Image sensor

1. An image sensor comprising a pixel assembly, each pixel comprising a photodiode and an insulated gate access transistor connected to a read circuit, wherein:

the photodiode and the access transistor are formed in and above a first semiconductor substrate;

all or part of the read circuit is formed in a second semiconductor substrate;

the second substrate is placed above the first substrate and separated therefrom by an intermediary insulating layer covering the insulated gate access transistor;

the photodiode receives incident photons arriving in the first semiconductor substrate on its lower surface side opposite to said intermediary insulating layer and comprises a heavily-doped P-type upper area placed at the surface of the first substrate and an N-type buried layer placed under the P-type upper area, said buried layer extending in a source/drain area of the access transistor, and another source/drain area of the access transistor being placed on the other side of its gate at the surface of the first substrate.

2. The image sensor of claim 1 , wherein the heavily-doped P-type upper area is connected to a bias voltage such as a ground via, among others, a metallization placed in the intermediary insulating layer above the heavily-doped P-type upper area.

3. The image sensor of claim 1 , wherein the read circuit comprises read transistors formed on the upper surface side of the second substrate, the second substrate and the read transistors being covered with an upper insulating layer, and a metallization, connecting the access transistor and the read circuit, being placed partly in openings of the intermediary insulating layer, partly in openings insulated from the second substrate, and partly in openings of the upper insulating layer.

4. The image sensor of claim 1 , wherein the read circuit comprises read transistors formed on the lower surface side of the second substrate, the read transistors being covered with said intermediary insulating layer, and a metallization, connecting the access transistor and the read circuit, being placed in said intermediary insulating layer.

5. The image sensor of claim 1 , comprising for each pixel a filter portion placed against the lower surface side of the first substrate.

6. The image sensor of claim 5 , comprising for each pixel a lens placed against the filter portion.

7. The image sensor of claim 1 , wherein a heavily-doped P-type area is formed at the surface of the first substrate on its lower surface side.

8. The image sensor of claim 2 , wherein a thickness and a doping of the N-type buried layer of the photodiode are such that without any photon capture, the N-type buried layer is entirely depleted.

9. The image sensor of claim 1 , comprising a control circuit having its semiconductor components formed in the first semiconductor substrate.

10. The image sensor of claim 5 , wherein the filter portion is configured to allow transmission of the incident photons exhibiting at least one wavelength within a plurality of predefined wavelengths.

11. The image sensor of claim 1 , wherein a plurality of read lines are formed in the intermediary insulating layer.

12. The image sensor of claim 11 , wherein at least one of the plurality of read lines is connected to the insulated gate access transistor.

13. The image sensor of claim 1 , wherein the read circuit receives a reset signal to reset the read circuit.

14. The image sensor of claim 1 , wherein an upper insulating layer is formed above the second semiconductor substrate and the upper insulating layer covers part of the read circuit.

15. The image sensor of claim 14 , wherein at least one metal contact is placed on the upper surface side of the upper insulating layer.

16. The image sensor of claim 14 , wherein at least one metal contact is placed in at least one insulated opening of the upper insulating layer.

17. An image sensor comprising a pixel assembly of at least one pixel, the at least one pixel comprising a photodiode and an insulated gate access transistor connected to a read circuit, wherein:

the photodiode and the insulated gate access transistor are formed in and above a first semiconductor substrate;

all or part of the read circuit is formed in a second semiconductor substrate;

the second semiconductor substrate is placed above the first substrate and separated from the first substrate by an intermediary insulating layer covering the insulated gate access transistor;

the photodiode receives incident photons arriving in the first semiconductor substrate on its lower surface side opposite to said intermediary insulating layer; and

a heavily-doped P-type area is formed at the surface of the first substrate on its lower surface side.

18. An image sensor, comprising:

a pixel assembly, each pixel of the pixel assembly comprising at least one photodiode, at least one insulated gate access transistor connected to the at least one photodiode and a read circuit, the read circuit comprising at least one read transistor;

a metallization connecting the at least one insulated gate access transistor to the read circuit;

a first insulating layer located above a first semiconductor substrate;

a second insulating layer located above a second semiconductor substrate and the first insulating layer;

wherein the at least one photodiode and the at least one insulated gate access transistor are formed in and above the first semiconductor substrate;

wherein the at least one photodiode comprises a first heavily-doped P-type upper area placed at an upper surface of the first semiconductor substrate and an N-type buried layer placed under the first heavily-doped P-type upper area;

wherein at least one part of the read circuit is formed in the second semiconductor substrate;

a second heavily-doped P-type area is placed at a lower surface side of the first semiconductor substrate; and

the at least one photodiode receives at least one incident photon on the lower surface side of the first semiconductor substrate.