Image sensor with controllable vertically integrated photodetectors
View Patent ↗An image sensor includes front-side and backside photodetectors of a first conductivity type disposed in a substrate layer of the first conductivity type. A front-side pinning layer of a second conductivity type is connected to a first contact. The first contact receives a predetermined potential. A backside pinning layer of the second conductivity type is connected to a second contact. The second contact receives an adjustable and programmable potential.
1. A method for reading charge out of a pixel in an image sensor comprising a plurality of pixels, wherein the pixel includes a front-side photodetector of a first conductivity type disposed in a substrate layer of the first conductivity type adjacent to a front-side of the substrate layer, a backside photodetector of the first conductivity type disposed in the substrate layer adjacent to a backside of the substrate layer, a front-side pinning layer of a second conductivity type spanning the front-side photodetector, a backside pinning layer of the second conductivity type spanning the backside photodetector, a front-side charge to voltage conversion region of the first conductivity type disposed in a front-side well of the second conductivity adjacent to the front-side photodetector, and a buried layer of the second conductivity type disposed in the substrate layer between the front-side and backside photodetectors, wherein the buried layer is patterned with a gap in the buried layer that is aligned with the front-side and backside photodetectors such that a continuous region of the substrate layer extends from the front-side photodetector through the gap to the backside photodetector, the method comprising:
setting the front-side pinning layer to a first potential;
producing an electrostatic barrier between the front-side photodetector and the backside photodetector by adjusting an adjustable and programmable second potential on the backside pinning layer to a second potential and adjusting an adjustable and programmable third potential on the buried layer to a third potential;
capturing an image by collecting photogenerated charge in the front-side photodetector and in the backside photodetector;
transferring the charge from the front-side photodetector to the charge to voltage conversion region;
removing the electrostatic barrier between the backside photodetector and the front-side photodetector and transferring the charge from the backside photodetector to the front-side photodetector by adjusting the adjustable and programmable second and third potentials to different potentials; and
transferring the charge from the front-side photodetector to the charge to voltage conversion region.
2. The method as in claim 1 , wherein the pixel further includes a transfer gate between the front-side photodetector and the front-side charge to voltage conversion region.
3. The method as in claim 1 , wherein transferring the charge from front-side photodetector to the charge to voltage conversion region comprises pulsing a signal applied to the transfer gate to transfer the charge from front-side photodetector to the charge to voltage conversion region.
4. The method as in claim 1 , further comprising resetting the charge to voltage conversion region to a known potential prior to collecting photogenerated charge in the front-side and backside photodetectors and prior to transferring the charge from the front-side photodetector to the charge to voltage conversion region.
5. The method as in claim 1 , wherein the first conductivity type is a p conductivity type and the second conductivity type is an n conductivity type.