US 3274024 A
Description (OCR text may contain errors)
Sept. 20, 1966 ET AL 3,274,024
ENERGY CONVERTER Filed Nov. 16, 1962 (YTTRIUM OXIDE) I8 (TANTALUM I6 (GOLD) F'ENTOXIDE) I4 I2 (TANTALUM) IO (GLASS) Fig. I.
24 (SILVER) (YTTRIUM OXIDE) l8 22 (SILICON (GOLD) 2O MONOXIDE) IO (GLASS) Fig. 2.
(SILVER) 24 3O (GADOLINIUM- (GOLD) 2O EUROPIUM OXIDE) IO (GLASS) Fig. 3.
ROBERT MATTESON HILL BURNELL VINCENT DORE United States Patent 3,274,024 ENERGY CONVERTER Robert Matteson Hill, Palo Alto, and Burnell Vincent Dore, Sunnyvale, Calif., assignors to General Telephone and Electronics Laboratories, Inc., a corporation of Delaware Filed Nov. 16, 1962, Ser. No. 238,299 4 Claims. (Cl. 117200) Our invention relates to devices for converting electrical energy into light and, more particularly, is directed toward a class of such devices wherein the energy conversion is attributed to internal quantum-mechanical processes.
According to classical physical theory, when an extremely thin film or barrier of poor conductivity is interposed between first and second electrically conductive layers and an electric field of relatively low intensity is established between these layers, the electrons present in the layers will have insuflicient energy to traverse the barrier, and no current should flow between the layers. Experimentally, however, it has been shown that some electrons have sufficient energy to traverse the barrier (and indeed to pass through one of the layers as well) since an appreciable current will flow between the layers under the conditions indicated. To provide an explanation for these experimental results, recourse is had to quantum theory. Consequently, the operation of such barrier structures is said to be based upon 'in-ternal quantum-mechanical processes.
We have succeeded in developing devices utilizing cathodoluminescent phosphors in combination with thin film or barrier structures of the type described above wherein light can be generated directly by the application of an electric field to the structure. It should be understood that our devices are not electroluminescent devices, since the cathodoluminescent phosphors are not excited directly by an electric field.
In accordance with the principles of our invention, a thin film or barrier is interposed between first and second electrically conductive layers. (This film is a poorly conductive material such as a semiconductor or a dielectric.) A cathodoluminescent phosphor layer can be applied over one layer, or can be interposed between the film and one of the layers, or can itself constitute the barrier film. In any event, application of a relatively low voltage between the first and second layers will result in the generation of light.
Illustrative embodiments of our invention will now be described with reference to the accompanying drawings wherein:
FIG. 1 illustrates one embodiment of our invention wherein the phosphor layer and the barrier film are positioned on opposite sides of an electrically conductive layer,
FIG. 2 illustrates a second embodiment wherein the phosphor layer and the barrier film are positioned adjacent each other between first and second electrically conductive layers; and
FIG. 3 illustrates a third embodiment wherein the phosphor layer also functions as a barrier film.
Referring now to FIG. 1, there is shown a glass substrate 10, one surface of which is coated with a tantalum layer 12. The top surface of this layer carries a thin film or barrier 14 of tantalum pentoxide. A gold layer 16 is applied over the film 14. A phosphor layer 18 is applied over layer 16. (This phosphor layer can be, for example, yttrium oxide containing about mole per cent of europium or can be any of the phosphors comprising a host material having the cubic C-type rare earth oxide structure incorporating up to about 20 mole 3,274,024 Patented Sept. 20, 1966 percent of a doping ion which can be a rare earth, a transition element or an actinide, as disclosed in the copending application of R. A. Lefever and K. A. Wickersheim, Serial No. 213,859, filed July 31, 1962. Alternatively, the phosphor can be yttrium oxide doped with cadmium, magnesium, copper or thorium or can be lanthanum oxide doped with a rare earth ion as disclosed in other copending applications of the same inventors, Serial No. 213,896 or 213,897, both filed on July 31, 1962.)
