Color separation in an active pixel cell imaging array using a triple-well structure

• US 5,965,875 A
• Filed: 04/24/1998
• Issued: 10/12/1999
• Est. Priority Date: 04/24/1998
• Status: Expired due to Term

• Current Assignee: Foveon, Inc. (Avis Budget Group Incorporated)
• Original Assignee: Foveon, Inc. (Avis Budget Group Incorporated)
• Inventors: Merrill, Richard Billings
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US09/065,939
• Time in Patent Office: 536 Days
• Field of Search: 250/226, 250/208.1, 250/214.1, 257/440, 257/458, 257/463
• US Class Current: 250/226
• CPC Class Codes: H01L 27/14623 Optical shielding
• CPC Class Codes: H01L 27/14647 Multicolour imagers having a stacked pixel-element structure, e.g. npn, npnpn or MQW elements
• CPC Class Codes: H04N 2209/047 using multispectral pick-up elements
• CPC Class Codes: H04N 25/134 based on three different wavelength filter elements
• CPC Class Codes: H04N 25/17 Colour separation based on photon absorption depth, e.g. full colour resolution obtained simultaneously at each pixel location

Abstract

A digital imager apparatus uses the differences in absorption length in silicon of light of different wavelengths for color separation. A preferred imaging array is based upon a three-color pixel sensor using a triple-well structure. The array results in elimination of color aliasing by measuring each of the three primary colors (RGB) in each pixel in the same location.

Claims

1. A color photosensing structure formed in a silicon substrate of a first conductivity type for separating light of differing wavelengths, the color photosensor structure comprising:

a first doped region of a second conductivity type opposite the first conductivity type formed in the silicon substrate, the junction between the first doped region and the silicon substrate being formed at a depth in the silicon substrate of about the absorption length in silicon of a first light wavelength to define a first photodiode;

a second doped region of the first conductivity type formed in the first doped region, the junction between the second doped region and the first doped region being formed at a depth in the first doped region of about the light absorption length in silicon of a second light wavelength to define a second photodiode;

a third doped region of the second conductivity type formed in the second doped region, the junction between the third doped region and the second doped region being formed at a depth in the second doped region of about the light absorption length in silicon of a third light wavelength to define a third photodiode; and

a photocurrent sensor connected to measure first, second and third photocurrents across the first, second and third photodiodes, respectively.

2. A color photosensing structure as in claim 1, and wherein

the junction between the first doped region and the silicon substrate is formed at a depth in the silicon substrate of about 1.5-3.0 microns;

the junction between the second doped region and the first doped region is formed at a depth in the first doped region of about 0.5-1.5 microns; and

the junction between the third doped region and the second doped region is formed at a depth in the second doped region of about 0.2-0.5 microns.

3. A color photosensing structure as in claim 1, and wherein

the junction between the first doped region and the silicon substrate is formed at a depth in the silicon substrate of about 2.0 microns;

the junction between the second doped region and the first doped region is formed at a depth in the first doped region of about 0.6 microns; and

the junction between the third doped region ad the second doped region is formed at a depth in the second doped region of about 0.2 microns.

4. A color photosensor structure formed in a silicon substrate of P-type conductivity for separating light of blue, green and red wavelength, wherein light of blue, green and red wavelength has respective first, second and third light absorption lengths in silicon, the color photosensor structure comprising:

a first deep region of N-type conductivity formed in the P-type silicon substrate, the junction between the deep N-type region and the P-type silicon substrate being formed at a depth in the P-type silicon substrate of about the third light absorption length to define a red photodiode;

a second region of P-type conductivity formed in the deep N-type region, the junction between the P-type region and the deep N-type region being formed at a depth in the deep N-type region of about the second light absorption length to define a green photodiode;

a third shallow region of N-type conductivity formed in the P-type region, the junction between the shallow N-type region and the P-type region being formed in the P-type region of about the first light absorption length to define a blue photodiode; and

photocurrent sensing means connected across the red, green and blue photodiodes for measuring red, green and blue photocurrents across the red, green and blue photodiodes, respectively.

5. An active pixel imaging array, the array comprising:

(a) a matrix of rows and columns of color photosensor structures formed in a silicon substrate having a first conductivity type, each color photosensor structure including;

(i) a first doped region of a second conductivity type opposite the first conductivity type formed in the silicon substrate, the junction between the first doped region and the silicon substrate being formed at a depth in the silicon substrate of about the absorption length in silicon of a first light wavelength to define a first photodiode;

(ii) a second doped region of the first conductivity type formed in the first doped region, the junction between the second doped region and the first doped region being formed at a depth in the first doped region of about the light absorption length in silicon of a second light wavelength to define a second photodiode;

(iii) a third doped region of the second conductivity type formed in the second doped region, the junction between the third doped region and the second doped region being formed at a depth in the second doped region of about the light absorption length in silicon of a third light wavelength to define a third photodiode; and

(iv) a photocurrent sensor connected to measure first, second and third photocurrents across the first, second and third photodiodes, respectively;

(b) for each row in said matrix, row select circuitry connected to each of the color photosensor structures in said row for selectively designating for outputting output signals representative of the first, second and third photocurrents generated in color photosensor structures in said row; and

(c) for each column in said matrix column output circuitry connected to each of the color photosensor structures in said column for selectively outputting output signals representative of the first, second and third photocurrents generated in color photosensor structures in said column.

