Image sensors with split photodiodes
An imaging device may have an array of image sensor pixels. Each image sensor pixel of the array of image sensor pixels may have split photodiodes that are symmetric about a shared floating diffusion region. The floating diffusion region may be coupled to each of the photodiodes. Each of the split photodiodes and the floating diffusion region may generate charge in response to light incident on the image sensor pixel. The split photodiodes and the floating diffusion region may be covered by a microlens. The charge generated by the photodiodes and the floating diffusion region may be compared and utilized by the imaging device in phase detection applications. The image sensor pixel may also include a dual conversion gain capacitor and a gain select transistor to produce high dynamic range (HDR) images.
1. An image sensor pixel that is configured to generate image signals in response to light, the image sensor pixel comprising:
a first photosensitive region that is configured to generate charge in response to the light;
a second photosensitive region that is configured to generate charge in response to the light;
a floating diffusion region that is configured to generate charge in response to the light, wherein the floating diffusion region is coupled to the first photosensitive region and the second photosensitive region and wherein the first photosensitive region and the second photosensitive region are symmetric about the floating diffusion region; and
a semiconductor substrate having opposing first and second surfaces, wherein the first and second photosensitive regions and the floating diffusion region extend from the first surface to the second surface.
2. The image sensor pixel defined in claim 1 , further comprising:
a microlens that covers the first photosensitive region, the second photosensitive region, and the floating diffusion region.
3. The image sensor pixel defined in claim 2 , further comprising:
isolation structures in the semiconductor substrate, wherein the isolation structures are interposed between the first photosensitive region, the second photosensitive region, and the floating diffusion region and wherein the first photosensitive region, the second photosensitive region, and the floating diffusion region are left uncovered by the isolation structures.
4. The image sensor pixel defined in claim 3 , wherein the isolation structures comprise deep trench isolation structures.
5. The image sensor pixel defined in claim 1 , further comprising:
a dual conversion gain capacitor coupled to the floating diffusion region, wherein the dual conversion gain capacitor is configured to store overflow charge generated by the floating diffusion region.
6. The image sensor pixel defined in claim 5 , further comprising:
a gain select transistor coupled between the floating diffusion region and the dual conversion gain capacitor, wherein the gain select transistor is configured to be turned on to electrically connect the floating diffusion region to the dual conversion gain capacitor and provide the floating diffusion region with additional capacitance.
7. The image sensor pixel defined in claim 6 , further comprising:
column readout circuitry coupled to the floating diffusion region, wherein the column readout circuitry is configured to read out the charge generated by the floating diffusion region and the first and second photosensitive regions.
8. The image sensor pixel defined in claim 7 wherein the gain select transistor is configured to be turned on while the charge generated by the floating diffusion region is read out and wherein the gain select transistor is configured to be turned off while the charge generated by the first and second photosensitive regions is read out.
9. An image sensor pixel, comprising:
a semiconductor substrate with first and second opposing surfaces;
a first photosensitive region in the semiconductor substrate that extends from the first surface towards the second surface and has a first height;
a second photosensitive region in the semiconductor substrate that extends from the first surface towards the second surface and has a second height; and
a floating diffusion region in the semiconductor substrate that is coupled to the first photosensitive region and the second photosensitive region, wherein the floating diffusion region extends from the first surface towards the second surface and has a third height, wherein the third height is within 20% of the first height, and wherein the third height is within 20% of the second height.
10. The image sensor pixel defined in claim 9 , further comprising:
a microlens that covers the first photosensitive region, the second photosensitive region, and the floating diffusion region.
11. The image sensor pixel defined in claim 9 , wherein the first photosensitive region, the second photosensitive region, and the floating diffusion region are each n-type doped regions of the semiconductor substrate.
12. The image sensor pixel defined in claim 11 , wherein the first photosensitive region, the second photosensitive region, and the floating diffusion region extend from the first surface to within 1 micron of the second surface.
13. A method of operating an image sensor pixel that includes first and second photosensitive regions, a floating diffusion region, a first transfer transistor between the first photosensitive region and the floating diffusion region, and a second transfer transistor between the second photosensitive region and the floating diffusion region, the method comprising:
with the first photosensitive region, the second photosensitive region, and the floating diffusion region, generating charge during an integration time;
after generating the charge, reading out charge generated by the floating diffusion region; and
after reading out the charge generated by the floating diffusion region, reading out charge generated by the first photosensitive region and the second photosensitive region.
14. The method defined in claim 13 , wherein reading out the charge generated by the first photosensitive region and the second photosensitive region comprises reading out the charge generated by the first photosensitive region and the second photosensitive region simultaneously.
15. The method defined in claim 14 , further comprising:
after reading out the charge generated by the floating diffusion region, resetting the floating diffusion region to a first reset value;
reading out the first reset value;
after reading out the first reset value, resetting the floating diffusion region to a second reset value; and
reading out the second reset value.
16. The method defined in claim 13 , wherein reading out the charge generated by the first photosensitive region and the second photosensitive region comprises reading out the charge generated by the first photosensitive region prior to reading out the charge generated by the second photosensitive region.
17. The method defined in claim 16 , further comprising:
after reading out the charge generated by the floating diffusion region, resetting the floating diffusion region to a first reset value;
reading out the first reset value;
after reading out the first reset value, resetting the floating diffusion region to a second reset value associated with the first photosensitive region;
reading out the second reset value;
after reading out the charge generated by the first photosensitive region, resetting the floating diffusion region to a third reset value associated with the second photosensitive region; and
reading out the third reset value.
18. The method defined in claim 13 , wherein the image sensor pixel further comprises a dual conversion gain capacitor coupled to the floating diffusion region and a gain select transistor coupled between the dual conversion gain capacitor and the floating diffusion region, the method further comprising:
after generating the charge during the integration time, activating the gain select transistor, wherein reading out the charge generated by the floating diffusion region comprises reading out the charge generated by the floating diffusion region while the gain select transistor is activated.
19. The method defined in claim 18 , further comprising:
after reading out the charge generated by the floating diffusion region, deactivating the gain select transistor, wherein reading out the charge generated by the first photosensitive region and the second photosensitive region comprises reading out the charge generated by the first photosensitive region and the second photosensitive region while the gain select transistor is deactivated.