Relative humidity sensor and method

1. A relative humidity sensor, comprising:

a first electrode and a second electrode disposed above a dielectric substrate;

a sensitive layer disposed above at least one of the first electrode and the second electrode, the sensitive layer is formed from a composition including a polyimide and a hydrophobic filler dispersed among the polyimide; and

a dust protection layer disposed above the sensitive layer.

2. The relative humidity sensor of claim 1 , wherein the hydrophobic filler is organic.

3. The relative humidity sensor of claim 2 , wherein the hydrophobic filler is one or more lignin.

4. The relative humidity sensor of claim 3 , wherein the one or more lignin is about 1 to about 10 weight percent based on a total weight of the composition.

5. The relative humidity sensor of claim 3 , wherein the one or more lignin has an average molecular weight between about 500 and about 1000 grams/mol.

6. The relative humidity sensor of claim 1 , wherein the hydrophobic filler is inorganic.

7. The relative humidity sensor of claim 6 , wherein the hydrophobic filler is talc nanoparticles.

8. The relative humidity sensor of claim 7 , wherein the talc nanoparticles is hydrated magnesium covered silica having the chemical formula Mg 3 Si 4 O 10 (OH) 2 .

9. The relative humidity sensor of claim 7 , wherein the talc nanoparticles are about 1 to about 5 weight percent based on a total weight of the composition.

10. The relative humidity sensor of claim 1 , wherein the sensitive layer is disposed above the first electrode and the second electrode is disposed above the sensitive layer.

11. The relative humidity sensor of claim 1 , wherein the first electrode and the second electrode are interdigitated and the sensitive layer is disposed above the first electrode and the second electrode.

12. The relative humidity sensor of claim 1 , wherein dust protection layer is more porous and less hydrophobic than the sensitive layer.

13. A method of forming a relative humidity sensor, the method comprising:

depositing a first electrode on a dielectric substrate;

applying a composition to an upper surface of the first electrode to form a sensitive layer, the composition including a polyimide and a hydrophobic filler dispersed among the polyimide;

depositing a second electrode on an upper surface of the sensitive layer; and

depositing a dust protection layer on an upper surface of the second electrode.

14. The method of claim 13 , wherein the hydrophobic filler is one of: one or more lignin and talc nanoparticles.

15. The method of claim 14 , wherein the hydrophobic filler is one or more lignin and the one or more lignin has an average molecular weight between about 500 and about 1000 grams/mol.

16. The method of claim 14 , wherein the hydrophobic filler is the talc nanoparticles and the talc nanoparticles are about 1 to about 5 weight percent based on a total weight of the composition.

17. The method of claim 16 , wherein the talc nanoparticles is hydrated magnesium covered silica having the chemical formula Mg 3 Si 4 O 10 (OH) 2 .

18. The method of claim 13 , wherein dust protection layer is more porous and less hydrophobic than the sensitive layer.

19. A method of forming a relative humidity sensor, the method comprising:

preparing a composition, the composition including a polyimide and a hydrophobic filler dispersed among the polyimide; and

depositing at least a portion of the composition on a dielectric substrate supporting a first electrode and a second electrode, wherein the first and second electrode are interdigitated, to form the relative humidity sensor.

20. The method of claim 19 , wherein preparing the composition includes:

functionalizing the polyimide using a chemical reduction of aryl diazonium salts;

preparing a solution including the hydrophobic filler and dimethylformamide (DMF), wherein the hydrophobic filler include talc nanoparticles; and

stirring the solution with the functionalized polyimide to form the composition.