When a low alternating or direct voltage is applied between the tantalum layer 12 and the gold layer 16, pink light was emitted from the phosphor layer.
Typically, the tantalum layer is 1 micron thick, the barrier is 100 angstroms thick, the gold layer is 100 angstrom units thick and the phosphor layer is 1 micron thick. The applied voltage can be, for example, 12 volts R.M.S. at 60 cycles per second and the current flowing between layers 12 and 16 can be 30 milliamperes. Alternatively, the same results ensue when a direct voltage of 8 volts is applied, the positive terminal of the voltage source being connected to the gold layer, the current in this case being milliamperes.
In forming the structure shown in FIG. 1, the substrate is first coated with tantalum. The tantalum is then electro-polished. The top surface of the tantalum layer is then anodized to produce the barrier; the gold is evaporated onto the anodized surface; and the structure is completed by vacuum depositing the phosphor layer on top of the gold layer.
Referring now to FIG. 2, there is shown a glass substrate 10, one surface of which is coated with a gold layer 20. A barrier 22 of vacuum deposited silicon monoxide is applied over the gold layer 20 and a semitransparent silver layer 24 is applied over the monoxide film 22. A phosphor layer 18 is interposed between barrier 22 and layer 24. Again application of an alternating or direct voltage between layers 20 and 24, can cause a pinkish glow to be viewed through the silver layer 24.
FIG. 3 shows another modification comprising a glass substitute 10, a gold layer 20, a phosphor barrier 30 and a semi-transparent silver layer 24. Application of an alternating or direct voltage can cause a pinkish glow as before. To form the structure of FIG. 3, the gold coated substrate was held above a molybdenum boat containing a suitable mixture of gadolinium and europium oxide powders [(Gd Eu O The boat was placed in an evacuator and heated to 1800 C., the evaporant being deposited upon the substrate as a phosphor film. After cooling to room temperature, the fired substrate was removed and inserted into an oven and reheated to 200 C. to activate the phosphor film. After cooling, the twice fired substrate was removed from the furnace and vacuum coated with silver in a conventional manner.
The thickness of the various layers is not particularly critical, but the barrier or film must be extremely thin varying from a lower limit of 20 angstroms to an upper limit of about 1000 angstroms.
The conductive layers can be formed of conventional materials other than gold as for example tin oxide or aluminum. The barrier can also be formed of conventional materials other than tantalum pentoxide or silicon monoxide, as for example A1 0 MgF TiO While we have shown and pointed out our invention as applied above, it will be apparent to those skilled in the art that many modifications can be made within the scope and sphere of our invention.
What is claimed is:
1. A device comprising first and second electrically conductive layers, a thin film or barrier having a thickness Within the range of 20 to 1000 angstroms interposed therebetween, and a cathodoluminescent phosphor layer associated with said first and second layers and said barrier.
2. A device comprising first and second electrically conductive layers, a thin film or barrier having a thickness within the range of 20 to 1000 angstroms interposed therebetween, and a cathodoluminescent phos phor layer interposed between said barrier and one of said first and second layers.
3. A device comprising first and second electrically conductive layers, a thin film or barrier having a thickness within the range of 20 to 1000 angstroms interposed therebetween, and a cathodoluminescent phosphor layer secured to the surface of one of said first and second layers remote from said barrier.
4. A device comprising first and second electrically conductive layers, and a thin film or barrier of a cathodoluminescent phosphor having a thickness within the 2 range of 20 to 1000 angstroms interposed between said layers.
References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Gobrecht et al.: Zeitschrift fur Physik, vol. 149 (pp. 504510), 1957.
Leverenz: Cathodoluminescence as Applied in Tele- 15 vision (Reprint from RCA Review, vol. V, No. 2, October 1940) (page 132 relied on).
ALFRED L. LEAVITT, Primary Examiner.
RICHARD D. NEVIUS, JOSEPH SPENCER, O Examiners.
W. L. JARVIS, Assistant Examiner.