Twin p-well CMOS imager
View Patent ↗A CMOS imager which includes a substrate voltage pump to bias a doped area of a substrate to prevent leakage into the substrate from the transistors formed in the doped area. The invention also provides a CMOS imager where a photodetector sensor array is formed in a first p-well and readout logic is formed in a second p-well. The first p-well can be selectively doped to optimize cross-talk, collection efficiency and transistor leakage, thereby improving the quantum efficiency of the sensor array while the second p-well can be selectively doped and/or biased to improve the speed and drive of the readout circuitry.
1. An imaging device comprising:
a substrate;
a photosensitive area within a first p-well formed in said substrate for accumulating photo-generated charge in said area; and
a periphery logic area within in a second p-well in said substrate; and
a n-well disposed between said first and second p-wells,
wherein said first p-well is deeper than said second p-well and said second p-well is doped to a higher ion concentration than said first p-well.
2. The imaging device according to claim 1 , wherein the accumulation of charge in said photosensitive area is controlled by a photogate.
3. The imaging device according to claim 1 , wherein said photosensitive area comprises a photodiode.
4. The imaging device according to claim 1 , wherein the accumulation of charge in said photosensitive area is controlled by a photoconductor.
5. The imaging device according to claim 1 , wherein said first p-well is doped to reduce cross-talk, increase collection efficiency and reduce transistor leakage in said imaging device.
6. The imaging device according to claim 5 , wherein said first p-well is doped with boron.
7. The imaging device according to claim 6 , wherein said first p-well is doped with boron implanted at a total dose of from about 1.0×10 11 ions/cm 2 to about 1.0×10 13 ions/cm 2 .
8. The imaging device according to claim 6 , wherein said first p-well is doped with boron implanted at a total dose of from about 2.0×10 11 ions/cm 2 to about 5.0×10 12 ions/cm 2 .
9. The imaging device according to claim 6 , wherein said first p-well is doped with boron implanted at a total dose of about 5.0×10 11 ions/cm 2 .
10. The imaging device according to claim 1 , wherein said first p-well has a depth of from about 2 to about 8 microns.
11. The imaging device according to claim 10 , wherein said first p-well has a depth of about 5 microns.
12. The imaging device according to claim 1 , wherein said second p-well is selectively doped to provide high speed in said imaging device.
13. The imaging device according to claim 12 , wherein said second p-well is doped with boron.
14. The imaging device according to claim 12 , wherein said second p-well is doped with boron implanted at a total dose of from about 5.0×10 11 ions/cm 2 to about 5.0×10 13 ions/cm 2 .
15. The imaging device according to claim 12 , wherein said second p-well is doped with boron implanted at a total dose of from about 1.0×10 12 ions/cm 2 to about 2.0×10 13 ions/cm 2 .
16. The imaging device according to claim 12 , wherein said second p-well is doped with boron implanted at a total dose of about 4.0×10 12 ions/cm 2 .
17. The imaging device according to claim 1 , wherein said first p-well is doped with boron at a total dose of from about 1.0×10 11 ions/cm 2 to about 1.0×10 13 ions/cm 2 and said second p-well is doped with boron at a total dose of from about 5.0×10 11 ions/cm 2 to about 5.0×10 13 ions/cm 2 .
18. The imaging device according to claim 17 , wherein said first p-well is doped with boron at a total dose of from about 2.0×10 11 ions/cm 2 to about 5.0×10 12 ions/cm 2 and said second p-well is doped with boron at a total dose of from about 1.0×10 12 ions/cm 2 to about 2.0×10 13 ions/cm 2 .
19. The imaging device according to claim 17 wherein said first p-well is doped with boron at a total dose of about 5×10 11 and has a depth of about 2 to 8 microns and said second p-well is doped with boron at a total dose of about 4×10 12 and has a depth of about 1 to 5 microns.
20. The imaging device according to claim 19 wherein said first p-well is doped with boron at a total dose of about 5×10 11 and has a depth of about 5 microns and said second p-well is doped with boron at a total dose of about 4×10 12 and has a depth of about 3 microns.
21. The imaging device according to claim 1 , wherein an n-well is formed in said substrate between said first p-well and said second p-well.
22. The imaging device according to claim 1 , wherein said second p-well is formed within an n-well.
23. The imaging device according to claim 1 , further comprising a first substrate voltage pump coupled to a supply voltage and connected to supply said first p-well with a first predetermined voltage.
24. The imaging device according to claim 23 , further comprising a second substrate voltage pump coupled to a supply voltage and connected to supply said second p-well with a second predetermined voltage.
