Methods and devices for improved charge management for three-dimensional and color sensing

1. A CMOS-implementable semiconductor photodetector useable in a system that illuminates a target with optical energy having a modulated periodic waveform that includes a high frequency component, generated in response to signal provided by a clock generator, and that detects a fraction of said optical energy reflected by said target with at least one said semiconductor photodetector, said photodetector comprising:

a semiconductor substrate having a surface upon which said incoming optical energy can impinge onto an optical energy sensitive region, said surface defining an x-direction and a y-direction;

at least a first elongate-shaped polysilicon gate disposed on said surface parallel to said y-direction, said first gate coupleable to a first bias clock signal, synchronously generated by said clock generator, that is high during a first bias regime to detect and collect charge generated by at least a fraction of said incoming optical energy;

a first source region formed in said substrate adjacent a distal end of said first gate;

at least a second elongate-shaped polysilicon gate disposed on said surface parallel to said first elongate-shaped gate and spaced-apart in said x-direction a distance substantially shorter than a length of either said gate, said second gate coupleable to a second bias clock signal synchronously generated by said clock generator;

a second source region formed in said substrate adjacent a distal end of said second gate;

wherein responsive to said first bias clock signal and said second bias clock signal, photoelectic charge generated in said substrate is moved in said x direction to become trapped beneath an elongate-shaped gate and is then moved in said y-direction to an adjacent source region for collection, charge movement in said y-direction being slower than charge movement in said x-direction, wherein modulation contrast of said photodetector is enhanced.

2. The photodetector of claim 1 , further including a potential barrier formed in said substrate in a spaced-apart elongated region between adjacent first and second gates, each said potential barrier being an implant region that reduces x-direction migration of collected charges trapped under a first elongate gate to a second adjacent elongate gate even when a maximum high or low bias clock signal magnitude is sufficient to increase modulation contrast for said photodetector.

3. The photodetector of claim 2 , wherein said substrate is p type material, said potential barrier region is p+ type material, and said source region is n+ type material.

4. The photodetector of claim 1 , further including a first bias gate disposed on said surface intermediate a distal end of a said first elongated gate and said first source region adjacent said distal end, said first bias gate biasable to controllably inhibit charge carrier transfer from said first source region to said first elongated gate.

5. The photodetector of claim 1 , further including a shallow trench isolation region defined in said surface so as to be spaced-apart from said source region a sufficient distance to reduce generation of dark current.

6. The photodetector of claim 1 , further including a shallow trench isolation region defined in said surface and spaced-apart from said optical energy sensitive region of said photodetector.

7. The photodetector of claim 6 , wherein said shallow trench isolation region is spaced-apart from said energy sensitive region by a distance of about 0.15 μm to about 0.45 μm.

8. The photodetector of claim 6 , wherein in plan view an interface of said shallow trench isolation region and a periphery of said energy sensitive region is defined by angles less than 90°.

9. The photodetector of claim 1 , wherein each said polysilicon gate includes at least one characteristic selected from a group consisting of an implant to promote electrical conductivity of said gate, said gate is formed of polysilicon substantially salicide free, said gate is formed of polysilicon substantially polycide free, an area between said polysilicon gates is substantially salicide free, and an area between said polysilicon gates is substantially polycide free.

10. The photodetector of claim 1 , wherein said photodetector is fabricated using at most x+1 process steps, where a standard CMOS process uses x process steps.

11. The photodetector of claim 1 , further including said system.

12. A CMOS-implementable semiconductor photodetector useable in a system that illuminates a target with optical energy having a modulated periodic waveform that includes a high frequency component, generated in response to a signal provided by a clock generator, and that detects a fraction of said optical energy reflected by said target with at least one said semiconductor photodetector, said photodetector comprising:

a semiconductor substrate having a surface upon which said incoming optical energy can impinge onto an optical energy sensitive region, said surface defining an x-direction and a y-direction;

at least a first elongate-shaped polysilicon gate disposed on said surface parallel to said y-direction, said first gate coupleable to a first bias clock signal, synchronously generated by said clock generator, that is high during a first bias regime to detect and collect charge generated by at least a fraction of said incoming optical energy;

a first source region formed in said substrate adjacent a distal end of said first gate;

a first bias gate disposed on said first surface intermediate a distal end of a said first elongated gate and said first source region adjacent said distal end, said first bias gate biasable to controllably inhibit carrier charge transfer from said first source region to said first elongated gate;

wherein responsive to said first bias clock signal, photoelectric charge trapped in a region of said substrate beneath said first elongated gate is moved in said y-direction to said source region for collection, wherein transfer of charge from said source region to said first elongated gate is inhibited, and wherein modulation contrast of said photodetector is enhanced.

