Twin p-well CMOS imager

Abstract

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.

What is claimed as new and desired to be protected by Letters Patent of the United States is: 
     
       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 transistor; 
 a periphery logic area formed in a second p-well in said substrate, said periphery logic area comprising a second transistor; 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. 
     
     
       80. A CMOS imager, comprising:
 a pixel array comprising a pixel coupled to a column output line to provide a pixel output signal to the column output line, the pixel including a first n-channel reset transistor comprising a first p-well region of the array, wherein the first n-channel reset transistor has a first threshold voltage;   a peripheral region, including a readout circuit coupled to the column output line, to receive the pixel output signal from the array, the peripheral region including a second n-channel transistor including a second p-well region of the periphery and a p-channel transistor including an n-well region of the periphery, wherein the second n-channel transistor has a second threshold voltage that is independent from the first threshold voltage, and the n-well region is disposed between the first and second p-well regions; and   a voltage pump to provide a negative voltage to the first n-channel reset transistor to turn off the n-channel reset transistor.   
     
     
       81. The CMOS imager of claim 80, wherein the voltage pump is coupled to the first p-well region. 
     
     
       82. The CMOS imager of claim 80, wherein the first threshold voltage is higher than the second threshold voltage.