Water-insensitive gas sensor using polymer-encapsulated Pt—AlGaN/GaN diodes
A hydrogen sensor can include a substrate, an Ohmic metal disposed on the substrate, a nitride layer disposed on the substrate and having a first window exposing the substrate, a Schottky metal placed in the first window and disposed on the substrate, a final metal disposed on the nitride layer and the Schottky metal and having a second window exposing the Schottky metal, and a polymethyl-methacrylate (PMMA) layer encapsulating the second window. The PMMA layer can fill the second window and be in contact with the Schottky metal.
1. A hydrogen sensor, comprising:
a substrate;
an Ohmic metal disposed on the substrate;
a nitride layer disposed on the substrate and having a first window exposing the substrate;
a Schottky metal placed in the first window and disposed on the substrate;
a final metal disposed on the nitride layer and the Schottky metal and having a second window exposing the Schottky metal; and
a polymethyl-methacrylate (PMMA) layer encapsulating the second window.
2. The hydrogen sensor according to claim 1 , wherein the PMMA layer covers a part of the Ohmic metal and a part of the final metal.
3. The hydrogen sensor according to claim 2 , wherein the PMMA layer fills the second window and is in contact with the Schottky metal.
4. The hydrogen sensor according to claim 3 , wherein the Schottky metal is in contact with a side surface and a top surface of the nitride layer.
5. The hydrogen sensor according to claim 4 , wherein the final metal is in contact with a side surface and a top surface of the Schottky metal.
6. The hydrogen sensor according to claim 3 , wherein the Ohmic metal and the Schottky metal are disposed on the same plane of the substrate.
7. The hydrogen sensor according to claim 6 , wherein the Schottky metal comprises platinum (Pt).
8. The hydrogen sensor according to claim 7 , wherein the substrate comprises a sapphire layer, a GaN layer on the sapphire layer, and an AlGaN layer on the GaN layer.
9. The hydrogen sensor according to claim 8 , wherein the GaN layer is a c-lane GaN layer and the AlGaN layer is an Al x Ga 1-x N layer, where x is in a range of 0 to 1.
10. The hydrogen sensor according to claim 8 , wherein the Ohmic metal comprises a titanium (Ti) layer, an aluminum (Al) layer, a nickel (Ni) layer, and a gold (Au) layer.
11. The hydrogen sensor according to claim 8 , wherein the final metal comprises a Ti layer and an Au layer.
12. The hydrogen sensor according to claim 3 , wherein a first width of the first window is larger than a second width of the second window.
13. The hydrogen sensor according to claim 3 , wherein the substrate comprises at least one of sapphire, SiC, and silicon.