Integrated capacitive humidity sensor

1. A method for forming a semiconductor device, comprising:

forming a first electrically conductive metal layer on a surface of an IC substrate;

electrografting a moisture-sensitive polymer layer onto the first electrically conductive metal layer;

forming a passivation layer over the substrate with the polymer layer exposed through one or more openings in the passivation layer;

wherein the polymer layer functions as a capacitive humidity sensing element when exposed to ambient air;

further comprising, prior to electrografting the polymer layer,

forming the first electrically conductive metal layer over an insulating layer on the substrate; and forming a patterned mask over the first electrically conductive metal layer;

wherein the polymer layer is electrographed onto an exposed area of the first electrically conductive metal layer;

further comprising, after electrografting the polymer layer, selectively removing the mask and conductive metal layer underlying the mask to expose the insulating layer on the substrate;

patterning the first electrically conductive metal layer to form an RDL layer comprising a contact area;

forming a passivation layer over the RDL layer;

forming an opening through the passivation layer to expose the contact area of the RDL layer;

forming a UBM structure on the contact area within the opening; and

forming a plurality of openings through the passivation layer and the RDL layer underlying the passivation layer to expose the polymer layer;

wherein the polymer layer functions as a capacitive humidity sensing element when exposed to ambient air;

further comprising, prior to electrografting the polymer layer,

forming the first electrically conductive metal layer over an insulating layer on the substrate; and

masking and patterning the first electrically conductive metal layer to form a pair of interdigitated sensing electrodes; and

forming a patterned photoresist mask over the substrate with the interdigitated sensing electrodes exposed;

wherein the polymer layer is electrographed onto the exposed interdigitated sensing electrodes.

2. The method of claim 1 , wherein the electrografting comprises:

applying an aqueous acidic electrografting composition to a surface of the first electrically conductive metal layer, wherein the composition comprises a solvent, an aryldiazonium salt, a vinyl ester monomer compound and an acidic component to maintain a pH of 1 to 2; and

applying an electric potential to the surface of the metal layer to form a primer layer of aryl radicals, followed by addition and polymerization of vinyl monomers onto the primer layer to form an electrografted polymer layer on the surface of the metal layer.

3. The method of claim 2 , wherein the polymer layer comprises a polyvinyl ester.

4. The method of claim 3 , wherein the polyvinyl ester is selected from the group consisting of polyvinyl methacrylate (PVM), polyvinyl benzoate (PVG), polyvinyl crotonate (PVCr), polyvinyl cinnamate (PVCi), and polymethyl methacrylate (PMMA), and

the polyvinyl ester comprises functional groups selected from the group consisting of carboxyl (—COOH), hydroxyl (—OH) and amino (—NH 2 ) groups.

5. The method of claim 1 , wherein the first electrically conductive metal layer comprises a pair of interdigitated sensing electrodes, and the polymer layer is electrographed to the pair of sensing electrodes.

6. The method of claim 1 , wherein the first electrically conductive metal layer comprises a metal selected from the group consisting of titanium, platinum, and gold, and combinations thereof.

7. The method of claim 1 , wherein the IC substrate comprises a CMOS substrate or an ASIC substrate.

8. A semiconductor device, comprising:

a moisture-sensitive polymer layer electrografted to a first electrically conductive metal layer situated on an IC substrate, and exposed within one or more openings through a passivation layer;

wherein the moisture-sensitive polymer layer functions as a capacitive humidity sensing element when exposed to ambient air;

wherein the IC substrate comprises an insulative layer on an upper surface;

the first electrically conductive metal layer over the insulative layer;

the moisture-sensitive polymer layer electrografted to the first electrically conductive metal layer;

an RDL layer overlying portions of the moisture-sensitive polymer layer;

wherein the passivation layer is over the RDL layer;

one or more of openings through the passivation layer and the RDL layer configured to expose the moisture-sensitive polymer layer;

wherein the openings extend through the passivation layer and underlying RDL layer with the moisture-sensitive polymer layer exposed within the openings to ambient air;

wherein the moisture-sensitive polymer layer functions as a capacitive humidity sensing element;

wherein the moisture-sensitive polymer layer is electrographed to a pair of interdigitated sensing electrodes;

wherein the moisture-sensitive polymer layer is exposed within the openings through the passivation layer and the RDL layer underlying the passivation layer.

9. The semiconductor device of claim 8 , wherein the semiconductor device is encapsulated as a package;

wherein an encapsulation process performed to cover the semiconductor device with a mold compound or mold encapsulant, which is then cured to produce the package.

10. The semiconductor device of claim 9 , wherein the package includes an opening for passage of ambient air to the moisture-sensitive polymer layer.

11. The semiconductor device of claim 10 , wherein the opening is situated along a side of the package as a space between the encapsulated semiconductor device and a substrate.

12. A method for forming a semiconductor device, comprising:

forming a first electrically conductive metal layer on a surface of an IC substrate;

electrografting a moisture-sensitive polymer layer onto the first electrically conductive metal layer; and

forming a passivation layer over the substrate with the polymer layer exposed through one or more openings in the passivation layer;

wherein the polymer layer functions as a capacitive humidity sensing element when exposed to ambient air;

further comprising, prior to electrografting the polymer layer, forming the first electrically conductive metal layer over an insulating layer on the substrate; and

masking and patterning the first electrically conductive metal layer to form a pair of interdigitated sensing electrodes; and

forming a patterned photoresist mask over the substrate with the interdigitated sensing electrodes exposed;

wherein the polymer layer is electrographed onto the exposed interdigitated sensing electrodes;

further comprising, after electrografting the polymer layer, removing the mask to expose the insulating layer on the substrate;

patterning the first electrically conductive metal layer to form an RDL layer comprising a contact area;

forming a passivation layer over the RDL layer and the polymer layer;

forming an opening through the passivation layer to expose the contact area of the RDL layer and the polymer layer; and

forming a UBM structure on the contact area within the opening; wherein the polymer layer functions as a capacitive humidity sensing element when exposed to ambient air;

further comprising, prior to electrografting the polymer layer,

forming the first electrically conductive metal layer over an insulating layer on the substrate; and

masking and patterning the first electrically conductive metal layer to form a pair of interdigitated sensing electrodes;

wherein the polymer layer is electrographed onto the interdigitated sensing electrodes.