CCD image sensors having multiple lateral overflow drain regions for a horizontal shift register
View Patent ↗A charge-coupled device (CCD) image sensor includes a layer of a semiconductor material having a first conductivity type. A horizontal CCD channel region of a second conductivity type is disposed in the layer of the semiconductor material. The horizontal CCD channel region includes multiple phases that are used to shift photo-generated charge through the horizontal CCD channel region. Distinct overflow drain regions are disposed in the layer of semiconducting material, with an overflow drain region electrically connected to only one particular phase of the horizontal CCD channel region.
1. A charge-coupled device (CCD) image sensor comprising:
an array of pixels each comprising a photodectector for conversion of incident light into electrical charge;
electrically connected to the array of pixels, a horizontal CCD channel region comprising a plurality of shift elements for receiving change from the array of pixels and transferring the charge out of the array for conversion into an image each shift element comprising a plurality of phases; and
associated with each shift element, a distinct overflow drain electrically connected to only one phase of the shift element, the phase being a drainable phase comprising (i) a first region proximate the array of pixels and (ii) a second region proximate the overflow drain,
wherein a channel width of the drainable phase in the second region is narrower than a channel width of the drainable phase in the first region, the narrower channel width in the second region forming a potential barrier having a height selected to prevent charge blooming from the drainable phase into a component other than the overflow drain to which the drainable phase is connected.
2. The CCD image sensor of claim 1 , further comprising a plurality of channel stop regions adjoining the second region of the drainable phase.
3. The CCD image sensor of claim 2 , wherein the narrower channel width in the second region is defined at least in part by dopants laterally diffused from the channel stop regions adjoining the second region.
4. The CCD image sensor of claim 1 , further comprising a conductive bus electrically connected to all of the distinct overflow drains.
5. The CCD image sensor of claim 4 , wherein the conductive bus comprises a metal.
6. The CCD image sensor of claim 5 , wherein the metal comprises at least one of aluminum or copper.
7. The CCD image sensor of claim 4 , further comprising a source of power supply bias electrically connected to the conductive bus.
8. The CCD image sensor of claim 1 , further comprising, for transferring charge from the pixels to the horizontal CCD channel region, a plurality of vertical CCD channel regions each electrically connected to (i) a plurality of pixels and (ii) the horizontal CCD channel region.
9. The CCD image sensor of claim 8 , wherein each vertical CCD channel region comprises a plurality of phases, one of the phases being directly connected to the horizontal CCD channel region.
10. The CCD image sensor of claim 9 , wherein, for each of the vertical CCD channel regions, the phase of the vertical CCD channel region directly connected to the horizontal CCD channel region is connected to the drainable phase of the horizontal CCD channel region.
11. The CCD image sensor of claim 9 , further comprising, electrically connected to the horizontal CCD channel region, circuitry for conversion of charge received from the horizontal CCD channel region into an image.
12. The CCD image sensor of claim 11 , wherein the circuitry comprises an output amplifier.