displays that employ thick dielectric layers subject to high processing temperatures to form and activate the phosphor films.
1. An improved phosphor film for a thick film dielectric electroluminescent display, said phosphor film selected from the group consisting of
(a) a rare earth activated alkaline earth phosphor having the formula AB x C y :RE wherein;
A is selected from one or more of the group consisting of Mg, Ca, Sr and Ba;
B is selected from one or more of the group consisting of Al, Ga and In;
C is selected from one or more of the group consisting of S and Se; and RE is a rare earth activator species;
(b) a rare earth or transition metal activated zinc selenide; and
(c) a rare earth or transition metal activated zinc sulfo-selenide, wherein said phosphor film of (a), (b) and (c) is provided with an aluminum nitride barrier layer on a top and/or bottom side of the phosphor film, and said aluminum nitride barrier layer has a thickness in a range of about 30 nm to about 50 nm when used in conjunction with said rare earth activated alkaline earth phosphor.
2. The phosphor film of claim 1 , wherein said rare earth activated alkaline earth phosphor comprises a thioaluminate phosphor.
3. The phosphor film of claim 2 , wherein C may also include oxygen at a relative atomic concentration that is less than 0.2 of the combined S and Se concentrations.
4. The phosphor film of claim 2 , wherein RE is selected from the group consisting of Eu and Ce.
5. The phosphor film of claim 1 , wherein said aluminum nitride barrier layer is provided on top of said phosphor of (a) to (c).
6. The phosphor film of claim 1 , wherein said aluminum nitride barrier layer is provided on the bottom of said phosphor of (a), (b), and (c).
7. The phosphor of claim 1 , wherein said aluminum nitride barrier layer is provided on the top and bottom of said phosphor of (a) to (c).
8. The phosphor of claim 1 , wherein said aluminum nitride barrier layer is about 30 nm to about 50 nm thick.
9. The phosphor of claim 8 , wherein said aluminum nitride barrier layer is deposited by sputtering.
10. The phosphor of claim 8 , wherein said aluminum nitride barrier layer is deposited by atomic layer chemical vapour deposition.
11. The phosphor of claim 8 , wherein said aluminum nitride barrier layer has a optical index of refraction of up to about 2.0.
12. The phosphor of claim 9 , wherein said sputtering is conducted in a sputtering atmosphere of gases at a pressure of about 0.65 Pa to 3.5 Pa having a nitrogen to argon ratio of about 0:50 to 20:50 and a power density of about 2 to 6 watts per square centimeter.
13. The phosphor of claim 12 , wherein oxygen is added to said sputtering atmosphere.
14. The phosphor of claim 1 , wherein said zinc sulfo-selenide is represented by the formula ZnS x Se 1-x :A where 0<×<1 and A is an activating element.
15. The phosphor of claim 1 , wherein said zinc selenide phosphor material is represented by ZnSe:A where A is an activating element.
16. A phosphor laminate for use in a thick film dielectric electroluminescent display, said phosphor laminate comprising; a phosphor thin film layer selected from the group consisting of
(a) a rare earth activated alkaline earth thioaluminate;
(b) a rare earth or transition metal activated zinc selenide; and
(c) a rare earth or transition metal activated zinc sulfo-selenide, an aluminum nitride layer provided directly adjacent a top and/or bottom side of the phosphor layer of (a), (b) and (c), and wherein said aluminum nitride barrier layer has a thickness of about 30 nm to about 50 nm.
17. The laminate of claim 16 , wherein said phosphor thin film layer is (a) and said aluminum nitride barrier layer is provided on the top side of said phosphor thin film layer.
18. A thick film dielectric electroluminescent device constructed on a glass or glass ceramic substrate and comprising a phosphor selected from the group consisting of
(a) a rare earth activated alkaline earth thioaluminate;
(b) a rare earth or transition metal activated zinc selenide; and
(c) a rare earth or transition metal activated zinc sulfo-selenide, wherein said phosphor film of (a), (b) and (c) is provided with an aluminum nitride barrier layer on a top and/or bottom side of the phosphor film.
19. The device of claim 18 , wherein said aluminum nitride barrier layer has a thickness of about 30 nm to about 50 nm.
20. A method for making a stabilized phosphor laminate for use in a thick film dielectric electroluminescent device, said method comprising
(i) deposition of a phosphor selected from the group consisting of:
(a) a rare earth activated alkaline earth thioaluminate;
(b) a rare earth or transition metal activated zinc selenide; and
(c) a rare earth or transition metal activated zinc sulfo-selenide, onto a glass or glass ceramic substrate incorporating a first set of address lines and a dielectric layer;
ii) deposition of a layer of aluminum nitride on top of said phosphor film of (a)-(c); and
iii) annealing said phosphor film at a temperature of up to about 1100° C.
21. The method of claim 20 , wherein said method further comprises deposition of a layer of aluminum nitride on the bottom of said phosphor film of (a), (b), and (c).
22. The method of claim 21 , wherein said aluminum nitride has a thickness of about 30 nm to about 50 nm.
23. The method of claim 22 , wherein said aluminum nitride barrier layer is deposited by sputtering.
24. The method of claim 23 , wherein said sputtering is conducted in a sputtering atmosphere of gases at a pressure of about 0.65 Pa to 3.5 Pa having a nitrogen to argon ratio of about 0:50 to 20:50 and a power density of about 2 to 6 watts per square centimeter.
25. The method of claim 24 , wherein oxygen is added to said sputtering atmosphere.
26. The method of claim 22 , wherein said aluminum nitride barrier layer is deposited by atomic layer chemical vapour deposition.
27. An improved phosphor film for a thick film dielectric electroluminescent display, said phosphor film selected from the group consisting of a transition metal activated zinc sulfide; wherein said phosphor film is provided with an aluminum nitride barrier layer on a top side of the phosphor film, said aluminum nitride barrier layer improving the stability of the interface between the phosphor film and the display; and further wherein said aluminum nitride barrier layer is about 30 nm to about 50 nm thick.
28. The phosphor of claim 27 , wherein said transition metal activated zinc sulfide is represented by the formula ZnS:A where A is selected from manganese and terbium.