Solid-state photodetector pixel and photodetecting method
View Patent ↗A pixel is formed in a semiconductor substrate (S) with a plane surface for use in a photodetector. It comprises an active region for converting incident light (In) into charge carriers, photogates (PGL, PGM, PGR) for generating a lateral electric potential (Φ(x)) across the active region, and an integration gate (IG) for storing charge carriers generated in the active region and a dump site (Ddiff). The pixel further comprises separation-enhancing means (SL) for additionally enhancing charge separation in the active region and charge transport from the active region to the integration gate (IG). The separation-enhancing means (SL) are for instance a shield layer designed such that for a given lateral electric potential (Φ(x)), the incident light (In) does not impinge on the section from which the charge carriers would not be transported to the integration gate (IG).
1. A pixel formed in a semiconductor substrate, comprising: an active region for converting incident electromagnetic radiation into charge carriers of a first and a second charge type, photogates for generating a lateral electric potential across the active region, charge storage areas for storing charge carriers of at least one said type generated in the active region, said charge storage areas being placed outside the active region, and at least two metal layers for shielding the charge storage areas with an insulating interlayer between them, the metal layers being arranged in different distances from a surface of the substrate, and one above the other and being terraced.
2. A pixel according to claim 1 , wherein at least one of the metal layers projects over part of the active region.
3. A pixel according to claim 1 , wherein at least one of the metal layers projects over part of the active region to expose the first section to the incident radiation and shields the second section from the incident radiation.
4. A pixel according to claim 1 , wherein a vertical opaque barrier is arranged above the charge-storage areas for shielding the charge storage areas from incident radiation with non-normal incidence.
5. A pixel according to claim 4 , wherein the vertical opaque barrier comprises insulating interlayer between the metal layers.
6. A pixel according to claim 4 , wherein vertical opaque barriers are made of metal and are provided between the metal layers.
7. A pixel according to claim 1 , wherein a transverse inhomogeneity is provided in the semiconductor substrate, to create an increased electric potential inside the substrate.
8. A pixel according to claim 7 , wherein the transverse inhomogeneity is a buried channel.
9. A pixel according to claim 1 , comprising a combination of a bulk substrate made of a material that impedes charge-carrier transport and/or supports charge-carrier recombination, and a detection layer made of a material that supports charge-carrier transport and/or impedes charge-carrier recombination, arranged on the surface of the substrate.
10. A pixel according to claim 9 wherein the detection layer is an epitaxial silicon layer with a thickness of 2 μm to 20 μm.
11. A pixel according to claim 1 , comprising an opaque and/or reflecting layer.
12. A pixel according to claim 11 , wherein the substrate is a silicon-on-insulator substrate and the opaque and/or reflecting layer is arranged beneath the insulator layer.
13. A pixel according to claim 1 , further comprising a processing unit for subtracting an offset that is constant for all charge storage areas from the number of charge carriers stored in each charge storage area.
14. A pixel according to claim 13 , wherein the processing unit applies a variable electric potential to a plurality of integration gates, and detects whether each integration gate yields charge carriers.
15. A pixel according to claim 14 , wherein the processing unit applies a variable electric potential to a plurality of integration gates, and detects whether an output of at least one integration gate is below saturation.
16. A solid-state image sensor comprising a plurality of the pixels as described in claim 1 , arranged in a two-dimensional array.
17. The image sensor according to claim 16 , wherein the image sensor is of the charge-coupled-device type, and is manufactured by a complementary-metal-oxide-semiconductor process.