Retrograde well structure for a CMOS imager
First Claim
1. A pixel sensor cell for an imaging device, said pixel sensor cell comprising:
- a retrograde well of a first conductivity type formed in a substrate;
a photosensitive region formed in said retrograde well;
a floating diffusion region of a second conductivity type formed in said retrograde well for receiving charges transferred from said photosensitive region;
a periphery well of one of said first or second conductivity type formed in said substrate in proximity to said retrograde well; and
peripheral devices formed in said periphery well.
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Abstract
A retrograde and periphery well structure for a CMOS imager is disclosed which improves the quantum efficiency and signal-to-noise ratio of the photosensing portion imager. The retrograde well comprises a doped region with a vertically graded dopant concentration that is lowest at the substrate surface, and highest at the bottom of the well. A single retrograde well may have a single pixel sensor cell, multiple pixel sensor cells, or even an entire array of pixel sensor cells formed therein. The highly concentrated region at the bottom of the retrograde well repels signal carriers from the photosensor so that they are not lost to the substrate, and prevents noise carriers from the substrate from diffusing up into the photosensor. The periphery well contains peripheral logic circuitry for the imager. By providing retrograde and peripheral wells, circuitry in each can be optimized. Also disclosed are methods for forming the retrograde and peripheral well.
57 Citations
81 Claims
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1. A pixel sensor cell for an imaging device, said pixel sensor cell comprising:
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a retrograde well of a first conductivity type formed in a substrate;
a photosensitive region formed in said retrograde well;
a floating diffusion region of a second conductivity type formed in said retrograde well for receiving charges transferred from said photosensitive region;
a periphery well of one of said first or second conductivity type formed in said substrate in proximity to said retrograde well; and
peripheral devices formed in said periphery well. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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28. A pixel sensor cell for an imaging device, said pixel sensor cell comprising:
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a retrograde well of a first conductivity type formed in a substrate;
a photosensor formed in said retrograde well;
a reset transistor having a gate stack formed in said retrograde well;
a floating diffusion region of a second conductivity type formed in said retrograde well between said photosensor and reset transistor for receiving charges from said photosensor, said reset transistor operating to periodically reset a charge level of said floating diffusion region;
a periphery well of one of said first and second conductivity type formed in said substrate adjacent said retrograde well; and
an output transistor having a gate electrically connected to said floating diffusion region, wherein said output transistor is formed in said periphery well. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53)
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54. A CMOS imager comprising:
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a substrate having at least one retrograde well of a first conductivity type;
an array of pixel sensor cells formed in said at least one retrograde well, wherein each pixel sensor cell has a photosensor;
at least one periphery well of said first or a second conductivity type formed in a substrate; and
a circuit formed in said periphery well, said circuit being electrically connected to receive and process output signals from said array. - View Dependent Claims (55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81)
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Specification
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Current AssigneeAptina Imaging Corporation (ON Semiconductor Corporation)
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Original AssigneeMicron Technology, Inc.
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InventorsRhodes, Howard E., Durcan, Mark
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Primary Examiner(s)Wilson, Allan R.
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Application NumberUS09/645,582Time in Patent Office739 DaysField of Search257/185, 257/431, 257/655, 257/917US Class Current257/185CPC Class CodesH01L 27/14601 Structural or functional de...H01L 27/14609 Pixel-elements with integra...
