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Title: Relative humidity detector
Claims: I claim: 1. A method for making a humidity detector, comprising: forming successive layers of a first electrical conductor, a hygroscopic material consisting essentially of Al.sub.2 O.sub.3, and a second electrical conductor upon a substrate, whereby the electrical impedance between said first and second electrical conductors varies with variations in humidity, submerging said successive layers into water, and subsequently exposing said successive layers to a temperature of about 120.degree. C., whereby said impedance variation is made essentially linear for variations in relative humidity between 0% and 100%. 2. The method of claim 1 wherein said submerging is for a time of about 12 hours. 3. The method of claim 1 wherein said heating comprises exposing said successive layers to said temperature for a time of between approximately 6 and 12 hours. 4. The method of claim 1 wherein said forming successive layers comprises: evaporating a layer of aluminum onto an amorphous quartz substrate, anodizing said aluminum layer to form said layer of Al.sub.2 O.sub.3, and, evaporating a layer of chrome and a layer of gold onto said layer of Al.sub.2 O.sub.3. 5. The method of claim 4 wherein said first layer of aluminum is of thickness of between approximately 15,000 and 20,000 A., said layer of Al.sub.2 O.sub.3 is of thickness of between approximately 5,000 and 10,000 A., and said third layer of chrome and gold is of thickness of about 1,500 A. 6. The method of claim 1 wherein said step for forming said second electrical conductor comprises providing a material selected from the group consisting of gold, silver, copper and platinum. 7. A method for making a humidity detector, comprising: evaporating an aluminum layer onto a substrate to a depth of between approximately 20,000 and 30,000 A.; forming a layer of Al.sub.2 O.sub.3 upon said substrate of thickness between 5,000 and 10,000 A.; evaporating chrome onto said layer of Al.sub.2 O.sub.3 to a depth of about 700 A.; evaporating gold onto said layer of chrome to a depth of approximately 800 A.; submerging the aforesaid layers into water for about 12 hours; and heating the aforesaid layers at a temperature less than the melting temperature of said Al.sub.2 O.sub.3 to evaporate said water therein and to relieve any intercrystalline stresses therein to produce a linear impedance relationship to humidity of said structure. 8. The method of claim 7 wherein said heating comprises exposing the aforesaid layers to a temperature of approximately 120.degree. C. for a time of between approximately 6 and 12 hours. 9. A humidity detector made in accordance with the method of claim 7. 10. A humidity detector made in accordance with the method of claim 1. 11. A method of linearizing the impedance response of a humidity detector of the type in which successive layers of aluminum, Al.sub.2 O.sub.3, and gold are formed on a substrate, comprising: submerging said detector into a bath of water, removing said detector from said bath, and exposing said detector to a temperature of approximately 120.degree. C. for a time sufficient to remove all of the water from said bath therein, and to relieve the intercrystalline stresses thereof. 12. The method of claim 11 wherein said heating step comprises heating said detector for a time of between approximately 6 and 12 hours. 13. A detector for measuring relative humidity comprising: a header, a substrate, mounted on said header, a layer of aluminum on said substrate of thickness of between approximately 10,000 and 20,000 A., a layer of Al.sub.2 O.sub.3 of thickness no more than 10,000 A., and no less than 5,000 A. on said layer of aluminum, a layer of metal formed on said layer of Al.sub.2 O.sub.3, said metal layer being selected from the group consisting of gold, platinum, copper and silver, said metal layer being of thickness of about 1,500 A., whereby water molecules from the surrounding air can pass through said metal layer and to said layer of Al.sub.2 O.sub.3, and a pair of electrodes connected directly to said layer of aluminum and said metal layer, respectively, whereby the impedance of said structure varies linearly with variations in the relative humidity between 0% and 100%. 14. The humidity detector of claim 13 wherein said metal layer is gold. 15. The humidity detector of claim 13 wherein said metal layer is platinum. 16. The humidity detector of claim 13 wherein said aluminum layer, said Al.sub.2 O.sub.3 layer, and said metal layer are free of intercrystalline stresses. 17. The humidity detector of claim 13 wherein said aluminum layer is of dimensions approximately 1/8 inch square. 18. The humidity detector of claim 13 further comprising: an alternating signal generator connected across said metal layer and said aluminum layer, an amplifier connected to receive the signal of said signal generator, and, a thermistor in proximity to said humidity detector connected to said signal generator to vary the gain thereof with variations in temperature, whereby the magnitude of the signal output of said amplifier indicates the impedance of said structure. 19. The humidity detector of claim 18 wherein said signal of said signal generator is of frequency of approximately 1,000 Hz. 20. The humidity detector of claim 14 further comprising an layer of chromium between said layer of Al.sub.2 O.sub.3 and said layer of gold of thickness of approximately 200 to 500 A. 21. A detector for measuring relative humidity comprising: a header, a substrate mounted on said header, a first electrode evaporated onto a portion of said substrate, a layer of aluminum on a portion of said substrate, overlying at least a portion of said first electrode, said layer of aluminum being of thickness between approximately 10,000 and 20,000 A., a layer of Al.sub.1 O.sub.3 of thickness of no more than 10,000 A. on said layer of aluminum, a layer of metal formed on said layer of Al.sub.2 O.sub.3, said metal layer being selected from the group consisting of gold, platinum, copper and silver, said metal layer being of thickness of about 1,500 A., whereby water molecules from the surrounding air can pass through said metal layer and to said layer of Al.sub.2 O.sub.3, a second electrode on said substrate, in contact with said layer of metal formed on said layer of Al.sub.2 O.sub.3, and a pair of electrodes bonded to said first and second electrodes, respectively, whereby the impedance of said structure measured upon said electrodes varies linearly with variations in the relative humidity between zero and 100%. 22. The humidity detector of claim 20 wherein said metal layer is gold. 23. The humidity detector of claim 20 wherein said aluminum layer, said Al.sub.2 O.sub.3 layer and said metal layer are free of intercrystalline stresses. Other info: Inventors: Bennewitz, Paul F. (Albuquerque, NM, US) Application Number: 635574 Filing Date: 1975-11-28 Publication_date: 1976-10-26 Assignee: Primary Class(es): 73/335.03 205/162, 338/35 Other Classes: US Patent Ref:
Other Refs: Other References: Storer, C. M., New Aluminum Oxide Humidity Element, (second report), Sandia Laboratories Publication SC-4667(RR), Mar. 1962. | |