Imaging sensor having floating region of imaging device on one substrate electrically coupled to another floating region formed on a second substrate
View Patent ↗An image sensor may include a symmetrical imaging pixel with a floating diffusion region. The floating diffusion region may be formed in the center of the imaging pixel. A shallow p-well may be formed around the floating diffusion region. A transfer gate configured to transfer charge from a photodiode to the floating diffusion region may be ring-shaped with an opening that overlaps the floating diffusion region. Isolation regions including deep trench isolation and a p-well may surround the photodiode of the imaging pixel. A p-stripe may couple the shallow p-well around the floating diffusion region to the isolation regions. The floating diffusion regions of neighboring pixels may be coupled together with additional conductive layers to implement shared configurations.
1. An imaging pixel comprising:
a photodiode with a center;
isolation regions that at least partially surround the photodiode;
a floating diffusion region formed over the center of the photodiode;
a transfer transistor configured to transfer charge from the photodiode to the floating diffusion region, wherein the transfer transistor comprises a transfer gate with an opening, and wherein the floating diffusion region is formed below the opening in the transfer gate; and
a p-type doped region between the isolation regions and the floating diffusion region, wherein the p-type doped region comprises a p-type doped strip that extends over the photodiode and divides the photodiode into first and second symmetric halves.
2. The imaging pixel defined in claim 1 , further comprising a shallow p-well formed around the floating diffusion region, wherein the p-type doped strip couples the isolation regions to the shallow p-well formed around the floating diffusion region.
3. The imaging pixel defined in claim 2 , wherein the isolation regions comprise deep trench isolation.
4. The imaging pixel defined in claim 3 , wherein the isolation regions further comprise a p-well.
5. The imaging pixel defined in claim 1 , wherein the transfer gate is donut shaped.
6. The imaging pixel defined in claim 1 , wherein the photodiode, the isolation regions, the floating diffusion region, and the p-type doped region between the isolation regions and the floating diffusion region are formed in a first substrate, the imaging pixel further comprising an interconnect layer that couples the floating diffusion region in the first substrate to a node in a second substrate.
7. The imaging pixel defined in claim 6 , further comprising:
a reset transistor formed in the second substrate that is coupled to the node; and
a source follower transistor formed in the second substrate that is coupled to the node.
8. The imaging pixel defined in claim 1 , further comprising a contact in the isolation regions that is coupled to ground.
9. The imaging pixel defined in claim 1 , further comprising:
a gate oxide formed underneath the transfer gate; and
an additional p-type doped region, wherein the gate oxide is interposed between the transfer gate and the additional p-type doped region.
10. An imaging sensor comprising an array of imaging pixels that are formed in at least first and second substrates, each imaging pixel of the array of imaging pixels comprising:
a photodiode formed in the first substrate;
a floating diffusion region formed in the first substrate;
a transfer transistor configured to transfer charge from the photodiode to the floating diffusion region, wherein the transfer transistor comprises a transfer gate with an opening that overlaps the floating diffusion region;
a shallow p-well that surrounds the floating diffusion region;
isolation regions; and
a p-stripe that couples the shallow p-well that surrounds the floating diffusion region to the isolation regions, wherein the p-stripe of each imaging pixel extendalong a longitudinal axis that defines an axis of symmetry for that imaging pixel.
11. The imaging sensor defined in claim 10 , wherein each imaging pixel further comprises:
an interconnect layer that couples the first substrate to the second substrate.
12. The imaging sensor defined in claim 11 , wherein each imaging pixel further comprises:
a node formed in the second substrate, wherein the interconnect layer couples the floating diffusion region in the first substrate to the node in the second substrate.
13. The imaging sensor defined in claim 12 , wherein each imaging pixel further comprises:
a reset transistor formed in the second substrate that is coupled to the node; and
a source follower transistor formed in the second substrate that is coupled to the node.
14. The imaging sensor defined in claim 10 , wherein the isolation regions of each imaging pixel comprise deep trench isolation.
15. The imaging sensor defined in claim 14 , wherein the isolation regions of each imaging pixel further comprise a p-well.
16. The imaging sensor defined in claim 15 , wherein the p-stripe of each imaging pixel comprises a strip of p-type doped silicon that extends along the longitudinal axis.
17. The imaging sensor defined in claim 10 , further comprising:
an additional conductive layer that connects at least first and second floating diffusion regions of respective first and second imaging pixels.
18. The imaging sensor defined in claim 10 , further comprising:
an additional conductive layer that connects at least first, second, third, and fourth floating diffusion regions of respective first second, third, and fourth imaging pixels.
19. The imaging sensor defined in claim 18 , wherein the first, second, third, and fourth imaging pixels are arranged in a 2×2 grid.