Front side illuminated, back-side contact double-sided PN-junction photodiode arrays
View Patent ↗The present invention is a photodiode detector array for use in computerized tomography (CT) and non-CT applications. Specifically, the present invention is a high-density photodiode arrays, with low dark current, low capacitance, high signal to noise ratio, high speed, and low crosstalk that can be fabricated on relatively large substrate wafers. More specifically the photodiode array of the present invention is fabricated such that the PN-junctions are located on both the front side and back side surfaces of the array, and wherein the front side PN-junction is in electrical communication with the back side PN-junction. Still more specifically, the present invention is a photodiode array awing PN-junctions that are electrically connected from the front to back surfaces and which can be operated in a fully depleted mode at low reverse bias.
1. A photodiode comprising:
a substrate with at least a front side and a back side;
a front side region within said front side of the substrate, wherein said front side region comprises at least one PN-junction, wherein said PN-junction comprises a first doped region of a first conductivity type, wherein said front side region comprises a second doped region of a second conductivity type, wherein said first doped region and second doped region are physically separated by a portion of said substrate, and wherein said first conductivity type is different than said second conductivity type;
a back side region within said back side of the substrate, wherein said back side region comprises at least one PN-junction, wherein said PN-junction comprises a first doped region of a first conductivity type, wherein said back side region comprises a second doped region of a second conductivity type, wherein said first doped region and second doped region are physically separated by a portion of said substrate, and wherein said first conductivity type is different than said second conductivity type; and
at least one conduit for forming an electrical connection from the PN-junction in the front side region to the PN-junction in the back side region, wherein the conduit comprises a) a p+ dopant layer and b) a polysilicon or polyimide filling, wherein said photodiode is manufactured from a silicon wafer having an n-type conductivity.
2. The photodiode of claim 1 wherein at least one of said first doped region or second doped region in the back side region is in electrical communication with a metallic area to form at least one back side cathode.
3. The photodiode of claim 2 wherein an inner edge of said cathode and said conduit are separated by a gap of approximately 0.060 mm.
4. The photodiode of claim 1 wherein said first doped region or second doped region in the back side region in electrical communication with a metallic area to form the at least one back side cathode is an n-type doped diffusion region.
5. The photodiode of claim 1 wherein at least one of said first doped region or second doped region in the back side region is in electrical communication with a metallic area to form at least one back side anode.
6. The photodiode of claim 5 wherein said first doped region or second doped region in the back side region in electrical communication with a metallic area to form at least one back side anode is a p-type doped diffusion region.
7. The photodiode of claim 1 wherein one of said first doped region or second doped region in the front side region has a p-type conductivity and one of said first doped region or second doped region in the front side region has an n-type conductivity.
8. The photodiode of claim 7 wherein said p-type conductivity doped region and said n-type conductivity doped region are separated by a gap of approximately 0.125 mm.
9. The photodiode of claim 1 wherein said conduit has a diameter of approximately 0.020 mm.
10. The photodiode of claim 1 wherein said silicon wafer has a thickness ranging from 0.210-0.260 mm.