25. The imaging device according to claim 22 , further comprising:
a first substrate voltage pump coupled to a supply voltage and connected to supply said first p-well with a first predetermined voltage;
a second substrate voltage pump coupled to a supply voltage and connected to supply said second p-well with a second predetermined voltage; and
a third substrate voltage pump coupled to a supply voltage and connected to supply said n-well with a third predetermined voltage.
26. The imaging device according to claim 1 , wherein the first and second p-wells are disjoint.
27. The imaging device according to claim 1 , wherein the n-well is in direct contact with the substrate.
28. An imaging device including a semiconductor integrated circuit substrate, said imaging device comprising:
a photosensitive device formed in a first p-well in said substrate for accumulating photo-generated charge in an underlying portion of said substrate, said photosensitive device comprising a first transitor;
a periphery logic area formed in a second p-well in said substrate, said periphery logic area comprising a second transitor; and
a n-well disposed between said first and second p-wells,
wherein said first transistor has a higher threshold voltage than said second transistor, said first p-well is deeper than said second p-well, and said second p-well is doped to a higher ion concentration than said first p-well.
29. The imaging device according to claim 28 , wherein said photosensitive device is a photogate.
30. The imaging device according to claim 28 , wherein said photosensitive device is a photodiode.
31. The imaging device according to claim 28 , wherein said photosensitive device is a photoconductor.
32. The imaging device according to claim 28 , wherein said first p-well is selectively doped to optimize the cross-talk, collection efficiency and transistor leakage in said imaging device.
33. The imaging device according to claim 32 , wherein said first p-well is doped with boron.
34. The imaging device according to claim 33 , wherein said first p-well is doped with boron implanted at a total dose of from about 1.0×10 11 ions/cm 2 to about 1.0×10 13 ions/cm 2 .
35. The imaging device according to claim 33 , wherein said first p-well is doped with boron implanted at a total dose of from about 2.0×10 11 ions/cm 2 to about 5.0×10 12 ions/cm 2 .
36. The imaging device according to claim 33 , wherein said first p-well is doped with boron implanted at a total dose of about 5.0×10 11 ions/cm 2 .
37. The imaging device according to claim 28 , wherein said first p-well has a depth of from about 2 to about 8 microns.
38. The imaging device according to claim 37 , wherein said first p-well has a depth of about 5 microns.
39. The imaging device according to claim 28 , wherein said second p-well is selectively doped to provide high speed in said imaging device.
40. The imaging device according to claim 39 , wherein said second p-well is doped with boron.
41. The imaging device according to claim 40 , wherein said second p-well is doped with boron implanted at a total dose of from about 5.0×10 11 ions/cm 2 to about 5.0×10 13 ions/cm 2 .
42. The imaging device according to claim 40 , wherein said second p-well is doped with boron implanted at a total dose of from about 1.0×10 12 ions/cm 2 to about 2.0×10 13 ions/cm 2 .
43. The imaging device according to claim 40 , wherein said second p-well is doped with boron at a concentration of about 4.0×10 12 ions/cm 2 .
44. The imaging device according to claim 28 , wherein said first p-well is doped with boron at a total dose of from about 1.0×10 11 ions/cm 2 to about 1.0×10 13 ions/cm 2 and said second p-well is doped with boron at a total dose of from about 5.0×10 11 ions/cm 2 to about 5.0×10 13 ions/cm 2 .
45. The imaging device according to claim 44 , wherein said first p-well is doped with boron at a total dose of from about 2.0×10 11 ions/cm 2 to about 5.0×10 12 ions/cm 2 and said second p-well is doped with boron at a total dose of from about 1.0×10 12 ions/cm 2 to about 2.0×10 13 ions/cm 2 .
46. The imaging device according to claim 43 wherein said first p-well is doped with boron at a total dose of about 5×10 11 and has a depth of about 2 to 8 microns and said second p-well is doped with boron at a total dose of about 4×10 12 and has a depth of about 1 to 5 micron.
47. The imaging device according to claim 28 , wherein said wells are formed in an n-type substrate.
48. The imaging device according to claim 28 , further comprising a substrate voltage pump coupled to a supply voltage and connected to supply said substrate with a voltage.
49. The imaging device according to claim 28 , further comprising a first substrate voltage pump coupled to a supply voltage and connected to supply said first p-well with a first predetermined voltage.
50. The imaging device according to claim 49 , further comprising a second substrate voltage pump coupled to a supply voltage and connected to supply said second p-well with a second predetermined voltage.