13. The photodetector of claim 12 , further including:

a second elongate-shaped polysilicon gate disposed on said surface parallel to said first elongate-shaped gate and spaced-apart in said x-direction a distance substantially shorter than a length of either said gate, said second gate coupleable to a second bias clock signal synchronously generated by said clock generator;

a second source region formed in said substrate adjacent a distal end of said second gate; and

a potential barrier formed in said substrate in a spaced-apart elongated region between adjacent first and second gates, each said potential barrier being an implant region that reduces x-direction migration of collected charges trapped under a first elongate gate to a second adjacent elongate gate even when high magnitude of a bias clock signal is sufficiently high to enhance modulation contrast for said photodetector.

14. The photodetector of claim 13 , wherein said substrate is p type material, said potential barrier region is p+ type material, and said source region is n+ type material.

15. The photodetector of claim 13 , further including a shallow trench isolation region defined in said surface so as to be spaced-apart from said source region a sufficient distance to reduce generation of dark current.

16. The photodetector of claim 13 , further including a shallow trench isolation region defined in said surface and spaced-apart from said optical energy sensitive region of said photodetector.

17. The photodetector of claim 16 , wherein said shallow trench isolation region is spaced-apart from said energy sensitive region by a distance of about 0.15 μm to about 0.45 μm.

18. The photodetector of claim 17 , wherein in plan view an interface of said shallow trench isolation region and a periphery of said energy sensitive region is defined by angles less than 90°.

19. The photodetector of claim 13 , wherein each said polysilicon gate includes at least one characteristic selected from a group consisting of an implant to promote electrical conductivity of said gate, said gate is formed of polysilicon substantially salicide free, said gate is formed of polysilicon substantially polycide free, an area between said polysilicon gates is substantially salicide free, and an area between polysilicon gates is substantially polycide free.

20. The photodetector of claim 12 , wherein said photodetector is implanted using at most x+1 process steps, where standard CMOS process uses x process steps.

21. The photodetector of claim 12 , further including said system.

22. A CMOS-implementable semiconductor photodetector usable in a system to determine spectral composition of light illuminating a target object with optical energy and to detect a fraction of said optical energy reflected by said target object with at least one said semiconductor photodetector, said photodetector comprising:

a semiconductor substrate having a surface upon which reflected said optical energy can impinge onto an optical energy sensitive region of said photodetector, said surface defining an x-direction and a y-direction;

at least a first elongate-shaped polysilicon gate disposed on said surface parallel to said y-direction, said first gate coupleable to a first bias signal that is high during a first bias regime to detect and collect charge generated by at least a fraction of reflected said optical energy;

a first source region formed in said substrate adjacent a distal end of said first gate;

at least a second elongate-shaped polysilicon gate disposed on said surface parallel to said first elongate-shaped gate and spaced-apart in said x-direction a distance substantially shorter than a length of either said gate, said second gate coupleable to a second bias signal that is high during the first bias regime;

a second source region formed in said substrate adjacent a distal end of said second gate;

wherein responsive to said first bias signal and said second bias signal, photoelectric charge generated in said substrate is moved in said x direction to become trapped beneath an elongate-shaped said gate and is then moved in said y-direction to an adjacent source region for collection, a relative amount of charge collected by each elongate shaped said gate being dependent upon wavelength of reflected said light and upon bias voltage magnitudes during said first bias regime.

23. The photodetector of claim 22 , wherein said first and said second bias signals have substantially different magnitudes during said first bias regime;

wherein difference in captured signal for said first gate and for said second gate is enhanced.