Split transfer gate for dark current suppression in an imager pixel
AssigneeMicron Technology, Inc.
InventorJohn Ladd
Life of this patent
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Abstract
A pixel with a photosensor and a transfer transistor having a split transfer gate. A first section of the transfer gate is connectable to a first voltage source while a second section of the transfer gate is connectable to a second voltage source. Thus, during a charge integration period of a photosensor, the two sections of the transfer gate may be oppositely biased to decrease dark current while controlling blooming of electrons within and out of the pixel cell. During charge transfer the two gate sections may be commonly connected to a positive voltage sufficient to transfer charge from the photosensor to a floating diffusion region.
Claims56
A pixel cell comprising:
- a photosensitive area;
- a storage region;
- and
- a transistor for transferring photo-charges from said photosensitive area of the pixel cell to said storage region, said transistor comprising:
- a gate structure between said photosensitive area and said storage region, said gate structure comprising:
- a dielectric layer;
- first and second gate electrode sections located over the dielectric layer;
- and
- an insulating region formed between the first and second gate electrode sections to electrically isolate said first and second gate electrode sections.
The pixel cell of claim 6, wherein the first gate electrode section is adjacent the photosensitive area on a first side and adjacent the insulating region on a second side.
A pixel cell comprising:
- a photosensitive element for generating charge in response to applied light;
- and
- a transfer transistor for transferring said generated charge to a storage node and having a split gate electrode, wherein a first section of said split electrode has a first terminal for connection to a first voltage source and a second section of said split electrode has a second terminal for connection to a second voltage source.
A pixel array comprising:
- an array of pixel sensor cells formed in a substrate, each pixel sensor cell comprising:
- an accumulation region formed in the substrate for accumulating photo-generated charges;
- and
- a transfer transistor for transferring said accumulated charges to a floating diffusion region and having a split gate electrode, wherein a first section of said split electrode is adapted for connection to a first voltage source and a second section of said split electrode is adapted for connection to a second voltage source.
An imager circuit comprising:
- a pixel cell comprising:
- a photosensitive area;
- a storage region;
- and
- a transistor for transferring photo-charges from said photosensitive area of the pixel cell to said storage region, said transistor comprising a gate having first and second gate electrode sections;
- and
- a circuit for applying a first voltage to said first gate section during a charge integration period and a second voltage to said second gate section during the charge integration period, wherein the first and second voltages are oppositely biased.
A processing system comprising:
- a processor;
- and
- an array of pixel sensor cells coupled to the processor, the array comprising a plurality of pixel sensor cells each comprising:
- a photosensitive element for generating and accumulating photo-generated charges in response to applied light;
- a floating diffusion region;
- and
- a transfer transistor for transferring said accumulated charges to said floating diffusion region and having a split gate electrode, wherein a first section of said split electrode is adapted for connection to a first voltage source and a second section of said split electrode is adapted for connection to a second voltage source.
A method of forming a pixel cell comprising the acts of:
- forming a photosensitive region in a substrate for generating photo-charges;
- forming a storage region in the substrate for storing the photo-charges;
- and
- forming a transistor for transferring the charges from the photosensitive region to the storage region, comprising the acts of:
- forming a gate oxide layer at a surface of the substrate;
- forming first and second gate electrode sections over the gate oxide layer in a location between the photosensitive region and the storage region;
- and
- forming an isolation region between the first and second gate electrode sections.
A method of forming an imager circuit comprising the acts of:
- forming a photosensitive area in a substrate;
- forming a charge storage region in the substrate;
- and
- forming a transfer transistor having a gatestack for transferring charge from said photosensitive area to said charge storage region, said forming of said transfer transistor comprising the acts of:
- forming first and second gate electrode sections located above the substrate;
- and
- forming an isolation region located between the first and second electrode sections;
- and
- forming a voltage supply circuit capable of supplying a first voltage to the first gate electrode section and a second voltage to the second gate electrode section during a charge integration period.
A method of operating a pixel cell comprising:
- applying light during an integration period to a photosensitive area of the pixel cell;
- storing transferred photo-generated charges in a storage region;
- applying a first voltage to a first section of a split gate electrode of a transfer transistor provided between the photosensitive area and the charge storage region during a charge integration period;
- and
- applying a second voltage to a second section of the split gate electrode during said charge integration period.
A method of operating a pixel cell comprising:
- biasing a first gate section of a transfer transistor, which is adjacent a photodiode in a substrate, to lower a depletion region associated with the photodiode from a top surface of the substrate during a charge integration period;
- and
- biasing a second gate section of a transfer transistor to facilitate the movement of electrons to a floating diffusion region during the charge integration period.
Dependencies are inferred from the claim text.