51. The imaging device according to claim 47 , further comprising:
a first substrate voltage pump coupled to a supply voltage and connected to supply said first p-well with a first predetermined voltage;
a second substrate voltage pump coupled to a supply voltage and connected to supply said second p-well with a second predetermined voltage; and
a third substrate voltage pump coupled to a supply voltage and connected to supply said n-type substrate with a third predetermined voltage.
52. The imaging device according to claim 28 , wherein the first and second p-wells are disjoint.
53. The imaging device according to claim 28 , wherein the n-well is in direct contact with the substrate.
54. An imaging system comprising:
a processor; and
a CMOS imaging device coupled to said processor and including:
a photosensitive area within a first p-well in a substrate for accumulating photo-generated charge in said area;
a periphery logic area formed in a second p-well in said substrate; and
a n-well disposed between said first and second p-wells,
wherein said first p-well is doped to a greater depth than said second p-well and said second p-well is doped to a higher ion concentration than said first p-well.
55. The system according to claim 54 , wherein the accumulation of charge in said photosensitive area is controlled by a photogate.
56. The system according to claim 54 , wherein said photosensitive area is a photodiode.
57. The system according to claim 54 , wherein said photosensitive area is controlled by a photoconductor.
58. The system according to claim 54 , wherein said first p-well is selectively doped to optimize the cross-talk, collection efficiency and transistor leakage.
59. The system according to claim 54 , wherein said first p-well is doped with boron.
60. The system according to claim 59 , wherein said first p-well is doped with boron implanted at a total dose of from about 1.0×10 11 ions/cm 2 to about 1.0×10 13 ions/cm 2 .
61. The system according to claim 59 , wherein said first p-well is doped with boron implanted at a total dose of from about 2.0×10 11 ions/cm 2 to about 5.0×10 12 ions/cm 2 .
62. The system according to claim 59 , wherein said first p-well is doped with boron implanted at a total dose of about 5.0×10 11 ions/cm 2 .
63. The system according to claim 54 , wherein said first p-well has a depth of from about 2 to about 8 microns.
64. The system according to claim 63 , wherein said first p-well has a depth of about 5 microns.
65. The system according to claim 54 , wherein said second p-well is selectively doped to provide high speed in said imaging device.
66. The system according to claim 65 , wherein said second p-well is doped with boron.
67. The system according to claim 65 , wherein said second p-well is doped with boron implanted at a total dose of from about 5.0×10 11 ions/cm 2 to about 5.0×10 13 ions/cm 2 .
68. The system according to claim 65 , wherein said second p-well is doped with boron implanted at a total dose of from about 1.0×10 12 ions/cm 2 to about 2.0×10 13 ions/cm 2 .
69. The system according to claim 65 , wherein said second p-well is doped with boron at a concentration of about 4.0×10 12 ions/cm 2 .
70. The imaging device according to claim 54 , wherein said first p-well is doped with boron at a total dose of from about 1.0×10 11 ions/cm 2 to about 1.0×10 13 ions/cm 2 and said second p-well is doped with boron at a total dose of from about 5.0×10 11 ions/cm 2 to about 5.0×10 13 ions/cm 2 .
71. The imaging device according to claim 70 , wherein said first p-well is doped with boron at a total dose of from about 2.0×10 11 ions/cm 2 to about 5.0×10 12 ions/cm 2 and said second p-well is doped with boron at a total dose of from about 1.0×10 12 ions/cm 2 to about 2.0×10 13 ions/cm 2 .
72. The imaging device according to claim 70 wherein said first p-well is doped with boron at a total dose of about 5×10 11 and has a depth of about 2 to 8 microns and said second p-well is doped with boron at a total dose of about 4×10 12 and has a depth of about 1 to 5 micron.
73. The system according to claim 54 , wherein said second p-well is formed within an n-well.
74. The system according to claim 54 , further comprising a substrate voltage pump coupled to a supply voltage and connected to supply said substrate with a voltage.
75. The system according to claim 54 , further comprising a first substrate voltage pump coupled to a supply voltage and connected to supply said first p-well with a first predetermined voltage.
76. The system according to claim 75 , further comprising a second substrate voltage pump coupled to a supply voltage and connected to supply said second p-well with a second predetermined voltage.
77. The system according to claim 73 , further comprising:
a first substrate voltage pump coupled to a supply voltage and connected to supply said first p-well with a first predetermined voltage;
a second substrate voltage pump coupled to a supply voltage and connected to supply said second p-well with a second predetermined voltage; and
a third substrate voltage pump coupled to a supply voltage and connected to supply said n-well with a third predetermined voltage.
78. The imaging device according to claim 54 , wherein the first and second p-wells are disjoint.
79. The imaging device according to claim 54 , wherein the n-well is in direct contact with the substrate.