6. An active pixel imaging array as in claim 5, and wherein

the junction between the first doped region and the silicon substrate is formed at a depth in the silicon substrate of about 1.5-3.0 microns;

the junction between the first second doped region and the first doped region is formed at a depth in the first doped region of about 0.5-1.5 microns; and

the junction between the third doped region and the second doped region is formed at a depth in the second doped region of about 0.2-0.5 microns.

7. An active pixel imaging array as in claim 5, and wherein

the junction between the first doped region and the silicon substrate is formed at a depth in the silicon substrate of about 2.0 microns;

the junction between the second doped region and the first doped region is formed at a depth in the first doped region of about 0.6 microns; and

the junction between the third doped region and the second doped region is formed at a depth in the second doped region at about 0.2 microns.

8. An active pixel imaging array as in claim 5, and wherein:

said row select circuitry comprises a row select line connected to the photocurrent sensor of each color photosensor structure in said row for designating the first second and third photocurrents for output; and

said column output circuitry comprises first, second and third column output lines connected to the photocurrent sensor of each color photosensor structure in said column for outputting the first, second and third photocurrents, respectively.

9. An active pixel imaging array as in claim 5, and wherein:

said row select circuitry comprises first, second and third row select lines connected to the photocurrent sensor of each color photosensor structure in said row for designating the first, second and third photocurrents, respectively for output; and

said column output circuitry comprises a column output line connected to the photocurrent sensor of each color photosensor structure in said column for outputting the first, second and third photocurrents.

10. A color photosensor structure formed in a silicon substrate of a first conductivity type for separating light of differing wavelengths, the color photosensor structure comprising:

a first doped region of a second conductivity type opposite the first conductivity type formed in the silicon substrate, the junction between the first doped region and the silicon substrate being formed at a depth in the silicon substrate of about the absorption length in silicon of a first light wavelength to define a first photodiode;

a second doped region of the first conductivity type formed in the first doped region, the junction between the second doped region and the first doped region being formed at a depth in the first doped region of about the light absorption length in silicon of a second light wavelength to define a second photodiode;

a third doped region of the second conductivity type formed in the second doped region, the junction between the third doped region and the second doped region being formed at a depth in the second doped region of about the light absorption length in silicon of a third light wavelength to define a third photodiode;

a fourth doped region of the first conductivity type, having substantially the same dopant concentration as the second doped region, formed in the silicon substrate and completely surrounding the first doped region; and

a plurality of field effect transistors of the second conductivity type formed in the fourth doped region and interconnected to provide a photocurrent sensor for measuring first, second and third photocurrents across the first, second and third photodiodes, respectively.

11. An active pixel imaging array, the array comprising:

(a) a matrix of row and columns of color photosensor structures formed in a silicon substrate having a first conductivity type, each color photosensor including;

(i) a first doped region of a second conductivity type opposite the first conductivity type formed in the silicon substrate, the junction between the first doped region and the silicon substrate being formed at a depth in the silicon substrate of about the absorption length in silicon of a first light wave length to define a first photodiode;

(ii) a second doped region of the first conductivity type formed in the first doped region, the junction between the second doped region and the first doped region being formed at a depth in the first doped region of about the light absorption length in silicon of a second light wavelength to define a second photodiode;

(iii) a third doped region of the second conductivity type formed in the second doped region, the junction between the third doped region and the second doped region being formed at a depth in the second doped region of about the light absorption length in silicon of a third light wavelength to define a third photodiode;

(iv) a fourth doped region of the first conductivity type, having substantially the same dopant concentration as the second doped region, formed in the silicon substrate and completely surrounding the first doped region; and

(v) a plurality of field effect transistors of the second conductivity type formed in the fourth doped region and interconnected to provide a photocurrent sensor for measuring first, second and third photocurrents across the first, second and third photodiodes, respectively;

(b) for each row in said matrix, row select circuitry connected to each of the color photosensor structures in said row for selectively designating for outputting output signals representative of the first, second and third photocurrents generated in color photosensor structures in said row; and

(c) for each column in said matrix, column output circuitry connected to each of the color photosensor structures in said column for selectively outputting output signals representative of the first, second and third photocurrents generated in color photosensor structures in said column.