Trench photosensor for a CMOS imager
View Patent ↗A trench photosensor for use in a CMOS imager having an improved charge capacity. The trench photosensor may be either a photogate or photodiode structure. The trench shape of the photosensor provides the photosensitive element with an increased surface area compared to a flat photosensor occupying a comparable area on a substrate. The trench photosensor also exhibits a higher charge capacity, improved dynamic range, and a better signal-to-noise ratio. Also disclosed are processes for forming the trench photosensor.
1. A method of sensing photons comprising:
receiving said photons into a trench, said trench disposed in a doped layer of a first conductivity type formed in a semiconductor substrate;
activating a diode formed in said substrate adjacent said trench by absorbing said photons, said diode including a first doped region of a second conductivity type formed in a sidewall and bottom of said trench;
receiving charges from said first doped region into a second doped region of said second conductivity type formed in said doped layer; and
resetting a charge level of said second doped region by receiving charges from said second doped region into a conductive signal line.
2. A method of sensing photons as defined in claim 1 wherein said resetting a charge level of said second doped region comprises transferring charges through a reset transistor.
3. A method of sensing photons as defined in claim 2 wherein said reset transistor includes a drain region and a gate and wherein said second doped region includes a source of said reset transistor.
4. A method of sensing photons as defined in claim 1 wherein receiving said photons into said trench comprises receiving said photons through an aperture in an upper surface of said semiconductor substrate.
5. A method of sensing photons as defined in claim 1 wherein activating said diode comprises energizing electrons in response to absorbing said photons into said semiconductor substrate.
6. A method of sensing photons as defined in claim 1 wherein activating said diode comprises absorbing said photons in a first region of a surface of said trench after reflecting said photons from a second region of said surface of said trench.
7. A method of sensing photons as defined in claim 1 wherein activating said diode comprises:
conducting said photons through a transparent layer disposed above an internal surface of said trench; and
absorbing said photons into said semiconductor substrate.
8. A method of sensing light comprising:
receiving said light through an aperture in a surface of a semiconductor substrate;
absorbing said light into an internal surface of said semiconductor substrate, said internal surface defining a cavity within said semiconductor substrate;
energizing an electron of said semiconductor substrate with said absorbed light; and
activating a switching device using said energized electron.
9. A method of sensing light as defined in claim 8 wherein said activating a switching device comprises activating a field effect transistor.
10. A method of sensing light as defined in claim 8 wherein said absorbing said light into said internal surface comprises receiving said light into said substrate through a layer of conductive material.
11. A method of sensing light as defined in claim 10 wherein said layer of conductive material comprises a photo-gate said method including applying an electrical potential to said photo-gate.
12. A method of sensing light as defined in claim 8 wherein said absorbing said light into said internal surface comprises receiving said light into said substrate through a layer of insulating material.
13. A method of sensing light as defined in claim 8 wherein said absorbing said light into said internal surface comprises receiving said light through a first region of substrate material having a first doping characteristic into a second region of substrate material having a second doping characteristic.
14. A method of sensing light as defined in claim 8 wherein said switching device includes a field effect transistor and wherein said activating a switching device using said energized electron comprises:
passing said energized electron through a first transistor to a floating diffusion region; and
elevating an electrical potential of a gate of said field effect transistor, said gate being electrically coupled to said floating diffusion region.