CMOS imager with improved sensitivity
First Claim
Patent Images
1. A CMOS image sensor element formed in a semiconductor substrate of a first doping type for converting impinging electromagnetic radiation into electric signals, the sensor element comprising:
- a first well formed in said substrate and doped with the first doping type to a higher doping level than the substrate, wherein at last a portion of said first well defines the gate region of a first transistor;
a second well formed in said first well and doped with a second doping type, said second well defining the source of the first transistor;
a third well formed substantially in said substrate and doped with the second doping type, said third well defining a photodiode and the drain of the first transistor; and
a fourth well formed in said substrate and doped with the first doping type to a higher doping level than the substrate, said fourth well defining the gate region of a second transistor;
so that electric charges generated by the electromagnetic radiation in the semiconductor substrate proximate to said third well and said fourth well are preferably collected in said third well whereby quantum efficiency can be maintained with reduced feature size of said sensor element.
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Abstract
An improved pixel design for a CMOS image sensor with a small feature size is described. In conventional image sensors of this type, the quantum efficiency is typically reduced as a result of the decreased thickness of the top n-type layer of the photodiode and the presence of an intervening p-type layer which is higher doped than the substrate. In the pixel design of the invention, the higher doped p-type layer underneath the photodiode is omitted while barrier regions channel the carriers generated by the impinging radiation towards the top n-layer of the photodiode. A high quantum efficiency is thereby attained in spite of a shrinking feature size. The novel pixel design can also incorporate anti-blooming protection.
55 Citations
16 Claims
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1. A CMOS image sensor element formed in a semiconductor substrate of a first doping type for converting impinging electromagnetic radiation into electric signals, the sensor element comprising:
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a first well formed in said substrate and doped with the first doping type to a higher doping level than the substrate, wherein at last a portion of said first well defines the gate region of a first transistor;
a second well formed in said first well and doped with a second doping type, said second well defining the source of the first transistor;
a third well formed substantially in said substrate and doped with the second doping type, said third well defining a photodiode and the drain of the first transistor; and
a fourth well formed in said substrate and doped with the first doping type to a higher doping level than the substrate, said fourth well defining the gate region of a second transistor;
so that electric charges generated by the electromagnetic radiation in the semiconductor substrate proximate to said third well and said fourth well are preferably collected in said third well whereby quantum efficiency can be maintained with reduced feature size of said sensor element. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
a plurality of fifth wells formed in said substrate and doped with the second doping type, wherein each of said plurality of fifth wells defines a respective source and drain of the second transistor;
wherein said fourth well extends at least partially along the periphery of said plurality of fifth wells, so that excess electric charges generated by the electromagnetic radiation proximate to said third well are preferably collected in said fifth wells to prevent blooming.
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4. The image sensor element of claim 1, wherein said substrate is p-type silicon.
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5. The image sensor element of claim 1, wherein said substrate is an epitaxial layer of p-type silicon disposed on a carrier.
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6. The image sensor element of claim 4, wherein the thickness of the third well is between 0.05 μ
- m and 1.0 μ
m.
- m and 1.0 μ
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7. The image sensor element of claim 4, wherein the third well is doped n-type and the dopant concentration in the third region is between 1×
- 1019 cm−
3 and 1×
1021 cm−
3.
- 1019 cm−
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8. The image sensor of claim 1, wherein the dopant concentration in the first well is between 1×
- 1016 cm3 and 1×
1018 cm−
3.
- 1016 cm3 and 1×
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9. An image sensor formed in a semiconductor substrate of a first doping type in the form of an array of pixel elements arranged in a matrix pattern of rows and columns, said substrate having a surface, wherein each of the pixel elements includes a photodiode for receiving electromagnetic radiation and converting said electromagnetic radiation into electric charges, a plurality of transistors for controlling and sensing said electric charges, each transistor having a source, a drain and a gate, and connections for interconnecting said photodiode and said transistor in a manner as to enable row-wise and column-wise addressing of said image sensor, the pixel comprising:
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a plurality of first regions formed in said substrate and doped with the first doping type at a higher dopant concentration than said substrate, said first regions forming the transistor gate regions;
a plurality of second regions formed in the substrate and doped with a second doping type, said second regions laterally defining the transistor source and drain regions;
a third region formed in said substrate and doped with the second doping type and laterally defining the photodiode, said third region laterally contiguous with the drain of at least one of the transistors;
wherein said first regions extend also along at least a portion of the peripheral marginal regions of the second and third regions, so that the electric charges generated proximate to said third region are preferably collected in said third region and excess electric charges are preferably collected in said second regions to prevent blooming. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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Specification
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Current AssigneeHanger Solutions, LLC (IP Investments Group LLC)
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Original AssigneePolaroid Corporation (PLR IP Holdings LLC)
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InventorsMcGrath, Robert Daniel
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Primary Examiner(s)WOJCIECHOWICZ, EDWARD JOSEPH
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Application NumberUS09/028,072Time in Patent Office1,044 DaysField of Search257/282, 257/369, 257/431, 257/444, 257/445US Class Current257/445CPC Class CodesH01L 27/14609 Pixel-elements with integra...H01L 27/14654 Blooming suppression
