Imaging with gate controlled charge storage
View Patent ↗A pixel cell comprises a photo-conversion device for generating charge and a gate controlled charge storage region for storing photo-generated charge under control of a control gate. The charge storage region can be a single CCD stage having a buried channel to obtain efficient charge transfer and low charge loss. The charge storage region is adjacent to a gate of a transistor. The transistor gate is adjacent to the photo-conversion device and, in conjunction with the control gate, transfers photo-generated charge from the photo-conversion device to the charge storage region.
1. A pixel cell comprising:
a photo-conversion device that generates charge;
a gate controlled charge storage region that stores the charge;
a first transistor having its gate between the photo-conversion device and the charge storage region for transferring charge from the photo-conversion device to the charge storage region; and
a control gate that controls the charge stored in the gate controlled charge storage region,
wherein the charge storage region comprises:
a doped region of a second conductivity type; and
a doped surface region of a first conductivity type over and in contact with the doped region of a second conductivity type, the control gate being over the doped surface region.
2. The pixel cell of claim 1 , wherein the charge storage region is part of a buried channel MOS capacitor.
3. The pixel cell of claim 1 , wherein the charge storage region is below a surface of the substrate.
4. The pixel cell of claim 1 , wherein the control gate comprises polysilicon doped with a first conductivity type dopant.
5. The pixel cell of claim 1 , wherein the first transistor is a shutter transistor for determining an integration time for the pixel cell.
6. The pixel cell of claim 1 , wherein the photo-conversion device is a pinned photodiode.
7. A pixel cell comprising:
a photo-conversion device that generates charge;
a gate controlled charge storage region that stores the charge, wherein the charge storage region comprises a doped region of a second conductivity type and a doped surface region of a first conductivity type over and in contact with the doped region of a second conductivity type;
a first transistor between the photo-conversion device and the charge storage region for transferring charge from the photo-conversion device to the charge storage region; and
a control gate that controls the charge stored in the gate controlled charge storage region, the control gate being located over the doped region.
8. The pixel cell of claim 7 , wherein the charge storage region is part of a buried channel metal oxide semiconductor (MOS) capacitor.