CMOS image sensor with non-contact structure
A complementary metal oxide semiconductor (CMOS) image sensor device includes a capacitive coupled photodiode that is formed within a region of a semiconductor substrate. The photodiode receives an incident light and generates a corresponding electric charge. The CMOS image sensor device includes a reset transistor coupled to the photodiode for reverse biasing the photodiode with a predetermined voltage. The CMOS image sensor device further includes a buffer circuit and a capacitor, which is interposed between the photodiode and the buffer circuit. The capacitor is configured to transfer the electric charge to the buffer circuit. The buffer circuit may include an emitter follower or a source follower transistor.
1. A complementary metal oxide semiconductor (CMOS) image sensor device including a capacitive coupled photodiode, the CMOS image sensing device comprising:
the photodiode configured to receive an incident light and generate an electric charge, the photodiode having an n-type doped region formed within a region of a semiconductor substrate, the n-type doped region configured to collect the generated electric charge;
a reset transistor coupled to the photodiode configured to reverse bias the photodiode with a predetermined voltage;
a capacitive element having a first plate overlying a portion of the n-type doped region and a second plate; and
a source follower transistor coupled to the second plate.
2. The CMOS image sensor device of claim 1 , wherein the capacitive element further comprises an insulation layer interposed between the first plate and the second plate.
3. The CMOS image sensor device of claim 2 , wherein the insulation layer comprises an oxide.
4. The CMOS image sensor device of claim 2 , wherein the insulation layer is a gate dielectric layer having a thickness substantially equal to a gate dielectric thickness of the reset transistor.
5. The CMOS image sensor device of claim 1 , wherein the first plate comprises a N− lightly doped region having a dopant concentration of less than 1018 ions/cm 3 .
6. The CMOS image sensor device of claim 1 , wherein the second plate is electrically coupled to a gate electrode of the source follower transistor.
7. The CMOS image sensor device of claim 1 , wherein the second plate comprises polysilicon.
8. The CMOS image sensor device of claim 7 , wherein the second plate is coplanar with the gate electrode of the source follower transistor.
9. The CMOS image sensor device of claim 1 , further comprising a select transistor coupled to the source follower transistor.
10. An image sensor device comprising:
a photodiode configured to generate an electric charge from an incident light;
a reset transistor coupled to the photodiode and being configured to reverse bias the photodiode with a predetermined voltage;
a buffer circuit; and
a capacitor having a first terminal connected to the photodiode and a second terminal connected to the buffer circuit, the capacitor being configured to transfer the electric charge to the buffer circuit.
11. The image sensor device of claim 10 , where the buffer circuit comprises a source follower transistor.
12. The image sensor device of claim 10 , further comprising a select transistor coupled to the buffer circuit.
13. The image sensor device of claim 10 , where the photodiode comprises:
an n-type doped charge collection region overlying a p-type semiconductor substrate; and
a p+ doped region overlying the n-type doped charge collection region.
14. The image sensor device of claim 10 , where the capacitor comprises:
a first plate coupled to the photodiode;
a second plate coupled to a gate electrode of the buffer circuit; and
an insulation layer interposed between the first plate and the second plate.
15. The image sensor device of claim 14 , wherein the first plate comprises a N− lightly doped region overlying the n-type doped charge collection region of the photodiode.
16. The image sensor device of claim 15 , wherein the N− lightly doped region comprises a concentration of less than 1018 ions/cm 3 .
17. The image sensor device of claim 14 , wherein the second plate comprises polysilicon.
18. The image sensor device of claim 17 , wherein the second plate is coplanar with a gate electrode of the reset transistor.
19. The image sensor device of claim 14 , wherein the insulation layer comprises oxide having a thickness substantially equal to a gate dielectric thickness of the reset transistor.