Image sensor pixels with conductive bias grids
An image sensor with an array of pixels is provided. In order to achieve high image quality, it may be desirable to improve well capacity of individual pixels within the array by forming deep photodiodes in a thick substrate. When forming the array of pixels, conductive contacts may be formed in a back surface of the substrate opposing ground contacts located on a front side of the substrate. A conductive grid layer may be formed over the conductive contacts. A color filter layer may be formed over the conductive grid layer that may include a barrier grid in which color filter material is deposited. The conductive grid layer and conductive contacts may be biased to a voltage to improve the strength of electric fields in the substrate. Conductive contacts will thereby improve charge collection and electrical isolation and prevent electrical crosstalk and blooming.
1. An electronic device having an array of image sensor pixels, comprising:
photosensitive elements formed in a semiconductor substrate having first and second opposing sides;
conductive contacts formed on the first side of the semiconductor substrate;
a conductive layer formed over the conductive contacts;
a color filter array formed over the first side of the semiconductor substrate;
an array of microlenses formed over the color filter array;
ground contacts formed on the second side of the semiconductor substrate; and
external voltage supply circuitry, wherein the external voltage supply circuitry is configured to apply a voltage to the conductive layer.
2. The electronic device defined in claim 1 , further comprising:
a bond pad formed at an edge of the array of image sensor pixels; and
a wire bond coupled between the bond pad and the external voltage supply circuitry.
3. The electronic device defined in claim 1 , further comprising:
a conductive via that is formed in the semiconductor substrate at an edge of the array of image sensor pixels and that is coupled between the conductive layer and the external voltage supply circuitry.
4. The electronic device defined in claim 1 , wherein the color filter array further comprises:
a grid of dielectric material having an array of openings; and
color filter elements formed in the openings in the grid of dielectric material.
5. The electronic device defined in claim 4 , wherein the conductive contacts are formed below intersections in the grid of dielectric material.
6. The electronic device defined in claim 4 , wherein the conductive layer is formed in a grid pattern that overlaps the grid of dielectric material.
7. The electronic device defined in claim 1 , wherein the conductive layer comprises doped dielectric material.
8. The electronic device defined in claim 1 , wherein the conductive layer comprises metal.
9. An image sensor having an array of pixels, comprising:
photodiodes formed in a semiconductor substrate;
conductive contacts formed in a first side of the semiconductor substrate;
a conductive grid layer formed over and in contact with the conductive contacts on the first side of the semiconductor substrate;
a color filter array formed on the first side of the semiconductor substrate comprising a grid of color filter barriers formed over the conductive grid layer and color filter elements disposed in cavities in the grid of color filter barriers;
a microlens array formed over the color filter array; and
metal contacts formed on a second side of the semiconductor substrate.
10. The image sensor defined in claim 9 , wherein the grid of color filter barriers comprises a conductive grid of color filter barriers.
11. The image sensor defined in claim 9 , wherein the grid of color filter barriers comprises electrically isolated metal formed in an insulating grid of color filter barriers.
12. The image sensor defined in claim 9 , wherein the conductive contacts are formed under respective intersections in the grid of color filter barriers.
13. The image sensor defined in claim 9 , wherein the grid of color filter barriers has a plurality of intersections and wherein the conductive contacts are formed under less than all of the intersections in the grid of color filter barriers.
14. The image sensor defined in claim 9 , wherein the color filter array comprises a Bayer color filter array.
15. The image sensor defined in claim 9 , wherein the conductive contacts overlap the metal contacts.
16. A system, comprising:
a central processing unit;
memory;
a lens;
input-output circuitry; and
an imaging device, wherein the imaging device comprises:
an array of pixels arranged in rows and columns, wherein the array of pixels comprises:
photodiodes formed in a substrate;
conductive contacts formed in a first side of the substrate, wherein the conductive contacts comprise doped semiconductor material;
a color filter array formed on the first side of the substrate, wherein the color filter array comprises a grid of metal barriers formed over the conductive contacts;
an array of microlenses formed over the color filter array; and
ground contacts formed on a second side of the substrate.
17. The system defined in claim 16 , wherein the conductive contacts are formed directly opposite the ground contacts.
18. The system defined in claim 16 , wherein the grid of metal barriers is coupled to external voltage supply circuitry that is configured to apply a voltage to the grid of metal barriers.